solanki

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Author name code: solanki
ADS astronomy entries on 2022-09-14
author:"Solanki, Sami K."

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Title: What drives decayless kink oscillations in active region
coronal loops on the Sun?
Authors: Mandal, Sudip; Chitta, Lakshmi P.; Antolin, Patrick; Peter,
Hardi; Solanki, Sami K.; Auchère, Frédéric; Berghmans, David;
Zhukov, Andrei N.; Teriaca, Luca; Cuadrado, Regina A.; Schühle,
Udo; Parenti, Susanna; Buchlin, Éric; Harra, Louise; Verbeeck, Cis;
Kraaikamp, Emil; Long, David M.; Rodriguez, Luciano; Pelouze, Gabriel;
Schwanitz, Conrad; Barczynski, Krzysztof; Smith, Phil J.
2022arXiv220904251M Altcode:
We study here the phenomena of decayless kink oscillations in a system
of active region (AR) coronal loops. Using high resolution observations
from two different instruments, namely the Extreme Ultraviolet Imager
(EUI) on board Solar Orbiter and the Atmospheric Imaging Assembly
(AIA) on board the Solar Dynamics Observatory, we follow these AR
loops for an hour each on three consecutive days. Our results show
significantly more resolved decayless waves in the higher-resolution
EUI data compared with the AIA data. Furthermore, the same system of
loops exhibits many of these decayless oscillations on Day-2, while on
Day-3, we detect very few oscillations and on Day-1, we find none at
all. Analysis of photospheric magnetic field data reveals that at most
times, these loops were rooted in sunspots, where supergranular flows
are generally absent. This suggests that supergranular flows, which
are often invoked as drivers of decayless waves, are not necessarily
driving such oscillations in our observations. Similarly, our findings
also cast doubt on other possible drivers of these waves, such as a
transient driver or mode conversion of longitudinal waves near the loop
footpoints. In conclusion, through our analysis we find that none of
the commonly suspected sources proposed to drive decayless oscillations
in active region loops seems to be operating in this event and hence,
the search for that elusive wave driver needs to continue.

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Title: Erratum: "Faculae Cancel out on the Surfaces of Active Suns"
(2022, ApJL, 934, L23)
Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.;
Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L.
2022ApJ...936L..17N Altcode:
No abstract at ADS

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Title: Faculae Cancel out on the Surfaces of Active Suns
Authors: Nèmec, N. -E.; Shapiro, A. I.; Işık, E.; Sowmya, K.;
Solanki, S. K.; Krivova, N. A.; Cameron, R. H.; Gizon, L.
2022ApJ...934L..23N Altcode: 2022arXiv220706816N
Surfaces of the Sun and other cool stars are filled with magnetic
fields, which are either seen as dark compact spots or more
diffuse bright structures like faculae. Both hamper detection and
characterization of exoplanets, affecting stellar brightness and
spectra, as well as transmission spectra. However, the expected facular
and spot signals in stellar data are quite different, for instance,
they have distinct temporal and spectral profiles. Consequently,
corrections of stellar data for magnetic activity can greatly benefit
from the insight on whether the stellar signal is dominated by spots or
faculae. Here, we utilize a surface flux transport model to show that
more effective cancellation of diffuse magnetic flux associated with
faculae leads to spot area coverages increasing faster with stellar
magnetic activity than that by faculae. Our calculations explain the
observed dependence between solar spot and facular area coverages and
allow its extension to stars that are more active than the Sun. This
extension enables anticipating the properties of stellar signal and its
more reliable mitigation, leading to a more accurate characterization
of exoplanets and their atmospheres.

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Title: Predictions of Astrometric Jitter for Sun-like Stars. III. Fast
Rotators
Authors: Sowmya, K.; Nèmec, N. -E.; Shapiro, A. I.; Işık, E.;
Krivova, N. A.; Solanki, S. K.
2022ApJ...934..146S Altcode: 2022arXiv220607702S
A breakthrough in exoplanet detections is foreseen with the
unprecedented astrometric measurement capabilities offered by
instrumentation aboard the Gaia space observatory. Besides, astrometric
discoveries of exoplanets are expected from the planned space mission,
Small-JASMINE. In this setting, the present series of papers focuses
on estimating the effect of the magnetic activity of G2V-type host
stars on the astrometric signal. This effect interferes with the
astrometric detections of Earth-mass planets. While the first two
papers considered stars rotating at the solar rotation rate, this paper
focuses on stars having solar effective temperature and metallicity
but rotating faster than the Sun, and consequently more active. By
simulating the distribution of active regions on such stars using the
Flux Emergence And Transport model, we show that the contribution of
magnetic activity to the astrometric measurements becomes increasingly
significant with increasing rotation rates. We further show that the
jitter for the most variable periodic Kepler stars is high enough to be
detected by Gaia. Furthermore, due to a decrease in the facula-to-spot
area ratio for more active stars, the magnetic jitter is found to be
spot dominated for rapid rotators. Our simulations of the astrometric
jitter have the potential to aid the interpretation of data from Gaia
and upcoming space astrometry missions.

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Title: A highly dynamic small-scale jet in a polar coronal hole
Authors: Mandal, Sudip; Chitta, Lakshmi Pradeep; Peter, Hardi;
Solanki, Sami K.; Cuadrado, Regina Aznar; Teriaca, Luca; Schühle,
Udo; Berghmans, David; Auchère, Frédéric
2022A&A...664A..28M Altcode: 2022arXiv220602236M
We present an observational study of the plasma dynamics at the base
of a solar coronal jet, using high resolution extreme ultraviolet
imaging data taken by the Extreme Ultraviolet Imager on board Solar
Orbiter, and by the Atmospheric Imaging Assembly on board Solar
Dynamics Observatory. We observed multiple plasma ejection events
over a period of ∼1 h from a dome-like base that is ca. 4 Mm wide
and is embedded in a polar coronal hole. Within the dome below the
jet spire, multiple plasma blobs with sizes around 1−2 Mm propagate
upwards to the dome apex with speeds of the order of the sound speed
(ca. 120 km s−1). Upon reaching the apex, some of these
blobs initiate flows with similar speeds towards the other footpoint
of the dome. At the same time, high speed super-sonic outflows
(∼230 km s−1) are detected along the jet spire. These
outflows as well as the intensity near the dome apex appear to be
repetitive. Furthermore, during its evolution, the jet undergoes
many complex morphological changes, including transitions between
the standard and blowout type eruption. These new observational
results highlight the underlying complexity of the reconnection
process that powers these jets and they also provide insights into
the plasma response when subjected to rapid energy injection. Movies associated to Figs. 1, 2, and 4 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202243765/olm">https://www.aanda.org</A>

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Title: Linking Small-scale Solar Wind Properties with Large-scale
Coronal Source Regions through Joint Parker Solar Probe-Metis/Solar
Orbiter Observations
Authors: Telloni, Daniele; Zank, Gary P.; Sorriso-Valvo, Luca;
D'Amicis, Raffaella; Panasenco, Olga; Susino, Roberto; Bruno, Roberto;
Perrone, Denise; Adhikari, Laxman; Liang, Haoming; Nakanotani, Masaru;
Zhao, Lingling; Hadid, Lina Z.; Sánchez-Cano, Beatriz; Verscharen,
Daniel; Velli, Marco; Grimani, Catia; Marino, Raffaele; Carbone,
Francesco; Mancuso, Salvatore; Biondo, Ruggero; Pagano, Paolo; Reale,
Fabio; Bale, Stuart D.; Kasper, Justin C.; Case, Anthony W.; de Wit,
Thierry Dudok; Goetz, Keith; Harvey, Peter R.; Korreck, Kelly E.;
Larson, Davin; Livi, Roberto; MacDowall, Robert J.; Malaspina, David
M.; Pulupa, Marc; Stevens, Michael L.; Whittlesey, Phyllis; Romoli,
Marco; Andretta, Vincenzo; Deppo, Vania Da; Fineschi, Silvano; Heinzel,
Petr; Moses, John D.; Naletto, Giampiero; Nicolini, Gianalfredo;
Spadaro, Daniele; Stangalini, Marco; Teriaca, Luca; Capobianco,
Gerardo; Capuano, Giuseppe E.; Casini, Chiara; Casti, Marta; Chioetto,
Paolo; Corso, Alain J.; Leo, Yara De; Fabi, Michele; Frassati,
Federica; Frassetto, Fabio; Giordano, Silvio; Guglielmino, Salvo L.;
Jerse, Giovanna; Landini, Federico; Liberatore, Alessandro; Magli,
Enrico; Massone, Giuseppe; Messerotti, Mauro; Pancrazzi, Maurizio;
Pelizzo, Maria G.; Romano, Paolo; Sasso, Clementina; Schühle, Udo;
Slemer, Alessandra; Straus, Thomas; Uslenghi, Michela; Volpicelli,
Cosimo A.; Zangrilli, Luca; Zuppella, Paola; Abbo, Lucia; Auchère,
Frédéric; Cuadrado, Regina Aznar; Berlicki, Arkadiusz; Ciaravella,
Angela; Lamy, Philippe; Lanzafame, Alessandro; Malvezzi, Marco;
Nicolosi, Piergiorgio; Nisticò, Giuseppe; Peter, Hardi; Solanki,
Sami K.; Strachan, Leonard; Tsinganos, Kanaris; Ventura, Rita; Vial,
Jean-Claude; Woch, Joachim; Zimbardo, Gaetano
2022ApJ...935..112T Altcode:
The solar wind measured in situ by Parker Solar Probe in the very
inner heliosphere is studied in combination with the remote-sensing
observation of the coronal source region provided by the METIS
coronagraph aboard Solar Orbiter. The coronal outflows observed near
the ecliptic by Metis on 2021 January 17 at 16:30 UT, between 3.5 and
6.3 R ⊙ above the eastern solar limb, can be associated
with the streams sampled by PSP at 0.11 and 0.26 au from the Sun,
in two time intervals almost 5 days apart. The two plasma flows
come from two distinct source regions, characterized by different
magnetic field polarity and intensity at the coronal base. It follows
that both the global and local properties of the two streams are
different. Specifically, the solar wind emanating from the stronger
magnetic field region has a lower bulk flux density, as expected,
and is in a state of well-developed Alfvénic turbulence, with low
intermittency. This is interpreted in terms of slab turbulence in the
context of nearly incompressible magnetohydrodynamics. Conversely,
the highly intermittent and poorly developed turbulent behavior of the
solar wind from the weaker magnetic field region is presumably due to
large magnetic deflections most likely attributed to the presence of
switchbacks of interchange reconnection origin.

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Title: Chromospheric extension of the MURaM code
Authors: Przybylski, D.; Cameron, R.; Solanki, S. K.; Rempel, M.;
Leenaarts, J.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.
2022A&A...664A..91P Altcode: 2022arXiv220403126P
Context. Detailed numerical models of the chromosphere and corona are
required to understand the heating of the solar atmosphere. An accurate
treatment of the solar chromosphere is complicated by the effects
arising from non-local thermodynamic equilibrium (NLTE) radiative
transfer. A small number of strong, highly scattering lines dominate the
cooling and heating in the chromosphere. Additionally, the recombination
times of ionised hydrogen are longer than the dynamical timescales,
requiring a non-equilibrium (NE) treatment of hydrogen ionisation. Aims: We describe a set of necessary additions to the MURaM code that
allow it to handle some of the important NLTE effects. We investigate
the impact on solar chromosphere models caused by NLTE and NE effects in
radiation magnetohydrodynamic simulations of the solar atmosphere. Methods: The MURaM code was extended to include the physical
process required for an accurate simulation of the solar chromosphere,
as implemented in the Bifrost code. This includes a time-dependent
treatment of hydrogen ionisation, a scattering multi-group radiation
transfer scheme, and approximations for NLTE radiative cooling. 
Results: The inclusion of NE and NLTE physics has a large impact on the
structure of the chromosphere; the NE treatment of hydrogen ionisation
leads to a higher ionisation fraction and enhanced populations in
the first excited state throughout cold inter-shock regions of the
chromosphere. Additionally, this prevents hydrogen ionisation from
buffering energy fluctuations, leading to hotter shocks and cooler
inter-shock regions. The hydrogen populations in the ground and first
excited state are enhanced by 102-103 in the
upper chromosphere and by up to 109 near the transition
region. Conclusions: Including the necessary NLTE physics
leads to significant differences in chromospheric structure and
dynamics. The thermodynamics and hydrogen populations calculated using
the extended version of the MURaM code are consistent with previous
non-equilibrium simulations. The electron number and temperature
calculated using the non-equilibrium treatment of the chromosphere
are required to accurately synthesise chromospheric spectral
lines. Movies associated to Fig. 2 are only available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141230/olm">https://www.aanda.org</A>

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Title: Solar cyclic activity over the last millennium
reconstructedfrom annual 14C data (Corrigendum)
Authors: Usoskin, I. G.; Solanki, S. K.; Krivova, N.; Hofer, B.;
Kovaltsov, G. A.; Wacker, L.; Brehm, N.; Kromer, B.
2022A&A...664C...3U Altcode:
No abstract at ADS

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Title: The on-ground data reduction and calibration pipeline for
SO/PHI-HRT
Authors: Sinjan, J.; Calchetti, D.; Hirzberger, J.; Orozco Suárez,
D.; Albert, K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero,
A.; Blanco Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero,
L.; Gutierrez Marquez, P.; Kahil, F.; Kolleck, M.; Solanki, S. K.; del
Toro Iniesta, J. C.; Volkmer, R.; Woch, J.; Fiethe, B.; Gómez Cama,
J. M.; Pérez-Grande, I.; Sanchis Kilders, E.; Balaguer Jiménez,
M.; Bellot Rubio, L. R.; Carmona, M.; Deutsch, W.; Fernandez-Rico,
G.; Fernández-Medina, A.; García Parejo, P.; Gasent Blesa, J. L.;
Gizon, L.; Grauf, B.; Heerlein, K.; Korpi-Lagg, A.; Lange, T.; López
Jiménez, A.; Maue, T.; Meller, R.; Michalik, H.; Moreno Vacas, A.;
Müller, R.; Nakai, E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub,
J.; Strecker, H.; Torralbo, I.; Valori, G.
2022arXiv220814904S Altcode:
The ESA/NASA Solar Orbiter space mission has been successfully launched
in February 2020. Onboard is the Polarimetric and Helioseismic Imager
(SO/PHI), which has two telescopes, a High Resolution Telescope
(HRT) and the Full Disc Telescope (FDT). The instrument is designed
to infer the photospheric magnetic field and line-of-sight velocity
through differential imaging of the polarised light emitted by the
Sun. It calculates the full Stokes vector at 6 wavelength positions
at the Fe I 617.3 nm absorption line. Due to telemetry constraints,
the instrument nominally processes these Stokes profiles onboard,
however when telemetry is available, the raw images are downlinked and
reduced on ground. Here the architecture of the on-ground pipeline
for HRT is presented, which also offers additional corrections not
currently available on board the instrument. The pipeline can reduce
raw images to the full Stokes vector with a polarimetric sensitivity
of $10^{-3}\cdot I_{c}$ or better.

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Title: Polarimetric calibration of the Sunrise UV Spectropolarimeter
and Imager
Authors: Iglesias, F. A.; Feller, A.; Gandorfer, A.; Lagg, A.;
Riethmüller, T. L.; Solanki, S. K.; Katsukawa, Y.; Kubo, M.;
Zucarelli, G.; Sanchez, M.; Sunrise Team
2022BAAA...63..305I Altcode:
Sunrise is an optical observatory mounted in a stratospheric balloon,
developed to study magnetic fields in the solar atmosphere with very
high resolution. In its third flight, Sunrise carry the Sunrise UV
Spectropolarimeter and Imager (SUSI), that operates in the 313-430 nm
range, covering thousands of spectral lines not accessible from the
ground and thus largely unexplored. SUSI does not include a polarimetric
calibration unit on board. We report about the development status of
SUSI and the preliminary results of its calibration.

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Title: Small-scale dynamo in cool stars. I. Changes in stratification
and near-surface convection for main-sequence spectral types
Authors: Bhatia, Tanayveer S.; Cameron, Robert H.; Solanki, Sami K.;
Peter, Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
2022A&A...663A.166B Altcode: 2022arXiv220600064B
Context. Some of the small-scale solar magnetic flux can
be attributed to a small-scale dynamo (SSD) operating in the
near-surface convection. The SSD fields have consequences for
solar granular convection, basal flux, and chromospheric heating. A
similar SSD mechanism is expected to be active in the near-surface
convection of other cool main-sequence stars, but this has not been
investigated thus far. Aims: We aim to investigate changes in
stratification and convection due to inclusion of SSD fields for F3V,
G2V, K0V, and M0V spectral types in the near-surface convection. Methods: We studied 3D magnetohydrodynamic (MHD) models of the four
stellar boxes, covering the subsurface convection zone up to the lower
photosphere in a small Cartesian box, based on the MURaM radiative-MHD
simulation code. We compared the SSD runs against reference hydrodynamic
runs. Results: The SSD is found to efficiently produce magnetic
field with energies ranging between 5% to 80% of the plasma kinetic
energy at different depths. This ratio tends to be larger for larger
Teff. The relative change in density and gas pressure
stratification for the deeper convective layers due to SSD magnetic
fields is negligible, except for the F-star. For the F-star, there is
a substantial reduction in convective velocities due to Lorentz force
feedback from magnetic fields, which, in turn, reduces the turbulent
pressure. Conclusions: The SSD in near-surface convection for
cool main-sequence stars introduces small but significant changes
in thermodynamic stratification (especially for the F-star) due to a
reduction in the convective velocities.

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Title: Historical Ca II K observations for irradiance reconstructions
Authors: Chatzistergos, Theodosios; Krivova, Natalie; Ermolli, Ilaria;
Leng Yeo, Kok; Solanki, Sami; Mandal, Sudip
2022cosp...44.1551C Altcode:
Solar irradiance has been measured by various instruments
from space since 1978 and exhibits variations on all accessible
timescales. Irradiance variations prior to satellite measurements,
knowledge of which is important for climate studies, can only be
recovered with models. Models have successfully been used to reconstruct
solar irradiance variations by attributing the variability on time
scales longer than about a day to the evolution of the solar surface
magnetic field. However, to account for the different contributions of
surface magnetic features, such as sunspots and faculae, models require
appropriate input data. Unfortunately, due to the scarcity of suitable
facular data prior to the period of direct irradiance measurements,
most available irradiance reconstructions rely on sunspot data alone or
on other, indirect data of solar magnetism. Historical Ca II K archives
carry direct information on facular regions, but they have not been
used to their full potential for irradiance reconstructions. The main
reasons limiting their use were the difficulty to account for the
non-linear response of the photographic plates along with plentiful
large-scale artefacts affecting the images. We have extensively studied
Ca II K data to overcome most issues affecting them thus paving the way
for them to be used for accurate irradiance reconstructions. We will
present our latest work on employment of Ca II K data for reconstructing
past irradiance variations.

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Title: The essential role of Earth-Sun L4 in solar particle event
forecasting for Lunar and Mars exploration
Authors: Posner, Arik; Toit Strauss, Du; Solanki, Sami K.; Effenberger,
Frederic; Gandorfer, Achim; Hirzberger, Johann; Kühl, Patrick; Heber,
Bernd; Malandraki, Olga; Folta, David; Jones, Sarah; Arge, Charles;
Sterken, Veerle; Henney, Carl J.; Staub, Jan; Hatten, Noble; Stcyr,
O. Chris
2022cosp...44.1157P Altcode:
We learned from the STEREO mission that solar particle events
originating from behind the west limb of the Sun, i.e., out of view
from Earth, make up about 30 percent of those significantly affecting
Earth's vicinity and thus could endanger human exploration of the
Moon. The Earth-Sun Lagrangian point 4 is a meta-stable location at 1
au from the Sun, 60° ahead of Earth's orbit. L4 has an uninterrupted
view of the solar photosphere centered on W60, the Earth's nominal
magnetic field connection to the Sun. The role of L4 observations
for improving several existing short-term SEP forecasting techniques,
including protons, ESPERTA, UMASEP and pps, for Lunar exploration will
be highlighted. We can show that BFO dose savings from short-term
solar energetic particle forecasts are critically important in a
worst-case scenario. Placing a mission at L4 is even a precondition
for any SEP all-clear forecasting for Lunar exploration. Furthermore,
we analyzed example trajectories of short-term Mars round trips that
may be considered for future human exploration of Mars and find that
L4-based SWx observations would have relevance for protecting Mars
explorers from radiation exposure.

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Title: Reconstruction of Coronal Magnetic Fields Using a
Poloidal-Toroidal Representation
Authors: Yi, Sibaek; Choe, G. S.; Cho, Kyung-Suk; Solanki, Sami K.;
Büchner, Jörg
2022arXiv220607189Y Altcode:
A new method for reconstruction of coronal magnetic fields as force-free
fields (FFFs) is presented. Our method employs poloidal and toroidal
functions to describe divergence-free magnetic fields. This magnetic
field representation naturally enables us to implement the boundary
conditions at the photospheric boundary, i.e., the normal magnetic field
and the normal current density there, in a straightforward manner. At
the upper boundary of the corona, a source-surface condition can be
employed, which accommodates magnetic flux imbalance at the bottom
boundary. Although our iteration algorithm is inspired by extant
variational methods, it is non-variational and requires much less
iteration steps than most of them. The computational code based on our
new method is tested against the analytical FFF solutions by Titov &amp;
Démoulin (1999). It is found to excel in reproducing a tightly wound
flux rope, a bald patch and quasi-separatrix layers with a hyperbolic
flux tube.

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Title: Stellar limb darkening. A new MPS-ATLAS library for Kepler,
TESS, CHEOPS, and PLATO passbands
Authors: Kostogryz, N. M.; Witzke, V.; Shapiro, A. I.; Solanki, S. K.;
Maxted, P. F. L.; Kurucz, R. L.; Gizon, L.
2022arXiv220606641K Altcode:
The detection of the first exoplanet paved the way into the era of
transit photometry space missions with a revolutionary photometric
precision that aim at discovering new exoplanetary systems around
different types of stars. With this high precision, it is possible
to derive very accurately the radii of exoplanets which is crucial
for constraining their type and composition. However, it requires an
accurate description of host stars, especially their center-to-limb
variation of intensities (so called limb darkening) as it affects the
planet-to-star radius ratio determination. We aim at improving the
accuracy of limb darkening calculations for stars with a wide range
of fundamental parameters. We used the recently developed 1D MPS-ATLAS
code to compute model atmosphere structures and to synthesize stellar
limb darkening on a very fine grid of stellar parameters. For the
computations we utilized the most accurate information on chemical
element abundances and mixing length parameters including convective
overshoot. The stellar limb darkening was fitted using the two most
accurate limb darkening laws: the power-2 and 4-parameters non-linear
laws. We present a new extensive library of stellar model atmospheric
structures, the synthesized stellar limb darkening curves, and the
coefficients of parameterized limb-darkening laws on a very fine grid of
stellar parameters in the Kepler, TESS, CHEOPS, and PLATO passbands. The
fine grid allows overcoming the sizable errors introduced by the need
to interpolate. Our computations of solar limb darkening are in a
good agreement with available solar measurements at different view
angles and wavelengths. Our computations of stellar limb darkening
agree well with available measurements of Kepler stars. A new grid of
stellar model structures, limb darkening and their fitted coefficients
in different broad filters is provided in CDS.

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Title: Making our star sparkle: The Sun's magnetic field, activity
and variability
Authors: Solanki, Sami
2022AAS...24040001S Altcode:
The magnetic field of the Sun relieves our star from the monotony of an
unchanging existence, at least unchanging on timescales between days
and millennia. Instead, it leads the Sun to display a large variety
of ever-changing features, such as sunspots and faculae at the solar
surface, a bright network in the chromosphere, and loops and plumes
in the corona, among many others. It also leads to variations of the
total brightness of the Sun. From time to time, the incessantly evolving
magnetic field causes great flashes of radiation in the form of flares,
or outbursts of particles in the form of coronal mass ejections. In
other words, the nuclear reactions in the Sun's core may make it shine,
but it takes the magnetic field to make our star sparkle. How
the solar magnetic field is structured, how it produces aspects of
solar activity and variability and how we learn more about it will be
subjects of this talk.

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Title: Magnetized supersonic downflows in the chromosphere. A
statistical study using the He I 10 830 Å lines
Authors: Sowmya, K.; Lagg, A.; Solanki, S. K.; Castellanos Durán,
J. S.
2022A&A...661A.122S Altcode: 2022arXiv220211679S
The chromosphere above active regions (ARs) on the Sun hosts
magnetized supersonic downflows. Studies of these supersonic downflows
help to decipher the magnetic fine structure and dynamics of the
chromosphere. We perform a statistical analysis of the magnetized
supersonic downflows in a number of ARs at different evolutionary stages
and survey their characteristics. We analyze spectro-polarimetric scans
of parts of 13 ARs obtained in the infrared He I 10 830 Å triplet
formed in the upper chromosphere recorded with the GREGOR Infrared
Spectrograph mounted at the GREGOR solar telescope. We retrieve
the line-of-sight velocities and the magnetic field vector using
the HELIX+ inversion code that assumes Milne-Eddington
atmospheres. We find magnetized supersonic downflows in all the ARs,
with larger area coverage by such flows in ARs observed during their
emerging phase. The fact that supersonic downflows were detected
in all scans, albeit only covering a small fraction, 0.2-6.4%, of
the observed field-of-view, suggests that they are a comparatively
common phenomenon in the upper chromospheres of ARs. The supersonic
downflows are found to be associated with many AR features, such as
pores, sunspot umbrae, sunspot penumbrae, light bridges, plages, He
I loops as part of arch filament systems characteristic of emerging
fields, and filaments. Although several mechanisms are identified to be
causing the supersonic downflows, by far the most common one appears to
be the draining of plasma along the legs of rising magnetic loops. The
loops mainly drain into forming pores. The line-of-sight velocities of
the supersonic downflows reach values of up to 49 km s−1,
and the velocity distribution shows multiple populations. Almost 92% of
these supersonic downflows coexist with a subsonic flow component. The
weaker, more horizontal fields associated with the supersonic component
suggests that it is formed above the subsonic component.

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Title: Multiwavelength Mitigation of Stellar Activity in Astrometric
Planet Detection
Authors: Kaplan-Lipkin, Avi; Macintosh, Bruce; Madurowicz, Alexander;
Sowmya, Krishnamurthy; Shapiro, Alexander; Krivova, Natalie; Solanki,
Sami K.
2022AJ....163..205K Altcode: 2021arXiv211206383K
Astrometry has long been a promising technique for exoplanet
detection. At the theoretical limits, astrometry would allow for
the detection of smaller planets than previously seen by current
exoplanet search methods, but stellar activity may make these
theoretical limits unreachable. Astrometric jitter of a Sun-like
star due to magnetic activity in its photosphere induces apparent
variability in the photocenter of order 0.5 mR ⊙. This
jitter creates a fundamental astrophysical noise floor preventing
detection of lower-mass planets in a single spectral band. By injecting
planet orbits into simulated solar data at five different passbands,
we investigate mitigation of this fundamental astrometric noise using
correlations across passbands. For a true solar analog and a planet at
1 au semimajor axis, the 6σ detection limit set by stellar activity for
an ideal telescope at the best single passband is 0.01 Earth masses. We
found that pairs of passbands with highly correlated astrometric jitter
due to stellar activity, but with less motion in the redder band,
enable higher-precision measurements of the common signal from the
planet. Using this method improves detectable planet masses at 1 au
by up to a factor of 10, corresponding to at best 0.005 Earth masses
for a Sun-like star with a perfect telescope. Given these results,
we recommend that future astrometry missions consider proceeding with
two or more passbands to reduce noise due to stellar activity.

---------------------------------------------------------
Title: The magnetic drivers of campfires seen by the Polarimetric
and Helioseismic Imager (PHI) on Solar Orbiter
Authors: Kahil, F.; Hirzberger, J.; Solanki, S. K.; Chitta, L. P.;
Peter, H.; Auchère, F.; Sinjan, J.; Orozco Suárez, D.; Albert,
K.; Albelo Jorge, N.; Appourchaux, T.; Alvarez-Herrero, A.; Blanco
Rodríguez, J.; Gandorfer, A.; Germerott, D.; Guerrero, L.; Gutiérrez
Márquez, P.; Kolleck, M.; del Toro Iniesta, J. C.; Volkmer, R.;
Woch, J.; Fiethe, B.; Gómez Cama, J. M.; Pérez-Grande, I.; Sanchis
Kilders, E.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Calchetti,
D.; Carmona, M.; Deutsch, W.; Fernández-Rico, G.; Fernández-Medina,
A.; García Parejo, P.; Gasent-Blesa, J. L.; Gizon, L.; Grauf, B.;
Heerlein, K.; Lagg, A.; Lange, T.; López Jiménez, A.; Maue, T.;
Meller, R.; Michalik, H.; Moreno Vacas, A.; Müller, R.; Nakai,
E.; Schmidt, W.; Schou, J.; Schühle, U.; Staub, J.; Strecker, H.;
Torralbo, I.; Valori, G.; Aznar Cuadrado, R.; Teriaca, L.; Berghmans,
D.; Verbeeck, C.; Kraaikamp, E.; Gissot, S.
2022A&A...660A.143K Altcode: 2022arXiv220213859K
Context. The Extreme Ultraviolet Imager (EUI) on board the Solar Orbiter
(SO) spacecraft observed small extreme ultraviolet (EUV) bursts,
termed campfires, that have been proposed to be brightenings near the
apexes of low-lying loops in the quiet-Sun atmosphere. The underlying
magnetic processes driving these campfires are not understood. Aims: During the cruise phase of SO and at a distance of 0.523
AU from the Sun, the Polarimetric and Helioseismic Imager on Solar
Orbiter (SO/PHI) observed a quiet-Sun region jointly with SO/EUI,
offering the possibility to investigate the surface magnetic field
dynamics underlying campfires at a spatial resolution of about 380
km. Methods: We used co-spatial and co-temporal data of the
quiet-Sun network at disc centre acquired with the High Resolution
Imager of SO/EUI at 17.4 nm (HRIEUV, cadence 2 s) and the
High Resolution Telescope of SO/PHI at 617.3 nm (HRT, cadence 2.5
min). Campfires that are within the SO/PHI−SO/EUI common field
of view were isolated and categorised according to the underlying
magnetic activity. Results: In 71% of the 38 isolated events,
campfires are confined between bipolar magnetic features, which seem to
exhibit signatures of magnetic flux cancellation. The flux cancellation
occurs either between the two main footpoints, or between one of the
footpoints of the loop housing the campfire and a nearby opposite
polarity patch. In one particularly clear-cut case, we detected the
emergence of a small-scale magnetic loop in the internetwork followed
soon afterwards by a campfire brightening adjacent to the location
of the linear polarisation signal in the photosphere, that is to
say near where the apex of the emerging loop lays. The rest of the
events were observed over small scattered magnetic features, which
could not be identified as magnetic footpoints of the campfire hosting
loops. Conclusions: The majority of campfires could be driven
by magnetic reconnection triggered at the footpoints, similar to the
physical processes occurring in the burst-like EUV events discussed
in the literature. About a quarter of all analysed campfires, however,
are not associated to such magnetic activity in the photosphere, which
implies that other heating mechanisms are energising these small-scale
EUV brightenings.

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Title: A solar coronal loop in a box: Energy generation and heating
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S. K.; Przybylski,
D.; Rempel, M.; Chitta, L. P.
2022A&A...658A..45B Altcode: 2021arXiv211211549B
Context. Coronal loops are the basic building block of the upper solar
atmosphere as seen in the extreme UV and X-rays. Comprehending how
these are energized, structured, and evolve is key to understanding
stellar coronae. Aims: Here we investigate how the energy
to heat the loop is generated by photospheric magneto-convection,
transported into the upper atmosphere, and how the internal
structure of a coronal magnetic loop forms. Methods: In a 3D
magnetohydrodynamics model, we study an isolated coronal loop rooted
with both footpoints in a shallow layer within the convection zone
using the MURaM code. To resolve its internal structure, we limited
the computational domain to a rectangular box containing a single
coronal loop as a straightened magnetic flux tube. Field-aligned heat
conduction, gray radiative transfer in the photosphere and chromosphere,
and optically thin radiative losses in the corona were taken into
account. The footpoints were allowed to interact self-consistently
with the granulation surrounding them. Results: The loop is
heated by a Poynting flux that is self-consistently generated through
small-scale motions within individual magnetic concentrations in
the photosphere. Turbulence develops in the upper layers of the
atmosphere as a response to the footpoint motions. We see little
sign of heating by large-scale braiding of magnetic flux tubes
from different photospheric concentrations at a given footpoint. The
synthesized emission, as it would be observed by the Atmospheric Imaging
Assembly or the X-Ray Telescope, reveals transient bright strands that
form in response to the heating events. Overall, our model roughly
reproduces the properties and evolution of the plasma as observed
within (the substructures of) coronal loops. Conclusions:
With this model we can build a coherent picture of how the energy
flux to heat the upper atmosphere is generated near the solar surface
and how this process drives and governs the heating and dynamics of
a coronal loop. Movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141451/olm">https://www.aanda.org</A>

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Title: Final Report for SAG 21: The Effect of Stellar Contamination
on Space-based Transmission Spectroscopy
Authors: Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana
V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris,
Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.;
Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas;
Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah
L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier,
Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg;
Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder,
Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh;
Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato,
Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson,
Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven;
Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.;
Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert,
Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik,
Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
2022arXiv220109905R Altcode:
Study Analysis Group 21 (SAG21) of the Exoplanet Exploration Program
Analysis Group (ExoPAG) was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method for
studying exoplanetary atmospheres by measuring the wavelength-dependent
radius of a planet as it transits its star. Transmission spectroscopy
relies on a precise understanding of the spectrum of the star being
occulted. However, stars are not homogeneous, constant light sources
but have temporally evolving photospheres and chromospheres with
inhomogeneities like spots, faculae, and plages. This SAG has brought
together an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar astrophysics,
planetary science, and exoplanetary atmosphere research communities,
to study the current needs that can be addressed in this context to
make the most of transit studies from current NASA facilities like
HST and JWST. The analysis produced 14 findings, which fall into
three Science Themes encompassing (1) how the Sun is used as our best
laboratory to calibrate our understanding of stellar heterogeneities
("The Sun as the Stellar Benchmark"), (2) how stars other than the Sun
extend our knowledge of heterogeneities ("Surface Heterogeneities of
Other Stars") and (3) how to incorporate information gathered for the
Sun and other stars into transit studies ("Mapping Stellar Knowledge
to Transit Studies").

---------------------------------------------------------
Title: Solar Surface Stereoscopy with Solar Orbiter's Polarimetric
Helioseismic Imager (SO/PHI)
Authors: Romero Avila, Amanda; Inhester, Bernd; Hirzberger, Johann;
Solanki, Sami
2021AGUFMSH25B2095R Altcode:
A compound method for a stereoscopic analysis of the height variations
in the solar photosphere is presented. This method allows to estimate
relevant quantities (i.e. the Wilson depression) and to study structures
in the solar photosphere and within sunspots. We will demonstrate
the feasibility of the method using simulated Stokes I continuum
observations derived from a radiative transfer model using the plasma
properties of a MHD simulation of the solar surface. The large scale
variations in our method are estimated by shifting and correlating
two signals of the same region as observed from two different view
directions. This result is then introduced as an initial height estimate
in a least squares optimization algorithm in order to reproduce smaller
scale structures. This method has been developed to be applied to the
high resolution images of the PHI instrument on board Solar Orbiter or
similar instruments on other Sun-observing spacecraft. It will allow
to perform direct stereoscopic studies of solar surface observations
in different wavelengths of the solar spectrum. Preliminary results,
advantages and limitations, applications and particular considerations
for PHI data will be discussed.

---------------------------------------------------------
Title: Propagating brightenings in small loop-like structures in
the quiet-Sun corona: Observations from Solar Orbiter/EUI
Authors: Mandal, Sudip; Peter, Hardi; Chitta, Lakshmi Pradeep;
Solanki, Sami K.; Aznar Cuadrado, Regina; Teriaca, Luca; Schühle,
Udo; Berghmans, David; Auchère, Frédéric
2021A&A...656L..16M Altcode: 2021arXiv211108106M
Brightenings observed in solar extreme-ultraviolet images are generally
interpreted as signatures of micro- or nanoflares occurring in the
transition region or at coronal temperatures. Recent observations
with the Extreme Ultraviolet Imager (EUI) on board Solar Orbiter have
revealed the smallest of such brightenings (called campfires) in the
quiet-Sun corona. Analyzing EUI 174 Å data obtained at a resolution
of about 400 km on the Sun with a cadence of 5 s on 30 May 2020,
we report here a number of cases in which these campfires exhibit
propagating signatures along their apparently small (3-5 Mm) loop-like
structures. The measured propagation speeds are generally between 25
km s−1 and 60 km s−1. If the loop plasma is
assumed to be at a million Kelvin, these apparent motions would be
slower than the local sound speed. Furthermore, these brightenings
exhibit nontrivial propagation characteristics such as bifurcation,
merging, reflection, and repeated plasma ejections. We suggest that
these features are manifestations of the internal dynamics of these
small-scale magnetic structures and could provide important insights
into the dynamic response (∼40 s) of the loop plasma to the heating
events and also into the locations of the heating events themselves. Movies associated to Figs 2-5, A.1, and B.1 are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142041/olm">https://www.aanda.org</A>

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Title: The first coronal mass ejection observed in both visible-light
and UV H I Ly-α channels of the Metis coronagraph on board Solar
Orbiter
Authors: Andretta, V.; Bemporad, A.; De Leo, Y.; Jerse, G.; Landini,
F.; Mierla, M.; Naletto, G.; Romoli, M.; Sasso, C.; Slemer, A.;
Spadaro, D.; Susino, R.; Talpeanu, D. -C.; Telloni, D.; Teriaca, L.;
Uslenghi, M.; Antonucci, E.; Auchère, F.; Berghmans, D.; Berlicki,
A.; Capobianco, G.; Capuano, G. E.; Casini, C.; Casti, M.; Chioetto,
P.; Da Deppo, V.; Fabi, M.; Fineschi, S.; Frassati, F.; Frassetto,
F.; Giordano, S.; Grimani, C.; Heinzel, P.; Liberatore, A.; Magli, E.;
Massone, G.; Messerotti, M.; Moses, D.; Nicolini, G.; Pancrazzi, M.;
Pelizzo, M. -G.; Romano, P.; Schühle, U.; Stangalini, M.; Straus,
Th.; Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Aznar
Cuadrado, R.; Bruno, R.; Ciaravella, A.; D'Amicis, R.; Lamy, P.;
Lanzafame, A.; Malvezzi, A. M.; Nicolosi, P.; Nisticò, G.; Peter,
H.; Plainaki, C.; Poletto, L.; Reale, F.; Solanki, S. K.; Strachan,
L.; Tondello, G.; Tsinganos, K.; Velli, M.; Ventura, R.; Vial, J. -C.;
Woch, J.; Zimbardo, G.
2021A&A...656L..14A Altcode:
Context. The Metis coronagraph on board Solar Orbiter offers a new
view of coronal mass ejections (CMEs), observing them for the first
time with simultaneous images acquired with a broad-band filter in
the visible-light interval and with a narrow-band filter around the
H I Ly-α line at 121.567 nm, the so-called Metis UV channel. 
Aims: We show the first Metis observations of a CME, obtained on 16
and 17 January 2021. The event was also observed by the EUI/FSI imager
on board Solar Orbiter, as well as by other space-based coronagraphs,
such as STEREO-A/COR2 and SOHO/LASCO/C2, whose images are combined here
with Metis data. Methods: Different images are analysed here
to reconstruct the 3D orientation of the expanding CME flux rope using
the graduated cylindrical shell model. This also allows us to identify
the possible location of the source region. Measurements of the CME
kinematics allow us to quantify the expected Doppler dimming in the
Ly-α channel. Results: Observations show that most CME features
seen in the visible-light images are also seen in the Ly-α images,
although some features in the latter channel appear more structured
than their visible-light counterparts. We estimated the expansion
velocity of this event to be below 140 km s−1. Hence,
these observations can be understood by assuming that Doppler dimming
effects do not strongly reduce the Ly-α emission from the CME. These
velocities are comparable with or smaller than the radial velocities
inferred from the same data in a similar coronal structure on the
east side of the Sun. Conclusions: The first observations by
Metis of a CME demonstrate the capability of the instrument to provide
valuable and novel information on the structure and dynamics of these
coronal events. Considering also its diagnostics capabilities regarding
the conditions of the ambient corona, Metis promises to significantly
advance our knowledge of such phenomena. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202142407/olm">https://www.aanda.org</A>

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Title: Capturing transient plasma flows and jets in the solar corona
Authors: Chitta, L. P.; Solanki, S. K.; Peter, H.; Aznar Cuadrado,
R.; Teriaca, L.; Schühle, U.; Auchère, F.; Berghmans, D.; Kraaikamp,
E.; Gissot, S.; Verbeeck, C.
2021A&A...656L..13C Altcode: 2021arXiv210915106C
Intensity bursts in ultraviolet (UV) to X-ray wavelengths and plasma
jets are typical signatures of magnetic reconnection and the associated
impulsive heating of the solar atmospheric plasma. To gain new insights
into the process, high-cadence observations are required to capture
the rapid response of plasma to magnetic reconnection as well as the
highly dynamic evolution of jets. Here, we report the first 2 s cadence
extreme-UV observations recorded by the 174 Å High Resolution Imager of
the Extreme Ultraviolet Imager on board the Solar Orbiter mission. These
observations, covering a quiet-Sun coronal region, reveal the onset
signatures of magnetic reconnection as localized heating events. These
localized sources then exhibit repeated plasma eruptions or jet
activity. Our observations show that this spatial morphological change
from localized sources to jet activity could occur rapidly on timescales
of about 20 s. The jets themselves are intermittent and are produced
from the source region on timescales of about 20 s. In the initial
phases of these events, plasma jets are observed to exhibit speeds,
as inferred from propagating intensity disturbances, in the range of
100 km s−1 to 150 km s−1. These jets then
propagate to lengths of about 5 Mm. We discuss examples of bidirectional
and unidirectional jet activity observed to have been initiated from
the initially localized bursts in the corona. The transient nature
of coronal bursts and the associated plasma flows or jets along with
their dynamics could provide a benchmark for magnetic reconnection
models of coronal bursts and jets. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202141683/olm">https://www.aanda.org</A>

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Title: Reconstructing solar irradiance from historical Ca II K
observations. I. Method and its validation
Authors: Chatzistergos, Theodosios; Krivova, Natalie A.; Ermolli,
Ilaria; Yeo, Kok Leng; Mandal, Sudip; Solanki, Sami K.; Kopp, Greg;
Malherbe, Jean-Marie
2021A&A...656A.104C Altcode: 2021arXiv210905844C
Context. Knowledge of solar irradiance variability is critical to
Earth's climate models and understanding the solar influence on Earth's
climate. Direct solar irradiance measurements have only been available
since 1978. Reconstructions of past variability typically rely on
sunspot data. However, sunspot records provide only indirect information
on the facular and network regions, which are decisive contributors to
irradiance variability on timescales of the solar cycle and longer. Aims: Our ultimate goal is to reconstruct past solar irradiance
variations using historical full-disc Ca II K observations to describe
the facular contribution independently of sunspot observations. Here,
we develop the method and test it extensively by using modern CCD-based
(charge-coupled device) Ca II K observations. We also carry out initial
tests on two photographic archives. Methods: We employ carefully
reduced and calibrated Ca II K images from 13 datasets, including some
of the most prominent series, such as those from the Meudon, Mt Wilson,
and Rome observatories. We convert them to unsigned magnetic field
maps and then use them as input to the adapted Spectral and Total
Irradiance Reconstruction (SATIRE) model to reconstruct total solar
irradiance (TSI) variations over the period 1978-2019, for which
direct irradiance measurements are available. Results: The
reconstructed irradiance from the analysed Ca II K archives agrees well
with direct irradiance measurements and existing reconstructions. The
model also returns good results on data taken with different bandpasses
and images with low spatial resolution. Historical Ca II K archives
suffer from numerous inconsistencies, but we show that these archives
can still be used to reconstruct TSI with reasonable accuracy provided
the observations are accurately processed and the effects of changes
in instrumentation and instrumental parameters are identified and
accounted for. The reconstructions are relatively insensitive to the
TSI reference record used to fix the single free parameter of the
model. Furthermore, even employment of a series, itself reconstructed
from Ca II K data, as a reference for further reconstructions returns
nearly equally accurate results. This will enable the Ca II K archives
without an overlap with direct irradiance measurements to be used to
reconstruct past irradiance. Conclusions: By using the unsigned
magnetic maps of the Sun reconstructed from modern high-quality Ca
II K observations as input into the SATIRE model, we can reconstruct
solar irradiance variations nearly as accurately as from directly
recorded magnetograms. Historical Ca II K observations can also be
used for past irradiance reconstructions but need additional care,
for example identifying and accounting for discontinuities and changes
in the quality of the data with time.

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Title: First observations from the SPICE EUV spectrometer on Solar
Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A.; Grundy, T.; Guest,
S.; Leeks, S.; Sidher, S.; Auchère, F.; Carlsson, M.; Hassler, D.;
Peter, H.; Aznar Cuadrado, R.; Buchlin, É.; Caminade, S.; DeForest,
C.; Fredvik, T.; Haberreiter, M.; Harra, L.; Janvier, M.; Kucera, T.;
Müller, D.; Parenti, S.; Schmutz, W.; Schühle, U.; Solanki, S. K.;
Teriaca, L.; Thompson, W. T.; Tustain, S.; Williams, D.; Young, P. R.;
Chitta, L. P.
2021A&A...656A..38F Altcode: 2021arXiv211011252F
 Aims: We present first science observations taken during the
commissioning activities of the Spectral Imaging of the Coronal
Environment (SPICE) instrument on the ESA/NASA Solar Orbiter
mission. SPICE is a high-resolution imaging spectrometer operating at
extreme ultraviolet (EUV) wavelengths. In this paper we illustrate
the possible types of observations to give prospective users a
better understanding of the science capabilities of SPICE. 
Methods: We have reviewed the data obtained by SPICE between April
and June 2020 and selected representative results obtained with
different slits and a range of exposure times between 5 s and 180
s. Standard instrumental corrections have been applied to the raw
data. Results: The paper discusses the first observations
of the Sun on different targets and presents an example of the full
spectra from the quiet Sun, identifying over 40 spectral lines from
neutral hydrogen and ions of carbon, oxygen, nitrogen, neon, sulphur,
magnesium, and iron. These lines cover the temperature range between
20 000 K and 1 million K (10 MK in flares), providing slices of the
Sun's atmosphere in narrow temperature intervals. We provide a list
of count rates for the 23 brightest spectral lines. We show examples
of raster images of the quiet Sun in several strong transition region
lines, where we have found unusually bright, compact structures in the
quiet Sun network, with extreme intensities up to 25 times greater
than the average intensity across the image. The lifetimes of these
structures can exceed 2.5 hours. We identify them as a transition
region signature of coronal bright points and compare their areas and
intensity enhancements. We also show the first above-limb measurements
with SPICE above the polar limb in C III, O VI, and Ne VIII lines, and
far off limb measurements in the equatorial plane in Mg IX, Ne VIII,
and O VI lines. We discuss the potential to use abundance diagnostics
methods to study the variability of the elemental composition that can
be compared with in situ measurements to help confirm the magnetic
connection between the spacecraft location and the Sun's surface,
and locate the sources of the solar wind. Conclusions: The
SPICE instrument successfully performs measurements of EUV spectra
and raster images that will make vital contributions to the scientific
success of the Solar Orbiter mission.

---------------------------------------------------------
Title: First light observations of the solar wind in the outer corona
with the Metis coronagraph
Authors: Romoli, M.; Antonucci, E.; Andretta, V.; Capuano, G. E.; Da
Deppo, V.; De Leo, Y.; Downs, C.; Fineschi, S.; Heinzel, P.; Landini,
F.; Liberatore, A.; Naletto, G.; Nicolini, G.; Pancrazzi, M.; Sasso,
C.; Spadaro, D.; Susino, R.; Telloni, D.; Teriaca, L.; Uslenghi,
M.; Wang, Y. -M.; Bemporad, A.; Capobianco, G.; Casti, M.; Fabi, M.;
Frassati, F.; Frassetto, F.; Giordano, S.; Grimani, C.; Jerse, G.;
Magli, E.; Massone, G.; Messerotti, M.; Moses, D.; Pelizzo, M. -G.;
Romano, P.; Schühle, U.; Slemer, A.; Stangalini, M.; Straus, T.;
Volpicelli, C. A.; Zangrilli, L.; Zuppella, P.; Abbo, L.; Auchère,
F.; Aznar Cuadrado, R.; Berlicki, A.; Bruno, R.; Ciaravella, A.;
D'Amicis, R.; Lamy, P.; Lanzafame, A.; Malvezzi, A. M.; Nicolosi,
P.; Nisticò, G.; Peter, H.; Plainaki, C.; Poletto, L.; Reale, F.;
Solanki, S. K.; Strachan, L.; Tondello, G.; Tsinganos, K.; Velli,
M.; Ventura, R.; Vial, J. -C.; Woch, J.; Zimbardo, G.
2021A&A...656A..32R Altcode: 2021arXiv210613344R
In this work, we present an investigation of the wind in the solar
corona that has been initiated by observations of the resonantly
scattered ultraviolet emission of the coronal plasma obtained with
UVCS-SOHO, designed to measure the wind outflow speed by applying
Doppler dimming diagnostics. Metis on Solar Orbiter complements the
UVCS spectroscopic observations that were performed during solar
activity cycle 23 by simultaneously imaging the polarized visible
light and the H I Lyman-α corona in order to obtain high spatial and
temporal resolution maps of the outward velocity of the continuously
expanding solar atmosphere. The Metis observations, taken on May 15,
2020, provide the first H I Lyman-α images of the extended corona
and the first instantaneous map of the speed of the coronal plasma
outflows during the minimum of solar activity and allow us to identify
the layer where the slow wind flow is observed. The polarized visible
light (580-640 nm) and the ultraviolet H I Lyα (121.6 nm) coronal
emissions, obtained with the two Metis channels, were combined in
order to measure the dimming of the UV emission relative to a static
corona. This effect is caused by the outward motion of the coronal
plasma along the direction of incidence of the chromospheric photons
on the coronal neutral hydrogen. The plasma outflow velocity was then
derived as a function of the measured Doppler dimming. The static
corona UV emission was simulated on the basis of the plasma electron
density inferred from the polarized visible light. This study leads
to the identification, in the velocity maps of the solar corona, of
the high-density layer about ±10° wide, centered on the extension
of a quiet equatorial streamer present at the east limb - the coronal
origin of the heliospheric current sheet - where the slowest wind
flows at about 160 ± 18 km s−1 from 4 R⊙
to 6 R⊙. Beyond the boundaries of the high-density layer,
the wind velocity rapidly increases, marking the transition between
slow and fast wind in the corona.

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Title: Similarities of magnetoconvection in the umbra and in the
penumbra of sunspots
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
2021A&A...655A..61L Altcode: 2021arXiv211001352L
Context. It is unclear why there is a rather sharp boundary in
sunspots between the umbra and the penumbra. Both regions exhibit
magnetoconvection, which manifests in penumbral filaments in the
penumbra and in umbral dots in the umbra. Aims: Here we compare
the physical properties of umbral dots and penumbral filaments. Our
goal is to understand how the properties of these convective features
change across the boundary between the umbra and the penumbra
and how this is related to the rapid increase in brightness at the
umbra-penumbra boundary. Methods: We derived ensemble averages
of the physical properties of different types of convective features
based on observations of two sunspots with Hinode. Results:
There are strong similarities between the convective features in the
outer parts of the umbra and the ones in the penumbra, with most
physical parameters being smooth and continuous functions of the
length of the features. Conclusions: Our results indicate
that the transition in brightness from the umbra to the penumbra
is solely caused by an increased effectiveness of magnetoconvection
within individual convective cells. There is no significant difference
in the number density of convective elements between the outer umbra
and the inner penumbra. Penumbral filaments exhibit a larger area and
a higher brightness compared to umbral dots. It is still unclear how
exactly the underlying magnetic field causes the increase in the size
and brightness of convective features in the penumbra.

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Title: First results of the CAST-RADES haloscope search for axions
at 34.67 μeV
Authors: Álvarez Melcón, A.; Arguedas Cuendis, S.; Baier, J.; Barth,
K.; Bräuninger, H.; Calatroni, S.; Cantatore, G.; Caspers, F.; Castel,
J. F.; Cetin, S. A.; Cogollos, C.; Dafni, T.; Davenport, M.; Dermenev,
A.; Desch, K.; Díaz-Morcillo, A.; Döbrich, B.; Fischer, H.; Funk,
W.; Gallego, J. D.; García Barceló, J. M.; Gardikiotis, A.; Garza,
J. G.; Gimeno, B.; Gninenko, S.; Golm, J.; Hasinoff, M. D.; Hoffmann,
D. H. H.; Irastorza, I. G.; Jakovčić, K.; Kaminski, J.; Karuza,
M.; Lakić, B.; Laurent, J. M.; Lozano-Guerrero, A. J.; Luzón,
G.; Malbrunot, C.; Maroudas, M.; Miralda-Escudé, J.; Mirallas, H.;
Miceli, L.; Navarro, P.; Ozbey, A.; Özbozduman, K.; Peña Garay, C.;
Pivovaroff, M. J.; Redondo, J.; Ruz, J.; Ruiz Chóliz, E.; Schmidt, S.;
Schumann, M.; Semertzidis, Y. K.; Solanki, S. K.; Stewart, L.; Tsagris,
I.; Vafeiadis, T.; Vogel, J. K.; Widmann, E.; Wuensch, W.; Zioutas, K.
2021JHEP...10..075A Altcode: 2021arXiv210413798A
We present results of the Relic Axion Dark-Matter Exploratory Setup
(RADES), a detector which is part of the CERN Axion Solar Telescope
(CAST), searching for axion dark matter in the 34.67 μeV mass range. A
radio frequency cavity consisting of 5 sub-cavities coupled by inductive
irises took physics data inside the CAST dipole magnet for the first
time using this filter-like haloscope geometry. An exclusion limit
with a 95% credibility level on the axion-photon coupling constant
of gaγ ≳ 4 × 10−13 GeV−1
over a mass range of 34.6738 μeV &lt; ma&lt; 34.6771 μeV
is set. This constitutes a significant improvement over the current
strongest limit set by CAST at this mass and is at the same time one of
the most sensitive direct searches for an axion dark matter candidate
above the mass of 25 μeV. The results also demonstrate the feasibility
of exploring a wider mass range around the value probed by CAST-RADES
in this work using similar coherent resonant cavities.

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Title: Predictions of Astrometric Jitter for Sun-like
Stars. II. Dependence on Inclination, Metallicity, and Active-region
Nesting
Authors: Sowmya, K.; Nèmec, N. -E.; Shapiro, A. I.; Işık, E.;
Witzke, V.; Mints, A.; Krivova, N. A.; Solanki, S. K.
2021ApJ...919...94S Altcode: 2021arXiv210701493S
Ultra-precise astrometry from the Gaia mission is expected to lead to
astrometric detections of more than 20,000 exoplanets in our Galaxy. One
of the factors that could hamper such detections is the astrometric
jitter caused by the magnetic activity of the planet host stars. In
our previous study, we modeled astrometric jitter for the Sun observed
equator-on. In this work, we generalize our model and calculate the
photocenter jitter as it would be measured by the Gaia and Small-JASMINE
missions for stars with solar rotation rate and effective temperature,
but with various values of the inclination angle of the stellar rotation
axis. In addition, we consider the effect of metallicity and of nesting
of active regions (i.e., the tendency of active regions to emerge in
the vicinity of each other). We find that, while the jitter of stars
observed equator-on does not have any long-term trends and can be
easily filtered out, the photocenters of stars observed out of their
equatorial planes experience systematic shifts over the course of
the activity cycle. Such trends allow the jitter to be detected with
continuous measurements, in which case it can interfere with planet
detectability. An increase in the metallicity is found to increase the
jitter caused by stellar activity. Active-region nesting can further
enhance the peak-to-peak amplitude of the photocenter jitter to a
level that could be detected by Gaia.

---------------------------------------------------------
Title: The relationship between bipolar magnetic regions and their
sunspots
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.; Jiang, J.
2021A&A...654A..28Y Altcode: 2021arXiv210914313Y
Context. The relationship between bipolar magnetic regions (BMRs)
and their sunspots is an important property of the solar magnetic
field, but it is not well constrained. One consequence is that it is a
challenge for surface flux transport models (SFTMs) based on sunspot
observations to determine the details of BMR emergence, which they
require as input, from such data. Aims: We aimed to establish
the relationship between the amount of magnetic flux in newly emerged
BMRs and the area of the enclosed sunspots, and examine the results
of its application to an established SFTM. Methods: Earlier
attempts to constrain BMR magnetic flux were hindered by the fact that
there is no extensive and reliable record of the magnetic and physical
properties of newly emerged BMRs currently available. We made use of
the empirical model of the relationship between the disc-integrated
facular and network magnetic flux and the total surface coverage by
sunspots reported in a recent study. The structure of the model is such
that it enabled us to establish, from these disc-integrated quantities,
an empirical relationship between the magnetic flux and sunspot area
of individual newly emerged BMRs, circumventing the lack of any proper
BMR database. Results: Applying the constraint on BMR magnetic
flux derived here to an established SFTM retained its key features,
in particular its ability to replicate various independent datasets
and the correlation between the model output polar field at the end
of each cycle and the observed strength of the following cycle. The
SFTM output indicates that facular and network magnetic flux rises
with increasing sunspot magnetic flux at a slowing rate such that
it appears to gradually saturate. This is analogous to what earlier
studies comparing disc-integrated quantities sensitive to the amount
of faculae and network present to sunspot indices had reported. The
activity dependence of the ratio of facular and network flux to sunspot
flux is consistent with the findings of recent studies: although the
Sun is faculae-dominated (such that its brightness is mostly positively
correlated with activity), it is only marginally so as facular and
network brightening and sunspot darkening appear to be closely balanced.

---------------------------------------------------------
Title: Correction of atmospheric stray light in restored slit spectra
Authors: Saranathan, S.; van Noort, M.; Solanki, S. K.
2021A&A...653A..17S Altcode: 2021arXiv211202648S
Context. A long-standing issue in solar ground-based observations has
been the contamination of data due to stray light, which is particularly
relevant in inversions of spectropolarimetric data. Aims: We aim
to build on a statistical method of correcting stray-light contamination
due to residual high-order aberrations and apply it to ground-based slit
spectra. Methods: The observations were obtained at the Swedish
Solar Telescope, and restored using the multi-frame blind deconvolution
restoration procedure. Using the statistical properties of seeing,
we created artificially degraded synthetic images generated from
magneto-hydrodynamic simulations. We then compared the synthetic data
with the observations to derive estimates of the amount of the residual
stray light in the observations. In the final step, the slit spectra
were deconvolved with a stray-light point spread function to remove
the residual stray light from the observations. Results: The RMS
granulation contrasts of the deconvolved spectra were found to increase
to approximately 12.5%, from 9%. Spectral lines, on average, were found
to become deeper in the granules and shallower in the inter-granular
lanes, indicating systematic changes to gradients in temperature. The
deconvolution was also found to increase the redshifts and blueshifts
of spectral lines, suggesting that the velocities of granulation in
the solar photosphere are higher than had previously been observed.

---------------------------------------------------------
Title: Ti I lines at 2.2 μm as probes of the cooler regions of
sunspots
Authors: Smitha, H. N.; Castellanos Durán, J. S.; Solanki, S. K.;
Tiwari, S. K.
2021A&A...653A..91S Altcode: 2021arXiv210701247S
Context. The sunspot umbra harbours the coolest plasma on the solar
surface due to the presence of strong magnetic fields. The atomic
lines that are routinely used to observe the photosphere have weak
signals in the umbra and are often swamped by molecular lines. This
makes it harder to infer the properties of the umbra, especially in
the darkest regions. Aims: The lines of the Ti I multiplet
at 2.2 μm are formed mainly at temperatures ≤4500 K and are not
known to be affected by molecular blends in sunspots. Since the first
systematic observations in the 1990s, these lines have been seldom
observed due to the instrumental challenges involved at these longer
wavelengths. We revisit these lines and investigate their formation
in different solar features. Methods: We synthesized the
Ti I multiplet using a snapshot from 3D magnetohydrodynamic (MHD)
simulations of a sunspot and explored the properties of two of its
lines in comparison with two commonly used iron lines, at 6302.5 Å and
1.5648 μm. Results: We find that the Ti I lines have stronger
signals than the Fe I lines in both intensity and polarization in the
sunspot umbra and in penumbral spines. They have little to no signal
in the penumbral filaments and the quiet Sun, at μ = 1. Their strong
and well-split profiles in the dark umbra are less affected by stray
light. Consequently, inside the sunspot, it is easier to invert these
lines and to infer the atmospheric properties as compared to the iron
lines. Conclusions: The Cryo-NIRSP instrument at the DKIST will
provide the first-ever high-resolution observations in this wavelength
range. In this preparatory study, we demonstrate the unique temperature
and magnetic sensitivities of the Ti multiplet by probing the Sun's
coolest regions, which are not favourable for the formation of other
commonly used spectral lines. We thus expect such observations to
advance our understanding of sunspot properties.

---------------------------------------------------------
Title: MPS-ATLAS: A fast all-in-one code for synthesising stellar
spectra
Authors: Witzke, V.; Shapiro, A. I.; Cernetic, M.; Tagirov, R. V.;
Kostogryz, N. M.; Anusha, L. S.; Unruh, Y. C.; Solanki, S. K.; Kurucz,
R. L.
2021A&A...653A..65W Altcode: 2021arXiv210513611W
Context. Stellar spectral synthesis is essential for various
applications, ranging from determining stellar parameters to
comprehensive stellar variability calculations. New observational
resources as well as advanced stellar atmosphere modelling, taking three
dimensional effects from radiative magnetohydrodynamics calculations
into account, require a more efficient radiative transfer. Aims:
For accurate, fast and flexible calculations of opacity distribution
functions (ODFs), stellar atmospheres, and stellar spectra, we developed
an efficient code building on the well-established ATLAS9 code. The new
code also paves the way for easy and fast access to different elemental
compositions in stellar calculations. Methods: For the generation
of ODF tables, we further developed the well-established DFSYNTHE code
by implementing additional functionality and a speed-up by employing
a parallel computation scheme. In addition, the line lists used can be
changed from Kurucz's recent lists. In particular, we implemented the
VALD3 line list. Results: A new code, the Merged Parallelised
Simplified ATLAS, is presented. It combines the efficient generation of
ODF, atmosphere modelling, and spectral synthesis in local thermodynamic
equilibrium, therefore being an all-in-one code. This all-in-one code
provides more numerical functionality and is substantially faster
compared to other available codes. The fully portable MPS-ATLAS code
is validated against previous ATLAS9 calculations, the PHOENIX code
calculations, and high-quality observations.

---------------------------------------------------------
Title: A Multi-Purpose Heliophysics L4 Mission
Authors: Posner, A.; Arge, C. N.; Staub, J.; StCyr, O. C.; Folta,
D.; Solanki, S. K.; Strauss, R. D. T.; Effenberger, F.; Gandorfer,
A.; Heber, B.; Henney, C. J.; Hirzberger, J.; Jones, S. I.; Kühl,
P.; Malandraki, O.; Sterken, V. J.
2021SpWea..1902777P Altcode:
The Earth-Sun Lagrangian point 4 is a meta-stable location at 1 AU from
the Sun, 60° ahead of Earth's orbit. It has an uninterrupted view of
the solar photosphere centered on W60, the Earth's nominal magnetic
field connection to the Sun. Such a mission on its own would serve
as a solar remote sensing observatory that would oversee the entire
solar radiation hemisphere with significant relevance for protecting
Moon and Mars explorers from radiation exposure. In combination with
appropriately planned observatories at L1 and L5, the three spacecraft
would provide 300° longitude coverage of photospheric magnetic field
structure, and allow continuous viewing of both solar poles, with
&gt;3.6° elevation. Ideally, the L4 and L5 missions would orbit the Sun
with a 7.2° inclination out of the heliographic equator, 14.5° out of
the ecliptic plane. We discuss the impact of extending solar magnetic
field observations in both longitude and latitude to improve global
solar wind modeling and, with the development of local helioseismology,
the potential for long-term solar activity forecasting. Such a mission
would provide a unique opportunity for interplanetary and interstellar
dust science. It would significantly add to reliability of operational
observations on fast coronal mass ejections directed at Earth and
for human Mars explorers on their round-trip journey. The L4 mission
concept is technically feasible, and is scientifically compelling.

---------------------------------------------------------
Title: Magnetic imaging of the outer solar atmosphere (MImOSA)
Authors: Peter, H.; Ballester, E. Alsina; Andretta, V.; Auchère, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; Alemán, T. del Pino; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Štěpán, J.; Teriaca, L.; Bueno, J. Trujillo
2021ExA...tmp...95P Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability of
planets orbiting these host stars. Although the magnetic field at the
surface of the Sun is reasonably well characterised by observations,
the information on the magnetic field in the higher atmospheric layers
is mainly indirect. This lack of information hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution
and high sensitivity. (b) An extreme-UV-to-IR coronagraph that is
designed to measure the large-scale magnetic field in the corona with
an aperture of about 40 cm. (c) An extreme-UV imaging polarimeter
based on a 30 cm telescope that combines high throughput in the
extreme UV with polarimetry to connect the magnetic measurements
of the other two instruments. Placed in a near-Earth orbit, the data
downlink would be maximised, while a location at L4 or L5 would provide
stereoscopic observations of the Sun in combination with Earth-based
observatories. This mission to measure the magnetic field will finally
unlock the driver of the dynamics in the outer solar atmosphere and
thereby will greatly advance our understanding of the Sun and the
heliosphere.

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Title: On the size distribution of spots within sunspot groups
Authors: Mandal, Sudip; Krivova, Natalie A.; Cameron, Robert; Solanki,
Sami K.
2021A&A...652A...9M Altcode: 2021arXiv210403534M
The size distribution of sunspots provides key information about
the generation and emergence processes of the solar magnetic
field. Previous studies of size distribution have primarily focused
on either the whole group or individual spot areas. In this paper we
investigate the organisation of spot areas within sunspot groups. In
particular, we analysed the ratio (R) of the area of the biggest spot
(Abig_spot) inside a group, to the total area of that group
(Agroup). We used sunspot observations from Kislovodsk,
Pulkovo, and Debrecen observatories, together covering solar cycles
17-24. We find that at the time when the group area reaches its maximum,
the single biggest spot in a group typically occupies about 60% of the
group area. For half of all groups, R lies in the range between roughly
50% and 70%. We also find R to change with Agroup, such that
R reaches a maximum of about 0.65 for groups with Agroup
≈ 200 μHem and then remains at about 0.6 for larger groups. Our
findings imply a scale-invariant emergence pattern, providing an
observational constraint on the emergence process. Furthermore,
extrapolation of our results to larger sunspot groups may have a
bearing on the giant unresolved starspot features found in Doppler
images of highly active Sun-like stars. Our results suggest that such
giant features are composed of multiple spots, with the largest spot
occupying roughly 55-75% of the total group area (i.e., the area of
the giant starspots seen in Doppler images).

---------------------------------------------------------
Title: Slow magneto-acoustic waves in simulations of a solar plage
region carry enough energy to heat the chromosphere
Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K.
2021A&A...652A..43Y Altcode: 2021arXiv210502932Y
 Aims: We study the properties of slow magneto-acoustic waves
that are naturally excited as a result of turbulent convection and we
investigate their role in the energy balance of a plage region using
three dimensional radiation magnetohydrodynamic simulations. 
Methods: To follow slow magneto-acoustic waves traveling along the
magnetic field lines, we selected 25 seed locations inside a strong
magnetic element and tracked the associated magnetic field lines both
in space and time. We calculate the longitudinal component (i.e.,
parallel to the field) of velocity at each grid point along the field
line and compute the temporal power spectra at various heights above
the mean solar surface. Additionally, the horizontally-averaged (over
the whole domain) frequency power spectra for both longitudinal and
vertical (i.e., the component perpendicular to the surface) components
of velocity are calculated using time series at fixed locations. To
compare our results with the observations, we degrade the simulation
data with Gaussian kernels having a full width at half maxium of 100
km and 200 km and calculate the horizontally-averaged power spectra
for the vertical component of velocity using time series at fixed
locations. Results: The power spectra of the longitudinal
component of velocity, averaged over 25 field lines in the core of
a kG magnetic flux concentration reveal that the dominant period
of oscillations shifts from ∼6.5 min in the photosphere to ∼4
min in the chromosphere. This behavior is consistent with earlier
studies that were restricted to vertically propagating waves. At the
same time, the velocity power spectra, averaged horizontally over
the whole domain, show that low frequency waves (∼6.5 min period)
may reach well into the chromosphere. In addition, the power spectra
at high frequencies follow a power law with an exponent close to
−5/3, suggestive of turbulent excitation. Moreover, waves with
frequencies above 5 mHz propagating along different field lines
are found to be out of phase with each other, even within a single
magnetic concentration. The horizontally-averaged power spectra of
the vertical component of velocity at various effective resolutions
show that the observed acoustic wave energy fluxes are underestimated
by a factor of three, even if determined from observations carried
out at a high spatial resolution of 200 km. Since the waves propagate
along the non-vertical field lines, measuring the velocity component
along the line-of-sight, rather than along the field, contributes
significantly to this underestimation. Moreover, this underestimation of
the energy flux indirectly indicates the importance of high-frequency
waves that are shown to have a smaller spatial coherence and are thus
more strongly influenced by the spatial averaging effect compared to
low-frequency waves. Conclusions: Inside a plage region, there
is on average a significant fraction of low frequency waves leaking
into the chromosphere due to inclined magnetic field lines. Our results
show that longitudinal waves carry (just) enough energy to heat the
chromosphere in the solar plage. However, phase differences between
waves traveling along different field lines within a single magnetic
concentration can lead to underestimations of the wave energy flux
due to averaging effects in degraded simulation data and, similarly,
in observations with lower spatial resolution. We find that current
observations (with spatial resolution around 200 km) underestimate the
energy flux by roughly a factor of three - or more if the observations
are carried out at a lower spatial resolution. We expect that even
at a very high resolution, which is expected with the next generation
of telescopes such as DKIST and the EST, less than half, on average,
of the energy flux carried by such waves will be detected if only the
line-of-sight component of the velocity is measured.

---------------------------------------------------------
Title: How rare are counter Evershed flows?
Authors: Castellanos Durán, J. S.; Lagg, A.; Solanki, S. K.
2021A&A...651L...1C Altcode: 2021arXiv210605592S
One of the main characteristics of sunspot penumbrae is the radially
outward-directed Evershed flow. Only recently have penumbral regions
been reported with similar characteristics to normal penumbral
filaments but with an opposite direction of the flow. Such flows
directed toward the umbra are known as counter Evershed flows
(CEFs). We aim to determine the occurrence frequency of CEFs in
active regions (ARs) and to characterize their lifetime and the
prevailing conditions in the ARs. We analyzed the continuum images,
Dopplergrams, and magnetograms recorded by SDO/HMI of 97 ARs that
appeared from 2011 to 2017. We followed the ARs for 9.6 ± 1.4 days
on average. We found 384 CEFs in total, with a median value of six
CEFs per AR. Counter Evershed flows are a rather common feature,
occurring in 83.5% of all ARs regardless of the magnetic complexity
of the AR. However, CEFs were only observed, on average, during 5.9%
of the mean total duration of all the observations analyzed here. The
lifetime of CEFs follows a log-normal distribution with a median value
of 10.6−6.0+12.4 h. In addition, we report two
populations of CEFs, those that are associated with light bridges and
those that are not. We explain that the rarity of reports of CEFs in
the literature is a result of highly incomplete coverage of ARs with
spectropolarimetric data. By using the continuous observations now
routinely available from space, we are able to overcome this limitation.

---------------------------------------------------------
Title: Radiative Transfer with Opacity Distribution Functions:
Application to Narrowband Filters
Authors: Anusha, L. S.; Shapiro, A. I.; Witzke, V.; Cernetic, M.;
Solanki, S. K.; Gizon, L.
2021ApJS..255....3A Altcode: 2021arXiv210413661A
Modeling of stellar radiative intensities in various spectral passbands
plays an important role in stellar physics. At the same time, direct
calculation of the high-resolution spectrum and then integration of it
over the given spectral passband is computationally demanding due to
the vast number of atomic and molecular lines. This is particularly so
when employing three-dimensional (3D) models of stellar atmospheres. To
accelerate the calculations, one can employ approximate methods, e.g.,
the use of opacity distribution functions (ODFs). Generally, ODFs
provide a good approximation of traditional spectral synthesis, i.e.,
computation of intensities through filters with strictly rectangular
transmission functions. However, their performance strongly deteriorates
when the filter transmission noticeably changes within its passband,
which is the case for almost all filters routinely used in stellar
physics. In this context, the aims of this paper are (a) to generalize
the ODFs method for calculating intensities through filters with
arbitrary transmission functions, and (b) to study the performance of
the standard and generalized ODFs methods for calculating intensities
emergent from 3D models of stellar atmospheres. For this purpose we
use the newly developed MPS-ATLAS radiative transfer code to compute
intensities emergent from 3D cubes simulated with the radiative
magnetohydrodynamics code MURaM. The calculations are performed
in the 1.5D regime, i.e., along many parallel rays passing through
the simulated cube. We demonstrate that the generalized ODFs method
allows accurate and fast syntheses of spectral intensities and their
center-to-limb variations.

---------------------------------------------------------
Title: Forward modelling of Kepler-band variability due to faculae
and spots
Authors: Johnson, Luke J.; Norris, Charlotte M.; Unruh, Yvonne C.;
Solanki, Sami K.; Krivova, Natalie; Witzke, Veronika; Shapiro,
Alexander I.
2021MNRAS.504.4751J Altcode: 2021arXiv210411544J; 2021MNRAS.tmp.1190J
Variability observed in photometric light curves of late-type stars (on
time-scales longer than a day) is a dominant noise source in exoplanet
surveys and results predominantly from surface manifestations of stellar
magnetic activity, namely faculae and spots. The implementation of
faculae in light-curve models is an open problem, with scaling typically
based on spectra equivalent to hot stellar atmospheres or assuming a
solar-derived facular contrast. We modelled rotational (single period)
light curves of active G2, K0, M0, and M2 stars, with Sun-like surface
distributions and realistic limb-dependent contrasts for faculae and
spots. The sensitivity of light-curve variability to changes in model
parameters such as stellar inclination, feature area coverage, spot
temperature, facular region magnetic flux density, and active band
latitudes is explored. For our light-curve modelling approach we used
ACTRESS, a geometrically accurate model for stellar variability. ACTRESS
generates two-sphere maps representing stellar surfaces and populates
them with user-prescribed spot and facular region distributions. From
this, light curves can be calculated at any inclination. Quiet star limb
darkening and limb-dependent facular contrasts were derived from MURaM
3D magnetoconvection simulations using ATLAS9. 1D stellar atmosphere
models were used for the spot contrasts. We applied ACTRESS in Monte
Carlo simulations, calculating light-curve variability amplitudes in
the Kepler band. We found that, for a given spectral type and stellar
inclination, spot temperature and spot area coverage have the largest
effect on variability of all simulation parameters. For a spot coverage
of $1{{\ \rm per\ cent}}$, the typical variability of a solar-type
star is around 2 parts per thousand. The presence of faculae clearly
affects the mean brightness and light-curve shape, but has relatively
little influence on the variability.

---------------------------------------------------------
Title: Coronal loops in a box: 3D models of their internal structure,
dynamics and heating
Authors: Breu, C. A.; Peter, H.; Cameron, R.; Solanki, S.; Przybylski,
D.; Chitta, L.
2021AAS...23810606B Altcode:
The corona of the Sun, and probably also of other stars, is built
up by loops defined through the magnetic field. They vividly appear
in solar observations in the extreme UV and X-rays. High-resolution
observations show individual strands with diameters down to a few 100
km, and so far it remains open what defines these strands, in particular
their width, and where the energy to heat them is generated. The
aim of our study is to understand how the magnetic field couples the
different layers of the solar atmosphere, how the energy generated
by magnetoconvection is transported into the upper atmosphere and
dissipated, and how this process determines the scales of observed
bright strands in the loop. To this end, we conduct 3D resistive
MHD simulations with the MURaM code. We include the effects of heat
conduction, radiative transfer and optically thin radiative losses.We
study an isolated coronal loop that is rooted with both footpoints
in a shallow convection zone layer. To properly resolve the internal
structure of the loop while limiting the size of the computational box,
the coronal loop is modelled as a straightened magnetic flux tube. By
including part of the convection zone, we drive the evolution of
the corona self-consistently by magnetoconvection. We find that
the energy injected into the loop is generated by internal coherent
motions within strong magnetic elements. The resulting Poynting
flux is channelled into the loop in vortex tubes forming a magnetic
connection between the photosphere and corona, where it is dissipated
and heats the upper atmosphere. The coronal emission as it would
be observed in solar extreme UV or X-ray observations, e.g. with AIA
or XRT, shows transient bright strands.The widths of these strands are
consistent with observations. From our model we find that the width
of the strands is governed by the size of the individual photospheric
magnetic field concentrations where the field line through these strands
are rooted. Essentially, each coronal strand is rooted in a single
magnetic patch in the photosphere, and the energy to heat the strand is
generated by internal motions within this magnetic concentration. With this model we can build a coherent picture of how energy and
matter are transported into the upper solar atmosphere and how these
processes structure the interior of coronal loops.

---------------------------------------------------------
Title: How wrong are the results of inverting Fe I lines when NLTE
and 3D radiative transfer effects are ignored?
Authors: Narayanamurthy, S.; Holzreuter, R.; van Noort, M.; Solanki, S.
2021AAS...23811305N Altcode:
The Fe I 6301.5 Å and 6302.5 Å lines are widely used to probe the
solar photosphere. They are known to be affected by the non-local
thermodynamic equilibrium (NLTE) conditions due to the ultraviolet
overionisation of iron atoms in the solar atmosphere. This leads
to deviations in their level populations based on Saha-Boltzmann
statistics. When inverting their Stokes profiles to determine
atmospheric parameters, the NLTE effects are often neglected and
other quantities are tweaked to compensate for deviations from the
LTE. In this work, we discuss how the routinely employed LTE inversion
introduces errors in the derived atmospheric quantities. We show that
when the NLTE effects are neglected, these errors can be as high
as 13% in temperature, and in line-of-sight velocity and magnetic
field strength the errors can even exceed 50%. Errors are found
at the sites of granules, intergranular lanes, magnetic elements,
and basically in every region with strong vertical gradients in the
atmosphere. Similarly, strong horizontal gradients in temperature
introduce 3D effects in these lines. We find that errors due to
neglecting the 3D effects are more localised and are lower than 5%
in temperature, and lower than 20% in both velocity and magnetic field
strength. The NLTE and 3D effects are found to persist when the Stokes
profiles are spatially and spectrally degraded to the resolution of
the Swedish Solar Telescope (SST) or Daniel K. Inouye Solar Telescope
(DKIST). Our findings have wide-ranging consequences since many results
derived in solar physics are based on inversions of these Fe I lines
carried out in LTE.

---------------------------------------------------------
Title: Small-scale Dynamo in Cool Main-Sequence Stars: Effect on
Stratification, Convection and Bolometric Intensity
Authors: Bhatia, T.; Cameron, R.; Solanki, S.; Peter, H.; Przybylski,
D.; Witzke, V.; Shapiro, A.
2021AAS...23830404B Altcode:
In cool main-sequence stars, the near-surface convection has an
impact on the center-to-limb variation of photospheric emission, with
implications for stellar lightcurves during planetary transits. In
the Sun, there is strong evidence for a small-scale dynamo (SSD)
maintaining the small-scale magnetic flux. This field could affect the
near-surface convection in other cool main-sequence stars. An SSD
could conceivably generate equipartition magnetic fields, which could
lead to non-negligible changes not only in convection and intensity
characteristics, but also in stratification. We aim to investigate these
changes for F, G, K and M stars. 3D MHD models of the four stellar types
covering the subsurface region to lower atmosphere in a small cartesian
box are studied using the MURaM rMHD simulation code. The MHD runs are
compared against a reference hydrodynamic (HD) run. The deviations
in stratification for the deeper convective layers is negligible,
except for the F-star, where reduction in turbulent pressure due to
magnetic fields is substantial. Convective velocities are reduced
by a similar percentage for all the cases due to inhibitory effect
of strong magnetic fields near the bottom boundary. All four cases
show small-scale brightenings in intergranular lanes, corresponding
to magnetic field concentrations, but overall effects on the r.m.s
contrast and spatial powerspectra are varied.

---------------------------------------------------------
Title: First Results of the Chromospheric MURaM code
Authors: Przybylski, D. F.; Cameron, R.; Solanki, S.; Rempel, M.
2021AAS...23810605P Altcode:
The solar chromosphere, spanning the region between the photosphere
and the transition to the corona, remains one of the least understood
parts of the Sun. This is partly because observing the chromosphere
and interpreting these observations is full of pitfalls. Also, the
simulation of the chromosphere is complex, as the particle densities
and collisional rates are too low to maintain local thermodynamic
equilibrium (LTE). Additionally, the recombination rates of hydrogen are
larger than the dynamical timescales and the populations must be solved
in non-equilibrium (NE). Realistic simulations of the chromosphere
must treat the magneto-hydrodynamics, time-dependant atomic and
molecular chemistry, and radiation transfer simultaneously. The
MURaM radiation-MHD code has previously been used for investigation
of the connection between the solar photosphere and corona, ranging
from small-scale dynamo generated 'quiet' sun fields to sunspots and
complex active regions. Until now these simulations have been performed
in LTE, greatly limiting their realism in the solar chromosphere. We
have extended MURaM to include NLTE effects following the prescriptions
used in the Bifrost code. The low viscocity and resistivity of the MURaM
code leads to turbulent convection in the photosphere with kilo-Gauss
mixed-polarity magnetic fields. This results in a dynamic chromosphere
with strong shocks and a finely structured magnetic field. We discuss
the implications of this new model towards observations of chromospheric
spectral lines.

---------------------------------------------------------
Title: Modeling Stellar Ca II H and K Emission Variations. I. Effect
of Inclination on the S-index
Authors: Sowmya, K.; Shapiro, A. I.; Witzke, V.; Nèmec, N. -E.;
Chatzistergos, T.; Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
2021ApJ...914...21S Altcode: 2021arXiv210313893S
The emission in the near-ultraviolet Ca II H and K lines is modulated
by stellar magnetic activity. Although this emission, quantified via
the S-index, has been serving as a prime proxy of stellar magnetic
activity for several decades, many aspects of the complex relation
between stellar magnetism and Ca II H and K emission are still
unclear. The amount of measured Ca II H and K emission is suspected
to be affected not only by the stellar intrinsic properties but
also by the inclination angle of the stellar rotation axis. Until
now, such an inclination effect on the S-index has remained largely
unexplored. To fill this gap, we develop a physics-based model to
calculate S-index, focusing on the Sun. Using the distributions of
solar magnetic features derived from observations together with Ca II
H and K spectra synthesized in non-local thermodynamic equilibrium,
we validate our model by successfully reconstructing the observed
variations of the solar S-index over four activity cycles. Further,
using the distribution of magnetic features over the visible solar
disk obtained from surface flux transport simulations, we obtain
S-index time series dating back to 1700 and investigate the effect
of inclination on S-index variability on both the magnetic activity
cycle and the rotational timescales. We find that when going from
an equatorial to a pole-on view, the amplitude of S-index variations
decreases weakly on the activity cycle timescale and strongly on the
rotational timescale (by about 22% and 81%, respectively, for a cycle
of intermediate strength). The absolute value of the S-index depends
only weakly on the inclination. We provide analytical expressions that
model such dependencies.

---------------------------------------------------------
Title: Modelling the evolution of the Sun's open and total magnetic
flux
Authors: Krivova, N. A.; Solanki, S. K.; Hofer, B.; Wu, C. -J.;
Usoskin, I. G.; Cameron, R.
2021A&A...650A..70K Altcode: 2021arXiv210315603K
Solar activity in all its varied manifestations is driven by the
magnetic field. Two global quantities are particularly important for
many purposes, the Sun's total and open magnetic flux, which can be
computed from sunspot number records using models. Such sunspot-driven
models, however, do not take into account the presence of magnetic
flux during grand minima, such as the Maunder minimum. Here we
present a major update of a widely used simple model, which now takes
into account the observation that the distribution of all magnetic
features on the Sun follows a single power law. The exponent of the
power law changes over the solar cycle. This allows for the emergence
of small-scale magnetic flux even when no sunspots have been present
for multiple decades and leads to non-zero total and open magnetic
flux also in the deepest grand minima, such as the Maunder minimum,
thus overcoming a major shortcoming of the earlier models. The results
of the updated model compare well with the available observations and
reconstructions of the solar total and open magnetic flux. This opens
up the possibility of improved reconstructions of the sunspot number
from time series of the cosmogenic isotope production rate.

---------------------------------------------------------
Title: Solar cyclic activity over the last millennium reconstructed
from annual 14C data
Authors: Usoskin, I. G.; Solanki, S. K.; Krivova, N. A.; Hofer, B.;
Kovaltsov, G. A.; Wacker, L.; Brehm, N.; Kromer, B.
2021A&A...649A.141U Altcode: 2021arXiv210315112U
 Aims: The 11-year solar cycle (Schwabe cycle) is the dominant
pattern of solar magnetic activity reflecting the oscillatory dynamo
mechanism in the Sun's convection zone. Solar cycles have been
directly observed since 1700, while indirect proxy data suggest their
existence over a much longer period of time, but generally without
resolving individual cycles and their continuity. Here we reconstruct
individual solar cycles for the last millennium using recently
obtained 14C data and state-of-the-art models. 
Methods: Starting with the 14C production rate determined
from the so far most precise measurements of radiocarbon content in
tree rings, solar activity was reconstructed in the following three
physics-based steps: (1) correction of the 14C production
rate for the changing geomagnetic field; (2) computation of the
open solar magnetic flux; and (3) conversion into sunspot numbers
outside of grand minima. All known uncertainties, including both
measurement and model uncertainties, were straightforwardly accounted
for by a Monte-Carlo method. Results: Cyclic solar activity is
reconstructed for the period 971-1900 (85 individual cycles) along with
its uncertainties. This more than doubles the number of solar cycles
known from direct solar observations. We found that the lengths and
strengths of well-defined cycles outside grand minima are consistent
with those obtained from the direct sunspot observations after 1750. The
validity of the Waldmeier rule (cycles with fast-rising phase tend to
be stronger) is confirmed at a highly significant level. Solar activity
is found to be in a deep grand minimum when the activity is mostly
below the sunspot formation threshold for about 250 years. Therefore,
although considerable cyclic variability in 14C is seen even
during grand minima, individual solar cycles can hardly be reliably
resolved therein. Three potential solar particle events, ca. 994,
1052, and 1279 AD, are shown to occur around the maximum phases of
solar cycles. Conclusions: A new approximately 1000-year-long
solar activity reconstruction, in the form of annual (pseudo) sunspot
numbers with the full assessment of all known uncertainties, is
presented based on new high-precision Δ14C measurements and
state-of-the-art models, more than doubling the number of individually
resolved solar cycles. This forms a solid basis for new, more detailed
studies of solar variability. Tabular data of the reconstructed
activity are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/649/A141">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/649/A141</A>

---------------------------------------------------------
Title: Signatures of coronal hole substructure in the solar wind:
combined Solar Orbiter remote sensing and in situ measurements
Authors: Horbury, T. S.; Laker, R.; Rodriguez, L.; Steinvall, K.;
Maksimovic, M.; Livi, S.; Berghmans, D.; Auchere, F.; Zhukov, A. N.;
Khotyaintsev, Yu. V.; Woodham, L.; Matteini, L.; Stawarz, J.; Woolley,
T.; Bale, S. D.; Rouillard, A.; O'Brien, H.; Evans, V.; Angelini,
V.; Owen, C.; Solanki, S. K.; Nicula, B.; Muller, D.; Zouganelis, I.
2021arXiv210414960H Altcode:
Context. The Sun's complex corona is the source of the solar wind
and interplanetary magnetic field. While the large scale morphology
is well understood, the impact of variations in coronal properties
on the scale of a few degrees on properties of the interplanetary
medium is not known. Solar Orbiter, carrying both remote sensing
and in situ instruments into the inner solar system, is intended
to make these connections better than ever before. Aims. We combine
remote sensing and in situ measurements from Solar Orbiter's first
perihelion at 0.5 AU to study the fine scale structure of the solar
wind from the equatorward edge of a polar coronal hole with the aim
of identifying characteristics of the corona which can explain the in
situ variations. Methods. We use in situ measurements of the magnetic
field, density and solar wind speed to identify structures on scales
of hours at the spacecraft. Using Potential Field Source Surface
mapping we estimate the source locations of the measured solar wind
as a function of time and use EUI images to characterise these solar
sources. Results. We identify small scale stream interactions in the
solar wind with compressed magnetic field and density along with speed
variations which are associated with corrugations in the edge of the
coronal hole on scales of several degrees, demonstrating that fine
scale coronal structure can directly influence solar wind properties
and drive variations within individual streams. Conclusions. This early
analysis already demonstrates the power of Solar Orbiter's combined
remote sensing and in situ payload and shows that with future, closer
perihelia it will be possible dramatically to improve our knowledge
of the coronal sources of fine scale solar wind structure, which is
important both for understanding the phenomena driving the solar wind
and predicting its impacts at the Earth and elsewhere.

---------------------------------------------------------
Title: Observing and modelling the young solar analogue EK Draconis:
starspot distribution, elemental abundances, and evolutionary status
Authors: Şenavcı, H. V.; Kılıçoğlu, T.; Işık, E.; Hussain,
G. A. J.; Montes, D.; Bahar, E.; Solanki, S. K.
2021MNRAS.502.3343S Altcode: 2021MNRAS.tmp..235S; 2021arXiv210107248S
Observations and modelling of stars with near-solar masses in their
early phases of evolution are critical for a better understanding
of how dynamos of solar-type stars evolve. We examine the chemical
composition and the spot distribution of the pre-main-sequence solar
analogue EK Dra. Using spectra from the HERMES Spectrograph (La Palma),
we obtain the abundances of 23 elements with respect to the solar
ones, which lead to a [Fe/H] = 0.03, with significant overabundance
of Li and Ba. The s-process elements Sr, Y, and Ce are marginally
overabundant, while Co, Ni, Cu, Zn are marginally deficient compared
to solar abundances. The overabundance of Ba is most likely due to the
assumption of depth-independent microturbulent velocity. Li abundance
is consistent with the age and the other abundances may indicate
distinct initial conditions of the pre-stellar nebula. We estimate a
mass of 1.04 M⊙ and an age of $27^{+11}_{-8}$ Myr using
various spectroscopic and photometric indicators. We study the surface
distribution of dark spots, using 17 spectra collected during 15 nights
using the CAFE Spectrograph (Calar Alto). We also conduct flux emergence
and transport (FEAT) simulations for EK Dra's parameters and produce
15-d-averaged synoptic maps of the likely starspot distributions. Using
Doppler imaging, we reconstruct the surface brightness distributions for
the observed spectra and FEAT simulations, which show overall agreement
for polar and mid-latitude spots, while in the simulations there is
a lack of low-latitude spots compared to the observed image. We find
indications that cross-equatorial extensions of mid-latitude spots
can be artefacts of the less visible southern-hemisphere activity.

---------------------------------------------------------
Title: The influence of NLTE effects in Fe I lines on an inverted
atmosphere. II. 6301 Å and 6302 Å lines formed in 3D NLTE
Authors: Smitha, H. N.; Holzreuter, R.; van Noort, M.; Solanki, S. K.
2021A&A...647A..46S Altcode: 2021arXiv210100506S
Context. This paper forms the second part of our study of how
neglecting non-local thermodynamic equilibrium (NLTE) conditions in
the formation of Fe I 6301.5 Å and the 6302.5 Å lines affects the
atmosphere that is obtained by inverting the Stokes profiles of these
lines in LTE. The main cause of NLTE effects in these lines is the line
opacity deficit that is due to the excess ionisation of Fe I atoms by
ultraviolet (UV) photons in the Sun. Aims: In the first paper,
these photospheric lines were assumed to have formed in 1D NLTE and the
effects of horizontal radiation transfer (RT) were neglected. In the
present paper, the iron lines are computed by solving the RT in 3D. We
investigate the effect of horizontal RT on the inverted atmosphere and
how it can enhance or reduce the errors that are due to neglecting 1D
NLTE effects. Methods: The Stokes profiles of the iron lines
were computed in LTE, 1D NLTE, and 3D NLTE. They were all inverted
using an LTE inversion code. The atmosphere from the inversion of
LTE profiles was taken as the reference model. The atmospheres from
the inversion of 1D NLTE profiles (testmodel-1D) and 3D NLTE profiles
(testmodel-3D) were compared with it. Differences between reference and
testmodels were analysed and correspondingly attributed to NLTE and 3D
effects. Results: The effects of horizontal RT are evident in
regions surrounded by strong horizontal temperature gradients. That is,
along the granule boundaries, regions surrounding magnetic elements,
and its boundaries with intergranular lanes. In some regions, the 3D
effects enhance the 1D NLTE effects, and in some, they weaken these
effects. In the small region analysed in this paper, the errors due to
neglecting the 3D effects are lower than 5% in temperature. In most of
the pixels, the errors are lower than 20% in both velocity and magnetic
field strength. These errors also persist when the Stokes profiles
are spatially and spectrally degraded to the resolution of the Swedish
Solar Telescope (SST) or Daniel K. Inouye Solar Telescope (DKIST). Conclusions: Neglecting horizontal RT introduces errors not only in
the derived temperature, but also in other atmospheric parameters. The
error sizes depend on the strength of the local horizontal temperature
gradients. Compared to the 1D NLTE effect, the 3D effects are more
localised in specific regions in the atmosphere and are weaker overall.

---------------------------------------------------------
Title: VizieR Online Data Catalog: 1000-year sunspot series (Usoskin+,
2021)
Authors: Usoskin, I. G.; Solanki, S. K.; Krivova, N.; Hofer, B.;
Kovaltsov, G. A.; Wacker, L.; Brehm, N.; Kromer, B.
2021yCat..36490141U Altcode:
A new quantitative reconstruction of annually resolved solar activity,
in the form of SNs (at least outside grand minima) with a full
uncertainty assessment, is presented for the period 971-1900. For the
first time, individual solar cycles are presented for the whole of the
last millennium, more than doubling the existing statistics of solar
cycles. Three tabular files are presented. File 'osf.dat'
contains annual reconstructions of the opens solar flux (OSF) [Fo]
along with its 1-sigma uncertainties [sF] and the smoothed (22-yr SSA --
see text) values [&lt;Fo&gt;]. This table corresponds to Figure 8 in
the text. File 'osn.dat' contains annual reconstructions of the
sunspot number (SN) [SN] along with its 1-sigma uncertainties [sSN]
and the smoothed (22-yr SSA -- see text) values [&lt;SN&gt;]. This
table corresponds to Figure 11 in the text. File 'table1.dat'
presents a textual tabular version of Table 1 in the text and contains
the internal cycle number [n], years of minimum [Ymin] and maximum
[Ymax] of each cycle, cycle-averaged sunspot number [&lt;SN&gt;], its
1-sigma uncertainty [sS], cycle length (min-to-min) [T], and quality
flag [q]. (3 data files).

---------------------------------------------------------
Title: Amplifying variability of solar-like stars by active longitudes
and nesting
Authors: Isik, Emre; Shapiro, Alexander I.; Solanki, Sami K.; Krivova,
Natalie A.
2021csss.confE.279I Altcode:
Many solar-type stars with near-solar rotation
periods exhibit much stronger variability than the Sun (<A
href="https://ui.adsabs.harvard.edu/abs/2020Sci...368..518R/abstract">Reinhold
et al. 2020</A>). Some of these stars even show very regular,
sine-like light curves. Motivated by solar activity complexes, we
developed a numerical model to quantify the effect of active-region (AR)
nesting and active longitudes on stellar brightness variations in the
rotational time scale. Modelling ARs with facular and spot components,
we simulated light curves covering four years and using the Kepler
passband. We found that the combined effect of the degree of nesting
and the activity level, both being somewhat higher than on the Sun,
can explain the whole range of observed light-curve amplitudes of
solar-like stars. While nesting at random longitudes can explain
variability amplitudes and light-curve morphology in many cases,
active-longitude-type nesting reproduces sine-like light curves and
the highest amplitude variability.

---------------------------------------------------------
Title: Modelling Solar Ca II H&amp;K Emission Variations
Authors: Krishnamurthy, Sowmya; Shapiro, Alexander I.; Witzke,
Veronika; Nèmec, Nina-E.; Chatzistergos, Theodosis; Yeo, Kok Leng;
Krivova, Natalie A.; Solanki, Sami K.
2021csss.confE.154K Altcode:
The emission in the near ultraviolet Ca II H&amp;K lines, often
quantified via the S-index, has been serving as a prime proxy of solar
and stellar magnetic activity. Despite the broad usage of the S-index,
the link between the coverage of a stellar disk by magnetic features
and Ca II H&amp;K emission is not fully understood. In order to fill
this gap we developed a physics-based model to calculate the solar
S-index. To this end, we made use of the distributions of the solar
magnetic features derived from the simulations of magnetic flux
emergence and surface transport, together with the Ca II H&amp;K
spectra synthesized using a non-local thermodynamic equilibrium
(non-LTE) radiative transfer code.We show that the value of the
solar S-index is influenced by the inclination angle between the
solar rotation axis and the observer's line-of-sight, i.e. the solar
S-index values obtained by an out-of-ecliptic observer are different
from those obtained by an ecliptic-bound observer. This is important
for comparing the magnetic activity of the Sun to other stars. We
computed time series of the S-index as they would be observed at
various inclinations dating back to 1700. We find that depending on
the inclination and period of observations, the activity cycle in solar
S-index can appear weaker or stronger than in stars with a solar-like
level of magnetic activity. We show that there is nothing unusual
about the solar chromospheric emission variations in the context of
stars with near-solar magnetic activity.

---------------------------------------------------------
Title: Small-scale dynamo in an F-star: effects on near-surface
stratification, convection and intensity
Authors: Bhatia, Tanayveer; Cameron, Robert; Solanki, Sami; Peter,
Hardi; Przybylski, Damien; Witzke, Veronika; Shapiro, Alexander
2021csss.confE..75B Altcode:
The emission from the photosphere of stars shows a systematic
center-to-limb variation. In cool main-sequence stars, the near-surface
convection has an impact on this variation, with implications for
lightcurves of stars during planetary transits. In the Sun, there
is strong evidence for a small-scale dynamo (SSD) maintaining the
small-scale magnetic flux. We aim to investigate what additional
effects such a field would play for other cool main-sequence
stars. In our work we first concentrate on F-stars. This is because
they have sonic velocities near the surface, implying a rough
equipartition between internal and kinetic energies. In addition,
an SSD might create a significant magnetic energy density to impact
the results. We investigate the interplay between internal, kinetic
and magnetic energies in 3D cartesian box MHD models of a F3V-star in
the near-surface convection, using the MURaM radiative-MHD simulation
code. Along with a reference hydrodynamic run, two MHD models with
self-consistently generated magnetic fields with two different lower
boundary conditions are considered. We find that the SSD process
creates a magnetic field with energy within an order of magnitude of the
internal and the kinetic energy. Compared to the hydrodynamic run, we
find slight (~1-3%) but significant deviations in density, gas pressure
and temperature stratification. At the surface, this corresponds to a
temperature difference of ~130 K. As expected, there is a significant
reduction in kinetic energy flux once the SSD is operational. The
changes in intensity are more subtle, both in total intensity and
granulation pattern. From this we conclude that the presence of an
SSD will have a significant impact on the atmospheric structure and
intensity characteristics seen at the surface. This makes it clear
that it would be important to consider the spatially and temporally
averaged effects of the SSD also for global stellar models.

---------------------------------------------------------
Title: Sunspot Simulations: Penumbra Formation and the Fluting
Instability
Authors: Panja, Mayukh; Cameron, Robert H.; Solanki, Sami K.
2021ApJ...907..102P Altcode: 2020arXiv201111447P
The fluting instability has been suggested as the driver of the
subsurface structure of sunspot flux tubes. We conducted a series
of numerical experiments where we used flux tubes with different
initial curvatures to study the effect of the fluting instability on
the subsurface structure of spots. We used the MURaM code, which has
previously been used to simulate complete sunspots, to first compute
four sunspots in the slab geometry and then two complete circular
spots of opposite polarities. We find that the curvature of a flux tube
indeed determines the degree of fluting the flux tube will undergo—the
more curved a flux tube is, the more fluted it becomes. In addition,
sunspots with strong curvature have strong horizontal fields at the
surface and therefore readily form penumbral filaments. The fluted
sunspots eventually break up from below, with lightbridges appearing
at the surface several hours after fluting commences.

---------------------------------------------------------
Title: Predictions of Astrometric Jitter for Sun-like Stars. I. The
Model and Its Application to the Sun as Seen from the Ecliptic
Authors: Shapiro, Alexander I.; Solanki, Sami K.; Krivova, Natalie A.
2021ApJ...908..223S Altcode: 2020arXiv201212312S
The advent of Gaia, capable of measuring stellar wobbles caused
by orbiting planets, raised interest in the astrometric detection
of exoplanets. Another source of such wobbles (often also called
jitter) is stellar magnetic activity. A quantitative assessment
of the stellar astrometric jitter is important for a more reliable
astrometric detection and characterization of exoplanets. We calculate
the displacement of the solar photocenter due to the magnetic activity
for an almost 16 yr period (1999 February 2-2014 August 1). We also
investigate how the displacement depends on the spectral passband chosen
for observations, including the wavelength range to be covered by the
upcoming Small-JASMINE mission of JAXA. This is done by extending the
SATIRE-S model for solar irradiance variability to calculating the
displacement of the solar photocenter caused by the magnetic features
on the surface of the Sun. We found that the peak-to-peak amplitude
of the solar photocenter displacement would reach 0.5 μas if the
Sun were located 10 pc away from the observer and observed in the
Gaia G filter. This is by far too small to be detected by the Gaia
mission. However, the Sun is a relatively inactive star so one can
expect significantly larger signals for younger, and, consequently,
more active stars. The model developed in this study can be combined
with the simulations of emergence and surface transport of magnetic
flux which have recently become available to model the astrometric
jitter over the broad range of magnetic activities.

---------------------------------------------------------
Title: Where Have All the Solar-like Stars Gone? Rotation Period
Detectability at Various Inclinations and Metallicities
Authors: Reinhold, Timo; Shapiro, Alexander I.; Witzke, Veronika;
Nèmec, Nina-E.; Işık, Emre; Solanki, Sami K.
2021ApJ...908L..21R Altcode: 2021arXiv210111426R
The plethora of photometric data collected by the Kepler space telescope
has promoted the detection of tens of thousands of stellar rotation
periods. However, these periods are not found to an equal extent
among different spectral types. Interestingly, early G-type stars with
near-solar rotation periods are strongly underrepresented among those
stars with known rotation periods. In this study we investigate whether
the small number of such stars can be explained by difficulties in the
period determination from photometric time series. For that purpose,
we generate model light curves of early G-type stars with solar
rotation periods for different inclination angles, metallicities, and
(magnitude-dependent) noise levels. We find that the detectability is
determined by the predominant type of activity (i.e., spot or faculae
domination) on the surface, which defines the degree of irregularity
of the light curve, and further depends on the level of photometric
noise. These two effects significantly complicate the period detection
and explain the lack of solar-like stars with known near-solar rotation
periods. We conclude that the rotation periods of the majority of
solar-like stars with near-solar rotation periods remain undetected
to date. Finally, we promote the use of new techniques to recover more
periods of near-solar rotators.

---------------------------------------------------------
Title: Coronal Heating and Solar Wind Formation in Quiet Sun and
Coronal Holes: A Unified Scenario
Authors: Tripathi, Durgesh; Nived, V. N.; Solanki, Sami K.
2021ApJ...908...28T Altcode: 2020arXiv201109803T
Coronal holes (CHs) are darker than the quiet Sun (QS) when observed
in coronal channels. This study aims to understand the similarities
and differences between CHs and QS in the transition region using
the Si IV 1394 Å line, recorded by the Interface Region Imaging
Spectrograph, by considering the distribution of magnetic field
measured by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. We find that Si IV intensities obtained in CHs
are lower than those obtained in QS for regions with identical magnetic
flux densities. Moreover, the difference in intensities between CHs
and QS increases with increasing magnetic flux. For the regions with
equal magnetic flux density, QS line profiles are more redshifted
than those measured in CHs. Moreover, the blueshifts measured in CHs
show an increase with increasing magnetic flux density unlike in
the QS. The non-thermal velocities in QS, as well as in CHs, show
an increase with increasing magnetic flux. However, no significant
difference was observed in QS and CHs, albeit a small deviation at
small flux densities. Using these results, we propose a unified model
for the heating of the corona in the QS and in CHs and the formation
of solar wind.

---------------------------------------------------------
Title: Vortex flow properties in simulations of solar plage region:
Evidence for their role in chromospheric heating
Authors: Yadav, N.; Cameron, R. H.; Solanki, S. K.
2021A&A...645A...3Y Altcode: 2020arXiv201014971Y
Context. Vortex flows exist across a broad range of spatial and
temporal scales in the solar atmosphere. Small-scale vortices are
thought to play an important role in energy transport in the solar
atmosphere. However, their physical properties remain poorly understood
due to the limited spatial resolution of the observations. 
Aims: We explore and analyze the physical properties of small-scale
vortices inside magnetic flux tubes using numerical simulations, and
investigate whether they contribute to heating the chromosphere in a
plage region. Methods: Using the three-dimensional radiative
magnetohydrodynamic simulation code MURaM, we perform numerical
simulations of a unipolar solar plage region. To detect and isolate
vortices we use the swirling strength criterion and select the locations
where the fluid is rotating with an angular velocity greater than
a certain threshold. We concentrate on small-scale vortices as they
are the strongest and carry most of the energy. We explore the spatial
profiles of physical quantities such as density and horizontal velocity
inside these vortices. Moreover, to learn their general characteristics,
a statistical investigation is performed. Results: Magnetic
flux tubes have a complex filamentary substructure harboring an
abundance of small-scale vortices. At the interfaces between vortices
strong current sheets are formed that may dissipate and heat the solar
chromosphere. Statistically, vortices have higher densities and higher
temperatures than the average values at the same geometrical height
in the chromosphere. Conclusions: We conclude that small-scale
vortices are ubiquitous in solar plage regions; they are denser and
hotter structures that contribute to chromospheric heating, possibly
by dissipation of the current sheets formed at their interfaces.

---------------------------------------------------------
Title: Magnetic Imaging of the Outer Solar Atmosphere (MImOSA):
Unlocking the driver of the dynamics in the upper solar atmosphere
Authors: Peter, H.; Alsina Ballester, E.; Andretta, V.; Auchere, F.;
Belluzzi, L.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Calcines, A.;
Chitta, L. P.; Dalmasse, K.; del Pino Aleman, T.; Feller, A.; Froment,
C.; Harrison, R.; Janvier, M.; Matthews, S.; Parenti, S.; Przybylski,
D.; Solanki, S. K.; Stepan, J.; Teriaca, L.; Trujillo Bueno, J.
2021arXiv210101566P Altcode:
The magnetic activity of the Sun directly impacts the Earth and human
life. Likewise, other stars will have an impact on the habitability
of planets orbiting these host stars. The lack of information on the
magnetic field in the higher atmospheric layers hampers our progress in
understanding solar magnetic activity. Overcoming this limitation would
allow us to address four paramount long-standing questions: (1) How
does the magnetic field couple the different layers of the atmosphere,
and how does it transport energy? (2) How does the magnetic field
structure, drive and interact with the plasma in the chromosphere and
upper atmosphere? (3) How does the magnetic field destabilise the outer
solar atmosphere and thus affect the interplanetary environment? (4)
How do magnetic processes accelerate particles to high energies? New
ground-breaking observations are needed to address these science
questions. We suggest a suite of three instruments that far exceed
current capabilities in terms of spatial resolution, light-gathering
power, and polarimetric performance: (a) A large-aperture UV-to-IR
telescope of the 1-3 m class aimed mainly to measure the magnetic
field in the chromosphere by combining high spatial resolution and high
sensitivity. (b) An extreme-UV-to-IR coronagraph that is designed to
measure the large-scale magnetic field in the corona with an aperture
of about 40 cm. (c) An extreme-UV imaging polarimeter based on a 30
cm telescope that combines high throughput in the extreme UV with
polarimetry to connect the magnetic measurements of the other two
instruments. This mission to measure the magnetic field will unlock
the driver of the dynamics in the outer solar atmosphere and thereby
greatly advance our understanding of the Sun and the heliosphere.

---------------------------------------------------------
Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP)
for SUNRISE III: optical design and performance
Authors: Tsuzuki, Toshihiro; Katsukawa, Yukio; Uraguchi, Fumihiro;
Hara, Hirohisa; Kubo, Masahito; Nodomi, Yoshifumi; Suematsu, Yoshinori;
Kawabata, Yusuke; Shimizu, Toshifumi; Gandorfer, Achim; Feller, Alex;
Grauf, Bianca; Solanki, Sami; Carlos del Toro Iniesta, Jose
2020SPIE11447E..AJT Altcode:
The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a
near-IR spectro-polarimeter instrument newly designed for Sunrise III,
which is a balloon-borne solar observatory equipped with a 1 m optical
telescope. To acquire high-quality 3D magnetic and velocity fields,
SCIP selects the two wavelength bands centered at 850 nm and 770 nm,
which contain many spectrum lines that are highly sensitive to magnetic
fields permeating the photosphere and chromosphere. To achieve high
spatial and spectral resolution (0.21 arcsec and 2 × 105),
SCIP optics adopt a quasi-Littrow configuration based on an echelle
grating and two high-order aspheric mirrors. Using different diffraction
orders of the echelle grating, dichroic beam splitter, and polarizing
beam-splitters, SCIP can obtain s- and p-polarization signals in the
two wavelength bands simultaneously within a relatively small space. We
established the wavefront error budget based on tolerance analysis,
surface figure errors, alignment errors, and environmental changes. In
addition, we performed stray light analysis, and designed light traps
and baffles needed to suppress unwanted reflections and diffraction
by the grating. In this paper, we present the details of this optical
system and its performance.

---------------------------------------------------------
Title: Reconstructing solar irradiance from Ca II K observations
Authors: Chatzistergos, T.; Krivova, N.; Ermolli, I.; Yeo, K. L.;
Solanki, S. K.; Puiu, C. C.; Giorgi, F.; Mandal, S.
2020AGUFMA237...10C Altcode:
To understand the influence of the Sun on Earth's system, long and
accurate measurements of solar irradiance are a prerequisite. The
available direct measurements of solar irradiance since 1978 are
clearly not sufficient for this purpose. This stimulated development
of models used to reconstruct past solar irradiance variations from
alternative observations. The main driver of the irradiance variations
on time scales of days to millennia is the evolution of the solar
surface magnetic field in form of dark sunspots and bright faculae
and network. Therefore, models require input data describing the
contributions of these various magnetic regions on the Sun at earlier
times. Unfortunately, records that can be used to describe the facular
and network contributions are barely longer than the direct irradiance
measurements. Thus, irradiance reconstructions to earlier periods have
to rely on sunspot data alone. Data that have hardly been used for solar
irradiance reconstructions until now are full-disc solar observations in
the Ca II K line. Such data exist since 1892 from various observatories
and include all the needed information describing faculae and the
network. However, they are plagued by a bunch of various problems and
artefacts, and recovering the non-linear response of the photographic
material to the radiation is non-trivial since the required information
is usually missing, too. We have developed a method to process Ca II K
observations from various sources and demonstrated the higher accuracy
achieved by our method compared to other techniques presented in the
literature. Here we use the carefully reduced Ca II K observations
from multiple archives to reconstruct solar irradiance variations.

---------------------------------------------------------
Title: Erratum: "Amplification of Brightness Variability by
Active-region Nesting in Solar-like Stars" (2020, ApJL, 901, L12)
Authors: Işık, Emre; Shapiro, Alexander I.; Solanki, Sami K.;
Krivova, Natalie A.
2020ApJ...905L..36I Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The magnetic fine structure of the Sun's polar region as
revealed by Sunrise
Authors: Prabhu, A.; Lagg, A.; Hirzberger, J.; Solanki, S. K.
2020A&A...644A..86P Altcode:
Context. Polar magnetic fields play a key role in the solar magnetic
cycle and they are the source of a significant portion of the
interplanetary magnetic field. However, observations of the poles
are challenging and hence our understanding of the polar magnetic
environment is incomplete. Aims: We deduce properties of
small-scale magnetic features in the polar region using high-resolution
data and specifically aim to determine the flux per patch above which
one magnetic polarity starts to dominate over the other. Methods:
We study the high spatial resolution, seeing-free observations of the
north solar polar region, obtained with the IMaX instrument on-board
the balloon-borne SUNRISE observatory during June 2009, at the solar
activity minimum. We performed inversions of the full Stokes vector
recorded by IMaX to retrieve atmospheric parameters of the Sun's
polar region, mainly the temperature stratification and the magnetic
field vector. Results: We infer kilo-Gauss (kG) magnetic fields
in patches harbouring polar faculae, without resorting to a magnetic
filling factor. Within these patches we find the maxima of the magnetic
field to be near the dark narrow lanes, which are shifted towards the
disc centre side in comparison to the maxima in continuum intensity. In
contrast, we did not find any fields parallel to the solar surface
with kG strengths. In addition to the kG patches, we found the polar
region to be covered in patches of both polarities, which have a range
of sizes. We find the field strength of these patches to increase with
increasing size and flux, with the smaller patches showing a significant
dispersion in field strength. The dominating polarity of the north
pole during this phase of the solar cycle is found to be maintained
by the larger patches with fluxes above 2.3 × 1017 Mx.

---------------------------------------------------------
Title: Multi-view magnetic synoptic maps with SO/PHI and SDO/HMI
Authors: Löschl, P.; Hirzberger, J.; Schou, J.; Solanki, S. K.
2020AGUFMSH0360028L Altcode:
With the recent launch of Solar Orbiter (SO) and the first data slowly
becoming available, it will soon be possible to simultaneously observe
the Sun from additional vantage points off the Earth-Sun line. One
of its instruments, the Polarimetric and Heliospheric Imager (PHI),
is the first spectro-polarimeter to operate outside of this line of
sight. This opens the possibility for joint observational campaigns
with similar instruments, such as the Heliospheric and Magnetic Imager
(HMI) on-board the Solar Dynamics Observatory (SDO). We utilise these
new observational possibilities to produce combined magnetic synoptic
maps from magnetograms of the PHI and HMI instruments. Building on the
existing software infrastructure for HMI synoptic maps, we extended
its current functionality to include PHI data and correct for the
different and varying relative orbital characteristics of the two
spacecraft. The result are joint magnetic synoptic maps, that can
be produced significantly faster than the approximately 27 days of
one solar rotation and therefore are less likely to suffer from the
evolution of the magnetic field over the observation period. Once Solar
Orbiter leaves the ecliptic plane, we will also be able to include
observations of the polar magnetic field into our synoptic maps,
which will give an unprecedented insight into the magnetic field of
the Sun. This work presents our preparatory modelling efforts and
gives an outlook for the future capabilities of this novel data product.

---------------------------------------------------------
Title: First results from SO/PHI's on-board data reduction
Authors: Albert, K.; Hirzberger, J.; Kolleck, M.; Albelo Jorge,
N.; Busse, D.; Blanco Rodriguez, J.; Cobos Carrascosa, J. P.;
Fiethe, B.; Gandorfer, A.; Germerott, D.; Guan, Y.; Guerrero, L.;
Gutierrez-Marques, P.; Hernández Expósito, D.; Lange, T.; Michalik,
H.; Orozco Suárez, D.; Schou, J.; Solanki, S. K.; Woch, J. G.
2020AGUFMSH038..05A Altcode:
The Polarimetric and Helioseismic Imager (PHI), on-board Solar
Orbiter (SO), is a spectropolarimeter imaging the solar photosphere
at the wavelengths of the Fe I 617.3 nm Zeeman sensitive absorption
line. SO/PHI's aim is to provide data about the magnetic structures and
the line-of-sight (LOS) velocity in the solar atmosphere. For this, it
takes time series of data sets consisting of 2048 x 2048 pixel images of
the Sun at 6 wavelengths, each in 4 different polarisation states. With
the minimum necessary 17 bits pixel depth, one data set amounts to
approx. 0.2 GB. The guaranteed data telemetry for PHI, in contrast,
is only 50 GiB/orbit which would also need to contain any calibration
data obtained on-board, i.e. our flat and dark fields. To cope with
this discrepancy, SO/PHI is performing full data reduction on-board,
including the inversion of the radiative transfer equation. The
downloaded results are science ready data, containing 5 final images: a
total intensity image from nearby the spectral line, the magnetic field
strength, azimuth and inclination (describing the magnetic vector) and
the LOS velocity. This process maximises the science return by reducing
the number of necessary images in a data set, as well as rendering the
download of calibration data unessential. In the commissioning phase
of SO/PHI we used the on-board data reduction system successfully
for the first time. We have calibrated the instrument to its optimal
operational parameters (calculation of exposure time, focus, etc.),
acquired and processed calibration data (dark and flat fields),
removed the most significant instrumental artefacts from the data
(dark field, flat field, polarimetric modulation and polarimetric
cross-talk), and performed the inversion of the radiative transfer
equation. The data have then been compressed to further maximise the
use of our telemetry. This contribution presents and discusses the
final results from this process.

---------------------------------------------------------
Title: Power spectrum of turbulent convection in the solar photosphere
Authors: Yelles Chaouche, L.; Cameron, R. H.; Solanki, S. K.;
Riethmüller, T. L.; Anusha, L. S.; Witzke, V.; Shapiro, A. I.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; van Noort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2020A&A...644A..44Y Altcode: 2020arXiv201009037Y
The solar photosphere provides us with a laboratory for understanding
turbulence in a layer where the fundamental processes of transport
vary rapidly and a strongly superadiabatic region lies very closely
to a subadiabatic layer. Our tools for probing the turbulence are
high-resolution spectropolarimetric observations such as have recently
been obtained with the two balloon-borne SUNRISE missions, and numerical
simulations. Our aim is to study photospheric turbulence with the
help of Fourier power spectra that we compute from observations
and simulations. We also attempt to explain some properties of the
photospheric overshooting flow with the help of its governing equations
and simulations. We find that quiet-Sun observations and smeared
simulations are consistent with each other and exhibit a power-law
behavior in the subgranular range of their Doppler velocity power
spectra with a power-law index of ≈ - 2. The unsmeared simulations
exhibit a power law that extends over the full range between the
integral and Taylor scales with a power-law index of ≈ - 2.25. The
smearing, reminiscent of observational conditions, considerably reduces
the extent of the power-law-like portion of the power spectra. This
suggests that the limited spatial resolution in some observations
might eventually result in larger uncertainties in the estimation of
the power-law indices. The simulated vertical velocity power spectra
as a function of height show a rapid change in the power-law index
(at the subgranular range) from roughly the optical depth unity layer,
that is, the solar surface, to 300 km above it. We propose that the
cause of the steepening of the power-law index is the transition from
a super- to a subadiabatic region, in which the dominant source of
motions is overshooting convection. A scale-dependent transport of
the vertical momentum occurs. At smaller scales, the vertical momentum
is more efficiently transported sideways than at larger scales. This
results in less vertical velocity power transported upward at small
scales than at larger scales and produces a progressively steeper
vertical velocity power law below 180 km. Above this height, the
gravity work progressively gains importance at all relevant scales,
making the atmosphere progressively more hydrostatic and resulting
in a gradually less steep power law. Radiative heating and cooling of
the plasma is shown to play a dominant role in the plasma energetics
in this region, which is important in terms of nonadiabatic damping
of the convective motions.

---------------------------------------------------------
Title: The SUNRISE UV Spectropolarimeter and imager for SUNRISE III
Authors: Feller, Alex; Gandorfer, Achim; Iglesias, Francisco A.;
Lagg, Andreas; Riethmüller, Tino L.; Solanki, Sami K.; Katsukawa,
Yukio; Kubo, Masahito
2020SPIE11447E..AKF Altcode:
Sunrise is a balloon-borne solar observatory dedicated to the
investigation of key processes of the magnetic field and the plasma
flows in the lower solar atmosphere. The observatory operates in
the stratosphere at an altitude of around 37 km in order to avoid
image degradation due to turbulence in the Earth's atmosphere and to
access the UV range. The third science flight of Sunrise will carry new
instrumentation which samples the solar spectrum over a broad wavelength
domain from the UV to the near IR and covers an extended height range in
the solar atmosphere. A key feature of the Sunrise UV Spectropolarimeter
and Imager (SUSI) operating between 309 nm and 417 nm, is its capability
to simultaneously record a large number of spectral lines. By combining
the spectral and polarization information of many individual lines
with different formation heights and sensitivities, the accuracy and
the height resolution of the inferred atmospheric parameters can be
significantly increased. The spectral bands of SUSI are selected one
at a time by rotating a diffraction grating with respect to a fixed
polarimetry unit. The spatial and spectral field of view on the 2k x
2k cameras is 59" and 2.0 - 2.3 nm, respectively. A further innovation
is the numerical restoration of the spectrograph scans by means of
synchronized 2D context imaging, a technique that has recently produced
impressive results at ground-based solar observatories.

---------------------------------------------------------
Title: The Solar-C (EUVST) mission: the latest status
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko; Suematsu,
Yoshinori; Hara, Hirohisa; Tsuzuki, Toshihiro; Katsukawa, Yukio; Kubo,
Masahito; Ishikawa, Ryoko; Watanabe, Tetsuya; Toriumi, Shin; Ichimoto,
Kiyoshi; Nagata, Shin'ichi; Hasegawa, Takahiro; Yokoyama, Takaaki;
Watanabe, Kyoko; Tsuno, Katsuhiko; Korendyke, Clarence M.; Warren,
Harry; De Pontieu, Bart; Boerner, Paul; Solanki, Sami K.; Teriaca,
Luca; Schuehle, Udo; Matthews, Sarah; Long, David; Thomas, William;
Hancock, Barry; Reid, Hamish; Fludra, Andrzej; Auchère, Frederic;
Andretta, Vincenzo; Naletto, Giampiero; Poletto, Luca; Harra, Louise
2020SPIE11444E..0NS Altcode:
Solar-C (EUVST) is the next Japanese solar physics mission to
be developed with significant contributions from US and European
countries. The mission carries an EUV imaging spectrometer with
slit-jaw imaging system called EUVST (EUV High-Throughput Spectroscopic
Telescope) as the mission payload, to take a fundamental step towards
answering how the plasma universe is created and evolves and how the
Sun influences the Earth and other planets in our solar system. In
April 2020, ISAS (Institute of Space and Astronautical Science) of JAXA
(Japan Aerospace Exploration Agency) has made the final down-selection
for this mission as the 4th in the series of competitively chosen
M-class mission to be launched with an Epsilon launch vehicle in mid
2020s. NASA (National Aeronautics and Space Administration) has selected
this mission concept for Phase A concept study in September 2019 and
is in the process leading to final selection. For European countries,
the team has (or is in the process of confirming) confirmed endorsement
for hardware contributions to the EUVST from the national agencies. A
recent update to the mission instrumentation is to add a UV spectral
irradiance monitor capability for EUVST calibration and scientific
purpose. This presentation provides the latest status of the mission
with an overall description of the mission concept emphasizing on key
roles of the mission in heliophysics research from mid 2020s.

---------------------------------------------------------
Title: Sunrise Chromospheric Infrared SpectroPolarimeter (SCIP)
for sunrise III: system design and capability
Authors: Katsukawa, Y.; del Toro Iniesta, J. C.; Solanki, S. K.;
Kubo, M.; Hara, H.; Shimizu, T.; Oba, T.; Kawabata, Y.; Tsuzuki,
T.; Uraguchi, F.; Nodomi, Y.; Shinoda, K.; Tamura, T.; Suematsu,
Y.; Ishikawa, R.; Kano, R.; Matsumoto, T.; Ichimoto, K.; Nagata, S.;
Quintero Noda, C.; Anan, T.; Orozco Suárez, D.; Balaguer Jiménez,
M.; López Jiménez, A. C.; Cobos Carrascosa, J. P.; Feller, A.;
Riethmueller, T.; Gandorfer, A.; Lagg, A.
2020SPIE11447E..0YK Altcode:
The Sunrise balloon-borne solar observatory carries a 1 m aperture
optical telescope and provides us a unique platform to conduct
continuous seeing-free observations at UV-visible-IR wavelengths from
an altitude of higher than 35 km. For the next flight planned for
2022, the post-focus instrumentation is upgraded with new spectro-
polarimeters for the near UV (SUSI) and the near-IR (SCIP), whereas
the imaging spectro-polarimeter Tunable Magnetograph (TuMag) is capable
of observing multiple spectral lines within the visible wavelength. A
new spectro-polarimeter called the Sunrise Chromospheric Infrared
spectroPolarimeter (SCIP) is under development for observing near-IR
wavelength ranges of around 770 nm and 850 nm. These wavelength ranges
contain many spectral lines sensitive to solar magnetic fields and
SCIP will be able to obtain magnetic and velocity structures in the
solar atmosphere with a sufficient height resolution by combining
spectro-polarimetric data of these lines. Polarimetric measurements are
conducted using a rotating waveplate as a modulator and polarizing beam
splitters in front of the cameras. The spatial and spectral resolutions
are 0.2" and 2 105, respectively, and a polarimetric sensitivity of
0.03 % (1σ) is achieved within a 10 s integration time. To detect
minute polarization signals with good precision, we carefully designed
the opto-mechanical system, polarization optics and modulation, and
onboard data processing.

---------------------------------------------------------
Title: Reconstructing solar irradiance from Ca II K observations
Authors: Chatzistergos, Theodosios; Krivova, Natalie A.; Ermolli,
Ilaria; Leng Yeo, Kok; Solanki, Sami K.; Puiu, Cosmin C.; Giorgi,
Fabrizio; Mandal, Sudip
2020AGUFM.A237..10C Altcode:
To understand the influence of the Sun on Earth's system, long and
accurate measurements of solar irradiance are a prerequisite. The
available direct measurements of solar irradiance since 1978 are
clearly not sufficient for this purpose. This stimulated development
of models used to reconstruct past solar irradiance variations from
alternative observations. The main driver of the irradiance variations
on time scales of days to millennia is the evolution of the solar
surface magnetic field in form of dark sunspots and bright faculae
and network. Therefore, models require input data describing the
contributions of these various magnetic regions on the Sun at earlier
times. Unfortunately, records that can be used to describe the facular
and network contributions are barely longer than the direct irradiance
measurements. Thus, irradiance reconstructions to earlier periods have
to rely on sunspot data alone. Data that have hardly been used for solar
irradiance reconstructions until now are full-disc solar observations in
the Ca II K line. Such data exist since 1892 from various observatories
and include all the needed information describing faculae and the
network. However, they are plagued by a bunch of various problems and
artefacts, and recovering the non-linear response of the photographic
material to the radiation is non-trivial since the required information
is usually missing, too. We have developed a method to process Ca II K
observations from various sources and demonstrated the higher accuracy
achieved by our method compared to other techniques presented in the
literature. Here we use the carefully reduced Ca II K observations
from multiple archives to reconstruct solar irradiance variations.

---------------------------------------------------------
Title: Solar Orbiter: connecting remote sensing and in situ
measurements
Authors: Horbury, T. S.; Auchere, F.; Antonucci, E.; Berghmans, D.;
Bruno, R.; Carlsson, M.; del Toro Iniesta, J. C.; Fludra, A.; Harra,
L.; Hassler, D.; Heinzel, P.; Howard, R. A.; Krucker, S.; Livi, S. A.;
Long, D.; Louarn, P.; Maksimovic, M.; Mueller, D.; Owen, C. J.; Peter,
H.; Rochus, P. L.; Rodriguez-Pacheco, J.; Romoli, M.; Schühle, U.;
Solanki, S. K.; Teriaca, L.; Wimmer-Schweingruber, R. F.; Zouganelis,
Y.; Laker, R.
2020AGUFMSH038..10H Altcode:
A key science goal of the Solar Orbiter mission is to make connections
between phenomena on the Sun and their manifestations in interplanetary
space. To that end, the spacecraft carries a carefully tailored
payload of six remote sensing instruments and four making in situ
measurements. During June 2020, while the spacecraft was around 0.5
AU from the Sun, the remote sensing instruments operated for several
days. While this was primarily an engineering activity, the resulting
observations provided outstanding measurements and represent the ideal
first opportunity to investigate the potential for making connections
between the remote sensing and in situ payloads on Solar Orbiter. We present a preliminary analysis of the available remote sensing and
in situ observations, showing how connections can be made, and discuss
the potential for further, more precise mapping to be performed as
the mission progresses.

---------------------------------------------------------
Title: Impulsive coronal heating during the interaction of surface
magnetic fields in the lower solar atmosphere
Authors: Chitta, L. P.; Peter, H.; Priest, E. R.; Solanki, S. K.
2020A&A...644A.130C Altcode: 2020arXiv201012560C
Coronal plasma in the cores of solar active regions is impulsively
heated to more than 5 MK. The nature and location of the magnetic
energy source responsible for such impulsive heating is poorly
understood. Using observations of seven active regions from the Solar
Dynamics Observatory, we found that a majority of coronal loops hosting
hot plasma have at least one footpoint rooted in regions of interacting
mixed magnetic polarity at the solar surface. In cases when co-temporal
observations from the Interface Region Imaging Spectrograph space
mission are available, we found spectroscopic evidence for magnetic
reconnection at the base of the hot coronal loops. Our analysis suggests
that interactions of magnetic patches of opposite polarity at the
solar surface and the associated energy release during reconnection
are key to impulsive coronal heating. Movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/202039099/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: Faculae-Spot dominance &amp;
rotation periods (Amazo-Gomez+, 2020)
Authors: Amazo-Gomez, E. M.; Shapiro, A. I.; Solanki, S. K.; Kopp,
G.; Oshagh, M.; Reinhold, T.; Reiners, A.
2020yCat..36420225A Altcode:
This table contains an example of the GPS outputs, the compared
rotation period values from GLS and ACF, and stellar parameters for
Kepler stars. In column 4 and 5 values of alpha-factor and its
2-sigma uncertainty are reported respectively. Prot GPS values in
column 6, as result of applying Eq. 1 using the factor alpha=0.19. 2)
Column 7 shows the Prot reported by Reinhold &amp; Gizon (2015,
Cat. J/A+A/583/A65). 3) Prot and variability values reported by
McQuillan et al. (2014, Cat. J/ApJS/211/24) in column 8. 4) Columns
10, 11 and 12 show the logg, [Fe/H], and Teff respectively, taken from
Huber et al. (2014, Cat J/ApJS/211/2). (1 data file).

---------------------------------------------------------
Title: Coordination within the remote sensing payload on the Solar
Orbiter mission
Authors: Auchère, F.; Andretta, V.; Antonucci, E.; Bach, N.;
Battaglia, M.; Bemporad, A.; Berghmans, D.; Buchlin, E.; Caminade,
S.; Carlsson, M.; Carlyle, J.; Cerullo, J. J.; Chamberlin, P. C.;
Colaninno, R. C.; Davila, J. M.; De Groof, A.; Etesi, L.; Fahmy,
S.; Fineschi, S.; Fludra, A.; Gilbert, H. R.; Giunta, A.; Grundy,
T.; Haberreiter, M.; Harra, L. K.; Hassler, D. M.; Hirzberger, J.;
Howard, R. A.; Hurford, G.; Kleint, L.; Kolleck, M.; Krucker, S.;
Lagg, A.; Landini, F.; Long, D. M.; Lefort, J.; Lodiot, S.; Mampaey,
B.; Maloney, S.; Marliani, F.; Martinez-Pillet, V.; McMullin, D. R.;
Müller, D.; Nicolini, G.; Orozco Suarez, D.; Pacros, A.; Pancrazzi,
M.; Parenti, S.; Peter, H.; Philippon, A.; Plunkett, S.; Rich, N.;
Rochus, P.; Rouillard, A.; Romoli, M.; Sanchez, L.; Schühle, U.;
Sidher, S.; Solanki, S. K.; Spadaro, D.; St Cyr, O. C.; Straus, T.;
Tanco, I.; Teriaca, L.; Thompson, W. T.; del Toro Iniesta, J. C.;
Verbeeck, C.; Vourlidas, A.; Watson, C.; Wiegelmann, T.; Williams,
D.; Woch, J.; Zhukov, A. N.; Zouganelis, I.
2020A&A...642A...6A Altcode:
Context. To meet the scientific objectives of the mission, the Solar
Orbiter spacecraft carries a suite of in-situ (IS) and remote sensing
(RS) instruments designed for joint operations with inter-instrument
communication capabilities. Indeed, previous missions have shown that
the Sun (imaged by the RS instruments) and the heliosphere (mainly
sampled by the IS instruments) should be considered as an integrated
system rather than separate entities. Many of the advances expected
from Solar Orbiter rely on this synergistic approach between IS and
RS measurements. Aims: Many aspects of hardware development,
integration, testing, and operations are common to two or more
RS instruments. In this paper, we describe the coordination effort
initiated from the early mission phases by the Remote Sensing Working
Group. We review the scientific goals and challenges, and give an
overview of the technical solutions devised to successfully operate
these instruments together. Methods: A major constraint for the
RS instruments is the limited telemetry (TM) bandwidth of the Solar
Orbiter deep-space mission compared to missions in Earth orbit. Hence,
many of the strategies developed to maximise the scientific return from
these instruments revolve around the optimisation of TM usage, relying
for example on onboard autonomy for data processing, compression,
and selection for downlink. The planning process itself has been
optimised to alleviate the dynamic nature of the targets, and an
inter-instrument communication scheme has been implemented which can
be used to autonomously alter the observing modes. We also outline the
plans for in-flight cross-calibration, which will be essential to the
joint data reduction and analysis. Results: The RS instrument
package on Solar Orbiter will carry out comprehensive measurements
from the solar interior to the inner heliosphere. Thanks to the close
coordination between the instrument teams and the European Space
Agency, several challenges specific to the RS suite were identified
and addressed in a timely manner.

---------------------------------------------------------
Title: Models and data analysis tools for the Solar Orbiter mission
Authors: Rouillard, A. P.; Pinto, R. F.; Vourlidas, A.; De Groof, A.;
Thompson, W. T.; Bemporad, A.; Dolei, S.; Indurain, M.; Buchlin, E.;
Sasso, C.; Spadaro, D.; Dalmasse, K.; Hirzberger, J.; Zouganelis, I.;
Strugarek, A.; Brun, A. S.; Alexandre, M.; Berghmans, D.; Raouafi,
N. E.; Wiegelmann, T.; Pagano, P.; Arge, C. N.; Nieves-Chinchilla,
T.; Lavarra, M.; Poirier, N.; Amari, T.; Aran, A.; Andretta, V.;
Antonucci, E.; Anastasiadis, A.; Auchère, F.; Bellot Rubio, L.;
Nicula, B.; Bonnin, X.; Bouchemit, M.; Budnik, E.; Caminade, S.;
Cecconi, B.; Carlyle, J.; Cernuda, I.; Davila, J. M.; Etesi, L.;
Espinosa Lara, F.; Fedorov, A.; Fineschi, S.; Fludra, A.; Génot,
V.; Georgoulis, M. K.; Gilbert, H. R.; Giunta, A.; Gomez-Herrero, R.;
Guest, S.; Haberreiter, M.; Hassler, D.; Henney, C. J.; Howard, R. A.;
Horbury, T. S.; Janvier, M.; Jones, S. I.; Kozarev, K.; Kraaikamp,
E.; Kouloumvakos, A.; Krucker, S.; Lagg, A.; Linker, J.; Lavraud,
B.; Louarn, P.; Maksimovic, M.; Maloney, S.; Mann, G.; Masson, A.;
Müller, D.; Önel, H.; Osuna, P.; Orozco Suarez, D.; Owen, C. J.;
Papaioannou, A.; Pérez-Suárez, D.; Rodriguez-Pacheco, J.; Parenti,
S.; Pariat, E.; Peter, H.; Plunkett, S.; Pomoell, J.; Raines, J. M.;
Riethmüller, T. L.; Rich, N.; Rodriguez, L.; Romoli, M.; Sanchez,
L.; Solanki, S. K.; St Cyr, O. C.; Straus, T.; Susino, R.; Teriaca,
L.; del Toro Iniesta, J. C.; Ventura, R.; Verbeeck, C.; Vilmer, N.;
Warmuth, A.; Walsh, A. P.; Watson, C.; Williams, D.; Wu, Y.; Zhukov,
A. N.
2020A&A...642A...2R Altcode:
Context. The Solar Orbiter spacecraft will be equipped with a wide
range of remote-sensing (RS) and in situ (IS) instruments to record
novel and unprecedented measurements of the solar atmosphere and
the inner heliosphere. To take full advantage of these new datasets,
tools and techniques must be developed to ease multi-instrument and
multi-spacecraft studies. In particular the currently inaccessible
low solar corona below two solar radii can only be observed
remotely. Furthermore techniques must be used to retrieve coronal
plasma properties in time and in three dimensional (3D) space. Solar
Orbiter will run complex observation campaigns that provide interesting
opportunities to maximise the likelihood of linking IS data to their
source region near the Sun. Several RS instruments can be directed
to specific targets situated on the solar disk just days before
data acquisition. To compare IS and RS, data we must improve our
understanding of how heliospheric probes magnetically connect to the
solar disk. Aims: The aim of the present paper is to briefly
review how the current modelling of the Sun and its atmosphere
can support Solar Orbiter science. We describe the results of a
community-led effort by European Space Agency's Modelling and Data
Analysis Working Group (MADAWG) to develop different models, tools,
and techniques deemed necessary to test different theories for the
physical processes that may occur in the solar plasma. The focus here
is on the large scales and little is described with regards to kinetic
processes. To exploit future IS and RS data fully, many techniques have
been adapted to model the evolving 3D solar magneto-plasma from the
solar interior to the solar wind. A particular focus in the paper is
placed on techniques that can estimate how Solar Orbiter will connect
magnetically through the complex coronal magnetic fields to various
photospheric and coronal features in support of spacecraft operations
and future scientific studies. Methods: Recent missions such as
STEREO, provided great opportunities for RS, IS, and multi-spacecraft
studies. We summarise the achievements and highlight the challenges
faced during these investigations, many of which motivated the Solar
Orbiter mission. We present the new tools and techniques developed
by the MADAWG to support the science operations and the analysis of
the data from the many instruments on Solar Orbiter. Results:
This article reviews current modelling and tool developments that ease
the comparison of model results with RS and IS data made available
by current and upcoming missions. It also describes the modelling
strategy to support the science operations and subsequent exploitation
of Solar Orbiter data in order to maximise the scientific output
of the mission. Conclusions: The on-going community effort
presented in this paper has provided new models and tools necessary
to support mission operations as well as the science exploitation of
the Solar Orbiter data. The tools and techniques will no doubt evolve
significantly as we refine our procedure and methodology during the
first year of operations of this highly promising mission.

---------------------------------------------------------
Title: The Dimmest State of the Sun
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.; Rempel, M.;
Anusha, L. S.; Shapiro, A. I.; Tagirov, R. V.; Witzke, V.
2020GeoRL..4790243Y Altcode: 2021arXiv210209487Y
How the solar electromagnetic energy entering the Earth's atmosphere
varied since preindustrial times is an important consideration in
the climate change debate. Detrimental to this debate, estimates
of the change in total solar irradiance (TSI) since the Maunder
minimum, an extended period of weak solar activity preceding the
industrial revolution, differ markedly, ranging from a drop of 0.75
W m-2 to a rise of 6.3 W m-2. Consequently, the
exact contribution by solar forcing to the rise in global temperatures
over the past centuries remains inconclusive. Adopting a novel approach
based on state-of-the-art solar imagery and numerical simulations, we
establish the TSI level of the Sun when it is in its least-active state
to be 2.0 ± 0.7 W m-2 below the 2019 level. This means TSI
could not have risen since the Maunder minimum by more than this amount,
thus restricting the possible role of solar forcing in global warming.

---------------------------------------------------------
Title: The Solar Orbiter Science Activity Plan. Translating solar
and heliospheric physics questions into action
Authors: Zouganelis, I.; De Groof, A.; Walsh, A. P.; Williams, D. R.;
Müller, D.; St Cyr, O. C.; Auchère, F.; Berghmans, D.; Fludra,
A.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic, M.;
Owen, C. J.; Rodríguez-Pacheco, J.; Romoli, M.; Solanki, S. K.;
Watson, C.; Sanchez, L.; Lefort, J.; Osuna, P.; Gilbert, H. R.;
Nieves-Chinchilla, T.; Abbo, L.; Alexandrova, O.; Anastasiadis, A.;
Andretta, V.; Antonucci, E.; Appourchaux, T.; Aran, A.; Arge, C. N.;
Aulanier, G.; Baker, D.; Bale, S. D.; Battaglia, M.; Bellot Rubio,
L.; Bemporad, A.; Berthomier, M.; Bocchialini, K.; Bonnin, X.; Brun,
A. S.; Bruno, R.; Buchlin, E.; Büchner, J.; Bucik, R.; Carcaboso,
F.; Carr, R.; Carrasco-Blázquez, I.; Cecconi, B.; Cernuda Cangas, I.;
Chen, C. H. K.; Chitta, L. P.; Chust, T.; Dalmasse, K.; D'Amicis, R.;
Da Deppo, V.; De Marco, R.; Dolei, S.; Dolla, L.; Dudok de Wit, T.;
van Driel-Gesztelyi, L.; Eastwood, J. P.; Espinosa Lara, F.; Etesi,
L.; Fedorov, A.; Félix-Redondo, F.; Fineschi, S.; Fleck, B.; Fontaine,
D.; Fox, N. J.; Gandorfer, A.; Génot, V.; Georgoulis, M. K.; Gissot,
S.; Giunta, A.; Gizon, L.; Gómez-Herrero, R.; Gontikakis, C.; Graham,
G.; Green, L.; Grundy, T.; Haberreiter, M.; Harra, L. K.; Hassler,
D. M.; Hirzberger, J.; Ho, G. C.; Hurford, G.; Innes, D.; Issautier,
K.; James, A. W.; Janitzek, N.; Janvier, M.; Jeffrey, N.; Jenkins,
J.; Khotyaintsev, Y.; Klein, K. -L.; Kontar, E. P.; Kontogiannis,
I.; Krafft, C.; Krasnoselskikh, V.; Kretzschmar, M.; Labrosse, N.;
Lagg, A.; Landini, F.; Lavraud, B.; Leon, I.; Lepri, S. T.; Lewis,
G. R.; Liewer, P.; Linker, J.; Livi, S.; Long, D. M.; Louarn, P.;
Malandraki, O.; Maloney, S.; Martinez-Pillet, V.; Martinovic, M.;
Masson, A.; Matthews, S.; Matteini, L.; Meyer-Vernet, N.; Moraitis,
K.; Morton, R. J.; Musset, S.; Nicolaou, G.; Nindos, A.; O'Brien,
H.; Orozco Suarez, D.; Owens, M.; Pancrazzi, M.; Papaioannou, A.;
Parenti, S.; Pariat, E.; Patsourakos, S.; Perrone, D.; Peter, H.;
Pinto, R. F.; Plainaki, C.; Plettemeier, D.; Plunkett, S. P.; Raines,
J. M.; Raouafi, N.; Reid, H.; Retino, A.; Rezeau, L.; Rochus, P.;
Rodriguez, L.; Rodriguez-Garcia, L.; Roth, M.; Rouillard, A. P.;
Sahraoui, F.; Sasso, C.; Schou, J.; Schühle, U.; Sorriso-Valvo, L.;
Soucek, J.; Spadaro, D.; Stangalini, M.; Stansby, D.; Steller, M.;
Strugarek, A.; Štverák, Š.; Susino, R.; Telloni, D.; Terasa, C.;
Teriaca, L.; Toledo-Redondo, S.; del Toro Iniesta, J. C.; Tsiropoula,
G.; Tsounis, A.; Tziotziou, K.; Valentini, F.; Vaivads, A.; Vecchio,
A.; Velli, M.; Verbeeck, C.; Verdini, A.; Verscharen, D.; Vilmer, N.;
Vourlidas, A.; Wicks, R.; Wimmer-Schweingruber, R. F.; Wiegelmann,
T.; Young, P. R.; Zhukov, A. N.
2020A&A...642A...3Z Altcode: 2020arXiv200910772Z
Solar Orbiter is the first space mission observing the solar plasma
both in situ and remotely, from a close distance, in and out of the
ecliptic. The ultimate goal is to understand how the Sun produces
and controls the heliosphere, filling the Solar System and driving
the planetary environments. With six remote-sensing and four in-situ
instrument suites, the coordination and planning of the operations are
essential to address the following four top-level science questions:
(1) What drives the solar wind and where does the coronal magnetic field
originate?; (2) How do solar transients drive heliospheric variability?;
(3) How do solar eruptions produce energetic particle radiation that
fills the heliosphere?; (4) How does the solar dynamo work and drive
connections between the Sun and the heliosphere? Maximising the
mission's science return requires considering the characteristics
of each orbit, including the relative position of the spacecraft
to Earth (affecting downlink rates), trajectory events (such
as gravitational assist manoeuvres), and the phase of the solar
activity cycle. Furthermore, since each orbit's science telemetry
will be downloaded over the course of the following orbit, science
operations must be planned at mission level, rather than at the level
of individual orbits. It is important to explore the way in which those
science questions are translated into an actual plan of observations
that fits into the mission, thus ensuring that no opportunities are
missed. First, the overarching goals are broken down into specific,
answerable questions along with the required observations and the
so-called Science Activity Plan (SAP) is developed to achieve this. The
SAP groups objectives that require similar observations into Solar
Orbiter Observing Plans, resulting in a strategic, top-level view of
the optimal opportunities for science observations during the mission
lifetime. This allows for all four mission goals to be addressed. In
this paper, we introduce Solar Orbiter's SAP through a series of
examples and the strategy being followed.

---------------------------------------------------------
Title: Inflection point in the power spectrum of stellar brightness
variations. III. Facular versus spot dominance on stars with known
rotation periods
Authors: Amazo-Gómez, E. M.; Shapiro, A. I.; Solanki, S. K.; Kopp,
G.; Oshagh, M.; Reinhold, T.; Reiners, A.
2020A&A...642A.225A Altcode: 2020arXiv200811492A
Context. Stellar rotation periods can be determined by observing
brightness variations caused by active magnetic regions transiting
visible stellar disk as the star rotates. Successful stellar photometric
surveys stemming from the Kepler and TESS observations have led to
the determination of rotation periods in tens of thousands of young
and active stars. However, there is still a lack of information on
the rotation periods of older and less active stars like the Sun. The
irregular temporal profiles of light curves caused by the decay times of
active regions, which are comparable to, or even shorter than, stellar
rotation periods, in combination with the random emergence of active
regions make period determination for such stars very difficult. 
Aims: We tested the performance of a new method for the determination
of stellar rotation periods against stars with previously determined
rotation periods. The method is based on calculating the gradient of the
power spectrum (GPS) and identifying the position of the inflection
point (i.e. point with the highest gradient). The GPS method is
specifically aimed at determining rotation periods of low-activity
stars like the Sun. Methods: We applied the GPS method to 1047
Sun-like stars observed by the Kepler telescope. We considered two
stellar samples individually: one with near-solar rotation periods
(24-27.4 d) and a broad range of effective temperatures (5000-6000 K)
and the other with near-solar effective temperatures (5700-5900 K)
and a broad range of rotation periods (15-40 d). Results: We
show that the GPS method returns precise values for stellar rotation
periods. Furthermore, it allows us to constrain the ratio between
facular and spot areas of active regions at the moment of their
emergence. We also show that the relative facular area decreases with
the stellar rotation rate. Conclusions: Our results suggest
that the GPS method can be successfully applied to retrieve the
periods of stars with both regular and non-regular light curves. Full Table 2 is only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A225">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/642/A225</A>

---------------------------------------------------------
Title: Autonomous on-board data processing and instrument calibration
software for the Polarimetric and Helioseismic Imager on-board the
Solar Orbiter mission
Authors: Albert, Kinga; Hirzberger, Johann; Kolleck, Martin; Jorge,
Nestor Albelo; Busse, Dennis; Rodríguez, Julian Blanco; Carrascosa,
Juan Pedro Cobos; Fiethe, Björn; Gandorfer, Achim; Germerott, Dietmar;
Guan, Yejun; Guerrero, Lucas; Gutierrez-Marques, Pablo; Expósito,
David Hernández; Lange, Tobias; Michalik, Harald; Suárez, David
Orozco; Schou, Jesper; Solanki, Sami K.; del Toro Iniesta, José
Carlos; Woch, Joachim
2020JATIS...6d8004A Altcode:
A frequent problem arising for deep space missions is the discrepancy
between the amount of data desired to be transmitted to the ground
and the available telemetry bandwidth. A part of these data consists
of scientific observations, being complemented by calibration data
to help remove instrumental effects. We present our solution for this
discrepancy, implemented for the Polarimetric and Helioseismic Imager
on-board the Solar Orbiter mission, the first solar spectropolarimeter
in deep space. We implemented an on-board data reduction system that
processes calibration data, applies them to the raw science observables,
and derives science-ready physical parameters. This process reduces
the raw data for a single measurement from 24 images to five, thus
reducing the amount of downlinked data, and in addition, renders the
transmission of the calibration data unnecessary. Both these on-board
actions are completed autonomously.

---------------------------------------------------------
Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Solanki, S. K.; del Toro Iniesta, J. C.; Woch, J.; Gandorfer,
A.; Hirzberger, J.; Alvarez-Herrero, A.; Appourchaux, T.; Martínez
Pillet, V.; Pérez-Grande, I.; Sanchis Kilders, E.; Schmidt, W.;
Gómez Cama, J. M.; Michalik, H.; Deutsch, W.; Fernandez-Rico, G.;
Grauf, B.; Gizon, L.; Heerlein, K.; Kolleck, M.; Lagg, A.; Meller, R.;
Müller, R.; Schühle, U.; Staub, J.; Albert, K.; Alvarez Copano, M.;
Beckmann, U.; Bischoff, J.; Busse, D.; Enge, R.; Frahm, S.; Germerott,
D.; Guerrero, L.; Löptien, B.; Meierdierks, T.; Oberdorfer, D.;
Papagiannaki, I.; Ramanath, S.; Schou, J.; Werner, S.; Yang, D.;
Zerr, A.; Bergmann, M.; Bochmann, J.; Heinrichs, J.; Meyer, S.;
Monecke, M.; Müller, M. -F.; Sperling, M.; Álvarez García, D.;
Aparicio, B.; Balaguer Jiménez, M.; Bellot Rubio, L. R.; Cobos
Carracosa, J. P.; Girela, F.; Hernández Expósito, D.; Herranz, M.;
Labrousse, P.; López Jiménez, A.; Orozco Suárez, D.; Ramos, J. L.;
Barandiarán, J.; Bastide, L.; Campuzano, C.; Cebollero, M.; Dávila,
B.; Fernández-Medina, A.; García Parejo, P.; Garranzo-García, D.;
Laguna, H.; Martín, J. A.; Navarro, R.; Núñez Peral, A.; Royo, M.;
Sánchez, A.; Silva-López, M.; Vera, I.; Villanueva, J.; Fourmond,
J. -J.; de Galarreta, C. Ruiz; Bouzit, M.; Hervier, V.; Le Clec'h,
J. C.; Szwec, N.; Chaigneau, M.; Buttice, V.; Dominguez-Tagle, C.;
Philippon, A.; Boumier, P.; Le Cocguen, R.; Baranjuk, G.; Bell,
A.; Berkefeld, Th.; Baumgartner, J.; Heidecke, F.; Maue, T.; Nakai,
E.; Scheiffelen, T.; Sigwarth, M.; Soltau, D.; Volkmer, R.; Blanco
Rodríguez, J.; Domingo, V.; Ferreres Sabater, A.; Gasent Blesa,
J. L.; Rodríguez Martínez, P.; Osorno Caudel, D.; Bosch, J.; Casas,
A.; Carmona, M.; Herms, A.; Roma, D.; Alonso, G.; Gómez-Sanjuan, A.;
Piqueras, J.; Torralbo, I.; Fiethe, B.; Guan, Y.; Lange, T.; Michel,
H.; Bonet, J. A.; Fahmy, S.; Müller, D.; Zouganelis, I.
2020A&A...642A..11S Altcode: 2019arXiv190311061S
 Aims: This paper describes the Polarimetric and Helioseismic
Imager on the Solar Orbiter mission (SO/PHI), the first magnetograph and
helioseismology instrument to observe the Sun from outside the Sun-Earth
line. It is the key instrument meant to address the top-level science
question: How does the solar dynamo work and drive connections between
the Sun and the heliosphere? SO/PHI will also play an important role
in answering the other top-level science questions of Solar Orbiter,
while hosting the potential of a rich return in further science. Methods: SO/PHI measures the Zeeman effect and the Doppler shift
in the Fe I 617.3 nm spectral line. To this end, the instrument
carries out narrow-band imaging spectro-polarimetry using a tunable
LiNbO3 Fabry-Perot etalon, while the polarisation modulation
is done with liquid crystal variable retarders. The line and the nearby
continuum are sampled at six wavelength points and the data are recorded
by a 2k × 2k CMOS detector. To save valuable telemetry, the raw data
are reduced on board, including being inverted under the assumption of
a Milne-Eddington atmosphere, although simpler reduction methods are
also available on board. SO/PHI is composed of two telescopes; one,
the Full Disc Telescope, covers the full solar disc at all phases of
the orbit, while the other, the High Resolution Telescope, can resolve
structures as small as 200 km on the Sun at closest perihelion. The high
heat load generated through proximity to the Sun is greatly reduced by
the multilayer-coated entrance windows to the two telescopes that allow
less than 4% of the total sunlight to enter the instrument, most of
it in a narrow wavelength band around the chosen spectral line. 
Results: SO/PHI was designed and built by a consortium having partners
in Germany, Spain, and France. The flight model was delivered to
Airbus Defence and Space, Stevenage, and successfully integrated into
the Solar Orbiter spacecraft. A number of innovations were introduced
compared with earlier space-based spectropolarimeters, thus allowing
SO/PHI to fit into the tight mass, volume, power and telemetry budgets
provided by the Solar Orbiter spacecraft and to meet the (e.g. thermal)
challenges posed by the mission's highly elliptical orbit.

---------------------------------------------------------
Title: The Solar Orbiter SPICE instrument. An extreme UV imaging
spectrometer
Authors: SPICE Consortium; Anderson, M.; Appourchaux, T.; Auchère, F.;
Aznar Cuadrado, R.; Barbay, J.; Baudin, F.; Beardsley, S.; Bocchialini,
K.; Borgo, B.; Bruzzi, D.; Buchlin, E.; Burton, G.; Büchel, V.;
Caldwell, M.; Caminade, S.; Carlsson, M.; Curdt, W.; Davenne, J.;
Davila, J.; Deforest, C. E.; Del Zanna, G.; Drummond, D.; Dubau,
J.; Dumesnil, C.; Dunn, G.; Eccleston, P.; Fludra, A.; Fredvik, T.;
Gabriel, A.; Giunta, A.; Gottwald, A.; Griffin, D.; Grundy, T.; Guest,
S.; Gyo, M.; Haberreiter, M.; Hansteen, V.; Harrison, R.; Hassler,
D. M.; Haugan, S. V. H.; Howe, C.; Janvier, M.; Klein, R.; Koller,
S.; Kucera, T. A.; Kouliche, D.; Marsch, E.; Marshall, A.; Marshall,
G.; Matthews, S. A.; McQuirk, C.; Meining, S.; Mercier, C.; Morris,
N.; Morse, T.; Munro, G.; Parenti, S.; Pastor-Santos, C.; Peter, H.;
Pfiffner, D.; Phelan, P.; Philippon, A.; Richards, A.; Rogers, K.;
Sawyer, C.; Schlatter, P.; Schmutz, W.; Schühle, U.; Shaughnessy,
B.; Sidher, S.; Solanki, S. K.; Speight, R.; Spescha, M.; Szwec, N.;
Tamiatto, C.; Teriaca, L.; Thompson, W.; Tosh, I.; Tustain, S.; Vial,
J. -C.; Walls, B.; Waltham, N.; Wimmer-Schweingruber, R.; Woodward,
S.; Young, P.; de Groof, A.; Pacros, A.; Williams, D.; Müller, D.
2020A&A...642A..14S Altcode: 2019arXiv190901183A; 2019arXiv190901183S
 Aims: The Spectral Imaging of the Coronal Environment (SPICE)
instrument is a high-resolution imaging spectrometer operating at
extreme ultraviolet wavelengths. In this paper, we present the concept,
design, and pre-launch performance of this facility instrument on the
ESA/NASA Solar Orbiter mission. Methods: The goal of this paper
is to give prospective users a better understanding of the possible
types of observations, the data acquisition, and the sources that
contribute to the instrument's signal. Results: The paper
discusses the science objectives, with a focus on the SPICE-specific
aspects, before presenting the instrument's design, including optical,
mechanical, thermal, and electronics aspects. This is followed by a
characterisation and calibration of the instrument's performance. The
paper concludes with descriptions of the operations concept and data
processing. Conclusions: The performance measurements of the
various instrument parameters meet the requirements derived from the
mission's science objectives. The SPICE instrument is ready to perform
measurements that will provide vital contributions to the scientific
success of the Solar Orbiter mission.

---------------------------------------------------------
Title: Understanding the origins of the heliosphere: integrating
observations and measurements from Parker Solar Probe, Solar Orbiter,
and other space- and ground-based observatories
Authors: Velli, M.; Harra, L. K.; Vourlidas, A.; Schwadron,
N.; Panasenco, O.; Liewer, P. C.; Müller, D.; Zouganelis, I.;
St Cyr, O. C.; Gilbert, H.; Nieves-Chinchilla, T.; Auchère, F.;
Berghmans, D.; Fludra, A.; Horbury, T. S.; Howard, R. A.; Krucker,
S.; Maksimovic, M.; Owen, C. J.; Rodríguez-Pacheco, J.; Romoli,
M.; Solanki, S. K.; Wimmer-Schweingruber, R. F.; Bale, S.; Kasper,
J.; McComas, D. J.; Raouafi, N.; Martinez-Pillet, V.; Walsh, A. P.;
De Groof, A.; Williams, D.
2020A&A...642A...4V Altcode:
Context. The launch of Parker Solar Probe (PSP) in 2018, followed
by Solar Orbiter (SO) in February 2020, has opened a new window in
the exploration of solar magnetic activity and the origin of the
heliosphere. These missions, together with other space observatories
dedicated to solar observations, such as the Solar Dynamics Observatory,
Hinode, IRIS, STEREO, and SOHO, with complementary in situ observations
from WIND and ACE, and ground based multi-wavelength observations
including the DKIST observatory that has just seen first light,
promise to revolutionize our understanding of the solar atmosphere
and of solar activity, from the generation and emergence of the Sun's
magnetic field to the creation of the solar wind and the acceleration of
solar energetic particles. Aims: Here we describe the scientific
objectives of the PSP and SO missions, and highlight the potential for
discovery arising from synergistic observations. Here we put particular
emphasis on how the combined remote sensing and in situ observations of
SO, that bracket the outer coronal and inner heliospheric observations
by PSP, may provide a reconstruction of the solar wind and magnetic
field expansion from the Sun out to beyond the orbit of Mercury in the
first phases of the mission. In the later, out-of-ecliptic portions of
the SO mission, the solar surface magnetic field measurements from SO
and the multi-point white-light observations from both PSP and SO will
shed light on the dynamic, intermittent solar wind escaping from helmet
streamers, pseudo-streamers, and the confined coronal plasma, and on
solar energetic particle transport. Methods: Joint measurements
during PSP-SO alignments, and magnetic connections along the same
flux tube complemented by alignments with Earth, dual PSP-Earth,
and SO-Earth, as well as with STEREO-A, SOHO, and BepiColumbo will
allow a better understanding of the in situ evolution of solar-wind
plasma flows and the full three-dimensional distribution of the
solar wind from a purely observational point of view. Spectroscopic
observations of the corona, and optical and radio observations,
combined with direct in situ observations of the accelerating solar
wind will provide a new foundation for understanding the fundamental
physical processes leading to the energy transformations from solar
photospheric flows and magnetic fields into the hot coronal plasma
and magnetic fields and finally into the bulk kinetic energy of the
solar wind and solar energetic particles. Results: We discuss
the initial PSP observations, which already provide a compelling
rationale for new measurement campaigns by SO, along with ground-
and space-based assets within the synergistic context described above.

---------------------------------------------------------
Title: The Solar Orbiter mission. Science overview
Authors: Müller, D.; St. Cyr, O. C.; Zouganelis, I.; Gilbert, H. R.;
Marsden, R.; Nieves-Chinchilla, T.; Antonucci, E.; Auchère, F.;
Berghmans, D.; Horbury, T. S.; Howard, R. A.; Krucker, S.; Maksimovic,
M.; Owen, C. J.; Rochus, P.; Rodriguez-Pacheco, J.; Romoli, M.;
Solanki, S. K.; Bruno, R.; Carlsson, M.; Fludra, A.; Harra, L.;
Hassler, D. M.; Livi, S.; Louarn, P.; Peter, H.; Schühle, U.;
Teriaca, L.; del Toro Iniesta, J. C.; Wimmer-Schweingruber, R. F.;
Marsch, E.; Velli, M.; De Groof, A.; Walsh, A.; Williams, D.
2020A&A...642A...1M Altcode: 2020arXiv200900861M
 Aims: Solar Orbiter, the first mission of ESA's Cosmic Vision
2015-2025 programme and a mission of international collaboration between
ESA and NASA, will explore the Sun and heliosphere from close up and
out of the ecliptic plane. It was launched on 10 February 2020 04:03
UTC from Cape Canaveral and aims to address key questions of solar and
heliospheric physics pertaining to how the Sun creates and controls
the Heliosphere, and why solar activity changes with time. To answer
these, the mission carries six remote-sensing instruments to observe
the Sun and the solar corona, and four in-situ instruments to measure
the solar wind, energetic particles, and electromagnetic fields. In
this paper, we describe the science objectives of the mission, and how
these will be addressed by the joint observations of the instruments
onboard. Methods: The paper first summarises the mission-level
science objectives, followed by an overview of the spacecraft and
payload. We report the observables and performance figures of each
instrument, as well as the trajectory design. This is followed by a
summary of the science operations concept. The paper concludes with a
more detailed description of the science objectives. Results:
Solar Orbiter will combine in-situ measurements in the heliosphere
with high-resolution remote-sensing observations of the Sun to address
fundamental questions of solar and heliospheric physics. The performance
of the Solar Orbiter payload meets the requirements derived from the
mission's science objectives. Its science return will be augmented
further by coordinated observations with other space missions and
ground-based observatories. ARRAY(0x207ce98)

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Title: The Solar Orbiter EUI instrument: The Extreme Ultraviolet
Imager
Authors: Rochus, P.; Auchère, F.; Berghmans, D.; Harra, L.; Schmutz,
W.; Schühle, U.; Addison, P.; Appourchaux, T.; Aznar Cuadrado,
R.; Baker, D.; Barbay, J.; Bates, D.; BenMoussa, A.; Bergmann, M.;
Beurthe, C.; Borgo, B.; Bonte, K.; Bouzit, M.; Bradley, L.; Büchel,
V.; Buchlin, E.; Büchner, J.; Cabé, F.; Cadiergues, L.; Chaigneau,
M.; Chares, B.; Choque Cortez, C.; Coker, P.; Condamin, M.; Coumar,
S.; Curdt, W.; Cutler, J.; Davies, D.; Davison, G.; Defise, J. -M.;
Del Zanna, G.; Delmotte, F.; Delouille, V.; Dolla, L.; Dumesnil, C.;
Dürig, F.; Enge, R.; François, S.; Fourmond, J. -J.; Gillis, J. -M.;
Giordanengo, B.; Gissot, S.; Green, L. M.; Guerreiro, N.; Guilbaud,
A.; Gyo, M.; Haberreiter, M.; Hafiz, A.; Hailey, M.; Halain, J. -P.;
Hansotte, J.; Hecquet, C.; Heerlein, K.; Hellin, M. -L.; Hemsley, S.;
Hermans, A.; Hervier, V.; Hochedez, J. -F.; Houbrechts, Y.; Ihsan,
K.; Jacques, L.; Jérôme, A.; Jones, J.; Kahle, M.; Kennedy, T.;
Klaproth, M.; Kolleck, M.; Koller, S.; Kotsialos, E.; Kraaikamp, E.;
Langer, P.; Lawrenson, A.; Le Clech', J. -C.; Lenaerts, C.; Liebecq,
S.; Linder, D.; Long, D. M.; Mampaey, B.; Markiewicz-Innes, D.;
Marquet, B.; Marsch, E.; Matthews, S.; Mazy, E.; Mazzoli, A.; Meining,
S.; Meltchakov, E.; Mercier, R.; Meyer, S.; Monecke, M.; Monfort,
F.; Morinaud, G.; Moron, F.; Mountney, L.; Müller, R.; Nicula, B.;
Parenti, S.; Peter, H.; Pfiffner, D.; Philippon, A.; Phillips, I.;
Plesseria, J. -Y.; Pylyser, E.; Rabecki, F.; Ravet-Krill, M. -F.;
Rebellato, J.; Renotte, E.; Rodriguez, L.; Roose, S.; Rosin, J.;
Rossi, L.; Roth, P.; Rouesnel, F.; Roulliay, M.; Rousseau, A.; Ruane,
K.; Scanlan, J.; Schlatter, P.; Seaton, D. B.; Silliman, K.; Smit,
S.; Smith, P. J.; Solanki, S. K.; Spescha, M.; Spencer, A.; Stegen,
K.; Stockman, Y.; Szwec, N.; Tamiatto, C.; Tandy, J.; Teriaca, L.;
Theobald, C.; Tychon, I.; van Driel-Gesztelyi, L.; Verbeeck, C.;
Vial, J. -C.; Werner, S.; West, M. J.; Westwood, D.; Wiegelmann, T.;
Willis, G.; Winter, B.; Zerr, A.; Zhang, X.; Zhukov, A. N.
2020A&A...642A...8R Altcode:
Context. The Extreme Ultraviolet Imager (EUI) is part of the remote
sensing instrument package of the ESA/NASA Solar Orbiter mission
that will explore the inner heliosphere and observe the Sun from
vantage points close to the Sun and out of the ecliptic. Solar Orbiter
will advance the "connection science" between solar activity and the
heliosphere. Aims: With EUI we aim to improve our understanding
of the structure and dynamics of the solar atmosphere, globally as well
as at high resolution, and from high solar latitude perspectives. 
Methods: The EUI consists of three telescopes, the Full Sun Imager and
two High Resolution Imagers, which are optimised to image in Lyman-α
and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere
up to corona. The EUI is designed to cope with the strong constraints
imposed by the Solar Orbiter mission characteristics. Limited telemetry
availability is compensated by state-of-the-art image compression,
onboard image processing, and event selection. The imposed power
limitations and potentially harsh radiation environment necessitate
the use of novel CMOS sensors. As the unobstructed field of view of
the telescopes needs to protrude through the spacecraft's heat shield,
the apertures have been kept as small as possible, without compromising
optical performance. This led to a systematic effort to optimise the
throughput of every optical element and the reduction of noise levels
in the sensor. Results: In this paper we review the design
of the two elements of the EUI instrument: the Optical Bench System
and the Common Electronic Box. Particular attention is also given to
the onboard software, the intended operations, the ground software,
and the foreseen data products. Conclusions: The EUI will
bring unique science opportunities thanks to its specific design,
its viewpoint, and to the planned synergies with the other Solar
Orbiter instruments. In particular, we highlight science opportunities
brought by the out-of-ecliptic vantage point of the solar poles,
the high-resolution imaging of the high chromosphere and corona,
and the connection to the outer corona as observed by coronagraphs.

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Title: PMI: The Photospheric Magnetic Field Imager
Authors: Staub, Jan; Fernandez-Rico, German; Gandorfer, Achim; Gizon,
Laurent; Hirzberger, Johann; Kraft, Stefan; Lagg, Andreas; Schou,
Jesper; Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Wiegelmann,
Thomas; Woch, Joachim
2020JSWSC..10...54S Altcode:
We describe the design and the capabilities of the Photospheric Magnetic
field Imager (PMI), a compact and lightweight vector magnetograph,
which is being developed for ESA's Lagrange mission to the Lagrange
L5 point. After listing the design requirements and give a scientific
justification for them, we describe the technical implementation and
the design solution capable of fulfilling these requirements. This is
followed by a description of the hardware architecture as well as the
operations principle. An outlook on the expected performance concludes
the paper.

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Title: Metis: the Solar Orbiter visible light and ultraviolet
coronal imager
Authors: Antonucci, Ester; Romoli, Marco; Andretta, Vincenzo; Fineschi,
Silvano; Heinzel, Petr; Moses, J. Daniel; Naletto, Giampiero; Nicolini,
Gianalfredo; Spadaro, Daniele; Teriaca, Luca; Berlicki, Arkadiusz;
Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
Mauro; Frassetto, Fabio; Heerlein, Klaus; Landini, Federico; Magli,
Enrico; Marco Malvezzi, Andrea; Massone, Giuseppe; Melich, Radek;
Nicolosi, Piergiorgio; Noci, Giancarlo; Pancrazzi, Maurizio; Pelizzo,
Maria G.; Poletto, Luca; Sasso, Clementina; Schühle, Udo; Solanki,
Sami K.; Strachan, Leonard; Susino, Roberto; Tondello, Giuseppe;
Uslenghi, Michela; Woch, Joachim; Abbo, Lucia; Bemporad, Alessandro;
Casti, Marta; Dolei, Sergio; Grimani, Catia; Messerotti, Mauro;
Ricci, Marco; Straus, Thomas; Telloni, Daniele; Zuppella, Paola;
Auchère, Frederic; Bruno, Roberto; Ciaravella, Angela; Corso,
Alain J.; Alvarez Copano, Miguel; Aznar Cuadrado, Regina; D'Amicis,
Raffaella; Enge, Reiner; Gravina, Alessio; Jejčič, Sonja; Lamy,
Philippe; Lanzafame, Alessandro; Meierdierks, Thimo; Papagiannaki,
Ioanna; Peter, Hardi; Fernandez Rico, German; Giday Sertsu, Mewael;
Staub, Jan; Tsinganos, Kanaris; Velli, Marco; Ventura, Rita; Verroi,
Enrico; Vial, Jean-Claude; Vives, Sebastien; Volpicelli, Antonio;
Werner, Stephan; Zerr, Andreas; Negri, Barbara; Castronuovo, Marco;
Gabrielli, Alessandro; Bertacin, Roberto; Carpentiero, Rita; Natalucci,
Silvia; Marliani, Filippo; Cesa, Marco; Laget, Philippe; Morea, Danilo;
Pieraccini, Stefano; Radaelli, Paolo; Sandri, Paolo; Sarra, Paolo;
Cesare, Stefano; Del Forno, Felice; Massa, Ernesto; Montabone, Mauro;
Mottini, Sergio; Quattropani, Daniele; Schillaci, Tiziano; Boccardo,
Roberto; Brando, Rosario; Pandi, Arianna; Baietto, Cristian; Bertone,
Riccardo; Alvarez-Herrero, Alberto; García Parejo, Pilar; Cebollero,
María; Amoruso, Mauro; Centonze, Vito
2020A&A...642A..10A Altcode: 2019arXiv191108462A
 Aims: Metis is the first solar coronagraph designed for a
space mission and is capable of performing simultaneous imaging of the
off-limb solar corona in both visible and UV light. The observations
obtained with Metis aboard the Solar Orbiter ESA-NASA observatory
will enable us to diagnose, with unprecedented temporal coverage and
spatial resolution, the structures and dynamics of the full corona
in a square field of view (FoV) of ±2.9° in width, with an inner
circular FoV at 1.6°, thus spanning the solar atmosphere from 1.7
R⊙ to about 9 R⊙, owing to the eccentricity
of the spacecraft orbit. Due to the uniqueness of the Solar Orbiter
mission profile, Metis will be able to observe the solar corona
from a close (0.28 AU, at the closest perihelion) vantage point,
achieving increasing out-of-ecliptic views with the increase of the
orbit inclination over time. Moreover, observations near perihelion,
during the phase of lower rotational velocity of the solar surface
relative to the spacecraft, allow longer-term studies of the off-limb
coronal features, thus finally disentangling their intrinsic evolution
from effects due to solar rotation. Methods: Thanks to a novel
occultation design and a combination of a UV interference coating of
the mirrors and a spectral bandpass filter, Metis images the solar
corona simultaneously in the visible light band, between 580 and 640
nm, and in the UV H I Lyman-α line at 121.6 nm. The visible light
channel also includes a broadband polarimeter able to observe the
linearly polarised component of the K corona. The coronal images in
both the UV H I Lyman-α and polarised visible light are obtained at
high spatial resolution with a spatial scale down to about 2000 km
and 15 000 km at perihelion, in the cases of the visible and UV light,
respectively. A temporal resolution down to 1 s can be achieved when
observing coronal fluctuations in visible light. Results: The
Metis measurements, obtained from different latitudes, will allow for
complete characterisation of the main physical parameters and dynamics
of the electron and neutral hydrogen/proton plasma components of the
corona in the region where the solar wind undergoes the acceleration
process and where the onset and initial propagation of coronal mass
ejections (CMEs) take place. The near-Sun multi-wavelength coronal
imaging performed with Metis, combined with the unique opportunities
offered by the Solar Orbiter mission, can effectively address crucial
issues of solar physics such as: the origin and heating/acceleration
of the fast and slow solar wind streams; the origin, acceleration,
and transport of the solar energetic particles; and the transient
ejection of coronal mass and its evolution in the inner heliosphere,
thus significantly improving our understanding of the region connecting
the Sun to the heliosphere and of the processes generating and driving
the solar wind and coronal mass ejections. Conclusions: This
paper presents the scientific objectives and requirements, the overall
optical design of the Metis instrument, the thermo-mechanical design,
and the processing and power unit; reports on the results of the
campaigns dedicated to integration, alignment, and tests, and to
the characterisation of the instrument performance; describes the
operation concept, data handling, and software tools; and, finally,
the diagnostic techniques to be applied to the data, as well as a brief
description of the expected scientific products. The performance of the
instrument measured during calibrations ensures that the scientific
objectives of Metis can be pursued with success. Metis website:
<A href="http://metis.oato.inaf.it">http://metis.oato.inaf.it</A>

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Title: Simulating Variability due to Faculae and Spots on GKM Stars
Authors: Johnson, Luke; Unruh, Yvonne; Norris, Charlotte; Solanki,
Sami; Krivova, Natalie; Witzke, Veronika; Shapiro, Alexander
2020EPSC...14..844J Altcode:
Stellar variability is a dominant noise source in exoplanet surveys
and results largely from the presence of photospheric faculae and
spots. The implementation of faculae in lightcurve models is an open
problem, with scaling based on spectra equivalent to hot stellar
atmospheres or assuming a solar-derived facular contrast. We model the
lightcurves of active late-type stars as they rotate, using emergent
intensity spectra calculated from 3D magnetoconvection simulations
of G, K and M-type stellar atmosphere regions at different viewing
angles to reproduce centre-to-limb brightness variations. We present
mean expected variability levels for several cases and compare with
solar and stellar observations. We also investigate the wavelength
dependence of variability. Fig. 1: Example of our geometrically
accurate lightcurve modelling approach. Top: normalised intensity
maps of a limb darkened, solar-type star viewed in the \textit{Kepler}
band at rotational phase 0.5 with stellar inclinations 90 deg (left)
and 30 deg (right). At 90 deg, the star is viewed equator-on. Middle:
Corresponding lightcurves calculated at inclinations 90 deg (black line)
and 30 deg (red line). Bottom: HealPix map representing the active
stellar surface, cosine-scaled in latitude and flattened in longitude
to resemble a solar synoptic map. The quiet photosphere is displayed
in orange, facular regions are bright yellow and spot regions are dark
blue. The crosses represent the centres of the stellar discs in the
top panel. Fig. 2: Example showing simulated lightcurves calculated
at different wavelengths. Rotational lightcurves are on the left,
transit lightcurves on the right. In the centre, one hemisphere of the
simulated stellar surface is shown, with a quarter of the disc shown
in each wavelength band. 'Giant' spots and facular regions are used
in this example. The transit path is highlighted in grey.

---------------------------------------------------------
Title: Amplification of Brightness Variability by Active-region
Nesting in Solar-like Stars
Authors: Işık, Emre; Shapiro, Alexander I.; Solanki, Sami K.;
Krivova, Natalie A.
2020ApJ...901L..12I Altcode: 2020arXiv200900692I
Kepler observations revealed that hundreds of stars with near-solar
fundamental parameters and rotation periods have much stronger and
more regular brightness variations than the Sun. Here we identify one
possible reason for the peculiar behavior of these stars. Inspired by
solar nests of activity, we assume that the degree of inhomogeneity
of active-region (AR) emergence on such stars is higher than on the
Sun. To test our hypothesis, we model stellar light curves by injecting
ARs consisting of spots and faculae on stellar surfaces at various
rates and nesting patterns, using solar AR properties and differential
rotation. We show that a moderate increase of the emergence frequency
from the solar value combined with the increase of the degree of nesting
can explain the full range of observed amplitudes of variability of
Sun-like stars with nearly the solar rotation period. Furthermore,
nesting in the form of active longitudes, in which ARs tend to emerge
in the vicinity of two longitudes separated by 180°, leads to highly
regular, almost sine-like variability patterns, rather similar to
those observed in a number of solar-like stars.

---------------------------------------------------------
Title: Simulations Show that Vortex Flows Could Heat the Chromosphere
in Solar Plage
Authors: Yadav, N.; Cameron, R.; Solanki, S.
2020SPD....5120107Y Altcode:
Recent advances in both, observational techniques and numerical
simulations have enabled us to detect small-scale vortices in the solar
atmosphere. Vortices are ubiquitous throughout the solar surface and
at all layers of the solar atmosphere existing over a wide range of
spatial and temporal scales. Small-scale vortices are suggested to play
an important role in the energy transport of the solar atmosphere,
however, their physical properties remain poorly understood due
to limited resolution. We explored the relationship between vortex
flows at different spatial scales, analyze their physical properties,
and investigate their contribution to Poynting flux transport. Using
three-dimensional (3D) radiative magnetohydrodynamic (MHD)simulation
code 'MURaM', we perform numerical simulations of a unipolar solar
plage region. For detecting and isolating vortices, we use the
'Swirling Strength' criterion. We explore the spatial profiles of
physical quantities viz. density, horizontal velocity, etc. inside
these vortices. Moreover, to apprehend their general characteristics,
a statistical investigation is performed. We found that magnetic flux
tubes have a complex filamentary substructure abundant of small-scale
vortices. On their interfaces strong current sheets are formed that
may dissipate and heat the solar chromosphere. Statistically, vortices
have higher densities and higher temperatures than the average values
at the same geometrical height. We also degrade our simulation data to
get an effective spatial resolution of 50 km, 100 km, 250 km, and 500
km, respectively. Analyzing simulation data at different effective
resolutions, we found vortex flows existing over various spatial
scales. In high-resolution simulation data, we detect a large number
of small-scale vortices. Whereas, in the degraded data with relatively
poor resolutions, smaller vortices are averaged-out and larger vortices
are detected. The Poynting flux over vortex locations is more than
adequate to compensate for the radiative losses in the chromosphere
indicating their possible role in the chromospheric heating.

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Title: A Coronal Loop in a Box: Energy Generation, Heating and
Dynamics
Authors: Breu, C.; Peter, H.; Cameron, R.; Solanki, S.; Chitta, P.;
Przybylski, D.
2020SPD....5121008B Altcode:
In our study we aim at an understanding how the energy to heat the
upper atmosphere is generated by the photospheric magneto-convection,
transported into the upper atmosphere, and how its dissipation governs
the formation of the internal structure of a coronal magnetic loop. In
a 3D MHD model we study a coronal loop that is rooted with both
footpoints in a shallow convection zone layer. Therefore the driving
at the coronal base arises self-consistently from magneto-convection
in plage-type areas. To fit into a cartesian box, we straighten the
coronal loop. This allows a high spatial resolution within the loop
that cannot be achieved in a model of a whole active region. To
conduct the numerical experiments we employ the MURaM code that
includes heat conduction, radiative transfer and optically thin
radiative losses. We find that the Poynting flux into the loop is
generated by small-scale photospheric motions within strong magnetic
flux concentrations. Turbulent behaviour develops in the upper layers
of the atmosphere as a response to the footpoint motions. Vortex flows
are found at various heights within the loop. These are organised in
swirls that form coherent structures with a magnetic connection from
the intergranular lanes in the photosphere through the chromosphere
up to several megameters into the corona. In the coronal part of
the loop plasma motions perpendicular to the magnetic axis of the
swirl are associated with an increased heating rate and thus enhanced
temperatures. At any given time, only part of the loop is filled with
swirls which leads to a substructure of the loop in terms of temperature
and density. Consequently the emission as it would be observed by AIA
or XRT reveals transient bright strands that form in response to the
heating events related to the swirls. With this model we can build a
coherent picture of how the energy flux to heat the upper atmosphere
is generated near the solar surface and how this process drives and
governs the heating and dynamics of a coronal loop

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Title: Effects of inclusion of small-scale dynamo in near-surface
structure of F-stars
Authors: Bhatia, T. S.; Cameron, R.; Solanki, S.; Peter, H.; Przbylski,
D.; Witzke, V.
2020SPD....5120704B Altcode:
The presence of (unresolved) small-scale mixed polarity regions in
the quiet Sun photosphere plays an important role in determining
the basal magnetic flux. Observationally, the magnitude of the
vertical component of this field is estimated to be ~50-100 G on the
Sun. This field is important for determining the energy balance in
the chromosphere and may also subtly affect the radiative properties
of the photosphere. These fields are believed to be the result of a
small-scale dynamo (SSD) operating near the surface. While significant
progress has been made in investigating the role of the SSD in the Sun,
it is unclear what effects SSDs have on other stars. In particular,
for F-stars, the photosheric kinetic and internal energies seem to be
of the same order of magnitude. Since there is a rough equipartition
in energies for a saturated SSD, deviations from a pure hydrodynamic
(HD) stratification are expected. We aim to characterize these
deviations. Box simulations of the upper convection zone and the
photosphere are carried out using the radiative MHD code MURaM. To
obtain SSD simulations, we use initial HD simulations and seed a
magnetic field of negligible strength and zero net flux, which we
then run till the magnetic field reaches saturation. We consider two
different lower boundary conditions (BCs) for the magnetic field to
characterize BC-effects: a) only vertical magnetic field is allowed, b)
both vertical and horizontal magnetic field is allowed. Both boundary
conditions exhibit SSD action. We observe slight increase (fraction
of a percent) in the horizontally-averaged temperature profile for
both the cases. Other thermodynamic quantities exhibit deviations (~
a percent) depending on the boundary condition considered. In addition,
the spatial power spectra of the bolometric intensity shows deviations
from the corresponding HD (without magnetic field) run, implying
larger power at smaller spatial scales for SSD case. The presence of
a SSD results in a significant amount of "quiet"-star magnetic flux
with associated changes in the stratification of the atmosphere and
spatial distribution of the bolometric intensity.

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Title: Magnetohydrostatic modeling of AR11768 based on a SUNRISE/IMaX
vector magnetogram
Authors: Zhu, X.; Wiegelmann, T.; Solanki, S. K.
2020A&A...640A.103Z Altcode: 2020arXiv200514332Z
Context. High-resolution magnetic field measurements are routinely
only done in the solar photosphere. Higher layers, such as the
chromosphere and corona, can be modeled by extrapolating these
photospheric magnetic field vectors upward. In the solar corona,
plasma forces can be neglected and the Lorentz force vanishes. This
is not the case in the upper photosphere and chromosphere where
magnetic and nonmagnetic forces are equally important. One way to
deal with this problem is to compute the plasma and magnetic field
self-consistently, in lowest order with a magnetohydrostatic (MHS)
model. The non-force-free layer is rather thin and MHS models require
high-resolution photospheric magnetic field measurements as the lower
boundary condition. Aims: We aim to derive the magnetic field,
plasma pressure, and density of AR11768 by applying the newly developed
extrapolation technique to the SUNRISE/IMaX data embedded in SDO/HMI
magnetogram. Methods: We used an optimization method for the MHS
modeling. The initial conditions consist of a nonlinear force-free field
(NLFFF) and a gravity-stratified atmosphere. During the optimization
procedure, the magnetic field, plasma pressure, and density are computed
self-consistently. Results: In the non-force-free layer, which
is spatially resolved by the new code, Lorentz forces are effectively
balanced by the gas pressure gradient force and gravity force. The
pressure and density are depleted in strong field regions, which is
consistent with observations. Denser plasma, however, is also observed
at some parts of the active region edges. In the chromosphere, the
fibril-like plasma structures trace the magnetic field nicely. Bright
points in SUNRISE/SuFI 3000 Å images are often accompanied by the
plasma pressure and electric current concentrations. In addition, the
average of angle between MHS field lines and the selected chromospheric
fibrils is 11.8°, which is smaller than those computed from the NLFFF
model (15.7°) and linear MHS model (20.9°). This indicates that the
MHS solution provides a better representation of the magnetic field
in the chromosphere.

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Title: Sunspot area catalog revisited: Daily cross-calibrated areas
since 1874
Authors: Mandal, Sudip; Krivova, Natalie A.; Solanki, Sami K.; Sinha,
Nimesh; Banerjee, Dipankar
2020A&A...640A..78M Altcode: 2020arXiv200414618M
Context. Long and consistent sunspot area records are important for
understanding long-term solar activity and variability. Multiple
observatories around the globe have regularly recorded sunspot
areas, but such individual records only cover restricted periods of
time. Furthermore, there are systematic differences between these
records and require cross-calibration before they can reliably be used
for further studies. Aims: We produce a cross-calibrated and
homogeneous record of total daily sunspot areas, both projected and
corrected, covering the period between 1874 and 2019. In addition,
we generated a catalog of calibrated individual group areas for
the same period. Methods: We compared the data from nine
archives: Royal Greenwich Observatory (RGO), Kislovodsk, Pulkovo,
Debrecen, Kodaikanal, Solar Optical Observing Network (SOON), Rome,
Catania, and Yunnan Observatories, covering the period between
1874 and 2019. Cross-comparisons of the individual records were
done to produce homogeneous and inter-calibrated records of daily
projected and corrected areas. As in earlier studies, the basis
of the composite is formed by the data from RGO. After 1976, the
only datasets used are those from Kislovodsk, Pulkovo, and Debrecen
observatories. This choice was made based on the temporal coverage
and the quality of the data. While there are still 776 days missing
in the final composite, these remaining gaps could not be filled
with data from the other archives as the missing days lie either
before 1922 or after 2016 and none of the additional archives cover
these periods. Results: In contrast to the SOON data used in
previous area composites for the post-RGO period, the properties of
the data from Kislovodsk and Pulkovo are very similar to those from
the RGO series. They also directly overlap the RGO data in time, which
makes their cross-calibration with RGO much more reliable. Indeed,
comparing our area catalog with previous such composites, we find
improvements both in data quality and coverage. We also computed the
daily Photometric Sunspot Index, which is widely used, for example,
in empirical reconstructions of solar irradiance. Generated
composites are available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A78">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/640/A78</A>
and at <A
href="http://www2.mps.mpg.de/projects/sun-climate/data.html">http://www2.mps.mpg.de/projects/sun-climate/data.html</A>

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Title: Radiative MHD Simulations of Starspots
Authors: Panja, M.; Cameron, R.; Solanki, S.
2020SPD....5121117P Altcode:
We have performed the first-ever, realistic 3D simulations of the
photospheric structure of complete starspots, including their penumbrae,
for a range of cool main-sequence stars, namely the spectral types M0V,
K0V, and G2V. We used the MHD code MURaM which includes radiative energy
transfer and the effects of partial ionization. We explore several
fundamental properties like umbral intensity contrast, temperature, and
magnetic field strength as functions of spectral type. Our simulations
show that there is an increase in spot contrast with the increase in
stellar surface temperature, which is consistent with observations. The
umbral field strength is determined by the depth at which the optical
surface forms and the surface pressures of the host stars. We will
present our results and discuss the physics behind them.

---------------------------------------------------------
Title: Analysis of full-disc Ca II K spectroheliograms. III. Plage
area composite series covering 1892-2019
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova,
Natalie A.; Solanki, Sami K.; Banerjee, Dipankar; Barata, Teresa;
Belik, Marcel; Gafeira, Ricardo; Garcia, Adriana; Hanaoka, Yoichiro;
Hegde, Manjunath; Klimeš, Jan; Korokhin, Viktor V.; Lourenço, Ana;
Malherbe, Jean-Marie; Marchenko, Gennady P.; Peixinho, Nuno; Sakurai,
Takashi; Tlatov, Andrey G.
2020A&A...639A..88C Altcode: 2020arXiv200501435C
Context. Studies of long-term solar activity and variability require
knowledge of the past evolution of the solar surface magnetism. The
archives of full-disc Ca II K observations that have been performed
more or less regularly at various sites since 1892 can serve as an
important source of such information. Aims: We derive the plage
area evolution over the last 12 solar cycles by employing data from all
Ca II K archives that are publicly available in digital form, including
several as-yet-unexplored Ca II K archives. Methods: We analysed
more than 290 000 full-disc Ca II K observations from 43 datasets
spanning the period between 1892-2019. All images were consistently
processed with an automatic procedure that performs the photometric
calibration (if needed) and the limb-darkening compensation. The
processing also accounts for artefacts affecting many of the images,
including some very specific artefacts, such as bright arcs found
in Kyoto and Yerkes data. Our employed methods have previously been
tested and evaluated on synthetic data and found to be more accurate
than other methods used in the literature to treat a subset of the data
analysed here. Results: We produced a plage area time-series
from each analysed dataset. We found that the differences between the
plage areas derived from individual archives are mainly due to the
differences in the central wavelength and the bandpass used to acquire
the data at the various sites. We empirically cross-calibrated and
combined the results obtained from each dataset to produce a composite
series of plage areas. The 'backbone' approach was used to bridge
the series together. We have also shown that the selection of the
backbone series has little effect on the final composite of the plage
area. We quantified the uncertainty of determining the plage areas
with our processing due to shifts in the central wavelength and found
it to be less than 0.01 in fraction of the solar disc for the average
conditions found on historical data. We also found the variable seeing
conditions during the observations to slightly increase the plage
areas during the activity maxima. Conclusions: We provide the
most complete so far time series of plage areas based on corrected
and calibrated historical and modern Ca II K images. Consistent
plage areas are now available on 88% of all days from 1892 onwards
and on 98% from 1907 onwards. The whole series described in
the paper are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/639/A88</A>

---------------------------------------------------------
Title: No universal connection between the vertical magnetic field
and the umbra-penumbra boundary in sunspots
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
2020A&A...639A.106L Altcode: 2020arXiv200602346L
Context. It has been reported that the boundary between the umbra and
the penumbra of sunspots occurs at a canonical value of the strength
of the vertical magnetic field, independently of the size of the
spot. This critical field strength is interpreted to be the threshold
for the onset of magnetoconvection. Aims: Here we investigate
the reasons why this criterion, also called the Jurčák criterion
in the literature, does not always identify the boundary between the
umbra and the penumbra. Methods: We performed a statistical
analysis of 23 sunspots observed with Hinode/SOT. We compared the
properties of the continuum intensity and the vertical magnetic
field between filaments and spines and how they vary between spots of
different sizes. Results: We find that the inner boundary of the
penumbra is not related to a universal value of the vertical magnetic
field. The properties of spines and filaments vary between spots of
different sizes. Both components are darker in larger spots and the
spines exhibit a stronger vertical magnetic field. These variations of
the properties of filaments and spines with the spot size are also the
reason for the reported invariance in the averaged vertical magnetic
field at 50% of the mean continuum intensity. Conclusions:
The formation of filaments and the onset of magnetoconvection are not
related to a canonical value of the strength of the vertical magnetic
field. The seemingly unique magnetic field strength is rather an effect
of the filling factor of spines and penumbral filaments.

---------------------------------------------------------
Title: How faculae and network relate to sunspots, and the
implications for solar and stellar brightness variations
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.
2020A&A...639A.139Y Altcode: 2020arXiv200614274Y
Context. How global faculae and network coverage relates to that
of sunspots is relevant to the brightness variations of the Sun and
Sun-like stars. Aims: We aim to extend and improve on earlier
studies that established that the facular-to-sunspot-area ratio
diminishes with total sunspot coverage. Methods: Chromospheric
indices and the total magnetic flux enclosed in network and faculae,
referred to here as "facular indices", are modulated by the amount
of facular and network present. We probed the relationship between
various facular and sunspot indices through an empirical model, taking
into account how active regions evolve and the possible non-linear
relationship between plage emission, facular magnetic flux, and sunspot
area. This model was incorporated into a model of total solar irradiance
(TSI) to elucidate the implications for solar and stellar brightness
variations. Results: The reconstruction of the facular indices
from the sunspot indices with the model presented here replicates
most of the observed variability, and is better at doing so than
earlier models. Contrary to recent studies, we found the relationship
between the facular and sunspot indices to be stable over the past four
decades. The model indicates that, like the facular-to-sunspot-area
ratio, the ratio of the variation in chromospheric emission and
total network and facular magnetic flux to sunspot area decreases
with the latter. The TSI model indicates the ratio of the TSI excess
from faculae and network to the deficit from sunspots also declines
with sunspot area, with the consequence being that TSI rises with
sunspot area more slowly than if the two quantities were linearly
proportional to one another. This explains why even though solar cycle
23 is significantly weaker than cycle 22, TSI rose to comparable levels
over both cycles. The extrapolation of the TSI model to higher activity
levels indicates that in the activity range where Sun-like stars are
observed to switch from growing brighter with increasing activity to
becoming dimmer instead, the activity-dependence of TSI exhibits a
similar transition. This happens as sunspot darkening starts to rise
more rapidly with activity than facular and network brightening. This
bolsters the interpretation of this behaviour of Sun-like stars as
the transition from a faculae-dominated to a spot-dominated regime.

---------------------------------------------------------
Title: Reply to the comment of T. Metcalfe and J. van Saders on the
Science report "The Sun is less active than other solar-like stars"
Authors: Reinhold, T.; Shapiro, A. I.; Solanki, S. K.; Montet, B. T.;
Krivova, N. A.; Cameron, R. H.; Amazo-Gómez, E. M.
2020arXiv200704817R Altcode:
This is our reply to the comment of T. Metcalfe and J. van Saders
on the Science report "The Sun is less active than other solar-like
stars" by T. Reinhold, A. I. Shapiro, S. K. Solanki, B. T. Montet,
N. A. Krivova, R. H. Cameron, E. M. Amazo-Gomez. We hope that both
the comment and our reply lead to fruitful discussions which of the
two presented scenarios is more likely.

---------------------------------------------------------
Title: Connecting measurements of solar and stellar brightness
variations
Authors: Nèmec, N. -E.; Işık, E.; Shapiro, A. I.; Solanki, S. K.;
Krivova, N. A.; Unruh, Y.
2020A&A...638A..56N Altcode: 2020arXiv200406974N
Context. A comparison of solar and stellar brightness variations is
hampered by the difference in spectral passbands that are used in
observations, and also by the possible difference in the inclination
of the solar and stellar rotation axes from the line of sight. 
Aims: We calculate the rotational variability of the Sun as it would
be measured in passbands used for stellar observations. In particular,
we consider the filter systems used by the CoRoT, Kepler, TESS, and
Gaia space missions. We also quantify the effect of the inclination
of the rotation axis on the solar rotational variability. 
Methods: We employed the spectral and total irradiance reconstruction
(SATIRE) model to calculate solar brightness variations in different
filter systems as observed from the ecliptic plane. We then combined
the simulations of the surface distribution of the magnetic features
at different inclinations using a surface flux transport model with
the SATIRE calculations to compute the dependence of the variability
on the inclination. Results: For an ecliptic-bound observer,
the amplitude of the solar rotational variability, as observed in
the total solar irradiance (TSI), is 0.68 mmag (averaged over solar
cycles 21-24). We obtained corresponding amplitudes in the Kepler
(0.74 mmag), CoRoT (0.73 mmag), TESS (0.62 mmag), Gaia G (0.74 mmag),
Gaia GRP (0.62 mmag), and Gaia GBP (0.86 mmag)
passbands. Decreasing the inclination of the rotation axis decreases
the rotational variability. For a sample of randomly inclined stars,
the variability is on average 15% lower in all filter systems we
considered. This almost compensates for the difference in amplitudes
of the variability in TSI and Kepler passbands, making the amplitudes
derived from the TSI records an ideal representation of the solar
rotational variability for comparison to Kepler stars with unknown
inclinations. Conclusions: The TSI appears to be a relatively
good measure of solar variability for comparisons with stellar
measurements in the CoRoT, Kepler, TESS Gaia G, and Gaia GRP
filters. Whereas the correction factors can be used to convert the
variability amplitude from solar measurements into the values expected
for stellar missions, the inclination affects the shapes of the light
curves so that a much more sophisticated correction than simple scaling
is needed to obtain light curves out of the ecliptic for the Sun.

---------------------------------------------------------
Title: On the Magnetic Nature of an Exploding Granule as Revealed
by Sunrise/IMaX
Authors: Guglielmino, Salvo L.; Martínez Pillet, Valentín; Ruiz
Cobo, Basilio; Bellot Rubio, Luis R.; del Toro Iniesta, José Carlos;
Solanki, Sami K.; Riethmüller, Tino L.; Zuccarello, Francesca
2020ApJ...896...62G Altcode: 2020arXiv200503371G
We study the photospheric evolution of an exploding granule
observed in the quiet Sun at high spatial (∼0"3) and temporal
(31.5 s) resolution by the imaging magnetograph Sunrise/IMaX in 2009
June. These observations show that the exploding granule is cospatial
to a magnetic flux emergence event occurring at mesogranular scale
(up to ∼12 Mm2 area). Using a modified version of the
SIR code for inverting the IMaX spectropolarimetric measurements, we
obtain information about the magnetic configuration of this photospheric
feature. In particular, we find evidence of highly inclined emerging
fields in the structure, carrying a magnetic flux content up to ∼4
× 1018 Mx. The balance between gas and magnetic pressure
in the region of flux emergence, compared with a very quiet region of
the Sun, indicates that the additional pressure carried by the emerging
flux increases the total pressure by about 5% and appears to allow the
granulation to be modified, as predicted by numerical simulations. The
overall characteristics suggest that a multipolar structure emerges
into the photosphere, resembling an almost horizontal flux sheet. This
seems to be associated with exploding granules. Finally, we discuss
the origin of such flux emergence events.

---------------------------------------------------------
Title: Detection of the Strongest Magnetic Field in a Sunspot
Light Bridge
Authors: Castellanos Durán, J. S.; Lagg, Andreas; Solanki, Sami K.;
van Noort, Michiel
2020ApJ...895..129C Altcode: 2020arXiv200312078C; 2020ApJ...895..129D
Traditionally, the strongest magnetic fields on the Sun have been
measured in sunspot umbrae. More recently, however, much stronger
fields have been measured at the ends of penumbral filaments carrying
the Evershed and counter-Evershed flows. Superstrong fields have
also been reported within a light bridge separating two umbrae of
opposite polarities. We aim to accurately determine the strengths of the
strongest fields in a light bridge using an advanced inversion technique
and to investigate their detailed structure. We analyze observations
from the spectropolarimeter on board the Hinode spacecraft of the
active region AR 11967. The thermodynamic and magnetic configurations
are obtained by inverting the Stokes profiles using an inversion scheme
that allows multiple height nodes. Both the traditional 1D inversion
technique and the so-called 2D coupled inversions, which take into
account the point-spread function of the Hinode telescope, are used. We
find a compact structure with an area of 32.7 arcsec2 within
a bipolar light bridge with field strengths exceeding 5 kG, confirming
the strong fields in this light bridge reported in the literature. Two
regions associated with downflows of ∼5 km s-1 harbor
field strengths larger than 6.5 kG, covering a total area of 2.97
arcsec2. The maximum field strength found is 8.2 kG, which
is the largest ever observed field in a bipolar light bridge up to now.

---------------------------------------------------------
Title: Simulations Show that Vortex Flows Could Heat the Chromosphere
in Solar Plage
Authors: Yadav, Nitin; Cameron, R. H.; Solanki, S. K.
2020ApJ...894L..17Y Altcode: 2020arXiv200413996Y
The relationship between vortex flows at different spatial scales
and their contribution to the energy balance in the chromosphere
is not yet fully understood. We perform three-dimensional (3D)
radiation-magnetohydrodynamic simulations of a unipolar solar plage
region at a spatial resolution of 10 km using the MURaM code. We
use the swirling-strength criterion that mainly detects the smallest
vortices present in the simulation data. We additionally degrade our
simulation data to smooth out the smaller vortices, so that also the
vortices at larger spatial scales can be detected. Vortex flows at
various spatial scales are found in our simulation data for different
effective spatial resolutions. We conclude that the observed large
vortices are likely clusters of much smaller ones that are not yet
resolved by observations. We show that the vertical Poynting flux
decreases rapidly with reduced effective spatial resolutions and
is predominantly carried by the horizontal plasma motions rather
than vertical flows. Since the small-scale horizontal motions or the
smaller vortices carry most of the energy, the energy transported by
vortices deduced from low-resolution data is grossly underestimated. In
full-resolution simulation data, the Poynting flux contribution due to
vortices is more than adequate to compensate for the radiative losses
in plage, indicating their importance for chromospheric heating.

---------------------------------------------------------
Title: Optical design of the multi-wavelength imaging coronagraph
Metis for the solar orbiter mission
Authors: Fineschi, S.; Naletto, G.; Romoli, M.; Da Deppo, V.;
Antonucci, E.; Moses, D.; Malvezzi, A. M.; Nicolini, G.; Spadaro,
D.; Teriaca, L.; Andretta, V.; Capobianco, G.; Crescenzio, G.;
Focardi, M.; Frassetto, F.; Landini, F.; Massone, G.; Melich, R.;
Nicolosi, P.; Pancrazzi, M.; Pelizzo, M. G.; Poletto, L.; Schühle,
U.; Uslenghi, M.; Vives, S.; Solanki, S. K.; Heinzel, P.; Berlicki,
A.; Cesare, S.; Morea, D.; Mottini, S.; Sandri, P.; Alvarez-Herrero,
A.; Castronuovo, M.
2020ExA....49..239F Altcode: 2020ExA...tmp...14F
This paper describes the innovative optical design of the Metis
coronagraph for the Solar Orbiter ESA-NASA mission. Metis is a
multi-wavelength, externally occulted telescope for the imaging
of the solar corona in both the visible and ultraviolet wavelength
ranges. Metis adopts a novel occultation scheme for the solar disk,
that we named "inverse external occulter", for reducing the extremely
high thermal load on the instrument at the spacecraft perihelion. The
core of the Metis optical design is an aplanatic Gregorian telescope
common to both the visible and ultraviolet channels. A suitable
dichroic beam-splitter, optimized for transmitting a narrow-band in
the ultraviolet (121.6 nm, HI Lyman-α) and reflecting a broadband
in the visible (580-640 nm) spectral range, is used to separate the
two optical paths. Along the visible light optical path, a liquid
crystal electro-optical modulator, used for the first time in space,
allows making polarimetric measurements.

---------------------------------------------------------
Title: Historical solar Ca II K observations at the Kyoto and
Sacramento Peak observatories
Authors: Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.
2020JPhCS1548a2007C Altcode:
Archives of full-disc solar Ca II K observations covering even short
periods of time can offer important data to fill observation gaps
and to allow a better transition from historical to modern data. Two
examples of such archives are those from the Kyoto and Sacramento
Peak observatories. As most other historical Ca II K data, they suffer
from artefacts that need to be accounted for to derive accurate plage
areas. Here we present the results of our analysis of these archives
of solar Ca II K images.

---------------------------------------------------------
Title: The SO/PHI instrument on Solar Orbiter and its data products
Authors: Solanki, Sami K.; Hirzberger, Johann; Wiegelmann, Thomas;
Gandorfer, Achim; Woch, Joachim; del Toro Iniesta, José Carlos
2020EGUGA..2217904S Altcode:
A central instrument of Solar Orbiter is the Polarimetric and
Helioseismic Imager, SO/PHI. It is a vector magnetograph that also
provides data for helioseismology. SO/PHI is composed of two telescopes,
a full-disk telescope (FDT) and a high-resolution telescope (HRT). The
HRT will observe at a resolution as high as 200 km on the solar
surface, while the FDT will obtain the magnetic field and velocity of
the full solar disc whenever it observes. SO/PHI will be the first
solar spectro-polarimeter to leave the Sun-Earth line, opening up
some unique perspectives, such as the first detailed view of the solar
poles. This will allow not just a more precise and exact mapping of the
polar magnetic field than possible so far, but will also enable us to
follow the dynamics of individual magnetic features at high latitudes
and to determine solar surface and sub-surface flows right up to the
poles. In addition to its standard data products (vector magnetograms,
continuum images and maps of the line-of-sight velocity), SO/PHI will
also provide higher-level data products. These will include synoptic
charts, local magnetic field extrapolations starting from HRT data and
global magnetic field extrapolations (from FDT data) with potential
field source-surface (PFSS) models and possibly also non-potential
models such as NLFFF (non-linear force-free fields), magnetostatics
and MHD. The SO/PHI data products will usefully complement the data
taken by other instruments on Solar Orbiter and on Solar Probe, as
well as instruments on the ground or in Earth orbit. Combining with
observations by Earth-based and near-Earth telescopes will enable
new types of investigations, such as stereoscopic polarimetry and
stereoscopic helioseismology.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Rotation periods of 97 solar-like
stars (Witzke+, 2020)
Authors: Witzke, V.; Reinhold, T.; Shapiro, A. I.; Krivova, N. A.;
Solanki, S. K.
2020yCat..36349009W Altcode:
The Kepler field of view was selected in order to contain a large
fraction of solar-like stars. Focusing on stars in the effective
temperature range of 5600K-5900K, it is challenging to determine their
rotational periods. Stellar fundamental parameters and rotation
periods of the 97 periodic stars are presented. (1 data file).

---------------------------------------------------------
Title: The Sun is less active than other solar-like stars
Authors: Reinhold, Timo; Shapiro, Alexander I.; Solanki, Sami K.;
Montet, Benjamin T.; Krivova, Natalie A.; Cameron, Robert H.;
Amazo-Gómez, Eliana M.
2020Sci...368..518R Altcode: 2020arXiv200501401R
The magnetic activity of the Sun and other stars causes their brightness
to vary. We investigated how typical the Sun’s variability is
compared with other solar-like stars, i.e., those with near-solar
effective temperatures and rotation periods. By combining 4 years
of photometric observations from the Kepler space telescope with
astrometric data from the Gaia spacecraft, we were able to measure
photometric variabilities of 369 solar-like stars. Most of those with
well-determined rotation periods showed higher variability than the Sun
and are therefore considerably more active. These stars appear nearly
identical to the Sun except for their higher variability. Therefore,
we speculate that the Sun could potentially also go through epochs of
such high variability.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Plage area composite series
(Chatzistergos+, 2020)
Authors: Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki,
S. K.; Banerjee, D.; Barata, T.; Belik, M.; Gafeira, R.; Garcia,
A.; Hanaoka, Y.; Hegde, M.; Klimes, J.; Korokhin, V. V.; Lourenco,
A.; Malherbe, J. -M.; Marchenko, G. P.; Peixinho, N.; Sakurai, T.;
Tlatov, A. G.
2020yCat..36390088C Altcode:
Annual, monthly, and daily values of the plage area composite series. The archives included are those from the Arcetri (Ar), Baikal (Ba),
Brussels (Br), Calern (CL), Catania (CT), Coimbra (Co), Kanzelhoehe
(Ka), Kenwood (Ke), Kharkiv (Kh), Kislovodsk (Ki), Kodaikanal taken with
the spectroheliograph (Ko), Kodaikanal taken with the Twin telescope
(KT), Kodaikanal taken with the White-Light Active Region Monitor (WARM)
telescope (KW), Kyoto (Ky), Manila (Ma), Mauna Loa (ML) taken with the
Precision Solar Photometric Telescope (PSPT), McMath-Hulbert (MM), Mees
(MS), Meudon taken with the spectroheliograph (MD1), Meudon taken with
an interference filter (MD2), Mitaka taken with the spectroheliograph
(Mi1), Mitaka taken with the Solar Flare Telescope with an interference
filter (Mi2), Mt Wilson (MW), Pic du Midi (PM), SOlar Diameter Imager
and Surface Mapper (SODISM) telescope on board the PICARD spacecraft
(PS), Rome taken with the equatorial bar at Monte Mario (Ro), Rome taken
with the PSPT (RP1), Rome taken with the PSPT with narrow bandwidth
(RP2), Sacramento Peak (SP), San Fernando taken with the Cartesian
Full-Disk Telescope (CFDT) 1 (SF1), San Fernando taken with the CFDT2
(SF2), Schauinsland (Sc), Teide (Te) taken with the Chromospheric
Telescope (ChroTel), Upice (UP), Valasske Mezirici (VM), Wendelstein
(WS), and Yerkes (YR) sites (3 data files).

---------------------------------------------------------
Title: Solar Disk Center Shows Scattering Polarization in the Sr I
4607 Å Line
Authors: Zeuner, Franziska; Manso Sainz, Rafael; Feller, Alex; van
Noort, Michiel; Solanki, Sami K.; Iglesias, Francisco A.; Reardon,
Kevin; Martínez Pillet, Valentín
2020ApJ...893L..44Z Altcode: 2020arXiv200403679Z
Magnetic fields in turbulent, convective high-β plasma naturally
develop highly tangled and complex topologies - the solar photosphere
being the paradigmatic example. These fields are mostly undetectable by
standard diagnostic techniques with finite spatio-temporal resolution
due to cancellations of Zeeman polarization signals. Observations of
resonance scattering polarization have been considered to overcome
these problems. But up to now, observations of scattering polarization
lack the necessary combination of high sensitivity and high spatial
resolution in order to directly infer the turbulent magnetic structure
at the resolution limit of solar telescopes. Here, we report the
detection of clear spatial structuring of scattering polarization
in a magnetically quiet solar region at disk center in the Sr I
4607 Å spectral line on granular scales, confirming theoretical
expectations. We find that the linear polarization presents a
strong spatial correlation with the local quadrupole of the radiation
field. The result indicates that polarization survives the dynamic and
turbulent magnetic environment of the middle photosphere and is thereby
usable for spatially resolved Hanle observations. This is an important
step toward the long-sought goal of directly observing turbulent
solar magnetic fields at the resolution limit and investigating their
spatial structure.

---------------------------------------------------------
Title: 3D Radiative MHD Simulations of Starspots
Authors: Panja, Mayukh; Cameron, Robert; Solanki, Sami K.
2020ApJ...893..113P Altcode: 2020arXiv200309656P
There are no direct spatially resolved observations of spots on stars
other than the Sun, and starspot properties are inferred indirectly
through lightcurves and spectropolarimetric data. We present the first
self-consistent 3D radiative MHD computations of starspots on G2V, K0V,
and M0V stars, which will help us to better understand observations of
activity, variability, and magnetic fields in late-type main-sequence
stars. We used the MURaM code, which has been extensively used to
compute "realistic" sunspots, for our simulations. We aim to study
how fundamental starspot properties such as intensity contrast,
temperature, and magnetic field strength vary with spectral type. We
first simulated in 2D multiple spots of each spectral type to find
out appropriate initial conditions for our 3D runs. We find that
with increasing stellar effective temperature, there is an increase
in the temperature difference between the umbra of the spot and its
surrounding photosphere, from 350 K on the M0V star to 1400 K on the
G2V star. This trend in our simulated starspots is consistent with
observations. The magnetic field strengths of all the starspot umbrae
are in the 3-4.5 kG range. The G2V and K0V umbrae have comparable
magnetic field strengths around 3.5 kG, while the M0V umbra has a
relatively higher field strength around 4 kG. We discuss the physical
reasons behind both these trends. All of the three starspots develop
penumbral filament-like structures with Evershed flows. The average
Evershed flow speed drops from 1.32 km s-1 in the G2V
penumbra to 0.6 km s-1 in the M0V penumbra.

---------------------------------------------------------
Title: Power spectra of solar brightness variations at various
inclinations
Authors: Nèmec, N. -E.; Shapiro, A. I.; Krivova, N. A.; Solanki,
S. K.; Tagirov, R. V.; Cameron, R. H.; Dreizler, S.
2020A&A...636A..43N Altcode: 2020arXiv200210895N
Context. Magnetic features on the surfaces of cool stars lead to
variations in their brightness. Such variations on the surface of
the Sun have been studied extensively. Recent planet-hunting space
telescopes have made it possible to measure brightness variations
in hundred thousands of other stars. The new data may undermine
the validity of setting the sun as a typical example of a variable
star. Putting solar variability into the stellar context suffers,
however, from a bias resulting from solar observations being carried
out from its near-equatorial plane, whereas stars are generally
observed at all possible inclinations. Aims: We model solar
brightness variations at timescales from days to years as they would
be observed at different inclinations. In particular, we consider the
effect of the inclination on the power spectrum of solar brightness
variations. The variations are calculated in several passbands that are
routinely used for stellar measurements. Methods: We employ the
surface flux transport model to simulate the time-dependent spatial
distribution of magnetic features on both the near and far sides of
the Sun. This distribution is then used to calculate solar brightness
variations following the Spectral And Total Irradiance REconstruction
approach. Results: We have quantified the effect of the
inclination on solar brightness variability at timescales down to a
single day. Thus, our results allow for solar brightness records to
be made directly comparable to those obtained by planet-hunting space
telescopes. Furthermore, we decompose solar brightness variations into
components originating from the solar rotation and from the evolution
of magnetic features.

---------------------------------------------------------
Title: Inflection point in the power spectrum of stellar brightness
variations. II. The Sun
Authors: Amazo-Gómez, E. M.; Shapiro, A. I.; Solanki, S. K.; Krivova,
N. A.; Kopp, G.; Reinhold, T.; Oshagh, M.; Reiners, A.
2020A&A...636A..69A Altcode: 2020arXiv200203455A
Context. Young and active stars generally have regular, almost
sinusoidal, patterns of variability attributed to their rotation,
while the majority of older and less active stars, including the Sun,
have more complex and non-regular light curves, which do not have clear
rotational-modulation signals. Consequently, the rotation periods have
been successfully determined only for a small fraction of the Sun-like
stars (mainly the active ones) observed by transit-based planet-hunting
missions, such as CoRoT, Kepler, and TESS. This suggests that only
a small fraction of such systems have been properly identified as
solar-like analogues. Aims: We aim to apply a new method of
determining rotation periods of low-activity stars, such as the Sun. The
method is based on calculating the gradient of the power spectrum
(GPS) of stellar brightness variations and identifying a tell-tale
inflection point in the spectrum. The rotation frequency is then
proportional to the frequency of that inflection point. In this paper,
we compare this GPS method to already-available photometric records of
the Sun. Methods: We applied GPS, auto-correlation functions,
Lomb-Scargle periodograms, and wavelet analyses to the total solar
irradiance (TSI) time series obtained from the Total Irradiance Monitor
on the Solar Radiation and Climate Experiment and the Variability of
solar IRradiance and Gravity Oscillations experiment on the SOlar
and Heliospheric Observatory missions. We analysed the performance
of all methods at various levels of solar activity. Results:
We show that the GPS method returns accurate values of solar rotation
independently of the level of solar activity. In particular, it performs
well during periods of high solar activity, when TSI variability
displays an irregular pattern, and other methods fail. Furthermore,
we show that the GPS and light curve skewness can give constraints
on facular and spot contributions to brightness variability. 
Conclusions: Our results suggest that the GPS method can successfully
determine the rotational periods of stars with both regular and
non-regular light curves. The two movies are available at <A
href="https://www.aanda.org/10.1051/0004-6361/201936925/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Solar-cycle irradiance variations over the last four billion
years
Authors: Shapiro, Anna V.; Shapiro, Alexander I.; Gizon, Laurent;
Krivova, Natalie A.; Solanki, Sami K.
2020A&A...636A..83S Altcode: 2020arXiv200208806S
Context. The variability of the spectral solar irradiance (SSI) over the
course of the 11-year solar cycle is one of the manifestations of solar
magnetic activity. There is strong evidence that the SSI variability
has an effect on the Earth's atmosphere. The faster rotation of the
Sun in the past lead to a more vigorous action of solar dynamo and
thus potentially to larger amplitude of the SSI variability on the
timescale of the solar activity cycle. This could lead to a stronger
response of the Earth's atmosphere as well as other solar system
planets' atmospheres to the solar activity cycle. Aims: We
calculate the amplitude of the SSI and total solar irradiance (TSI)
variability over the course of the solar activity cycle as a function
of solar age. Methods: We employed the relationship between the
stellar magnetic activity and the age based on observations of solar
twins. Using this relation, we reconstructed solar magnetic activity
and the corresponding solar disk area coverages by magnetic features
(i.e., spots and faculae) over the last four billion years. These disk
coverages were then used to calculate the amplitude of the solar-cycle
SSI variability as a function of wavelength and solar age. 
Results: Our calculations show that the young Sun was significantly
more variable than the present Sun. The amplitude of the solar-cycle TSI
variability of the 600 Myr old Sun was about ten times larger than that
of the present Sun. Furthermore, the variability of the young Sun was
spot-dominated (the Sun being brighter at the activity minimum than
in the maximum), that is, the Sun was overall brighter at activity
minima than at maxima. The amplitude of the TSI variability decreased
with solar age until it reached a minimum value at 2.8 Gyr. After this
point, the TSI variability is faculae-dominated (the Sun is brighter
at the activity maximum) and its amplitude increases with age.

---------------------------------------------------------
Title: Solar Photosphere
Authors: Chitta, L. P.; Smitha, H. N.; Solanki, S. K.
2020orep.bookE...1C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: VizieR Online Data Catalog: Sunspot area catalogue revisited
(1874-2019) (Mandal+, 2020)
Authors: Mandal, S.; Krivova, N.; Solanki, S. K.; Sinha, N.;
Banerjee, D.
2020yCat..36400078M Altcode:
A number of observatories around the globe have carried
out measurements of sunspot areas and positions over the last
century. RGO, the longest sunspot area database to date, started its
campaign in 1874 and after continuing for a century, stopped it in
1976. Several other observatories from different parts of the world
(e.g., Kodaikanal, Kislovodsk, Debrecen, Rome etc.) also carried out
such observing programs throughout the 20th century. Sunspot area
datasets are invaluable historical records of solar magnetic fields
and are key to understanding the solar variability and its historical
reconstructions. In this work, we analyze and compare sunspot group
areas from a total of nine observatories (RGO, Kislovodsk, Pulkovo,
Debrecen, Kodaikanal, SOON, Rome, Catania, Yunnan). It turns out that
data from only four observatories (RGO, Kislovodsk, Pulkovo, Debrecen)
are sufficient to produce cross-calibrated, up-to-date (1874-2019)
catalogs of daily total and individual group areas. The remaining
gaps (776 days in total) could not be filled with data from the other
archives as the missing days lie either before 1922 or after 2016 and
none of the other archives cover these periods. (2 data files).

---------------------------------------------------------
Title: Connecting the Wilson depression to the magnetic field
of sunspots
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
2020A&A...635A.202L Altcode: 2020arXiv200207484L
Context. In sunspots, the geometric height of continuum optical depth
unity is depressed compared to the quiet Sun. This so-called Wilson
depression is caused by the Lorentz force of the strong magnetic
field inside the spots. However, it is not understood in detail yet
how the Wilson depression is related to the strength and geometry
of the magnetic field or to other properties of the sunspot. 
Aims: We aim to study the dependence of the Wilson depression on the
properties of the magnetic field of the sunspots and how exactly the
magnetic field contributes to balancing the Wilson depression with
respect to the gas pressure of the surroundings of the spots. Methods: Our study is based on 24 spectropolarimetric scans of
12 individual sunspots performed with Hinode. We derived the Wilson
depression for each spot using both a recently developed method that
is based on minimizing the divergence of the magnetic field and an
approach that was developed earlier, which enforces an equilibrium
between the gas pressure and the magnetic pressure inside the spot and
the gas pressure in the quiet Sun, thus neglecting the influence of the
curvature force. We then performed a statistical analysis by comparing
the Wilson depression resulting from the two techniques with each other
and by relating them to various parameters of the sunspots, such as
their size or the strength of the magnetic field. Results: We
find that the Wilson depression becomes larger for spots with a stronger
magnetic field, but not as much as one would expect from the increased
magnetic pressure. This suggests that the curvature integral provides
an important contribution to the Wilson depression, particularly
for spots with a weak magnetic field. Our results indicate that the
geometry of the magnetic field in the penumbra is different between
spots with different strengths of the average umbral magnetic field.

---------------------------------------------------------
Title: Effect of metallicity on the detectability of rotational
periods in solar-like stars
Authors: Witzke, V.; Reinhold, T.; Shapiro, A. I.; Krivova, N. A.;
Solanki, S. K.
2020A&A...634L...9W Altcode: 2020arXiv200101934W
The accurate determination of stellar rotation periods is important
for estimating stellar ages and for understanding stellar activity
and evolution. While rotation periods can be determined for about
thirty thousand stars in the Kepler field, there are over one
hundred thousand stars, especially with low photometric variability
and irregular pattern of variations, for which rotational periods
are unknown. Here we investigate the effect of metallicity on the
detectability of rotation periods. This is done by synthesising light
curves of hypothetical stars that are identical to our Sun with the
exception of the metallicity. These light curves are then used as an
input to the period determination algorithms. We find that the success
rate for recovering the rotation signal has a minimum close to the solar
metallicity value. This can be explained by the compensation effect
of facular and spot contributions. In addition, selecting solar-like
stars with near-solar effective temperature and photometric variability,
and with metallicity between M/H = -0.35 and M/H = 0.35 from the Kepler
sample, we analyse the fraction of stars for which rotational periods
have been detected as a function of metallicity. In agreement with
our theoretical estimate we find a local minimum for the detection
fraction close to the solar metallicity. We further report rotation
periods of 87 solar-like Kepler stars for the first time.

---------------------------------------------------------
Title: The influence of NLTE effects in Fe I lines on an inverted
atmosphere. I. 6301 Å and 6302 Å lines formed in 1D NLTE
Authors: Smitha, H. N.; Holzreuter, R.; van Noort, M.; Solanki, S. K.
2020A&A...633A.157S Altcode: 2019arXiv191207007S
Context. Ultraviolet overionisation of iron atoms in the solar
atmosphere leads to deviations in their level populations based on
Saha-Boltzmann statistics. This causes their line profiles to form in
non-local thermodynamic equilibrium (NLTE) conditions. When inverting
such profiles to determine atmospheric parameters, the NLTE effects
are often neglected and other quantities are tweaked to compensate for
deviations from the LTE. Aims: We investigate how the routinely
employed LTE inversion of iron lines formed in NLTE underestimates
or overestimates atmospheric quantities, such as temperature (T),
line-of-sight velocity (vLOS), magnetic field strength (B),
and inclination (γ) while the earlier papers have focused mainly
on T. Our findings has wide-ranging consequences since many results
derived in solar physics are based on inversions of Fe I lines carried
out in LTE. Methods: We synthesized the Stokes profiles of Fe I
6301.5 Å and 6302.5 Å lines in both LTE and NLTE using a snapshot of
a 3D magnetohydrodynamic simulation. The profiles were then inverted
in LTE. We considered the atmosphere inferred from the inversion of
LTE profiles as the fiducial model and compared it to the atmosphere
resulting from the inversion of NLTE profiles. The observed differences
have been attributed to NLTE effects. Results: Neglecting the
NLTE effects introduces errors in the inverted atmosphere. While the
errors in T can go up to 13%, in vLOS and B, the errors can
go as high as 50% or above. We find these errors to be present at all
three inversion nodes. Importantly, they survive degradation from the
spatial averaging of the profiles. Conclusions: We provide an
overview of how neglecting NLTE effects influences the values of T,
vLOS, B, and γ that are determined by inverting the Fe I
6300 Å line pair, as observed, for example, by Hinode/SOT/SP. Errors
are found at the sites of granules, intergranular lanes, magnetic
elements, and basically in every region susceptible to NLTE effects. For
an accurate determination of the atmospheric quantities and their
stratification, it is, therefore, important to take the NLTE effects
into account.

---------------------------------------------------------
Title: Inflection point in the power spectrum of stellar brightness
variations. I. The model
Authors: Shapiro, A. I.; Amazo-Gómez, E. M.; Krivova, N. A.; Solanki,
S. K.
2020A&A...633A..32S Altcode: 2019arXiv191008351S
Context. Considerable effort has gone into using light curves observed
by such space telescopes as CoRoT, Kepler, and TESS for determining
stellar rotation periods. While rotation periods of active stars
can be reliably determined, the light curves of many older and less
active stars, such as stars that are similar to the Sun, are quite
irregular. This hampers the determination of their rotation periods. Aims: We aim to examine the factors causing these irregularities in
stellar brightness variations and to develop a method for determining
rotation periods for low-activity stars with irregular light curves. Methods: We extended the Spectral And Total Irradiance Reconstruction
approach for modeling solar brightness variations to Sun-like stars. We
calculated the power spectra of stellar brightness variations for
various combinations of parameters that define the surface configuration
and evolution of stellar magnetic features. Results: The short
lifetime of spots in comparison to the stellar rotation period, as well
as the interplay between spot and facular contributions to brightness
variations of stars with near solar activity, cause irregularities in
their light curves. The power spectra of such stars often lack a peak
associated with the rotation period. Nevertheless, the rotation period
can still be determined by measuring the period where the concavity
of the power spectrum plotted in the log-log scale changes its sign,
that is, by identifying the position of the inflection point. 
Conclusions: The inflection point of the (log-log) power spectrum is
found to be a new diagnostic for stellar rotation periods which is
shown to work even in cases where the power spectrum shows no peak at
the rotation rate.

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Title: Fast downflows in a chromospheric filament
Authors: Sowmya, K.; Lagg, A.; Solanki, S. K.; Castellanos Durán,
J. S.
2020IAUS..354..454S Altcode: 2019arXiv191206586S
An active region filament in the upper chromosphere is studied using
spectropolarimetric data in He i 10830 Å from the GREGOR telescope. A
Milne-Eddingon based inversion of the Unno-Rachkovsky equations is
used to retrieve the velocity and the magnetic field vector of the
region. The plasma velocity reaches supersonic values closer to the feet
of the filament barbs and coexist with a slow velocity component. Such
supersonic velocities result from the acceleration of the plasma as it
drains from the filament spine through the barbs. The line-of-sight
magnetic fields have strengths below 200 G in the filament spine and
in the filament barbs where fast downflows are located, their strengths
range between 100 - 700 G.

---------------------------------------------------------
Title: First results on the search for chameleons with the KWISP
detector at CAST
Authors: Arguedas Cuendis, S.; Baier, J.; Barth, K.; Baum, S.; Bayirli,
A.; Belov, A.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Castel,
J. F.; Cetin, S. A.; Dafni, T.; Davenport, M.; Dermenev, A.; Desch,
K.; Döbrich, B.; Fischer, H.; Funk, W.; García, J. A.; Gardikiotis,
A.; Garza, J. G.; Gninenko, S.; Hasinoff, M. D.; Hoffmann, D. H. H.;
Iguaz, F. J.; Irastorza, I. G.; Jakovčić, K.; Kaminski, J.; Karuza,
M.; Krieger, C.; Lakić, B.; Laurent, J. M.; Luzón, G.; Maroudas, M.;
Miceli, L.; Neff, S.; Ortega, I.; Ozbey, A.; Pivovaroff, M. J.; Rosu,
M.; Ruz, J.; Chóliz, E. Ruiz; Schmidt, S.; Schumann, M.; Semertzidis,
Y. K.; Solanki, S. K.; Stewart, L.; Tsagris, I.; Vafeiadis, T.; Vogel,
J. K.; Vretenar, M.; Yildiz, S. C.; Zioutas, K.
2019PDU....2600367A Altcode: 2019arXiv190601084A
We report on a first measurement with a sensitive opto-mechanical force
sensor designed for the direct detection of coupling of real chameleons
to matter. These dark energy candidates could be produced in the Sun
and stream unimpeded to Earth. The KWISP detector installed on the
CAST axion search experiment at CERN looks for tiny displacements of a
thin membrane caused by the mechanical effect of solar chameleons. The
displacements are detected by a Michelson interferometer with a homodyne
readout scheme. The sensor benefits from the focusing action of the
ABRIXAS X-ray telescope installed at CAST, which increases the chameleon
flux on the membrane. A mechanical chopper placed between the telescope
output and the detector modulates the incoming chameleon stream. We
present the results of the solar chameleon measurements taken at CAST in
July 2017, setting an upper bound on the force acting on the membrane
of 80 pN at 95% confidence level. The detector is sensitive for direct
coupling to matter 104 ≤βm ≤ 108
, where the coupling to photons is locally bound to βγ
≤ 1011 .

---------------------------------------------------------
Title: The Polarimetric and Helioseismic Imager on Solar Orbiter
Authors: Mueller, D.; Solanki, S. K.; del Toro Iniesta, J. C.
2019AGUFMSH21D3292M Altcode:
The Polarimetric and Helioseismic Imager on the Solar Orbiter mission
(SO/PHI) is the first magnetograph and helioseismology instrument
to observe the Sun from outside the Sun-Earth line. It is the key
instrument meant to address the top-level science question: How does
the solar dynamo work and drive connections between the Sun and the
heliosphere? SO/PHI will also play an important role in answering the
other top-level science questions of Solar Orbiter. It will provide
valuable supporting observations for Parker Solar Probe. The
instrument carries out narrow-band imaging spectro-polarimetry using a
tunable LiNbO3 Fabry-Perot etalon, while the polarisation modulation is
done with liquid crystal variable retarders (LCVRs). The line and the
nearby continuum are sampled at six wavelength points and the data are
recorded by a 2k x 2k CMOS detector. To save valuable telemetry, the
raw data are reduced already on board, including being inverted under
the assumption of a Milne-Eddington atmosphere. SO/PHI is composed of
two telescopes, the Full Disc Telescope (FDT), covers the full solar
disc at all phases of the orbit, while the High Resolution Telescope
(HRT), can resolve structures as small as 200 km on the Sun at closest
perihelion. The standard data products of SO/PHI are maps of the
photospheric magnetic field vector, line-of-sight velocity and continuum
intensity with a highest cadence of one minute. The operational modes
of SO/PHI are kept highly flexible allowing to adjust to the actual
science goal chosen for a Solar Orbiter operation window.

---------------------------------------------------------
Title: Readdressing the UV solar variability with SATIRE-S: non-LTE
effects
Authors: Tagirov, R. V.; Shapiro, A. I.; Krivova, N. A.; Unruh, Y. C.;
Yeo, K. L.; Solanki, S. K.
2019A&A...631A.178T Altcode: 2019arXiv190911736T
Context. Solar spectral irradiance (SSI) variability is one of the key
inputs to models of the Earth's climate. Understanding solar irradiance
fluctuations also helps to place the Sun among other stars in terms of
their brightness variability patterns and to set detectability limits
for terrestrial exoplanets. Aims: One of the most successful
and widely used models of solar irradiance variability is Spectral
And Total Irradiance REconstruction model (SATIRE-S). It uses spectra
of the magnetic features and surrounding quiet Sun that are computed
with the ATLAS9 spectral synthesis code under the assumption of local
thermodynamic equilibrium (LTE). SATIRE-S has been at the forefront
of solar variability modelling, but due to the limitations of the LTE
approximation its output SSI has to be empirically corrected below
300 nm, which reduces the physical consistency of its results. This
shortcoming is addressed in the present paper. Methods: We
replaced the ATLAS9 spectra of all atmospheric components in SATIRE-S
with spectra that were calculated using the Non-LTE Spectral SYnthesis
(NESSY) code. To compute the spectrum of the quiet Sun and faculae,
we used the temperature and density stratification models of the FAL
set. Results: We computed non-LTE contrasts of spots and faculae
and combined them with the corresponding fractional disc coverages,
or filling factors, to calculate the total and spectral irradiance
variability during solar cycle 24. The filling factors have been derived
from solar full-disc magnetograms and continuum images recorded by
the Helioseismic and Magnetic Imager on Solar Dynamics Observatory
(SDO/HMI). Conclusions: The non-LTE contrasts yield total and
spectral solar irradiance variations that are in good agreement with
empirically corrected LTE irradiance calculations. This shows that
the empirical correction applied to the SATIRE-S total and spectral
solar irradiance is consistent with results from non-LTE computations.

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Title: Superstrong photospheric magnetic fields in sunspot penumbrae
Authors: Siu-Tapia, A.; Lagg, A.; van Noort, M.; Rempel, M.; Solanki,
S. K.
2019A&A...631A..99S Altcode: 2019arXiv190913619S
Context. Recently, there have been some reports of unusually strong
photospheric magnetic fields (which can reach values of over 7 kG)
inferred from Hinode SOT/SP sunspot observations within penumbral
regions. These superstrong penumbral fields are even larger than the
strongest umbral fields on record and appear to be associated with
supersonic downflows. The finding of such fields has been controversial
since they seem to show up only when spatially coupled inversions
are performed. Aims: Here, we investigate and discuss the
reliability of those findings by studying in detail observed spectra
associated with particularly strong magnetic fields at the inner edge
of the penumbra of active region 10930. Methods: We applied
classical diagnostic methods and various inversions with different
model atmospheres to the observed Stokes profiles in two selected
pixels with superstrong magnetic fields, and compared the results
with a magnetohydrodynamic simulation of a sunspot whose penumbra
contains localized regions with strong fields (nearly 5 kG at τ = 1)
associated with supersonic downflows. Results: The different
inversions provide different results: while the SPINOR 2D inversions
consider a height-dependent single-component model and return B &gt;
7 kG and supersonic positive vLOS (corresponding to a
counter-Evershed flow), height-dependent two-component inversions
suggest the presence of an umbral component (almost at rest)
with field strengths ∼4 - 4.2 kG and a penumbral component with
vLOS ∼ 16 - 18 km s-1 and field strengths up
to ∼5.8 kG. Likewise, height-independent two-component inversions
find a solution for an umbral component and a strongly redshifted
(vLOS ∼ 15 - 17 km s-1) penumbral component
with B ∼ 4 kG. According to a Bayesian information criterion,
the inversions providing a better balance between the quality of
the fits and the number of free parameters considered by the models
are the height-independent two-component inversions, but they lie
only slightly above the SPINOR 2D inversions. Since it is expected
that the physical parameters all display considerable gradients with
height, as supported by magnetohydrodynamic (MHD) sunspot simulations,
the SPINOR 2D inversions are the preferred ones. Conclusions:
According to the MHD sunspot simulation analyzed here, the presence
of counter-Evershed flows in the photospheric penumbra can lead to
the necessary conditions for the observation of ∼5 kG fields at the
inner penumbra. Although a definite conclusion about the potential
existence of fields in excess of 7 kG cannot be given, their nature
could be explained (based on the simulation results) as the consequence
of the extreme dynamical effects introduced by highly supersonic
counter-Evershed flows (vLOS &gt; 10 km s-1
and up to ∼30 km s-1 according to SPINOR 2D). The latter
are much faster and more compressive downflows than those found in
the MHD simulations and therefore could lead to field intensification
up to considerably stronger fields. Also, a lower gas density would
lead to a deeper depression of the τ = 1 surface, making possible
the observation of deeper-lying stronger fields. The superstrong
magnetic fields are expected to be nearly force-free, meaning that
they can attain much larger strengths than expected when considering
only balance between magnetic pressure and the local gas pressure.

---------------------------------------------------------
Title: Delving into the Historical Ca II K Archive from the Kodaikanal
Observatory: The Potential of the Most Recent Digitized Series
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Solanki, Sami K.;
Krivova, Natalie A.; Banerjee, Dipankar; Jha, Bibhuti K.; Chatterjee,
Subhamoy
2019SoPh..294..145C Altcode: 2019arXiv190805493C
Full-disc Ca II K photographic observations of the Sun carry direct
information as regards the evolution of solar-plage regions for more
than a century and are therefore a unique dataset for solar-activity
studies. For a long time Ca II K observations were barely explored, but
recent digitizations of multiple archives have allowed their extensive
analysis. However, various studies have reported diverse results partly
due to the insufficient quality of the digitized data. Furthermore,
inhomogeneities have been identified within the individual archives,
which, at least partly, could be due to the digitization. As a result,
some of the archives, e.g. that from the Kodaikanal observatory, were
re-digitized. The results obtained by different authors who analyzed the
data from the new digitization of the Kodaikanal archive differ from
each other and from those derived from the old digitization. Since
the data were processed and analyzed using different techniques,
it is not clear, however, whether the differences are due to the
digitization or the processing of the data. To understand the reasons
for such discrepancies, we analyze here the data from the two most
recent digitizations of this archive. We use the same techniques
to consistently process the images from both archives and to derive
the plage areas from them. Some issues have been identified in both
digitizations, implying that they are intrinsic characteristics of
the data. Moreover, errors in timing of the observations plague both
digitizations. Overall, the most recent 16-bit digitization offers an
improvement over the earlier 8-bit one. It also includes considerably
more data and should be preferred.

---------------------------------------------------------
Title: A comparison between solar plage and network properties
Authors: Buehler, D.; Lagg, A.; van Noort, M.; Solanki, S. K.
2019A&A...630A..86B Altcode: 2019arXiv190807464B
 Aims: We compare the properties of kG magnetic structures
in the solar network and in active region plage at high spatial
resolution. Methods: Our analysis used six SP scans of the solar
disc centre aboard Hinode SOT and inverted the obtained spectra of the
photospheric 6302 Å line pair using the 2D SPINOR code. Results:
Photospheric magnetic field concentrations in network and plage areas
are on average 1.5 kG strong with inclinations of 10° -20°, and have
&lt; 400 m s-1 internal and 2-3 km s-1 external
downflows. At the disc centre, the continuum intensity of magnetic
field concentrations in the network are on average 10% brighter than the
mean quiet Sun, whilst their plage counterparts are 3% darker. A more
detailed analysis revealed that all sizes of individual kG patches in
the network have 150 G higher field strengths on average, 5% higher
continuum contrasts, and 800 m s-1 faster surrounding
downflows than similarly sized patches in the plage. The speed of
the surrounding downflows also correlates with the patch area, and
patches containing pores can produce supersonic flows exceeding 11 km
s-1 in individual pixels. Furthermore, the magnetic canopies
of kG patches are on average 9° more horizontal in the plage compared
to the network. Conclusions: Most of the differences between the
network and plage are due to their different patch size distributions,
but the intrinsic differences between similarly sized patches likely
results from the modification of the convection photospheric convection
with increasing amounts of magnetic flux.

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Title: Performance Analysis of the SO/PHI Software Framework for
On-board Data Reduction
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Rodríguez, J. Blanco;
Castellanos Duran, J. S.; Cobos Carrascosa, J. P.; Fiethe, B.;
Gandorfer, A.; Guan, Y.; Kolleck, M.; Lagg, A.; Lange, T.; Michalik,
H.; Solanki, S. K.; del Toro Iniesta, J. C.
2019ASPC..523..151A Altcode: 2019arXiv190508690A
The Polarimetric and Helioseismic Imager (PHI) is the first deep-space
solar spectropolarimeter, on-board the Solar Orbiter (SO) space
mission. It faces: stringent requirements on science data accuracy, a
dynamic environment, and severe limitations on telemetry volume. SO/PHI
overcomes these restrictions through on-board instrument calibration
and science data reduction, using dedicated firmware in FPGAs. This
contribution analyses the accuracy of a data processing pipeline by
comparing the results obtained with SO/PHI hardware to a reference
from a ground computer. The results show that for the analyzed pipeline
the error introduced by the firmware implementation is well below the
requirements of SO/PHI.

---------------------------------------------------------
Title: Achievements of Hinode in the first eleven years
Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick;
Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks,
David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio;
Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra,
Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.;
Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao,
Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota,
Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu,
Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin;
Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young,
Peter R.
2019PASJ...71R...1H Altcode:
Hinode is Japan's third solar mission following Hinotori (1981-1982)
and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in
operation currently. Hinode carries three instruments: the Solar Optical
Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These
instruments were built under international collaboration with the
National Aeronautics and Space Administration and the UK Science and
Technology Facilities Council, and its operation has been contributed
to by the European Space Agency and the Norwegian Space Center. After
describing the satellite operations and giving a performance evaluation
of the three instruments, reviews are presented on major scientific
discoveries by Hinode in the first eleven years (one solar cycle long)
of its operation. This review article concludes with future prospects
for solar physics research based on the achievements of Hinode.

---------------------------------------------------------
Title: Solar irradiance variability over last four billion years
Authors: Shapiro, Anna V.; Shapiro, Alexander I.; Gizon, Laurent;
Krivova, Natalie A.; Solanki, Sami K.
2019EPSC...13.2071S Altcode:
The action of dynamo generates magnetic field in the solar
interior. This field then travels through the convective zone and
emerges on the solar surface, leading to a various manifestations
of solar magnetic activity. One of the most appealing among them
is the variations of Spectral Solar Irradiance (SSI). There is an
evidence that these variations have substantial effect on the Earth's
climate system. The faster rotation of the Sun in the past led to
a more vigorous dynamo and consequently larger amplitude of solar
spectral irradiance variability. This could led to a stronger effect
of the SSI variability on the Earth. The main goal of our study is to
calculate the amplitude of the SSI variability over the course of the
solar activity cycle (which presently lasts 11 years but could have
different duration in the past) as a function of solar age. We utilise
recently published relation between the stellar chromospheric activity
and stellar age to reconstruct solar chromospheric activity back in
time. It is used to calculate solar disk coverages by magnetic features,
i.e. solar spots and faculae. Corresponding brightness variations are
then computed using the SATIRE (which stands for Spectral and Total
Irradiance Reconstruction) approach. Our study shows that the facular
component of the irradiance variability over the solar activity cycle
decreases slower with the solar age than the spot component. This
makes the dependence of the amplitude of the solar variability on the
age non-monotonic. The am- plitude decreases for the young Sun till
it reaches minimum value and then gradually increases again. The
variability of the Total Solar Irradiance (TSI, i.e. irradiance
integrated over the entire spectral domain) changes from being spot- to
facular-dominated at the solar age of about 2.8 Gyr. Our calculations
show that the amplitude of the TSI variability of 600-Myr Sun was one
order of magnitude larger than the present-day value. We have found that
the age of the transition between spot- and facular-dominated regimes
of the variability depends on the wavelength. For example, it is about
1.3 Gyr for the 210-400 nm spectral domain and becomes approximately
3.7 Gyr for the 400-700 nm spectral range. Our calculations of the past
solar irradiance variability on the activity cycle timescale might be
of interest for paleoclimate researchers as well as for modelling of
atmospheres of exoplanets.

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Title: The Solar-C_EUVST mission
Authors: Shimizu, Toshifumi; Imada, Shinsuke; Kawate, Tomoko;
Ichimoto, Kiyoshi; Suematsu, Yoshinori; Hara, Hirohisa; Katsukawa,
Yukio; Kubo, Masahito; Toriumi, Shin; Watanabe, Tetsuya; Yokoyama,
Takaaki; Korendyke, Clarence M.; Warren, Harry P.; Tarbell, Ted; De
Pontieu, Bart; Teriaca, Luca; Schühle, Udo H.; Solanki, Sami; Harra,
Louise K.; Matthews, Sarah; Fludra, A.; Auchère, F.; Andretta, V.;
Naletto, G.; Zhukov, A.
2019SPIE11118E..07S Altcode:
Solar-C EUVST (EUV High-Throughput Spectroscopic Telescope) is a
solar physics mission concept that was selected as a candidate for
JAXA competitive M-class missions in July 2018. The onboard science
instrument, EUVST, is an EUV spectrometer with slit-jaw imaging
system that will simultaneously observe the solar atmosphere from the
photosphere/chromosphere up to the corona with seamless temperature
coverage, high spatial resolution, and high throughput for the first
time. The mission is designed to provide a conclusive answer to the
most fundamental questions in solar physics: how fundamental processes
lead to the formation of the solar atmosphere and the solar wind, and
how the solar atmosphere becomes unstable, releasing the energy that
drives solar flares and eruptions. The entire instrument structure
and the primary mirror assembly with scanning and tip-tilt fine
pointing capability for the EUVST are being developed in Japan, with
spectrograph and slit-jaw imaging hardware and science contributions
from US and European countries. The mission will be launched and
installed in a sun-synchronous polar orbit by a JAXA Epsilon vehicle in
2025. ISAS/JAXA coordinates the conceptual study activities during the
current mission definition phase in collaboration with NAOJ and other
universities. The team is currently working towards the JAXA final
down-selection expected at the end of 2019, with strong support from
US and European colleagues. The paper provides an overall description
of the mission concept, key technologies, and the latest status.

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Title: Stellar Physics with High-Resolution UV Spectropolarimetry
Authors: Morin, Julien; Bouret, Jean-Claude; Neiner, Coralie; Aerts,
Conny; Bagnulo, Stefano; Catala, Claude; Charbonnel, Corinne;
Evans, Chris; Fossati, Luca; Garcia, Miriam; Gómez de Castro,
Ana I; Herrero, Artemio; Hussain, Gaitee; Kaper, Lex; Kochukhov,
Oleg; Konstantinova-Antova, Renada; de Koter, Alex; Kraus, Michaela;
Jiří\K{r}tička; Lèbre, Agnes; Lueftinger, Theresa; Meynet, Georges;
Petit, Pascal; Shore, Steve; Solanki, Sami; Stelzer, Beate; Strugarek,
Antoine; Vidotto, Aline; Vink, Jorick S
2019arXiv190801545M Altcode:
Current burning issues in stellar physics, for both hot and cool
stars, concern their magnetism. In hot stars, stable magnetic fields
of fossil origin impact their stellar structure and circumstellar
environment, with a likely major role in stellar evolution. However,
this role is complex and thus poorly understood as of today. It
needs to be quantified with high-resolution UV spectropolarimetric
measurements. In cool stars, UV spectropolarimetry would provide
access to the structure and magnetic field of the very dynamic upper
stellar atmosphere, providing key data for new progress to be made
on the role of magnetic fields in heating the upper atmospheres,
launching stellar winds, and more generally in the interaction of
cool stars with their environment (circumstellar disk, planets) along
their whole evolution. UV spectropolarimetry is proposed on missions
of various sizes and scopes, from POLLUX on the 15-m telescope LUVOIR
to the Arago M-size mission dedicated to UV spectropolarimetry.

---------------------------------------------------------
Title: Cosmic-ray variability on the multi-millennial time scale:
A new multi-proxy reconstruction
Authors: Usoskin, I.; Wu, C. J.; Krivova, N.; Solanki, S. K.;
Kovaltsov, G.; Baroni, M.; Bard, E.
2019ICRC...36.1164U Altcode: 2019PoS...358.1164U
No abstract at ADS

---------------------------------------------------------
Title: Opacity distribution functions for stellar spectra synthesis
Authors: Cernetic, M.; Shapiro, A. I.; Witzke, V.; Krivova, N. A.;
Solanki, S. K.; Tagirov, R. V.
2019A&A...627A.157C Altcode: 2019arXiv190603112C
Context. Stellar spectra synthesis is essential for the characterization
of potential planetary hosts. In addition, comprehensive stellar
variability calculations with fast radiative transfer are needed
to disentangle planetary transits from stellar magnetically driven
variability. The planet-hunting space telescopes, such as CoRoT, Kepler,
and TESS, bring vast quantities of data, rekindling the interest in
fast calculations of the radiative transfer. Aims: We revisit
the opacity distribution functions (ODF) approach routinely applied to
speed up stellar spectral synthesis. To achieve a considerable speedup
relative to the state of the art, we further optimize the approach and
search for the best ODF configuration. Furthermore, we generalize the
ODF approach for fast calculations of flux in various filters often
used in stellar observations. Methods: In a parameter-sweep
fashion, we generated ODF in the spectral range from UV to IR with
different setups. The most accurate ODF configuration for each spectral
interval was determined. We adapted the wavelength grid based on the
transmission curve for calculations of the radiative fluxes through
filters before performing the normal ODF procedure. Results:
Our optimum ODF configuration allows for a three-fold speedup, compared
to the previously used ODF configurations. The ODF generalization to
calculate fluxes through filters results in a speedup of more than
two orders of magnitude.

---------------------------------------------------------
Title: ALMA detection of dark chromospheric holes
Authors: White, Stephen M.; Loukitcheva, Maria A.; Solanki, Sami K.
2019AAS...23421704W Altcode:
Atacama Large Millimeter/submillimeter Array (ALMA) observations of a
quiet-Sun region at a wavelength of 3 mm are compared with available
chromospheric observations in the UV and visible as well as with
photospheric magnetograms. The ALMA images clearly reveal the presence
of distinctive cold areas in the millimeter maps having temperatures of
around 60% of the normal quiet Sun at 3 mm, which are not seen in the
other data. We speculate that ALMA is sensing cool chromospheric gas,
whose presence had earlier been inferred from infrared CO spectra.

---------------------------------------------------------
Title: ALMA Detection of Dark Chromospheric Holes in the Quiet Sun
Authors: Loukitcheva, Maria A.; White, Stephen M.; Solanki, Sami K.
2019ApJ...877L..26L Altcode: 2019arXiv190506763L
We present Atacama Large Millimeter/submillimeter Array (ALMA)
observations of a quiet-Sun region at a wavelength of 3 mm, obtained
during the first solar ALMA cycle on 2017 April 27, and compare them
with available chromospheric observations in the UV and visible as
well as with photospheric magnetograms. ALMA images clearly reveal the
presence of distinct particularly dark/cool areas in the millimeter
maps with temperatures as low as 60% of the normal quiet Sun at 3 mm,
which are not seen in the other data. We speculate that ALMA is sensing
cool chromospheric gas, whose presence had earlier been inferred from
infrared CO spectra.

---------------------------------------------------------
Title: Recovering the unsigned photospheric magnetic field from Ca
II K observations
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Solanki, Sami K.;
Krivova, Natalie A.; Giorgi, Fabrizio; Yeo, Kok Leng
2019A&A...626A.114C Altcode: 2019arXiv190503453C
Context. A number of studies have aimed at defining the exact form
of the relation between magnetic field strength and Ca II H and K
core brightness. All previous studies have however been restricted
to isolated regions on the solar disc or to a limited set of
observations. Aims: We reassess the relationship between the
photospheric magnetic field strength and the Ca II K intensity for
a variety of surface features as a function of the position on the
disc and the solar activity level. This relationship can be used to
recover the unsigned photospheric magnetic field from images recorded
in the core of Ca II K line. Methods: We have analysed 131
pairs of high-quality, full-disc, near-co-temporal observations from
the Helioseismic and Magnetic Imager (SDO/HMI) and Precision Solar
Photometric Telescope (Rome/PSPT) spanning half a solar cycle. To
analytically describe the observationally determined relation, we
considered three different functions: a power law with an offset,
a logarithmic function, and a power-law function of the logarithm
of the magnetic flux density. We used the obtained relations to
reconstruct maps of the line-of-sight component of the unsigned
magnetic field (unsigned magnetograms) from Ca II K observations,
which were then compared to the original magnetograms. Results:
We find that both power-law functions represent the data well, while
the logarithmic function is good only for quiet periods. We see
no significant variation over the solar cycle or over the disc in
the derived fit parameters, independently of the function used. We
find that errors in the independent variable, which are usually
not accounted for, introduce attenuation bias. To address this, we
binned the data with respect to the magnetic field strength and Ca II
K contrast separately and derived the relation for the bisector of
the two binned curves. The reconstructed unsigned magnetograms show
good agreement with the original ones. Root mean square differences
are less than 90 G. The results were unaffected by the stray-light
correction of the SDO/HMI and Rome/PSPT data. Conclusions:
Our results imply that accurately processed and calibrated Ca II K
observations can be used to reconstruct unsigned magnetograms by using
the relations derived in our study.

---------------------------------------------------------
Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A.; Riethmueller, T.; Solanki, S. K.; Lagg, A.
2019ASPC..526..307K Altcode:
Moving magnetic features (MMFs) are small-scale magnetic elements
observed to move radially outward from sunspots. Some studies have
reported the presence of MMFs around pores as well. We analyzed data
from SunriseII/IMaX observations obtained on 2013 June 12 between
23:39:10 and 23:55:37 UT. IMaX scanned the Fe I 5250.225 Å spectral
line at eight wavelength positions and recorded the full Stokes vector
at each of these positions. The field of view covered a large pore
(μ = 0.93) with pixel scale of 0″.055. MMFs of opposite (positive)
and same (negative) polarity as the pore were observed to stream
from the pore boundary. We carried out a statistical analysis of the
physical properties of MMFs and the main results are: 1) the number
of opposite polarity MMFs within 1.5 Mm from the pore border, when
they were first identified, is twice that of the same polarity MMFs. 2)
Only 11% of the chosen MMFs appear to be monopolar and they all have the
same polarity as the pore. 3) Majority of MMFs of both polarities move
away from the pore border with an average speed of 1.5 km/s. However,
they do not always follow a smooth radial track and some of them even
move in tangential direction to the pore. 4) MMFs of opposite polarity
show a preferential up-flow whereas those of the same polarity do not
show any preference. 5) MMFs of both polarities are characterized by
inclined fields. This work, presented in an oral contribution
at this Workshop, has been published on The Astrophysical Journal
Supplement Series (Kaithakkal et al. 2017).

---------------------------------------------------------
Title: Fast Solar Polarimeter (Prototype): Preliminary Results of
Stokes Measurements in the Sr I 4607 Å Line at VTT/TESOS
Authors: Zeuner, F.; Feller, A.; Iglesias, F. A.; Solanki, S. K.
2019ASPC..526..295Z Altcode:
Scattering polarization measurements at spatial scales in the
0.1″-1″ regime are a very promising complementary diagnostic for the
Sun's atmosphere and magnetism at small spatial scales (e.g., Trujillo
Bueno et al. 2004). So far, for the Sr I line at 4607.3 Å, which
exhibits a large scattering polarization signal (Stenflo et al. 1997;
Gandorfer 2002), only theoretical predictions for the strength and
spatial distribution of linear polarization signals at sub-arcsecond
scales close to disk center are made available by Trujillo Bueno &amp;
Shchukina (2007), whereas observational feedback is still very rare. Here, we present preliminary results of two observational campaigns
with the prototype of the Fast Solar Polarimeter (FSP, Iglesias et
al. 2016) attached to the TESOS filtergraph, which is located at the
German Vacuum Tower Telescope (VTT) in Tenerife, Spain. We
measured the center-to-limb variation of spatially averaged Stokes
Q/I profiles in the Sr I line at 11 wavelength positions to check
for systematic errors and to compare with previous results by other
instruments. We find that our results are in agreement with previous
findings reported in the literature (i.e., Stenflo et al. 1997). In May 2015, we observed the Sr I line in the quiet Sun at
μ=0.6 from the north solar limb with a spatial sampling of 0.08″
pixel-1 and noise levels significantly below 1% per pixel
for linear polarized signals with 1.25 s integration time. To obtain
lower noise levels (&lt; 0.1%), while conserving sufficient spatial
resolution to resolve solar granulation, we carefully used spatial,
spectral, and temporal averaging, as well as a MOMFBD restoration
(see van Noort et al. 2005). We compare our findings in the Sr I line
with the neighboring, but not scattering sensitive Fe I line at 4607.6
Å. Our statistical analysis of Stokes Q/I signals in the line
core of Sr I reveals that the polarization amplitude is correlating
with the intensity of the continuum image. We find stronger linear
polarimetric signals corresponding to intergranular lanes of the Stokes
I image, which is in contrast to the findings of Malherbe et al. (2007)
at μ=0.3. The results have been published as an article entitled
"Detection of spatially structured scattering polarization of Sr I
4607.3 Å with the Fast Solar Polarimeter" (Zeuner et al. 2018).

---------------------------------------------------------
Title: On the Magnetic Nature of Solar Exploding Granules
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
B.; Bellot Rubio, L. R.; del Toro Iniesta, J. C.; Solanki, S. K.;
Zuccarello, F.
2019ASPC..526..299G Altcode:
We report on spectropolarimetric observations acquired by the imaging
magnetograph SUNRISE/IMaX at high spatial 0.”3 and temporal (31.5 s)
resolution during the first science flight of this balloon-borne solar
observatory. We describe the photospheric evolution of an exploding
granule observed in the quiet Sun. This granule is cospatial with
a magnetic flux emergence event occurring at mesogranular scales
(up to ∼12 Mm2 area). Using a modified version of the
SIR code, we show that we can estimate the longitudinal field also
in the presence of a residual cross-talk in these IMaX longitudinal
measurements. We determine the magnetic flux content of the structure
(∼3 ×1018 Mx), which appears to have a multipolar
configuration, and discuss the origin of such flux emergence events.

---------------------------------------------------------
Title: GPS, decrypting brightness variations of the Sun and Sun-like
Authors: Amazo-Gómez, Eliana Maritza; Shapiro, Alexander I.; Solanki,
Sami K.; Kopp, Greg; Oshagh, Mahmoudreza; Reinhold, Timo; Krivova,
Natalie A.; Reiners, Ansgar
2019shin.confE.109A Altcode:
The rotation period is in general detectable in the light curves of
young and active stars. Even after successful stellar surveys stemmed
from Kepler mission, there is still a lack of information in photometric
records of rotation periods in Sun-like stars. Non-periodic light-curve
profiles, low variability contrast -therefore low modulation amplitude-
short lifetime evolution and random emergence of magnetic features
(in comparison to the rotation time-scale) are the main reasons of
unreliable determination of rotation periodicity in the Sun and its
closer analogs. This indicates that only a small fraction of solar-like
systems have been properly analyzed. We show that the rotation periods
of those stars can be reliably determined from the profile of the
gradient of the power spectra, GPS. By analysing periodic patterns
in high-accuracy measurements of the total solar irradiance, TSI,
by SORCE/TIM and SoHO/VIRGO missions, here we test and validate
GPS, linking the variability by transits of magnetic features over
the stellar surface with a clear and enhanced signal of the solar
rotation. GPS method retrieves accurate and stable values of rotation
period during different regimes of solar activity cycle and could
be applied to stars of comparable and higher activity - where other
methods underperform. Furthermore, GPS gives us constraints on the
faculae to spot driver ratio and consequently help us to interpret
the stellar surface.

---------------------------------------------------------
Title: Spectropolarimetric Observations of an Arch Filament System
with GREGOR
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kučera, A.; Schwartz, P.; Berkefeld, T.; Collados, M.;
Denker, C.; Feller, A.; Hofmann, A.; Schlichenmaier, R.; Schmidt,
D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau,
D.; Staude, J.; Strassmeier, K. G.; von der Lühe, O.
2019ASPC..526..217B Altcode: 2018arXiv180401789B
We observed an arch filament system (AFS) in a sunspot group with the
GREGOR Infrared Spectrograph attached to the GREGOR solar telescope. The
AFS was located between the leading sunspot of negative polarity and
several pores of positive polarity forming the following part of the
sunspot group. We recorded five spectro-polarimetric scans of this
region. The spectral range included the spectral lines Si I 1082.7
nm, He I 1083.0 nm, and Ca I 1083.9 nm. In this work we concentrate
on the silicon line which is formed in the upper photosphere. The
line profiles are inverted with the code 'Stokes Inversion based
on Response functions' to obtain the magnetic field vector. The
line-of-sight velocities are determined independently with a Fourier
phase method. Maximum velocities are found close to the ends of AFS
fibrils. These maximum values amount to 2.4 km s-1 next
to the pores and to 4 km s-1 at the sunspot side. Between
the following pores, we encounter an area of negative polarity that
is decreasing during the five scans. We interpret this by new emerging
positive flux in this area canceling out the negative flux. In summary,
our findings confirm the scenario that rising magnetic flux tubes
cause the AFS.

---------------------------------------------------------
Title: Photospheric Magnetic Fields of the Trailing Sunspots in
Active Region NOAA 12396
Authors: Verma, M.; Balthasar, H.; Denker, C.; Böhm, F.; Fischer,
C. E.; Kuckein, C.; González Manrique, S. J.; Sobotka, M.; Bello
González, N.; Diercke, A.; Berkefeld, T.; Collados, M.; Feller, A.;
Hofmann, A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar,
A.; Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K.; Volkmer,
R.; von der Lühe, O.; Waldmann, T.
2019ASPC..526..291V Altcode: 2018arXiv180507752V
The solar magnetic field is responsible for all aspects of solar
activity. Sunspots are the main manifestation of the ensuing solar
activity. Combining high-resolution and synoptic observations has
the ambition to provide a comprehensive description of the sunspot
growth and decay processes. Active region NOAA 12396 emerged on 2015
August 3 and was observed three days later with the 1.5-meter GREGOR
solar telescope on 2015 August 6. High-resolution spectropolarimetric
data from the GREGOR Infrared Spectrograph (GRIS) are obtained in the
photospheric lines Si I λ1082.7 nm and Ca I λ1083.9 nm, together
with the chromospheric He I λ1083.0 nm triplet. These near-infrared
spectropolarimetric observations were complemented by synoptic
line-of-sight magnetograms and continuum images of the Helioseismic
and Magnetic Imager (HMI) and EUV images of the Atmospheric Imaging
Assembly (AIA) on board the Solar Dynamics Observatory (SDO).

---------------------------------------------------------
Title: Formation of the Penumbra and Start of the Evershed Flow
Authors: Murabito, M.; Romano, P.; Guglielmino, S. L.; Zuccarello,
F.; Solanki, S. K.
2019ASPC..526..243M Altcode:
We analyze high-resolution observations of Active Region NOAA 11490,
acquired on 2012 May 28 and 29. Spectropolarimetric measurements of
the photospheric lines of Fe I at 617.3 nm and 630.25 nm were taken
with the Interferometric BIdimensional Spectrometer (IBIS), mounted on
NSO/DST, during about 30 minutes for each day. To study the evolution
of continuum intensity, LOS velocity, inclination and strength of the
magnetic field during the entire time interval, we also used data taken
by SDO/HMI. We used the SIR code to invert the Stokes profiles observed
with IBIS, using different initial models to take into account the
physical conditions of the plasma in the region of umbra, penumbra,
and quiet Sun. From the analysis of the SIR results, we found that,
before the formation of the penumbra, the annular zone is characterized
by downflows in the inner part. Furthermore, we observed that the onset
of the classical Evershed flow occurs on a short time scale, 1-3 hours,
while the penumbra is forming. In order to investigate the conditions
that lead to the establishment of the classical Evershed flow, we
analyzed the evolution of the continuum intensity, LOS velocity,
inclination and strength of the magnetic field in a segment in the
north-western part of the leading spot. In about 1 hour, we noted a
clear evolution from redshift to blueshift in the penumbral filaments
along the selected segment. We propose a scenario in which the penumbra
is formed by magnetic flux dragged down from the canopy surrounding
the initial pore: the Evershed flow starts when the sinking magnetic
field dips below the solar surface and magnetoconvection sets in.

---------------------------------------------------------
Title: Analysis of full disc Ca II K spectroheliograms. II. Towards
an accurate assessment of long-term variations in plage areas
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova, Natalie
A.; Solanki, Sami K.
2019A&A...625A..69C Altcode: 2019arXiv190207122C
Context. Reconstructions of past irradiance variations require suitable
data on solar activity. The longest direct proxy is the sunspot number,
and it has been most widely employed for this purpose. These data,
however, only provide information on the surface magnetic field
emerging in sunspots, while a suitable proxy of the evolution of the
bright magnetic features, specifically faculae/plage and network,
is missing. This information can potentially be extracted from the
historical full-disc observations in the Ca II K line. Aims: We
use several historical archives of full-disc Ca II K observations to
derive plage areas over more than a century. Employment of different
datasets allows the identification of systematic effects in the
images, such as changes in instruments and procedures, as well as
an assessment of the uncertainties in the results. Methods:
We have analysed over 100 000 historical images from eight digitised
photographic archives of the Arcetri, Kodaikanal, McMath-Hulbert,
Meudon, Mitaka, Mt Wilson, Schauinsland, and Wendelstein observatories,
and one archive of modern observations from the Rome/PSPT. The analysed
data cover the period 1893-2018. We first performed careful photometric
calibration and compensation for the centre-to-limb variation, and
then segmented the images to identify plage regions. This has been
consistently applied to both historical and modern observations. Results: The plage series derived from different archives are
generally in good agreement with each other. However, there are also
clear deviations that most likely hint at intrinsic differences in the
data and their digitisation. We showed that accurate image processing
significantly reduces errors in the plage area estimates. Accurate
photometric calibration also allows precise plage identification on
images from different archives without the need to arbitrarily adjust
the segmentation parameters. Finally, by comparing the plage area
series from the various records, we found the conversion laws between
them. This allowed us to produce a preliminary composite of the plage
areas obtained from all the datasets studied here. This is a first
step towards an accurate assessment of the long-term variation of plage
regions. The data are only available at the CDS via anonymous ftp
to <A href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/625/A69">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/625/A69</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: Plage area composite series
(Chatzistergos+, 2019)
Authors: Chatzistergos, T.; Ermolli, I.; Krivova, N. A.; Solanki, S. K.
2019yCat..36250069C Altcode:
Annual, monthly, and daily values of the plage area composite series
produced in the paper. (3 data files).

---------------------------------------------------------
Title: The potential of many-line inversions of photospheric
spectropolarimetric data in the visible and near UV
Authors: Riethmüller, T. L.; Solanki, S. K.
2019A&A...622A..36R Altcode: 2018arXiv181203757R
Our knowledge of the lower solar atmosphere is mainly obtained from
spectropolarimetric observations, which are often carried out in the red
or infrared spectral range and almost always cover only a single or a
few spectral lines. Here we compare the quality of Stokes inversions of
only a few spectral lines with many-line inversions. In connection with
this, we have also investigated the feasibility of spectropolarimetry
in the short-wavelength range, 3000 Å-4300 Å, where the line density
but also the photon noise are considerably higher than in the red,
so that many-line inversions could be particularly attractive in
that wavelength range. This is also timely because this wavelength
range will be the focus of a new spectropolarimeter in the third
science flight of the balloon-borne solar observatory SUNRISE. For
an ensemble of state-of-the-art magneto-hydrodynamical atmospheres we
synthesize exemplarily spectral regions around 3140 Å (containing 371
identified spectral lines), around 4080 Å (328 lines), and around
6302 Å (110 lines). The spectral coverage is chosen such that at a
spectral resolving power of 150 000 the spectra can be recorded by a
2K × 2K detector. The synthetic Stokes profiles are degraded with a
typical photon noise and afterward inverted. The atmospheric parameters
of the inversion of noisy profiles are compared with the inversion
of noise-free spectra. We find that significantly more information
can be obtained from many-line inversions than from a traditionally
used inversion of only a few spectral lines. We further find that
information on the upper photosphere can be significantly more reliably
obtained at short wavelengths. In the mid and lower photosphere, the
many-line approach at 4080 Å provides equally good results as the
many-line approach at 6302 Å for the magnetic field strength and the
line-of-sight (LOS) velocity, while the temperature determination is
even more precise by a factor of three. We conclude from our results
that many-line spectropolarimetry should be the preferred option in
the future, and in particular at short wavelengths it offers a high
potential in solar physics.

---------------------------------------------------------
Title: Cancelation of small-scale magnetic features
Authors: Kaithakkal, A. J.; Solanki, S. K.
2019A&A...622A.200K Altcode: 2018arXiv181211496K
 Aims: We investigate small-scale flux cancelations in a young
active region observed with the high-resolution imaging magnetograph
IMaX on the SUNRISE balloon-borne solar observatory. Methods: The
observed Stokes profiles of the photospheric Fe I 5250.2 Å line were
inverted using the SPINOR code to obtain the atmospheric parameters,
including magnetic field vector and the line-of-sight velocity. We then
identified 11 opposite-polarity canceling pairs using an automatic
detection code, studied their evolution in detail, and derived
their statistical properties. We classified the cancelations into two
groups. Class I events are those for which cancelation happens between
a pre-existing large magnetic feature of one polarity and a smaller
feature of the other polarity that emerged or appeared nearby. For
Class II events cancelations occur between two pre-existing, previously
unconnected features that converge. Results: All studied events
have an apparent cancelation time of less than ten minutes and display
a significant transient linear polarization signal along the polarity
inversion line. The cancelation events are characterized by a flux decay
rate of about 1015 Mx s-1. For Class I events,
the Doppler velocity of the disappearing patch gradually switches
from blueshift during the initial phase of cancelation to redshift
toward the end of the cancelation. For class II events, the Doppler
velocity is consistently redshifted. Horizontal convergence speeds
of Class II pairs fall between 0.3 and 1.22 km s-1. The
elements often do not converge directly toward each other, so that
the proper motion speeds of the individual elements is higher,
in the range of 1-2.7 km s-1. Conclusions: We
propose that these cancelation events result from either field-line
submergence (Class I), or reconnection followed by submergence
(Class II and/or Class I). Ohmic dissipation of magnetic energy
could also play a role for both classes. The dynamics and evolution
of these events are influenced by neighboring granular motions. We
also propose that, at least for the Class II events, the granular
motions could possibly be driving magnetic reconnection, rather than
the supergranular motions proposed for the larger cancelation events
studied earlier. Specific flux cancelation rates of the Class II events
seem to indicate that they belong to somewhat different category
of cancelations when compared with those studied in SOT/Hinode and
MDI/SOHO data. A movie associated to Fig. 5 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833770/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Chapter 3 - The Sun's Atmospher
Authors: Shapiro, Alexander I.; Peter, Hardi; Solanki, Sami K.
2019sgsp.book...59S Altcode:
The solar atmosphere covers a broad range of temperatures and densities
from the solar surface, via the chromosphere and transition region, and
to the corona. Although one-dimensional (1D) models of the atmospheric
structure have reached a high level of maturity, high-spatial
resolution observations have cast some doubt on their validity. Thus,
such observations have revealed a richness of highly variable spatial
structure, often reaching down to the current resolution limit
of 0.1 arcsec, or roughly 70 km on the Sun, in the photosphere and
chromosphere. These observational advances have led to a new generation
of models that describe the solar atmosphere self-consistently using 3D
magnetohydrodynamic approximation simulations, including 3D radiative
energy transport for those that cover the lower atmosphere, while
simplistically taking into account the complex magnetic structure and
energy dissipation processes in the upper atmosphere. These models have
achieved considerable success in explaining the best observations,
although there are still a number of open questions. Nonetheless,
thanks to modern advances, the solar atmosphere now provides an
excellent setting to test models of stellar atmospheres critically.

---------------------------------------------------------
Title: Intensity contrast of solar plage as a function of magnetic
flux at high spatial resolution
Authors: Kahil, F.; Riethmüller, T. L.; Solanki, S. K.
2019A&A...621A..78K Altcode: 2018arXiv181105759K
Magnetic elements have an intensity contrast that depends on the type
of region they are located in (for example quiet Sun, or active region
plage). Observed values also depend on the spatial resolution of the
data. Here we investigate the contrast-magnetic field dependence in
active region plage observed near disk center with SUNRISE during
its second flight in 2013. The wavelengths under study range from
the visible at 525 nm to the near ultraviolet (NUV) at 300 nm and
397 nm. We use quasi-simultaneous spectropolarimetric and photometric
data from the Imaging Magnetograph eXperiment (IMaX) and the Sunrise
Filter Imager (SuFI), respectively. We find that in all wavelength
bands, the contrast exhibits a qualitatively similar dependence on
the line-of-sight magnetic field, BLOS, as found in the
quiet Sun, with the exception of the continuum at 525 nm. There, the
contrast of plage magnetic elements peaks for intermediate values of
BLOS and decreases at higher field strengths. By comparison,
the contrast of magnetic elements in the quiet Sun saturates at its
maximum value at large BLOS. We find that the explanation
of the turnover in contrast in terms of the effect of finite spatial
resolution of the data is incorrect with the evidence provided by the
high-spatial resolution SUNRISE data, as the plage magnetic elements are
larger than the quiet Sun magnetic elements and are well-resolved. The
turnover comes from the fact that the core pixels of these larger
magnetic elements are darker than the quiet Sun. We find that plages
reach lower contrast than the quiet Sun at disk center at wavelength
bands formed deep in the photosphere, such as the visible continuum
and the 300 nm band. This difference decreases with formation height
and disappears in the Ca II H core, in agreement with empirical models
of magnetic element atmospheres.

---------------------------------------------------------
Title: Historical solar Ca II K observations at the Rome and Catania
observatories
Authors: Chatzistergos, T.; Ermolli, I.; Falco, M.; Giorgi, F.;
Guglielmino, S. L.; Krivova, N. A.; Romano, P.; Solanki, S. K.
2019NCimC..42....5C Altcode: 2019arXiv190207483C
Here we present the little explored Ca II K archives from the Rome
and the Catania observatories and analyse the digitised images from
these archives to derive plage areas.

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Title: Improved search for solar chameleons with a GridPix detector
at CAST
Authors: Anastassopoulos, V.; Aune, S.; Barth, K.; Belov, A.;
Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Castel, J. F.; Cetin,
S. A.; Christensen, F.; Dafni, T.; Davenport, M.; Dermenev, A.; Desch,
K.; Döbrich, B.; Eleftheriadis, C.; Fanourakis, G.; Ferrer-Ribas,
E.; Fischer, H.; Funk, W.; Garcimatha, J. A.; Gardikiotis, A.; Garza,
J. G.; Gazis, E. N.; Geralis, T.; Giomataris, I.; Gninenko, S.; Hailey,
C. J.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.; Irastorza,
I. G.; Jakobsen, A.; Jacoby, J.; Jakovčić, K.; Kaminski, J.; Karuza,
M.; Kostoglou, S.; Kralj, N.; Krčmar, M.; Krieger, C.; Lakić, B.;
Laurent, J. M.; Liolios, A.; Ljubičić, A.; Luzón, G.; Maroudas,
M.; Miceli, L.; Neff, S.; Ortega, I.; Papaevangelou, T.; Paraschou,
K.; Pivovaroff, M. J.; Raffelt, G.; Rosu, M.; Ruz, J.; Ruiz Chóliz,
E.; Savvidis, I.; Schmidt, S.; Semertzidis, Y. K.; Solanki, S. K.;
Stewart, L.; Vafeiadis, T.; Vogel, J. K.; Vretenar, M.; Wuensch, W.;
Yildiz, S. C.; Zioutas, K.; Brax, P.
2019JCAP...01..032A Altcode: 2018arXiv180800066A
We report on a new search for solar chameleons with the CERN
Axion Solar Telescope (CAST). A GridPix detector was used to
search for soft X-ray photons in the energy range from 200 eV
to 10 keV from converted solar chameleons. No significant excess
over the expected background has been observed in the data taken
in 2014 and 2015. We set an improved limit on the chameleon
photon coupling, βγlesssim#5.7×1010 for
1&lt;βm&lt;106 at 95% C.L. improving our previous
results by a factor two and for the first time reaching sensitivity
below the solar luminosity bound for tachocline magnetic fields up to
12.5 T.

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Title: Solar total and spectral irradiance reconstruction over the
last 9000 years
Authors: Wu, C. -J.; Krivova, N. A.; Solanki, S. K.; Usoskin, I. G.
2018A&A...620A.120W Altcode: 2018arXiv181103464W
Context. Changes in solar irradiance and in its spectral distribution
are among the main natural drivers of the climate on Earth. However,
irradiance measurements are only available for less than four decades,
while assessment of solar influence on Earth requires much longer
records. Aims: The aim of this work is to provide the most
up-to-date physics-based reconstruction of the solar total and spectral
irradiance (TSI/SSI) over the last nine millennia. Methods:
The concentrations of the cosmogenic isotopes 14C and
10Be in natural archives have been converted to decadally
averaged sunspot numbers through a chain of physics-based models. TSI
and SSI are reconstructed with an updated SATIRE model. Reconstructions
are carried out for each isotope record separately, as well as
for their composite. Results: We present the first ever
SSI reconstruction over the last 9000 years from the individual
14C and 10Be records as well as from their
newest composite. The reconstruction employs physics-based models to
describe the involved processes at each step of the procedure. Conclusions: Irradiance reconstructions based on two different
cosmogenic isotope records, those of 14C and 10Be,
agree well with each other in their long-term trends despite their
different geochemical paths in the atmosphere of Earth. Over the last
9000 years, the reconstructed secular variability in TSI is of the
order of 0.11%, or 1.5 W m-2. After the Maunder minimum,
the reconstruction from the cosmogenic isotopes is consistent with
that from the direct sunspot number observation. Furthermore, over
the nineteenth century, the agreement of irradiance reconstructions
using isotope records with the reconstruction from the sunspot number
by Chatzistergos et al. (2017, A&amp;A, 602, A69) is better than that
with the reconstruction from the WDC-SILSO series (Clette et al. 2014,
Space Sci. Rev., 186, 35), with a lower χ2-value.

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Title: Activity variation driven by flux emergence and transport on
Sun-like stars
Authors: Işık, Emre; Solanki, Sami K.; Krivova, Natalie A.; Shapiro,
Alexander I.
2018arXiv181208976I Altcode:
In G dwarfs, the surface distribution, coverage and lifetimes
of starspots deviate from solar-like patterns as the rotation
rate increases. We set up a numerical platform which includes the
large-scale rotational and surface flow effects, aiming to simulate
evolving surface patterns over an activity cycle for up to 8 times the
solar rotation and flux emergence rates. At the base of the convection
zone, we assume a solar projected butterfly diagram. We then follow
the rotationally distorted trajectories of rising thin flux tubes to
obtain latitudes and tilt angles. Using them as source distributions,
we run a surface flux transport model with solar parameters. Our model
predicts surface distributions of the signed radial fields and the
starspots that qualitatively agree with observations.

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Title: Forward modelling of brightness variations in Sun-like
stars. I. Emergence and surface transport of magnetic flux
Authors: Işık, E.; Solanki, S. K.; Krivova, N. A.; Shapiro, A. I.
2018A&A...620A.177I Altcode: 2018arXiv181006728I
Context. The latitudinal distribution of starspots deviates
from the solar pattern with increasing rotation rate. Numerical
simulations of magnetic flux emergence and transport can help model
the observed stellar activity patterns and the associated brightness
variations. Aims: We set up a composite model for the processes
of flux emergence and transport on Sun-like stars to simulate stellar
brightness variations for various levels of magnetic activity and
rotation rates. Methods: Assuming that the distribution of
magnetic flux at the base of the convection zone follows solar scaling
relations, we calculate the emergence latitudes and tilt angles of
bipolar regions at the surface for various rotation rates, using
thin-flux-tube simulations. Taking these two quantities as input to a
surface flux transport (SFT) model, we simulate the diffusive-advective
evolution of the radial field at the stellar surface, including
effects of active region nesting. Results: As the rotation
rate increases, (1) magnetic flux emerges at higher latitudes and an
inactive gap opens around the equator, reaching a half-width of 20° for
8 Ω⊙; and (2) the tilt angles of freshly emerged bipolar
regions show stronger variations with latitude. Polar spots can form
at 8 Ω⊙ by accumulation of follower-polarity flux from
decaying bipolar regions. From 4 Ω⊙ to 8 Ω⊙,
the maximum spot coverage changes from 3 to 20%, respectively, compared
to 0.4% in the solar model. Nesting of activity can lead to strongly
non-axisymmetric spot distributions. Conclusions: On Sun-like
stars rotating at 8 Ω⊙ (Prot ≃ 3 days),
polar spots can form, owing to higher levels of flux emergence rate and
tilt angles. Defining spots by a threshold field strength yields global
spot coverages that are roughly consistent with stellar observations.

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Title: Detection of spatially structured scattering polarization of
Sr I 4607.3 Å with the Fast Solar Polarimeter
Authors: Zeuner, F.; Feller, A.; Iglesias, F. A.; Solanki, S. K.
2018A&A...619A.179Z Altcode: 2018arXiv180806539Z
Context. Scattering polarization in the Sr I 4607.3 Å line observed
with high resolution is an important diagnostic of the Sun's atmosphere
and magnetism at small spatial scales. Investigating the scattering
polarization altered by the Hanle effect is key to constraining the
role of small-scale magnetic activity in solar atmospheric activity
and energy balance. At present, spatially resolved observations of
this diagnostic are rare and have not been reported as close to the
disk center as for μ = 0.6. Aims: Our aim is to measure the
scattering polarization in the Sr I line at μ = 0.6 and to identify the
spatial fluctuations with a statistical approach. Methods: Using
the Fast Solar Polarimeter (FSP) mounted on the TESOS filtergraph at the
German Vacuum Tower Telescope (VTT) in Tenerife, Spain, we measured both
the spatially resolved full Stokes parameters of the Sr I line at μ =
0.6 and the center-to-limb variation of the spatially averaged Stokes
parameters. Results: We find that the center-to-limb variation
of the scattering polarization in the Sr I line measured with FSP
is consistent with previous measurements. A statistical analysis of
Stokes Q/I (i.e., the linear polarization component parallel to the
solar limb), sampled with 0.16″ pixel-1 in the line core
of Sr I reveals that the signal strength is inversely correlated with
the intensity in the continuum. We find stronger linear polarimetric
signals corresponding to dark areas in the Stokes I continuum image
(intergranular lanes). In contrast, independent measurements at μ =
0.3 show a positive correlation of Q/I with respect to the continuum
intensity. We estimate that the subregion diameter responsible for the
excess Q/I signal is on the order of 0.5″-1″. Conclusions:
The presented observations and the statistical analysis of Q/I signals
at μ = 0.6 complement reported scattering polarization observations
as well as simulations. The FSP has proven to be a suitable instrument
to measure spatially resolved scattering polarization signals. In
the future, a systematic center-to-limb series of observations with
subgranular spatial resolution and increased polarimetric sensitivity
(&lt;10-3) compared to that in the present study is needed
in order to investigate the change in trend with μ that the comparison
of our results with the literature suggests.

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Title: From solar to stellar brightness variations. The effect
of metallicity
Authors: Witzke, V.; Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.;
Schmutz, W.
2018A&A...619A.146W Altcode: 2018arXiv180904360W
Context. Comparison studies of Sun-like stars with the Sun suggest an
anomalously low photometric variability of the Sun compared to Sun-like
stars with similar magnetic activity. Comprehensive understanding
of stellar variability is needed to find a physical reason for this
observation. Aims: We investigate the effect of metallicity
and effective temperature on the photometric brightness change
of Sun-like stars seen at different inclinations. The considered
range of fundamental stellar parameters is sufficiently small so
the stars investigated here still count as Sun-like or even as solar
twins. Methods: To model the brightness change of stars with
solar magnetic activity, we extended a well-established model of
solar brightness variations based on solar spectra, Spectral And
Total Irradiance REconstruction (SATIRE), to stars with different
fundamental parameters. For this we calculated stellar spectra for
different metallicities and effective temperature using the radiative
transfer code ATLAS9. Results: We show that even a small change
(e.g. within the observational error range) of metallicity or effective
temperature significantly affects the photometric brightness change
compared to the Sun. We find that for Sun-like stars, the amplitude
of the brightness variations obtained for Strömgren (b + y)/2 reaches
a local minimum for fundamental stellar parameters close to the solar
metallicity and effective temperature. Moreover, our results show that
the effect of inclination decreases for metallicity values greater than
the solar metallicity. Overall, we find that an exact determination of
fundamental stellar parameters is crucially important for understanding
stellar brightness changes.

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Title: Measuring the Wilson depression of sunspots using the
divergence-free condition of the magnetic field vector
Authors: Löptien, B.; Lagg, A.; van Noort, M.; Solanki, S. K.
2018A&A...619A..42L Altcode: 2018arXiv180806867L
Context. The Wilson depression is the difference in geometric height of
unit continuum optical depth between the sunspot umbra and the quiet
Sun. Measuring the Wilson depression is important for understanding
the geometry of sunspots. Current methods suffer from systematic
effects or need to make assumptions on the geometry of the magnetic
field. This leads to large systematic uncertainties of the derived
Wilson depressions. Aims: We aim to develop a robust method
for deriving the Wilson depression that only requires the information
about the magnetic field that is accessible from spectropolarimetry,
and that does not rely on assumptions on the geometry of sunspots
or on their magnetic field. Methods: Our method is based on
minimizing the divergence of the magnetic field vector derived from
spectropolarimetric observations. We have focused on large spatial
scales only in order to reduce the number of free parameters. 
Results: We tested the performance of our method using synthetic Hinode
data derived from two sunspot simulations. We find that the maximum and
the umbral averaged Wilson depression for both spots determined with
our method typically lies within 100 km of the true value obtained
from the simulations. In addition, we applied the method to Hinode
observations of a sunspot. The derived Wilson depression (∼600 km) is
consistent with results typically obtained from the Wilson effect. We
also find that the Wilson depression obtained from using horizontal
force balance gives 110-180 km smaller Wilson depressions than both,
what we find and what we deduce directly from the simulations. This
suggests that the magnetic pressure and the magnetic curvature force
contribute to the Wilson depression by a similar amount.

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Title: Observations of solar chromospheric heating at sub-arcsec
spatial resolution
Authors: Smitha, H. N.; Chitta, L. P.; Wiegelmann, T.; Solanki, S. K.
2018A&A...617A.128S Altcode: 2018arXiv180701078S
A wide variety of phenomena such as gentle but persistent
brightening, dynamic slender features (∼100 km), and compact
(∼1″) ultraviolet (UV) bursts are associated with the heating of
the solar chromosphere. High spatio-temporal resolution is required to
capture the finer details of the likely magnetic reconnection-driven,
rapidly evolving bursts. Such observations are also needed to reveal
their similarities to large-scale flares, which are also thought to be
reconnection driven, and more generally their role in chromospheric
heating. Here we report observations of chromospheric heating in
the form of a UV burst obtained with the balloon-borne observatory
SUNRISE. The observed burst displayed a spatial morphology similar
to that of a large-scale solar flare with a circular ribbon. While
the co-temporal UV observations at 1.5″ spatial resolution and
24 s cadence from the Solar Dynamics Observatory showed a compact
brightening, the SUNRISE observations at diffraction-limited spatial
resolution of 0.1″ at 7 s cadence revealed a dynamic substructure
of the burst that it is composed of an extended ribbon-like feature
and a rapidly evolving arcade of thin (∼0.1″) magnetic loop-like
features, similar to post-flare loops. Such a dynamic substructure
reveals the small-scale nature of chromospheric heating in these
bursts. Furthermore, based on magnetic field extrapolations, this
heating event is associated with a complex fan-spine magnetic
topology. Our observations strongly hint at a unified picture of
magnetic heating in the solar atmosphere from some large-scale
flares to small-scale bursts, all associated with such a magnetic
topology. The movie associated to Fig. 2 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833276/olm">https://www.aanda.org/</A>

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Title: Emission of solar chromospheric and transition region features
related to the underlying magnetic field
Authors: Barczynski, K.; Peter, H.; Chitta, L. P.; Solanki, S. K.
2018A&A...619A...5B Altcode: 2018arXiv180702372B
Context. The emission of the upper atmosphere of the Sun is closely
related to magnetic field concentrations at the solar surface. 
Aims: It is well established that this relation between chromospheric
emission and magnetic field is nonlinear. Here we investigate
systematically how this relation, characterised by the exponent
of a power-law fit, changes through the atmosphere, from the upper
photosphere through the temperature minimum region and chromosphere
to the transition region. Methods: We used spectral maps from
the Interface Region Imaging Spectrograph (IRIS) covering Mg II and
its wings, C II, and Si IV together with magnetograms and UV continuum
images from the Solar Dynamics Observatory. After a careful alignment
of the data we performed a power-law fit for the relation between each
pair of observables and determine the power-law index (or exponent) for
these. This was done for different spatial resolutions and different
features on the Sun. Results: While the correlation between
emission and magnetic field drops monotonically with temperature,
the power-law index shows a hockey-stick-type variation: from the
upper photosphere to the temperature-minimum it drops sharply and then
increases through the chromosphere into the transition region. This
is even seen through the features of the Mg II line, this is,
from k1 to k2 and k3. It is irrespective of spatial resolution or
whether we investigate active regions, plage areas, quiet Sun, or
coronal holes. Conclusions: In accordance with the general
picture of flux-flux relations from the chromosphere to the corona,
above the temperature minimum the sensitivity of the emission to the
plasma heating increases with temperature. Below the temperature
minimum a different mechanism has to govern the opposite trend of
the power-law index with temperature. We suggest four possibilities,
in other words, a geometric effect of expanding flux tubes filling the
available chromospheric volume, the height of formation of the emitted
radiation, the dependence on wavelength of the intensity-temperature
relationship, and the dependence of the heating of flux tubes on the
magnetic flux density.

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Title: Quiet-Sun and Coronal Hole in Mg II k Line as Observed by IRIS
Authors: Kayshap, Pradeep; Tripathi, Durgesh; Solanki, Sami K.;
Peter, Hardi
2018ApJ...864...21K Altcode: 2018arXiv180703494K
Coronal hole (CH) regions are dark in comparison to the quiet Sun (QS)
at coronal temperatures. However, at chromospheric and transition
region temperatures, the QS and CHs are hardly distinguishable. In
this study, we have used the Mg II 2796.35 Å spectral line recorded
by the Interface Region Imaging Spectrometer (IRIS) to understand
the similarities and differences in the QS and CH at chromospheric
levels. Our analysis reveals that the emission from Mg II k3 and k2v
that originates in the chromosphere is significantly lower in CH than
in QS for the regions with similar magnetic field strength. The wing
emissions of Mg II k that originates from the photospheric layer,
however, do not show any difference between QS and CH. The difference
in Mg II k3 intensities between QS and CH increases with increasing
magnetic field strength. We further studied the effects of spectral
resolution on these differences and found that the difference in
the intensities decreases with decreasing spectral resolution. For
a resolution of 11 Å, the difference completely disappears. These
findings are not only important for mass and energy supply from the
chromosphere to the corona but also provides essential ingredients for
the modeling of the solar spectral irradiance for the understanding
of the Sun-climate relationships.

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Title: Dark Structures in Sunspot Light Bridges
Authors: Zhang, Jingwen; Tian, Hui; Solanki, Sami K.; Wang, Haimin;
Peter, Hardi; Ahn, Kwangsu; Xu, Yan; Zhu, Yingjie; Cao, Wenda; He,
Jiansen; Wang, Linghua
2018ApJ...865...29Z Altcode: 2018arXiv180900146Z
We present unprecedented high-resolution TiO images and Fe I 1565
nm spectropolarimetric data of two light bridges taken by the 1.6
m Goode Solar Telescope at Big Bear Solar Observatory. In the first
light bridge (LB1), we find striking knot-like dark structures within
the central dark lane. Many dark knots show migration away from the
penumbra along the light bridge. The sizes, intensity depressions,
and apparent speeds of their proper motion along the light bridges of
33 dark knots identified from the TiO images are mainly in the ranges
of 80 ∼ 200 km, 30% ∼ 50%, and 0.3 ∼ 1.2 km s-1,
respectively. In the second light bridge (LB2), a faint central dark
lane and striking transverse intergranular lanes were observed. These
intergranular lanes have sizes and intensity depressions comparable
to those of the dark knots in LB1 and also migrate away from the
penumbra at similar speeds. Our observations reveal that LB2 is made
up of a chain of evolving convection cells, as indicated by patches of
blueshift surrounded by narrow lanes of redshift. The central dark lane
generally corresponds to blueshifts, supporting the previous suggestion
of central dark lanes being the top parts of convection upflows. In
contrast, the intergranular lanes are associated with redshifts and
located at two sides of each convection cell. The magnetic fields are
stronger in intergranular lanes than in the central dark lane. These
results suggest that these intergranular lanes are manifestations of
convergent convective downflows in the light bridge. We also provide
evidence that the dark knots observed in LB1 may have a similar origin.

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Title: Temporal evolution of arch filaments as seen in He I 10 830 Å
Authors: González Manrique, S. J.; Kuckein, C.; Collados, M.; Denker,
C.; Solanki, S. K.; Gömöry, P.; Verma, M.; Balthasar, H.; Lagg,
A.; Diercke, A.
2018A&A...617A..55G Altcode: 2018arXiv180700728G
 Aims: We study the evolution of an arch filament system (AFS)
and of its individual arch filaments to learn about the processes
occurring in them. Methods: We observed the AFS at the
GREGOR solar telescope on Tenerife at high cadence with the very
fast spectroscopic mode of the GREGOR Infrared Spectrograph (GRIS)
in the He I 10 830 Å spectral range. The He I triplet profiles
were fitted with analytic functions to infer line-of-sight (LOS)
velocities to follow plasma motions within the AFS. Results:
We tracked the temporal evolution of an individual arch filament
over its entire lifetime, as seen in the He I 10 830 Å triplet. The
arch filament expanded in height and extended in length from 13″ to
21″. The lifetime of this arch filament is about 30 min. About 11
min after the arch filament is seen in He I, the loop top starts to
rise with an average Doppler velocity of 6 km s-1. Only two
minutes later, plasma drains down with supersonic velocities towards
the footpoints reaching a peak velocity of up to 40 km s-1
in the chromosphere. The temporal evolution of He I 10 830 Å profiles
near the leading pore showed almost ubiquitous dual red components of
the He I triplet, indicating strong downflows, along with material
nearly at rest within the same resolution element during the whole
observing time. Conclusions: We followed the arch filament as it
carried plasma during its rise from the photosphere to the corona. The
material then drained toward the photosphere, reaching supersonic
velocities, along the legs of the arch filament. Our observational
results support theoretical AFS models and aids in improving future
models. The movie associated to Fig. 3 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201832684/olm">https://www.aanda.org/</A>

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Title: Sunrise Chromospheric Infrared spectroPolarimeter (SCIP)
for the SUNRISE balloon-borne solar observatory
Authors: Suematsu, Yoshinori; Katsukawa, Yukio; Hara, Hirohisa;
Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito; Barthol,
Peter; Riethmueller, Tino; Gandorfer, Achim; Feller, Alex; Orozco
Suárez, David; Del Toro Iniesta, Jose Carlos; Kano, Ryouhei; Ishikawa,
Shin-nosuke; Ishikawa, Ryohko; Tsuzuki, Toshihiro; Uraguchi, Fumihiro;
Quintero Noda, Carlos; Tamura, Tomonori; Oba, Takayoshi; Kawabata,
Yusuke; Nagata, Shinichi; Anan, Tetsu; Cobos Carrascosa, Juan Pedro;
Lopez Jimenez, Antonio Carlos; Balaguer Jimenez, Maria; Solanki, Sami
2018cosp...42E3285S Altcode:
The SUNRISE balloon-borne solar observatory carries a 1 m aperture
optical telescope, and allows us to perform seeing-free continuous
observations at visible-IR wavelengths from an altitude higher than
35 km. In the past two flights, in 2009 and 2013, observations mainly
focused on fine structures of photospheric magnetic fields. For the
third flight planned for 2021, we are developing a new instrument
for conducting spectro-polarimetry of spectral lines formed over a
larger height range in the solar atmosphere from the photosphere to
the chromosphere. Targets of the spectro-polarimetric observation
are (1) to determine 3D magnetic structure from the photosphere to
the chromosphere, (2) to trace MHD waves from the photosphere to the
chromosphere, and (3) to reveal the mechanism driving chromospheric
jets, by measuring height- and time-dependent velocities and magnetic
fields. To achieve these goals, a spectro-polarimeter called SCIP
(Sunrise Chromospheric Infrared spectroPolarimeter) is designed to
observe near-infrared spectrum lines sensitive to solar magnetic
fields. The spatial and spectral resolutions are 0.2 arcsec and
200,000, respectively, while 0.03% polarimetric sensitivity is
achieved within a 10 sec integration time. The optical system employs
an Echelle grating and off-axis aspheric mirrors to observe the two
wavelength ranges centered at 850 nm and 770 nm simultaneously by
two cameras. Polarimetric measurements are performed using a rotating
waveplate and polarization beam-splitters in front of the cameras. For
detecting minute polarization signals with good precision, we carefully
assess the temperature dependence of polarization optics, and make
the opto-structural design that minimizes the thermal deformation
of the spectrograph optics. Another key technique is to attain good
(better than 30 msec) synchronization among the rotating phase of
the waveplate, read-out timing of cameras, and step timing of a
slit-scanning mirror. On-board accumulation and data processing are
also critical because we cannot store all the raw data read-out from the
cameras. We demonstrate that we can reduce the data down to almost 10%
with loss-less image compression and without sacrificing polarimetric
information in the data. The SCIP instrument is developed by internal
collaboration among Japanese institutes including Japan Aerospace
Exploration Agency (JAXA), the Spanish Sunrise consortium, and the
German Max Planck Institute for Solar System Research (MPS) with a
leadership of the National Astronomical Observatory of Japan (NAOJ).

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Title: ACTReSS: ACTive Rotating Star Simulator
Authors: Johnson, Luke Jonathan; Norris, Charlotte; Unruh, Yvonne;
Solanki, Sami; Krivova, Natalie
2018csss.confE..58J Altcode:
Variability of late-type stars on timescales of days or longer is
largely due to magnetic surface features (starspots and faculae). We
present ACTReSS, a software tool to calculate rotational lightcurves
of stars. The model uses limb-dependent intensities derived from
MURaM 3-D magneto-convection simulations (Beeck et al. 2014) for
quiet stellar photospheres and bright active regions. This allows us
to investigate the dependence of the flux variation on spectral type,
inclination and wavelength.

---------------------------------------------------------
Title: Solar irradiance variability on time scales of decades to
millennia
Authors: Krivova, Natalie; Solanki, Sami K.; Leng Yeo, Kok; Wu, Chi-Ju
2018cosp...42E1847K Altcode:
Reconstructions of past solar irradiance changes over as long periodsof
time as possible are crucial to our understanding of solarinfluence on
climate. They are only possible with the help of suitablemodels, based
on detailed understanding of the mechanisms of thevariability. With
the advance of such models, also the pastreconstructions are becoming
more reliable. Nevertheless, theremaining uncertainties spread out when
extrapolating back over longperiods of time. They are further amplified
by the increasingly pooreramount and quality of the available data that
bear information on pastsolar activity. We will discuss the progress
and the uncertainties ofirradiance reconstructions on time scales of
decades to millennia.

---------------------------------------------------------
Title: Solar Activity and Irradiance Reconstruction over the Holocene
Authors: Wu, Chi-Ju; Usoskin, Ilya; Krivova, Natalie; Solanki, Sami
K.; Kovaltsov, Gennady A.; Baroni, Melanie; Bard, Edouard
2018cosp...42E3695W Altcode:
Direct measurements of the solar irradiance are only available since
1978. To understand the solar influence on Earth's climate, longer
records and thus reconstructions of the solar variability in the past
are needed. The directly observed sunspot number allows going back
to 1610 A.D, although with progressively increasing uncertainty. To
assess solar variability at earlier times, one has to rely on indirect
proxies of solar activity, such as concentrations of cosmogenic isotopes
10Be and 14C in terrestrial archives. They are produced mostly in
the upper atmosphere by impinging galactic cosmic rays (GCRs). The
flux of GCRs is modulated by both the heliospheric magnetic field and
the geomagnetic field. Therefore, the isotope signals retrieved from
various sites around the globe show a very high degree of similarity,
reflecting changes in the solar activity. Still, short-and mid-term
deviations can be observed due to various systematic effects, such as
different geochemical production, atmospheric distribution processes
and local climatic conditions. To account for these differences, we
have constructed a state-of-the-art consistent multi-isotope composite
from one global 14C and six regional 10Be data sets. This composite is
then used to reconstruct decadal values of the total and spectral solar
irradiance over the Holocene with the semi-empirical SATIRE-M model,
while the quasi-11 year solar cycle has been simulated statistically.

---------------------------------------------------------
Title: Image compression on reconfigurable FPGA for the SO/PHI
space instrument
Authors: Hernández Expósito, D.; Cobos Carrascosa, J. P.; Ramos
Mas, J. L.; Rodríguez Valido, M.; Orozco Suárez, D.; Hirzberger,
J.; Woch, J.; Solanki, S.; del Toro Iniesta, J. C.
2018SPIE10707E..2FH Altcode:
In this paper we present a novel FPGA implementation of the Consultative
Committee for Space Data Systems Image Data Compression (CCSDS-IDC
122.0-B-1) for performing image compression aboard the Polarimetric
Helioseismic Imager instrument of the ESA's Solar Orbiter mission. This
is a System-On-Chip solution based on a light multicore architecture
combined with an efficient ad-hoc Bit Plane Encoder core. This hardware
architecture performs an acceleration of 30 times with respect to a
software implementation running into space-qualified processors, like
LEON3. The system stands out over other FPGA implementations because
of the low resource usage, which does not use any external memory,
and of its configurability.

---------------------------------------------------------
Title: Solar activity over nine millennia: A consistent multi-proxy
reconstruction
Authors: Wu, C. J.; Usoskin, I. G.; Krivova, N.; Kovaltsov, G. A.;
Baroni, M.; Bard, E.; Solanki, S. K.
2018A&A...615A..93W Altcode: 2018arXiv180401302W
 Aims: The solar activity in the past millennia can only
be reconstructed from cosmogenic radionuclide proxy records in
terrestrial archives. However, because of the diversity of the proxy
archives, it is difficult to build a homogeneous reconstruction. All
previous studies were based on individual, sometimes statistically
averaged, proxy datasets. Here we aim to provide a new consistent
multi-proxy reconstruction of the solar activity over the last 9000
yr, using all available long-span datasets of 10Be and
14C in terrestrial archives. Methods: A new method,
based on a Bayesian approach, was applied for the first time to solar
activity reconstruction. A Monte Carlo search (using the χ2
statistic) for the most probable value of the modulation potential was
performed to match data from different datasets for a given time. This
provides a straightforward estimate of the related uncertainties. We
used six 10Be series of different lengths (from 500-10
000 yr) from Greenland and Antarctica, and the global 14C
production series. The 10Be series were resampled to match
wiggles related to the grand minima in the 14C reference
dataset. The stability of the long data series was tested. 
Results: The Greenland Ice-core Project (GRIP) and the Antarctic EDML
(EPICA Dronning Maud Land) 10Be series diverge from each
other during the second half of the Holocene, while the 14C
series lies in between them. A likely reason for the discrepancy is the
insufficiently precise beryllium transport and deposition model for
Greenland, which leads to an undercorrection of the GRIP series for
the geomagnetic shielding effect. A slow 6-7 millennia variability
with lows at ca. 5500 BC and 1500 AD in the long-term evolution
of solar activity is found. Two components of solar activity can
be statistically distinguished: the main component, corresponding
to the "normal" moderate level, and a component corresponding to
grand minima. A possible existence of a component representing
grand maxima is indicated, but it cannot be separated from the main
component in a statistically significant manner. Conclusions:
A new consistent reconstruction of solar activity over the last nine
millennia is presented with the most probable values of decadal sunspot
numbers and their realistic uncertainties. Independent components
of solar activity corresponding to the main moderate activity
and the grand-minimum state are identified; they may be related
to different operation modes of the dynamo. A table with the
reconstructed SN series is available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>(ftp://130.79.128.5)
or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/615/A93">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/615/A93</A>

---------------------------------------------------------
Title: Getting Ready for the Third Science Flight of SUNRISE
Authors: Barthol, Peter; Katsukawa, Yukio; Lagg, Andreas; Solanki,
Sami K.; Kubo, Masahito; Riethmueller, Tino; Martínez Pillet,
Valentin; Gandorfer, Achim; Feller, Alex; Berkefeld, . Thomas; Orozco
Suárez, David; Del Toro Iniesta, Jose Carlos; Bernasconi, Pietro;
Álvarez-Herrero, Alberto; Quintero Noda, Carlos
2018cosp...42E.215B Altcode:
SUNRISE is a balloon-borne, stratospheric solar observatory dedicated
to the investigation of the structure and dynamics of the Sun's
magnetic field and its interaction with convective plasma flows and
waves. The previous science flights of SUNRISE in 2009 and 2013 have
led to many new scientific results, so far described in around 90
refereed publications. This success has shown the huge potential of the
SUNRISE concept and the recovery of the largely intact payload offers
the opportunity for a third flight.The scientific instrumentation of
SUNRISE 3 will have extended capabilities in particular to measure
magnetic fields, plasma velocities and temperatures with increased
sensitivity and over a larger height range in the solar atmosphere, from
the convectively dominated photosphere up to the still poorly understood
chromosphere. The latter is the key interaction region between magnetic
field, waves and radiation and plays a central role in transporting
energy to the outer layers of the solar atmosphere including the
corona.SUNRISE 3 will carry 2 new grating-based spectro-polarimeters
with slit-scanning and context imaging with slitjaw cameras. The
SUNRISE UV Spectro-polarimeter and Imager (SUSI) will explore the rich
near-UV range between 300 nm and 430 nm which is poorly accessible
from the ground. The SUNRISE Chromospheric Infrared spectro-Polarimeter
(SCIP) will sample 2 spectral windows in the near-infrared, containing
many spectral lines highly sensitive to magnetic fields at different
formation heights. In addition to the two new instruments the Imaging
Magnetograph eXperiment (IMaX), an etalon-based tunable filtergraph and
spectro-polarimeter flown on both previous missions, will be upgraded
to IMaX+, enhancing its cadence and giving access to 2 spectral lines
in the visible spectral range. All three instruments will allow
investigating both the photosphere and the chromosphere and will
ideally complement each other in terms of sensitivity, height coverage
and resolution.A new gondola with a sophisticated attitude control
system including roll damping will provide improved pointing/tracking
performance. Upgraded image stabilization with higher bandwidth will
further reduce residual jitter, maximizing the quality of the science
data.SUNRISE 3 is a joint project of the German Max-Planck-Institut für
Sonnensystemforschung together with the Spanish SUNRISE consortium, the
Johns Hopkins University Applied Physics Laboratory, USA, the German
Kiepenheuer Institut für Sonnenphysik, the National Astronomical
Observatory of Japan and the Japan Aerospace eXploraion Agency (JAXA).

---------------------------------------------------------
Title: Nature of the energy source powering solar coronal loops
driven by nanoflares
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.
2018A&A...615L...9C Altcode: 2018arXiv180611045C
Context. Magnetic energy is required to heat the corona, the outer
atmosphere of the Sun, to millions of degrees. Aims: We study the
nature of the magnetic energy source that is probably responsible for
the brightening of coronal loops driven by nanoflares in the cores of
solar active regions. Methods: We consider observations of two
active regions (ARs), 11890 and 12234, in which nanoflares have been
detected. To this end, we use ultraviolet (UV) and extreme ultraviolet
(EUV) images from the Atmospheric Imaging Assembly (AIA) onboard the
Solar Dynamics Observatory (SDO) for coronal loop diagnostics. These
images are combined with the co-temporal line-of-sight magnetic
field maps from the Helioseismic and Magnetic Imager (HMI) onboard
SDO to investigate the connection between coronal loops and their
magnetic roots in the photosphere. Results: The core of
these ARs exhibit loop brightening in multiple EUV channels of AIA,
particularly in its 9.4 nm filter. The HMI magnetic field maps reveal
the presence of a complex mixed polarity magnetic field distribution
at the base of these loops. We detect the cancellation of photospheric
magnetic flux at these locations at a rate of about 1015
Mx s-1. The associated compact coronal brightenings directly
above the cancelling magnetic features are indicative of plasma heating
due to chromospheric magnetic reconnection. Conclusions:
We suggest that the complex magnetic topology and the evolution of
magnetic field, such as flux cancellation in the photosphere and
the resulting chromospheric reconnection, can play an important role
in energizing active region coronal loops driven by nanoflares. Our
estimate of magnetic energy release during flux cancellation in the
quiet Sun suggests that chromospheric reconnection can also power the
quiet corona. The movie associated to Fig. 1 is available at <A
href="https://www.aanda.org/10.1051/0004-6361/201833404/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Autonomous on-board data processing and instrument calibration
software for the SO/PHI
Authors: Albert, K.; Hirzberger, J.; Busse, D.; Lange, T.; Kolleck, M.;
Fiethe, B.; Orozco Suárez, D.; Woch, J.; Schou, J.; Blanco Rodriguez,
J.; Gandorfer, A.; Guan, Y.; Cobos Carrascosa, J. P.; Hernández
Expósito, D.; del Toro Iniesta, J. C.; Solanki, S. K.; Michalik, H.
2018SPIE10707E..0OA Altcode: 2018arXiv181003493A
The extension of on-board data processing capabilities is an
attractive option to reduce telemetry for scientific instruments
on deep space missions. The challenges that this presents, however,
require a comprehensive software system, which operates on the limited
resources a data processing unit in space allows. We implemented such
a system for the Polarimetric and Helioseismic Imager (PHI) on-board
the Solar Orbiter (SO) spacecraft. It ensures autonomous operation
to handle long command-response times, easy changing of the processes
after new lessons have been learned and meticulous book-keeping of all
operations to ensure scientific accuracy. This contribution presents
the requirements and main aspects of the software implementation,
followed by an example of a task implemented in the software frame,
and results from running it on SO/PHI. The presented example shows
that the different parts of the software framework work well together,
and that the system processes data as we expect. The flexibility of
the framework makes it possible to use it as a baseline for future
applications with similar needs and limitations as SO/PHI.

---------------------------------------------------------
Title: The High Resolution Telescope (HRT) of the Polarimetric and
Helioseismic Imager (PHI) onboard Solar Orbiter
Authors: Gandorfer, A.; Grauf, B.; Staub, J.; Bischoff, J.; Woch, J.;
Hirzberger, J.; Solanki, S. K.; Álvarez-Herrero, A.; García Parejo,
P.; Schmidt, W.; Volkmer, R.; Appourchaux, T.; del Toro Iniesta, J. C.
2018SPIE10698E..4NG Altcode:
Solar Orbiter is a joint mission of ESA and NASA scheduled for
launch in 2020. Solar Orbiter is a complete and unique heliophysics
mission, combining remote sensing and in-situ analysis; its special
elliptical orbit allows viewing the Sun from a distance of only 0.28
AU, and - leaving the ecliptic plane - to observe the solar poles from
a hitherto unexplored vantage point. One of the key instruments for
Solar Orbiter's science is the "Polarimetric and Helioseismic Imager"
(PHI), which will provide maps of the solar surface magnetic fields and
the gas flows on the visible solar surface. Two telescopes, a full disc
imager, and a high resolution channel feed a common Fabry-Perot based
tunable filter and thus allow sampling a single Fraunhofer line at 617.3
nm with high spectral resolution; a polarization modulation system
makes the system sensitive to the full state of polarization. From
the analysis of the Doppler shift and the magnetically induced Zeeman
polarization in this line, the magnetic field and the line-of-sight
gas motions can be detected for each point in the image. In this
paper we describe the opto-mechanical system design of the high
resolution telescope. It is based on a decentred Ritchey-Chrétien
two-mirror telescope. The telescope includes a Barlow type magnifier
lens group, which is used as in-orbit focus compensator, and a beam
splitter, which sends a small fraction of the collected light onto
a fast camera, which provides the error signals for the actively
controlled secondary mirror compensating for spacecraft jitter and other
disturbances. The elliptical orbit of the spacecraft poses high demands
on the thermo-mechanical stability. The varying size of the solar disk
image requires a special false-light suppression architecture, which is
briefly described. In combination with a heat-rejecting entrance window,
the optical energy impinging on the polarimetric and spectral analysis
system is efficiently reduced. We show how the design can preserve the
diffraction-limited imaging performance over the design temperature
range of -20°C to +60°C. The decentred hyperbolical mirrors require
special measures for the inter-alignment and their alignment with
respect to the mechanical structure. A system of alignment flats and
mechanical references is used for this purpose. We will describe the
steps of the alignment procedure, and the dedicated optical ground
support equipment, which are needed to reach the diffraction limited
performance of the telescope. We will also report on the verification
of the telescope performance, both - in ambient condition - and in
vacuum at different temperatures.

---------------------------------------------------------
Title: Effect of Transport Coefficients on Excitation of Flare-induced
Standing Slow-mode Waves in Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.;
Davila, Joseph M.
2018ApJ...860..107W Altcode: 2018arXiv180503282W
Standing slow-mode waves have been recently observed in flaring loops by
the Atmospheric Imaging Assembly of the Solar Dynamics Observatory. By
means of the coronal seismology technique, transport coefficients in
hot (∼10 MK) plasma were determined by Wang et al., revealing that
thermal conductivity is nearly suppressed and compressive viscosity is
enhanced by more than an order of magnitude. In this study, we use 1D
nonlinear MHD simulations to validate the predicted results from the
linear theory and investigate the standing slow-mode wave excitation
mechanism. We first explore the wave trigger based on the magnetic
field extrapolation and flare emission features. Using a flow pulse
driven at one footpoint, we simulate the wave excitation in two types
of loop models: Model 1 with the classical transport coefficients and
Model 2 with the seismology-determined transport coefficients. We
find that Model 2 can form the standing wave pattern (within about
one period) from initial propagating disturbances much faster than
Model 1, in better agreement with the observations. Simulations of
the harmonic waves and the Fourier decomposition analysis show that
the scaling law between damping time (τ) and wave period (P) follows
τ ∝ P 2 in Model 2, while τ ∝ P in Model 1. This
indicates that the largely enhanced viscosity efficiently increases
the dissipation of higher harmonic components, favoring the quick
formation of the fundamental standing mode. Our study suggests that
observational constraints on the transport coefficients are important
in understanding both the wave excitation and damping mechanisms.

---------------------------------------------------------
Title: Initial features of an X-class flare observed with SUMER
and TRACE
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.
2018arXiv180510418W Altcode:
A class X1.5 flare started on the solar limb at 00:43 UT on 21 April
2002, which was associated with a CME observed at 01:27 UT by LASCO
C2. The coordinated analyses of this flare include TRACE 195 Å images
and SUMER spectra in lines of Fe XXI, Fe XII, and C II. We find that:
1) The flare began with a jet seen by TRACE, which was detected by
SUMER in the C II line as a strong brightening with blue shifts up
to 170 km s$^{-1}$. At that time only weak emission was detected
in Fe XII and Fe XXI. 2) Subsequently, a weak looplike brightening
started south of the jet, moving outwards with an average speed of
about 150 km s$^{-1}$. The SUMER spectra responded this moving loop
as separatingly brightenings, visible only in the Fe XXI line. The
southwards moving component contains red- and blue-shifted emission
features and has an apparent speed of $\sim$120 km s$^{-1}$. The absence
of signatures in Fe XII and C II lines indicates that the moving weak
loop seen by TRACE corresponds to the emission from very hot plasma,
in a blend line in the 195 Å bandpass due to Fe XXIV formed at T &gt;
10 MK. 3) The trigger mechanism of the flare and associated CME can
be interpreted in the same way as that proposed by Wang et al. (2002)
for an event with similar initial features.

---------------------------------------------------------
Title: Excitation and Damping of Standing Slow-Mode Waves in Flaring
Coronal Loops
Authors: Wang, Tongjiang; Ofman, Leon; Sun, Xudong; Solanki, Sami K.;
Davila, Joseph M.
2018tess.conf22204W Altcode:
We analyze and model a flare-induced longitudinal oscillation event
detected by SDO/AIA. The magnetic field extrapolation and flare emission
features suggest that the wave event is generated by slipping and
null-point-type reconnections in a closed fan-spine magnetic topology,
and the large spine loop appears to be heated impulsively to the flare
temperature before the wave disturbances travel along it. By means of
the seismology technique, we determined the transport coefficients
in hot (about 10 MK) plasma, and found that thermal conductivity is
nearly suppressed and compressive viscosity is enhanced by more than
an order of magnitude from the observed wave properties. Using a flow
pulse injected at the loop's footpoint constrained by the observation,
we simulate the excitation of slow-mode waves in two types of 1D loop
models. We find that the models with the seismology-determined transport
coefficients can excite the standing waves quickly as observed, while
the models with the classical transport coefficients excites basically
the reflecting propagating waves. Simulations of harmonic waves and
the Fourier decomposition analysis reveal a scaling between damping
time and wave period as Td ~ P in the former type of models,
while Td ~ P2 in the latter type. This suggests
that anomalously large viscosity can efficiently enhance the dissipation
of higher harmonic components, favoring quick setup of the fundamental
standing mode. Our study indicates that observational constraints on
the transport coefficients are crucial in understanding both the wave
excitation and damping mechanisms.

---------------------------------------------------------
Title: Reconstructing Total Solar Irradiance with the help of MHD
simulations
Authors: Leng Yeo, Kok; Solanki, Sami; Noris, Charlotte; Unruh,
Yvonne; Krivova, Natalie; Beeck, Benjamin
2018EGUGA..20.8166L Altcode:
The variation in the solar irradiance is an important input into the
climate system. Whereas it is commonly thought that solar irradiance
variability is driven by the evolving surface magnetism, verifying this
assumption has been more difficult. Making use of 3D MHD simulations
of the solar atmosphere layers and state-of-the-art solar magnetograms
from the Solar Dynamics Observatory, we present a model of total solar
irradiance (TSI) that does not require any calibration of the modeled
TSI by the measured TSI. I.e., the modeled irradiance variability
is entirely independent of the observational record, except for the
absolute level. The model replicates 95% of the observed variability
between April 2010 and July 2016, leaving little scope for alternative
drivers of solar irradiance variability, at least over the time scales
examined (days to years).

---------------------------------------------------------
Title: Physical Processes on The Sun's Surface
Authors: Solanki, Sami
2018iss..confE..35S Altcode:
The Sun, as our nearest star, allows us to probe the surface of a
main sequence G star in great detail and to determine the features and
processes acting there with the help of high-resolution observations and
MHD simulations. These features (possibly in somewhat different guises)
and processes are thought to be present/acting also on other cool stars,
whose spectra they influence and whose variability and activity they
are responsible for. In this presentation a brief introduction will be
given to the main physical processes acting in the solar photosphere
and the structures and dynamics that they produce. An attempt will also
be made to work out what influence these processes and structures have
on the Sun seen as an unresolved star.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Reconstructed decadal sunspot
numbers (Wu+, 2018)
Authors: Wu, C. J.; Usoskin, I. G.; Krivova, N.; Kovaltsov, G. A.;
Baroni, M.; Bard, E.; Solanki, S. K.
2018yCat..36150093W Altcode:
The file contains the decadal numbers of sunspot groups including
the decade central year [Y], the low [Sl], the mean [SM]
and the upper [S_u] 1-sigma (68% bounds). (1 data file).

---------------------------------------------------------
Title: Solar polarimetry in the K I D2 line : A novel
possibility for a stratospheric balloon
Authors: Quintero Noda, C.; Villanueva, G. L.; Katsukawa, Y.; Solanki,
S. K.; Orozco Suárez, D.; Ruiz Cobo, B.; Shimizu, T.; Oba, T.; Kubo,
M.; Anan, T.; Ichimoto, K.; Suematsu, Y.
2018A&A...610A..79Q Altcode: 2018arXiv180101655Q
Of the two solar lines, K I D1 and D2, almost
all attention so far has been devoted to the D1 line, as
D2 is severely affected by an O2 atmospheric
band. This, however, makes the latter appealing for balloon and space
observations from above (most of) the Earth's atmosphere. We estimate
the residual effect of the O2 band on the K I D2
line at altitudes typical for stratospheric balloons. Our aim is to
study the feasibility of observing the 770 nm window. Specifically,
this paper serves as a preparation for the third flight of the Sunrise
balloon-borne observatory. The results indicate that the absorption
by O2 is still present, albeit much weaker, at the expected
balloon altitude. We applied the obtained O2 transmittance
to K I D2 synthetic polarimetric spectra and found that in
the absence of line-of-sight motions, the residual O2 has
a negligible effect on the K I D2 line. On the other hand,
for Doppler-shifted K I D2 data, the residual O2
might alter the shape of the Stokes profiles. However, the residual
O2 absorption is sufficiently weak at stratospheric levels
that it can be divided out if appropriate measurements are made,
something that is impossible at ground level. Therefore, for the
first time with Sunrise III, we will be able to perform polarimetric
observations of the K I D2 line and, consequently, we will
have improved access to the thermodynamics and magnetic properties of
the upper photosphere from observations of the K I lines.

---------------------------------------------------------
Title: Long-term Datasets for the Understanding of Solar and Stellar
Magnetic Cycles
Authors: Banerjee, D.; Jiang, J.; Kusano, K.; Solanki, S.
2018IAUS..340.....B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Ca II K spectroheliograms for studies of long-term changes
in solar irradiance
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Krivova, Natalie
A.; Solanki, Sami K.
2018IAUS..340..125C Altcode: 2018arXiv180503928C
We address the importance of historical full-disc Ca II K
spectroheliograms for solar activity and irradiance reconstruction
studies. We review our work on processing such data to enable them to
be used in irradiance reconstructions. We also present our preliminary
estimates of the plage areas from five of the longest available
historical Ca II K archives.

---------------------------------------------------------
Title: The potential of Ca II K observations for solar activity and
variability studies
Authors: Ermolli, Ilaria; Chatzistergos, Theodosios; Krivova, Natalie
A.; Solanki, Sami K.
2018IAUS..340..115E Altcode: 2018arXiv180504483E
Several observatories around the globe started regular full-disc imaging
of the solar atmosphere in the Ca II K line in the early decades of
the 20th century. These observations are continued today
at a few sites with either old spectroheliographs or modern telescopes
equipped with narrow-band filters. The Ca II K time series are unique
in representing long-term variations of the Sun's chromospheric magnetic
field. However, meaningful results from their analysis require accurate
processing of the available data and robust merging of the information
stored in different archives. This paper provides an overview of the
historical and modern full-disc Ca II K observations, with focus on
their quality and the main results obtained from their analysis over
the last decade.

---------------------------------------------------------
Title: Frequently Occurring Reconnection Jets from Sunspot Light
Bridges
Authors: Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Solanki, Sami
K.; Young, Peter R.; Ni, Lei; Cao, Wenda; Ji, Kaifan; Zhu, Yingjie;
Zhang, Jingwen; Samanta, Tanmoy; Song, Yongliang; He, Jiansen; Wang,
Linghua; Chen, Yajie
2018ApJ...854...92T Altcode: 2018arXiv180106802T
Solid evidence of magnetic reconnection is rarely reported within
sunspots, the darkest regions with the strongest magnetic fields
and lowest temperatures in the solar atmosphere. Using the world’s
largest solar telescope, the 1.6 m Goode Solar Telescope, we detect
prevalent reconnection through frequently occurring fine-scale jets
in the Hα line wings at light bridges, the bright lanes that may
divide the dark sunspot core into multiple parts. Many jets have an
inverted Y-shape, shown by models to be typical of reconnection in a
unipolar field environment. Simultaneous spectral imaging data from
the Interface Region Imaging Spectrograph show that the reconnection
drives bidirectional flows up to 200 km s-1, and that the
weakly ionized plasma is heated by at least an order of magnitude up
to ∼80,000 K. Such highly dynamic reconnection jets and efficient
heating should be properly accounted for in future modeling efforts
of sunspots. Our observations also reveal that the surge-like activity
previously reported above light bridges in some chromospheric passbands
such as the Hα core has two components: the ever-present short surges
likely to be related to the upward leakage of magnetoacoustic waves
from the photosphere, and the occasionally occurring long and fast
surges that are obviously caused by the intermittent reconnection jets.

---------------------------------------------------------
Title: Solar Magnetic Fields
Authors: Balogh, André; Cliver, Edward; Petrie, Gordon; Solanki,
Sami; Thompson, Michael; von Steiger, Rudolf
2018smf..book.....B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Magnetoconvection and Small-Scale Dynamo
Authors: Borrero, J. M.; Jafarzadeh, S.; Schüssler, M.; Solanki, S. K.
2018smf..book..275B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Influence of Metallicity on Stellar Differential Rotation
and Magnetic Activity
Authors: Karoff, Christoffer; Metcalfe, Travis S.; Santos, Ângela
R. G.; Montet, Benjamin T.; Isaacson, Howard; Witzke, Veronika;
Shapiro, Alexander I.; Mathur, Savita; Davies, Guy R.; Lund, Mikkel N.;
Garcia, Rafael A.; Brun, Allan S.; Salabert, David; Avelino, Pedro P.;
van Saders, Jennifer; Egeland, Ricky; Cunha, Margarida S.; Campante,
Tiago L.; Chaplin, William J.; Krivova, Natalie; Solanki, Sami K.;
Stritzinger, Maximilian; Knudsen, Mads F.
2018ApJ...852...46K Altcode: 2017arXiv171107716K
Observations of Sun-like stars over the past half-century have improved
our understanding of how magnetic dynamos, like that responsible for the
11 yr solar cycle, change with rotation, mass, and age. Here we show
for the first time how metallicity can affect a stellar dynamo. Using
the most complete set of observations of a stellar cycle ever obtained
for a Sun-like star, we show how the solar analog HD 173701 exhibits
solar-like differential rotation and a 7.4 yr activity cycle. While
the duration of the cycle is comparable to that generated by the solar
dynamo, the amplitude of the brightness variability is substantially
stronger. The only significant difference between HD 173701 and the
Sun is its metallicity, which is twice the solar value. Therefore,
this provides a unique opportunity to study the effect of the
higher metallicity on the dynamo acting in this star and to obtain a
comprehensive understanding of the physical mechanisms responsible
for the observed photometric variability. The observations can be
explained by the higher metallicity of the star, which is predicted to
foster a deeper outer convection zone and a higher facular contrast,
resulting in stronger variability.

---------------------------------------------------------
Title: Analysis of full disc Ca II K spectroheliograms. I. Photometric
calibration and centre-to-limb variation compensation
Authors: Chatzistergos, Theodosios; Ermolli, Ilaria; Solanki, Sami K.;
Krivova, Natalie A.
2018A&A...609A..92C Altcode: 2017arXiv171004949C
Context. Historical Ca II K spectroheliograms (SHG) are unique in
representing long-term variations of the solar chromospheric magnetic
field. They usually suffer from numerous problems and lack photometric
calibration. Thus accurate processing of these data is required to get
meaningful results from their analysis. Aims: In this paper we
aim at developing an automatic processing and photometric calibration
method that provides precise and consistent results when applied
to historical SHG. Methods: The proposed method is based on
the assumption that the centre-to-limb variation of the intensity in
quiet Sun regions does not vary with time. We tested the accuracy of
the proposed method on various sets of synthetic images that mimic
problems encountered in historical observations. We also tested our
approach on a large sample of images randomly extracted from seven
different SHG archives. Results: The tests carried out on the
synthetic data show that the maximum relative errors of the method are
generally &lt;6.5%, while the average error is &lt;1%, even if rather
poor quality observations are considered. In the absence of strong
artefacts the method returns images that differ from the ideal ones by
&lt;2% in any pixel. The method gives consistent values for both plage
and network areas. We also show that our method returns consistent
results for images from different SHG archives. Conclusions:
Our tests show that the proposed method is more accurate than other
methods presented in the literature. Our method can also be applied
to process images from photographic archives of solar observations at
other wavelengths than Ca II K.

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Title: Evershed and Counter-Evershed Flows in Sunspot MHD Simulations
Authors: Siu-Tapia, A. L.; Rempel, M.; Lagg, A.; Solanki, S. K.
2018ApJ...852...66S Altcode: 2017arXiv171201202S
There have been a few reports in the literature of counter-Evershed
flows observed in well-developed sunspot penumbrae, i.e., flows
directed toward the umbra along penumbral filaments. Here, we
investigate the driving forces of such counter-Evershed flows in a
radiative magnetohydrodynamic simulation of a sunspot, and compare
them to the forces acting on the normal Evershed flow. The simulation
covers a timespan of 100 solar hours and generates an Evershed outflow
exceeding 8 km s-1 in the penumbra along radially aligned
filaments where the magnetic field is almost horizontal. Additionally,
the simulation produces a fast counter-Evershed flow (i.e., an inflow
near τ =1) in some regions within the penumbra, reaching peak flow
speeds of ∼12 km s-1. The counter-Evershed flows are
transient and typically last a few hours before they turn into outflows
again. By using the kinetic energy equation and evaluating its various
terms in the simulation box, we found that the Evershed flow occurs
due to overturning convection in a strongly inclined magnetic field,
while the counter-Evershed flows can be well-described as siphon flows.

---------------------------------------------------------
Title: Solar Spectral Irradiance Reconstruction over 9 Millennia
from a Composite 14C and 10Be Series
Authors: Wu, C. J.; Usoskin, I. G.; Krivova, N.; Kovaltsov, G.;
Solanki, S. K.
2017AGUFMSH42A..03W Altcode:
The Sun is the main external energy source to the Earth and thus the
knowledge of solar variability on different time scales is important
for understanding the solar influence on the terrestrial atmosphere
and climate. The overall energy input and its spectral distribution
are described by the total (TSI) and spectral (SSI) solar irradiance,
respectively. Direct measurements of the solar irradiance provide
information on solar variability on the decadal and shorter time
scales, while the sunspot number record covers four centuries. On
yet longer time scales only indirect proxies can be used, such
as the concentrations of the cosmogenic isotopes 10Be and 14C in
terrestrial archives. These isotopes are produced in the terrestrial
atmosphere by impinging cosmic rays, whose flux is modulated by solar
activity. Therefore the isotope data retrieved from various natural
archives around the globe show a very high degree of similarity
reflecting changes in the solar activity. Nevertheless, significant
short-term deviations can be observed due to the different geochemical
production processes and local climatic conditions. We will present
the newest TSI/SSI reconstruction over the last 9000 years based
on a new consistent composite multi-isotope proxy series. The solar
irradiance reconstruction reveals the global and robust pattern of
solar variability in the past.

---------------------------------------------------------
Title: Probing photospheric magnetic fields with new spectral
line pairs
Authors: Smitha, H. N.; Solanki, S. K.
2017A&A...608A.111S Altcode: 2017arXiv170908926S
Context. The magnetic line ratio (MLR) method has been extensively
used in the measurement of photospheric magnetic field strength. It
was devised for the neutral iron line pair at 5247.1 Å and 5250.2 Å
(5250 Å pair). Other line pairs as well-suited as this pair have not
been reported in the literature. Aims: The aim of the present
work is to identify new line pairs useful for the MLR technique and to
test their reliability. Methods: We used a three-dimensional
magnetohydrodynamic 3D MHD simulation representing the quiet Sun
atmosphere to synthesize the Stokes profiles. Then, we applied the MLR
technique to the Stokes V profiles to recover the fields in the MHD
cube both at original resolution and after degrading with a point spread
function. In both these cases, we aim to empirically represent the field
strengths returned by the MLR method in terms of the field strengths
in the MHD cube. Results: We have identified two new line pairs
that are very well adapted to be used for MLR measurements. The first
pair is in the visible, Fe I 6820-6842 Å, whose intensity profiles
have previously been used to measure stellar magnetic fields, and
the other pair is in the infrared (IR), Fe I 15 534-15 542 Å. The
lines in these pairs reproduce the magnetic fields in the MHD cube
rather well and, in fact, somewhat better than the original 5250 Å
pair. Conclusions: The newly identified line pairs complement
the old pairs. The lines in the new IR pair, because of their higher
Zeeman sensitivity, are ideal for the measurement of weak fields. The
new visible pair works best above 300 G. The new IR pair, due to its
large Stokes V signal samples more fields in the MHD cube than the old
IR pair at 1.56 μm, even in the presence of noise, and hence likely
also on the real Sun. Owing to their low formation heights (100-200 km
above τ5000 = 1), both the new line pairs are well suited
for probing magnetic fields in the lower photosphere.

---------------------------------------------------------
Title: ALMA Discovery of Solar Umbral Brightness Enhancement at λ =
3 mm
Authors: Iwai, K.; Loukitcheva, M.; Shimojo, M.; Solanki, S. K.;
White, S. M.
2017AGUFMSH43A2806I Altcode:
We report the discovery of a brightness enhancement in the center of
a large sunspot umbra at a wavelength of 3 mm using the Atacama Large
Millimeter/sub-millimeter Array (ALMA). Sunspots are among the most
prominent features on the solar surface, but many of their aspects are
surprisingly poorly understood. We analyzed a λ = 3 mm (100 GHz) mosaic
image obtained by ALMA that includes a large sunspot within the active
region AR12470, on 2015 December 16. The 3 mm map has a 300”×300”
field of view and 4.9”×2.2” spatial resolution, which is the highest
spatial resolution map of an entire sunspot in this frequency range. We
find a gradient of 3 mm brightness from a high value in the outer
penumbra to a low value in the inner penumbra/outer umbra. Within the
inner umbra, there is a marked increase in 3 mm brightness temperature,
which we call an umbral brightness enhancement. This enhanced emission
corresponds to a temperature excess of 800 K relative to the surrounding
inner penumbral region and coincides with excess brightness in the
1330 and 1400 Å slit-jaw images of the Interface Region Imaging
Spectrograph (IRIS), adjacent to a partial lightbridge. This λ = 3 mm
brightness enhancement may be an intrinsic feature of the sunspot umbra
at chromospheric heights, such as a manifestation of umbral flashes, or
it could be related to a coronal plume, since the brightness enhancement
was coincident with the footpoint of a coronal loop observed at 171 Å.

---------------------------------------------------------
Title: METIS, the Multi Element Telescope for Imaging and
Spectroscopy: an instrument proposed for the solar orbiter mission
Authors: Antonucci, E.; Andretta, V.; Cesare, S.; Ciaravella, A.;
Doschek, G.; Fineschi, S.; Giordano, S.; Lamy, P.; Moses, D.; Naletto,
G.; Newmark, J.; Poletto, L.; Romoli, M.; Solanki, S.; Spadaro, D.;
Teriaca, L.; Zangrilli, L.
2017SPIE10566E..0LA Altcode:
METIS, the Multi Element Telescope for Imaging and Spectroscopy,
is an instrument proposed to the European Space Agency to be part of
the payload of the Solar Orbiter mission. The instrument design has
been conceived for performing extreme ultraviolet (EUV) spectroscopy
both on the solar disk and off-limb, and near-Sun coronagraphy
and spectroscopy. The proposed instrument suite consists of three
different interconnected elements, COR, EUS and SOCS, sharing the
same optical bench, electronics, and S/C heat shield aperture. COR is
a visible-EUV multiband coronagraph based on a classical externally
occulted design. EUS is the component of the METIS EUV disk spectrometer
which includes the telescope and all the related mechanisms. Finally,
SOCS is the METIS spectroscopic component including the dispersive
system and the detectors. The capability of inserting a small telescope
collecting coronal light has been added to perform also EUV coronal
spectroscopy. METIS can simultaneously image the visible and ultraviolet
emission of the solar corona and diagnose, with unprecedented temporal
coverage and space resolution the structure and dynamics of the full
corona in the range from 1.2 to 3.0 (1.6 to 4.1) solar radii (R⊙,
measured from Sun centre) at minimum (maximum) perihelion during the
nominal mission. It can also perform spectroscopic observations of the
solar disk and out to 1.4 R⊙ within the 50-150 nm spectral region,
and of the geo-effective coronal region 1.7-2.7 R⊙ within the 30-125
nm spectral band.

---------------------------------------------------------
Title: Normal and counter Evershed flows in the photospheric penumbra
of a sunspot. SPINOR 2D inversions of Hinode-SOT/SP observations
Authors: Siu-Tapia, A.; Lagg, A.; Solanki, S. K.; van Noort, M.;
Jurčák, J.
2017A&A...607A..36S Altcode: 2017arXiv170907386S
Context. The Evershed effect, a nearly horizontal outflow of material
seen in the penumbrae of sunspots in the photospheric layers, is a
common characteristic of well-developed penumbrae, but is still not well
understood. Even less is known about photospheric horizontal inflows in
the penumbra, also known as counter Evershed flows. Aims: Here we
present a rare feature observed in the penumbra of the main sunspot of
AR NOAA 10930. This spot displays the normal Evershed outflow in most
of the penumbra, but harbors a fast photospheric inflow of material
over a large sector of the disk-center penumbra. We investigate the
driving forces of both, the normal and the counter Evershed flows. Methods: We invert the spectropolarimetric data from Hinode SOT/SP
using the spatially coupled version of the SPINOR inversion code,
which allows us to derive height-dependent maps of the relevant
physical parameters in the sunspot. These maps show considerable fine
structure. Similarities and differences between the normal Evershed
outflow and the counter Evershed flow are investigated. Results:
In both the normal and the counter Evershed flows, the material flows
from regions with field strengths of the order of 1.5-2 kG to regions
with stronger fields. The sources and sinks of both penumbral flows
display opposite field polarities, with the sinks (tails of filaments)
harboring local enhancements in temperature, which are nonetheless
colder than their sources (heads of filaments). Conclusions:
The anti-correlation of the gradients in the temperature and magnetic
pressure between the endpoints of the filaments from the two distinct
penumbral regions is compatible with both the convective driver and
the siphon flow scenarios. A geometrical scale of the parameters is
necessary to determine which is the dominant force driving the flows.

---------------------------------------------------------
Title: Solar ALMA Observations: Constraining the Chromosphere above
Sunspots
Authors: Loukitcheva, Maria A.; Iwai, Kazumasa; Solanki, Sami K.;
White, Stephen M.; Shimojo, Masumi
2017ApJ...850...35L Altcode: 2017arXiv171003812L
We present the first high-resolution Atacama Large
Millimeter/Submillimeter Array (ALMA) observations of a sunspot at
wavelengths of 1.3 and 3 mm, obtained during the solar ALMA Science
Verification campaign in 2015, and compare them with the predictions
of semi-empirical sunspot umbral/penumbral atmosphere models. For
the first time, millimeter observations of sunspots have resolved
umbral/penumbral brightness structure at the chromospheric heights,
where the emission at these wavelengths is formed. We find that the
sunspot umbra exhibits a radically different appearance at 1.3 and 3
mm, whereas the penumbral brightness structure is similar at the two
wavelengths. The inner part of the umbra is ∼600 K brighter than the
surrounding quiet Sun (QS) at 3 mm and is ∼700 K cooler than the QS
at 1.3 mm, being the coolest part of sunspot at this wavelength. On
average, the brightness of the penumbra at 3 mm is comparable to
the QS brightness, while at 1.3 mm it is ∼1000 K brighter than
the QS. Penumbral brightness increases toward the outer boundary in
both ALMA bands. Among the tested umbral models, that of Severino et
al. provides the best fit to the observational data, including both
the ALMA data analyzed in this study and data from earlier works. No
penumbral model among those considered here gives a satisfactory fit
to the currently available measurements. ALMA observations at multiple
millimeter wavelengths can be used for testing existing sunspot models,
and serve as an important input to constrain new empirical models.

---------------------------------------------------------
Title: The Small-scale Structure of Photospheric Convection Retrieved
by a Deconvolution Technique Applied to Hinode/SP Data
Authors: Oba, T.; Riethmüller, T. L.; Solanki, S. K.; Iida, Y.;
Quintero Noda, C.; Shimizu, T.
2017ApJ...849....7O Altcode: 2017arXiv170906933O
Solar granules are bright patterns surrounded by dark channels, called
intergranular lanes, in the solar photosphere and are a manifestation of
overshooting convection. Observational studies generally find stronger
upflows in granules and weaker downflows in intergranular lanes. This
trend is, however, inconsistent with the results of numerical
simulations in which downflows are stronger than upflows through the
joint action of gravitational acceleration/deceleration and pressure
gradients. One cause of this discrepancy is the image degradation caused
by optical distortion and light diffraction and scattering that takes
place in an imaging instrument. We apply a deconvolution technique to
Hinode/SP data in an attempt to recover the original solar scene. Our
results show a significant enhancement in both the convective upflows
and downflows but particularly for the latter. After deconvolution,
the up- and downflows reach maximum amplitudes of -3.0 km s-1
and +3.0 km s-1 at an average geometrical height of roughly
50 km, respectively. We found that the velocity distributions after
deconvolution match those derived from numerical simulations. After
deconvolution, the net LOS velocity averaged over the whole field of
view lies close to zero as expected in a rough sense from mass balance.

---------------------------------------------------------
Title: The Maximum Entropy Limit of Small-scale Magnetic Field
Fluctuations in the Quiet Sun
Authors: Gorobets, A. Y.; Berdyugina, S. V.; Riethmüller, T. L.;
Blanco Rodríguez, J.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Gizon, L.; Hirzberger, J.; van Noort, M.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..233....5G Altcode: 2017arXiv171008361G
The observed magnetic field on the solar surface is characterized by a
very complex spatial and temporal behavior. Although feature-tracking
algorithms have allowed us to deepen our understanding of this behavior,
subjectivity plays an important role in the identification and tracking
of such features. In this paper, we continue studies of the temporal
stochasticity of the magnetic field on the solar surface without relying
either on the concept of magnetic features or on subjective assumptions
about their identification and interaction. We propose a data analysis
method to quantify fluctuations of the line-of-sight magnetic field by
means of reducing the temporal field’s evolution to the regular Markov
process. We build a representative model of fluctuations converging to
the unique stationary (equilibrium) distribution in the long time limit
with maximum entropy. We obtained different rates of convergence to the
equilibrium at fixed noise cutoff for two sets of data. This indicates
a strong influence of the data spatial resolution and mixing-polarity
fluctuations on the relaxation process. The analysis is applied to
observations of magnetic fields of the relatively quiet areas around an
active region carried out during the second flight of the Sunrise/IMaX
and quiet Sun areas at the disk center from the Helioseismic and
Magnetic Imager on board the Solar Dynamics Observatory satellite.

---------------------------------------------------------
Title: Flows along arch filaments observed in the GRIS `very fast
spectroscopic mode'
Authors: González Manrique, S. J.; Denker, C.; Kuckein, C.; Pastor
Yabar, A.; Collados, M.; Verma, M.; Balthasar, H.; Diercke, A.;
Fischer, C. E.; Gömöry, P.; Bello González, N.; Schlichenmaier,
R.; Cubas Armas, M.; Berkefeld, T.; Feller, A.; Hoch, S.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Schmidt, D.; Schmidt,
W.; Sigwarth, M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude,
J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2017IAUS..327...28G Altcode: 2017arXiv170102206G
A new generation of solar instruments provides improved spectral,
spatial, and temporal resolution, thus facilitating a better
understanding of dynamic processes on the Sun. High-resolution
observations often reveal multiple-component spectral line profiles,
e.g., in the near-infrared He i 10830 Å triplet, which provides
information about the chromospheric velocity and magnetic fine
structure. We observed an emerging flux region, including two small
pores and an arch filament system, on 2015 April 17 with the `very
fast spectroscopic mode' of the GREGOR Infrared Spectrograph (GRIS)
situated at the 1.5-meter GREGOR solar telescope at Observatorio del
Teide, Tenerife, Spain. We discuss this method of obtaining fast (one
per minute) spectral scans of the solar surface and its potential to
follow dynamic processes on the Sun. We demonstrate the performance
of the `very fast spectroscopic mode' by tracking chromospheric
high-velocity features in the arch filament system.

---------------------------------------------------------
Title: Spectral variability of photospheric radiation due to
faculae. I. The Sun and Sun-like stars
Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne C.;
Solanki, Sami K.; Krivova, Natalie A.; Yeo, Kok Leng
2017A&A...605A..45N Altcode: 2017arXiv170504455N
Context. Stellar spectral variability on timescales of a day and
longer, arising from magnetic surface features such as dark spots
and bright faculae, is an important noise source when characterising
extra-solar planets. Current 1D models of faculae do not capture the
geometric properties and fail to reproduce observed solar facular
contrasts. Magnetoconvection simulations provide facular contrasts
accounting for geometry. Aims: We calculate facular contrast
spectra from magnetoconvection models of the solar photosphere with
a view to improve (a) future parameter determinations for planets
with early G type host stars and (b) reconstructions of solar spectral
variability. Methods: Regions of a solar twin (G2, log g = 4.44)
atmosphere with a range of initial average vertical magnetic fields
(100 to 500 G) were simulated using a 3D radiation-magnetohydrodynamics
code, MURaM, and synthetic intensity spectra were calculated from
the ultraviolet (149.5 nm) to the far infrared (160 000 nm) with the
ATLAS9 radiative transfer code. Nine viewing angles were investigated
to account for facular positions across most of the stellar disc. Results: Contrasts of the radiation from simulation boxes with
different levels of magnetic flux relative to an atmosphere with no
magnetic field are a complicated function of position, wavelength
and magnetic field strength that is not reproduced by 1D facular
models. Generally, contrasts increase towards the limb, but at UV
wavelengths a saturation and decrease are observed close to the
limb. Contrasts also increase strongly from the visible to the UV;
there is a rich spectral dependence, with marked peaks in molecular
bands and strong spectral lines. At disc centre, a complex relationship
with magnetic field was found and areas of strong magnetic field
can appear either dark or bright, depending on wavelength. Spectra
calculated for a wide variety of magnetic fluxes will also serve to
improve total and spectral solar irradiance reconstructions.

---------------------------------------------------------
Title: Solar Irradiance Variability is Caused by the Magnetic Activity
on the Solar Surface
Authors: Yeo, K. L.; Solanki, S. K.; Norris, C. M.; Beeck, B.; Unruh,
Y. C.; Krivova, N. A.
2017PhRvL.119i1102Y Altcode: 2017arXiv170900920Y
The variation in the radiative output of the Sun, described in terms
of solar irradiance, is important to climatology. A common assumption
is that solar irradiance variability is driven by its surface
magnetism. Verifying this assumption has, however, been hampered by
the fact that models of solar irradiance variability based on solar
surface magnetism have to be calibrated to observed variability. Making
use of realistic three-dimensional magnetohydrodynamic simulations
of the solar atmosphere and state-of-the-art solar magnetograms from
the Solar Dynamics Observatory, we present a model of total solar
irradiance (TSI) that does not require any such calibration. In doing
so, the modeled irradiance variability is entirely independent of the
observational record. (The absolute level is calibrated to the TSI
record from the Total Irradiance Monitor.) The model replicates 95%
of the observed variability between April 2010 and July 2016, leaving
little scope for alternative drivers of solar irradiance variability
at least over the time scales examined (days to years).

---------------------------------------------------------
Title: Solar Magnetoconvection and Small-Scale Dynamo. Recent
Developments in Observation and Simulation
Authors: Borrero, J. M.; Jafarzadeh, S.; Schüssler, M.; Solanki, S. K.
2017SSRv..210..275B Altcode: 2015SSRv..tmp..113B; 2015arXiv151104214B
A number of observational and theoretical aspects of solar
magnetoconvection are considered in this review. We discuss recent
developments in our understanding of the small-scale structure of
the magnetic field on the solar surface and its interaction with
convective flows, which is at the centre of current research. Topics
range from plage areas in active regions over the magnetic network
shaped by supergranulation to the ubiquituous `turbulent' internetwork
fields. On the theoretical side, we focus upon magnetic field generation
by small-scale dynamo action.

---------------------------------------------------------
Title: Three-dimensional magnetic structure of a sunspot: Comparison
of the photosphere and upper chromosphere
Authors: Joshi, Jayant; Lagg, Andreas; Hirzberger, Johann; Solanki,
Sami K.
2017A&A...604A..98J Altcode: 2017arXiv170508404J
 Aims: We investigate the magnetic field of a sunspot in the
upper chromosphere and compare it to the photospheric properties
of the field. Methods: We observed the main leading sunspot
of the active region NOAA 11124 during two days with the Tenerife
Infrared Polarimeter-2 (TIP-2) mounted at the German Vacuum Tower
Telescope (VTT). Through inversion of Stokes spectra of the He I
triplet at 10 830 Å, we obtained the magnetic field vector of the
upper chromosphere. For comparison with the photosphere, we applied
height-dependent inversions of the Si I 10 827.1 Å and Ca I 10 833.4 Å
lines. Results: We found that the umbral magnetic field strength
in the upper chromosphere is lower by a factor of 1.30-1.65 compared
to the photosphere. The magnetic field strength of the umbra decreases
from the photosphere toward the upper chromosphere by an average rate of
0.5-0.9 G km-1. The difference in the magnetic field strength
between both atmospheric layers steadily decreases from the sunspot
center to the outer boundary of the sunspot; the field, in particular
its horizontal component, is stronger in the chromopshere outside the
spot and this is suggestive of a magnetic canopy. The sunspot displays
a twist that on average is similar in the two layers. However, the
differential twist between the photosphere and chromosphere increases
rapidly toward the outer penumbral boundary. The magnetic field
vector is more horizontal with respect to the solar surface by roughly
5-20° in the photosphere compared to the upper chromosphere. Above
a lightbridge, the chromospheric magnetic field is equally strong as
that in the umbra, whereas the field of the lightbridge is weaker than
its surroundings in the photosphere by roughly 1 kG. This suggests a
cusp-like magnetic field structure above the lightbridge.

---------------------------------------------------------
Title: The Solar Ultraviolet Imaging Telescope on-board Aditya-L1
Authors: Tripathi, Durgesh; Ramaprakash, A. N.; Khan, Aafaque;
Ghosh, Avyarthana; Chatterjee, Subhamoy; Banerjee, Dipankar; Chordia,
Pravin; Gandorfer, Achim; Krivova, Natalie; Nandy, Dibyendu; Rajarshi,
Chaitanya; Solanki, Sami K.
2017CSci..113..616T Altcode: 2022arXiv220407732T
The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument
onboard the Aditya-L1 mission of ISRO that will measure and monitor
the solar radiation emitted in the near-ultraviolet wavelength range
(200-400 nm). SUIT will simultaneously map the photosphere and the
chromosphere of the Sun using 11 filters sensitive to different
wavelengths and covering different heights in the solar atmosphere
and help us understand the processes involved in the transfer of
mass and energy from one layer to the other. SUIT will also allow us
to measure and monitor spatially resolved solar spectral irradiance
that governs the chemistry of oxygen and ozone in the stratosphere of
Earth's atmosphere. This is central to our understanding of the Sun
climate relationship.

---------------------------------------------------------
Title: The nature of solar brightness variations
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Cameron,
R. H.; Yeo, K. L.; Schmutz, W. K.
2017NatAs...1..612S Altcode: 2017arXiv171104156S
Determining the sources of solar brightness variations1,2,
often referred to as solar noise3, is important because
solar noise limits the detection of solar oscillations3,
is one of the drivers of the Earth's climate system4,5 and
is a prototype of stellar variability6,7—an important
limiting factor for the detection of extrasolar planets. Here,
we model the magnetic contribution to solar brightness variability
using high-cadence8,9 observations from the Solar Dynamics
Observatory (SDO) and the Spectral And Total Irradiance REconstruction
(SATIRE)10,11 model. The brightness variations caused by
the constantly evolving cellular granulation pattern on the solar
surface were computed with the Max Planck Institute for Solar System
Research (MPS)/University of Chicago Radiative Magnetohydrodynamics
(MURaM)12 code. We found that the surface magnetic field
and granulation can together precisely explain solar noise (that
is, solar variability excluding oscillations) on timescales from
minutes to decades, accounting for all timescales that have so far
been resolved or covered by irradiance measurements. We demonstrate
that no other sources of variability are required to explain the
data. Recent measurements of Sun-like stars by the COnvection ROtation
and planetary Transits (CoRoT)13 and Kepler14
missions uncovered brightness variations similar to that of the Sun,
but with a much wider variety of patterns15. Our finding
that solar brightness variations can be replicated in detail with
just two well-known sources will greatly simplify future modelling of
existing CoRoT and Kepler as well as anticipated Transiting Exoplanet
Survey Satellite16 and PLAnetary Transits and Oscillations
of stars (PLATO)17 data.

---------------------------------------------------------
Title: The variability of magnetic activity in solar-type stars
Authors: Fabbian, D.; Simoniello, R.; Collet, R.; Criscuoli, S.;
Korhonen, H.; Krivova, N. A.; Oláh, K.; Jouve, L.; Solanki, S. K.;
Alvarado-Gómez, J. D.; Booth, R.; García, R. A.; Lehtinen, J.;
See, V.
2017AN....338..753F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Association of solar coronal loops to photospheric magnetic
field
Authors: Pradeep Chitta, Lakshmi; Peter, Hardi; Solanki, Sami
2017SPD....4810630P Altcode:
Magnetic connectivity and its evolution from the solar photosphere
to the corona will play a crucial role in the energetics of the
solar atmosphere. To explore this connectivity, we use high spatial
resolution magnetic field observations of an active region from the
balloon-borne SUNRISE telescope, in combination with the observations
of coronal loops imaged in extreme ultraviolet by SDO/AIA. We show
that photospheric magnetic field at the base of coronal loops is
rapidly evolving through small-scale flux emergence and cancellation
events with rates on the order of 10^15 Mx/s. When observed at high
spatial resolution better than 0.5 arcsec, we find that basically
all coronal loops considered so far are rooted in the photosphere
above small-scale opposite polarity magnetic field patches. In the
photosphere, the magnetic field threading coronal loops is interacting
with opposite polarity parasitic magnetic concentrations leading to
dynamic signatures in the upper atmosphere. Chromospheric small-scale
jets aligned to coronal loops are observed at these locations. We
will present preliminary results from 3D MHD simulations of coronal
loops driven by realistic magneto-convection and discuss what role
the magnetic interactions at coronal loop footpoints could play in
the evolution of coronal loops and their heating.

---------------------------------------------------------
Title: The Sunrise balloon-borne observatory: Results from the second
flight and outlook on the third flight
Authors: Solanki, Sami K.
2017SPD....4810507S Altcode:
The balloon-borne solar observatory Sunrise flew for a second time in
June 2013 and provided seeing-free UV images and spectropolarimetric
data at close to the diffraction limit of the 1m telescope. The data
analysis has so far concentrated on a time series of the heart of
an active region recorded in the Stokes vector of the Fe I 525.02 nm
line and a time series of UV images of the same region. First results
were published in a special issue of the ApJ Supplement, vol. 229,
in April 2017. The data suggest the presence of very strong fields
in pores, a low-lying canopy of slender fibrils and different types
of waves propagating along these fibrils. Furthermore, properties of
the complex emergence of magnetic flux, of moving magnetic features
around a pore and of a siphon flow along a low-lying slender magnetic
loop are determined. A novel technique for inversions of Stokes
profiles including constraints to make the results more physically
consistent has also been developed and for the first time applied
to Sunrise II data. In addition, the presence of small-scale mixed
polarities and chromospheric jets was detected at the footpoints of
particularly bright coronal loops. These and more results will be
briefly presented. Preparations for the next flight of Sunrise have
started. Many new features are being designed for this flight, which
will allow it to reach considerably extended science goals. Thus it
will feature two new spectropolarimeters, one exploring the near
UV (from MPS), the other concentrating on chromospheric fields
and their connection to the photosphere (led by NAOJ). The IMaX
vector-magnetograph (provided by a Spanish consortium) will also
be updated to be able to sample multiple spectral lines. Finally,
Sunrise will have a new gondola (coming from APL) and an improved
image stabilization system (from KIS).

---------------------------------------------------------
Title: ALMA Discovery of Solar Umbral Brightness Enhancement at λ =
3 mm
Authors: Iwai, Kazumasa; Loukitcheva, Maria; Shimojo, Masumi; Solanki,
Sami K.; White, Stephen M.
2017ApJ...841L..20I Altcode: 2017arXiv170503147I
We report the discovery of a brightness enhancement in the center
of a large sunspot umbra at a wavelength of 3 mm using the Atacama
Large Millimeter/sub-millimeter Array (ALMA). Sunspots are among
the most prominent features on the solar surface, but many of their
aspects are surprisingly poorly understood. We analyzed a λ = 3 mm
(100 GHz) mosaic image obtained by ALMA that includes a large sunspot
within the active region AR12470, on 2015 December 16. The 3 mm map
has a 300″ × 300″ field of view and 4.″9 × 2.″2 spatial
resolution, which is the highest spatial resolution map of an entire
sunspot in this frequency range. We find a gradient of 3 mm brightness
from a high value in the outer penumbra to a low value in the inner
penumbra/outer umbra. Within the inner umbra, there is a marked increase
in 3 mm brightness temperature, which we call an umbral brightness
enhancement. This enhanced emission corresponds to a temperature
excess of 800 K relative to the surrounding inner penumbral region
and coincides with excess brightness in the 1330 and 1400 Å slit-jaw
images of the Interface Region Imaging Spectrograph (IRIS), adjacent
to a partial lightbridge. This λ = 3 mm brightness enhancement may be
an intrinsic feature of the sunspot umbra at chromospheric heights,
such as a manifestation of umbral flashes, or it could be related to
a coronal plume, since the brightness enhancement was coincident with
the footpoint of a coronal loop observed at 171 Å.

---------------------------------------------------------
Title: New reconstruction of the sunspot group numbers since 1739
using direct calibration and "backbone" methods
Authors: Chatzistergos, Theodosios; Usoskin, Ilya G.; Kovaltsov,
Gennady A.; Krivova, Natalie A.; Solanki, Sami K.
2017A&A...602A..69C Altcode: 2017arXiv170206183C
Context. The group sunspot number (GSN) series constitute the longest
instrumental astronomical database providing information on solar
activity. This database is a compilation of observations by many
individual observers, and their inter-calibration has usually been
performed using linear rescaling. There are multiple published series
that show different long-term trends for solar activity. Aims:
We aim at producing a GSN series, with a non-linear non-parametric
calibration. The only underlying assumptions are that the differences
between the various series are due to different acuity thresholds
of the observers, and that the threshold of each observer remains
constant throughout the observing period. Methods: We used a
daisy chain process with backbone (BB) observers and calibrated all
overlapping observers to them. We performed the calibration of each
individual observer with a probability distribution function (PDF)
matrix constructed considering all daily values for the overlapping
period with the BB. The calibration of the BBs was carried out in a
similar manner. The final series was constructed by merging different
BB series. We modelled the propagation of errors straightforwardly
with Monte Carlo simulations. A potential bias due to the selection
of BBs was investigated and the effect was shown to lie within the 1σ
interval of the produced series. The exact selection of the reference
period was shown to have a rather small effect on our calibration
as well. Results: The final series extends back to 1739 and
includes data from 314 observers. This series suggests moderate
activity during the 18th and 19th century, which is significantly
lower than the high level of solar activity predicted by other recent
reconstructions applying linear regressions. Conclusions:
The new series provides a robust reconstruction, based on modern and
non-parametric methods, of sunspot group numbers since 1739, and it
confirms the existence of the modern grand maximum of solar activity in
the second half of the 20th century. Values of the group sunspot
number series are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(<A href="http://130.79.128.5">http://130.79.128.5</A>) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A69">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A69</A>

---------------------------------------------------------
Title: Millimeter radiation from a 3D model of the solar
atmosphere. II. Chromospheric magnetic field
Authors: Loukitcheva, M.; White, S. M.; Solanki, S. K.; Fleishman,
G. D.; Carlsson, M.
2017A&A...601A..43L Altcode: 2017arXiv170206018L
 Aims: We use state-of-the-art, three-dimensional non-local
thermodynamic equilibrium (non-LTE) radiative magnetohydrodynamic
simulations of the quiet solar atmosphere to carry out detailed tests
of chromospheric magnetic field diagnostics from free-free radiation at
millimeter and submillimeter wavelengths (mm/submm). Methods:
The vertical component of the magnetic field was deduced from the
mm/submm brightness spectra and the degree of circular polarization
synthesized at millimeter frequencies. We used the frequency bands
observed by the Atacama Large Millimeter/Submillimeter Array (ALMA)
as a convenient reference. The magnetic field maps obtained describe
the longitudinal magnetic field at the effective formation heights of
the relevant wavelengths in the solar chromosphere. Results:
The comparison of the deduced and model chromospheric magnetic fields
at the spatial resolution of both the model and current observations
demonstrates a good correlation, but has a tendency to underestimate
the model field. The systematic discrepancy of about 10% is probably
due to averaging of the restored field over the heights contributing
to the radiation, weighted by the strength of the contribution. On
the whole, the method of probing the longitudinal component of the
magnetic field with free-free emission at mm/submm wavelengths
is found to be applicable to measurements of the weak quiet-Sun
magnetic fields. However, successful exploitation of this technique
requires very accurate measurements of the polarization properties
(primary beam and receiver polarization response) of the antennas,
which will be the principal factor that determines the level to which
chromospheric magnetic fields can be measured. Conclusions:
Consequently, high-resolution and high-precision observations of
circularly polarized radiation at millimeter wavelengths can be a
powerful tool for producing chromospheric longitudinal magnetograms.

---------------------------------------------------------
Title: Erratum: Morphological Properties of
Slender CaII H Fibrils Observed by sunrise II (<A
href="http://doi.org/10.3847/1538-4365/229/1/6">ApJS 229, 1, 6</A>)
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..230...11G Altcode:
No abstract at ADS

---------------------------------------------------------
Title: High-frequency Oscillations in Small Magnetic Elements Observed
with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Stangalini, M.; Steiner,
O.; Cameron, R. H.; Danilovic, S.
2017ApJS..229...10J Altcode: 2016arXiv161109302J
We characterize waves in small magnetic elements and investigate
their propagation in the lower solar atmosphere from observations at
high spatial and temporal resolution. We use the wavelet transform to
analyze oscillations of both horizontal displacement and intensity
in magnetic bright points found in the 300 nm and the Ca II H 396.8
nm passbands of the filter imager on board the Sunrise balloon-borne
solar observatory. Phase differences between the oscillations at the
two atmospheric layers corresponding to the two passbands reveal
upward propagating waves at high frequencies (up to 30 mHz). Weak
signatures of standing as well as downward propagating waves are also
obtained. Both compressible and incompressible (kink) waves are found
in the small-scale magnetic features. The two types of waves have
different, though overlapping, period distributions. Two independent
estimates give a height difference of approximately 450 ± 100 km
between the two atmospheric layers sampled by the employed spectral
bands. This value, together with the determined short travel times of
the transverse and longitudinal waves provide us with phase speeds of 29
± 2 km s-1 and 31 ± 2 km s-1, respectively. We
speculate that these phase speeds may not reflect the true propagation
speeds of the waves. Thus, effects such as the refraction of fast
longitudinal waves may contribute to an overestimate of the phase speed.

---------------------------------------------------------
Title: Slender Ca II H Fibrils Mapping Magnetic Fields in the Low
Solar Chromosphere
Authors: Jafarzadeh, S.; Rutten, R. J.; Solanki, S. K.; Wiegelmann, T.;
Riethmüller, T. L.; van Noort, M.; Szydlarski, M.; Blanco Rodríguez,
J.; Barthol, P.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon, L.;
Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Schmidt, W.
2017ApJS..229...11J Altcode: 2016arXiv161003104J
A dense forest of slender bright fibrils near a small solar active
region is seen in high-quality narrowband Ca II H images from the SuFI
instrument onboard the Sunrise balloon-borne solar observatory. The
orientation of these slender Ca II H fibrils (SCF) overlaps with the
magnetic field configuration in the low solar chromosphere derived
by magnetostatic extrapolation of the photospheric field observed
with Sunrise/IMaX and SDO/HMI. In addition, many observed SCFs are
qualitatively aligned with small-scale loops computed from a novel
inversion approach based on best-fit numerical MHD simulation. Such
loops are organized in canopy-like arches over quiet areas that differ
in height depending on the field strength near their roots.

---------------------------------------------------------
Title: EMPIRE: A robust empirical reconstruction of solar irradiance
variability
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
2017JGRA..122.3888Y Altcode: 2017arXiv170407652Y
We present a new empirical model of total and spectral solar irradiance
(TSI and SSI) variability entitled EMPirical Irradiance REconstruction
(EMPIRE). As with existing empirical models, TSI and SSI variability
is given by the linear combination of solar activity indices. In
empirical models, UV SSI variability is usually determined by
fitting the rotational variability in activity indices to that in
measurements. Such models have to date relied on ordinary least
squares regression, which ignores the uncertainty in the activity
indices. In an advance from earlier efforts, the uncertainty in the
activity indices is accounted for in EMPIRE by the application of
an error-in-variables regression scheme, making the resultant UV SSI
variability more robust. The result is consistent with observations and
unprecedentedly, with that from other modeling approaches, resolving
the long-standing controversy between existing empirical models and
other types of models. We demonstrate that earlier empirical models,
by neglecting the uncertainty in activity indices, underestimate UV
SSI variability. The reconstruction of TSI and visible and IR SSI from
EMPIRE is also shown to be consistent with observations. The EMPIRE
reconstruction is of utility to climate studies as a more robust
alternative to earlier empirical reconstructions.

---------------------------------------------------------
Title: Magneto-static Modeling from Sunrise/IMaX: Application to an
Active Region Observed with Sunrise II
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki, S. K.;
Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller,
T. L.; van Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229...18W Altcode: 2017arXiv170101458N; 2017arXiv170101458W
Magneto-static models may overcome some of the issues facing force-free
magnetic field extrapolations. So far they have seen limited use
and have faced problems when applied to quiet-Sun data. Here we
present a first application to an active region. We use solar vector
magnetic field measurements gathered by the IMaX polarimeter during
the flight of the Sunrise balloon-borne solar observatory in 2013
June as boundary conditions for a magneto-static model of the higher
solar atmosphere above an active region. The IMaX data are embedded
in active region vector magnetograms observed with SDO/HMI. This work
continues our magneto-static extrapolation approach, which was applied
earlier to a quiet-Sun region observed with Sunrise I. In an active
region the signal-to-noise-ratio in the measured Stokes parameters
is considerably higher than in the quiet-Sun and consequently the
IMaX measurements of the horizontal photospheric magnetic field allow
us to specify the free parameters of the model in a special class of
linear magneto-static equilibria. The high spatial resolution of IMaX
(110-130 km, pixel size 40 km) enables us to model the non-force-free
layer between the photosphere and the mid-chromosphere vertically
by about 50 grid points. In our approach we can incorporate some
aspects of the mixed beta layer of photosphere and chromosphere, e.g.,
taking a finite Lorentz force into account, which was not possible with
lower-resolution photospheric measurements in the past. The linear model
does not, however, permit us to model intrinsic nonlinear structures
like strongly localized electric currents.

---------------------------------------------------------
Title: The Second Flight of the Sunrise Balloon-borne Solar
Observatory: Overview of Instrument Updates, the Flight, the Data,
and First Results
Authors: Solanki, S. K.; Riethmüller, T. L.; Barthol, P.; Danilovic,
S.; Deutsch, W.; Doerr, H. -P.; Feller, A.; Gandorfer, A.; Germerott,
D.; Gizon, L.; Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.;
Lagg, A.; Meller, R.; Tomasch, G.; van Noort, M.; Blanco Rodríguez,
J.; Gasent Blesa, J. L.; Balaguer Jiménez, M.; Del Toro Iniesta,
J. C.; López Jiménez, A. C.; Orozco Suarez, D.; Berkefeld, T.;
Halbgewachs, C.; Schmidt, W.; Álvarez-Herrero, A.; Sabau-Graziati,
L.; Pérez Grande, I.; Martínez Pillet, V.; Card, G.; Centeno, R.;
Knölker, M.; Lecinski, A.
2017ApJS..229....2S Altcode: 2017arXiv170101555S
The Sunrise balloon-borne solar observatory, consisting of a 1 m
aperture telescope that provides a stabilized image to a UV filter
imager and an imaging vector polarimeter, carried out its second science
flight in 2013 June. It provided observations of parts of active regions
at high spatial resolution, including the first high-resolution images
in the Mg II k line. The obtained data are of very high quality, with
the best UV images reaching the diffraction limit of the telescope
at 3000 Å after Multi-Frame Blind Deconvolution reconstruction
accounting for phase-diversity information. Here a brief update is
given of the instruments and the data reduction techniques, which
includes an inversion of the polarimetric data. Mainly those aspects
that evolved compared with the first flight are described. A tabular
overview of the observations is given. In addition, an example time
series of a part of the emerging active region NOAA AR 11768 observed
relatively close to disk center is described and discussed in some
detail. The observations cover the pores in the trailing polarity of
the active region, as well as the polarity inversion line where flux
emergence was ongoing and a small flare-like brightening occurred in
the course of the time series. The pores are found to contain magnetic
field strengths ranging up to 2500 G, and while large pores are clearly
darker and cooler than the quiet Sun in all layers of the photosphere,
the temperature and brightness of small pores approach or even exceed
those of the quiet Sun in the upper photosphere.

---------------------------------------------------------
Title: Estimation of the Magnetic Flux Emergence Rate in the Quiet
Sun from Sunrise Data
Authors: Smitha, H. N.; Anusha, L. S.; Solanki, S. K.; Riethmüller,
T. L.
2017ApJS..229...17S Altcode: 2016arXiv161106432S
Small-scale internetwork (IN) features are thought to be the major
source of fresh magnetic flux in the quiet Sun. During its first science
flight in 2009, the balloon-borne observatory Sunrise captured images of
the magnetic fields in the quiet Sun at a high spatial resolution. Using
these data we measure the rate at which the IN features bring magnetic
flux to the solar surface. In a previous paper it was found that the
lowest magnetic flux in small-scale features detected using the Sunrise
observations is 9 × 1014 Mx. This is nearly an order of
magnitude smaller than the smallest fluxes of features detected in
observations from the Hinode satellite. In this paper, we compute the
flux emergence rate (FER) by accounting for such small fluxes, which
was not possible before Sunrise. By tracking the features with fluxes
in the range {10}15{--}{10}18 Mx, we measure an
FER of 1100 {Mx} {{cm}}-2 {{day}}-1. The smaller
features with fluxes ≤slant {10}16 Mx are found to be the
dominant contributors to the solar magnetic flux. The FER found here
is an order of magnitude higher than the rate from Hinode, obtained
with a similar feature tracking technique. A wider comparison with the
literature shows, however, that the exact technique of determining the
rate of the appearance of new flux can lead to results that differ by
up to two orders of magnitude, even when applied to similar data. The
causes of this discrepancy are discussed and first qualitative
explanations proposed.

---------------------------------------------------------
Title: Vertical magnetic field gradient in the photospheric layers
of sunspots
Authors: Joshi, Jayant; Lagg, Andreas; Hirzberger, Johann; Solanki,
Sami K.; Tiwari, Sanjiv K.
2017A&A...599A..35J Altcode: 2016arXiv161000500J
 Aims: We investigate the vertical gradient of the magnetic
field of sunspots in the photospheric layer. Methods:
Independent observations were obtained with the Solar Optical
Telescope/Spectropolarimeter (SOT/SP) on board the Hinode spacecraft and
with the Tenrife Infrared Polarimeter-2 (TIP-2) mounted at the German
Vacuum Tower Telescope (VTT). We apply state-of-the-art inversion
techniques to both data sets to retrieve the magnetic field and the
corresponding vertical gradient along with other atmospheric parameters
in the solar photosphere. Results: In the sunspot penumbrae we
detected patches of negative vertical gradients of the magnetic field
strength, I.e., the magnetic field strength decreases with optical depth
in the photosphere. The negative gradient patches are located in the
inner and partly in the middle penumbrae in both data sets. From the
SOT/SP observations we found that the negative gradient patches are
restricted mainly to the deep photospheric layers and are concentrated
near the edges of the penumbral filaments. Magnetohydrodynamic (MHD)
simulations also show negative gradients in the inner penumbrae, also
at the locations of filaments. In the observations and the simulation
negative gradients of the magnetic field vs. optical depth dominate
at some radial distances in the penumbra. The negative gradient with
respect to optical depth in the inner penumbrae persists even after
averaging in the azimuthal direction in the observations and, to a
lesser extent, in the MHD simulations. If the gradients in the MHD
simulations are determined with respect to geometrical height, then
the azimuthal averages are always positive within the sunspot (above
log τ = 0), corresponding to magnetic field increasing with depth,
as generally expected. Conclusions: We interpret the observed
localized presence of negative vertical gradient of the magnetic
field strength in the observations as a consequence of stronger field
from spines expanding with height and closing above the weaker field
inter-spines. The presence of the negative gradients with respect
to optical depth after azimuthal averaging can be explained by two
different mechanisms: the high corrugation of equal optical depth
surfaces and the cancellation of polarized signal due to the presence
of unresolved opposite polarity patches in the deeper layers of the
penumbra.

---------------------------------------------------------
Title: A Tale of Two Emergences: Sunrise II Observations of Emergence
Sites in a Solar Active Region
Authors: Centeno, R.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.;
Solanki, S. K.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger,
J.; Riethmüller, T. L.; van Noort, M.; Orozco Suárez, D.; Berkefeld,
T.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229....3C Altcode: 2016arXiv161003531C
In 2013 June, the two scientific instruments on board the second Sunrise
mission witnessed, in detail, a small-scale magnetic flux emergence
event as part of the birth of an active region. The Imaging Magnetograph
Experiment (IMaX) recorded two small (∼ 5\prime\prime )
emerging flux patches in the polarized filtergrams of a photospheric Fe
I spectral line. Meanwhile, the Sunrise Filter Imager (SuFI) captured
the highly dynamic chromospheric response to the magnetic fields pushing
their way through the lower solar atmosphere. The serendipitous capture
of this event offers a closer look at the inner workings of active
region emergence sites. In particular, it reveals in meticulous detail
how the rising magnetic fields interact with the granulation as they
push through the Sun’s surface, dragging photospheric plasma in
their upward travel. The plasma that is burdening the rising field
slides along the field lines, creating fast downflowing channels at
the footpoints. The weight of this material anchors this field to the
surface at semi-regular spatial intervals, shaping it in an undulatory
fashion. Finally, magnetic reconnection enables the field to release
itself from its photospheric anchors, allowing it to continue its
voyage up to higher layers. This process releases energy that lights
up the arch-filament systems and heats the surrounding chromosphere.

---------------------------------------------------------
Title: Photospheric Response to an Ellerman Bomb-like Event—An
Analogy of Sunrise/IMaX Observations and MHD Simulations
Authors: Danilovic, S.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van Noort, M.;
Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez, D.;
Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229....5D Altcode: 2016arXiv160903817D
Ellerman Bombs are signatures of magnetic reconnection, which is an
important physical process in the solar atmosphere. How and where they
occur is a subject of debate. In this paper, we analyze Sunrise/IMaX
data, along with 3D MHD simulations that aim to reproduce the exact
scenario proposed for the formation of these features. Although
the observed event seems to be more dynamic and violent than the
simulated one, simulations clearly confirm the basic scenario for the
production of EBs. The simulations also reveal the full complexity of
the underlying process. The simulated observations show that the Fe I
525.02 nm line gives no information on the height where reconnection
takes place. It can only give clues about the heating in the aftermath
of the reconnection. However, the information on the magnetic field
vector and velocity at this spatial resolution is extremely valuable
because it shows what numerical models miss and how they can be
improved.

---------------------------------------------------------
Title: Transverse Oscillations in Slender Ca II H Fibrils Observed
with Sunrise/SuFI
Authors: Jafarzadeh, S.; Solanki, S. K.; Gafeira, R.; van Noort, M.;
Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco Suárez, D.;
Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....9J Altcode: 2016arXiv161007449J
We present observations of transverse oscillations in slender Ca II
H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long
time series of high- (spatial and temporal-) resolution seeing-free
observations in a 1.1 Å wide passband covering the line core of Ca
II H 3969 Å from the second flight of the Sunrise balloon-borne solar
observatory. The entire field of view, spanning the polarity inversion
line of an active region close to the solar disk center, is covered with
bright, thin, and very dynamic fine structures. Our analysis reveals
the prevalence of transverse waves in SCFs with median amplitudes and
periods on the order of 2.4 ± 0.8 km s-1 and 83 ± 29 s,
respectively (with standard deviations given as uncertainties). We
find that the transverse waves often propagate along (parts of) the
SCFs with median phase speeds of 9 ± 14 km s-1. While the
propagation is only in one direction along the axis in some of the
SCFs, propagating waves in both directions, as well as standing waves
are also observed. The transverse oscillations are likely Alfvénic
and are thought to be representative of magnetohydrodynamic kink
waves. The wave propagation suggests that the rapid high-frequency
transverse waves, often produced in the lower photosphere, can
penetrate into the chromosphere with an estimated energy flux of ≈15
kW m-2. Characteristics of these waves differ from those
reported for other fibrillar structures, which, however, were observed
mainly in the upper solar chromosphere.

---------------------------------------------------------
Title: Kinematics of Magnetic Bright Features in the Solar Photosphere
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Barthol, P.;
Blanco Rodríguez, J.; del Toro Iniesta, J. C.; Gandorfer, A.; Gizon,
L.; Hirzberger, J.; Knölker, M.; Martínez Pillet, V.; Orozco Suárez,
D.; Riethmüller, T. L.; Schmidt, W.; van Noort, M.
2017ApJS..229....8J Altcode: 2016arXiv161007634J
Convective flows are known as the prime means of transporting magnetic
fields on the solar surface. Thus, small magnetic structures are good
tracers of turbulent flows. We study the migration and dispersal
of magnetic bright features (MBFs) in intergranular areas observed
at high spatial resolution with Sunrise/IMaX. We describe the flux
dispersal of individual MBFs as a diffusion process whose parameters are
computed for various areas in the quiet-Sun and the vicinity of active
regions from seeing-free data. We find that magnetic concentrations
are best described as random walkers close to network areas (diffusion
index, γ =1.0), travelers with constant speeds over a supergranule
(γ =1.9{--}2.0), and decelerating movers in the vicinity of flux
emergence and/or within active regions (γ =1.4{--}1.5). The three
types of regions host MBFs with mean diffusion coefficients of 130
km2 s-1, 80-90 km2 s-1,
and 25-70 km2 s-1, respectively. The MBFs in
these three types of regions are found to display a distinct kinematic
behavior at a confidence level in excess of 95%.

---------------------------------------------------------
Title: Spectropolarimetric Evidence for a Siphon Flow along an
Emerging Magnetic Flux Tube
Authors: Requerey, Iker S.; Ruiz Cobo, B.; Del Toro Iniesta, J. C.;
Orozco Suárez, D.; Blanco Rodríguez, J.; Solanki, S. K.; Barthol,
P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.;
van Noort, M.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229...15R Altcode: 2016arXiv161106732R
We study the dynamics and topology of an emerging magnetic flux
concentration using high spatial resolution spectropolarimetric data
acquired with the Imaging Magnetograph eXperiment on board the sunrise
balloon-borne solar observatory. We obtain the full vector magnetic
field and the line of sight (LOS) velocity through inversions of
the Fe I line at 525.02 nm with the SPINOR code. The derived vector
magnetic field is used to trace magnetic field lines. Two magnetic flux
concentrations with different polarities and LOS velocities are found
to be connected by a group of arch-shaped magnetic field lines. The
positive polarity footpoint is weaker (1100 G) and displays an upflow,
while the negative polarity footpoint is stronger (2200 G) and shows
a downflow. This configuration is naturally interpreted as a siphon
flow along an arched magnetic flux tube.

---------------------------------------------------------
Title: Morphological Properties of Slender Ca II H Fibrils Observed
by SUNRISE II
Authors: Gafeira, R.; Lagg, A.; Solanki, S. K.; Jafarzadeh, S.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....6G Altcode: 2016arXiv161200319G
We use seeing-free high spatial resolution Ca II H data obtained by
the SUNRISE observatory to determine properties of slender fibrils
in the lower solar chromosphere. In this work we use intensity images
taken with the SuFI instrument in the Ca II H line during the second
scientific flight of the SUNRISE observatory to identify and track
elongated bright structures. After identification, we analyze theses
structures to extract their morphological properties. We identify
598 slender Ca II H fibrils (SCFs) with an average width of around
180 km, length between 500 and 4000 km, average lifetime of ≈400
s, and average curvature of 0.002 arcsec-1. The maximum
lifetime of the SCFs within our time series of 57 minutes is ≈2000
s. We discuss similarities and differences of the SCFs with other
small-scale, chromospheric structures such as spicules of type I and
II, or Ca II K fibrils.

---------------------------------------------------------
Title: A New MHD-assisted Stokes Inversion Technique
Authors: Riethmüller, T. L.; Solanki, S. K.; Barthol, P.; Gandorfer,
A.; Gizon, L.; Hirzberger, J.; van Noort, M.; Blanco Rodríguez, J.;
Del Toro Iniesta, J. C.; Orozco Suárez, D.; Schmidt, W.; Martínez
Pillet, V.; Knölker, M.
2017ApJS..229...16R Altcode: 2016arXiv161105175R
We present a new method of Stokes inversion of spectropolarimetric
data and evaluate it by taking the example of a Sunrise/IMaX
observation. An archive of synthetic Stokes profiles is obtained
by the spectral synthesis of state-of-the-art magnetohydrodynamics
(MHD) simulations and a realistic degradation to the level of the
observed data. The definition of a merit function allows the archive
to be searched for the synthetic Stokes profiles that best match the
observed profiles. In contrast to traditional Stokes inversion codes,
which solve the Unno-Rachkovsky equations for the polarized radiative
transfer numerically and fit the Stokes profiles iteratively, the new
technique provides the full set of atmospheric parameters. This gives
us the ability to start an MHD simulation that takes the inversion
result as an initial condition. After a relaxation process of half an
hour solar time we obtain physically consistent MHD data sets with
a target similar to the observation. The new MHD simulation is used
to repeat the method in a second iteration, which further improves
the match between observation and simulation, resulting in a factor
of 2.2 lower mean {χ }2 value. One advantage of the new
technique is that it provides the physical parameters on a geometrical
height scale. It constitutes a first step toward inversions that give
results consistent with the MHD equations.

---------------------------------------------------------
Title: Oscillations on Width and Intensity of Slender Ca II H Fibrils
from Sunrise/SuFI
Authors: Gafeira, R.; Jafarzadeh, S.; Solanki, S. K.; Lagg, A.;
van Noort, M.; Barthol, P.; Blanco Rodríguez, J.; del Toro Iniesta,
J. C.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; Knölker, M.; Orozco
Suárez, D.; Riethmüller, T. L.; Schmidt, W.
2017ApJS..229....7G Altcode: 2017arXiv170102801G
We report the detection of oscillations in slender Ca II H fibrils
(SCFs) from high-resolution observations acquired with the Sunrise
balloon-borne solar observatory. The SCFs show obvious oscillations in
their intensity, but also their width. The oscillatory behaviors are
investigated at several positions along the axes of the SCFs. A large
majority of fibrils show signs of oscillations in intensity. Their
periods and phase speeds are analyzed using a wavelet analysis. The
width and intensity perturbations have overlapping distributions
of the wave period. The obtained distributions have median values
of the period of 32 ± 17 s and 36 ± 25 s, respectively. We
find that the fluctuations of both parameters propagate in
the SCFs with speeds of {11}-11+49 km
s-1 and {15}-15+34 km s-1,
respectively. Furthermore, the width and intensity oscillations have a
strong tendency to be either in anti-phase or, to a smaller extent, in
phase. This suggests that the oscillations of both parameters are caused
by the same wave mode and that the waves are likely propagating. Taking
all the evidence together, the most likely wave mode to explain all
measurements and criteria is the fast sausage mode.

---------------------------------------------------------
Title: Solar Coronal Loops Associated with Small-scale Mixed Polarity
Surface Magnetic Fields
Authors: Chitta, L. P.; Peter, H.; Solanki, S. K.; Barthol, P.;
Gandorfer, A.; Gizon, L.; Hirzberger, J.; Riethmüller, T. L.; van
Noort, M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco
Suárez, D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229....4C Altcode: 2016arXiv161007484C
How and where are coronal loops rooted in the solar lower
atmosphere? The details of the magnetic environment and its evolution
at the footpoints of coronal loops are crucial to understanding the
processes of mass and energy supply to the solar corona. To address
the above question, we use high-resolution line-of-sight magnetic
field data from the Imaging Magnetograph eXperiment instrument on the
Sunrise balloon-borne observatory and coronal observations from the
Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory
of an emerging active region. We find that the coronal loops are
often rooted at the locations with minor small-scale but persistent
opposite-polarity magnetic elements very close to the larger dominant
polarity. These opposite-polarity small-scale elements continually
interact with the dominant polarity underlying the coronal loop through
flux cancellation. At these locations we detect small inverse Y-shaped
jets in chromospheric Ca II H images obtained from the Sunrise Filter
Imager during the flux cancellation. Our results indicate that magnetic
flux cancellation and reconnection at the base of coronal loops due
to mixed polarity fields might be a crucial feature for the supply of
mass and energy into the corona.

---------------------------------------------------------
Title: Moving Magnetic Features around a Pore
Authors: Kaithakkal, A. J.; Riethmüller, T. L.; Solanki, S. K.; Lagg,
A.; Barthol, P.; Gandorfer, A.; Gizon, L.; Hirzberger, J.; vanNoort,
M.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.; Orozco Suárez,
D.; Schmidt, W.; Martínez Pillet, V.; Knölker, M.
2017ApJS..229...13K Altcode: 2016arXiv160905664K
Spectropolarimetric observations from Sunrise/IMaX, obtained in 2013
June, are used for a statistical analysis to determine the physical
properties of moving magnetic features (MMFs) observed near a pore. MMFs
of the same and opposite polarity, with respect to the pore, are found
to stream from its border at an average speed of 1.3 km s-1
and 1.2 km s-1, respectively, with mainly same-polarity MMFs
found further away from the pore. MMFs of both polarities are found to
harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs
are blueshifted, whereas same-polarity MMFs do not show any preference
for up- or downflows. Most of the MMFs are found to be of sub-arcsecond
size and carry a mean flux of ∼1.2 × 1017 Mx.

---------------------------------------------------------
Title: Brightness of Solar Magnetic Elements As a Function of Magnetic
Flux at High Spatial Resolution
Authors: Kahil, F.; Riethmüller, T. L.; Solanki, S. K.
2017ApJS..229...12K Altcode: 2017arXiv170100759K
We investigate the relationship between the photospheric magnetic
field of small-scale magnetic elements in the quiet-Sun (QS) at disk
center and the brightness at 214, 300, 313, 388, 397, and 525.02
nm. To this end, we analyzed spectropolarimetric and imaging time
series acquired simultaneously by the Imaging Magnetograph eXperiment
magnetograph and the SuFI filter imager on board the balloon-borne
observatory {{S}}{{UNRISE}} during its first science flight in 2009,
with high spatial and temporal resolution. We find a clear dependence
of the contrast in the near ultraviolet and the visible on the
line-of-sight component of the magnetic field, B LOS, which
is best described by a logarithmic model. This function effectively
represents the relationship between the Ca II H-line emission and
B LOS and works better than the power-law fit adopted
by previous studies. This, along with the high contrast reached
at these wavelengths, will help with determining the contribution
of small-scale elements in the QS to the irradiance changes for
wavelengths below 388 nm. At all wavelengths, including the continuum
at 525.40 nm, the intensity contrast does not decrease with increasing
B LOS. This result also strongly supports the fact that
{{S}}{{UNRISE}} has resolved small strong magnetic field elements in the
internetwork, resulting in constant contrasts for large magnetic fields
in our continuum contrast at 525.40 nm versus the B LOS
scatterplot, unlike the turnover obtained in previous observational
studies. This turnover is due to the intermixing of the bright magnetic
features with the dark intergranular lanes surrounding them.

---------------------------------------------------------
Title: Convectively Driven Sinks and Magnetic Fields in the Quiet-Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
Schmidt, Wolfgang
2017ApJS..229...14R Altcode: 2016arXiv161007622R
We study the relation between mesogranular flows, convectively
driven sinks and magnetic fields using high spatial resolution
spectropolarimetric data acquired with the Imaging Magnetograph
eXperiment on board Sunrise. We obtain the horizontal velocity
flow fields of two quiet-Sun regions (31.2 × 31.2 Mm2)
via local correlation tracking. Mesogranular lanes and the central
position of sinks are identified using Lagrange tracers. We find
6.7× {10}-2 sinks per Mm2 in the two observed
regions. The sinks are located at the mesogranular vertices and turn
out to be associated with (1) horizontal velocity flows converging to a
central point and (2) long-lived downdrafts. The spatial distribution
of magnetic fields in the quiet-Sun is also examined. The strongest
magnetic fields are preferentially located at sinks. We find that 40% of
the pixels with longitudinal components of the magnetic field stronger
than 500 G are located in the close neighborhood of sinks. In contrast,
the small-scale magnetic loops detected by Martínez González et al. in
the same two observed areas do not show any preferential distribution
at mesogranular scales. The study of individual examples reveals
that sinks can play an important role in the evolution of quiet-Sun
magnetic features.

---------------------------------------------------------
Title: Overview of the Special Issue on the First Science Results
from the Second Flight of Sunrise
Authors: Solanki, Sami K.
2017ApJS..229....1S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Statistical evolution of quiet-Sun small-scale magnetic
features using Sunrise observations
Authors: Anusha, L. S.; Solanki, S. K.; Hirzberger, J.; Feller, A.
2017A&A...598A..47A Altcode: 2016arXiv160808499A
The evolution of small magnetic features in quiet regions of the Sun
provides a unique window for probing solar magneto-convection. Here
we analyze small-scale magnetic features in the quiet Sun, using the
high resolution, seeing-free observations from the Sunrise balloon
borne solar observatory. Our aim is to understand the contribution of
different physical processes, such as splitting, merging, emergence
and cancellation of magnetic fields to the rearrangement, addition
and removal of magnetic flux in the photosphere. We have employed a
statistical approach for the analysis and the evolution studies are
carried out using a feature-tracking technique. In this paper we provide
a detailed description of the feature-tracking algorithm that we have
newly developed and we present the results of a statistical study
of several physical quantities. The results on the fractions of the
flux in the emergence, appearance, splitting, merging, disappearance
and cancellation qualitatively agrees with other recent studies. To
summarize, the total flux gained in unipolar appearance is an order of
magnitude larger than the total flux gained in emergence. On the other
hand, the bipolar cancellation contributes nearly an equal amount to
the loss of magnetic flux as unipolar disappearance. The total flux
lost in cancellation is nearly six to eight times larger than the
total flux gained in emergence. One big difference between our study
and previous similar studies is that, thanks to the higher spatial
resolution of Sunrise, we can track features with fluxes as low as
9 × 1014 Mx. This flux is nearly an order of magnitude
lower than the smallest fluxes of the features tracked in the highest
resolution previous studies based on Hinode data. The area and flux
of the magnetic features follow power-law type distribution, while
the lifetimes show either power-law or exponential type distribution
depending on the exact definitions used to define various birth and
death events. We have also statistically determined the evolution
of the flux within the features in the course of their lifetime,
finding that this evolution depends very strongly on the birth and
death process that the features undergo.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Group sunspot number series since
1739 (Chatzistergos+, 2017)
Authors: Chatzistergos, T.; Usoskin, I. G.; Kovaltsov, G. A.; Krivova,
N. A.; Solanki, S. K.
2017yCat..36020069C Altcode:
Annual, monthly, and daily values of the Group sunspot number series
produced in the paper. (3 data files).

---------------------------------------------------------
Title: Fan Loops Observed by IRIS, EIS, and AIA
Authors: Ghosh, Avyarthana; Tripathi, Durgesh; Gupta, G. R.; Polito,
Vanessa; Mason, Helen E.; Solanki, Sami K.
2017ApJ...835..244G Altcode: 2017arXiv170101617G
A comprehensive study of the physical parameters of active region fan
loops is presented using the observations recorded with the Interface
Region Imaging Spectrometer (IRIS), the EUV Imaging Spectrometer (EIS)
on board Hinode, and the Atmospheric Imaging Assembly (AIA) and the
Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics
Observatory (SDO). The fan loops emerging from non-flaring AR 11899
(near the disk center) on 2013 November 19 are clearly discernible in
AIA 171 Å images and in those obtained in Fe viii and Si vii images
using EIS. Our measurements of electron densities reveal that the
footpoints of these loops are at an approximately constant pressure
with electron densities of {log} {N}e=10.1 cm-3 at
{log} [T/K]=5.15 (O IV), and {log} {N}e=8.9 cm-3
at {log} [T/K]=6.15 (Si x). The electron temperature diagnosed
across the fan loops by means of EM-Loci suggest that two temperature
components exist at {log} [T/K]=4.95 and 5.95 at the footpoints. These
components are picked up by IRIS lines and EIS lines, respectively. At
higher heights, the loops are nearly isothermal at {log} [T/K]=5.95,
which remained constant along the loop. The measurement of the Doppler
shift using IRIS lines suggests that the plasma at the footpoints of
these loops is predominantly redshifted by 2-3 km s-1 in C
II, 10-15 km s-1 in Si IV, and 15-20 km s-1 in O
IV, reflecting the increase in the speed of downflows with increasing
temperature from {log} [T/K]=4.40 to 5.15. These observations can
be explained by low-frequency nanoflares or impulsive heating, and
provide further important constraints on the modeling of the dynamics
of fan loops.

---------------------------------------------------------
Title: The dark side of solar photospheric G-band bright points
Authors: Riethmüller, T. L.; Solanki, S. K.
2017A&A...598A.123R Altcode: 2016arXiv161207887R
Bright, small-scale magnetic elements found mainly in intergranular
lanes at the solar surface are named bright points (BPs). They show
high contrasts in Fraunhofer G-band observations and are described
by nearly vertical slender flux tubes or sheets. A recent comparison
between BP observations in the ultraviolet (UV) and visible spectral
range recorded with the balloon-borne observatory Sunrise and
state-of-the-art magnetohydrodynamical (MHD) simulations revealed
a kilogauss magnetic field for 98% of the synthetic BPs. Here we
address the opposite question, namely which fraction of pixels hosting
kilogauss fields coincides with an enhanced G-band brightness. We
carried out 3D radiation MHD simulations for three magnetic activity
levels (corresponding to the quiet Sun, weak and strong plage)
and performed a full spectral line synthesis in the G-band. Only 7%
of the kilogauss pixels in our quiet-Sun simulation coincide with a
brightness lower than the mean quiet-Sun intensity, while 23% of the
pixels in the weak-plage simulation and even 49% in the strong-plage
simulation are associated with a local darkening. Dark strong-field
regions are preferentially found in the cores of larger flux patches
that are rare in the quiet Sun, but more common in plage regions,
often in the vertices of granulation cells. The significant brightness
shortfall in the core of larger flux patches coincides with a slight
magnetic field weakening. Kilogauss elements in the quiet Sun are,
on average, brighter than similar features in plage regions. Almost
all strong-field pixels display a more or less vertical magnetic field
orientation. Hence, in the quiet Sun, G-band BPs correspond almost
one-to-one with kilogauss elements. In weak plage, the correspondence
is still very good, but not perfect.

---------------------------------------------------------
Title: Flux emergence rate in the quiet Sun from Sunrise data
Authors: Smitha, H. N.; Anusha, L. S.; Solanki, S. K.; Riethmüller,
T. L.
2017psio.confE.106S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Lambda-shaped jets from a penumbral intrusion into a sunspot
umbra: a possibility for magnetic reconnection
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
2017A&A...597A.127B Altcode:
We present the results of high resolution co-temporal and co-spatial
photospheric and chromospheric observations of sunspot penumbral
intrusions. The data were taken with the Swedish Solar Telescope
(SST) on the Canary Islands. Time series of Ca II H images show
a series of transient jets extending roughly 3000 km above a
penumbral intrusion into the umbra. For most of the time series,
jets were seen along the whole length of the intruding bright
filament. Some of these jets develop a clear λ-shaped structure,
with a small loop appearing at their footpoint and lasting for around
a minute. In the framework of earlier studies, the observed transient
λ shape of these jets suggests that they could be caused by magnetic
reconnection between a curved arcade-like or flux rope-like field in
the lower part of the penumbral intrusion and the more vertical umbral
magnetic field forming a cusp-shaped structure above the penumbral
intrusion. Movies associated to Figs. 1 and 2 are available at
<A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Handling Historical Ca II K Spectroheliogram Observation
Authors: Solanki, S. K.; Chatzistergos, T.; Ermolli, I.; Krivova, N.
2016AGUFMSA51B2429S Altcode:
The total solar irradiance has been continuously monitored since 1978,
but climate studies require time-series extending further back in
time. Models assuming that the irradiance variations are due to the
evolution of the solar surface magnetic field manifesting itself
as bright faculae and dark sunspots have been quite successful in
reproducing the measured changes. Unfortunately full-disk observations
of the magnetic field exist only for the last four decades. Sunspot
observations (areas or numbers) have been employed to reconstruct past
irradiance changes, however they provide information about the plage
regions only indirectly. Information about the evolution of the plage
regions can potentially be obtained from Ca II K spectroheliograms that
are available for the last century. Such observational programs have
been carried out at several observatories and some of these photographic
archives have been digitised. However, analysis of such data is plagued
by numerous problems affecting the images and the lack of photometric
calibration. Here we present a new method to process historical Ca II K
spectroheliograms in order to perform the photometric calibration and
compensate for the centre-to-limb variations and artefacts affecting
the data. The method is tested on synthetic images with known artefacts
and a sample of images from various historical archives.

---------------------------------------------------------
Title: Solar Total and Spectral Irradiance Reconstruction over Last
9000 Years
Authors: Wu, C. J.; Krivova, N.; Solanki, S. K.; Usoskin, I. G.
2016AGUFMSA51B2430W Altcode:
Although the mechanisms of solar influence on Earth climate system
are not yet fully understood, solar total and spectral irradiance are
considered to be among the main determinants. Solar total irradiance
is the total flux of solar radiative energy entering Earth's climate
system, whereas the spectral irradiance describes this energy is
distributed over the spectrum. Solar irradiance in the UV band is of
special importance since it governs chemical processes in the middle and
upper atmosphere. On timescales of the 11-year solar cycle and shorter,
solar irradiance is measured by space-based instruments while models
are needed to reconstruct solar irradiance on longer timescale. The
SATIRE-M model (Spectral And Total Irradiance Reconstruction over
millennia) is employed in this study to reconstruct solar irradiance
from decadal radionuclide isotope data such as 14C and 10Be stored in
tree rings and ice cores, respectively. A reconstruction over the last
9000 years will be presented.

---------------------------------------------------------
Title: Non-linear re-calibration of group sunspot number series back
to 1819
Authors: Chatzistergos, T.; Usoskin, I. G.; Kovaltsov, G.; Solanki,
S. K.; Krivova, N.
2016AGUFMSH31B2547C Altcode:
Sunspot numbers form the longest series of direct observations
that give information about the activity of the Sun. It consists in
numerous records from different observers with different instruments
and techniques, and unavoidably requires a calibration of individual
observers to a standard reference condition. Such calibrations pose a
challenge and are still a subject of debate. Most of the calibration
methods are based on a simple linear scaling of data from one observer
to the other, proposed in the mid-19th century by Rudolf Wolf. This
method is still used in many recent reconstructions. However, this
linear method is shown, on both real and synthetic data, to be
very rough and incorrect because of the essentially non-linearity
of the relation.Here we present a new reconstruction of the
group sunspot number series back to 1819 attempting to take into
account the non-linearity of the relation between data of different
observers. We use an approach incorporating several overlapping backbone
observers (similar to Svalgaard and Schatten, 2016) and perform the
straightforward non-linear calibration of each observer to the backbone
(and the backbones with each other) based on the actual statistics of
the common daily values.

---------------------------------------------------------
Title: Lower solar atmosphere and magnetism at ultra-high spatial
resolution
Authors: Collet, Remo; Criscuoli, Serena; Ermolli, Ilaria; Fabbian,
Damian; Guerreiro, Nuno; Haberreiter, Margit; Peck, Courtney; Pereira,
Tiago M. D.; Rempel, Matthias; Solanki, Sami K.; Wedemeyer-Boehm, Sven
2016arXiv161202348C Altcode:
We present the scientific case for a future space-based telescope
aimed at very high spatial and temporal resolution imaging of the
solar photosphere and chromosphere. Previous missions (e.g., HINODE,
SUNRISE) have demonstrated the power of observing the solar photosphere
and chromosphere at high spatial resolution without contamination from
Earth's atmosphere. We argue here that increased spatial resolution
(from currently 70 km to 25 km in the future) and high temporal cadence
of the observations will vastly improve our understanding of the
physical processes controlling solar magnetism and its characteristic
scales. This is particularly important as the Sun's magnetic field
drives solar activity and can significantly influence the Sun-Earth
system. At the same time a better knowledge of solar magnetism can
greatly improve our understanding of other astrophysical objects.

---------------------------------------------------------
Title: Far side Helioseismology with Solar Orbiter
Authors: Appourchaux, T.; Birch, A.; Gizon, L. C.; Löptien, B.;
Schou, J.; Solanki, S. K.; del Toro Iniesta, J. C.; Gandorfer, A.;
Hirzberger, J.; Alvarez-Herrero, A.; Woch, J. G.; Schmidt, W.
2016AGUFMSH43A2554A Altcode:
The Solar Orbiter mission, to be launched in October 2018, will
carry a suite of remote sensing and in-situ instruments, including
the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
high-cadence images of the Sun in intensity and Doppler velocity
suitable for carrying out novel helioseismic studies. The orbit
of the Solar Orbiter spacecraft will reach a solar latitude up to
34 degrees by the end of the extended mission and thus will enable
the first local helioseismology studies of the polar regions. The
full range of Earth-Sun-spacecraft angles provided by the orbit will
enable helioseismology from two vantage points by combining PHI with
another instrument: stereoscopic helioseismology will allow the study
of the deep solar interior and a better understanding of the physics
of solar oscillations in both quiet Sun and sunspots. In this paper
we will review the helioseismic objectives achievable with PHI, and
will also give a short status report of the development of the Flight
Model of PHI.

---------------------------------------------------------
Title: Relationship between supergranulation flows, magnetic
cancellation and network flares
Authors: Attie, R.; Innes, D. E.; Solanki, S. K.; Glassmeier, K. H.
2016A&A...596A..15A Altcode: 2017arXiv170510389A
Context. Photospheric flows create a network of often mixed-polarity
magnetic field in the quiet Sun, where small-scale eruptions and network
flares are commonly seen. Aims: The aim of this paper is (1)
to describe the characteristics of the flows that lead to these energy
releases, (2) to quantify the energy build up due to photospheric flows
acting on the magnetic field, and (3) to assess its contribution to the
energy of small-scale, short-lived X-ray flares in the quiet Sun. 
Methods: We used photospheric and X-ray data from the SoHO and Hinode
spacecraft combined with tracking algorithms to analyse the evolution
of five network flares. The energy of the X-ray emitting thermal plasma
is compared with an estimate of the energy built up due to converging
and sheared flux. Results: Quiet-Sun network flares occur above
sites of converging opposite-polarity magnetic flux that are often found
on the outskirts of network cell junctions, sometimes with observable
vortex-like motion. In all studied flares the thermal energy was more
than an order of magnitude higher than the magnetic free energy of the
converging flux model. The energy in the sheared field was always higher
than in the converging flux but still lower than the thermal energy. Conclusions: X-ray network flares occur at sites of magnetic energy
dissipation. The energy is probably built up by supergranular flows
causing systematic shearing of the magnetic field. This process appears
more efficient near the junction of the network lanes. Since this work
relies on 11 case studies, our results call for a follow-up statistical
analysis to test our hypothesis throughout the quiet Sun.

---------------------------------------------------------
Title: Slipping reconnection in a solar flare observed in high
resolution with the GREGOR solar telescope
Authors: Sobotka, M.; Dudík, J.; Denker, C.; Balthasar, H.; Jurčák,
J.; Liu, W.; Berkefeld, T.; Collados Vera, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Kuckein, C.; Lagg, A.; Louis, R. E.; von der Lühe, O.;
Nicklas, H.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.;
Volkmer, R.; Waldmann, T.
2016A&A...596A...1S Altcode: 2016arXiv160500464S
A small flare ribbon above a sunspot umbra in active region 12205 was
observed on November 7, 2014, at 12:00 UT in the blue imaging channel
of the 1.5 m GREGOR telescope, using a 1 Å Ca II H interference
filter. Context observations from the Atmospheric Imaging Assembly
(AIA) onboard the Solar Dynamics Observatory (SDO), the Solar Optical
Telescope (SOT) onboard Hinode, and the Interface Region Imaging
Spectrograph (IRIS) show that this ribbon is part of a larger one
that extends through the neighboring positive polarities and also
participates in several other flares within the active region. We
reconstructed a time series of 140 s of Ca II H images by means of the
multiframe blind deconvolution method, which resulted in spatial and
temporal resolutions of 0.1″ and 1 s. Light curves and horizontal
velocities of small-scale bright knots in the observed flare ribbon
were measured. Some knots are stationary, but three move along the
ribbon with speeds of 7-11 km s-1. Two of them move in the
opposite direction and exhibit highly correlated intensity changes,
which provides evidence of a slipping reconnection at small spatial
scales. Movies associated to Figs. 1 and 2 are available at <A
href="http://www.aanda.org/10.1051/0004-6361/201527966/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Deep probing of the photospheric sunspot penumbra: no evidence
of field-free gaps
Authors: Borrero, J. M.; Asensio Ramos, A.; Collados, M.;
Schlichenmaier, R.; Balthasar, H.; Franz, M.; Rezaei, R.; Kiess, C.;
Orozco Suárez, D.; Pastor Yabar, A.; Berkefeld, T.; von der Lühe,
O.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Soltau, D.; Volkmer, R.;
Waldmann, T.; Denker, C.; Hofmann, A.; Staude, J.; Strassmeier, K. G.;
Feller, A.; Lagg, A.; Solanki, S. K.; Sobotka, M.; Nicklas, H.
2016A&A...596A...2B Altcode: 2016arXiv160708165B
Context. Some models for the topology of the magnetic field in
sunspot penumbrae predict regions free of magnetic fields or with
only dynamically weak fields in the deep photosphere. Aims:
We aim to confirm or refute the existence of weak-field regions in
the deepest photospheric layers of the penumbra. Methods:
We investigated the magnetic field at log τ5 = 0 is
by inverting spectropolarimetric data of two different sunspots
located very close to disk center with a spatial resolution of
approximately 0.4-0.45”. The data have been recorded using the GRIS
instrument attached to the 1.5-m solar telescope GREGOR at the El
Teide observatory. The data include three Fe I lines around 1565 nm,
whose sensitivity to the magnetic field peaks half a pressure scale
height deeper than the sensitivity of the widely used Fe I spectral
line pair at 630 nm. Before the inversion, the data were corrected
for the effects of scattered light using a deconvolution method with
several point spread functions. Results: At log τ5
= 0 we find no evidence of regions with dynamically weak (B&lt;
500 Gauss) magnetic fields in sunspot penumbrae. This result is much
more reliable than previous investigations made on Fe I lines at 630
nm. Moreover, the result is independent of the number of nodes employed
in the inversion, is independent of the point spread function used to
deconvolve the data, and does not depend on the amount of stray light
(I.e., wide-angle scattered light) considered.

---------------------------------------------------------
Title: Spectropolarimetric observations of an arch filament system
with the GREGOR solar telescope
Authors: Balthasar, H.; Gömöry, P.; González Manrique, S. J.;
Kuckein, C.; Kavka, J.; Kučera, A.; Schwartz, P.; Vašková, R.;
Berkefeld, T.; Collados Vera, M.; Denker, C.; Feller, A.; Hofmann,
A.; Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pastor Yabar, A.;
Rezaei, R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth,
M.; Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1050B Altcode: 2016arXiv160901514B
Arch filament systems occur in active sunspot groups, where a fibril
structure connects areas of opposite magnetic polarity, in contrast to
active region filaments that follow the polarity inversion line. We
used the GREGOR Infrared Spectrograph (GRIS) to obtain the full
Stokes vector in the spectral lines Si I λ1082.7 nm, He I λ1083.0
nm, and Ca I λ1083.9 nm. We focus on the near-infrared calcium line
to investigate the photospheric magnetic field and velocities, and
use the line core intensities and velocities of the helium line to
study the chromospheric plasma. The individual fibrils of the arch
filament system connect the sunspot with patches of magnetic polarity
opposite to that of the spot. These patches do not necessarily coincide
with pores, where the magnetic field is strongest. Instead, areas are
preferred not far from the polarity inversion line. These areas exhibit
photospheric downflows of moderate velocity, but significantly higher
downflows of up to 30 km s-1 in the chromospheric helium
line. Our findings can be explained with new emerging flux where the
matter flows downward along the field lines of rising flux tubes,
in agreement with earlier results.

---------------------------------------------------------
Title: Magnetic fields of opposite polarity in sunspot penumbrae
Authors: Franz, M.; Collados, M.; Bethge, C.; Schlichenmaier, R.;
Borrero, J. M.; Schmidt, W.; Lagg, A.; Solanki, S. K.; Berkefeld,
T.; Kiess, C.; Rezaei, R.; Schmidt, D.; Sigwarth, M.; Soltau, D.;
Volkmer, R.; von der Luhe, O.; Waldmann, T.; Orozco, D.; Pastor Yabar,
A.; Denker, C.; Balthasar, H.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Feller, A.; Nicklas, H.; Kneer, F.; Sobotka, M.
2016A&A...596A...4F Altcode: 2016arXiv160800513F
Context. A significant part of the penumbral magnetic field returns
below the surface in the very deep photosphere. For lines in the
visible, a large portion of this return field can only be detected
indirectly by studying its imprints on strongly asymmetric and
three-lobed Stokes V profiles. Infrared lines probe a narrow layer
in the very deep photosphere, providing the possibility of directly
measuring the orientation of magnetic fields close to the solar
surface. Aims: We study the topology of the penumbral magnetic
field in the lower photosphere, focusing on regions where it returns
below the surface. Methods: We analyzed 71 spectropolarimetric
datasets from Hinode and from the GREGOR infrared spectrograph. We
inferred the quality and polarimetric accuracy of the infrared data
after applying several reduction steps. Techniques of spectral
inversion and forward synthesis were used to test the detection
algorithm. We compared the morphology and the fractional penumbral
area covered by reversed-polarity and three-lobed Stokes V profiles for
sunspots at disk center. We determined the amount of reversed-polarity
and three-lobed Stokes V profiles in visible and infrared data of
sunspots at various heliocentric angles. From the results, we computed
center-to-limb variation curves, which were interpreted in the context
of existing penumbral models. Results: Observations in visible
and near-infrared spectral lines yield a significant difference in the
penumbral area covered by magnetic fields of opposite polarity. In
the infrared, the number of reversed-polarity Stokes V profiles is
smaller by a factor of two than in the visible. For three-lobed Stokes
V profiles the numbers differ by up to an order of magnitude.

---------------------------------------------------------
Title: Horizontal flow fields in and around a small active region. The
transition period between flux emergence and decay
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016A&A...596A...3V Altcode: 2016arXiv160507462V
Context. The solar magnetic field is responsible for all aspects
of solar activity. Thus, emergence of magnetic flux at the surface
is the first manifestation of the ensuing solar activity. 
Aims: Combining high-resolution and synoptic observations aims to
provide a comprehensive description of flux emergence at photospheric
level and of the growth process that eventually leads to a mature
active region. Methods: The small active region NOAA 12118
emerged on 2014 July 17 and was observed one day later with the 1.5-m
GREGOR solar telescope on 2014 July 18. High-resolution time-series
of blue continuum and G-band images acquired in the blue imaging
channel (BIC) of the GREGOR Fabry-Pérot Interferometer (GFPI) were
complemented by synoptic line-of-sight magnetograms and continuum
images obtained with the Helioseismic and Magnetic Imager (HMI) onboard
the Solar Dynamics Observatory (SDO). Horizontal proper motions and
horizontal plasma velocities were computed with local correlation
tracking (LCT) and the differential affine velocity estimator (DAVE),
respectively. Morphological image processing was employed to measure
the photometric and magnetic area, magnetic flux, and the separation
profile of the emerging flux region during its evolution. 
Results: The computed growth rates for photometric area, magnetic
area, and magnetic flux are about twice as high as the respective
decay rates. The space-time diagram using HMI magnetograms of five days
provides a comprehensive view of growth and decay. It traces a leaf-like
structure, which is determined by the initial separation of the two
polarities, a rapid expansion phase, a time when the spread stalls,
and a period when the region slowly shrinks again. The separation
rate of 0.26 km s-1 is highest in the initial stage, and
it decreases when the separation comes to a halt. Horizontal plasma
velocities computed at four evolutionary stages indicate a changing
pattern of inflows. In LCT maps we find persistent flow patterns such
as outward motions in the outer part of the two major pores, a diverging
feature near the trailing pore marking the site of upwelling plasma and
flux emergence, and low velocities in the interior of dark pores. We
detected many elongated rapidly expanding granules between the two
major polarities, with dimensions twice as large as the normal granules.

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Title: A New Calibrated Sunspot Group Series Since 1749: Statistics
of Active Day Fractions
Authors: Usoskin, I. G.; Kovaltsov, G. A.; Lockwood, M.; Mursula,
K.; Owens, M.; Solanki, S. K.
2016SoPh..291.2685U Altcode: 2016SoPh..tmp....6U; 2015arXiv151206421U
Although sunspot-number series have existed since the mid-nineteenth
century, they are still the subject of intense debate, with the largest
uncertainty being related to the "calibration" of the visual acuity
of individual observers in the past. A daisy-chain regression method
is usually applied to inter-calibrate the observers, which may lead
to significant bias and error accumulation. Here we present a novel
method for calibrating the visual acuity of the key observers to the
reference data set of Royal Greenwich Observatory sunspot groups for the
period 1900 - 1976, using the statistics of the active-day fraction. For
each observer we independently evaluate their observational thresholds
[SS] defined such that the observer is assumed to miss all
of the groups with an area smaller than SS and report all
the groups larger than SS. Next, using a Monte-Carlo method,
we construct a correction matrix for each observer from the reference
data set. The correction matrices are significantly non-linear and
cannot be approximated by a linear regression or proportionality. We
emphasize that corrections based on a linear proportionality between
annually averaged data lead to serious biases and distortions of the
data. The correction matrices are applied to the original sunspot-group
records reported by the observers for each day, and finally the
composite corrected series is produced for the period since 1748. The
corrected series is provided as supplementary material in electronic
form and displays secular minima around 1800 (Dalton Minimum) and 1900
(Gleissberg Minimum), as well as the Modern Grand Maximum of activity in
the second half of the twentieth century. The uniqueness of the grand
maximum is confirmed for the last 250 years. We show that the adoption
of a linear relationship between the data of Wolf and Wolfer results
in grossly inflated group numbers in the eighteenth and nineteenth
centuries in some reconstructions.

---------------------------------------------------------
Title: Upper chromospheric magnetic field of a sunspot penumbra:
observations of fine structure
Authors: Joshi, J.; Lagg, A.; Solanki, S. K.; Feller, A.; Collados,
M.; Orozco Suárez, D.; Schlichenmaier, R.; Franz, M.; Balthasar,
H.; Denker, C.; Berkefeld, T.; Hofmann, A.; Kiess, C.; Nicklas, H.;
Pastor Yabar, A.; Rezaei, R.; Schmidt, D.; Schmidt, W.; Sobotka, M.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; von der Lühe,
O.; Waldmann, T.
2016A&A...596A...8J Altcode: 2016arXiv160801988J
 Aims: The fine-structure of the magnetic field in a sunspot
penumbra in the upper chromosphere is to be explored and compared
to that in the photosphere. Methods: Spectropolarimetric
observations with high spatial resolution were recorded with the 1.5-m
GREGOR telescope using the GREGOR Infrared Spectrograph (GRIS). The
observed spectral domain includes the upper chromospheric Hei triplet
at 10 830 Å and the photospheric Sii 10 827.1 Å and Cai 10 833.4 Å
spectral lines. The upper chromospheric magnetic field is obtained
by inverting the Hei triplet assuming a Milne-Eddington-type model
atmosphere. A height-dependent inversion was applied to the Sii 10
827.1 Å and Cai 10 833.4 Å lines to obtain the photospheric magnetic
field. Results: We find that the inclination of the magnetic
field varies in the azimuthal direction in the photosphere and in the
upper chromosphere. The chromospheric variations coincide remarkably
well with the variations in the inclination of the photospheric field
and resemble the well-known spine and interspine structure in the
photospheric layers of penumbrae. The typical peak-to-peak variations
in the inclination of the magnetic field in the upper chromosphere
are found to be 10°-15°, which is roughly half the variation in
the photosphere. In contrast, the magnetic field strength of the
observed penumbra does not vary on small spatial scales in the upper
chromosphere. Conclusions: Thanks to the high spatial resolution
of the observations that is possible with the GREGOR telescope at 1.08
microns, we find that the prominent small-scale fluctuations in the
magnetic field inclination, which are a salient part of the property
of sunspot penumbral photospheres, also persist in the chromosphere,
although at somewhat reduced amplitudes. Such a complex magnetic
configuration may facilitate penumbral chromospheric dynamic phenomena,
such as penumbral micro-jets or transient bright dots.

---------------------------------------------------------
Title: Active region fine structure observed at 0.08 arcsec resolution
Authors: Schlichenmaier, R.; von der Lühe, O.; Hoch, S.; Soltau, D.;
Berkefeld, T.; Schmidt, D.; Schmidt, W.; Denker, C.; Balthasar, H.;
Hofmann, A.; Strassmeier, K. G.; Staude, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Collados, M.; Sigwarth, M.; Volkmer, R.; Waldmann,
T.; Kneer, F.; Nicklas, H.; Sobotka, M.
2016A&A...596A...7S Altcode: 2016arXiv160707094S
Context. The various mechanisms of magneto-convective energy transport
determine the structure of sunspots and active regions. 
Aims: We characterise the appearance of light bridges and other
fine-structure details and elaborate on their magneto-convective
nature. Methods: We present speckle-reconstructed images taken
with the broad-band imager (BBI) at the 1.5 m GREGOR telescope in the
486 nm and 589 nm bands. We estimate the spatial resolution from the
noise characteristics of the image bursts and obtain 0.08″ at 589
nm. We describe structure details in individual best images as well
as the temporal evolution of selected features. Results: We
find branched dark lanes extending along thin (≈1″) light bridges
in sunspots at various heliocentric angles. In thick (≳ 2″) light
bridges the branches are disconnected from the central lane and have a Y
shape with a bright grain toward the umbra. The images reveal that light
bridges exist on varying intensity levels and that their small-scale
features evolve on timescales of minutes. Faint light bridges show
dark lanes outlined by the surrounding bright features. Dark lanes are
very common and are also found in the boundary of pores. They have a
characteristic width of 0.1″ or smaller. Intergranular dark lanes of
that width are seen in active region granulation. Conclusions: We
interpret our images in the context of magneto-convective simulations
and findings: while central dark lanes in thin light bridges are
elevated and associated with a density increase above upflows, the dark
lane branches correspond to locations of downflows and are depressed
relative to the adjacent bright plasma. Thick light bridges with central
dark lanes show no projection effect. They have a flat elevated plateau
that falls off steeply at the umbral boundary. There, Y-shaped filaments
form as they do in the inner penumbra. This indicates the presence of
inclined magnetic fields, meaning that the umbral magnetic field is
wrapped around the convective light bridge.

---------------------------------------------------------
Title: Probing deep photospheric layers of the quiet Sun with high
magnetic sensitivity
Authors: Lagg, A.; Solanki, S. K.; Doerr, H. -P.; Martínez González,
M. J.; Riethmüller, T.; Collados Vera, M.; Schlichenmaier, R.;
Orozco Suárez, D.; Franz, M.; Feller, A.; Kuckein, C.; Schmidt, W.;
Asensio Ramos, A.; Pastor Yabar, A.; von der Lühe, O.; Denker, C.;
Balthasar, H.; Volkmer, R.; Staude, J.; Hofmann, A.; Strassmeier,
K.; Kneer, F.; Waldmann, T.; Borrero, J. M.; Sobotka, M.; Verma, M.;
Louis, R. E.; Rezaei, R.; Soltau, D.; Berkefeld, T.; Sigwarth, M.;
Schmidt, D.; Kiess, C.; Nicklas, H.
2016A&A...596A...6L Altcode: 2016arXiv160506324L
Context. Investigations of the magnetism of the quiet Sun are hindered
by extremely weak polarization signals in Fraunhofer spectral
lines. Photon noise, straylight, and the systematically different
sensitivity of the Zeeman effect to longitudinal and transversal
magnetic fields result in controversial results in terms of the strength
and angular distribution of the magnetic field vector. Aims:
The information content of Stokes measurements close to the diffraction
limit of the 1.5 m GREGOR telescope is analyzed. We took the effects of
spatial straylight and photon noise into account. Methods: Highly
sensitive full Stokes measurements of a quiet-Sun region at disk center
in the deep photospheric Fe I lines in the 1.56 μm region were obtained
with the infrared spectropolarimeter GRIS at the GREGOR telescope. Noise
statistics and Stokes V asymmetries were analyzed and compared to a
similar data set of the Hinode spectropolarimeter (SOT/SP). Simple
diagnostics based directly on the shape and strength of the profiles
were applied to the GRIS data. We made use of the magnetic line ratio
technique, which was tested against realistic magneto-hydrodynamic
simulations (MURaM). Results: About 80% of the GRIS spectra
of a very quiet solar region show polarimetric signals above a 3σ
level. Area and amplitude asymmetries agree well with small-scale
surface dynamo-magneto hydrodynamic simulations. The magnetic line ratio
analysis reveals ubiquitous magnetic regions in the ten to hundred Gauss
range with some concentrations of kilo-Gauss fields. Conclusions:
The GRIS spectropolarimetric data at a spatial resolution of ≈0.̋4
are so far unique in the combination of high spatial resolution scans
and high magnetic field sensitivity. Nevertheless, the unavoidable
effect of spatial straylight and the resulting dilution of the weak
Stokes profiles means that inversion techniques still bear a high risk
of misinterpretating the data.

---------------------------------------------------------
Title: Flow and magnetic field properties in the trailing sunspots
of active region NOAA 12396
Authors: Verma, M.; Denker, C.; Böhm, F.; Balthasar, H.; Fischer,
C. E.; Kuckein, C.; Bello González, N.; Berkefeld, T.; Collados,
M.; Diercke, A.; Feller, A.; González Manrique, S. J.; Hofmann, A.;
Lagg, A.; Nicklas, H.; Orozco Suárez, D.; Pator Yabar, A.; Rezaei,
R.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.;
Sobotka, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K. G.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1090V Altcode:
Improved measurements of the photospheric and chromospheric
three-dimensional magnetic and flow fields are crucial for a precise
determination of the origin and evolution of active regions. We present
an illustrative sample of multi-instrument data acquired during a
two-week coordinated observing campaign in August 2015 involving,
among others, the GREGOR solar telescope (imaging and near-infrared
spectroscopy) and the space missions Solar Dynamics Observatory (SDO)
and Interface Region Imaging Spectrograph (IRIS). The observations
focused on the trailing part of active region NOAA 12396 with complex
polarity inversion lines and strong intrusions of opposite polarity
flux. The GREGOR Infrared Spectrograph (GRIS) provided Stokes IQUV
spectral profiles in the photospheric Si I λ1082.7 nm line, the
chromospheric He I λ1083.0 nm triplet, and the photospheric Ca I
λ1083.9 nm line. Carefully calibrated GRIS scans of the active region
provided maps of Doppler velocity and magnetic field at different
atmospheric heights. We compare quick-look maps with those obtained
with the “Stokes Inversions based on Response functions” (SIR)
code, which furnishes deeper insight into the magnetic properties
of the region. We find supporting evidence that newly emerging flux
and intruding opposite polarity flux are hampering the formation
of penumbrae, i.e., a penumbra fully surrounding a sunspot is only
expected after cessation of flux emergence in proximity to the sunspots.

---------------------------------------------------------
Title: Three-dimensional structure of a sunspot light bridge
Authors: Felipe, T.; Collados, M.; Khomenko, E.; Kuckein, C.; Asensio
Ramos, A.; Balthasar, H.; Berkefeld, T.; Denker, C.; Feller, A.;
Franz, M.; Hofmann, A.; Joshi, J.; Kiess, C.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Pastor Yabar, A.; Rezaei, R.; Schlichenmaier,
R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka, M.; Solanki,
S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.;
von der Lühe, O.; Waldmann, T.
2016A&A...596A..59F Altcode: 2016arXiv161104803F
Context. Active regions are the most prominent manifestations of solar
magnetic fields; their generation and dissipation are fundamental
problems in solar physics. Light bridges are commonly present during
sunspot decay, but a comprehensive picture of their role in the
removal of the photospheric magnetic field is still lacking. 
Aims: We study the three-dimensional configuration of a sunspot,
and in particular, its light bridge, during one of the last stages of
its decay. Methods: We present the magnetic and thermodynamical
stratification inferred from full Stokes inversions of the photospheric
Si I 10 827 Å and Ca I 10 839 Å lines obtained with the GREGOR
Infrared Spectrograph of the GREGOR telescope at the Observatorio del
Teide, Tenerife, Spain. The analysis is complemented by a study of
continuum images covering the disk passage of the active region, which
are provided by the Helioseismic and Magnetic Imager on board the Solar
Dynamics Observatory. Results: The sunspot shows a light bridge
with penumbral continuum intensity that separates the central umbra from
a smaller umbra. We find that in this region the magnetic field lines
form a canopy with lower magnetic field strength in the inner part. The
photospheric light bridge is dominated by gas pressure (high-β),
as opposed to the surrounding umbra, where the magnetic pressure
is higher. A convective flow is observed in the light bridge. This
flow is able to bend the magnetic field lines and to produce field
reversals. The field lines merge above the light bridge and become
as vertical and strong as in the surrounding umbra. We conclude that
this occurs because two highly magnetized regions approach each other
during the sunspot evolution. Movies associated to Figs. 2 and 13
are available at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Inference of magnetic fields in the very quiet Sun
Authors: Martínez González, M. J.; Pastor Yabar, A.; Lagg, A.;
Asensio Ramos, A.; Collados, M.; Solanki, S. K.; Balthasar, H.;
Berkefeld, T.; Denker, C.; Doerr, H. P.; Feller, A.; Franz, M.;
González Manrique, S. J.; Hofmann, A.; Kneer, F.; Kuckein, C.;
Louis, R.; von der Lühe, O.; Nicklas, H.; Orozco, D.; Rezaei, R.;
Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma, M.; Waldman,
T.; Volkmer, R.
2016A&A...596A...5M Altcode: 2018arXiv180410089M
Context. Over the past 20 yr, the quietest areas of the solar surface
have revealed a weak but extremely dynamic magnetism occurring
at small scales (&lt;500 km), which may provide an important
contribution to the dynamics and energetics of the outer layers of
the atmosphere. Understanding this magnetism requires the inference
of physical quantities from high-sensitivity spectro-polarimetric
data with high spatio-temporal resolution. Aims: We present
high-precision spectro-polarimetric data with high spatial resolution
(0.4”) of the very quiet Sun at 1.56 μm obtained with the GREGOR
telescope to shed some light on this complex magnetism. Methods:
We used inversion techniques in two main approaches. First, we assumed
that the observed profiles can be reproduced with a constant magnetic
field atmosphere embedded in a field-free medium. Second, we assumed
that the resolution element has a substructure with either two constant
magnetic atmospheres or a single magnetic atmosphere with gradients of
the physical quantities along the optical depth, both coexisting with
a global stray-light component. Results: Half of our observed
quiet-Sun region is better explained by magnetic substructure within
the resolution element. However, we cannot distinguish whether this
substructure comes from gradients of the physical parameters along the
line of sight or from horizontal gradients (across the surface). In
these pixels, a model with two magnetic components is preferred, and
we find two distinct magnetic field populations. The population with
the larger filling factor has very weak ( 150 G) horizontal fields
similar to those obtained in previous works. We demonstrate that the
field vector of this population is not constrained by the observations,
given the spatial resolution and polarimetric accuracy of our data. The
topology of the other component with the smaller filling factor is
constrained by the observations for field strengths above 250 G:
we infer hG fields with inclinations and azimuth values compatible
with an isotropic distribution. The filling factors are typically
below 30%. We also find that the flux of the two polarities is not
balanced. From the other half of the observed quiet-Sun area 50% are
two-lobed Stokes V profiles, meaning that 23% of the field of view
can be adequately explained with a single constant magnetic field
embedded in a non-magnetic atmosphere. The magnetic field vector and
filling factor are reliable inferred in only 50% based on the regular
profiles. Therefore, 12% of the field of view harbour hG fields with
filling factors typically below 30%. At our present spatial resolution,
70% of the pixels apparently are non-magnetised.

---------------------------------------------------------
Title: Fitting peculiar spectral profiles in He I 10830Å absorption
features
Authors: González Manrique, S. J.; Kuckein, C.; Pastor Yabar, A.;
Collados, M.; Denker, C.; Fischer, C. E.; Gömöry, P.; Diercke, A.;
Bello González, N.; Schlichenmaier, R.; Balthasar, H.; Berkefeld, T.;
Feller, A.; Hoch, S.; Hofmann, A.; Kneer, F.; Lagg, A.; Nicklas, H.;
Orozco Suárez, D.; Schmidt, D.; Schmidt, W.; Sigwarth, M.; Sobotka,
M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier, K. G.; Verma,
M.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016AN....337.1057G Altcode: 2016arXiv160300679G
The new generation of solar instruments provides better
spectral, spatial, and temporal resolution for a better
understanding of the physical processes that take place on the
Sun. Multiple-component profiles are more commonly observed with these
instruments. Particularly, the He I 10830 Å triplet presents such
peculiar spectral profiles, which give information on the velocity
and magnetic fine structure of the upper chromosphere. The purpose
of this investigation is to describe a technique to efficiently fit
the two blended components of the He I 10830 Å triplet, which are
commonly observed when two atmospheric components are located within
the same resolution element. The observations used in this study were
taken on 2015 April 17 with the very fast spectroscopic mode of the
GREGOR Infrared Spectrograph (GRIS) attached to the 1.5-m GREGOR solar
telescope, located at the Observatorio del Teide, Tenerife, Spain. We
apply a double-Lorentzian fitting technique using Levenberg-Marquardt
least-squares minimization. This technique is very simple and much
faster than inversion codes. Line-of-sight Doppler velocities can
be inferred for a whole map of pixels within just a few minutes. Our
results show sub- and supersonic downflow velocities of up to 32 km
s-1 for the fast component in the vicinity of footpoints of
filamentary structures. The slow component presents velocities close
to rest.

---------------------------------------------------------
Title: Variability Of The Sun And Sun-Like Stars On Different
Timescales
Authors: Solanki, Sami K.
2016csss.confE..16S Altcode:
Although many features can be seen moving across it at various
wavelengths, the Sun is an almost constant star with regard to its
radiative output. Its radiative variability has generally only been
discovered after the beginning of the space age. For Sun-like stars
it is easier to measure their small levels of variability from the
ground, leading to some unexpected discoveries that seemed to suggest
a behaviour rather different than that displayed by the Sun. However,
revisions of the measurements as well as advances in modelling have
in recent years shown that some of the main differences between the
Sun and stars can be reconciled. A much richer data set of short and
medium-term variability has been provided by the COROT and Kepler
missions. Although a number of exciting results have already been
obtained from these data, many more are expected in the coming years as
the data are more thoroughly analysed and models of solar variability
are extended to describe stars which, while similar to the Sun, are
not exact solar analogs.

---------------------------------------------------------
Title: The statistical study of global properties of sunspots observed
by SoHO/MDI continuum images over solar cycle 23
Authors: Goel, Suruchi; Krivova, Natalie; Solanki, Sami K.; Mathew,
Shibu K.
2016cosp...41E.687G Altcode:
A better understanding of inter-dependency of various sunspot parameters
such as magnetic field, intensity, temperature, size etc., and also
their variation with strength of solar activity cycle is important to
understand the magneto-convection process involved in sunspot formation
and evolution and hence to develop a consistent sunspot model. We have
investigated global sunspot properties using parameters of sunspots
identified from stray-light-corrected continuum images from SoHO/MDI
spanning from years 1996 to 2011. We find that the non-linear relation
between umbral core (minimum) intensity and sunspot area is best
represented by an exponential function, which reaches an asymptotic
value at 600 MSH. For the first time we have also observed that the
core intensity depends on shape of umbrae, i.e., circular umbrae
are statistically darker compared to the elongated ones. The core
intensity increases slightly towards the limb (by value of ~0.1 from
disk center to the limb). From sunspots sampled over the complete solar
cycle 23 and during the rising phase of cycle 24, we did not find any
solar-cycle variation in umbral core intensity. The penumbra to umbra
area ratio is found to be not a constant parameter, instead it shows a
quadratic decrease with sunspot area. Leading and following sunspots
usually have different morphological features, however in this study
we did not observe significant differences in their core intensity
and penumbra-umbra area ratio relation with the sunspot area.

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Title: Formation of the Penumbra and Start of the Evershed Flow
Authors: Murabito, M.; Romano, P.; Guglielmino, S. L.; Zuccarello,
F.; Solanki, S. K.
2016ApJ...825...75M Altcode: 2016arXiv160405610M
We studied the variations of line of sight photospheric plasma flows
during the formation phase of the penumbra around a pore in active
region NOAA 11490. We used a high spatial, spectral, and temporal
resolution data set acquired by the Interferometric BIdimensional
Spectrometer operating at the NSO/Dunn Solar Telescope as well as
data taken by the Helioseismic and Magnetic Imager on board the
Solar Dynamics Observatory satellite (SDO/HMI). Before the penumbra
formed we observed a redshift of the spectral line in the inner part
of the annular zone surrounding the pore as well as a blueshift of
material associated with opposite magnetic polarity farther away from
the pore. We found that the onset of the classical Evershed flow
occurs on a very short timescale (1 to 3 hr) while the penumbra is
forming. During the same time interval we found changes in the magnetic
field inclination in the penumbra, with the vertical field actually
changing sign near the penumbral edge, while the total magnetic field
showed a significant increase, about 400 G. To explain these and other
observations related to the formation of the penumbra and the onset
of the Evershed flow we propose a scenario in which the penumbra is
formed by magnetic flux dragged down from the canopy surrounding the
initial pore. The Evershed flow starts when the sinking magnetic field
dips below the solar surface and magnetoconvection sets in.

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Title: Solar total and spectral irradiance reconstruction over last
9000 years
Authors: Wu, Chi-Ju; Usoskin, Ilya; Krivova, Natalie; Solanki, Sami K.
2016cosp...41E2072W Altcode:
Although the mechanisms of solar influence on Earth climate system
are not yet fully understood, solar total and spectral irradiance are
considered to be among the main determinants. Solar total irradiance
is the total flux of solar radiative energy entering Earth's climate
system, whereas the spectral irradiance describes this energy is
distributed over the spectrum. Solar irradiance in the UV band is of
special importance since it governs chemical processes in the middle and
upper atmosphere. On timescales of the 11-year solar cycle and shorter,
solar irradiance is measured by space-based instruments while models
are needed to reconstruct solar irradiance on longer timescale. The
SATIRE-M model (Spectral And Total Irradiance Reconstruction over
millennia) is employed in this study to reconstruct solar irradiance
from decadal radionuclide isotope data such as 14C and 10Be stored in
tree rings and ice cores, respectively. A reconstruction over the last
9000 years will be presented.

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Title: The Solar Ultraviolet Imaging Telescope onboard Aditya-L1
Authors: Ghosh, Avyarthana; Chatterjee, Subhamoy; Khan, Aafaque R.;
Tripathi, Durgesh; Ramaprakash, A. N.; Banerjee, Dipankar; Chordia,
Pravin; Gandorfer, Achim M.; Krivova, Natalie; Nandy, Dibyendu;
Rajarshi, Chaitanya; Solanki, Sami K.; Sriram, S.
2016SPIE.9905E..03G Altcode:
The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument onboard
the Aditya-L1 spacecraft, the first dedicated solar mission of the
Indian Space Research Organization (ISRO), which will be put in a
halo orbit at the Sun-Earth Langrage point (L1). SUIT has an off-axis
Ritchey-Chrétien configuration with a combination of 11 narrow and
broad bandpass filters which will be used for full-disk solar imaging
in the Ultravoilet (UV) wavelength range 200-400 nm. It will provide
near simultaneous observations of lower and middle layers of the solar
atmosphere, namely the Photosphere and Chromosphere. These observations
will help to improve our understanding of coupling and dynamics of
various layers of the solar atmosphere, mechanisms responsible for
stability, dynamics and eruption of solar prominences and Coronal Mass
ejections, and possible causes of solar irradiance variability in the
Near and Middle UV regions, which is of central interest for assessing
the Sun's influence on climate.

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Title: Long-term solar irradiance variability: knowns and unknowns
Authors: Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria;
Leng Yeo, Kok; Wu, Chi-Ju
2016cosp...41E1066K Altcode:
Long-term reconstructions of solar irradiance variability are crucial
to our understanding of solar influence on climate. They are only
possible with the help of suitable models, which in turn require a
thorough understanding of the mechanisms of this variability. With the
advance of such models, also the past reconstructions are becoming
more reliable. Nevertheless, the remaining uncertainties spread out
when extrapolating back over long periods of time, amplified by the
increasingly poorer quality and reliability of the available data that
bear information on past solar activity. We will discuss the progress
and the reliability of irradiance reconstructions on time scales of
decades to millennia.

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Title: EMPIRE reconstruction of TSI and SSI since 1947
Authors: Leng Yeo, Kok; Krivova, Natalie; Solanki, Sami K.
2016cosp...41E2107L Altcode:
TSI and SSI, at least in the UV, have been monitored from space
since 1978. This is accompanied by the development of models aimed
at reproducing TSI and SSI by relating the variability to solar
magnetism. We present a reconstruction of TSI and SSI, spanning 1947
to 2016, based on the EMPirical Irradiance REconstruction (EMPIRE)
model. EMPIRE is what is termed a proxy model, based on the regression
of solar activity indices to measured solar irradiance. One of the main
open questions in our understanding of solar irradiance variability,
and consequently its influence on the Earth's climate, is the
variation in UV SSI over the solar cycle. Solar cycle variability
in UV SSI in preceding proxy models, such as NRLSSI, NRLSSI2 and
MGNM, is significantly weaker than that indicated by other types
of models longwards of around 240 nm. We demonstrate here that this
discrepancy arises from previous proxy models neglecting the influence
of measurement uncertainty on regression analyses. EMPIRE is based
on the same activity indices as NRLSSI(2) but by taking measurement
uncertainty into account, reproduces variability consistent with other
modelling approaches and measurements. As such, EMPIRE supersedes
earlier proxy models, including NRLSSI(2) and MGNM.

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Title: Solar electromagnetic emission and climate
Authors: Solanki, Sami K.
2016cosp...41E1831S Altcode:
Ever since the first solar radiometer flew in space it has been known
that the level of emission of electromagnetic radiation from the Sun
(the Sun's total irradiance) varies with time. This record now covers
roughly 3.5 solar cycles. With time the quality of the observations has
improved and the set of quantities that are observed have increased
(now including the spectral solar irradiance over a wide range of
wavelengths). At the same time, our understanding of the processes
leading to variations in the Sun's radiative output and our ability to
model such variations quantitatively have steadily improved, so that
we are at a stage where we can reconstruct solar total and spectral
irradiance over most of the Holocene, with increasing accuracy the
closer we come to recent decades. The variable solar radiative output
drives changes in the Earth's atmosphere, with such changes being
well-documented in the upper and middle atmosphere of the Earth and
becoming increasingly more subtle with depth in the atmosphere. In
particular, uncovering the influence of the variable Sun on the
troposphere, where the Earth's climate change mainly plays out, is
a challenging task. In this talk an overview will be given of the
chain from the Sun to the Earth, with the emphasis lying more on the
solar part.

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Title: The origin of Total Solar Irradiance variability on timescales
less than a day
Authors: Shapiro, Alexander; Krivova, Natalie; Schmutz, Werner;
Solanki, Sami K.; Leng Yeo, Kok; Cameron, Robert; Beeck, Benjamin
2016cosp...41E1774S Altcode:
Total Solar Irradiance (TSI) varies on timescales from minutes to
decades. It is generally accepted that variability on timescales of
a day and longer is dominated by solar surface magnetic fields. For
shorter time scales, several additional sources of variability have
been proposed, including convection and oscillation. However, available
simplified and highly parameterised models could not accurately explain
the observed variability in high-cadence TSI records. We employed the
high-cadence solar imagery from the Helioseismic and Magnetic Imager
onboard the Solar Dynamics Observatory and the SATIRE (Spectral And
Total Irradiance Reconstruction) model of solar irradiance variability
to recreate the magnetic component of TSI variability. The recent 3D
simulations of solar near-surface convection with MURAM code have been
used to calculate the TSI variability caused by convection. This allowed
us to determine the threshold timescale between TSI variability caused
by the magnetic field and convection. Our model successfully replicates
the TSI measurements by the PICARD/PREMOS radiometer which span the
period of July 2010 to February 2014 at 2-minute cadence. Hence,
we demonstrate that solar magnetism and convection can account for
TSI variability at all timescale it has ever been measured (sans the
5-minute component from p-modes).

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Title: Modelling the Spectral Contrasts of Stellar Faculae.
Authors: Norris, Charlotte M.; Beeck, Benjamin; Unruh, Yvonne; Solanki,
Sami; Yeo, Kok Leng; Krivova, Natalie
2016csss.confE..63N Altcode:
Facular contrasts are an important parameter in modelling stellar
variability and exoplanet transits. The ultimate goal of this work
will be to model the contrasts of faculae for different spectral types
and thus improve the modelling of solar and stellar photospheric
variability. This is done by using a radiative transfer algorithm
(ATLAS9) on magneto-convection simulations. Starting with solar twins,
we derive facular contrasts as a function of limb angle and discuss
their wavelength dependence.

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Title: Diagnostics of Coronal Magnetic Fields Through the Hanle
Effect in UV and IR Lines
Authors: Raouafi, Nour E.; Riley, Pete; Gibson, Sarah; Fineschi,
Silvano; Solanki, Sami K.
2016FrASS...3...20R Altcode: 2016arXiv160608493R
The plasma thermodynamics in the solar upper atmosphere, particularly in
the corona, are dominated by the magnetic field, which controls the flow
and dissipation of energy. The relative lack of knowledge of the coronal
vector magnetic field is a major handicap for progress in coronal
physics. This makes the development of measurement methods of coronal
magnetic fields a high priority in solar physics. The Hanle effect in
the UV and IR spectral lines is a largely unexplored diagnostic. We
use magnetohydrodynamic (MHD) simulations to study the magnitude of the
signal to be expected for typical coronal magnetic fields for selected
spectral lines in the UV and IR wavelength ranges, namely the HI Ly-α
and the He I 10830 Å lines. We show that the selected lines are useful
for reliable diagnosis of coronal magnetic fields. The results show
that the combination of polarization measurements of spectral lines
with different sensitivities to the Hanle effect may be most appropriate
for deducing coronal magnetic properties from future observations.

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Title: Formation of a solar Hα filament from orphan penumbrae
Authors: Buehler, D.; Lagg, A.; van Noort, M.; Solanki, S. K.
2016A&A...589A..31B Altcode: 2016arXiv160305899B
 Aims: The formation and evolution of an Hα filament in active
region (AR) 10953 is described. Methods: Observations from the
Solar Optical Telescope (SOT) aboard the Hinode satellite starting
from UT 18:09 on 27th April 2007 until UT 06:08 on 1st May 2007 were
analysed. 20 scans of the 6302 Å Fe I line pair recorded by SOT/SP were
inverted using the spatially coupled version of the SPINOR code. The
inversions were analysed together with co-spatial SOT/BFI G-band and
Ca II H and SOT/NFI Hα observations. Results: Following the
disappearance of an initial Hα filament aligned along the polarity
inversion line (PIL) of the AR, a new Hα filament formed in its place
some 20 h later, which remained stable for, at least, another 1.5
days. The creation of the new Hα filament was driven by the ascent of
horizontal magnetic fields from the photosphere into the chromosphere
at three separate locations along the PIL. The magnetic fields at
two of these locations were situated directly underneath the initial
Hα filament and formed orphan penumbrae already aligned along the Hα
filament channel. The 700 G orphan penumbrae were stable and trapped in
the photosphere until the disappearance of the overlying initial Hα
filament, after which they started to ascend into the chromosphere at
10 ± 5 m/s. Each ascent was associated with a simultaneous magnetic
flux reduction of up to 50% in the photosphere. The ascended orphan
penumbrae formed dark seed structures in Hα in parallel with the PIL,
which elongated and merged to form an Hα filament. The filament channel
featured horizontal magnetic fields of on average 260 G at log (τ) =
-2 suspended above the nearly field-free lower photosphere. The fields
took on an overall inverse configuration at log (τ) = -2 suggesting
a flux rope topology for the new Hα filament. The destruction of the
initial Hα filament was likely caused by the flux emergence at the
third location along the PIL. Conclusions: We present a new
interpretation of the Hα filament formation in AR 10953 whereby the
mainly horizontal fields of orphan penumbrae, aligned along the Hα
filament channel, ascend into the chromosphere, forming seed fragments
for a new, second Hα filament. The orphan penumbral fields ascend
into the chromosphere ~9-24 h before the Hα filament is fully formed.

---------------------------------------------------------
Title: Reconstruction of spectral solar irradiance since 1700 from
simulated magnetograms
Authors: Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.;
Unruh, Y. C.; Yeo, K. L.
2016A&A...590A..63D Altcode: 2016arXiv160502039D
 Aims: We present a reconstruction of the spectral solar
irradiance since 1700 using the SATIRE-T2 (Spectral And Total Irradiance
REconstructions for the Telescope era version 2) model. This model
uses as input magnetograms simulated with a surface flux transport
model fed with semi-synthetic records of emerging sunspot groups. Methods: The record of sunspot group areas and positions from the
Royal Greenwich Observatory (RGO) is only available since 1874. We
used statistical relationships between the properties of sunspot
group emergence, such as the latitude, area, and tilt angle, and the
sunspot cycle strength and phase to produce semi-synthetic sunspot
group records starting in the year 1700. The semi-synthetic records
are fed into a surface flux transport model to obtain daily simulated
magnetograms that map the distribution of the magnetic flux in active
regions (sunspots and faculae) and their decay products on the solar
surface. The magnetic flux emerging in ephemeral regions is accounted
for separately based on the concept of extended cycles whose length
and amplitude are linked to those of the sunspot cycles through the
sunspot number. The magnetic flux in each surface component (sunspots,
faculae and network, and ephemeral regions) was used to compute the
spectral and total solar irradiance (TSI) between the years 1700
and 2009. This reconstruction is aimed at timescales of months or
longer although the model returns daily values. Results: We
found that SATIRE-T2, besides reproducing other relevant observations
such as the total magnetic flux, reconstructs the TSI on timescales
of months or longer in good agreement with the PMOD composite of
observations, as well as with the reconstruction starting in 1878
based on the RGO-SOON data. The model predicts an increase in the TSI
of 1.2+0.2-0.3 Wm-2 between 1700
and the present. The spectral irradiance reconstruction is in good
agreement with the UARS/SUSIM measurements as well as the Lyman-α
composite. The complete total and spectral (115 nm-160 μm)
irradiance reconstructions since 1700 will be available from <A
href="http://www2.mps.mpg.de/projects/sun-climate/data.html">http://www2.mps.mpg.de/projects/sun-climate/data.html</A>

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Title: High-resolution, high-sensitivity, ground-based solar
spectropolarimetry with a new fast imaging polarimeter. I. Prototype
characterization
Authors: Iglesias, F. A.; Feller, A.; Nagaraju, K.; Solanki, S. K.
2016A&A...590A..89I Altcode: 2016arXiv160401521I
Context. Remote sensing of weak and small-scale solar magnetic fields is
of utmost relevance when attempting to respond to a number of important
open questions in solar physics. This requires the acquisition of
spectropolarimetric data with high spatial resolution (~10-1
arcsec) and low noise (10-3 to 10-5 of the
continuum intensity). The main limitations to obtain these measurements
from the ground, are the degradation of the image resolution produced
by atmospheric seeing and the seeing-induced crosstalk (SIC). Aims: We introduce the prototype of the Fast Solar Polarimeter
(FSP), a new ground-based, high-cadence polarimeter that tackles the
above-mentioned limitations by producing data that are optimally suited
for the application of post-facto image restoration, and by operating
at a modulation frequency of 100 Hz to reduce SIC. Methods:
We describe the instrument in depth, including the fast pnCCD camera
employed, the achromatic modulator package, the main calibration steps,
the effects of the modulation frequency on the levels of seeing-induced
spurious signals, and the effect of the camera properties on the image
restoration quality. Results: The pnCCD camera reaches 400
fps while keeping a high duty cycle (98.6%) and very low noise (4.94
e- rms). The modulator is optimized to have high (&gt;80%)
total polarimetric efficiency in the visible spectral range. This allows
FSP to acquire 100 photon-noise-limited, full-Stokes measurements per
second. We found that the seeing induced signals that are present in
narrow-band, non-modulated, quiet-sun measurements are (a) lower than
the noise (7 × 10-5) after integrating 7.66 min, (b) lower
than the noise (2.3 × 10-4) after integrating 1.16 min and
(c) slightly above the noise (4 × 10-3) after restoring
case (b) by means of a multi-object multi-frame blind deconvolution. In
addition, we demonstrate that by using only narrow-band images (with
low S/N of 13.9) of an active region, we can obtain one complete set
of high-quality restored measurements about every 2 s.

---------------------------------------------------------
Title: Are solar brightness variations faculae- or spot-dominated?
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Yeo, K. L.;
Schmutz, W. K.
2016A&A...589A..46S Altcode: 2016arXiv160204447S
Context. Regular spaceborne measurements have revealed that
solar brightness varies on multiple timescales, variations on
timescales greater than a day being attributed to a surface magnetic
field. Independently, ground-based and spaceborne measurements suggest
that Sun-like stars show a similar, but significantly broader pattern
of photometric variability. Aims: To understand whether the
broader pattern of stellar variations is consistent with the solar
paradigm, we assess relative contributions of faculae and spots to
solar magnetically-driven brightness variability. We investigate
how the solar brightness variability and its facular and spot
contributions depend on the wavelength, timescale of variability,
and position of the observer relative to the ecliptic plane. 
Methods: We performed calculations with the SATIRE model, which
returns solar brightness with daily cadence from solar disc area
coverages of various magnetic features. We took coverages as seen by
an Earth-based observer from full-disc SoHO/MDI and SDO/HMI data and
projected them to mimic out-of-ecliptic viewing by an appropriate
transformation. Results: Moving the observer away from the
ecliptic plane increases the amplitude of 11-year variability as it
would be seen in Strömgren (b + y)/2 photometry, but decreases the
amplitude of the rotational brightness variations as it would appear
in Kepler and CoRoT passbands. The spot and facular contributions to
the 11-year solar variability in the Strömgren (b + y)/2 photometry
almost fully compensate each other so that the Sun appears anomalously
quiet with respect to its stellar cohort. Such a compensation does not
occur on the rotational timescale. Conclusions: The rotational
solar brightness variability as it would appear in the Kepler and
CoRoT passbands from the ecliptic plane is spot-dominated, but the
relative contribution of faculae increases for out-of-ecliptic viewing
so that the apparent brightness variations are faculae-dominated for
inclinations less than about I = 45°. Over the course of the 11-year
activity cycle, the solar brightness variability is faculae-dominated
shortwards of 1.2 μm independently of the inclination.

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Title: An update on the Axion Helioscopes front: current activities
at CAST and the IAXO project
Authors: Dafni, T.; Arik, M.; Armengaud, E.; Aune, S.; Avignone, F. T.;
Barth, K.; Belov, A.; Betz, M.; Bräuninger, H.; Brax, P.; Breijnholt,
N.; Brun, P.; Cantatore, G.; Carmona, J. M.; Carosi, G. P.; Caspers,
F.; Caspi, S.; Cetin, S. A.; Chelouche, D.; Christensen, F. E.;
Collar, J. I.; Dael, A.; Davenport, M.; Derbin, A. V.; Desch, K.;
Diago, A.; Döbrich, B.; Dratchnev, I.; Dudarev, A.; Eleftheriadis, C.;
Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.; Galán, J.; García,
J. A.; Gardikiotis, A.; Garza, J. G.; Gazis, E. N.; Georgiopoulou,
E.; Geralis, T.; Gimeno, B.; Giomataris, I.; Gninenko, S.; Gómez,
H.; González-Díaz, D.; Gruber, E.; Guendelman, E.; Guthörl, T.;
Hailey, C. J.; Hartmann, R.; Hauf, S.; Haug, F.; Hasinoff, M. D.;
Hiramatsu, T.; Hoffmann, D. H. H.; Horns, D.; Iguaz, F. J.; Irastorza,
I. G.; Isern, J.; Imai, K.; Jacoby, J.; Jaeckel, J.; Jakobsen, A. C.;
Jakovčić, K.; Kaminski, J.; Kawasaki, M.; Karuza, M.; Königsmann,
K.; Kotthaus, R.; Krčmar, M.; Kousouris, K.; Krieger, C.; Kuster, M.;
Lakić, B.; Laurent, J. M.; Limousin, O.; Lindner, A.; Liolios, A.;
Ljubičić, A.; Luzón, G.; Matsuki, S.; Muratova, V. N.; Neff, S.;
Niinikoski, T.; Nones, C.; Ortega, I.; Papaevangelou, T.; Pivovaroff,
M. J.; Raffelt, G.; Redondo, J.; Riege, H.; Ringwald, A.; Rodríguez,
A.; Rosu, M.; Russenschuck, S.; Ruz, J.; Saikawa, K.; Savvidis, I.;
Sekiguchi, T.; Semertzidis, Y. K.; Shilon, I.; Sikivie, P.; Silva,
H.; Solanki, S. K.; Stewart, L.; ten Kate, H. H. J.; Tomas, A.;
Troitsky, S.; Vafeiadis, T.; van Bibber, K.; Vedrine, P.; Villar,
J. A.; Vogel, J. K.; Walckiers, L.; Weltman, A.; Wester, W.; Yildiz,
S. C.; Zioutas, K.
2016NPPP..273..244D Altcode:
Although they have not yet been detected, axions and axion-like
particles (ALPs) continue to maintain the interest (even increasingly
so) of the rare-event searches community as viable candidates for the
Dark Matter of the Universe but also as a solution for several other
puzzles of astrophysics. Their property of coupling to photons has
inspired different experimental methods for their detection, one of
which is the helioscope technique. The CERN Axion Solar Telescope
(CAST) is the most sensitive helioscope built up to date and has
recently published part of the latest data taken with the magnet
bores gradually filled with 3He, probing the mass range
up to 1.17 eV. The International AXion Observatory (IAXO) is being
proposed as a facility where different axion studies can be performed,
with the primary goal to study axions coming from the Sun. Designed to
maximize sensitivity, it will improve the levels reached by CAST by
almost 5 orders of magnitude in signal detection, that is more than
one order of magnitude in terms of gaγ. Here
we will summarize the most important aspects of the helioscopes,
and focus mainly on IAXO, based on the recent papers [1, 2].

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Title: Modelling Solar and Stellar Brightness Variabilities
Authors: Yeo, K. L.; Shapiro, A. I.; Krivova, N. A.; Solanki, S. K.
2016ASPC..504..273Y Altcode:
Total and spectral solar irradiance, TSI and SSI, have been measured
from space since 1978. This is accompanied by the development of
models aimed at replicating the observed variability by relating
it to solar surface magnetism. Despite significant progress,
there remains persisting controversy over the secular change and the
wavelength-dependence of the variation with impact on our understanding
of the Sun's influence on the Earth's climate. We highlight the recent
progress in TSI and SSI modelling with SATIRE. Brightness variations
have also been observed for Sun-like stars. Their analysis can profit
from knowledge of the solar case and provide additional constraints
for solar modelling. We discuss the recent effort to extend SATIRE to
Sun-like stars.

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Title: Flows in and around Active Region NOAA12118 Observed with
the GREGOR Solar Telescope and SDO/HMI
Authors: Verma, M.; Denker, C.; Balthasar, H.; Kuckein, C.; González
Manrique, S. J.; Sobotka, M.; Bello González, N.; Hoch, S.; Diercke,
A.; Kummerow, P.; Berkefeld, T.; Collados, M.; Feller, A.; Hofmann,
A.; Kneer, F.; Lagg, A.; Löhner-Böttcher, J.; Nicklas, H.; Pastor
Yabar, A.; Schlichenmaier, R.; Schmidt, D.; Schmidt, W.; Schubert,
M.; Sigwarth, M.; Solanki, S. K.; Soltau, D.; Staude, J.; Strassmeier,
K.; Volkmer, R.; von der Lühe, O.; Waldmann, T.
2016ASPC..504...29V Altcode: 2016arXiv160301109V
Accurate measurements of magnetic and velocity fields in and around
solar active regions are key to unlocking the mysteries of the
formation and the decay of sunspots. High spatial resolution images
and spectral sequences with a high cadence obtained with the GREGOR
solar telescope give us an opportunity to scrutinize 3-D flow fields
with local correlation tracking and imaging spectroscopy. We present
GREGOR early science data acquired in 2014 July - August with the GREGOR
Fabry-Pérot Interferometer and the Blue Imaging Channel. Time-series
of blue continuum (λ 450.6 nm) images of the small active region
NOAA 12118 were restored with the speckle masking technique to derive
horizontal proper motions and to track the evolution of morphological
changes. In addition, high-resolution observations are discussed in
the context of synoptic data from the Solar Dynamics Observatory.

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Title: Solar Science with the Atacama Large Millimeter/Submillimeter
Array—A New View of Our Sun
Authors: Wedemeyer, S.; Bastian, T.; Brajša, R.; Hudson, H.;
Fleishman, G.; Loukitcheva, M.; Fleck, B.; Kontar, E. P.; De Pontieu,
B.; Yagoubov, P.; Tiwari, S. K.; Soler, R.; Black, J. H.; Antolin,
P.; Scullion, E.; Gunár, S.; Labrosse, N.; Ludwig, H. -G.; Benz,
A. O.; White, S. M.; Hauschildt, P.; Doyle, J. G.; Nakariakov, V. M.;
Ayres, T.; Heinzel, P.; Karlicky, M.; Van Doorsselaere, T.; Gary,
D.; Alissandrakis, C. E.; Nindos, A.; Solanki, S. K.; Rouppe van
der Voort, L.; Shimojo, M.; Kato, Y.; Zaqarashvili, T.; Perez, E.;
Selhorst, C. L.; Barta, M.
2016SSRv..200....1W Altcode: 2015SSRv..tmp..118W; 2015arXiv150406887W
The Atacama Large Millimeter/submillimeter Array (ALMA) is a new
powerful tool for observing the Sun at high spatial, temporal, and
spectral resolution. These capabilities can address a broad range
of fundamental scientific questions in solar physics. The radiation
observed by ALMA originates mostly from the chromosphere—a complex
and dynamic region between the photosphere and corona, which plays a
crucial role in the transport of energy and matter and, ultimately,
the heating of the outer layers of the solar atmosphere. Based on
first solar test observations, strategies for regular solar campaigns
are currently being developed. State-of-the-art numerical simulations
of the solar atmosphere and modeling of instrumental effects can help
constrain and optimize future observing modes for ALMA. Here we present
a short technical description of ALMA and an overview of past efforts
and future possibilities for solar observations at submillimeter and
millimeter wavelengths. In addition, selected numerical simulations
and observations at other wavelengths demonstrate ALMA's scientific
potential for studying the Sun for a large range of science cases.

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Title: Exploiting Four Historical Ca II K Spectroheliogram Archives
Authors: Chatzistergos, T.; Ermolli, I.; Solanki, S. K.; Krivova, N. A.
2016ASPC..504..227C Altcode:
Here we briefly review the status of the project aimed to analyse
the potential of historical Ca II K archives for studies of long-term
(decades to a century) solar variability.

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Title: Fast Solar Polarimeter: Prototype Characterization and
First Results
Authors: Iglesias, F. A.; Feller, A.; Krishnappa, N.; Solanki, S. K.
2016ASPC..504..325I Altcode:
Due to the differential and non-simultaneous nature of polarization
measurements, seeing induced crosstalk (SIC) and seeing limited spatial
resolution can easily counterbalance the benefits of solar imaging
polarimetry from the ground. The development of instrumental techniques
to treat these issues is necessary to fully exploit the next generation
of large-aperture solar facilities, and maintain ground-based data at
a competitive level with respect to its space-based counterpart. In
particular, considering that many open questions in modern solar
physics demand data with challenging specifications of resolution
and polarimetric sensitivity that can only be achieved with large
telescope apertures (Stenflo 1999). Even if state-of-the-art adaptive
optics systems greatly improve image quality, their limited correction
—due to finite bandwidth, mode number and seeing anisoplanat-
ism— produces large residual values of SIC (Krishnappa &amp; Feller
2012). Dual beam polarimeters are commonly used to reduce SIC between
the intensity and polarization signals, however, they cannot compensate
for the SIC introduced between circular and linear polarization,
which can be relevant for high-precision polarimetry. It is known
that fast modulation effectively reduces SIC, but the demodulation of
the corresponding intensity signals imposes hard requirements on the
frame rate of the associated cameras. One way to avoid a fast sensor,
is to decouple the camera readout from the intensity demodulation
step. This concept is the cornerstone of the very successful Zurich
Imaging Polarimeter (ZIMPOL). Even though the ZIMPOL solution allows
the detection of very faint signals (∼10-5), its design is
not suitable for high-spatial-resolution applications. We are developing
a polarimeter that focuses on both spatial resolution (&lt;0.5 arcsec)
and polarimetric sensitivity (10-4). The prototype of this
Fast Solar Polarimeter (FSP, see Feller et al. 2014), employs a high
frame-rate (400 fps), low-noise (&lt;4 e- RMS), pnCCD camera (Hartmann
et al. 2006) that is read in synchronization with a polarization
modulator based on ferroelectric liquid crystals. The modulator package
is similar to the SOLIS (Keller et al. 2003) design and optimized to
have an achromatic total polarimetric efficiency above 80 % in the
400-700 nm wavelength range. The fast modulation frequency of FSP,
yielding up to 100 full-Stokes measurements per second, and high duty
cycle (&gt;95%), have the double benefit of reducing seeing induced
artifacts and improving the final spatial resolution by providing an
optimal regime for the application of post-facto image reconstruction
techniques. In this poster we describe the FSP prototype, including
the characterization results, a technique to correct image smearing
due to the sensor frame transfer (Iglesias et al. 2015) and some of
the first measurements obtained with the 68-cm Vacuum Tower Telescope
located at the Observatorio del Teide, Spain.

---------------------------------------------------------
Title: Variation of the Mn I 539.4 nm line with the solar cycle
Authors: Danilovic, S.; Solanki, S. K.; Livingston, W.; Krivova, N.;
Vince, I.
2016A&A...587A..33D Altcode: 2015arXiv151101286D
Context. As a part of the long-term program at Kitt Peak National
Observatory (KPNO), the Mn I 539.4 nm line has been observed for
nearly three solar cycles using the McMath telescope and the 13.5 m
spectrograph in double-pass mode. These full-disk spectrophotometric
observations revealed an unusually strong change of this line's
parameters over the solar cycle. Aims: Optical pumping by the Mg
II k line was originally proposed to explain these variations. More
recent studies have proposed that this is not required and that
the magnetic variability (I.e., the changes in solar atmospheric
structure due to faculae) might explain these changes. Magnetic
variability is also the mechanism that drives the changes in total
solar irradiance variations (TSI). With this work we investigate this
proposition quantitatively by using the same model that was earlier
successfully employed to reconstruct the irradiance. Methods:
We reconstructed the changes in the line parameters using the model
SATIRE-S, which takes only variations of the daily surface distribution
of the magnetic field into account. We applied exactly the same model
atmospheres and value of the free parameter as were used in previous
solar irradiance reconstructions to now model the variation in the Mn
I 539.4 nm line profile and in neighboring Fe I lines. We compared
the results of the theoretical model with KPNO observations. 
Results: The changes in the Mn I 539.4 nm line and a neighbouring Fe
I 539.52 nm line over approximately three solar cycles are reproduced
well by the model without additionally tweaking the model parameters,
if changes made to the instrument setup are taken into account. The
model slightly overestimates the change for the strong Fe I 539.32 nm
line. Conclusions: Our result confirms that optical pumping
of the Mn II 539.4 nm line by Mg II k is not the main cause of its
solar cycle change. It also provides independent confirmation of solar
irradiance models which are based on the assumption that irradiance
variations are caused by the evolution of the solar surface magnetic
flux. The result obtained here also supports the spectral irradiance
variations computed by these models.

---------------------------------------------------------
Title: Probing the Sun with ALMA: Observations and Simulations
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.; Carlsson, M.
2015ASPC..499..349L Altcode: 2015arXiv150805686L
ALMA will open a new chapter in the study of the Sun by providing a leap
in spatial resolution and sensitivity compared to currently available
mm wavelength observations. In preparation of ALMA, we have carried out
a large number of observational tests and state-of-the-art radiation
MHD simulations. Here we review the best available observations of
the Sun at millimeter wavelengths.Using state of the art radiation
MHD simulations of the solar atmosphere we demonstrate the huge
potential of ALMA observations for uncovering the nature of the solar
chromosphere. We show that ALMA will not only provide a reliable probe
of the thermal structure and dynamics of the chromosphere, it will also
open up a powerful new diagnostic of magnetic field at chromospheric
heights, a fundamentally important, but so far poorly known parameter.

---------------------------------------------------------
Title: Sunspot areas and tilt angles for solar cycles 7-10
Authors: Senthamizh Pavai, V.; Arlt, R.; Dasi-Espuig, M.; Krivova,
N. A.; Solanki, S. K.
2015A&A...584A..73S Altcode: 2015arXiv150807849S
 Aims: Extending the knowledge about the properties of solar
cycles into the past is essential for understanding the solar
dynamo. This paper aims to estimate areas of sunspots observed by
Schwabe in 1825-1867 and to calculate the tilt angles of sunspot
groups. Methods: The sunspot sizes in Schwabe's drawings are
not to scale and need to be converted into physical sunspot areas. We
employed a statistical approach assuming that the area distribution
of sunspots was the same in the 19th century as it was in the 20th
century. Results: Umbral areas for about 130 000 sunspots
observed by Schwabe were obtained, as well as the tilt angles of
sunspot groups assuming them to be bipolar. There is, of course,
no polarity information in the observations. The annually averaged
sunspot areas correlate reasonably with sunspot number. We derived
an average tilt angle by attempting to exclude unipolar groups with
a minimum separation of the two alleged polarities and an outlier
rejection method which follows the evolution of each group and detects
the moment it turns unipolar at its decay. As a result, the tilt angles,
although displaying considerable scatter, average to 5̊.85 ± 0, with
the leading polarity located closer to the equator, in good agreement
with tilt angles obtained from 20th century data sets. Sources of
uncertainties in the tilt angle determination are discussed and need to
be addressed whenever different data sets are combined. The sunspot area
and tilt angle data are provided at the CDS. The sunspot area and
tilt angle data are only available at the CDS via anonymous ftp to <A
href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A73">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/584/A73</A>

---------------------------------------------------------
Title: Helioseismology with Solar Orbiter
Authors: Löptien, Björn; Birch, Aaron C.; Gizon, Laurent; Schou,
Jesper; Appourchaux, Thierry; Blanco Rodríguez, Julián; Cally,
Paul S.; Dominguez-Tagle, Carlos; Gandorfer, Achim; Hill, Frank;
Hirzberger, Johann; Scherrer, Philip H.; Solanki, Sami K.
2015SSRv..196..251L Altcode: 2014arXiv1406.5435L; 2014SSRv..tmp...31L
The Solar Orbiter mission, to be launched in July 2017, will
carry a suite of remote sensing and in-situ instruments, including
the Polarimetric and Helioseismic Imager (PHI). PHI will deliver
high-cadence images of the Sun in intensity and Doppler velocity
suitable for carrying out novel helioseismic studies. The orbit of
the Solar Orbiter spacecraft will reach a solar latitude of up to
21∘ (up to 34∘ by the end of the extended
mission) and thus will enable the first local helioseismology studies of
the polar regions. Here we consider an array of science objectives to be
addressed by helioseismology within the baseline telemetry allocation
(51 Gbit per orbit, current baseline) and within the science observing
windows (baseline 3×10 days per orbit). A particularly important
objective is the measurement of large-scale flows at high latitudes
(rotation and meridional flow), which are largely unknown but play an
important role in flux transport dynamos. For both helioseismology
and feature tracking methods convection is a source of noise in
the measurement of longitudinally averaged large-scale flows, which
decreases as T -1/2 where T is the total duration of the
observations. Therefore, the detection of small amplitude signals (e.g.,
meridional circulation, flows in the deep solar interior) requires long
observation times. As an example, one hundred days of observations at
lower spatial resolution would provide a noise level of about three m/s
on the meridional flow at 80∘ latitude. Longer time-series
are also needed to study temporal variations with the solar cycle. The
full range of Earth-Sun-spacecraft angles provided by the orbit will
enable helioseismology from two vantage points by combining PHI with
another instrument: stereoscopic helioseismology will allow the study
of the deep solar interior and a better understanding of the physics
of solar oscillations in both quiet Sun and sunspots. We have used a
model of the PHI instrument to study its performance for helioseismology
applications. As input we used a 6 hr time-series of realistic solar
magneto-convection simulation (Stagger code) and the SPINOR radiative
transfer code to synthesize the observables. The simulated power
spectra of solar oscillations show that the instrument is suitable for
helioseismology. In particular, the specified point spread function,
image jitter, and photon noise are no obstacle to a successful mission.

---------------------------------------------------------
Title: Magneto-static Modeling of the Mixed Plasma Beta Solar
Atmosphere Based on Sunrise/IMaX Data
Authors: Wiegelmann, T.; Neukirch, T.; Nickeler, D. H.; Solanki,
S. K.; Martínez Pillet, V.; Borrero, J. M.
2015ApJ...815...10W Altcode: 2015arXiv151105568W
Our aim is to model the three-dimensional magnetic field structure
of the upper solar atmosphere, including regions of non-negligible
plasma beta. We use high-resolution photospheric magnetic field
measurements from SUNRISE/IMaX as the boundary condition for a
magneto-static magnetic field model. The high resolution of IMaX
allows us to resolve the interface region between the photosphere
and corona, but modeling this region is challenging for the following
reasons. While the coronal magnetic field is thought to be force-free
(the Lorentz force vanishes), this is not the case in the mixed plasma
β environment in the photosphere and lower chromosphere. In our model,
pressure gradients and gravity forces are self-consistently taken into
account and compensate for the non-vanishing Lorentz force. Above a
certain height (about 2 Mm) the non-magnetic forces become very weak
and consequently the magnetic field becomes almost force-free. Here,
we apply a linear approach where the electric current density consists
of a superposition of a field-line parallel current and a current
perpendicular to the Sun's gravity field. We illustrate the prospects
and limitations of this approach and give an outlook for an extension
toward a nonlinear model.

---------------------------------------------------------
Title: Sunrise Mission Highlights
Authors: Riethmüller, Tino L.; Solanki, Sami K.
2015arXiv151103487R Altcode:
Solar activity is controlled by the magnetic field, which also causes
the variability of the solar irradiance that in turn is thought to
influence the climate on Earth. The magnetic field manifests itself
in the form of structures of different sizes, starting with sunspots
(10-50 Mm) down to the smallest known magnetic features that often
have spatial extents of 100 km or less. The study of the fine scale
structure of the Sun's magnetic field has been hampered by the limited
spatial resolution of the available observations. This has recently
changed thanks to new space and ground-based telescopes. A significant
step forward has been taken by the Sunrise observatory, built around
the largest solar telescope to leave the ground, and containing two
science instruments. Sunrise had two successful long-duration science
flights on a stratospheric balloon in June 2009 (solar activity minimum)
and in June 2013 (at a high activity level) and a number of scientific
results have been obtained that have greatly advanced our understanding
of solar magnetism, with data analysis still ongoing. After a brief
introduction to the Sunrise mission, an overview of a selection of
these results will be given.

---------------------------------------------------------
Title: Depth-dependent global properties of a sunspot observed by
Hinode using the Solar Optical Telescope/Spectropolarimeter
Authors: Tiwari, Sanjiv K.; van Noort, Michiel; Solanki, Sami K.;
Lagg, Andreas
2015A&A...583A.119T Altcode: 2015arXiv150804830T
Context. For the past two decades, the three-dimensional structure
of sunspots has been studied extensively. A recent improvement in the
Stokes inversion technique prompts us to revisit the depth-dependent
properties of sunspots. Aims: In the present work, we aim to
investigate the global depth-dependent thermal, velocity, and magnetic
properties of a sunspot, as well as the interconnection between
various local properties. Methods: We analysed high-quality
Stokes profiles of the disk-centred, regular, leading sunspot of NOAA
AR 10933, acquired by the Solar Optical Telescope/Spectropolarimeter
(SOT/SP) on board the Hinode spacecraft. To obtain depth-dependent
stratification of the physical parameters, we used the recently
developed, spatially coupled version of the SPINOR inversion code. Results: First, we study the azimuthally averaged physical parameters
of the sunspot. We find that the vertical temperature gradient in the
lower- to mid-photosphere is at its weakest in the umbra, while it is
considerably stronger in the penumbra, and stronger still in the spot's
surroundings. The azimuthally averaged field becomes more horizontal
with radial distance from the centre of the spot, but more vertical
with height. At continuum optical depth unity, the line-of-sight
velocity shows an average upflow of ~300 ms-1 in the inner
penumbra and an average downflow of ~1300 ms-1 in the
outer penumbra. The downflow continues outside the visible penumbral
boundary. The sunspot shows, at most, a moderate negative twist of
&lt;5° at log (τ) = 0, which increases with height. The sunspot umbra
and the spines of the penumbra show considerable similarity with regard
to their physical properties, albeit with some quantitative differences
(weaker, somewhat more horizontal fields in spines, commensurate
with their location being further away from the sunspot's core). The
temperature shows a general anti-correlation with the field strength,
with the exception of the heads of penumbral filaments, where a weak
positive correlation is found. The dependence of the physical parameters
on each other over the full sunspot shows a qualitative similarity to
that of a standard penumbral filament and its surrounding spines. 
Conclusions: The large-scale variation in the physical parameters of
a sunspot at various optical depths is presented. Our results suggest
that the spines in the penumbra are basically the outward extension
of the umbra. The spines and the penumbral filaments, together, are
the basic elements that form a sunspot penumbra.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Sunspot areas and tilt angles
(Senthamizh Pavai+, 2015)
Authors: Senthamizh Pavai, V.; Arlt, R.; Dasi-Espuig, M.; Krivova,
N.; Solanki, S.
2015yCat..35840073S Altcode:
We present sunspot positions and areas from historical observations
of sunspots by Samuel Heinrich Schwabe from Dessau, Germany. He has
recorded his observations of sunspots from 1825-1867 as drawings in
small circles of about 5cm diameter (representing the solar disk). Even
though he has used quite a number of telescopes for his observations,
the majority of the full-disk drawings were made with a 3-1/2-foot
telescope from Fraunhofer. His observing log books are stored in the
library of the Royal Astronomical Society in London. Those drawings
were digitized photographically with a resolution of 2912x4378 pixels
per page. The sizes and positions of the sunspots were measured using
a dozen of circular mouse cursor shapes with different diameters. The
sunspot sizes in Schwabe's drawings are not to scale and need to
be converted into physical sunspot areas. We employed a statistical
approach assuming that the area distribution of sunspots was the same
in the 19th century as it was in the 20th century. Umbral areas for
about 130,000 sunspots observed by Schwabe were obtained, as well as
the tilt angles of sunspot groups assuming them to be bipolar (two
or more spots). There is, of course, no polarity information in the
observations. Both an updated sunspot database and a tilt angle
database are available at http://www.aip.de/Members/rarlt/ sunspots
for further study. (2 data files).

---------------------------------------------------------
Title: Flarelike brightenings of active region loops observed
with SUMER
Authors: Wang, T. J.; Innes, D. E.; Solanki, S. K.; Curdt, W.
2015arXiv151000337W Altcode:
Coronal loops on the east limb of the Sun were observed by SUMER on
SOHO for several days. Small flare-like brightenings are detected very
frequently in the hot flare line Fe~{\small XIX}. We find that the
relatively intense events are in good coincidence with the transient
brightenings seen by Yohkoh/SXT. A statistical analysis shows that these
brightenings have durations of 5-84 min and extensions along the slit
of 2-67 Mm. The integrated energy observed in Fe~{\small XIX} for each
event is in the range of $3\times10^{18}-5\times10^{23}$ ergs, and the
estimated thermal energy ranges from $10^{26}-10^{29}$ ergs. Application
of the statistical method proposed by Parnell \&amp; Jupp (2000) yields
a value of 1.5 to 1.8 for the index of a power law relation between
the frequency of the events and the radiated energy in Fe~{\small XIX},
and a value of 1.7 to 1.8 for the index of the frequency distribution of
the thermal energy in the energy range $&gt;10^{27}$ ergs. We examine
the possibility that these small brightenings give a big contribution
to heating of the active region corona.

---------------------------------------------------------
Title: Three-dimensional non-LTE radiative transfer effects in Fe
i lines. III. Line formation in magneto-hydrodynamic atmospheres
Authors: Holzreuter, R.; Solanki, S. K.
2015A&A...582A.101H Altcode: 2015arXiv150704224H
Non-local thermodynamic equilibrium (NLTE) effects in diagnostically
important solar Fe i lines are important because of the strong
sensitivity of Fe i to ionizing UV radiation, which may lead to
a considerable underpopulation of the Fe i levels in the solar
atmosphere and, therefore, to a sizeable weakening of Fe i lines. These
NLTE effects may be intensified or weakened by horizontal radiative
transfer (RT) in a three-dimensionally (3D) structured atmosphere. We
analyze the influence of horizontal RT on commonly used Fe i lines in
a snapshot of a 3D radiation magneto-hydrodynamic (MHD) simulation of
a plage region. NLTE and horizontal RT effects occur with considerable
strength (up to 50% in line depth or equivalent width) in the analyzed
snapshot. Because they may have either sign, and both signs occur with
approximately the same frequency and strength, the net effects are small
when considering spatially averaged quantities. The situation in the
plage atmosphere turns out to be rather complex. Horizontal transfer
leads to line weakening relative to 1D NLTE transfer near the boundaries
of kG magnetic elements. Around the centers of these elements, however,
we find line strengthening, which is often significant. This behavior
contrasts with what is expected from previous 3D RT computations in
idealized flux-tube models, which only display line weakening. The
origin of this unexpected behavior lies in the fact that magnetic
elements are surrounded by dense and relatively cool downflowing gas,
which forms the walls of the magnetic elements. The continuum in these
dense walls is often formed in colder gas than in the central part of
the magnetic elements. Consequently, the central parts of the magnetic
element experience a subaverage UV-irradiation leading to the observed
3D NLTE line strengthening.

---------------------------------------------------------
Title: ADAHELI: exploring the fast, dynamic Sun in the x-ray, optical,
and near-infrared
Authors: Berrilli, Francesco; Soffitta, Paolo; Velli, Marco; Sabatini,
Paolo; Bigazzi, Alberto; Bellazzini, Ronaldo; Bellot Rubio, Luis
Ramon; Brez, Alessandro; Carbone, Vincenzo; Cauzzi, Gianna; Cavallini,
Fabio; Consolini, Giuseppe; Curti, Fabio; Del Moro, Dario; Di Giorgio,
Anna Maria; Ermolli, Ilaria; Fabiani, Sergio; Faurobert, Marianne;
Feller, Alex; Galsgaard, Klaus; Gburek, Szymon; Giannattasio, Fabio;
Giovannelli, Luca; Hirzberger, Johann; Jefferies, Stuart M.; Madjarska,
Maria S.; Manni, Fabio; Mazzoni, Alessandro; Muleri, Fabio; Penza,
Valentina; Peres, Giovanni; Piazzesi, Roberto; Pieralli, Francesca;
Pietropaolo, Ermanno; Martinez Pillet, Valentin; Pinchera, Michele;
Reale, Fabio; Romano, Paolo; Romoli, Andrea; Romoli, Marco; Rubini,
Alda; Rudawy, Pawel; Sandri, Paolo; Scardigli, Stefano; Spandre,
Gloria; Solanki, Sami K.; Stangalini, Marco; Vecchio, Antonio;
Zuccarello, Francesca
2015JATIS...1d4006B Altcode:
Advanced Astronomy for Heliophysics Plus (ADAHELI) is a project concept
for a small solar and space weather mission with a budget compatible
with an European Space Agency (ESA) S-class mission, including launch,
and a fast development cycle. ADAHELI was submitted to the European
Space Agency by a European-wide consortium of solar physics research
institutes in response to the "Call for a small mission opportunity
for a launch in 2017," of March 9, 2012. The ADAHELI project builds
on the heritage of the former ADAHELI mission, which had successfully
completed its phase-A study under the Italian Space Agency 2007 Small
Mission Programme, thus proving the soundness and feasibility of
its innovative low-budget design. ADAHELI is a solar space mission
with two main instruments: ISODY: an imager, based on Fabry-Pérot
interferometers, whose design is optimized to the acquisition of
highest cadence, long-duration, multiline spectropolarimetric images
in the visible/near-infrared region of the solar spectrum. XSPO: an
x-ray polarimeter for solar flares in x-rays with energies in the 15
to 35 keV range. ADAHELI is capable of performing observations that
cannot be addressed by other currently planned solar space missions,
due to their limited telemetry, or by ground-based facilities, due to
the problematic effect of the terrestrial atmosphere.

---------------------------------------------------------
Title: The Polarimetric and Helioseismic Imager for Solar Orbiter:
SO/PHI
Authors: Solanki, Sami K.; del Toro Iniesta, Jose Carlos; Woch,
Joachim; Gandorfer, Achim; Hirzberger, Johann; Schmidt, Wolfgang;
Appourchaux, Thierry; Alvarez-Herrero, Alberto
2015IAUS..305..108S Altcode: 2015arXiv150203368S
The Solar Orbiter is the next solar physics mission of the European
Space Agency, ESA, in collaboration with NASA, with a launch planned in
2018. The spacecraft is designed to approach the Sun to within 0.28 AU
at perihelion of a highly eccentric orbit. The proximity with the Sun
will also allow its observation at uniformly high resolution at EUV and
visible wavelengths. Such observations are central for learning more
about the magnetic coupling of the solar atmosphere. At a later phase
in the mission the spacecraft will leave the ecliptic and study the
enigmatic poles of the Sun from a heliographic latitude of up to 33°.

---------------------------------------------------------
Title: Search for chameleons with CAST
Authors: Anastassopoulos, V.; Arik, M.; Aune, S.; Barth, K.; Belov,
A.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.;
Christensen, F.; Collar, J. I.; Dafni, T.; Davenport, M.; Desch, K.;
Dermenev, A.; Eleftheriadis, C.; Fanourakis, G.; Ferrer-Ribas, E.;
Friedrich, P.; Galán, J.; García, J. A.; Gardikiotis, A.; Garza,
J. G.; Gazis, E. N.; Geralis, T.; Giomataris, I.; Hailey, C.; Haug,
F.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.; Irastorza,
I. G.; Jacoby, J.; Jakobsen, A.; Jakovčić, K.; Kaminski, J.; Karuza,
M.; Kavuk, M.; Krčmar, M.; Krieger, C.; Krüger, A.; Lakić, B.;
Laurent, J. M.; Liolios, A.; Ljubičić, A.; Luzón, G.; Neff, S.;
Ortega, I.; Papaevangelou, T.; Pivovaroff, M. J.; Raffelt, G.; Riege,
H.; Rosu, M.; Ruz, J.; Savvidis, I.; Solanki, S. K.; Vafeiadis, T.;
Villar, J. A.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.; Brax, P.;
Lavrentyev, I.; Upadhye, A.
2015PhLB..749..172A Altcode: 2015arXiv150304561A
In this work we present a search for (solar) chameleons with the CERN
Axion Solar Telescope (CAST). This novel experimental technique,
in the field of dark energy research, exploits both the chameleon
coupling to matter (βm) and to photons (βγ)
via the Primakoff effect. By reducing the X-ray detection energy
threshold used for axions from 1 keV to 400 eV CAST became sensitive
to the converted solar chameleon spectrum which peaks around 600
eV. Even though we have not observed any excess above background, we
can provide a 95% C.L. limit for the coupling strength of chameleons to
photons of βγ ≲1011 for 1 &lt;βm
&lt;106.

---------------------------------------------------------
Title: The Maunder minimum (1645-1715) was indeed a grand minimum:
A reassessment of multiple datasets
Authors: Usoskin, Ilya G.; Arlt, Rainer; Asvestari, Eleanna; Hawkins,
Ed; Käpylä, Maarit; Kovaltsov, Gennady A.; Krivova, Natalie;
Lockwood, Michael; Mursula, Kalevi; O'Reilly, Jezebel; Owens, Matthew;
Scott, Chris J.; Sokoloff, Dmitry D.; Solanki, Sami K.; Soon, Willie;
Vaquero, José M.
2015A&A...581A..95U Altcode: 2015arXiv150705191U
 Aims: Although the time of the Maunder minimum (1645-1715) is
widely known as a period of extremely low solar activity, it is still
being debated whether solar activity during that period might have
been moderate or even higher than the current solar cycle #24. We have
revisited all existing evidence and datasets, both direct and indirect,
to assess the level of solar activity during the Maunder minimum. 
Methods: We discuss the East Asian naked-eye sunspot observations, the
telescopic solar observations, the fraction of sunspot active days,
the latitudinal extent of sunspot positions, auroral sightings at
high latitudes, cosmogenic radionuclide data as well as solar eclipse
observations for that period. We also consider peculiar features of
the Sun (very strong hemispheric asymmetry of the sunspot location,
unusual differential rotation and the lack of the K-corona) that imply
a special mode of solar activity during the Maunder minimum. 
Results: The level of solar activity during the Maunder minimum is
reassessed on the basis of all available datasets. Conclusions:
We conclude that solar activity was indeed at an exceptionally low
level during the Maunder minimum. Although the exact level is still
unclear, it was definitely lower than during the Dalton minimum of
around 1800 and significantly below that of the current solar cycle
#24. Claims of a moderate-to-high level of solar activity during the
Maunder minimum are rejected with a high confidence level.

---------------------------------------------------------
Title: The role of the Fraunhofer lines in solar brightness
variability
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Tagirov,
R. V.; Schmutz, W. K.
2015A&A...581A.116S Altcode: 2015arXiv150705437S
Context. The solar brightness varies on timescales from minutes to
decades. A clear identification of the physical processes behind such
variations is needed for developing and improving physics-based models
of solar brightness variability and reconstructing solar brightness
in the past. This is, in turn, important for better understanding
the solar-terrestrial and solar-stellar connections. Aims:
We estimate the relative contributions of the continuum, molecular,
and atomic lines to the solar brightness variations on different
timescales. Methods: Our approach is based on the assumption that
variability of the solar brightness on timescales greater than a day
is driven by the evolution of the solar surface magnetic field. We
calculated the solar brightness variations employing the solar
disc area coverage of magnetic features deduced from the MDI/SOHO
observations. The brightness contrasts of magnetic features relative
to the quiet Sun were calculated with a non-LTE radiative transfer
code as functions of disc position and wavelength. By consecutive
elimination of molecular and atomic lines from the radiative transfer
calculations, we assessed the role of these lines in producing solar
brightness variability. Results: We show that the variations
in Fraunhofer lines define the amplitude of the solar brightness
variability on timescales greater than a day and even the phase of
the total solar irradiance variability over the 11-year cycle. We also
demonstrate that molecular lines make substantial contribution to solar
brightness variability on the 11-year activity cycle and centennial
timescales. In particular, our model indicates that roughly a quarter
of the total solar irradiance variability over the 11-year cycle
originates in molecular lines. The maximum of the absolute spectral
brightness variability on timescales greater than a day is associated
with the CN violet system between 380 and 390 nm.

---------------------------------------------------------
Title: Magnetic reconnection as a source of jets from a penumbral
intrusion into a sunspot umbra
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
2015arXiv150902123B Altcode:
We present the results of high resolution co-temporal and co-spatial
photospheric and chromospheric observations of sunspot penumbral
intrusions. The data was taken with the Swedish Solar Telescope (SST)
on the Canary Islands. Time series of Ca\,II H images show a series of
transient jets extending roughly 3000 km above a penumbral intrusion
into the umbra. For most of the time series jets were seen along
the whole length of the intruding bright filament. Some of these jets
develop a clear $\lambda$-shaped structure, with a small loop appearing
at their footpoint and lasting for around a minute. In the framework
of earlier studies, the observed transient $\lambda$ shape of these
jets strongly suggests that they are caused by magnetic reconnection
between a curved arcade-like or flux-rope like field in the lower part
of the penumbral intrusion and the more vertical umbral magnetic field
forming a cusp-shaped structure above the penumbral intrusion.

---------------------------------------------------------
Title: Dynamics of Multi-cored Magnetic Structures in the Quiet Sun
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Martínez Pillet, Valentín; Solanki, Sami K.;
Schmidt, Wolfgang
2015ApJ...810...79R Altcode: 2015arXiv150806998R
We report on the dynamical interaction of quiet-Sun magnetic fields and
granular convection in the solar photosphere as seen by Sunrise. We
use high spatial resolution (0.″15-0.″18) and temporal cadence
(33 s) spectropolarimetric Imaging Magnetograph eXperiment data,
together with simultaneous CN and Ca ii H filtergrams from Sunrise
Filter Imager. We apply the SIR inversion code to the polarimetric
data in order to infer the line of sight velocity and vector magnetic
field in the photosphere. The analysis reveals bundles of individual
flux tubes evolving as a single entity during the entire 23 minute data
set. The group shares a common canopy in the upper photospheric layers,
while the individual tubes continually intensify, fragment and merge in
the same way that chains of bright points in photometric observations
have been reported to do. The evolution of the tube cores are driven
by the local granular convection flows. They intensify when they
are “compressed” by surrounding granules and split when they are
“squeezed” between two moving granules. The resulting fragments
are usually later regrouped in intergranular lanes by the granular
flows. The continual intensification, fragmentation and coalescence of
flux results in magnetic field oscillations of the global entity. From
the observations we conclude that the magnetic field oscillations first
reported by Martínez González et al. correspond to the forcing by
granular motions and not to characteristic oscillatory modes of thin
flux tubes.

---------------------------------------------------------
Title: Solar extreme ultraviolet variability of the quiet Sun
Authors: Shakeri, F.; Teriaca, L.; Solanki, S. K.
2015A&A...581A..51S Altcode: 2015arXiv150705786S
The last solar minimum has been unusually quiet compared to the previous
minima (since space-based radiometric measurements are available). The
Sun's magnetic flux was substantially lower during this minimum. Some
studies also show that the total solar irradiance during the minimum
after cycle 23 may have dropped below the values known from the two
minima prior to that. For chromospheric and coronal radiation, the
situation is less clear-cut. The Sun's 10.7 cm flux shows a decrease of
~4% during the solar minimum in 2008 compared to the previous minimum,
but Ca ii K does not. Here we consider additional wavelengths in
the extreme ultraviolet (EUV), specifically transitions of He i at
584.3 Å and O v at 629.7 Å, of which the CDS spectrometer aboard
SOHO has been taking regular scans along the solar central meridian
since 1996. We analysed this unique dataset to verify if and how the
radiance distribution undergoes measurable variations between cycle
minima. To achieve this aim we determined the radiance distribution
of quiet areas around the Sun centre. Concentrating on the last two
solar minima, we found out that there is very little variation in the
radiance distribution of the chromospheric spectral line He i between
these minima. The same analysis shows a modest, although significant,
4% variation in the radiance distribution of the TR spectral line O
v. These results are comparable to those obtained by earlier studies
employing other spectral features, and they confirm that chromospheric
indices display a small variation, whereas in the transition region
a more significant reduction of the brighter features is visible.

---------------------------------------------------------
Title: Modelling stellar brightness variations
Authors: Shapiro, Alexander; Solanki, Sami K.; Krivova, Natalie
2015IAUGA..2256741S Altcode:
We develop a model that attributes the variability of the stellar
brightness to the imbalance between starspot darkening and facular
brightening. Our approach is based on the assumption that the
photometric variability of the Sun and Sun-like stars have the same
fundamental causes so that we can describe stellar variability by
extrapolating the solar model. Our results suggest that the solar
paradigm is remarkably successful in explaining the stellar variability
on the activity cycle time-scale. In particular, the model reproduces
the observed reversal of the in-phase activity-brightness relationship
for low-activity stars to an anti-phase one for more active stars.We
simulate the solar variability as it would be measured out-of-ecliptic
by Kepler and CoRoT and discuss the relative contributions of spots
and faculae to the photometric stellar variability.

---------------------------------------------------------
Title: Statistical analysis of supersonic downflows in sunspot
penumbrae.
Authors: Kim, Hyunnam; Lagg, Andreas; Solanki, Sami K.; Narayan,
Gautam; van Noort, Michiel; Kim, Kap-Sung
2015IAUGA..2254868K Altcode:
Supersonic downflow patches was found in the outer edge of sunspot
penumbra. These patches are believed to be the return channels of the
Evershed flow. There was previous study to investigate their structure
in detail using Hinode SOT/SP observations (M. van Noort et al. 2013)
but their data sample was only two sunspots. To make general description
it needs to check more sunspot data sample.We selected 242 downflow
patches of 16 sunspots using Hinode SOT/SP observations from 2006 to
2012. Height-dependent maps of atmospheric parameters of these downflows
was produced by using HeLix which was height dependent LTE inversion
code of Stokes profiles.Statistical analysis of magnetic field strength,
inclination angle of field line, temperature and line-of-sight velocity
are presented. The recovered atmospheric data tell us that downflow
patches have different physical signatures comparing normal penumbra
properties. Furthermore, our results of three height-dependent layer
support that heating process should occur on the downflow patches in
the middle of layer.

---------------------------------------------------------
Title: UV solar irradiance in observations and the NRLSSI and
SATIRE-S models
Authors: Yeo, K. L.; Ball, W. T.; Krivova, N. A.; Solanki, S. K.;
Unruh, Y. C.; Morrill, J.
2015JGRA..120.6055Y Altcode: 2015arXiv150701224Y
Total solar irradiance and UV spectral solar irradiance has been
monitored since 1978 through a succession of space missions. This is
accompanied by the development of models aimed at replicating solar
irradiance by relating the variability to solar magnetic activity. The
Naval Research Laboratory Solar Spectral Irradiance (NRLSSI) and
Spectral And Total Irradiance REconstruction for the Satellite era
(SATIRE-S) models provide the most comprehensive reconstructions of
total and spectral solar irradiance over the period of satellite
observation currently available. There is persistent controversy
between the various measurements and models in terms of the wavelength
dependence of the variation over the solar cycle, with repercussions on
our understanding of the influence of UV solar irradiance variability
on the stratosphere. We review the measurement and modeling of UV solar
irradiance variability over the period of satellite observation. The
SATIRE-S reconstruction is consistent with spectral solar irradiance
observations where they are reliable. It is also supported by an
independent, empirical reconstruction of UV spectral solar irradiance
based on Upper Atmosphere Research Satellite/Solar Ultraviolet Spectral
Irradiance Monitor measurements from an earlier study. The weaker
solar cycle variability produced by NRLSSI between 300 and 400 nm is
not evident in any available record. We show that although the method
employed to construct NRLSSI is principally sound, reconstructed solar
cycle variability is detrimentally affected by the uncertainty in the
SSI observations it draws upon in the derivation. Based on our findings,
we recommend, when choosing between the two models, the use of SATIRE-S
for climate studies.

---------------------------------------------------------
Title: Models of Solar Irradiance Variability
Authors: Solanki, Sami K.
2015IAUGA..2250049S Altcode:
Models of solar irradiance variability have an important role to
play due to the relatively short (although steadily increasing)
length of measured irradiance time series. Advanced models also allow
identifying the source of solar irradiance variations and give insight
into the variation of irradiance as a function of wavelength. The
first generation of models of solar irradiance were proxy-based,
i.e. purely empirical. These were followed by models that combine
spectra computed from semi-empirical model atmospheres, with a
measure of solar activity variations. In future, models will build
increasingly on 3D MHD simulations instead of 1D model atmospheres
to compute the spectra. On longer timescales models are generally
simpler, although there too considerable progress has been made,
with irradiance reconstructions now available for multiple millennia,
albeit with lower resolution and accuracy than at shorter timescales.

---------------------------------------------------------
Title: The Maunder minimum: A reassessment from multiple dataset
Authors: Usoskin, Ilya; Arlt, Rainer; Asvestari, Eleanna; Kovaltsov,
Gennady; Krivova, Natalie; Lockwood, Michael; Käpylä, Maarit; Owens,
Matthew; Sokoloff, Dmitry D.; Solanki, Sami; Soon, Willie; Vaquero,
Jose; Scott, Chris
2015IAUGA..2253036U Altcode:
The Maunder minimum (MM) in 1645-1715 was a period of the lowest ever
known solar activity recorded via sunspot numbers since 1610. Since
it is the only Grand minimum of solar activity directly observed,
it forms a benchmark for the solar variability studies. Therefore,
it is crucially important to assess the level and other features
of temporal and spatial solar magnetic variability during that
time. However, because of uncertainties related mostly to ambiguity
of some historical sunspot observation records, the exact level of
solar activity during the MM is somewhat unclear, leaving room for
continuous discussions and speculations. Many of these issues have been
addressed by Jack Eddy in his cornerstone papers of 1976 and 1983,
but since then numerous new pieces of evidence and datasets have
appeared, making it possible to verify the paradigm of the Maunder
minimum with far greater certainty than before.Here we provide a full
reassessment of the Maunder minimum using all the available datasets:
augmented sunspot counts and drawings; revisited historical archives;
both well-known and newly revealed records of auroral observations;
cosmic ray variability via cosmogenic isotope records of 14C
in tree trunks, 10Be in ice cores and 44Ti in
fallen meteorites. We show that, while the exact level of the activity
is not easy to determine, the Sun indeed exhibited exceptionally low
magnetic activity during the MM, in comparison to other periods of
moderate or decreased activity, such as the Dalton minimum (ca. 1800),
the Gleissberg minimum (ca. 1900) and the present weak solar cycle #
24. We show that a scenario of moderate or strong activity during the
MM contradicts all the available datasets.Thus, we confirm, using
all the presently available datasets of different nature, that the
period of the Maunder minimum in 1645-1715 was indeed a Grand minimum,
with very low solar surface magnetic activity, low intensity of the
interplanetary magnetic field, as well as lower frequency and higher
geographical latitude of auroral occurrence. Meanwhile some indications
of the continuation, but at a very low level, of the 11-year solar
cycle can be found in the data.

---------------------------------------------------------
Title: Solar cycle variation in UV solar spectral irradiance
Authors: Leng Yeo, Kok; Krivova, Natalie; Solanki, Sami K.
2015IAUGA..2253798L Altcode:
Solar spectral irradiance, SSI, in the UV has been measured from space,
almost without interruption, since 1978. This is accompanied by the
development of models aimed at reconstructing SSI by relating its
variability to solar magnetic activity. The various satellite records
and model reconstructions differ significantly in terms of the variation
over the solar cycle, with the consequence that their application to
climate models yield qualitatively different results. Here, we highlight
the key discrepancies between available records and reconstructions,
and discuss the possible underlying causes.

---------------------------------------------------------
Title: New solar axion search using the CERN Axion Solar Telescope
with 4He filling
Authors: Arik, M.; Aune, S.; Barth, K.; Belov, A.; Bräuninger,
H.; Bremer, J.; Burwitz, V.; Cantatore, G.; Carmona, J. M.; Cetin,
S. A.; Collar, J. I.; Da Riva, E.; Dafni, T.; Davenport, M.; Dermenev,
A.; Eleftheriadis, C.; Elias, N.; Fanourakis, G.; Ferrer-Ribas, E.;
Galán, J.; García, J. A.; Gardikiotis, A.; Garza, J. G.; Gazis,
E. N.; Geralis, T.; Georgiopoulou, E.; Giomataris, I.; Gninenko, S.;
Gómez Marzoa, M.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.;
Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza, M.; Kavuk,
M.; Krčmar, M.; Kuster, M.; Lakić, B.; Laurent, J. M.; Liolios,
A.; Ljubičić, A.; Luzón, G.; Neff, S.; Niinikoski, T.; Nordt,
A.; Ortega, I.; Papaevangelou, T.; Pivovaroff, M. J.; Raffelt, G.;
Rodríguez, A.; Rosu, M.; Ruz, J.; Savvidis, I.; Shilon, I.; Solanki,
S. K.; Stewart, L.; Tomás, A.; Vafeiadis, T.; Villar, J.; Vogel,
J. K.; Yildiz, S. C.; Zioutas, K.; CAST Collaboration
2015PhRvD..92b1101A Altcode: 2015arXiv150300610A
The CERN Axion Solar Telescope (CAST) searches for a →γ conversion
in the 9 T magnetic field of a refurbished LHC test magnet that can
be directed toward the Sun. Two parallel magnet bores can be filled
with helium of adjustable pressure to match the x-ray refractive mass
mγ to the axion search mass ma. After the vacuum
phase (2003-2004), which is optimal for ma≲0.02 eV , we
used 4He in 2005-2007 to cover the mass range of 0.02-0.39
eV and 3He in 2009-2011 to scan from 0.39 to 1.17 eV. After
improving the detectors and shielding, we returned to 4He
in 2012 to investigate a narrow ma range around 0.2 eV
("candidate setting" of our earlier search) and 0.39-0.42 eV, the
upper axion mass range reachable with 4He, to "cross the
axion line" for the KSVZ model. We have improved the limit on the
axion-photon coupling to ga γ&lt;1.47 ×10-10
GeV-1 (95% C.L.), depending on the pressure settings. Since
2013, we have returned to the vacuum and aim for a significant increase
in sensitivity.

---------------------------------------------------------
Title: Properties of solar plage from a spatially coupled inversion
of Hinode SP data
Authors: Buehler, D.; Lagg, A.; Solanki, S. K.; van Noort, M.
2015A&A...576A..27B Altcode: 2015arXiv150101151B
 Aims: The properties of magnetic fields forming an extended
plage region in AR 10953 were investigated. Methods:
Stokes spectra of the Fe I line pair at 6302 Å recorded by the
spectropolarimeter aboard the Hinode satellite were inverted using
the SPINOR code. The code performed a 2D spatially coupled inversion
on the Stokes spectra, allowing the retrieval of gradients in optical
depth within the atmosphere of each pixel, whilst accounting for the
effects of the instrument's PSF. Consequently, no magnetic filling
factor was needed. Results: The inversion results reveal that
plage is composed of magnetic flux concentrations (MFCs) with typical
field strengths of 1520 G at log (τ) = -0.9 and inclinations of
10°-15°. The MFCs expand by forming magnetic canopies composed of
weaker and more inclined magnetic fields. The expansion and average
temperature stratification of isolated MFCs can be approximated well
with an empirical plage thin flux tube model. The highest temperatures
of MFCs are located at their edges in all log (τ) layers. Whilst
the plasma inside MFCs is nearly at rest, each is surrounded by a
ring of downflows of on average 2.4 km s-1 at log (τ)
= 0 and peak velocities of up to 10 km s-1, which are
supersonic. The downflow ring of an MFC weakens and shifts outwards
with height, tracing the MFC's expansion. Such downflow rings often
harbour magnetic patches of opposite polarity to that of the main MFC
with typical field strengths below 300 G at log (τ) = 0. These opposite
polarity patches are situated beneath the canopy of their main MFC. We
found evidence of a strong broadening of the Stokes profiles in MFCs
and particularly in the downflow rings surrounding MFCs (expressed
by a microturbulence in the inversion). This indicates the presence
of strong unresolved velocities. Larger magnetic structures such as
sunspots cause the field of nearby MFCs to be more inclined.

---------------------------------------------------------
Title: Millimeter radiation from a 3D model of the solar
atmosphere. I. Diagnosing chromospheric thermal structure
Authors: Loukitcheva, M.; Solanki, S. K.; Carlsson, M.; White, S. M.
2015A&A...575A..15L Altcode: 2015arXiv150102898L
 Aims: We use advanced 3D non-local thermodynamic equilibrium
radiative magnetohydrodynamic simulations of the solar atmosphere to
carry out detailed tests of chromospheric diagnostics at millimeter and
submillimeter wavelengths. Methods: We focused on the diagnostics
of the thermal structure of the chromosphere in the wavelength bands
from 0.4 mm up to 9.6 mm that can be accessed with the Atacama Large
Millimeter/Submillimeter Array (ALMA) and investigated how these
diagnostics are affected by the instrumental resolution. Results:
We find that the formation height range of the millimeter radiation
depends on the location in the simulation domain and is related to the
underlying magnetic structure. Nonetheless, the brightness temperature
is a reasonable measure of the gas temperature at the effective
formation height at a given location on the solar surface. There is
considerable scatter in this relationship, but this is significantly
reduced when very weak magnetic fields are avoided. Our results
indicate that although instrumental smearing reduces the correlation
between brightness and temperature, millimeter brightness can still
be used to reliably diagnose electron temperature up to a resolution
of 1”. If the resolution is more degraded, then the value of the
diagnostic diminishes rapidly. Conclusions: We conclude that
millimeter brightness can image the chromospheric thermal structure
at the height at which the radiation is formed. Thus multiwavelength
observations with ALMA with a narrow step in wavelength should provide
sufficient information for a tomographic imaging of the chromosphere.

---------------------------------------------------------
Title: Simulated magnetic flows in the solar photosphere
Authors: Danilovic, S.; Cameron, R. H.; Solanki, S. K.
2015A&A...574A..28D Altcode: 2014arXiv1408.6159D
Context. Recent Sunrise/IMaX observations have revealed supersonic
magnetic flows. Aims: Our aim is to determine the origin of
these flows by using realistic magnetohydrodynamics simulations. Methods: We simulated cancellation and emergence of magnetic
flux through the solar photosphere. Our first numerical experiment
started with a magnetic field of both polarities. To simulate
emergence into a region with pre-existing field, we introduced a
large-scale horizontally uniform sheet of a horizontal field. We
followed the subsequent evolution and created synthetic polarimetric
observations, including known instrumental effects of the Sunrise/IMaX
and Hinode/SP instruments. We compared the simulated and observed
spectropolarimetric signals. Results: Strongly blue- and
redshifted Stokes V signals are produced in locations where strong
line-of-sight velocities coincide with the strong line-of-sight
component of the magnetic field. The size and strength of simulated
events is smaller than observed, and they are mostly associated with
downflows, contrary to observations. In a few cases where they appear
above a granule, single blue-lobed Stokes V are produced by strong
gradients in magnetic field and velocity. No change of magnetic field
sign is detected along the line of sight in these instances. More
high-speed magnetised flows occurred when an emergence was simulated
than when no horizontal field was added. Conclusions: The
simulations indicate that the observed events result from magnetic flux
emergences in which reconnection may take place, but does not seem to
be necessary. The movies are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201423779/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Centre-to-limb properties of small, photospheric quiet-Sun jets
Authors: Rubio da Costa, F.; Solanki, S. K.; Danilovic, S.; Hizberger,
J.; Martínez-Pillet, V.
2015A&A...574A..95R Altcode: 2014arXiv1412.1620R
Context. Strongly Doppler-shifted Stokes V profiles have been detected
in the quiet Sun with the IMaX instrument on-board the SUNRISE
stratospheric balloon-borne telescope. High velocities are required
to produce such signals, hence these events have been interpreted as
jets, although other sources are also possible. Aims: We aim
to characterize the variation of the main properties of these events
(occurrence rate, lifetime, size, and velocities) with their position on
the solar disk between disk centre and the solar limb. Methods:
These events were identified in SUNRISE/IMaX data according to the same
objective criteria at all available positions on the solar disk. Their
properties were determined using standard techniques. Results:
Our study yielded a number of new insights into this phenomenon. Most
importantly, the number density of these events is independent of
the heliocentric angle, meaning that the investigated supersonic
flows are nearly isotropically distributed. Size and lifetime are
also nearly independent of the heliocentric angle, while their
intensity contrast increases towards the solar limb. The Stokes V
jets are associated with upflow velocities deduced from Stokes I,
which are stronger towards the limb. Their intensity decreases with
time, while their line-of-sight velocity does not display a clear
temporal evolution. Their association with linear polarization signals
decreases towards the limb. Conclusions: The density of events
appears to be independent of heliocentric angle, establishing that they
are directed nearly randomly. If these events are jets triggered by
magnetic reconnection between emerging magnetic flux and the ambient
field, then our results suggest that there is no preferred geometry
for the reconnection process.

---------------------------------------------------------
Title: Solar Cycle Variation in Solar Irradiance
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
2015sac..book..137Y Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Formation and Disintegration of Magnetic Bright Points
Observed by Sunrise/IMaX
Authors: Utz, D.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.;
Jurčák, J.; Martínez Pillet, V.; Solanki, S. K.; Schmidt, W.
2014ApJ...796...79U Altcode: 2014arXiv1411.3240U
The evolution of the physical parameters of magnetic bright points
(MBPs) located in the quiet Sun (mainly in the interwork) during
their lifetime is studied. First, we concentrate on the detailed
description of the magnetic field evolution of three MBPs. This
reveals that individual features follow different, generally complex,
and rather dynamic scenarios of evolution. Next, we apply statistical
methods on roughly 200 observed MBP evolutionary tracks. MBPs are found
to be formed by the strengthening of an equipartition field patch,
which initially exhibits a moderate downflow. During the evolution,
strong downdrafts with an average velocity of 2.4 km s-1
set in. These flows, taken together with the concurrent strengthening of
the field, suggest that we are witnessing the occurrence of convective
collapses in these features, although only 30% of them reach kG field
strengths. This fraction might turn out to be larger when the new 4
m class solar telescopes are operational as observations of MBPs with
current state of the art instrumentation could still be suffering from
resolution limitations. Finally, when the bright point disappears
(although the magnetic field often continues to exist) the magnetic
field strength has dropped to the equipartition level and is generally
somewhat weaker than at the beginning of the MBP's evolution. Also,
only relatively weak downflows are found on average at this stage of
the evolution. Only 16% of the features display upflows at the time
that the field weakens, or the MBP disappears. This speaks either for
a very fast evolving dynamic process at the end of the lifetime, which
could not be temporally resolved, or against strong upflows as the cause
of the weakening of the field of these magnetic elements, as has been
proposed based on simulation results. It is noteworthy that in about 10%
of the cases, we observe in the vicinity of the downflows small-scale
strong (exceeding 2 km s-1) intergranular upflows related
spatially and temporally to these downflows. The paper is complemented
by a detailed discussion of aspects regarding the applied methods,
the complementary literature, and in depth analysis of parameters
like magnetic field strength and velocity distributions. An important
difference to magnetic elements and associated bright structures in
active region plage is that most of the quiet Sun bright points display
significant downflows over a large fraction of their lifetime (i.e.,
in more than 46% of time instances/measurements they show downflows
exceeding 1 km s-1).

---------------------------------------------------------
Title: Magnetic Flux Transport at the Solar Surface
Authors: Jiang, J.; Hathaway, D. H.; Cameron, R. H.; Solanki, S. K.;
Gizon, L.; Upton, L.
2014SSRv..186..491J Altcode: 2014SSRv..tmp...43J; 2014arXiv1408.3186J
After emerging to the solar surface, the Sun's magnetic field displays a
complex and intricate evolution. The evolution of the surface field is
important for several reasons. One is that the surface field, and its
dynamics, sets the boundary condition for the coronal and heliospheric
magnetic fields. Another is that the surface evolution gives us insight
into the dynamo process. In particular, it plays an essential role
in the Babcock-Leighton model of the solar dynamo. Describing this
evolution is the aim of the surface flux transport model. The model
starts from the emergence of magnetic bipoles. Thereafter, the model is
based on the induction equation and the fact that after emergence the
magnetic field is observed to evolve as if it were purely radial. The
induction equation then describes how the surface flows—differential
rotation, meridional circulation, granular, supergranular flows,
and active region inflows—determine the evolution of the field (now
taken to be purely radial). In this paper, we review the modeling of
the various processes that determine the evolution of the surface
field. We restrict our attention to their role in the surface flux
transport model. We also discuss the success of the model and some of
the results that have been obtained using this model.

---------------------------------------------------------
Title: Solar Cycle Variation in Solar Irradiance
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.
2014SSRv..186..137Y Altcode: 2014arXiv1407.4249Y; 2014SSRv..tmp...25Y
The correlation between solar irradiance and the 11-year solar activity
cycle is evident in the body of measurements made from space, which
extend over the past four decades. Models relating variation in solar
irradiance to photospheric magnetism have made significant progress
in explaining most of the apparent trends in these observations. There
are, however, persistent discrepancies between different measurements
and models in terms of the absolute radiometry, secular variation and
the spectral dependence of the solar cycle variability. We present an
overview of solar irradiance measurements and models, and discuss the
key challenges in reconciling the divergence between the two.

---------------------------------------------------------
Title: The magnetic field in the solar atmosphere
Authors: Wiegelmann, Thomas; Thalmann, Julia K.; Solanki, Sami K.
2014A&ARv..22...78W Altcode: 2014arXiv1410.4214W
This publication provides an overview of magnetic fields in the solar
atmosphere with the focus lying on the corona. The solar magnetic field
couples the solar interior with the visible surface of the Sun and with
its atmosphere. It is also responsible for all solar activity in its
numerous manifestations. Thus, dynamic phenomena such as coronal mass
ejections and flares are magnetically driven. In addition, the field
also plays a crucial role in heating the solar chromosphere and corona
as well as in accelerating the solar wind. Our main emphasis is the
magnetic field in the upper solar atmosphere so that photospheric and
chromospheric magnetic structures are mainly discussed where relevant
for higher solar layers. Also, the discussion of the solar atmosphere
and activity is limited to those topics of direct relevance to the
magnetic field. After giving a brief overview about the solar magnetic
field in general and its global structure, we discuss in more detail
the magnetic field in active regions, the quiet Sun and coronal holes.

---------------------------------------------------------
Title: A New SATIRE-S Spectral Solar Irradiance Reconstruction for
Solar Cycles 21-23 and Its Implications for Stratospheric Ozone*
Authors: Ball, William T.; Krivova, Natalie A.; Unruh, Yvonne C.;
Haigh, Joanna D.; Solanki, Sami K.
2014JAtS...71.4086B Altcode: 2014arXiv1408.0365B
We present a revised and extended total and spectral solar irradiance
(SSI) reconstruction, which includes a wavelength-dependent uncertainty
estimate, spanning the last three solar cycles using the SATIRE-S
model. The SSI reconstruction covers wavelengths between 115 and
160,000 nm and all dates between August 1974 and October 2009. This
represents the first full-wavelength SATIRE-S reconstruction to
cover the last three solar cycles without data gaps and with an
uncertainty estimate. SATIRE-S is compared with the NRLSSI model and
SORCE/SOLSTICE ultraviolet (UV) observations. SATIRE-S displays similar
cycle behaviour to NRLSSI for wavelengths below 242 nm and almost twice
the variability between 242 and 310 nm. During the decline of last
solar cycle, between 2003 and 2008, SSI from SORCE/SOLSTICE version
12 and 10 typically displays more than three times the variability of
SATIRE-S between 200 and 300 nm. All three datasets are used to model
changes in stratospheric ozone within a 2D atmospheric model for a
decline from high solar activity to solar minimum. The different flux
changes result in different modelled ozone trends. Using NRLSSI leads
to a decline in mesospheric ozone, while SATIRE-S and SORCE/SOLSTICE
result in an increase. Recent publications have highlighted increases
in mesospheric ozone when considering version 10 SORCE/SOLSTICE
irradiances. The recalibrated SORCE/SOLSTICE version 12 irradiances
result in a much smaller mesospheric ozone response than when using
version 10 and now similar in magnitude to SATIRE-S. This shows that
current knowledge of variations in spectral irradiance is not sufficient
to warrant robust conclusions concerning the impact of solar variability
on the atmosphere and climate.

---------------------------------------------------------
Title: Evolution of Small Scale Magnetic Structures from Sunrise Data
Authors: Anusha, L. S.; Feller, A.; Hirzberger, J.; Solanki, S. K.
2014ASPC..489...83A Altcode:
We present the results of an analysis of small scale magnetic features
in the quiet Sun, observed with the Sunrise balloon borne telescope. Our
aim is to understand the contribution of different physical processes
that drive the evolution of magnetic features in quiet regions of
the photosphere. To this end, we study the rearrangement, addition,
and removal of magnetic flux through splitting, merging, cancellation,
and emergence of magnetic fields.

---------------------------------------------------------
Title: Discriminant analysis of solar bright points and faculae
II. Contrast and morphology analysis
Authors: Kobel, P.; Hirzberger, J.; Solanki, S. K.
2014arXiv1410.5354K Altcode:
Taken at a high spatial resolution of 0.1 arcsec, Bright Points (BPs)
are found to coexist with faculae in images and the latter are often
resolved as adjacent striations. Understanding the properties of these
different features is fundamental to carrying out proxy magnetometry. To
shed light on the relationship between BPs and faculae, we studied
them separately after the application of a classification method,
developed and described in a previous paper) on active region images
at various heliocentric angles. In this Paper, we explore different
aspects of the photometric properties of BPs and faculae, namely
their G-band contrast profiles, their peak contrast in G-band and
continuum, as well as morphological parameters. We find that: (1)
the width of the contrast profiles of the classified BPs and faculae
are consistent with studies of disk center BPs at and limb faculae,
which indirectly confirms the validity of our classification, (2) the
profiles of limb faculae are limbward skewed on average, while near
disk center they exhibit both centerward and limbward skewnesses due
to the distribution of orientations of the faculae, (3) the relation
between the peak contrasts of BPs and faculae and their apparent area
discloses a trend reminiscent of magnetogram studies. The skewness
of facular profiles provides a novel constraint for 3D MHD models of
faculae. As suggested by the asymmetry and orientation of their contrast
profiles, faculae near disk center could be induced by inclined fields,
while apparent BPs near the limb seem to be in fact small faculae
misidentified. The apparent area of BPs and faculae could be possibly
exploited for proxy magnetometry.

---------------------------------------------------------
Title: Modelling total solar irradiance since 1878 from simulated
magnetograms
Authors: Dasi-Espuig, M.; Jiang, J.; Krivova, N. A.; Solanki, S. K.
2014A&A...570A..23D Altcode: 2014arXiv1409.1941D
 Aims: We present a new model of total solar irradiance (TSI)
based on magnetograms simulated with a surface flux transport model
(SFTM) and the Spectral And Total Irradiance REconstructions (SATIRE)
model. Our model provides daily maps of the distribution of the
photospheric field and the TSI starting from 1878. Methods:
The modelling is done in two main steps. We first calculate the
magnetic flux on the solar surface emerging in active and ephemeral
regions. The evolution of the magnetic flux in active regions (sunspots
and faculae) is computed using a surface flux transport model fed
with the observed record of sunspot group areas and positions. The
magnetic flux in ephemeral regions is treated separately using the
concept of overlapping cycles. We then use a version of the SATIRE
model to compute the TSI. The area coverage and the distribution of
different magnetic features as a function of time, which are required by
SATIRE, are extracted from the simulated magnetograms and the modelled
ephemeral region magnetic flux. Previously computed intensity spectra
of the various types of magnetic features are employed. Results:
Our model reproduces the PMOD composite of TSI measurements starting
from 1978 at daily and rotational timescales more accurately than the
previous version of the SATIRE model computing TSI over this period of
time. The simulated magnetograms provide a more realistic representation
of the evolution of the magnetic field on the photosphere and also
allow us to make use of information on the spatial distribution
of the magnetic fields before the times when observed magnetograms
were available. We find that the secular increase in TSI since 1878
is fairly stable to modifications of the treatment of the ephemeral
region magnetic flux.

---------------------------------------------------------
Title: Reconstruction of total and spectral solar irradiance from
1974 to 2013 based on KPVT, SoHO/MDI, and SDO/HMI observations
Authors: Yeo, K. L.; Krivova, N. A.; Solanki, S. K.; Glassmeier, K. H.
2014A&A...570A..85Y Altcode: 2014arXiv1408.1229Y
Context. Total and spectral solar irradiance are key parameters in the
assessment of solar influence on changes in the Earth's climate. 
Aims: We present a reconstruction of daily solar irradiance obtained
using the SATIRE-S model spanning 1974 to 2013 based on full-disc
observations from the KPVT, SoHO/MDI, and SDO/HMI. Methods:
SATIRE-S ascribes variation in solar irradiance on timescales
greater than a day to photospheric magnetism. The solar spectrum
is reconstructed from the apparent surface coverage of bright
magnetic features and sunspots in the daily data using the modelled
intensity spectra of these magnetic structures. We cross-calibrated
the various data sets, harmonizing the model input so as to yield a
single consistent time series as the output. Results: The model
replicates 92% (R2 = 0.916) of the variability in the PMOD
TSI composite including the secular decline between the 1996 and 2008
solar cycle minima. The model also reproduces most of the variability
in observed Lyman-α irradiance and the Mg II index. The ultraviolet
solar irradiance measurements from the UARS and SORCE missions are
mutually consistent up to about 180 nm before they start to exhibit
discrepant rotational and cyclical variability, indicative of unresolved
instrumental effects. As a result, the agreement between model and
measurement, while relatively good below 180 nm, starts to deteriorate
above this wavelength. As with earlier similar investigations,
the reconstruction cannot reproduce the overall trends in SORCE/SIM
SSI. We argue, from the lack of clear solar cycle modulation in the
SIM record and the inconsistency between the total flux recorded
by the instrument and TSI, that unaccounted instrumental trends are
present. Conclusions: The daily solar irradiance time series
is consistent with observations from multiple sources, demonstrating
its validity and utility for climate models. It also provides further
evidence that photospheric magnetism is the prime driver of variation
in solar irradiance on timescales greater than a day.

---------------------------------------------------------
Title: Nonlinear Force-free Field Modeling of the Solar Magnetic
Carpet and Comparison with SDO/HMI and Sunrise/IMaX Observations
Authors: Chitta, L. P.; Kariyappa, R.; van Ballegooijen, A. A.;
DeLuca, E. E.; Solanki, S. K.
2014ApJ...793..112C Altcode: 2014arXiv1408.0497C
In the quiet solar photosphere, the mixed polarity fields form a
magnetic carpet that continuously evolves due to dynamical interaction
between the convective motions and magnetic field. This interplay is a
viable source to heat the solar atmosphere. In this work, we used the
line-of-sight (LOS) magnetograms obtained from the Helioseismic and
Magnetic Imager on the Solar Dynamics Observatory, and the Imaging
Magnetograph eXperiment instrument on the Sunrise balloon-borne
observatory, as time-dependent lower boundary conditions, to study the
evolution of the coronal magnetic field. We use a magneto-frictional
relaxation method, including hyperdiffusion, to produce a time series
of three-dimensional nonlinear force-free fields from a sequence
of photospheric LOS magnetograms. Vertical flows are added up to a
height of 0.7 Mm in the modeling to simulate the non-force-freeness
at the photosphere-chromosphere layers. Among the derived quantities,
we study the spatial and temporal variations of the energy dissipation
rate and energy flux. Our results show that the energy deposited in
the solar atmosphere is concentrated within 2 Mm of the photosphere and
there is not sufficient energy flux at the base of the corona to cover
radiative and conductive losses. Possible reasons and implications are
discussed. Better observational constraints of the magnetic field in
the chromosphere are crucial to understand the role of the magnetic
carpet in coronal heating.

---------------------------------------------------------
Title: Fast Solar Polarimeter: Description and First Results
Authors: Feller, A.; Iglesias, F. A.; Nagaraju, K.; Solanki, S. K.;
Ihle, S.
2014ASPC..489..271F Altcode:
We are developing a novel fast solar imaging polarimeter with an
emphasis on significantly increased polarimetric accuracy and high
spatial resolution. The instrument is based on a fast pnCCD sensor
and shall work at frame rates of up to 400 fps, which suppresses
spurious polarization signals induced by external disturbances such
as atmospheric turbulence or jitter. The much higher polarimetric
accuracy that can be achieved with the new instrument is in particular
expected to extend studies of the enigmatic small-scale magnetic field
in the quiet Sun, and of chromospheric magnetic fields. Here we will
report on some key concepts of the polarimeter, and on first results
obtained with an evaluation model at the spectrograph of the Vacuum
Tower Telescope on Tenerife.

---------------------------------------------------------
Title: Inclinations of small quiet-Sun magnetic features based on
a new geometric approach
Authors: Jafarzadeh, S.; Solanki, S. K.; Lagg, A.; Bellot Rubio,
L. R.; van Noort, M.; Feller, A.; Danilovic, S.
2014A&A...569A.105J Altcode: 2014arXiv1408.2443J
Context. High levels of horizontal magnetic flux have been reported
in the quiet-Sun internetwork, often based on Stokes profile
inversions. Aims: Here we introduce a new method for deducing
the inclination of magnetic elements and use it to test magnetic field
inclinations from inversions. Methods: We determine accurate
positions of a set of small, bright magnetic elements in high spatial
resolution images sampling different photospheric heights obtained by
the Sunrise balloon-borne solar observatory. Together with estimates
of the formation heights of the employed spectral bands, these provide
us with the inclinations of the magnetic features. We also compute
the magnetic inclination angle of the same magnetic features from the
inversion of simultaneously recorded Stokes parameters. Results:
Our new, geometric method returns nearly vertical fields (average
inclination of around 14° with a relatively narrow distribution
having a standard deviation of 6°). In strong contrast to this, the
traditionally used inversions give almost horizontal fields (average
inclination of 75 ± 8°) for the same small magnetic features,
whose linearly polarised Stokes profiles are adversely affected by
noise. We show that for such magnetic features inversions overestimate
the flux in horizontal magnetic fields by an order of magnitude. 
Conclusions: The almost vertical field of bright magnetic features from
our geometric method is clearly incompatible with the nearly horizontal
magnetic fields obtained from the inversions. This indicates that the
amount of magnetic flux in horizontal fields deduced from inversions is
overestimated in the presence of weak Stokes signals, in particular if
Stokes Q and U are close to or under the noise level. Inversions should
be used with great caution when applied to data with no clear Stokes Q
and no U signal. By combining the proposed method with inversions we are
not just improving the inclination, but also the field strength. This
technique allows us to analyse features that are not reliably treated
by inversions, thus greatly extending our capability to study the
complete magnetic field of the quiet Sun.

---------------------------------------------------------
Title: Variability of Sun-like stars: reproducing observed photometric
trends
Authors: Shapiro, A. I.; Solanki, S. K.; Krivova, N. A.; Schmutz,
W. K.; Ball, W. T.; Knaack, R.; Rozanov, E. V.; Unruh, Y. C.
2014A&A...569A..38S Altcode: 2014arXiv1406.2383S
Context. The Sun and stars with low magnetic activity levels become
photometrically brighter when their activity increases. Magnetically
more active stars display the opposite behavior and become fainter
when their activity increases. Aims: We reproduce the observed
photometric trends in stellar variations with a model thattreats stars
as hypothetical suns with coverage by magnetic features different from
that of the Sun. Methods: The model attributes the variability
of stellar spectra to the imbalance between the contributions from
different components of the solar atmosphere, such as dark starspots
and bright faculae. A stellar spectrum is calculated from spectra
of the individual components by weighting them with corresponding
disk-area coverages. The latter are obtained by extrapolating
the solar dependences of spot and facular disk-area coverages
on chromospheric activity to stars with different levels of mean
chromospheric activity. Results: We find that the contribution
by starspots to the variability increases faster with chromospheric
activity than the facular contribution. This causes the transition from
faculae-dominated variability and direct activity-brightness correlation
to spot-dominated variability and inverse activity-brightness
correlation with increasing chromospheric activity level. We show that
the regime of the variability also depends on the angle between the
stellar rotation axis and the line-of-sight and on the latitudinal
distribution of active regions on the stellar surface. Our model
can be used as a tool for extrapolating the observed photometric
variability of the Sun to Sun-like stars at different activity levels,
which makes a direct comparison between solar and stellar irradiance
data possible. Appendices are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201323086/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Comparison of solar photospheric bright points between Sunrise
observations and MHD simulations
Authors: Riethmüller, T. L.; Solanki, S. K.; Berdyugina, S. V.;
Schüssler, M.; Martínez Pillet, V.; Feller, A.; Gandorfer, A.;
Hirzberger, J.
2014A&A...568A..13R Altcode: 2014arXiv1406.1387R
Bright points (BPs) in the solar photosphere are thought to be the
radiative signatures (small-scale brightness enhancements) of magnetic
elements described by slender flux tubes or sheets located in the darker
intergranular lanes in the solar photosphere. They contribute to the
ultraviolet (UV) flux variations over the solar cycle and hence may
play a role in influencing the Earth's climate. Here we aim to obtain
a better insight into their properties by combining high-resolution
UV and spectro-polarimetric observations of BPs by the Sunrise
Observatory with 3D compressible radiation magnetohydrodynamical
(MHD) simulations. To this end, full spectral line syntheses are
performed with the MHD data and a careful degradation is applied
to take into account all relevant instrumental effects of the
observations. In a first step it is demonstrated that the selected
MHD simulations reproduce the measured distributions of intensity at
multiple wavelengths, line-of-sight velocity, spectral line width,
and polarization degree rather well. The simulated line width also
displays the correct mean, but a scatter that is too small. In
the second step, the properties of observed BPs are compared with
synthetic ones. Again, these are found to match relatively well,
except that the observations display a tail of large BPs with strong
polarization signals (most likely network elements) not found in the
simulations, possibly due to the small size of the simulation box. The
higher spatial resolution of the simulations has a significant effect,
leading to smaller and more numerous BPs. The observation that most BPs
are weakly polarized is explained mainly by the spatial degradation,
the stray light contamination, and the temperature sensitivity of the Fe
i line at 5250.2 Å. Finally, given that the MHD simulations are highly
consistent with the observations, we used the simulations to explore
the properties of BPs further. The Stokes V asymmetries increase with
the distance to the center of the mean BP in both observations and
simulations, consistent with the classical picture of a production
of the asymmetry in the canopy. This is the first time that this has
been found also in the internetwork. More or less vertical kilogauss
magnetic fields are found for 98% of the synthetic BPs underlining
that basically every BP is associated with kilogauss fields. At the
continuum formation height, the simulated BPs are on average 190 K
hotter than the mean quiet Sun, the mean BP field strength is found to
be 1750 G, and the mean inclination is 17°, supporting the physical
flux-tube paradigm to describe BPs. On average, the synthetic BPs
harbor downflows increasing with depth. The origin of these downflows
is not yet understood very well and needs further investigation.

---------------------------------------------------------
Title: Vigorous convection in a sunspot granular light bridge
Authors: Lagg, Andreas; Solanki, Sami K.; van Noort, Michiel;
Danilovic, Sanja
2014A&A...568A..60L Altcode: 2014arXiv1407.1202L
Context. Light bridges are the most prominent manifestation of
convection in sunspots. The brightest representatives are granular
light bridges composed of features that appear to be similar to
granules. Aims: An in-depth study of the convective motions,
temperature stratification, and magnetic field vector in and around
light bridge granules is presented with the aim of identifying
similarities and differences to typical quiet-Sun granules. 
Methods: Spectropolarimetric data from the Hinode Solar Optical
Telescope were analyzed using a spatially coupled inversion technique
to retrieve the stratified atmospheric parameters of light bridge and
quiet-Sun granules. Results: Central hot upflows surrounded by
cooler fast downflows reaching 10 km s-1 clearly establish
the convective nature of the light bridge granules. The inner part
of these granules in the near surface layers is field free and is
covered by a cusp-like magnetic field configuration. We observe
hints of field reversals at the location of the fast downflows. The
quiet-Sun granules in the vicinity of the sunspot are covered by a
low-lying canopy field extending radially outward from the spot. Conclusions: The similarities between quiet-Sun and light bridge
granules point to the deep anchoring of granular light bridges in
the underlying convection zone. The fast, supersonic downflows are
most likely a result of a combination of invigorated convection
in the light bridge granule due to radiative cooling into the
neighboring umbra and the fact that we sample deeper layers, since the
downflows are immediately adjacent to the slanted walls of the Wilson
depression. The two movies are available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201424071/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Scattered Lyman-α radiation of comet 2012/S1 (ISON) observed
by SUMER/SOHO
Authors: Curdt, W.; Boehnhardt, H.; Vincent, J. -B.; Solanki, S. K.;
Schühle, U.; Teriaca, L.
2014A&A...567L...1C Altcode: 2014arXiv1406.4343C
During its sungrazing perihelion passage, comet ISON appeared in
the field of view of the SUMER spectrometer and allowed unique
observations at far-ultraviolet wavelengths with high spatial and
temporal resolution. We report results of these observations completed
on November 28, 2013, when the comet was only 2.82 Rʘ
away from the Sun. Our data show the arrow-shaped dust tail in Ly-α
emission trailing behind the predicted position of the nucleus, but
offset from the trajectory. We interpret the emission as sunlight
that is scattered at μm-sized dust particles. We modeled the dust
emission and dynamics to reproduce the appearance of the tail. We
were unable to detect any signature of cometary gas or plasma around
the expected position of the nucleus and conclude that the outgassing
processes must have stopped before the observation started. Moreover,
the model we used to reproduce the observed dust tail needs a sharp
fall-off of the dust production hours before perihelion transit. We
compare the radiances of the disk and the dust tail for an estimate
of the dust column density and tail mass.

---------------------------------------------------------
Title: The History of a Quiet-Sun Magnetic Element Revealed by
IMaX/SUNRISE
Authors: Requerey, Iker S.; Del Toro Iniesta, Jose Carlos; Bellot
Rubio, Luis R.; Bonet, José A.; Martínez Pillet, Valentín; Solanki,
Sami K.; Schmidt, Wolfgang
2014ApJ...789....6R Altcode: 2014arXiv1405.2837R
Isolated flux tubes are considered to be fundamental magnetic building
blocks of the solar photosphere. Their formation is usually attributed
to the concentration of magnetic field to kG strengths by the convective
collapse mechanism. However, the small size of the magnetic elements in
quiet-Sun areas has prevented this scenario from being studied in fully
resolved structures. Here, we report on the formation and subsequent
evolution of one such photospheric magnetic flux tube, observed in
the quiet Sun with unprecedented spatial resolution (0.”15-0.”18)
and high temporal cadence (33 s). The observations were acquired by
the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne
solar observatory. The equipartition field strength magnetic element
is the result of the merging of several same polarity magnetic flux
patches, including a footpoint of a previously emerged loop. The
magnetic structure is then further intensified to kG field strengths
by convective collapse. The fine structure found within the flux
concentration reveals that the scenario is more complex than can be
described by a thin flux tube model with bright points and downflow
plumes being established near the edges of the kG magnetic feature. We
also observe a daisy-like alignment of surrounding granules and a
long-lived inflow toward the magnetic feature. After a subsequent
weakening process, the field is again intensified to kG strengths. The
area of the magnetic feature is seen to change in anti-phase with the
field strength, while the brightness of the bright points and the speed
of the downflows varies in phase. We also find a relation between the
brightness of the bright point and the presence of upflows within it.

---------------------------------------------------------
Title: Scattered Lyman-alpha radiation of comet 2012/S1 (ISON)
observed by SUMER/SOHO
Authors: Curdt, W.; Boehnhardt, H.; Germerott, D.; Schuehle, U.;
Solanki, S.; Teriaca, L.; Vincent, J.
2014acm..conf..119C Altcode:
During its recent perihelion passage, comet ISON came so close to
the Sun that it appeared in the field of view (FOV) of the SUMER
spectrometer on SOHO and allowed unique observations at far-UV
wavelengths with high spatial and temporal resolution. We report results
of these observations completed during the comet's encounter with the
Sun on November 28.75, 2013. Our data show the dust tail trailing behind
the predicted position of the nucleus seen in Lyman-alpha emission
as light from the solar disk that is scattered by micron-sized dust
particles. The arrow-shaped tail is offset from the trajectory and not
aligned with it. We model the dust emission and dynamics to reproduce
the appearance of the tail. We could not detect any signature of
cometary gas or plasma around the expected position of the nucleus
and conclude that the out-gassing processes must have stopped before
the comet entered our FOV. Also the model we used to reproduce the
observed dust tail needs a sharp fall-off of the dust production hours
before perihelion. We compare the radiance of the dust tail to the
Lyman-alpha emission of the disk for an estimate of the dust column
density. After observing 18 years mostly solar targets, this was the
first time that SUMER completed spectroscopic observations of a comet.

---------------------------------------------------------
Title: Search for Solar Axions by the CERN Axion Solar Telescope
with He3 Buffer Gas: Closing the Hot Dark Matter Gap
Authors: Arik, M.; Aune, S.; Barth, K.; Belov, A.; Borghi, S.;
Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.; Collar,
J. I.; Da Riva, E.; Dafni, T.; Davenport, M.; Eleftheriadis, C.;
Elias, N.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.; Galán,
J.; García, J. A.; Gardikiotis, A.; Garza, J. G.; Gazis, E. N.;
Geralis, T.; Georgiopoulou, E.; Giomataris, I.; Gninenko, S.; Gómez,
H.; Gómez Marzoa, M.; Gruber, E.; Guthörl, T.; Hartmann, R.; Hauf,
S.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.;
Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza, M.; Königsmann,
K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Lakić, B.; Lang, P. M.;
Laurent, J. M.; Liolios, A.; Ljubičić, A.; Luzón, G.; Neff, S.;
Niinikoski, T.; Nordt, A.; Papaevangelou, T.; Pivovaroff, M. J.;
Raffelt, G.; Riege, H.; Rodríguez, A.; Rosu, M.; Ruz, J.; Savvidis,
I.; Shilon, I.; Silva, P. S.; Solanki, S. K.; Stewart, L.; Tomás,
A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.; Villar, J.; Vogel,
J. K.; Yildiz, S. C.; Zioutas, K.; CAST Collaboration
2014PhRvL.112i1302A Altcode: 2013arXiv1307.1985A
The CERN Axion Solar Telescope has finished its search for
solar axions with He3 buffer gas, covering the search range
0.64 eV≲ma≲1.17 eV. This closes the gap to the
cosmological hot dark matter limit and actually overlaps with
it. From the absence of excess x rays when the magnet was pointing
to the Sun we set a typical upper limit on the axion-photon coupling
of gaγ≲3.3×10-10 GeV-1 at 95%
C.L., with the exact value depending on the pressure setting. Future
direct solar axion searches will focus on increasing the sensitivity
to smaller values of gaγ, for example by the currently
discussed next generation helioscope International AXion Observatory.

---------------------------------------------------------
Title: Comparison between Mg II k and Ca II H Images Recorded by
SUNRISE/SuFI
Authors: Danilovic, S.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
S. K.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.; Knölker,
M.; Schmidt, W.; Blanco Rodríguez, J.; Del Toro Iniesta, J. C.
2014ApJ...784...20D Altcode:
We present a comparison of high-resolution images of the solar surface
taken in the Mg II k and Ca II H channels of the Filter Imager on the
balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled
with 0.48 nm and 0.11 nm wide filters, respectively. The two channels
show remarkable qualitative and quantitative similarities in the quiet
Sun, in an active region plage and during a small flare. However, the Mg
filtergrams display 1.4-1.7 times higher intensity contrast and appear
more smeared and smoothed in the quiet Sun. In addition, the fibrils
in a plage are wider. Although the exposure time is 100 times longer
for Mg images, the evidence suggests that these differences cannot be
explained only with instrumental effects or the evolution of the solar
scene. The differences at least partially arise because of different
line-formation heights, the stronger response of Mg k emission peaks
to the higher temperatures, and the larger height range sampled by
the broad Mg filter used here. This is evidently manifested during
the flare when a surge in Mg evolves differently than in Ca.

---------------------------------------------------------
Title: Migration of Ca II H bright points in the internetwork
Authors: Jafarzadeh, S.; Cameron, R. H.; Solanki, S. K.; Pietarila,
A.; Feller, A.; Lagg, A.; Gandorfer, A.
2014A&A...563A.101J Altcode: 2014arXiv1401.7522J
Context. The migration of magnetic bright point-like features (MBP)
in the lower solar atmosphere reflects the dispersal of magnetic
flux as well as the horizontal flows of the atmospheric layer they
are embedded in. Aims: We analyse trajectories of the proper
motion of intrinsically magnetic, isolated internetwork Ca ii H MBPs
(mean lifetime 461 ± 9 s) to obtain their diffusivity behaviour. Methods: We use seeing-free high spatial and temporal resolution
image sequences of quiet-Sun, disc-centre observations obtained in
the Ca ii H 3968 Å passband of the Sunrise Filter Imager (SuFI)
onboard the Sunrise balloon-borne solar observatory. Small MBPs in
the internetwork are automatically tracked. The trajectory of each
MBP is then calculated and described by a diffusion index (γ) and
a diffusion coefficient (D). We also explore the distribution of the
diffusion indices with the help of a Monte Carlo simulation. 
Results: We find γ = 1.69 ± 0.08 and D = 257 ± 32 km2
s-1 averaged over all MBPs. Trajectories of most MBPs are
classified as super-diffusive, i.e. γ &gt; 1, with the determined γ
being the largest obtained so far to our knowledge. A direct correlation
between D and timescale (τ) determined from trajectories of all MBPs is
also obtained. We discuss a simple scenario to explain the diffusivity
of the observed, relatively short-lived MBPs while they migrate within
a small area in a supergranule (i.e. an internetwork area). We show
that the scatter in the γ values obtained for individual MBPs is due
to their limited lifetimes. Conclusions: The super-diffusive
MBPs can be described as random walkers (due to granular evolution and
intergranular turbulence) superposed on a large systematic (background)
velocity, caused by granular, mesogranular, and supergranular flows.

---------------------------------------------------------
Title: Magnetic structure of an activated filament in a flaring
active region
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
2014A&A...561A..98S Altcode: 2013arXiv1312.2781S
 Aims: While the magnetic field in quiescent prominences has
been widely investigated, less is known about the field in activated
prominences. We report observational results on the magnetic field
structure of an activated filament in a flaring active region. In
particular, we studied its magnetic structure and line-of-sight flows
during its early activated phase, shortly before it displayed signs
of rotation. Methods: We inverted the Stokes profiles of the
chromospheric He i 10 830 Å triplet and the photospheric Si i 10 827
Å line observed in this filament by the Vacuum Tower Telescope on
Tenerife. Using these inversion results, we present and interpret the
first maps of the velocity and magnetic field obtained in an activated
filament, both in the photosphere and the chromosphere. Results:
Up to five different magnetic components are found in the chromospheric
layers of the filament, while outside the filament a single component is
sufficient to reproduce the observations. Magnetic components displaying
an upflow are preferentially located towards the centre of the filament,
while the downflows are concentrated along its periphery. Moreover,
the upflowing gas is associated with an opposite-polarity magnetic
configuration with respect to the photosphere, while the downflowing gas
is associated with a same-polarity configuration. Conclusions:
The activated filament has a very complex structure. Nonetheless,
it is compatible with a flux rope, albeit a distorted one, in
the normal configuration. The observations are best explained
by a rising flux rope in which part of the filament material is
still stably stored (upflowing material, rising with the field),
while the rest is no longer stably stored and flows down along the
field lines. The movie is available in electronic form at <A
href="http://www.aanda.org/10.1051/0004-6361/201322481/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: The chromosphere above sunspots at millimeter wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
2014A&A...561A.133L Altcode: 2014arXiv1403.3436L
 Aims: The aim of this paper is to demonstrate that millimeter
wave data can be used to distinguish between various atmospheric models
of sunspots, whose temperature structure in the upper photosphere
and chromosphere has been the source of some controversy. 
Methods: We use observations of the temperature contrast (relative
to the quiet Sun) above a sunspot umbra at 3.5 mm obtained with
the Berkeley-Illinois-Maryland Array (BIMA), complemented by submm
observations from Lindsey &amp; Kopp (1995) and 2 cm observations
with the Very Large Array. These are compared with the umbral contrast
calculated from various atmospheric models of sunspots. Results:
Current mm and submm observational data suggest that the brightness
observed at these wavelengths is low compared to the most widely used
sunspot models. These data impose strong constraints on the temperature
and density stratifications of the sunspot umbral atmosphere, in
particular on the location and depth of the temperature minimum and the
location of the transition region. Conclusions: A successful
model that is in agreement with millimeter umbral brightness should
have an extended and deep temperature minimum (below 3000 K). Better
spatial resolution as well as better wavelength coverage are needed
for a more complete determination of the chromospheric temperature
stratification above sunspot umbrae.

---------------------------------------------------------
Title: Time evolution of a single, quiet-Sun magnetic structure
Authors: Requerey, Iker S.; Bonet, José Antonio; Solanki, Sami K.;
Bellot Rubio, L. R.; Del Toro Iniesta, Jose Carlos
2014cosp...40E2828R Altcode:
Isolated flux tubes are considered to be fundamental magnetic building
blocks of the solar photosphere. Their formation is usually attributed
to the concentration of magnetic field to kG strengths by the convective
instability mechanism. However, the small size of the magnetic elements
in quiet-Sun areas has prevented this scenario from being studied
in fully resolved structures. Here we report on the formation and
subsequent evolution of a photospheric magnetic flux tube, observed
in the quiet Sun with unprecedented spatial resolution (0. (”) 15 -
0. (”) 18) and high temporal cadence (33 s). The observations were
acquired by the Imaging Magnetograph Experiment (IMaX) aboard the
textsc{Sunrise} balloon-borne solar observatory. The equipartition
field strength magnetic element is reached from the merging of
several magnetic flux patches in a mesogranule-sized sink. The
magnetic structure is then further intensified to kG field strengths by
convective collapse and granular compression. The fine structure found
within the flux concentration reveal that the scenario is more complex
than a canonical flux tube model. After a subsequent weakening process,
the field is further intensified to kG strengths. Seen as a whole, the
evolution of the magnetic structure is compatible with oscillations in
all basic physical quantities. A discussion on whether this evolution
fits to the current theoretical descriptions is also presented.

---------------------------------------------------------
Title: Point spread function of SDO/HMI and the effects of stray
light correction on the apparent properties of solar surface phenomena
Authors: Yeo, K. L.; Feller, A.; Solanki, S. K.; Couvidat, S.;
Danilovic, S.; Krivova, N. A.
2014A&A...561A..22Y Altcode: 2013arXiv1310.4972Y
 Aims: We present a point spread function (PSF) for the
Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO) and discuss the effects of its removal on the
apparent properties of solar surface phenomena in HMI data. 
Methods: The PSF was retrieved from observations of Venus in transit
by matching it to the convolution of a model of the Venusian disc and
solar background with a guess PSF. We described the PSF as the sum of
five Gaussian functions, the amplitudes of which vary sinusoidally with
azimuth. This relatively complex functional form was required by the
data. Observations recorded near in time to the transit of Venus were
corrected for instrumental scattered light by the deconvolution with the
PSF. We also examined the variation in the shape of the solar aureole in
daily data, as an indication of PSF changes over time. Results:
Granulation contrast in restored HMI data is greatly enhanced relative
to the original data and exhibit reasonable agreement with numerical
simulations. Image restoration enhanced the apparent intensity and
pixel averaged magnetic field strength of photospheric magnetic features
significantly. For small-scale magnetic features, restoration enhanced
intensity contrast in the continuum and core of the Fe I 6173 Å line
by a factor of 1.3, and the magnetogram signal by a factor of 1.7. For
sunspots and pores, the enhancement varied strongly within and between
features, being more acute for smaller features. Magnetic features are
also rendered smaller, as signal smeared onto the surrounding quiet
Sun is recovered. Image restoration increased the apparent amount of
magnetic flux above the noise floor by a factor of about 1.2, most
of the gain coming from the quiet Sun. Line-of-sight velocity due to
granulation and supergranulation is enhanced by a factor of 1.4 to 2.1,
depending on position on the solar disc. The shape of the solar aureole
varied, with time and between the two CCDs. There are also indications
that the PSF varies across the FOV. However, all these variations were
found to be relatively small, such that a single PSF can be applied to
HMI data from both CCDs, over the period examined without introducing
significant error. Conclusions: Restoring HMI observations
with the PSF presented here returns a reasonable estimate of the stray
light-free intensity contrast. Image restoration affects the measured
radiant, magnetic and dynamic properties of solar surface phenomena
sufficiently to significantly impact interpretation.

---------------------------------------------------------
Title: Reconstructions of solar irradiance on centennial time scales
Authors: Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria;
Kok Leng, Yeo
2014cosp...40E1664K Altcode:
Solar irradiance is the main external source of energy to Earth's
climate system. The record of direct measurements covering less than 40
years is too short to study solar influence on Earth's climate, which
calls for reconstructions of solar irradiance into the past with the
help of appropriate models. An obvious requirement to a competitive
model is its ability to reproduce observed irradiance changes, and a
successful example of such a model is presented by the SATIRE family of
models. As most state-of-the-art models, SATIRE assumes that irradiance
changes on time scales longer than approximately a day are caused by
the evolving distribution of dark and bright magnetic features on the
solar surface. The surface coverage by such features as a function of
time is derived from solar observations. The choice of these depends
on the time scale in question. Most accurate is the version of the
model that employs full-disc spatially-resolved solar magnetograms and
reproduces over 90% of the measured irradiance variation, including
the overall decreasing trend in the total solar irradiance over
the last four cycles. Since such magnetograms are only available
for about four decades, reconstructions on time scales of centuries
have to rely on disc-integrated proxies of solar magnetic activity,
such as sunspot areas and numbers. Employing a surface flux transport
model and sunspot observations as input, we have being able to produce
synthetic magnetograms since 1700. This improves the temporal resolution
of the irradiance reconstructions on centennial time scales. The most
critical aspect of such reconstructions remains the uncertainty in
the magnitude of the secular change.

---------------------------------------------------------
Title: Analysis of magnetic fields in a plage region using a spatially
coupled 2D inversion technique
Authors: Buehler, David; Lagg, Andreas; Solanki, Sami K.; Van Noort,
Michiel
2014cosp...40E.427B Altcode:
The properties of magnetic features (MFCs) within a plage region
in the vicinity of a sunspot were investigated at high spatial
resolution. Stokes spectra of the 630nm line pair recorded by the
spectropolarimeter aboard Hinode were inverted using an extended
version of the SPINOR code. The code preformed a spatially coupled
inversion of the Stokes spectra using three log(tau) nodes in optical
depth. No magnetic filling factors was employed. The analysis of the
inversion results reveals that the MFCs have typical field strengths
of 1500G at log(tau)=-0.9 and inclinations between 10-15 degrees in
all three log(tau) nodes. The MFCs expand by forming magnetic canopies
composed of weaker and more inclined magnetic fields. The expansion of
the magnetic field and temperature stratification of MFCs with optical
depth is in good agreement with a thin flux tube model. Whilst the gas
inside magnetic flux concentrations is typically at rest, the majority
of MFCs were surrounded by a ring of downflows with an average value
of 2.5km/s at log(tau)=0. The ring gradually shifts outwards following
the expansion of the MFC. Within the downflow rings of MFCs small
magnetic patches of opposite polarity to that of the main MFC were
identified, which are predominantly situated beneath the canopy of
its main MFC. We found evidence for a strong broadening of the Stokes
profiles within MFCs and their surrounding downflow rings (expressed
by a microturbulence in the inversion). This indicates the presence
of strong unresolved velocities.

---------------------------------------------------------
Title: Total solar irradiance reconstruction since 1700 using a flux
transport model
Authors: Dasi Espuig, Maria; Krivova, Natalie; Solanki, Sami K.;
Jiang, Jie
2014cosp...40E.634D Altcode:
Reconstructions of solar irradiance into the past are crucial for
studies of solar influence on climate. Models based on the assumption
that irradiance changes are caused by the evolution of the photospheric
magnetic fields have been most successful in reproducing the measured
irradiance variations. Daily magnetograms, such as those from MDI and
HMI, provide the most detailed information on the changing distribution
of the photospheric magnetic fields. Since such magnetograms are
only available from 1974, we used a surface flux transport model to
describe the evolution of the magnetic fields on the solar surface
due to the effects of differential rotation, meridional circulation,
and turbulent diffusivity, before 1974. In this model, the sources of
magnetic flux are the active regions, which are introduced based on
sunspot group areas, positions, and tilt angles. The RGO record is,
however, only available since 1874. Here we present a model of solar
irradiance since 1700, which is based on a semi-synthetic sunspot
record. The semi-synthetic record was obtained using statistical
relationships between sunspot group properties (areas, positions,
tilt angles) derived from the RGO record on one hand, and the cycle
strength and phase derived from the sunspot group number (Rg) on the
other. These relationships were employed to produce daily records
of sunspot group positions, areas, and tilt angles before 1874. The
semi-synthetic records were fed into the surface flux transport model
to simulate daily magnetograms since 1700. By combining the simulated
magnetograms with a SATIRE-type model, we then reconstructed total
solar irradiance since 1700.

---------------------------------------------------------
Title: Sunrise Mission Highlights
Authors: Riethmüller, T.; Solanki, S. K.; Sunrise Team
2014frap.confE..34R Altcode: 2014PoS...237E..34R
No abstract at ADS

---------------------------------------------------------
Title: Fast Solar Polarimeter: First Light Results
Authors: Krishnappa, N.; Feller, A.; Iglesia, F. A.; Solanki, S.
2013AGUFMSM53A2213K Altcode:
Accurate measurements of magnetic fields on the Sun are crucial
to understand various physical processes that take place in the
solar atmosphere such as solar eruptions, coronal heating, solar
wind acceleration, etc. The Fast Solar Polarimeter (FSP) is a new
instrument that is being developed to probe magnetic fields on the
Sun. One of the main goals of this polarimeter is to carry out high
precision spectropolarimetric observations with spatial resolution
close to the telescope diffraction limit. The polarimeter is based
on pnCCD technology with split frame transfer and simultaneous
multi-channel readout, resulting in frame rate upto 1 kHz. The FSP
prototype instrument uses a small format pnCCD of 264x264 pixels
which has been developed by PNSensor and by the semiconductor lab of
the Max Planck Society. The polarization modulator is based on two
ferro-electric liquid crystals (FLCs) interlaced between two static
retarders. The first solar observations have been carried out with this
prototype during May-June, 2013 at German Vacuum Tower Telescope (VTT)
on Tenerife, Canary Islands, Spain. Here we present the instrument
performance assessments and the first results on the magnetic field
measurements. Further, we briefly discuss about the next phase of FSP
which will be a dual beam system with 1k x 1k CCDs.

---------------------------------------------------------
Title: Three-dimensional non-LTE radiative transfer effects in Fe
i lines. II. Line formation in 3D radiation hydrodynamic simulations
Authors: Holzreuter, R.; Solanki, S. K.
2013A&A...558A..20H Altcode: 2013arXiv1308.2490H
Here we investigate the effects of horizontal radiative transfer
(RT) in combination with non-local thermodynamic equilibrum (NLTE)
on important diagnostic iron lines in a realistic atmosphere. Using
a snapshot of a 3D radiation-hydrodynamic (HD) simulation and a
multilevel iron atom, we computed widely used Fe i line profiles at
three different levels of approximation of the RT (3D NLTE, 1D NLTE,
LTE). By comparing the resulting line profiles and the circumstances of
their formation, we gain new insight into the importance of horizontal
RT. We find that the influence of horizontal RT is of the same order
of magnitude as that of NLTE, although spatially more localized. Also,
depending on the temperature of the surroundings, horizontal RT is
found to either weaken or strengthen spectral lines. Line depths
and equivalent width may differ by up to 20% from the corresponding
LTE value if 3D RT is applied. Residual intensity contrasts in LTE
are found to be larger than those in 3D NLTE by up to a factor of
two. When compared to 1D NLTE, we find that horizontal RT weakens the
contrast by up to 30% almost independently of the angle of line of
sight. While the center-to-limb variation (CLV) of the 1D and 3D NLTE
contrasts have a similar form, the LTE contrast CLV shows a different
run. Determination of temperatures by 1D NLTE inversions of spatially
resolved observations may produce errors of up to 200 K if one neglects
3D RT. We find a linear correlation between the intensity difference
of 1D and 3D NLTE and a simple estimate of the temperature in the
horizontal environment of the line formation region. This correlation
could be used to coarsely correct inversions done in 1D NLTE for some
of the effects of horizontal RT. Horizontal RT is less important if
one considers spatially averaged line profiles because local line
strengthening and weakening occur with similar frequency in our HD
atmosphere. Thus, the iron abundance is underestimated by 0.012 dex if
calculated using 1D NLTE RT. Since effects of horizontal RT are greatest
for spatially resolved quantities, the use of 3D RT is particularly
important for interpreting high spatial resolution observations.

---------------------------------------------------------
Title: Temporal relation between quiet-Sun transverse fields and
the strong flows detected by IMaX/SUNRISE
Authors: Quintero Noda, C.; Martínez Pillet, V.; Borrero, J. M.;
Solanki, S. K.
2013A&A...558A..30Q Altcode: 2013arXiv1309.0627Q
Context. Localized strongly Doppler-shifted Stokes V signals were
detected by IMaX/SUNRISE. These signals are related to newly emerged
magnetic loops that are observed as linear polarization features. Aims: We aim to set constraints on the physical nature and causes
of these highly Doppler-shifted signals. In particular, the temporal
relation between the appearance of transverse fields and the strong
Doppler shifts is analyzed in some detail. Methods: We calculated
the time difference between the appearance of the strong flows and the
linear polarization. We also obtained the distances from the center
of various features to the nearest neutral lines and whether they
overlap or not. These distances were compared with those obtained from
randomly distributed points on observed magnetograms. Various cases of
strong flows are described in some detail. Results: The linear
polarization signals precede the appearance of the strong flows by on
average 84 ± 11 s. The strongly Doppler-shifted signals are closer
(0.″19) to magnetic neutral lines than randomly distributed points
(0.″5). Eighty percent of the strongly Doppler-shifted signals are
close to a neutral line that is located between the emerging field and
pre-existing fields. That the remaining 20% do not show a close-by
pre-existing field could be explained by a lack of sensitivity or
an unfavorable geometry of the pre-existing field, for instance, a
canopy-like structure. Conclusions: Transverse fields occurred
before the observation of the strong Doppler shifts. The process is
most naturally explained as the emergence of a granular-scale loop
that first gives rise to the linear polarization signals, interacts
with pre-existing fields (generating new neutral line configurations),
and produces the observed strong flows. This explanation is indicative
of frequent small-scale reconnection events in the quiet Sun.

---------------------------------------------------------
Title: First High-resolution Images of the Sun in the 2796 Å Mg II
k Line
Authors: Riethmüller, T. L.; Solanki, S. K.; Hirzberger, J.;
Danilovic, S.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Gizon, L.;
Knölker, M.; Schmidt, W.; Del Toro Iniesta, J. C.
2013ApJ...776L..13R Altcode: 2013arXiv1309.5213R
We present the first high-resolution solar images in the Mg II k 2796
Å line. The images, taken through a 4.8 Å broad interference filter,
were obtained during the second science flight of Sunrise in 2013 June
by the Sunrise Filter Imager (SuFI) instrument. The Mg II k images
display structures that look qualitatively very similar to images taken
in the core of Ca II H. The Mg II images exhibit reversed granulation
(or shock waves) in the internetwork regions of the quiet Sun, at
intensity contrasts that are similar to those found in Ca II H. Very
prominent in Mg II are bright points, both in the quiet Sun and in plage
regions, particularly near the disk center. These are much brighter than
at other wavelengths sampled at similar resolution. Furthermore, Mg II k
images also show fibril structures associated with plage regions. Again,
the fibrils are similar to those seen in Ca II H images, but tend to
be more pronounced, particularly in weak plage.

---------------------------------------------------------
Title: Peripheral downflows in sunspot penumbrae
Authors: van Noort, M.; Lagg, A.; Tiwari, S. K.; Solanki, S. K.
2013A&A...557A..24V Altcode: 2013arXiv1308.0466V
Context. Sunspot penumbrae show high-velocity patches along
the periphery. Aims: The high-velocity downflow patches
are believed to be the return channels of the Evershed flow. We
aim to investigate their structure in detail using Hinode SOT/SP
observations. Methods: We employ Fourier interpolation in
combination with spatially coupled height dependent LTE inversions
of Stokes profiles to produce high-resolution, height-dependent maps
of atmospheric parameters of these downflows and investigate their
properties. Results: High-speed downflows are observed over
a wide range of viewing angles. They have supersonic line-of-sight
velocities, some in excess of 20 km s-1, and very high
magnetic field strengths, reaching values of over 7 kG. A relation
between the downflow velocities and the magnetic field strength is
found, in good agreement with MHD simulations. Conclusions:
The coupled inversion at high resolution allows for the accurate
determination of small-scale structures. The recovered atmospheric
structure indicates that regions with very high downflow velocities
contain some of the strongest magnetic fields that have ever been
measured on the Sun. Two movies are available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Structure of sunspot penumbral filaments: a remarkable
uniformity of properties
Authors: Tiwari, Sanjiv Kumar; van Noort, Michiel; Lagg, Andreas;
Solanki, Sami K.
2013A&A...557A..25T Altcode: 2013arXiv1307.3668T
Context. The sunspot penumbra comprises numerous thin, radially
elongated filaments that are central for heat transport within
the penumbra, but whose structure is still not clear. Aims:
We aim to investigate the fine-scale structure of these penumbral
filaments. Methods: We perform a depth-dependent inversion of
spectropolarimetric data of a sunspot very close to solar disk center
obtained by Solar Optical Telescope/Spectropolarimeter onboard the
Hinode spacecraft. We have used a recently developed, spatially coupled
2D inversion scheme, which allows us to analyze the fine structure
of individual penumbral filaments up to the diffraction limit of
the telescope. Results: Filaments of different sizes in all
parts of the penumbra display very similar magnetic field strengths,
inclinations, and velocity patterns. The temperature structure is also
similar, although the filaments in the inner penumbra have cooler
tails than those in the outer penumbra. The similarities allowed
us to average all these filaments and to subsequently extract the
physical properties common to all of them. This average filament
shows upflows associated with an upward-pointing field at its inner,
umbral end (head) and along its axis, as well as downflows along the
lateral edge and strong downflows in the outer end (tail) associated
with a nearly vertical, strong, and downward-pointing field. The
upflowing plasma is significantly, i.e., up to 800 K, hotter than the
downflowing plasma. The hot, tear-shaped head of the averaged filament
can be associated with a penumbral grain. The central part of the
filament shows nearly horizontal fields with strengths in the range
of 1 kG. The field above the filament converges, whereas a diverging
trend is seen in the deepest layers near the head of the filament. The
fluctuations in the physical parameters along and across the filament
increase rapidly with depth. Conclusions: We put forward a
unified observational picture of a sunspot penumbral filament. It
is consistent with such a filament being a magneto-convective cell,
in line with recent magnetohydrodynamic simulations. The uniformity
of its properties over the penumbra sets constraints on penumbral
models and simulations. The complex and inhomogeneous structure of the
filament provides a natural explanation for a number of long-running
controversies in the literature.

---------------------------------------------------------
Title: Solar Irradiance Variability and Climate
Authors: Solanki, Sami K.; Krivova, Natalie A.; Haigh, Joanna D.
2013ARA&A..51..311S Altcode: 2013arXiv1306.2770S
The brightness of the Sun varies on all timescales on which it has been
observed, and there is increasing evidence that this has an influence
on climate. The amplitudes of such variations depend on the wavelength
and possibly the timescale. Although many aspects of this variability
are well established, the exact magnitude of secular variations (going
beyond a solar cycle) and the spectral dependence of variations are
under discussion. The main drivers of solar variability are thought
to be magnetic features at the solar surface. The climate response
can be, on a global scale, largely accounted for by simple energetic
considerations, but understanding the regional climate effects is more
difficult. Promising mechanisms for such a driving have been identified,
including through the influence of UV irradiance on the stratosphere and
dynamical coupling to the surface. Here, we provide an overview of the
current state of our knowledge, as well as of the main open questions.

---------------------------------------------------------
Title: Sunspot group tilt angles and the strength of the solar cycle
(Corrigendum)
Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron,
R.; Peñuela, T.
2013A&A...556C...3D Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Quiet Sun magnetic fields observed by Hinode: Support for a
local dynamo
Authors: Buehler, D.; Lagg, A.; Solanki, S. K.
2013A&A...555A..33B Altcode: 2013arXiv1307.0789B
Context. The Hinode mission has revealed copious amounts of horizontal
flux covering the quiet Sun. Local dynamo action has been proposed
to explain the presence of this flux. Aims: We sought to
test whether the quiet Sun flux detected by Hinode is due to a
local or the global dynamo by studying long-term variations in the
polarisation signals detectable at the disc centre of the quiet Sun
between November 2006 and May 2012, with particular emphasis on weak
signals in the internetwork. Methods: The investigation focusses
on line-integrated circular polarisation Vtot and linear
polarisation LPtot profiles obtained from the Fe I 6302.5
Å absorption line in Hinode SOT/SP. Results: Both circular and
linear polarisation signals show no overall variation in the fraction
of selected pixels from 2006 until 2012. There is also no variation
in the magnetic flux in this interval of time. The probability density
functions (PDF) of the line-of-sight magnetic flux can be fitted with
a power law from 1.17 × 1017 Mx to 8.53 × 1018
Mx with index α = -1.82 ± 0.02 in 2007. The variation of α's across
all years does not exceed a significance of 1σ. Linearly polarised
features are also fitted with a power law, with index α = -2.60 ±
0.06 in 2007. Indices derived from linear polarisation PDFs of other
years also show no significant variation. Conclusions: Our
results show that the ubiquitous horizontal polarisation on the edges
of bright granules seen by Hinode are invariant during the minimum of
cycle 23. This supports the notion that the weak circular and linear
polarisation is primarily caused by an independent local dynamo.

---------------------------------------------------------
Title: Chromospheric magnetic field of an active region filament
using the He I triplet and the primary observation of filaments
(prominences) using New Vacuum Solar Tower of China
Authors: Xu, Zhi; Lagg, A.; Solanki, S.; Liu, Z.; New Vacuum Solar
Telescope Observers
2013SPD....4410504X Altcode:
There are two parts in my presentation. In the first part I present the
magnetic field measurement of an active region filament using the full
Stokes profiles of He I 10830 and Si I 10827 band when the filament in
its stable phase. This observation was fulfilled using German Vacuum
Tower Telescope (VTT). The vector magnetic field and Doppler velocity
map both in the photosphere and chromosphere were observed and analyzed
co-temporally and co-spatially. The observation findings reveal that we
were observing the emergence of a flux rope with a subsequent formation
of a filament. In the second part, I would like to exhibit another
ground-based observation facility, 1m New Vacuum Solar Telescope
(NVST) located in Fu-Xian Lake Solar Observatory of China. After
the basic introduction including the location and instrumentations,
I give some high lights including granulation, faculae, micro-flares,
jets, and filaments or prominence since the first running in 2010,
showing our potential ability to do high-resolution solar observation
from the ground. Observation proposals from the international solar
community are well appreciated in future.

---------------------------------------------------------
Title: Vertical flows and mass flux balance of sunspot umbral dots
Authors: Riethmüller, T. L.; Solanki, S. K.; van Noort, M.; Tiwari,
S. K.
2013A&A...554A..53R Altcode: 2013arXiv1305.1164R
A new Stokes inversion technique that greatly reduces the effect of the
spatial point spread function of the telescope is used to constrain
the physical properties of umbral dots (UDs). The depth-dependent
inversion of the Stokes parameters from a sunspot umbra recorded
with Hinode SOT/SP revealed significant temperature enhancements and
magnetic field weakenings in the core of the UDs in deep photospheric
layers. Additionally, we found upflows of around 960 m/s in peripheral
UDs (i.e., UDs close to the penumbra) and ≈600 m/s in central UDs. For
the first time, we also detected systematic downflows for distances
larger than 200 km from the UD center that balance the upflowing mass
flux. In the upper photosphere, we found almost no difference between
the UDs and their diffuse umbral background.

---------------------------------------------------------
Title: First evidence of interaction between longitudinal and
transverse waves in solar magnetic elements
Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.; Martínez
Pillet, V.
2013A&A...554A.115S Altcode: 2013arXiv1304.7088S
Small-scale magnetic fields are thought to play an important role in
the heating of the outer solar atmosphere. By taking advantage of
the unprecedented high-spatial and temporal cadence of the Imaging
Magnetograph eXperiment (IMaX), the filter vector polarimeter on board
the Sunrise balloon-borne observatory, we study the transversal and
longitudinal velocity oscillations in small magnetic elements. The
results of this analysis are then compared to magnetohydrodynamic (MHD)
simulations, showing excellent agreement. We found buffeting-induced
transverse oscillations with velocity amplitudes of the order of 1-2
km s-1 to be common along with longitudinal oscillations
with amplitudes ~0.4 km s-1. Moreover, we also found an
interaction between transverse oscillations and longitudinal velocity
oscillations, showing a ± 90° phase lag at the frequency at which
they exhibit the maximum coherence in the power spectrum. Our results
are consistent with the theoretical picture in which MHD longitudinal
waves are excited inside small magnetic elements as a response of the
flux tube to the forcing action of the granular flows.

---------------------------------------------------------
Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, Thomas; Solanki, Sami; Borrero, Juan; Peter,
Hardi; Sunrise Team
2013EGUGA..15.5251W Altcode:
Observations with the balloon-borne Sunrise/ Imaging Magnetograph
eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
disk center) measurements of the magnetic field in the photosphere of
the quiet Sun. To investigate the magnetic structure of the chromosphere
and corona, we extrapolate these photospheric measurements into
the upper solar atmosphere and analyse a 22-minute long time series
with a cadence of 33 seconds. Using the extrapolated magnetic-field
lines as tracer, we investigate temporal evolution of the magnetic
connectivity in the quiet Sun's atmosphere. The majority of magnetic
loops are asymmetric in the sense that the photospheric field strength
at the loop footpoints is very different. We find that the magnetic
connectivity of the loops changes rapidly with a typical connection
recycling time of about 3 ± 1 minutes in the upper solar atmosphere and
12 ± 4 minutes in the photosphere. This is considerably shorter than
previously found. Nonetheless, our estimate of the energy released by
the associated magnetic-reconnection processes is not likely to be the
sole source for heating the chromosphere and corona in the quiet Sun.

---------------------------------------------------------
Title: A Collaborative FP7 Effort towards the First European
Comprehensive SOLar Irradiance Data Exploitation (SOLID)
Authors: Haberreiter, Margit; Dasi, Maria; Delouille, Veronique; Del
Zanna, Giulio; Dudok de Wit, Thierry; Ermolli, Ilaria; Kretzschmar,
Matthieu; Krivova, Natalie; Mason, Helen; Qahwaji, Rami; Schmutz,
Werner; Solanki, Sami; Thuillier, Gerard; Tourpali, Kleareti; Unruh,
Yvonne; Verbeeck, Cis; Weber, Mark; Woods, Tom
2013EGUGA..1513079H Altcode:
Variations of solar irradiance are the most important natural factor
in the terrestrial climate and as such, the time dependent spectral
solar irradiance is a crucial input to any climate modelling. There
have been previous efforts to compile solar irradiance but it is
still uncertain by how much the spectral and total solar irradiance
changed on yearly, decadal and longer time scales. Observations of
irradiance data exist in numerous disperse data sets. Therefore, it
is important to bring together the European expertise in the field
to analyse and merge the complete set of European irradiance data,
complemented by archive data that include data from non-European
missions. We report on the initiation of a collaborative effort to unify
representatives from all European solar space experiments and European
teams specialized in multi-wavelength solar image processing. It is
intended to include the European groups involved in irradiance modelling
and reconstruction. They will work with two different state of the art
approaches to produce reconstructed spectral and total solar irradiance
data as a function of time. These results will be used to bridge
gaps in time and wavelength coverage of the observational data. This
will allow the proposing SOLID team to reduce the uncertainties in
the irradiance time series - an important requirement by the climate
community - and to provide uniform data sets of modelled and observed
solar irradiance data from the beginning of the space era to the
present including proper error and uncertainty estimates. Climate
research needs these data sets and therefore, the primary benefit
is for the climate community, but the stellar community, planetary,
lunar, and ionospheric researchers are also interested in having at
their disposition incident radiation of the Sun. The proposing team
plans to realize a wide international synergy in solar physics from
7 European countries, and collaborators from the US, complemented by
representatives from the climate community, who will accompany their
research work with wide dissemination activities.

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Title: The AD775 cosmic event revisited: the Sun is to blame
Authors: Usoskin, I. G.; Kromer, B.; Ludlow, F.; Beer, J.; Friedrich,
M.; Kovaltsov, G. A.; Solanki, S. K.; Wacker, L.
2013A&A...552L...3U Altcode: 2013arXiv1302.6897U
 Aims: Miyake et al. (2012, Nature, 486, 240, henceforth M12)
recently reported, based on 14C data, an extreme cosmic
event in about AD775. Using a simple model, M12 claimed that the event
was too strong to be caused by a solar flare within the standard
theory. This implied a new paradigm of either an impossibly strong
solar flare or a very strong cosmic ray event of unknown origin that
occurred around AD775. However, as we show, the strength of the event
was significantly overestimated by M12. Several subsequent works have
attempted to find a possible exotic source for such an event, including
a giant cometary impact upon the Sun or a gamma-ray burst, but they are
all based on incorrect estimates by M12. We revisit this event with
analysis of new datasets and consistent theoretical modelling. Methods: We verified the experimental result for the AD775 cosmic
ray event using independent datasets including 10Be series
and newly measured 14C annual data. We surveyed available
historical chronicles for astronomical observations for the period
around the AD770s to identify potential sightings of aurorae borealis
and supernovae. We interpreted the 14C measurements using
an appropriate carbon cycle model. Results: We show that:
(1) The reality of the AD775 event is confirmed by new measurements
of 14C in German oak; (2) by using an inappropriate
carbon cycle model, M12 strongly overestimated the event's strength;
(3) the revised magnitude of the event (the global 14C
production Q = (1.1 - 1.5) × 108 atoms/cm2)
is consistent with different independent datasets (14C,
10Be, 36Cl) and can be associated with a
strong, but not inexplicably strong, solar energetic particle event
(or a sequence of events), and provides the first definite evidence
for an event of this magnitude (the fluence &gt;30 MeV was about
4.5 × 1010 cm-2) in multiple datasets; (4)
this interpretation is in agreement with increased auroral activity
identified in historical chronicles. Conclusions: The results
point to the likely solar origin of the event, which is now identified
as the greatest solar event on a multi-millennial time scale, placing
a strong observational constraint on the theory of explosive energy
releases on the Sun and cool stars.

---------------------------------------------------------
Title: Modeling the variability of Sun-like stars
Authors: Shapiro, Alexander; Knaack, Reto; Krivova, Natalie; Schmutz,
Werner; Solanki, Sami; Unruh, Yvonne
2013EGUGA..15.9981S Altcode:
We present a model which attributes the variability of the stellar
radiative energy flux to the imbalance between the contributions from
dark starspots and bright faculae. The stellar radiative energy flux
variations are modeled from the individual component's spectra, by
weighting them with corresponding filling factors. The filling factors
are deduced by extrapolating the sunspot and facular filling factors
dependencies on solar CaII S-index to stars with different levels
of the chromospheric activity. Our approach allows us to model the
stellar photometric variability vs. activity dependency and reproduce
the transition from spot-dominated to facula-dominated regimes of
variability. We show how the effect of inclination (arising due to the
random position of the Earth-bound observer relative to the directions
of stellar rotational axis) can affect these dependencies and present
the modeling of the individual stellar photometric light curves.

---------------------------------------------------------
Title: What can we learn about the Sun with PREMOS/PICARD?
Authors: Cessateur, Gaël; Shapiro, Alexander; Schmutz, Werner;
Krivova, Natalie; Solanki, Sami K.; Yeo, Kok Leng; Thuillier, Gérard
2013EGUGA..1511720C Altcode:
Total and Spectral Solar Irradiance are key input parameters to
atmospheric/oceanic and space weather models. We present here
spectral solar irradiance data from the radiometer PREMOS onboard
the PICARD satellite. This instrument convers the solar spectrum from
the Ultraviolet to near-infrared, and provides valuable information
and nourishes theoretical models. Based on redundancy strategies,
instrumental degradation has been mostly corrected, revealing
surprising behavior from the visible and near-infrared filters. We
compare these data with those from the VIRGO/SOHO and SOLSTIC/SORCE
experiments. Finally we use COSI to model the variability of the
irradiance, assuming that the latter is determined by the evolution
of the solar surface magnetic field as seen with SDO/HMI data. A
direct comparison shows a very good correlation for most of channels
from PREMOS.

---------------------------------------------------------
Title: Analysis of Ca II K images aiming to determine long-term
trends in solar irradiance variability
Authors: Kar, Anuradha; Ermolli, Ilaria; Krivova, Natalie; Solanki,
Sami
2013EGUGA..15..330K Altcode:
The change in radiative output of the Sun on time scales longer than
a day is attributed to the variability in solar surface magnetic
fields. Direct irradiance measurements are only available for less
than four decades. To reconstruct long term trends in solar total and
spectral irradiance, proxies of solar surface magnetism like sunspot,
facular and network areas are needed. Currently, sunspot records
alone are used for this purpose, from which the deduction of facular
and network areas is rather indirect. Historical records of full disk
images of the Sun taken in the Ca II K spectral line (393.3 nm) have the
potential to provide far more direct information about the distribution
and evolution of faculae and network elements. The latter appear as
bright regions in the Ca II K spectroheliograms and their intensity
is correlated with the magnetic field strength of the features on the
solar surface. Solar full disk images in the Ca II K line have been
recorded since the beginning of the 20th century at a number of solar
observatories such as at Arcetri (Italy), Mount Wilson(California,
US) and Kodaikanal (India). The images are available in digitized
archives that contain the data processed for standard instrumental
calibrations. To utilize these records for irradiance studies, the next
step is to identify the bright magnetic features from the images using
feature recognition techniques. We test different feature identification
methods which are first applied to a set of recent images from the PSPT
instrument at the Osservatorio Astronomico di Roma, taken during three
periods characterized by high, medium and low levels of activity. Then
the performance of these methods to historical images from Arcetri,
Mt. Wilson and Kodaikanal archives is tested. The results will be
presented and discussed here.

---------------------------------------------------------
Title: Evolution of the Fine Structure of Magnetic Fields in the
Quiet Sun: Observations from Sunrise/IMaX and Extrapolations
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Peter,
H.; Barthol, P.; Gandorfer, A.; Martínez Pillet, V.; Schmidt, W.;
Knölker, M.
2013SoPh..283..253W Altcode:
Observations with the balloon-borne Sunrise/Imaging Magnetograph
eXperiment (IMaX) provide high spatial resolution (roughly 100 km at
disk center) measurements of the magnetic field in the photosphere of
the quiet Sun. To investigate the magnetic structure of the chromosphere
and corona, we extrapolate these photospheric measurements into
the upper solar atmosphere and analyze a 22-minute long time series
with a cadence of 33 seconds. Using the extrapolated magnetic-field
lines as tracer, we investigate temporal evolution of the magnetic
connectivity in the quiet Sun's atmosphere. The majority of magnetic
loops are asymmetric in the sense that the photospheric field strength
at the loop foot points is very different. We find that the magnetic
connectivity of the loops changes rapidly with a typical connection
recycling time of about 3±1 minutes in the upper solar atmosphere and
12±4 minutes in the photosphere. This is considerably shorter than
previously found. Nonetheless, our estimate of the energy released by
the associated magnetic-reconnection processes is not likely to be the
sole source for heating the chromosphere and corona in the quiet Sun.

---------------------------------------------------------
Title: Fine structures in the atmosphere above a sunspot umbra
Authors: Bharti, L.; Hirzberger, J.; Solanki, S. K.
2013A&A...552L...1B Altcode: 2013arXiv1302.2772B
We present simultaneous photospheric and chromospheric observations
of the trailing sunspot in NOAA 10904, obtained with the Swedish
Solar Telescope (SST) La Palma, Canary Islands. Time series of high
resolution Ca ii H images show transient jet-like structures in sunspot
umbrae are elongated, which we call umbral microjets. These jets are
directed roughly parallel to nearby penumbral microjets, suggesting
that they are aligned with the background magnetic field. In general,
first a bright dot-like structure appears, from which a jet later
emerges, although some jets appear without an associated chromospheric
dot. Bright photospheric umbral dots are associated with umbral
microjets arising in the outer umbra. Nevertheless, a one-to-one
correspondence between jet-like events and underlying umbral dots
is not seen. They are typically less than 1” long and less than 0.3
arcsec wide. The typical lifetime of umbral microjets is around one
minute. The brightness of these structures increases from the center of
the umbra toward the umbra-penumbra boundary along with the brightness
of the local background.

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Title: Recent variability of the solar spectral irradiance and its
impact on climate modelling
Authors: Ermolli, I.; Matthes, K.; Dudok de Wit, T.; Krivova,
N. A.; Tourpali, K.; Weber, M.; Unruh, Y. C.; Gray, L.; Langematz,
U.; Pilewskie, P.; Rozanov, E.; Schmutz, W.; Shapiro, A.; Solanki,
S. K.; Woods, T. N.
2013ACP....13.3945E Altcode: 2012ACPD...1224557E; 2013arXiv1303.5577E
The lack of long and reliable time series of solar spectral irradiance
(SSI) measurements makes an accurate quantification of solar
contributions to recent climate change difficult. Whereas earlier SSI
observations and models provided a qualitatively consistent picture of
the SSI variability, recent measurements by the SORCE (SOlar Radiation
and Climate Experiment) satellite suggest a significantly stronger
variability in the ultraviolet (UV) spectral range and changes in the
visible and near-infrared (NIR) bands in anti-phase with the solar
cycle. A number of recent chemistry-climate model (CCM) simulations
have shown that this might have significant implications on the
Earth's atmosphere. Motivated by these results, we summarize here
our current knowledge of SSI variability and its impact on Earth's
climate. We present a detailed overview of existing SSI
measurements and provide thorough comparison of models available to
date. SSI changes influence the Earth's atmosphere, both directly,
through changes in shortwave (SW) heating and therefore, temperature
and ozone distributions in the stratosphere, and indirectly, through
dynamical feedbacks. We investigate these direct and indirect effects
using several state-of-the art CCM simulations forced with measured
and modelled SSI changes. A unique asset of this study is the use
of a common comprehensive approach for an issue that is usually
addressed separately by different communities. We show
that the SORCE measurements are difficult to reconcile with earlier
observations and with SSI models. Of the five SSI models discussed
here, specifically NRLSSI (Naval Research Laboratory Solar Spectral
Irradiance), SATIRE-S (Spectral And Total Irradiance REconstructions
for the Satellite era), COSI (COde for Solar Irradiance), SRPM (Solar
Radiation Physical Modelling), and OAR (Osservatorio Astronomico di
Roma), only one shows a behaviour of the UV and visible irradiance
qualitatively resembling that of the recent SORCE measurements. However,
the integral of the SSI computed with this model over the entire
spectral range does not reproduce the measured cyclical changes of the
total solar irradiance, which is an essential requisite for realistic
evaluations of solar effects on the Earth's climate in CCMs. We show that within the range provided by the recent SSI observations
and semi-empirical models discussed here, the NRLSSI model and SORCE
observations represent the lower and upper limits in the magnitude
of the SSI solar cycle variation. The results of the
CCM simulations, forced with the SSI solar cycle variations estimated
from the NRLSSI model and from SORCE measurements, show that the direct
solar response in the stratosphere is larger for the SORCE than for the
NRLSSI data. Correspondingly, larger UV forcing also leads to a larger
surface response. Finally, we discuss the reliability
of the available data and we propose additional coordinated work,
first to build composite SSI data sets out of scattered observations
and to refine current SSI models, and second, to run coordinated
CCM experiments.

---------------------------------------------------------
Title: Intensity contrast of solar network and faculae
Authors: Yeo, K. L.; Solanki, S. K.; Krivova, N. A.
2013A&A...550A..95Y Altcode: 2013arXiv1302.1442Y
 Aims: This study aims at setting observational constraints
on the continuum and line core intensity contrast of network and
faculae, specifically, their relationship with magnetic field and
disc position. Methods: Full-disc magnetograms and intensity
images by the Helioseismic and Magnetic Imager (HMI) onboard the Solar
Dynamics Observatory (SDO) were employed. Bright magnetic features,
representing network and faculae, were identified and the relationship
between their intensity contrast at continuum and line core with
magnetogram signal and heliocentric angle examined. Care was taken
to minimize the inclusion of the magnetic canopy and straylight from
sunspots and pores as network and faculae. Results: In line
with earlier studies, network features, on a per unit magnetic flux
basis, appeared brighter than facular features. Intensity contrasts
in the continuum and line core differ considerably, most notably, they
exhibit opposite centre-to-limb variations. We found this difference in
behaviour to likely be due to the different mechanisms of the formation
of the two spectral components. From a simple model based on bivariate
polynomial fits to the measured contrasts we confirmed spectral line
changes to be a significant driver of facular contribution to variation
in solar irradiance. The discrepancy between the continuum contrast
reported here and in the literature was shown to arise mainly from
differences in spatial resolution and treatment of magnetic signals
adjacent to sunspots and pores. Conclusions: HMI is a source of
accurate contrasts and low-noise magnetograms covering the full solar
disc. For irradiance studies it is important to consider not just the
contribution from the continuum but also from the spectral lines. In
order not to underestimate long-term variations in solar irradiance,
irradiance models should take the greater contrast per unit magnetic
flux associated with magnetic features with low magnetic flux into
account.

---------------------------------------------------------
Title: Solar irradiance variability
Authors: Solanki, S. K.; Unruh, Y. C.
2013AN....334..145S Altcode: 2013csss...17..145S; 2012arXiv1210.5911S
The Sun has long been considered a constant star, to the extent
that its total irradiance was termed the solar constant. It required
radiometers in space to detect the small variations in solar irradiance
on timescales of the solar rotation and the solar cycle. A part of
the difficulty is that there are no other constant natural daytime
sources to which the Sun's brightness can be compared. The discovery
of solar irradiance variability rekindled a long-running discussion on
how strongly the Sun affects our climate. A non-negligible influence is
suggested by correlation studies between solar variability and climate
indicators. The mechanism for solar irradiance variations that fits
the observations best is that magnetic features at the solar surface,
i.e. sunspots, faculae and the magnetic network, are responsible for
almost all variations (although on short timescales convection and
p-mode oscillations also contribute). In spite of significant progress
important questions are still open. Thus there is a debate on how
strongly irradiance varies on timescales of centuries (i.e. how much
darker the Sun was during the Maunder minimum than it is today). It is
also not clear how the solar spectrum changes over the solar cycle. Both
these questions are of fundamental importance for working out just how
strongly the Sun influences our climate. Another interesting question
is how solar irradiance variability compares with that of other cool
dwarfs, particularly now that observations from space are available
also for stars.

---------------------------------------------------------
Title: European Solar Physics: moving from SOHO to Solar Orbiter
and beyond
Authors: Solanki, S. K.; Teriaca, L.; Barthol, P.; Curdt, W.;
Inhester, B.
2013MmSAI..84..286S Altcode:
When ESA and NASA launched the Solar and Heliospheric Observatory (SOHO)
to the Sun-Earth L1 point, they also launched European solar physics
into a steep upward trajectory. Thanks to the battery of instruments
on SOHO our picture of the Sun changed dramatically from that of a
sedate, nearly static star into that of a highly structured, dynamic
one. Subsequent solar missions have probed higher energy radiation,
gazed at the Sun from new vantage points in the ecliptic, analysed
the Sun at higher spatial resolution and imaged the whole Sun in many
wavelengths at high cadence. Nonetheless, SOHO is still going strong and
still delivering unique data. In the meantime European solar physicists
are working hard on the next major mission, Solar Orbiter, now being
implemented as the M1 mission of ESA's Cosmic Vision program. Solar
Orbiter will leave the Earth's orbit and move ever closer to the Sun,
reaching a perihelion inside the orbit of Mercury. This will allow it
to sample the Sun's dynamic inner heliosphere in situ, while probing
the source regions of the ambient solar wind with its remote sensing
instruments, a unique combination. Solar Orbiter will also leave the
ecliptic and, for the first time, image the Sun's poles. This will
bring us closer to finding the missing pieces of the puzzle on how
the solar dynamo works. Beyond Solar Orbiter are further exciting
prospects, such as the Solar-C mission, or the large European Solar
Telescope. Here an overview of solar missions and telescopes and the
associated science is given from a European perspective.

---------------------------------------------------------
Title: Structure and dynamics of isolated internetwork Ca II H bright
points observed by SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Feller, A.; Lagg, A.;
Pietarila, A.; Danilovic, S.; Riethmüller, T. L.; Martínez Pillet, V.
2013A&A...549A.116J Altcode: 2012arXiv1211.4836J
 Aims: We aim to improve our picture of the low chromosphere in
the quiet-Sun internetwork by investigating the intensity, horizontal
velocity, size and lifetime variations of small bright points (BPs;
diameter smaller than 0.3 arcsec) observed in the Ca II H 3968 Å
passband along with their magnetic field parameters, derived from
photospheric magnetograms. Methods: Several high-quality
time series of disc-centre, quiet-Sun observations from the Sunrise
balloon-borne solar telescope, with spatial resolution of around 100
km on the solar surface, have been analysed to study the dynamics
of BPs observed in the Ca II H passband and their dependence on the
photospheric vector magnetogram signal. Results: Parameters such
as horizontal velocity, diameter, intensity and lifetime histograms of
the isolated internetwork and magnetic Ca II H BPs were determined. Mean
values were found to be 2.2 km s-1, 0.2 arcsec (≈150 km),
1.48 ⟨ ICa ⟩ and 673 s, respectively. Interestingly, the
brightness and the horizontal velocity of BPs are anti-correlated. Large
excursions (pulses) in horizontal velocity, up to 15 km s-1,
are present in the trajectories of most BPs. These could excite kink
waves travelling into the chromosphere and possibly the corona, which we
estimate to carry an energy flux of 310 W m-2, sufficient to
heat the upper layers, although only marginally. Conclusions:
The stable observing conditions of Sunrise and our technique for
identifying and tracking BPs have allowed us to determine reliable
parameters of these features in the internetwork. Thus we find, e.g.,
that they are considerably longer lived than previously thought. The
large velocities are also reliable, and may excite kink waves. Although
these wave are (marginally) energetic enough to heat the quiet corona,
we expect a large additional contribution from larger magnetic elements
populating the network and partly also the internetwork.

---------------------------------------------------------
Title: Pathway to the Square Kilometre Array - The German White
Paper -
Authors: Aharonian, F.; Arshakian, T. G.; Allen, B.; Banerjee, R.;
Beck, R.; Becker, W.; Bomans, D. J.; Breitschwerdt, D.; Brüggen,
M.; Brunthaler, A.; Catinella, B.; Champion, D.; Ciardi, B.; Crocker,
R.; de Avillez, M. A.; Dettmar, R. J.; Engels, D.; Enßlin, T.; Enke,
H.; Fieseler, T.; Gizon, L.; Hackmann, E.; Hartmann, B.; Henkel, C.;
Hoeft, M.; Iapichino, L.; Innes, D.; James, C.; Jasche, J.; Jones,
D.; Kagramanova, V.; Kauffmann, G.; Keane, E.; Kerp, J.; Klöckner,
H. -R.; Kokkotas, K.; Kramer, M.; Krause, M.; Krause, M.; Krupp, N.;
Kunz, J.; Lämmerzahl, C.; Lee, K. J.; List, M.; Liu, K.; Lobanov,
A.; Mann, G.; Merloni, A.; Middelberg, E.; Niemeyer, J.; Noutsos,
A.; Perlick, V.; Reich, W.; Richter, P.; Roy, A.; Saintonge, A.;
Schäfer, G.; Schaffner-Bielich, J.; Schinnerer, E.; Schleicher, D.;
Schneider, P.; Schwarz, D. J.; Sedrakian, A.; Sesana, A.; Smolčić,
V.; Solanki, S.; Tuffs, R.; Vetter, M.; Weber, E.; Weller, J.; Wex,
N.; Wucknitz, O.; Zwaan, M.
2013arXiv1301.4124A Altcode:
The Square Kilometre Array (SKA) is the most ambitious radio telescope
ever planned. With a collecting area of about a square kilometre,
the SKA will be far superior in sensitivity and observing speed to
all current radio facilities. The scientific capability promised by
the SKA and its technological challenges provide an ideal base for
interdisciplinary research, technology transfer, and collaboration
between universities, research centres and industry. The SKA in
the radio regime and the European Extreme Large Telescope (E-ELT)
in the optical band are on the roadmap of the European Strategy Forum
for Research Infrastructures (ESFRI) and have been recognised as the
essential facilities for European research in astronomy. This "White
Paper" outlines the German science and R&amp;D interests in the SKA
project and will provide the basis for future funding applications to
secure German involvement in the Square Kilometre Array.

---------------------------------------------------------
Title: Inversions of L12-2 IMaX data of an emerging flux mantle
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo,
B.; del Toro Iniesta, J. C.; Bellot Rubio, L. R.; Solanki, S. K.;
Sunrise/IMaX Team
2013MmSAI..84..355G Altcode:
We present the analysis of a flux emergence event observed with
the IMaX magnetograph flown aboard the SUNRISE balloon. IMaX took a
15' sequence with cadence of 31 s along the Fe I line at 525.0 nm,
acquiring only Stokes I and V at 12 line positions (L12-2 mode). This
sequence shows the emergence of a flux mantle at mesogranular scale,
cospatial with a large exploding granule. An undesired cross-talk
between Stokes U and V was found in such L12-2 data. We show that the
use of a modified version of the SIR inversion code is able to remove
such effect in inferring the physical quantities of interest.

---------------------------------------------------------
Title: MHD waves in small magnetic elements: comparing IMaX
observations to simulations.
Authors: Stangalini, M.; Solanki, S. K.; Cameron, R.
2013MmSAI..84..444S Altcode:
Small-scale magnetic fields are thought to play an important role in the
heating of the outer solar atmosphere. By exploiting the high-spatial
and temporal resolution of IMaX, the bidimensional spectropolarimeter on
board the Sunrise balloon-borne observatory, we study the excitation of
MHD waves in small magnetic elements, providing clues on the interaction
of the magnetic structures with the photospheric forcing and the ambient
acoustic field. The large fraction of magnetic features observed by
IMaX made it possible to study the interaction between the photospheric
granulation and the flux tubes from a statistical point-of-view. In
particular we find a 90 degree phase lag with an high confidence level
between the horizontal displacements of the flux tubes and the velocity
perturbations measured inside them. We also find that the observational
results are in excellent agreement with MHD simulations. This result
suggests that the horizontal displacement of small-scale magnetic
features by the surrounding granulation excites longitudinal waves
within the magnetic elements.

---------------------------------------------------------
Title: The GREGOR Solar Telescope on Tenerife
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello González, N.; Berkefeld, T.;
Collados Vera, M.; Hofmann, A.; Kneer, F.; Lagg, A.; Puschmann, K. G.;
Schmidt, D.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.
2012ASPC..463..365S Altcode: 2012arXiv1202.4289S
2011 was a successful year for the GREGOR project. The telescope was
finally completed in May with the installation of the 1.5-meter primary
mirror. The installation of the first-light focal plane instruments was
completed by the end of the year. At the same time, the preparations
for the installation of the high-order adaptive optics were finished,
its integration to the telescope is scheduled for early 2012. This
paper describes the telescope and its instrumentation in their present
first-light configuration, and provides a brief overview of the science
goals of GREGOR.

---------------------------------------------------------
Title: The GREGOR Solar Telescope
Authors: Denker, C.; Lagg, A.; Puschmann, K. G.; Schmidt, D.; Schmidt,
W.; Sobotka, M.; Soltau, D.; Strassmeier, K. G.; Volkmer, R.; von
der Luehe, O.; Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.;
Berkefeld, T.; Collados Vera, M.; Hofmann, A.; Kneer, F.
2012IAUSS...6E.203D Altcode:
The 1.5-meter GREGOR solar telescope is a new facility for
high-resolution observations of the Sun. The telescope is located at the
Spanish Observatorio del Teide on Tenerife. The telescope incorporates
advanced designs for a foldable-tent dome, an open steel-truss telescope
structure, and active and passive means to minimize telescope and mirror
seeing. Solar fine structure can be observed with a dedicated suite
of instruments: a broad-band imaging system, the "GREGOR Fabry-Perot
Interferometer", and the "Grating Infrared Spectrograph". All post-focus
instruments benefit from a high-order (multi-conjugate) adaptive optics
system, which enables observations close to the diffraction limit of
the telescope. The inclusion of a spectrograph for stellar activity
studies and the search for solar twins expands the scientific usage
of the GREGOR to the nighttime domain. We report on the successful
commissioning of the telescope until the end of 2011 and the first
steps towards science verification in 2012.

---------------------------------------------------------
Title: Doppler shift of hot coronal lines in a moss area of an
active region
Authors: Dadashi, N.; Teriaca, L.; Tripathi, D.; Solanki, S. K.;
Wiegelmann, T.
2012A&A...548A.115D Altcode: 2012arXiv1211.5473D
The moss is the area at the footpoint of the hot (3 to 5 MK) loops
forming the core of the active region where emission is believed to
result from the heat flux conducted down to the transition region from
the hot loops. Studying the variation of Doppler shift as a function
of line formation temperatures over the moss area can give clues
on the heating mechanism in the hot loops in the core of the active
regions. We investigate the absolute Doppler shift of lines formed
at temperatures between 1 MK and 2 MK in a moss area within active
region NOAA 11243 using a novel technique that allows determining the
absolute Doppler shift of EUV lines by combining observations from
the SUMER and EIS spectrometers. The inner (brighter and denser) part
of the moss area shows roughly constant blue shift (upward motions)
of 5 km s-1 in the temperature range of 1 MK to 1.6 MK. For
hotter lines the blue shift decreases and reaches 1 km s-1
for Fe xv 284 Å (~2 MK). The measurements are discussed in relation
to models of the heating of hot loops. The results for the hot coronal
lines seem to support the quasi-steady heating models for nonsymmetric
hot loops in the core of active regions.

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Title: A retrospective of the GREGOR solar telescope in scientific
literature
Authors: Denker, C.; von der Lühe, O.; Feller, A.; Arlt, K.;
Balthasar, H.; Bauer, S. -M.; Bello González, N.; Berkefeld, Th.;
Caligari, P.; Collados, M.; Fischer, A.; Granzer, T.; Hahn, T.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Kentischer, T.; Klva{ňa,
M.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Rendtel, J.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Solanki, S. K.;
Soltau, D.; Staude, J.; Strassmeier, K. G.; Volkmer, R.; Waldmann,
T.; Wiehr, E.; Wittmann, A. D.; Woche, M.
2012AN....333..810D Altcode: 2012arXiv1210.3167D
In this review, we look back upon the literature, which had the
GREGOR solar telescope project as its subject including science cases,
telescope subsystems, and post-focus instruments. The articles date
back to the year 2000, when the initial concepts for a new solar
telescope on Tenerife were first presented at scientific meetings. This
comprehensive bibliography contains literature until the year 2012,
i.e., the final stages of commissioning and science verification. Taking
stock of the various publications in peer-reviewed journals and
conference proceedings also provides the “historical” context
for the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.

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Title: Three-dimensional non-LTE radiative transfer effects in Fe
I lines. I. Flux sheet and flux tube geometries
Authors: Holzreuter, R.; Solanki, S. K.
2012A&A...547A..46H Altcode: 2012arXiv1209.0559H
In network and active region plages, the magnetic field is concentrated
into structures often described as flux tubes (FTs) and sheets
(FSs). Three-dimensional (3D) radiative transfer is important for
energy transport in these concentrations. It is also expected to be
important for diagnostic purposes but has rarely been applied for
that purpose. Using true 3D, non-local thermodynamic-equilibrium
(non-LTE or NLTE) radiative transfer (RT) in FT and FS models, we
compute iron line profiles commonly used to diagnose the Sun's magnetic
field by using and comparing the results with those obtained from LTE
or one-dimensional (1D) NLTE calculations. Employing a multilevel
iron atom, we study the influence of several basic parameters such
as either FS or FT Wilson depression, wall thickness, radius/width,
thermal stratification or magnetic field strength on Stokes I and the
polarized Stokes parameters in the thin-tube approximation. The use
of different levels of approximations of RT (3D NLTE, 1D NLTE, LTE)
may lead to considerable differences in profile shapes, intensity
contrasts, equivalent widths, and the determination of magnetic field
strengths. In particular, LTE, which often provides a good approach in
planar 1D atmospheres, is a poor approximation in our flux sheet model
for some of the most important diagnostic Fe i lines (524.7 nm, 525.0
nm, 630.1 nm, and 630.2 nm). The observed effects depend on parameters
such as the height of line formation, field strength, and internal
temperature stratification. Differences between the profile shapes may
lead to errors in the determination of magnetic fields on the order of
10% to 20%, while errors in the determined temperature can reach 300-400
K. The empirical FT models NET and PLA turn out to minimize the effects
of 3D RT, so that results obtained with these models by applying LTE may
also remain valid for 3D NLTE calculations. Finally, horizontal RT is
found to only insignificantly smear out structures such as the optically
thick walls of flux tubes and sheets, allowing features as narrow as
10 km to remain visible. Appendices are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>

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Title: The 1.5 meter solar telescope GREGOR
Authors: Schmidt, W.; von der Lühe, O.; Volkmer, R.; Denker, C.;
Solanki, S. K.; Balthasar, H.; Bello Gonzalez, N.; Berkefeld, Th.;
Collados, M.; Fischer, A.; Halbgewachs, C.; Heidecke, F.; Hofmann,
A.; Kneer, F.; Lagg, A.; Nicklas, H.; Popow, E.; Puschmann, K. G.;
Schmidt, D.; Sigwarth, M.; Sobotka, M.; Soltau, D.; Staude, J.;
Strassmeier, K. G.; Waldmann , T. A.
2012AN....333..796S Altcode:
The 1.5 m telescope GREGOR opens a new window to the understanding
of solar small-scale magnetism. The first light instrumentation
includes the Gregor Fabry Pérot Interferometer (GFPI), a filter
spectro-polarimeter for the visible wavelength range, the GRating
Infrared Spectro-polarimeter (GRIS) and the Broad-Band Imager (BBI). The
excellent performance of the first two instruments has already been
demonstrated at the Vacuum Tower Telescope. GREGOR is Europe's largest
solar telescope and number 3 in the world. Its all-reflective Gregory
design provides a large wavelength coverage from the near UV up to at
least 5 microns. The field of view has a diameter of 150 arcsec. GREGOR
is equipped with a high-order adaptive optics system, with a subaperture
size of 10 cm, and a deformable mirror with 256 actuators. The science
goals are focused on, but not limited to, solar magnetism. GREGOR
allows us to measure the emergence and disappearance of magnetic flux
at the solar surface at spatial scales well below 100 km. Thanks to its
spectro-polarimetric capabilities, GREGOR will measure the interaction
between the plasma flows, different kinds of waves, and the magnetic
field. This will foster our understanding of the processes that heat the
chromosphere and the outer layers of the solar atmosphere. Observations
of the surface magnetic field at very small spatial scales will shed
light on the variability of the solar brightness.

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Title: GRIS: The GREGOR Infrared Spectrograph
Authors: Collados, M.; López, R.; Páez, E.; Hernández, E.; Reyes,
M.; Calcines, A.; Ballesteros, E.; Díaz, J. J.; Denker, C.; Lagg,
A.; Schlichenmaier, R.; Schmidt, W.; Solanki, S. K.; Strassmeier,
K. G.; von der Lühe, O.; Volkmer, R.
2012AN....333..872C Altcode:
This paper describes the main characteristics of GRIS (GREGOR Infrared
Spectrograph), the grating spectrograph installed in the recently
inaugurated (May 2012) 1.5-meter GREGOR telescope located at the
Observatorio del Teide in Tenerife. The spectrograph has a standard
Czerny-Turner configuration with parabolic collimator and camera mirrors
that belong to the same conic surface. Although nothing prevents its
use at visible wavelengths, the spectrograph will be initially used
in combination with the infrared detector of the Tenerife Infrared
Polarimeter (TIP-II) in standard spectroscopic mode as well as for
spectropolarimetric measurements.

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Title: LEMUR: Large European module for solar Ultraviolet
Research. European contribution to JAXA's Solar-C mission
Authors: Teriaca, Luca; Andretta, Vincenzo; Auchère, Frédéric;
Brown, Charles M.; Buchlin, Eric; Cauzzi, Gianna; Culhane, J. Len;
Curdt, Werner; Davila, Joseph M.; Del Zanna, Giulio; Doschek, George
A.; Fineschi, Silvano; Fludra, Andrzej; Gallagher, Peter T.; Green,
Lucie; Harra, Louise K.; Imada, Shinsuke; Innes, Davina; Kliem,
Bernhard; Korendyke, Clarence; Mariska, John T.; Martínez-Pillet,
Valentin; Parenti, Susanna; Patsourakos, Spiros; Peter, Hardi; Poletto,
Luca; Rutten, Robert J.; Schühle, Udo; Siemer, Martin; Shimizu,
Toshifumi; Socas-Navarro, Hector; Solanki, Sami K.; Spadaro, Daniele;
Trujillo-Bueno, Javier; Tsuneta, Saku; Dominguez, Santiago Vargas;
Vial, Jean-Claude; Walsh, Robert; Warren, Harry P.; Wiegelmann,
Thomas; Winter, Berend; Young, Peter
2012ExA....34..273T Altcode: 2011ExA...tmp..135T; 2011arXiv1109.4301T
The solar outer atmosphere is an extremely dynamic environment
characterized by the continuous interplay between the plasma and the
magnetic field that generates and permeates it. Such interactions play a
fundamental role in hugely diverse astrophysical systems, but occur at
scales that cannot be studied outside the solar system. Understanding
this complex system requires concerted, simultaneous solar observations
from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at
high spatial resolution (between 0.1” and 0.3”), at high temporal
resolution (on the order of 10 s, i.e., the time scale of chromospheric
dynamics), with a wide temperature coverage (0.01 MK to 20 MK,
from the chromosphere to the flaring corona), and the capability of
measuring magnetic fields through spectropolarimetry at visible and
near-infrared wavelengths. Simultaneous spectroscopic measurements
sampling the entire temperature range are particularly important. These
requirements are fulfilled by the Japanese Solar-C mission (Plan B),
composed of a spacecraft in a geosynchronous orbit with a payload
providing a significant improvement of imaging and spectropolarimetric
capabilities in the UV, visible, and near-infrared with respect to
what is available today and foreseen in the near future. The Large
European Module for solar Ultraviolet Research (LEMUR), described
in this paper, is a large VUV telescope feeding a scientific payload
of high-resolution imaging spectrographs and cameras. LEMUR consists
of two major components: a VUV solar telescope with a 30 cm diameter
mirror and a focal length of 3.6 m, and a focal-plane package composed
of VUV spectrometers covering six carefully chosen wavelength ranges
between 170 Å and 1270 Å. The LEMUR slit covers 280” on the Sun with
0.14” per pixel sampling. In addition, LEMUR is capable of measuring
mass flows velocities (line shifts) down to 2 km s - 1 or
better. LEMUR has been proposed to ESA as the European contribution
to the Solar C mission.

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Title: Spectroscopic observations of propagating disturbances in a
polar coronal hole: evidence of slow magneto-acoustic waves
Authors: Gupta, G. R.; Teriaca, L.; Marsch, E.; Solanki, S. K.;
Banerjee, D.
2012A&A...546A..93G Altcode: 2012arXiv1209.3524G
 Aims: We focus on detecting and studying quasi-periodic
propagating features that have been interpreted in terms of both slow
magneto-acoustic waves and of high-speed upflows. Methods:
We analyzed long-duration spectroscopic observations of the on-disk
part of the south polar coronal hole taken on 1997 February 25 by
the SUMER spectrometer onboard SOHO. We calibrated the velocity
with respect to the off-limb region and obtained time-distance maps
in intensity, Doppler velocity, and line width. We also performed a
cross-correlation analysis on different time series curves at different
latitudes. We studied average spectral line profiles at the roots
of propagating disturbances and along the propagating ridges, and
performed a red-blue asymmetry analysis. Results: We clearly
find propagating disturbances in intensity and Doppler velocity with
a projected propagation speed of about 60 ± 4.8 km s-1
and a periodicity of ≈14.5 min. To our knowledge, this is the first
simultaneous detection of propagating disturbances in intensity as
well as in Doppler velocity in a coronal hole. During the propagation,
an intensity enhancement is associated with a blueshifted Doppler
velocity. These disturbances are clearly seen in intensity also
at higher latitudes (i.e., closer to the limb), while disturbances
in Doppler velocity become faint there. The spectral line profiles
averaged along the propagating ridges are found to be symmetric, to
be well fitted by a single Gaussian, and have no noticeable red-blue
asymmetry. Conclusions: Based on our analysis, we interpret
these disturbances in terms of propagating slow magneto-acoustic waves.

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Title: Resolving the Internal Magnetic Structure of the Solar Network
Authors: Martínez González, M. J.; Bellot Rubio, L. R.; Solanki,
S. K.; Martínez Pillet, V.; Del Toro Iniesta, J. C.; Barthol, P.;
Schmidt, W.
2012ApJ...758L..40M Altcode: 2012arXiv1209.2584M
We analyze the spectral asymmetry of Stokes V (circularly polarized)
profiles of an individual network patch in the quiet Sun observed
by Sunrise/IMaX. At a spatial resolution of 0farcs15-0farcs18, the
network elements contain substructure which is revealed by the spatial
distribution of Stokes V asymmetries. The area asymmetry between the
red and blue lobes of Stokes V increases from nearly zero at the core
of the structure to values close to unity at its edges (single-lobed
profiles). Such a distribution of the area asymmetry is consistent
with magnetic fields expanding with height, i.e., an expanding
magnetic canopy (which is required to fulfill pressure balance and
flux conservation in the solar atmosphere). Inversion of the Stokes
I and V profiles of the patch confirms this picture, revealing a
decreasing field strength and increasing height of the canopy base
from the core to the periphery of the network patch. However, the
non-roundish shape of the structure and the presence of negative area
and amplitude asymmetries reveal that the scenario is more complex than
a canonical flux tube expanding with height surrounded by downflows.

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Title: Nitrate in Polar Ice: A New Tracer of Solar Variability
Authors: Traversi, R.; Usoskin, I. G.; Solanki, S. K.; Becagli, S.;
Frezzotti, M.; Severi, M.; Stenni, B.; Udisti, R.
2012SoPh..280..237T Altcode: 2012SoPh..tmp..169T
Knowledge of the long-term variability of solar activity is of
both astrophysical and geoscientific interest. Reconstructions of
solar activity over multiple millennia are traditionally based on
cosmogenic isotopes 14C or 10Be measured in
natural terrestrial archives, but the two isotopes exhibit significant
differences on millennial time scales, so that our knowledge of solar
activity at this time scale remains somewhat uncertain. Here we present
a new potential proxy of solar activity on the centennial-millennial
time scale, based on a chemical tracer, viz. nitrate content in an ice
core drilled at Talos Dome (Antarctica). We argue that this location
is optimal for preserving the solar signal in the nitrate content
during the Holocene. By using the firn core from the same location
we show that the 11-year and Gleissberg cycles are present with the
variability of 10 - 25 % in nitrate content in the pre-industrial
epoch. This is consistent with the results of independent efforts of
modeling HNO3 and NOy in Antarctic near surface
air. However, meteorological noise on the interannual scale makes
it impossible to resolve individual solar cycles. Based on different
processes of formation and transport compared to cosmogenic isotopes,
it provides new, independent insight into long-term solar activity
and helps resolve the uncertainties related to cosmogenic isotopes as
diagnostics of solar activity.

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Title: Results and perspectives of the solar axion search with the
CAST experiment
Authors: Ferrer-Ribas, E.; Arik, M.; Aune, S.; Barth, K.; Belov,
A.; Borghi, S.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.;
Cetin, S. A.; Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis,
C.; Elias, N.; Ezer, C.; Fanourakis, G.; Friedrich, P.; Galán, J.;
García, J. A.; Gardikiotis, A.; Garza, J. G.; Gazis, E. N.; Geralis,
T.; Giomataris, I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl,
T.; Hartmann, R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.;
Iguaz, F. J.; Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza,
M.; Königsmann, K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Lakić,
B.; Laurent, J. M.; Liolios, A.; Ljubičić, A.; Lozza, V.; Lutz, G.;
Luzón, G.; Morales, J.; Niinikoski, T.; Nordt, A.; Papaevangelou, T.;
Pivovaroff, M. J.; Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez,
A.; Rosu, M.; Ruz, J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.;
Stewart, L.; Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.;
Villar, J.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.
2012arXiv1209.6347F Altcode:
The status of the solar axion search with the CERN Axion Solar Telescope
(CAST) will be presented. Recent results obtained by the use of $^3$He
as a buffer gas has allowed us to extend our sensitivity to higher axion
masses than our previous measurements with $^4$He. With about 1 h of
data taking at each of 252 different pressure settings we have scanned
the axion mass range 0.39 eV$ \le m_{a} \le $ 0.64 eV. From the absence
of an excess of x rays when the magnet was pointing to the Sun we set
a typical upper limit on the axion-photon coupling of g$_{a\gamma} \le
2.3\times 10^{-10}$ GeV$^{-1}$ at 95% C.L., the exact value depending
on the pressure setting. CAST published results represent the best
experimental limit on the photon couplings to axions and other similar
exotic particles dubbed WISPs (Weakly Interacting Slim Particles)
in the considered mass range and for the first time the limit enters
the region favored by QCD axion models. Preliminary sensitivities for
axion masses up to 1.16 eV will also be shown reaching mean upper limits
on the axion-photon coupling of g$_{a\gamma} \le 3.5\times 10^{-10}$
GeV$^{-1}$ at 95% C.L. Expected sensibilities for the extension of the
CAST program up to 2014 will be presented. Moreover long term options
for a new helioscope experiment will be evoked.

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Title: Multi Element Telescope for Imaging and Spectroscopy (METIS)
coronagraph for the Solar Orbiter mission
Authors: Antonucci, Ester; Fineschi, Silvano; Naletto, Giampiero;
Romoli, Marco; Spadaro, Daniele; Nicolini, Gianalfredo; Nicolosi,
Piergiorgio; Abbo, Lucia; Andretta, Vincenzo; Bemporad, Alessandro;
Auchère, Frédéric; Berlicki, Arkadiusz; Bruno, Roberto; Capobianco,
Gerardo; Ciaravella, Angela; Crescenzio, Giuseppe; Da Deppo, Vania;
D'Amicis, Raffaella; Focardi, Mauro; Frassetto, Fabio; Heinzel,
Peter; Lamy, Philippe L.; Landini, Federico; Massone, Giuseppe;
Malvezzi, Marco A.; Moses, J. Dan; Pancrazzi, Maurizio; Pelizzo,
Maria-Guglielmina; Poletto, Luca; Schühle, Udo H.; Solanki, Sami K.;
Telloni, Daniele; Teriaca, Luca; Uslenghi, Michela
2012SPIE.8443E..09A Altcode:
METIS, the “Multi Element Telescope for Imaging and Spectroscopy”,
is a coronagraph selected by the European Space Agency to be part of
the payload of the Solar Orbiter mission to be launched in 2017. The
unique profile of this mission will allow 1) a close approach to the
Sun (up to 0.28 A.U.) thus leading to a significant improvement in
spatial resolution; 2) quasi co-rotation with the Sun, resulting in
observations that nearly freeze for several days the large-scale outer
corona in the plane of the sky and 3) unprecedented out-of-ecliptic
view of the solar corona. This paper describes the experiment concept
and the observational tools required to achieve the science drivers
of METIS. METIS will be capable of obtaining for the first time: •
simultaneous imaging of the full corona in polarized visible-light
(590-650 nm) and narrow-band ultraviolet HI Lyman α (121.6 nm); •
monochromatic imaging of the full corona in the extreme ultraviolet
He II Lyman α (30.4 nm); • spectrographic observations of the HI
and He II Ly α in corona. These measurements will allow a complete
characterization of the three most important plasma components of
the corona and the solar wind, that is, electrons, hydrogen, and
helium. This presentation gives an overview of the METIS imaging and
spectroscopic observational capabilities to carry out such measurements.

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Title: METIS: a novel coronagraph design for the Solar Orbiter mission
Authors: Fineschi, Silvano; Antonucci, Ester; Naletto, Giampiero;
Romoli, Marco; Spadaro, Daniele; Nicolini, Gianalfredo; Abbo, Lucia;
Andretta, Vincenzo; Bemporad, Alessandro; Berlicki, Arkadiusz;
Capobianco, Gerardo; Crescenzio, Giuseppe; Da Deppo, Vania; Focardi,
Mauro; Landini, Federico; Massone, Giuseppe; Malvezzi, Marco A.;
Moses, J. Dan; Nicolosi, Piergiorgio; Pancrazzi, Maurizio; Pelizzo,
Maria-Guglielmina; Poletto, Luca; Schühle, Udo H.; Solanki, Sami K.;
Telloni, Daniele; Teriaca, Luca; Uslenghi, Michela
2012SPIE.8443E..3HF Altcode:
METIS (Multi Element Telescope for Imaging and Spectroscopy) METIS,
the “Multi Element Telescope for Imaging and Spectroscopy”,
is a coronagraph selected by the European Space Agency to be part
of the payload of the Solar Orbiter mission to be launched in
2017. The mission profile will bring the Solar Orbiter spacecraft
as close to the Sun as 0.3 A.U., and up to 35° out-of-ecliptic
providing a unique platform for helio-synchronous observations of
the Sun and its polar regions. METIS coronagraph is designed for
multi-wavelength imaging and spectroscopy of the solar corona. This
presentation gives an overview of the innovative design elements of
the METIS coronagraph. These elements include: i) multi-wavelength,
reflecting Gregorian-telescope; ii) multilayer coating optimized for
the extreme UV (30.4 nm, HeII Lyman-α) with a reflecting cap-layer
for the UV (121.6 nm, HI Lyman-α) and visible-light (590-650); iii)
inverse external-occulter scheme for reduced thermal load at spacecraft
peri-helion; iv) EUV/UV spectrograph using the telescope primary mirror
to feed a 1st and 4th-order spherical varied
line-spaced (SVLS) grating placed on a section of the secondary mirror;
v) liquid crystals electro-optic polarimeter for observations of the
visible-light K-corona. The expected performances are also presented.

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Title: Grand minima of solar activity during the last millennia
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Kovaltsov, Gennady A.
2012IAUS..286..372U Altcode:
In this review we discuss the occurrence and statistical properties of
Grand minima based on the available data covering the last millennia. In
particular, we consider the historical record of sunspot numbers
covering the last 400 years as well as records of cosmogenic isotopes
in natural terrestrial archives, used to reconstruct solar activity
for up to the last 11.5 millennia, i.e. throughout the Holocene. Using
a reconstruction of solar activity from cosmogenic isotope data, we
analyze statistics of the occurrence of Grand minima. We find that: the
Sun spends about most of the time at moderate activity, 1/6 in a Grand
minimum and some time also in a Grand maximum state; Occurrence of Grand
minima is not a result of long-term cyclic variations but is defined
by stochastic/chaotic processes; There is a tendency for Grand minima
to cluster with the recurrence rate of roughly 2000-3000 years, with
a weak ~210-yr periodicity existing within the clusters. Grand minima
occur of two different types: shorter than 100 years (Maunder-type)
and long ~150 years (Spörer-type). It is also discussed that solar
cycles (most possibly not sunspots cycle) could exist during the
Grand minima, perhaps with stretched length and asymmetric sunspot
latitudinal distribution. These results set new observational
constraints on long-term solar and stellar dynamo models.

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Title: A reconstruction of solar irradiance using a flux transport
model
Authors: Dasi Espuig, Maria; Krivova, Natalie; Solanki, Sami K.;
Jiang, Jie
2012cosp...39..418D Altcode: 2012cosp.meet..418D
Solar irradiance is one of the important drivers of the Earth's
global climate, but it has only been measured for the past 33
years. Its reconstructions are therefore crucial to study longer
term variations relevant to climate timescales. Most successful in
reproducing the measured irradiance variations have being the models
that are based on the assumption that irradiance changes are caused by
the evolution of the photospheric magnetic field. Our SATIRE-S model
is one of these, which uses solar full-disc magnetograms as an input,
and these are available for less than four decades. To reconstruct the
irradiance back to times when no observed magnetograms are available,
we combine the SATIRE-S model with synthetic magnetograms, produced
using a surface flux transport model. The model is fed with daily,
observed or modelled statistically, records of sunspot positions,
areas, and tilt angles. The concept of overlapping ephemeral region
cycles is used to describe the secular change in the irradiance.

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Title: Solar Spectral Irradiance as observed by LYRA/PROBA2 and
PREMOS/PICARD
Authors: Cessateur, Gaël.; Kretzschmar, Matthieu; Krivova, Natalie;
Schmutz, Werner; Solanki, Sami K.; Thuillier, Gerard; Shapiro,
Alexander; Schoell, Micha; Shapiro, Anna; Dominique, Marie; Tagirov,
Rinat; Wehrli, Christoph; Yeo, Kok Leng
2012cosp...39..287C Altcode: 2012cosp.meet..287C
No abstract at ADS

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Title: Spectroscopic Observations of Propagating Disturbances in
Polar Coronal Hole
Authors: Gupta, Girjesh R.; Marsch, Eckart; Solanki, Sami K.; Banerjee,
Dipankar; Teriaca, Luca
2012cosp...39..689G Altcode: 2012cosp.meet..689G
We focus on long duration spectroscopic observations of the south
polar coronal hole taken on 1997 February 25 by the Solar Ultraviolet
Measurements of Emitted Radiation (SUMER) spectrometer aboard SOHO. We
analyze the data in the on-disk part of the coronal hole to find any
signature of propagating waves or high speed up-flows. We find the
clear presence of propagating disturbances in intensity and Doppler
velocity with a projected propagation speed of about 60~km~s^{-1} and
a periodicity of ≈14.5~min. During the propagation, the intensity
enhancement is associated with a blue-shifted Doppler velocity. These
disturbances are clearly seen in intensity at higher latitudes
(i.e. closer to the limb), whereas disturbances in Doppler velocity
becomes faint there. We study average spectral line profiles at the
roots of these disturbances and along the propagating ridge. Based on
our analysis, we interpret these disturbances in terms of propagating
slow magneto-acoustic waves.

---------------------------------------------------------
Title: Long-term reconstructions of total solar irradiance
Authors: Krivova, Natalie; Solanki, Sami K.; Dasi Espuig, Maria
2012cosp...39..985K Altcode: 2012cosp.meet..985K
Solar irradiance is the main external driver of the Earth's climate,
although its relative contribution compared to other internal and
anthropogenic factors is not yet well determined. Variations of total
solar irradiance have being measured for over three decades and are
relatively well understood. Reconstructions of the irradiance into the
past remain, however, rather uncertain. In particular, the magnitude of
the secular change is highly debated. The reason is the lack of direct
and well-sampled proxies of solar magnetic activity on time scales
longer than a few decades. Reconstructions on time scales of centuries
rely on sunspot observations available since 1610. Reconstructions on
millennial time scales use concentrations of the cosmogenic isotopes
in terrestrial archives. We will review long-term reconstructions of
the solar irradiance using the SATIRE set of models, compare them with
other recent models and discuss the remaining uncertainties.

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Title: Nitrate in polar ice as a new index of solar variability
Authors: Traversi, Rita; Usoskin, Ilya; Solanki, Sami K.; Becagli,
Silvia; Frezzotti, Massimo; Severi, Mirko; Stenni, Barbara; Udisti,
Roberto
2012cosp...39.2001T Altcode: 2012cosp.meet.2001T
The Sun affects Earth's climate and environment in multiple ways and
on different time scales but understanding if and how the variations
in solar radiative output might drive global climatic change has
revealed to be a complex and controversial issue. In order to address
the question about the Sun's role on the climate in the past, present
and, eventually, in the future, a reliable reconstruction of solar
activity is mandatory. Over millennia time scales, a quantitative
information about past solar activity can only be obtained through
proxies recorded in natural stratified archives (e.g., tree rings or
ice cores), such as the cosmogenic isotopes 14C and 10Be. Nonetheless,
the two isotopes exhibit significant differences on millennial time
scales, making our knowledge of solar activity at this time scale less
certain. Here we present a new potential proxy of solar activity on the
centennial-millennial time scale, namely nitrate content in the TALDICE
ice core (Talos Dome, placeEast Antarctica). Talos Dome site was shown
to be favourably located to minimize possible local climate effects,
which may be dominant in other coastal sites and, due to a sufficiently
high snow accumulation rate throughout the Holocene, such a reversibly
deposited species as nitrate is preserved here (in contrast to inland
Antarctic sites) making it a potential paleomarker. Comparing the
TALDICE nitrate record with the two traditionally used cosmogenic
proxies of solar activity, we observed that a highly significant
agreement on the millennial and multi-millennial time scales over the
Holocene. The relation at centennial time scales is less significant,
likely due to ice core dating uncertainties. No statistical relationship
was found between the nitrate data series and other chemical markers
of local climate/transport. Consequently, the coherence between
nitrate and cosmogenic isotopes univocally suggests a common origin
of their long-term variability. As concerning the more recent times,
we show that the 11-year and Gleissberg cycles are present at a level
of 10-25% in nitrate content in the pre-industrial epoch after the
Maunder minimum, which is in agreement with model results. However, the
“meteorological noise” on the interannual scale makes it impossible
to resolve individual solar cycles. Since nitrate is characterised by
different processes of formation and transport, compared to cosmogenic
isotopes, we conclude that nitrate in this Antarctic ice core forms
a novel proxy of solar activity on the centennial and longer time
scales and could help in reconciling the discrepancies between the
two cosmogenic isotopes as diagnostics of solar activity.

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Title: Status and perspectives of the CAST experiment
Authors: Lakić, B.; Arik, M.; Aune, S.; Barth, K.; Belov, A.;
Borghi, S.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin,
S. A.; Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis, C.;
Elias, N.; Ezer, C.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.;
Galán, J.; García, J. A.; Gardikiotis, A.; Gazis, E. N.; Geralis,
T.; Giomataris, I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl,
T.; Hartmann, R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.;
Iguaz, F. J.; Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza,
M.; Königsmann, K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Laurent,
J. M.; Liolios, A.; Ljubičić, A.; Lozza, V.; Lutz, G.; Luzón, G.;
Morales, J.; Niinikoski, T.; Nordt, A.; Papaevangelou, T.; Pivovaroff,
M. J.; Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez, A.; Rosu, M.;
Ruz, J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.; Stewart, L.;
Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.; Villar, J.;
Vogel, J. K.; Yildiz, S. C.; Zioutas, K.; Cast Collaboration
2012JPhCS.375b2001L Altcode:
The CERN Axion Solar Telescope (CAST) is currently the most sensitive
axion helioscope designed to search for axions produced by the Primakoff
process in the solar core. CAST is using a Large Hadron Collider (LHC)
test magnet where axions could be converted into X-rays with energies
up to 10 keV. During the phase I, the experiment operated with vacuum
inside the magnet bores and covered axion masses up to 0.02 eV. In
the phase II, the magnet bores were filled with a buffer gas (first
4He and later 3He) at various densities in order
to extend the sensitivity to higher axion masses (up to f .18 eV). The
phase II data taking was completed in 2011. So far, no evidence of axion
signal has been found and CAST set the most restrictive experimental
limit on the axion-photon coupling constant over a broad range of axion
masses. The latest CAST results with 3He data in the mass
range 0.39 eV &lt; ma &lt; 0.64 eV will be presented.

---------------------------------------------------------
Title: Waves as the Source of Apparent Twisting Motions in Sunspot
Penumbrae
Authors: Bharti, L.; Cameron, R. H.; Rempel, M.; Hirzberger, J.;
Solanki, S. K.
2012ApJ...752..128B Altcode: 2012arXiv1204.2221B
The motion of dark striations across bright filaments in a sunspot
penumbra has become an important new diagnostic of convective gas
flows in penumbral filaments. The nature of these striations has,
however, remained unclear. Here, we present an analysis of small-scale
motions in penumbral filaments in both simulations and observations. The
simulations, when viewed from above, show fine structure with dark lanes
running outward from the dark core of the penumbral filaments. The
dark lanes either occur preferentially on one side or alternate
between both sides of the filament. We identify this fine structure
with transverse (kink) oscillations of the filament, corresponding to
a sideways swaying of the filament. These oscillations have periods in
the range of 5-7 minutes and propagate outward and downward along the
filament. Similar features are found in observed G-band intensity time
series of penumbral filaments in a sunspot located near disk center
obtained by the Broadband Filter Imager on board the Hinode. We also
find that some filaments show dark striations moving to both sides
of the filaments. Based on the agreement between simulations and
observations we conclude that the motions of these striations are
caused by transverse oscillations of the underlying bright filaments.

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Title: Chromospheric magnetic fields of an active region filament
Authors: Xu, Z.; Solanki, S.; Lagg, A.
2012EAS....55..163X Altcode:
Vector magnetic fields of an active region filament are co-spatially
and co-temporally mapped in photosphere and upper chromosphere, by
using spectro-polarimetric observations made by Tenerife Infrared
Polarimeter (TIP II) at the German Vacuum Tower Telescope (VTT). A
Zeeman-based ME inversion is performed on the full Stokes vectors
of both the photospheric Si I 1082.7 nm and the chromospheric He
I 1083.0 nm lines. We found that the strong magnetic fields, with
the field strength of 600 - 800 G in the He I line formation height,
are not uncommon among AR filaments. But such strong magnetic field
is not always found in AR filaments.

---------------------------------------------------------
Title: The continuum intensity as a function of magnetic
field. II. Local magnetic flux and convective flows
Authors: Kobel, P.; Solanki, S. K.; Borrero, J. M.
2012A&A...542A..96K Altcode: 2014arXiv1402.3474K
Context. To deepen our understanding of the role of small-scale magnetic
fields in active regions (ARs) and in the quiet Sun (QS) on the solar
irradiance, it is fundamental to investigate the physical processes
underlying their continuum brightness. Previous results showed that
magnetic elements in the QS reach larger continuum intensities than
in ARs at disk center, but left this difference unexplained. 
Aims: We use Hinode/SP disk center data to study the influence of
the local amount of magnetic flux on the vigour of the convective
flows and the continuum intensity contrasts. Methods: The
apparent (i.e. averaged over a pixel) longitudinal field strength
and line-of-sight (LOS) plasma velocity were retrieved by means
of Milne-Eddington inversions (VFISV code). We analyzed a series
of boxes taken over AR plages and the QS, to determine how the
continuum intensity contrast of magnetic elements, the amplitude of
the vertical flows and the box-averaged contrast were affected by the
mean longitudinal field strength in the box (which scales with the total
unsigned flux in the box). Results: Both the continuum brightness
of the magnetic elements and the dispersion of the LOS velocities
anti-correlate with the mean longitudinal field strength. This can
be attributed to the "magnetic patches" (here defined as areas where
the longitudinal field strength is above 100 G) carrying most of the
flux in the boxes. There the velocity amplitude and the spatial scale
of convection are reduced. Due to this hampered convective transport,
these patches appear darker than their surroundings. Consequently, the
average brightness of a box decreases as the the patches occupy a larger
fraction of it and the amount of embedded flux thereby increases. 
Conclusions: Our results suggest that as the magnetic flux increases
locally (e.g. from weak network to strong plage), the heating of the
magnetic elements is reduced by the intermediate of a more suppressed
convective energy transport within the larger and stronger magnetic
patches. This, together with the known presence of larger magnetic
features, could explain the previously found lower contrasts of the
brightest magnetic elements in ARs compared to the QS. The inhibition
of convection also affects the average continuum brightness of a
photospheric region, so that at disk center, an area of photosphere in
strong network or plage appears darker than a purely quiet one. This
is qualitatively consistent with the predictions of 3D MHD simulations.

---------------------------------------------------------
Title: First Results from the SUNRISE Mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Jafarzadeh, S.; Lagg, A.; Riethmüller,
T. L.; Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; González,
M. J. M.; Pillet, V. M.; Khomenko, E.; Yelles Chaouche, L.; Iniesta,
J. C. d. T.; Domingo, V.; Palacios, J.; Knölker, M.; González,
N. B.; Borrero, J. M.; Berkefeld, T.; Franz, M.; Roth, M.; Schmidt,
W.; Steiner, O.; Title, A. M.
2012ASPC..455..143S Altcode:
The SUNRISE balloon-borne solar observatory consists of a 1m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that reveal the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. Here we describe very briefly the mission and the first results
obtained from the SUNRISE data, which include a number of discoveries.

---------------------------------------------------------
Title: Detection of Vortex Tubes in Solar Granulation from
Observations SUNRISE
Authors: Steiner, O.; Franz, M.; González, N. B.; Nutto, C.; Rezaei,
R.; Pillet, V. M.; Bonet, J. A.; Iniesta, J. C. d. T.; Domingo, V.;
Solanki, S. K.; Knölker, M.; Schmidt, W.; Barthol, P.; Gandorfer, A.
2012ASPC..455...35S Altcode:
We investigated a time series of continuum intensity maps and
Dopplergrams of granulation in a very quiet solar region at the disk
center, recorded with the Imaging Magnetograph eXperiment (IMaX)
on board the balloon-borne solar observatory SUNRISE. We find that
granules frequently show substructure in the form of lanes composed of
a leading bright rim and a trailing dark edge, which move together
from the boundary of a granule into the granule itself. We find
strikingly similar events in synthesized intensity maps from an ab
initio numerical simulation of solar surface convection. We conclude
that these granular lanes are the visible signature of (horizontally
oriented) vortex tubes. The characteristic optical appearance of vortex
tubes at the solar surface is explained. This paper is a summary and
update of the results previously presented in Steiner et al. (2010).

---------------------------------------------------------
Title: Supersonic Magnetic Flows in the Quiet Sun Observed with
SUNRISE/IMaX
Authors: Borrero, J. M.; Pillet, V. M.; Schlichenmaier, R.; Schmidt,
W.; Berkefeld, T.; Solanki, S. K.; Bonet, J. A.; Iniesta, J. C. d. T.;
Domingo, V.; Barthol, P.; Gandorfer, A.
2012ASPC..455..155B Altcode: 2012arXiv1202.4354B
In this contribution we describe some recent observations of high-speed
magnetized flows in the quiet Sun granulation. These observations
were carried out with the Imaging Magnetograph eXperiment (IMaX)
onboard the stratospheric balloon SUNRISE, and possess an unprecedented
spatial resolution and temporal cadence. These flows were identified as
highly shifted circular polarization (Stokes V) signals. We estimate
the LOS velocity responsible for these shifts to be larger than 6 km
s-1, and therefore we refer to them as supersonic magnetic
flows. The average lifetime of the detected events is 81.3 s and
they occupy an average area of about 23 000 km2. Most of
the events occur within granular cells and correspond therefore to
upflows. However some others occur in intergranular lanes or bear no
clear relation to the convective velocity pattern. We analyze a number
of representative examples and discuss them in terms of magnetic loops,
reconnection events, and convective collapse.

---------------------------------------------------------
Title: Reconstruction of total solar irradiance 1974-2009
Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.;
Wenzler, T.; Mortlock, D. J.; Jaffe, A. H.
2012A&A...541A..27B Altcode: 2012arXiv1202.3554B
Context. The study of variations in total solar irradiance (TSI)
is important for understanding how the Sun affects the Earth's
climate. Aims: Full-disk continuum images and magnetograms are
now available for three full solar cycles. We investigate how modelled
TSI compares with direct observations by building a consistent modelled
TSI dataset. The model, based only on changes in the photospheric
magnetic flux can then be tested on rotational, cyclical and secular
timescales. Methods: We use Kitt Peak and SoHO/MDI continuum
images and magnetograms in the SATIRE-S model to reconstruct TSI over
cycles 21-23. To maximise independence from TSI composites, SORCE/TIM
TSI data are used to fix the one free parameter of the model. We compare
and combine the separate data sources for the model to estimate an
uncertainty on the reconstruction and prevent any additional free
parameters entering the model. Results: The reconstruction
supports the PMOD composite as being the best historical record of
TSI observations, although on timescales of the solar rotation the
IRMB composite provides somewhat better agreement. Further to this,
the model is able to account for 92% of TSI variations from 1978
to 2009 in the PMOD composite and over 96% during cycle 23. The
reconstruction also displays an inter-cycle, secular decline of
0.20+0.12-0.09 W m-2 between cycle
23 minima, in agreement with the PMOD composite. Conclusions:
SATIRE-S is able to recreate TSI observations on all timescales of a
day and longer over 31 years from 1978. This is strong evidence that
changes in photospheric magnetic flux alone are responsible for almost
all solar irradiance variations over the last three solar cycles.

---------------------------------------------------------
Title: Solar Spectral Irradiance as observed by LYRA/PROBA2 and
PREMOS/PICARD
Authors: Cessateur, G.; Shapiro, A. I.; Dominique, M.; Kretzschmar,
M.; Krivova, N.; Shapiro, A. V.; Schmutz, W.; Schoell, M.; Solanki,
S.; Tagirov, R.; Thuillier, G.; Wehrli, C.; Yeo, K. L.
2012EGUGA..14.8254C Altcode:
Total and Spectral Solar Irradiance are key input parameters to
atmospheric/oceanic and space weather models. Both vary on time-scales
ranging from days to millennia, although a complete picture of the
solar irradiance variability is still missing. The recent launch of
two European missions PROBA-2 with LYRA radiometer onboard and PICARD
with PREMOS package onboard provides therefore valuable information and
nourishes theoretical models. Both instruments covers the solar spectrum
from the EUV to near-infrared. Here we present spectral solar irradiance
data from these two recent missions. After a proper correction of the
degradation and non-solar signatures, we compare these data with those
from the VIRGO/SOHO and SOLSTICE+SIM/SORCE experiments. Both LYRA and
PREMOS have also observed several solar eclipses, which allows us to
accurately retrieve the center-to-limb variations (CLVs) of the quiet
Sun's brightness at the wavelengths of the corresponding channels. CLVs
play indeed an important role in modelling of the solar irradiance
variability. We show that calculations with the published COde for
Solar Irradiance (COSI) yield CLVs that are in good agreement with
measurements. Finally we use COSI to model the variability of the
irradiance, assuming that the latter is determined by the evolution
of the solar surface magnetic field as seen with SDO/HMI data. These
theoretical results are compared to PREMOS and LYRA measurements.

---------------------------------------------------------
Title: Break up of returning plasma after the 7 June 2011 filament
eruption by Rayleigh-Taylor instabilities
Authors: Innes, D. E.; Cameron, R. H.; Fletcher, L.; Inhester, B.;
Solanki, S. K.
2012A&A...540L..10I Altcode: 2012arXiv1202.4981I
Context. A prominence eruption on 7 June 2011 produced spectacular
curtains of plasma falling through the lower corona. At the solar
surface they created an incredible display of extreme ultraviolet
brightenings. Aims: To identify and analyze some of the local
instabilities which produce structure in the falling plasma. 
Methods: The structures were investigated using SDO/AIA 171 Å and
193 Å images in which the falling plasma appeared dark against
the bright coronal emission. Results: Several instances of
the Rayleigh-Taylor instability were investigated. In two cases the
Alfvén velocity associated with the dense plasma could be estimated
from the separation of the Rayleigh-Taylor fingers. A second type of
feature, which has the appearance of self-similar branching horns was
discussed. Appendix A and two movies are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Long-term magnetic field monitoring of the Sun-like star ξ
Bootis A
Authors: Morgenthaler, A.; Petit, P.; Saar, S.; Solanki, S. K.; Morin,
J.; Marsden, S. C.; Aurière, M.; Dintrans, B.; Fares, R.; Gastine,
T.; Lanoux, J.; Lignières, F.; Paletou, F.; Ramírez Vélez, J. C.;
Théado, S.; Van Grootel, V.
2012A&A...540A.138M Altcode: 2011arXiv1109.5066M
 Aims: We aim to investigate the long-term temporal evolution
of the magnetic field of the solar-type star ξ Bootis A, both from
direct magnetic field measurements and from the simultaneous estimate
of indirect activity indicators. Methods: We obtained seven
epochs of high-resolution, circularly-polarized spectra from the
NARVAL spectropolarimeter between 2007 and 2011, for a total of 76
spectra. Using approximately 6100 photospheric spectral lines covering
the visible domain, we employed a cross-correlation procedure to compute
a mean polarized line profile from each spectrum. The large-scale
photospheric magnetic field of the star was then modelled by means
of Zeeman-Doppler Imaging, allowing us to follow the year-to-year
evolution of the reconstructed magnetic topology. Simultaneously, we
monitored the width of several magnetically sensitive spectral lines,
the radial velocity, the line asymmetry of intensity line profiles,
and the chromospheric emission in the cores of the Ca II H and Hα
lines. Results: During the highest observed activity states,
in 2007 and 2011, the large-scale field of ξ Bootis A is almost
completely axisymmetric and is dominated by its toroidal component. The
toroidal component persists with a constant polarity, containing
a significant fraction of the magnetic energy of the large-scale
surface field through all observing epochs. The magnetic topologies
reconstructed for these activity maxima are very similar, suggesting
a form of short cyclicity in the large-scale field distribution. The
mean unsigned large-scale magnetic flux derived from the magnetic
maps varies by a factor of about 2 between the lowest and highest
observed magnetic states. The chromospheric flux is less affected and
varies by a factor of 1.2. Correlated temporal evolution, due to both
rotational modulation and seasonal variability, is observed between
the Ca II emission, the Hα emission and the width of magnetically
sensitive lines. The rotational dependence of polarimetric magnetic
measurements displays a weak correlation with other activity proxies,
presumably due to the different spatial scales and centre-to-limb
darkening associated with polarimetric signatures, as compared to
non-polarized activity indicators. Better agreement is observed on the
longer term. When measurable, the differential rotation reveals a strong
latitudinal shear in excess of 0.2 rad d-1. Based on
observations obtained at the Bernard Lyot Telescope (TBL, Pic du Midi,
France) of the Midi-Pyrénées Observatory, which is operated by the
Institut National des Sciences de l'Univers of the Centre National de la
Recherche Scientifique of France.Tables 3-6 are available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Solar magnetism eXplorer (SolmeX). Exploring the magnetic
field in the upper atmosphere of our closest star
Authors: Peter, Hardi; Abbo, L.; Andretta, V.; Auchère, F.; Bemporad,
A.; Berrilli, F.; Bommier, V.; Braukhane, A.; Casini, R.; Curdt,
W.; Davila, J.; Dittus, H.; Fineschi, S.; Fludra, A.; Gandorfer, A.;
Griffin, D.; Inhester, B.; Lagg, A.; Landi Degl'Innocenti, E.; Maiwald,
V.; Sainz, R. Manso; Martínez Pillet, V; Matthews, S.; Moses, D.;
Parenti, S.; Pietarila, A.; Quantius, D.; Raouafi, N. -E.; Raymond, J.;
Rochus, P.; Romberg, O.; Schlotterer, M.; Schühle, U.; Solanki, S.;
Spadaro, D.; Teriaca, L.; Tomczyk, S.; Trujillo Bueno, J.; Vial, J. -C.
2012ExA....33..271P Altcode: 2011arXiv1108.5304P; 2011ExA...tmp..134P
The magnetic field plays a pivotal role in many fields of
Astrophysics. This is especially true for the physics of the solar
atmosphere. Measuring the magnetic field in the upper solar atmosphere
is crucial to understand the nature of the underlying physical
processes that drive the violent dynamics of the solar corona—that
can also affect life on Earth. SolmeX, a fully equipped solar space
observatory for remote-sensing observations, will provide the first
comprehensive measurements of the strength and direction of the
magnetic field in the upper solar atmosphere. The mission consists
of two spacecraft, one carrying the instruments, and another one in
formation flight at a distance of about 200 m carrying the occulter to
provide an artificial total solar eclipse. This will ensure high-quality
coronagraphic observations above the solar limb. SolmeX integrates two
spectro-polarimetric coronagraphs for off-limb observations, one in
the EUV and one in the IR, and three instruments for observations on
the disk. The latter comprises one imaging polarimeter in the EUV for
coronal studies, a spectro-polarimeter in the EUV to investigate the low
corona, and an imaging spectro-polarimeter in the UV for chromospheric
studies. SOHO and other existing missions have investigated the emission
of the upper atmosphere in detail (not considering polarization),
and as this will be the case also for missions planned for the near
future. Therefore it is timely that SolmeX provides the final piece of
the observational quest by measuring the magnetic field in the upper
atmosphere through polarimetric observations.

---------------------------------------------------------
Title: Magnetic Fields of an Active Region Filament from Full Stokes
Analysis of Si I 1082.7 nm and He I 1083.0 nm
Authors: Xu, Z.; Lagg, A.; Solanki, S.; Liu, Y.
2012ApJ...749..138X Altcode: 2012arXiv1202.4562X
Vector magnetic fields of an active region filament in the photosphere
and upper chromosphere are obtained from spectro-polarimetric
observations recorded with the Tenerife Infrared Polarimeter (TIP II) at
the German Vacuum Tower Telescope. We apply Milne-Eddington inversions
on full Stokes vectors of the photospheric Si I 1082.7 nm and the upper
chromospheric He I triplet at 1083.0 nm to obtain the magnetic field
vector and velocity maps in two atmosphere layers. We find that (1) a
complete filament was already present in Hα at the beginning of the TIP
II data acquisition. Only a partially formed one, composed of multiple
small threads, was present in He I. (2) The AR filament comprises two
sections. One shows strong magnetic field intensities, about 600-800
G in the upper chromosphere and 800-1000 G in the photosphere. The
other exhibits only comparatively weak magnetic field strengths in both
layers. (3) The Stokes V signal is indicative of a dip in the magnetic
field strength close to the chromospheric PIL. (4) In the chromosphere,
consistent upflows are found along the PIL flanked by downflows. (5)
The transversal magnetic field is nearly parallel to the PIL in the
photosphere and inclined by 20°-30° in the chromosphere. (6) The
chromospheric magnetic field around the filament is found to be in
normal configuration, while the photospheric field presents a concave
magnetic topology. The observations are consistent with the emergence
of a flux rope with a subsequent formation of a filament.

---------------------------------------------------------
Title: Diffusivity of Isolated Internetwork Ca II H Bright Points
Observed by SuFI/SUNRISE
Authors: Jafarzadeh, S.; Solanki, S. K.; Cameron, R. H.; Feller, A.;
Pietarila, A.; Lagg, A.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A.
2012decs.confE..99J Altcode:
We analyze trajectories of the proper motion of intrinsically magnetic,
isolated internetwork Ca II H BPs (with mean lifetime of 461 sec) to
obtain their diffusivity behaviors. We use high spatial and temporal
resolution image sequences of quiet-Sun, disc-centre observations
obtained in the Ca II H 397 nm passband of the Sunrise Filter Imager
(SuFI) on board the SUNRISE balloon-borne solar observatory. In
order to avoid misidentification, the BPs are semi-manually selected
and then automatically tracked. The trajectory of each BP is then
calculated and its diffusion index is described by a power law
exponent, using which we classify the BPs' trajectories into sub-,
normal and super- diffusive. In addition, the corresponding diffusion
coefficients (D) based on the observed displacements are consequently
computed. We find a strong super-diffusivity at a height sampled by the
SuFI/SUNRISE Ca II H passband (i.e. a height corresponding roughly to
the temperature minimum). We find that 74% of the identified tiny BPs
are super-diffusive, 18% move randomly (i.e. their motion corresponds
to normal diffusion) and only 8% belong to the sub-diffusion regime. In
addition, we find that 53% of the super-diffusion regime (i.e. 39% of
all BPs) have the diffusivity index of 2 which are termed as "Ballistic
BPs". Finally, we explore the distribution of diffusion index with the
help of a simple simulation. The results suggest that the BPs are random
walkers superposed by a systematic (background) velocity in which the
magnitude of each component (and hence their ratio) depends on the time
and spatial scales. We further discuss a simple sketch to explain the
diffusivity of observed BPs while they migrate within a supergranule
(i.e. internetwork areas) or close to the network regions.

---------------------------------------------------------
Title: The Frontier between Small-scale Bipoles and Ephemeral Regions
in the Solar Photosphere: Emergence and Decay of an Intermediate-scale
Bipole Observed with SUNRISE/IMaX
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.;
del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.;
Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.
2012ApJ...745..160G Altcode: 2011arXiv1110.1405G
We report on the photospheric evolution of an intermediate-scale (≈4
Mm footpoint separation) magnetic bipole, from emergence to decay,
observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s)
resolution. The observations were acquired by the Imaging Magnetograph
Experiment imaging magnetograph during the first science flight of the
SUNRISE balloon-borne solar observatory. The bipole flux content is 6 ×
1017 Mx, representing a structure bridging the gap between
granular scale bipoles and the smaller ephemeral regions. Footpoints
separate at a speed of 3.5 km s-1 and reach a maximum
distance of 4.5 Mm before the field dissolves. The evolution of the
bipole is revealed to be very dynamic: we found a proper motion of
the bipole axis and detected a change of the azimuth angle of 90° in
300 s, which may indicate the presence of some writhe in the emerging
structure. The overall morphology and behavior are in agreement with
previous analyses of bipolar structures emerging at the granular scale,
but we also found several similarities with emerging flux structures
at larger scales. The flux growth rate is 2.6 × 1015 Mx
s-1, while the mean decay rate is one order of magnitude
smaller. We describe in some detail the decay phase of the bipole
footpoints that includes break up into smaller structures, and
interaction with preexisting fields leading to cancellation, but it
appears to be dominated by an as-yet unidentified diffusive process
that removes most of the flux with an exponential flux decay curve. The
diffusion constant (8 × 102 km2 s-1)
associated with this decay is similar to the values used to describe
the large-scale diffusion in flux transport models.

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Title: The influence of spectral solar irradiance data on
stratospheric heating rates during the 11 year solar cycle
Authors: Oberländer, S.; Langematz, U.; Matthes, K.; Kunze, M.; Kubin,
A.; Harder, J.; Krivova, N. A.; Solanki, S. K.; Pagaran, J.; Weber, M.
2012GeoRL..39.1801O Altcode: 2012GeoRL..3901801O
Heating rate calculations with the FUBRad shortwave (SW) radiation
parameterization have been performed to examine the effect of
prescribed spectral solar fluxes from the NRLSSI, MPS and IUP
data sets on SW heating rates over the 11 year solar cycle 22. The
corresponding temperature response is derived from perpetual January
General Circulation Model (GCM) simulations with prescribed ozone
concentrations. The different solar flux input data sets induce clear
differences in SW heating rates at solar minimum, with the established
NRLSSI data set showing the smallest solar heating rates. The stronger
SW heating in the middle and upper stratosphere in the MPS data
warms the summer upper stratosphere by 2 K. Over the solar cycle,
SW heating rate differences vary up to 40% between the irradiance
data sets, but do not result in a significant change of the solar
temperature signal. Lower solar fluxes in the newer SIM data lead
to a significantly cooler stratosphere and mesosphere when compared
to NRLSSI data for 2007. Changes in SW heating from 2004 to 2007 are
however up to six times stronger than for the NRLSSI data.

---------------------------------------------------------
Title: Magnetic field emergence in mesogranular-sized exploding
granules observed with sunrise/IMaX data
Authors: Palacios, J.; Blanco Rodríguez, J.; Vargas Domínguez, S.;
Domingo, V.; Martínez Pillet, V.; Bonet, J. A.; Bellot Rubio, L. R.;
Del Toro Iniesta, J. C.; Solanki, S. K.; Barthol, P.; Gandorfer, A.;
Berkefeld, T.; Schmidt, W.; Knölker, M.
2012A&A...537A..21P Altcode: 2011arXiv1110.4555P
We report on magnetic field emergences covering significant
areas of exploding granules. The balloon-borne mission Sunrise
provided high spatial and temporal resolution images of the solar
photosphere. Continuum images, longitudinal and transverse magnetic
field maps and Dopplergrams obtained by IMaX onboard Sunrise are
analyzed by local correlation traking (LCT), divergence calculation
and time slices, Stokes inversions and numerical simulations are also
employed. We characterize two mesogranular-scale exploding granules
where ~1018 Mx of magnetic flux emerges. The emergence
of weak unipolar longitudinal fields (~100 G) start with a single
visible magnetic polarity, occupying their respective granules' top
and following the granular splitting. After a while, mixed polarities
start appearing, concentrated in downflow lanes. The events last around
20 min. LCT analyses confirm mesogranular scale expansion, displaying
a similar pattern for all the physical properties, and divergence
centers match between all of them. We found a similar behaviour
with the emergence events in a numerical MHD simulation. Granule
expansion velocities are around 1 kms-1 while magnetic
patches expand at 0.65 kms-1. One of the analyzed events
evidences the emergence of a loop-like structure. Advection of
the emerging magnetic flux features is dominated by convective
motion resulting from the exploding granule due to the magnetic
field frozen in the granular plasma. Intensification of the
magnetic field occurs in the intergranular lanes, probably
because of being directed by the downflowing plasma. Movies
associated to Figs. 2-4 are available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Search for Sub-eV Mass Solar Axions by the CERN Axion Solar
Telescope with He3 Buffer Gas
Authors: Arik, M.; Aune, S.; Barth, K.; Belov, A.; Borghi, S.;
Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.;
Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis, C.; Elias,
N.; Ezer, C.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.;
Galán, J.; García, J. A.; Gardikiotis, A.; Gazis, E. N.; Geralis,
T.; Giomataris, I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl,
T.; Hartmann, R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.;
Iguaz, F. J.; Irastorza, I. G.; Jacoby, J.; Jakovčić, K.; Karuza,
M.; Königsmann, K.; Kotthaus, R.; Krčmar, M.; Kuster, M.; Lakić,
B.; Laurent, J. M.; Liolios, A.; Ljubičić, A.; Lozza, V.; Lutz, G.;
Luzón, G.; Morales, J.; Niinikoski, T.; Nordt, A.; Papaevangelou, T.;
Pivovaroff, M. J.; Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez,
A.; Rosu, M.; Ruz, J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.;
Stewart, L.; Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.;
Villar, J. A.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.
2011PhRvL.107z1302A Altcode: 2011arXiv1106.3919A
The CERN Axion Solar Telescope (CAST) has extended its search for
solar axions by using He3 as a buffer gas. At T=1.8K this allows
for larger pressure settings and hence sensitivity to higher axion
masses than our previous measurements with He4. With about 1 h
of data taking at each of 252 different pressure settings we have
scanned the axion mass range 0.39eV≲ma≲0.64eV. From
the absence of excess x rays when the magnet was pointing to the
Sun we set a typical upper limit on the axion-photon coupling
of gaγ≲2.3×10-10GeV-1
at 95% C.L., the exact value depending on the pressure
setting. Kim-Shifman-Vainshtein-Zakharov axions are excluded
at the upper end of our mass range, the first time ever for any
solar axion search. In the future we will extend our search to
ma≲1.15eV, comfortably overlapping with cosmological hot
dark matter bounds.

---------------------------------------------------------
Title: Fast Up-flows Observed on Granules with Sunrise
Authors: Macdonald, G. A.; Hirzberger, J.; Solanki, S.; Choudhary,
D. P.
2011AGUFMSH13B1985M Altcode:
We present results from a rigorous study of fast granular up flows
observed with the Imaging Magnetograph eXperiment (IMaX) aboard
the SUNRISE balloon-borne observatory. A time series ∼ 23 minutes
long made June 9, 2009 with a cadence of ∼ 33sec and resolution
of 0.15--0.18” was used. Our study concentrates on up
flows with a LOS speeds in excess of 2km/s. These flows occur most
frequently on the bright areas of the smallest granules, and less
so on the bright edges of larger granules. The maximum up flow speed
tends to scale with its area which scales with the size of the host
granule. The longest-lived up flows are located on larger granules,
while shorter-lived ones tend to be located on smaller granules. Results
from simulations carried out in other studies suggest that the fastest
granular up flows occur chiefly during two scenarios: 1) on the edges
of granules when their centers cool, before the granules subsequently
split and 2) when a granule is forced under the surface by powerful
down flows from adjacent granules. Our observations provide evidence
for these results.

---------------------------------------------------------
Title: Evolution of the fine structure of magnetic fields in the
quiet Sun: Combining Sunrise observations and modelling
Authors: Wiegelmann, T.; Solanki, S.; Borrero, J.; Martinez Pillet,
V.; Sunrise Team
2011AGUFMSH41B..06W Altcode:
Observations with the balloon borne SUNRISE/IMAX instrument provide
us with unprecedented high spatial resolution (pixel size 40 km)
measurements of the magnetic field in the photosphere of the quiet
Sun. To investigate the magnetic structure of the chromosphere and
corona we extrapolate these photospheric measurements into the upper
solar atmosphere and analyse a timeseries with a cadence of 33s. We find
that the majority of closed loops which reach into the chromosphere
or corona have one foot point in strong photospheric magnetic field
regions (B&gt;300 G). Most loops are asymmetric and the weaker foot
point is often located in the internetwork. We find that the magnetic
connectivity of the loops changes rapidly with a typical recycling
time of about 2 min in the upper solar atmosphere and 14 min in the
photosphere. We discuss, to which extend the observed topological
changes can be interpreted as evidence for magnetic reconnection and
the relevance of these processes for coronal heating.

---------------------------------------------------------
Title: Chromospheric Observations of a Kink Wave in an On-disk Active
Region Fibril
Authors: Pietarila, A. M.; Aznar Cuadrado, R.; Hirzberger, J.;
Solanki, S.
2011AGUFMSH13B1951P Altcode:
Most observations of kink and Alfven waves in the chromosphere are
made in off-limb spicules. Here we present observations of a kink wave
in high spatial and temporal resolution Ca II 8542 data of an active
region fibril on the solar disk. The properties of the observed wave
are similar to kink waves in spicules. From the inferred wave phase
and period we estimate the lower limit for the field strength in the
chromospheric fibril to be a few hundred Gauss. The observations
indicate that the event may have been triggered by a small-scale
reconnection event higher up in the atmosphere.

---------------------------------------------------------
Title: Zeeman Broadening in Optical Stokes I of Solar-like Stars
Authors: Anderson, R. I.; Reiners, A.; Solanki, S. K.
2011ASPC..448.1061A Altcode: 2010arXiv1012.2968A; 2011csss...16.1061A
We present our analysis aimed at inferring average magnetic fields in
slowly-rotating solar-like stars. Using the spectral line inversion code
SPINOR, we perform high-accuracy line profile fitting and investigate
whether Zeeman broadening can be reliably detected in optical data
of unprecedented quality. We argue that our usage of both high-
and low-geff lines does provide a certain sensitivity to
magnetic fields that may, indeed, be detected. However, the measurement
is subject to a model dependence and prone to ambiguities, e.g. due to
spectral blends. Hence, while a field may be successfully recovered,
the quantification of this field is subject to large uncertainties,
even for the highest-quality optical data.

---------------------------------------------------------
Title: Long-term Magnetic Field Monitoring of the Sun-like Star ζ
Bootis A
Authors: Morgenthaler, A.; Petit, P.; Aurière, M.; Dintrans, B.;
Fares, R.; Gastine, T.; Lanoux, J.; Lignières, F.; Morin, J.; Ramirez,
J.; Saar, S.; Solanki, S. K.; Théado, S.; Van Grootel V., V.
2011ASPC..448.1203M Altcode: 2011csss...16.1203M
Phase-resolved observations of the solar-type star ζ Bootis A were
obtained using the NARVAL spectropolarimeter at the Telescope Bernard
Lyot (Pic du Midi, France) during years 2007, 2008, 2009 and 2010. The
data sets enable us to study both the rotational modulation and the
long-term evolution of various magnetic and activity tracers. Here,
we focus on the large-scale photospheric magnetic field (reconstructed
by Zeeman-Doppler Imaging), the Zeeman broadening of the FeI 846.84
nm magnetic line, and the chromospheric CaII H and Hα emission.

---------------------------------------------------------
Title: Analyzing Solar Cycles
Authors: Solanki, Sami K.; Krivova, Natalie A.
2011Sci...334..916S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The quiet Sun average Doppler shift of coronal lines up to 2 MK
Authors: Dadashi, N.; Teriaca, L.; Solanki, S. K.
2011A&A...534A..90D Altcode: 2011arXiv1109.4493D
Context. The average Doppler shift shown by spectral lines formed
from the chromosphere to the corona reveals important information
on the mass and energy balance of the solar atmosphere, providing
an important observational constraint to any models of the solar
corona. Previous spectroscopic observations of vacuum ultra-violet
(VUV) lines have revealed a persistent average wavelength shift of
lines formed at temperatures up to 1 MK. At higher temperatures,
the behaviour is still essentially unknown. Aims: Here we
analyse combined SUMER (Solar Ultraviolet Measurements of Emitted
Radiation)/SoHO (Solar and Heliospheric Observatory) and EIS (EUV
Imaging Spectrometer)/Hinode observations of the quiet Sun around
disk centre to determine, for the first time, the average Doppler
shift of several spectral lines formed between 1 and 2 MK, where the
largest part of the quiet coronal emission is formed. Methods:
The measurements are based on a novel technique applied to EIS spectra
to measure the difference in Doppler shift between lines formed at
different temperatures. Simultaneous wavelength-calibrated SUMER spectra
allow establishing the absolute value at the reference temperature of
T ≈ 1 MK. Results: The average line shifts at 1 MK &lt; T &lt;
1.8 MK are modestly, but clearly bluer than those observed at 1 MK. By
accepting an average blue shift of about (-1.8 ± 0.6) km s-1
at 1 MK (as provided by SUMER measurements), this translates into a
maximum Doppler shift of (-4.4 ± 2.2) km s-1 around 1.8
MK. The measured value appears to decrease to about (-1.3 ± 2.6) km
s-1 at the Fe xv formation temperature of 2.1 MK. 
Conclusions: The measured average Doppler shift between 0.01 and 2.1
MK, for which we provide a parametrisation, appears to be qualitatively
and roughly quantitatively consistent with what foreseen by 3D coronal
models where heating is produced by dissipation of currents induced
by photospheric motions and by reconnection with emerging magnetic flux.

---------------------------------------------------------
Title: Erratum:"Convective Nature of Sunspot Penumbral
Filaments: Discovery of Downflows in the Deep Photosphere" <A
href="/abs/2011ApJ...734L..18J">(2011, ApJ, 734, L18)</A>
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
Aznar Cuadrado, R.; Merenda, L.
2011ApJ...740L..55J Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Kink Waves in an Active Region Dynamic Fibril
Authors: Pietarila, A.; Aznar Cuadrado, R.; Hirzberger, J.; Solanki,
S. K.
2011ApJ...739...92P Altcode: 2011arXiv1107.3113P
We present high spatial and temporal resolution Ca II 8542 Å
observations of a kink wave in an on-disk chromospheric active region
fibril. The properties of the wave are similar to those observed in
off-limb spicules. From the observed phase and period of the wave we
determine a lower limit for the field strength in the chromospheric
active region fibril located at the edge of a sunspot to be a few
hundred gauss. We find indications that the event was triggered by a
small-scale reconnection event higher up in the atmosphere.

---------------------------------------------------------
Title: Variation of quiet Sun magnetic elements between 2006 and
2011 using Hinode SOT/SP
Authors: Buehler, D.; Lagg, A.; Solanki, S. K.
2011sdmi.confE..76B Altcode:
The Hinode satellite has revealed copious amounts of horizontal flux
covering the quiet Sun, nurturing the notion of local dynamo action
operating close to the solar surface. We sought to investigate the
variation in the occurrence as well as the strength of circular and
linear polarisation on the quiet Sun during the minimum of cycle
23, covering a period from November 2006 until August 2011. This
investigation used Hinode SOT/SP images of the disk centre and a large
FOV and focussed on line-integrated linear and circular polarisation
signals obtained from the Fe I 6302.5 Å absorption line. The circular
polarisation showed an overall linear decline in occurrence from
November 2006 until August 2011. By comparing PDFs we found that
this decline is associated in particular with network elements. The
internetwork on the other hand showed a 10% decrease in occurrence
from November 2010 until June 2009, followed by an equal increase
until August 2011. The investigation also revealed a reduction of 30%
in the occurrence of linear polarisation signals between November 2006
and December 2009. From August 2010 until August 2011 the occurrence of
linear polarisation was increasing again. Hence, our results show that
the occurrence of the ubiquitous linear polarisation of the internetwork
as seen by Hinode is measurably influenced by the solar cycle. This
implies that an independent local dynamo process is unlikely to be
the sole cause responsible for the generation of this magnetic flux.

---------------------------------------------------------
Title: Chromosphere above sunspots as seen at millimeter wavelengths
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen M.
2011IAUS..273..408L Altcode:
Millimeter emission is known to be a sensitive diagnostic of temperature
and density in the solar chromosphere. In this work we use millimeter
wave data to distinguish between various atmospheric models of sunspots,
whose temperature structure in the upper photosphere and chromosphere
has been the source of some controversy. From mm brightness simulations
we expect a radio umbra to change its appearance from dark to bright
(compared to the Quiet Sun) at a given wavelength in the millimeter
spectrum (depending on the exact temperature in the model used). Thereby
the millimeter brightness observed above an umbra at several wavelengths
imposes strong constraints on temperature and density stratification of
the sunspot atmosphere, in particular on the location and depth of the
temperature minimum and the location of the transition region. Current
mm/submm observational data suggest that brightness observed at
short wavelengths is unexpectedly low compared to the most widely
used sunspot models such as of Maltby et al. (1986). A successful
model that is in agreement with millimeter umbral brightness should
have an extended and deep temperature minimum (below 3000 K), such as
in the models of Severino et al. (1994). However, we are not able to
resolve the umbra cleanly with the presently available observations
and better resolution as well as better wavelength coverage are
needed for accurate diagnostics of umbral brightness at millimeter
wavelengths. This adds one more scientific objective for the Atacama
Large Millimeter/Submillimeter Array (ALMA).

---------------------------------------------------------
Title: The Sun at high resolution: first results from the Sunrise
mission
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller,
A.; Gandorfer, A.; Hirzberger, J.; Lagg, A.; Riethmüller, T. L.;
Schüssler, M.; Wiegelmann, T.; Bonet, J. A.; Pillet, V. Martínez;
Khomenko, E.; del Toro Iniesta, J. C.; Domingo, V.; Palacios, J.;
Knölker, M.; González, N. Bello; Borrero, J. M.; Berkefeld, T.;
Franz, M.; Roth, M.; Schmidt, W.; Steiner, O.; Title, A. M.
2011IAUS..273..226S Altcode:
The Sunrise balloon-borne solar observatory consists of a 1m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system and further infrastructure. The first
science flight of Sunrise yielded high-quality data that reveal the
structure, dynamics and evolution of solar convection, oscillations
and magnetic fields at a resolution of around 100 km in the quiet
Sun. Here we describe very briefly the mission and the first results
obtained from the Sunrise data, which include a number of discoveries.

---------------------------------------------------------
Title: The height of chromospheric loops in an emerging flux region
Authors: Merenda, L.; Lagg, A.; Solanki, S. K.
2011A&A...532A..63M Altcode: 2012arXiv1202.1113M
Context. The chromospheric layer observable with the He i 10 830 Å
triplet is strongly warped. The analysis of the magnetic morphology of
this layer therefore requires a reliable technique to determine the
height at which the He i absorption takes place. Aims: The He
i absorption signature connecting two pores of opposite polarity in an
emerging flux region is investigated. This signature is suggestive of a
loop system connecting the two pores. We aim to show that limits can be
set on the height of this chromospheric loop system. Methods: The
increasing anisotropy in the illumination of a thin, magnetic structure
intensifies the linear polarization signal observed in the He i triplet
with height. This signal is altered by the Hanle effect. We apply an
inversion technique incorporating the joint action of the Hanle and
Zeeman effects, with the absorption layer height being one of the
free parameters. Results: The observed linear polarization
signal can be explained only if the loop apex is higher than ≈ 5
Mm. Best agreement with the observations is achieved for a height of
6.3 Mm. Conclusions: The strength of the linear polarization
signal in the loop apex is inconsistent with the assumption of a He
i absorption layer at a constant height level. The determined height
supports the earlier conclusion that dark He 10 830 Å filaments in
emerging flux regions trace emerging loops.

---------------------------------------------------------
Title: Latest results and prospects of the CERN Axion Solar Telescope
Authors: Irastorza, I. G.; Aune, S.; Barth, K.; Belov, A.; Borghi,
S.; Bräuninger, H.; Cantatore, G.; Carmona, J. M.; Cetin, S. A.;
Collar, J. I.; Dafni, T.; Davenport, M.; Eleftheriadis, C.; Elias,
N.; Ezer, C.; Fanourakis, G.; Ferrer-Ribas, E.; Friedrich, P.;
Galán, J.; Gardikiotis, A.; Gazis, E. N.; Geralis, T.; Giomataris,
I.; Gninenko, S.; Gómez, H.; Gruber, E.; Guthörl, T.; Hartmann,
R.; Haug, F.; Hasinoff, M. D.; Hoffmann, D. H. H.; Iguaz, F. J.;
Jacoby, J.; Jakovčić, K.; Karuza, M.; Königsmann, K.; Kotthaus,
R.; Krčmar, M.; Kuster, M.; Lakić, B.; Laurent, J. M.; Liolios,
A.; Ljubičić, A.; Lozza, V.; Lutz, G.; Luzón, G.; Morales, J.;
Niinikoski, T.; Nordt, A.; Papaevangelou, T.; Pivovaroff, M. J.;
Raffelt, G.; Rashba, T.; Riege, H.; Rodríguez, A.; Rosu, M.; Ruz,
J.; Savvidis, I.; Silva, P. S.; Solanki, S. K.; Soufli, R.; Stewart,
L.; Tomás, A.; Tsagri, M.; van Bibber, K.; Vafeiadis, T.; Villar,
J.; Vogel, J. K.; Yildiz, S. C.; Zioutas, K.
2011JPhCS.309a2001I Altcode:
The CERN Axion Solar Telescope (CAST) experiment searches for axions
from the Sun converted into few keV photons via the inverse Primakoff
effect in the high magnetic field of a superconducting Large Hadron
Collider (LHC) decommissioned test magnet. After results obtained
with vacuum in the magnet pipes (phase I of the experiment) as well
as with 4He the collaboration is now immersed in the data
taking with 3He, to be finished in 2011. The status of
the experiment will be presented, including a preliminary exclusion
plot of the first 3He data. CAST is currently sensitive to
realistic QCD axion models at the sub-eV scale, and with axion-photon
couplings down to the ~ 2 × 10-10 GeV-1,
compatible with solar life limits. Future plans include revisiting
vaccuum and 4He configurations with improved sensitivity,
as well as possible additional search for non-standard signals from
chamaleons, paraphotons or other WISPs. For the longer term, we
study the feasibility of an altogether improved version of the axion
helioscope concept, with a jump in sensitivity of about one order of
magnitude in gaγ beyond CAST.

---------------------------------------------------------
Title: Exploring the magnetic topologies of cool stars
Authors: Morin, J.; Donati, J. -F.; Petit, P.; Albert, L.; Auriére,
M.; Cabanac, R.; Catala, C.; Delfosse, X.; Dintrans, B.; Fares,
R.; Forveille, T.; Gastine, T.; Jardine, M.; Konstantinova-Antova,
R.; Lanoux, J.; Lignires, F.; Morgenthaler, A.; Paletou, F.; Velez,
J. C. Ramirez; Solanki, S. K.; Thado, S.; Van Grootel, V.
2011IAUS..273..181M Altcode: 2010arXiv1009.2589M
Magnetic fields of cool stars can be directly investigated through
the study of the Zeeman effect on photospheric spectral lines using
several approaches. With spectroscopic measurement in unpolarised
light, the total magnetic flux averaged over the stellar disc can
be derived but very little information on the field geometry is
available. Spectropolarimetry provides a complementary information
on the large-scale magnetic topology. With Zeeman-Doppler Imaging
(ZDI), this information can be retrieved to produce a map of the vector
magnetic field at the surface of the star, and in particular to assess
the relative importance of the poloidal and toroidal components as
well as the degree of axisymmetry of the field distribution. The
development of high-performance spectropolarimeters associated with
multi-lines techniques and ZDI allows us to explore magnetic topologies
throughout the Hertzsprung-Russel diagram, on stars spanning a wide
range of mass, age and rotation period. These observations bring novel
constraints on magnetic field generation by dynamo effect in cool
stars. In particular, the study of solar twins brings new insight on
the impact of rotation on the solar dynamo, whereas the detection of
strong and stable dipolar magnetic fields on fully convective stars
questions the precise role of the tachocline in this process.

---------------------------------------------------------
Title: Modelling solar irradiance variability on time scales from
minutes to months
Authors: Seleznyov, A. D.; Solanki, S. K.; Krivova, N. A.
2011A&A...532A.108S Altcode: 2013arXiv1303.1961S
We analyze and model total solar irradiance variability on time scales
from minutes to months, excluding variations due to p-mode oscillations,
using a combination of convective and magnetic components. These include
granulation, the magnetic network, faculae and sunspots. Analysis of
VIRGO data shows that on periods of a day or longer solar variability
depends on magnetic activity, but is nearly independent at shorter
periods. We assume that only granulation affects the solar irradiance
variability on time scales from minutes to hours. Granulation is
described as a large sample of bright cells and dark lanes that
evolve according to rules deduced from observations and radiation
hydrodynamic simulations. Comparison of this model combined with a high
time resolution magnetic-field based irradiance reconstruction, with
solar data reveals a good correspondence except at periods of 10 to 30
h. This suggests that the model is missing some power at these periods,
which may be due to the absence of supergranulation or insufficient
sensitivity of MDI magnetograms used for the reconstruction of the
magnetic field-based irradiance reconstructions. Our model also shows
that even for spatially unresolved data (such as those available for
stars) the Fourier or wavelet transform of time series sampled at high
cadence may allow properties of stellar granulation, in particular
granule lifetimes to be determined.

---------------------------------------------------------
Title: Continuous upflows and sporadic downflows observed in active
regions
Authors: Kamio, S.; Peter, H.; Curdt, W.; Solanki, S. K.
2011A&A...532A..96K Altcode: 2011arXiv1107.1993K
 Aims: We present a study of the temporal evolution of coronal
loops in active regions and its implications for the dynamics in coronal
loops. Methods: We analyzed images of the Atmospheric Imaging
Assembly (AIA) on the Solar Dynamics Observatory (SDO) at multiple
temperatures to detect apparent motions in the coronal loops. 
Results: Quasi-periodic brightness fluctuations propagate upwards from
the loop footpoint in hot emission at 1 MK, while sporadic downflows
are seen in cool emission below 1 MK. The upward motion in hot
emission increases just after the cool downflows. Conclusions:
The apparent propagating pattern suggests a hot upflow from the
loop footpoints, and is considered to supply hot plasma into the
coronal loop, but a wavelike phenomenon cannot be ruled out. Coronal
condensation occasionally happens in the coronal loop, and the cool
material flows down to the footpoint. Emission from cool plasma could
have a significant contribution to hot AIA channels in the event of
coronal condensation.

---------------------------------------------------------
Title: Evolution of the solar irradiance during the Holocene
Authors: Vieira, L. E. A.; Solanki, S. K.; Krivova, N. A.; Usoskin, I.
2011A&A...531A...6V Altcode: 2011arXiv1103.4958V
Context. Long-term records of solar radiative output are vital for
understanding solar variability and past climate change. Measurements
of solar irradiance are available for only the last three decades,
which calls for reconstructions of this quantity over longer time
scales using suitable models. Aims: We present a physically
consistent reconstruction of the total solar irradiance for the
Holocene. Methods: We extend the SATIRE (Spectral And Total
Irradiance REconstruction) models to estimate the evolution of the
total (and partly spectral) solar irradiance over the Holocene. The
basic assumption is that the variations of the solar irradiance are
due to the evolution of the dark and bright magnetic features on the
solar surface. The evolution of the decadally averaged magnetic flux
is computed from decadal values of cosmogenic isotope concentrations
recorded in natural archives employing a series of physics-based
models connecting the processes from the modulation of the cosmic
ray flux in the heliosphere to their record in natural archives. We
then compute the total solar irradiance (TSI) as a linear combination
of the jth and jth + 1 decadal values of the open magnetic flux. In
order to evaluate the uncertainties due to the evolution of the Earth's
magnetic dipole moment, we employ four reconstructions of the open flux
which are based on conceptually different paleomagnetic models. 
Results: Reconstructions of the TSI over the Holocene, each valid for
a different paleomagnetic time series, are presented. Our analysis
suggests that major sources of uncertainty in the TSI in this model
are the heritage of the uncertainty of the TSI since 1610 reconstructed
from sunspot data and the uncertainty of the evolution of the Earth's
magnetic dipole moment. The analysis of the distribution functions
of the reconstructed irradiance for the last 3000 years, which is the
period that the reconstructions overlap, indicates that the estimates
based on the virtual axial dipole moment are significantly lower at
earlier times than the reconstructions based on the virtual dipole
moment. We also present a combined reconstruction, which represents
our best estimate of total solar irradiance for any given time during
the Holocene. Conclusions: We present the first physics-based
reconstruction of the total solar irradiance over the Holocene, which
will be of interest for studies of climate change over the last 11 500
years. The reconstruction indicates that the decadally averaged total
solar irradiance ranges over approximately 1.5 W/m2 from
grand maxima to grand minima. Appendix A is available in electronic
form at <A href="http://www.aanda.org">http://www.aanda.org</A>The
TSI data is only available at the CDS via anonymous
ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A6">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/531/A6</A>

---------------------------------------------------------
Title: The continuum intensity as a function of magnetic
field. I. Active region and quiet Sun magnetic elements
Authors: Kobel, P.; Solanki, S. K.; Borrero, J. M.
2011A&A...531A.112K Altcode: 2011arXiv1105.1958K
Context. Small-scale magnetic fields are major contributors to
the solar irradiance variations. Hence, the continuum intensity
contrast of magnetic elements in the quiet Sun (QS) network and in
active region (AR) plage is an essential quantity that needs to be
measured reliably. Aims: By using Hinode/SP disk center data
at a constant, high spatial resolution, we aim at updating results of
earlier ground-based studies of contrast vs. magnetogram signal, and to
look for systematic differences between AR plages and QS network. Methods: The field strength, filling factor and inclination of the
field was retrieved by means of a Milne-Eddington inversion (VFISV
code). As in earlier studies, we then performed a pixel-by-pixel study
of 630.2 nm continuum contrast vs. apparent (i.e. averaged over a pixel)
longitudinal magnetic field over large fields of view in ARs and in the
QS. Results: The continuum contrast of magnetic elements reaches
larger values in the QS (on average 3.7%) than in ARs (on average
1.3%). This could not be attributed to any systematic difference in
the chosen contrast references, so that it mainly reflects an intrinsic
brightness difference. The larger contrasts in the QS are in agreement
with earlier, lower resolution results, although our values are larger
due to our better spatial resolution. At Hinode's spatial resolution,
moreover, the relationship between contrast and apparent longitudinal
field strength exhibits a peak at around 700 G in both the QS and ARs,
whereas earlier lower resolution studies only found a peak in the QS and
a monotonic decrease in ARs. We attribute this discrepancy both to our
careful removal of the pores and their close surroundings affected by
the telescope diffraction, as well as to the enhanced spatial resolution
and very low scattered light of the Hinode Solar Optical Telescope. We
verified that the magnetic elements producing the peak in the contrast
curve are rather vertical in the AR and in the QS, so that the larger
contrasts in the QS cannot be explained by larger inclinations, as had
been proposed earlier. The opposite polarities in ARs do not exhibit
any noticeable difference in inclination either, although they reach
different contrasts when the amount of flux is significantly unbalanced
between the polarities. Conclusions: According to our inversions,
the magnetic elements producing the peak of the contrast curves have
similar properties (field strength, inclination, filling factor) in ARs
and in the QS, so that the larger brightness of magnetic elements in the
QS remains unexplained. Indirect evidence suggests that the contrast
difference is not primarily due to any difference in average size of
the magnetic elements. A possible explanation lies in the different
efficiencies of convective energy transport in the QS and in ARs,
which will be the topic of a second paper.

---------------------------------------------------------
Title: EUV jets, type III radio bursts and sunspot waves investigated
using SDO/AIA observations
Authors: Innes, D. E.; Cameron, R. H.; Solanki, S. K.
2011A&A...531L..13I Altcode: 2011arXiv1106.3417I
Context. Quasi-periodic plasma jets are often ejected from the Sun
into interplanetary space. The commonly observed signatures are
day-long sequences of type III radio bursts. Aims: The aim is
to identify the source of quasi-periodic jets observed on 3 Aug. 2010
in the Sun's corona and in interplanetary space. Methods:
Images from the Solar Dynamics Observatory (SDO) at 211 Å are used
to identify the solar source of the type III radio bursts seen in
WIND/WAVES dynamic spectra. We analyse a 2.5 h period during which six
strong bursts are seen. The radio signals are cross-correlated with
emission from extreme ultraviolet (EUV) jets coming from the western
side of a sunspot in AR 11092. The jets are further cross-correlated
with brightening at a small site on the edge of the sunspot umbra,
and the brightening with 3-min sunspot intensity oscillations. 
Results: The radio bursts correlate very well with the EUV jets. The
EUV jet emission also correlates well with brightening at what looks
like their footpoint at the edge of the umbra. The jet emission lags
the radio signals and the footpoint brightening by about 30 s because
the EUV jets take time to develop. For 10-15 min after strong EUV jets
are ejected, the footpoint brightens at roughly 3 min intervals. In
both the EUV images and the extracted light curves, it looks as though
the brightening is related to the 3-min sunspot oscillations, although
the correlation coefficient is rather low. The only open field near
the jets is rooted in the sunspot. Conclusions: Active region
EUV/X-ray jets and interplanetary electron streams originate on the
edge of the sunspot umbra. They form along a current sheet between
the sunspot open field and closed field connecting to underlying
satellite flux. Sunspot running penumbral waves cause roughly 3-min
jet footpoint brightening. The relationship between the waves and
jets is less clear. Movie is available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Convective Nature of Sunspot Penumbral Filaments: Discovery
of Downflows in the Deep Photosphere
Authors: Joshi, Jayant; Pietarila, A.; Hirzberger, J.; Solanki, S. K.;
Aznar Cuadrado, R.; Merenda, L.
2011ApJ...734L..18J Altcode: 2011arXiv1105.1877J
We study the velocity structure of penumbral filaments in the deep
photosphere to obtain direct evidence for the convective nature of
sunspot penumbrae. A sunspot was observed at high spatial resolution
with the 1 m Swedish Solar Telescope in the deep photospheric C I 5380
Å absorption line. The Multi-Object Multi-Frame Blind Deconvolution
method is used for image restoration and straylight is filtered out. We
report here the discovery of clear redshifts in the C I 5380 Å line
at multiple locations in sunspot penumbral filaments. For example,
bright head of filaments show larger concentrated blueshift and are
surrounded by darker, redshifted regions, suggestive of overturning
convection. Elongated downflow lanes are also located beside bright
penumbral fibrils. Our results provide the strongest evidence yet
for the presence of overturning convection in penumbral filaments and
highlight the need to observe the deepest layers of the penumbra in
order to uncover the energy transport processes taking place there.

---------------------------------------------------------
Title: Solar irradiance variability: a six-year comparison between
SORCE observations and the SATIRE model
Authors: Ball, W. T.; Unruh, Y. C.; Krivova, N. A.; Solanki, S.;
Harder, J. W.
2011A&A...530A..71B Altcode: 2011arXiv1104.0885B
 Aims: We investigate how well modeled solar irradiances agree
with measurements from the SORCE satellite, both for total solar
irradiance and broken down into spectral regions on timescales of
several years. Methods: We use the SATIRE model and compare
modeled total solar irradiance (TSI) with TSI measurements over the
period 25 February 2003 to 1 November 2009. Spectral solar irradiance
over 200-1630 nm is compared with the SIM instrument on SORCE over
the period 21 April 2004 to 1 November 2009. We discuss the overall
change in flux and the rotational and long-term trends during this
period of decline from moderate activity to the recent solar minimum
in ~10 nm bands and for three spectral regions of significant interest:
the UV integrated over 200-300 nm, the visible over 400-691 nm and the
IR between 972-1630 nm. Results: The model captures 97% of the
observed TSI variation. This is on the order at which TSI detectors
agree with each other during the period considered. In the spectral
comparison, rotational variability is well reproduced, especially
between 400 and 1200 nm. The magnitude of change in the long-term
trends is many times larger in SIM at almost all wavelengths while
trends in SIM oppose SATIRE in the visible between 500 and 700 nm and
again between 1000 and 1200 nm. We discuss the remaining issues with
both SIM data and the identified limits of the model, particularly
with the way facular contributions are dealt with, the limit of flux
identification in MDI magnetograms during solar minimum and the model
atmospheres in the IR employed by SATIRE. However, it is unlikely that
improvements in these areas will significantly enhance the agreement
in the long-term trends. This disagreement implies that some mechanism
other than surface magnetism is causing SSI variations, in particular
between 2004 and 2006, if the SIM data are correct. Since SATIRE
was able to reproduce UV irradiance between 1991 and 2002 from UARS,
either the solar mechanism for SSI variation fundamentally changed
around the peak of cycle 23, or there is an inconsistency between UARS
and SORCE UV measurements. We favour the second explanation.

---------------------------------------------------------
Title: Small-scale flux emergence events observed by Sunrise/IMaX
Authors: Guglielmino, S. L.; Pillet, V. Martínez; del Toro Iniesta,
J. C.; Rubio, L. R. Bellot; Zuccarello, F.; Solanki, S. K.; Solanki
2011IAUS..274..140G Altcode:
Thanks to the unprecedented combination of high spatial resolution
(0”.2) and high temporal cadence (33 s) spectropolarimetric
measurements, the IMaX magnetograph aboard the Sunrise balloon-borne
telescope is revealing new insights about the plasma dynamics
of the all-pervasive small-scale flux concentrations in the quiet
Sun. We present the result of a case study concerning the appearance
of a bipole, with a size of about 4” and a flux content of 5 ×
1017 Mx, with strong signal of horizontal fields during
the emergence. We analyze the data set using the SIR inversion code
and obtain indications about the three-dimensional shape of the bipole
and its evolution with time.

---------------------------------------------------------
Title: Solar total irradiance in cycle 23
Authors: Krivova, N. A.; Solanki, S. K.; Schmutz, W.
2011A&A...529A..81K Altcode: 2011arXiv1102.3077K
Context. The most recent minimum of solar activity was deeper and
longer than the previous two minima as indicated by different proxies
of solar activity. This is also true for the total solar irradiance
(TSI) according to the PMOD composite. Aims: The apparently
unusual behaviour of the TSI has been interpreted as evidence against
solar surface magnetism as the main driver of the secular change
in the TSI. We test claims that the evolution of the solar surface
magnetic field does not reproduce the observed TSI in cycle 23. Methods: We use sensitive, 60-min averaged MDI magnetograms and
quasi-simultaneous continuum images as an input to our SATIRE-S model
and calculate the TSI variation over cycle 23, sampled roughly every
two weeks. The computed TSI is then compared with the PMOD composite of
TSI measurements and with the data from two individual instruments,
SORCE/TIM and UARS/ACRIM II, that monitored the TSI during the
declining phase of cycle 23 and over the previous minimum in 1996,
respectively. Results: Excellent agreement is found between the
trends shown by the model and almost all sets of measurements. The
only exception is the early, i.e. 1996 to 1998, PMOD data. Whereas
the agreement between the model and the PMOD composite over the
period 1999-2009 is almost perfect, the modelled TSI shows a steeper
increase between 1996 and 1999 than implied by the PMOD composite. On
the other hand, the steeper trend in the model agrees remarkably well
with the ACRIM II data. A closer look at the VIRGO data, which are the
basis of the PMOD composite after 1996, reveals that only one of the
two VIRGO instruments, the PMO6V, shows the shallower trend present
in the composite, whereas the DIARAD measurements indicate a steeper
trend. Conclusions: Based on these results, we conclude that (1)
the sensitivity changes of the PMO6V radiometers within VIRGO during
the first two years have very likely not been correctly evaluated;
and that (2) the TSI variations over cycle 23 and the change in the
TSI levels between the minima in 1996 and 2008 are consistent with
the solar surface magnetism mechanism.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Evolution of solar irradiance
during Holocene (Vieira+, 2011)
Authors: Vieira, L. E. A.; Solanki, S. K.; Krivova, N. A.; Usoskin, I.
2011yCat..35310006V Altcode: 2011yCat..35319006V
This is a composite total solar irradiance (TSI) time series for 9495BC
to 2007AD constructed as described in Sect. 3.3 of the paper. Since
the TSI is the main external heat input into the Earth's climate
system, a consistent record covering as long period as possible
is needed for climate models. This was our main motivation for
constructing this composite TSI time series. In order to
produce a representative time series, we divided the Holocene into
four periods according to the available data for each period. Table
4 (see below) summarizes the periods considered and the models
available for each period. After the end of the Maunder Minimum we
compute daily values, while prior to the end of the Maunder Minimum
we compute 10-year averages. For the period for which both solar disk
magnetograms and continuum images are available (period 1) we employ
the SATIRE-S reconstruction (Krivova et al. 2003A&amp;A...399L...1K;
Wenzler et al. 2006A&amp;A...460..583W). SATIRE-T (Krivova et
al. 2010JGRA..11512112K) reconstruction is used from the beginning of
the Maunder Minimum (approximately 1640AD) to 1977AD. Prior to 1640AD
reconstructions are based on cosmogenic isotopes (this paper). Different
models of the Earth's geomagnetic field are available before and after
approximately 5000BC. Therefore we treat periods 3 and 4 (before and
after 5000BC) separately. Further details can be found in the paper. We
emphasize that the reconstructions based on different proxies have
different time resolutions. (1 data file).

---------------------------------------------------------
Title: Performance validation of phase diversity image reconstruction
techniques
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Gandorfer,
A.; Solanki, S. K.
2011A&A...529A.132H Altcode:
We present a performance study of a phase diversity (PD) image
reconstruction algorithm based on artificial solar images obtained
from MHD simulations and on seeing-free data obtained with the SuFI
instrument on the Sunrise balloon borne observatory. The artificial
data were altered by applying different levels of degradation with
synthesised wavefront errors and noise. The PD algorithm was modified
by changing the number of fitted polynomials, the shape of the pupil and
the applied noise filter. The obtained reconstructions are evaluated by
means of the resulting rms intensity contrast and by the conspicuousness
of appearing artifacts. The results show that PD is a robust method
which consistently recovers the initial unaffected image contents. The
efficiency of the reconstruction is, however, strongly dependent on the
number of used fitting polynomials and the noise level of the images. If
the maximum number of fitted polynomials is higher than 21, artifacts
have to be accepted and for noise levels higher than 10-3
the commonly used noise filtering techniques are not able to avoid
amplification of spurious structures.

---------------------------------------------------------
Title: The Continuum Contrast of Magnetic Elements as a Function of
Magnetic Field (Disk Center): Early Studies and Hinode/SP Results
Authors: Kobel, P.; Solanki, S. K.; Borrero, J. M.
2011ASPC..437..297K Altcode:
To deepen our understanding of the role of small-scale magnetic
fields on the solar irradiance, it is essential to quantify the
continuum contrast of magnetic elements in the quiet Sun (QS)
network and in active region (AR) plage. By using Hinode/SP disk
center data at constant spatial resolution, we aimed at updating
results of earlier ground-based studies of contrast vs. magnetogram
signal, and to look for systematic differences between AR plages
and QS network. We performed a pixel-per-pixel study of continuum
contrast vs. longitudinal flux density over large fields of view in
AR and in QS (as in earlier studies). Even at Hinode's resolution,
the contrast of magnetic elements reaches larger values in the QS than
in ARs. We show that this difference cannot be explained by different
inclinations of magnetic elements in ARs and QS. We compared our
contrast vs. magnetic flux density with earlier studies and attributed
the differences both to our proper removal of the pores and their
surrounding diffraction-spread radiation, as well as to our enhanced
spatial resolution and quasi-absence of scattered light. At Hinode's
resolution, the contrast of magnetic elements peaks on average at
similar magnetic flux densities in ARs and in the QS, which indicates
that the brightest flux tubes have similar sizes in ARs and QS.

---------------------------------------------------------
Title: Unnoticed Magnetic Field Oscillations in the Very Quiet Sun
Revealed by SUNRISE/IMaX
Authors: Martínez González, M. J.; Asensio Ramos, A.; Manso Sainz,
R.; Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; López Ariste,
A.; Schmidt, W.; Barthol, P.; Gandorfer, A.
2011ApJ...730L..37M Altcode: 2011arXiv1103.0145M
We present observational evidence for oscillations of magnetic flux
density in the quiet areas of the Sun. The majority of magnetic
fields on the solar surface have strengths of the order of or lower
than the equipartition field (300-500 G). This results in a myriad of
magnetic fields whose evolution is largely determined by the turbulent
plasma motions. When granules evolve they squash the magnetic field
lines together or pull them apart. Here, we report on the periodic
deformation of the shapes of features in circular polarization observed
at high resolution with SUNRISE. In particular, we note that the
area of patches with a constant magnetic flux oscillates with time,
which implies that the apparent magnetic field intensity oscillates
in antiphase. The periods associated with this oscillatory pattern
are compatible with the granular lifetime and change abruptly, which
suggests that these oscillations might not correspond to characteristic
oscillatory modes of magnetic structures, but to the forcing by granular
motions. In one particular case, we find three patches around the same
granule oscillating in phase, which means that the spatial coherence
of these oscillations can reach 1600 km. Interestingly, the same kind
of oscillatory phenomenon is also found in the upper photosphere.

---------------------------------------------------------
Title: Transport of Magnetic Flux from the Canopy to the Internetwork
Authors: Pietarila, A.; Cameron, R. H.; Danilovic, S.; Solanki, S. K.
2011ApJ...729..136P Altcode: 2011arXiv1102.1397P
Recent observations have revealed that 8% of linear polarization
patches in the internetwork (INW) quiet Sun are fully embedded in
downflows. These are not easily explained with the typical scenarios for
the source of INW fields which rely on flux emergence from below. Using
radiative MHD simulations, we explore a scenario where magnetic flux
is transported from the magnetic canopy overlying the INW into the
photosphere by means of downward plumes associated with convective
overshoot. We find that if a canopy-like magnetic field is present in
the simulation, the transport of flux from the canopy is an important
process for seeding the photospheric layers of the INW with magnetic
field. We propose that this mechanism is relevant for the Sun as well,
and it could naturally explain the observed INW linear polarization
patches entirely embedded in downflows.

---------------------------------------------------------
Title: Intensity contrast from MHD simulations and HINODE observations
Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.;
Lagg, A.; Vögler, A.
2011A&A...526A.120A Altcode: 2010arXiv1011.6102A
Context. Changes in the solar surface area, which is covered by
small-scale magnetic elements, are thought to cause long-term changes
in the solar spectral irradiance, which are important for determining
the impact on Earth's climate. Aims: To study the effect of
small-scale magnetic elements on the total and spectral irradiance,
we derive their contrasts from 3-D MHD simulations of the solar
atmosphere. These calculations are necessary because measurements of
small-scale flux tube contrasts are confined to a few wavelengths and
affected by scattered light and instrument defocus, even for space
observations. Methods: To test the contrast calculations,
we compare rms contrasts from simulations with those obtained with
the broad-band filter imager mounted on the Solar Optical Telescope
(SOT) onboard the Hinode satellite and also analyse centre-to-limb
variations (CLV). The 3-D MHD simulations include the interaction
between convection and magnetic flux tubes. They are performed by
assuming non-grey radiative transfer and using the MURaM code. The
simulations have an average vertical magnetic field of 0 G, 50 G, and
200 G. Emergent intensities are calculated with the spectral synthesis
code ATLAS9 and are convolved with a theoretical point-spread function
to account for the properties of the observations' optical system. Results: We find reasonable agreement between simulated and observed
intensity distributions in the visible continuum bands. Agreement is
poorer for the CN and G-bands. The analysis of the simulations uncovers
a potentially more realistic centre-to-limb behaviour than calculations
based on 1-D model atmospheres. Conclusions: We conclude that
starting from 3-D MHD simulations represents a powerful approach
to obtaining intensity contrasts for a wide wavelength coverage and
different positions across on the solar disk. This also paves the way
for future calculations of facular and network contrast as a function
of magnetic fluxes.

---------------------------------------------------------
Title: The Role of Active Region Loop Geometry. II. Symmetry Breaking
in Three-dimensional Active Region: Why are Vertical Kink Oscillations
Observed so Rarely?
Authors: Selwa, M.; Solanki, S. K.; Ofman, L.
2011ApJ...728...87S Altcode:
We present numerical results of simulations of kink oscillations of
coronal loops in an idealized active region (AR) that is initialized
as a potential dipole magnetic configuration with gravitationally
stratified density. We consider loops, with density higher than
the surrounding plasma, embedded into the dipolar AR. We study the
excitation of kink oscillations of such loops by velocity pulses at
different positions, of a given duration and amplitude. The position of
the pulse varies in the parametric studies. For a central (symmetric)
loop within the AR, we find that the amplitude of vertical kink
oscillations is significantly amplified in comparison to horizontal
kink oscillations for exciters located centrally (symmetrically) below
the loop. For pulses initiated further from such a symmetric loop a
combination of vertical and horizontal oscillations is excited. The
scenario changes significantly when we study an inclined loop
(non-symmetric within a dipole field). In this case, we do not
see vertical kink oscillations of any significant amplitude being
excited, while horizontal ones can be easily detected. These results
indicate that the reason why vertical kink oscillations are observed so
rarely is that their excitation requires a set of conditions to occur
simultaneously: the exciting pulse must be located roughly below the
loop apex and the loop itself must be located symmetrically within
the group of loops. The new findings of the present study show the
importance of not only the position of the pulse, but mainly of the
location of the loop within the set of field lines having the same
magnetic connectivity. We find that the slow propagating wave is excited
in all the studied loops and its excitation does not depend either on
the geometry of the loop or the pulse. We discuss TRACE observations
of coronal loop oscillations in view of our findings and find that
our results can be used for identifying the polarization of the kink
mode based on the location of the loop within the set of field lines
of the same connectivity and the position of the flare.

---------------------------------------------------------
Title: Towards a long-term record of solar total and spectral
irradiance
Authors: Krivova, N. A.; Solanki, S. K.; Unruh, Y. C.
2011JASTP..73..223K Altcode: 2009arXiv0911.4002K
The variation of total solar irradiance (TSI) has been measured since
1978 and that of the spectral irradiance for an even shorter amount of
time. Semi-empirical models are now available that reproduce over 80%
of the measured irradiance variations. An extension of these models into
the more distant past is needed in order to serve as input to climate
simulations. Here we review our most recent efforts to model solar
total and spectral irradiance on time scales from days to centuries and
even longer. Solar spectral irradiance has been reconstructed since
1947. Reconstruction of solar total irradiance goes back to 1610 and
suggests a value of about 1-1.5W/m2 for the increase in
the cycle-averaged TSI since the end of the Maunder minimum, which
is significantly lower than previously assumed but agrees with other
modern models. First steps have also been made towards reconstructions
of solar total and spectral irradiance on time scales of millennia.

---------------------------------------------------------
Title: Multicomponent He I 10 830 Å profiles in an active filament
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
2011A&A...526A..42S Altcode: 2011arXiv1101.5563S
 Aims: We present new spectropolarimetric observations of the
chromospheric He i 10 830 Å multiplet observed in a filament during
its phase of activity. Methods: The data were recorded with the
new Tenerife Infrared Polarimeter (TIP-II) at the German Vacuum Tower
Telescope (VTT) on 2005 May 18. We inverted the He Stokes profiles
using multiple atmospheric components. Results: The observed
He Stokes profiles display a remarkably wide variety of shapes. Most
of the profiles show very broad Stokes I absorptions and complex and
spatially variable Stokes V signatures. The inversion of the profiles
shows evidence of different atmospheric blue- and redshifted components
of the He i lines within the resolution element (~1 arcsec), with
supersonic velocities of up to ~100 km s-1. Up to five
different atmospheric components are found in the same profile. We
show that even these complex profiles can be reliably inverted.

---------------------------------------------------------
Title: Mesogranulation and the Solar Surface Magnetic Field
Distribution
Authors: Yelles Chaouche, L.; Moreno-Insertis, F.; Martínez Pillet,
V.; Wiegelmann, T.; Bonet, J. A.; Knölker, M.; Bellot Rubio, L. R.;
del Toro Iniesta, J. C.; Barthol, P.; Gandorfer, A.; Schmidt, W.;
Solanki, S. K.
2011ApJ...727L..30Y Altcode: 2010arXiv1012.4481Y
The relation of the solar surface magnetic field with mesogranular
cells is studied using high spatial (≈100 km) and temporal (≈30
s) resolution data obtained with the IMaX instrument on board
SUNRISE. First, mesogranular cells are identified using Lagrange
tracers (corks) based on horizontal velocity fields obtained through
local correlation tracking. After ≈20 minutes of integration, the
tracers delineate a sharp mesogranular network with lanes of width
below about 280 km. The preferential location of magnetic elements in
mesogranular cells is tested quantitatively. Roughly 85% of pixels with
magnetic field higher than 100 G are located in the near neighborhood
of mesogranular lanes. Magnetic flux is therefore concentrated in
mesogranular lanes rather than intergranular ones. Second, magnetic
field extrapolations are performed to obtain field lines anchored in
the observed flux elements. This analysis, therefore, is independent
of the horizontal flows determined in the first part. A probability
density function (PDF) is calculated for the distribution of distances
between the footpoints of individual magnetic field lines. The PDF has
an exponential shape at scales between 1 and 10 Mm, with a constant
characteristic decay distance, indicating the absence of preferred
convection scales in the mesogranular range. Our results support
the view that mesogranulation is not an intrinsic convective scale
(in the sense that it is not a primary energy-injection scale of solar
convection), but also give quantitative confirmation that, nevertheless,
the magnetic elements are preferentially found along mesogranular lanes.

---------------------------------------------------------
Title: The Solar Orbiter Mission and its Polarimetric and Helioseismic
Imager (SO/PHI)
Authors: Gandorfer, Achim; Solanki, Sami K.; Woch, Joachim; Martínez
Pillet, Valentin; Álvarez Herrero, Alberto; Appourchaux, Thierry
2011JPhCS.271a2086G Altcode:
We briefly outline the scientific and instrumental aspects of ESA's
Solar Orbiter mission. Special emphasis is given to the Polarimetric
and Helioseismic Imager, the instrument with the highest relevance for
helioseismology applications, which will observe gas motions and the
vector magnetic field in the photosphere at high spatial and temporal
resolution.

---------------------------------------------------------
Title: The Imaging Magnetograph eXperiment (IMaX) for the Sunrise
Balloon-Borne Solar Observatory
Authors: Martínez Pillet, V.; del Toro Iniesta, J. C.;
Álvarez-Herrero, A.; Domingo, V.; Bonet, J. A.; González Fernández,
L.; López Jiménez, A.; Pastor, C.; Gasent Blesa, J. L.; Mellado, P.;
Piqueras, J.; Aparicio, B.; Balaguer, M.; Ballesteros, E.; Belenguer,
T.; Bellot Rubio, L. R.; Berkefeld, T.; Collados, M.; Deutsch, W.;
Feller, A.; Girela, F.; Grauf, B.; Heredero, R. L.; Herranz, M.;
Jerónimo, J. M.; Laguna, H.; Meller, R.; Menéndez, M.; Morales, R.;
Orozco Suárez, D.; Ramos, G.; Reina, M.; Ramos, J. L.; Rodríguez,
P.; Sánchez, A.; Uribe-Patarroyo, N.; Barthol, P.; Gandorfer, A.;
Knoelker, M.; Schmidt, W.; Solanki, S. K.; Vargas Domínguez, S.
2011SoPh..268...57M Altcode: 2010SoPh..tmp..181M; 2010arXiv1009.1095M
The Imaging Magnetograph eXperiment (IMaX) is a spectropolarimeter
built by four institutions in Spain that flew on board the Sunrise
balloon-borne solar observatory in June 2009 for almost six days over
the Arctic Circle. As a polarimeter, IMaX uses fast polarization
modulation (based on the use of two liquid crystal retarders),
real-time image accumulation, and dual-beam polarimetry to reach
polarization sensitivities of 0.1%. As a spectrograph, the instrument
uses a LiNbO3 etalon in double pass and a narrow band
pre-filter to achieve a spectral resolution of 85 mÅ. IMaX uses the
high-Zeeman-sensitive line of Fe I at 5250.2 Å and observes all four
Stokes parameters at various points inside the spectral line. This
allows vector magnetograms, Dopplergrams, and intensity frames to be
produced that, after reconstruction, reach spatial resolutions in the
0.15 - 0.18 arcsec range over a 50×50 arcsec field of view. Time
cadences vary between 10 and 33 s, although the shortest one only
includes longitudinal polarimetry. The spectral line is sampled in
various ways depending on the applied observing mode, from just two
points inside the line to 11 of them. All observing modes include
one extra wavelength point in the nearby continuum. Gauss equivalent
sensitivities are 4 G for longitudinal fields and 80 G for transverse
fields per wavelength sample. The line-of-sight velocities are estimated
with statistical errors of the order of 5 - 40 m s−1. The
design, calibration, and integration phases of the instrument,
together with the implemented data reduction scheme, are described in
some detail.

---------------------------------------------------------
Title: The Wave-Front Correction System for the Sunrise Balloon-Borne
Solar Observatory
Authors: Berkefeld, T.; Schmidt, W.; Soltau, D.; Bell, A.;
Doerr, H. P.; Feger, B.; Friedlein, R.; Gerber, K.; Heidecke, F.;
Kentischer, T.; v. d. Lühe, O.; Sigwarth, M.; Wälde, E.; Barthol,
P.; Deutsch, W.; Gandorfer, A.; Germerott, D.; Grauf, B.; Meller, R.;
Álvarez-Herrero, A.; Knölker, M.; Martínez Pillet, V.; Solanki,
S. K.; Title, A. M.
2011SoPh..268..103B Altcode: 2010SoPh..tmp..236B; 2010arXiv1009.3196B
This paper describes the wave-front correction system developed for
the Sunrise balloon telescope, and it provides information about its
in-flight performance. For the correction of low-order aberrations,
a Correlating Wave-Front Sensor (CWS) was used. It consisted of a
six-element Shack - Hartmann wave-front sensor (WFS), a fast tip-tilt
mirror for the compensation of image motion, and an active telescope
secondary mirror for focus correction. The CWS delivered a stabilized
image with a precision of 0.04 arcsec (rms), whenever the coarse
pointing was better than ± 45 arcsec peak-to-peak. The automatic
focus adjustment maintained a focus stability of 0.01 waves in the
focal plane of the CWS. During the 5.5 day flight, good image quality
and stability were achieved during 33 hours, containing 45 sequences,
which lasted between 10 and 45 min.

---------------------------------------------------------
Title: The Sunrise Mission
Authors: Barthol, P.; Gandorfer, A.; Solanki, S. K.; Schüssler,
M.; Chares, B.; Curdt, W.; Deutsch, W.; Feller, A.; Germerott, D.;
Grauf, B.; Heerlein, K.; Hirzberger, J.; Kolleck, M.; Meller, R.;
Müller, R.; Riethmüller, T. L.; Tomasch, G.; Knölker, M.; Lites,
B. W.; Card, G.; Elmore, D.; Fox, J.; Lecinski, A.; Nelson, P.;
Summers, R.; Watt, A.; Martínez Pillet, V.; Bonet, J. A.; Schmidt,
W.; Berkefeld, T.; Title, A. M.; Domingo, V.; Gasent Blesa, J. L.;
del Toro Iniesta, J. C.; López Jiménez, A.; Álvarez-Herrero, A.;
Sabau-Graziati, L.; Widani, C.; Haberler, P.; Härtel, K.; Kampf,
D.; Levin, T.; Pérez Grande, I.; Sanz-Andrés, A.; Schmidt, E.
2011SoPh..268....1B Altcode: 2010arXiv1009.2689B; 2010SoPh..tmp..224B
The first science flight of the balloon-borne Sunrise telescope took
place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset
Island in northern Canada. We describe the scientific aims and
mission concept of the project and give an overview and a description
of the various hardware components: the 1-m main telescope with its
postfocus science instruments (the UV filter imager SuFI and the imaging
vector magnetograph IMaX) and support instruments (image stabilizing
and light distribution system ISLiD and correlating wavefront sensor
CWS), the optomechanical support structure and the instrument mounting
concept, the gondola structure and the power, pointing, and telemetry
systems, and the general electronics architecture. We also explain
the optimization of the structural and thermal design of the complete
payload. The preparations for the science flight are described,
including AIV and ground calibration of the instruments. The course
of events during the science flight is outlined, up to the recovery
activities. Finally, the in-flight performance of the instrumentation
is discussed.

---------------------------------------------------------
Title: The Filter Imager SuFI and the Image Stabilization and Light
Distribution System ISLiD of the Sunrise Balloon-Borne Observatory:
Instrument Description
Authors: Gandorfer, A.; Grauf, B.; Barthol, P.; Riethmüller, T. L.;
Solanki, S. K.; Chares, B.; Deutsch, W.; Ebert, S.; Feller, A.;
Germerott, D.; Heerlein, K.; Heinrichs, J.; Hirche, D.; Hirzberger,
J.; Kolleck, M.; Meller, R.; Müller, R.; Schäfer, R.; Tomasch,
G.; Knölker, M.; Martínez Pillet, V.; Bonet, J. A.; Schmidt, W.;
Berkefeld, T.; Feger, B.; Heidecke, F.; Soltau, D.; Tischenberg, A.;
Fischer, A.; Title, A.; Anwand, H.; Schmidt, E.
2011SoPh..268...35G Altcode: 2010SoPh..tmp..176G; 2010arXiv1009.1037G
We describe the design of the Sunrise Filter Imager (SuFI) and the
Image Stabilization and Light Distribution (ISLiD) unit onboard the
Sunrise balloon borne solar observatory. This contribution provides the
necessary information which is relevant to understand the instruments'
working principles, the relevant technical data, and the necessary
information about calibration issues directly related to the science
data.

---------------------------------------------------------
Title: The Role of Active Region Loop Geometry. I. How Can it Affect
Coronal Seismology?
Authors: Selwa, M.; Ofman, L.; Solanki, S. K.
2011ApJ...726...42S Altcode:
We present numerical results of coronal loop oscillation excitation
using a three-dimensional (3D) MHD model of an idealized active region
(AR) field. The AR is initialized as a potential dipole magnetic
configuration with gravitationally stratified density and contains a
loop with a higher density than its surroundings. We study different
ways of excitation of vertical kink oscillations of this loop by
velocity: as an initial condition, and as an impulsive excitation
with a pulse of a given position, duration, and amplitude. We vary the
geometry of the loop in the 3D MHD model and find that it affects both
the period of oscillations and the synthetic observations (difference
images) that we get from oscillations. Due to the overestimated
effective length of the loop in the case of loops which have maximum
separation between their legs above the footpoints (&gt;50% of observed
loops), the magnetic field obtained from coronal seismology can also
be overestimated. The 3D MHD model shows how the accuracy of magnetic
field strength determined from coronal seismology can be improved. We
study the damping mechanism of the oscillations and find that vertical
kink waves in 3D stratified geometry are damped mainly due to wave
leakage in the horizontal direction.

---------------------------------------------------------
Title: Reconstruction of solar spectral irradiance since the Maunder
minimum
Authors: Krivova, N. A.; Vieira, L. E. A.; Solanki, S. K.
2010JGRA..11512112K Altcode:
Solar irradiance is the main external driver of the Earth's
climate. Whereas the total solar irradiance is the main source of
energy input into the climate system, solar UV irradiance exerts
control over chemical and physical processes in the Earth's upper
atmosphere. The time series of accurate irradiance measurements are,
however, relatively short and limit the assessment of the solar
contribution to the climate change. Here we reconstruct solar total
and spectral irradiance in the range 115-160,000 nm since 1610. The
evolution of the solar photospheric magnetic flux, which is a central
input to the model, is appraised from the historical record of the
sunspot number using a simple but consistent physical model. The model
predicts an increase of 1.25 W/m2, or about 0.09%, in the
11-year averaged solar total irradiance since the Maunder minimum. Also,
irradiance in individual spectral intervals has generally increased
during the past four centuries, the magnitude of the trend being higher
toward shorter wavelengths. In particular, the 11-year averaged Ly-α
irradiance has increased by almost 50%. An exception is the spectral
interval between about 1500 and 2500 nm, where irradiance has slightly
decreased (by about 0.02%).

---------------------------------------------------------
Title: SUNRISE: Instrument, Mission, Data, and First Results
Authors: Solanki, S. K.; Barthol, P.; Danilovic, S.; Feller, A.;
Gandorfer, A.; Hirzberger, J.; Riethmüller, T. L.; Schüssler, M.;
Bonet, J. A.; Martínez Pillet, V.; del Toro Iniesta, J. C.; Domingo,
V.; Palacios, J.; Knölker, M.; Bello González, N.; Berkefeld, T.;
Franz, M.; Schmidt, W.; Title, A. M.
2010ApJ...723L.127S Altcode: 2010arXiv1008.3460S
The SUNRISE balloon-borne solar observatory consists of a 1 m aperture
Gregory telescope, a UV filter imager, an imaging vector polarimeter,
an image stabilization system, and further infrastructure. The first
science flight of SUNRISE yielded high-quality data that revealed the
structure, dynamics, and evolution of solar convection, oscillations,
and magnetic fields at a resolution of around 100 km in the quiet
Sun. After a brief description of instruments and data, the first
qualitative results are presented. In contrast to earlier observations,
we clearly see granulation at 214 nm. Images in Ca II H display narrow,
short-lived dark intergranular lanes between the bright edges of
granules. The very small-scale, mixed-polarity internetwork fields
are found to be highly dynamic. A significant increase in detectable
magnetic flux is found after phase-diversity-related reconstruction
of polarization maps, indicating that the polarities are mixed right
down to the spatial resolution limit and probably beyond.

---------------------------------------------------------
Title: Supersonic Magnetic Upflows in Granular Cells Observed with
SUNRISE/IMAX
Authors: Borrero, J. M.; Martínez-Pillet, V.; Schlichenmaier, R.;
Solanki, S. K.; Bonet, J. A.; del Toro Iniesta, J. C.; Schmidt, W.;
Barthol, P.; Gandorfer, A.; Domingo, V.; Knölker, M.
2010ApJ...723L.144B Altcode: 2010arXiv1009.1227B
Using the IMaX instrument on board the SUNRISE stratospheric balloon
telescope, we have detected extremely shifted polarization signals
around the Fe I 5250.217 Å spectral line within granules in the solar
photosphere. We interpret the velocities associated with these events
as corresponding to supersonic and magnetic upflows. In addition, they
are also related to the appearance of opposite polarities and highly
inclined magnetic fields. This suggests that they are produced by the
reconnection of emerging magnetic loops through granular upflows. The
events occupy an average area of 0.046 arcsec2 and last for
about 80 s, with larger events having longer lifetimes. These supersonic
events occur at a rate of 1.3 × 10-5 occurrences per second
per arcsec2.

---------------------------------------------------------
Title: Detection of Vortex Tubes in Solar Granulation from
Observations with SUNRISE
Authors: Steiner, O.; Franz, M.; Bello González, N.; Nutto, Ch.;
Rezaei, R.; Martínez Pillet, V.; Bonet Navarro, J. A.; del Toro
Iniesta, J. C.; Domingo, V.; Solanki, S. K.; Knölker, M.; Schmidt,
W.; Barthol, P.; Gandorfer, A.
2010ApJ...723L.180S Altcode: 2010arXiv1009.4723S
We have investigated a time series of continuum intensity maps and
corresponding Dopplergrams of granulation in a very quiet solar region
at the disk center, recorded with the Imaging Magnetograph eXperiment
(IMaX) on board the balloon-borne solar observatory SUNRISE. We
find that granules frequently show substructure in the form of lanes
composed of a leading bright rim and a trailing dark edge, which move
together from the boundary of a granule into the granule itself. We
find strikingly similar events in synthesized intensity maps from an
ab initio numerical simulation of solar surface convection. From cross
sections through the computational domain of the simulation, we conclude
that these granular lanes are the visible signature of (horizontally
oriented) vortex tubes. The characteristic optical appearance of vortex
tubes at the solar surface is explained. We propose that the observed
vortex tubes may represent only the large-scale end of a hierarchy of
vortex tubes existing near the solar surface.

---------------------------------------------------------
Title: On detectability of Zeeman broadening in optical spectra of F-
and G-dwarfs
Authors: Anderson, R. I.; Reiners, A.; Solanki, S. K.
2010A&A...522A..81A Altcode: 2010arXiv1008.2213A
We investigate the detectability of Zeeman broadening in optical Stokes
I spectra of slowly rotating sun-like stars. To this end, we apply the
LTE spectral line inversion package SPINOR to very-high quality CES
data and explore how fit quality depends on the average magnetic field,
Bf. One-component (OC) and two-component (TC) models are adopted. In
OC models, the entire surface is assumed to be magnetic. Under this
assumption, we determine formal 3σ upper limits on the average magnetic
field of 200 G for the Sun, and 150 G for 61 Vir (G6V). Evidence
for an average magnetic field of ~500 G is found for 59 Vir (G0V),
and of ~ 1000 G for HD 68456 (F6V). A distinction between magnetic
and non-magnetic regions is made in TC models, while assuming a
homogeneous distribution of both components. In our TC inversions
of 59 Vir, we investigate three cases: both components have equal
temperatures; warm magnetic regions; cool magnetic regions. Our TC
model with equal temperatures does not yield significant improvement
over OC inversions for 59 Vir. The resulting Bf values are consistent
for both. Fit quality is significantly improved, however, by using two
components of different temperatures. The inversions for 59 Vir that
assume different temperatures for the two components yield results
consistent with 0-450 G at the formal 3σ confidence level. We thus
find a model dependence of our analysis and demonstrate that the
influence of an additional temperature component can dominate over
the Zeeman broadening signature, at least in optical data. Previous
comparable analyses that neglected effects due to multiple temperature
components may be prone to the same ambiguities. Based on
observations collected at the European Southern Observatory,
La Silla.Appendix A is only available in electronic form at <A
href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Where the Granular Flows Bend
Authors: Khomenko, E.; Martínez Pillet, V.; Solanki, S. K.; del Toro
Iniesta, J. C.; Gandorfer, A.; Bonet, J. A.; Domingo, V.; Schmidt,
W.; Barthol, P.; Knölker, M.
2010ApJ...723L.159K Altcode: 2010arXiv1008.0517K
Based on IMaX/SUNRISE data, we report on a previously undetected
phenomenon in solar granulation. We show that in a very narrow region
separating granules and intergranular lanes, the spectral line width
of the Fe I 5250.2 Å line becomes extremely small. We offer an
explanation of this observation with the help of magneto-convection
simulations. These regions with extremely small line widths correspond
to the places where the granular flows bend from upflow in granules
to downflow in intergranular lanes. We show that the resolution and
image stability achieved by IMaX/SUNRISE are important requisites to
detect this interesting phenomenon.

---------------------------------------------------------
Title: Bright Points in the Quiet Sun as Observed in the Visible
and Near-UV by the Balloon-borne Observatory SUNRISE
Authors: Riethmüller, T. L.; Solanki, S. K.; Martínez Pillet, V.;
Hirzberger, J.; Feller, A.; Bonet, J. A.; Bello González, N.; Franz,
M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; del Toro Iniesta,
J. C.; Domingo, V.; Gandorfer, A.; Knölker, M.; Schmidt, W.
2010ApJ...723L.169R Altcode: 2010arXiv1009.1693R
Bright points (BPs) are manifestations of small magnetic elements
in the solar photosphere. Their brightness contrast not only gives
insight into the thermal state of the photosphere (and chromosphere) in
magnetic elements, but also plays an important role in modulating the
solar total and spectral irradiance. Here, we report on simultaneous
high-resolution imaging and spectropolarimetric observations of
BPs using SUNRISE balloon-borne observatory data of the quiet Sun
at the disk center. BP contrasts have been measured between 214 nm
and 525 nm, including the first measurements at wavelengths below
388 nm. The histograms of the BP peak brightness show a clear trend
toward broader contrast distributions and higher mean contrasts at
shorter wavelengths. At 214 nm, we observe a peak brightness of up to
five times the mean quiet-Sun value, the highest BP contrast so far
observed. All BPs are associated with a magnetic signal, although in
a number of cases it is surprisingly weak. Most of the BPs show only
weak downflows, the mean value being 240 m s-1, but some
display strong down- or upflows reaching a few km s-1.

---------------------------------------------------------
Title: Transverse Component of the Magnetic Field in the Solar
Photosphere Observed by SUNRISE
Authors: Danilovic, S.; Beeck, B.; Pietarila, A.; Schüssler, M.;
Solanki, S. K.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta,
J. C.; Domingo, V.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knölker, M.; Schmidt, W.; Title, A. M.
2010ApJ...723L.149D Altcode: 2010arXiv1008.1535D
We present the first observations of the transverse component of
a photospheric magnetic field acquired by the imaging magnetograph
SUNRISE/IMaX. Using an automated detection method, we obtain statistical
properties of 4536 features with significant linear polarization
signal. We obtain a rate of occurrence of 7 × 10-4
s-1 arcsec-2, which is 1-2 orders of magnitude
larger than the values reported by previous studies. We show that
these features have no characteristic size or lifetime. They appear
preferentially at granule boundaries with most of them being caught
in downflow lanes at some point. Only a small percentage are entirely
and constantly embedded in upflows (16%) or downflows (8%).

---------------------------------------------------------
Title: Detection of Large Acoustic Energy Flux in the Solar Atmosphere
Authors: Bello González, N.; Franz, M.; Martínez Pillet, V.; Bonet,
J. A.; Solanki, S. K.; del Toro Iniesta, J. C.; Schmidt, W.; Gandorfer,
A.; Domingo, V.; Barthol, P.; Berkefeld, T.; Knölker, M.
2010ApJ...723L.134B Altcode: 2010arXiv1009.4795B
We study the energy flux carried by acoustic waves excited by convective
motions at sub-photospheric levels. The analysis of high-resolution
spectropolarimetric data taken with IMaX/SUNRISE provides a total
energy flux of ~6400-7700 W m-2 at a height of ~250 km
in the 5.2-10 mHz range, i.e., at least twice the largest energy
flux found in previous works. Our estimate lies within a factor of
two of the energy flux needed to balance radiative losses from the
chromosphere according to the estimates of Anderson &amp; Athay and
revives interest in acoustic waves for transporting energy to the
chromosphere. The acoustic flux is mainly found in the intergranular
lanes but also in small rapidly evolving granules and at the bright
borders, forming dark dots and lanes of splitting granules.

---------------------------------------------------------
Title: Magnetic Loops in the Quiet Sun
Authors: Wiegelmann, T.; Solanki, S. K.; Borrero, J. M.; Martínez
Pillet, V.; del Toro Iniesta, J. C.; Domingo, V.; Bonet, J. A.;
Barthol, P.; Gandorfer, A.; Knölker, M.; Schmidt, W.; Title, A. M.
2010ApJ...723L.185W Altcode: 2010arXiv1009.4715W
We investigate the fine structure of magnetic fields in the atmosphere
of the quiet Sun. We use photospheric magnetic field measurements from
SUNRISE/IMaX with unprecedented spatial resolution to extrapolate
the photospheric magnetic field into higher layers of the solar
atmosphere with the help of potential and force-free extrapolation
techniques. We find that most magnetic loops that reach into the
chromosphere or higher have one footpoint in relatively strong magnetic
field regions in the photosphere. Ninety-one percent of the magnetic
energy in the mid-chromosphere (at a height of 1 Mm) is in field
lines, whose stronger footpoint has a strength of more than 300 G,
i.e., above the equipartition field strength with convection. The
loops reaching into the chromosphere and corona are also found to be
asymmetric in the sense that the weaker footpoint has a strength B &lt;
300 G and is located in the internetwork (IN). Such loops are expected
to be strongly dynamic and have short lifetimes, as dictated by the
properties of the IN fields.

---------------------------------------------------------
Title: SUNRISE/IMaX Observations of Convectively Driven Vortex Flows
in the Sun
Authors: Bonet, J. A.; Márquez, I.; Sánchez Almeida, J.; Palacios,
J.; Martínez Pillet, V.; Solanki, S. K.; del Toro Iniesta, J. C.;
Domingo, V.; Berkefeld, T.; Schmidt, W.; Gandorfer, A.; Barthol, P.;
Knölker, M.
2010ApJ...723L.139B Altcode: 2010arXiv1009.1992B
We characterize the observational properties of the convectively driven
vortex flows recently discovered on the quiet Sun, using magnetograms,
Dopplergrams, and images obtained with the 1 m balloon-borne SUNRISE
telescope. By visual inspection of time series, we find some 3.1
× 10-3 vortices Mm-2 minute-1,
which is a factor of ~1.7 larger than previous estimates. The mean
duration of the individual events turns out to be 7.9 minutes, with
a standard deviation of 3.2 minutes. In addition, we find several
events appearing at the same locations along the duration of the time
series (31.6 minutes). Such recurrent vortices show up in the proper
motion flow field map averaged over the time series. The typical
vertical vorticities are lsim6 × 10-3 s-1,
which corresponds to a period of rotation of some 35 minutes. The
vortices show a preferred counterclockwise sense of rotation, which
we conjecture may have to do with the preferred vorticity impinged by
the solar differential rotation.

---------------------------------------------------------
Title: Radiative emission of solar features in the Ca II K line:
comparison of measurements and models
Authors: Ermolli, I.; Criscuoli, S.; Uitenbroek, H.; Giorgi, F.;
Rast, M. P.; Solanki, S. K.
2010A&A...523A..55E Altcode: 2010arXiv1009.0227E
Context. The intensity of the Ca II K resonance line observed with
spectrographs and Lyot-type filters has long served as a diagnostic of
the solar chromosphere. However, the literature contains a relative
lack of photometric measurements of solar features observed at this
spectral range. Aims: We study the radiative emission of various
types of solar features, such as quiet Sun, enhanced network, plage,
and bright plage regions, identified on filtergrams taken in the Ca II
K line. Methods: We analysed full-disk images obtained with the
PSPT, by using three interference filters that sample the Ca II K line
with different bandpasses. We studied the dependence of the radiative
emission of disk features on the filter bandpass. We also performed a
non-local thermal equilibrium (NLTE) spectral synthesis of the Ca II
K line integrated over the bandpass of PSPT filters. The synthesis
was carried out by utilizing the partial frequency redistribution
(PRD) with the most recent set of semi-empirical atmosphere models
in the literature and some earlier atmosphere models. As the studied
models were computed by assuming the complete redistribution formalism
(CRD), we also performed simulations with this approximation for
comparison. Results: We measured the center-to-limb variation
of intensity values for various solar features identified on PSPT
images and compared the results obtained with those derived from the
synthesis. We find that CRD calculations derived using the most recent
quiet Sun model, on average, reproduce the measured values of the
quiet Sun regions slightly more accurately than PRD computations with
the same model. This may reflect that the utilized atmospheric model
was computed assuming CRD. Calculations with PRD on earlier quiet Sun
model atmospheres reproduce measured quantities with a similar accuracy
as to that achieved here by applying CRD to the recent model. We
also find that the median contrast values measured for most of the
identified bright features, disk positions, and filter bandpasses
are, on average, a factor ≈1.9 lower than those derived from PRD
simulations performed using the recent bright feature models. The
discrepancy between measured and modeled values decreases by ≈12%
after taking into account straylight effects on PSPT images. When
moving towards the limb, PRD computations display closer agreement with
the data than performed in CRD. Moreover, PRD computations on either
the most recent or the earlier atmosphere models of bright features
reproduce measurements from plage and bright plage regions with a
similar accuracy. Appendix A is only available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Surface Waves in Solar Granulation Observed with SUNRISE
Authors: Roth, M.; Franz, M.; Bello González, N.; Martínez Pillet,
V.; Bonet, J. A.; Gandorfer, A.; Barthol, P.; Solanki, S. K.;
Berkefeld, T.; Schmidt, W.; del Toro Iniesta, J. C.; Domingo, V.;
Knölker, M.
2010ApJ...723L.175R Altcode: 2010arXiv1009.4790R
Solar oscillations are expected to be excited by turbulent flows in
the intergranular lanes near the solar surface. Time series recorded
by the IMaX instrument on board the SUNRISE observatory reveal solar
oscillations at high spatial resolution, which allow the study of
the properties of oscillations with short wavelengths. We analyze
two time series with synchronous recordings of Doppler velocity and
continuum intensity images with durations of 32 minutes and 23 minutes,
respectively, recorded close to the disk center of the Sun to study
the propagation and excitation of solar acoustic oscillations. In
the Doppler velocity data, both the standing acoustic waves and the
short-lived, high-degree running waves are visible. The standing
waves are visible as temporary enhancements of the amplitudes of the
large-scale velocity field due to the stochastic superposition of
the acoustic waves. We focus on the high-degree small-scale waves by
suitable filtering in the Fourier domain. Investigating the propagation
and excitation of f- and p 1-modes with wavenumbers k&gt;1.4
Mm-1, we also find that exploding granules contribute to
the excitation of solar p-modes in addition to the contribution of
intergranular lanes.

---------------------------------------------------------
Title: Fully Resolved Quiet-Sun Magnetic flux Tube Observed with
the SUNRISE/IMAX Instrument
Authors: Lagg, A.; Solanki, S. K.; Riethmüller, T. L.; Martínez
Pillet, V.; Schüssler, M.; Hirzberger, J.; Feller, A.; Borrero,
J. M.; Schmidt, W.; del Toro Iniesta, J. C.; Bonet, J. A.; Barthol, P.;
Berkefeld, T.; Domingo, V.; Gandorfer, A.; Knölker, M.; Title, A. M.
2010ApJ...723L.164L Altcode: 2010arXiv1009.0996L
Until today, the small size of magnetic elements in quiet-Sun areas has
required the application of indirect methods, such as the line-ratio
technique or multi-component inversions, to infer their physical
properties. A consistent match to the observed Stokes profiles could
only be obtained by introducing a magnetic filling factor that specifies
the fraction of the observed pixel filled with magnetic field. Here,
we investigate the properties of a small magnetic patch in the quiet
Sun observed with the IMaX magnetograph on board the balloon-borne
telescope SUNRISE with unprecedented spatial resolution and low
instrumental stray light. We apply an inversion technique based on
the numerical solution of the radiative transfer equation to retrieve
the temperature stratification and the field strength in the magnetic
patch. The observations can be well reproduced with a one-component,
fully magnetized atmosphere with a field strength exceeding 1 kG and
a significantly enhanced temperature in the mid to upper photosphere
with respect to its surroundings, consistent with semi-empirical flux
tube models for plage regions. We therefore conclude that, within the
framework of a simple atmospheric model, the IMaX measurements resolve
the observed quiet-Sun flux tube.

---------------------------------------------------------
Title: Quiet-sun Intensity Contrasts in the Near-ultraviolet as
Measured from SUNRISE
Authors: Hirzberger, J.; Feller, A.; Riethmüller, T. L.; Schüssler,
M.; Borrero, J. M.; Afram, N.; Unruh, Y. C.; Berdyugina, S. V.;
Gandorfer, A.; Solanki, S. K.; Barthol, P.; Bonet, J. A.; Martínez
Pillet, V.; Berkefeld, T.; Knölker, M.; Schmidt, W.; Title, A. M.
2010ApJ...723L.154H Altcode:
We present high-resolution images of the Sun in the near-ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1 m SUNRISE balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range are
among the highest values ever obtained for quiet-Sun solar surface
structures—up to 32.8% at a wavelength of 214 nm. We compare the
rms contrasts obtained from the observational data with theoretical
intensity contrasts obtained from numerical magnetohydrodynamic
simulations. For 388 nm and 312 nm the observations agree well with
the numerical simulations whereas at shorter wavelengths discrepancies
between observed and simulated contrasts remain.

---------------------------------------------------------
Title: Evidence for Convection in Sunspot Penumbrae
Authors: Bharti, L.; Solanki, S. K.; Hirzberger, J.
2010ApJ...722L.194B Altcode: 2010arXiv1009.2919B
We present an analysis of twisting motions in penumbral filaments in
sunspots located at heliocentric angles from 30° to 48° using three
time series of blue continuum images obtained by the Broadband Filter
Imager (BFI) on board Hinode. The relations of the twisting motions to
the filament brightness and the position within the filament and within
the penumbra, respectively, are investigated. Only certain portions
of the filaments show twisting motions. In a statistical sense, the
part of the twisting portion of a filament located closest to the
umbra is brightest and possesses the fastest twisting motion, with a
mean twisting velocity of 2.1 km s-1. The middle and outer
sections of the twisting portion of the filament (lying increasingly
further from the umbra), which are less bright, have mean velocities
of 1.7 km s-1 and 1.35 km s-1, respectively. The
observed reduction of brightness and twisting velocity toward the
outer section of the filaments may be due to reducing upflow along the
filament's long axis. No significant variation of twisting velocity as
a function of viewing angles was found. The obtained correlation of
brightness and velocity suggests that overturning convection causes
the twisting motions observed in penumbral filament and may be the
source of the energy needed to maintain the brightness of the filaments.

---------------------------------------------------------
Title: Reply to comment by P. Foukal on “A homogeneous database
of sunspot areas covering more than 130 years”
Authors: Balmaceda, L. A.; Solanki, S. K.; Krivova, N. A.; Foster, S.
2010JGRA..115.9103B Altcode: 2010JGRA..11509103B
<A href="/journals/ja/ja1009/2010JA015375/">Abstract Available</A>
from <A href="http://www.agu.org">http://www.agu.org</A>

---------------------------------------------------------
Title: Magnetic structures of an emerging flux region in the solar
photosphere and chromosphere
Authors: Xu, Z.; Lagg, A.; Solanki, S. K.
2010A&A...520A..77X Altcode:
 Aims: We investigate the vector magnetic field and Doppler
velocity in the photosphere and upper chromosphere of a young
emerging flux region of the sun close to disk center. Methods:
Spectropolarimetric scans of a young active region made using the
second generation Tenerife Infrared Polarimeter (TIP II) on the German
Vacuum Tower Telescope (VTT) are analyzed. The scanned area contained
multiple sunspots and an emerging flux region. An inversion based on
the Milne-Eddington approximation was performed on the full Stokes
vector of the chromospheric He I 10 830 Å and the photospheric Si I
10 827.1 Å lines. This provided the magnetic vector and line-of-sight
velocity at each spatial point in both atmospheric layers. 
Results: A clear difference is seen between the complex magnetic
structure of the emerging flux region (EFR) in the photosphere and
the much simpler structure in the upper chromosphere. The upper
chromospheric structure is consistent with a set of emerging loops
following elongated dark structures seen in the He I 10 830 Å triplet,
similar to arch filament systems (AFS), while in the photosphere we
infer the presence of U-loops within the emergence zone. Nonetheless, in
general the upper chromospheric field has a similar linear relationship
between inclination angle and field strength as the photospheric field:
the field is weak (≈300 G) and horizontal in the emergence zone,
but strong (up to 850 G) and more vertical near its edges. The field
strength decreases from the photosphere to the upper chromosphere
by approximately 0.1-0.2 G km-1 (or even less) within the
emergence zone and by 0.3-0.6 G km-1 in sunspots located
at its edge. We reconstructed the magnetic field in 3D based on the
chromospheric vector field under the assumption that the He I 10 830 Å
triplet forms along the magnetic field loops. The reconstructed loops
are quite flat with supersonic downflows at both footpoints. Arguments
and evidence for an enhanced formation height of He I 10 830 Å in
arch-filaments seen in this line are provided, which support the
validity of the reconstructed loops. Conclusions: The main
chromospheric properties of EFRs previously deduced for a single region
NOAA 9451 are shown to be valid for another region as well, suggesting
that the main original results may have a wider application. The main
exception is that only the first region displayed a current sheet in
the chromosphere. We propose a scenario in which the relatively complex
photospheric structure evolves into the simpler chromospheric one.

---------------------------------------------------------
Title: Quiet-Sun intensity contrasts in the near ultraviolet
Authors: Hirzberger, Johann; Feller, Alex; Riethmüller, Tino L.;
Schüssler, Manfred; Borrero, Juan M.; Afram, Nadine; Unruh, Yvonne C.;
Berdyugina, Svetlana V.; Gandorfer, Achim; Solanki, Sami K.; Barthol,
Peter; Bonet, Jose A.; Martínez Pillet, Valentin; Berkefeld, Thomas;
Knölker, Michael; Schmidt, Wolfgang; Title, Alan M.
2010arXiv1009.1050H Altcode:
We present high-resolution images of the Sun in the near ultraviolet
spectral range between 214 nm and 397 nm as obtained from the first
science flight of the 1-m Sunrise balloon-borne solar telescope. The
quiet-Sun rms intensity contrasts found in this wavelength range
are among the highest values ever obtained for quiet-Sun solar
surface structures - up to 32.8% at a wavelength of 214 nm. We
compare with theoretical intensity contrasts obtained from numerical
magneto-hydrodynamic simulations. For 388 nm and 312 nm the observations
agree well with the numerical simulations whereas at shorter wavelengths
discrepancies between observed and simulated contrasts remain.

---------------------------------------------------------
Title: Sunspot group tilt angles and the strength of the solar cycle
Authors: Dasi-Espuig, M.; Solanki, S. K.; Krivova, N. A.; Cameron,
R.; Peñuela, T.
2010A&A...518A...7D Altcode: 2010arXiv1005.1774D
Context. It is well known that the tilt angles of active regions
increase with their latitude (Joy's law). It has never been checked
before, however, whether the average tilt angles change from one cycle
to the next. Flux transport models show the importance of tilt angles
for the reversal and build up of magnetic flux at the poles, which is in
turn correlated to the strength of the next cycle. Aims: Here we
analyse time series of tilt angle measurements and look for a possible
relationship of the tilt angles with other solar cycle parameters,
in order to glean information on the solar dynamo and to estimate
their potential for predicting solar activity. Methods: We
employed tilt angle data from Mount Wilson and Kodaikanal observatories
covering solar cycles 15 to 21. We analyse the latitudinal distribution
of the tilt angles (Joy's law), their variation from cycle to cycle,
and their relationship to other solar cycle parameters, such as the
strength (or total area covered by sunspots in a cycle), amplitude,
and length. Results: The two main results of our analysis
follow. 1. We find an anti-correlation between the mean normalised
tilt angle of a given cycle and the strength (or amplitude) of that
cycle, with a correlation coefficient of rc = -0.95 (99.9%
confidence level) and rc = -0.93 (99.76% confidence level)
for Mount Wilson and Kodaikanal data, respectively. 2. The product
of the cycle's averaged tilt angle and the strength of the same cycle
displays a significant correlation with the strength of the next cycle
(rc = 0.65 at 89% confidence level and rc =
0.70 at 92% confidence level for Mount Wilson and Kodaikanal data,
respectively). An even better correlation is obtained between the
source term of the poloidal flux in Babcock-Leighton-type dynamos (which
contains the tilt angle) and the amplitude of the next cycle. Further we
confirm the linear relationship (Joy's law) between the tilt angle and
latitude with slopes of 0.26 and 0.28 for Mount Wilson and Kodaikanal
data, respectively. In addition, we obtain good positive correlations
between the normalised-area-weighted tilt angle and the length of the
following cycle, whereas the strength or the amplitude of the next cycle
does not appear to be correlated to the tilt angles of the current cycle
alone. Conclusions: The results of this study indicate that,
in combination with the cycle strength, the active region tilt angles
play an important role in building up the polar fields at cycle minimum.

---------------------------------------------------------
Title: GREGOR telescope: start of commissioning
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Halbgewachs,
C.; Heidecke, F.; Hofmann, A.; Klvana, M.; Kneer, F.; Lagg, A.; Popow,
E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau, D.; Strassmeier, K.
2010SPIE.7733E..0KV Altcode: 2010SPIE.7733E..18V
With the integration of a 1-meter Cesic primary mirror the GREGOR
telescope pre-commissioning started. This is the first time, that
the entire light path has seen sunlight. The pre-commissioning period
includes testing of the main optics, adaptive optics, cooling system,
and pointing system. This time was also used to install a near-infrared
grating spectro-polarimeter and a 2D-spectropolarimeter for the visible
range as first-light science instruments. As soon as the final 1.5
meter primary mirror is installed, commissioning will be completed,
and an extended phase of science verification will follow. In the near
future, GREGOR will be equipped with a multi-conjugate adaptive optics
system that is presently under development at KIS.

---------------------------------------------------------
Title: Accelerating Waves in Polar Coronal Holes as Seen by EIS
and SUMER
Authors: Gupta, G. R.; Banerjee, D.; Teriaca, L.; Imada, S.;
Solanki, S.
2010ApJ...718...11G Altcode: 2010arXiv1005.3453G
We present EIS/Hinode and SUMER/SOHO observations of propagating
disturbances detected in coronal lines in inter-plume and plume
regions of a polar coronal hole. The observation was carried out on
2007 November 13 as part of the JOP196/HOP045 program. The SUMER
spectroscopic observation gives information about fluctuations in
radiance and on both resolved (Doppler shift) and unresolved (Doppler
width) line-of-sight velocities, whereas EIS 40” wide slot images
detect fluctuations only in radiance but maximize the probability
of overlapping field of view between the two instruments. From
distance-time radiance maps, we detect the presence of propagating
waves in a polar inter-plume region with a period of 15-20 minutes
and a propagation speed increasing from 130 ± 14 km s-1
just above the limb to 330 ± 140 km s-1 around 160” above
the limb. These waves can be traced to originate from a bright region
of the on-disk part of the coronal hole where the propagation speed
is in the range of 25 ± 1.3 to 38 ± 4.5 km s-1, with the
same periodicity. These on-disk bright regions can be visualized as the
base of the coronal funnels. The adjacent plume region also shows the
presence of propagating disturbances with the same range of periodicity
but with propagation speeds in the range of 135 ± 18 to 165 ± 43 km
s-1 only. A comparison between the distance-time radiance
map of the two regions indicates that the waves within the plumes are
not observable (may be getting dissipated) far off-limb, whereas this
is not the case in the inter-plume region. A correlation analysis was
also performed to find out the time delay between the oscillations at
several heights in the off-limb region, finding results consistent with
those from the analysis of the distance-time maps. To our knowledge,
this result provides first spectroscopic evidence of the acceleration of
propagating disturbances in the polar region close to the Sun (within
1.2 R/R sun), which provides clues to the understanding of
the origin of these waves. We suggest that the waves are likely either
Alfvénic or fast magnetoacoustic in the inter-plume region and slow
magnetoacoustic in the plume region. This may lead to the conclusion
that inter-plumes are a preferred channel for the acceleration of the
fast solar wind.

---------------------------------------------------------
Title: Expansion of magnetic flux concentrations: a comparison of
Hinode SOT data and models
Authors: Pietarila, A.; Cameron, R.; Solanki, S. K.
2010A&A...518A..50P Altcode: 2010arXiv1005.3405P
Context. The expansion of network magnetic fields with height is a
fundamental property of flux tube models. A rapid expansion is required
to form a magnetic canopy. Aims: We characterize the observed
expansion properties of magnetic network elements and compare them
with the thin flux tube and sheet approximations, as well as with
magnetoconvection simulations. Methods: We used data from
the Hinode SOT NFI NaD1 channel and spectropolarimeter to
study the appearance of magnetic flux concentrations seen in circular
polarization as a function of position on the solar disk. We compared
the observations with synthetic observables from models based on the
thin flux tube approximation and magnetoconvection simulations with two
different upper boundary conditions for the magnetic field (potential
and vertical). Results: The observed circular polarization signal
of magnetic flux concentrations changes from unipolar at disk center to
bipolar near the limb, which implies an expanding magnetic field. The
observed expansion agrees with expansion properties derived from the
thin flux sheet and tube approximations. Magnetoconvection simulations
with a potential field as the upper boundary condition for the magnetic
field also produce bipolar features near the limb while a simulation
with a vertical field boundary condition does not. Conclusions:
The near-limb apparent bipolar magnetic features seen in high-resolution
Hinode observations can be interpreted using a simple flux sheet
or tube model. This lends further support to the idea that magnetic
features with vastly varying sizes have similar relative expansion
rates. The numerical simulations presented here are less useful in
interpreting the expansion since the diagnostics we are interested in
are strongly influenced by the choice of the upper boundary condition
for the magnetic field in the purely photospheric simulations.

---------------------------------------------------------
Title: Flight control software for the wave-front sensor of SUNRISE
1m balloon telescope
Authors: Bell, Alexander; Barthol, Peter; Berkefeld, Thomas; Feger,
Bernhard; Gandorfer, Achim M.; Heidecke, Frank; Knoelker, Michael;
Martinez Pillet, Valentin; Schmidt, Wolfgang; Sigwarth, Michael;
Solanki, Sami K.; Soltau, Dirk; Title, Alan M.
2010SPIE.7740E..03B Altcode: 2010SPIE.7740E...2B
This paper describes the flight control software of the wave-front
correction system that flew on the 2009 science flight of the Sunrise
balloon telescope. The software discussed here allowed fully automated
operations of the wave-front sensor, communications with the adaptive
optics sub-system, the pointing system, the instrument control unit
and the main telescope controller. The software was developed using
modern object oriented analysis and design techniques, and consists
of roughly 13.000 lines of C++ code not counting code written for the
on-board communication layer. The software operated error free during
the 5.5 day flight.

---------------------------------------------------------
Title: SUNRISE Impressions from a successful science flight
Authors: Schmidt, W.; Solanki, S. K.; Barthol, P.; Berkefeld, T.;
Gandorfer, A.; Knölker, M.; Martínez Pillet, V.; Schüssler, M.;
Title, A.
2010AN....331..601S Altcode:
SUNRISE is a balloon-borne telescope with an aperture of one meter. It
is equipped with a filter imager for the UV wavelength range between
214 nm and 400 nm (SUFI), and with a spectro-polarimeter that measures
the magnetic field of the photosphere using the Fe I line at 525.02
nm that has a Landé factor of 3. SUNRISE performed its first science
flight from 8 to 14 June 2009. It was launched at the Swedish ESRANGE
Space Center and cruised at an altitude of about 36 km and geographic
latitudes between 70 and 74 degrees to Somerset Island in northern
Canada. There, all data, the telescope and the gondola were successfully
recovered. During its flight, Sunrise achieved high pointing stability
during 33 hours, and recorded about 1.8 TB of science data. Already at
this early stage of data processing it is clear that SUNRISE recorded
UV images of the solar photosphere, and spectropolarimetric measurements
of the quiet Sun's magnetic field of unprecedented quality.

---------------------------------------------------------
Title: Spectropolarimetric analysis of 3D MHD sunspot simulations
Authors: Borrero, J. M.; Rempel, M.; Solanki, S. K.
2010AN....331..567B Altcode:
We have employed 3D non-grey MHD simulations of sunspots to compute
theoretical Stokes profiles and compare the levels of circular and
linear polarization in the simulations with those observed in a real
sunspot. We find that the spatial distribution and average values
of these quantities agree very well with the observations, although
the polarization levels in the simulations are slightly larger. This
can be explained by a slightly larger magnetic field strength or a
larger temperature gradient in the simulated penumbra as compared to
the observations.

---------------------------------------------------------
Title: Sideways displacement of penumbral fibrils by the solar flare
on 2006 December 13
Authors: Zhang, Jun; Li, Leping; Solanki, S. K.
2010arXiv1007.0056Z Altcode:
Flares are known to restructure the magnetic field in the corona and
to accelerate the gas between the field lines, but their effect on
the photosphere is less well studied. New data of the Solar Optical
Telescope (SOT) onboard Hinode provide unprecedented opportunity to
uncover the photospheric effect of a solar flare, which associates
with an active region NOAA AR 10930 on 2006 December 13. We find a
clear lateral displacement of sunspot penumbral regions scanned by two
flare ribbons. In the impulsive phase of the flare, the flare ribbons
scan the sunspot at a speed of around 18 km/s, derived from Ca II and
G-band images. We find instantaneous horizontal shear of penumbral
fibrils, with initial velocities of about 1.6 km/s, produced when
a flare ribbon passes over them. This velocity decreases rapidly at
first, then gradually decays, so that about one hour later, the fibrils
return to a new equilibrium. During the one hour interval, the total
displacement of these fibrils is around 2.0 Mm, with an average shear
velocity of 0.55 km/s. This lateral motion of the penumbral fibrils
indicates that the magnetic footpoints of these field lines being
rearranged in the corona also move.

---------------------------------------------------------
Title: GREGOR solar telescope: Design and status
Authors: Volkmer, R.; von der Lühe, O.; Denker, C.; Solanki, S. K.;
Balthasar, H.; Berkefeld, T.; Caligari, P.; Collados, M.; Fischer, A.;
Halbgewachs, C.; Heidecke, F.; Hofmann, A.; Klvaňa, M.; Kneer, F.;
Lagg, A.; Popow, E.; Schmidt, D.; Schmidt, W.; Sobotka, M.; Soltau,
D.; Strassmeier, K. G.
2010AN....331..624V Altcode:
The integration and verification phase of the GREGOR telescope
reached an important milestone with the installation of the
interim 1 m SolarLite primary mirror. This was the first time
that the entire light path had seen sunlight. Since then extensive
testing of the telescope and its subsystems has been carried out. The
integration and verification phase will culminate with the delivery and
installation of the final 1.5 m Zerodur primary mirror in the summer of
2010. Observatory level tests and science verification will commence in
the second half of 2010 and in 2011. This phase includes testing of the
main optics, adaptive optics, cooling and pointing systems. In addition,
assuming the viewpoint of a typical user, various observational modes
of the GREGOR Fabry-Pérot Interferometer (GFPI), the Grating Infrared
Spectrograph (GRIS), and high-speed camera systems will be tested to
evaluate if they match the expectations and science requirements. This
ensures that GREGOR will provide high-quality observations with its
combination of (multi-conjugate) adaptive optics and advanced post-focus
instruments. Routine observations are expected for 2012.

---------------------------------------------------------
Title: Are cold winters in Europe associated with low solar activity?
Authors: Lockwood, M.; Harrison, R. G.; Woollings, T.; Solanki, S. K.
2010ERL.....5b4001L Altcode:
Solar activity during the current sunspot minimum has fallen to levels
unknown since the start of the 20th century. The Maunder minimum
(about 1650-1700) was a prolonged episode of low solar activity
which coincided with more severe winters in the United Kingdom and
continental Europe. Motivated by recent relatively cold winters in
the UK, we investigate the possible connection with solar activity. We
identify regionally anomalous cold winters by detrending the Central
England temperature (CET) record using reconstructions of the northern
hemisphere mean temperature. We show that cold winter excursions from
the hemispheric trend occur more commonly in the UK during low solar
activity, consistent with the solar influence on the occurrence of
persistent blocking events in the eastern Atlantic. We stress that
this is a regional and seasonal effect relating to European winters
and not a global effect. Average solar activity has declined rapidly
since 1985 and cosmogenic isotopes suggest an 8% chance of a return
to Maunder minimum conditions within the next 50 years (Lockwood 2010
Proc. R. Soc. A 466 303-29): the results presented here indicate that,
despite hemispheric warming, the UK and Europe could experience more
cold winters than during recent decades.

---------------------------------------------------------
Title: Probing quiet Sun magnetism using MURaM simulations and
Hinode/SP results: support for a local dynamo
Authors: Danilovic, S.; Schüssler, M.; Solanki, S. K.
2010A&A...513A...1D Altcode: 2010arXiv1001.2183D
Context. Owing to the limited spatial resolution and the weak
polarization signal coming from the quietest regions on the Sun, the
organization of the magnetic field on the smallest scales is largely
unknown. Aims: We obtain information about the magnetic flux
present in the quiet Sun by comparing radiative MHD simulations with
observations, with particular emphasis on the role of surface dynamo
action. Methods: We synthesized Stokes profiles on the basis of
the MHD simulation results. The profiles are degraded by taking the
properties of the spectropolarimeter (SP) into account onboard the
Hinode satellite. We used simulation runs with different magnetic
Reynolds numbers (Rm) and observations at different
heliocentric angles with different levels of noise. Results:
Simulations with an imposed mixed-polarity field and Rm
below the threshold for dynamo action reproduce the observed vertical
flux density, but do not display a high enough horizontal flux
density. Surface dynamo simulations at the highest Rm
feasible at the moment yield a ratio of the horizontal and vertical
flux density consistent with observational results, but the overall
amplitudes are too low. Based on the properties of the local dynamo
simulations, a tentative scaling of the magnetic field strength
by a factor 2-3 reproduces the signal observed in the internetwork
regions. Conclusions: We find agreement with observations at
different heliocentric angles. The mean field strength in internetwork
implied by our analysis is roughly 170 G at the optical depth unity. Our
study shows that surface dynamo could be responsible for most of the
magnetic flux in the quiet Sun outside the network, given that the
extrapolation to higher Rm is valid.

---------------------------------------------------------
Title: Excitation of vertical kink waves in a solar coronal arcade
loop by a periodic driver
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Ofman, L.
2010A&A...512A..76S Altcode:
 Aims: We study an oscillatory driver as a possible excitation
mechanism of vertical kink loop oscillations in the ideal MHD
regime. Methods: We consider a solar coronal magnetic arcade
with a dense photospheric layer. The two-dimensional numerical model
that we implement includes the effects of nonlinearity and line
curvature on the excitation and attenuation of fast magnetosonic kink
waves. We investigate the effects of a driven sinusoidal pressure
pulse and compare it with the impulsive excitation by a pressure
pulse that impacts the overlying loop. Results: Our numerical
simulations reveal wave signatures that are reminiscent of vertical
loop oscillations seen in TRACE observational data. Conclusions:
We conclude that attenuation of vertical kink oscillations can be
reduced to the value observed by adopting an oscillatory instead of an
impulsive excitation. An oscillatory driver also naturally explains why
only a small subset of all loops is excited to oscillate transversally
in an active region.

---------------------------------------------------------
Title: A comparison of measured and simulated solar network contrast
Authors: Afram, N.; Unruh, Y. C.; Solanki, S. K.; Schüssler, M.;
Mathew, S. K.
2010IAUS..264...63A Altcode: 2009arXiv0910.0976A
Long-term trends in the solar spectral irradiance are important to
determine the impact on Earth's climate. These long-term changes are
thought to be caused mainly by changes in the surface area covered by
small-scale magnetic elements. The direct measurement of the contrast
to determine the impact of these small-scale magnetic elements
is, however, limited to a few wavelengths, and is, even for space
instruments, affected by scattered light and instrument defocus. In
this work we calculate emergent intensities from 3-D simulations of
solar magneto-convection and validate the outcome by comparing with
observations from Hinode/SOT. In this manner we aim to construct the
contrast at wavelengths ranging from the NUV to the FIR.

---------------------------------------------------------
Title: Observations of a rotating macrospicule associated with an
X-ray jet
Authors: Kamio, S.; Curdt, W.; Teriaca, L.; Inhester, B.; Solanki,
S. K.
2010A&A...510L...1K Altcode: 2010arXiv1001.1924K
 Aims: We attempt to understand the driving mechanism of a
macrospicule and its relationship with a coronal jet. Methods:
We study the dynamics of a macrospicule and an associated coronal jet
captured by multi-spacecraft observations. Doppler velocities in both
the macrospicule and the coronal jet are determined by EIS and SUMER
spectra. Their temporal evolution is studied using X-ray and He II λ304
images. Results: A blueshift of -120 ± 15 km s-1
is detected on one side of the macrospicule, while a redshift of 50
± 6 km s-1 is found at the base of the other side. The
inclination angle of the macrospicule inferred from a stereoscopic
analysis with STEREO suggests that the measured Doppler velocities can
be attributed to a rotating motion of the macrospicule rather than
a radial flow or an expansion. Conclusions: The macrospicule
is driven by the unfolding motion of a twisted magnetic flux rope,
while the associated X-ray jet is a radial outflow.

---------------------------------------------------------
Title: Nonlinear force-free modelling: influence of inaccuracies in
the measured magnetic vector
Authors: Wiegelmann, T.; Yelles Chaouche, L.; Solanki, S. K.; Lagg, A.
2010A&A...511A...4W Altcode: 2009arXiv0912.3002W
Context. Solar magnetic fields are regularly extrapolated into the
corona starting from photospheric magnetic measurements that can
be affected by significant uncertainty. Aims: We study how
inaccuracies introduced into the maps of the photospheric magnetic
vector by the inversion of ideal and noisy Stokes parameters influence
the extrapolation of nonlinear force-free magnetic fields. 
Methods: We compute nonlinear force-free magnetic fields based on
simulated vector magnetograms, by the inversion of Stokes profiles
that were computed by a 3-D radiation MHD simulation snapshot. These
extrapolations are compared with extrapolations that originate directly
in the field in the MHD simulations, which is our reference. We
investigate how line formation and instrumental effects such as noise,
limited spatial resolution, and the effect of employing a filter
instrument influence the resulting magnetic field structure. The
comparison is performed qualitatively by visually inspecting the
magnetic field distribution and quantitatively by different metrics. Results: The reconstructed field is most accurate if ideal Stokes
data are inverted and becomes less accurate if instrumental effects
and noise are included. The results demonstrate that the nonlinear
force-free field extrapolation method tested here is relatively
insensitive to the effects of noise in measured polarization spectra
at levels consistent with present-day instruments. Conclusions:
Our results show that we can reconstruct the coronal magnetic field as
a nonlinear force-free field from realistic photospheric measurements
with an accuracy of a few percent, at least in the absence of sunspots.

---------------------------------------------------------
Title: Convective Motions and Net Circular Polarization in Sunspot
Penumbrae
Authors: Borrero, J. M.; Solanki, S. K.
2010ApJ...709..349B Altcode: 2009arXiv0911.2570B
We have employed a penumbral model, which includes the Evershed flow
and convective motions inside penumbral filaments, to reproduce the
azimuthal variation of the net circular polarization (NCP) in sunspot
penumbrae at different heliocentric angles for two different spectral
lines. The theoretical NCP fits the observations as satisfactorily
as penumbral models based on flux tubes. The reason for this is that
the effect of convective motions on the NCP is very small compared
to the effect of the Evershed flow. In addition, the NCP generated by
convective upflows cancels out the NCP generated by the downflows. We
have also found that, in order to fit the observed NCP, the strength
of the magnetic field inside penumbral filaments must be very close
to 1000 G. In particular, field-free or weak-field filaments fail to
reproduce both the correct sign of the NCP and its dependence on the
azimuthal and heliocentric angles.

---------------------------------------------------------
Title: Evolution of the solar magnetic flux on time scales of years
to millenia
Authors: Vieira, L. E. A.; Solanki, S. K.
2010A&A...509A.100V Altcode: 2009arXiv0911.4396V
 Aims: We improve the description of the evolution of the Sun's
open and total magnetic flux on time scales of years to millenia. 
Methods: In the model employed here the evolution of the solar total
and open magnetic flux is computed from the flux emerging at the solar
surface in the form of bipolar magnetic features, which is related to
the sunspot number cycle parameters and can be estimated from historical
records. Compared to earlier versions of the model in addition to the
long-lived open flux, now also a more rapidly decaying component of
the open flux is considered. The model parameters are constrained by
comparing its output with observations of the total surface magnetic
flux and with a reconstruction of the open magnetic flux based on the
geomagnetic indexes. A method to compute the Sun's total magnetic flux
and the sunspot number during the Holocene, starting from the open flux
obtained from cosmogenic isotopes records, is also presented. 
Results: By considering separately a rapidly evolving and a slowly
evolving component of the open flux the model reproduces the Sun's
open flux, as reconstructed based on the aa-index, much better and
a reasonable description of the radial component of interplanetary
magnetic field data is obtained. The greatest improvement is in the
reproduction of the cyclic variation of the open flux, including
the amplitudes of individual cycles. Furthermore, we found that
approximately 25% of the modeled open flux values since the end of
the Maunder minimum are lower than the averaged value over 2008,
i.e. during the current low minimum. The same proportion is observed
in reconstructions of the open flux during the Holocene based on
cosmogenic isotopes, which suggests that the present solar minimum
conditions are below average, but not exceptional in terms of the
heliospheric magnetic flux.

---------------------------------------------------------
Title: Evolution of the solar radiative forcing on climate during
the Holocene
Authors: Vieira, Luis Eduardo; Solanki, Sami K.; Krivova, Natalie
2010cosp...38.1785V Altcode: 2010cosp.meet.1785V
The main external heating source of the Earth's coupled atmosphere-ocean
system is the solar radiative energy input. The variability of
this energy source produces corresponding changes on the coupled
system. However, there is still significant uncertainty on the level of
changes. One way to distinguish the influence of the Sun on the climate
from other sources is to search for its influence in the pre-industrial
period, when the influence of human activities on the atmosphere
composition and Earth's surface properties can be neglected. Such
studies require long time series of solar and geophysical parameters,
ideally covering the whole Holocene. Here, we compute the total and
spectral irradiance for the Holocene employing the reconstructions of
the open flux and sunspot number obtained from the cosmogenic isotope
14C. The model employed in this study is identical to the spectral
and total irradiance reconstruction (SATIRE) models employed to study
these parameters on time scales from days to centuries, but adapted
to work with decadal averaged data. The model is tested by comparing
to the total and spectral solar irradiance reconstructions from the
sunspot number for the last 4 centuries. We also discuss limits and
uncertainties of the model.

---------------------------------------------------------
Title: Is the current solar activity minimum special?
Authors: Solanki, Sami K.; Krivova, Natalie; Antunes Vieira, Luis
Eduardo
2010cosp...38.1693S Altcode: 2010cosp.meet.1693S
Is the current solar activity minimum special? Sami K. Solanki(1,2),
Natalie Krivova(1), Luis E. Vieira(1,3) (1) Max Planck Institute
for Solar System Research, Katlenburg-Lindau, Germany (2) Kyung-Hee
University, Yongin, Gyeonggi, Korea (3) Laboratory for Physics and
Chemistry of the Terrestrial Environment/CNRS, Or-leans, France In many
respects the current minimum of solar activity is rather different
from other minima during the last half century, which has seen the
Sun in a state of unusually high activity. This uncommon minimum
has fascinated solar physicists. Of particular importance for our
understanding is the behaviour of the magnetic field, which is the
source of all activity observed in the solar atmosphere, including the
heliosphere. Furthermore, the evolution of dark and bright magnetic
features on the solar surface modulates the solar irradiance, which
could directly influence the Earth's climate. In this presentation
observations and models of the evolution of the Sun's magnetic field,
sunspots and irradiance are reviewed. After discussing the variation
of these quantities over the solar cycle and from cycle to cycle,
the current minimum is considered in greater detail. It is compared
to earlier minima going back to the Maunder minimum and, in a more
averaged sense, to solar activity and irradiance during the whole
Holocene. Questions that will be onsidered are: Are we leaving the
period of high solar activity (a grand maximum) to enter into a phase
of more moderate activity, or even into a grand minimum? How could
such a change in the level of the magnetic field and irradiance aid
us in gaining further insight into the nature of the Sun's influence
on the Earth's climate?

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Title: Temperatures of small scale magnetic structures in deep solar
photospheric layers
Authors: Oklay, Nilda; Gandorfer, Achim; Lagg, Andreas; Solanki,
Sami K.; Bianda, Michele; Ramelli, Renzo
2010cosp...38.2857O Altcode: 2010cosp.meet.2857O
With current solar instrumentation, small scale magnetic
structures still remain unresolved. Nevertheless, it is possible
to retrieve information about these unresolved magnetic structures
via spectropolarimetry. For this reason, IRSOL (Istituto Ricerche
Solari Locarno) facility is used to obtain simultaneously recorded
spectra of Stokes I and Stokes V/I of CI (5380.3 A), FeI (5379.6 A,
5383.4 A) and TiII (5381.0 A) lines on an active region using the
ZIMPOL II (Zurich Imaging Polarimeter II) instrument. We used Stokes V
amplitude ratios technique to investigate temperatures of unresolved
magnetic features down to deep photospheric layers. Atmospheric
parameters are obtained from the inversions done with the SPINOR code
(Stokes-Profile-INversion-O-Routines). Then the results are compared
with the results from the realistic MHD simulations obtained from
MURaM code (MPS/University of Chicago radiative MHD). Comparisons of
the results from observations, inversions and numerical simulations
show a good agreement, which confirms the usage of this technique as
a temperature diagnostic tool.

---------------------------------------------------------
Title: Observations of the solar chromosphere at millimeter
wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
2010MmSAI..81..592L Altcode:
Millimeter wavelengths provide a powerful tool to study the thermal
structure of the solar chromosphere and its response to dynamic
processes. We present initial studies of chromospheric fine structure
and its dynamics obtained from observations of the quiet Sun with
BIMA at 3.5 mm with a resolution of 12 arcsec. The two-dimensional
millimeter maps of the solar chromosphere reveal brightness features
corresponding to supergranular network boundaries and bright points
within cells. Significant intensity oscillations with frequencies of
1.5 - 8.0 mHz with a tendency toward shorter-period oscillations in
the internetwork and longer periods in network regions are found in
the data. However, higher spatial resolution is required for a more
detailed study. We discuss the requirements imposed on observations in
the millimeter domain that might provide an insight into the fundamental
questions of solar physics. We also review the capabilities of the
current and future millimeter-wave interferometers, including the
CARMA and ALMA arrays.

---------------------------------------------------------
Title: Solar Spectral Irradiance variations: the long-term view
Authors: Solanki, Sami K.
2010cosp...38...19S Altcode: 2010cosp.meet...19S
Solar Spectral Irradiance variations: the long-term view S.K. Solanki
Max Planck Institute for Solar System Research, Katlenburg-Lindau,
Germany The total and spectral irradiance of the Sun are prime
candidates for external forcing of the Earth's climate system. Whereas
variations of total solar irradiance have been observed and modelled
with great success, our corresponding knowledge of the variation of
spectral irradi-ance is, by comparison, still in its infancy. Although,
on short time-scales multiple measured time series and models are
now available, on longer time-scales models are the only source of
information. Until recently even the models were rather restricted,
being either based purely on proxies, or limited in spectral range. A
new generation of models is now available, which goes beyond the
limitations of the earlier approaches. An overview of the models and
their results is given, with the emphasis being placed on the most
recent ones.

---------------------------------------------------------
Title: How do inaccuracies and unresolved structures in the measured
solar photospheric magnetic vector influence the accuracy of coronal
magnetic field models?
Authors: Wiegelmann, Thomas; Yelles, Lotfi; Solanki, Sami; Lagg,
Andreas
2010cosp...38.2827W Altcode: 2010cosp.meet.2827W
Solar magnetic fields are usually extrapolated into the corona
starting from photospheric mag-netic measurements that can suffer from
significant uncertainties caused by the presence of unresolved fine
structures due to a limited spatial resolution and by the limited
polarimet-ric accuracy and spectral resolution. We investigate
how these inaccuracies in the measured photospheric magnetic field
vector influence the accuracy of the extrapolated coronal mag-netic
field. We compare non-linear force-free coronal magnetic field
extrapolations from a 3-D radiation MHD simulation snapshot with
corresponding extrapolations from synthetic vector magnetograms. The
synthetic magnetograms contain instrumental effects such as noise,
limited spatial and spectral resolution and the effect of employing a
filter instrument. The parameters are chosen in particular to mimic the
effects of the Hinode/SOT and the future Solar Orbiter PHI instruments,
respectively. We discuss, how photospheric structures, which are
inherent in the MHD snapshot, but not resolved in the photospheric
magnetic field measurements, influence the quality of the computed
coronal magnetic field model.

---------------------------------------------------------
Title: Accelerating disturbances in polar plume and inter-plume
Authors: Gupta, Girjesh R.; Banerjee, Dipankar; Teriaca, Luca; Imada,
Shinsuke; Solanki, Sami
2010cosp...38.2937G Altcode: 2010cosp.meet.2937G
We present EIS/Hinode &amp; SUMER/SoHO joint observations allowing the
first spectroscopic detection of accelerating disturbances as recorded
with coronal lines in inter-plume and plume regions of a polar coronal
hole. From time-distance radiance maps, we detect the presence of
propagating disturbances in a polar inter-plume region with a period
of 15 to 20 min and a propagation speed increasing from 130±14 km/s
just above the limb, to 330±140 km/s around 160" above the limb. These
disturbances can also be traced to originate from a bright region of
the on-disk part of the coronal hole where the propagation speed was
found to be in the range of 25±1.3 to 38±4.5 km/s, with the same
periodicity. These on-disk bright regions can be vi-sualized as the
base of the coronal funnels. The adjacent plume region also shows the
presence of propagating disturbance with the same range of period but
with propagation speeds in the range of 135±18 to 165±43 km/s only. A
comparison between the time-distance radiance map of both regions,
indicate that the disturbances within the plumes are not observable (may
be getting dissipated) far off-limb whereas this is not the case in the
inter-plume region. Conclu-sions drawn from these observations in terms
of accelerating waves or high speed jets/upflows will be discussed.

---------------------------------------------------------
Title: High resolution imaging and polarimetry with SUNRISE, a
balloon-borne stratospheric solar observatory
Authors: Barthol, Peter; Chares, Bernd; Deutsch, Werner; Feller, Alex;
Gandorfer, Achim; Grauf, Bianca; Hirzberger, Johann; Meller, Reinhard;
Riethmueller, Tino; Schuessler, Manfred; Solanki, Sami K.; Knoelker,
Michael; Martinez Pillet, Valentin; Schmidt, Wolfgang; Title, Alan
2010cosp...38.4063B Altcode: 2010cosp.meet.4063B
SUNRISE is an international collaboration for the development
and operation of a meter-class balloon-borne stratospheric solar
observatory. Prime science goal is the study of structure and dynamics
of the magnetic field in the solar atmosphere and the interaction of
the magnetic field with convective plasma flows. These processes are
studied by high resolution imaging in the UV and polarimetry at visible
wavelengths. The instrument has been successfully launched on June 8,
2009 from ESRANGE, Kiruna, Northern Sweden. During the more than 5
days flight about 1.5 TByte of scientific data were collected. The
paper gives an overview of the instrument and mission, examples of
the scientific output will also be presented. SUNRISE is a joint
project of the Max-Planck-Institut fuer Sonnensystemforschung (MPS),
Katlenburg-Lindau, with the Kiepenheuer-Institut fuer Sonnenphysik
(KIS), Freiburg, the High-Altitude Observatory (HAO), Boulder, the
Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto, and
the Spanish IMaX consortium.

---------------------------------------------------------
Title: The Ultraviolet Filter Imager (SuFI) onboard the Sunrise
balloon-borne solar observatory: Instrument description and first
results
Authors: Gandorfer, Achim; Barthol, Peter; Feller, Alex; Grauf,
Bianca; Hirzberger, Johann; Riethmueller, Tino; Solanki, Sami K.;
Berkefeld, Thomas; Knoelker, Michael; Martinez Pillet, Valentin;
Schmidt, Wolfgang; Title, Alan
2010cosp...38.4064G Altcode: 2010cosp.meet.4064G
We describe the design of the near UV filter imager SuFi onboard
Sunrise, which was successfully flown in the stratosphere in June
2009. During its five days flight SuFI captured the highest contrast
images of solar granulation ever. SuFI is a diffraction limited filter
imager with an effective focal length of 121m, working in 5 distinct
wavelength bands between 210nm and 397nm. It is based on a two mirror
modified Schwarzschild microscope, which is integral part of the central
Image stabilization and light Distribution unit (ISLiD) of Sunrise,
which acts as the reimaging optics between the 1m telescope and the
science instruments. The key technical features of the instrument are
presented under the view of the specific demands of balloon-borne
optical systems. First results obtained with the instrument are
presented to demonstrate the capabilities of the instrument.

---------------------------------------------------------
Title: UV intensity distributions of the quiet Sun observed with
Sunrise
Authors: Hirzberger, Johann; Feller, A.; Riethmueller, T.; Borrero,
J. M.; Schüssler, M.; Barthol, P.; Berkefeld, T.; Gandorfer, A.;
Knoelker, M.; Martínez Pillet, V.; Schmidt, W.; Solanki, S.; Title, A.
2010cosp...38.1735H Altcode: 2010cosp.meet.1735H
High resolution solar images in the near UV have been obtained with
the Solar UV Filtergraph (SUFI) onboard the Sunrise balloon borne
observatory, amongst others in wavelength regions not accessible
from the ground. We present intensity distributions of the quiet
Sun at different heliocentric angles, from disk center to the solar
limb. These results, obtained in spectral windows at 214 nm, 313 nm
(OH band), 388 nm (CN band) and 396.7 nm (CaIIH), represent an important
validation of numerical models of the solar photosphere and are, thus,
fundamental ingredients for our understanding of the thermal processes
in the solar surface region.

---------------------------------------------------------
Title: Magnetic field intensification: comparison of 3D MHD
simulations with Hinode/SP results
Authors: Danilovic, S.; Schüssler, M.; Solanki, S. K.
2010A&A...509A..76D Altcode: 2009arXiv0910.1211D
Context. Recent spectro-polarimetric observations have provided detailed
measurements of magnetic field, velocity and intensity during events of
magnetic field intensification in the solar photosphere. Aims:
By comparing with synthetic observations derived from MHD simulations,
we investigate the physical processes underlying the observations,
as well as verify the simulations and the interpretation of the
observations. Methods: We consider the temporal evolution of
the relevant physical quantities for three cases of magnetic field
intensification in a numerical simulation. In order to compare with
observations, we calculate Stokes profiles and take into account the
spectral and spatial resolution of the spectropolarimeter (SP) on
board Hinode. We determine the evolution of the intensity, magnetic
flux density and zero-crossing velocity derived from the synthetic
Stokes parameters, using the same methods as applied to the Hinode/SP
observations to derive magnetic field and velocity information from
the spectro-polarimetric data. Results: The three events
considered show a similar evolution: advection of magnetic flux to a
granular vertex, development of a strong downflow, evacuation of the
magnetic feature, increase of the field strength and the appearance
of the bright point. The magnetic features formed have diameters of
0.1-0.2´´. The downflow velocities reach maximum values of 5-10
km s-1 at τ = 1. In the largest feature, the downflow
reaches supersonic speed in the lower photosphere. In the same case,
a supersonic upflow develops approximately 200 s after the formation of
the flux concentration. We find that synthetic and real observations
are qualitatively consistent and, for one of the cases considered,
also agree very well quantitatively. The effect of finite resolution
(spatial smearing) is most pronounced in the case of small features,
for which the synthetic Hinode/SP observations miss the bright point
formation and also the high-velocity downflows during the formation
of the smaller magnetic features. Conclusions: The observed
events are consistent with the process of field intensification by
flux advection, radiative cooling, and evacuation by strong downflow
found in MHD simulations. The quantitative agreement of synthetic and
real observations indicates the validity of both the simulations and
the interpretations of the spectro-polarimetric observations.

---------------------------------------------------------
Title: Radiative emission of solar features in Ca II K
Authors: Criscuoli, S.; Ermolli, I.; Fontenla, J.; Giorgi, F.; Rast,
M.; Solanki, S. K.; Uitenbroek, H.
2010MmSAI..81..773C Altcode: 2010arXiv1002.0244C
We investigated the radiative emission of different types of solar
features in the spectral range of the Ca II K line. We analyzed
full-disk 2k × 2k observations from the Precision Solar Photometric
Telescope (PSPT). The data were obtained by using three narrow-band
interference filters that sample the Ca II K line with different pass
bands. Two filters are centered in the line core, the other in the red
wing of the line. We measured the intensity and contrast of various
solar features, specifically quiet Sun (inter-network), network,
enhanced network, plage, and bright plage (facula) regions. Moreover,
we compared the results obtained with those derived from the numerical
synthesis performed for the three PSPT filters with a widely used
radiative code on a set of reference semi-empirical atmosphere models.

---------------------------------------------------------
Title: Analysis of Ca II K spectroheliogram time-series for solar
irradiance studies
Authors: Ermolli, Ilaria; Krivova, Natalie; Solanki, Sami K.
2010cosp...38..133E Altcode: 2010cosp.meet..133E
Historic Ca II K observations constitute an extremely valuable
resource for many research topics, including investigations of solar
activity and irradiance variations on century timescales. In fact,
the intensities measured on these observations can serve as proxies for
magnetic activity, due to the strong correlation found between the Ca
II K emission and the line-of-sight magnetic flux density. We analyzed
three time-series of historic Ca II K observations, specifically those
obtained by the digitization of the Arcetri, Kodaikanal, and Mt Wilson
spectroheliohram archives. We examined the quality of these data,
in order to estimate their value for irradiance studies focusing
on time-scales longer than the solar cycle. We employ different
processing techniques in order to investigate whether uniform results
on the evolution of the solar magnetic field, both in quiet and active
regions, can be obtained for the three analyzed series. ——-Session
A1.1 Atmosphere Chemistry and Physics (i) Solar Spectral Irradiance
Variations and Their Influence on the Earth's Atmosphere

---------------------------------------------------------
Title: Relation between the Sunrise photospheric magnetic field and
the Ca II H bright features
Authors: Jafarzadeh, Shahin; Hirzberger, J.; Feller, A.; Lagg, A.;
Solanki, S. K.; Pietarila, A.; Danilovic, S.; Riethmueller, T.;
Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knülker, M.; Martínez
Pillet, V.; Schmidt, W.; Schüssler, M.; Title, A.
2010cosp...38.2856J Altcode: 2010cosp.meet.2856J
Recent observations from the Sunrise balloon-borne solar telescope
have enabled us to reach an unprecedented high spatial resolution
on the solar surface with the near-ultraviolet photo-spheric and
chromospheric images as well as the magnetograms. We use these high
resolution observations to investigate the structure of the solar
upper photosphere and lower chromosphere as well as their temporal
evolutions. We study the relation between the inter-granular Ca II
397 nm bright structures in images obtained by the Sunrise Filter
Imager (SuFI) and their corresponding photospheric vector magnetic
field computed from the Imaging Magnetogram eXperiment (IMaX)
observations. The targets under study are in a quiet Sun region and
close to disc-centre.

---------------------------------------------------------
Title: Total and spectral irradiance comparisons between SIM and
the SATIRE model in the declining phase of cycle 23
Authors: Ball, Will; Unruh, Yvonne; Krivova, Natalie; Solanki, Sami
K.; Harder, Jerald
2010cosp...38..136B Altcode: 2010cosp.meet..136B
Climate models rely on accurate total and spectral solar irradiance
inputs, but until 2003 con-tinuous spectral irradiance information
across a large portion of the solar spectrum was lacking. Since the
launch of the Solar Radiation and Climate Experiment (SORCE), with the
Spectral Irradiance Monitor (SIM) observing the UV, visible and IR,
data have been accumulating and now cover a significant portion of
a cycle. For the first time this allows spectral models to be tested
over periods greater than a solar rotation. We present six years of
total and spectral irradiance reconstructions using the SATIRE model
that incorporates SOHO/MDI continuum and magnetogram images for the
period April 2004 to November 2009 in the declining phase of cycle 23
and through the recent unusual minimum. We compare these results with
the SIM instrument and so cover the spectral region 200 -1600 nm. While
detrended, short-term, variation is recreated well by the model, there
are discrepancies in longer-term trends between observations and the
model. This may become important when considering the radiative forcing
from the Sun used in climate research and so understanding why there is
such a significant disagreement is an important area of investigation.

---------------------------------------------------------
Title: Center-to-Limb Variation of the continuum contrast of quiet
Sun magnetic features from Hinode/SP
Authors: Kobel, Philippe; Borrero Santiago, Juan Manuel; Solanki,
Sami K.
2010cosp...38.1788K Altcode: 2010cosp.meet.1788K
The center-to-limb variation (CLV) of the continuum contrast of
magnetic features represents an important constraint for flux tube
models, as well as a useful input to reproduce the total solar
irradiance. However, precise measurements are difficult because
the contrast depends on the atmospheric and magnetic parameters of
those features, and is severely affected by the observing conditions
(seeing). Here we present the first assessment of the dependence of
the continuum contrast of magnetic features on both the heliocentric
angle and on their magnetic properties, inferred from high spatial
resolution spectro-polarimetric maps (Hinode/SP). At the same time,
it allowed us to improve the results of previous lower resolution
studies of contrast as a function of magnetogram signal. The magnetic
parameters (field strength, filling factor and inclination) were
inferred by Milne-Eddington inversions (VFISV) of spectro-polarimetric
maps covering a continuous range of mu between 1 and 0.2 in the
quiet Sun. Our contrasts reach positive values at disk center,
and the peak of the contrast as a function of magnetogram signal
at different are larger than in previous studies. The contrast was
found to behave differently in two distinct regimes of "apparent flux
density", characterizing fields that are tied to granulation and strong
network-like magnetic features, respectively. The weak fields seem to be
"wrapped" around granules and the contrasts reflects their location:
pixels with horizontal fields are on average located within granules
and are brighter, while pixels with more vertical fields are preferably
located in the intergranular lanes and are thus darker. For the stronger
fields, the contrast CLV was found to depend essentially on the apparent
flux density, with a rather symmetric dependence on the field strength
and on the filling factor, while the fields are quasi-vertical.

---------------------------------------------------------
Title: Long term variability of solar magnetic activity: the
solar-stellar connection
Authors: Solanki, Sami K.
2010cosp...38.2890S Altcode: 2010cosp.meet.2890S
Long term variability of solar magnetic activity: the solar-stellar
connection S.K. Solanki Max Planck Institute for Solar System
Research, Katlenburg-Lindau, Germany The dominant time-scales of
solar variability are the solar rotation period and in particular
the length of the solar cycle, but variations of solar activity on
longer time scales are also present. Variations of stellar activity
are also well documented on time scales up to stellar activity
cycles, although secular variations on longer time scales are
somewhat less well established, due to the limited length of the
available observational time series. Multi-wavelength observations
of solar variability is mainly limited to the space age, while
direct observations of sunspots are available back to the year 1610,
i.e. over the whole era of telescopic astronomy. In the last decades
considerable progress has been made in extending our knowledge of solar
activity to pre-telescopic times, using records of the concentration of
cosmogenic isotopes in terrestrial archives.Such studies have shown,
e.g., that in addition to grand minima, the Sun has also enjoyed
times of significantly anhanced activity, so called grand maxima. The
recent decades formed a particularly prominent such grand maximum. The
current peculiar minimum has shown strong indications that we are in
the process of leaving this last grand maximum. There is also strong
evidence that there are significant secular changes of the magnetic
flux and other active phenomena. Although the period over which we
have data on stellar activity is far shorter than for the Sun, these
data allow stars of different types to be sampled (i.e. stars with
different activity levels, of different spectral types, at different
evolutionary stages, etc.) that display the full variety of active
phenomena, including cycles, but also chaotic variability. After an
overview of our knowledge and understanding of the longer-term evolution
of solar activity, comparisons with observations of stellar activity
time series are presented and some implications for our understanding
of stellar activity variations are deduced.

---------------------------------------------------------
Title: Expansion of Magnetic Flux Concentrations with Height:
A Comparison of Hinode SOT Data and MHD Simulations
Authors: Pietarila, A.; Cameron, R.; Solanki, S.
2009ASPC..415...91P Altcode:
The Hinode SOT (Tsuneta et al. 2008) NFI Na I D1 and SP Fe I
data sampled at different positions on the solar disk provide a unique
diagnostic for studying the expansion of magnetic flux concentrations
with height. We make a comparative study of SOT observations and
2-dimensional (2D) radiative MHD-simulations to see how well the
simulations capture the expansion properties. The expansion of flux
concentrations is clearly seen in the SOT Na I D1 data,
where most of the magnetic features appear unipolar at disk center while
close to the limb bipolar appearance strongly dominates. This trend,
albeit not as strong, is seen in the SP data as well. Some aspects of
the observations are qualitatively reproduced by simulations with a
potential (as opposed to vertical) upper boundary condition for the
magnetic field.

---------------------------------------------------------
Title: Simulation of a flux emergence event and comparison with
observations by Hinode
Authors: Yelles Chaouche, L.; Cheung, M. C. M.; Solanki, S. K.;
Schüssler, M.; Lagg, A.
2009A&A...507L..53Y Altcode: 2009arXiv0910.5737Y
Aims: We study the observational signature of flux emergence in
the photosphere using synthetic data from a 3D MHD simulation of the
emergence of a twisted flux tube. Methods: Several stages in the
emergence process are considered. At every stage we compute synthetic
Stokes spectra of the two iron lines Fe I 6301.5 Å and Fe I 6302.5
Å and degrade the data to the spatial and spectral resolution of
Hinode's SOT/SP. Then, following observational practice, we apply
Milne-Eddington-type inversions to the synthetic spectra in order
to retrieve various atmospheric parameters and compare the results
with recent Hinode observations. Results: During the emergence
sequence, the spectral lines sample different parts of the rising
flux tube, revealing its twisted structure. The horizontal component
of the magnetic field retrieved from the simulations is close to the
observed values. The flattening of the flux tube in the photosphere is
caused by radiative cooling, which slows down the ascent of the tube
to the upper solar atmosphere. Consistent with the observations, the
rising magnetized plasma produces a blue shift of the spectral lines
during a large part of the emergence sequence. Figure 3 is only
available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Internetwork Horizontal Magnetic Fields in the Quiet Sun
Chromosphere: Results from a Joint Hinode/VTT Study
Authors: Lagg, A.; Ishikawa, R.; Merenda, L.; Wiegelmann, T.; Tsuneta,
S.; Solanki, S. K.
2009ASPC..415..327L Altcode:
We present results from a joint Hinode/VTT campaign (May
2008). Spectropolarimetric data of a quiet Sun super-granular network
cell at a heliocentric angle of 28° in the He I 10830 Å line were
analyzed using an inversion code incorporating Hanle and Zeeman effects
(HeLIx^+) to retrieve magnetic field strength and direction in the upper
chromosphere. Simultaneously recorded Hinode SOT/SP data reveal the
photospheric magnetic field morphology, clearly showing magnetic flux
concentrations in the internetwork. The photospheric magnetic field
maps are used to feed potential field extrapolations similar to the
work by Schrijver &amp; Title (2003). The extrapolated magnetic field
structure is compared with the magnetic field configuration resulting
from the He 10830 inversions. These inversions also reveal horizontal
magnetic structures extending over a length of up to 20 Mm above the
internetwork, indicative of the presence of a magnetic canopy. The
photospheric magnetic flux concentrations in the internetwork are
obviously not sufficiently strong to prevent the formation of a canopy
at chromospheric heights.

---------------------------------------------------------
Title: Solar magnetic field and irradiance: how unusual is the
current minimum? (Invited)
Authors: Solanki, S. K.; Krivova, N.; Vieira, L. A.
2009AGUFM.U34A..01S Altcode:
In many respects the current minimum of solar activity is rather
different from other minima during the last half century, which has
seen the Sun in a state of unusually high activity. This uncommon
minimum has fascinated solar physicists. Of particular importance for
our understanding is the behaviour of the magnetic field, which is the
source of all activity observed in the solar atmosphere, including the
heliosphere. Furthermore, the evolution of dark and bright magnetic
features on the solar surface modulates the solar irradiance, which
could directly influence the Earth's climate. In this presentation
observations and models of the evolution of the Sun's magnetic field
and irradiance are reviewed. After discussing the variation of these
quantities over the solar cycle and from cycle to cycle, the current
minimum is considered in greater detail. It is compared to earlier
minima going back to the Maunder minimum and, in a more averaged sense,
to solar activity and irradiance during the whole Holocene. Questions
that will be considered are: Are we leaving the period of high solar
activity (a grand maximum) to enter into a phase of more moderate
activity, or even into a grand minimum? How could such a change in the
level of the magnetic field and irradiance aid us in gaining further
insight into the nature of the Sun's influence on the Earth's climate?

---------------------------------------------------------
Title: The Local Dust Foregrounds in the Microwave Sky. I. Thermal
Emission Spectra
Authors: Dikarev, Valeri; Preuß, Oliver; Solanki, Sami; Krüger,
Harald; Krivov, Alexander
2009ApJ...705..670D Altcode: 2009arXiv0910.1317D
Analyses of the cosmic microwave background (CMB) radiation maps made by
the Wilkinson Microwave Anisotropy Probe (WMAP) have revealed anomalies
not predicted by the standard inflationary cosmology. In particular, the
power of the quadrupole moment of the CMB fluctuations is remarkably
low, and the quadrupole and octopole moments are aligned mutually
and with the geometry of the solar system. It has been suggested in
the literature that microwave sky pollution by an unidentified dust
cloud in the vicinity of the solar system may be the cause for these
anomalies. In this paper, we simulate the thermal emission by clouds
of spherical homogeneous particles of several materials. Spectral
constraints from the WMAP multi-wavelength data and earlier infrared
observations on the hypothetical dust cloud are used to determine the
dust cloud's physical characteristics. In order for its emissivity
to demonstrate a flat, CMB-like wavelength dependence over the WMAP
wavelengths (3 through 14 mm), and to be invisible in the infrared
light, its particles must be macroscopic. Silicate spheres of several
millimeters in size and carbonaceous particles an order of magnitude
smaller will suffice. According to our estimates of the abundance of
such particles in the zodiacal cloud and trans-Neptunian belt, yielding
the optical depths of the order of 10-7 for each cloud,
the solar system dust can well contribute 10 μK (within an order of
magnitude) in the microwaves. This is not only intriguingly close to
the magnitude of the anomalies (about 30 μK), but also alarmingly
above the presently believed magnitude of systematic biases of the
WMAP results (below 5 μK) and, to an even greater degree, of the
future missions with higher sensitivities, e.g., Planck.

---------------------------------------------------------
Title: ACRIM-gap and total solar irradiance revisited: Is there a
secular trend between 1986 and 1996?
Authors: Krivova, N. A.; Solanki, S. K.; Wenzler, T.
2009GeoRL..3620101K Altcode: 2009arXiv0911.3817K
A gap in the total solar irradiance (TSI) measurements between
ACRIM-1 and ACRIM-2 led to the ongoing debate on the presence or not
of a secular trend between the minima preceding cycles 22 (in 1986)
and 23 (1996). It was recently proposed to use the SATIRE model of
solar irradiance variations to bridge this gap. When doing this, it is
important to use the appropriate SATIRE-based reconstruction, which we
do here, employing a reconstruction based on magnetograms. The accuracy
of this model on months to years timescales is significantly higher
than that of a model developed for long-term reconstructions used by
the ACRIM team for such an analysis. The constructed ‘mixed’ ACRIM
— SATIRE composite shows no increase in the TSI from 1986 to 1996,
in contrast to the ACRIM TSI composite.

---------------------------------------------------------
Title: High-resolution spectro-polarimetry of a flaring sunspot
penumbra
Authors: Hirzberger, J.; Riethmüller, T.; Lagg, A.; Solanki, S. K.;
Kobel, P.
2009A&A...505..771H Altcode: 2009arXiv0908.3803H
We present simultaneous photospheric and chromospheric observations
of the trailing sunspot in NOAA 10904 during a weak flare eruption
(GOES magnitude B7.8), obtained with the Swedish Solar Telescope
(SST) in La Palma, Canary Islands. High-resolution Ca II H images
show a typical two-ribbon structure that has been hitherto only
known for larger flares, and the flare appears in a confined region
that is discernible by a bright border. The underlying photosphere
shows a disturbed penumbral structure with intersecting branches of
penumbral filaments. High-resolution Doppler- and vector-magnetograms
exhibit oppositely directed Evershed flows and magnetic field vectors
in the individual penumbral branches, resulting in several regions
of magnetic azimuth discontinuity and several islands where the
vertical magnetic field is reversed. The discontinuity regions are
co-spatial with the locations of the onset of the flare ribbons. From
the results, we conclude that the confined flare region is detached
from the global magnetic field structure by a separatrix marked by the
bright border visible in C II H. We further conclude that the islands
of reversed vertical field appear because of flux emergence and that
the strong magnetic shear appearing in the regions of magnetic azimuth
discontinuity triggers the flare. Movies are only available in
electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Comparison of the thin flux tube approximation with 3D MHD
simulations
Authors: Yelles Chaouche, L.; Solanki, S. K.; Schüssler, M.
2009A&A...504..595Y Altcode: 2009arXiv0910.1796Y
Context: The structure and dynamics of small vertical photospheric
magnetic flux concentrations has been often treated in the framework
of an approximation based upon a low-order truncation of the Taylor
expansions of all quantities in the horizontal direction, together
with the assumption of instantaneous total pressure balance at
the boundary to the non-magnetic external medium. Formally, such
an approximation is justified if the diameter of the structure (a
flux tube or a flux sheet) is small compared to all other relevant
length scales (scale height, radius of curvature, wavelength,
etc.). The advent of realistic 3D radiative MHD simulations opens
the possibility of checking the consistency of the approximation with
the properties of the flux concentrations that form in the course of
a simulation. Aims: We carry out a comparative analysis between
the thin flux tube/sheet models and flux concentrations formed in a 3D
radiation-MHD simulation. Methods: We compare the distribution
of the vertical and horizontal components of the magnetic field in a 3D
MHD simulation with the field distribution in the case of the thin flux
tube/sheet approximation. We also consider the total (gas plus magnetic)
pressure in the MHD simulation box. Results: Flux concentrations
with super-equipartition fields are reasonably well reproduced by
the second-order thin flux tube/sheet approximation. The differences
between approximation and simulation are due to the asymmetry and the
dynamics of the simulated structures.

---------------------------------------------------------
Title: Reconstruction of solar UV irradiance since 1974
Authors: Krivova, N. A.; Solanki, S. K.; Wenzler, T.; Podlipnik, B.
2009JGRD..114.0I04K Altcode: 2009arXiv0907.1500K; 2009JGRD..11400I04K
Variations of the solar UV irradiance are an important driver of
chemical and physical processes in the Earth's upper atmosphere and may
also influence global climate. Here we reconstruct solar UV irradiance
in the range 115-400 nm over the period 1974-2007 by making use of
the recently developed empirical extension of the Spectral And Total
Irradiance Reconstruction (SATIRE) models employing Solar Ultraviolet
Spectral Irradiance Monitor (SUSIM) data. The evolution of the solar
photospheric magnetic flux, which is a central input to the model,
is described by the magnetograms and continuum images recorded at
the Kitt Peak National Solar Observatory between 1974 and 2003 and
by the Michelson Doppler Imager instrument on SOHO since 1996. The
reconstruction extends the available observational record by 1.5
solar cycles. The reconstructed Ly-α irradiance agrees well with
the composite time series by Woods et al. (2000). The amplitude of
the irradiance variations grows with decreasing wavelength and in
the wavelength regions of special interest for studies of the Earth's
climate (Ly-α and oxygen absorption continuum and bands between 130
and 350 nm) is 1-2 orders of magnitude stronger than in the visible
or if integrated over all wavelengths (total solar irradiance).

---------------------------------------------------------
Title: Bright fibrils in Ca II K
Authors: Pietarila, A.; Hirzberger, J.; Zakharov, V.; Solanki, S. K.
2009A&A...502..647P Altcode: 2009arXiv0905.3124P
Context: Except for the Ca II resonance lines, fibrils are ubiquitously
present in most high-resolution observations of chromospheric lines. Aims: We show that fibrils are also a prevailing feature in Ca II K,
provided the spatial-resolution is sufficiently high. Methods:
We present high spatial resolution observations of an active region in
the Ca II K line from the Swedish Solar Telescope. Through a comparison
between photospheric intensity and magnetic field data, we study the
connection between bright chromospheric fibrils and photospheric
structures. Additionally, using Fourier analysis we study how the
fibrils are linked to the observed dynamics. Results: We find
that very narrow, bright fibrils are a prevailing feature over large
portions of the observed field. We also find a clear connection between
the fibril footpoints and photospheric magnetic features. We show that
the fibrils play two distinct roles in the observed dynamics: depending
on their location they can act as a canopy suppressing oscillations or
they can channel low-frequency oscillations into the chromosphere. Conclusions: The Ca II K fibrils share many characteristics with
fibrils observed in other chromospheric lines, but some features,
such as the very small widths, are unique to these observations.

---------------------------------------------------------
Title: Solar Surface Magnetism and Irradiance on Time Scales from
Days to the 11-Year Cycle
Authors: Domingo, V.; Ermolli, I.; Fox, P.; Fröhlich, C.; Haberreiter,
M.; Krivova, N.; Kopp, G.; Schmutz, W.; Solanki, S. K.; Spruit, H. C.;
Unruh, Y.; Vögler, A.
2009SSRv..145..337D Altcode:
The uninterrupted measurement of the total solar irradiance during the
last three solar cycles and an increasing amount of solar spectral
irradiance measurements as well as solar imaging observations
(magnetograms and photometric data) have stimulated the development
of models attributing irradiance variations to solar surface
magnetism. Here we review the current status of solar irradiance
measurements and modelling efforts based on solar photospheric
magnetic fields. Thereby we restrict ourselves to the study of solar
variations from days to the solar cycle. Phenomenological models
of the solar atmosphere in combination with imaging observations of
solar electromagnetic radiation and measurements of the photospheric
magnetic field have reached high enough quality to show that a large
fraction (at least, about 80%) of the solar irradiance variability
can be explained by the radiative effects of the magnetic activity
present in the photosphere. Also, significant progress has been made
with magnetohydrodynamic simulations of convection that allow us to
relate the radiance of the photospheric magnetic structures to the
observations.

---------------------------------------------------------
Title: Stray light correction and contrast analysis of Hinode
broad-band images
Authors: Mathew, S. K.; Zakharov, V.; Solanki, S. K.
2009A&A...501L..19M Altcode: 2009arXiv0906.2451M
The contrasts of features in the quiet Sun are studied using filtergrams
recorded by the broad-band filter imager mounted on the Hinode/Solar
Optical Telescope. In a first step, the scattered light originating
in the instrument is modeled using Mercury transit data. Combinations
of four two-dimensional Gaussians with different widths and weights
were employed to retrieve the point-spread functions (PSF) of the
instrument at different wavelengths, which also describe instrumental
scattered light. The parameters of the PSFs at different wavelengths
are tabulated. The observed images were then deconvolved using the
PSFs. The corrected images were used to determine the contrasts of
features such as bright points and granulation in different wavelength
bands. After correction, rms contrasts of the granulation of between
0.11 (at 668 nm) and 0.22 (at 388 nm) were obtained. Similarly, bright
point contrasts ranging from 0.07 (at 668 nm) to 0.78 (at 388 nm) are
found, which are a factor of 1.8 to 2.8 higher than those obtained
before PSF deconvolution. The mean contrast of the bright points is
found to be somewhat higher in the CN-band than in the G-band, which
confirms theoretical predictions. Appendices are only available
in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: A homogeneous database of sunspot areas covering more than
130 years
Authors: Balmaceda, L. A.; Solanki, S. K.; Krivova, N. A.; Foster, S.
2009JGRA..114.7104B Altcode: 2009JGRA..11407104B; 2009arXiv0906.0942B
The historical record of sunspot areas is a valuable and widely used
proxy of solar activity and variability. The Royal Greenwich Observatory
regularly measured this and other parameters between 1874 and
1976. After that time records from a number of different observatories
are available. These, however, show systematic differences and often
have significant gaps. Our goal is to obtain a uniform and complete
sunspot area time series by combining different data sets. A homogeneous
composite of sunspot areas is essential for different applications
in solar physics, among others for irradiance reconstructions. Data
recorded simultaneously at different observatories are statistically
compared in order to determine the intercalibration factors. Using
these data we compile a complete and cross-calibrated time series. The
Greenwich data set is used as a basis until 1976, the Russian data
(a compilation of observations made at stations in the former USSR)
are used between 1977 and 1985, and data compiled by the USAF network
are used since 1986. Other data sets (Rome, Yunnan, and Catania)
are used to fill up the remaining gaps. Using the final sunspot areas
record the Photometric Sunspot Index is calculated. We also show that
the use of uncalibrated sunspot areas data sets can seriously affect
the estimate of irradiance variations. Our analysis implies that there
is no basis for the claim that UV irradiance variations have a much
smaller influence on climate than total solar irradiance variations.

---------------------------------------------------------
Title: Stereoscopic Polar Plume Reconstructions from STEREO/SECCHI
Images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wilhelm, K.;
Wiegelmann, T.; Podlipnik, B.; Howard, R. A.; Plunkett, S. P.; Wuelser,
J. P.; Gan, W. Q.
2009ApJ...700..292F Altcode: 2009arXiv0908.2365F
We present stereoscopic reconstructions of the location and
inclination of polar plumes of two data sets based on the two
simultaneously recorded images taken by the EUVI telescopes in the
SECCHI instrument package onboard the Solar TErrestrial RElations
Observatory spacecraft. The 10 plumes investigated show a superradial
expansion in the coronal hole in three dimensions (3D) which is
consistent with the two-dimensional results. Their deviations from the
local meridian planes are rather small with an average of 6fdg47. By
comparing the reconstructed plumes with a dipole field with its axis
along the solar rotation axis, it is found that plumes are inclined
more horizontally than the dipole field. The lower the latitude is, the
larger is the deviation from the dipole field. The relationship between
plumes and bright points has been investigated and they are not always
associated. For the first data set, based on the 3D height of plumes
and the electron density derived from SUMER/SOHO Si VIII line pair,
we found that electron densities along the plumes decrease with height
above the solar surface. The temperature obtained from the density
scale height is 1.6-1.8 times larger than the temperature obtained
from Mg IX line ratios. We attribute this discrepancy to a deviation
of the electron and the ion temperatures. Finally, we have found that
the outflow speeds studied in the O VI line in the plumes corrected
by the angle between the line of sight and the plume orientation are
quite small with a maximum of 10 km s-1. It is unlikely
that plumes are a dominant contributor to the fast solar wind.

---------------------------------------------------------
Title: Discriminant analysis of solar bright points and
faculae. I. Classification method and center-to-limb distribution
Authors: Kobel, P.; Hirzberger, J.; Solanki, S. K.; Gandorfer, A.;
Zakharov, V.
2009A&A...502..303K Altcode: 2010arXiv1001.5143K
Context: While photospheric magnetic elements appear mainly as
Bright Points (BPs) at the disk center and as faculae near the limb,
high-resolution images reveal the coexistence of BPs and faculae over a
range of heliocentric angles. This is not explained by a “hot wall”
effect through vertical flux tubes, and suggests that the transition
from BPs to faculae needs to be quantitatively investigated. Aims:
To achieve this, we made the first recorded attempt to discriminate
BPs and faculae, using a statistical classification approach based
on Linear Discriminant Analysis (LDA). This paper gives a detailed
description of our method, and shows its application on high-resolution
images of active regions to retrieve a center-to-limb distribution of
BPs and faculae. Methods: Bright “magnetic” features were
detected at various disk positions by a segmentation algorithm using
simultaneous G-band and continuum information. By using a selected
sample of those features to represent BPs and faculae, suitable
photometric parameters were identified for their discrimination. We
then carried out LDA to find a unique discriminant variable, defined
as the linear combination of the parameters that best separates the
BPs and faculae samples. By choosing an adequate threshold on that
variable, the segmented features were finally classified as BPs and
faculae at all the disk positions. Results: We thus obtained
a Center-to-Limb Variation (CLV) of the relative number of BPs and
faculae, revealing the predominance of faculae at all disk positions
except close to disk center (μ ≥ 0.9). Conclusions: Although
the present dataset suffers from limited statistics, our results are
consistent with other observations of BPs and faculae at various disk
positions. The retrieved CLV indicates that at high resolution, faculae
are an essential constituent of active regions all across the solar
disk. We speculate that the faculae near disk center as well as the BPs
away from disk center are associated with inclined fields. Figures
11-14 are only available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Center to Limb Distribution of Bright Points and Faculae:
First Results of an Automated Detection Algorithm
Authors: Kobel, P.; Hirzberger, J.; Zakharov, V.; Gandorfer, A.;
Solanki, S. K.
2009ASPC..405..211K Altcode:
Center to limb variations (CLV) of photospheric Bright Points (BPs)
and faculae are important to understand the fundamental relationship
between these magnetic features. In this context, we present a
statistical study of the center to limb distribution of BPs and faculae
in active regions. Magnetic brightenings were detected at various disk
positions by an automated segmentation algorithm based on joint G-band
and continuum information. They were then classified as BPs or faculae
according to a linear discriminant analysis, which allowed to determine
the relative fraction of the two classes at each disk position.

---------------------------------------------------------
Title: Spectropolarimetric Investigations of the Deep Photospheric
Layers of Solar Magnetic Structures
Authors: Oklay, N.; Gandorfer, A.; Solanki, S. K.; Bianda, M.;
Ramelli, R.
2009ASPC..405..233O Altcode:
Solar surface magnetism manifests itself in a variety of structures
with sizes often comparable or even below our spatial resolution
capabilities. Nevertheless, sub-resolution information about
the intrinsic atmospheric structure can be obtained via indirect
techniques. We use state-of-the-art spectropolarimetric observations
in carefully selected photospheric lines which include C~I~(5380.3~Å)
as well as strong lines of Fe~I, Ti~I covering also the deep layers of
the photosphere and obtain ratios of their Stokes V amplitudes. From
there we deduce that the temperature within magnetic features is higher
at locations of smaller magnetic flux.

---------------------------------------------------------
Title: Reconstructed and measured total solar irradiance: Is there
a secular trend between 1978 and 2003?
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.
2009GeoRL..3611102W Altcode: 2009arXiv0909.2975W
Total solar irradiance reconstructed between 1978 and 2003 using solar
surface magnetic field distributions is compared with three composites
of total solar irradiance measurements. A good correspondence is found
with the total solar irradiance composite from PMOD/WRC, with no bias
between the three cycles. The agreement with the other composites
(the ACRIM composite, mainly based on the Active Cavity Radiometer
Irradiance Monitors I, II, and III, and the IRMB composite from the
Institut Royal Meteorologique Belgique) is significantly poorer. In
particular, a secular increase in the irradiance exhibited by these
composites is not present in the reconstructions. Hence any secular
trend in total solar irradiance between 1978 and 2003 is not due to
magnetic fields at the solar surface.

---------------------------------------------------------
Title: Photospheric Magnetic Field: Quiet Sun
Authors: Solanki, S. K.
2009ASPC..405..135S Altcode:
The solar photosphere is the layer in which the magnetic field has been
most reliably and most often measured. Zeeman- and Hanle-effect based
probes have revealed many details of a rich variety of structures and
dynamic processes, but the number of open and debated questions has
remained large. The magnetic field in the quiet Sun has maintained
a particularly large number of secrets and has been a topic of a
particularly lively debate as new observations and analysis techniques
have revealed new and often unexpected aspects of its organization,
physical structure and origin.

---------------------------------------------------------
Title: Spectropolarimetric Diagnostics at the Solar Photosphere near
the Limb
Authors: Yelles Chaouche, L.; Solanki, S. K.; Rouppe van der Voort,
L.; van Noort, M.
2009ASPC..405..189Y Altcode: 2009arXiv0910.2885Y
In the present work, we investigate the formation of Stokes profiles
and spectro-polarimetric diagnostics in an active region plage near
the limb. We use 3-D radiation-MHD simulations with unipolar fields
of an average strength of 400 G, which is largely concentrated in
flux tubes in which the field reaches typical kilo-Gauss values. We
generate synthetic Stokes spectra by radiative transfer calculations,
then we degrade the simulated Stokes signal to account for observational
conditions. The synthetic data treated in this manner are compared with
and found to roughly reproduce spectro-polarimetric high-resolution
observations at μ=0.39 obtained by the SOUP instrument with the
Swedish 1-m Solar Telescope at the beginning of 2006.

---------------------------------------------------------
Title: Full Magnetic Field Vector of an Emerging Flux Region
Authors: Xu, Z.; Lagg, A.; Solanki, S. K.
2009ASPC..405..223X Altcode:
We present maps of the full magnetic field vector of an emerging flux
region in both the photosphere and chromosphere. The magnetic and
velocity structure of freshly emerged loops is determined.

---------------------------------------------------------
Title: Comparison Among Ca II K Spectroheliogram Time Series with
an Application to Solar Activity Studies
Authors: Ermolli, I.; Solanki, S. K.; Tlatov, A. G.; Krivova, N. A.;
Ulrich, R. K.; Singh, J.
2009ApJ...698.1000E Altcode:
Various observatories around the globe started regular full-disk imaging
of the solar atmosphere in the Ca II K line in the early decades of
the 20th century. The archives made by these observations have the
potential of providing far more detailed information on solar magnetism
than just the sunspot number and area records to which most studies
of solar activity and irradiance changes are restricted. We evaluate
the image quality and contents of three Ca II K spectroheliogram time
series, specifically those obtained by the digitization of the Arcetri,
Kodaikanal, and Mt Wilson photographic archives, in order to estimate
their value for studies focusing on timescales longer than the solar
cycle. We analyze the quality of these data and compare the results
obtained with those achieved for similar present-day observations
taken with the Meudon spectroheliograph and with the Rome-PSPT. We
also investigate whether image-segmentation techniques, such as
those developed for identification of plage regions on present-day Ca
II K observations, can be used to process historic series. We show
that historic data suffer from stronger geometrical distortions and
photometric uncertainties than similar present-day observations. The
latter uncertainties mostly originate from the photographic calibration
of the original data and from stray-light effects. We also show that
the image contents of the three analyzed series vary in time. These
variations are probably due to instrument changes and aging of the
spectrographs used, as well as changes of the observing programs. The
segmentation technique tested in this study gives reasonably consistent
results for the three analyzed series after application of a simple
photographic calibration. Although the plage areas measured from the
three analyzed series differ somewhat, the difference to previously
published results is larger.

---------------------------------------------------------
Title: Multi-Channel Observations of a Solar Flare
Authors: Hirzberger, J.; Riethmüller, T.; Solanki, S. K.; Kobel, P.
2009ASPC..405..125H Altcode:
On August 13, 2006 we performed simultaneous observations in Ca IIH,
G-band and Fe I 6303 Å of a complex sunspot in NOAA~10904 with
the Swedish Solar Telescope (SST) on La Palma, Canary Islands. From
spectro-polarimetric scans through the Fe I line with the tunable
SOUP filter we computed the full Stokes vectors at each pixel of the
field of view. At 8:47 UT a weak flare eruption (GOES class B7.8) was
registered in the line core of Ca IIH. We present the changing magnetic
field and flow topologies in the underneath penumbral photosphere
during the flaring phase. The unmatched spatial resolution of SST
observations allows detailed simultaneous mapping of chromospheric
and photospheric events.

---------------------------------------------------------
Title: Hanle Effect Diagnostics of the Coronal Magnetic Field:
A Test Using Realistic Magnetic Field Configurations
Authors: Raouafi, N. -E.; Solanki, S. K.; Wiegelmann, T.
2009ASPC..405..429R Altcode: 2008arXiv0801.2202R
Our understanding of coronal phenomena, such as coronal plasma
thermodynamics, faces a major handicap caused by missing coronal
magnetic field measurements. Several lines in the UV wavelength range
present suitable sensitivity to determine the coronal magnetic field
via the Hanle effect. The latter is a largely unexplored diagnostic
of coronal magnetic fields with a very high potential. Here we study
the magnitude of the Hanle-effect signal to be expected outside the
solar limb due to the Hanle effect in polarized radiation from the
H I Lyα and β lines, which are among the brightest lines in the
off-limb coronal FUV spectrum. For this purpose we use a magnetic field
structure obtained by extrapolating the magnetic field starting from
photospheric magnetograms. The diagnostic potential of these lines for
determining the coronal magnetic field, as well as their limitations
are studied. We show that these lines, in particular H I Lyβ, are
useful for such measurements.

---------------------------------------------------------
Title: Propagating waves in polar coronal holes as seen by SUMER
&amp; EIS
Authors: Banerjee, D.; Teriaca, L.; Gupta, G. R.; Imada, S.; Stenborg,
G.; Solanki, S. K.
2009A&A...499L..29B Altcode: 2009arXiv0905.1013B
Context: To study the dynamics of coronal holes and the role of waves in
the acceleration of the solar wind, spectral observations were performed
over polar coronal hole regions with the SUMER spectrometer on SoHO and
the EIS spectrometer on Hinode. Aims: Using these observations,
we aim to detect the presence of propagating waves in the corona and
to study their properties. Methods: The observations analysed
here consist of SUMER spectra of the Ne viii 770 Å line (T = 0.6 MK)
and EIS slot images in the Fe xii 195 Å line (T = 1.3 MK). Using the
wavelet technique, we study line radiance oscillations at different
heights from the limb in the polar coronal hole regions. Results:
We detect the presence of long period oscillations with periods of 10
to 30 min in polar coronal holes. The oscillations have an amplitude
of a few percent in radiance and are not detectable in line-of-sight
velocity. From the time distance maps we find evidence for propagating
velocities from 75 km s-1 (Ne viii) to 125 km s-1
(Fe xii). These velocities are subsonic and roughly in the same ratio
as the respective sound speeds. Conclusions: We interpret the
observed propagating oscillations in terms of slow magneto-acoustic
waves. These waves can be important for the acceleration of the fast
solar wind.

---------------------------------------------------------
Title: Constraints on O5+ Ions Kinetic Temperature Anisotropies in
the Polar Coronal Holes
Authors: Raouafi, Noureddine; Solanki, S.
2009SPD....40.1404R Altcode:
We present new constraints on the kinetic temperature anisotropies of
the O5+ ions in the polar coronal holes. Our analysis is based on the
observations of the Ultraviolet Coronagraph Spectrometer (UVCS) on the
Solar and Heliospheric Observatory (SOHO) spacecraft. We find that the
observations are consistently reproduced when considering anisotropies
less than 5 between heliocentric distances 2.0 Rsun and 2.7
Rsun. Below 2.0 Rsun and above 2.7 Rsun
no anisotropies or Tperpendicular/Tparallel
significantly smaller than 5 are sufficient to obtain the observed
spectral line profiles. Our analysis provides also height dependencies
of Tperpendicular and Tparallel. We also discuss
the possible existence of other mechanisms that may reduce kinetic
temperature anisotropies in the polar coronal holes.

---------------------------------------------------------
Title: On the relation between photospheric magnetic field and
chromospheric emission in the quiet Sun
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen M.
2009IAUS..259..185L Altcode:
In this contribution we present an observational study of the
interaction of the photosphere with different chromospheric layers. We
study the correlations between emissions at varying temperature from the
temperature minimum region (UV continuum at 1600 Å from TRACE) through
the low chromosphere (CaII K-line from BBSO) to the middle chromosphere
(continuum at 3.5 mm from BIMA) and photospheric magnetic field from
MDI/SOHO. For the first time millimeter observational data are included
in such analysis. We report a high degree of correlation between
considered emissions formed at different heights in the chromosphere. A
power law is found to be a good representation for the relationship
between photospheric magnetic field and chromospheric emissions at
all considered wavelengths. Our analysis shows that the dependence
of chromospheric intensities on magnetic field is different for the
network and internetwork regions. In the network a power law provides
the best fit with the exponent being close to 0.5-0.6, while almost
no dependence of chromospheric intensity on magnetic flux is found for
the cell interiors. The obtained results support the idea of different
heating mechanisms acting in the network (magnetic) and cell interiors
(acoustic).

---------------------------------------------------------
Title: The relationship between chromospheric emissions and magnetic
field strength
Authors: Loukitcheva, M.; Solanki, S. K.; White, S. M.
2009A&A...497..273L Altcode: 2009arXiv0910.1985L
Aims: We analyze observational data from 4 instruments to study the
correlations between chromospheric emission, spanning the heights
from the temperature minimum region to the middle chromosphere,
and photospheric magnetic field. Methods: The data consist of
radio images at 3.5 mm from the Berkeley-Illinois-Maryland Array
(BIMA), UV images at 1600 Å from TRACE, Ca II K-line filtergrams
from BBSO, and MDI/SOHO longitudinal photospheric magnetograms. For
the first time interferometric millimeter data with the highest
currently available resolution are included in such an analysis. We
determine various parameters of the intensity maps and correlate the
intensities with each other and with the magnetic field. Results:
The chromospheric diagnostics studied here show a pronounced similarity
in their brightness structures and map out the underlying photospheric
magnetic field relatively well. We find a power law to be a good
representation of the relationship between photospheric magnetic field
and emission from chromospheric diagnostics at all wavelengths. The
dependence of chromospheric brightness on magnetic field is found to
be different for network and internetwork regions.

---------------------------------------------------------
Title: Small-Scale Solar Magnetic Fields
Authors: de Wijn, A. G.; Stenflo, J. O.; Solanki, S. K.; Tsuneta, S.
2009SSRv..144..275D Altcode: 2008SSRv..tmp..190D; 2008SSRv..tmp..191D; 2008arXiv0812.4465D
As we resolve ever smaller structures in the solar atmosphere,
it has become clear that magnetism is an important component of
those small structures. Small-scale magnetism holds the key to many
poorly understood facets of solar magnetism on all scales, such as the
existence of a local dynamo, chromospheric heating, and flux emergence,
to name a few. Here, we review our knowledge of small-scale photospheric
fields, with particular emphasis on quiet-sun field, and discuss the
implications of several results obtained recently using new instruments,
as well as future prospects in this field of research.

---------------------------------------------------------
Title: Magnetic geometries of Sun-like stars: exploring the
mass-rotation plane
Authors: Petit, Pascal; Dintrans, B.; Aurière, M.; Catala, C.; Donati,
J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morgenthaler, A.;
Morin, J.; Paletou, F.; Ramirez Velez, J.; Solanki, S. K.; Théado, S.
2009IAUS..259..441P Altcode:
Sun-like stars are able to continuously generate a large-scale
magnetic field through the action of a dynamo. Various physical
parameters of the star are able to affect the dynamo output, in
particular the rotation and mass. Using the NARVAL spectropolarimeter
(Observatoire du Pic du Midi, France), it is now possible to measure
the large-scale magnetic field of solar analogues (i.e. stars very
close to the Sun in the mass-rotation plane, including strict solar
twins). From spectropolarimetric time-series, tomographic inversion
enables one to reconstruct the field geometry and its progressive
distortion under the effect of surface differential rotation. We
show the first results obtained on a sample of main-sequence dwarfs,
probing masses between 0.7 and 1.4 solar mass and rotation rates
between 1 and 3 solar rotation rate.

---------------------------------------------------------
Title: On the common solar signal in different cosmogenic isotope
data sets
Authors: Usoskin, Ilya G.; Horiuchi, Kazuho; Solanki, Sami; Kovaltsov,
Gennady A.; Bard, Edouard
2009JGRA..114.3112U Altcode: 2009JGRA..11403112U
In this article, we aim to determine frequency ranges and intervals
of time in which the solar signal dominates in different cosmogenic
isotope data. From a 14C-based reconstruction of cosmic ray
intensity over the last millennia, we computed expected 10Be
variations in two Antarctic sites (Dom Fuji and South Pole) and two
Greenland sites (Dye-3 and GISP-2) and compared them with the actually
measured 10Be abundance at the sites. By applying different
methods of analysis, such as bivariate correlation, conventional
FFT coherence, and wavelet coherence, we found the following: (1)
The modeled series, on the basis of 14C data, are in good
agreement with the measured 10Be data sets, on different
timescales and at different locations, confirming the existence of a
common solar signal in both isotope data. (2) The 10Be data
are driven by the solar signal on timescales from about 100 years up
to 1000 years or even to multimillennial scales (at the longer scales,
paleomagnetism plays an increasingly important role). (3) The local
climate dominates the 10Be data mostly on short (&lt;100
years) timescales, but the solar signal becomes important even at short
scales during periods of Grand minima of solar activity. (4) There is an
indication of a possible systematic uncertainty in the early Holocene,
likely due to a not-perfectly-stable thermohaline circulation, which
requires additional studies. We have shown that both 14C- and
10Be-based records are consistent with each other over a wide
range of timescales and time intervals. They form a robust basis for
quantitative reconstructions of solar activity variations in the past.

---------------------------------------------------------
Title: Multiple-spacecraft study of an extended magnetic structure
in the solar wind
Authors: Ruan, P.; Korth, A.; Marsch, E.; Inhester, B.; Solanki, S.;
Wiegelmann, T.; Zong, Q. -G.; Bucik, R.; Fornacon, K. -H.
2009JGRA..114.2108R Altcode: 2009JGRA..11402108R
An extended magnetic structure was observed consecutively by five
spacecraft (ACE, WIND, STEREO A and B, and CLUSTER) in the solar wind on
15 January 2007. The similar bipolar magnetic field variations from five
spacecraft suggest that the magnetic structure is two-dimensional. The
abrupt disappearance of the beam electrons in the core of the structure
suggests that the core of the structure is magnetically isolated from
the surrounding environment. Our analysis shows that this magnetic
structure is a magnetic flux rope, which extends over at least 180 R
E in space. The length and orientation of the flux rope were
determined by a local minimum variance analysis (MVA) from individual
spacecraft observations of the magnetic field and a timing analysis
based on the joint observations by all five spacecraft. The results
show that the orientation of the flux rope stays constant in space
and time. The flux rope is embedded in a corotating interaction region
(CIR), which followed a magnetic cloud.

---------------------------------------------------------
Title: Zeeman Broadening in Cool Stars
Authors: Anderson, Richard I.; Reiners, Ansgar; Solanki, Sami K.;
Lagg, Andreas
2009AIPC.1094..708A Altcode: 2009csss...15..708A
We investigate detectability of magnetic fields by Zeeman broadening
of well-isolated spectral lines in F, G and K type stars. Data of
unprecedented quality were taken with CES1 mounted on the 3.6
m ESO telescope at La Silla, Chile, in three campaigns in the optical
range between 5770 Å and 6280 Å, each with a wavelength coverage
of roughly 40 Å. We use the SPINOR/STOPRO (cf. Frutiger et al. [1])
package developed by ETH2 and MPS3 to perform
spectral line inversion via χ2 minimization. Starting from
constraints given by previous measurements of stellar parameters,
we fit a number of extracted spectral lines. Eventually, our goal
is to determine the product of the magnetic field strength B and the
surface filling factor, B×f. Our work is in progress and thus
no final measurements can be presented at this stage.

---------------------------------------------------------
Title: Slow magnetoacoustic standing waves in a curved solar
coronal slab
Authors: Ogrodowczyk, R.; Murawski, K.; Solanki, S. K.
2009A&A...495..313O Altcode:
Aims: We consider a model of a two-dimensional solar coronal arcade to
explore the effects of a curved magnetic field topology on excitation
and attenuation of slow magnetoacoustic standing waves. Methods:
The time-dependent ideal magnetohydrodynamic equations are solved
numerically to find the spatial and temporal signatures of these
waves. Results: A pulse in gas pressure initially launched at
a loop footpoint excites the fundamental mode of slow magnetoacoustic
standing waves. The typical excitation time of such a wave mode is 2.5
wave periods, with a similar attenuation timescale. These values are
remarkably similar to those recovered from observations by SOHO/SUMER in
an Fe XIX line. Conclusions: Slow magnetoacoustic standing waves
are excited and attenuated more efficiently in curved magnetic field
lines than in a straight magnetic slab topology. The waves supported
by the magnetic arcade are in far closer agreement with observations.

---------------------------------------------------------
Title: Towards Long-Term Solar Irradiance Modelling: Network Contrasts
from Magneto-Convection Simulations
Authors: Unruh, Y. C.; Solanki, S. K.; Schüssler, M.; Vögler, A.;
Garcia-Alvarez, D.
2009AIPC.1094..768U Altcode: 2009csss...15..768U
Solar irradiance changes on a wide range of time scales and is a key
driver of the Earth's climate where secular variability in particular is
relevant. This is, however, not well understood and our knowledge relies
on reconstructions based on sunspot numbers and similar proxies. The prime candidate to produce secular variability is a change
in the surface coverage of small-scale magnetic elements. Direct
observational determination of the flux emitted by these magnetic
elements is difficult, especially as information covering a large
spectral range is needed. Here we present a theoretical approach
to this problem using intensity calculations from 3-D simulations
of solar magneto-convection and compare these with the intensity
calculations used in the successful semi-empirical S ATIRE models at
disk centre. Eventually, such a comparison should lead to the removal
of the last free parameter from S ATIRE-based irradiance reconstruction.

---------------------------------------------------------
Title: Faculae and Plague
Authors: Solanki, Sami; Krivova, Natalie
2009LanB...4B..153S Altcode: 2009LanB...4B.4124S
No abstract at ADS

---------------------------------------------------------
Title: Sunspots
Authors: Solanki, Sami; Krivova, Natalie
2009LanB...4B..141S Altcode: 2009LanB...4B.4123S
No abstract at ADS

---------------------------------------------------------
Title: The Origin and Dynamics of Solar Magnetism
Authors: Thompson, M. J.; Balogh, A.; Culhane, J. L.; Nordlund, Å.;
Solanki, S. K.; Zahn, J. -P.
2009odsm.book.....T Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Space Missions: present and future
Authors: Solanki, Sami K.; Marsch, Eckart
2009RvMA...21..229S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Solar Chromosphere: Old Challenges, New Frontiers
Authors: Ayres, T.; Uitenbroek, H.; Cauzzi, G.; Reardon, K.; Berger,
T.; Schrijver, C.; de Pontieu, B.; Judge, P.; McIntosh, S.; White,
S.; Solanki, S.
2009astro2010S...9A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Activity Cycle
Authors: Solanki, Sami; Krivova, Natalie
2009LanB...4B..124S Altcode: 2009LanB...4B.4122S
No abstract at ADS

---------------------------------------------------------
Title: Dynamos and magnetic fields of the Sun and other cool stars,
and their role in the formation and evolution of stars and in the
habitability of planets
Authors: Schrijver, Karel; Carpenter, Ken; Karovska, Margarita; Ayres,
Tom; Basri, Gibor; Brown, Benjamin; Christensen-Dalsgaard, Joergen;
Dupree, Andrea; Guinan, Ed; Jardine, Moira; Miesch, Mark; Pevtsov,
Alexei; Rempel, Matthias; Scherrer, Phil; Solanki, Sami; Strassmeier,
Klaus; Walter, Fred
2009astro2010S.262S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Small-Scale Solar Magnetic Fields
Authors: de Wijn, A. G.; Stenflo, J. O.; Solanki, S. K.; Tsuneta, S.
2009odsm.book..275D Altcode:
As we resolve ever smaller structures in the solar atmosphere,
it has become clear that magnetism is an important component of
those small structures. Small-scale magnetism holds the key to many
poorly understood facets of solar magnetism on all scales, such as the
existence of a local dynamo, chromospheric heating, and flux emergence,
to name a few. Here, we review our knowledge of small-scale photospheric
fields, with particular emphasis on quiet-sun field, and discuss the
implications of several results obtained recently using new instruments,
as well as future prospects in this field of research.

---------------------------------------------------------
Title: German Data Center for the Solar Dynamics Observatory:
A model for the PLATO mission?
Authors: Burston, R.; Gizon, L.; Saidi, Y.; Solanki, S. K.
2008CoAst.157..293B Altcode:
The German Data Center for the Solar Dynamics Observatory
(GDC-SDO), hosted by the Max Planck Institute for Solar System
Research in Germany, will provide access to SDO data for the
German solar physics community. The GDC-SDO will make available
all the relevant Helioseismic and Magnetic Imager (HMI) data
for helioseismology and smaller se- lected Atmospheric Imaging
Assembly (AIA) data sets. This project commenced in August 2007
and is funded by the German Aerospace Center (Deutsches zentrum
fuer Luft- und Raumfahrt or DLR) until December 2012. An important
component of the GDC-SDO is the Data Record Management System (DRMS),
developed in collaboration with the Stan- ford/Lockheed Joint Science
Operations Center (JSOC). The PEGASUS workflow manage- ment system
will be used to implement GDC-SDO data analysis pipelines. This
makes use of the CONDOR High Throughput Computing Project for
optimal job scheduling and also the GLOBUS Toolkit to enable grid
technologies. Additional information about the GDC-SDO can be found at
http://www.mps.mpg.de/projects/seismo/GDC1/index.html. Here, we sug-
gest a similar structure and philosophy should be ideal for the PLATO
mission, which looks for planetary transits and stellar oscillations
and is being studied by ESA for an M-Mission slot in Cosmic Vision.

---------------------------------------------------------
Title: A nanoflare model for active region radiance: application of
artificial neural networks
Authors: Bazarghan, M.; Safari, H.; Innes, D. E.; Karami, E.; Solanki,
S. K.
2008A&A...492L..13B Altcode: 2008arXiv0808.3925B
Context: Nanoflares are small impulsive bursts of energy that blend with
and possibly make up much of the solar background emission. Determining
their frequency and energy input is central to understanding the
heating of the solar corona. One method is to extrapolate the energy
frequency distribution of larger individually observed flares to
lower energies. Only if the power law exponent is greater than 2 is
it considered possible that nanoflares contribute significantly to
the energy input. Aims: Time sequences of ultraviolet line
radiances observed in the corona of an active region are modelled
with the aim of determining the power law exponent of the nanoflare
energy distribution. Methods: A simple nanoflare model based
on three key parameters (the flare rate, the flare duration, and
the power law exponent of the flare energy frequency distribution)
is used to simulate emission line radiances from the ions Fe XIX,
Ca XIII, and Si III, observed by SUMER in the corona of an active
region as it rotates around the east limb of the Sun. Light curve
pattern recognition by an Artificial Neural Network (ANN) scheme is
used to determine the values. Results: The power law exponents,
α≈2.8, 2.8, and 2.6 are obtained for Fe XIX, Ca XIII, and Si III
respectively. Conclusions: The light curve simulations imply
a power law exponent greater than the critical value of 2 for all
ion species. This implies that if the energy of flare-like events is
extrapolated to low energies, nanoflares could provide a significant
contribution to the heating of active region coronae.

---------------------------------------------------------
Title: Brightness, distribution, and evolution of sunspot umbral dots
Authors: Riethmüller, T. L.; Solanki, S. K.; Zakharov, V.;
Gandorfer, A.
2008A&A...492..233R Altcode: 2008arXiv0812.0477R
Context: Umbral Dots (UDs) are thought to be manifestations
of magnetoconvection in sunspot umbrae. Recent advances in their
theoretical description point to the need for a thorough study of their
properties and evolution based on data with the highest currently
achievable resolution. Aims: Our UD analysis aims to provide
parameters such as lifetimes, diameters, horizontal velocities, and
peak intensities, as well as the evolution of selected parameters. Methods: We present a 106-min TiO (705.7 nm) time series of high
spatial and temporal resolution that contains thousands of UDs in
the umbra of a mature sunspot in the active region NOAA 10667 at μ =
0.95. The data were acquired with the 1-m Swedish Solar Telescope (SST)
on La Palma. With the help of a multilevel tracking (MLT) algorithm the
sizes, brightnesses, and trajectories of 12 836 umbral dots were found
and extensively analyzed. The MLT allows UDs with very low contrast to
be reliably identified. Results: Inside the umbra we determine a
UD filling factor of 11%. The histogram of UD lifetimes is monotonic,
i.e. a UD does not have a typical lifetime. Three quarters of the UDs
lived for less than 150 s and showed no or little motion. The histogram
of the UD diameters exhibits a maximum at 225 km, i.e. most of the
UDs are spatially resolved. UDs display a typical horizontal velocity
of 420 m s-1 and a typical peak intensity of 51% of the
mean intensity of the quiet photosphere, making them on average 20%
brighter than the local umbral background. Almost all mobile UDs (large
birth-death distance) were born close to the umbra-penumbra boundary,
move towards the umbral center, and are brighter than average. Notably
bright and mobile UDs were also observed along a prominent UD chain,
both ends of which are located at the umbra-penumbra boundary. Their
motion started primarily at either of the ends of the chain, continued
along the chain, and ended near the chain's center. We observed the
splitting and merging of UDs and the temporal succession of both. For
the first time the evolution of brightness, size, and horizontal speed
of a typical UD could be determined in a statistically significant
way. Considerable differences between the evolution of central and
peripheral UDs are found, which point to a difference in origin.

---------------------------------------------------------
Title: Future high-latitude observations anticipated from the Solar
Orbiter mission
Authors: Woch, J.; Solanki, S. K.; Marsch, E.
2008AGUFMSH44A..08W Altcode:
As one of the cornerstones of the HELEX programme, the Solar Orbiter
mission is currently scheduled for launch in 2015. After an initial
cruise phase, Solar Orbiter will reach its science orbit in 2018. This
orbit comprises initially a nearly Sun-synchronous phase at a distance
of only 0.22 AU from Sun center. In a later stage, the orbital
inclination will be raised, thus allowing Solar Orbiter to reach
solar latitudes of about 35 degrees, and making it the first mission
after Ulysses to study the Sun from a high-latitude vantage point. In
contrast to Ulysses, however, Solar Orbiter will carry a complementary
suite of both, in-situ and remote- sensing instruments, which will
allow the study of the solar atmosphere to be extended to the largely
unexplored polar regions of the Sun. The polar magnetic fields are
responsible for the polar coronal holes driving the fast solar wind,
but are poorly known. From its vantage point outside the ecliptic,
Solar Orbiter will uncover the surface and sub-surface flows at the
poles, the polar magnetic field structure and its evolution. It will
provide new insights into the formation of the polar coronal holes,
the nature of their boundaries and the acceleration of the fast
solar wind emanating from the holes. The potential of Solar Orbiter
for investigating the acceleration mechanism of the fast wind, the
plumes and X-ray jets at the poles, and the high-latitude meridional
circulation will be discussed.

---------------------------------------------------------
Title: Magnetic geometries of Sun-like stars : impact of rotation
Authors: Petit, P.; Dintrans, B.; Aurière, M.; Catala, C.; Donati,
J. -F.; Fares, R.; Gastine, T.; Lignières, F.; Morin, J.; Paletou,
F.; Ramirez, J.; Solanki, S. K.; Théado, S.
2008sf2a.conf..523P Altcode:
Sun-like stars are able to continuously generate a large-scale magnetic
field through the action of a dynamo. Various physical parameters
of the star are able to affect the dynamo output, in particular the
rotation and mass. Using new generation stellar spectropolarimeters
(ESPaDOnS@CFHT, NARVAL@TBL), it is now possible to measure the
large-scale magnetic field of solar analogues (i.e. stars very close
to the Sun in the stellar-parameter plane, including strict solar
twins). From spectropolarimetric time-series, tomographic inversion
of polarized Zeeman signatures allows us to reconstruct the field
geometry and its progressive distortion under the effect of surface
differential rotation. We detail the first results obtained on a sample
of four main-sequence dwarfs, with masses close to 1 solar mass and
rotation rates between 1 and 3 solar rotation rate.

---------------------------------------------------------
Title: Are There Field-Free Gaps near τ = 1 in Sunspot Penumbrae?
Authors: Borrero, J. M.; Solanki, S. K.
2008ApJ...687..668B Altcode: 2008arXiv0806.4454B
The vertical stratification of the magnetic field strength in sunspot
penumbrae is investigated by means of spectropolarimetric observations
at high spatial resolution from the Hinode spacecraft. Assuming that
the magnetic field changes linearly with optical depth we find that, in
those regions where the magnetic field is more inclined and the Evershed
flow is strongest (penumbral intraspines), the magnetic field can either
increase or decrease with depth. Allowing more degrees of freedom to the
magnetic field stratification reveals that the magnetic field initially
decreases from log τ5 = - 3 until log τ5simeq -
1.0, but increases again below that. The presence of strong magnetic
fields near the continuum is at odds with the existence of regions
void of magnetic fields at, or right below, the τ5 = 1
level in the penumbra. However, they are compatible with the presence
of a horizontal flux-tube-like field embedded in a magnetic atmosphere.

---------------------------------------------------------
Title: SUMER observations of the inverse Evershed effect in the
transition region above a sunspot
Authors: Teriaca, L.; Curdt, W.; Solanki, S. K.
2008A&A...491L...5T Altcode: 2009arXiv0901.3317T
Aims: We analyse SUMER spectral scans of a large sunspot within active
region NOAA 10923, obtained on 14-15 November 2006, to determine
the morphology and dynamics of the sunspot atmosphere at different
heights/temperatures. Methods: The data analysed here consist
of spectroheliograms in the continuum around 142.0 nm and in the Si
iv 140.2 nm, O iii 70.3 nm, N iv 76.5 nm, and O iv 79.0 nm spectral
lines. Gaussian-fitting of the observed profiles provides line-of-sight
velocity and Doppler-width maps. Results: The data show an
asymmetric downflow pattern compatible with the presence of the inverse
Evershed flow in a region within roughly twice the penumbral radius
at transition-region temperatures up to 0.18 MK. The motions, highly
inhomogeneous on small scales, seem to occur in a collar of radially
directed filamentary structures, with an average width less than the 1
Mm spatial resolution of SUMER and characterised by different plasma
speeds. Assuming that the flows are directed along the field lines,
we deduce that such field lines are inclined by 10° to 25° with
respect to the solar surface.

---------------------------------------------------------
Title: Identification of different types of kink modes in coronal
loops: principles and application to TRACE results
Authors: Wang, T. J.; Solanki, S. K.; Selwa, M.
2008A&A...489.1307W Altcode: 2008arXiv0808.0685W
We explore the possible observational signatures of different types of
kink modes (horizontal and vertical oscillations in their fundamental
mode and second harmonic) that may arise in coronal loops, with the
aim of determining how well the individual modes can be uniquely
identified from time series of images. A simple, purely geometrical
model is constructed to describe the different types of kink-mode
oscillations. These are then “observed” from a given direction. In
particular, we employ the 3D geometrical parameters of 14 TRACE loops
of transverse oscillations to try to identify the correct observed wave
mode. We find that for many combinations of viewing and loop geometry
it is not straightforward to distinguish between at least two types of
kink modes just using time series of images. We also considered Doppler
signatures and find that these can help obtain unique identifications of
the oscillation modes when employed in combination with imaging. We then
compare the modeled spatial signatures with the observations of 14 TRACE
loops. We find that out of three oscillations previously identified
as fundamental horizontal mode oscillations, two cases appear to be
fundamental vertical mode oscillations (but possibly combined with the
fundamental horizontal mode), and one case appears to be a combination
of the fundamental vertical and horizontal modes, while in three cases
it is not possible to clearly distinguish between the fundamental mode
and the second-harmonic of the horizontal oscillation. In five other
cases it is not possible to clearly distinguish between a fundamental
horizontal mode and the second-harmonic of a vertical mode.

---------------------------------------------------------
Title: Loop Morphology and Flows and their Relation to the Magnetic
Field
Authors: Teriaca, L.; Wiegelmann, T.; Lagg, A.; Solanki, S. K.; Curdt,
W.; Sekii, T.
2008ASPC..397..196T Altcode:
In November 2006 we obtained several rasters of a large sunspot
and its trailing region using the SUMER spectrometer on SOHO. The
observations consist of spectroheliograms in the continuum around
142 nm and in several spectral lines formed between 80000 K and
0.6 MK, covering the temperature range from the chromosphere to
the lower corona. The observed profiles provide LOS velocity and
Doppler width maps. TRACE images in the EUV passbands and in the 160
nm continuum provide a clear picture of the coronal loops and the
chromosphere near their footpoints. The same target was also observed
by all the instruments aboard Hinode and, in particular, by the SOT
spectro-polarimeter measuring the photospheric magnetic vector. We
combined SOT and MDI data (covering a larger FOV) to infer the coronal
magnetic field of the active region by a nonlinear force-free field
extrapolation. The observed radiance and velocity patterns at the
various heights/temperatures throughout the solar atmosphere are
compared with the field topology.

---------------------------------------------------------
Title: Fibrils in Ca II K
Authors: Pietarila, A.; Solanki, S.; Hirzberger, J.; Zakharov, V.
2008ESPM...12.2.51P Altcode:
High spatial resolution observations have revealed that fibril-like
structures are a ubiquitous feature of the solar chromosphere. They are
observed in most chromospheric lines, e.g., H-? and Ca II IRT. Until
recently, there have been no reports of these structures in the Ca
II H and K lines. Instead, these lines have revealed a hazy, uniform
chromosphere and only in the highest resolution images have there been
any indications of fibril structures. We present high spatial
resolution Ca II K observations from the Swedish Solar Telescope
which show that fibrils are a prevailing feature in regions where
the bulk of the signal is chromospheric. Based on the cotemporal
continuum and nearly cotemporal magnetic field observations it is
clear that the fibril foot points originate from photospheric magnetic
concentrations. The fibrils share many characteristics, e.g. lifetime
and dynamics, with fibrils observed in other spectral lines. They are
also found to play an important role in the dynamics: in the plage
they channel low frequency waves into the chromosphere while in the
more quiet regions the highly inclined fibrils form a multi-layer
canopy that suppresses oscillations from below.

---------------------------------------------------------
Title: The Magnetic Vector Structure of an Active Region Plage Field
Authors: Meling, M. H. M.; Lagg, A.; Solanki, S. K.
2008ESPM...12.2.58M Altcode:
We present scans of the active region plage associated with NOAA 10953,
recorded with the Tenerife Infrared Polarimeter 2 (TIP-2) mounted
behind the German Vacuum Tower Telescope (VTT) on Tenerife and the
SOT-SP instrument on-board the HINODE spacecraft. TIP-2 recorded the
full Stokes vector close to the diffraction limit of the telescope over
a 20 angstroem wavelength range containing six magnetically sensitive
FeI lines in the infrared including the g=3 line FeI 15648.5. With
these lines we use the advantage that the Zeeman splitting dominates
over the Doppler broadening for kG fields. The iron lines used by
HINODE are FeI 6301.501and FeI 6302.494. We analyzed the data by
applying a Milne-Eddington type inversion to it. In the context of a
two-component model we found a bimodal distribution of field strengths,
strong fields whose field strength distribution peaks at 1400 [G]
and a weak field distribution, which may be associated with quiet sun
regions bordering on the plage.

---------------------------------------------------------
Title: Spectropolarimetric Investigations of the Deep Photospheric
Layers of Magnetic Elements
Authors: Oklay, N.; Gandorfer, A.; Solanki, S. K.
2008ESPM...12.2.49O Altcode:
We observed simultaneously Stokes I and Stokes V/I profiles of Fe I
(5379.574Å), C I(5380.332Å), Ti II(5381.021Å) and Fe I(5383.369Å)
using the ZIMPOL II spectropolarimeter at the IRSOL (Istituto Ricerche
Solari Locarno) facility. This set of spectral lines covers not only
the mid-photosphere but also the deep photospheric layers, where
the temperature sensitive C I line is formed. We analyzed ratios
and asymmetries of their Stokes V amplitudes and areas. Further,
the spectral profiles were analyzed using the SPINOR inversion code
(Frutiger et al. 2000) to constrain the temperature structure of
the magnetic elements down to deep photospheric layers. In this way,
our understanding of the lowest photospheric layers of solar magnetic
elements can be tested.

---------------------------------------------------------
Title: Structure and Evolution of Supergranulation from Local
Helioseismology
Authors: Hirzberger, Johann; Gizon, Laurent; Solanki, Sami K.; Duvall,
Thomas L.
2008SoPh..251..417H Altcode: 2008SoPh..tmp..106H
Supergranulation is visible at the solar surface as a cellular
pattern of horizontal outflows. Although it does not show a distinct
intensity pattern, it manifests itself indirectly in, for example,
the chromospheric network. Previous studies have reported significant
differences in the inferred basic parameters of the supergranulation
phenomenon. Here we study the structure and temporal evolution of a
large sample of supergranules, measured by using local helioseismology
and SOHO/MDI data from the year 2000 at solar activity minimum. Local
helioseismology with f modes provides maps of the horizontal divergence
of the flow velocity at a depth of about 1 Mm. From these divergence
maps supergranular cells were identified by using Fourier segmentation
procedures in two dimensions and in three dimensions (two spatial
dimensions plus time). The maps that we analyzed contain more than
105 supergranular cells and more than 103
lifetime histories, which makes possible a detailed analysis with high
statistical significance. We find that the supergranular cells have
a mean diameter of 27.1 Mm. The mean lifetime is estimated to be 1.6
days from the measured distribution of lifetimes (three-dimensional
segmentation), with a clear tendency for larger cells to live longer
than smaller ones. The pair and mark correlation functions do not
show pronounced features on scales larger than the typical cell size,
which suggests purely random cell positions. The temporal histories of
supergranular cells indicate a smooth evolution from their emergence
and growth in the first half of their lives to their decay in the
second half of their lives (unlike exploding granules, which reach
their maximum size just before they fragment).

---------------------------------------------------------
Title: Evidence of convective rolls in a sunspot penumbra
Authors: Zakharov, V.; Hirzberger, J.; Riethmüller, T. L.; Solanki,
S. K.; Kobel, P.
2008A&A...488L..17Z Altcode: 2008arXiv0808.2317Z
Aims: We study the recently discovered twisting motion of bright
penumbral filaments with the aim of constraining their geometry and
the associated magnetic field. Methods: A large sunspot located
40° from disk center was observed at high resolution with the 1-m
Swedish Solar Telescope. Inversions of multi-wavelength polarimetric
data and speckle reconstructed time series of continuum images were
used to determine proper motions, as well as the velocity and magnetic
structure in penumbral filaments. Results: The continuum movie
reveals apparent lateral motions of bright and dark structures inside
bright filaments oriented parallel to the limb, confirming recent
Hinode results. In these filaments we measure upflows of ≈1.1
km s-1 on their limbward side and weak downflows on
their centerward side. The magnetic field in them is significantly
weaker and more horizontal than in the adjacent dark filaments. Conclusions: The data indicate the presence of vigorous convective
rolls in filaments with a nearly horizontal magnetic field. These
are separated by filaments harbouring stronger, more vertical
fields. Because of reduced gas pressure, we see deeper into the
latter. When observed near the limb, the disk-centerward side of the
horizontal-field filaments appear bright due to the hot wall effect
known from faculae. We estimate that the convective rolls transport
most of the energy needed to explain the penumbral radiative flux.

---------------------------------------------------------
Title: Discriminant Analysis of Bright Points and Faculae:
Center-to-Limb Distribution, Contrast and Morphology
Authors: Kobel, P.; Hirzberger, J.; Gandorfer, A.; Solanki, S. K.;
Zakharov, V.
2008ESPM...12.2.60K Altcode:
High-resolution images of the solar photosphere reveal an intriguing
mixture of Brights Points (BPs) and faculae at several disk positions,
which is not explained by the conventional "hot wall” model. Together
with quantitative discrepancies between observations and simulations
of faculae, it stresses that the fundamental relationship between BPs
and faculae is not yet clear: How are BPs and faculae distributed on
the solar disk? How do the photometric properties of BPs and faculae
differ and vary with disk position? To tackle these issues, a
necessary step is to sort the BPs and faculae at various disk positions,
in order to treat them separately. We present here the first attempt
to discriminate BPs and faculae, using a statistical classification
approach based on Linear Discriminant Analysis (LDA). This has never
been done so far, presumably due to the lack of known automated methods
to distinguish such features, and to the difficulty to obtain a coherent
dataset of high-resolution images recorded in the same conditions. We
applied our method to high-resolution G-band and continuum images
of active regions recorded at the Swedish Solar Telescope, covering
several disk positions where the transition from BPs to faculae
is expected. This allowed us to retrieve a first estimate of
the center-to-limb variation of the relative distribution of both
species. The center-to-limb distribution of BPs and faculae reveals
the predominance of faculae at all disk positions except close to disk
center. We argue that these ubiquitous faculae could be the transient
signatures of swaying flux tubes with a wide range of inclination
angles. Moreover, we statistically compared the G-band and continuum
contrast of BPs and faculae, and characterized their morphology. Both
the G-band and continuum contrast of BPs and faculae are found to
similarly increase from center to limb. But when comparing G-band
to continuum, BPs and faculae exhibit slightly different behaviours,
which are related to radiative transfer processes. By orienting the
features in local coordinate frames corresponding to the principal axes
of their contrast moment of inertia, we could retrieve characteristic
G-band contrast profiles exhibiting the typical predicted asymmetry
for faculae. Finally, our BPs and faculae were found to have very
similar morphological properties. Although our study is essentially
descriptive and based on purely photometric information, we hope that it
will provide novel useful constraints for future BPs/faculae MHD models.

---------------------------------------------------------
Title: The Solar Chromosphere at Millimeter Wavelengths
Authors: Loukitcheva, M.; Solanki, S. K.; White, S.
2008ESPM...12.2.18L Altcode:
The solar chromosphere remains the least understood layer of the
solar atmosphere. There is yet no answer to the question concerning
its structure. Is it better described by the classical picture of a
steady temperature rise as a function of height, with superposed weak
oscillations, or does the temperature keep dropping outwards, with hot
shocks producing strong localized heating? Observations in the UV and
the IR give contrasting results, since they only sample either the
hot or the cool parts of the chromosphere. Computations carried out
with sophisticated dynamic models of the solar chromosphere demonstrate
that millimeter emission is extremely sensitive to dynamic processes in
the chromosphere and the appropriate wavelengths to look for dynamic
signatures are in the range 0.8-5.0 mm. The models also suggest
that high resolution observations at mm wavelengths have the unique
property of reacting to both the hot and the cool gas, and thus have the
potential of distinguishing between models. In this contribution
we use high-resolution millimeter-interferometer observations, obtained
with the Berkeley-Illinois-Maryland Array at 3.5 mm (resolution of
12 arcsec), as a diagnostic tool to study the thermal structure of
the solar chromosphere and its response to dynamic processes. Our initial results obtained from the observations of the quiet
Sun reveal brightness features corresponding to supergranular network
boundaries and bright points within the cells. We found significant
intensity oscillations with frequencies of 1.5-8 mHz with a tendency
toward short-period oscillations in internetwork and longer periods in
network regions. However higher spatial resolution is required for a
clean separation between the brightness features and for an adequate
comparison with the output of the comprehensive dynamic simulations.

---------------------------------------------------------
Title: Magnetic Structure of a Filament during its Phase of Activity
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
2008ESPM...12.2.19S Altcode:
We analyze and interpret spectropolarimetric observations of an active
region filament located close to the solar disc center, during its
phase of activity. The observations are obtained in the chromospheric
He I lines at 1083.0 nm. We provide novel observational results on the
magnetic field measurements in solar filaments to give constraints
to the theoretical models of their support in the solar corona. Our
main goal is to interpret the behavior of the atmospheric parameters
retrieved from the spectropolarimetric data to give a picture of
the magnetic structure of the observed filament. The analysis of the
observed polarization of the He I 1083.0 nm multiplet in the filament,
carried out by inverting the Stokes profiles, reveals the presence of
different unresolved atmospheric components of the He lines, coexisting
within the resolution element (1.2 arcsec). The different components,
belonging to different magnetic field lines, show supersonic up-
and downflows, sometimes within the same resolution element. The He
blueshifted components belong to mostly transversal field lines in
the body of the filament. These field lines are found to be curving
upwards on both sides. This picture suggests the presence of dipped
field lines that are moving upward, carrying with them the filament
material. During this movement, we also observe filament material
flowing down along field lines having the same polarity as the
photospheric field (i.e. they have the opposite inclination with
respect to the dipped field lines). These downflows are faster at the
filament end points and can reach values close to 10 times the speed of
sound. The field lines are found to be almost parallel to the filament
axis in the plane perpendicular to the line of sight. We use the two
main theoretical models of prominence support (dip or flux rope models)
to interpret the results obtained.

---------------------------------------------------------
Title: Comparison of Magnetoconvection Simulations with the
Approximation of Thin Flux Tubes
Authors: Yelles Chaouche, L.; Solanki, S.; Schuessler, M.
2008ESPM...12..3.8Y Altcode:
The structure and dynamics of small vertical photospheric magnetic
flux concentrations has been often treated in the framework of
an approximation based upon a low-order truncation of the Taylor
expansions of all quantities in the horizontal direction, together with
the assumption of instantaneous total pressure balance at the boundary
to the non-magnetic external medium. Formally, such an approximation
is justified if the diameter of the structure (a flux tube or a
flux sheet) is small compared to all other relevant length scales
(scale height, radius of curvature, wavelength, etc.). The advent of
realistic 3D radiative MHD simulations opens the possibility to check
the consistency of the approximation with the properties of the flux
concentrations that form in the course of the simulation. We make
a comparative analysis between the thin flux tube/sheet model and
flux concentrations existing in a 3D radiation-MHD simulation. We
have found that for flux concentration well above the equipartition
distribution, the MHD magnetic structures are reasonably well reproduced
by the second-order thin flux tube/sheet approximation. The differences
between approximation and simulation are due to the asymmetry and the
dynamics of the simulated structures.

---------------------------------------------------------
Title: Evidence for Polar Jets as Precursors of Polar Plume Formation
Authors: Raouafi, N. -E.; Petrie, G. J. D.; Norton, A. A.; Henney,
C. J.; Solanki, S. K.
2008ApJ...682L.137R Altcode: 2008arXiv0806.3045R
Observations from the Hinode/XRT telescope and STEREO/SECCHI/EUVI
are utilized to study polar coronal jets and plumes. The study
focuses on the temporal evolution of both structures and their
relationship. The data sample, spanning 2007 April 7-8, shows that
over 90% of the 28 observed jet events are associated with polar
plumes. EUV images (STEREO/SECCHI) show plume haze rising from the
location of approximately 70% of the polar X-ray (Hinode/XRT) and EUV
jets, with the plume haze appearing minutes to hours after the jet was
observed. The remaining jets occurred in areas where plume material
previously existed, causing a brightness enhancement of the latter after
the jet event. Short-lived, jetlike events and small transient bright
points are seen (one at a time) at different locations within the base
of preexisting long-lived plumes. X-ray images also show instances
(at least two events) of collimated thin jets rapidly evolving into
significantly wider plumelike structures that are followed by the
delayed appearance of plume haze in the EUV. These observations provide
evidence that X-ray jets are precursors of polar plumes and in some
cases cause brightenings of plumes. Possible mechanisms to explain
the observed jet and plume relationship are discussed.

---------------------------------------------------------
Title: SUNRISE: High resolution UV/VIS observations of the sun from
the stratosphere
Authors: Sunrise Team; Barthol, P.; Gandorfer, A. M.; Solanki,
S. K.; Knölker, M.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.;
SUNRISE Team
2008AdSpR..42...70S Altcode:
SUNRISE is an international project for the development, construction
and operation of a balloon-borne solar telescope with an aperture
of 1 m, working in the UV/VIS spectral domain. The main scientific
goal of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
near diffraction-limited images of the photosphere and chromosphere
with an unprecedented resolution down to 35 km on the solar surface
at wavelengths around 220 nm. Active in-flight alignment and image
stabilization techniques are used. The focal-plane instrumentation
consists of a polarization sensitive spectrograph, a Fabry Perot
filter magnetograph and a phase-diverse filter imager working in
the near UV. The first stratospheric long-duration balloon flight
of SUNRISE is planned in summer 2009 from the Swedish ESRANGE
station. SUNRISE is a joint project of the German Max-Planck-Institut
für Sonnensystemforschung (MPS), Katlenburg-Lindau, with the
Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, Germany, the
High-Altitude Observatory (HAO), Boulder, USA, the Lockheed-Martin
Solar and Astrophysics Laboratory (LMSAL), Palo Alto, USA, and the
Spanish IMaX consortium. This paper will give an overview about the
mission and a description of its scientific and technological aspects.

---------------------------------------------------------
Title: Toroidal versus poloidal magnetic fields in Sun-like stars:
a rotation threshold
Authors: Petit, P.; Dintrans, B.; Solanki, S. K.; Donati, J. -F.;
Aurière, M.; Lignières, F.; Morin, J.; Paletou, F.; Ramirez Velez,
J.; Catala, C.; Fares, R.
2008MNRAS.388...80P Altcode: 2008MNRAS.tmp..715P; 2008arXiv0804.1290P
From a set of stellar spectropolarimetric observations, we report
the detection of surface magnetic fields in a sample of four
solar-type stars, namely HD 73350, HD 76151, HD 146233 (18 Sco) and HD
190771. Assuming that the observed variability of polarimetric signal
is controlled by stellar rotation, we establish the rotation periods of
our targets, with values ranging from 8.8 d (for HD 190771) to 22.7 d
(for HD 146233). Apart from rotation, fundamental parameters of the
selected objects are very close to the Sun's, making this sample
a practical basis to investigate the specific impact of rotation
on magnetic properties of Sun-like stars. We reconstruct the
large-scale magnetic geometry of the targets as a low-order (l &lt; 10)
spherical harmonic expansion of the surface magnetic field. From the set
of magnetic maps, we draw two main conclusions. (i) The magnetic energy
of the large-scale field increases with rotation rate. The increase
in chromospheric emission with the mean magnetic field is flatter than
observed in the Sun. Since the chromospheric flux is also sensitive to
magnetic elements smaller than those contributing to the polarimetric
signal, this observation suggests that a larger fraction of the surface
magnetic energy is stored in large scales as rotation increases. (ii)
Whereas the magnetic field is mostly poloidal for low rotation rates,
more rapid rotators host a large-scale toroidal component in their
surface field. From our observations, we infer that a rotation period
lower than ~12 d is necessary for the toroidal magnetic energy to
dominate over the poloidal component.

---------------------------------------------------------
Title: Spectral irradiance variations: comparison between observations
and the SATIRE model on solar rotation time scales
Authors: Unruh, Y. C.; Krivova, N. A.; Solanki, S. K.; Harder, J. W.;
Kopp, G.
2008A&A...486..311U Altcode: 2008arXiv0802.4178U
Aims: We test the reliability of the observed and calculated spectral
irradiance variations between 200 and 1600 nm over a time span of
three solar rotations in 2004. Methods: We compare our model
calculations to spectral irradiance observations taken with SORCE/SIM,
SoHO/VIRGO, and UARS/SUSIM. The calculations assume LTE and are based
on the SATIRE (Spectral And Total Irradiance REconstruction) model. We
analyse the variability as a function of wavelength and present time
series in a number of selected wavelength regions covering the UV to
the NIR. We also show the facular and spot contributions to the total
calculated variability. Results: In most wavelength regions,
the variability agrees well between all sets of observations and the
model calculations. The model does particularly well between 400 and
1300 nm, but fails below 220 nm, as well as for some of the strong NUV
lines. Our calculations clearly show the shift from faculae-dominated
variability in the NUV to spot-dominated variability above approximately
400 nm. We also discuss some of the remaining problems, such as the low
sensitivity of SUSIM and SORCE for wavelengths between approximately
310 and 350 nm, where currently the model calculations still provide
the best estimates of solar variability.

---------------------------------------------------------
Title: SOHO/SUMER observations of prominence oscillation before
eruption
Authors: Chen, P. F.; Innes, D. E.; Solanki, S. K.
2008A&A...484..487C Altcode: 2008arXiv0802.1961C
Context: Coronal mass ejections (CMEs), as a large-scale eruptive
phenomenon, often reveal some precursors in the initiation phase, e.g.,
X-ray brightening, filament darkening, etc., which are useful for CME
modelling and space weather forecasting. Aims: With the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) spectroscopic
observations of the 2000 September 26 CME, we propose another
precursor for CMEs, namely, long-time prominence oscillations. Methods: We observed the prominence oscillation-and-eruption event by
ground-based Hα telescopes and space-borne white-light, EUV imaging,
and spectroscopic instruments. In particular, the SUMER slit was
observing the prominence in a sit-and-stare mode. Results:
The observations indicate that a siphon flow was moving from the
proximity of the prominence to a site at a projected distance of 270”,
which was followed by repetitive Hα surges and continual prominence
oscillations. The oscillation lasted 4 hours before the prominence
erupted as a blob-like CME. The analysis of the multiwavelength
data indicates that the whole series of processes fits well into the
emerging flux trigger mechanism for CMEs. In this mechanism, emerging
magnetic flux drives a siphon flow due to increased gas pressure
where the background polarity emerges. It also drives Hα surges
through magnetic reconnection where the opposite polarity emerges. The
magnetic reconnection triggers the prominence oscillations, as well
as its loss of equilibrium, which finally leads to the eruption of the
prominence. It is also found that the reconnection between the emerging
flux and the pre-existing magnetic loop proceeds in an intermittent,
probably quasi-periodic, way.

---------------------------------------------------------
Title: Understanding the WMAP Results: Low-Order Multipoles and Dust
in the Vicinity of the Solar System
Authors: Dikarev, Valeri; Preuß, Oliver; Solanki, Sami; Krüger,
Harald; Krivov, Alexander
2008EM&P..102..555D Altcode: 2007EM&P..tmp...47D
Analyses of the cosmic microwave background (CMB) radiation maps
produced by the Wilkinson Microwave Anisotropy Probe (WMAP) have
revealed anomalies not predicted by the standard cosmological
theory. It has been suggested that a dust cloud in the vicinity of
the Solar system may be the cause for these anomalies. In this paper,
the thermal emission by particles from two known interplanetary
meteoroid complexes is tested against the CMB maps. Conclusions are
drawn based on the geometry of cloud projections onto the WMAP sky
whether these clouds are likely to explain the observed anomaly. The
smooth background Zodiacal cloud and one of the Taurid meteor complex
branches do not explain the WMAP anomaly.

---------------------------------------------------------
Title: Models of solar irradiance variations: Current status
Authors: Krivova, Natalie A.; Solanki, Sami K.
2008JApA...29..151K Altcode:
Regular monitoring of solar irradiance has been carried out since 1978
to show that solar total and spectral irradiance varies at different
time scales. Whereas variations on time scales of minutes to hours
are due to solar oscillations and granulation, variations on longer
time scales are driven by the evolution of the solar surface magnetic
field. Here the most recent advances in modelling of solar irradiance
variations on time scales longer than a day are briefly reviewed.

---------------------------------------------------------
Title: The intensity contrast of solar granulation: comparing Hinode
SP results with MHD simulations
Authors: Danilovic, S.; Gandorfer, A.; Lagg, A.; Schüssler, M.;
Solanki, S. K.; Vögler, A.; Katsukawa, Y.; Tsuneta, S.
2008A&A...484L..17D Altcode: 2008arXiv0804.4230D
Context: The contrast of granulation is an important quantity
characterizing solar surface convection. Aims: We compare the
intensity contrast at 630 nm, observed using the Spectro-Polarimeter
(SP) aboard the Hinode satellite, with the 3D radiative MHD simulations
of Vögler &amp; Schüssler (2007, A&amp;A, 465, L43). Methods:
A synthetic image from the simulation is degraded using a theoretical
point-spread function of the optical system, and by considering other
important effects. Results: The telescope aperture and the
obscuration by the secondary mirror and its attachment spider, reduce
the simulated contrast from 14.4% to 8.5%. A slight effective defocus
of the instrument brings the simulated contrast down to 7.5%, close to
the observed value of 7.0%. Conclusions: A proper consideration
of the effects of the optical system and a slight defocus, lead to
sufficient degradation of the synthetic image from the MHD simulation,
such that the contrast reaches almost the observed value. The remaining
small discrepancy can be ascribed to straylight and slight imperfections
of the instrument, which are difficult to model. Hence, Hinode SP data
are consistent with a granulation contrast which is predicted by 3D
radiation MHD simulations.

---------------------------------------------------------
Title: Moments of the latitudinal dependence of the sunspot cycle:
a new diagnostic of dynamo models
Authors: Solanki, S. K.; Wenzler, T.; Schmitt, D.
2008A&A...483..623S Altcode:
Aims: The latitude-distribution of solar activity as represented by
sunspots is studied. Methods: We first determined the latitudinal
distribution of a sunspot cycle by integrating the butterfly diagram
at each latitude over the length of each cycle. We then formed the five
lowest moments of the latitudinal distribution of all complete sunspot
cycles since 1874 and compared these moments with each other. Results: The three lowest moments correlate remarkably well with
each other. For example, the mean latitude of the sunspots during a
cycle and the latitude range are correlated at the 0.96 level. A clear
asymmetry is seen between the two hemispheres, with the southern solar
hemisphere showing consistently stronger and more positive correlations
than the northern hemisphere. When applied to different simple dynamo
models, the same analysis reveals significant differences between the
models and demonstrates that such moments are a useful diagnostic in
distinguishing between dynamo models. Remarkably, dynamos without a
meridional flow provide results closer to those of the Sun's northern
hemisphere, while a dynamo with a meridional flow produces fields more
like those in the Sun's southern hemisphere. This may provide a clue
to the cause of the well-known north-south asymmetry of solar activity.

---------------------------------------------------------
Title: Multiheight Analysis of Asymmetric Stokes Profiles in a Solar
Active Region
Authors: Deng, N.; Choudhary, D.; Solanki, S. K.; Lagg, A.
2008AGUSMSP51D..06D Altcode:
Parameters characterizing Stokes asymmetries are derived from full
Stokes I,Q,U,V spectra of FeI λλ 630.15, 630.25~nm line pair
(formed at two different heights in the photosphere) and MgI b
517.27~nm line (formed at lower chromosphere) in a solar active
region near disc center. The spectropolarimetric observations were
taken with the National Solar Observatory/High Altitude Observatory
Advanced Stokes Polarimeter. The observed active region consists
of a α sunspot, a δ sunspot, several pores and granulation. The
line center shifts and bi-sectors derived from Stokes-I profiles
describe the line-of-sight Doppler velocity and Stokes-I asymmetry,
respectively. Stokes-V amplitude and area asymmetries are defined by
the normalized difference of respective quantities between blue and
red lobes of circular polarization profiles. The same can be derived
from linear polarization profiles ([Q2+U2]1/2). The Stokes asymmetries
are compared for different regions and at multiple heights. Neutral
line regions of the δ spot and outer penumbral regions show distinct
large Stokes asymmetries. Both Stokes-V amplitude and area asymmetries
become larger from lower to higher atmosphere in neutral line regions
that have strong transverse field and mixed polarities. The Stokes-V
area asymmetry of outer edge of penumbrae changes from positive in
the photosphere to negative in lower chromosphere. Detailed results
and interpretation will be presented.

---------------------------------------------------------
Title: The nature of running penumbral waves revealed
Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K.
2008IAUS..247...55B Altcode: 2007IAUS..247...55B
We seek to clarify the nature of running penumbral (RP) waves:
are they chromospheric trans-sunspot waves or a visual pattern of
upward-propagating waves? Full Stokes spectropolarimetric time series
of the photospheric Sii10827 Å line and the chromospheric Hei10830 Å
multiplet were inverted using a Milne-Eddington code. Spatial pixels
were paired between the outer umbral/inner penumbral photosphere
and the penumbral chromosphere using inclinations retrieved by the
inversion and the dual-height pairings of line-of-sight velocity time
series were studied for signatures of wave propagation using a Fourier
phase difference analysis. The dispersion relation for radiatively
cooling acoustic waves, modified to incorporate an inclined propagation
direction, fits well the observed phase differences between the pairs
of photospheric and chromospheric pixels. We have thus demonstrated
that RP waves are in effect low-β slow-mode waves propagating along
the magnetic field.

---------------------------------------------------------
Title: Identification of types of kink modes in coronal loops:
principles and application to TRACE results
Authors: Wang, T.; Solanki, S.; Selwa, M.; Ofman, L.
2008AGUSMSP31C..08W Altcode:
We explore the possible signatures of different types of kink modes
(horizontal and vertical oscillations in their fundamental mode and
second harmonic) which may arise in coronal loops. Based on the 3D
geometrical parameters of 14 TRACE loops of transverse oscillations,
we simulate qualitatively the loop displacements due to these types
of kink mode oscillations. We find that for many combinations of
viewing and loop geometry it is not straightforward to distinguish
between the two types of kink modes. We have also considered Doppler
signatures and found that these can in principle help to obtain
unique identifications of the oscillation modes. We then compared
the simulated spatial signatures with the observations for 14
TRACE loops. We find that two cases of loop oscillations previously
identified as a fundamental horizontal mode appear to be a fundamental
vertical mode, while in two other cases it is not possible to clearly
distinguish between a horizontal oscillation of the fundamental
mode and the second-harmonic, and in six cases it is not possible
to clearly distinguish between a fundamental horizontal mode and a
second-harmonic vertical mode. In addition, for the particular case
that the oscillating loop has a S-shape, we find that the fundamental
vertical oscillation can take on the appearance of the horizontal second
harmonic due to projection effects. We also present numerical results
of three dimensional MHD model of an idealized active region field with
S-shaped field-lines. The active region is initialized as a force-free
dipole magnetic configuration with uniform density and contains a loop
with a higher density than its surroundings. We introduce a velocity
pulse which models the impact of a flare on surrounding fields. Both
the qualitative study and the MHD simulation support the conclusion
of the presence of fundamental mode of vertical kink oscillations in
an S-shaped loop. Our interpretation can naturally solve the puzzle of
the absence of the fundamental mode and the apparent presence of second
harmonic oscillations observed in a TRACE loop by De Moortel and Brady
(2007).

---------------------------------------------------------
Title: Stratification of Sunspot Umbral Dots from Inversion of Stokes
Profiles Recorded by Hinode
Authors: Riethmüller, T. L.; Solanki, S. K.; Lagg, A.
2008ApJ...678L.157R Altcode: 2008arXiv0805.4324R
This work aims to constrain the physical nature of umbral dots (UDs)
using high-resolution spectropolarimetry. Full Stokes spectra recorded
by the spectropolarimeter on Hinode of 51 UDs in a sunspot close to the
disk center are analyzed. The height dependence of the temperature,
magnetic field vector, and line-of-sight velocity across each UD
is obtained from an inversion of the Stokes vectors of the two Fe I
lines at 630 nm. No difference is found at higher altitudes [-3 &lt;=
log (τ500) &lt;= - 2] between the UDs and the diffuse
umbral background. Below that level the difference rapidly increases,
so that at the continuum formation level [log (τ500) = 0]
we find on average a temperature enhancement of 570 K, a magnetic field
weakening of 510 G, and upflows of 800 m s-1 for peripheral
UDs, whereas central UDs display an excess temperature of on average
550 K, a field weakening of 480 G, and no significant upflows. The
results for, in particular, the peripheral UDs, including cuts of
magnetic vector and velocity through them, look remarkably similar to
the output of recent radiation MHD simulations. They strongly suggest
that UDs are produced by convective upwellings.

---------------------------------------------------------
Title: First stereoscopic polar plume reconstructions from
STEREO/SECCHI images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wiegelmann, T.;
Podlipnik, B.; Howard, R.; Plunkett, S.; Wuelser, J.; Gan, W.
2008AGUSMSH23A..01F Altcode:
We present the first stereoscopic reconstruction of the
three-dimensional structures of polar plumes based on the two
simultaneously recorded images taken by the EUVI telescopes in
the SECCHI instrument package onboard the recently launched STEREO
mission. The reconstructed polar plumes were observed on April 7th,
2007 when the two spacecraft were well below the solar equatorial
plane, an appropriate time for the observation of the plumes in the
south polar coronal hole. The heliocentric separation of the two
spacecraft was 3.6 degrees at that time. We determine locations of
the footpoints of five EUV polar plumes on the solar surface as well
as their inclinations relative to the line-of-sight and to their
local radial directions. The five plumes are all within 21 degrees
of the south pole and their inclinations to the line-of-sight of
STEREO A(head) and radial directions are on average 107 degrees and
28 degrees, respectively. A simple dipole model for the south pole's
magnetic field does not provide a good correspondence with the obtained
inclinations. Of the three plumes in front of the limb only one is
associated with an EUV bright point.

---------------------------------------------------------
Title: The FeH F4Δ-X4Δ system. Creating a
valuable diagnostic tool to explore solar and stellar magnetic fields
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.;
Lagg, A.
2008A&A...482..387A Altcode:
Context: Lines of diatomic molecules are ideal tools for studying
cool stellar atmospheres and the internal structure of sunspots
and starspots, given their temperature and pressure sensitivities,
which are typically higher than in atomic lines. The Wing-Ford FeH
F4Δ-X4Δ system represents such a diatomic
molecule that is, in addition, highly sensitive to magnetic fields. The
current theoretical description of those transitions that include the
involved molecular constants, however, are only based on intensity
measurements because polarimetric observations have not been available
until now, which limits their diagnostic value. Furthermore, the theory
has so far been optimized to reproduce energy levels and line strengths
without taking magnetic sensitivities into account. Aims: The
FeH F4Δ-X4Δ system is produced by transitions
between two electronic states with the coupling of the angular momenta
that is intermediate between limiting Hund's cases (a) and (b). Our goal
is to investigate the diagnostic capabilities of the current theoretical
description of the molecule FeH. Methods: Using the most precise
available Hamiltonian, we carried out the perturbation calculation
of the molecular Zeeman effect for this transition and computed the
Landé factors of the energy levels and of transitions. We extracted
Landé factors from a comparison of observed and calculated Stokes
I and V profiles. Certain spectral lines, most frequently with high
magnetic sensitivity, exhibited discrepancies between the theory and
observations. We extended the theoretical model with a semi-empirical
approach to obtain a diagnostic tool that is able to reproduce many
of the interesting spectral lines. Results: We find that the
current theory successfully reproduces the magnetic properties of
a large number of lines in the FeH F4Δ-X4Δ
system and that the modified Hamiltonian allows us to synthesize
and successfully reproduce the most sensitive lines. Thus, our
observations have provided valuable constraints for determining
empirical molecular constants and Landé factors. Conclusions:
The FeH F4Δ-X4Δ system is found to be a very
sensitive magnetic diagnostic tool. Polarimetric data of these lines,
in contrast to intensity measurements, provide us with more direct
and detailed information to study the coolest parts of sunspot and
starspot umbrae, as well as cool active dwarfs.

---------------------------------------------------------
Title: A first step in reconstructing the solar corona
self-consistently with a magnetohydrostatic model during solar
activity minimum
Authors: Ruan, P.; Wiegelmann, T.; Inhester, B.; Neukirch, T.; Solanki,
S. K.; Feng, L.
2008A&A...481..827R Altcode:
Aims: We compute the distribution of the magnetic field and the plasma
in the global corona with a self-consistent magnetohydrostatic (MHS)
model. Methods: Because direct measurements of the solar coronal
magnetic field and plasma are extremely difficult and inaccurate, we
use a modeling approach based on observational quantities, e.g. the
measured photospheric magnetic field, to reconstruct the structure
of the global solar corona. We take an analytic magnetohydrostatic
model to extrapolate the magnetic field in the corona from photospheric
magnetic field measurement. In the model, the electric current density
can be decomposed into two components: one component is aligned with the
magnetic field lines, whereas the other component flows in spherical
shells. The second component of the current produces finite Lorentz
forces that are balanced by the pressure gradient and the gravity
force. We derive the 3D distribution of the magnetic field and plasma
self-consistently in one model. The boundary conditions are given by
a synoptic magnetogram on the inner boundary and by a source surface
model at the outer boundary. Results: The density in the model is
higher in the equatorial plane than in the polar region. We compare the
magnetic field distribution of our model with potential and force-free
field models for the same boundary conditions and find that our model
differs noticeably from both. We discuss how to apply the model and
how to improve it.

---------------------------------------------------------
Title: Evidence of magnetic field wrapping around penumbral filaments
Authors: Borrero, J. M.; Lites, B. W.; Solanki, S. K.
2008A&A...481L..13B Altcode: 2007arXiv0712.2548B
We employ high-spatial resolution spectropolarimetric observations
from the Solar Optical Telescope on-board the Hinode spacecraft to
investigate the fine structure of the penumbral magnetic fields. The
Stokes vector of two neutral iron lines at 630 nm is inverted at every
spatial pixel to retrieve the depth-dependence of the magnetic field
vector, line-of-sight velocity and thermodynamic parameters. We show
that the azimuthal angle of the magnetic field vector has opposite sign
on both sides above the penumbral filaments. This is consistent with
the wrapping of an inclined field around the horizontal filaments. The
wrapping effect is stronger for filaments with larger horizontal
extensions. In addition, we find that the external magnetic field can
penetrate into the intraspines, leading to non-radial magnetic fields
inside them. These findings shed some light on the controversial
small-scale structure of the sunspot penumbra.

---------------------------------------------------------
Title: Theoretical modeling for the stereo mission
Authors: Aschwanden, Markus J.; Burlaga, L. F.; Kaiser, M. L.; Ng,
C. K.; Reames, D. V.; Reiner, M. J.; Gombosi, T. I.; Lugaz, N.;
Manchester, W.; Roussev, I. I.; Zurbuchen, T. H.; Farrugia, C. J.;
Galvin, A. B.; Lee, M. A.; Linker, J. A.; Mikić, Z.; Riley, P.;
Alexander, D.; Sandman, A. W.; Cook, J. W.; Howard, R. A.; Odstrčil,
D.; Pizzo, V. J.; Kóta, J.; Liewer, P. C.; Luhmann, J. G.; Inhester,
B.; Schwenn, R. W.; Solanki, S. K.; Vasyliunas, V. M.; Wiegelmann, T.;
Blush, L.; Bochsler, P.; Cairns, I. H.; Robinson, P. A.; Bothmer,
V.; Kecskemety, K.; Llebaria, A.; Maksimovic, M.; Scholer, M.;
Wimmer-Schweingruber, R. F.
2008SSRv..136..565A Altcode: 2006SSRv..tmp...75A
We summarize the theory and modeling efforts for the STEREO mission,
which will be used to interpret the data of both the remote-sensing
(SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The
modeling includes the coronal plasma, in both open and closed magnetic
structures, and the solar wind and its expansion outwards from the Sun,
which defines the heliosphere. Particular emphasis is given to modeling
of dynamic phenomena associated with the initiation and propagation
of coronal mass ejections (CMEs). The modeling of the CME initiation
includes magnetic shearing, kink instability, filament eruption, and
magnetic reconnection in the flaring lower corona. The modeling of CME
propagation entails interplanetary shocks, interplanetary particle
beams, solar energetic particles (SEPs), geoeffective connections,
and space weather. This review describes mostly existing models of
groups that have committed their work to the STEREO mission, but is by
no means exhaustive or comprehensive regarding alternative theoretical
approaches.

---------------------------------------------------------
Title: On the potential value of Ca II K spectroheliogram time-series
for solar activity and irradiance studies
Authors: Ermolli, I.; Solanki, S. K.; Tlatov, A. G.; Krivova, N. A.;
Ulrich, R. K.; Singh, J.
2008arXiv0802.3806E Altcode:
Various observatories around the globe started regular full-disk imaging
of the solar atmosphere in the Ca II K line since the early decades
of the 20th century. The archives made by these observations have the
potential of providing far more detailed information on solar magnetism
than just the sunspot number and area records to which most studies
of solar activity and irradiance changes are restricted. We evaluate
the image contents of three Ca II K spectroheliogram time-series,
specifically those obtained by the digitization of the Arcetri,
Kodaikanal, and Mt Wilson photographic archives. We describe the
main problems afflicting these data and analyze their quality by
expressing the image contents through several quantities. We compare
the results obtained with those for similar present-day observations
taken with the Meudon spectroheliograph and with the Rome-PSPT. We show
that historic data suffer from stronger geometrical distortions and
photometric uncertainties than similar present-day observations. The
latter uncertainties mostly originate from the photographic calibration
of the original data and from stray-light effects. We also show that
the image contents of the three analyzed series vary in time. These
variations are probably due to instrument changes and aging of the
spectrographs used, as well as changes of the observing programs. Our
results imply that the main challenge for the analysis of historic data
is their accurate photometric calibration. This problem must be solved
before they can provide reliable information about solar magnetism and
activity over the last century. Moreover, inter-calibration of results
obtained from independent time-series is required to reliably trace
changes of solar properties with time from the analysis of such data.

---------------------------------------------------------
Title: SOHO/SUMER observations of prominence oscillation before
eruption
Authors: Chen, P. F.; Innes, D. E.; Solanki, Sami
2008cosp...37..502C Altcode: 2008cosp.meet..502C
Coronal mass ejections (CMEs) often reveal some precursors in the
initiation phase, such as X- ray brightening and filament darkening,
which are useful for CME modeling and space weather forecast. With the
SOHO/SUMER spectroscopic observations of the 2000 September 26 event,
we propose another precursor for CME eruptions, namely, long-time
prominence oscillations. The observations indicate that a siphon
flow was moving from the proximity of the prominence to a far site,
which was followed by repetitive Hα surges and continual prominence
oscillations. The oscillation lasted 4 hours before the prominence
erupted as a blob-like CME. The analysis of the multiwavelength
data indicates that the whole series of processes fits well into the
emerging flux trigger mechanism for CMEs. In this mechanism, emerging
magnetic flux drives a siphon flow due to increased gas pressure
where the background polarity emerges. It also drives Hα surges
through magnetic reconnection where the opposite polarity emerges. The
magnetic reconnection triggers the prominence oscillations, as well
as its loss of equilibrium, which finally leads to the eruption of the
prominence. It is also found that the reconnection between the emerging
flux and the pre-existing magnetic loop proceeds in an intermittent,
probably quasiperiodic, way.

---------------------------------------------------------
Title: 3D MHD model of kink waves in a loop anchored in a realistic
active region
Authors: Selwa, Malgorzata; Ofman, Leon; Wang, Tongjiang; Solanki, Sami
2008cosp...37.2804S Altcode: 2008cosp.meet.2804S
We present numerical results of three dimensional MHD model of the
active region field. The active region is initialized using MDI data
of 15 May 2001, 02:57 UT and potential extrapolation of the magnetic
field with gravitationally stratified density and contains a loop
with a higher density than its surroundings. The potential model
imitates the original TRACE AR quite well, however, the choice of
particular loop within AR is inaccurate due to limitation of the
plane-of-the-sky view. This study represents an extension to the
model of Ofman (2007). We introduce a velocity pulse based on TRACE
observations to model the impact of a flare on surrounding fields, and
study the resulting loop oscillations. The flare is initialized as a
semispherical velocity pulse at the bottom of AR and corresponds to the
event between loop's footpoints captured by TRACE. We investigate the
influence of a realistic dense loop on the excitation and damping of
the oscillations and compare our results with TRACE observations. By
the means of 3D computer simulation we confirm that considering
combination of viewing and loop geometry and Doppler signatures it
is straightforward to distinguish between at least two types of kink
modes: horizontal and vertical in the real loop observed by Aschwanden
et al. (2002). We find that oscillation previously identified as a
fundamental horizontal mode (Aschwanden et al. 2002) appears to be a
fundamental vertical mode. As such vertical kink oscillations are not
as rare compared to horizontal ones as previously thought.

---------------------------------------------------------
Title: Grand minima and maxima of solar activity on multi-millennial
scale
Authors: Usoskin, Ilya; Solanki, Sami; Kovaltsov, Gennady
2008cosp...37.3264U Altcode: 2008cosp.meet.3264U
Using a reconstruction of sunspot numbers stretching over multiple
millennia, we analyze the statistics of the occurrence of grand minima
and maxima and set new observational constraints on long-term solar
and stellar dynamo models. We present an updated reconstruction of
sunspot number over multiple millennia, from 14C data by means of
a physics-based model, using an updated model of the evolution of
the solar open magnetic flux. A list of grand minima and maxima of
solar activity is presented for the Holocene (since 9500 BC) and
the statistics of both the length of individual events as well as
the waiting time between them are analyzed. It is discussed that the
occurrence of grand minima/maxima is driven not by long-term cyclic
variability, but by a stochastic/chaotic process. The waiting time
distribution of the occurrence of grand minima/maxima deviates from an
exponential distribution, implying that these events tend to cluster
together with long event-free periods between the clusters. Two
different types of grand minima are observed: short (30-90 years)
minima of Maunder type and long (&gt;110 years) minima of Sp¨rer type,
implying that a deterministic behaviour of the dynamo during o a grand
minimum defines its length. The duration of grand maxima follows an
exponential distribution, suggesting that the duration of a grand
maximum is determined by a random process.

---------------------------------------------------------
Title: Variability of solar irradiance from the UV to the NIR from
GOME and SCIAMACHY for use in atmospheric models
Authors: Ambrose Pagaran, Joseph; Weber, Mark; Ambrose Pagaran, Joseph;
Burrows, John P.; Krivova, Natalie; Solanki, Sami; Floyd, Linton
2008cosp...37.2329A Altcode: 2008cosp.meet.2329A
The Sun is the primary energy source that drives the Earth's
climate system. Its radiative output is known to vary in time,
for instance, with the 11-year solar cycle and 27-day solar
rotation period. Variations in the solar spectral irradiance (SSI)
affect the thermal structure and chemical composition of the Earth's
atmosphere. Although the largest solar variations are observed in the UV
spectral region, a large fraction of the total solar irradiance (TSI,
solar constant) variation over a solar cycle comes from the visible
and near IR spectral range. In order to understand how SSI variations
cause a detectable change in climate, we need to quantify UV, visible,
and near IR variation in the solar spectral irradiance to a high level
of certainty both over the short term solar rotation 27-day period and
11-year solar cycle. Using daily solar irradiance observations from
SUSIM (1992-2005), GOME (1995-present), and SCIAMACHY (2002-present),
we study solar variations over 27-day solar rotations from 120 nm to
1600 nm. The variability is modelled by parameterizing SSI in terms
of faculae brightening (using the Mg II core-to-wing ratio proxy)
and sunspot darkening (using the photospheric sunspot index). Since
the variations in the visible and NIR are well below 1

---------------------------------------------------------
Title: ALMA as the ideal probe of the solar chromosphere
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen
2008Ap&SS.313..197L Altcode: 2007arXiv0704.0023L; 2007Ap&SS.tmp..371L
The very nature of the solar chromosphere, its structuring and
dynamics, remains far from being properly understood, in spite of
intensive research. Here we point out the potential of chromospheric
observations at millimeter wavelengths to resolve this long-standing
problem. Computations carried out with a sophisticated dynamic model
of the solar chromosphere due to Carlsson and Stein demonstrate that
millimeter emission is extremely sensitive to dynamic processes in
the chromosphere and the appropriate wavelengths to look for dynamic
signatures are in the range 0.8 5.0 mm. The model also suggests that
high resolution observations at mm wavelengths, as will be provided
by ALMA, will have the unique property of reacting to both the hot
and the cool gas, and thus will have the potential of distinguishing
between rival models of the solar atmosphere. Thus, initial results
obtained from the observations of the quiet Sun at 3.5 mm with the
BIMA array (resolution of 12″) reveal significant oscillations with
amplitudes of 50 150 K and frequencies of 1.5 8 mHz with a tendency
toward short-period oscillations in internetwork and longer periods
in network regions. However higher spatial resolution, such as that
provided by ALMA, is required for a clean separation between the
features within the solar atmosphere and for an adequate comparison
with the output of the comprehensive dynamic simulations.

---------------------------------------------------------
Title: The Nature of Running Penumbral Waves Revealed
Authors: Bloomfield, D. Shaun; Lagg, Andreas; Solanki, Sami K.
2007ApJ...671.1005B Altcode: 2007arXiv0709.3731B
We seek to clarify the nature of running penumbral (RP) waves:
are they chromospheric trans-sunspot waves or a visual pattern of
upward-propagating waves? Full Stokes spectropolarimetric time series of
the photospheric Si I λ10827 line and the chromospheric He I λ10830
multiplet were inverted using a Milne-Eddington atmosphere. Spatial
pixels were paired between the outer umbral/inner penumbral photosphere
and the penumbral chromosphere using inclinations retrieved by the
inversion and the dual-height pairings of line-of-sight velocity time
series were studied for signatures of wave propagation using a Fourier
phase difference analysis. The dispersion relation for radiatively
cooling acoustic waves, modified to incorporate an inclined propagation
direction, fits well the observed phase differences between the pairs
of photospheric and chromospheric pixels. We have thus demonstrated
that RP waves are in effect low-β slow-mode waves propagating along
the magnetic field.

---------------------------------------------------------
Title: First Stereoscopic Coronal Loop Reconstructions from STEREO
SECCHI Images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wiegelmann, T.;
Podlipnik, B.; Howard, R. A.; Wuelser, J. -P.
2007ApJ...671L.205F Altcode: 2008arXiv0802.0773F
We present the first reconstruction of the three-dimensional shape of
magnetic loops in an active region from two different vantage points
based on simultaneously recorded images. The images were taken by the
two EUVI telescopes of the SECCHI instrument on board the recently
launched STEREO spacecraft when the heliocentric separation of the
two space probes was 12°. We demonstrate that these data allow us to
obtain a reliable three-dimensional reconstruction of sufficiently
bright loops. The result is compared with field lines derived from
a coronal magnetic field model extrapolated from a photospheric
magnetogram recorded nearly simultaneously by SOHO MDI. We attribute
discrepancies between reconstructed loops and extrapolated field lines
to the inadequacy of the linear force-free field model used for the
extrapolation.

---------------------------------------------------------
Title: First Stereoscopic Coronal Loop Reconstructions From
STEREO/SECCHI Images
Authors: Feng, L.; Inhester, B.; Solanki, S. K.; Wiegelmann, T.;
Podlipnik, B.; Howard, R. A.
2007AGUFMSH41B..06F Altcode:
We for the first time use simultaneously observed EUV images to
reconstruct the 3D shape of magnetic loops which emerge from an active
region. The images were taken by the two EUVI cameras of the SECCHI
telescopes onboard the STEREO spacecraft. At the time the data was
taken, the heliocentric separation of the two STEREO probes was 12
degrees. We show that under these conditions it is possible to obtain
a reliable three- dimensional reconstruction of sufficiently bright
loops as they usually emerge from an active region. The result is
compared with field lines derived from a coronal magnetic field model
extrapolated from a surface magnetogram. The magnetogram was abserved
by SOHO/MDI only 9 seconds before the the EUV images were taken.

---------------------------------------------------------
Title: Discovery of inward moving magnetic enhancements in sunspot
penumbrae
Authors: Zhang, J.; Solanki, S. K.; Woch, J.
2007A&A...475..695Z Altcode: 2007arXiv0705.0604Z
Context: Sunspot penumbrae show a fine structure in continuum intensity
which displays considerable dynamics. The magnetic field, in contrast,
although also highly structured, has been shown to be relatively static
in earlier studies. Aims: We report on the discovery of inward
moving magnetic enhancements in the penumbrae of two regular sunspots,
and characterize their fundamental properties. Methods: Using
continuum images, longitudinal magnetograms and Dopplergrams, recorded
in high resolution mode by the Michelson Doppler Imager (MDI) instrument
on the Solar and Heliospheric Observatory (SOHO), we have probed the
evolution of magnetic features in the inner penumbra. The relationship
between magnetic features, corresponding brightness in continuum images
and Dopplergrams is also considered. Results: Local enhancements
of the line-of-sight (LOS) component of the magnetic field in the inner
part of the penumbral region move inward towards the umbra-penumbra
boundary with a radial speed of about 0.3 km s-1. These local
inward-moving enhancements of the LOS component of the magnetic fields
appear to be relatively common. They are associated with dark structures
and tend to display downflows relative to the penumbral background. We
also confirm the presence of outward moving magnetic enhancments in
the outer half of the penumbra. Possible explanations are discussed.

---------------------------------------------------------
Title: The Fraction of DA White Dwarfs with Kilo--Gauss Magnetic
Fields
Authors: Jordan, S.; Aznar Cuadrado, R.; Napiwotzki, R.; Schmid,
H. M.; Solanki, S. K.
2007ASPC..372..169J Altcode: 2006astro.ph.10881J
Current estimates for white dwarfs with fields in excess of 1 MG are
about 10%; according to our first high-precision circular-polarimetric
study of 12 bright white dwarfs with the VLT tep{p26_Aznar-etal:04}
this number increases up to about 25%\ in the kG regime. With our
new sample of ten white dwarf observations (plus one sdO star) we
wanted to improve the sample statistics to determine the incident
of kG magnetic fields in white dwarfs. In one of our objects (LTT
7987) we detected a statistically significant (97% confidence level)
longitudinal magnetic field varying between (-1± 0.5) kG and (+1±
0.5) kG. This would be the weakest magnetic field ever found in a
white dwarf, but at this level of accuracy, systematic errors cannot
completely be ruled out. Together with previous investigations, the
fraction of kG magnetic fields in white dwarfs amounts to about 11-15%
, which is close to current estimates for highly magnetic white dwarfs
(&gt;1 MG).

---------------------------------------------------------
Title: A bright coronal downflow seen in multi-wavelength
observations: evidence of a bifurcating flux-rope?
Authors: Tripathi, D.; Solanki, S. K.; Mason, H. E.; Webb, D. F.
2007A&A...472..633T Altcode: 2008arXiv0802.3616T
Aims:We study the origin and characteristics of a bright coronal
downflow seen after a coronal mass ejection associated with
erupting prominences on 5 March 2000. Methods: This study
extends that of Tripathi et al. (2006b, A&amp;A, 449, 369) based
on the Extreme-ultraviolet Imaging Telescope (EIT), the Soft X-ray
Telescope (SXT) and the Large Angle Spectrometric Coronagraph (LASCO)
observations. We combined those results with an analysis of the
observations taken by the Hα and the Mk4 coronagraphs at the Mauna Loa
Solar Observatory (MLSO). The combined data-set spans a broad range of
temperature as well as continuous observations from the solar surface
out to 30 R⊙. Results: The downflow started at
around 1.6 R⊙ and contained both hot and cold gas. The
downflow was observed in the Hα and the Mk4 coronagraphs as well as
the EIT and the SXT and was approximately co-spatial and co-temporal
providing evidence of multi-thermal plasma. The Hα and Mk4 images
show cusp-shaped structures close to the location where the downflow
started. Mk4 observations reveal that the speed of the downflow in
the early phase was substantially higher than the free-fall speed,
implying a strong downward acceleration near the height at which
the downflow started. Conclusions: The origin of the downflow
was likely to have been magnetic reconnection taking place inside
the erupting flux rope that led to its bifurcation. Movies are
available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: The velocity structure of moving magnetic feature pairs around
sunspots: support for the U-loop model
Authors: Zhang, J.; Solanki, S. K.; Woch, J.; Wang, J.
2007A&A...471.1035Z Altcode: 2007arXiv0705.2507Z
Context: Moving magnetic feature (MMF) pairs are among the most
significant fine-scale structures around sunspots. Several models have
been proposed to interpret the origin and evolution of MMF pairs. These
models provide important clues to understanding MMF pairs. Aims:
We present an analysis of the velocity structure of MMF pairs in
order to put further constrains on the MMF models. Methods:
Using continuum images, longitudinal magnetograms and Dopplergrams,
recorded by the Michelson Doppler Imager (MDI) instrument on the
Solar and Heliospheric Observatory (SOHO), we have traced 123 pairs
of opposite magnetic polarity moving magnetic features (MMFs) in three
active regions NOAA ARs 8375, 0330 and 9575. At the time of observation,
AR 8375 was young, AR 0330 mature, and AR 9575 decaying. Results:
The vertical velocity, measured from MDI Dopplergrams for the three
active regions, indicates that the elements of MMF pairs with polarity
opposite to that of the sunspot support a downflow (Doppler redshift)
of around 50-100 m s-1. The average Doppler shift difference
between negative and positive elements of an MMF pair is about 150 m
s-1 in AR 8375, 100 m s-1 in AR 0330, and 20 m
s-1 in AR 9575. These observational results are in agreement
with the model where MMF pairs are part of a U-loop emanating from the
sunspot's magnetic canopy. According to this model, the downflow is
caused by the Evershed flow returning below the solar surface. For AR
8375, the horizontal velocity of MMFs ranges from 0.1 km s-1
to 0.7 km s-1, and on average, the velocity of an MMF
pair decreases significantly (from 0.6 km s-1 to 0.35 km
s-1) with increasing distance from the MMF's birth place. In
contrast, the decrease of the average velocity is far less obvious
from 0.5 km s-1 to 0.4 km s-1 with increasing
distance from the sunspot. This result suggests that the change in
MMF flow speed does not reflect the radial structure of the moat flow,
but rather is intrinsic to the evolution of the MMF pairs. This result
is also in agreement with the U-loop model of MMF pairs. We also find
that properties of MMF pairs, most strikingly the lifetime, depend on
the evolution stages of the parent sunspot. The mean lifetimes of MMF
pairs in ARs 9575 and 0330 are 0.7 h and 1.6 h, respectively, which is
considerably shorter than the 4 h lifetime previously found for AR 8375.

---------------------------------------------------------
Title: Grand minima and maxima of solar activity: new observational
constraints
Authors: Usoskin, I. G.; Solanki, S. K.; Kovaltsov, G. A.
2007A&A...471..301U Altcode: 2007arXiv0706.0385U
Aims:Using a reconstruction of sunspot numbers stretching over
multiple millennia, we analyze the statistics of the occurrence of
grand minima and maxima and set new observational constraints on
long-term solar and stellar dynamo models. Methods: We present
an updated reconstruction of sunspot number over multiple millennia,
from 14C data by means of a physics-based model, using an
updated model of the evolution of the solar open magnetic flux. A
list of grand minima and maxima of solar activity is presented for
the Holocene (since 9500 BC) and the statistics of both the length
of individual events as well as the waiting time between them are
analyzed. Results: The occurrence of grand minima/maxima is
driven not by long-term cyclic variability, but by a stochastic/chaotic
process. The waiting time distribution of the occurrence of grand
minima/maxima deviates from an exponential distribution, implying that
these events tend to cluster together with long event-free periods
between the clusters. Two different types of grand minima are observed:
short (30-90 years) minima of Maunder type and long (&gt;110 years)
minima of Spörer type, implying that a deterministic behaviour of
the dynamo during a grand minimum defines its length. The duration of
grand maxima follows an exponential distribution, suggesting that the
duration of a grand maximum is determined by a random process. Conclusions: These results set new observational constraints upon
the long-term behaviour of the solar dynamo.

---------------------------------------------------------
Title: Solar irradiance variability
Authors: Solanki, Sami K.
2007HiA....14..279S Altcode:
We study solar irradiance variability. The current generation of models
show that the irradiance since then has increased by between 0.9 and
1.5 W m-2.

---------------------------------------------------------
Title: Attenuation of Alfvén waves in straight and curved coronal
slabs
Authors: Gruszecki, M.; Murawski, K.; Solanki, S. K.; Ofman, L.
2007A&A...469.1117G Altcode:
Aims:We consider impulsively generated Alfvén waves in coronal loops
to investigate the role of energy leakage on wave attenuation, which
includes lateral leakage, leakage into dense photospheric regions and
nonlinear driving of magnetosonic waves. Methods: A coronal loop
is modelled either as a straight magnetic slab or as a curved slab
of smooth mass density profiles. We perform numerical simulations of
2.5D ideal magnetohydrodynamic equations to determine the signatures of
Alfvén waves. Results: The numerical results show that lateral
leakage of Alfvén waves is significant in comparison to leakage into
the photospheric regions for realistic corona to photospheric density
ratios. Energy leakage is enhanced by curvature of magnetic field lines
and for large amplitude Alfvén waves for which nonlinear driving of
magnetosonic waves is more significant than in the linear regime.

---------------------------------------------------------
Title: Low-lying magnetic loops in the solar internetwork
Authors: Martínez González, M. J.; Collados, M.; Ruiz Cobo, B.;
Solanki, S. K.
2007A&A...469L..39M Altcode: 2007arXiv0705.1319M
Aims:We study the structure of the magnetic field vector in the
internetwork and search for the presence of small-scale loops. Methods: We invert 1.56 μm spectropolarimetric observations of
internetwork regions at disc centre by applying the SIR code. This
allows us to recover the atmospheric parameters that play a role in
the formation of these spectral lines. We are mainly interested in the
structure of the magnetic field vector. Results: We find that
many opposite polarity elements of the internetwork are connected by
short (2-6´´), low-lying (photospheric) loops. These loops connect
at least the 10-20% of the internetwork flux visible in our data. Also
we have some evidence that points towards a dynamic scenario that can
be produced by the emergence of internetwork magnetic flux.

---------------------------------------------------------
Title: Modified p-modes in penumbral filaments?
Authors: Bloomfield, D. S.; Solanki, S. K.; Lagg, A.; Borrero, J. M.;
Cally, P. S.
2007A&A...469.1155B Altcode: 2007arXiv0705.0481B
Aims:The primary objective of this study is to search for and identify
wave modes within a sunspot penumbra. Methods: Infrared
spectropolarimetric time series data are inverted using a model
comprising two atmospheric components in each spatial pixel. Fourier
phase difference analysis is performed on the line-of-sight velocities
retrieved from both components to determine time delays between the
velocity signals. In addition, the vertical separation between the
signals in the two components is calculated from the Stokes velocity
response functions. Results: The inversion yields two atmospheric
components, one permeated by a nearly horizontal magnetic field, the
other with a less-inclined magnetic field. Time delays between the
oscillations in the two components in the frequency range 2.5-4.5 mHz
are combined with speeds of atmospheric wave modes to determine wave
travel distances. These are compared to expected path lengths obtained
from response functions of the observed spectral lines in the different
atmospheric components. Fast-mode (i.e., modified p-mode) waves exhibit
the best agreement with the observations when propagating toward the
sunspot at an angle ~50° to the vertical.

---------------------------------------------------------
Title: Stokes diagnostics of simulated solar magneto-convection
Authors: Shelyag, S.; Schüssler, M.; Solanki, S. K.; Vögler, A.
2007A&A...469..731S Altcode: 2007astro.ph..3490S
We present results of synthetic spectro-polarimetric diagnostics of
radiative MHD simulations of solar surface convection with magnetic
fields. Stokes profiles of Zeeman-sensitive lines of neutral iron in
the visible and infrared spectral ranges emerging from the simulated
atmosphere have been calculated in order to study their relation to the
relevant physical quantities and compare with observational results. We
have analyzed the dependence of the Stokes-I line strength and width as
well as of the Stokes-V signal and asymmetries on the magnetic field
strength. Furthermore, we have evaluated the correspondence between
the actual velocities in the simulation with values determined from
the Stokes-I (Doppler shift of the centre of gravity) and Stokes-V
profiles (zero-crossing shift). We confirm that the line weakening in
strong magnetic fields results from a higher temperature (at equal
optical depth) in the magnetic flux concentrations. We also confirm
that considerable Stokes-V asymmetries originate in the peripheral
parts of strong magnetic flux concentrations, where the line of sight
cuts through the magnetopause of the expanding flux concentration into
the surrounding convective donwflow.

---------------------------------------------------------
Title: News and Views: Does the Sun affect the Earth's climate?
Authors: Priest, Eric; Lockwood, Mike; Solanki, Sami; Wolfendale,
Arnold; Coustenis, A.
2007A&G....48c...7P Altcode: 2007A&G....48c...7C
Svensmark's article in the February issue (A&amp;G 2007 48 1.18)
presented a possible mechanism for the way the Sun could influence
the Earth's climate. He suggested that water droplets condense in the
ionization trail left by cosmic rays, whose flux varies inversely with
solar activity: when the magnetic field of the solar wind is stronger,
it shields the Earth from galactic cosmic rays and so decreases their
flux on the Earth; according to Svensmark's ideas, this produces fewer
clouds and thereby heats the Earth.

---------------------------------------------------------
Title: Observations of Running Waves in a Sunspot Chromosphere
Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K.
2007ASPC..368..239B Altcode: 2007astro.ph..2056B
Spectropolarimetric time series data of the primary spot of active
region NOAA 9448 were obtained in the Si I 10827 Å line and the He I
10830 Å multiplet with the Tenerife Infrared Polarimeter. Throughout
the time series the spectrograph slit was fixed over a region covering
umbra, a light bridge, penumbra, and quiet sun. We present speeds
of running penumbral waves in the chromosphere, their relation to
both photospheric and chromospheric umbral oscillations, and their
dependence on the magnetic field topology.

---------------------------------------------------------
Title: Solar Cycle Variation of Chromospheric Radiation
Authors: Solanki, S. K.
2007ASPC..368..481S Altcode:
Radiation emitted by the Sun's chromospheric gas displays a significant
cyclic variation. The magnitude of this variability and the shape of
the light curve differs from that exhibited by photospheric radiation,
or total solar irradiance. The amplitude of the cyclic variation of
chromospheric radiation is larger and less affected by the contribution
of sunspots. Consequently, the influence of small-scale magnetic
features forming plage and the network dominates. Here a brief
introduction is given to the solar cycle variation of chromospheric
radiation, its connection with the magnetic field, its quantitative
modeling and related questions, such as the solar cycle variability
of the quiet Sun chromosphere and its cause. Finally, some thoughts
on the possible secular change of chromospheric (and total) irradiance
are presented.

---------------------------------------------------------
Title: Solar Activity and Irradiance Studies with Ca II
Spectroheliograms: Potential and Problems
Authors: Ermolli, I.; Tlatov, A.; Solanki, S. K.; Krivova, N. A.;
Singh, J.
2007ASPC..368..533E Altcode:
Various observatories around the globe carried out synoptic full-disk
observations of the Sun since the beginning of the 20th century. The
archives created by these observations, especially those including
Ca II spectroheliograms, have the potential of providing far more
detailed information on solar activity than the indices usually used to
study activity variations, solar cycle and irradiance changes. However,
these data suffer significantly from various problems including numerous
defects in the photographic plates, missing or inaccurate calibration of
the blackening curve, changes in the positioning of the exit slit with
respect to the spectral line and variable seeing. Here we discuss the
quality of images obtained by the digitization of three historic Ca II
K time series, specifically those stored by the Arcetri, Kodaikanal
and Mt Wilson Observatories. The aim of this work is to evaluate
the potential value of these data for studies of solar activity and
variability. It also shows the importance of the detailed and accurate
image processing technique, in order to obtain uniform and trustable
results from images coming from different historic archives.

---------------------------------------------------------
Title: Tenerife Infrared Polarimeter II
Authors: Collados, M.; Lagg, A.; Díaz Garcí A, J. J.; Hernández
Suárez, E.; López López, R.; Páez Mañá, E.; Solanki, S. K.
2007ASPC..368..611C Altcode:
Since May 2005 the Tenerife Infrared Polarimeter II (TIP-II) has been
operational at the Vacuum Tower Telescope on Tenerife. The core of the
polarimeter is a 1024×1020 pixel infrared camera allowing for high
precision measurements of the full Stokes vector with a pixel size of
0.18 arcsec, corresponding to the diffraction limit of the telescope at
1 μm. The polarimeter is able to reach a polarimetric accuracy of a few
times 10-4, covering a wavelength range of 1 to 1.8 μm. With
an upgrade in July 2006, the slit size has been increased to 77 arcsec
allowing most active regions to be covered with a single scan. Here
we present the technical details of the polarimeter and the camera. We
also show some data illustrating the power of this new instrumentation.

---------------------------------------------------------
Title: 2d Simulations Of Excitation And Damping Of Vertical Kink Waves
Authors: Selwa, Malgorzata; Murawski, K.; Solanki, S. K.; Ofman, L.
2007AAS...210.9115S Altcode: 2007BAAS...39S.206S
We consider different kinds of excitation of fast vertical kink
standing waves in a solar coronal loop that is embedded in a potential
arcade. The two dimensional numerical model we implement includes the
effects of field line curvature and nonlinearity on the excitation
and damping of standing fast magnetosonic waves. We investigate the
effects of a driven sinusodial pressure pulse and compare it with an
impulsive excitation by a pressure pulse that impacts the overlaying
loop. The results of the numerical simulations reveal wave signatures
which are characteristic of vertical loop oscillations seen in recent
TRACE observational data.

---------------------------------------------------------
Title: Reconstruction of the Long-Term Irradiance Variations
Authors: Balmaceda, L.; Krivova, N.; Solanki, S.
2007AGUSMGP54A..05B Altcode:
Solar irradiance variations have been recorded only since 1978. Clearly,
there is a need to extend these records into the past in order to
evaluate their possible influence on the Earth's climate. Here, a
reconstruction of solar irradiance back to the Maunder minimum from
the surface magnetic flux is presented. The reconstruction is based on
a simple physical model that builds on the sunspot number records and
sunspot areas where available. Since the sunspot area records generally
consist of a compilation of data from multiple observatories, a proper
cross-calibration is essential. The use of data of different sources
directly combined can lead to errors in estimating the increase of
solar irradiance during the past centuries. Thus, a brief description
of the cross-calibration of sunspot areas is also presented.

---------------------------------------------------------
Title: Reconstruction of solar total irradiance since 1700 from the
surface magnetic flux
Authors: Krivova, N. A.; Balmaceda, L.; Solanki, S. K.
2007A&A...467..335K Altcode:
Context: Total solar irradiance changes by about 0.1% between solar
activity maximum and minimum. Accurate measurements of this quantity are
only available since 1978 and do not provide information on longer-term
secular trends. Aims: In order to reliably evaluate the Sun's
role in recent global climate change, longer time series are, however,
needed. They can only be assessed with the help of suitable models. Methods: The total solar irradiance is reconstructed from the end of
the Maunder minimum to the present based on variations of the surface
distribution of the solar magnetic field. The latter is calculated
from the historical record of the sunspot number using a simple but
consistent physical model. Results: Our model successfully
reproduces three independent data sets: total solar irradiance
measurements available since 1978, total photospheric magnetic
flux since 1974 and the open magnetic flux since 1868 empirically
reconstructed using the geomagnetic aa-index. The model predicts an
increase in the solar total irradiance since the Maunder minimum of
1.3^+0.2_-0.4 Wm-2.

---------------------------------------------------------
Title: Full-Stokes Observations and Analysis of He I 10830 Å in a
Flaring Region
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.; Aznar Cuadrado, R.;
Collados, M.
2007ASPC..368..467S Altcode:
We present observations of the full Stokes vector in a flaring
region, taken in the chromospheric He I 10830 Å multiplet. The data
were recorded with the new Tenerife Infrared Polarimeter (TIP 2)
at the German Vacuum Tower Telescope (VTT) during May 2005. The He
profiles during the flare are extraordinary, showing extremely broad
Stokes I absorption and very complex and spatially variable Stokes V
signatures. We give first results on the line-of-sight velocities and
the magnetic field vector values in the chromosphere for one observed
Stokes profile by applying an inversion code to the He I lines.

---------------------------------------------------------
Title: Magnetic Stereoscopy of Coronal Loops in NOAA 8891
Authors: Feng, L.; Wiegelmann, T.; Inhester, B.; Solanki, S.; Gan,
W. Q.; Ruan, P.
2007SoPh..241..235F Altcode:
The Solar TErrestrial RElations Observatory (STEREO) requires powerful
tools for the three-dimensional (3D) reconstruction of the solar
corona. Here we test such a program with data from SOHO and TRACE. By
taking advantage of solar rotation, a newly developed stereoscopy tool
for the reconstruction of coronal loops is applied to the solar active
region NOAA 8891 observed from 1 March to 2 March 2000. The stereoscopic
reconstruction is composed of three steps. First, we identify loop
structures in two TRACE images observed from two vantage viewpoints
approximately 17 degrees apart, which corresponds to observations
made about 30 hours apart. In the second step, we extrapolate the
magnetic field in the corona with the linear force-free field model
from the photospheric line-of-sight SOHO/MDI data. Finally, combining
the extrapolated field lines and one-dimensional loop curves from two
different viewpoints, we obtain the 3D loop structures with the magnetic
stereoscopy tool. We demonstrate that by including the magnetic modeling
this tool is more powerful than pure geometrical stereoscopy, especially
in resolving the ambiguities generated by classical stereoscopy. This
work will be applied to the STEREO mission in the near future.

---------------------------------------------------------
Title: Properties of sunspots in cycle 23. I. Dependence of brightness
on sunspot size and cycle phase
Authors: Mathew, S. K.; Martínez Pillet, V.; Solanki, S. K.; Krivova,
N. A.
2007A&A...465..291M Altcode: 2007astro.ph..1401M
Aims:In this paper we investigate the dependence of umbral core
brightness, as well as the mean umbral and penumbral brightness on the
phase of the solar cycle and on the size of the sunspot. Methods:
Albregtsen &amp; Maltby (1978, Nature, 274, 41) reported an increase
in umbral core brightness from the early to the late phase of solar
cycle from the analysis of 13 sunspots which cover solar cycles 20
and 21. Here we revisit this topic by analysing continuum images
of more than 160 sunspots observed by the MDI instrument on board
the SOHO spacecraft for the period between 1998 March to 2004 March,
i.e. a sizable part of solar cycle 23. The advantage of this data set
is its homogeneity, with no seeing fluctuations. A careful stray light
correction, which is validated using the Mercury transit of 7th May,
2003, is carried out before the umbral and penumbral intensities are
determined. The influence of the Zeeman splitting of the nearby Ni I
spectral line on the measured "continuum" intensity is also taken into
account. Results: We did not observe any significant variation
in umbral core, mean umbral and mean penumbral intensities with solar
cycle, which is in contrast to earlier findings for the umbral core
intensity. We do find a strong and clear dependence of the umbral
brightness on sunspot size, however. The penumbral brightness also
displays a weak dependence. The brightness-radius relationship has
numerous implications, some of which, such as those for the energy
transport in umbrae, are pointed out.

---------------------------------------------------------
Title: Properties of Solar Polar Coronal Plumes Constrained by
Ultraviolet Coronagraph Spectrometer Data
Authors: Raouafi, N. -E.; Harvey, J. W.; Solanki, S. K.
2007ApJ...658..643R Altcode: 2007astro.ph..3745R
We investigate the plasma dynamics (outflow speed and turbulence)
inside polar plumes. We compare line profiles (mainly of O VI) observed
by the Ultraviolet Coronagraph Spectrometer (UVCS) instrument on
SOHO at the minimum of solar cycle 22-23 with model calculations. We
consider Maxwellian velocity distributions with different widths in
plume and interplume regions. Electron densities are assumed to be
enhanced in plumes and to approach interplume values with increasing
height. Different combinations of the outflow and turbulence velocity
in the plume regions are considered. We compute line profiles and total
intensities of the H I Lyα and the O VI doublets. The observed profile
shapes and intensities are reproduced best by a small solar wind speed
at low altitudes in plumes that increases with height to reach ambient
interplume values above roughly 3-4 Rsolar, combined with
a similar variation of the width of the velocity distribution of the
scattering atoms/ions. We also find that plumes very close to the
pole give narrow profiles at heights above 2.5 Rsolar,
which are not observed. This suggests a tendency for plumes to be
located away from the pole. We find that the inclusion of plumes in
the model computations provides an improved correspondence with the
observations and confirms previous results showing that published UVCS
observations in polar coronal holes can be roughly reproduced without
the need for large temperature anisotropy. The latitude distributions
of plumes and magnetic flux distributions are studied by analyzing
data from different instruments on SOHO and with SOLIS.

---------------------------------------------------------
Title: Magnetic flux transport on active cool stars and starspot
lifetimes
Authors: Işik, E.; Schüssler, M.; Solanki, S. K.
2007A&A...464.1049I Altcode: 2006astro.ph.12399I
Context: Many rapidly rotating cool stars show signatures of large
magnetic regions at all latitudes. Mid-latitude starspots and magnetic
regions have characteristic lifetimes of 1 month or less, as indicated
by observations using (Zeeman-) Doppler imaging techniques. Aims: We aim to estimate the lifetimes of bipolar magnetic regions
and starspots on the surfaces of cool stars. We consider different
possible configurations for starspots and compare their flux variations
and lifetimes based on a magnetic flux transport model. Methods:
We carry out numerical simulations of the surface evolution of bipolar
magnetic regions (BMRs) and magnetic spots on stars, which have radii
and surface rotational shears of <ASTROBJ>AB Doradus</ASTROBJ>, the Sun,
and the <ASTROBJ>HR 1099</ASTROBJ> primary. The surface flux transport
model is based on the magnetic induction equation for radial fields
under the effects of surface differential rotation, meridional flow,
and turbulent diffusion due to convective flow patterns. We calculate
the flux evolution and the lifetimes of BMRs and unipolar starspots,
varying the emergence latitude, surface shear rate, and tilt angle. Results: For BMRs comparable to the largest observed on the Sun, we
find that varying the surface flows and the tilt angle modifies the
lifetimes over a range of one month. For very large BMRs (area ~10%
of the stellar surface) the assumption of a tilt angle increasing with
latitude leads to a significant increase of lifetime, as compared to
the case without tilt. Such regions can evolve to polar spots that live
more than a year. Adopting the observed weak latitudinal shear and the
radius of the active subgiant component of HR 1099, we find longer
BMR lifetimes as compared to the more strongly sheared <ASTROBJ>AB
Dor</ASTROBJ> case. Random emergence of six additional tilted bipoles
in an activity belt at 60° latitude enhanced the lifetimes of polar
caps up to 7 years. We have also compared the evolution and lifetime
of monolithic starspots with those of conglomerates of smaller spots
of similar total area. We find similar decay patterns and lifetimes
for both configurations.

---------------------------------------------------------
Title: Energy leakage as an attenuation mechanism for vertical kink
oscillations in solar coronal wave guides
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Wang, T. J.
2007A&A...462.1127S Altcode:
Aims:We study wave leakage as a possible attenuation mechanism of
coronal loop oscillations in the ideal MHD regime. Methods:
We consider impulsively generated oscillations in solar coronal
magnetic wave guides such as a straight slab and a curved arcade
loop. The two-dimensional numerical model we implement includes the
effects of nonlinearity and line curvature on attenuation of fast
magnetosonic kink waves. Results: We show that these waves
are more strongly attenuated in the arcade loop than in the slab and
provide evidence that the curvature of magnetic field lines results in
excess energy leakage. For parameters appropriate for a coronal loop
the kink oscillation is too efficiently attenuated by energy leakage,
suggesting that in the solar atmosphere wave leakage must be reduced
compared to our simulations. We conclude that energy leakage is an
efficient source of attenuation of coronal loop oscillations.

---------------------------------------------------------
Title: The fraction of DA white dwarfs with kilo-Gauss magnetic fields
Authors: Jordan, S.; Aznar Cuadrado, R.; Napiwotzki, R.; Schmid,
H. M.; Solanki, S. K.
2007A&A...462.1097J Altcode: 2006astro.ph.10875J
Context: Weak magnetic fields have been searched for on only a small
number of white dwarfs. Current estimates find that about 10% of all
white dwarfs have fields in excess of 1 MG; according to previous
studies this number increases up to about 25% in the kG regime. Aims: Our aim is to improve on these statistics by a new sample
of ten white dwarfs in order to determine the ratio of magnetic to
field-free white dwarfs. Methods: Mean longitudinal magnetic
fields strengths were determined by means of high-precision circular
polarimetry of Hβ and Hγ with the FORS1 spectrograph of the VLT
"Kueyen" 8 m telescope. Results: In one of our objects (LTT
7987), we detected a statistically significant (97% confidence level)
longitudinal magnetic field varying between (-1± 0.5) kG and (+1±
0.5) kG. This would be the weakest magnetic field ever found in a
white dwarf, but systematic errors cannot completely be ruled out at
this level of accuracy. We also observed the sdO star EC 11481-2303 but
could not detect a magnetic field. Conclusions: . VLT observations
with uncertainties typically of 1000 G or less suggest that 15-20% of
WDs have kG fields. Together with previous investigations, the fraction
of kG magnetic fields in white dwarfs amounts to about 11-15%, which is
close to the current estimations for highly magnetic white dwarfs (&gt;1
MG). Based on observations made with ESO Telescopes at the La Silla
or Paranal Observatories under programme ID 073.D-0356. Figures A.1
and A.2 are only available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Supersonic downflows in the vicinity of a growing
pore. Evidence of unresolved magnetic fine structure at chromospheric
heights
Authors: Lagg, A.; Woch, J.; Solanki, S. K.; Krupp, N.
2007A&A...462.1147L Altcode:
Aims:The velocity and magnetic fine structure of the chromosphere at
the leg of an emerging magnetic loop is investigated at a location
of supersonic downflows. Methods: We analyze a time series of
spectropolarimetric data in the He i 1083 nm triplet covering a time
interval of ≈70 min. The temporal evolution as well as the topology
of the magnetic field in the downflow region are investigated. We
apply an inversion technique based on a genetic algorithm using the
Milne-Eddington approach. The technique is very reliable and robust in
retrieving maps of the velocity and the magnetic field vector for both
atmospheric components separately. Results: We observe redshifts
corresponding to a downflow speed of up to 40 km s-1 in the
vicinity of a growing pore. These supersonic downflows always coexist
with a second atmospheric component almost at rest (slow component)
within the same resolution element. The redshifted component is more
inclined to the solar normal than the slow component and has a different
field strength. Conclusions: .We interpret this downflow as a
consequence of the draining of the rising loops. The different magnetic
field orientation of the redshifted and the slow component give rise to
two possible interpretations: an uncombed structure of the chromosphere,
similar to the differently inclined flux-tubes in the penumbra of
a sunspot, or a cloud-like structure containing gas at different
velocities in two separate height layers of the solar atmosphere.

---------------------------------------------------------
Title: T he Lower Transition Region As Seen In The H I Lyman-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
2007ESASP.641E..84T Altcode:
The SUMER spectrometer aboard SOHO has been used to acquire several
raster images and temporal series of quiet-Sun targets at both disk
centre and the limb. Spectra have been recorded simultaneously in the
H I Lyman α and the Si III 120.6 nm line. Both spatial and temporal
maps of the integrated radiances appear very similar in the two lines,
despite the huge difference in optical thickness, a result showing the
H I Lyman α to be a good diagnostic of the dynamics and morphology of
the lower transition region. Oscillations can be detected and studied
at all observed locations. At disk centre, the 3 minute oscillations are
sporadically observed in the inter-network but also at locations at the
edges of network lanes, while 5 minute oscillations clearly dominate
the network. At the limb, evidence of 3 to 5 minute oscillations is
found at the base of spicules. Moreover, H I Lyman α spectra shows a
high degree of variability, revealing also the signature of explosive
events. The combination of high spectral purity images and slit spectra
in the H I Lyman α line would therefore be an exceptional new tool
to investigate the nature of the solar transition region. This line
is therefore of interest for both, a high resolution channel in the
EUI instrument and for the EUS spectrometer.

---------------------------------------------------------
Title: T he Lower Transitio n Region As Seen In The H I Lyman-α Line.
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
2007ESASP.641E..36T Altcode:
The SUMER spectrometer aboard SOHO has been used to acquire several
raster images and temporal series of quiet-Sun targets at both disk
centre and the limb. Spectra have been recorded simultaneously in the
H I Lyman α and the Si III 120.6 nm line. Both spatial and temporal
maps of the integrated radiances appear very similar in the two lines,
despite the huge difference in optical thickness, a result showing the
H I Lyman α to be a good diagnostic of the dynamics and morphology of
the lower transition region. Oscillations can be detected and studied
at all observed locations. At disk centre, the 3 minute oscillations are
sporadically observed in the inter-network but also at locations at the
edges of network lanes, while 5 minute oscillations clearly dominate
the network. At the limb, evidence of 3 to 5 minute oscillations is
found at the base of spicules. Moreover, H I Lyman α spectra shows a
high degree of variability, revealing also the signature of explosive
events. The combination of high spectral purity images and slit spectra
in the H I Lyman α line would therefore be an exceptional new tool
to investigate the nature of the solar transition region. This line
is therefore of interest for both, a high resolution channel in the
EUI instrument and for the EUS spectrometer.

---------------------------------------------------------
Title: SUNRISE: High resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Gandorfer, A. M.; Solanki, S. K.; Barthol, P.; Martínez
Pillet, V.; Schmidt, W.; Title, A. M.; Knölker, M.
2007msfa.conf...69G Altcode:
SUNRISE is an international project for the development, construction,
and operation of a balloon-borne solar telescope with an aperture
of 1 m, working in the UV/VIS spectral domain. The main scientific
goal of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
near diffraction-limited images of the photosphere and chromosphere
with an unpredecented resolution down to 35 km on the solar surface at
wavelengths around 220 nm. The focal-plane instrumentation consists of a
polarization sensitive spectrograph, a Fabry-Perot filter magnetograph,
and a phase-diverse filter imager working in the near UV. The first
stratospheric long-duration balloon flight of SUNRISE is planned in
summer 2009 from the Swedish ESRANGE station. SUNRISE is a joint project
of the German Max-Planck-Institut für Sonnensystemforschung (MPS),
Katlenburg-Lindau, with the Kiepenheuer-Institut für Sonnenphysik
(KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder,
USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo
Alto, USA, and the Spanish IMaX consortium. In this paper we will
present a brief description of the scientific and technological aspects
of SUNRISE.

---------------------------------------------------------
Title: Magnetic source of the solar cycle variation of the Mn I
539.4 nm line
Authors: Danilović, S.; Solanki, S. K.; Livingston, W.; Krivova,
N.; Vince, I.
2007msfa.conf..189D Altcode:
As a part of the long term program at KPNO, the Mn I 539.4 nm line has
been observed for nearly three solar cycles using the McMath telescope
and the 13.5 m spectrograph in double pass mode. These full-disk
spectrophotometric observations revealed an unusually large amplitude
change of its parameters over the solar cycle and its correlation with
Ca II K intensity. One of the proposed explanations for this phenomenon
is the optical pumping by the Mg II k line. With this work we would like
to show that this may not be the main mechanism behind the change. We
reconstructed the changes of the line parameters using a model that
takes into account only changes of the daily surface distributions of
magnetic field. This model has already been used to successfully model
total solar irradiance. We now apply it for modelling the Mn I line,
as well as its neighboring Fe I line using exactly the same value
of the free parameter as used for the reconstruction of total solar
irradiance. We reproduce well the Mn I and Fe I line changes over the
cycle purely with LTE modelling. This indicates that optical pumping
of the Mn I line by Mg II k is not the main cause of its solar cycle
change and sets an independent constraint on solar irradiance models.

---------------------------------------------------------
Title: Structure and evolution of supergranulation from local
helioseismology
Authors: Hirzberger, J.; Gizon, L.; Solanki, S. K.; Duvall, T. L.
2007msfa.conf..103H Altcode:
Maps of the horizontal divergence of the near-surface velocity field
have been calculated using local helioseismology and SOHO/MDI full-disk
Dopplergrams. These maps provide a continuous coverage for two to
three months each year with a cadence of 12 hours. Geometrical and
evolutional properties of individual supergranular cells have been
studied. Supergranular cells have sizes in a range around 650Mm2
(circular diameter of 28.77 Mm) with lifetimes of up to 4.5 days. We
also observe a clear trend for larger cells to have stronger divergence
values and larger lifetimes than smaller ones.

---------------------------------------------------------
Title: EUI, The Ultraviolet Imaging Telescopes Of Solar Orbiter
Authors: Hochedez, J. -F.; Appourchaux, T.; Defise, J. -M.; Harra,
L. K.; Schühle, U.; Auchère, F.; Curdt, W.; Hancock, B.; Kretzschmar,
M.; Lawrence, G.; Leclec'h, J. -C.; Marsch, E.; Mercier, R.; Parenti,
S.; Podladchikova, E.; Ravet, M. -F.; Rochus, P.; Rodriguez, L.;
Rouesnel, F.; Solanki, S.; Teriaca, L.; Van Driel, L.; Vial, J. -C.;
Winter, B.; Zhukov, A.
2007ESASP.641E..33H Altcode:
The scientific objectives of Solar Orbiter rely ubiquitously on EUI,
its suite of solar atmosphere imaging telescopes. In the configuration
discussed here, EUI includes three co-aligned High Resolution Imagers
(HRI) and one Full Sun Imager (FSI). FSI and two HRIs observe in extreme
ultraviolet passbands, dominated by coronal emission. Another HRI is
designed for the hydrogen Lyman α radiation in the far UV, imaging the
Chromosphere and the lower Transition Region. The current EUI design
and some of its development challenges are highlighted. EUI profits from
co-rotation phases, solar proximity and departure from the ecliptic. In
synergy with the other S.O. payload, EUI probes the dynamics of the
solar atmosphere, provides context data for all investigations and helps
to link in-situ and remote-sensing observations. In short, it serves all
four top-level goals of the mission. For these reasons, the EUI suite
is keenly anticipated in the European scientific community and beyond.

---------------------------------------------------------
Title: Nanoflare model of emission line radiance distributions in
active region coronae
Authors: Safari, H.; Innes, D. E.; Solanki, S. K.; Pauluhn, A.
2007msfa.conf..359S Altcode:
Nanoflares are small impulsive bursts of energy that blend with and
possibly make up much of the solar background emission. Determining
their overall contribution is central to understanding the heating of
the solar corona. Here, a simple nanoflare model based on three key
parameters: the flare rate, the flare damping time, and the power-law
slope of the flare energy frequency distribution has been used to
simulate emission line radiances observed by SUMER in the corona
above an active region. The three lines analysed, Fe XIX, Ca XIII,
and Si III have very different formation temperatures, damping times
and flare rates but all suggest a power-law slope greater than 2. Thus
it is possible that nanoflares provide a significant fraction of the
flare energy input to active region coronae.

---------------------------------------------------------
Title: A nanoflare model of quiet Sun EUV emission
Authors: Pauluhn, A.; Solanki, S. K.
2007A&A...462..311P Altcode: 2006astro.ph.12585P
Nanoflares have been proposed as the main source of heating of the
solar corona. However, detecting them directly has so far proved
elusive, and extrapolating to them from the properties of larger
brightenings gives unreliable estimates of the power-law exponent
α characterising their distribution. Here we take the approach of
statistically modelling light curves representative of the quiet Sun
as seen in EUV radiation. The basic assumption is that all quiet-Sun
EUV emission is due to micro- and nanoflares, whose radiative energies
display a power-law distribution. Radiance values in the quiet Sun
follow a lognormal distribution. This is irrespective of whether the
distribution is made over a spatial scan or over a time series. We show
that these distributions can be reproduced by our simple model. By
simultaneously fitting the radiance distribution function and the
power spectrum obtained from the light curves emitted by transition
region and coronal lines the power-law distribution of micro- and
nanoflare brightenings is constrained. A good statistical match to the
measurements is obtained for a steep power-law distribution of nanoflare
energies, with power-law exponent α&gt; 2. This is consistent with
the dominant heat input to the corona being provided by nanoflares,
i.e., by events with energies around 1023 erg. In order to
reproduce the observed SUMER time series approximately 103
to 104 nanoflares are needed per second throughout the
atmosphere of the quiet Sun (assuming the nanoflares to cover an
average area of 1013 m2).

---------------------------------------------------------
Title: Reconstruction of solar irradiance using the Group sunspot
number
Authors: Balmaceda, L.; Krivova, N. A.; Solanki, S. K.
2007AdSpR..40..986B Altcode: 2007astro.ph..3147B
We present a reconstruction of total solar irradiance since 1610 to
the present based on variations of the surface distribution of the
solar magnetic field. The latter is calculated from the historical
record of the Group sunspot number using a simple but consistent
physical model. Our model successfully reproduces three independent
data sets: total solar irradiance measurements available since 1978,
total photospheric magnetic flux from 1974 and the open magnetic
flux since 1868 (as empirically reconstructed from the geomagnetic
aa-index). The model predicts an increase in the total solar irradiance
since the Maunder Minimum of about 1.3 Wm -2.

---------------------------------------------------------
Title: T he Performance Of The SOLO-VIM Instrument: Effects Of
Instrumental Noise And Lossy Data Compression
Authors: Lagg, A.; Yelles, L.; Hirzberger, J.; Woch, J.; Solanki, S. K.
2007ESASP.641E..69L Altcode:
Spectropolarimetric observations in photospheric lines reveal a
wealth of information on physical parameters of the solar atmosphere
like magnetic field strength and di rection or the line-of sight
velocity. These observations require the measurement of the four Stokes
parameters at a sample of N wavelength positions around the core of the
spectral line, resulting in 4N images for one observation. The Visible
light Imager and Magnetograph (VIM) instrument on board Solar Orbiter
is capable of performing these measurements. However, the data rate
required to transfer all 4N images with the required cadence is well
beyond the telemetry limit. Here we use realistic, three-dimensional
MHD simulations in order to simulate science data provided by VIM which
are then used to test various compression techniques. We conclude that
lossy data compression and instrumental noise have similar effects on
the output data.

---------------------------------------------------------
Title: S imulations Of Science Data Of The Solo-VIM Instrument
Authors: Yelles, L.; Hirzberger, J.; Lagg, A.; Woch, J.; Solanki,
S. K.; Vögler, A.
2007ESASP.641E..34Y Altcode:
The SolO-VIM instrument will be a two-dimensional full-Stokes
spectro-polarimeter which will provide diffraction-limited
vector-magnetograms, Dopplergrams, and continuum images of the solar
photosphere. The instrument's performance depends on various parameters
such as aperture diameter, filter characteristics, spectral- line
sampling, and orbital position. Here we compute Stokes profiles in
realistic 3D MHD simulations. These synthetic data are then degraded to
match the output ex- pected from the VIM instrument, and subsequently
inverted using a Milne-Eddington atmosphere. We present parameter
studies in order to set up minimum require- ments on limitations of
VIM's capabilities.

---------------------------------------------------------
Title: Velocity distribution of chromospheric downflows
Authors: Aznar Cuadrado, R.; Solanki, S. K.; Lagg, A.
2007msfa.conf..173A Altcode:
Infrared spectropolarimetric observations were obtained with the
Tenerife Infrared Polarimeter (TIP) at the German Vacuum Tower
Telescope (VTT) of the Spanish observatory of Izana, Tenerife. We
present the velocity distributions of a large dataset composed of
maps of the Stokes I, Q, U, and V profiles of active and quiet sun
regions obtained in the chromospheric He I 1083.0 nm triplet. The
line-of-sight velocities were determined by applying a multi-Gaussian
fit to the intensity profiles. Single and double component fits were
carried out for all datasets. We find that 18.7% of all observed
pixels show strong downflows as evidenced by a second line profile
component, generally shifted by more than 8 km s-1 relative to the rest
wavelegth. The distribution of these strong down-flows displays two
distinct populations. The slower one (near sonic and weakly supersonic
flows) has line-of-sight velocities up to 17 km s-1 and is associated
with moderate to strong magnetic signal (up to √(Q2 + U2 + V2)/Ic =
0.08). Strongly supersonic downflows (reaching up to 60 km s-1) are
found at places with weak to moderate magnetic signal, with √(Q2 +
U2 + V2)/Ic values mainly between 0.01 and 0.03.

---------------------------------------------------------
Title: Spectropolarimetry in the chromospheric He I 1083.0 nm
multiplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
2007waas.work...43S Altcode:
Spectropolarimetry in the He I 1083.0 nm multiplet has a great
potential to obtain information on the magnetic field in the solar
upper chromosphere. We apply an inversion technique to infrared
spectropolarimetric observations, to retrieve the full magnetic vector
and the line-of sight velocity. The observations, obtained with the
Tenerife Infrared Polarimeter (TIP) II at the German Vacuum Tower
Telescope (VTT), provide maps in the Stokes parameters I, Q, U and V.

---------------------------------------------------------
Title: Magnetic flux transport and the lifetimes of spots on active
cool stars
Authors: Işik, E.; Schüssler, M.; Solanki, S. K.
2007msfa.conf..367I Altcode:
We present results of numerical simulations of magnetic flux transport
on the surfaces of cool stars with radii of 1 Rm and 3.3 Rm. The
effects of differential rotation and the tilt angle on the lifetimes
of stellar bipolar magnetic regions are discussed. The existence of
long-lasting polar spots can be explained by high-latitude persistent
emergence of bipolar regions.

---------------------------------------------------------
Title: High-resolution CN spectroscopy of small-scale solar magnetic
features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
2007msfa.conf..161Z Altcode:
High-resolution spectroscopic observations of small-scale magnetic
elements in the solar photosphere were carried out in the spectral
region 387.5388.4 nm with the 1-m Swedish Solar Telescope (SST). This
part of the spectrum covers not only the violet CN band-head, but also
contains some lines of the CH molecule. The analysis of the line-core
intensity contrasts of the CN and CH lines in bright points (BPs)
yielded that on average the BPs appear brighter, thus providing a higher
rms contrast, in the CN than in the CH lines in the same spectral band.

---------------------------------------------------------
Title: Wavelet-based method for coronal loop oscillations analysis
Authors: Tothova, D.; Innes, D. E.; Solanki, S. K.
2007msfa.conf..265T Altcode:
We study the properties of Doppler shift oscillations observed
in hot coronal loops by SoHO/SUMER. These oscillations have been
identified as magnetoacoustic slow mode standing waves and may be an
important magnetic field diagnostic for the oscillating loops. Visual
inspection of the SUMER data suggests that one in three microflares
trigger oscillation. So for an average active region we can expect
several oscillation events per hour. To study the statistics of
the oscillations, automatic identification and classification of
the events is required. We have performed a Wavelet analysis on a 12
hour time series of SUMER Fe XIX data and find that almost all of the
oscillation events in the data set are identified by this technique,
with very few false positives. The method is expected to be useful
for the analysis of future Ca XVII and Fe XXIV spectra of microflares
observed with HINODE/EIS.

---------------------------------------------------------
Title: Modified p-modes in penumbral filaments
Authors: Bloomfield, D. S.; Lagg, A.; Solanki, S. K.; Borrero, J. M.
2007msfa.conf..241B Altcode:
A time series analysis was performed on velocity signals in a sunspot
penumbra to search for possible wave modes. The spectropolarimetric
photospheric data obtained by the Tenerife Infrared Polarimeter were
inverted using the SPINOR code. An atmospheric model comprising two
magnetic components and one stray-light component gave an optimal fit
to the data. Fourier phase difference analysis between line-of-sight
velocities of both magnetic components provided time delays between
the two atmospheres. These delays were combined with the speeds of
atmospheric wave modes and compared to height separations derived from
velocity response functions to determine the wave mode.

---------------------------------------------------------
Title: Nonlinear Force-Free Magnetic Field Modelling For VIM On SO
Authors: Wiegelmann, T.; Solanki, S. K.; Yelles, L.; Lagg, A.
2007ESASP.641E..19W Altcode:
The aim of this work is to investigate how photon noise and errors
in the retrieval of solar magnetic parameters from measured Stokes
profiles influences the extrapolartion of nonlinear force-free
coronal magnetic fields from photospheric vector magnetograms. To
do so we use a nonlinear force-free extrapolation code based on an
optimization principle. The extrapolation methods has been extensively
tested and applied to data from various telescopes. Here we apply the
code artificial vector magnetograms obtained from 3-D radiation-MHD
simulations. As a reference case we compute the coronal magnetic field
from an ideal magnetogram and compare the result with more realistic
magnetograms based on simulated Solar Orbiter/VIM-measurements. We
investigate the effect of noise, ambiguities, spatial resolution,
inversion mechanism, of Stokes profiles etc. We rate the quality of
the reconstructed coronal magnetic field qualitatively by magnetic
field line plots and quantitatively by a number of comparison metrices,
e.g., the vector correlation with the exact solution and how accurate
the free magnetic energy is computed. Not surprisingly, the instrument
effects and noise influence the quality of the nonlinear force-free
coronal magnetic field model. The extrapolations from realistic vector
magnetograms show a reasonable agreement with the ideal reconstruction,
however, and are in particular significantly better than extrapolations
based on line-of-sight magnetograms only. High quality VIM data
will thus allow reasonably accurate extrapolations that can serve
as the basis for magnetic coupling science through a comparison with
observations from EUS and EUI.

---------------------------------------------------------
Title: S pace Qualification Of A Thin Wafer Lithium Niobate Etalon
For The Visible Light Imager And Magnetograph (Vim)
Authors: Schühle, U.; Mathew, S. K.; Wedemeier, M.; Hartwig, H.;
Ballesteros, E.; Martinez Pillet, V.; Solanki, S. K.
2007ESASP.641E..82S Altcode:
For the Visible Light Imager and Magnetograph (VIM) a high-resolution
filtergraph is under design. The system takes advantage of a lithium
niobate (LiNbO3) crystal which can be used as a scanning filter using
high voltage for tuning. We have undertaken first studies to qualify
a lithium niobate wafer of 70 mm aperture size for deployment and use
in space. We show the results of the mechanical mounting and vibration
and thermal cycling tests as well as stability tests under fast voltage
tuning in vacuum. Although these tests have all been very successful,
further environmental testing is necessary to fully space-qualify the
filter for the Solar Orbiter mission.

---------------------------------------------------------
Title: Spectro-Polarimetry of a Sunspot in Atomic and Molecular
Lines with THEMIS
Authors: Arnaud, J.; Berdyugina, S. V.; Fluri, D. M.; Afram, N.;
Solanki, S. K.; Raouafi, N. -E.
2006ASPC..358..319A Altcode:
We present spectro-polarimetric observations of a sunspot, which were
recorded simultaneously with THEMIS in various atomic and molecular
lines. These observations include the first full Stokes measurements
of the band-head of TiO around 7055 Å.

---------------------------------------------------------
Title: Molecular Diagnostics of the Internal Structure of Starspots
and Sunspots
Authors: Afram, N.; Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.;
Lagg, A.; Petit, P.; Arnaud, J.
2006ASPC..358..375A Altcode:
We have analyzed the usefulness of molecules as a diagnostic tool for
studying solar and stellar magnetism with the molecular Zeeman and
Paschen-Back effects. In the first part we concentrate on molecules
that are observed in sunspots such as MgH and TiO. We present calculated
molecular line profiles obtained by assuming magnetic fields of 2-3 kG
and compare these synthetic Stokes profiles with spectro-polarimetric
observations in sunspots. The good agreement between the theory and
observations allows us to turn our attention in the second part to
starspots to gain insight into their internal structure. We investigate
the temperature range in which the selected molecules can serve as
indicators for magnetic fields on highly active cool stars and compare
synthetic Stokes profiles with our recent observations.

---------------------------------------------------------
Title: The Molecular Paschen-Back Effect
Authors: Berdyugina, S. V.; Fluri, D. M.; Solanki, S. K.
2006ASPC..358..329B Altcode:
The molecular Paschen-Back effect (PBE) lacks a detailed description
since the problem was first addressed by Hill in 1929. However,
many diatomic molecules exhibit the PBE at field strengths typical of
sunspots and active cool stars. Recently we have presented a complete
theoretical description of the molecular PBE in Hund's cases (a), (b),
and all intermediate cases. This description allows us to compute the
splitting of levels of any multiplicity and the transitions between
them. We find that in the partial PBE regime strongly asymmetric
Stokes profiles are produced, whose strengths and asymmetries depend
sensitively on the magnetic field. Also, the strength of the forbidden
and satellite transitions increases rapidly with field strength,
while the strength of the main branch transitions decreases. These
signatures hold promise to form the basis of new diagnostics of solar
and stellar magnetic fields.

---------------------------------------------------------
Title: Measuring the Magnetic Vector with the He I 10830 Å Line:
A Rich New World
Authors: Solanki, S. K.; Lagg, A.; Aznar Cuadrado, R.; Orozco Suárez,
D.; Collados, M.; Wiegelmann, T.; Woch, J.; Sasso, C.; Krupp, N.
2006ASPC..358..431S Altcode:
The triplet of the He I transitions around 10830 Å not only shows a
rich variety of Stokes profiles, but also allows the full magnetic
vector in the upper chromosphere to be probed, thus revealing
the magnetic structure of loops, current sheets, finely structured
supersonic downflows, the chromospheric layers of sunspots (supporting
the presence of uncombed fields in the penumbra), flares, and the
quiet Sun. A very brief overview of some of the observations and
results obtained so far is given.

---------------------------------------------------------
Title: Reconstruction of solar irradiance variations in cycles 21-23
based on surface magnetic fields
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.; Fröhlich, C.
2006A&A...460..583W Altcode:
Aims.We present a reconstruction of total solar irradiance (TSI) back
to 1974, i.e. from the minimum of cycle 21 to the declining phase of
cycle 23. We also present a cross-calibration between the magnetograms
obtained by the 512 channel magnetograph and the spectromagnetograph
at Kitt Peak. Methods: .The TSI reconstruction is carried out
using data from the 512-channel Diode Array Magnetograph and the newer
spectromagnetograph on Kitt Peak. The model is based on the assumption
that all irradiance changes on time-scales of a day and longer are
entirely due to the variations of the surface distribution of the
solar magnetic field. The reconstructed irradiance is compared with
the composite of total solar irradiance measurements from PMOD/WRC
(version 41). Results: .A good correspondence is found with the
PMOD TSI composite, with no bias between the three cycles on time-scales
longer than the solar rotation period, although the accuracy of the
TSI reconstruction is somewhat lower when 512 channel magnetograph
data are used. This suggests that the same driver of the irradiance
variations, namely the evolution of the magnetic flux at the solar
surface, is acting in cycles 21-23. Different methods of comparing
the magnetograms obtained by the two Kitt Peak magnetographs give
somewhat different results, with factors by which 512 channel data
must be divided in the range 1.38-1.63 being found. This is due to the
non-linearity of the relationship between the magnetic field measured
by the two instruments.

---------------------------------------------------------
Title: The Uncombed Penumbra
Authors: Borrero, J. M.; Rempel, M.; Solanki, S. K.
2006ASPC..358...19B Altcode: 2006astro.ph..2130B
The uncombed penumbral model explains the structure of the sunspot
penumbra in terms of thick magnetic fibrils embedded in a surrounding,
magnetic atmosphere. This model has been successfully applied to explain
the polarization signals emerging from the sunspot penumbra. Thick
penumbral fibrils face some physical problems, however. In this
contribution we will offer possible solutions to these shortcomings.

---------------------------------------------------------
Title: Supersonic Downflows in the Vicinity of a Solar Pore
Authors: Lagg, A.; Woch, J.; Solanki, S. K.; Gandorfer, A.
2006ASPC..358..437L Altcode:
At the footpoints of magnetic arcades spanning over a site of flux
emergence we observe strong redshifts in the He I triplet at 1083
nm. These redshifts are associated with downflow speeds of up to
40 km s-1. Within the spatial resolution of our data (1
arcsec-2 arcsec) obtained with the Tenerife Infrared Polarimeter at
the VTT we find an almost unshifted atmospheric component coexisting
with the redshifted component. We were able to retrieve the magnetic
field configuration in both the unshifted and the redshifted component
simultaneously and infer an uncombed, fibril-like structure of the
upper chromosphere. The supersonic downflow speeds are interpreted as
a consequence of a significantly reduced pressure scale height above
the pore, where the magnetic arcades are rooted. A temporal series of
the fast downflow region reveals that the supersonic flow is maintained
for more than one hour. Making use of the increased spatial resolution
of the new TIP2 instrument we are working on reducing the upper limit
on the size of the fibril-like flux channels in the upper chromosphere.

---------------------------------------------------------
Title: Secular variations of solar activity and irradiance
Authors: Solanki, S.
2006AGUFMSH41A..01S Altcode:
Regular direct measurements of solar activity started around 1611
when sunspots detected by telescopic means began to be counted. Solar
irradiance variations have been recorded for a much shorter time, only
since 1978. Clearly, there is a need to extend both of these records
into the past. In this talk reconstructions of solar irradiance back
to the Maunder minimum and of sunspot number over multiple millenia
are introduced. A comparison with climate reconstructions over the
last millenium is shown and the next necessary steps in this line of
research are considered.

---------------------------------------------------------
Title: Long-term solar activity reconstructions: direct test by
cosmogenic 44Ti in meteorites
Authors: Usoskin, I. G.; Solanki, S. K.; Taricco, C.; Bhandari, N.;
Kovaltsov, G. A.
2006A&A...457L..25U Altcode:
Aims.Long-term solar activity in the past is usually estimated from
cosmogenic isotopes, 10Be or 14C, deposited in
terrestrial archives such as ice cores and tree rings. A number of such
reconstruction models have been proposed which differ from each other
significantly. This approach suffers, however, from uncertainties due
to the sensitivity of the data to several terrestrial processes. Here
we propose a method to constrain these solar activity reconstructions
using cosmogenic 44Ti activity in meteorites which is
not affected by terrestrial processes. Methods: .We test the
veracity of recent solar activity reconstructions using the data on
the activity of cosmogenic isotope 44Ti in meteorites which
fell during the past 235 years, and provide an independent and direct
measure of the cosmic ray flux near the Earth and allow decoupling of
solar activity variations from terrestrial influences. Results:
.We demonstrate that the 44Ti data can distinguish between
various reconstructions of past solar activity based on cosmogenic
isotope data in terrestrial archives, allowing unrealistic models to
be ruled out. We also show that a model based on the sunspot number
record is consistent with the data on 44Ti activity in
meteorites, thus confirming the validity of the method. In particular
the 44Ti data confirm significant secular variations of
the solar magnetic flux during the last century.

---------------------------------------------------------
Title: High-resolution millimeter-interferometer observations of
the solar chromosphere
Authors: White, S. M.; Loukitcheva, M.; Solanki, S. K.
2006A&A...456..697W Altcode:
The use of millimeter-interferometer data for the study of chromospheric
structure and dynamics is tested using 85 GHz observations with the
10-element Berkeley-Illinois-Maryland Array (BIMA). Interferometer
data have the advantage over single-dish data that they allow both high
spatial resolution and dense temporal sampling simultaneously. However,
snapshot imaging of the quiet solar atmosphere with a small number of
dishes is challenging. We demonstrate that techniques are available to
carry out this task successfully using maximum entropy deconvolution
from a default image constructed from the entire observation: one of
our results is that the solar chromosphere at millimeter wavelengths
exhibits features that are long-lasting and the map of the entire
observation is significant provided that atmospheric phase errors do
not prevent deconvolution. We compare observations of quiet Sun, active
region and coronal hole targets. The interferometer is not sensitive
to the disk emission and the positivity constraint of the maximum
entropy algorithm used forces the zero level in the images to be at
the temperature of the coolest feature in each field. The brightest
features in the images are typically 1000-1500 K above the zero level,
with a snapshot noise level of order 100 K. We use extensive tests to
determine whether oscillation power can be recovered from sequences of
snapshot images and show that individual sources can be down to quite
weak levels at locations in the image where significant flux is present;
oscillation power located in cool regions of the image is not well
recovered due to the deconvolution method used and may be redistributed
to brighter regions of the millimeter image. We then investigate
whether the data do show oscillation power using uninterrupted 30-min
scans of the target regions. Intensity oscillations with significant
power in the frequency range 1.5-8.0 mHz are found in the quiet-Sun
and active region targets. For the quiet-Sun region we compare the
oscillation properties of network boundaries and cell interiors
(internetwork) in the spatially-resolved time series. In agreement
with investigations at other wavelengths, in the millimeter data the
power in the network tends to be at periods of 5 min and longer while
power in the internetwork is present also at shorter (3-min) periods.

---------------------------------------------------------
Title: The dynamics of the solar chromosphere: comparison of model
predictions with millimeter-interferometer observations
Authors: Loukitcheva, M.; Solanki, S. K.; White, S.
2006A&A...456..713L Altcode:
We analyze the millimeter intensity spectrum expected from the dynamic
model of Carlsson &amp; Stein together with the interferometric
observations of the quiet Sun obtained at a wavelength of 3.5 mm with
the Berkeley-Illinois-Maryland Array. The observational data products
(Fourier and wavelet spectra, brightness histograms) are compared
with the corresponding products obtained for the Carlsson &amp;
Stein (CS) models. We estimate how the limited spatial resolution
of the observations influences the comparison with the predictions
of chromospheric dynamic models and discuss the limitations of a
one-dimensional non-magnetic modeling approach. In addition, we test the
effect of the integration time of the BIMA observations on the dynamic
signatures. The dependence of the observed brightness variations on
spatial resolution is studied by employing artificial image degradation
and approximating the obtained dependence by power laws. We are able
to establish a correspondence between the CS model predictions and
the observational data under assumptions on the horizontal coherence
length of the oscillations. The reconstructed brightness rms values
indicate that, assuming the coherence length of oscillating elements
to be of order of 1”, the oscillation power in the observations
recorded with 10” resolution agrees within a factor of 2 with the
power predicted by the CS model. We argue that millimeter continuum
observations promise to be an important diagnostic of chromospheric
structure and dynamics. Based on the analysis carried out in this work,
the appropriate wavelengths to look for dynamic signatures are in the
range 0.8-5.0 mm. Further millimeter interferometric observations with
longer sequences and higher spatial resolution are highly desirable
along with the development of realistic three-dimensional radiation
magnetohydrodynamic simulations.

---------------------------------------------------------
Title: Fe XIX observations of active region brightenings in the corona
Authors: Wang, T. J.; Innes, D. E.; Solanki, S. K.
2006A&A...455.1105W Altcode:
Small flarelike brightenings seen in the hot flare line, Fe XIX,
by the spectrometer SUMER on SOHO are analysed. We observe active
region coronae about 30 Mm off the limb of the Sun for a period of
several days. Brightenings are observed with a frequency 3-14 per hour
and their lifetimes range from 5-150 min, with an average of about
25 min. The measured size of the events along the spectrometer slit
range from 2-67 Mm, but most are around 7 Mm. Like soft X-ray active
region transient brightenings, they range in estimated thermal energy
from 1026 to 1029 erg with a power law index of
1.7 to 1.8, beyond 1027 erg. We conclude that they are the
coronal parts of loops heated to &gt; 6 MK by soft X-ray microflares.

---------------------------------------------------------
Title: Milne-Eddington inversions of the He &lt;sf&gt;I&lt;/sf&gt;
10 830 Å Stokes profiles: influence of the Paschen-Back effect
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
2006A&A...456..367S Altcode: 2011arXiv1102.0898S
Context: .The Paschen-Back effect influences the Zeeman sublevels
of the He I multiplet at 10 830 Å, leading to changes in strength
and in position of the Zeeman components of these lines. Aims:
.We illustrate the relevance of this effect using synthetic Stokes
profiles of the He I 10 830 Å multiplet lines and investigate its
influence on the inversion of polarimetric data. Methods: .We
invert data obtained with the Tenerife Infrared Polarimeter (TIP)
at the German Vacuum Tower Telescope (VTT). We compare the results of
inversions based on synthetic profiles calculated with and without the
Paschen-Back effect being included. Results: .We find that when
taking into account the incomplete Paschen-Back effect, on average 16%
higher field strength values are obtained. We also show that this effect
is not the main cause for the area asymmetry exhibited by many He I
10 830 Stokes V-profiles. This points to the importance of velocity
and magnetic field gradients over the formation height range of these
lines.

---------------------------------------------------------
Title: Vector tomography for the coronal magnetic
field. I. Longitudinal Zeeman effect measurements
Authors: Kramar, M.; Inhester, B.; Solanki, S. K.
2006A&A...456..665K Altcode:
Aims.We study the possibility of applying tomographic techniques in
order to reconstruct the 3D magnetic field configuration in the solar
corona. Our simulations are based on data which can be obtained from
longitudinal Zeeman-effect (or from Faraday rotation) measurements
obtained during a solar rotation. Methods: .The Zeeman effect
provides essentially the integrated line-of-sight component of the
magnetic field. The reconstruction problem relates to a family of
similar problems termed vector tomography. For inversion of this type
problems it is known that the curl-free part of a vector field cannot
be reconstructed from the integrated along line-of-sight data. To
remove the resulting ambiguity of the reconstruction we include the
additional constraint, ∇\cdotB=0, into the inversion similar to
smoothing constraints in Tikhonov regularization problems. 
Results: .It is shown that Zeeman data obtained from vantage points
in the ecliptic plane alone is sensitive only to certain magnetic
field structures. For a full reconstruction it is necessary either to
have also observations from viewing directions at higher heliographic
latitudes, or to combine the longitudinal Zeeman-effect data with
observations that provide the transverse component of the field,
e.g. from the Hanle effect.

---------------------------------------------------------
Title: Solar Variability of Possible Relevance for Planetary Climates
Authors: Solanki, S. K.; Krivova, N. A.
2006SSRv..125...25S Altcode: 2006SSRv..tmp...97S
The global variability of the Sun of relevance for planetary climates
has been directly measured for the past few decades. For longer
stretches of time models are required. Semi-empirical models can now
accurately reproduce the measured records of solar total and spectral
irradiance, as well as of the magnetic flux. They can also provide
reconstructions of these quantities on longer time scales. Here a
summary is given of some of the modelling efforts and of the results
achieved so far.

---------------------------------------------------------
Title: Multi-component analysis of a flaring region in the
chromospheric He I 1083.0 nm triplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
2006IAUJD...3E..31S Altcode:
We present infrared spectropolarimetric observations of the solar active
region NOAA 0763 obtained with the new Tenerife Infrared Polarimeter
(TIP 2) at the German Vacuum Tower Telescope (VTT) during May 2005,
taken in the chromospheric He I 1083.0 nm multiplet. The region was
in the initial phase of a C2.0 flare. We observe up to 4 atmospheric
components within the spatial resolution of our observations. The
components are clearly separated in wavelength, the largest separation
corresponding to downflow velocities of up to 64 km/s. We give
preliminary results on the magnetic vector and the line-of sight
velocity obtained by inverting the Stokes I, Q, U and V profiles of
the He 1083.0 nm triplet.

---------------------------------------------------------
Title: High-Resolution CN Spectroscopy of Small-Scale Solar Magnetic
Features
Authors: Zakharov, V. V.; Gandorfer, A.; Solanki, S. K.
2006IAUJD...3E..87Z Altcode:
High-resolution spectroscopic observations of the Sun have been
carried out with the TRIPPEL spectrograph installed at the new 1-m
Swedish Solar Telescope (SST) using realtime AO correction. A detailed
spectroscopic analysis of individual photospheric bright points (BP)
and faculae-like structures simultaneously in two spectral domains,
i.e 387.588&lt;λ&lt;388.473 nm (violet CN band) and in a blue spectral
band at 436.1&lt;λ&lt;436.9 nm, containing absorption lines of CH,
obtained at the disc center and near the limb is presented. The
estimated spatial resolution of the obtained spectra is around
0.25 arcsec while the spectral resolving power is around 130.000
in the first domain, and 76.000 in the second spectral region,
respectivlely. The first spectral band covers absorption lines of
both, CH and CN molecules, as well as many atomic lines. This enabled
us to make a quantitative comparison of their absorption and Doppler
shifts in the different photospheric features. The absorption lines
of the CN molecule and many atoms are depressed in a BP's interior
with respect to those in the quiet Sun. Our quantitative comparison
of the relative line depression of CH lines with respect to CN lines
showed that the latter have weaker absorption by a factor of 1.28 at
the disc centre and 1.32 near the limb. The CN line-core intensity,
at the disc centre, has higher BP contrast than the contrast in the
CH line-core by a factor of 1.9, and the ratio of these contrasts
is decreasing with increasing continuum intensity of the BPs. This
trend is similar to that obtained from previous simultaneous G-band
and violet CN-band imaging observations. Measurements of contrasts and
rms contrasts of line-core, integrated and local continuum intensities
are provided. Analysis of Doppler shifts and line broadening of an
Fe I line at 387.777 nm revealed an increase of the FWHM in the BP's
interior and in dark intergranular lanes and a decrease with increasing
intensity of the granules. The first results of a direct comparison
of observed CN spectra with those simulated in MHD models in different
photospheric features is presented.

---------------------------------------------------------
Title: Flux Emergence In The Solar Photosphere - Diagnostics Based
On 3-D Rradiation-MHD Simulations
Authors: Yelles Chaouche, L.; Cheung, M.; Lagg, A.; Solanki, S.
2006IAUJD...3E..75Y Altcode:
We investigate flux tube emergence in the solar photosphere using a
diagnostic procedure based on analyzing Stokes signals from different
spectral lines calculated in 3-D radiation-MHD simulations. The
simulations include the effects of radiative transport and partial
ionization and cover layers both above and below the solar surface. The
simulations consider the emergence of a twisted magnetic flux tube
through the solar surface. We consider different stages in the emergence
process, starting from the early appearance of the flux tube at the
solar surface, and following the emergence process until the emerged
flux looks similar to a normal bipolar region. At every stage we compute
line profiles by numerically solving the Unno-Rachkovsky equations at
every horizontal grid point. Then, following observational practice,
we apply Milne-Eddington-type inversions to the synthetic spectra in
order to retrieve different atmospheric parameters. We include the
influence of spatial smearing on the deduced atmospheric parameters
to identify signatures of different stages of flux emergence in the
solar photosphere.

---------------------------------------------------------
Title: Variations of solar irradiance
Authors: Solanki, S. K.
2006IAUJD...8E..43S Altcode:
Since 1978 satellite based radiometers have been measuring changes
in solar irradiance, so that the available record now covers almost 3
solar cycles. In addition, spectral irradiance has been measured with
increasing precision time has passed. These data have uncoverd a rich
structure of the variable solar irradiance. In addition, the physical
understanding of irradiance variations and the detailed reconstruction
of this quantity (both for the time in which observations are available
and for earlier times) have made great strides over the last years. It
is now possible to reproduce both the total and spectral irradiance
variations with very high precision. In this talk an overview of
the measurements and the modelling of total and spectral irradiance
variations is given, highlighting in particular the progress of the
last few years.

---------------------------------------------------------
Title: Magnetic Flux Transport on Active Cool Stars and Starspot
Lifetimes
Authors: Isik, E.; Schüssler, M.; Solanki, S. K.
2006IAUJD...8E..21I Altcode:
Rapidly rotating cool stars are known to have large magnetic regions
at mid- to high-latitudes. Mid-latitude starspots and magnetic regions
have characteristic lifetimes on the order of one month as observed
using (Zeeman-) Doppler imaging techniques. The structure and detailed
morphology of starspots are not observable at present. In this study,
we present numerical simulations of the surface transport of bipolar
magnetic regions (BMRs) and magnetic spots on stars which have radii
and surface rotational shears of AB Doradus, the Sun, and the HR 1099
primary. The surface flux transport model is based on the magnetic
induction equation for radial fields under the effects of surface
differential rotation, meridional flow, and turbulent diffusion due to
supergranulation. We calculate flux evolution and lifetimes of BMRs with
different emergence latitudes, surface shear rates, and tilt angles. For
BMRs comparable to the largest ones on the Sun, we find that varying
the surface flows and tilt angle modifies the lifetimes over a range
of a month. For very large BMRs (area fraction ~ 0.1) the assumption
of Joy's law for the tilt angle - as compared to the case with zero
tilt - leads to a significant increase of lifetime. Such regions can
evolve to form circumpolar spots that live more than a year. Taking the
observed weak latitudinal shear and the radius of the active subgiant
component of HR 1099, we find longer BMR lifetimes as compared to
the more strongly sheared AB Dor case. We have also considered the
effect on decay and lifetimes of starspots if they are monolithic or
a conglomerate of smaller spots of similar total size. We find these
different configurations differ neither in their decay patterns,
nor in their lifetimes. We also give an analytical explanation for
the linear decay of magnetic flux in the monolithic-spot simulation.

---------------------------------------------------------
Title: Quiet Sun magnetic fields
Authors: Solanki, S. K.
2006IAUJD...3E..69S Altcode:
The amount of magnetic flux in the quiet Sun, its distribution on the
solar surface, its origin and evolution are topics that have been
strongly debated in recent years. Here a critical overview will be
given of some of the results obtained from high-sensitivity polarimetric
data and from numerical 3-D radiation-MHD simulations.

---------------------------------------------------------
Title: Numerical simulations of impulsively generated vertical
oscillations in a solar coronal arcade loop
Authors: Selwa, M.; Solanki, S. K.; Murawski, K.; Wang, T. J.;
Shumlak, U.
2006A&A...454..653S Altcode:
Aims.The main aims of the paper are to carry out numerical simulations
of the vertical oscillations in a coronal loop in order to determine
their dependence on various parameters and to compare them with recent
TRACE observations. Methods: .We consider impulsively generated
oscillations in a solar coronal arcade loop. The two-dimensional
numerical model we implement in the ideal MHD regime includes the
effects of nonlinearity and line curvature. We perform parametric
studies by varying both the position and the width/strength of
the pulse. Results: .A pulse launched below a loop is in
general found to excite multiple wave modes, in particular a vertical
oscillation with many properties of a kink mode, fast mode oscillations
and a slow mode pulse (or two slow mode pulses, depending on the
location of the original pulse). From our parametric studies we deduce
that wave periods and attenuation times of the excited waves depend
on the position below the loop summit, as well as on the width of the
pulse. Wider pulses launched closer to a foot-point and to the loop's
apex trigger wave packets of longer period waves which are more strongly
attenuated. A perturbed loop does not return to its initial state but
is instead stretched, with its apex shifted upwards. As a result the
perturbations propagate along the stretched loop and consequently
stronger and wider pulses which stretch a loop more lead to longer
period oscillations. A pulse located near one of the foot-points is
found to excite a distortion mode leading to asymmetric oscillations
which are distinct from the vertical or horizontal kink modes that
have been identified in TRACE data.

---------------------------------------------------------
Title: Microflares and Loop Oscillations
Authors: Innes, D. E.; Wang, T. J.; Solanki, S. K.; Tothova, D.
2006ESASP.617E.132I Altcode: 2006soho...17E.132I
No abstract at ADS

---------------------------------------------------------
Title: Properties of Plasma Dynamics In The Polar Coronal Plumes
Authors: Raouafi, N. -E.; Harvey, J. W.; Solanki, S. K.
2006ESASP.617E..16R Altcode: 2006soho...17E..16R
No abstract at ADS

---------------------------------------------------------
Title: Large Temperature Anisotropies in Polar Coronal Holes: How
Reliable are they?
Authors: Raouafi, N. -E.; Solanki, S. K.
2006ESASP.617E.105R Altcode: 2006soho...17E.105R
No abstract at ADS

---------------------------------------------------------
Title: Solar Coronal Magnetic Field Mapper
Authors: Solanki, S. K.; Raouafi, N. -E.; Gandorfer, A.; Schühle,
U.; Lagg, A.
2006ESASP.617E.160S Altcode: 2006soho...17E.160S
No abstract at ADS

---------------------------------------------------------
Title: Solar Microscopy: Unveiling the Sun's Basic Physical Processes
at their Intrinsic Scales
Authors: Solanki, S. K.; Marsch, E.
2006ESASP.617E..34S Altcode: 2006soho...17E..34S
No abstract at ADS

---------------------------------------------------------
Title: The Dynamic Nature of the Lower Transition Region as Revealed
by Spectroscopy of the Hydrogen Lyman-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
2006ESASP.617E..77T Altcode: 2006soho...17E..77T
No abstract at ADS

---------------------------------------------------------
Title: SUNRISE: high resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Gandorfer, A. M.; Solanki, S. K.; Barthol, P.; Lites, B. W.;
Martínez Pillet, V.; Schmidt, W.; Soltau, D.; Title, A. M.
2006SPIE.6267E..0SG Altcode: 2006SPIE.6267E..25G
SUNRISE is an international project for the development, construction,
and operation of a balloon-borne solar telescope with an aperture
of 1 m, working in the UV/VIS spectral domain. The main scientific
goal of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
near diffraction-limited images of the photosphere and chromosphere
with an unpredecented resolution down to 35 km on the solar surface at
wavelengths around 220 nm. The focal-plane instrumentation consists of a
polarization sensitive spectrograph, a Fabry-Perot filter magnetograph,
and a phase-diverse filter imager working in the near UV. The first
stratospheric long-duration balloon flight of SUNRISE is planned
in Summer 2009 from the swedish ESRANGE station. SUNRISE is a joint
project of the german Max-Planck-Institut fur Sonnensystemforschung
(MPS), Katlenburg-Lindau, with the Kiepenheuer-Institut fur Sonnenphysik
(KIS), Freiburg, Germany, the High-Altitude Observatory (HAO), Boulder,
USA, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL), Palo Alto,
USA, and the spanish IMaX consortium. In this paper we will present
an actual update on the mission and give a brief description of its
scientific and technological aspects.

---------------------------------------------------------
Title: Reconstruction of solar UV irradiance in cycle 23
Authors: Krivova, N. A.; Solanki, S. K.; Floyd, L.
2006A&A...452..631K Altcode:
Solar irradiance variations show a strong wavelength dependence. Whereas
the total solar irradiance varies by about 0.1% during the course
of the solar cycle, variations at the wavelengths around the Ly-α
emission line near 121.6 nm range up to 50-100%. These variations may
have a significant impact on the Earth's climate system. Being almost
completely absorbed in the upper atmosphere, solar UV radiation below
300 nm affects stratospheric chemistry and controls production and
destruction of ozone. Models of the solar UV irradiance remain far from
perfect, even though considerable progress has been made in modelling
the irradiance variations longwards of about 200-300 nm. We show that
after correcting for the exposure dependent degradation of the SUSIM
channels sampling irradiance at λ &gt;240 nm (making use of the Mg
II core-to-wing ratio) the agreement between model and measurement is
significantly improved. At shorter wavelengths the LTE approximation
usually made in such models fails, which makes a reconstruction of the
solar UV irradiance a rather intricate problem. We choose an alternative
approach and use the observed SUSIM UV spectra to extrapolate available
models to shorter wavelengths. The model reproduces observed solar
cycle variations of the irradiance at wavelengths down to 115 nm and
indicates an important role of UV irradiance variability: up to 60%
of the total irradiance variations over the solar cycle might be
produced at wavelengths below 400 nm.

---------------------------------------------------------
Title: Observation of a bright coronal downflow by SOHO/EIT
Authors: Tripathi, D.; Solanki, S. K.; Schwenn, R.; Bothmer, V.;
Mierla, M.; Stenborg, G.
2006A&A...449..369T Altcode:
A distinct coronal downflow has been discovered in the course of a
prominence eruption associated coronal mass ejection (CME) imaged by
EIT (Extreme ultraviolet Imaging Telescope) and LASCO (Large Angle
Spectrometric Coronagraph) on board SOHO (Solar and Heliospheric
Observatory) on 5-Mar.-2000. Evolution of the prominences seen by EIT
was tracked into the LASCO/C2 and C3 field-of-view where they developed
as the core of a typical three-part CME. In contrast to the inflow
structures reported earlier in the literatures, which were dark and
were interpreted as plasma voids moving down, the downflow reported
here was bright. The downflow, which was only seen in EIT FOV had an
onset time that coincided with the deceleration phase of the core
of the CME. The downflow showed a rapid acceleration followed by a
strong deceleration. The downflow followed a curved path which may be
explained by material following the apex of a contracting magnetic loop
sliding down along other field lines, although other explanations are
also possible. Irrespective of the detailed geometry, this observation
provides support for the pinching off of the field lines drawn-out by
the erupting prominences and the contraction of the arcade formed by
the reconnection.

---------------------------------------------------------
Title: On the fine structure of sunspot penumbrae. III. The vertical
extension of penumbral filaments
Authors: Borrero, J. M.; Solanki, S. K.; Lagg, A.; Socas-Navarro,
H.; Lites, B.
2006A&A...450..383B Altcode: 2005astro.ph.10586B
In this paper we study the fine structure of the penumbra as inferred
from the uncombed model (flux tube embedded in a magnetic surrounding)
when applied to penumbral spectropolarimetric data from the neutral
iron lines at 6300 Å. The inversion infers very similar radial
dependences in the physical quantities (LOS velocity, magnetic field
strength etc.) as those obtained from the inversion of the Fe I 1.56
μm lines. In addition, the large Stokes V area asymmetry exhibited
by the visible lines helps to constrain the size of the penumbral
flux tubes. As we demonstrate here, the uncombed model is able to
reproduce the area asymmetry with striking accuracy, returning flux
tubes as thick as 100-300 kilometers in the vertical direction, in
good agreement with previous investigations.

---------------------------------------------------------
Title: Solar proton events in cosmogenic isotope data
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Kovaltsov, Gennady A.;
Beer, Jürg; Kromer, Bernd
2006GeoRL..33.8107U Altcode:
A possible contribution of solar energetic particle events to the
production of cosmogenic 10Be and 14C in the
atmosphere is studied. The solar particle effect is negligible in
the 14C data, but extreme events may be detectable in
high-resolution 14C data. Although the overall effect
is small in the 10Be data, strong events may contribute
notably on the inter-annual time scale. In combination with the
11-year solar modulation of galactic cosmic rays, it may lead to an
intermittent 5.5-year periodicity, which is seen in high resolution
10Be data. We have identified ten episodes during 1750-1950
when 10Be may hold signatures of strong solar proton
events. This opens a new possibility to study extreme solar particle
events in the past using high resolution cosmogenic isotope data.

---------------------------------------------------------
Title: Solar activity reconstructed over the last 7000 years: The
influence of geomagnetic field changes
Authors: Usoskin, I. G.; Solanki, S. K.; Korte, M.
2006GeoRL..33.8103U Altcode:
The long-term solar activity, as manifested by sunspot number,
has been recently reconstructed on multi-millennium time scales
by S. K. Solanki et al. (2004) from the measured concentration of
14C in tree rings. The exact level of the reconstructed
solar activity depends, however, on independently evaluated data of
the geomagnetic dipole strength variations. Recently, a new series
of the palaeomagnetic dipole moment reconstruction for the last 7000
years has been presented by M. Korte and C. G. Constable (2005a) on the
basis of a thorough analysis of global samples. The new palaeomagnetic
series yields a systematically lower dipole moment in the past,
compared to the earlier geomagnetic reconstructions. We have revised
the earlier sunspot activity reconstruction since 5000 BC, using the
new geomagnetic data series, and found that it is roughly consistent
with the previous results during most of the period, although the
revised sunspot number values are in general higher. Nonetheless, it
is confirmed with the new palaeomagnetic series that the Sun spends
only 2-3% of the time in a state of high activity, similar to the
modern episode. This strengthens the conclusion that the modern high
activity level is very unusual during the last 7000 years.

---------------------------------------------------------
Title: The solar magnetic field
Authors: Solanki, Sami K.; Inhester, Bernd; Schüssler, Manfred
2006RPPh...69..563S Altcode: 2010arXiv1008.0771S
The magnetic field of the Sun is the underlying cause of the many
diverse phenomena combined under the heading of solar activity. Here
we describe the magnetic field as it threads its way from the bottom
of the convection zone, where it is built up by the solar dynamo, to
the solar surface, where it manifests itself in the form of sunspots
and faculae, and beyond into the outer solar atmosphere and, finally,
into the heliosphere. On the way it transports energy from the surface
and the subsurface layers into the solar corona, where it heats the
gas and accelerates the solar wind.

---------------------------------------------------------
Title: The uncombed penumbra
Authors: Borrero, J. M.; Rempel, M.; Solanki, S. K.
2006astro.ph..2129B Altcode:
The uncombed penumbral model explains the structure of the sunspot
penumbra in terms of thick magnetic fibrils embedded in a magnetic
surrounding atmosphere. This model has been successfully applied
to explain the polarization signals emerging from the sunspot
penumbra. Thick penumbral fibrils face some physical problems,
however. In this contribution we will offer possible solutions to
these shortcomings.

---------------------------------------------------------
Title: Plasma dynamics in the polar coronal plumes
Authors: Raouafi, N. -E.; Harvey, J. W.; Solanki, S. K.
2006IAUS..233..193R Altcode:
We use the spectral shapes of the EUV line profiles to study the plasma
dynamics, acceleration and heating, in polar plumes (PP). We find
that the observed profiles are reproduced fairly well when considering
low plume wind speeds and velocity turbulence (α_S) at low altitudes
followed by a rapid acceleration and heating of the plasma to reach
the properties of inter-plumes (IP) by ≈3-4~R_⊙. We also find that
plumes very close to the pole give narrow profiles at all heights
that are not observed above ≈2.5~R_⊙. This suggests a tendency
for plume footpoints to lie more than 10° away from the pole. High
resolution magnetograms of SOLIS and EUV images support this hypothesis.

---------------------------------------------------------
Title: Acoustic shock waves in the solar chromosphere from millimeter
observations
Authors: Loukitcheva, Maria A.; Solanki, Sami K.; White, Stephen
2006IAUS..233..104L Altcode:
We argue that millimeter continuum observations promise to be an
important diagnostic of chromospheric dynamics and the appropriate
wavelengths to look for dynamic signatures are in the range 0.8-5.0
mm. We have analyzed the millimeter intensity spectrum expected from
the dynamic model of the solar non-magnetic atmosphere of Carlsson
&amp; Stein (1992, 1995, 1997, 2002, hereafter CS) together with the
interferometric observations of the quiet Sun obtained at a wavelength
of 3.5 mm with the Berkeley-Illinois-Maryland Array. Model radio
emission at millimeter wavelengths is found to be extremely sensitive
to dynamic processes in the chromosphere, if these are spatially and
temporally resolved. The estimated millimeter brightness temperatures
are time-dependent, following changes in the atmospheric parameters,
and result in clear signatures of waves with a period of 180 s seen
in the radio intensity as a function of time. At the same time,
the interferometric observations of the internetwork regions reveal
significant oscillations with amplitudes of 50-150 K in the frequency
range 1.5-8 mHz. We give an estimate of the influence of the limited
available spatial resolution of observations on the comparison with the
predictions of dynamic models. We are able to establish a correspondence
between the CS model predictions and the observational data if we
assume that the horizontal coherence length of the oscillations is on
the order of 1 arcsec.

---------------------------------------------------------
Title: Multi-millennium changes of the geomagnetic field and solar
activity
Authors: Usoskin, I. G.; Solanki, S.; Korte, M.
2006cosp...36.2281U Altcode: 2006cosp.meet.2281U
The long-term solar activity has been recently reconstructed on
the multi-millennium time scale Solanki et al Nature 431 384 2004
from the measured concentration of radiocarbon 14 C in tree rings
The exact level of the reconstructed solar activity depends however
on independently evaluated data of the geomagnetic dipole strength
variations Recently a new series of the palaeomagnetic dipole moment
reconstruction for the last 7000 years has been presented by Korte and
Constable Earth Plan Sci Lett 236 348 2005 on the basis of a thorough
complex analysis of global samples The new palaeomagnetic series yields
systematically lower dipole moment in the past compared to the earlier
geomagnetic reconstructions We have revised the earlier sunspot activity
reconstruction since 5000 BC using the new geomagnetic data and found
that it is consistent with the previous results during most of the
period although it yields a slightly higher level of the reconstructed
sunspot activity The earlier finding on the very unusual level of the
contemporary solar activity over the last millennia is confirmed with
the new palaeomagnetic series The Sun spent only 2-3 of the time in
a high activity state similar to the modern episode implying that the
modern high activity level is very unusual during the last 7000 years On
the other hand grand minima occupy about 12 of the time in the recent
history of the Sun The new reconstruction allows for a comparative
study of solar-terrestrial relations in the multi-millennium time scale

---------------------------------------------------------
Title: Influence of the Paschen-Back effect on the results of
polarimetric inversions of the He I 10830 Å triplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.; Socas-Navarro, H.
2006MSAIS...9..126S Altcode:
The He I triplet at 10830 Å has a great potential for determining the
magnetic field vector in the upper chromosphere. The triplet is Zeeman
sensitive (Landé factors 2.0, 1.75 and 1.25) and shows the signature of
the Hanle effect under appropriate conditions. Additionally, the Zeeman
sublevels are influenced by the Paschen-Back effect leading to changes
in strength and in position of the Zeeman components of the transitions
forming the triplet. In this work we calculate the influence of the
Paschen-Back effect on the Stokes profiles and investigate its relevance
to inversions on spectro-polarimetric data obtained with the Tenerife
Infrared Polarimeter (TIP) at the German Vacuum Tower Telescope (VTT).

---------------------------------------------------------
Title: SUNRISE: high-resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Solanki, S. K.; Barthol, P.; Gandorfer, A.; Schüssler, M.;
Lites, B. W.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.
2006cosp...36.2416S Altcode: 2006cosp.meet.2416S
SUNRISE is a balloon-borne solar telescope with an aperture of 1m
working in the UV VIS optical domain The main scientific goal of
SUNRISE is to study the structure and dynamics of the magnetic field
in the atmosphere of the Sun at high spatial resolution SUNRISE will
provide diffraction-limited images of the photosphere and chromosphere
with an unprecedented resolution down to 35km at wavelengths around
220nm Focal-plane instruments are a UV filter imager a Fabry-Perot
filter magnetograph and a spectrograph polarimeter Stratospheric
long-duration balloon flights of SUNRISE over the North Atlantic
and or Antarctica are planned SUNRISE is a joint project of the
Max-Planck-Institut fuer Sonnensystemforschung MPS Katlenburg-Lindau
with the Kiepenheuer-Institut fuer Sonnenphysik KIS Freiburg the
High-Altitude Observatory HAO Boulder the Lockheed-Martin Solar and
Astrophysics Lab LMSAL Palo Alto and the spanish IMaX consortium The
presentation will give an overview about the mission and a description
of the instrumentation now at the beginning of the hardware construction
phase

---------------------------------------------------------
Title: Sensitivity of solar off-limb line profiles to electron
density stratification and the velocity distribution anisotropy
Authors: Raouafi, N. -E.; Solanki, S. K.
2006A&A...445..735R Altcode: 2007arXiv0704.1127R
The effect of the electron density stratification on the intensity
profiles of the H I Ly-α line and the O VI and Mg X doublets formed
in solar coronal holes is investigated. We employ an analytical 2-D
model of the large scale coronal magnetic field that provides a good
representation of the corona at the minimum of solar activity. We use
the mass-flux conservation equation to determine the outflow speed of
the solar wind at any location in the solar corona and take into account
the integration along the line of sight (LOS). The main assumption we
make is that no anisotropy in the kinetic temperature of the coronal
species is considered. We find that at distances greater than 1
Rsun from the solar surface the widths of the emitted lines
of O VI and Mg X are sensitive to the details of the adopted electron
density stratification. However, Ly-α, which is a pure radiative line,
is hardly affected. The calculated total intensities of Ly-α and the O
VI doublet depend to a lesser degree on the density stratification and
are comparable to the observed ones for most of the considered density
models. The widths of the observed profiles of Ly-α and Mg X are well
reproduced by most of the considered electron density stratifications,
while for the O VI doublet only few stratifications give satisfying
results. The densities deduced from SOHO data result in O VI profiles
whose widths and intensity ratio are relatively close to the values
observed by UVCS although only isotropic velocity distributions are
employed. These density profiles also reproduce the other considered
observables with good accuracy. Thus the need for a strong anisotropy
of the velocity distribution (i.e. a temperature anisotropy) is not so
clear cut as previous investigations of UVCS data suggested. However,
these results do not rule completely out the existence of some degree
of anisotropy in the corona. The results of the present computations
also suggest that the data can also be reproduced if protons, heavy
ions and electrons have a common temperature, if the hydrogen and
heavy-ion spectral lines are also non-thermally broadened by a roughly
equal amount.

---------------------------------------------------------
Title: Magnetic field measurements at different levels in the solar
atmosphere and magnetic coupling
Authors: Solanki, S. K.; Lagg, A.
2006cosp...36..916S Altcode: 2006cosp.meet..916S
The magnetic field couples the different layers of the solar atmosphere
with each other To unravel this coupling we need to be able to
measure the field at all the relevant levels Most measurements of
the magnetic field refer to the photosphere where magnetographs
and spectropolarimetry using the Zeeman effect have allowed the
magnetic structure and its evolution to be studied Observations of
the field at higher layers in the atmosphere are more rare although
a number of techniques are available These include Zeeman-effect and
Hanle effect based measurements in the chromosphere and the corona
as well as radio observations of coronal magnetic field These direct
measurements are complemented by magnetic field extrapolations starting
from the photosphere A brief overview of results obtained by various
techniques of magnetic field measurements is given and a more detailed
discussion of the main results of recent measurements of the field in
the photosphere and the upper chromosphere are presented

---------------------------------------------------------
Title: How reliable are the large temperature anisotropies in polar
coronal holes?
Authors: Raouafi, N. -E.; Solanki, S. K.
2006IAUS..233..185R Altcode:
We examine the influence of different electron density stratifications
on the coronal LOS-integrated profiles of H I Ly-α and O VI
lines at 103nm. We find that the widths of the emitted lines are
significantly affected by the details of the adopted electron density
profiles. Densities deduced from SOHO data result in O VI profiles
whose widths and intensity ratio are relatively close to the values
observed by UVCS although only isotropic kinetic temperatures are
employed. Hence we expect the magnitude of the anisotropy to depend
strongly on the density stratification adopted when analyzing the data.

---------------------------------------------------------
Title: Chromospheric Dynamics: Model Predictions and Comparison
With Observations
Authors: Loukitcheva, M.; Solanki, S. K.; White, S.
2006apri.meet...38L Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Fundamental parameters and granulation properties of Alpha
Centauri A and B obtained from inversions of their spectra
Authors: Frutiger, C.; Solanki, S. K.; Mathys, G.
2005A&A...444..549F Altcode:
Properties of stellar granulation are obtained by inverting spectra
of the late-type stars α Centauri A and B. Our inversions are based
on a multi-component model of the stellar photosphere and take into
account the center-to-limb variation and rotational broadening. The
different atmospheric components describe the areas harboring up-,
down- and horizontal flows. The inversions are constrained by
fitting not only the flux profiles, but also their line bisectors,
and by using a simple mass conservation scheme. The inversions return
the properties of convection at the stellar surface, including the
stratification of the thermodynamic parameters, as well as fundamental
parameters such as the gravitational acceleration, v sin i and the
element abundances. For α Cen A (G2V) the derived stratifications of
the temperature and convective velocity are very similar to the Sun,
while for α Cen B (K1V) we find similar up- and downflow velocities,
but lower horizontal speeds and a reduced overshoot. The latter is
consistent with the smaller scale height of the atmosphere, while mass
conservation arguments taken with the lower horizontal speed imply
that the granules on α Cen B are smaller than on the Sun. Both these
properties are in good agreement with the hydrodynamic simulation of
Nordlund &amp; Dravins (1990, A&amp;A, 228, 155). The inversions also
return the fundamental parameters (T_eff, log g, abundances, v sin i,
etc.) of the two stars. These values are on the whole in good agreement
with literature values. Also, most of them do not strongly depend on the
details of the inversion. However, importantly, the element abundances
are 0.1 to 0.15 dex lower when a 2- or 3-component inversion is carried
out than with a 1-component inversion. Based on observations
collected at the European Southern Observatories, La Silla, Chile.

---------------------------------------------------------
Title: Flarelike Brightenings of Active Region Loops Observed
with SUMER
Authors: Wang, T. J.; Innes, D. E.; Solanki, S. K.; Curdt, W.
2005ESASP.600E.105W Altcode: 2005ESPM...11..105W; 2005dysu.confE.105W
No abstract at ADS

---------------------------------------------------------
Title: On the size distribution of sunspot groups in the Greenwich
sunspot record 1874-1976
Authors: Baumann, I.; Solanki, S. K.
2005A&A...443.1061B Altcode: 2005astro.ph.10516B
We investigate the size distribution of the maximum areas and the
instantaneous distribution of areas of sunspot groups using the
Greenwich sunspot group record spanning the interval 1874-1976. Both
distributions are found to be well described by log-normal
functions. Using a simple model we can transform the maximum area
distribution into the instantaneous area distribution if the sunspot
area decay rates are also distributed log-normally. For single-valued
decay rates the resulting snapshot distribution is incompatible with the
observations. The current analysis therefore supports the results of
Howard (1992, Sol. Phys., 137, 51) and Martínez Pillet et al. (1993,
A&amp;A, 274, 521). It is not possible to distinguish between a linear
and a quadratic decay law, however, with the employed data set.

---------------------------------------------------------
Title: The Dynamics of the Lower Transition Region as Inferred from
Spectroscopy of the Hydrogen LYMAN-α Line
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
2005ESASP.600E.100T Altcode: 2005ESPM...11..100T; 2005dysu.confE.100T
No abstract at ADS

---------------------------------------------------------
Title: The molecular Zeeman effect and diagnostics of solar and
stellar magnetic fields. III. Theoretical spectral patterns in the
Paschen-Back regime
Authors: Berdyugina, S. V.; Braun, P. A.; Fluri, D. M.; Solanki, S. K.
2005A&A...444..947B Altcode:
Many diatomic molecules present in the atmospheres of the Sun and cool
stars exhibit the Paschen-Back effect at field strengths typical of
sunspots and active cool stars. Here we present a complete theoretical
description of the molecular Paschen-Back efect in Hund's cases (a),
(b) and all cases intermediate to them. This description allows
us to compute the splitting of levels of any multiplicity and the
transitions between them. We also introduce a generalized description
of the effective magnetic Landé factor applicable not just in the
Zeeman regime, but also in the Paschen-Back regime. We find that in
the regime of the partial Paschen-Back effect strongly asymmetric
Stokes profiles are produced, whose strengths and asymmetries depend
sensitively on the magnetic field. In the regime of the complete
Paschen-Back effect the profiles become symmetric again (although
they may be strongly shifted). The strength of the forbidden and
satellite transitions increases rapidly with field strength in the
partial Paschen-Back regime, while the strength of the main branch
transitions decreases. These signatures hold promise to form the basis
of new diagnostics of solar and stellar magnetic fields.

---------------------------------------------------------
Title: Diagnostics of a Simulated Flux Tube Emergence
Authors: Yelles Chaouche, L.; Cheung, M.; Lagg, A.; Solanki, S.
2005ESASP.600E..74Y Altcode: 2005ESASP.600E..74C; 2005ESPM...11...74C; 2005dysu.confE..74C
No abstract at ADS

---------------------------------------------------------
Title: Impulsive Generation of Vertical Oscillations of a Solar
Coronal Arcade Loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Wang, T. J.;
Shumlak, U.
2005ESASP.596E..43S Altcode: 2005ccmf.confE..43S
No abstract at ADS

---------------------------------------------------------
Title: Influence of the Paschen-Back Effect on the Stokes Profiles
of the he 10830 Å Triplet
Authors: Sasso, C.; Lagg, A.; Solanki, S. K.
2005ESASP.596E..64S Altcode: 2005ccmf.confE..64S
No abstract at ADS

---------------------------------------------------------
Title: Stokes diagnostics of simulations of magnetoconvection of
mixed-polarity quiet-Sun regions
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vögler, A.
2005A&A...442.1059K Altcode:
Realistic solar magneto-convection simulations including the
photospheric layers are used to study the polarization of the Fe i
Zeeman-sensitive spectral lines at 6301.5, 6302.5, 15 648 and 15 652
Å. The Stokes spectra are synthesized in a series of snapshots with
a mixed-polarity magnetic field whose average unsigned strength varies
from &lt; B &gt; = 10 to 140 G. The effects of spatial resolution and
of the amount of magnetic flux in the simulation box on the profiles
shapes, amplitudes and shifts are discussed. The synthetic spectra show
many properties in common with those observed in quiet solar regions. In
particular, the simulations reproduce the width and depth of spatially
averaged Stokes I profiles, the basic classes of the Stokes V profiles
and their amplitude and area asymmetries, as well as the abundance of
the irregular-shaped Stokes V profiles. It is demonstrated that the
amplitudes of the 1.56 μm lines observed in the inter-network are
consistent with a "true" average unsigned magnetic field strength of
20 G. We show that observations using these and visible lines, carried
out under different seeing conditions (e.g., simultaneous observations
at different telescopes), may result in different asymmetries and
even opposite polarities of the profiles in the two spectral regions
observed at the same spatial point.

---------------------------------------------------------
Title: Photospheric and Chromospheric Magnetic Structure of a Sunspot
Authors: Orozco Suarez, D.; Lagg, A.; Solanki, S. K.
2005ESASP.596E..59O Altcode: 2005ccmf.confE..59O
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Loops: a Comparison of Extrapolations from the
Photosphere with Chromospheric Measurements
Authors: Wiegelmann, T.; Lagg, A.; Solanki, S.; Inhester, B.; Woch, J.
2005ESASP.596E...7W Altcode: 2005ccmf.confE...7W
No abstract at ADS

---------------------------------------------------------
Title: The Structure of the Lower Transition Region as Inferred from
the Hydrogen LYMAN-α Line Radiance
Authors: Teriaca, L.; Schühle, U.; Solanki, S. K.; Curdt, W.;
Marsch, E.
2005ESASP.596E..66T Altcode: 2005ccmf.confE..66T
No abstract at ADS

---------------------------------------------------------
Title: Supersonic Downflows in the Solar Chromosphere are Very Common
Authors: Aznar Cuadrado, R.; Solanki, S. K.; Lagg, A.
2005ESASP.596E..49A Altcode: 2005ccmf.confE..49A
No abstract at ADS

---------------------------------------------------------
Title: Polar Coronal Holes During Solar Cycles 22 and 23
Authors: Zhang, Jun; Woch, J.; Solanki, S.
2005ChJAA...5..531Z Altcode:
Data from the Solar Wind Ion Composition Spectrometer (SWICS) on
Ulysses and synoptic maps from Kitt Peak are used to analyze the
polar coronal holes of solar activity cycles 22 and 23 (from 1990
to end of 2003). In the beginning of the declining phase of solar
cycles 22 and 23, the north polar coronal holes (PCHs) appear about
one year earlier than the ones in the south polar region. The solar
wind velocity and the solar wind ionic charge composition exhibit a
characteristic dependence on the solar wind source position within
a PCH. From the center toward the boundary of a young PCH, the solar
wind velocity decreases, coinciding with a shift of the ionic charge
composition toward higher charge states. However, for an old PCH, the
ionic charge composition does not show any obvious change, although the
latitude evolution of the velocity is similar to that of a young PCH.

---------------------------------------------------------
Title: Solar activity, cosmic rays, and Earth's temperature: A
millennium-scale comparison
Authors: Usoskin, I. G.; Schüssler, M.; Solanki, S. K.; Mursula, K.
2005JGRA..11010102U Altcode:
Previous studies of a solar influence on climate variations have often
suffered from the relatively short length of continuous direct solar
observations of less than 400 years. We use two recently reconstructed
series of the sunspot number and the cosmic ray flux to study this
question over time intervals of up to nearly 1800 years. Comparison of
the Sun-related data sets with various reconstructions of terrestrial
Northern Hemisphere mean surface temperatures reveals consistently
positive correlation coefficients for the sunspot numbers and
consistently negative correlation coefficients for the cosmic rays. The
significance levels reach up to 99% but vary strongly for the different
data sets. The major part of the correlation is due to the similarity
of the long-term trends in the data sets. The trend of the cosmic ray
flux correlates somewhat better with the terrestrial temperature than
the sunspot numbers derived from the same cosmogenic isotope data.

---------------------------------------------------------
Title: Numerical simulations of vertical oscillations of a solar
coronal loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.; Wang, T. J.;
Tóth, G.
2005A&A...440..385S Altcode:
We consider the impulsive excitation of fast vertical kink standing
waves in a solar coronal loop that is embedded in a potential
arcade. The two-dimensional numerical model we implement includes the
effects of field line curvature and nonlinearity on the excitation
and damping of standing fast magnetosonic waves. The results of the
numerical simulations reveal wave signatures which are characteristic
of vertical loop oscillations seen in recent TRACE observational data.

---------------------------------------------------------
Title: Detection of planetary transits using wavelet analysis and
genetic algorithms.
Authors: Husser, T. -O.; Dreizler, S.; Solanki, S.; Thomas, R.
2005AN....326R.628H Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Gravity-induced birefringence within the framework of Poincaré
gauge theory
Authors: Preuss, Oliver; Solanki, Sami K.; Haugan, Mark P.; Jordan,
Stefan
2005PhRvD..72d2001P Altcode: 2005gr.qc.....7071P
Gauge theories of gravity provide an elegant and promising extension
of general relativity. In this paper we show that the Poincaré gauge
theory exhibits gravity-induced birefringence under the assumption
of a specific gauge invariant nonminimal coupling between torsion
and Maxwell’s field. Furthermore we give for the first time an
explicit expression for the induced phase shift between two orthogonal
polarization modes within the Poincaré framework. Since such a phase
shift can lead to a depolarization of light emitted from an extended
source this effect is, in principle, observable. We use white dwarf
polarimetric data to constrain the essential coupling constant
responsible for this effect.

---------------------------------------------------------
Title: Kilo-Gauss Magnetic Fields in Three DA White Dwarfs
Authors: Aznar Cuadrado, R.; Jordan, S.; Napiwotzki, R.; Schmid,
H. M.; Solanki, S. K.; Mathys, G.
2005ASPC..334..159A Altcode: 2005astro.ph..1191A; 2005astro.ph..1191C
We have detected longitudinal magnetic fields between 2 and 4 kG in
three normal DA white dwarfs (WD 0446-790, WD 1105-048, WD 2359-434)
out of a sample of 12 by using optical spectropolarimetry done with
the VLT Antu 8 m telescope equipped with FORS1. With the exception of
40 Eri B (4 kG) these are the first positive detections of magnetic
fields in white dwarfs below 30 kG. A detection rate of 25 % (3/12)
may indicate now for the first time that a substantial fraction of
white dwarfs have weak magnetic fields. This result, if confirmed by
future observations, would form a cornerstone for our understanding
of the evolution of stellar magnetic fields.

---------------------------------------------------------
Title: A comparative study of the contrast of solar magnetic elements
in CN and CH
Authors: Zakharov, V.; Gandorfer, A.; Solanki, S. K.; Löfdahl, M.
2005A&A...437L..43Z Altcode:
Photospheric bright points were investigated in three different
wavelength bands using interference filters centered at 436.5 nm
(continuum), 430.5 nm (Fraunhofer's G-band dominated by absorption due
to CH), and 388.7 nm (absorption band of CN). Such bright points serve
as proxies of small-scale solar magnetic elements. Near diffraction
limited imaging was achieved by real-time frame selection and
subsequent joint phase diverse speckle reconstruction. Comparison of
the filtergrams of NOAA0670 taken in CH and CN shows that the contrast
of bright points is on average 1.4 times higher in CN than in
G-band, which is in good quantitative agreement with the predictions
of Berdyugina et al. (2003, A&amp;A, 412, 513) and Rutten et al. (2001,
ASP Conf. Ser., 236, 445).

---------------------------------------------------------
Title: Constraining Gravitational Theories by Observing Magnetic
White Dwarfs
Authors: Preuss, O.; Jordan, S.; Haugan, M. P.; Solanki, S. K.
2005ASPC..334..265P Altcode: 2004astro.ph.11688P
Under the assumption of a specific nonminimal coupling of torsion
to electromagnetism, spacetime is birefringent in the presence of a
gravitational field leading to depolarization of light emitted from
extended astrophysical sources. We use polarimetric data of the magnetic
white dwarf RE J0317-853 to set for the very first time constraints on
the essential coupling constant for this effect, giving k2
∼ (22 m)2.

---------------------------------------------------------
Title: Climate: How unusual is today's solar activity? (reply)
Authors: Solanki, S. K.; Usoskin, I. G.; Kromer, B.; Schüssler, M.;
Beer, J.
2005Natur.436E...4S Altcode:
Muscheler et al. claim that the solar activity affecting cosmic rays
was much higher in the past than we deduced from 14C
measurements. However, this claim is based on a problematic
normalization and is in conflict with independent results, such as
the 44Ti activity in meteorites and the 10Be
concentration in ice cores.

---------------------------------------------------------
Title: Magnetic flux in the internetwork quiet Sun
Authors: Khomenko, E. V.; Martínez González, M. J.; Collados, M.;
Vögler, A.; Solanki, S. K.; Ruiz Cobo, B.; Beck, C.
2005A&A...436L..27K Altcode:
We report a direct comparison of the amplitudes of Stokes spectra of the
Fe i 630 nm and 1.56 μm lines produced by realistic MHD simulations
with simultaneous observations in the same spectral regions. The
Stokes spectra were synthesized in snapshots with a mixed polarity
magnetic field having a spatially averaged strength, &lt; B &gt;,
between 10 and 30 G. The distribution of Stokes V amplitudes depends
sensitively on &lt; B &gt;. A quiet inter-network region was observed
at the German VTT simultaneously with TIP (1.56 μm) and POLIS (630
nm). We find that the Stokes V amplitudes of both infrared and visible
observations are best reproduced by the simulation snapshot with &lt;
B &gt; = 20 G. In observations with 1 resolution, up to 2/3 of the
magnetic flux can remain undetected.

---------------------------------------------------------
Title: Excitation and damping of slow magnetosonic standing waves
in a solar coronal loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.
2005A&A...436..701S Altcode:
We consider slow magnetosonic standing waves that are impulsively
excited in a solar coronal loop. The one-dimensional numerical model
we implement includes the effects of nonlinearity, optionally thermal
conduction, heating, and cooling of the solar plasma. We numerically
evaluate excitation and damping times of a standing wave in hot coronal
loops on the basis of a parametric study. Results of the numerical
simulations reveal that initially launched impulses mainly trigger
the fundamental mode and its first harmonic, depending on the location
of these pulses in space. Parametric study shows that these standing
waves are excited in a dozen or so wave periods corresponding roughly
to 13 min and that they are strongly damped over a similar time-scale.

---------------------------------------------------------
Title: On the fine structure of sunspot penumbrae. II. The nature
of the Evershed flow
Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Collados, M.
2005A&A...436..333B Altcode: 2005astro.ph..3677B
We investigate the fine structure of the sunspot penumbra by means of
a model that allows for a flux tube in horizontal pressure balance
with the magnetic background atmosphere in which it is embedded. We
apply this model to spectropolarimetric observations of two neutral
iron lines at 1.56 μm and invert several radial cuts in the penumbra
of the same sunspot at two different heliocentric angles. In the inner
part of the penumbra we find hot flux tubes that are somewhat inclined
to the horizontal. They become gradually more horizontal and cooler
with increasing radial distance. This is accompanied by an increase
in the velocity of the plasma and a decrease of the gas pressure
difference between flux tube and the background component. At large
radial distances the flow speed exceeds the critical speed and evidence
is found for the formation of a shock front. These results are in good
agreement with simulations of the penumbral fine structure and provide
strong support for the siphon flow as the physical mechanism driving
the Evershed flow.

---------------------------------------------------------
Title: Millimeter-Interferometer Observations of Oscillations in
the Solar Chromosphere
Authors: White, S. M.; Loukitcheva, M.; Solanki, S. K.
2005AGUSMSH12A..03W Altcode:
The use of millimeter-interferometer data for the study of chromospheric
structure and dynamics is tested using 85 GHz observations with the
10-element Berkeley-Illinois-Maryland Array (BIMA). Interferometer
data have the advantage over single-dish data that they allow both high
spatial resolution and dense temporal sampling simultaneously. However,
snapshot imaging of the quiet solar atmosphere with a small number of
dishes is challenging. We demonstrate that techniques are available to
carry out this task successfully. We compare observations of quiet Sun,
active region and coronal hole targets using images with 10 arcsec
resolution at 15 second cadence. The brightest features in the images
are typically 1500 K above the background level, with a snapshot noise
level of order 100 K. We use extensive tests to determine whether
oscillation power can be recovered from sequences of snapshot images
and show that they can down to quite weak levels. Intensity oscillations
with significant power in the frequency range 1.5-8.0 mHz are found in
the quiet-Sun and active region targets. For the quiet-Sun region we
use the spatially-resolved time series to investigate the properties
of network boundaries and cell interiors (internetwork) separately. In
agreement with investigations at other wavelengths, the millimeter
data show that power in the network tends to be at periods of 5 minutes
and longer while power in the internetwork is present also at shorter
(3-minute) periods.

---------------------------------------------------------
Title: Initiation of hot coronal loop oscillations: Spectral features
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.
2005A&A...435..753W Altcode:
We explore the excitation of hot loop oscillations observed with the
SUMER spectrograph on SOHO by analysing Fe XIX and Fe XXI spectral
line profiles in the initial phase of the events. We investigate all
54 Doppler shift oscillations in 27 flare-like events, whose physical
parameters have been measured so far. In nearly 50% of the cases, the
spectral evolution reveals the presence of two spectral components,
one of them almost undisturbed, the other highly shifted. We find that
the shifted component reaches maximum Doppler shift (on the order of
100-300 km s-1) and peak intensity almost simultaneously. The
velocity amplitude of the shifted component has no correlation with
the oscillation amplitudes. These features imply that in these events
the initial shifts are not caused by the locally oscillating plasma
(or waves), but most likely by a pulse of hot plasma travelling
along the loop through the slit position. This interpretation is also
supported by several examples showing that standing slow mode waves
are set up immediately after the initial line shift pulse (standing
slow mode waves are inferred from the 1/4-period phase relationship
between the velocity and intensity oscillations). We re-measure the
physical parameters of the 54 Doppler oscillations by fitting the time
profiles excluding the first peak, and find that the periods are almost
unchanged, damping times are shorter by 5%, and amplitudes are smaller
by 37% than measured when the first peak is included. We also measure
the velocity of the net (background) flow during the oscillations,
which is found to be nearly zero. Our result of initial hot flows
supports the model of single footpoint (asymmetric) excitation, but
contradicts chromospheric evaporation as the trigger.

---------------------------------------------------------
Title: How To Use Magnetic Field Information For Coronal Loop
Identification
Authors: Wiegelmann, T.; Inhester, B.; Lagg, A.; Solanki, S. K.
2005SoPh..228...67W Altcode: 2008arXiv0801.4573W
The structure of the solar corona is dominated by the magnetic field
because the magnetic pressure is about four orders of magnitude
higher than the plasma pressure. Due to the high conductivity the
emitting coronal plasma (visible, e.g., in SOHO/EIT) outlines the
magnetic field lines. The gradient of the emitting plasma structures
is significantly lower parallel to the magnetic field lines than
in the perpendicular direction. Consequently information regarding
the coronal magnetic field can be used for the interpretation of
coronal plasma structures. We extrapolate the coronal magnetic field
from photospheric magnetic field measurements into the corona. The
extrapolation method depends on assumptions regarding coronal currents,
e.g., potential fields (current-free) or force-free fields (current
parallel to magnetic field). As a next step we project the reconstructed
3D magnetic field lines on an EIT-image and compare with the emitting
plasma structures. Coronal loops are identified as closed magnetic
field lines with a high emissivity in EIT and a small gradient of the
emissivity along the magnetic field.

---------------------------------------------------------
Title: Comparing magnetic field extrapolations with measurements of
magnetic loops
Authors: Wiegelmann, T.; Lagg, A.; Solanki, S. K.; Inhester, B.;
Woch, J.
2005A&A...433..701W Altcode: 2008arXiv0801.4519W
We compare magnetic field extrapolations from a photospheric magnetogram
with the observationally inferred structure of magnetic loops in
a newly developed active region. This is the first time that the
reconstructed 3D-topology of the magnetic field is available to test
the extrapolations. We compare the observations with potential fields,
linear force-free fields and non-linear force-free fields. This
comparison reveals that a potential field extrapolation is not
suitable for a reconstruction of the magnetic field in this young,
developing active region. The inclusion of field-line-parallel
electric currents, the so called force-free approach, gives much better
results. Furthermore, a non-linear force-free computation reproduces
the observations better than the linear force-free approximation,
although no free parameters are available in the former case.

---------------------------------------------------------
Title: Can surface magnetic fields reproduce solar irradiance
variations in cycles 22 and 23?
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.
2005A&A...432.1057W Altcode:
Total solar irradiance is reconstructed using data from the
spectromagnetograph on Kitt Peak for 1992 2003 (covering parts of cycles
22 and 23) and compared with observational data. The model assumes
that solar irradiance variations are caused by surface magnetism and
its single free parameter is kept at the same value for both cycles. A
good correspondence is found for the whole period of time, with no bias
between the two cycles on time-scales longer than the solar rotation
period. This is in agreement with the recent results of [CITE], but it
is in contrast to the earlier analysis of [CITE], and suggests that the
source of the irradiance variations is the same for cycles 22 and 23,
namely the evolution of the magnetic flux at the solar surface.

---------------------------------------------------------
Title: Solar activity over the last 1150 years: does it correlate
with climate?
Authors: Usoskin, I. G.; Schüssler, M.; Solanki, S. K.; Mursula, K.
2005ESASP.560...19U Altcode: 2005csss...13...19U
No abstract at ADS

---------------------------------------------------------
Title: SoHO/EIT Observation of a Coronal Inflow
Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.;
Mierla, M.; Stenborg, G.
2005IAUS..226..133T Altcode:
A distinct coronal inflow has been discovered after ∼90 min
of prominence eruption associated coronal mass ejection (CME) on
05-Mar-2000 by EIT (Extreme ultraviolet Imaging Telescope) aboard SoHO
(Solar and Heliospheric Observatory). Evolution of the prominence seen
by EIT was tracked into the LASCO/C2 and C3 field-of-view (FOV; 4-10
R⊙) where it developed as the core of a typical three-part
CME. The speed of the inflow, which was only seen in EIT FOV, was 70-80
km/s at a height between 1.5-1.2 R⊙ coinciding with the
deceleration phase of the core of the CME in LASCO/C2. In contrast to
dark inflow structures observed earlier and interpreted as plasma void
moving down, the inflow reported here was bright. The inflow showed a
constant deceleration and followed a curved path suggesting the apex
of a contracting magnetic loop sliding down along other field lines.

---------------------------------------------------------
Title: Modelling of irradiance variations through atmosphere models .
Authors: Krivova, N. A.; Solanki, S. K.
2005MmSAI..76..834K Altcode:
Regular space-based measurements of solar total and spectral irradiance
reveal its variations on time scales from minutes to decades. About
90% of these variations are reproduced by recent models assuming
that the evolution of the solar surface magnetic fields is their
main cause. Circumstantial evidence suggests that variations on yet
longer time scales, which are of special interest for climate studies,
are also possible. Once good understanding of the directly observed
variations has been gained, we can then attempt to extend the models
back in time. Here a brief overview of our recent efforts to reconstruct
solar total and spectral irradiance on time scales of days to centuries
is given.

---------------------------------------------------------
Title: A cross-calibrated sunspot areas time series since 1874
Authors: Balmaceda, L.; Solanki, S. K.; Krivova, N.
2005MmSAI..76..929B Altcode:
A complete and homogeneous historical record of sunspot areas is
a valuable proxy of solar variability, and is widely used, e.g.,
to understand the behaviour of total and spectral solar irradiance
at earlier times. Since 1874, the Royal Greenwich Observatory (RGO)
regularly carried out these and other measurements until December
1976. After that time the records from a number of different
observatories are available. These, however, show some systematic
differences and often have a lot of gaps. In order to compile a
complete and cross-calibrated time series we compare the data from
different observatories when they overlap and find the corresponding
correction factors. The Greenwich data set is used as a basis until
1976, the Russian data (stations from the former USSR) between 1977
and 1985 and the Mt. Wilson data since 1986. Other data sets (Rome,
Yunnan, Catania) are used to fill in the remaining gaps.

---------------------------------------------------------
Title: Reconstruction of solar UV irradiance
Authors: Krivova, N. A.; Solanki, S. K.
2005AdSpR..35..361K Altcode:
Understanding solar influence on the Earth’s climate requires
a reconstruction of solar irradiance for the pre-satellite
period. Considerable advances have been made in modelling the irradiance
variations at wavelengths longer than 200 nm. At shorter wavelengths,
however, the LTE approximation usually taken in such models fails, which
makes a reconstruction of the solar UV irradiance a rather intricate
problem. We choose an alternative approach and use the observed SUSIM
UV spectra to extrapolate available models to shorter wavelengths.

---------------------------------------------------------
Title: Irradiance models
Authors: Solanki, S. K.; Krivova, N. A.; Wenzler, T.
2005AdSpR..35..376S Altcode:
Measurements of solar irradiance have revealed variations at all the
sampled time scales (ranging from minutes to the length of the solar
cycle). One important task of models is to identify the causes of the
observed (total and spectral) irradiance variations. Another major
aim is to reconstruct irradiance over time scales longer than sampled
by direct measurements in order to consider if and to what extent
solar irradiance variations may be responsible for global climate
change. Here, we describe recent efforts to model solar irradiance
over the current and the previous two solar cycles. These irradiance
models are remarkably successful in reproducing the observed total and
spectral irradiance, although further improvements are still possible.

---------------------------------------------------------
Title: Shock Wave Driven by an Expanding System of Loops
Authors: Raouafi, N. -E.; Mancuso, S.; Solanki, S. K.; Inhester, B.;
Mierla, M.; Stenborg, G.; Delaboudinière, J. P.; Benna, C.
2005IAUS..226..127R Altcode:
We report on a Coronal Mass Ejection (CME) observed on June 27
1999 by the UltraViolet Coronagraph Spectrometer (UVCS) telescope
operating on board the SOHO spacecraft. The CME was also observed
by LASCO (SOHO). Emission of hot material has been recorded by UVCS
propagating in front of an opening system of loops generated by the
CME. The evolution of the UVCS structure is highly correlated to the
evolution of the opening loop. The data reveal excess broadening of
the O VI doublet lines and an enhancement in the intensity of the Si
XII λ 520.66 and λ499.37 lines due to the motion of the expanding hot
gas. The hot gas emission seems to be due to a shock wave propagating in
front of a very fast gas bubble traveling along the opening loop system.

---------------------------------------------------------
Title: Mechanisms of secular magnetic field variations.
Authors: Solanki, S. K.; Schüssler, M.
2005MmSAI..76..781S Altcode:
The variability of the solar magnetic field on time scales of decades
and longer lies at the root of the various mechanisms by which the
changing Sun could affect Earth's climate. We discuss the origin of
the secular variability of both the open heliospheric flux and the
total unsigned solar surface flux and review models that have been put
forward to describe these variations. We propose that a combination of
the effects of overlapping activity cycles and the long decay time of
large-scale magnetic patterns is responsible for the secular variability
of the solar magnetic field.

---------------------------------------------------------
Title: Excitation and Damping of Slow Magnetosonic Standing Waves
in a Solar Coronal Loop
Authors: Selwa, M.; Murawski, K.; Solanki, S. K.
2004ESASP.575...91S Altcode: 2004soho...15...91S
No abstract at ADS

---------------------------------------------------------
Title: Signature of Current Sheets as Seen by Tip at VTT in the HeI
Multiplet at 1083.0 nm
Authors: Aznar Cuadrado, R.; Solanki, S. K.; Lagg, A.; Thomas, R. M.
2004ESASP.575..593A Altcode: 2004soho...15..593A
No abstract at ADS

---------------------------------------------------------
Title: Small-Scale Flares as the Cause of Quiet Sun EUV Emission
Authors: Pauluhn, A.; Solanki, S. K.
2004ESASP.575..501P Altcode: 2004soho...15..501P
No abstract at ADS

---------------------------------------------------------
Title: Sensitivity of Solar Off-Limb Line Profiles to Electron
Density Stratification and the Velocity Distribution Anisotropy
Authors: Raouafi, N. -E.; Solanki, S. K.
2004ESASP.575..170R Altcode: 2004soho...15..170R
No abstract at ADS

---------------------------------------------------------
Title: Why are Coronal Holes Indistinguishable from the Quiet Sun
in Transition Region Radiation?
Authors: Wiegelmann, T.; Solanki, S. K.
2004ESASP.575...35W Altcode: 2004soho...15...35W
No abstract at ADS

---------------------------------------------------------
Title: Similarities and Differences between Coronal Holes and the
Quiet Sun: Are Loop Statistics the Key?
Authors: Wiegelmann, T.; Solanki, S. K.
2004SoPh..225..227W Altcode: 2008arXiv0802.0120W
Coronal holes (CH) emit significantly less at coronal temperatures
than quiet-Sun regions (QS), but can hardly be distinguished in most
chromospheric and lower transition region lines. A key quantity for the
understanding of this phenomenon is the magnetic field. We use data from
SOHO/MDI to reconstruct the magnetic field in coronal holes and the
quiet Sun with the help of a potential magnetic model. Starting from
a regular grid on the solar surface we then trace field lines, which
provide the overall geometry of the 3D magnetic field structure. We
distinguish between open and closed field lines, with the closed field
lines being assumed to represent magnetic loops. We then try to compute
some properties of coronal loops. The loops in the coronal holes (CH)
are found to be on average flatter than in the QS. High and long closed
loops are extremely rare, whereas short and low-lying loops are almost
as abundant in coronal holes as in the quiet Sun. When interpreted in
the light of loop scaling laws this result suggests an explanation for
the relatively strong chromospheric and transition region emission
(many low-lying, short loops), but the weak coronal emission (few
high and long loops) in coronal holes. In spite of this contrast
our calculations also suggest that a significant fraction of the cool
emission in CHs comes from the open flux regions. Despite these insights
provided by the magnetic field line statistics further work is needed
to obtain a definite answer to the question if loop statistics explain
the differences between coronal holes and the quiet Sun.

---------------------------------------------------------
Title: Comparison between KPVT/SPM and SoHO/MDI magnetograms with
an application to solar irradiance reconstructions
Authors: Wenzler, T.; Solanki, S. K.; Krivova, N. A.; Fluri, D. M.
2004A&A...427.1031W Altcode:
To be able to use both space- and ground-based solar magnetograms and
construct long time series of derived parameters it is important to
cross-calibrate them so that we can estimate their reliability and
combine them. Using two different techniques, we compare magnetograms
as well as continuum images recorded by the Spectropolarimeter (SPM)
on Kitt Peak and the Michelson Doppler Interferometer (MDI) on board
SoHO. We find that the result obtained depends on the method used. The
method we favour gives almost identical umbral and penumbral areas and
very similar total magnetic fluxes in faculae. The magnetic fluxes in
umbrae and penumbrae returned by the two instruments, however, differ
considerably. We also demonstrate that SPM data can be employed to
reconstruct total solar irradiance variations with almost the same
accuracy as recently shown for MDI data.

---------------------------------------------------------
Title: Small-Scale Solar Magnetic Elements: Simulations and
Observations
Authors: Solanki, S. K.; Schüssler, M.
2004ASPC..325..105S Altcode:
Both the small-scale and large-scale properties of solar features,
such as sunspots and the solar corona, are influenced strongly by
the small-scale structure of the underlying magnetic field. Even
some global properties of the Sun, such as variations of the Sun's
irradiance, depend on the local properties of small-scale magnetic
features. We briefly describe these dependences, as well as recent
results concerning the small-scale magnetic elements deduced from
radiation MHD simulations and spectropolarimetric observations. The
simulations reproduce a number of sensitive observational tests and
explain, e.g. why G-band images allow only a part of the magnetic flux
to be identified.

---------------------------------------------------------
Title: The Magnetic Field from the Solar Interior to the Heliosphere
Authors: Solanki, Sami K.
2004ASSL..317..373S Altcode: 2004shis.conf..373S
No abstract at ADS

---------------------------------------------------------
Title: G-band spectral synthesis and diagnostics of simulated solar
magneto-convection
Authors: Shelyag, S.; Schüssler, M.; Solanki, S. K.; Berdyugina,
S. V.; Vögler, A.
2004A&A...427..335S Altcode:
Realistic simulations of radiative magneto-convection in the solar
(sub)photosphere are used for a spectral synthesis of Fraunhofer's G
band, which is dominated by spectral lines from the CH molecule. It
is found that the spatial pattern of integrated G-band brightness
closely matches the spatial structure of magnetic flux concentrations
in the convective downflow regions. The brightness contrast is mainly
caused by the weakening of CH lines due to the reduced CH abundance
and the resulting shift of the optical depth scale in the hot and
tenuous magnetic flux concentrations. Various properties of the
synthetic brightness images agree well with G-band observations. These
results lends credit to the observational usage of G-band bright
features as proxies for magnetic flux concentrations in the solar
photosphere. However, the converse is only correct in a limited sense:
only a fraction of the magnetic flux concentrations turn out to be
bright in the G band.

---------------------------------------------------------
Title: Apparent solar radius variations. The influence of magnetic
network and plage
Authors: Bruls, J. H. M. J.; Solanki, S. K.
2004A&A...427..735B Altcode:
Solar radius measurements, a by-product of the magnetograms recorded
several times daily at Mt. Wilson Observatory over a period of a few
decades, have revealed apparent variations of about 0.4 arcsec that are
correlated with the solar cycle. We note that the radius definition
used for the analysis of those magnetograms automatically converts
intensity variations near the limb into apparent radius variations. A
change in the average temperature structure of the quiet Sun can be
ruled out as the source of these variations, since such a change would
need to be very significant and would lead to other easily measurable
consequences that are not observed. We show that plage emission near
the solar limb associated with the magnetic activity variation during a
solar cycle produces apparent radius changes of the correct sign. The
use of plane-parallel or spherically-symmetric models to describe
the faculae gives apparent radius variations that are a factor of
4-10 too small in magnitude. If the Mt. Wilson results are correct,
then this implies that the small-scale structure of faculae produces
limb extensions that are considerably larger than those returned by
a plane-parallel or spherically-symmetric model.

---------------------------------------------------------
Title: Effect of the electron density stratification on off-limb O
VI line profiles: How large is the velocity distribution anisotropy
in the solar corona?
Authors: Raouafi, N. -E.; Solanki, S. K.
2004A&A...427..725R Altcode:
Coronagraphic spectral observations carried out with UVCS on SoHO
have shown that the velocity distribution in the solar corona is
highly anisotropic. Here we examine the influence of the density
stratification on the interpretation of such observations. In
particular, we investigate the profiles of O VI lines emitted in
the corona by employing an analytical 2-D model of the large scale
coronal magnetic field and solar wind. We concentrate on the polar
coronal holes and take into account the integration along the line of
sight. We find that at distances greater than 1 R⊙ from
the solar surface the widths of the emitted lines are significantly
affected by the details of the adopted electron density profiles. In
particular, the densities deduced by Doyle et al. (\cite{Doyle1999a},b)
from SoHO data result in O VI profiles whose widths and intensity ratio
are relatively close to the values observed by UVCS/SoHO although only
isotropic velocity distributions are employed. Hence we expect that
the magnitude of anisotropy of the velocity distribution deduced from
UVCS data depends strongly on the adopted density profile.

---------------------------------------------------------
Title: Evolution of the large-scale magnetic field on the solar
surface: A parameter study
Authors: Baumann, I.; Schmitt, D.; Schüssler, M.; Solanki, S. K.
2004A&A...426.1075B Altcode:
Magnetic flux emerging on the Sun's surface in the form of bipolar
magnetic regions is redistributed by supergranular diffusion, a poleward
meridional flow and differential rotation. We perform a systematic and
extensive parameter study of the influence of various parameters on the
large-scale field, in particular the total unsigned surface flux and the
flux in the polar caps, using a flux transport model. We investigate
both, model parameters and source term properties. We identify the
average tilt angle of the emerging bipolar regions, the diffusion
coefficient (below a critical value), the total emergent flux and,
for the polar field, the meridional flow velocity and the cycle length
as parameters with a particularly large effect. Of special interest is
the influence of the overlap between successive cycles. With increasing
overlap, an increasing background field (minimum flux at cycle minimum)
is built up, which is of potential relevance for secular trends of
solar activity and total irradiance.

---------------------------------------------------------
Title: SUNRISE: high-resolution UV/VIS observations of the Sun from
the stratosphere
Authors: Gandorfer, Achim M.; Solanki, Sami K.; Schüssler, Manfred;
Curdt, Werner; Lites, Bruce W.; Martínez Pillet, Valentin; Schmidt,
Wolfgang; Title, Alan M.
2004SPIE.5489..732G Altcode:
SUNRISE is a balloon-borne solar telescope with an aperture of 1m,
working in the UV/VIS optical domain. The main scientific goal
of SUNRISE is to understand the structure and dynamics of the
magnetic field in the atmosphere of the Sun. SUNRISE will provide
diffraction-limited images of the photosphere and chromosphere with
an unpredecented resolution down to 35km at wavelengths around
220nm. Focal-plane instruments are a spectrograph/polarimeter,
a Fabry-Perot filter magnetograph, and a filter imager. The first
stratospheric long-duration balloon flight of SUNRISE over Antarctica
is planned in winter 2006/2007. SUNRISE is a joint project of the
Max-Planck-Institut fur Sonnensystemforschung (MPS), Katlenburg-Lindau,
with the Kiepenheuer-Institut für Sonnenphysik (KIS), Freiburg, the
High-Altitude Observatory (HAO), Boulder, the Lockheed-Martin Solar and
Astrophysics Lab. (LMSAL), Palo Alto, and the Instituto de Astrofisica
de Canarias, La Laguna, Tenerife. In this paper we will present an
overview on the mission and give a description of the instrumentation,
now, at the beginning of the hardware construction phase.

---------------------------------------------------------
Title: Solar Irradiance Variations: From Current Measurements to
Long-Term Estimates
Authors: Solanki, Sami K.; Krivova, Natalie A.
2004SoPh..224..197S Altcode: 2005SoPh..224..197S
Variations of solar total and spectral irradiance are prime
solar quantities purported to have an influence on the Earth's
climate. Quantitative estimates of irradiance over as long a time
as possible are needed to judge their effectiveness in forcing the
climate. In order to do this reliably, first the measured record must
be reproduced and a feeling for the physics underlying the irradiance
variations must be developed. With the help of this knowledge combined
with the available proxy data, reconstructions of irradiance in the
past, generally since the Maunder minimum, are attempted. Here a brief
introduction to some of the irradiance reconstruction work aiming at
irradiance on time scales of days to the solar cycle is given, followed
by a brief and incomplete overview of the longer-term reconstructions.

---------------------------------------------------------
Title: Unusual activity of the Sun during recent decades compared
to the previous 11,000 years
Authors: Solanki, S. K.; Usoskin, I. G.; Kromer, B.; Schüssler, M.;
Beer, J.
2004Natur.431.1084S Altcode:
Direct observations of sunspot numbers are available for the past
four centuries, but longer time series are required, for example,
for the identification of a possible solar influence on climate
and for testing models of the solar dynamo. Here we report a
reconstruction of the sunspot number covering the past 11,400 years,
based on dendrochronologically dated radiocarbon concentrations. We
combine physics-based models for each of the processes connecting
the radiocarbon concentration with sunspot number. According to our
reconstruction, the level of solar activity during the past 70 years is
exceptional, and the previous period of equally high activity occurred
more than 8,000 years ago. We find that during the past 11,400 years
the Sun spent only of the order of 10% of the time at a similarly high
level of magnetic activity and almost all of the earlier high-activity
periods were shorter than the present episode. Although the rarity
of the current episode of high average sunspot numbers may indicate
that the Sun has contributed to the unusual climate change during the
twentieth century, we point out that solar variability is unlikely
to have been the dominant cause of the strong warming during the past
three decades.

---------------------------------------------------------
Title: Shock wave driven by an expanding system of loops
Authors: Raouafi, N. -E.; Mancuso, S.; Solanki, S. K.; Inhester, B.;
Mierla, M.; Stenborg, G.; Delaboudinière, J. P.; Benna, C.
2004A&A...424.1039R Altcode:
We report on a Coronal Mass Ejection (CME) observed on June 27, 1999 by
the UltraViolet Coronagraph Spectrometer (UVCS) telescope operating on
board the SOHO spacecraft. The CME was also observed by the Large Angle
Spectroscopic Coronagraph (LASCO). Emission of hot material has been
recorded by UVCS propagating in front of an opening system of loops
generated by the CME. The evolution of the UVCS structure is highly
correlated with the evolution of the opening loop. The data reveal
excess broadening of the O VI doublet lines and an enhancement in the
intensity of the Si XII λ520.66 and λ499.37 lines due to the motion
of the expanding hot gas. The hot gas emission seems to be due to a
shock wave propagating in front of a very fast gas bubble traveling
along the opening loop system.

---------------------------------------------------------
Title: Discovery of kilogauss magnetic fields in three DA white dwarfs
Authors: Aznar Cuadrado, R.; Jordan, S.; Napiwotzki, R.; Schmid,
H. M.; Solanki, S. K.; Mathys, G.
2004A&A...423.1081A Altcode: 2004astro.ph..5308C; 2004astro.ph..5308A
We have detected longitudinal magnetic fields between 2 and 4 kG in
three (WD 0446-790, WD 1105-048, WD 2359-434) out of a sample of 12
normal DA white dwarfs by using optical spectropolarimetry done with the
VLT Antu 8 m telescope equipped with FORS1. With the exception of 40 Eri
B (4 kG) these are the first positive detections of magnetic fields in
white dwarfs below 30 kG. Although suspected, it was not clear whether
a significant fraction of white dwarfs contain magnetic fields at this
level. These fields may be explained as relics from magnetic fields in
the main-sequence progenitors considerably enhanced by magnetic flux
conservation during the shrinkage of the core. A detection rate of 25%
(3/12) may indicate now for the first time that a substantial fraction
of white dwarfs have a weak magnetic field. This result, if confirmed
by future observations, would form a cornerstone for our understanding
of the evolution of stellar magnetic fields. Based on observations
collected at the European Southern Observatory, Paranal, Chile, under
programme ID 70.D-0259.

---------------------------------------------------------
Title: An astronomical search for evidence of new physics: Limits
on gravity-induced birefringence from the magnetic white dwarf
REJ0317-853
Authors: Preuss, Oliver; Haugan, Mark P.; Solanki, Sami K.; Jordan,
Stefan
2004PhRvD..70f7101P Altcode: 2004gr.qc.....5068P
The coupling of the electromagnetic field directly with gravitational
gauge fields leads to new physical effects that can be tested using
astronomical data. Here we consider a particular case for closer
scrutiny, a specific nonminimal coupling of torsion to electromagnetism,
which enters into a metric-affine geometry of space-time. We show
that under the assumption of this nonminimal coupling, space-time is
birefringent in the presence of such a gravitational field. This leads
to the depolarization of light emitted from extended astrophysical
sources. We use polarimetric data of the magnetic white dwarf
REJ0317-853 to set, for the very first time, constraints on the
essential coupling constant for this effect, giving k2≲(19
m)2.

---------------------------------------------------------
Title: Thermal-magnetic relation in a sunspot and a map of its
Wilson depression
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.;
Borrero, J. M.; Berdyugina, S.
2004A&A...422..693M Altcode:
We present relations between thermal and magnetic quantities in a
simple, isolated sunspot, as deduced from the inversion of 1.56 μm
spectropolarimetric data. We used a combination of two infrared Fe I
lines at 15 648.5 Å and 15 652.8 Å/ in the inversions. Due to the
high Zeeman sensitivity of these lines, we can study this relationship
in the entire sunspot. The relevant parameters were derived both as a
function of location within the sunspot and of height in the atmosphere
using an inversion technique based on response functions. In this paper
we relate the magnetic vector with temperature. We find a non-linear
relationship between the various components of the magnetic vector and
temperature, which confirm the results from earlier investigations. We
also computed the Wilson depression and the plasma β for the observed
sunspot and compare our results with earlier findings.

---------------------------------------------------------
Title: On the fine structure of sunspot penumbrae. I. A quantitative
comparison of two semiempirical models with implications for the
Evershed effect
Authors: Borrero, J. M.; Solanki, S. K.; Bellot Rubio, L. R.; Lagg,
A.; Mathew, S. K.
2004A&A...422.1093B Altcode:
Sunspot penumbrae exhibit prominent fine structure. Different
interpretations of spectropolarimetric observations suggest different,
sometimes contradictory, properties of this fine structure. In this
paper we show that the results of inversions of penumbral infrared
profiles based on one-component models with gradients of the atmospheric
parameters and two-component models without gradients are compatible
with each other. Our analysis reconciles the results of previous
investigations and provides further support for the picture that sunspot
penumbrae are composed of penumbral flux tubes embedded in a magnetic
background. The magnetic field in the tubes is more horizontal and
weaker than that of the background atmosphere. While the tubes carry
most of the Evershed flow, the background is essentially at rest. We
notice also that the magnetic field strength in the flux tubes drops
much more slowly with radial distance than the background field. This
finding is discussed as a possible driver for the Evershed flow.

---------------------------------------------------------
Title: Vertical oscillations of a coronal loop observed by TRACE
Authors: Wang, T. J.; Solanki, S. K.
2004A&A...421L..33W Altcode:
We report on a loop oscillation event observed by TRACE in the
195 Åbandpass at the solar limb. The difference images reveal the
first evidence for vertical kink oscillations of the loop, i.e.,
alternately expanding and shrinking motions, in contrast to horizontal
transverse loop oscillations reported before, which exhibit swaying
motions. Based on the 3D geometry of the oscillating loop derived from
the observation by fitting with a circular or elliptical loop model,
we simulate these two kinds of global kink modes and find that only
the vertical oscillations produce a signature in the difference images
in agreement with the observations. We also find that the oscillating
loop is associated with intensity variations. Based on the measured
displacement amplitude, the simulation predicts an intensity variation
of about 13% due to density changes produced by the change of the
loop length. The observed intensity changes have the same sign but
are considerably larger than the predictions although the error bars
are also large. This suggests that these oscillations are compressible.

---------------------------------------------------------
Title: Line profile characteristics of solar explosive event bursts
Authors: Ning, Z.; Innes, D. E.; Solanki, S. K.
2004A&A...419.1141N Altcode:
The spatial structure and temporal evolution of explosive events
are explored using spectral observations of the Si IV 1393 Å line
obtained with the Solar Ultraviolet Measurements of Emitted Radiation
spectrograph (SUMER). Three areas of quiet Sun near disk center,
8 arcsec×120 arcsec each, were rastered with a cadence of less than
1 min for a period of over half an hour. Events were identified by a
non-Gaussian excess in the blue and/or red wings of the line. We found
21 sites where events re-occur. The sites are clustered near regions of
evolving network fields seen in low resolution Michelson Doppler Imager
(MDI) magnetic field images. Events tend to expand and shrink across the
surface with a speed ∼ 25 km s-1. Individual events were
also seen to move at this speed across the solar surface. Consecutive
events often have different line profile characteristics and sizes,
suggesting changes in the structure of the accelerated plasma from event
to event. In the majority of events, blue and red wing brightenings do
not produce a simultaneous line intensity increase. Also, the red and
blue wing emission is mostly co-spatial implying either non-directed
flow or jets orientated along the line-of-sight (i.e. out from and
towards the solar surface). The explosive events within a burst are
in some cases separated by 3-5 min, suggesting that oscillations,
which are known to have such periods, may play a role in triggering
the individual events of a burst.

---------------------------------------------------------
Title: Millimeter observations and chromospheric dynamics
Authors: Loukitcheva, M.; Solanki, S. K.; Carlsson, M.; Stein, R. F.
2004A&A...419..747L Altcode:
The intensities of submillimeter and millimeter continua, which are
formed in LTE and depend linearly on temperature, may be able to provide
a test of models of the Solar chromosphere. We have taken a collection
of submillimeter and millimeter wave observed brightness temperatures
Tb of the quiet Sun from the literature and compared it
with brightness temperatures computed from the standard static models
of Fontenla, Avrett and Loeser (FAL) and the dynamic simulations of
Carlsson &amp; Stein (CS). The analysis of the dynamic simulations
of Carlsson &amp; Stein reveals that radio emission at millimeter
wavelengths is extremely sensitive to dynamic processes in the
chromosphere, if these are spatially and temporally resolved. The most
striking result is that the dynamic picture of the solar internetwork
chromosphere is consistent with currently available millimeter and
submillimeter brightness observations. The spectrum obtained by
averaging over the spectra from all time-steps of CS simulations
provides a good fit to observed temporally and spatially averaged
millimeter data in spite of the absence of a permanent temperature
rise at low chromospheric heights in the simulations. This does not by
itself rule out the presence of a chromospheric temperature rise as
present in the FAL models, since a combination of such models also
reproduces the (low resolution) data relatively well. Millimeter
observations indicate that using radio techniques it is possible
to extend observations of the solar oscillatory component to the
heights above those previously observed in the photospheric and low
chromospheric spectral lines and submillimeter continuum. For more
precise diagnostics of chromospheric dynamics, high temporal and spatial
resolution interferometric observations in the millimeter-wavelength
region would be particularly useful. Table \ref{tab:table} is
only available in electronic form at http://www.edpsciences.org

---------------------------------------------------------
Title: Usoskin et al. Reply:
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Schüssler, Manfred;
Mursula, Kalevi
2004PhRvL..92s9002U Altcode:
A Reply to the Comment by G. M. Raisbeck and F. Yiou.

---------------------------------------------------------
Title: Measuring Stellar Differential rotation with asteroseismology
Authors: Gizon, Laurent; Solanki, Sami K.
2004SoPh..220..169G Altcode:
The variation of rotation with latitude is poorly known on stars
other than the Sun. Several indirect techniques, photometric and
spectroscopic, have been used to search for departure from rigid
rotation for sufficiently fast rotators. Here we investigate the
possibility of measuring stellar differential rotation for solar-type
stars through asteroseismology. Rotationally split frequencies of
global oscillation provide information about rotation at different
latitudes depending on the azimuthal order, m, of the mode of
pulsation. We present a method to estimate differential rotation
based on the realization that the m = ±1 and m = ±2 components
of quadrupole oscillations can be observed simultaneously in
asteroseismology. Rotational frequency splittings can be inverted
to provide an estimate of the difference in stellar angular velocity
between the equator and 45° latitude. The precision of the method,
assessed through Monte Carlo simulations, depends on the value of the
mean rotation and on the inclination angle between the rotation axis
and the line of sight.

---------------------------------------------------------
Title: Effect of spatial resolution on estimating the Sun's magnetic
flux
Authors: Krivova, N. A.; Solanki, S. K.
2004A&A...417.1125K Altcode:
A critical question related to a possible secular trend in the Sun's
total magnetic flux and consequently in solar irradiance is the total
amount of magnetic flux present on the Sun and how it is distributed
between active regions and the quiet Sun. NSO/Kitt Peak synoptic
charts have in the past been used to estimate the total flux and the
fraction of the flux in active regions and in the quiet Sun. Since a
single pixel of these synoptic charts is much bigger than individual
small-scale magnetic elements and opposite polarities may be present
within the same pixel, some magnetic flux escaped notice. Here we
estimate the fraction of the magnetic flux escaping detection in Kitt
Peak synoptic charts. By artificially reducing the spatial resolution of
MDI full-disc and high-resolution magnetograms we study the influence
of the resolution on the measured total magnetic flux. Noise in the
data poses the main difficulty to this approach and is carefully
studied. It is concluded that at least half of the magnetic flux in
the quiet Sun remains undetected in Kitt Peak synoptic charts and that
the total flux present on the solar surface at maxima of activity is
around twice the flux present at activity minima.

---------------------------------------------------------
Title: Distribution of magnetically confined circumstellar matter
in oblique rotators
Authors: Preuss, O.; Schüssler, M.; Holzwarth, V.; Solanki, S. K.
2004A&A...417..987P Altcode: 2004astro.ph..1599P
We consider the mechanical equilibrium and stability of matter trapped
in the magnetosphere of a rapidly rotating star. Assuming a dipolar
magnetic field and arbitrary inclination of the magnetic axis with
respect to the axis of rotation we find stable equilibrium positions a)
in a (warped) disk roughly aligned with the magnetic equatorial plane
and b) at two locations above and below the disk, whose distance from
the star increases with decreasing inclination angle between dipole and
rotation axis. The distribution of matter is not strongly affected by
allowing for a spatial offset of the magnetic dipole. These results
provide a possible explanation for some observations of corotating
localized mass concentrations in hot magnetic stars.

---------------------------------------------------------
Title: Towards understanding the β Pictoris dust stream
Authors: Krivov, A. V.; Krivova, N. A.; Solanki, S. K.; Titov, V. B.
2004A&A...417..341K Altcode:
The recent radar detection by \citet{baggaley-2000} of a collimated
stream of interstellar meteoroids postulated to be sourced at β
Pictoris, a nearby star with a prominent dust disk, presents a challenge
to theoreticians. Two mechanisms of possible dust ejection from β
Pic have been proposed: ejection of dust by radiation pressure from
comets in eccentric orbits and by gravity of a hypothetical planet
in the disk. Here we re-examine observational data and reconsider
theoretical scenarios, substantiating them with detailed modeling
to test whether they can explain quantitatively and simultaneously
the masses, speeds, and fluxes. Our analysis of the stream geometry
and kinematics confirms that β Pic is the most likely source of the
stream and suggests that an intensive dust ejection phase took place
∼0.7 Myr ago. Our dynamical simulations show that high ejection
speeds retrieved from the observations can be explained by both
planetary ejection and radiation pressure mechanisms, providing,
however, several important constraints. In the planetary ejection
scenario, only a “hot Jupiter”-type planet with a semimajor axis
of less than 1 AU can be responsible for the stream, and only if the
disk was dynamically “heated” by a more distant massive planet. The
radiation pressure scenario also requires the presence of a relatively
massive planet at several AU or more, that had heated the cometesimal
disk before the ejection occurred. Finally, the dust flux measured at
Earth can be brought into reasonable agreement with both scenarios,
provided that β Pic's protoplanetary disk recently passed through an
intensive short-lasting (∼0.1 Myr) clearance stage by nascent giant
planets, similar to what took place in the early solar system.

---------------------------------------------------------
Title: Solar constraints on new couplings between electromagnetism
and gravity
Authors: Solanki, S. K.; Preuss, O.; Haugan, M. P.; Gandorfer, A.;
Povel, H. P.; Steiner, P.; Stucki, K.; Bernasconi, P. N.; Soltau, D.
2004PhRvD..69f2001S Altcode: 2004gr.qc.....2055S
The unification of quantum field theory and general relativity is a
fundamental goal of modern physics. In many cases, theoretical efforts
to achieve this goal introduce auxiliary gravitational fields, ones
in addition to the familiar symmetric second-rank tensor potential
of general relativity, and lead to nonmetric theories because of
direct couplings between these auxiliary fields and matter. Here,
we consider an example of a metric-affine gauge theory of gravity in
which torsion couples nonminimally to the electromagnetic field. This
coupling causes a phase difference to accumulate between different
polarization states of light as they propagate through the metric-affine
gravitational field. Solar spectropolarimetric observations are reported
and used to set strong constraints on the relevant coupling constant k:
k2&lt;(2.5 km)2.

---------------------------------------------------------
Title: Spot sizes on Sun-like stars
Authors: Solanki, S. K.; Unruh, Y. C.
2004MNRAS.348..307S Altcode: 2003astro.ph.11310S
The total area coverage by starspots is of interest for a variety
of reasons, but direct techniques only provide estimates of this
important quantity. Sunspot areas exhibit a lognormal size distribution
irrespective of the phase of the activity cycle, implying that most
sunspots are small. Here we explore the consequences if starspot areas
were similarly distributed. The solar data allow for an increase in
the fraction of larger sunspots with increasing activity. Taking
this difference between the size distribution at sunspot maximum
and minimum, we extrapolate to higher activity levels, assuming
different dependences of the parameters of the lognormal distribution
on total spot coverage. We find that, even for very heavily spotted
(hypothetical) stars, a large fraction of the spots are smaller than
the current resolution limit of Doppler images and hence might be
missed on traditional Doppler maps.

---------------------------------------------------------
Title: Retrieval of the full magnetic vector with the He I multiplet
at 1083 nm. Maps of an emerging flux region
Authors: Lagg, A.; Woch, J.; Krupp, N.; Solanki, S. K.
2004A&A...414.1109L Altcode:
A technique is presented to invert Stokes profiles of the He I 1083
nm multiplet lines in order to obtain the full magnetic vector and the
line-of-sight velocity. The technique makes use of spectropolarimetry
connected with the Zeeman effect supplemented by a simple Hanle effect
based diagnostic when appropriate. It takes into account effects
like line saturation, magnetooptieffects, etc. and is coupled with a
genetic algorithm, which ensures that the global minimum in a goodness
of fit hypersurface is found. Tests using both artificial and real
data demonstrated the robustness of the method. As an illustration
maps of deduced parameters of an emerging flux region are shown and
briefly discussed.

---------------------------------------------------------
Title: Dynamic Behaviors of the Quiet Sun Seen by SUMER
Authors: Ning, Z.; Innes, D. E.; Solanki, S. K.
2004ESASP.547..297N Altcode: 2004soho...13..297N
No abstract at ADS

---------------------------------------------------------
Title: Radiance Emission by Flaring Activity
Authors: Pauluhn, A.; Solanki, S. K.
2004ESASP.547..323P Altcode: 2004soho...13..323P
Radiance values in the quiet Sun follow a lognormal distribution, with
shape and scaling parameters varying significantly over the temperature
range from chromosphere to corona. We show that these distributions
can be reproduced by a simple model, which assumes that the radiance
is produced by a stochastic (micro-, nano-) flaring process. This
allows the diagnostic capabilities of the radiance distribution to
be judged, performing, e.g., estimates of the true damping times of
the flares. Several energy distributions are tested for the flaring
process, like a Gaussian and a power law. The resulting time series
are compared with SUMER time series of equivalent sampling, after
adjustment of the parameters of the simulation. A good statistical match
of the measurements is obtained for a steep power law distribution of
nanoflare energies.

---------------------------------------------------------
Title: Magnetic Coupling and Topological Change
Authors: Solanki, S. K.
2004ESASP.547..155S Altcode: 2004soho...13..155S
Magnetic field lines thread the convective layers of the Sun's interior
and its atmosphere. They couple these parts of the Sun in the sense
that energy is transported from the Sun's interior and surface into
its atmosphere, where it is deposited, leading to a heating of the
gas present there. One way of energy release is through magnetic
reconnection, which leads to a change of the magnetic topology. Both
these topics are briefly discussed and some recent results are reviewed,
including, new measurements of the magnetic vector near the base of
the corona which reveal the magnetic structure of loops and have led to
the first detection of a magnetic current sheet in the solar atmosphere.

---------------------------------------------------------
Title: Reconstruction of solar UV irradiance
Authors: Krivova, N. A.; Solanki, S. K.
2004cosp...35..504K Altcode: 2004cosp.meet..504K
Understanding solar influence on the Earth's climate requires
a reconstruction of solar irradiance for the pre-satellite
period. Considerable advances have been made in modelling the irradiance
variations at wavelengths longer than 300 nm. At shorter wavelengths,
however, the LTE approximation usually taken in such models fails, which
makes a reconstruction of the solar UV irradiance a rather intricate
problem. We choose an alternative approach and use the observed SUSIM
UV spectra to extrapolate available models to shorter wavelengths.

---------------------------------------------------------
Title: Effect of the electron density stratification on the off-limb
O VI line profiles
Authors: Raouafi, N. -E.; Solanki, S. K.
2004IAUS..223..481R Altcode: 2005IAUS..223..481R
Coronagraphic spectral observations carried out with UVCS on SoHO
above polar coronal holes have shown that the velocity distribution
is highly anisotropic. Here we examine the influence of the density
stratification on the interpretation of such observations. In
particular, we investigate the profiles of O VI spectral lines emitted
in polar coronal holes. We find that at distances greater than 1
R_{odot} from the solar surface the widths of the emitted lines are
significantly affected by the details of the adopted electron density
profiles. In particular, the densities deduced by Doyle et al. (1999)
from SoHO data result in O VI profiles whose widths and intensity
ratio are relatively close to the values observed by UVCS although
only isotropic velocity distributions are employed. Hence we expect
that the magnitude of the anisotropy of the velocity distribution
deduced from UVCS data depends strongly on the adopted density profile.

---------------------------------------------------------
Title: Stokes diagnostics of magneto-convection. Profile shapes
and asymmetries
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vögler, A.;
Schüssler, M.
2004IAUS..223..635K Altcode: 2005IAUS..223..635K
We discuss the polarization signals produced in recent realistic 3D
simulations of solar magnetoconvection. The Stokes profiles of the
Fe I 6301.5, 6302.5, 15648 and 15652 mathrm{Å} Zeeman-sensitive
spectral lines are synthesised and smeared to simulate the image
degradation caused by the Earth's atmosphere and finite telescope
resolution. A Principal Component Analysis approach is applied to
classify the profiles. We find that the classes of Stokes V profiles
as well as their amplitude and area asymmetries are very close to the
observations in the network and inter-network regions.

---------------------------------------------------------
Title: Structure of the solar chromosphere
Authors: Solanki, Sami K.
2004IAUS..223..195S Altcode: 2005IAUS..223..195S
The chromosphere is an intriguing part of the Sun that has stubbornly
resisted all attempts at a comprehensive description. Thus, observations
carried out in different wavelength bands reveal very different,
seemingly incompatible properties. Not surprisingly, a debate is raging
between supporters of the classical picture of the chromosphere as
a nearly plane parallel layer exhibiting a gentle temperature rise
from the photosphere to the transition region and proponents of a
highly dynamical atmosphere that includes extremely cool gas. New
data are required in order settle this issue. Here a brief overview
of the structure and dynamics of the solar chromosphere is given,
with particular emphasis on the chromospheric structure of the quiet
Sun. The structure of the magnetic field is also briefly discussed,
although filaments and prominences are not considered. Besides the
observations, contrasting models are also critically discussed.

---------------------------------------------------------
Title: Temporal evolution of chromospheric downflows
Authors: Lagg, Andreas; Woch, J.; Krupp, N.; Gandorfer, A.; Solanki,
S. K.
2004IAUS..223..279L Altcode: 2005IAUS..223..279L
At the footpoints of loops spanning a site of flux emergence, earlier
investigated in the papers by Solanki et al. (2003) and Lagg et
al. (2004), we find large redshifts in the He 1083 nm line coexisting
with an almost unshifted component. The speed associated with these
redshifts reaches values as high as 40 km/s. We interpret these
downflows in the context of several models: the free-fall downflow of
matter along vertical field lines (Schmidt et al. 2000), the redshift
by downward propagating acoustic waves (Hansteen 1993) and the motion
of condensation regions to either side of loop footpoints (Müller et
al. 2003). We present the temporal evolution of these redshifts and
reconstruct the magnetic field vector in these regions for both the
redshifted and the unshifted atmospheric component.

---------------------------------------------------------
Title: Overview of Slow Mode Oscillations in Hot Coronal Loops
Observed by SUMER
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.
2004IAUS..219..712W Altcode: 2003IAUS..219E..70W
No abstract at ADS

---------------------------------------------------------
Title: Understanding Solar Variability as a Groundwork for Planet
Transit Detection
Authors: Seleznyov, A. D.; Krivova, N. A.; Solanki, S. K.
2004IAUS..219..815S Altcode: 2003IAUS..219E...7K
Detection of planetary transits holds the greatest promise for
the search of terrestrial planets. However intrinsic stellar
variability can mask real transits or lead to 'false' planet transit
detections. Understanding the origin of stellar variability can
help to estimate the minimum sizes of planets detectable with this
technique around different types of stars and to identify the best
wavelength range for such measurements. The only star for which data
with sufficient photometric accuracy and temporal sampling exist is
the Sun. We analyze and model solar variability on timescales relevant
for planetary transits (hours to several days) using a variety of
components such as granulation network (supergranulation) faculae
and sunspots. This study extends our successful work to model solar
irradiance variations on days to years timescales (Fligge et al. 2000;
Krivova et al. 2003).

---------------------------------------------------------
Title: Plasma dynamics of a prominence associated coronal mass
ejection
Authors: Tripathi, D.; Bothmer, V.; Solanki, S. K.; Schwenn, R.;
Mierla, M.; Stenborg, G.
2004IAUS..223..401T Altcode: 2005IAUS..223..401T
An erupting prominence seen by SOHO/EIT was tracked into the field of
view of the LASCO C2 and C3 coronagraphs where it developed into the
core of a structured CME. The erupting prominence was deflected by an
angle of sim 20^{circ} towards the north pole whereas the consequent
core of the CME and it's leading edge propagated in the outer corona at
constant position angle. The prominence material underwent a constant
acceleration phase until a height of sim1.5 solar radii before it
started to decelerate up to a distance of 5.0 solar radii. An inflow
of plasma with a speed of about 70-80 km/s was discovered in the EIT
observations at a height of 1.5-1.2 solar radii in the course of the
prominence eruption, matching in time the prominence deceleration
phase. The downflowing material followed a curved path, suggestive
of the apex of a contracting magnetic loop sliding down along other
field lines.

---------------------------------------------------------
Title: The solar chromosphere as seen in high-resolution millimeter
observations
Authors: Loukitcheva, M. A.; Solanki, S. K.; White, S.
2004IAUS..223..643L Altcode: 2005IAUS..223..643L
We report on chromospheric oscillations studied with 15 sec
cadence observations obtained at a wavelength of 3.5 mm with the
Berkeley-Illinois-Maryland Array (BIMA). Different solar structures,
including active and quiet-Sun regions, are analyzed. We compare the
high-resolution millimeter 2-D images with Ca II K line images from Big
Bear Solar Observatory. Using Fourier and wavelet time series analysis
techniques we find signatures of intensity oscillations with periods
in the range of 2-7 minutes. We discuss the results in the context of
the dynamical model of the solar atmosphere by Carlsson &amp; Stein
(1995, 1997).

---------------------------------------------------------
Title: Stokes Diagnostics of Magnetoconvection. Profile shapes
and asymmetries.
Authors: Khomenko, E. V.; Shelyag, S.; Solanki, S. K.; Vogler, A.;
Schussler, M.
2004cosp...35.2131K Altcode: 2004cosp.meet.2131K
Stokes profiles observed in the quiet Sun have a broad range of
asymmetries and show a variety of shapes. These asymmetries are the
result of the velocity and magnetic field gradients both in horizontal
and vertical directions. We use the most recent realistic 3D simulations
of magnetoconvection at the solar surface to synthesize Stokes profiles
of some photospheric lines and to compare them with observations. Such
comparison provides an important constrains on the MHD models allowing
to conclude about their realism and, thus, to understand the nature of
solar magnetoconvection. The following Zeeman-sensitive spectral lines
are considered: Fe I 6301.5, 6302.5, 15648 and 15652 Å. These lines are
extensively used in observations. The computed Stokes profiles of these
lines were spatially smeared to simulate the effects of a telescope and
atmospheric seeing. A Principal Component Analysis approach is applied
to classify the profiles. The effects of spatial resolution and the
amount of the magnetic flux in the MHD model on the profile shapes are
discussed. The profiles of different classes are clustered together and
form patches on the surface. The size of these patches decreases with
increasing spatial resolution. The distributions of the amplitude and
area asymmetries of Stokes V profiles are very close to the observations
in network and inter-network regions. Some 15% of the profiles smeared
with a 0.”5 seeing have irregular shape with 3 or more lobes. Finally,
we show that simultaneous observations of the same area of the solar
disc using infrared Fe I 15648, 15652 Å and the visible Fe I 6301.5,
6302.5 Å lines done under different seeing conditions (for example
in the case of simultaneous observations at different telescopes)
may result in different asymmetries and even different polarities
of the profiles in two spectral regions observed at the same spatial
point. This work was partially supported by INTAS grant 00-00084.

---------------------------------------------------------
Title: Reconstruction of solar activity for the last millennium
using 10Be data
Authors: Usoskin, I. G.; Mursula, K.; Solanki, S.; Schüssler, M.;
Alanko, K.
2004A&A...413..745U Altcode: 2003astro.ph..9556U
In a recent paper (Usoskin et al. 2002a), we have reconstructed
the concentration of the cosmogenic 10Be isotope in ice
cores from the measured sunspot numbers by using physical models
for 10Be production in the Earth's atmosphere, cosmic ray
transport in the heliosphere, and evolution of the Sun's open magnetic
flux. Here we take the opposite route: starting from the 10Be
concentration measured in ice cores from Antarctica and Greenland, we
invert the models in order to reconstruct the 11-year averaged sunspot
numbers since 850 AD. The inversion method is validated by comparing
the reconstructed sunspot numbers with the directly observed sunspot
record since 1610. The reconstructed sunspot record exhibits a prominent
period of about 600 years, in agreement with earlier observations
based on cosmogenic isotopes. Also, there is evidence for the century
scale Gleissberg cycle and a number of shorter quasi-periodicities
whose periods seem to fluctuate in the millennium time scale. This
invalidates the earlier extrapolation of multi-harmonic representation
of sunspot activity over extended time intervals.

---------------------------------------------------------
Title: Solar variability and global warming: a statistical comparison
since 1850
Authors: Krivova, N. A.; Solanki, S. K.
2004AdSpR..34..361K Altcode:
The magnitude of the Sun's influence on climate has been a subject
of intense debate. Estimates of this magnitude are generally based on
assumptions regarding the forcing due to solar irradiance variations
entering climate modelling. Given the complexity of the climate system,
however, such modelling is perforce based on simplifying assumptions,
which leaves it open to criticism. We take a complementary approach. We
assume that the Sun has been responsible for climate change prior to
1970 and that their interrelation remained unchanged afterwards. Then,
employing reconstructions and measured records of relevant solar
quantities as well as of the cosmic-ray flux, we estimate statistically
which fraction of the dramatic temperature rise after that date could
be due to the influence of the Sun. We show that at least in the most
recent past (since about 1970) the solar influence on climate cannot
have been significant.

---------------------------------------------------------
Title: Irradiance models
Authors: Solanki, S. K.
2004cosp...35..318S Altcode: 2004cosp.meet..318S
Measurements of solar irradiance have revealed variations at all the
sampled time scales (ranging from minutes to the length of the solar
cycle). One important task of models is to identify the causes of the
observed (total and spectral) irradiance variations. Another major
aim is to reconstruct irradiance over time scales longer than sampled
by direct measurements in order to consider if and to what extent
solar irradiance variations may be responsible for global climate
change. Here I describe recent efforts to model solar irradiance
both on the short-term and at longer time scales. On time scales up
to the solar cycle the irradiance models are remarkably successful
in reproducing the observed total and spectral irradiance, although
further improvements are still possible. On longer time scales,
in spite of considerable advances, some uncertainties still remain,
although there is hope of reducing these in the near future.

---------------------------------------------------------
Title: Solar activity and climate during the last millennium
Authors: Solanki, S. K.; Usoskin, I.; Schüssler, M.
2004cosp...35.2535S Altcode: 2004cosp.meet.2535S
The sunspot number is the longest running direct index of solar
activity, with direct measurements starting in 1610. For many purposes,
e.g., for comparisons with climate indices, it is still too short. We
present a reconstruction of the cycle-averaged sunspot number over the
last millennium based on 10Be concentrations in Greenland
and Antarctic ice cores. As intermediate steps of the method, we also
reconstruct the cosmic ray flux at Earth and the Sun's open magnetic
flux. The reconstructions are validated by comparison with direct
measurements or independent reconstructions. We also compare with
records of global climate, in particular with the global temperature
("hockey stick") curve of Mann et al (1998). A reasonable agreement
is found for the entire millennium, excluding only the last decades,
when the two curves start diverging from each other.

---------------------------------------------------------
Title: Effect of the Line-of-Sight Integration on the Profiles of
Coronal Lines
Authors: Raouafi, N. -E.; Solanki, S. K.
2004ESASP.547..401R Altcode: 2004soho...13..401R
We reexamine the interpretation of coronal observations aiming at
the determination of the coronal magnetic field and/or the solar
wind velocity vectors. In particular we investigate the effect of the
integration along the line-of-sight on the profiles of O vi spectral
lines emitted in the corona employing a simple model of the large scale
coronal magnetic field and solar wind. Here we present preliminary
results. We concentrate on the polar coronal holes and find that
although the line-of-sight integration is not important at small
heights, the width of the emitted line is increasingly affected when
moving outwards from the solar disk. At distances of 2.5 R and greater
the width of the profile integrated along the LOS is more than 2 times
as larger as the line profile obtained from an elementary emitting
volume on the polar axis.

---------------------------------------------------------
Title: Interpretation of the Coronal EUV Signature of the CME Event
on June 27 1999
Authors: Raouafi, N. -E.; Mancuso, S.; Solanki, S. K.; Inhester, B.;
Benna, C.; Delaboudinière, J. P.; Stenborg, G.; Mierla, M.
2004ESASP.547..317R Altcode: 2004soho...13..317R
We report the observation of a Coronal Mass Ejection (CME) detected
on June 27 1999 by the UltraViolet Coronagraph Spectrometer (UVCS)
telescope operating on board the SOHO spacecraft. The CME, whose
leading edge was expanding at a projected speed of about 1200 km s,
was observed in white light by the Large Angle Spectroscopic Coronagraph
(LASCO). The UVCS spectra reveal excess broadening of the O VI doublet
lines and enhancement in the intensity of the Si XII lines due to the
motion of expanding hot material. The evolution of the UVCS structure
is highly correlated to the evolution of the CME observed by LASCO
in white light, so that the hot gas emission could be attributable to
the passage of a shock wave propagating just in front of the fast CME.

---------------------------------------------------------
Title: Effect of anisotropic velocity distribution on the linear
polarization of coronal lines. Does the ion cyclotron exist in the
inner corona?
Authors: Raouafi, N. -E.; Solanki, S. K.
2003A&A...412..271R Altcode:
The effect of an anisotropic velocity field distribution of scattering
ions on the polarization parameters of a spectral line emitted by
resonance scattering is considered. The anisotropy of the velocity field
distribution can be interpreted in terms of the ion-cyclotron effect
that is believed to influence some heavy ions in the solar corona. We
present a theoretical study of the Stokes parameters of a spectral
line emitted by atoms or ions in the presence of a bi-Maxwellian
velocity field distribution. It is found from test calculations that
such a distribution measurably changes the polarization properties
of the \ion {O}{vi} D_2 coronal line. Consequently, measurements of
the linear polarization of this line may serve as a new diagnostic
of a possible bi-Maxwellian velocity distribution. As a preliminary
application, the obtained theoretical results are used to interpret
the polarization parameters of the O Vi D_2 coronal line (lambda1031
.92) measured using SUMER/SoHO observations. The obtained results
are compatible with SUMER's observations for more reasonable solar
wind parameters than for an isotropic velocity field distribution
of the scattering ions. Thus, the outflow velocity field vector of
the emitting ions is less inclined with respect to the polar axis of
the Sun (the minimal value of the polar angle eta is 8deg
for an anisotropic velocity distribution versus 17deg for
an isotropic velocity field distribution). These results are obtained
assuming that the re-emitted photons come from a small area in the
center of the coronal polar hole, with zero magnetic field. Since
SUMER/SoHO observations integrate over the line of sight, the results of
the current analysis must be considered preliminary pending computations
including an integration along the line of sight.

---------------------------------------------------------
Title: Models of Solar Irradiance on Time Scales of Minutes to
Centuries
Authors: Solanki, S. K.
2003AGUFMSH31C..01S Altcode:
Solar irradiance varies on all time scales accessible to observations
from minutes to the solar cycle. For the Earth's climate even longer
time scales are of relevance, from centuries to millennia. A series of
models have been or are being constructed to account for the irradiance
variations at these different time scales, which are dominated by
different physical processes. The results of the modelling are described
and, where possible, are compared with the data and are discussed.

---------------------------------------------------------
Title: The molecular Zeeman effect and diagnostics of solar and
stellar magnetic fields. II. Synthetic Stokes profiles in the
Zeeman regime
Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C.
2003A&A...412..513B Altcode:
Recent advances in the computation of the Zeeman splitting of
molecular lines have paved the way for their use as diagnostics
of solar and stellar magnetic fields. A systematic study of their
diagnostic capabilities had not been carried out so far, however. Here
we investigate how molecular lines can be used to deduce the magnetic
and thermal structure of sunspots, starspots and cool stars. First, we
briefly describe the Stokes radiative transfer of Zeeman-split molecular
lines. Then, we compute Stokes spectra of TiO, OH, CH and FeH lines and
investigate their diagnostic capabilities. We also compare the synthetic
profiles with observations. Spectra of TiO, OH and FeH are found to be
interesting diagnostics of sunspot magnetic fields. This is also true
for cool stars, where, however, the OH Stokes V profiles may require
very high S/N data to be reliably employed. Finally we investigate
the potential of various molecular bands for high-contrast imaging
of the solar surface. The violet CN and CH bands turn out to be most
promising for imaging the photosphere, the TiO bands are excellent for
imaging sunspot umbrae, while the UV OH band can be used for imaging
both the photosphere and sunspots.

---------------------------------------------------------
Title: Successful Measurement of the Full Magnetic Vector Near the
Base of the Solar Corona
Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Landi
Degl'Innocenti, E.; Collados, M.
2003AGUFMSH41D..05S Altcode:
The measurement of coronal fields has in the past generally been
restricted to the field strength or to only some of the components of
the magnetic vector. We present here a technique for measuring the full
magnetic vector near the base of the solar corona. As an application
we report on observations of a developing active region with ongoing
magnetic flux emergence. The data allow the first measurement of the 3-D
structure of magnetic loops. They also provide the first detection of an
electric current sheet located near the base of the solar corona. Such
current sheets or tangential discontinuities of the coronal magnetic
field have long been thought to be a major source of coronal heating.

---------------------------------------------------------
Title: Why Solar Magnetic Flux Concentrations Are Bright in Molecular
Bands
Authors: Schüssler, M.; Shelyag, S.; Berdyugina, S.; Vögler, A.;
Solanki, S. K.
2003ApJ...597L.173S Altcode:
Using realistic ab initio simulations of radiative magnetoconvection,
we show that the bright structures in images taken in the “G band,”
a spectral band dominated by lines of the CH molecule, precisely
outline small-scale concentrations of strong magnetic fields on the
visible solar surface. The brightening is caused by a depletion of CH
molecules in the hot and tenuous magnetic structures, thus confirming
the model of radiatively heated magnetic flux concentrations. These
results provide a firm basis for observational studies of the evolution
and dynamics of the small-scale solar magnetic field derived through
“proxy magnetometry” with G-band images.

---------------------------------------------------------
Title: Millennium-Scale Sunspot Number Reconstruction: Evidence for
an Unusually Active Sun since the 1940s
Authors: Usoskin, Ilya G.; Solanki, Sami K.; Schüssler, Manfred;
Mursula, Kalevi; Alanko, Katja
2003PhRvL..91u1101U Altcode: 2003astro.ph.10823U
The extension of the sunspot number series backward in time is of
considerable interest for dynamo theory, solar, stellar, and climate
research. We have used records of the 10Be concentration in
polar ice to reconstruct the average sunspot activity level for the
period between the year 850 to the present. Our method uses physical
models for processes connecting the 10Be concentration with
the sunspot number. The reconstruction shows reliably that the period
of high solar activity during the last 60years is unique throughout
the past 1150years. This nearly triples the time interval for which
such a statement could be made previously.

---------------------------------------------------------
Title: Spatial and temporal fluctuations in sunspots derived from
MDI data
Authors: Solanki, S. K.; Rüedi, I.
2003A&A...411..249S Altcode:
The penumbra radiates an energy flux that is 0.75-0.8 times the
photospheric value. One mechanism proposed to bring this flux to the
surface is interchange convection according to which hot flux tubes
rise to the surface, lie horizontally there while they cool and finally
sink down again. We search for possible signatures of such a process
using time series of magnetograms and continuum images recorded by the
Michelson Doppler Imager (MDI) in its high resolution mode (0.6\arcsec
pixels). The data reveal that at the spatial scales accessible to MDI,
magnetic structures are on average smaller in the azimuthal direction
than brightness features. The small-scale magnetic pattern resolvable
by MDI lives for well over two hours, i.e. longer than the brightness
pattern. As shown in a parallel paper (Schlichenmaier &amp; Solanki
\cite{Sch03}) this result, taken together with theoretical predictions,
suggests that interchange convection is unable to account for the
observed penumbral radiative flux. The need for higher resolution data
obtained under stable conditions is pointed out.

---------------------------------------------------------
Title: On the heat transport in a sunspot penumbra
Authors: Schlichenmaier, R.; Solanki, S. K.
2003A&A...411..257S Altcode:
The penumbra radiates an energy flux that is roughly 75% of the
quiet-sun value. One mechanism proposed to bring this flux to the
surface is interchange convection of magnetic flux tubes according
to which hot flux tubes rise to the surface, cool off their heat
by radiation and sink down again. Another way to deposit heat in
the penumbral photosphere is by steady upflows along magnetic flux
tubes. We discuss these two mechanisms and elaborate on consequences
that can be compared with and constrained by observations. We estimate
the time scales for variations of the intensity and the magnetic field
pattern. By comparing them with the corresponding observed time scales,
we find that pure interchange convection is unable to account for the
observed penumbral heat flux. Heating the penumbra by steady upflows
along magnetic flux tubes, however, turns out to be sufficient to
explain the penumbral brightness, under the condition that significant
magnetic return flux is present within the penumbra. Associated with
the magnetic return flux, downflows within the penumbra should be
present, in accordance with recent observational findings of such
downflows. Exploring other possible heating mechanisms, we find that
dissipation of magnetic energy is negligible, while dissipation of the
kinetic energy of the Evershed flow could contribute significantly to
the brightness of the penumbra.

---------------------------------------------------------
Title: Three dimensional structure of a regular sunspot from the
inversion of IR Stokes profiles
Authors: Mathew, S. K.; Lagg, A.; Solanki, S. K.; Collados, M.;
Borrero, J. M.; Berdyugina, S.; Krupp, N.; Woch, J.; Frutiger, C.
2003A&A...410..695M Altcode:
The magnetic, thermal and velocity structure of a regular sunspot,
observed close to solar disk center is presented. Spectropolarimetric
data obtained with the Tenerife Infrared Polarimeter (TIP) in two
infrared FeI lines at 15 648.5 Å and 15 652.8 Å are inverted
employing a technique based on response functions to retrieve the
atmospheric stratification at every point in the sunspot. In order
to improve the results for the umbra, profiles of Zeeman split OH
lines blending the FeI 15 652.8 Å are also consistently fit. Thus
we obtain maps of temperature, line-of-sight velocity, magnetic
field strength, inclination, and azimuth, as a function of both
location within the sunspot and height in the atmosphere. We present
these maps for an optical depth range between log tau5 =
0 and log tau5 = -1.5, where these lines provide accurate
results. We find decreasing magnetic field strength with increasing
height all over the sunspot, with a particularly large vertical field
gradient of ~ -4 G km-1 in the umbra. We also observe the
so called “spine” structures in the penumbra, i.e. extended radial
features with a stronger and more vertical magnetic field than the
surroundings. Also we found that the magnetic field zenith angle
increases with height. From the velocity map it is clear that the
Evershed flow avoids the spines and mostly concentrates in the more
inclined intervening field. The field inclination at a few locations
in the outer penumbra in lower layers goes beyond 90o. These
locations coincide with the strongest flows in the velocity map.

---------------------------------------------------------
Title: Three-dimensional magnetic field topology in a region of
solar coronal heating
Authors: Solanki, S. K.; Lagg, A.; Woch, J.; Krupp, N.; Collados, M.
2003Natur.425..692S Altcode:
Flares and X-ray jets on the Sun arise in active regions where magnetic
flux emerges from the solar interior amd interacts with the ambient
magnetic field. The interactions are believed to occur in electric
current sheets separating regions of opposite magnetic polarity. The
current sheets located in the corona or upper chromosphere have long
been thought to act as an important source of coronal heating, requiring
their location in the corona or upper chromosphere. The dynamics and
energetics of these sheets are governed by a complex magnetic field
structure that, until now, has been difficult to measure. Here we report
the determination of the full magnetic vector in an interaction region
near the base of the solar corona. The observations reveal two magnetic
features that characterize young active regions on the Sun: a set of
rising magnetic loops and a tangential discontinuity of the magnetic
field direction, the latter being the observational signature of an
electric current sheet. This provides strong support for coronal heating
models based on the dissipation of magnetic energy at current sheets.

---------------------------------------------------------
Title: On the origin of solar variability, with an application to
the search for extrasolar planets
Authors: Seleznyov, A. D.; Solanki, S. K.; Krivova, N. A.
2003ESASP.539..589S Altcode: 2003toed.conf..589S
Detection of planetary transits holds great promise for the search of
terrestrial planets. However, most stars are variable at the level of
the signal produced by the transit of an Earth-like planet. Hence,
intrinsic stellar variability can lead to "false" planet transit
detections. An understanding of the origin of the stellar variability
is needed to ensure reliable transit detections. We consider the
Sun as the closest and best studied star and analyze its variability
on timescales relevant to the transit effect, namely from an hour to
several days. Total and spectral solar irradiance measurements obtained
by the VIRGO instrument on board the SOHO spacecraft have been analyzed
by applying Fourier and wavelet techniques. Preliminary results suggest
that at the time scales of interest solar variability is driven partly
by solar magnetic activity, which dominates at longer time scales,
and convection, in particular solar granulation, which dominates at
shorter time scales. As part of a more quantitative analysis a simple
numerical model of the irradiance variations due to granulation has
been constructed. Irradiance variability of stars with different surface
gravity was calculated in the frequency band of relevance to transits.

---------------------------------------------------------
Title: Molecular Lines as Diagnostics of Solar and Stellar Magnetic
Fields
Authors: Berdyugina, S. V.; Solanki, S. K.; Lagg, A.
2003csss...12..210B Altcode:
Thanks to recent advances in theory we can now calculate molecular
line profiles in the presence of magnetic fields with high accuracy,
both in the Zeeman and Paschen-Back regimes (Berdyugina et al. 2000;
Berdyugina &amp; Solanki 2001a). The synthetic Stokes profiles of
various molecular species (e.g. TiO, OH, MgH, CN, FeH) have been
compared with profiles observed in sunspots. The agreement between
the theory and observations is remarkable. For example, the mutually
opposite polarities of different OH lines are reproduced without
invoking any free parameters, except the magnetic field strength and
sunspot temperature. Introducing molecular lines into the inversion
of sunspot spectra leads to significant improvements in the deduced
magnetic field vector. Here we investigate how molecular lines can be
used to deduce magnetic parameters of cool stars. We find that such
lines are of great interest for measuring magnetic fields on cooler
stars and in starspots.

---------------------------------------------------------
Title: Solar total and spectral irradiance: modelling and a possible
impact on climate
Authors: Krivova, N. A.; Solanki, S. K.
2003ESASP.535..275K Altcode: 2003iscs.symp..275K
There is growing evidence that solar variability influences the
Earth's climate, although the underlying mechanism is not yet
understood. Variations in the solar total and spectral irradiance
often play a central role within various processes that have been
suggested. Whereas changes in the total irradiance can affect the
overall energy balance of the Earth's atmosphere, variations in its
spectral distribution, in particular in the UV, have a pronounced effect
on the chemistry of the Earth's upper atmosphere. Measurements of the
solar total irradiance are only available since 1978 and the spectral
irradiance record is even shorter. This calls for a reconstruction of
irradiance variations at earlier times with the help of models. We first
outline our current understanding of the main mechanism responsible
for irradiance variations and describe the efforts to reconstruct
them. The reconstructed total and UV irradiance is then employed to
estimate the solar contribution to global warming, with particular
emphasis to the period since 1970.

---------------------------------------------------------
Title: Solar irradiance fluctuations on short timescales
Authors: Solanki, S. K.; Seleznyov, A. D.; Krivova, N. A.
2003ESASP.535..285S Altcode: 2003iscs.symp..285S
Although solar irradiance variability at time-scales of days to the
solar cycle has been well studied, comparatively little is known about
the causes of such variations on shorter time-scales. We present an
analysis that aims to distinguish between magnetic and convective
causes. It suggests that on time-scales longer than 1-2 days magnetic
structures are the dominant source while for time-scales shorter than
a few hours convection appears to dominate. We also present a simple
granulation model that includes the various paths of granule birth
and death and compare its output with VIRGO data.

---------------------------------------------------------
Title: Quiet-Sun inter-network magnetic fields observed in the
infrared
Authors: Khomenko, E. V.; Collados, M.; Solanki, S. K.; Lagg, A.;
Trujillo Bueno, J.
2003A&A...408.1115K Altcode:
This paper presents the results of an investigation of the quiet Sun's
magnetic field based on high-resolution infrared spectropolarimetric
observations obtained with the Tenerife Infrared Polarimeter (TIP)
at the German VTT of the Observatorio del Teide. We observed two very
quiet regions at disc centre. The seeing was exceptionally good during
both observing runs, being excellent during one of them. In both cases
the network was intentionally avoided to the extent possible, to focus
the analysis on the characteristics of the weak polarization signals
of the inter-network regions. We find that the Stokes V profile of
Fe I 15648 Å line in almost 50% of the pixels and Stokes Q and/or
U in 20% of the pixels have a signal above 10-3 (in units
of continuum intensity Ic), which is significantly above
the noise level of 2-3 x 10-4. This implies that we detect
fluxes as low as 2 x 1015 Mx/px. We find evidence that we
have detected most of the net flux that is in principle detectable at
1” resolution with the Zeeman effect. The observed linear
polarization resulting from the transverse Zeeman effect indicates that
the magnetic fields have a broad range of inclinations, although most
of the pixels show polarization signatures which imply an inclination
of about 20o. Nearly 30% of the selected V-profiles have
irregular shapes with 3 or more lobes, suggesting mixed polarities with
different LOS velocity within the resolution element. The profiles are
classified using a single value decomposition approach. The spatial
distribution of the magnetic signal shows that profiles of different
classes (having different velocities, splitting, asymmetries) are
clustered together and form patches, close to the spatial resolution
in size. Most of the field is found to be located in intergranular
lanes. The statistical properties of the mainly inter-network field
sampled by these observations are presented, showing that most of
the observed fields are weak with relatively few kG features. The
field strength distribution peaks at 350 G and has a FWHM of 300
G. Other parameters, such as profile asymmetries, filling factors and
line-of-sight velocities are also determined and discussed. Based
on observations with the German Vacuum Tower Telescope (VTT) operated by
the Kiepenheuer-Institut für Sonnenphysik at the Spanish Observatorio
del Teide of the Instituto de Astrofísica de Canarias (IAC).

---------------------------------------------------------
Title: Dependence of UV radiance of the quiet Sun on the solar cycle:
Surface magnetic fields as the cause
Authors: Pauluhn, A.; Solanki, S. K.
2003A&A...407..359P Altcode:
The quiet-Sun UV radiance depends on the solar cycle, as shown by
data collected by the SUMER spectrograph on the Solar and Heliospheric
Observatory (SOHO). The cause of this dependence is still unclear. Here
the hypothesis is tested for the He I 584 Å line that these variations
are due to changes in the magnetic network. The quiet-Sun variability
is investigated with the two EUV instruments CDS (Coronal Diagnostic
Spectrometer) and SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) and the MDI (Michelson Doppler Imager) magnetograph
on SOHO. Using a monthly data set of co-spatial and co-temporal
observations of quiet Sun areas near disk centre we follow the
evolution of the quiet Sun over four years from solar cycle minimum
to maximum conditions and find that the magnetic flux of the quiet
network increases during this period. Furthermore, its variation is
well correlated with the radiance change in the He I 584 Å line. Also,
we find that the largest fractional change is in the flux of the strong
network elements (largest average field strengths), while the weaker
elements do not exhibit a significant change.

---------------------------------------------------------
Title: Hot coronal loop oscillations observed with SUMER: Examples
and statistics
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
Dammasch, I. E.; Kliem, B.
2003A&A...406.1105W Altcode:
We give an extensive overview of Doppler shift oscillations in
hot active region loops obtained with SUMER. The oscillations have
been detected in loops sampled 50-100 arcsec off the limb of the
Sun in ultraviolet lines, mainly Fe Xix and Fe Xxi, with formation
temperature greater than 6 MK. The spectra were recorded along a
300 arcsec slit placed at a fixed position in the corona above the
active regions. Oscillations are usually seen along an extended
section of the slit and often appear to be from several different
portions of the loops (or from different loops). Different portions
are sometimes in phase, sometimes out of phase and sometimes show
phase shifts along the slit. We measure physical parameters of 54
Doppler shift oscillations in 27 flare-like events and give geometric
parameters of the associated hot loops when soft X-ray (SXR) images
are available. The oscillations have periods in the range 7-31 min,
with decay times 5.7-36.8 min, and show an initial large Doppler
shift pulse with peak velocities up to 200 km s-1. The
oscillation periods are on average a factor of three longer than the
TRACE transverse loop oscillations. The damping times and velocity
amplitude are roughly the same, but the derived displacement amplitude
is four or five times larger than the transverse oscillation amplitude
measured in TRACE images. Unlike TRACE oscillations, only a small
fraction of them are triggered by large flares, and they often recur
2-3 times within a couple of hours. All recurring events show initial
shifts of the same sign. These data provide the following evidence to
support the conclusion that these oscillations are slow magnetoacoustic
standing waves in hot loops: (1) the phase speeds derived from observed
periods and loop lengths roughly agree with the sound speed; (2)
the intensity fluctuation lags the Doppler shifts by 1/4 period; (3)
The scaling of the dissipation time of slow waves with period agrees
with the observed scaling for 49 cases. They seem to be triggered
by micro- or subflares near a footpoint, as revealed in one example
with SXR image observations. However other mechanisms cannot as yet
be ruled out. Some oscillations showed phase propagation along the
slit in one or both directions with apparent speeds in the range of
8-102 km s-1, together with distinctly different intensity
and line width distributions along the slit. These features can be
explained by the excitation of the oscillation at a footpoint of an
inhomogeneous coronal loop, e.g. a loop with fine structure. Table
\ref{osctab} and Appendices A and B are only available in electronic
form at http://www.edpsciences.org

---------------------------------------------------------
Title: Long-Term Cosmic Ray Intensities: Physical Reconstruction
Authors: Usoskin, I. G.; Mursula, K.; Solanki, S. K.; Schuessler,
M.; Kovaltsov, G. A.
2003ICRC....7.4041U Altcode: 2003ICRC...28.4041U
Solanki et al. (2000) have recently calculated the open solar magnetic
flux for the last 400 years from sunspot data. Using this reconstructed
magnetic flux as an input to a simple spherically symmetric quasi-steady
state model of the heliosphere, we calculate the expected differential
spectra and integral intensity of galactic cosmic rays at the Earth's
orbit since 1610. The calculated cosmic ray integral intensity is in
good agreement with the neutron monitor measurements during the last
50 years. Moreover, using the specific yield function of cosmogenic
10 Be radionuclide production in the atmosphere, we also calculate
the expected 10 Be production rate which exhibits an excellent
agreement with the actual 10 Be abundance in polar ice over the
last 400 years. Here we present a physical model for the long-term
reconstruction of cosmic ray intensity at 1 AU. The reconstruction
is based on a combination of the solar magnetic flux model and a
heliospheric model. This model allows us to calculate the expected
intensity of galactic cosmic rays (GCR) at the Earth's orbit for the
last 400 years. Details can be found in [25]. Using the numerical recip
e of Solanki et al. [21] and the group sunspot number series (Fig. 1.a)
[11] we have calculated the open solar magnetic flux Fo since 1610 as
shown in Fig. 1.b. In order to calculate galactic cosmic ray (GCR)
spectra we use a spherically symmetric quasi-steady sto chastic
simulation model described in detail elsewhere [24], which reliably
describes the long-term GCR modulation during the last 50 years. In this
model, the most important parameter of the heliospheric modulation of
GCR is the modulation strength [10]: Φ = (D - rE )V /(3κo), where D
= 100 AU is the heliospheric boundary and rE = 1 AU, V = 400 km/s is
the constant solar wind velocity and κo is the rigidity indep endent
part of the diffusion coefficient. Thus, all changes in the modulation
strength Φ in our model are related to the changing diffusion

---------------------------------------------------------
Title: Overview of Recent Results on Coronal Loop Oscillations
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.
2003ANS...324...19W Altcode: 2003ANS...324..B18W
No abstract at ADS

---------------------------------------------------------
Title: Infrared Polarimetry at the MPAe: The Solar Atmosphere from
the Photosphere to the Upper Chromosphere
Authors: Lagg, Andreas; Woch, Joachim; Solanki, Sami K.; Mathew,
Shibu; Borrero, Juan M.; Krupp, N.; Raouafi, N. E.
2003ANS...324...29L Altcode: 2003ANS...324..D04L
No abstract at ADS

---------------------------------------------------------
Title: SUNRISE: Balloon-borne High-Resolution Observation of the Sun
Authors: Solanki, S. K.; Curdt, W.; Gandorfer, A.; Schüssler,
M.; Lites, B. W.; Martinez Pillet, V.; Schmidt, W.; Title, A. M.;
Sunrise Team
2003ANS...324..113S Altcode: 2003ANS...324..P20S
No abstract at ADS

---------------------------------------------------------
Title: Determining the Inclination of the Rotation Axis of a
Sun-like Star
Authors: Gizon, L.; Solanki, S. K.
2003ApJ...589.1009G Altcode:
Asteroseismology provides us with the possibility of determining the
angle, i, between the direction of the rotation axis of a pulsating
Sun-like star and the line of sight. A knowledge of i is important
not just for obtaining improved stellar parameters, but also in order
to determine the true masses of extrasolar planets detected from the
radial velocity shifts of their central stars. By means of Monte Carlo
simulations, we estimate the precision of the measurement of i and
other stellar parameters. We find that the inclination angle can be
retrieved accurately when i&gt;~30deg for stars that rotate
at least twice as fast as the Sun.

---------------------------------------------------------
Title: Slow-mode standing waves observed by SUMER in hot coronal
loops
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.;
Marsch, E.
2003A&A...402L..17W Altcode:
We report the first detection of postflare loop oscillations seen in
both Doppler shift and intensity. The observations were recorded in
an Fe Xix line by the SUMER spectrometer on SOHO in the corona about
70 min after an M-class flare on the solar limb. The oscillation has a
period of about 17 min in both the Doppler velocity and the intensity,
but their decay times are different (i.e., 37 min for the velocity and
21 min for the intensity). The fact that the velocity and the intensity
oscillations have exactly a 1/4-period phase difference points to the
existence of slow-mode standing waves in the oscillating loop. This
interpretation is also supported by two other pieces of evidence:
(1) the wave period and (2) the amplitude relationship between the
intensity and velocity are as expected for a slow-mode standing wave.

---------------------------------------------------------
Title: Variability of EUV-spectra from the quiet upper solar
atmosphere: Intensity and Doppler shift
Authors: Brković, A.; Peter, H.; Solanki, S. K.
2003A&A...403..725B Altcode:
We have studied SUMER and CDS time series of spectra and images of
quiet-Sun regions at the solar disc centre. The data contain ultraviolet
emission lines sampling temperatures of the chromosphere, transition
region and corona. We find a high correlation between average net
Doppler shifts and relative brightness variabilities of the studied
lines (correlation coefficient of 0.92), suggesting a connection between
the two quantities. The anti-correlation between differential emission
measures and relative brightness variabilities is weaker (correlation
coefficient of -0.78). We discuss the observed relationships on the
basis of differential emission measures and linear wave calculations.

---------------------------------------------------------
Title: Can solar variability explain global warming since 1970?
Authors: Solanki, S. K.; Krivova, N. A.
2003JGRA..108.1200S Altcode:
The magnitude of the Sun's influence on climate has been a subject
of intense debate. Estimates of this magnitude are generally based on
assumptions regarding the forcing due to solar irradiance variations
and climate modeling. This approach suffers from uncertainties that
are difficult to estimate. Such uncertainties are introduced because
the employed models may not include important but complex processes
or mechanisms or may treat these in too simplified a manner. Here
we take a more empirical approach. We employ time series of the most
relevant solar quantities, the total and UV irradiance between 1856
and 1999 and the cosmic rays flux between 1868 and 1999. The time
series are constructed using direct measurements wherever possible and
reconstructions based on models and proxies at earlier times. These
time series are compared with the climate record for the period 1856 to
1970. The solar records are scaled such that statistically the solar
contribution to climate is as large as possible in this period. Under
this assumption we repeat the comparison but now including the period
1970-1999. This comparison shows without requiring any recourse to
modeling that since roughly 1970 the solar influence on climate (through
the channels considered here) cannot have been dominant. In particular,
the Sun cannot have contributed more than 30% to the steep temperature
increase that has taken place since then, irrespective of which of the
three considered channels is the dominant one determining Sun-climate
interactions: tropospheric heating caused by changes in total solar
irradiance, stratospheric chemistry influenced by changes in the solar
UV spectrum, or cloud coverage affected by the cosmic ray flux.

---------------------------------------------------------
Title: A stream of particles from the begin {equation}ta Pictoris
disc: A possible ejection mechanism
Authors: Krivova, N. A.; Solanki, S. K.
2003A&A...402L...5K Altcode:
Recently, a stream of particles originating from the direction of begin
{equation}ta Pictoris, a young main sequence star surrounded by a dust
disc, has been reported (Baggaley \cite{baggaley-2000}). Standard
mechanisms of particle ejection from a disc fail to reproduce
the properties of this stream. We find that scattering by a giant
proto-planet with properties taken from the literature is consistent
with the observations. The fact that a straightforward ejection
mechanism reproduces the data supports the identification of the
particle stream's source with beta Pic. Our work also indicates that
protoplanetary dust discs form a potentially rich source of large
interstellar grains, as widely detected in the Solar System.

---------------------------------------------------------
Title: Interplanetary and solar surface properties of coronal holes
observed during solar maximum
Authors: Zhang, J.; Woch, J.; Solanki, S. K.; von Steiger, R.;
Forsyth, R.
2003JGRA..108.1144Z Altcode:
Data from the Solar Wind Ion Composition Spectrometer (SWICS) on board
the Ulysses spacecraft and synoptic maps from Kitt Peak are used to
analyze the relatively short-lived coronal holes which exist during
the maximum phase of the solar activity cycle 23. They are compared
with the persistent polar coronal holes which prevail around solar
minimum. A solar wind velocity increase coinciding with a shift of
the ionic charge composition toward lower charge states serves as a
robust criterion for identifying solar wind streams emanating from
solar maximum holes. This allows an unambiguous association of every
stream identified in interplanetary space with a coronal hole on the
solar surface with consistent magnetic polarity. Solar wind streams
emanating from the solar maximum holes generally show lower velocities
of 400 to 600 km/s compared to the polar hole stream velocities of
700 to 800 km/s. However, the SWICS O7+/O6+
charge-state ratios, which are a proxy for coronal temperatures, do not
reveal a consistent difference. Though a number of solar maximum holes
have a significantly, up to three times, higher temperature compared
to the polar coronal holes, the majority of the investigated holes and
specifically those with new cycle polarity have a coronal temperature
within the range of polar hole temperatures. Likewise, the magnetic flux
density in the solar maximum holes and in the polar coronal holes, as
derived from the synoptic maps, is not strikingly different. Therefore
any intrinsic difference between solar maximum holes and polar coronal
holes is small. The striking discrepancy in their kinetic properties,
namely the slower velocity of the solar wind streams emanating from
solar maximum holes, may partly be attributed to deceleration of the
solar wind during propagation to the spacecraft. The discrepancy may
also be influenced by active regions in close proximity to the coronal
holes, which presumably is more likely for smaller holes. There may,
however, be a tendency for the faster wind streams to emanate from
cooler holes.

---------------------------------------------------------
Title: Ejection of Dust from Planetary Systems into Interstellar Space
Authors: Krivov, A.; Krivova, N.; Solanki, S.; Titov, V.
2003EAEJA.....4264K Altcode:
Extensive observational and theoretical research of the last two decades
have made it clear that young exoplanetary systems comprise not only
planets themselves, but also disks of small bodies and of dust-sized
material these bodies replenish. In much the same way as in the young
Solar System, interaction of the solids in a circumstellar disk with
planets at late stages of planet formation should hang the material on
the outskirts of the system, creating exosolar Kuiper belts and Oort
clouds. A portion of the material is ejected by the exoplanets from the
disks into interstellar space, which may represent an important source
of large interstellar dust grains in the Galaxy. Here we study how
the efficiency of the ejection mechanism and the involved timescales
depend on the mass and orbital parameters of the planet, as well
as on the `unperturbed' spatial distribution of disk particles. We
also derive the distribution of the final velocities of the ejected
material. The study is done semianalytically with the aid of the
Oepik-Weidenschilling statistical theory of planetary encounters and
numerically with direct Monte-Carlo orbital simulations. The results
may have particular implications to the beta Pictoris system: they
lend further support to the idea (Krivova and Solanki 2002) that a
collimated stream of interstellar radiometeors detected by Baggaley
(2000) originates at beta Pic and consists of grains ejected by a
presumed jovian planet orbiting this star.

---------------------------------------------------------
Title: Cycles and cyclicities of the Sun
Authors: Solanki, S. K.; Krivova, N. A.
2003ASPC..292..423S Altcode: 2003ipc..conf..423S
The solar activity cycle is discussed in the broader context of solar
variability. It is pointed out that the Sun exhibits periodic, cyclic,
chaotic and stochastic phenomena. The origins of solar variability
are mentioned and the importance of secular variations of the solar
cycle for a putative influence of the Sun on the Earth's climate is
briefly discussed.

---------------------------------------------------------
Title: SUNRISE: a balloon-borne telescope for high resolution solar
observations in the visible and UV
Authors: Solanki, Sami K.; Gandorfer, Achim M.; Schuessler, Manfred;
Curdt, W.; Lites, Bruce W.; Martinez-Pillet, Valentin; Schmidt,
Wolfgang; Title, Alan M.
2003SPIE.4853..129S Altcode:
Sunrise is a light-weight solar telescope with a 1 m aperture for
spectro-polarimetric observations of the solar atmosphere. The telescope
is planned to be operated during a series of long-duration balloon
flights in order to obtain time series of spectra and images at the
diffraction-limit and to study the UV spectral region down to ~200 nm,
which is not accessible from the ground. The central aim of Sunrise
is to understand the structure and dynamics of the magnetic field in
the solar atmosphere. Through its interaction with the convective flow
field, the magnetic field in the solar photosphere develops intense
field concentrations on scales below 100 km, which are crucial for the
dynamics and energetics of the whole solar atmosphere. In addition,
Sunrise aims to provide information on the structure and dynamics
of the solar chromosphere and on the physics of solar irradiance
changes. Sunrise is a joint project of the Max-Planck-Institut fuer
Aeronomie (MPAe), Katlenburg-Lindau, with the Kiepenheuer-Institut fuer
Sonnenphysik (KIS), Freiburg, the High-Altitude Observatory (HAO),
Boulder, the Lockheed-Martin Solar and Astrophysics Lab. (LMSAL),
Palo Alto, and the Instituto de Astrofi sica de Canarias, La Laguna,
Tenerife. In addition, there are close contacts with associated
scientists from a variety of institutes.

---------------------------------------------------------
Title: On the nature of moving magnetic feature pairs around sunspots
Authors: Zhang, Jun; Solanki, S. K.; Wang, Jingxiu
2003A&A...399..755Z Altcode:
Employing data recorded by the Michelson Doppler Imager (MDI) instrument
on the Solar and Heliospheric Observatory (SOHO), we have identified
144 pairs of opposite magnetic polarity moving magnetic features
(MMFs) in two active regions (NOAA ARs 8375 and 9236). The following
results are obtained: (1) The majority of MMF pairs first appears at
a distance of 1000 to 5000 km from the outer boundary of the sunspot,
although MMF pairs appearing closer to the sunspot may be missed. (2)
MMF bipoles are not randomly oriented. The member of an MMF pair further
from the sunspot has the polarity of the parent sunspot in 85% of the
cases. Furthermore, the orientations of MMF pairs are associated with
the twist of the sunspot superpenumbra deduced from Hα images. (3) The
mean lifetime of the studied MMFs is around 4 hours. (4) The separation
between the two polarities of the MMFs falls in the range of 1100-1700
km. This separation remains almost unchanged, even decreases slightly
as the MMF pairs move outwards. (5) MMFs are observed to cluster at
particular azimuths around the parent sunspot, in particular in AR
8375. (6) MMF pairs move approximately radially outward from sunspots
at an average speed of around 0.5 km s-1. Their motion is
deflected towards large concentrations of magnetic flux of opposite
polarity to that of the parent sunspot. A qualitative model based on
these and other observations is presented. MMF pairs are proposed to be
part of a U-loop emanating from the sunspot's magnetic canopy. Possible
mechanisms leading to the formation of such a loop are discussed.

---------------------------------------------------------
Title: Reconstruction of solar irradiance variations in cycle 23:
Is solar surface magnetism the cause?
Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.; Unruh, Y. C.
2003A&A...399L...1K Altcode:
A model of solar irradiance variations is presented which is based
on the assumption that solar surface magnetism is responsible for all
total irradiance changes on time scales of days to years. A time series
of daily magnetograms and empirical models of the thermal structure
of magnetic features (sunspots, faculae) are combined to reconstruct
total (and spectral) irradiance from 1996 to 2002. Comparisons with
observational data reveal an excellent correspondence, although the
model only contains a single free parameter. This provides strong
support for the hypothesis that solar irradiance variations are caused
by changes in the amount and distribution of magnetic flux at the
solar surface.

---------------------------------------------------------
Title: Intercalibration of SUMER and CDS on SOHO. III. SUMER and
CDS-GIS
Authors: Pauluhn, Anuschka; Lang, Jim; Breeveld, Eddie R.; Solanki,
Sami K.; Schühle, Udo
2003ApOpt..42..657P Altcode:
Simultaneous observation of the same solar sources with different
instruments is one way to test prelaunch radiometric calibrations and
to detect changes in responsivity with time of extreme-ultraviolet
instruments in space. Here we present the results of intercalibration
of the SUMER (Solar Ultraviolet Measurements of Emitted Radiation)
spectrometer (detectors A and B) and the GIS (Grazing Incidence
Spectrometer), one of two spectrometers that compose the CDS (Coronal
Diagnostic Spectrometer) on the Solar and Heliospheric Observatory
(SOHO). The two instruments observed simultaneously radiances of
emission lines at or near the center of the solar disk. The emission
line chosen for intercomparison was Ne viii at 770 Å. However,
such an intercomparison of the SUMER and CDS-GIS measurements means
comparing two data sets with large differences in resolution and field
of view. The latter difference, especially, introduces differences
in the measured intensities caused by the solar variability that is
relatively strong in the 770- Å line. Using a statistical approach to
overcome this problem, we found that the ratio of the GIS to the SUMER
average radiances amounted to 2.6 +/- 0.9 before the SOHO ’s loss of
attitude and to 2.1 +/- 0.7 afterward. These findings confirm earlier
estimates of the GIS ’s responsivity being too low, and an update
of the GIS calibration is recommended. Despite the large differences
in resolution and field of view of the two instruments, the shapes of
their normalized and rescaled histograms of the radiances agree well
and therefore represent characteristic features of the Ne viii line.

---------------------------------------------------------
Title: The Magnetic Field from the Sun to the Interstellar Medium
Authors: Solanki, Sami K.
2003IAUJD...7E..11S Altcode:
The magnetic field of the Sun is responsible for a vast variety of
phenomena on the Sun and in the heliosphere. The field extends from
the bottom of the convection zone into the interstellar medium and
is the main agent that couples the various layers of the atmosphere
together. The strength structure spatial scales complexity and evolution
of the magnetic field changes very significantly with distance from
the solar surface. In particular the energy density of the field
compared to that of the gas (thermal kinetic) is a strong function of
location. Furthermore although the global magnetic structure becomes
simpler with increasing height complex fine-scale features are seen
at all heights.

---------------------------------------------------------
Title: New Molecular Indicators of Sunspot Magnetic Fields: Infrared
OH Lines
Authors: Berdyugina, S. V.; Solanki, S. K.; Lagg, A.
2003ASPC..286..299B Altcode: 2003ctmf.conf..299B
No abstract at ADS

---------------------------------------------------------
Title: Molecular lines observations with THEMIS
Authors: Arnaud, J.; Faurobert, M.; Raouafi, N. -E.; Solanki, S. K.
2003sf2a.conf..111A Altcode: 2003sf2a.confE..39A
Lines of molecules like MgH, C2, TiO, ... represent powerful tools
for the study of the solar atmosphere. Their observations on the
Sun can also help to constrain the polarizability and Lande factors
calculations which are much more complex than for atomic lines. We will
present THEMIS polarimetric observations of these lines to illustrate
some aspects of their use for solar physics.

---------------------------------------------------------
Title: Structure of a simple sunspot from the inversion of IR
spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.;
Berdyugina, S. V.; Frutiger, C.; Krupp, N.; Woch, J.
2003AN....324..388M Altcode:
Analysis of spectral data of two neighboring infrared lines, Fe i
15648.5 Å (g = 3) and Fe i 15652.9 Å (g_eff = 1.53) are carried out
for a simple sunspot when it was near the solar disk center (mu = 0.92),
to understand the basic structure of sunspot magnetic field. Inversions
of Stokes profiles are carried out to derive different atmospheric
parameters both as a function of location within the sunspot and height
in the atmosphere. As a result of the inversion we have obtained maps
of magnetic field strength, temperature, line-of-sight velocity, field
inclination and azimuth for different optical depth layers between log
(tau_ {5}) = 0 and log (tau_ {5}) = -2.0 . In this paper we present
few results from our inversion for a layer averaged between log (tau_
{5}) from 0.0 to -0.5.

---------------------------------------------------------
Title: Doppler Oscillations of Active Region Loops: Steps towards
Coronal Seismology
Authors: Curdt, W.; Wang, T. J.; Dammasch, I. E.; Solanki, S. K.
2003HvaOB..27...83C Altcode:
Oscillations of coronal loops -- subject of theoretical work for a long
time -- can help to determine coronal plasma parameters not otherwise
accessible. Therefore, the Doppler oscillations recently observed by
the SUMER spectrometer on SOHO are of extreme interest and constitute a
significant contribution to the old, but rejuvenated field of coronal
seismology. High-velocity oscillation events in hot EUV flare lines
are seen almost every time these lines brighten. Such events seem to
be a common feature of active region loops. The oscillations always
have an impulsive trigger and are strongly damped while they cool
down. Lines formed at normal coronal temperatures do not show any
signature of these oscillations.

---------------------------------------------------------
Title: Commission 12: Solar radiation and structure (Rayonnement et
structure solaires)
Authors: Solanki, Sami K.
2003IAUTA..25...90S Altcode: 2003IAUTr..25A..90S
No abstract at ADS

---------------------------------------------------------
Title: Sunspots: An overview
Authors: Solanki, Sami K.
2003A&ARv..11..153S Altcode:
Sunspots are the most readily visible manifestations of solar
magnetic field concentrations and of their interaction with the Sun's
plasma. Although sunspots have been extensively studied for almost
400 years and their magnetic nature has been known since 1908,
our understanding of a number of their basic properties is still
evolving, with the last decades producing considerable advances. In the
present review I outline our current empirical knowledge and physical
understanding of these fascinating structures. I concentrate on the
internal structure of sunspots, in particular their magnetic and
thermal properties and on some of their dynamical aspects.

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Title: Hot loop oscillations seen by SUMER
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
Dammasch, I. E.
2003AN....324..340W Altcode:
No abstract at ADS

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Title: Magnetic Elements Near the Solar Limb: Inversions Based on
a Flux-tube Model
Authors: Frutiger, C.; Solanki, S. K.; Gandorfer, A.
2003ASPC..307..344F Altcode:
No abstract at ADS

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Title: Molecules as Diagnostics of Solar and Stellar Magnetic Fields
Authors: Berdyugina, S. V.; Solanki, S. K.; Stenflo, J. O.
2003ASPC..307..181B Altcode:
No abstract at ADS

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Title: Modeling the Fine Structure of a Sunspot Penumbra through
the Inversion of Stokes Profiles
Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Frutiger, C.;
Collados, M.; Bellot Rubio, L. R.
2003ASPC..286..235B Altcode: 2003ctmf.conf..235B
No abstract at ADS

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Title: Asteroseismic Determination of a Star
Authors: Gizon, Laurent; Solanki, Sami K.
2003IAUJD..12E..19G Altcode:
Asteroseismology provides us with the possibility of determining the
angle i between the direction of the rotation axis of a pulsating
Sun-like star and the line of sight. A knowledge of i is important
not just for obtaining improved stellar parameters but also in order
to determine the true masses of extra-solar planets detected from the
radial velocity shifts of their central stars. By means of Monte-Carlo
simulations we estimate the precision of the measurement of i and
other stellar parameters. We find that the inclination angle can be
retrieved accurately for sufficiently large i for stars that rotate
at least twice faster than the Sun.

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Title: Doppler oscillations in hot coronal loops
Authors: Curdt, W.; Wang, T. J.; Innes, D. E.; Solanki, S. K.;
Dammasch, I. E.; Kliem, B.; Ofman, L.
2002ESASP.506..581C Altcode: 2002ESPM...10..581C; 2002svco.conf..581C
Recently, a new kind of damped oscillations of hot coronal loops was
revealed by the Solar Ultraviolet Measurements of Emitted Radiation
(SUMER) spectrometer on SOHO. Such events seem to be a common feature
observed in active region loops, seen very often when these lines
brighten. The oscillations always have an impulsive trigger and
are strongly damped while they cool down. However, in lines formed
at coronal temperatures of ≍2 MK never any signature of these
oscillations has been observed. In this study, we present the main
properties of Doppler oscillations derived from a statistical study
of 17 flare-like events, and a comparison with TRACE transverse loop
oscillations. We also discuss the oscillation modes and their damping
mechanism.

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Title: Was one sunspot cycle in the 18th century really lost?
Authors: Krivova, N. A.; Solanki, S. K.; Beer, J.
2002A&A...396..235K Altcode:
The unusually long 4th solar cycle has recently been proposed by
Usoskin et al. (2001) to be composed of two cycles. They argue that
a weak and short cycle might have been lost in sparse sunspot data at
the end of the 18th century. Here we check this hypothesis in different
ways. First, we consider the sunspot number record in greater detail
and compare in a statistical sense the sunspot observations of the
period in question with those at other times. In a statistical sense the
sunspot numbers recorded at the time of the proposed new cycle minimum
are extremely untypical for other minima in the solar cycle record,
but quite usual for the declining phase of the solar cycle. We also
analyse other available proxies of solar activity, such as variations
of the cosmogenic nuclides 10Be and 14C as well
as auroral activity. These historical records are sufficiently long
and provide an independent testimony of the cyclic behaviour of solar
activity at the end of the 18th century. We found no evidence for a lost
cycle in any of these data sets. Finally, we compare the proposed new
cycle with the other cycles in the sunspot record. This reveals that
the proposed “missing” cycle has very unusual properties, much more
so than the original, standard cycle 4. Taken together, the evidence
from these various tests strongly suggests that no cycle was missed and
that the official sunspot cycle numbering and parameters are correct.

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Title: Search for a relationship between solar cycle amplitude
and length
Authors: Solanki, S. K.; Krivova, N. A.; Schüssler, M.; Fligge, M.
2002A&A...396.1029S Altcode:
The cross-correlation between time series of solar cycle length
and amplitude suggests that the length precedes the amplitude. The
relationship between the two is found to be more complex than a simple
lag or phase shift, however. A simple empirical model is constructed
which allows the amplitude of a given cycle to be predicted with
relatively high accuracy from the lengths of earlier cycles. This
result not only adds to the means at our disposal for predicting the
amplitudes of future cycles, but also implies that the solar dynamo
carries a memory of the length of one cycle over into the next. It may
also have a bearing on why solar cycle length correlates better with
the Earth's temperature record than cycle amplitude (Friis-Christensen
&amp; Lassen \cite{Friis-Christensen:Lassen:1991}). Thoughts on possible
physical causes are presented.

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Title: A physical reconstruction of cosmic ray intensity since 1610
Authors: Usoskin, Ilya G.; Mursula, Kalevi; Solanki, Sami K.;
Schüssler, Manfred; Kovaltsov, Gennady A.
2002JGRA..107.1374U Altcode:
The open solar magnetic flux has been recently reconstructed by [2000,
2002] for the last 400 years from sunspot data. Using this reconstructed
magnetic flux as an input to a spherically symmetric quasi-steady
state model of the heliosphere, we calculate the expected intensity
of galactic cosmic rays at the Earth's orbit since 1610. This new,
physical reconstruction of the long-term cosmic ray intensity is
in good agreement with the neutron monitor measurements during the
last 50 years. Moreover, it resolves the problems related to previous
reconstruction for the last 140 years based on linear correlations. We
also calculate the flux of 2 GeV galactic protons and compare it to
the cosmogenic 10Be level in polar ice in Greenland and
Antarctica. An excellent agreement between the calculated and measured
levels is found over the last 400 years.

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Title: The 1.3-year and 156-day periodicities in sunspot data:
Wavelet analysis suggests a common origin
Authors: Krivova, N. A.; Solanki, S. K.
2002A&A...394..701K Altcode:
Helioseismic data have revealed a 1.3-year periodicity in the solar
rotation rate near the bottom of the solar convection zone. In order
to test whether these rotation rate variations have a significant
impact on the solar dynamo, we search for such a periodicity in
tracers of relatively freshly emerged flux at the solar surface,
namely sunspots. Sunspot areas and sunspot number time series are
studied with the help of the wavelet transform. Significant power
at this period (1.28 years) is indeed found and is observed to vary
strongly with time. This provides independent support for the presence
of a 1.3 year periodicity in solar data. The power at the 154-158-day
Rieger period of solar flares is seen to vary approximately in phase
with the 1.28-year period. Based on this we propose that the Rieger
period is the third harmonic (3x 156 days= 1.28 years) of the 1.3-year
period. If the rotation rate of the Sun does vary with 1.3 years then
the enhanced flaring with the Rieger period may finally be driven by
the 1.3 year periodicity. However, the power in both periods is also
found to approximately follow the total number of sunspots. Therefore
we cannot rule out that the 1.3-year and 156-day periods are harmonics
of the solar activity cycle. Finally, our analysis of a calibrated
sunspot area record reveals that the 156-day period continues into
the most recent cycles, in contrast to earlier results.

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Title: Sunrise: a 1-m balloon borne solar telescope
Authors: Solanki, S. K.; Schüssler, M.; Curdt, W.; Lites, B. W.;
Martinez Pillet, V.; Schmidt, W.; Title, A. M.; Sunrise Team
2002ESASP.505...27S Altcode: 2002solm.conf...27S; 2002IAUCo.188...27S
Sunrise is a light-weight solar telescope with a 1 m aperture
for spectro-polarimetric observations of the solar atmosphere. The
telescope is planned to be operated during a series of long-duration
balloon flights in order to obtain time series of spectra and images
at the diffraction-limit and to study the UV spectral region down to
≅200 nm, which is not accessible from the ground. The central aim of
Sunrise is to understand the structure and dynamics of the magnetic
field in the solar atmosphere. Interacting with the convective flow
field, the magnetic field in the solar photosphere develops intense
field concentrations on scales below 100 km, which are crucial for the
dynamics and energetics of the whole solar atmosphere. In addition,
Sunrise aims to provide information on the structure and dynamics of
the solar chromosphere and on the physics of solar irradiance changes.

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Title: Thermal-magnetic relation of a sunspot as inferred from the
inversion of 1.5 μm spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Krupp, N.; Woch,
J.; Collados, M.; Berdyugina, S.; Frutiger, C.
2002ESASP.505..501M Altcode: 2002IAUCo.188..501M; 2002solm.conf..501M
We present the thermal-magnetic relation in a simple, isolated sunspot
deduced from the inversion of 1.56 μm spectropolarimetric data. Due to
the high Zeeman sensitivity of the g = 3, Fe I 1.5648 μm line, we can
study this relationship in the entire sunspot. An inversion technique
based on response functions is used to derive various parameters,
both as a function of location within the sunspot and of height in the
atmosphere. In this paper we attempt to relate field strength, vertical
and radial field components and the field inclination with temperature.

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Title: Initial features of an X-class flare observed with SUMER
and TRACE
Authors: Wang, T. J.; Solanki, S. K.; Innes, D. E.; Curdt, W.
2002ESASP.505..607W Altcode: 2002IAUCo.188..607W; 2002solm.conf..607W
A class X1.5 flare started on the solar limb at 00:43 UT on 21 April
2002, which was associated with a CME observed at 01:27 UT by LASCO
C2. The coordinated analyses of this flare include TRACE 195 Å images
and SUMER spectra in lines of Fe XXI, Fe XII, and C II. We find that:
1) The flare began with a jet seen by TRACE, which was detected by
SUMER in the C II line as a strong brightening with blue shifts up to
170 km s-1. At that time only weak emission was detected
in Fe XII and Fe XXI. 2) Subsequently, a weak looplike brightening
started south of the jet, moving outwards with an average speed of
about 150 km s-1. The SUMER spectra responded this moving
loop as separatingly brightenings, visible only in the Fe XXI line. The
southwards moving component contains red- and blue-shifted emission
features and has an apparent speed of ~120 km s-1. The
absence of signatures in Fe XII and C II lines indicates that the
moving weak loop seen by TRACE corresponds to the emission from very
hot plasma, in a blend line in the 195 Å bandpass due to Fe XXIV
formed at T &gt; 10 MK. 3) The trigger mechanism of the flare and
associated CME can be interpreted in the same way as that proposed by
Wang et al. (2002) for an event with similar initial features.

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Title: Harold Jeffreys Lecture: Solar variability and climate change:
is there a link?
Authors: Solanki, Sami K.
2002A&G....43e...9S Altcode:
Radiation from the Sun makes Earth a habitable planet. Fluctuations in
the solar output are therefore likely to affect the climate on Earth,
but establishing both how the output of he Sun varies and how such
variations influence Earth's climate have proved tricky. But increased
amounts of data from the Sun and about the climate on Earth over
recent years mean that rapid progress is being made. In this paper,
I review the current debate on the influence of the Sun and summarize
the state of play in this area of solar physics.

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Title: Statistical properties of magnetic fields in intranetwork
Authors: Khomenko, E. V.; Collados, M.; Lagg, A.; Solanki, S. K.;
Trujillo Bueno, J.
2002ESASP.505..445K Altcode: 2002IAUCo.188..445K; 2002solm.conf..445K
We report a study of the quiet sun's magnetic field based
on high-resolution infrared spectropolarimetric observations
(TIP/VTT). We find that in almost 50% of the pixels Stokes V and in 15%
the Stokes Q and/or U profiles have a signal above 10-3. The
statistical properties of the mainly intranetwork field sampled by these
observations are presented, showing that most of the observed fields
are weak (the field strength distribution peaks at 350 G and has a FWHM
of 300 G) with very few kG features. The magnetized regions occupy a
very small fill fractions (about 2%). The field changes properties on
granular spatial scales and the size of the patches formed by similar
profiles is close to 1". Most of the parameters of the observed
polarization profiles show correlations with granulation parameters.

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Title: How large is the Sun's total magnetic flux?
Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.
2002ESASP.505..461K Altcode: 2002solm.conf..461K; 2002IAUCo.188..461K
Variations in the radiative output of the Sun are directly allied
to changes in the amount and distribution of solar surface magnetic
field. The variability of irradiance on time-scales significantly
shorter than a solar cycle can be produced by the spatial and temporal
evolution of active regions, whereas its secular variations ensue
from changes of the quiet-Sun magnetic flux on longer time-scales. The
relative amounts of the magnetic flux in active regions and in the quiet
Sun as well as their cyclic evolution have been studied by Harvey (1994)
on the basis of the NSO/Kitt Peak synoptic maps. Since a single pixel of
such a map is much bigger than individual small-scale magnetic elements
and opposite polarities may be present within the same pixel, some
magnetic flux went uncounted, so that the flux obtained by Harvey (1994)
represents a lower limit to the true amount of magnetic flux present
on the Sun. We use MDI full-disc and high-resolution magnetograms to
estimate the total magnetic flux of the Sun.

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Title: Surface magnetic fields and UV radiance of the quiet Sun
Authors: Pauluhn, A.; Solanki, S. K.
2002ESASP.505..521P Altcode: 2002solm.conf..521P; 2002IAUCo.188..521P
In order to investigate the correspondence between the quiet-Sun UV
radiance and changes in the magnetic network during the solar cycle,
we study the quiet-Sun variability with the two EUV instruments
CDS (Coronal Diagnostic Spectrometer) and SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) and the MDI (Michelson Doppler
Imager) magnetograph on SOHO. Using a monthly data set of co-spatial and
co-temporal observations of quiet-Sun areas near disk centre we follow
the evolution of the quiet Sun over four years from solar minimum to
solar maximum conditions. Although the magnetic flux of the quiet
network increases by a rather low percentage over the solar cycle,
its variation is well correlated with the radiance change in the He
I 584 Å line. We test our data set of quiet-Sun measurements for a
pixelwise relation between magnetic flux density and radiance.

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Title: Hot loop oscillations seen by SUMER: examples and statistics
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
Dammasch, I. E.
2002ESASP.505..199W Altcode: 2002solm.conf..199W; 2002IAUCo.188..199W
We measure physical parameters of Doppler-shift oscillations in
17 flare-like events. These events have been recorded by the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
on SOHO, along a slit fixed above limb active regions. The selected
spectral windows contain emission lines with formation temperatures
from ~104 to 107K. The events were only
detected in hot flare lines, without any signature in lines formed
around 2×106K. Similarly, the Doppler shift oscillations
occur in regions coincident with hot soft X-ray loops, but not with
EUV loops. The oscillations have periods of 11 - 31 min, with an
exponential decay time of 5.5 - 29 min, and show an initial large
shift pulse with peak velocities up to 200 km s-1. Several
indications suggest that the Doppler oscillations are incompressible
coronal loop oscillations, that are usually excited impulsively by
weak flare (or microflare) events that also produced a strong emission
increase at 5 - 8×106K.

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Title: Doppler Shift Oscillations of Hot Solar Coronal Plasma Seen
by SUMER: A Signature of Loop Oscillations?
Authors: Wang, Tongjiang; Solanki, S. K.; Curdt, W.; Innes, D. E.;
Dammasch, I. E.
2002ApJ...574L.101W Altcode:
We report observations of strongly damped Doppler shift oscillations
detected in a flare line, Fe XIX, with the Solar Ultraviolet
Measurement of Emitted Radiation spectrometer. Spectra were recorded
above an active region at the western limb of the Sun, from lines
with formation temperatures ranging from 0.01 to 10 MK. However, the
oscillations were seen only in the hot plasma (&gt;6 MK) lines. The
Doppler oscillations have periods of 14-18 minutes, with an exponential
decay time of 12-19 minutes, and show an initial large blueshift pulse
with peak velocities up to 77 km s-1. Several indications
suggest that the Doppler oscillations are incompressible coronal loop
oscillations that are excited impulsively by a flarelike event that
also produced a strong increase in Fe XIX emission.

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Title: The magnetic structure of sunspots and starspots
Authors: Solanki, S. K.
2002AN....323..165S Altcode:
The single most important quantity determining the properties of
sunspots and presumably starspots is their magnetic field. First
an overview of the magnetic structure of sunspots is given, some
of the progress made in recent years is described and some of the
unsolved questions are pointed out. Both observational and theoretical
aspects are dealt with. Finally, the magnetic structure of starspots
is discussed. After presenting the evidence for (and against) their
magnetic nature the signature of starspots in Zeeman Doppler images
is described. It is pointed out that if the properties of sunspots
are extrapolated to giant spots on rapidly rotating stars then the
observed signature can be at least qualitatively explained.

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Title: Modelling solar irradiance variations: separate models for
the network and active region faculae
Authors: Wenzler, T.; Solanki, S. K.; Fluri, D. M.; Frutiger, C.;
Fligge, M.; Ortiz, A.
2002ESASP.508..231W Altcode: 2002soho...11..231W
In order to determine to what extent solar surface magnetism
affects solar irradiance we need to reconstruct the irradiance from
magnetograms. This process requires the use of model atmospheres. Here
we present two model atmospheres describing faculae in active regions
and the network. The models have been constructed such that they
reproduce various data sets simultaneously.

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Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schühle, U.; Solanki, S. K.; Wilhelm,
K.; Pike, C. D.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber,
M. C. E.
2002ESASP.508..223P Altcode: 2002soho...11..223P
The outcome of the Joint Observing Programme (JOP) Intercal-01, which
is the intercalibration of the SUMER (Solar Ultraviolet Measurements
of Emitted Radiation) instrument (detectors A and B) and the two CDS
(Coronal Diagnostic Spectrometer) instruments, the Normal Incidence
Spectrometer (NIS) and the Grazing Incidence Spectrometer (GIS),
is presented. Recent calibration updates of both instruments have
been employed, and the results indicate a very good correlation and
agreement of the measured radiances within the individual uncertainties.

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Title: Relative brightness variability vs. averaged Doppler shift
in the quiet Sun
Authors: Brković, A.; Peter, H.; Solanki, S. K.
2002ESASP.508..281B Altcode: 2002soho...11..281B
We studied SUMER and CDS time series of spectra and images of quiet-Sun
regions at disc centre. Ultraviolet emission lines sampling temperatures
of the chromosphere, transition region and corona were recorded. We
found a high correlation between average net Doppler shifts and
relative brightness variabilities of the studied lines. We point to
some basic ideas which could eventually model the variability-Doppler
shift relationship.

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Title: How does the magnetic cycle change radiance and irradiance
of the Sun?
Authors: Solanki, Sami K.
2002ESASP.508..173S Altcode: 2002soho...11..173S
The Sun's magnetic field, which is concentrated into flux tubes in the
photosphere, affects the radiance. Depending on the size of a flux
tube it radiates more (for slender tubes) or less (for broad tubes)
strongly than the quiet Sun. The Sum of all magnetic features on the
whole solar disc affects the Sun's irradiance. As the number and the
size distribution of the flux tubes changes over the solar cycle it
produces a variation of total irradiance, which is very similar to the
observed variation. There is also evidence that the Sun's magnetic
field exhibits a secular variation, which is expected to produce a
slow irradiance change, whose amplitude is expected to be larger than
the cyclic variation. In this review some of the relevant processes
taking place in flux tubes are pointed out and models describing the
irradiance variations over the solar cycle based on the Sun's magnetic
field are discussed. Finally, the results of the modelling of the
secular variation of the Sun's magnetic field are presented.

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Title: Total solar magnetic flux: dependence on spatial resolution
of magnetograms
Authors: Krivova, N. A.; Solanki, S. K.; Fligge, M.
2002ESASP.508..155K Altcode: 2002soho...11..155K
The variability of the solar radiative output is tied to the evolution
of the surface magnetic field. Irradiance changes on time-scales of the
solar rotation are governed by the varying distribution of the magnetic
features and the evolution of sunspots and individual active regions,
whereas the total amount of magnetic flux in particular small-scale
magnetic elements seems to dominate the irradiance variations on the
time scale of the solar cycle. Possibly of even greater relevance for
climate on Earth are secular variations of solar irradiance, which
are at least partly caused by changes in the quiet-Sun magnetic flux
on long time scales. Using NSO/Kitt Peak synoptic charts Harvey (1994)
found that the total magnetic flux in active regions at activity maximum
is about 3 times higher than the flux at activity minimum. The size of
small-scale magnetic elements is, however, far below the resolution of
currently obtainable magnetograms. At the same time, their distribution
on the solar surface is highly non-uniform, with magnetic elements of
opposite polarities often being grouped close together. This leads to
an apparent cancellation of the flux within a relatively large pixel
of a Kitt Peak synoptic chart and underestimates the total magnetic
flux, mainly in the quiet Sun. Using MDI full-disc and high-resolution
magnetograms and artificially reducing their spatial resolution by
binning several pixels together we study the influence of the resolution
on the measured total magnetic flux.

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Title: On the intensity contrast of solar photospheric faculae and
network elements
Authors: Ortiz, A.; Solanki, S. K.; Domingo, V.; Fligge, M.;
Sanahuja, B.
2002A&A...388.1036O Altcode: 2002astro.ph..7008O
Sunspots, faculae and the magnetic network contribute to solar
irradiance variations. The contribution due to faculae and the network
is of basic importance, but suffers from considerable uncertainty. We
determine the contrasts of active region faculae and the network,
both as a function of heliocentric angle and magnetogram signal. To
achieve this, we analyze near-simultaneous full disk images of
photospheric continuum intensity and line-of-sight magnetic field
provided by the Michelson Doppler Interferometer (MDI) on board
the SOHO spacecraft. Starting from the surface distribution of
the solar magnetic field we first construct a mask, which is then
used to determine the brightness of magnetic features, and the
relatively field-free part of the photosphere separately. By sorting
the magnetogram signal into different bins we are able to distinguish
between the contrasts of different concentrations of magnetic field. We
find that the center-to-limb variation (CLV) of the contrast changes
strongly with magnetogram signal. Thus, the contrasts of active region
faculae (large magnetogram signal) and the network (small signal)
exhibit a very different CLV, showing that the populations of magnetic
flux tubes that underly the two kinds of features are different. The
results are compatible with, on average, larger flux tubes in faculae
than in the network. This implies that these elements need to be treated
separately when reconstructing variations of the total solar irradiance
with high precision. We have obtained an analytical expression for
the contrast of photospheric magnetic features as a function of both
position on the disk and spatially averaged magnetic field strength,
by performing a 2-dimensional fit to the observations. We also provide
a linear relationship between magnetogram signal and the mu =cos (theta
), where theta is the heliocentric angle, at which the contrast is
maximal. Finally, we show that the maximum contrast per unit magnetic
flux decreases rapidly with increasing magnetogram signal, supporting
earlier evidence that the intrinsic contrast of magnetic flux tubes
in the network is higher.

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Title: Oscillating hot loops observed by SUMER
Authors: Wang, T. J.; Solanki, S. K.; Curdt, W.; Innes, D. E.;
Dammasch, I. E.
2002ESASP.508..465W Altcode: 2002soho...11..465W
We report observations of Doppler shift oscillations in hot flare lines
emitted from active region loops. The Solar Ultraviolet Measurements
of Emitted Radiation (SUMER) spectrometer on SOHO recorded spectra
of limb active regions loops in several emission lines with formation
temperatures from ~104 to 107K. The events were
only detected in the hot flare lines, without any signature in lines
formed around 2×106K. There is a large shift pulse of up
to 190 km s-1 during the rising phase of the flux which
is followed by two or three periods of strongly damped alternating
red and blue shift oscillations with periods in the range 12-31
min. Slow mode standing waves match the observed period. However,
the initial large Doppler shift pulse suggests that the waves are
impulsively generated. Unlike the oscillating loops seen in the TRACE
images, these Doppler shift oscillations are sometimes seen without
an associated flare.

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Title: Variation of the facular and network contrast during the
rising phase of cycle 23
Authors: Ortiz, A.; Domingo, V.; Sanahuja, B.; Solanki, S. K.
2002ESASP.508..185O Altcode: 2002soho...11..185O
Magnetic activity contributes to solar irradiance variations, both on
short and long time-scales. While sunspots and active region faculae
are the dominant contributors to irradiance changes on time-scales of
days to weeks, the origin of the long-term increase of the irradiance
between activity minimum and maximum (~0.1%) is still debated. It
has been proposed that the small-scale magnetic elements composing the
enhanced and quiet network contribute substantially to this increase. To
contribute to this debate, we attempt to see if there is a change in
the radiative properties of these elements along the solar cycle,
and to evaluate such a change. We use near-simultaneous full disk
magnetograms and images of the photospheric continuum intensity provided
by MDI/SOHO. We have studied the center-to-limb variations (CLV) of the
contrast as a function of magnetic strength and we are now analyzing how
the noise level of the images changes throughout time, as a preliminary
step towards an analysis of the temporal irradiance variations.

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Title: Dependence of UV radiance of the quiet Sun on the solar cycle
Authors: Pauluhn, A.; Solanki, S. K.
2002ESASP.508..227P Altcode: 2002soho...11..227P
Recent SOHO measurements of UV radiance of the quiet Sun show
a dependence of the radiance on the solar cycle. We study the
hypothesis that changes in the magnetic network are causing these
variations. The quiet-Sun variability is investigated with the two
EUV instruments CDS and SUMER and the MDI magnetograph on SOHO. We
find that although the magnetic flux of the quiet network increases
by a rather low percentage over the rising part of the solar cycle,
its variation is well correlated with the radiance change in the He I
584 Å line. The main change occurs in the flux of the strong network
elements while the weaker elements do not exhibit a significant change.

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Title: The Sun at solar minimum: North - south asymmetry of the
polar coronal holes
Authors: Zhang, J.; Woch, J.; Solanki, S. K.; von Steiger, R.
2002GeoRL..29.1236Z Altcode: 2002GeoRL..29h..77Z
Data from the Solar Wind Ion Composition Spectrometer (SWICS) on
Ulysses and synoptic charts derived from Kitt Peak magnetograms are
used to compare the south and north polar coronal holes which existed
during the declining/minimum phase of the solar activity cycle from
1992 to 1997. The kinetic properties of the solar wind emanating from
the two polar coronal holes, as represented by solar wind speed, do
not differ significantly. However, the electron temperature in the
two coronal holes inferred from ionic charge composition data, namely
the O7+/O6+ ratio, show consistent differences,
with the south polar hole being 10 to 15% hotter. The ground-based
magnetograms show that the north polar coronal hole covers a larger
part of the solar surface than the southern one. The total magnetic
flux and, specifically, the flux density of the north polar coronal
hole is considerably lower for the whole interval of time between 1992
and 1997. This strongly indicates that the difference in coronal hole
temperature between the southern and northern coronal hole is intrinsic
and is not due to the fact that the Ulysses observations in the south
and north coronal hole streams were made at different phases of the
solar cycle. Thus the differences found represent a real north-south
asymmetry during this time period.

---------------------------------------------------------
Title: Quiet-Sun variability observed with SUMER and CDS
Authors: Brković, A.; Solanki, S. K.; Rüedi, I.
2002A&A...385..257B Altcode:
Brightness variations of solar features are investigated using time
series of images and spectra of quiet-Sun regions at disc centre
obtained with the Coronal Diagnostic Spectrometer (CDS) and the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) instrument onboard
the SOHO spacecraft. Ultraviolet emission lines sampling temperatures
of the chromosphere, transition region and corona were recorded, with
the \hei 584.3 Å and \oxv 629.7 Å lines being recorded simultaneously
by both instruments. A comparison shows that both instruments give
similar results except that SUMER reveals a factor of three higher
absolute and relative variability than CDS. Simple tests suggest
that the higher spatial resolution of SUMER compared to CDS, and the
broad slit used for the CDS observations, are responsible for this
difference. This points to the need for higher spatial resolution for
future variability studies. The SUMER results confirm and extend to
lower temperatures the trends deduced in an earlier paper from CDS data.

---------------------------------------------------------
Title: The molecular Zeeman effect and diagnostics of solar and
stellar magnetic fields. I. Theoretical spectral patterns in the
Zeeman regime
Authors: Berdyugina, S. V.; Solanki, S. K.
2002A&A...385..701B Altcode:
An overview of the theory of the Zeeman effect in diatomic molecules
for the limiting Hund's cases (a) and (b) is given and a numerical
approach for the intermediate coupling case (a-b) is developed. In
contrast to earlier derivations, which were limited to doublets, this
approach is valid for terms of any multiplicity. General properties
of the Zeeman effect for the various cases are deduced. Finally,
calculated Landé factors for prominent molecular bands in sunspot
and cool-star spectra are employed to predict the general behaviour of
these bands in the presence of a magnetic field below the Paschen-Back
limit. The limiting field strength is calculated and listed.

---------------------------------------------------------
Title: Solar irradiance variations and climate
Authors: Solanki, S. K.; Fligge, M.
2002JASTP..64..677S Altcode: 2002JATP...64..677S
The irradiance of the Sun is observed to vary in phase with the solar
cycle at an amplitude of /~0.1% and a period of roughly 11 years. There
is indirect evidence that the irradiance also exhibits a larger secular
variation. Direct measurements only cover the last 21/2 solar cycles
and a longer record is needed to study the possible coupling with
climate. Therefore, it is necessary to develop successful models
of solar irradiance variations and to reconstruct it back into the
past. In the present paper, the current observational knowledge and
the state-of-the-art of the modelling are introduced and reviewed.

---------------------------------------------------------
Title: Models for solar magnetic loops. II. Comparison with SOHO-CDS
observations on the solar disk
Authors: Brković, A.; Landi, E.; Landini, M.; Rüedi, I.; Solanki,
S. K.
2002A&A...383..661B Altcode:
The present work describes a detailed comparison between SOHO-CDS
observations of active region loops with a static, isobaric loop
model developed assuming a temperature-independent heating function
in the energy balance equation and a variable loop cross-section. The
loop model is described in Landini &amp; Landi (2002). Observations
of an active region recorded by CDS have been analyzed. Additional
data from the EIT and MDI instruments on board the SOHO satellite,
and broad band soft X-rays images from the Yohkoh satellite, have
been used to complement the CDS dataset. CDS monochromatic images
from lines at different temperatures have been co-aligned with EIT,
MDI and Yohkoh images and a loop structure has been identified. Two
other loop structures are visible but their footpoints are not clearly
identified, and have not been analyzed. Electron density, temperature
and pressure along the selected loop structure have been measured by
means of line ratio techniques. These quantities have been used to test
the assumption of constant pressure adopted in the theoretical model,
and to compare their values with its predictions. The loop filling
factor has also been estimated from the CDS data after assumptions on
the loop geometry have been made. Comparison with CDS data has shown
that a classical model is not able to reproduce the observations;
despite the large uncertainties, mainly given by the limited CDS
spatial resolution, indications suggest that agreement occurs only if an
“ad hoc” isothermal region is added on top of the loop and a large
conductive flux at the base is assumed. Suggestions for improvements
of theoretical loop models and further studies with the EIS instrument
on Solar-B, due for launch in 2005, are given.

---------------------------------------------------------
Title: Secular variation of the Sun's magnetic flux
Authors: Solanki, S. K.; Schüssler, M.; Fligge, M.
2002A&A...383..706S Altcode:
We present an extension of the model of \citet{Solanki:etal:2000}
that allows us to reconstruct the time evolution of both the total
and the open magnetic flux at the solar surface since 1700. The flux
emerging in large active regions is determined using the sunspot number
as a proxy, while the flux emergence in small ephemeral regions is
described by an extended cycle whose amplitude and length are related
to the corresponding sunspot cycle. Both types of regions contribute
to the open flux, which is the source of the heliospheric field. The
overlap of the activity cycles of ephemeral regions leads to a secular
variation of the total cycle-related magnetic flux (active region
flux + ephemeral region flux + open flux). The model results indicate
that the total surface flux has doubled in the first half of the last
century. The evolution of the open flux is in good agreement with the
reconstruction by \citet{Lockwood:etal:1999}.

---------------------------------------------------------
Title: Solar variability and global warming
Authors: Krivova, N.; Solanki, S.
2002cosp...34E.274K Altcode: 2002cosp.meetE.274K
The magnitude of the Sun's influence on climate has been a subject
of intense debate. Estimates of this magnitude are generally based on
assumptions regarding the forcing due to solar irradiance variations
entering climate modelling. Given the complexity of the climate system,
however, such modelling is perforce based on simplifying assumptions,
which leaves it open to criticism. We take a complementary approach. We
assume that the Sun has been responsible for climate change prior to
1970. Then, using reconstructions and measured records of relevant
solar quantities as well as of the cosmic-ray flux, we estimate which
fraction of the dramatic temperature rise after that date could be
due to the influence of the Sun. We show that at least in the most
recent past (since 1970) the solar influence on climate cannot have
been significant.

---------------------------------------------------------
Title: The solar atmosphere
Authors: Solanki, S. K.; Hammer, R.
2002css1.book.1065S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Irradiance Medels based on Magnetic Activity
Authors: Solanki, S.; Krivova, N.; Unruh, Y.
2002cosp...34E1357S Altcode: 2002cosp.meetE1357S
An introduction is given to the modelling of irradiance variations
based on solar surface magnetism. We describe how a time series of daily
magnetograms and empirical models of the thermal structure of magnetic
features (sunspots, magnetic elements) are combined to reconstruct total
and spectral irradiance on a time scale of weeks to years. Comparisons
with observational data reveal an excellent correspondence. On a
longer time scale of decades to centuries we first need to know how
the Sun's magnetic field evolved. Hence reconstructions of the Sun's
total magnetic flux are briefly introduced, before we present longer
term reconstructions of the total and spectral irradiance since the
Maunder minimum.

---------------------------------------------------------
Title: Physical reconstruction of the long-term heliospheric
modulation of cosmic rays
Authors: Usoskin, I.; Mursula, K.; Solanki, S.; Shuessler, M.;
Kovaltsov, G.
2002cosp...34E.902U Altcode: 2002cosp.meetE.902U
Open solar magnetic flux has been recently reconstructed by Solanki
et al. (2000, 2002) for the last 400 years from sunspot data. Using
this reconstructed magnetic flux as an input to a spherically symmetric
quasi-steady state model of the heliosphere, we calculate the expected
intensity of galactic cosmic rays at the Earth's orbit since 1610. This
calculated cosmic ray intensity is in good agreement with the neutron
monitor measurements during the last 50 years. Moreover, we calculate
the flux of 2 GeV galactic protons and compare it to the cosmogenic
10 B e level in polar ice in Greenland and Antarctica. An excellent
agreement between the calculated and actual levels is found over the
last 400 years.

---------------------------------------------------------
Title: Solar Variability
Authors: Solanki, S. K.
2002ISSIR...2....1S Altcode: 2002rcs..conf....1S; 2002ESASR...2....1S
With increasing sensitivity, wavelength coverage and photometric
accuracy (including reliability in calibrations) it is becoming
ever more clear that the Sun is a variable star at practically all
wavelengths and timescales. A short and incomplete overview is given
of the forms which this variability can take. Some of the underlying
physics is also very briefly touched upon.

---------------------------------------------------------
Title: The Sun At Solar Minimum: North - South Asymmetry of The
Polar Coronal Holes
Authors: Woch, J.; Zhang, J.; Solanki, S. K.; von Steiger, R.
2002EGSGA..27.4007W Altcode:
Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses
and synoptic charts derived from Kitt Peak magnetograms are used to
compare the south and north polar coronal holes which existed during
the declining/minimum phase of the solar activity cycle from 1992 to
1997. The kinetic properties of the solar wind emanating from the two
polar coronal holes, as represented by solar wind speed, do not differ
significantly. However, the electron temperature in the two coronal
holes inferred from ionic charge composition data, namely the O7+/O6+
ratio, show consis- tent differences, with the south polar hole being
10 to 15% hotter. The ground-based magnetograms show that the north
polar coronal hole covers a larger part of the so- lar surface than
the southern one. The total magnetic flux and, specifically, the flux
density of the north polar coronal hole is considerably lower for the
whole interval of time between 1992 and 1997. This strongly indicates
that the difference in coronal hole temperature between the southern
and northern coronal hole is intrinsic and is not due to the fact that
the Ulysses observations in the south and north coronal hole streams
were made at different phases of the solar cycle Thus the differences
found represents a real north-south asymmetry.

---------------------------------------------------------
Title: Interplanetary and solar surface properties of coronal holes
Authors: Woch, J.; Zhang, J.; Solanki, S.; von Steiger, R.
2002cosp...34E.967W Altcode: 2002cosp.meetE.967W
Data from the Solar Wind Ion Composition Spectrometer (SWICS) on
Ulysses and synoptic maps from Kitt Peak are used to analyse coronal
holes throughout the solar activity cycle. The large polar coronal
holes existing during the declining/minimum phase of solar cycle 22
show a persistent north-south asymmetry. The coronal temperature,
inferred from ionic charge-state distributions, and the magnetic flux
density are significantly lower in the north polar coronal hole. The
temperature of the emerging north polar hole of solar cycle 23 is
remarkably similar to that of solar cycle 22, confirming that the
coronal temperatures of the polar coronal holes do not evolve in the
course of the activity cycle. Solar wind streams emanating from the
small-scale coronal holes observed around solar maximum generally show
lower velocities compared to the polar coronal hole streams. However,
the coronal temperatures do not reveal a consistent difference. Though
a large number of solar maximum holes have a significantly higher
temperature compared to the polar coronal holes the majority has a
coronal temperature within the range of polar hole temperatures. Above
all, the latter holds for solar maximum coronal holes having a magnetic
polarity consistent with the polarity of the new solar cycle. Likewise,
the magnetic flux density in the solar maximum holes and in the polar
coronal holes, as derived from the synoptic maps, is not strikingly
different. Therefore, it can be concluded that there is no indication
for an intrinsic difference of solar maximum and polar coronal holes.

---------------------------------------------------------
Title: How much of the solar irradiance variations is caused by the
magnetic field at the solar surface?
Authors: Solanki, S. K.; Fligge, M.
2002AdSpR..29.1933S Altcode:
The contribution to total solar irradiance variations by the magnetic
field at the solar surface is estimated. Detailed models of the
irradiance changes on the basis of magnetograms show that magnetic
features at the solar surface account for over 90% of the irradiance
variations on a solar rotation time scale and at least 70% on a solar
cycle time scale. If the correction to the VIRGO record proposed by
Fröhlich &amp; Finsterle (2001) is accepted, then magnetic features
at the solar surface are responsible for over 90% of the solar cycle
irradiance variations as well.

---------------------------------------------------------
Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schuhle, U.; Solanki, S. K.; Wilhelm,
K.; Thompson, W. T.; Pike, C. D.; Ruedi, I.; Hollandt, J.; Huber,
M. C. E.
2002ISSIR...2..235P Altcode: 2002rcs..conf..235P; 2002ESASR...2..235P
Simultaneous observations of the same solar features with different
instruments provide a way to compare radiometric calibrations and
detect changes in responsivity with time of EUV instruments in space
within the combined uncertainties of the individual instruments. Here
we present the intercalibration of the SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) instrument (detectors A and B) and
the two CDS (Coronal Diagnostic Spectrometer) instruments, the Normal
Incidence Spectrometer (NIS) and the Grazing Incidence Spectrometer
(GIS) on the Solar and Heliospheric Observatory (SOHO). This work
describes the results of the Joint Observing Programme Intercal 01
and presents quiet-Sun comparisons from March 1996 up to February
2001, which represents the complete set of all available Intercal
01 measurements. Recent calibration updates of both instruments are
employed, and the results indicate a very good correlation and agreement
of the measured radiances within the combined uncertainties.

---------------------------------------------------------
Title: Properties of ultraviolet lines observed with the Coronal
Diagnostic Spectrometer (CDS/SOHO) in coronal holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Pike, C. D.; Schühle, U.;
Rüedi, I.; Pauluhn, A.; Brković, A.
2002A&A...381..653S Altcode:
We present an analysis of 14 ultraviolet emission lines belonging to
different atoms and ions observed inside polar coronal holes and in
the normal quiet Sun. The observations were made with the Coronal
Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric
Observatory (SOHO). This study extends previous investigations made
with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer to higher temperatures. We compare line intensities,
shifts and widths in coronal holes with the corresponding values
obtained in the quiet Sun. While all lines formed at temperatures above
7 x 105 K show clearly the presence of the hole in their
intensities, differences in line width are more subtle, with cooler
lines being broader in coronal holes, while hotter lines tend to be
narrower. According to the present data all lines are blueshifted inside
the coronal hole compared to the normal quiet Sun. Almost all the lines
formed between 80 000 K and 600 000 K (i.e. transition-region lines)
show a correlation between blueshifts and brightness within coronal
holes. This is in agreement with the conclusion reached by Hassler et
al. (\cite{Hassler1999}) that the fast solar wind emanates from the
network and supports our previous study (Stucki et al. 2000b). For
coronal lines, this trend seems to be reversed.

---------------------------------------------------------
Title: Reconstruction of Cosmic Ray Intensity Since 1610
Authors: Usoskin, I. G.; Mursula, K.; Solanki, S. K.; Schüssler,
M.; Kovaltsov, G. A.
2002EGSGA..27.5173U Altcode:
Open solar magnetic flux has been recently reconstructed by Solanki
et al. (2000, 2002) for the last 400 years from sunspot data. Using
this reconstructed magnetic flux as an input to a spherically symmetric
quasi-steady state model of the heliosphere, we calculate the expected
intensity of galactic cosmic rays at the Earth's orbit since 1610. This
calculated cosmic ray intensity is in good agreement with the neutron
monitor measurements during the last 50 years. Moreover, we calculate
the flux of 2 GeV galactic protons and compare it to the cosmogenic
10Be level in polar ice in Greenland and Antarctica. An excellent
agreement between the calculated and actual levels is found over the
last 400 years.

---------------------------------------------------------
Title: Physical reconstruction of long-term solar activity
Authors: Usoskin, I.; Solanki, S.; Schuessler, M.; Mursula, K.;
Kovaltsov, G.
2002cosp...34E.901U Altcode: 2002cosp.meetE.901U
For many applications in dynamo theory and solar-terrestrial research
it is important to know the evolution of solar activity on long time
scales (centuries to millennia). Previous reconstructions were based
upon either multi-harmonic backward extrapolation of the known sunspot
records or on the assumption of a linear relation between terrestrial
proxies (e.g., cosmogenic isotope abundance) and solar activity. Here
we present, for the first time, a physical reconstruction of sunspot
activity on long time scales from the cosmogenic 10 Be records. We
use a numerical inversion of a combined physical solar-heliospheric
model (Usoskin et al., 2002), which is essentially non-linear. Using
physical rather than empirical relations on all steps, we present a
reconstruction of sunspot activity since the 15th century. Uncertainties
of the reconstruction are discussed in details. It is important that
the current high level of sunspot activity is unique on the millennium
time scale.

---------------------------------------------------------
Title: Coronal Holes During Solar Maximum: Swics/ulysses and Kitt
Peak Observations
Authors: Zhang, J.; Woch, J.; Solanki, S. K.; von Steiger, R.
2002EGSGA..27.4034Z Altcode:
Synoptic maps of the solar coronal magnetic field from Kitt Peak show
the existence of small-scale coronal holes at low and mid latitudes
during the maximum phase of the present solar cycle. The solar
wind originating from the most prominent holes can be unambiguously
identified in interplanetary space at distances of 2 to 4 AU with
the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses. The
coronal hole plasma is characterized by an enhanced velocity and a
decreased O7+/O6+ ratio com- pared to the ambient solar wind. The
decreased ratio is indicative for a lower coronal temperature in the
source region on the Sun. Though clearly distinguishable from the
ambient solar wind plasma, the solar wind originating from small
scale coronal holes has a lower velocity and less reduced O7+/O6+
ratio than the solar wind emanating from the large-scale polar coronal
holes during solar minimum. This difference is re- flected in synoptic
coronal hole maps and magnetograms. The magnetic flux density of the
small scale coronal holes is considerably lower compared to the flux
density of the polar coronal holes. We suggest that the two types of
coronal holes are intrinsically different.

---------------------------------------------------------
Title: Noise reduction in helioseismic power spectra\ by
non-orthogonal wavelets
Authors: Solanki, S. K.; Régulo, C.; Fligge, M.; Kosovichev, A. G.
2001A&A...379.1039S Altcode:
We present a method to reduce noise in helioseismic power spectra
using a non-orthogonal wavelet transform based on quadratic spline
functions. The quality of our method is tested by applying it to
artificially generated time-series approximating solar p-modes. The
mode frequencies and line widths obtained from least-squares fits to
the smoothed spectra are compared with the corresponding parameters
deduced from maximum likelihood fits to the original spectra. The
results from both approaches are very similar and suggest that there
is no major bias in either of these rather independent approaches. As a
practical example we denoise parts of the power spectrum obtained from
the two first years of operation of the GOLF instrument onboard SOHO.

---------------------------------------------------------
Title: Zeeman-split opposite-polarity OH lines in sunspot spectra:
Resolution of a puzzle
Authors: Berdyugina, S. V.; Solanki, S. K.
2001A&A...380L...5B Altcode:
We present the first synthetic Zeeman-split Stokes I and V profiles
of OH lines. They explain the puzzling observations reported by Harvey
(\cite{har85}) of two pairs of lines from the infrared (2, 0) band with
Stokes V profiles exhibiting opposite polarities. Our new perturbation
calculations of the Zeeman effect in diatomic molecules, which allow
states of any multiplicity to be treated, resolve the puzzle. They
reveal that the unusual behaviour of these lines stems from the fact
that the two pairs have effective Landé factors of similar magnitude,
but of opposite signs.

---------------------------------------------------------
Title: Intercalibration of SUMER and CDS on SOHO. II. SUMER detectors
A and B and CDS NIS
Authors: Pauluhn, Anuschka; Rüedi, Isabelle; Solanki, Sami K.;
Schühle, Udo; Wilhelm, Klaus; Lang, Jim; Thompson, William T.;
Hollandt, Jörg
2001ApOpt..40.6292P Altcode:
Results of an intercalibration between the extreme-ultraviolet
spectrometers Coronal Diagnostic Spectrometer (CDS) and Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) on board the Solar
and Heliospheric Observatory (SOHO) are reported. The results of the
joint observing program Intercal_01 are described, and intercalibration
results up to July 2000 of both SUMER detectors A and B and of the
CDS Normal Incidence Spectrometer (NIS) are presented. The instruments
simultaneously observed radiance of emission lines at the center of the
Sun, and three lines have been chosen for intercomparison: He I 584 Å,
Mg X 609 Å, and Mg X 624 Å. Initially the same area was observed by
both instruments, but, after restrictions were imposed by the scanning
mechanism of SUMER in November 1996, the instruments viewed areas of
different sizes. Nevertheless, the temporal correlation between the
two instruments remained good through June 1998, when contact with
the SOHO spacecraft was lost. Until then the CDS instrument measured
(33+/-5)% and (38+/-7)% (+/-1σ) higher intensity than SUMER in the
Hz I 584-Å line on average for detectors A and B, respectively. Data
from SUMER detector B agreed well for Mg X 609 Å and Mg X 624 Å
with the CDS intensities, showing offsets of (2+/-10)% and (9+/-15)%,
much less than the data of detector A with offsets of (7+/-8)% and
(16+/-7)% for the two lines, respectively, relative to CDS. Finally,
the intercalibration measurements after the loss and recovery of the
SOHO spacecraft are analyzed. The data for observations from November
1998 to July 2000 are compared, and it is shown that, although the
responses of the instruments have changed, the CDS and the SUMER still
perform well, and their temporal correlation is good.

---------------------------------------------------------
Title: High-resolution solar polarimetry with Sunrise
Authors: Schmidt, W.; Solanki, S. K.; Lites, B. W.; Title, A. M.;
Martínez Pillet, V.
2001AN....322..363S Altcode:
Sunrise is a solar telescope with an aperture of 1 m, and is dedicated
for spectropolarimetric measurements in the visible and the near
UV. The total wavelength range is 200 to 1000 nm for narrowband imaging
and diagnostic spectroscopy. Sunrise is planned as a stratospheric
long-duration balloon mission with a first flight in 2006

---------------------------------------------------------
Title: A formation mechanism of magnetic elements in regions of
mixed polarity
Authors: Gadun, A. S.; Solanki, S. K.; Sheminova, V. A.; Ploner,
S. R. O.
2001SoPh..203....1G Altcode:
We present 2-D, fully compressible radiation-MHD simulations of
the solar photospheric and subphotospheric layers that run for
2 hours of solar time starting from a magnetic configuration
with mixed polarities. In the atmospheric layers the simulation
reveals a correlation between field strength and inclination, with a
nearly vertical strong-field magnetic component and a more horizontal
weak-field component, in agreement with the observations. Our simulation
also shows that magnetic flux is converted from one of these states to
the other. In particular, magnetic flux sheets can also be formed when
a new downflow lane starts due to granule fragmentation. The dynamics
of the granulation and field-line reconnection are found to play a
role in the initial stages of a magnetic element's formation. The
simulation predicts that during or shortly after their formation
magnetic elements could be associated with oppositely polarized flux
at a small spatial scale.

---------------------------------------------------------
Title: The sun's variable spectrum and its terrestrial effects
Authors: Fligge, M.; Solanki, S. K.
2001A&AT...20..467F Altcode:
The solar radiation exhibits strong temporal variations not only in
intensity but also in its spectrum which are linked to the evolution of
the Sun through its magnetic activity cycle. The irradiance variability
increases from longer to shorter wavelengths, with variations in the
UV being orders of magnitude larger than those in the visible. While
99% of the total solar radiative output occurs at wavelengths longer
than 300 nm, solar UV radiation accounts for up to 30% of the total
variation. The continuous rise of the Earth's surface temperature over
the last decades urgently raises a question about the physical origin
of so-called global warming. A reliable estimate of the influence
of human activity on the Earth's climate requires detailed knowledge
about the natural sources of variability. One of the unknown boundary
conditions for models of the evolution of the Earth's climate is the
variation of the solar irradiance.

---------------------------------------------------------
Title: The influence of an inclined rotation axis on solar irradiance
variations
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2001A&A...376.1080K Altcode:
Compared with Sun-like stars, the irradiance variations of the
Sun over the solar cycle appear to be relatively small for its
average activity level (Lockwood et al. \cite{Lockwood:etal:1992};
Radick et al. \cite{Radick:etal:1998}). It has been proposed that
the special position of Earth-based observers in the ecliptic plane
may give the impression of a subdued solar photometric variability
(Schatten \cite{Schatten:1993}). The aim of the present paper is to
examine the influence on irradiance variations of a solar rotation
axis inclined towards the observer. A three-component model is
used to calculate relative flux variations of a given active-region
distribution on the surface of the Sun as a function of inclination
and wavelength. Wavelength-dependent intensity spectra are used to
describe the contributions of the undisturbed photosphere, sunspots and
faculae. The spectra result from models that have successfully been
used to reproduce a host of solar data and thus represent realistic
estimates of the radiative output from these solar features. We find
that an inclined rotation axis increases the total solar irradiance
variations maximally by 40%. The most probable value is approximately
6%. This is much less than that suggested by former studies, which
were based on simple contrast functions. In the averaged Strömgren
filters we estimate a most probable increase of the solar variability
of 30%. In addition, we estimate the dependence of the flux in the
chromospheric Ca II H&amp;K lines on inclination. We find that the
average chromospheric activity level depends only slightly on the
inclination angle. The chromospheric variability of Sun-like stars,
however, is significantly affected. Nonetheless, our results indicate
that a different average inclination of stellar rotation axes relative
to the observer cannot explain the discrepancy between the brightness
variations of the Sun and Sun-like stars.

---------------------------------------------------------
Title: Variations of solar spectral irradiance from near UV to the
infrared-measurements and results
Authors: Fligge, M.; Solanki, S. K.; Pap, J. M.; Fröhlich, C.;
Wehrli, C.
2001JASTP..63.1479F Altcode: 2001JATP...63.1479F
Solar spectral irradiance variations are known to exhibit a strong
wavelength dependence with the amount of variability increasing towards
shorter wavelengths. The bulk of solar radiation is emitted at visible
and infrared wavelengths. Thus, the spectral radiation length of 300nm
accounts for 99% of the total solar radiative output. Deposited in the
Earth's troposphere and biosphere, this part of the solar irradiance
spectrum determines direct solar radiative forcing and is therefore
of particular interest for climate studies. First, measurements of
solar irradiance and irradiance variability from near UV to the IR are
reviewed with particular emphasis on the results obtained from the
Variability of Irradiance and Gravity Oscillations (VIRGO) on SOHO
and Solar Spectrum Measurement (SOLSPEC) instruments. In the second
part a model is presented which describes solar spectral irradiance
variations in terms of the changing distribution of solar surface
magnetic features.

---------------------------------------------------------
Title: The lower polar atmosphere and the solar dynamo: perspectives
for the Solar Orbiter
Authors: Solanki, Sami K.
2001ESASP.493...35S Altcode: 2001sefs.work...35S
The Solar Orbiter will, by flying out of the ecliptic, allow its battery
of remote-sensing instruments to focus on the Sun's polar regions,
providing solar physicists with a unique opportunity to study this
enigmatic part of the Sun for the first time. Some of the scientific
questions which may be addressed by the Solar Orbiter in its out of
the ecliptic phase are presented here, with emphasis being placed on
those related to the lower solar atmosphere and the solar interior.

---------------------------------------------------------
Title: Analysis of blinkers and EUV brightenings in the quiet Sun
observed with CDS
Authors: Brković, A.; Solanki, S. K.; Rüedi, I.
2001A&A...373.1056B Altcode:
Movies of quiet Sun regions at disc centre obtained with the
Coronal Diagnostic Spectrometer (CDS) onboard the SOHO spacecraft
are used to study the properties of transient brightenings seen in
the extreme ultraviolet (EUV), so-called blinkers, at three different
temperatures sampled simultaneously in the chromospheric He I 584.3
Å (2 x 104 K), the transition region O V 629.7 Å (2.5
x 105 K) and coronal Mg IX 368.1 Å (106 K)
lines. Blinkers, here defined somewhat differently than in previous
studies, were clearly detected in the O V and He I lines. Brightenings
of the Mg IX line were also seen. A thorough analysis of blinker
properties is carried out and their detailed properties are
determined. Blinkers are found to be present in both bright (network)
and dark (intranetwork) regions, but their number density is larger
in the brighter areas (in O V) although the rest of their properties
appear to be unaffected. The average sizes of brightenings range
from 2.8 Mm2 in Mg IX, 12.4 Mm2 in He I to 23.5
Mm2 in O V. The durations of blinkers are in the range 3-110
min, with the average durations being 23 min in He I, about 16 min in
O V and 12 min in Mg IX. The frequency distributions of ratio of peak
to background intensity, excess energy and size follow power laws with
exponents &lt;-5 for the intensity ratio, and between -1 and -3 for
the other two parameters. The correlation coefficients between pairs of
ratio, energy and size are at least 0.5, while other pairs of parameters
describing the blinkers appear to be uncorrelated. The best correlation
is between size and energy. The blinker durations exhibit a distribution
whose form is compatible with a log-normal function. Finally, blinkers
in the 3 lines (i.e. 3 temperature regimes) are poorly correlated; with
the correlation coefficient being always less than 0.4. This suggests
that to a large extent the transition region reacts independently of the
corona and chromosphere to energy deposition, so that these parts of the
atmosphere are at least partly decoupled from each other. This agrees
with the expectations from models having separate transition-region
loops, but contradicts the classical picture of the transition region,
as being heated dominantly by energy conduction from the corona.

---------------------------------------------------------
Title: Small-Scale Magnetic Elements in 2-D Nonstationary
Magnetogranulation
Authors: Gadun, A. S.; Solanki, S. K.
2001ASSL..259..295G Altcode: 2001dysu.conf..295G
2-D simulations of magnetogranulation provide evidence of a close
connection between the magnetic field and nonstationary thermal
convection. Fragmentation of large granules can lead to the formation
of compact nearly vertical magnetic tubes from a weaker horizontal
field. Conversely, the dissolution of granules can lead to a merging
of magnetic elements and either to field cancellation (leading to the
transformation of strong vertical field to its weaker horizontal state)
or to the formation of broader and stronger magnetic structures.

---------------------------------------------------------
Title: Diagnostics from Spectral Irradiance Measurements
Authors: Unruh, Y. C.; Solanki, S. K.
2001AGUSM..SP32B01U Altcode:
Solar irradiance varies in tune with solar activity. The irradiance
changes show a strong wavelength dependence, being an order of magnitude
larger in the UV than in the visible. The spectral dependence of the
irradiance variations can be used to differentiate between mechanisms
that may be responsible for the irradiance changes. I review some of
the mechanisms that have been invoked in the past to explain the solar
irradiance variations and compare their predicted spectral irradiance
changes with solar irradiance measurements. The comparisons imply
that surface magnetic features alone are sufficient to explain solar
irradiance data.

---------------------------------------------------------
Title: Comparison of quiet-Sun radiances measured by CDS and SUMER
on SOHO
Authors: Pauluhn, A.; Solanki, S. K.; Schühle, U.; Wilhelm, K.;
Lang, J.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber, M. C. E.
2001SSRv...97...63P Altcode:
Since the beginning of the SOHO (Solar and Heliospheric Observatory)
mission an intercalibration programme was carried out which included
simultaneous observations of the EUV instruments CDS (Coronal Diagnostic
Spectrometer) and SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) of common targets on the quiet Sun. The observations in the
chromospheric line of He i (584 Å) and the two coronal lines of Mg x
(609 Å and 624 Å) thus cover the long period of 4 years and provide a
data set highly suitable not only for instrumental comparison but also
for studies of the quiet Sun's long term variability. Up to the SOHO
accident, both instruments show a very good temporal correlation and
stability. Even after the loss and recovery of the spacecraft, when
the instruments had been exposed to extreme temperature conditions,
the performance of the CDS and SUMER instruments is still good, as is
the temporal correlation. However, the ratio between the efficiencies
of the two instruments, which remained constant with time until the
SOHO accident seems to have changed afterwards. In the coronal lines
both instruments show an increase of average radiances towards the
solar maximum.

---------------------------------------------------------
Title: Empirical models of solar magnetic flux-tubes and their
non-magnetic surroundings
Authors: Frutiger, C.; Solanki, S. K.
2001A&A...369..646F Altcode:
A powerful method for the analysis of the structure of small
scale magnetic elements in the solar photosphere is the
inversion of Stokes spectra. In previous papers based on such
inversions \cite{BellotRubio:etal:1997, BellotRubio:etal:1999}
and \cite{Frutiger:etal:1999} have argued in favor of models with
rather different dynamic properties. In this paper we return to
this debate and compare results returned by inversions based on
new multi-component models applied to several Fe i, Fe ii and C i
spectral line profiles obtained in active region plage with a Fourier
Transform Spectrometer. These inversions differ from earlier ones by
the fact that mass conservation is strictly imposed both inside the
magnetic elements and on the surrounding external flow field. These
flux-tube models are not only able to reproduce the characteristic
Stokes V asymmetries and line-shifts observed in active regions
plages or network elements, but also the Stokes I line profiles,
including line bisectors. It is confirmed that from the quality of the
fits alone it is not possible to distinguish between the steady flow
proposed by \cite{BellotRubio:etal:1997} and the oscillatory model of
\cite{Frutiger:Solanki:1998}. If, however, physical constraints are
imposed (e.g. mass conservation or that the flow retains the same
direction over height in the flux tube) then the oscillatory model
is found to be superior. In addition, the current investigation also
provides the first inversion-based model of abnormal granulation.

---------------------------------------------------------
Title: Large Doppler Shifts in X-Ray Plasma: An Explosive Start to
Coronal Mass Ejection
Authors: Innes, D. E.; Curdt, W.; Schwenn, R.; Solanki, S.; Stenborg,
G.; McKenzie, D. E.
2001ApJ...549L.249I Altcode:
We report observations, taken with the Solar Ultraviolet Measurements
of Emitted Radiation spectrometer, of spatially resolved high red and
blue Doppler shifts (up to 650 km s-1) from X-ray-emitting
plasma in the corona above a flare. The high Doppler shifts are seen
minutes after a fast, faint optical front is seen racing through the
same part of the corona in images taken with the Mirror Coronagraph
for Argentina. The association of the large-scale fast optical emission
front with soft X-ray emission and high Doppler shifts suggests plasma
heating and acceleration in the wake of a shock.

---------------------------------------------------------
Title: Division II: Sun and Heliosphere
Authors: Benz, Arnold O.; Bogdan, T.; Foukal, P. V.; Melrose, D. B.;
Solanki, S.; Vandas, M.; Webb, D. F.
2001IAUTB..24..110B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Formation of One-Lobed Stokes V Profiles in an
Inhomogeneous Atmosphere
Authors: Ploner, S. R. O.; Schussler, M.; Solanki, S. K.; Sheminova,
V. A.; Gadun, A. S.; Frutiger, C.
2001ASPC..236..371P Altcode: 2001aspt.conf..371P
We assess the diagnostic potential of the observed pathological Stokes V
profiles that differ strongly from the customary, nearly antisymmetric
two-lobed shape. In particular, we consider the formation of one-lobed
Stokes V profiles using the results of an MHD simulation. We find
that the majority of one-lobed profiles is produced in regions of
weak horizontal field with significant cancellation caused by mixed
polarity along the line of sight. A minority of one-lobed profiles
originates close to strong magnetic field concentrations with strong
gradients of velocity and magnetic field strength.

---------------------------------------------------------
Title: Stellar Irradiance Variations Caused by Magnetic Activity:
The Influence of an Inclined Rotation Axis
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2001ASPC..248..227K Altcode: 2001mfah.conf..227K
No abstract at ADS

---------------------------------------------------------
Title: A Model for the Decline of Coronal X-ray Emission of Cool
Giant Stars
Authors: Holzwarth, V.; Schüssler, M.; Solanki, S. K.
2001ASPC..248..259H Altcode: 2001mfah.conf..259H
No abstract at ADS

---------------------------------------------------------
Title: Are the Sun's Brightness Variations Really Tamer than Those of
Other Comparable Solar-type Stars? (CD-ROM Directory: contribs/unruh1)
Authors: Unruh, Y. C.; Knaack, R.; Fligge, M.; Solanki, S. K.
2001ASPC..223..748U Altcode: 2001csss...11..748U
No abstract at ADS

---------------------------------------------------------
Title: Consistent Empirical Models of Solar Magnetic Flux Tubes and
the Surrounding Convection (CD-ROM Directory: contribs/frutige2)
Authors: Frutiger, C.; Solanki, S. K.
2001ASPC..223..632F Altcode: 2001csss...11..632F
No abstract at ADS

---------------------------------------------------------
Title: The Quiet-Sun Variability as seen by CDS and by SUMER
Authors: Brkovic, A.; Solanki, S. K.; Rüedi, I.
2001IAUS..203..381B Altcode:
Blinkers are transient brightenings seen in the extreme
ultraviolet. These brightenings are candidates for microflare
activity. Here we determine their properties, using co-aligned
observations with SUMER and CDS, in the latter case with an open
slit. We use CDS to find evidence for blinkers in the quiet Sun, and
SUMER to measure the velocities, and line width changes associated
with them.

---------------------------------------------------------
Title: Magnetic Splitting of Molecular Lines in Sunspot
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.
2001IAUS..203..254B Altcode:
A study of molecular lines in sunspots is of particular interest
because of their high temperature and pressure sensitivity. Many of
them are also magnetically sensitive, but this was not yet widely
investigated. With high-resolution, high signal-to-noise Fourier
spectroscopy in four Stokes parameters now available, the use of
molecular lines for studying the structure of sunspots brings real
gains. One is the extension of spot models, including magnetic field,
up to layers, where atomic lines suffer from NLTE effects but molecules
can still be treated in the LTE approximation. Equally important is the
fact that since molecular lines are extremely temperature sensitive
they can be used to probe the thermal and magnetic structure of the
coolest parts of sunspots. We present calculations of splitting and
the Stokes parameters for a number of molecular lines in the visible
and near-infrared regions. Our first selections are the green system of
MgH A2Π-X2σ and the TiO triplet α, γ' and γ
systems as the most studied band systems in the sunspot spectrum. The
calculations involve different regimes of the molecular Zeeman effect,
up to the complete Paschen-Back effect for individual lines. We look
for molecular lines which can be used along with atomic lines to derive
magnetic, thermal and dynamic properties of the umbra.

---------------------------------------------------------
Title: An Example of Reconnection and Magnetic Flux Recycling near
the Solar Surface
Authors: Ploner, S. R. O.; Schüssler, M.; Solanki, S. K.; Gadun, A. S.
2001ASPC..236..363P Altcode: 2001aspt.conf..363P
No abstract at ADS

---------------------------------------------------------
Title: Statistical Features of the Quiet Sun in EUV
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
Schühle, U.
2001IAUS..203..416P Altcode:
The frequency distribution of the extreme ultraviolet (EUV) intensities
in the quiet Sun has in the past usually been modelled using two
Gaussians. Here we test this and other distribution functions against
observed distributions with exceptional statistics. The data were
obtained in a number of spectral lines observed with two extreme
ultraviolet spectrometers, CDS (Coronal Diagnostic Spectrometer)
and SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on
board the Solar and Heliospheric Observatory (SOHO). We show that the
frequency distribution of the radiance is best modelled by a lognormal
distribution or by a sum of a lognormal and a Gaussian. The fact that
the radiance distribution of the quiet Sun including the network and
the intranetwork is better reproduced by a single lognormal distribution
function than by two Gaussians suggests that the same heating processes
are acting in both types of features. The shape of the distribution
function shows a clear temperature dependence.

---------------------------------------------------------
Title: Small-scale Photospheric Structure of the Solar Magnetic
Fields outside Sunspots
Authors: Solanki, S. K.
2001ASPC..248...45S Altcode: 2001mfah.conf...45S
No abstract at ADS

---------------------------------------------------------
Title: The Molecular Zeeman Effect and Solar Magnetic Fields
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingston,
W.
2001ASPC..236..551B Altcode: 2001aspt.conf..551B
No abstract at ADS

---------------------------------------------------------
Title: Solar and Stellar Magnetic Fields: the Molecular Zeeman Effect
as a Probe
Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C.
2001ASPC..248...99B Altcode: 2001mfah.conf...99B
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Fields in Cool Stars (CD-ROM Directory:
contribs/moreno)
Authors: Moreno Insertis, F.; Saar, S. H.; Solanki, S. K.
2001ASPC..223..435M Altcode: 2001csss...11..435M
No abstract at ADS

---------------------------------------------------------
Title: Empirical Models of Stellar Convection (CD-ROM Directory:
contribs/frutige1)
Authors: Frutiger, C.; Solanki, S. K.
2001ASPC..223..626F Altcode: 2001csss...11..626F
No abstract at ADS

---------------------------------------------------------
Title: Buried Flux Tubes in the Coronal Graveyard (CD-ROM Directory:
contribs/schussle)
Authors: Schüssler, M.; Holzwarth, V.; Solanki, S. K.; Charbonnel, C.
2001ASPC..223.1114S Altcode: 2001csss...11.1114S
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Fields Across the Hertzsprung-Russell Diagram
Authors: Mathys, G.; Solanki, S. K.; Wickramasinghe, D. T.
2001ASPC..248.....M Altcode: 2001mfah.conf.....M
No abstract at ADS

---------------------------------------------------------
Title: Variations of the Solar Spectral Irradiance
Authors: Solanki, S. K.; Fligge, M.; Unruh, Y. C.
2001IAUS..203...66S Altcode:
Not just the total solar irradiance is known to vary, but also the
solar spectrum. Observations and models of solar spectral irradiance
variations are presented.

---------------------------------------------------------
Title: Radiance of Solar Spectral Lines observed with CDS and SUMER
on SOHO (CD-ROM Directory: contribs/pauluhn)
Authors: Pauluhn, A.; Schühle, U.; Solanki, S. K.; Rüedi, I.; Lang,
J.; Pike, C. D.; Thompson, W. T.; Huber, M. C. E.
2001ASPC..223..721P Altcode: 2001csss...11..721P
No abstract at ADS

---------------------------------------------------------
Title: Noise Reduction in GOLF Spectra Using Wavelets (CD-ROM
Directory: contribs/regulo)
Authors: Régulo, C.; Roca Cortés, T.; Solanki, S. K.; Fligge, M.;
GOLF Team
2001ASPC..223..734R Altcode: 2001csss...11..734R
No abstract at ADS

---------------------------------------------------------
Title: High-resolution Solar Polarimetry with Sunrise
Authors: Schmidt, W.; Solanki, S. K.; Schüssler, M.; Curdt, W.;
Lites, B. W.; Title, A. M.; Martinez Pillet, V.
2001AGM....18S1001S Altcode:
Sunrise is a 1m balloon-borne solar telescope. It is equipped with
a spectrograph polarimeter which combines vector-polarimetry in the
visible with diagnostic spectroscopy in the visible and the UV, down
to 200 nm. The instrumentation includes a filter-magnetograph and a
medium-band filtergraph. The wavelength bands of the latter include
the CH-band (430.6 nm) and a UV continuum at 205 nm. Diffraction
limited resolution in the UV will be achieved by employing a phase
diversity technique. The main telescope is based on a lightweight
silicon-carbide mirror, developed within the Solar Lite program. During
the long-duration flight at Antarctica, foreseen for late 2005, Sunrise
will continuously observe the sun for a period of about ten days,
with constant image quality across the full field of view. In-flight
alignment of the telescope optics will be controlled by a wavefront
sensor. The main goal of Sunrise is to understand the structure and
dynamics of the magnetic field in the atmosphere of the sun. To this
end, Sunrise will observe small magnetic flux concentrations with
dimensions of less than 70 km with high polarimetric accuracy. At the
same time, Sunrise will provide diffraction-limited filtergrams of
the photosphere and chromosphere with a resolution down to 35 km at
a wavelength of 200 nm.

---------------------------------------------------------
Title: Successful spectral synthesis of Zeeman-split molecular bands
in sunspot spectra
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingstone,
W.
2000A&A...364L.101B Altcode:
We present the first spectral synthesis of Zeeman-split Stokes profiles
of the MgH A2Pi -X2BLAigma green system and
TiO gamma -system. The calculations involve different regimes of the
molecular Zeeman effect, up to the complete Paschen-Back effect for
individual lines. The synthetic spectra are compared with observations
of Stokes I and V in sunspot umbrae. We find that although the Stokes
I spectra are reasonably reproduced, some lines are obviously still
missing from the employed line lists. The Stokes V spectra turn
out to be much cleaner since the missing lines do not appear to
be Zeeman-split. We thus provide the first good fit to Zeeman-split
molecular lines, including profiles with unconventional Stokes V shapes,
determined by the Paschen-Back effect. Based on observations from
the Canada-France-Hawaii Telescope operated by the National Research
Council of Canada, the Centre National de la Recherche Scientifique
de France and the University of Hawaii

---------------------------------------------------------
Title: Comparison of far-ultraviolet emission lines formed in coronal
holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Schühle, U.; Rüedi, I.; Wilhelm,
K.; Stenflo, J. O.; Brković, A.; Huber, M. C. E.
2000A&A...363.1145S Altcode:
We present an analysis of 26 far-ultraviolet emission lines belonging
to 19 atoms and ions observed on both sides of the boundary of polar
coronal holes as well as other quiet Sun areas along the limb. The
observations were made with the SUMER instrument (Solar Ultraviolet
Measurements of Emitted Radiation) onboard the Solar and Heliospheric
Observatory (SOHO). We compare line intensities, shifts and widths
in coronal holes with the corresponding values obtained in the quiet
Sun. We find that with increasing formation temperature, spectral
lines show on average an increasingly stronger blueshift in coronal
holes relative to the quiet Sun at equal heliospheric angle, with the
coolest lines in our sample (formation temperature ~ 104
K) indicating a small relative redshift. With respect to the rest
wavelength, however, only lines formed above 5 * 105 K
show blueshifts in coronal holes, which is not very different from
the quiet Sun. The width of the lines is generally larger (by a few
kilometers per second) inside the coronal hole. Intensity measurements
clearly show the presence of the coronal hole in Ne VIII lines as well
as in Fe XII, and provide evidence for a slightly enhanced emission
in polar coronal holes for lines formed below 105 K. This
last result is, however, less certain than the rest due to relatively
poor statistics. Intensity histograms also exhibit distinct differences
between coronal hole and quiet-Sun data. For cooler chromospheric lines,
such as Ni II, the coronal holes display a greater spread in intensities
than the quiet Sun. Transition-region lines, e.g. O IV, do not reveal
such differences, while Ne VIII shows characteristics of a coronal line
with lower average intensity and lower intensity spread inside holes.

---------------------------------------------------------
Title: Sunspot Magnetic Fields
Authors: Solanki, S.
2000eaa..bookE2298S Altcode:
The magnetic field is the central quantity determining the property of
a SUNSPOT. It permeates every part of sunspots and by greatly reducing
the convective transport of heat from below is also responsible for
sunspot darkness. Conversely, sunspots were the first astronomical
objects recognized (by G E Hale in 1908) to harbor a magnetic field....

---------------------------------------------------------
Title: Evolution of the Sun's large-scale magnetic field since the
Maunder minimum
Authors: Solanki, S. K.; Schüssler, M.; Fligge, M.
2000Natur.408..445S Altcode:
The most striking feature of the Sun's magnetic field is its cyclic
behaviour. The number of sunspots, which are dark regions of strong
magnetic field on the Sun's surface, varies with a period of about
11 years. Superposed on this cycle are secular changes that occur on
timescales of centuries and events like the Maunder minimum in the
second half of the seventeenth century, when there were very few
sunspots. A part of the Sun's magnetic field reaches out from the
surface into interplanetary space, and it was recently discovered
that the average strength of this interplanetary field has doubled
in the past 100 years. There has hitherto been no clear explanation
for this doubling. Here we present a model describing the long-term
evolution of the Sun's large-scale magnetic field, which reproduces
the doubling of the interplanetary field. The model indicates that
there is a direct connection between the length of the sunspot cycle
and the secular variations.

---------------------------------------------------------
Title: Modelling solar irradiance variations: Comparison with
observations, including line-ratio variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
2000SSRv...94..145U Altcode:
Solar irradiance variations show a strong temporal and spectral
dependence. The progression of the Sun through its activity cycle as
well as solar rotation are mirrored in the irradiance variations. The
spectral dependence is such that the variations are several magnitudes
larger in the EUV than in the visible or infrared. We present a simple
3-component model that is based on the assumption that changes in
the solar flux are exclusively due to changes in spot and facular
coverage. We compare our model to observations of the spectral solar
irradiance variations. Despite its simplicity, we find that the
agreement between our model and the observations is surprisingly
good. We also explore the reliability and the limitations of our
approach by comparing observations of the solar facular contrast and
of the changes in spectral line depths with our calculations.

---------------------------------------------------------
Title: Modelling Short-Term Spectral Irradiance Variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2000SSRv...94..139F Altcode:
On time-scales of the solar rotation most of the solar irradiance
variations are caused by the changing distribution of solar surface
magnetic features. We model these short-term irradiance variations
using calculations of sunspot and facular contrasts as a function of
wavelength and limb angle on the Sun. The position of active regions on
the solar disc is derived from the MDI magnetograms. The reconstructed
irradiance variations are compared with total and spectral irradiance
measurements obtained by the VIRGO experiment on SOHO.

---------------------------------------------------------
Title: Sunspot Models
Authors: Solanki, S.
2000eaa..bookE2300S Altcode:
Models of SUNSPOTS aim either to reproduce observed properties
of sunspots, or to understand the physical processes occurring in
them. Sunspot models are of very diverse types, ranging from empirically
derived models of their thermal stratification to MHD models of their
magnetic configuration and evolution. The final aim of all modelling
is to obtain a consistent and detailed description and und...

---------------------------------------------------------
Title: Reconstruction of Past Solar Irradiance
Authors: Solanki, S. K.; Fligge, M.
2000SSRv...94..127S Altcode:
Accurate measurements of solar irradiance started in 1978, but a much
longer time series is needed in order to uncover a possible influence
on the Earth's climate. In order to reconstruct the irradiance prior to
1978 we require both an understanding of the underlying causes of solar
irradiance variability as well as data describing the state of the Sun
(in particular its magnetic field) at the relevant epochs. Evidence
is accumulating that on the time-scale of the solar cycle or less,
variations in solar irradiance are produced mainly by changes in the
amount and distribution of magnetic flux on the solar surface. The main
solar features contributing to a darkening of the Sun are sunspots,
while active-region faculae and the network lead to a brightening. There
is also increasing evidence for secular changes of the solar magnetic
field and the associated of solar brightness variability. In part
the behavior of sun-like stars is used as a guide of such secular
changes. Under the assumption that solar irradiance variations are due
to solar surface magnetism on all relevant time scales it is possible to
reconstruct the irradiance with some reliability from today to around
1874, and with lower accuracy back to the Maunder minimum. One major
problem is the decreasing amount and accuracy of the relevant data with
age. In this review the various reconstructions of past solar irradiance
are presented and the assumptions underlying them are scrutinized.

---------------------------------------------------------
Title: Solar Photospheric Magnetic Flux Tubes: Observations
Authors: Solanki, S.
2000eaa..bookE2013S Altcode:
The magnetic field on the solar surface (SOLAR MAGNETIC FIELD)
is highly filamentary, with a considerable fraction being in the
form of flux tubes (roughly speaking bundles of concentrated field
lines). Small-scale flux tubes have diameters below approximately 400
km. They appear bright and are the basic magnetic features underlying
the magnetic network and active region plages (SOLAR CHROMOSPHER...

---------------------------------------------------------
Title: Statistics of quiet Sun extreme ultraviolet intensities
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
Schühle, U.
2000A&A...362..737P Altcode:
The frequency distribution of the extreme ultraviolet (EUV) emission
line intensities in the quiet Sun has in the past often been modelled
using two Gaussians. This gives adequate fits to observed distributions
of average statistical significance. In this paper we test this
and other distribution functions against observed distributions with
exceptional statistical significance. The data were obtained in a number
of spectral lines observed with two extreme ultraviolet spectrometers
on board the Solar and Heliospheric Observatory (SOHO). In this way,
the influence of spatial resolution and other instrument-specific
parameters can be identified. The observations span a period of
more than two years and provide a very large data set of radiance
measurements of the quiet Sun at or near solar disk centre. We show
that the frequency distribution of the radiance is best modelled by
a lognormal distribution. The fact that the radiance distribution of
the quiet Sun including the network and the intranetwork is better
reproduced by a single lognormal distribution function than by two
Gaussians suggests that the same heating processes are acting in both
types of features. The parameters of the lognormal fit show a clear
temperature dependence, with the transition region lines exhibiting the
largest skewness of the distribution and the chromospheric intensity
distributions being the most symmetric.

---------------------------------------------------------
Title: On the relationship between shift and intensity of ultraviolet
lines in coronal holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Schühle, U.; Rüedi, I.
2000A&A...362L..49S Altcode:
We study the relationship between wavelength shifts and intensities
of chromospheric, transition-region and coronal ultraviolet emission
lines in polar coronal holes and in the normal quiet Sun using SUMER
data. Within coronal holes almost all the lines showing the network
and formed above 30 000 K show a correlation between blueshifts
and brightness. This extends and supports the conclusion reached
by Hassler et al. (1999) that the fast solar wind emanates from the
network. In the normal quiet Sun, however, we find that only lines
formed above 2-3 * 105 K show such a trend, the cooler
lines being more redshifted in the network. This suggests that either
there is a fundamental difference in the initial acceleration of
the solar wind in coronal holes and the normal quiet Sun, or that
the wavelength-shift versus brightness relationship in the quiet Sun
stems from other processes or structures (loops) than in coronal holes
(open field lines).

---------------------------------------------------------
Title: Size-dependent properties of simulated 2-D solar granulation
Authors: Gadun, A. S.; Hanslmeier, A.; Pikalov, K. N.; Ploner,
S. R. O.; Puschmann, K. G.; Solanki, S. K.
2000A&AS..146..267G Altcode:
Two time-dependent sets of two-dimensional hydrodynamic models of solar
granulation have been analyzed to obtain dependence of simulated thermal
convection on the horizontal size of the convection cells. The two
sets of models treat thermal convection either as fully non-stationary,
multiscale convection (granular convection is a surface phenomenon) or
as quasi-steady-state convection cells (they treat granular convection
as a collection of deep-formed cells). The following results were
obtained: 1) quasi-steady convection cells can be divided into 3
groups according to their properties and evolution, namely small-scale
(up to L ~ 900 km), intermediate-scale (1000-1500 km) and large-scale
(larger 1500 km) convection cells. For the first group thermal damping
due to radiative exchange of energy, mostly in the horizontal direction,
is very important. Large-scale cells build up a pressure excess, which
can lead to their total fragmentation. Similar processes also acts on
the fully non-stationary convection. 2) The largest horizontal size
of convection cells for which steady-state solutions can be obtained
is about 1500 km. This corresponds to granules, i.e. the bright
parts of the convection cells, with a diameter of about 1000 km. 3)
In addition to the zone of high convective instability associated
with the partial ionization of hydrogen, we identify another layer
harboring important dynamic processes in steady-state models. Just
below the hydrogen-ionization layer pressure fluctuations and the
acoustic flux are reduced. Steady-state models with reflecting lateral
boundaries even exhibit an inversion of pressure fluctuations there. 4)
From observational point of view the surface convection differs from
steady-state deep treatment of thermal convection in the dependence
of vertical granular velocities on their sizes for small-scale
inhomogeneous. However, they cannot be distinguished by the dependence
of temperature or emergent intensity of brightness structures. 5) Both
kinds of models demonstrate the inversion of density in subphotospheric
layers. It is more pronounced in small-scale cells and inside hot
upflows. 6) The brightness of simulated granules linearly increases
with their size for small granules and is approximately constant or
even decreases slightly for larger granules. For intergranular lanes
the simulations predict a decrease of their brightness with increasing
size. It falls very rapidly for narrow lanes and remains unchanged
for broader lanes. 7) A quantitative comparison of the brightness
properties of simulated granulation with real observations shows
that the strong size-dependence of the properties of the smallest
simulated granules is not accessible to current observations due to
their limited spatial resolution. The observed size dependences result
rather from spatial smoothing and the granule-finding algorithm. We
do not exclude, however, an influence of the limitations of the 2-D
treatment of thermal convection on the present results.

---------------------------------------------------------
Title: The solar spectral irradiance since 1700
Authors: Fligge, M.; Solanki, S. K.
2000GeoRL..27.2157F Altcode:
The change in the irradiance spectrum of the Sun from 1700 to the
last solar minimum is determined and compared to the change in the
spectrum between activity minimum and maximum. For this purpose we have
used detailed model flux spectra of solar magnetic features. Also,
time-series of the solar spectral irradiance since 1700 in different
wavelength bands are reconstructed. We expect that these reconstructions
are more accurate than previously published ones, although they suffer
(like all reconstructions of solar irradiance on such time-scales)
from uncertainties in our knowledge of the evolution of the solar
network with time.

---------------------------------------------------------
Title: Spin and orbital angular momentum exchange in binary star
systems. II. Ascending the giant branch: a new path to FK Comae stars
Authors: Keppens, R.; Solanki, S. K.; Charbonnel, C.
2000A&A...359..552K Altcode:
Using the model by Keppens (1997), we investigate the angular momentum
(AM) evolution in asymmetric binary star systems from Zero-Age Main
Sequence times until at least one component has ascended the giant
branch. We concentrate on stars ranging in mass from 0.9 Msun
- 1.7 Msun, in almost synchronous, short period systems
(P_orb&lt;9 days). We address synchronization and circularization
by tidal interaction, allowing for structural evolution and
stellar winds. A Weber-Davis prescription is used to quantify the
wind influence, thereby accounting for changes in its acceleration
mechanism from the interplay of the evolving thermal-magneto-centrifugal
effects. We identify a scenario for fast in-spiraling components with d
ln P_orb/dt =~ -{cal O}(10-8) which is primarily driven by
fast structural evolution as the heaviest component ascends the giant
branch. This leads to the formation of contact systems, which ultimately
coalesce and form FK Comae-like objects on relatively short timescales
due to the continuing expansion of the primary. The obtained mass loss
rates and orbital period variations d ln P_orb/dt are confronted with
their observed ranges. The predicted mass loss rates agree with the
solar value on the main sequence and with the Reimers relation in the
giant phase. Observations of period evolution in close, active binaries
suggest, however, that other influences than those considered here must
play an important role. Finally, we point out how the mass asymmetry of
the binary system can be a crucial ingredient in the angular momentum
evolution: while the primary dictates the spin-orbital AM exchange
in the system, the slowly evolving lighter component can develop an
efficient magneto-centrifugally driven wind and thereby drain the AM
from the system.

---------------------------------------------------------
Title: Cyclic Evolution of Sunspots: Gleaning New Results from
Old Data
Authors: Solanki, S. K.; Fligge, M.; Pulkkinen, P.; Hoyng, P.
2000JApA...21..163S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Properties of the solar granulation obtained from the inversion
of low spatial resolution spectra
Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J.
2000A&A...358.1109F Altcode:
The spectra of cool stars are rich in information on elemental
abundances, convection and non-thermal heating. Extracting this
information is by no means straightforward, however. Here we demonstrate
that an inversion technique may not only provide the stratification of
the classical parameters describing a model atmosphere, but can also
determine the properties of convection at the stellar surface. The
inversion technique is applied to spectra of photospheric lines, one
recorded at the quiet solar disk center, the other integrated over the
whole disk. We find that a model based on a single plane-parallel
atmosphere gives unsatisfactory fits to the spectral lines and
suffers from considerable uncertainties in the derived temperature
stratification. Also, the elemental abundances returned by the inversion
are not particularly reliable. These problems are greatly reduced if
two atmospheric components, corresponding to granular up- and downflows
are allowed for. The best results are obtained if the line profiles
and bisectors of a neutral and ionized species are fit and the results
are constrained using a simple mass conservation scheme. We find that
inversions based on two- and three-component models of disk-integrated
spectra give similar results to inversions of disk-center observations,
although with somewhat lower accuracy. This similarity is promising
for future applications of line profile inversions to the study of
late-type stars and in particular their convection.

---------------------------------------------------------
Title: Properties of Flux Tubes and the Relation with Solar Irradiance
Variability
Authors: Fligge, M.; Solanki, S. K.
2000JApA...21..275F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Is solar mesogranulation a surface phenomenon?
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.
2000A&A...356.1050P Altcode:
Convection is the main form of energy transport in the subsurface
layers of the sun and other cool stars. The imprint of cellular
convection can be directly observed on the solar surface, with
a hierarchy of four size scales. The smallest observed convection
cells, called granules, have typical horizontal sizes of 1,000-2,000
km and have been successfully reproduced by numerical simulations
\citep{spruit:97,stein:nordlund:98}. Cells at three larger scales are
also detected \citep{leighton:etal:62,november:etal:81,beck:etal:98},
but these have so far not been amenable to numerical modelling,
so that their formation scenarios remain untested. Here we present
a numerical simulation which resolves both the granular and the next
larger, mesogranular, scale. The mesogranules have horizontal extents
of 5,000-10,000 km. Our 2D simulation reproduces key properties of both
granules and mesogranules. In addition, our simulation demonstrates
that the observed mesogranulation is driven close to the solar surface
and therefore rules out the text-book explanation of mesogranulation
as cellular convection driven by superadiabaticity in the deeper
layer where neutral helium ionizes. By proxy, this result also casts
doubt on the traditional explanation of supergranulation, even larger
convection cells with diameters of 20,000-30,000 km, as being driven
by the yet deeper second ionization of helium.

---------------------------------------------------------
Title: Distribution of magnetic flux on the solar surface and
low-degree p-modes
Authors: Moreno-Insertis, F.; Solanki, S. K.
2000MNRAS.313..411M Altcode:
The frequencies of solar p-modes are known to change over the solar
cycle. There is also recent evidence that the relation between frequency
shift of low-degree modes and magnetic flux or other activity indicators
differs between the rising and falling phases of the solar cycle,
leading to a hysteresis in such diagrams. We consider the influence
of the changing large-scale surface distribution of the magnetic
flux on low-degree (l&lt;=3) p-mode frequencies. To that end, we use
time-dependent models of the magnetic flux distribution and study the
ensuing frequency shifts of modes with different order and degree as a
function of time. The resulting curves are periodic functions (in simple
cases just sine curves) shifted in time by different amounts for the
different modes. We show how this may easily lead to hysteresis cycles
comparable to those observed. Our models suggest that high-latitude
fields are necessary to produce a significant difference in hysteresis
between odd- and even-degree modes. Only magnetic field distributions
within a small parameter range are consistent with the observations
by Jiménez-Reyes et al. Observations of p-mode frequency shifts
are therefore capable of providing an additional diagnostic of the
magnetic field near the solar poles. The magnetic distribution that
is consistent with the p-mode observations also appears reasonable
compared with direct measurements of the magnetic field.

---------------------------------------------------------
Title: Reconstruction of Past Solar Irradiance
Authors: Solanki, S. K.; Fligge, M.
2000svc..book..127S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Long-Term Changes in Solar Irradiance
Authors: Solanki, S.; Fligge, M.
2000ESASP.463...51S Altcode: 2000sctc.proc...51S
No abstract at ADS

---------------------------------------------------------
Title: Modelling irradiance variations from the surface distribution
of the solar magnetic field
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2000A&A...353..380F Altcode:
An important question in solar physics is to what extent solar surface
magnetism affects the solar irradiance. Previous attempts to answer this
question have employed proxies of the magnetic field to reconstruct the
irradiance and compare it with observations. Here we present the first
model calculations of solar irradiance variations based on variations
of the surface distribution of the solar magnetic field. The irradiance
reconstruction makes use of sunspot and facular contrasts calculated
as a function of wavelength and limb angle on the Sun. The position
and size of magnetic features on the solar disk are extracted from
full-disk magnetograms obtained by the Michelson Doppler Interferometer
(MDI) onboard the SOHO spacecraft. The reconstructed spectral irradiance
variations are compared with total and spectral contrast measurements
obtained by the VIRGO instrument onboard SOHO. Our reconstructions are
able to reproduce variations on the time-scale of the solar rotation
with much greater accuracy than previous models based on disk-integrated
magnetic proxies.

---------------------------------------------------------
Title: The influence of an inclined rotation axis on solar irradiance
variations
Authors: Knaack, R.; Fligge, M.; Solanki, S. K.; Unruh, Y. C.
2000ssls.work...45K Altcode:
The irradiance variations of the Sun over the solar cycle are relatively
small compared with sun-like stars (Radick et al., 1998). It has been
proposed that a random distribution of stellar rotation axes relative to
the ecliptic plane could explain their larger variability (Schatten,
1993). We examine the influence on total irradiance variations of
the inclination of the solar rotation axis relative to an observer. A
three-component model is used to calculate the relative flux variations
of a given distribution of active regions on the surface of the Sun as
a function of the inclination. One component is the quiet Sun, another
is a sunspot component and the third describes the faculae. We find
that the inclination effect increases the total irradiance variations
of the Sun maximally by 40%. The most probable value is approximately
5%. This is much less than former studies (Schatten, 1993, Radick et
al., 1998) suggested.

---------------------------------------------------------
Title: Commission 12: Solar Radiation and Structure (Radiation et
Structure Solaires)
Authors: Foukal, Peter; Solanki, Sami; Mariska, J.; Baliunas, S.;
Dravins, D.; Duvall, T.; Fang, C.; Gaizauskas, V.; Heinzel, P.;
Kononovich, E.; Koutchmy, S.; Melrose, D.; Stix, M.; Suematsu, Y.;
Deubner, F.
2000IAUTA..24...73F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar Surface Magnetism and the Increase of Solar Irradiance
between Activity Minimum and Maximum
Authors: Fligge, M.; Solanki, Sami K.; Meunier, Nadege; Unruh,
Yvonne C.
2000ESASP.463..117F Altcode: 2000sctc.proc..117F
No abstract at ADS

---------------------------------------------------------
Title: On the Contrast of Faculae and Small Magnetic Features
Authors: Ortiz, A.; Solanki, S. K.; Fligge, M.; Domingo, V.;
Sanahuja, B.
2000ESASP.463..399O Altcode: 2000sctc.proc..399O
Sunspots, faculae and the magnetic network contribute to solar
irradiance variations. The contribution due to faculae and the network
is important for understanding solar irradiance variations, but suffers
from considerable uncertainty. We focus our study on the faculae and
the network which produce an increase in the irradiance. Data from
the Michelson Doppler Interferometer (MDI) are employed. Starting from
the surface distribution of the solar magnetic field we build a mask
to detect bright features and study their contrast dependence on limb
angle and magnetic field. By sorting the magnetic field strength into
different bins we can distinguish between different associated bright
features. We find that the contrast of active region faculae and the
network exhibits different centre to limb variations, implying that
they need to be treated separately when reconstructing variations of
the total solar irradiance.

---------------------------------------------------------
Title: Modelling Solar Irradiance Variations: Comparison with
Observations, Including Line-Ratio Variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
2000svc..book..145U Altcode:
No abstract at ADS

---------------------------------------------------------
Title: EUV brightness variations in the quiet Sun
Authors: Brković, A.; Rüedi, I.; Solanki, S. K.; Fludra, A.;
Harrison, R. A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
2000A&A...353.1083B Altcode:
The Coronal Diagnostic Spectrometer (CDS) onboard the SOHO satellite has
been used to obtain movies of quiet Sun regions at disc centre. These
movies were used to study brightness variations of solar features at
three different temperatures sampled simultaneously in the chromospheric
He I 584.3 Ä (2 * 104 K), the transition region O V 629.7
Ä (2.5 * 105 K) and coronal Mg IX 368.1 Ä (106
K) lines. In all parts of the quiet Sun, from darkest intranetwork to
brightest network, we find significant variability in the He I and O
V line, while the variability in the Mg IX line is more marginal. The
relative variability, defined by rms of intensity normalised to the
local intensity, is independent of brightness and strongest in the
transition region line. Thus the relative variability is the same
in the network and the intranetwork. More than half of the points
on the solar surface show a relative variability, determined over a
period of 4 hours, greater than 15.5% for the O V line, but only 5%
of the points exhibit a variability above 25%. Most of the variability
appears to take place on time-scales between 5 and 80 minutes for the
He I and O V lines. Clear signs of “high variability” events are
found. For these events the variability as a function of time seen
in the different lines shows a good correlation. The correlation is
higher for more variable events. These events coincide with the (time
averaged) brightest points on the solar surface, i.e. they occur in
the network. The spatial positions of the most variable points are
identical in all the lines.

---------------------------------------------------------
Title: Division II: The Sun and Heliosphere: (Le Soleil et
Heliosphere)
Authors: Foukal, Peter; Ai, Guoxiang; Benz, Arnold; Engvold, Oddbjorn;
Solanki, Sami; Vandas, Marek; Verheest, Frank
2000IAUTA..24...65F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The evolution of solar granules deduced from 2-D simulations
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.
1999A&A...352..679P Altcode:
The evolution of solar granules is investigated on the basis of two
dimensional numerical solutions of the hydrodynamic equations describing
a compressible, radiatively coupled and gravitationally stratified
medium representative of the solar surface layers. The simulation covers
17 Mm on the solar surface and was run for over 5 h of solar time,
hence allowing the evolution of over 400 granules to be followed. A
statistical investigation of the temporal evolution of granules
therefore becomes feasible. Two types of granules can be distinguished
by their means of death: fragmenting and dissolving granules. Properties
and average evolutionary histories of these two types of granules
are considered. It is found that fragmenting granules are in general
large at birth and expand further with time. It is confirmed that
fragmentation into two (or more) parts is produced by buoyancy braking,
which in turn is initiated by the stronger horizontal flows in larger
granules. This last property, finally, is due to mass conservation. The
expansion, however, is due to a pressure excess relative to neighbouring
granules. The pressure excess is particularly marked if the neighbours
are dissolving granules. In contrast, dissolving granules are born
small and shrink before finally disappearing. The shrinkage is caused
by their neighbours which generally posses excess gas pressure and
larger horizontal flows. In summary, according our findings the fate
of a granule is decided by its properties at birth and the company
it keeps. Evidence is presented suggesting that the evolution of both
types of granules is driven by events near the solar surface.

---------------------------------------------------------
Title: Is the FIP effect present inside solar photospheric magnetic
flux tubes?
Authors: Sheminova, V. A.; Solanki, S. K.
1999A&A...351..701S Altcode:
The first determination of the elemental composition in the photospheric
layers of solar magnetic flux tubes is described. Stokes I and V
profiles of 13 elements observed in solar active region plage and in
the network are analysed. The abundances are obtained for elements
with high (C, O) and low (Al, Ca, Cr, Na, Ni, Sc, Si, Ti, Y, Zn) first
ionization potential (FIP) in order to investigate to what extent the
abundance anomalies observed in the upper solar atmosphere (FIP-effect)
are already present in the photospheric layers of flux tubes, which
are the source of much of the gas in the upper atmosphere. Various
sources of error are considered and the uncertainties introduced by
them are estimated. There are hints of a weak FIP-effect in the flux
tubes, corresponding to an overabundance of a factor of 1.1-1.2 of
the low-FIP elements relative to high-FIP elements, as compared to
the quiet photosphere. However, our data set a firm upper limit of
1.3-1.6 on this factor, which is well below the enhancement seen in
many parts of the upper solar atmosphere.

---------------------------------------------------------
Title: Relationship between Line Shift and Intensity Inside Coronal
Holes
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Schüehle, U.
1999ESASP.446..633S Altcode: 1999soho....8..633S
We analyse SUMER spectra of a group of lines belonging to chromospheric,
transition region and coronal ions obtained on both sides of the
boundary of polar coronal holes as well as at other locations along the
limb. We study the relationship between line shifts and intensities in
coronal holes and compare to values obtained in the quiet Sun. We find
that within coronal holes, a trend can be detected in some transition
region lines, like O V and N V, in the sense that the lines are more
strongly blueshifted in brighter regions. This is in agreement with
the conclusion reached by Hassler et al. (1999, Science 283, 810-813)
that the fast solar wind emanates from the network. Furthermore,
a correlation of line shifts of ions formed at higher temperatures
(Ne VIII, Fe XII) with intensities of lines showing network structures
(Si I, N III) is presented.

---------------------------------------------------------
Title: Hanle effect observations with the CA BT I 4227 Å line
Authors: Bianda, M.; Stenflo, J. O.; Solanki, S. K.
1999A&A...350.1060B Altcode:
The Hanle effect in the Ca i 4227 Ä line has been explored through
the analysis of a large number of Stokes profile recordings obtained
on the quiet Sun with the beam-splitter polarimeter system at IRSOL
(Istituto Ricerche Solari Locarno). In contrast to previous Hanle
observations with this line, which were limited to the Stokes I and
Q parameters, we are now in a position to study the combined effects
of Hanle depolarization (via Stokes Q) and rotation of the plane
of linear polarization (via Stokes U) with the same methods that
we recently applied to the Sr ii 4078 Ä line. The Hanle histograms
for the distributions of the depolarization and rotation parameters
are very similar for the two lines and show that there must be mixed
contributions to the Hanle signals from spatially unresolved magnetic
fields with random orientations (which do not contribute to Stokes U)
and partially resolved magnetic fields with a net orientation of the
field vectors. Field strengths in the range 5-10 G are preferred. We
also determine the “Hanle efficiency profile”, which shows how the
Hanle effect is confined to the Doppler core but vanishes in the line
wings. It is wider than the corresponding profile for the Sr line,
as expected from the difference in atomic weight and wavelength
between the two lines. The Q/I profiles of the Ca i 4227 Ä line
have minima around the Doppler core which turn negative (polarization
perpendicular to the limb) for limb distances mu =cos theta &gt;~ 0.2,
a likely signature of partial redistribution effects.

---------------------------------------------------------
Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brkovic, A.; Landi, E.; Rüedi, I.; Solanki, S.
1999ESASP.446..423L Altcode: 1999soho....8..423L
SOHO CDS, GIS and NIS, observations are used to evaluate the
electron temperature, density and pressure of active region loops. The
measurements are used to constrain empirical models of loops, which are
compared with an improved version of theoretical models from Landini
and Monsignori Fossi 1975. Energy balance is investigated to evaluate
temperature, pressure and heating release along the loop.

---------------------------------------------------------
Title: Magnetic Field Structuring
Authors: Solanki, S. K.
1999ESASP.446...25S Altcode: 1999soho....8...25S
No abstract at ADS

---------------------------------------------------------
Title: Two-dimensional simulation of solar granulation: description
of technique and comparison with observations
Authors: Gadun, A. S.; Solanki, S. K.; Johannesson, A.
1999A&A...350.1018G Altcode:
The physical properties of the solar granulation are analyzed on the
basis of 2-D fully compressible, radiation-hydrodynamic simulations and
the synthetic spectra they produce. The basic physical and numerical
treatment of the problem as well as tests of this treatment are
described. The simulations are compared with spatially averaged spectral
observations made near disk centre and high resolution spectra recorded
near the solar limb. The present simulations reproduce a significant
number of observed features, both at the centre of the solar disc and
near the solar limb. Reproduced observables include the magnitude of
continuum and line-core intensity fluctuations, line bisectors and
correlations between different line parameters. Spatially averaged
line shifts near disc centre, however, are not so well reproduced,
as are individual correlations between line parameters near the solar
limb. Possible causes of these discrepancies are discussed. The present
models predict the existence of two photospheric layers at which the
temperature fluctuations change sign. We point out a diagnostic of
the hitherto undetected upper sign reversal based on high spatial
resolution spectral observations of a sample of lines formed over a
wide range of heights in the photosphere.

---------------------------------------------------------
Title: Characteristics Of Blinkers Observed With CDS
Authors: Brkovic, A.; Ruedi, I.; Solanki, S. K.
1999ESASP.446..191B Altcode: 1999soho....8..191B
Blinkers are transient brightenings seen in the extreme
ultraviolet. They probably can not heat the corona, but are candidates
for microflare activity. Here we determine their properties on the
basis of a larger sample than previously studied. We used the Normal
Incidence Spectrometer of the Coronal Diagnostic Spectrometer (CDS)
onboard the SOHO satellite in its movie mode, i.e. 90"x240" slit,
to find evidence for blinkers in the quiet Sun. The He I 584.3 A
(20'000 K), the O V 629.7 (250'000 K) and the Mg IX 368.1 (1'000'000
K) lines are recorded simultaneously at a cadence of 31 seconds
for a duration of 4 hours each on December 3 1996. Harrison (1997)
defined the blinker as a phenomenon showing an enhancement of a factor
2-3 in the flux of transition region lines at network junctions. The
criterion we used was similar to his. We applied the threshold to the
O V line, and identified 74 distinct blinkers. The average properties
of these blinkers and the scatter around these mean values were then
determined. These properties include the duration of the blinker, the
energy content of the event, ratio of maximum to minimum brightness and
the sizes of these brightenings. We find that the overall brightening
is often composed of a number of shorter events. Finally, we checked
if these blinkers were also present in the images obtained in the two
other lines, of He I and Mg IX. In the He I line we found 65 events and
in the Mg IX line 16 events. On average the brightening was smaller
in these lines than in O V. The work is still in progress. We plan
to investigate how the locations of these events are related to the
distribution of the magnetic field and if they are also related to other
phenomena. References: Harrison, R.A.: 1997, Solar Physics 162, 467.

---------------------------------------------------------
Title: Oscillations of Sunspot Magnetic Fields: MDI Observations of
a Symmetrical Sunspot
Authors: Rüedi, I.; Solanki, S. K.
1999ASPC..184..131R Altcode:
We report on sunspot magnetic field oscillations observed using the
MDI instrument on the SOHO spacecraft. Clear oscillations are seen in
both the 3- and 5-min bands, but appear to be intermittent.

---------------------------------------------------------
Title: A reconstruction of total solar irradiance since 1700
Authors: Solanki, S. K.; Fligge, M.
1999GeoRL..26.2465S Altcode:
The irradiance of the Sun is reconstructed from 1700 to the present,
whereby the contributions of active regions and the quiet Sun are
modelled separately. A method is proposed which allows the contribution
of active-region faculae and sunspots to irradiance changes to be
isolated even when only a single proxy of solar activity, such as
sunspot relative number, Rz, is available. The resulting
reconstruction explicitly takes the non-linear relationship between
Rz and irradiance variations into account. Nevertheless,
due to the decreasing accuracy of the solar proxy data the accuracy of
the reconstruction decreases at earlier epochs. The main uncertainty,
however, lies in the reconstruction of the quiet-sun irradiance
variations.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic
features. XV. Evershed flow in cool, weak penumbral fields
Authors: Rüedi, I.; Solanki, S. K.; Keller, C. U.
1999A&A...348L..37R Altcode:
Observations of Ti I lines at 2.2 mu m show that the Evershed flow takes
place in cool, almost horizontal channels with a low magnetic field
strength (~ 500-900 G) that does not appear to change significantly
across the penumbra. This property might allow an outward directed
siphon flow to exist along such cool flux tubes.

---------------------------------------------------------
Title: Expansion of solar magnetic flux tubes large and small
Authors: Solanki, S. K.; Finsterle, W.; Rüedi, I.; Livingston, W.
1999A&A...347L..27S Altcode:
In the solar photosphere the magnetic field of magnetic elements and
sunspots is known to expand with height. In the case of sunspots this
expansion is known to be very rapid, with the field forming an almost
horizontal canopy. In this contribution we present new results on
the superpenumbral canopy of sunspots based on fits to Stokes I and
V profiles of infrared spectral lines. The new models take pressure
balance across the boundary of the canopy field into account, which
leads to significantly lower canopy base heights than previously
determined from similar data. Due to the lower canopy base height,
the density above the canopy base is larger, so that estimates of
the mass transported by the Evershed effect in the canopy need to be
revised upwards: approximately 15-50% of the mass flowing through the
penumbra travels beyond the sunspot boundary above the canopy base. A
comparison with small flux tubes leads to the surprising result that
although the two types of features have magnetic fluxes that differ by
5-6 orders of magnitude, their relative rate of expansion with height
is very similar, suggesting that at least in this respect sunspots
can be described by the thin-tube approximation. The remaining small
differences between the relative expansion of the two types of flux
tubes is qualitatively compatible with the presence of magnetic flux
that returns into the solar interior at the spot boundary, as has been
proposed by Westendorp Plaza et al. (1997).

---------------------------------------------------------
Title: Determination of solar cycle length variations using the
continuous wavelet transform
Authors: Fligge, M.; Solanki, S. K.; Beer, J.
1999A&A...346..313F Altcode:
The length of the sunspot cycle determined by Friis-Christensen
&amp; Lassen (1991) correlates well with indicators of terrestrial
climate, but has been criticized as being subjective. In the
present paper we present a more objective and general cycle-length
determination. Objectivity is achieved by using the continuous
wavelet transform based on Morlet wavelets and carrying out a careful
error analysis. Greater generality comes from the application of this
technique to different records of solar activity, e.g. sunspot number,
sunspot area, plage area or (10) Be records. The use of different
indicators allows us to track cycle length variations back to the 15th
century. All activity indicators give cycle length records which agree
with each other within the error bars, whereby the signal due to the
solar cycle is weaker within (10) Be than in the other indicators. In
addition, all records exhibit cycle length variations which are, within
the error bars, in accordance with the record originally proposed by
Friis-Christensen &amp; Lassen (1991). In the 16th century, however,
the (10) Be record suggests a much longer cycle than the auroral
record used by Friis-Christensen &amp; Lassen. Also, the presence
of a distinct 11-year cycle in the (10) Be record during the Maunder
Minimum is confirmed. By combining the results from all the indicators
a composite of the solar cycle length is constructed, which we expect
to be more reliable than the length derived from individual records.

---------------------------------------------------------
Title: The spectral dependence of facular contrast and solar
irradiance variations
Authors: Unruh, Y. C.; Solanki, S. K.; Fligge, M.
1999A&A...345..635U Altcode:
We present model calculations of facular and sunspot contrasts as a
function of wavelength and limb angle on the Sun. These are the first
such calculations; they assume LTE and are based on opacity distribution
functions (ODFs). The calculated facular contrasts as a function of
limb angle fit into the general picture of contrast measurements,
and the behaviour of the contrast with wavelength at a given limb
angle is in excellent agreement with the measurements. The calculated
intensity spectra are used to construct the solar flux spectrum for
different levels of solar activity. It is assumed that the irradiance
or flux variations are due to changes in the sunspot and facular
filling factors. The model atmosphere used to calculate the facular
intensities has been tuned so that the calculated irradiance variations
match the observed total and spectral irradiance variations during
the last solar cycles. The model calculations have also been used
to estimate the relative importance of continuum and spectral-line
variations in producing irradiance variations. The results suggest
that the continuum variations only contribute negligibly to the total
irradiance variations on solar-cycle time scales.

---------------------------------------------------------
Title: Influence of torsional waves in solar magnetic flux tubes on
spectral lines
Authors: Ploner, S. R. O.; Solanki, S. K.
1999A&A...345..986P Altcode:
The influence of torsional waves propagating along a thin, vertical,
photospheric flux tube on Zeeman-split polarized line profiles (Stokes
profiles) is investigated using a simple MHD model. In the presence of
such a wave spatially resolved Stokes profiles are found to oscillate
strongly in wavelength, amplitude and blue-red asymmetry. Qualitatively,
torsional waves induce similar changes into the line profiles as kink
waves (Ploner &amp; Solanki 1997). The magnitude of the line parameter
variation depends strongly on the observed location with respect to
the flux-tube axis. The spatially averaged Stokes V and Q profiles
are found to follow the torsional wave with double the wave frequency,
some parameters of Stokes U fluctuate directly at the wave frequency,
however. The other main feature of the spatially averaged profiles is
their comparatively small reaction to the wave. The reason for the
latter is that most polarized light is produced near the centre of
the flux tube where, however, the torsional wave produces only weak
perturbations. Temporally and spatially averaged Stokes profiles are
found to be only negligibly shifted, but strongly broadened. The sign
of the small remaining asymmetry is opposite in Stokes Q to that in
V and U. The amplitude of the wave and the location of the flux tube
on the solar disk have a strong influence on the magnitude of the
perturbation of the Stokes profiles.

---------------------------------------------------------
Title: Formation of small-scale magnetic elements: surface mechanism
Authors: Gadun, A. S.; Sheminova, V. A.; Solanki, S. K.
1999KFNT...15..387G Altcode: 2012arXiv1210.3499G; 1999KFNT...15e.387G
The first results of a two-dimensional MHD simulation of solar
magnetogranulation are given. The medium was treated as compressible,
gravitationally stratified, radiatively coupled, partially ionized,
and turbulent. The evolution of magnetogranulation was simulated in
course of 2 hours of hydrodynamic (solar) time. A surface (magnetic
plume-like) mechanism which forms thin magnetic elements was found to
exist. This sort of field formation occurs due to fragmentation of
large-scale granules. Active role of such mechanism shows that the
magnetogranulation not only concentrates and intensifies the global
magnetic flux at the boundaries of convective cells but also forms
nearly vertical compact magnetic tubes by involving the weak horizontal
field of the photosphere, which in general may be of local nature.

---------------------------------------------------------
Title: Limits on gravity-induced depolarization of light from the
white dwarf Grw +70°8247
Authors: Solanki, Sami K.; Haugan, Mark P.; Mann, R. B.
1999PhRvD..59d7101S Altcode:
We use measurements of the polarization of light from a magnetic white
dwarf to impose sharp constraints on the gravity-induced birefringence
of space predicted by a broad class of nonmetric gravitation
theories. Since gravity-induced birefringence violates the Einstein
equivalence principle, our measurements test this foundation of general
relativity and other metric gravitation theories in a new setting.

---------------------------------------------------------
Title: Can Chromospheric Activity mimic a Polar Spot?
Authors: Bruls, J. H. M. J.; Schüssler, M.; Solanki, S. K.
1999ASPC..158..182B Altcode: 1999ssa..conf..182B
No abstract at ADS

---------------------------------------------------------
Title: Solar Line Bisectors in the Infrared
Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K.
1999ASSL..239..227P Altcode: 1999msa..proc..227P
In the present work we made some analysis with respect to shifts
and asymmetries of infrared solar spectral lines to get information
about vertical velocity fields in the deep layers of the Solar
Photosphere. For the analysis of shifts and asymmetries of bisectors
were used. We averaged bisectors belonging to a group of similar line
parameter. Therefore it was possible, to analyse correlations between
asymmetries and line shifts and corresponding vertical velocities with
line parameters and to discuss the results with other literature.

---------------------------------------------------------
Title: Inversion of Stokes profiles
Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J.
1999ASSL..243..281F Altcode: 1999sopo.conf..281F
No abstract at ADS

---------------------------------------------------------
Title: Observations of the Hanle effect in the Ca I 4227 and Sr II
4078 Å lines
Authors: Bianda, M.; Stenflo, J. O.; Solanki, S. K.
1999ASSL..243...31B Altcode: 1999sopo.conf...31B
No abstract at ADS

---------------------------------------------------------
Title: Formation of small-scale magnetic elements: surface mechanism.
Authors: Gadun, A. S.; Sheminova, V. A.; Solanki, S. K.
1999KPCB...15..291G Altcode:
The authors present results of a two-dimensional MHD simulation of the
solar magnetogranulation. The medium was assumed to be compressible,
gravitationally stratified, radiatively coupled, partially ionized,
and turbulent. The simulated magnetogranulation evolved over the
course of two hours of hydrodynamic (solar) time. A surface (magnetic
plume-like) mechanism which forms thin magnetic elements was found to
operate during the process of granule fragmentation. The activity of
such a mechanism suggests that the magnetogranulation can concentrate
and intensify the global magnetic flux at the boundaries of convective
cells and can also form nearly vertical compact magnetic flux tubes
by involving the weak horizontal photospheric field, which may be,
in general, of local (turbulent) nature.

---------------------------------------------------------
Title: Coronal Hole Properties Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
Brković , A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
1999SSRv...87..315S Altcode:
We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained
on both sides of the boundary of polar coronal holes as well as at
other locations along the limb. We compare line intensities, shifts
and widths in coronal holes with values obtained in the quiet Sun. We
find that with increasing formation temperature, spectral lines show
an increasingly stronger blueshift in coronal holes relative to the
quiet Sun at an equal heliospheric angle. The width of the lines is
generally larger (by a few km/s) inside the coronal hole. Intensity
measurements show the presence of the coronal hole in Ne VIII lines
as well as in Fe XII, with evidence for a slightly enhanced emission
in polar coronal holes for lines formed below 105 K.

---------------------------------------------------------
Title: Coronal Holes Versus Normal Quiet Sun Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
Brković, A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
1999Ap&SS.264...53S Altcode: 1998Ap&SS.264...53S
We present a preliminary analysis of spectral lines obtained with the
SUMER instrument (Solar Ultraviolet Measurements of Emitted Radiation)
onboard the Solar and Heliospheric Observatory (SOHO), as observed
during three observing campaigns. From the 70 observed spectral lines,
we selected 12, representing 9 ions or atoms, in order to analyse line
intensities, shifts and widths in polar coronal holes as well as in the
normal quiet Sun. We find that coronal lines show a distinct blueshift
in coronal holes relative to the quiet Sun at equal heliospheric
angle, while there is no evidence for such a shift for lines formed at
temperatures below 10^5 K. The widths of lines formed at temperatures
above 3 - 10^4 K are slightly increased inside the coronal hole,
but unaffected for lower temperatures. Intensity measurements clearly
show the center-to-limb variation, as well as an intensity diminution
inside the coronal hole for lines formed above approximately 10^5 K.

---------------------------------------------------------
Title: Spots and Plages: the Solar Perspective
Authors: Solanki, S. K.
1999ASPC..158..109S Altcode: 1999ssa..conf..109S
No abstract at ADS

---------------------------------------------------------
Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brković , A.; Landi, E.; Rüedi, I.; Solanki, S.
1999SSRv...87..245L Altcode:
The Coronal Diagnostic Spectrometer (CDS) on SOHO is a grazing/normal
incidence spectrograph, aimed to produce stigmatic spectra of selected
regions of the solar surface in six spectral windows of the extreme
ultraviolet from 150 Å to 785 Å (Harrison et al. 1995). In the
present work, CDS, EIT, MDI and Yohkoh observations of active region
lops have been analyzed. These observations are part of JOP 54. CDS
monochromatic images from lines at different temperatures have been
co-aligned with EIT and MDI images, and loop structures have been
clearly identified using Fe XVI emission lines. Density sensitive
lines and lines from adjacent stages of ionization of Fe ions have
been used to measure electron density and temperature along the loop
length; these measurements have been used to determine the electron
pressure along the loop and test the constant pressure assumption
commonly used in loop modeling. The observations have been compared
with a static, isobaric loop model (Landini and Monsignori Fossi 1975)
assuming a temperature-constant heating function in the energy balance
equation. Good agreement is found for the temperature distribution
along the loop at the coronal level. The model pressure is somewhat
higher than obtained from density sensitive line ratios.

---------------------------------------------------------
Title: Granulation Near the Solar Limb: Observations and 2-D Modeling
Authors: Gadun, A. S.; Solanki, S. K.; Johannesson, A.
1999ASSL..239..201G Altcode: 1999msa..proc..201G
Based on high spatial resolution spectra and using 2-D fully
compressible, HD simulations of granules we analyze the correlations
between spectral line parameters: their CLV, height-dependence and
sensitivity to spatial resolution. We also point out some discrepancies
between the model results and observations.

---------------------------------------------------------
Title: Signatures of Coronal Hole Spectra Between 660 Å and 1460
Å Measured with SUMER on SOHO
Authors: Schühle, U.; Curdt, W.; Wilhelm, K.; Solanki, S. K.;
Stucki, K.
1999SSRv...87..299S Altcode:
Spectra of the northern polar coronal hole measured with the SUMER
spectrometer on SOHO on 25 October 1996 are analyzed. We present spectra
taken at locations on the solar disk where part of the spectrometer
slit intersects a polar coronal hole region and an area of brighter
emission from outside of the coronal hole area. By comparing the line
intensities between the parts of the spectrum taken inside the "dark"
area of the coronal holes and the brighter regions, we work out the
signatures of the specific coronal hole in the chromosphere, transition
region and lower corona. We find that emissions of neutral atom lines,
of which there are many in the spectrum of SUMER, show no difference
between the coronal hole and the bright boundary areas, whereas all
ionized species show strong intensity enhancements, including the
continuum emissions of carbon and hydrogen. These enhancements are
larger than in normal quiet Sun areas.

---------------------------------------------------------
Title: On the expansion of large and small flux tubes with height
Authors: Solanki, S. K.; Rüedi, I.; Finsterle, W.; Livingston, W.
1999ASSL..243..397S Altcode: 1999sopo.conf..397S
No abstract at ADS

---------------------------------------------------------
Title: Sunspot magnetic oscillations: Comparison between observations
and models
Authors: Rüedi, I.; Solanki, S. K.; Bogdan, T.; Cally, P.
1999ASSL..243..337R Altcode: 1999sopo.conf..337R
No abstract at ADS

---------------------------------------------------------
Title: Brightness Variations in the Solar Atmosphere as Seen by SOHO
Authors: Brkovic, A.; Rüedi, I.; Solanki, S. K.; Huber, M. C. E.;
Stenflo, J. O.; Stucki, K.; Harrison, R.; Fludra, A.
1999ASSL..239..231B Altcode: 1999msa..proc..231B
We present preliminary results of a statistical analysis of the
brightness variations of solar features at different levels in
the solar atmosphere. We observed quiet Sun regions at disc centre
using the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and
Heliospheric Observatory (SOHO). We find significant variability at all
time scales in all parts of the quiet Sun, from darkest intranetwork
to brightest network. Such variations are observed simultaneously in
the chromospheric He I 584.33 Angstroms (2 \cdot 10^4 K) line, the
transition region O V 629.74 Angstroms (2.5 \cdot 10^5 K) and coronal
Mg IX 368.06 Angstroms (10^6 K) line. The relative variability is
independent of brightness and most of the variability appears to take
place on time scales longer than 5 minutes for all 3 spectral lines. No
significant differences are observed between the different data sets.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. XIV. TI
i and the cool components of sunspots
Authors: Rueedi, I.; Solanki, S. K.; Keller, C. U.; Frutiger, C.
1998A&A...338.1089R Altcode:
The first systematic observations of sunspot umbrae using the lines
of the Ti Ii multiplet at 2.2 mu m are presented. Their diagnostic
capabilities are investigated, developed and used to investigate the
magnetic and velocity structure of a sunspot. These lines are most
sensitive to cool plasma. In addition, they are extremely Zeeman
sensitive. We find that a sunspot is composed of two distinct cool
magnetic components. One of them is fairly vertical, has a large
magnetic field strength and is associated with the central (umbral)
part of the sunspot. The other component is strongest near the outer
boundary of the spot (penumbra), is much more inclined, has a very
low magnetic field strength and shows the signature of the Evershed
effect. In contrast to the smooth transition of field strength from
the darkest part of the umbra to the outer penumbral boundary usually
visible in observations carried out in other spectral lines, the Ti
Ii lines exhibit a sharp transition between the two magnetic components.

---------------------------------------------------------
Title: Hanle diagnostics of solar magnetic fields: the SR II 4078
Angstrom line
Authors: Bianda, M.; Stenflo, J. O.; Solanki, S. K.
1998A&A...337..565B Altcode:
The Hanle depolarization and rotation effects in the Sr ii
4078\tsAngstroms line have been explored with the instrumentation at
IRSOL (Istituto Ricerche Solari Locarno) by recording the Stokes I,
Q, and U line profiles with high spectral resolution and polarimetric
accuracy in a large number of regions across the solar disk. &gt;From
the extracted line parameters we have constructed “Hanle histograms”
showing the statistical distributions of the Hanle rotation and
depolarization effects. Comparison with theoretical calculations allow
these histograms to be understood in terms of magnetic fields with a
strength of about 5-10\ts G, which is similar to the field strengths
previously found through analysis of Q/I Hanle depolarization in the
Ca i 4227\tsAngstroms line. While small-scale magnetic fields with
spatially unresolved angular distributions contribute to the observed
Hanle depolarization effects, the observed Hanle rotation effects in
Stokes U are due to spatially resolved fields with net large-scale
orientations (e.g. global or canopy-type fields). We have also for the
first time determined empirical “Hanle efficiency profiles”, derived
independently for the Hanle rotation and depolarization effects. They
show how the Hanle efficiency has its maximum in the Doppler core of
the line and then rapidly decreases to become zero in the line wings.

---------------------------------------------------------
Title: Doppler imaging: the polar SPOT controversy
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Schuessler, M.
1998A&A...336..231B Altcode:
Doppler imaging studies have revealed that most rapidly rotating cool
stars have high-latitude spots, which in many cases cover the stellar
poles. The spectroscopic signature of polar spots is a filling in
of the cores of spectral lines, which become flat-bottomed and may
show bumps. Although the existence of polar spots is corroborated by
spectroscopic and photometric measurements, and although theoretical
models predict polar spots, they remain controversial. Most notably, it
has been proposed that the line core filling in might also be caused by
chromospheric activity. We present a NLTE radiative transfer analysis
of 14 of the most-used Doppler-imaging lines which demonstrates that
chromospheric activity can produce filling in of the observed line
profiles only in a few of these lines. Moreover, such filling in is in
general not of the type observed in the spectra of active stars. We
are able to produce a flat-bottomed line core by concentrating the
chromospheric activity near the poles, but only for two of the strongest
lines, Fe i 5497 Angstroms and Fe i 6430 Angstroms. In the observations,
however, also the weaker lines have flat-bottomed cores. Therefore, it
is unlikely that polar spots are an artifact due to misinterpretation
of the spectral signature of chromospheric activity. Nevertheless, we
cannot exclude that chromospheric activity provides part of the filling
in of the cores of some stronger lines; we present a diagnostic that may
help to separate the contributions of chromospheric activity and spots.

---------------------------------------------------------
Title: Do solar magnetic elements harbor downflows?
Authors: Frutiger, C.; Solanki, S. K.
1998A&A...336L..65F Altcode:
In a recent paper Bellot Rubio et al. (1997) inverted Zeeman split
Stokes profiles to infer the stratification of the temperature,
velocity and magnetic field in the photospheric layers of solar
magnetic elements (modeled as thin flux tubes). One controversial
result of their inversions is the presence of a strong downflow
within the flux tubes. In the model underlying their inversion such
a downflow is necessary to reproduce the asymmetric shape of the
observed V profiles. We present inversions based on two different
flux-tube models, both of which reproduce the Stokes I and V profiles
obtained in plages and the network with high accuracy, including the
V profile asymmetry. One model is almost identical to that employed
by Bellot Rubio et al. (1997), and results in a significant downflow
within the flux tube. The other, although similar in most respects,
has mass conservation enforced inside the flux tubes, i.e. they contain
both an upflow and a downflow which could arise from oscillations or
siphon flows. Hence, current data may not be sufficiently sensitive
to distinguish between the two velocity structures, so that there is
no compelling evidence for a net downflow of matter inside magnetic
elements. From a physical point of view the model incorporating mass
conservation is to be preferred.

---------------------------------------------------------
Title: Oscillations of sunspot magnetic fields
Authors: Rueedi, I.; Solanki, S. K.; Stenflo, J. O.; Tarbell, T.;
Scherrer, P. H.
1998A&A...335L..97R Altcode:
We report on velocity and magnetic field oscillations observed
in sunspots using the MDI instrument onboard SOHO. In addition to
the well-known velocity oscillations, the data clearly show highly
localised oscillations of the magnetogram signal in different parts
of the sunspots. We show that only oscillations of the magnetic field
vector can produce the observed magnetogram oscillations, and that the
observed phase relations suggest an origin in terms of magnetoacoustic
gravity waves.

---------------------------------------------------------
Title: A model of solar total and spectral irradiance variations
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y. C.; Froehlich, C.;
Wehrli, Ch.
1998A&A...335..709F Altcode:
We model solar spectral irradiance variations under the assumption
that they are produced by sunspots and faculae alone. The model is
based on three components, i.e. quiet Sun, assumed to be temporally
invariant, sunspots and faculae whose temporal variations are mimicked
using time series of sunspot areas and Mg II core-to-wing ratios. The
detailed flux spectrum for each component is employed. The results
are compared to spectral irradiance measurements at 402 nm, 500 nm
and 862 nm obtained between February 22 and December 31, 1996 by
the three-channel sunphotometers (SPM) which are part of the VIRGO
package onboard SOHO. Our model shows a good correlation with the
measured variations of the three colour channels and of the total
irradiance. Since it also successfully reproduces changes in the UV
spectral irradiance, irradiance variations and observed variations
of the faculae-to-spots filling factor ratio since 1978, our model
supports earlier suggestions that a large part of the solar irradiance
variations is caused by magnetic fields at the solar surface. Finally,
we use the model to test whether the difference between the magnitude
of solar and stellar brightness variations reported by Lockwood et
al. (1992) is due to the particular filters they use for their stellar
observations. Our results suggest that this effect can explain only
a small part of the discrepancy.

---------------------------------------------------------
Title: On the reliability of Stokes diagnostics of magnetic elements
away from solar disc centre
Authors: Solanki, S. K.; Steiner, O.; Buente, M.; Murphy, G.; Ploner,
S. R. O.
1998A&A...333..721S Altcode:
{The spectropolarimetric signature of models of small-scale magnetic
features is well understood at the centre of the solar disc, but
has been little studied near the solar limb, mainly because the
detailed geometry of the flux tubes must then be taken into account
in a realistic analysis. We present multi-ray calculations of Stokes
profiles through arrays of 2-D magnetohydrostatic models of small flux
tubes. We compare the Stokes profile shapes and Stokes based diagnostics
(Q to V ratio, V amplitude, magnetic line ratio, centre of gravity
wavelengths, etc.) resulting from plane-parallel and 2-D flux-tube
models at different limb distances for two lines in the visible and
an infrared H-band line. For the visible lines around 5250 Angstroms
all the diagnostics we have studied, with the exception of the Q and U
to V ratio, are significantly affected by the finite size of the flux
tubes and the passage of the rays through non-magnetic material near
the limb. We show that magnetic filling factors and the global magnetic
flux may be underestimated using the usual calibration techniques. In
addition, near the solar limb the magnetic line ratio can move into
a regime that is forbidden according to simpler models. The spatially
averaged longitudinal field derived from the centre-of-gravity method
also becomes strongly model dependent. The thermal structure of the
non-magnetic atmosphere appears to play a particularly important role
in determining the values of these diagnostic parameters. The infrared
line at 1.5648 mu m, on the one hand, reacts little to the external
atmosphere and provides superior diagnostics of both the magnetic field
strength and filling factor. On the other hand, for a flux tube with
a sharp boundary this line shows little dependence on the flux-tube
diameter, in contrast to the earlier findings of Zayer et al. (1989). }

---------------------------------------------------------
Title: Temporal Evolution of Artificial Solar Granules
Authors: Ploner, S. R. O.; Solanki, S. K.; Gadun, A. S.; Hanslmeier, A.
1998SSRv...85..261P Altcode:
We study the evolution of artificial granulation on the basis of 2-D
hydrodynamical simulations. These clearly show that granules die in
two different ways. One route to death is the well known bifurcation
or fragmentation of a large granule into 2 smaller ones (exploding
granules). The other pathway to death is characterized by merging
intergranular lanes and the accompanying dissolution of the granule
located between them. It is found that the lifetime and maximum
brightness is independent of the way in which granules evolve and
die. They clearly differ in size, however, with exploding granules
being in general significantly larger.

---------------------------------------------------------
Title: Structure of the Solar Photosphere
Authors: Solanki, Sami K.
1998SSRv...85..175S Altcode:
The majority of measured solar abundances refer to the solar
photosphere. In general, when determining photospheric abundances a
plane-parallel atmosphere and LTE are assumed. However, the photosphere
is structured by granulation, magnetic fields and p-modes. They change
line profiles by the thermal inhomogeneities and wavelength shifts they
introduce. A brief description of the first two of these phenomena
is given and some of the ways in which they influence abundances are
pointed out. Departures from LTE also occur. The magnitude of the errors
introduced into elemental abundances by neglecting such departures is
also briefly discussed.

---------------------------------------------------------
Title: Foreword
Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger,
R.
1998SSRv...85...11F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Long-term behavior of emission from solar faculae: steps
towards a robust index
Authors: Fligge, M.; Solanki, S. K.
1998A&A...332.1082F Altcode:
Facular emission is one of the major contributors to long-term solar
irradiance variations. Reconstructions of past facular variations,
however, are strongly hampered by the lack of reliable proxies,
particularly on time-scales longer than a solar cycle. We consider
the five potential facular proxies with records covering more than
40 years. By suitably weighting and combining them we create a new
proxy. In comparison with sunspot relative number the combined proxy
exhibits enhanced values during solar cycles 16 and 17. This suggests
that the Sun may have been brighter during those cycles than earlier
models, which used sunspot numbers as the facular proxy, indicate.

---------------------------------------------------------
Title: Hanle depolarisation in the solar chromosphere
Authors: Bianda, M.; Solanki, S. K.; Stenflo, J. O.
1998A&A...331..760B Altcode:
A new polarimeter and an extension of the polarimetric technique of
Donati et al. (1990) to higher polarisation values are presented. With
this system, which allows low-noise polarimetric observations in the
blue and near-UV part of the solar spectrum, we have recorded more than
200 Q/I profiles of Ca I 4227 Angstroms with an accuracy of 2-3x 10(-4)
. We find that while the Q/I line shape outside the line core is very
stable from one part of the solar surface to the next, the line core
exhibits large variations relative to the rest of the profile. These
variations are best interpreted in terms of partial depolarisation
produced by the Hanle effect in the presence of weak fields. We obtain
a quantitative and model-independent estimate of the depolarisation,
from which we deduce field strengths of 5-15 G at the level of line-core
formation, i.e. in the low to mid chromosphere. We also find evidence
that the field strength is distributed around these average values
with a FWHM that is approximately the same as the average value.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. XIII. The
relative flux in weak and strong quiet-sun magnetic fields
Authors: Meunier, N.; Solanki, S. K.; Livingston, W. C.
1998A&A...331..771M Altcode:
An estimate of the fraction of magnetic flux in intrinsically weak-field
form, i.e. fields with less than 1 kG intrinsic strength, in the
quiet Sun is presented. We find that on average approximately 2/3 of
the flux is in weak-field form, although our data allow a range of
values between 25%\ and 85%. These estimates have been derived with
the help of radiative transfer model calculations from low-noise
scans through the quiet Sun at fixed wavelengths within a Zeeman
sensitive spectral line at 1.56 mu m. They represent the first rapidly
modulated polarimetric observations of solar 1.56 mu m radiation. These
scans show that the polarimetric signature near the core of the line
exhibits a very different spatial structure than in the outer line
wings. Since the outer part of the line profile is only sensitive to
intrinsically strong magnetic fields, while the central part reacts
also to intrinsically weak fields, this implies that intrinsically weak
fields are distributed differently on the surface than strong fields
are (weak-field features lie closer together). The spatial distribution
suggests that the strong fields we are observing are network elements,
whereas the weak fields are intranetwork features. Further results,
such as the average distance between weak and strong field features,
flux distribution, spatial power spectra and the Stokes asymmetry
of intrinsically weak fields are also presented. In particular, we
find that the flux per magnetic feature is distributed lognormally,
in agreement with a similar finding for sunspot umbral areas by Bogdan
et al. (1988).

---------------------------------------------------------
Title: Solar irradiance since 1874 revisited
Authors: Solanki, S. K.; Fligge, M.
1998GeoRL..25..341S Altcode:
We reconstruct the solar irradiance since 1874 employing an evolved
version of previously published models and improved sunspot and
facular data. A good correlation between reconstructed irradiance
and Earth's global air temperature on time scales longer than the
solar cycle is obtained and, in contrast to many earlier models, solar
irradiance does not on average lag behind global temperature prior to
1975, although the exact time lag between the two quantities depends
somewhat on details of the reconstruction. Since that epoch, however,
air temperatures have increased by 0.2 K, whereas solar irradiance
has risen a disproportionately smaller amount. Therefore, unless the
influence of solar variability on Earth is very strongly non-linear,
at least this most recent temperature increase reflects the influence of
man-made greenhouse gases or non-solar sources of natural variability.

---------------------------------------------------------
Title: Velocity fields below the magnetic canopy of solar flux tubes:
evidence for high-speed downflows?
Authors: Briand, C.; Solanki, S. K.
1998A&A...330.1160B Altcode:
It is well-established that velocities in the immediate surroundings of
solar magnetic elements produce an asymmetry in the Stokes V profiles
emerging from the magnetic feature. Conversely, the observed Stokes V
asymmetry can be used to infer the velocity field. Taking as constraints
the area asymmetries of the Stokes V profiles of two lines of neutral
magnesium (lambda 457nm and lambda 517nm) observed near the center of
the solar disk, the (vertical) component of the velocity field below
the magnetic canopy of flux tubes is investigated. We find that the
strong Mg I b_2 line at 517nm qualitatively extends the diagnostic
capabilities of Stokes V asymmetry, mainly due to the fact that it is
sensitive to velocities over a large range of heights and hence also at
relatively large distances from the flux tube axis. In order to retrieve
the observed area asymmetry of both lines, up- as well as downflows
have to be introduced in the models. If the temperature differences
between the two flows are neglected then a downflow of 1.5 - 2km s(-1)
close to the edge of the flux tube and an almost equally strong upflow
at greater distances (corresponding to the central part of a granule)
reproduces the observed area asymmetries. If we take into account
that the temperature in the downflow is lower than in the upflow,
we can only reproduce the observations if the downflow is fast (&gt;=
5 km s(-1) ) and concentrated into narrow lanes.

---------------------------------------------------------
Title: The photospheric sources of jets
Authors: Solanki, S. K.
1998ESASP.421..115S Altcode: 1998sjcp.conf..115S
No abstract at ADS

---------------------------------------------------------
Title: Complex magnetic fields in an active region
Authors: Bernasconi, P. N.; Keller, C. U.; Solanki, S. K.; Stenflo,
J. O.
1998A&A...329..704B Altcode:
High-resolution observations of the full Stokes vector in Fe\sc i
spectral lines around 5250 Angstroms obtained at the Swedish Vacuum
Solar Telescope on La Palma with the ZIMPOL I Stokes polarimeter in a
complex active region reveal the presence of anomalously shaped Stokes
profiles indicating the coexistence of at least two magnetic components
within the same spatial resolution element. These Stokes profiles have
been analyzed with an inversion code based on a 3-component atmospheric
model with two magnetic and one field-free component. The fits to
the observations in a magnetic region that resembles a small penumbra
reveal the presence of a horizontal magnetic field component with an
average field strength of /line{B}=840 G, a mean filling factor of
/lineα=0.12, and an average temperature /line{T}=5400 K at log {tau_
{5000}}=-1.5 embedded in the main “penumbral” magnetic field that
has /line{B}=1500 G, /lineα=0.56, and /line{T}=4900 K. The horizontal
component exhibits a mean outflow of 2.7 km s(-1) which is mainly due
to the Evershed flow. In a region where there are strong downflows up
to 7 km s(-1) , we infer the possible presence of a shock front whose
height changes along the slit. The height variation can be explained by
a change of the gas pressure at the base of the photosphere below the
shock front as proposed by Thomas &amp; Montesinos (1991). Small plages
with field strengths below 900 G have been observed in the vicinity
of some pores. Finally, we present a puzzling field structure at the
boundary between two adjacent pores. Ambiguous results suggest that
although the inversion code is able to successfully invert even very
complex Stokes profiles, we are far from a complete description of the
field structure in complex magnetic regions. We warn that magnetograms
and fits to data involving only a single magnetic component may hide
the true complexity of the magnetic structure in at least some parts
of active regions.

---------------------------------------------------------
Title: Solar Composition and Its Evolution -- From Core to Corona
Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger,
R.
1998sce..conf.....F Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Search for a Robust Index of Long-Term Facular Variations
Authors: Fligge, M.; Solanki, S. K.
1998ASPC..140..317F Altcode: 1998ssp..conf..317F
No abstract at ADS

---------------------------------------------------------
Title: Kink Waves in Solar Flux Tubes and Polarized Line Profiles
Authors: Ploner, S. R. O.; Solanki, S. K.
1998ASPC..154..679P Altcode: 1998csss...10..679P
Waves are thought to play a fundamental role in the heating processes
of the chromosphere and corona of the Sun and other cool stars. Of
particular interest are periodic motions in so called flux tubes,
elements of concentrated magnetic field. We investigate the influence
of kink waves in flux tubes on polarized line profiles and demonstrate
that they have a large effect. This should help us to set limits on
the energy flux in such waves.

---------------------------------------------------------
Title: A Non-LTE Analysis of Doppler Imaging Lines
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Schussler, M.
1998ASPC..154.1959B Altcode: 1998csss...10.1959B
Doppler imaging studies have revealed that most stars with high activity
levels have polar spots. Although their existence is corroborated by
spectroscopic and photometric measurements, and although theoretical
models have been produced that include polar spots, their existence
remains controversial. Based on a NLTE radiative transfer analysis
of the most-used Doppler-imaging lines we reject the claim that
chromospheric activity might be responsible for the features in the
spectral lines that are commonly interpreted as polar spots.

---------------------------------------------------------
Title: Torsional waves in solar flux tubes and polarized line
profiles.
Authors: Ploner, S. R. O.; Solanki, S. K.
1998joso.proc..113P Altcode:
Waves are thought to play a fundamental role in the heating of the
chromosphere and corona of the Sun and other cool stars. Of particular
interest are periodic motions in so called flux tubes, elements of
concentrated magnetic field. The authors investigate the influence of
torsional waves from different locations in flux tubes on polarized
line profiles. They find that the magnitude of the influence of those
waves strongly depends on the location within the flux tube.

---------------------------------------------------------
Title: A model of the wavelength dependence of solar irradiance
variations
Authors: Solanki, S. K.; Unruh, Y. C.
1998A&A...329..747S Altcode:
The variation of the solar irradiance over the solar cycle has a strong
wavelength dependence, being larger at shorter wavelengths. Here
we present simple models of the spectral dependence of irradiance
variations between solar activity maximum and minimum. We find that the
observations (which concentrate on the UV) cannot be reproduced by a
change in effective temperature of the Sun (or of parts of its surface)
alone. We can, however, reproduce the data with either a 2-component or
a 3-component model, of which one component is the quiet Sun, another
is a facular component, and the third (in the case of the 3-component
model) represents the temperature stratification of sunspots. The
facular component is found to be very close to the facular models F
or P of Fontenla et al. (1993). The success of these models supports
the assumption underlying many studies of total solar irradiance
variations that these are caused mainly by magnetic fields at the solar
surface. Our investigation also allows an improved estimate of the
relative contribution of the various layers in the solar photosphere and
of the different wavelength regions to the total irradiance variations.

---------------------------------------------------------
Title: The Wavelength Dependence of Solar Irradiance Variations
Authors: Unruh, Yvonne C.; Solanki, Sami K.
1998ASPC..154..700U Altcode: 1998csss...10..700U
The observed irradiance variations over a solar cycle show a strong
wavelength dependence; the variations are strongest in the UV and
very weak in the visible. Here we present a simple model of the
spectral dependence of the solar irradiance. We can exclude models that
postulate a change in the effective temperature of the Sun or of parts
of the Sun. However, we find that the observed irradiance variations
can be matched with a model that includes the different temperature
stratification of the quiet photosphere, the faculae and the sunspots.

---------------------------------------------------------
Title: Structure of the Solar Photosphere
Authors: Solanki, S. K.
1998sce..conf..175S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Manifestations of Solar Magnetic Fields
Authors: Solanki, S. K.
1998HiA....11..857S Altcode:
The magnetism of the Sun manifests itself in innumerable ways, many
of which constitute what is referred to as solar magnetic activity,
while others are counted among the phenomena of the quiet Sun. After
a brief overview of the structure of the solar magnetic field, a few
examples of its manifestations are pointed out.

---------------------------------------------------------
Title: Modelling Spectral Irradiance Variations obtained by VIRGO
Authors: Fligge, M.; Solanki, S. K.; Unruh, Y.; Frohlich, C.;
Wehrli, Ch.
1998ASPC..140..311F Altcode: 1998ssp..conf..311F
No abstract at ADS

---------------------------------------------------------
Title: The flare of November 29, 1996 observed by SOHO/CDS
Authors: Czaykowska, A.; Rank, G.; Ruedi, I.; Solanki, S. K.; de
Pontieu, B.
1998cee..workE..32C Altcode:
We present flare and post-flare observations obtained with the Coronal
Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric
Observatory (SOHO) on November 29, 1996. On this day at around 20:40
UT, an M 1.0/1F flare occurred in the solar active region NOAA 7999 and
was accidentally observed by the Normal Incidence Spectrometer (NIS),
one of the two spectrometers of CDS (Harrison et al., 1995). The
data consist of two rasters lasting for 135 minutes each and both
cover an area of 4 times 4 arcminutes. The first raster is pointed at
the northern part of the active region during the flare whereas the
second one covers the southern part of the active region after the main
phase of the flare. The observations were part of the Joint Observing
Program (JOP) 54 which is aimed at the investigation of scaling laws in
coronal loops. Consequently the details of observations such as line
list and exposure time weren't convenient for flare observations. In
addition a flare can lead to over-exposures, i.e., saturation of the
CCD detector pixels, and a burn-in degeneration of the detector in
bright lines. Therefore observations of flares with CDS are avoided
and the flare from November 29, 1996, is so far the only noteworthy
flare observed by CDS. In our case we have remarkable saturation in
the chromospheric He I line at 584 AA and the coronal Fe XVI lines
at 335 AA and 361 AA, which are formed at an equilibrium temperature
of about 2.5 cdot 10^6 K. Another effect of illumination on the CCD
detector being too high is that the electron well of each pixel may
fill and hence bleed to adjacent pixels. This effect is clearly seen
in our data. As the flare occurred, the 2 times 240 arcseconds slit
was being rastered across the active region from west to east. We thus
have a convolution of spatial and temporal effects which are not easy
to separate. However, we have spectral information of each pixel in all
lines and exposures which are not saturated. Hence, line parameters such
as intensity and relative Doppler shifts can be calculated. Moreover,
the line list contains two density sensitive line pairs, Fe XII 338
AA/364 AA and Fe XIII 348 AA / 360 AA (see, e.g., Mason et al., 1997)
which can be used to determine the electron density. Using this data we
intend to study the temporal evolution of characteristics and geometry
of the loop during the flare.

---------------------------------------------------------
Title: Solar Magnetic Fields: an Introduction
Authors: Solanki, Sami K.
1998LNP...507...41S Altcode: 1998sspt.conf...41S
The magnetic field of the Sun is thought to be produced by a dynamo
in the solar interior and exhibits its greatest influence on the
solar plasma in the tenuous outer layers of the solar atmosphere,
where it lies at the heart of almost every major phenomenon. Most
direct observations of the magnetic field are restricted to the solar
surface, however. Both observational and theoretical methods have
been employed heavily to obtain information on and an understanding
of solar magnetism. It is the aim of these lecture notes to impart
some of this knowledge to the reader: knowledge both of the magnetic
field and of some of the methods used to investigate it.

---------------------------------------------------------
Title: Sunspot Oscillations Observed with MDI
Authors: Rüedi, I.; Solanki, S. K.; Stenflo, J. O.; Scherrer, P. H.
1998ESASP.417..281R Altcode: 1998cesh.conf..281R
No abstract at ADS

---------------------------------------------------------
Title: Solar composition and its evolution - from core to
corona. Proceedings. ISSI (International Space Science Institute)
Workshop, Bern (Switzerland), 26 - 30 Jan 1998.
Authors: Fröhlich, C.; Huber, M. C. E.; Solanki, S. K.; von Steiger,
R.
1998SSRv...85.....F Altcode:
The following topics were dealt with: solar composition, solar
evolution, the solar interior, helioseismology, photosphere,
chromosphere, solar corona, solar wind, the Sun as a Sun-like star.

---------------------------------------------------------
Title: Evolved Stars: What Happens to Activity Off the Main Sequence
Authors: Strassmeier, K. G.; Fekel, F. C.; Gray, D. F.; Hatzes, A. P.;
Schmitt, J. H. M. M.; Solanki, S. K.
1998ASPC..154..257S Altcode: 1998csss...10..257S
Magnetic activity on the main sequence has been well studied, in
contrast to researches on sub-giants, giants, and supergiant stars. In
this discussion we will address three main topics associated with
activity in evolved stars: (1) rotation regimes for evolved stars;
(2) rotation-activity relations in the H-R diagram; (3) polar spots.

---------------------------------------------------------
Title: Noise Reduction in Astronomical Spectra: A New Wavelet-Based
Method
Authors: Fligge, M.; Solanki, S. K.
1998ASPC..154..833F Altcode: 1998csss...10..833F
We present a wavelet technique to de-noise astronomical spectra based on
non-orthogonal wavelet packets and compare it to Fourier-smoothing and
other wavelet-based de-noising algorithms. It is found to give better
results than any other tested de-noising algorithm and is particularly
successful in recovering weak signals that are practically drowned by
the noise.

---------------------------------------------------------
Title: Solar Oscillations in CO at 4.6 Microns
Authors: Livingston, W.; Solanki, S.; Muglach, K.; Wallace, L.
1998ASPC..135..186L Altcode: 1998hcsp.conf..186L
The fundamental band lines of CO originate in the solar temperature
minimum and lower cool parts of the chromosphere. We have observed
velocity and intensity oscillations in the quiet sun disk center
and extreme limb, sunspots, and plage. We have also looked for CO
oscillations in the Sun-as-a-star (but detect nothing). We compare the
power spectra of these various features, noting well separated 3 min and
5 min peaks. We interpret our observations in terms of the models of
Carlsson and Stein (1995), and Solanki, et al., (1994). Active Region
Seismology: Results from TON Project Bala Balachandran (Dept. Physics,
National Tsing Hua University, Hsinchu, Taiwan 30043, R.O.C.) Taiwan
Oscillation Network (TON) is a ground based observation facility
for the study of solar oscillations. The data consists of full-disc
K-line images taken at every minute. Using the 512 images time series,
we have tried to infer the location of the magnetic field below the
photosphere using the property of the active regions to absorb the
p-mode power. Two consecutive days, one just when the magnetic flux
appears on the surface and the other the day before the emergence, were
analysed. For this, an annular region of 15 deg. around the region of
emerging flux was chosen for the analysis. The modes were decomposed
into incoming and outgoing waves and the absorption coefficient was
calculated as the fractional difference of the two types. We found
that the absorption is stronger after the emergence of the flux and
the flux was at a depth of about 4000 km below the surface just before
its appearance on the surface; that is about 15 hrs before. It was also
reported earlier by other groups that the quiet sun exhibits acoustic
emission. It is believed to be an observational effect and the cause is
yet to find out. We have carried out a systematic analysis of the quiet
sun emission using 512 images. The analysis is similar to the active
region study, but the region of interest is the solar disc centre. We
found that there exists negative absoption or emission for most modes
and the negative absorption increases with the angular distance from
the centre of the sun.

---------------------------------------------------------
Title: Wavelength Dependence of Solar Irradiance Variability from
VIRGO Onboard SOHO
Authors: Wehrli, C.; Fröhlich, C.; Anklin, M.; Fligge, M.; SOlanki,
S. K.; Unruh, Y.
1997ESASP.415..497W Altcode: 1997cpsh.conf..497W
No abstract at ADS

---------------------------------------------------------
Title: Polar spots and stellar spindown: is dynamo saturation needed?
Authors: Solanki, S. K.; Motamen, S.; Keppens, R.
1997A&A...325.1039S Altcode:
Dynamo saturation is often invoked when calculating the rotational
evolution of cool stars. At rapid rotation rates a saturated
dynamo reduces the angular momentum carried away by the stellar
wind. This, in turn, may explain the high rotation rates present in
the distribution of rotation periods in young clusters. Here we point
out that concentration of magnetic flux near the poles of rapidly
rotating cool stars provides an alternative to dynamo saturation. A
high-latitude concentration of field on rapid rotators saturates
the angular momentum loss induced by the stellar wind, due to the
reduced torque arm. We show that the inclusion of this effect in
model calculations is able to reproduce the observed high rotation
rates without the need for dynamo saturation. Taken together with the
results of O'Dell et al. (1995A&amp;A...294..715O) this argues against
dynamo saturation at low rotation rates.

---------------------------------------------------------
Title: Noise reduction in astronomical spectra using wavelet packets
Authors: Fligge, M.; Solanki, S. K.
1997A&AS..124..579F Altcode:
The wavelet representation of a signal offers greater flexibility in
de-noising astronomical spectra than classical Fourier smoothing due
to the additional wavelength resolution of the decomposed signal. We
present here a new wavelet-based approach to noise reduction. It is
similar to an application of the splitting algorithm of a wavelet
packets analysis using non-orthogonal wavelets. It clearly separates
the signal from the noise, in particular also at the noise-dominated
highest frequencies. This allows a better suppression of the noise,
so that the spectrum de-noised in this manner provides a closer
approximation of the uncorrupted signal than in the case of a single
wavelet transformation or a Fourier transform. We test this method on
intensity and circularly polarized spectra of the sun and compare with
Fourier and other wavelet-based de-noising algorithms. Our technique
is found to give better results than any other tested de-noising
algorithm. It is shown to be particularly successful in recovering
weak signals that are practically drowned by the noise.

---------------------------------------------------------
Title: Influence of kink waves in solar magnetic flux tubes on
spectral lines.
Authors: Ploner, S. R. O.; Solanki, S. K.
1997A&A...325.1199P Altcode:
The kink-mode waves in solar magnetic flux tubes have been proposed
as the carriers of significant amounts of energy into the upper
atmosphere. Their observational signature, i.e. their influence
on polarized spectral lines, is investigated theoretically using a
simple MHD model and radiative transfer calculations. The results of
a large model grid are presented. The wave is found to periodically
shift, broaden, strengthen and change the asymmetry of circularly
and linearly polarized profiles (Stokes V and Q, respectively). For
most, but not all line parameters it exhibits its largest influence
close to the limb. The time fluctuations of all quantities are in
phase for Stokes Q and V, except for their amplitudes, which are in
antiphase. The signal of the wave in time-averaged profiles depends
on the wave frequency. Stokes Q and V exhibit opposite senses of the
blue-red asymmetry and wavelength shift. This behaviour is found to be
a result of the dependence on frequency of the phase relation between
velocity and flux tube inclination. As the wave frequency approaches
the cutoff frequency the phase relation changes and the time-averaged
line asymmetry and shift decrease rapidly. High frequency kink waves are
found to be an extremely efficient source of Stokes Q and V asymmetry,
while maintaining a small line shift.

---------------------------------------------------------
Title: Simulations of Zeeman-split CA II K-line Stokes profiles with
angle-dependent partial redistribution.
Authors: Bruls, J. H. M. J.; Solanki, S. K.
1997A&A...325.1179B Altcode:
The formulation of the polarized radiative transfer equations
for Zeeman-split spectral lines is still incomplete for cases
with frequency-dependent line source function, e.g. when partial
frequency distribution (PRD) of line photons occurs (strong resonance
lines). Under the well-founded assumption that the field-free
approximation works equally well for lines with partial redistribution
as for lines with complete redistribution (CRD), we decouple the
computation of the level populations (accounting for PRD effects) from
the formal Stokes vector solution. The level populations are obtained
with the Hubeny &amp; Lites (1995ApJ...455..376H) version of Carlsson's
(1986UppOR..33....1C) MULTI code, and the formal solution follows
by means of a modified version of the Murphy &amp; Rees (1990, NCAR
Technical Note NCAR/TN-348+IA) SPSR code. Due to lack of the appropriate
equations concerning the combination of partial redistribution and
Zeeman splitting of spectral lines, an ad hoc partial redistribution
approach (basically allowing for wavelength dependence of the line
source function) is implemented in the SPSR code. This combination
of codes is used to study the relevance of partial redistribution
to the Caii K-line diagnostics of solar plage regions using grids of
flux-tube models. In addition to magnetic fields, velocity fields play
an important role in the formation of the K-line profiles, but these
invalidate the commonly-used angle-averaged PRD formalism. We therefore
extended the Hubeny &amp; Lites (1995ApJ...455..376H) angle-averaged
PRD version of MULTI code to the angle-dependent case, which allows
line profiles to be computed under PRD conditions for arbitrary (but
not too large) velocity fields. This code is subsequently used to
perform the non-magnetic non-LTE statistical equilibrium computations
for a few schematic velocity structures in plage flux tubes and in the
surrounding non-magnetic atmosphere. The SPSR code is again used to
obtain the K-line Stokes profiles. We investigate in particular the
asymmetry of the K line intensity and circularly polarized profiles
produced by the velocity fields.

---------------------------------------------------------
Title: Polar spots and stellar spindown: is dynamo saturation needed?
Authors: Solanki, S. K.; Motamen, S.; Keppens, R.
1997A&A...324..943S Altcode:
Dynamo saturation is often invoked when calculating the rotational
evolution of cool stars. At rapid rotation rates a saturated
dynamo reduces the angular momentum carried away by the stellar
wind. This, in turn, may explain the high rotation rates present in
the distribution of rotation periods in young clusters. Here we point
out that concentration of magnetic flux near the poles of rapidly
rotating cool stars provides an alternative to dynamo saturation. A
high-latitude concentration of field on rapid rotators saturates
the angular momentum loss induced by the stellar wind, due to the
reduced torque arm. We show that the inclusion of this effect in
model calculations is able to reproduce the observed high rotation
rates without the need for dynamo saturation. Taken together with the
results of O'Dell et al. (1995A&amp;A...294..715O) this argues against
dynamo saturation at low rotation rates.

---------------------------------------------------------
Title: Inter-Cycle Variations of Solar Irradiance: Sunspot Areas as
a Pointer
Authors: Fligge, M.; Solanki, S. K.
1997SoPh..173..427F Altcode:
Most of the present models and reconstructions of solar irradiance
use the concept of Photometric Sunspot Index (PSI) to account for
the influence of sunspots on solar brightness. Since PSI is based on
measured sunspot areas a firm database of such areas is essential. We
show, however, that a significant disagreement exists between the
data provided by the Royal Greenwich Observatory (from 1874 to 1976)
and newer measurements provided by the observatories of Rome, Yunnan,
Catania, and the US Air Force. The overlap of the time intervals over
which sunspot areas were measured at Greenwich and Rome allows us to
quantify the difference between the Greenwich and other data sets. We
find that the various data sets differ, at least in a statistical sense,
mainly by a correction factor of between 1.15 and 1.25.

---------------------------------------------------------
Title: Center-to-limb variation of the second solar spectrum.
Authors: Stenflo, J. O.; Bianda, M.; Keller, C. U.; Solanki, S. K.
1997A&A...322..985S Altcode:
The linear polarization that is caused by scattering processes in the
solar atmosphere has been refered to as the "second solar spectrum",
since it is structurally as rich as the ordinary intensity spectrum
but quite different in appearance and information contents. One
of the most used and theoretically best understood lines in the
second solar spectrum is the SrI 4607Å line, which has served as a
diagnostic tool for determinations of spatially unresolved, turbulent
magnetic fields via the Hanle effect. Here we present the detailed
center-to-limb variation of the scattering polarization in this line
for a number of new data sets obtained both with an electrooptical
modulation system (ZIMPOL) and a non-modulating beam splitter system
(at IRSOL, Locarno), to provide improved observational constraints for
theoretical modelling. The amplitude and width of the polarization
profile, the amount of continuum polarization, as well as the depth
and width of the intensity profile have been evaluated and carefully
corrected for spectral broadening and stray light. While there is
generally good agreement between the five data sets, some systematic
differences are shown to be of solar rather than instrumental origin,
most likely due to spatially varying Hanle depolarization across the
solar disk. A number of other spectral lines have been observed with
the ZIMPOL system at two different limb distances (μ=0.1 and 0.2) to
allow us to compare the steepness of the center-to-limb variation of
their polarization amplitudes. The steepest variation is exhibited by
the continuum polarization, which declines by approximately a factor of
6 when going the 15 arcsec distance from μ=0.1 to μ=0.2. The spectral
lines with the steepest center-to-limb variation are molecular lines,
the CaII infrared triplet, and Hα. In contrast the SrI 4607 and BaII
4554Å lines have only moderately steeper center-to-limb variations
than that of an ideal, purely dipole-scattering atmosphere, for
which the polarization ratio between μ=0.1 and μ=0.2 is 1.38. These
center-to-limb variations may be used to constrain temperature-density
models of the upper photosphere and chromosphere.

---------------------------------------------------------
Title: Translimb Spectroscopy with SOHO/SUMER
Authors: Ayres, T. R.; Lemaire, P.; Schuhle, U.; Wilhelm, K.; Ruedi,
I.; Solanki, S.
1997SPD....28.0104A Altcode: 1997BAAS...29..879A
We have used SUMER to obtain deep exposures of the 1300--1400 Angstroms
spectrum, at the extreme limb and off-limb. Previous “translimb”
studies in the thermal infrared had revealed remarkable extensions
of cold material (T ~ 3000 K)---traced by carbon monoxide emission
lines---into the heart of the hot chromosphere. A main objective of
our program was to search for corresponding far-UV signatures of the
“thermally-bifurcated” low chromosphere; for example, radiatively
fluoresced emissions of the CO A--X 4th-positive system (collisional
excitation would be negligible in cold gas). We conducted two separate
observing programs with SUMER. Both made use of the 1(”) -diameter
circular aperture, translated across the limb in the minimum motor
step increments of 0.(”) 375, along the central meridian in the
Northern polar coronal hole. The first program executed for nine hours
beginning 19UT 25 Oct 1996. The full wavelength range was 1340--1400
Angstroms. It was recorded in two overlapping segments, placing key
regions of the spectrum alternately on the KBr and bare parts of
the detector, to help isolate 2nd-order features. Each segment was
integrated for 500 s, and 32 pairs were obtained to span a 12(”)
swath centered on the optical limb. The second program was conducted
00--09UT 01 Dec 1996. It consisted of a single wavelength setting
(1300--1340 Angstroms) with exposure time 500 s, but twice the spatial
coverage of the earlier series: 64 steps, for a total displacement
of 24(”) . The strong chromospheric resonance lines of atomic oxygen
(1302--1305 Angstroms) and ionized carbon (1334--1335 Angstroms) were
observed on the bare part of the MCP camera. We report our progress
in cataloging the rich, diverse translimb emission spectrum; and our
efforts to deduce fundamental properties of the thermally heterogeneous
chromosphere. [-3mm] SOHO is a project of international cooperation;
the participation of TRA was supported by NASA grant NAG5-3226.

---------------------------------------------------------
Title: Magnetic field measurements on moderately active cool dwarfs.
Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H.
1997A&A...318..429R Altcode:
We present a careful analysis of 13 high-quality optical spectra
of low to moderately active late-type dwarfs (G1-K5) aimed at
determining their magnetic parameters. Among our sample only one
star, ɛ Eri (spatially averaged field strength=~165+/-30G), exhibits
the unambiguous signature of a magnetic field, a few are candidates
and the remaining show no sign of a magnetic field in the observed
spectra. Our analysis is based on an inversion of the spectra using
detailed numerical solutions of the Unno-Rachkovsky equations, for
multiple spectral lines at different positions on the stellar disk,
and including magneto-optical effects. It gives results for ɛ Eri
which are in good agreement with the detailed analysis of infrared
spectra by Valenti et al. (1995ApJ...439..939V). However, the low
value of the spatially averaged field strength of these recent analyses
imply that most values of the magnetic flux determined previously for
moderately active stars are probably too large, often by considerable
amounts. We find that the magnetic flux can be reliably determined if
considerable care is taken in the analysis, but the magnetic field
strength and filling factor cannot be determined separately for
moderately active stars with optical spectra of spectral resolution
&lt;=10^5^ and S/N&lt;=250. In the case of ɛ Eri we are able to
constrain the temperature of the detected magnetic features, which we
find to be similar to or hotter than the non-magnetic surroundings,
providing the first direct evidence that the detected field is in the
form of plages. We also find that if an inversion approach is used,
which determines various line broadening parameters simultaneously
in a self-consistent manner, the presence of a magnetic field is not
as obvious as some previous analyses have suggested. In addition,
we determine fundamental parameters of the stellar sample.

---------------------------------------------------------
Title: Properties of Brightenings Seen in CDS Movies
Authors: Rüedi, I.; Brkovic, A.; Solanki, S. K.; Harrison, R.;
Fludra, A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
1997ESASP.404..641R Altcode: 1997cswn.conf..641R
No abstract at ADS

---------------------------------------------------------
Title: Dynamics of Flux Tubes in the Solar Atmosphere: Observations
Authors: Solanki, S. K.
1997LNP...489...49S Altcode: 1997shpp.conf...49S
Ground-based observations of the dynamics of solar magnetic flux tubes
are reviewed. First a brief overview of the range of dynamic phenomena
observed in both the largest and smallest flux tubes, i.e. in sunspots
and magnetic elements, is given. Then three such phenomena — the
Evershed effect, steady flows in small-scale magnetic features and
oscillations in such features — are selected and discussed in detail.

---------------------------------------------------------
Title: Empirical Modelling and Thermal Structure of Sunspots
Authors: Solanki, Sami K.
1997ASPC..118..178S Altcode: 1997fasp.conf..178S
An overview of empirical models of sunspot thermal structure is
presented. First a few remarks are made on empirical modelling in
general. After that the literature on the various types of models,
1- and 2-component models of the umbra and penumbra, is reviewed. The
evidence for or against the dependence of umbral temperature on various
parameters like sunspot size, magnetic field strength and phase of
the solar cycle is critically reviewed.

---------------------------------------------------------
Title: Umbral Polarimetric Measurements Using the TI I Multiplet at
2.2 MU M %The temperature gradient of a sunspot umbra
Authors: Ruedi, I.; Solanki, S. K.; Livingston, W.
1997ASPC..118..237R Altcode: 1997fasp.conf..237R
We present the first measurements of sunspot magnetic fields using the
lines of the Ti I multiplet at 2.2 mu m. These lines are most sensitive
to the plasma in the umbra. The observed line profiles suggest that
the temperature gradient in mid-photospheric layers of a sunspot
umbra is steeper than that of the standard sunspot models of Maltby
et al. (1986).

---------------------------------------------------------
Title: Velocity fields around magnetic flux tubes.
Authors: Briand, C.; Solanki, S. K.
1997joso.proc...55B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The beat of the solar chromosphere's cold heart.
Authors: Solanki, S. K.; Livingston, W.; Muglach, K.; Wallace, L.
1996A&A...315..303S Altcode:
The cold heart of the solar chromosphere is best investigated using
fundamental band lines of carbon monoxide, CO, at 4.7μm. We have
obtained time series of CO spectra in the quiet sun and in active-region
plage at the solar limb and at disk centre. In addition, we have
recorded time series in sunspot umbrae located near disk centre. The
power spectra and RMS amplitudes of the quiet-sun oscillations at
disk centre and at the limb are not compatible with a generally
hot chromosphere which is periodically cooled, but support recent
suggestions that the low chromosphere is pervasively cool, interspersed
with hot, possibly shocked material. In the plage the CO oscillations
provide indirect evidence for the expansion of hot material (probably
inside magnetic elements) with height. In umbrae the CO lines exhibit
well-separated 3min and 5min peaks. We also present spectra of the phase
shift between velocity and intensity oscillations of CO lines. At disk
centre in the quiet sun the phase shift is on the whole similar to that
seen in atomic lines formed near the classical temperature minimum,
although with some properties peculiar to CO. In plages the quality
of the phase shift is marginal, but suggests either large radiative
damping or propagating waves in the 4 mHz frequency range. Finally,
in sunspots the phase shift resembles that of atomic chromospheric
lines in some umbrae.

---------------------------------------------------------
Title: Distribution of starspots on cool stars. I. Young and main
sequence stars of 1Msun_.
Authors: Schuessler, M.; Caligari, P.; Ferriz-Mas, A.; Solanki, S. K.;
Stix, M.
1996A&A...314..503S Altcode:
Sunspots are restricted to a latitude band within 30degof the solar
equator. In contrast, the latitudes of spots on the surfaces of
rapidly rotating cool stars can range from their polar regions, for
RS CVn systems and for T Tauri stars leaving the Hayashi track, to
mid latitudes for stars close to or on the main sequence. In order to
find an explanation for these observed spot latitudes we have applied
the criteria for the undulatory instability (Parker instability) of
a toroidal magnetic flux tube embedded in the convective overshoot
layer below the outer convection zone and calculated the non-linear
evolution of the rising magnetic loops formed by this instability. We
describe the results for a star of one solar mass in different phases
of its evolution before and on the main sequence. We find that there
usually is a range of latitudes at which magnetic flux can emerge on
the stellar surface. The mean latitude of emergence shifts towards
the poles for increasingly rapid rotation. The internal structure
of the star, however, plays an almost equally important role in
determining the latitude of magnetic emergence. For stars of solar
mass only the youngest objects, with extremely deep convection zones,
should show spots emerging at the stellar poles. Pre-main sequence
stars at an age of 10^7^ y (convection zone reaching down half-way to
the centre) exhibit high latitude, but not truly polar spots, while
a main sequence star of one solar mass, even at high rotation rates,
only shows intermediate latitude spots. These results are found to be
in good agreement with Doppler images of young rapid rotators.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic
features. XII. Magnetic flux tubes: evidence of convective collapse?
Authors: Solanki, S. K.; Zufferey, D.; Lin, H.; Rueedi, I.; Kuhn, J. R.
1996A&A...310L..33S Altcode:
The magnetic field in the solar photosphere is mainly composed of
magnetic flux tubes. Their formation is not well understood, largely due
to an absence of observational tests of theoretical predictions. Here we
use infrared polarimetric data to test and confirm the prediction that
whereas the field strength of large flux tubes is almost independent
of their magnetic flux, small flux tubes show a strong dependence. Our
work thus strengthens the case for convective collapse as the source of
concentrated solar magnetic fields. We also present the first direct
measurement of the intrinsic field strength of typical intranetwork
elements. A significant fraction of them is in equipartition with the
kinetic energy of convection. Nevertheless, our results suggest that
as far as their internal structure is concerned intranetwork magnetic
features are better described by flux tubes than by turbulent fields.

---------------------------------------------------------
Title: Book Review: The Sun as a variable star ; solar and stellar
irradiance variations (IAU colloquium 143) / Cambridge U Press, 1994
Authors: Pap, J. M.; Fröhlich, C.; Hudson, H. D.; Solanki, S. K.
1996SSRv...76..354P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the detection of shocks in the solar granulation.
Authors: Solanki, S. K.; Rueedi, I.; Bianda, M.; Steffen, M.
1996A&A...308..623S Altcode:
We investigate the spectral signature of a hydrodynamic simulation of
solar granulation and compare it with high resolution observations. The
model gives the correct qualitative trend of increasing line width
with decreasing continuum intensity seen by Nesis et al. (1992)
and interpreted by them as a sign of post-shock turbulence. We find,
however, that the profiles in the dark downflow lanes are broader even
when there is no horizontal transonic flow or shock in the vicinity. We
conclude that the observations of Nesis et al. do not provide any firm
evidence for the presence of granular transonic flows. Nevertheless,
the simulation predicts a promising diagnostic of shocked horizontal
flows. We find that at the locations of the shocks the line profiles
are particularly broad, especially near the solar limb. We present
observations of quiet solar regions that show this specific signature
of shocks and thus support the theoretical prediction of transonic
granular flows.

---------------------------------------------------------
Title: Measurement of the full Stokes vector of He I 10830 Å
Authors: Rüedi, I.; Keller, C. U.; Solanki, S. K.
1996SoPh..164..265R Altcode:
First observations of the full Stokes vector in the upper chromosphere
are presented. The He I 10830 Å line, which has been shown to give
reliable measurements of the line-of-sight component of the magnetic
field vector, has been used for this purpose. It is shown that the
difference between the appearance of chromospheric and photospheric
magnetic structures observed close to the solar limb is largely
due to the difference in height to which they refer and projection
effects. The observations do suggest, however, that the magnetic field
above sunspot penumbrae is somewhat more vertical in the chromosphere
than in the photosphere.

---------------------------------------------------------
Title: The Influence of Sunspot Canopies on Magnetic Inclination
Measurements in Solar Plages
Authors: Solanki, Sami K.; Finsterle, Wolfgang; Rüedi, Isabelle
1996SoPh..164..253S Altcode:
Sunspots are known to have large, low-lying magnetic canopies,
i.e. horizontal magnetic fields overlying a field-free medium,
that cover substantial fractions of active region plage. In this
paper we consider the influence of such canopies on the inclination
of plage magnetic fields. We find that for observations in spectral
lines like 5250.2Å the neglect of a sunspot canopy when determining
magnetic inclination angles of plage fields can introduce errors
exceeding 5-10°. This is particularly true if the observations
do not have high spatial resolution. Thus this effect may explain
some of the measurements of substantially inclined fields in solar
plages. Furthermore we find that the Fe I 15648 Å line is far superior
in giving correct flux-tube inclinations in the presence of a sunspot
magnetic canopy. Finally, the inversion of full Stokes profiles is shown
to produce more reliable results than results obtained by considering
only ratios of individual Stokes profile parameters.

---------------------------------------------------------
Title: Inversion of Stokes Vector Profiles in Terms of a 3-Component
Model
Authors: Bernasconi, P. N.; Solanki, S. K.
1996SoPh..164..277B Altcode:
Various spectropolarimetric observations show peculiar Stokes profiles
that reveal the coexistence of at least two magnetic components in
the same resolution element. An example is given by observations of
the full Stokes vector in a complex active region performed with the
ZIMPOL I Stokes polarimeter. In order to deduce the physical parameters
of the observed regions from such measured profiles, we have extended
an existing inversion code, so that it can now fit the data with models
composed of up to three different atmospheric components. Two of these
components are magnetic and may possess different field strengths,
field geometries, temperature stratifications, and velocity fields. The
third component describes the field free atmosphere surrounding the
magnetic features.

---------------------------------------------------------
Title: Flux Tube Dynamics in Active Stars
Authors: Caligari, P.; Schüssler, M.; Solanki, S. K.; Schaerer, D.;
Stix, M.
1996ApL&C..34...17C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: New constraints on gravity-induced birefringence
Authors: Solanki, Sami K.; Haugan, Mark P.
1996PhRvD..53..997S Altcode:
A wide class of gravitation theories predicts gravity-induced
birefringence. For Moffat's NGT, the prototypical theory of this type,
Gabriel, Haugan, Mann, and Palmer used the predicted gravitational
birefringence and observations of solar polarization to constrain
the Sun's nonsymmetric charge lsolar. We improve on this
constraint by making use of improved knowledge of the solar source
of polarization and of a refined analysis procedure. We obtain
l2solar&lt; (305 km)2.

---------------------------------------------------------
Title: PRD vs. CRD CaII K Stokes profiles from solar plage
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Uitenbroek, H.
1996ASPC..109..113B Altcode: 1996csss....9..113B
No abstract at ADS

---------------------------------------------------------
Title: Solar and stellar magnetic flux tubes (review)
Authors: Solanki, S. K.
1996IAUS..176..201S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observing stellar surface structure with the ESO-VLT
interferometer
Authors: von der Luhe, O.; Solanki, S.; Reinheimer, Th.
1996IAUS..176..147V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Interesting lines in the infrared solar spectrum. III. A
polarimetric survey between 1.05 and 2.50 μm.
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W.; Harvey, J.
1995A&AS..113...91R Altcode:
We present a survey of Stokes I, V and Q in the near infrared
spectral range between 1.05 and 2.50μm, based on Fourier transform
spectrometer data obtained in a sunspot umbra and in an active region
plage. We discuss the diagnostic potential of a number of lines for
studying solar magnetic features. These include the Ti I multiplet near
22000A, the Fe I g=3 line at 15648.5A, He I 10830A, high excitation C I
lines, as well as CO and CN lines. As an example, we provide the first
estimate of the field strength gradient averaged over the height range
covered by the photosphere and chromosphere. We also identify lines
that show large Stokes V or Q amplitudes and analyze their profile
asymmetries. In our J-band plage spectrum the Stokes V and Q profiles
show an extremely large blue-red asymmetry, whose origin is not yet
clear. As an incidental result we obtain the first measured value of the
vertical gradient of the magnetic field strength in a plage. Averaged
over approximately 1500-2000km it corresponds to roughly 0.6G/km.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic
features. XI. Structure of a sunspot umbra with a light bridge.
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W.
1995A&A...302..543R Altcode:
We investigate the magnetic structure of an umbra and the light bridge
it contains using spectra at 1.56μm. The magnetic field strength in
the umbra reaches over 3500G on the first day of observation and 3200G
on the second and third days, while the field strength in the light
bridge is reduced by 1000-1400G relative to the nearby umbra. The
magnetic vector is also found to be much more horizontal in the light
bridge. There is evidence that the boundary between the strong and
weak magnetic field is less than 1" wide, implying the presence of
large currents there. At some locations a downflow of up to 1.5km/s is
seen in the light bridge relative to the umbral material. Finally, we
discuss the blending of the 1.5648μm line in sunspots and develop the
depth of the OH 15650.7A line as a diagnostic of umbral temperatures.

---------------------------------------------------------
Title: Interesting lines in the infrared solar spectrum. II. Unblended
lines between λ1.0 and λ1.8 μm.
Authors: Ramsauer, J.; Solanki, S. K.; Biemont, E.
1995A&AS..113...71R Altcode:
We list 603 spectral lines between 1.0 and 1.8μm that are judged
to be relatively unblended from a visual inspection of spectra of
the quiet sun. Much of the atomic data of relevance to studies of
solar and stellar magnetism, convection and atmospheric structure are
also provided. Particular attention is paid to blending by telluric
lines. We determine the level of blending both in the presence and
the absence of telluric lines. We also describe how telluric blends
may be removed from spectra with high spectral resolution.

---------------------------------------------------------
Title: Book Review: Planetary systems : formation, evolution and
detection / Kluwer, 1994
Authors: Solanki, S. K.; Švestka, Zdeněk; Svestka, Z.
1995SoPh..159..403S Altcode: 1995SoPh..159..403B
No abstract at ADS

---------------------------------------------------------
Title: Empirical models of solar magnetic elements: constraints
imposed by MgI Stokes profiles.
Authors: Briand, C.; Solanki, S. K.
1995A&A...299..596B Altcode:
Although the temperature structure of small-scale magnetic features
in the lower and middle photosphere has been constrained quite well,
there are still considerable uncertainties in the upper photospheric
and lower chromospheric thermal structure. As a step towards an
improvement of this situation we investigate, using a non-LTE analysis,
the diagnostic capabilities of the Stokes I and V profiles of the Mg
I b_2_ 517.3nm and the Mg I 457.1nm lines. We find that the V profile
of the former line can constrain the magnetic element thermal and
velocity structure near the temperature minimum, which goes beyond
the capabilities of the commonly used Fe I and II lines. The λ457.1nm
line, on the other hand, does not provide any additional information
on its own. A comparison of synthetic profiles with plage and network
Stokes I and V spectra confirms the findings of Bruls &amp; Solanki
(???) that the chromospheric temperature rise starts at a substantially
lower height in magnetic elements than in the quiet Sun. Some of the
ambiguities in previous empirical models of magnetic elements are also
removed. We confirm that small-scale magnetic features are associated
with larger line broadening velocities than the quiet Sun, particularly
in the higher layers. Finally, the Mg I b_2_ line is revealed to be
a direct diagnostic of the merging height of magnetic elements.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Lines in the infrared solar
spectrum (Ramsauer+, 1995)
Authors: Ramsauer, J.; Solanki, S. K.; Biemont, E.
1995yCat..41130071R Altcode:
We list 603 spectral lines between 1.0, 1.8um that are judged to
be relatively unblended from a visual inspection of spectra of the
quiet sun. Much of the atomic data of relevance to studies of solar
and stellar magnetism, convection and atmospheric structure are also
provided. Particular attention is paid to blending by telluric lines. We
determine the level of blending both in the presence and the absence
of telluric lines. We also describe how telluric blends may be removed
from spectra with high spectral resolution. (4 data files).

---------------------------------------------------------
Title: The Evershed effect: rise and fall of the wave model.
Authors: Buente, M.; Solanki, S. K.
1995A&A...297..861B Altcode:
Adiabatic surface and trapped body waves have recently been proposed
as the source of the Evershed effect. We show that such waves fail to
simultaneously reproduce the main features of the Evershed effect in a
set of spectral lines with different temperature sensitivities. This
result sets constraints on all models that attempt to explain the
Evershed effect on the basis of a wave-like correlation between
temperature and velocity. In the photospheric layers in which
the waves are expected to propagate, dissipative effects due to
radiative diffusion are likely to damp the wave-induced temperature
perturbations. We show, however, that in the line forming penumbral
layers radiatively damped ("isothermal") waves shift spectral lines of
neutral and ionized species in opposite directions. We conclude that,
in spite of a number of highly attractive features, linear wave models
have great difficulty in explaining the Evershed effect.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. IX. MgI
12μm diagnostics of solar plage.
Authors: Bruls, J. H. M. J.; Solanki, S. K.
1995A&A...293..240B Altcode:
The MgI 12.32μm line is a prime diagnostic for studying upper
photospheric magnetic fields on the Sun. We study for the first time
its behavior using flux-tube models with magnetic field strengths and
filling factors characteristic of solar plage in order to establish
the line's capabilities for measuring plage magnetic fields. We
show that this line is only moderately sensitive to the range of
temperatures expected for solar plages, including the chromospheric
temperature rise. This low sensitivity considerably enhances this line
as a magnetic field diagnostic for the upper photosphere of plages. We
find that besides being highly sensitive to the field strength in flux
tubes, the shape and Zeeman splitting of this line are almost equally
sensitive to the magnetic filling factor at the flux-tube base. This
combined sensitivity leads to the large range of profile shapes observed
in plages. Not only can the 12μm emission lines be used to determine
the sub-spatial-resolution distribution of flux-tube field strengths,
but also the sub-spatial-resolution distribution of filling factors
(i.e. they can provide an estimate of the "clumpiness" of the flux-tube
distribution on a small scale). We also provide evidence that simple
two-component modeling of magnetic flux tubes, without taking into
account the height-dependence of the flux-tube size, may lead to
erroneous conclusions in the case of the MgI 12μm lines, and that at
least 1.5-D computations are required to adequately model these lines
in magnetic flux tubes. Computations also show that standard flux-tube
models simultaneously reproduce the observed splitting of the g=3 FeI
lines at 1.5648μm (formed in the low photosphere) and at 525.02nm
(middle photosphere), as well as of the 12.32μm emission line (upper
photosphere). Our computations thus support the currently standard
view that solar plages are composed of flux tubes with kGauss fields
in the lower and mid photosphere, and that the thin-tube approximation
is an adequate representation of the magnetic stratification in these
flux tubes.

---------------------------------------------------------
Title: FTS Polarimetric Survey of the Infrared Solar Spectrum Between
1.0 and 2.5 MU M
Authors: Ruedi, I.; Solanki, S. K.; Livingston, W.; Harvey, J.
1995ASPC...81..107R Altcode: 1995lahr.conf..107R
No abstract at ADS

---------------------------------------------------------
Title: Oscillations in Active Plage Regions as Observed in 1.56
Micron Lines
Authors: Muglach, K.; Solanki, S. K.; Livingston, W. C.
1995itsa.conf..387M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. VIII. MgI
12μm diagnostics of sunspots.
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson,
M.
1995A&A...293..225B Altcode:
Due to their large Zeeman sensitivity, the MgI lines at 12μm are
important diagnostics of solar magnetism. The formation of their
central emission features is now understood, enabling quantitative
modeling and diagnostic application of these lines. We supply the
first systematic analysis of solar MgI 12μm Stokes profiles employing
detailed line-profile synthesis. We compute Stokes profiles of MgI
12.32μm for the quiet Sun, for sunspot penumbrae and for the extended
("superpenumbral") magnetic canopies surrounding sunspots. We use these
computations to analyze recent MgI 12μm observations by Hewagama
et al. (1993). Our results are the following: (1) -Saha-Boltzmann
temperature sensitivity explains that the emission peaks are stronger in
penumbrae than in the quiet Sun, and that they disappear in umbrae. (2)
-The formation heights of the emission features are approximately the
same in penumbrae and in the quiet Sun, namely τ_500_=~10^-3^. (3)
-The simple Seares formula allows relatively accurate determinations
of field strength and magnetic inclination. (4) -The observed excess
broadening of the σ-component peaks compared with the π component
in penumbrae is well explained by primarily horizontal, smooth radial
variation of the magnetic field strength. Additional small-scale
variations are less than {DELTA}B =~200G. (5) -The vertical field
gradients dB/dz in penumbrae range from 0.7G/km to 3G/km; the larger
gradients occur near the umbra, the smaller ones near the outer edge of
the penumbra. (6) -The MgI 12μm lines are well-suited to measure the
base heights of superpenumbral magnetic canopies. These heights range
between 300km and 500km above τ_500_=1 out to twice the sunspot radius,
in excellent agreement with determinations from other infrared lines.

---------------------------------------------------------
Title: Solar line bisectors in the infrared
Authors: Puschmann, K.; Hanslmeier, A.; Solanki, S. K.
1995IAUS..176P.117P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Observation of Surface Activity on Cool Giants with the VLT
Interferometer
Authors: von der Lühe, O.; Schüssler, M.; Solanki, S. K.; Caligari,
P.
1995svlt.conf...94V Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Field Measurements in the Infrared
Authors: Solanki, S. K.
1995itsa.conf..341S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. X. HeI
10830A as a diagnostic of chromospheric magnetic fields.
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W. C.
1995A&A...293..252R Altcode:
The need for a simple but quantitative diagnostic of upper chromospheric
magnetic fields is keenly felt. We develop the HeI 10830A line as such a
diagnostic. An application to observations of an active region allows us
to compare the magnetic field in the upper chromosphere with the field
in the underlying photosphere. In general, the magnetic field in the
chromosphere is found to be significantly more homogeneous. We find that
dB/dz in the umbra of a large sunspot (0.4-0.6G/km) is similar to other
determinations of this quantity over an equivalent height range. Also,
dB/dz decreases outwards in the spot. Thus, in the outer penumbra it
has dropped to 0.1-0.3 G/km. A comparison of these values with the
results of dB/dz measurements in the photosphere suggests that dB/dz
decreases with height. We also find evidence for magnetic canopies near
sunspots and for the conservation of magnetic flux with height in solar
plages when averaged horizontally over a few arc s. Observations of
complex Stokes V profiles at the neutral line in a sunspot penumbra
(crossover effect) suggest that the upper chromospheric penumbral
magnetic field is not fluted to the same extent as the photospheric
field. The large line broadening of He I (up to 10km/s) is found to
be due to motions which are largely field aligned.

---------------------------------------------------------
Title: Magnetic flux observed over entire solar disk
Authors: Livingston, Willam; Solanki, Sami
1994AAS...18512306L Altcode: 1994BAAS...26.1523L
A single channel Babock-type magnetograph, using the favorable Fe
1.5648 microns (g=3) line, reveals fields everywhere from equator to
the polar limb. Good seeing is essential. Experimental setup includes
a 2.5 arcsec image slicer as the input, the NIM modulator driven at
20Hz, and an exit slit of 0.20 Angstroms. Noise is 5 (10(-3) ) percent
polarization with a time constant of 3 sec and is negligible. Presumably
we mainly sense the intranetwork fields in agreement with S. Martin
(1988). New results are that the fields (flux) may strengthen near the
limb and that the best signal is obtained at line center. The latter
could indicate unresolved doppler shifts or the transverse Zeeman
effect. (Both circular and linear polarized light is detected by the
modulator). Field strength will be deduced by a statistical analysis
of signal vs. position on the line profile.

---------------------------------------------------------
Title: New contribution functions for Zeeman split spectral lines
Authors: Solanki, S. K.; Bruls, J. H. M. J.
1994A&A...286..269S Altcode:
The recently introduced emergent line radiation contribution function
(Achmad + de Jager + Nieuwenhuijzen 1991; Gurtovenko + Sheminova +
Sarychev 1991) is extended to the Stokes vector of Zeeman split spectral
lines. This contribution function is compared to the line depresssion
contribution function on the basis of an analytical relation and of
numerical NLTE computations of a set of spectral lines. In general the
two contribution functions give very similar results, although in some
cases the one or the other of them is more suitable.

---------------------------------------------------------
Title: The deep layers of solar magnetic elements
Authors: Grossmann-Doerth, U.; Knoelker, M.; Schuessler, M.; Solanki,
S. K.
1994A&A...285..648G Altcode:
We compare self-consistent theoretical models of solar magnetic
flux sheets with spectropolarimetric observations of a solar plage
and a network region. Our observational diagnostics mainly provide
information on temperature and magnetic field of the deep photospheric
layers. They are used to constrain the two free parameters of the
models, viz. width and initial evacuation of the flux sheets. We find
that the width of flux sheets in the network is approximately 200 km,
while it is 300-350 km in an active plage. The flux sheets turn out
to be less evacuated than previously thought, so they have continuum
intensities close to unity. Since these are average values, however,
our results do not exclude the presence of either smaller and brighter
or larger and darker magnetic structures.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. 7:
On the nature of the Evershed effect in sunspots
Authors: Solanki, S. K.; Montavon, C. A. P.; Livingston, W.
1994A&A...283..221S Altcode:
Stokes I and V profiles of 1.56 micron lines are observed in sunspots
and their surroundings near the solar limb. An analysis of these
observations confirms that the magnetic field of the sunspots continues
beyond their visible boundaries in the form of an extensive, low-lying
(supernumbral) canopy. We also find that the V profiles, which are
only formed above the canopy base, exhibit the Evershed effect with
line shifts of 0.5-2 km/s, while the non-magnetic material below the
canopy is at rest. The deduced geometry of the flow outside the sunspot
suggests a resolution of the long standing dispute about the existence
or not of an Evershed flow outside the visible sunspot. In addition,
the low density of the gas above the canopy base implies that the mass
flux in the magnetic canopy is much smaller (approximately equals 10%)
than the mass flux in the penumbra, where the 1.5 micron lines exhibit
wavelength shifts of approximately 4 km/s. The present observations
cast doubt on the standard interpretation of the photospheric Evershed
effect in terms of a steady flow, in particular if it is driven by
the siphon-flow mechanism.

---------------------------------------------------------
Title: 1.5 MU M Observations the Depth of Sunspot Penumbrae
Authors: Solanki, S. K.; Ruedi, I.; Livingston, W.; Schmidt, H. U.
1994IAUS..154..471S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Field Strength and Filling Factor Sensitivity of
the MgI 12 MU M Infrared Lines in Solar Plage
Authors: Bruls, J. H. M. J.; Solanki, S. K.
1994ASPC...68..294B Altcode: 1994sare.conf..294B
No abstract at ADS

---------------------------------------------------------
Title: Flux Tube Shredding Its Infrared Signature
Authors: Bunte, M.; Steiner, O.; Solanki, S. K.; Pizzo, V. J.
1994IAUS..154..459B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Are Magnetic Features on epsilon ERI Cold or Hot?
Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H.
1994ASPC...64..465R Altcode: 1994csss....8..465R
We analyse high-quality spectra of epsilon Eri with the aim of
determining its magnetic and thermal parameters. From a careful analysis
we conclude that it is not possible to separate the field strength
and filling factor of this star based on data obtained in the visible
spectral range. The data do suggest, however, that the magnetic field
of the star is concentrated in cool, starspot-like structures.

---------------------------------------------------------
Title: How Accurate Are Stellar Magnetic Field
Measurements? II. Analysis of Disk-Integrated Flux Tube Models
Authors: Saar, S. H.; Buente, M.; Solanki, S. K.
1994ASPC...64..474S Altcode: 1994csss....8..474S
We analyze disk-integrated line profiles generated in atmospheres
embedded with fluxtubes to test the accuracy of simple radiative
transfer (RT) analyses in determining stellar magnetic parameters.

---------------------------------------------------------
Title: Distribution of Magnetic Flux on the Surface of Rapidly
Rotating Stars
Authors: Caligari, P.; Schussler, M.; Stix, M.; Solanki, S. K.
1994ASPC...64..387C Altcode: 1994csss....8..387C
No abstract at ADS

---------------------------------------------------------
Title: New Light on the Heart of Darkness of the Solar Chromosphere
Authors: Solanki, S. K.; Livingston, W.; Ayres, T.
1994Sci...263...64S Altcode:
Solar carbon monoxide spectra indicate the existence of a cool (less
than 4000 kelvin) component to the solar chromosphere coexisting with
the hot, bright gas at 6000 to 7000 kelvin. However, both the existence
and the location of the cool component have been controversial. New
high-resolution spectra show that carbon monoxide goes into emission
just beyond the limb, allowing it to be probed without photospheric
contamination. The cool component has temperatures as low as 3000 to
3500 kelvin and appears to cover 50 to 85 percent of the quiet solar
surface. There is a steep temperature rise to normal chromospheric
temperatures at a height of 900 to 1100 kilometers. Large horizontal
velocities are seen, suggesting that the cool component is maintained
by the supersonic adiabatic expansion of upwelling gas in overshooting
granules.

---------------------------------------------------------
Title: Some consequences of an uncombed and inhomogeneous penumbra
Authors: Solanki, S. K.; Montavon, C. A. P.
1994ASIC..433..239S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Preliminary properties of pores derived from 1.56 micron lines
Authors: Muglach, K.; Solanki, S. K.; Livingston, W. C.
1994ASIC..433..127M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Poster Proceedings from IAU Colloquium 143: The Sun as a
Variable Star: Solar and Stellar Irradiance Variations
Authors: Pap, J. M.; Frohlich, C.; Hudson, H. S.; Solanki, S. K.
1994svsp.coll.....P Altcode: 1994IAUCo.143P....P
No abstract at ADS

---------------------------------------------------------
Title: The upper photosphere and lower chromosphere of small-scale
magnetic features
Authors: Solanki, S. K.; Bruls, J. H. M. J.; Steiner, O.; Ayres, T.;
Livingston, W.; Uitenbroek, H.
1994ASIC..433...91S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Properties of Magnetic Features from the Analysis of
Near-Infrared Spectral Lines
Authors: Solanki, S. K.
1994IAUS..154..393S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Must the Magnetic Field Saturate on Rapidly Rotating Stars?
Authors: Solanki, S. K.
1994ASPC...64..477S Altcode: 1994csss....8..477S
No abstract at ADS

---------------------------------------------------------
Title: Solar Magnetic Elements: Models Compared with Observations
Authors: Grossmann-Doerth, U.; Knolker, M.; Schussler, M.; Solanki,
S. K.
1994ASPC...68...96G Altcode: 1994sare.conf...96G
No abstract at ADS

---------------------------------------------------------
Title: Solar line bisectors in the infrared.
Authors: Puschmann, K.; Anslmeier, A.; Solanki, S.
1994AGAb...10..117P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On the nature of the Evershed effect
Authors: Solanki, S. K.; Montavon, C. A. P.; Livingston, W.
1994smf..conf..173S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic fields in the upper chromosphere: He I 10830 Å as
an almost ideal diagnostic
Authors: Rüedi, I.; Solanki, S. K.; Livingston, W. C.
1994smf..conf..363R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Flux tube dynamics in pre-main-sequence and giant stars.
Authors: Caligari, P.; Schaerer, D.; Schüssler, M.; Solanki, S.
1994AGAb...10...92C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: MgI 12 μm diagnostics of sunspot penumbrae
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson,
M.
1994smf..conf..191B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Irradiance Effects of Small-Scale Magnetic Fields on the Sun
Authors: Solanki, S. K.
1994svsp.coll..226S Altcode: 1994IAUCo.143P.226S
No abstract at ADS

---------------------------------------------------------
Title: Surface waves: Origin of the Evershed phenomenon?
Authors: Bünte, M.; Solanki, S. K.
1994smf..conf..179B Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A Search for Sunspot Canopies Using a Vector Magnetograph
Authors: Adams, M.; Solanki, S. K.; Hagyard, M.; Moore, R. L.
1993SoPh..148..201A Altcode:
Using a magnetograph, we examine four sunspots for evidence of a
magnetic canopy at the penumbra/photosphere boundary. The penumbral
edge is determined from the photometric intensity and is defined
to correspond to the value of the average intensity minus twice the
standard deviation from the average. From a comparison of the location
of this boundary with the location of contours of the vertical and
horizontal components of the magnetic field, we conclude that the
data are best represented by canopy-type fields close to all four
sunspots. There is some evidence that the magnetic inclination in the
canopies is 5°-15° with respect to the horizontal and that the canopy
base height lies in the middle/upper photosphere. The observations
further suggest that the magnetic canopy of a sunspot begins at its
outer penumbral boundary.

---------------------------------------------------------
Title: Evidence for siphon flows with shocks in solar magnetic
flux tubes
Authors: Degenhardt, D.; Solanki, S. K.; Montesinos, B.; Thomas, J. H.
1993A&A...279L..29D Altcode:
We synthesize profiles of the infrared line Fe I 15648.5 A (g = 3) for a
recently developed theoretical model of siphon flows along photospheric
magnetic loops. The synthesized line profiles are compared with the
observations from which Rueedi et al. (1992) deduced the presence of
such flows across the neutral line of an active region plage. This
comparison supports the interpretation of Rueedi et al. (1992). It
also suggests that the average footpoint separation of the observed
loops carrying the siphon flow is 8-15 sec and that the siphon flow
experiences a standing tube shock in the downstream leg near the top
of the arch.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. VI. The
thermal-magnetic relation and Wilson depression of a simple sunspot
Authors: Solanki, S. K.; Walther, U.; Livingston, W.
1993A&A...277..639S Altcode:
We analyse the relationship between the temperature and the magnetic
vector, as derived from 1.56 μm spectra, in a simple sunspot. Due to
the high Zeeman sensitivity of the = 3, 1.56 μm line, we can study this
relationship throughout the sunspot. We confirm the field-strength, B,
vs. temperature, T, relationship found by Kopp &amp; Rabin (1992). In
addition, we also find a linear relation between the magnetic
inclination angle, γ‧, and T. An analysis based on the assumption
of magnetohydrostatic force balance gives an estimate of the Wilson
depression, ZW, throughout the sunspot. Our analysis supports
a jump in ZW of 200-500 km at the umbral boundary and agrees
with a relatively constant ZW in the penumbra. In addition,
we constrain various gradients of magnetic parameters and judge the
strength of magnetic curvature forces. For example, we set tight limits
on the vertical gradient of γ‧, the magnetic inclination angle to
the vertical, in the penumbra. Finally, we discuss the consequences
for, e.g., the model proposed by Sanchez Almeida &amp; Lites (1992)
to explain the broad-band circular polarization measured in sunspots.

---------------------------------------------------------
Title: Uncombed fields as the source of the broad-band circular
polarization of sunspots.
Authors: Solanki, S. K.; Montavon, C. A. P.
1993A&A...275..283S Altcode:
We investigate the production of broad-band circular polarization (BBC)
of sunspots using a model inspired by the discovery of small-scale
variations of magnetic inclination in sunspot penumbrae. The proposed
model is a simple representation of a horizontal magnetic flux tube
embedded in an inclined magnetic field, with a flow in either one
or both components (Evershed flow). This model is shown to produce a
sizable BBC without requiring substantial net vertical gradients of the
magnetic vector. It reproduces the BBC observations in a qualitatively
correct and quantitatively acceptable manner for reasonable values of
its free parameters. In addition, our model also explains the crossover
effect observed in sunspot penumbrae. The fits to the observations
support the presence of a larger velocity in the horizontal magnetic
filaments than in the inclined field. We point out that the BBC is
complementary to high resolution images in that it diagnoses the
height variation of the small-scale structure of sunspot magnetic
fields. By combining the results from both techniques we outline the
3-D fine-scale structure of the magnetic field in the photospheric
layers of sunspot penumbrae. The most important result is that the
two differently inclined components of the field do not simply form
vertical sheets, but rather must have a horizontal interface near the
level of line formation.

---------------------------------------------------------
Title: Surface waves as the origin of the Evershed phenomenon
Authors: Bunte, M.; Darconza, G.; Solanki, S. K.
1993A&A...274..478B Altcode:
We investigate the spectral signature of magnetoacoustic-gravity surface
waves (MAGS-waves), which we expect to exist at the interface between
the lower boundary of the magnetic field of the sunspot penumbra and
the non-magnetic gas below. MAGS-waves have a number of properties
that make them attractive candidates for explaining the photo spheric
Evershed effect: 1. Since they transport only energy but no mass,
they resolve the problem of mass conservation at the outer penumbral
boundary. 2. Since they are restricted to magnetic interfaces, they
are only (or dominantly) present in the penumbra and absent in the
umbra. 3. The phase relation between the temperature, the horizontal,
and vertical velocity perturbations leads to line shifts and asymmetries
in observations at the limb, but none at disc centre. 4. The amplitude
of the velocity perturbation drops approximately exponentially with
height, in good agreement with observations. 5. Waves travelling in
opposite directions with respect to the observer produce oppositely
directed line shifts and asymmetries, making it straightforward to
explain the opposite shifts and asymmetries observed in the limb-side
and centre-side penumbra.

---------------------------------------------------------
Title: The chromospheric temperature rise in solar magnetic flux tubes
Authors: Bruls, J. H. M. J.; Solanki, S. K.
1993A&A...273..293B Altcode:
We set constraints on the location and steepness of the chromospheric
temperature rise in solar magnetic flux tubes by synthesizing Stokes
V profiles in non-local thermodynamic equilibrium (NLTE) of a set of
"clean" Fe I and Fe II lines of different strengths. We compute profiles
for several flux-tube models of the magnetic features within solar
network and plage. Comparison with observed V profiles indicates that
both in network and plage the chromospheric temperature rise starts
at larger optical depth within the flux tubes than in the surrounding
non-magnetic atmosphere. The exact onset cannot be determined with the
present set of lines because they cannot easily distinguish between
the location and initial steepness of the temperature rise. Assuming
a similar T(τ) gradient as in quiet-Sun models, the chromosphere
sets in 200 - 300 km deeper in flux tubes than in the quiet Sun. The
similarity between the plage and network results suggests that in the
low chromosphere the heating per flux tube is almost independent of
magnetic filling factor.

---------------------------------------------------------
Title: Smallscale Solar Magnetic Fields - an Overview
Authors: Solanki, Sami K.
1993SSRv...63....1S Altcode:
An overview is given of the observational and the theoretical
methods used to investigate solar magnetic fields. It includes an
introduction to the Stokes parameters, their radiative transfer in the
presence of a magnetic field, and empirical techniques used to measure
various properties of solar magnetic features, such as the strength
and direction of the magnetic field, magnetic flux, temperature,
velocity, size and lifetime. The MHD equations are introduced and
some of the most common simplifications used to describe solar
magnetic features are outlined. The application of these techniques
to small-scale magnetic features is surveyed. The results of empirical
and theoretical investigations of small-scale solar magnetic features
are reviewed. Current views on their magnetic structure, thermal
stratification, velocity field, size, distribution and evolution are
presented. Finally, some open questions concerning small-scale solar
magnetic fields are listed.

---------------------------------------------------------
Title: Centre-to-limb variation of the Stokes V asymmetry in solar
magnetic flux tubes
Authors: Buente, M.; Solanki, S. K.; Steiner, O.
1993A&A...268..736B Altcode:
The center-to-limb variation (CLV) of synthetic Stokes V line
profiles of the spectral lines Fe 15250.22 A and Fe I 5083.35 A is
computed and compared with observations. The basic elements of the
hydromagnetic model used to calculate the Stokes V profiles consist
of a vertical cylindrical flux tube surrounded by a field-free plasma
in stationary motion with a downflow along the tube boundary and
an upflow further away from it. It is shown that an array of such
magnetic flux tubes reproduces the peculiar observed CLV of the Stokes
V asymmetry, in particular the sign reversal of the asymmetry near the
limb. We determine a minimum number of model components needed for the
reproduction of the Stokes V area asymmetry and study the influence of
various free model parameters on it. Satisfactory agreement between
synthetic and observed Stokes V profiles can only be achieved by
including a considerable amount of realism into the model such as
a granular temperature-velocity correlation. This suggests that the
basic picture of magnetic structures in the quiet solar network and
active region plages is correct.

---------------------------------------------------------
Title: Field Strength vs. Temperature Relation and the Structure
of Sunspots
Authors: Solanki, S. K.; Walther, U.; Livingston, W.
1993ASPC...46...48S Altcode: 1993IAUCo.141...48S; 1993mvfs.conf...48S
No abstract at ADS

---------------------------------------------------------
Title: Siphon Flow Across the Magnetic Neutral-Line of an Active
Region
Authors: Solanki, S. K.; Ruedi, I.; Rabin, D.
1993ASPC...46..534S Altcode: 1993IAUCo.141..534S; 1993mvfs.conf..534S
No abstract at ADS

---------------------------------------------------------
Title: Are sunspot penumbrae deep or shallow?
Authors: Solanki, S. K.; Schmidt, H. U.
1993A&A...267..287S Altcode:
From the strength and inclination of the magnetic field measured
across large symmetric sunspots, we estimate the fraction of the
total magnetic flux of the sunspot passing through the solar surface
in the penumbra. It is found that on average approximately 1/2-2/3 of
the total magnetic flux of the spot emerges in its penumbra. Sunspot
penumbrae are therefore deep, i.e. the tau = 1 level does not correspond
to the lower magnetic boundary of the spot in its penumbra (except
perhaps near its outer edge). Furthermore, the analyzed data do not
support the passage of any significant amount of magnetic flux through
the solar surface (in either direction) at or beyond the edge of the
sunspot. The observations support models of the sunspot magnetic field
which are bounded by a relatively sharp current sheet. Evidence for a
substantial deviation from a potential field in the penumbra is found
in the analyzed symmetric sunspots. Finally, at the height of line
formation the field strength averaged over the whole umbra of all the
analyzed sunspots is approximately 2250 G, while the field strength
averaged over the whole sunspot is roughly 1350 G. The latter value is
similar to the field strength measured in small-scale magnetic features.

---------------------------------------------------------
Title: Evershed Effect in Sunspots and Their Canopies
Authors: Solanki, S. K.; Montavon, C.; Livingston, W.
1993ASPC...46...52S Altcode: 1993IAUCo.141...52S; 1993mvfs.conf...52S
No abstract at ADS

---------------------------------------------------------
Title: Why rapid rotators have polar spots.
Authors: Schuessler, M.; Solanki, S. K.
1992A&A...264L..13S Altcode:
Starspots on magnetically active, cool stars preferentially appear near
the poles. We suggest that this preference of high latitudes is due
to the rapid rotation to these stars which leads to a dominance of the
Coriolis force over the buoyancy force in the dynamics of magnetic flux
tubes. As a consequence, flux tubes erupting from the deep parts of the
stellar convection zone follow a path nearly parallel to the axis of
rotation and thus necessarily surface at high latitudes, unless their
initial field strength exceeds a critical value for which buoyancy
becomes dominant again. It is shown that for stars with rotation
periods below about 10 days flux tubes with such large field strength
(of the order of 10 exp 6 G) cannot be formed and stored since they are
unstable with respect to non-axisymmetric disturbances. Consequently,
magnetically active stars with rapid rotation exhibit magnetic flux
eruption at high latitudes and polar starspots.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. V -
The magnetic structure of a simple sunspot and its canopy
Authors: Solanki, S. K.; Rueedi, I.; Livingston, W.
1992A&A...263..339S Altcode:
The Zeeman Lande g = 3 Fe I line at 15648 A is used here to determine
the strength and inclination of the magnetic field of a simple,
relatively symmetric sunspot. The largest field strength observed in
the sunspot is approximately 3100 G. The field strength at different
points along the outer penumbral edge varies beween 800 and 1000 G. The
angle of inclination at the outer penumbral boundary is close to 80
deg. A low-lying, almost horizontal superpenumbral magnetic canopy best
reproduces the observations. The magnetic field strength in the canopy
is consistent with a magnetic monopole. Evidence of small magnetic
elements underlying the superpenumbral canopy is presented.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. I -
A many-line analysis of a network region
Authors: Muglach, K.; Solanki, S. K.
1992A&A...263..301M Altcode:
The results are presented of an analysis of a Fourier transform
spectrometer Stokes I and V spectrum in the H band of a solar network
region. From a many-line statistical analysis of the measured Stokes F
profiles, it is concluded that there is no evidence for s systematic
up or downflow greater than 200-300 m/s within the magnetic element
of the observed region. The Stokes V profiles in the H band show
a blue-red asymmetry having the same sign as in the visible, but
a smaller magnitude. The lines with g(eff) greater than about 1.5
are more or less completely Zeeman split in the observed region, and
only lines with g(eff) values well below unity can be considered to
be in the weak-field regime. An analysis based on radiative transfer
calculations of 16 selected spectral lines in a flux tube model shows
that a thin tube with a field strength of 2050 G at tau (1.6) = 1 ,
corresponding to 1500 G at z = 0, fits the profiles best.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. II -
Diagnostic capabilities of Fe I 15648.5 A and 15652.9 A
Authors: Solanki, S. K.; Rueedi, I. K.; Livingston, W.
1992A&A...263..312S Altcode:
The properties of two Fe I lines at 15648.5 A and 15652.9 A in the
infrared H-band are investigated using numerical radiative transfer
calculations. It is shown that using this combination of a Lande g = 3
and a g(eff) = 1.53 line it is possible to measure the field strength in
solar magnetic features simply and with great accuracy. The g = 3 line
alone allows field strengths as low as 300-600 G to be measured. By
forming the line ratio between the V profiles of these lines it is,
in principle, possible to measure field strengths as low as 100 G,
thus achieving a sensitivity otherwise only possible with the emission
lines near 12 microns. Other diagnostic capabilities of these lines
are also analyzed.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. III -
Strong and weak magnetic fields in plages
Authors: Rueedi, I.; Solanki, S. K.; Livingston, W.; Stenflo, J. O.
1992A&A...263..323R Altcode:
The diagnostics developed by Zayer et al. 1989 are applied to 27
Stokes V spectra of solar plates. The 1.5 micron lines at 15648 A and
15652 A are used to measure magnetic field strengths between 400 G
and 1700 G at z = 0 in active region plages with an accuracy of up
to 2-3 percent. The results confirm the accuracy of the line-ratio
technique of Stenflo (1973). It is estimated that the fraction of net
magnetic flux in strong-field form is close to 90 percent, supporting
the view that the small-scale magnetic fields are concentrated very
efficiently. The data clearly contradict the claims of Zirin and Popp
(1989) based on 12 micron lines that there is at most indirect evidence
for kG fields in solar plages. They also contradict the large fraction
of weak-field flux reported by Del Toro et al. (1990).

---------------------------------------------------------
Title: Continuum brightness of solar magnetic elements
Authors: Solanki, S. K.; Brigljevic, V.
1992A&A...262L..29S Altcode:
Ratios between the Stokes V profiles of C I lines and Fe II lines are
used to determine the temperature of the continuum-forming layers of
solar magnetic features. From the derived temperature stratification
the continuum intensity of the spatially unresolved magnetic features
is obtained independently of spatial resolution. First results suggest
that whereas magnetic features have, on average, a brighter continuum
than the quiet sun in a region of small magnetic filling, they are
darker in a region with large filling factor. Consequences for flux-tube
sizes and the interpretation of the global solar luminosity variation
are discussed.

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. IV -
Discovery of a siphon flow
Authors: Rueedi, I.; Solanki, S. K.; Rabin, D.
1992A&A...261L..21R Altcode:
Spectra of two neighboring IR lines, Fe I 15648.5 A and Fe I 15652.9 A,
are analyzed. The spectra were obtained with an IR array detector in
active region plages with the entrance slit of the spectrograph placed
across the polarity-inversion (neutral) line. Near the neutral line the
positive polarity field is weaker (about 1200 G) and shows an upflow
of up to 2 km/s, while the negative polarity field is stronger (about
1500 G) and exhibits a downflow of up to 1 km/s. This configuration
corresponds to the expected signature of a siphon flow along a loop
connecting flux tubes across the neutral line.

---------------------------------------------------------
Title: Waves in solar magnetic flux tubes - The observational
signature of undamped longitudinal tube waves
Authors: Solanki, S. K.; Roberts, B.
1992MNRAS.256...13S Altcode:
Linear calculations of undamped magnetoacoustic waves utilizing
the thin-tube approximation are presented and their influence on the
Stokes I and V line parameters of a set of photospheric spectral lines
is analyzed. To improve the observational diagnostics of flux tube
waves, the dependence of various line parameters, such as the Stokes V
zero-crossing wavelength, Stokes V amplitude, width area and asymmetry,
on wave parameters is studied. It is determined that it is possible
to set a lower limit on the energy flux transported by longitudinal
tube waves by measuring time series of the Stokes V zero-crossing
wavelength of a selected group of lines.

---------------------------------------------------------
Title: Polarimetry with an imaging FTS.
Authors: Stenflo, J. O.; Solanki, S. K.
1992ESASP.344..197S Altcode: 1992spai.rept..197S
The concept of an imaging FTS polarimeter based on piezoelastic
modulation and direct demodulation in partially masked CCDs is
outlined. To illustrate its principle the currently operational FTS
polarimeter at the McMath telescope as well as the detection scheme
of the ETH polarimeter, based on partially masked CCD cameras, are
briefly described.

---------------------------------------------------------
Title: Small-scale physics of convection and magnetic fields.
Authors: Solanki, S. K.
1992ESASP.344...27S Altcode: 1992spai.rept...27S
An overview is given of the current knowledge of the properties and
the physics of small-scale magnetic features, magnetoconvection and
convection. This review concentrates on the theoretical aspects. Some
examples are given of features or processes which require very high
spatial resolution to be observed.

---------------------------------------------------------
Title: CA II K Line Diagnostics of Two Dimensional Models of the
Solar Chromosphere
Authors: Solanki, S. K.; Buente, M.; Steiner, O.; Uitenbroek, H.
1992ASPC...26..294S Altcode: 1992csss....7..294S
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Fields in Stellar Photospheres (Invited Review)
Authors: Solanki, S.
1992ASPC...26..211S Altcode: 1992csss....7..211S
No abstract at ADS

---------------------------------------------------------
Title: How Accurate are Stellar Magnetic Field Measurements?
Authors: Saar, S. H.; Solanki, S. K. .
1992ASPC...26..259S Altcode: 1992csss....7..259S
We study the accuracy of two magnetic analysis methods by applying
them to a large grid of lines computed using detailed 1.5-D radiative
transfer (RT) calculations in a variety of stellar atmospheres
imbedded with fluxtubes. We find errors of &lt; +/- 20% when using
the more realistic analysis method if the fluxtube and external quiet
atmospheres are similar; errors can increase substantially if this
condition is relaxed.

---------------------------------------------------------
Title: The Chromospheric Temperature Rise in Fluxtubes
Authors: Bruls, J. H. M. J.; Solanki, S. K.
1992ASPC...26..512B Altcode: 1992csss....7..512B
No abstract at ADS

---------------------------------------------------------
Title: Strong; Weak Solar Magnetic Fields
Authors: Solanki, S. K.; Ruedi, I.; Livingston, W. C.; Stenflo, J. O.
1992ASPC...26..262S Altcode: 1992csss....7..262S
No abstract at ADS

---------------------------------------------------------
Title: Two-dimensional models of the solar chromosphere. I - The CA
II K line as a diagnostic: 1.5-D radiative transfer
Authors: Solanki, S. K.; Steiner, O.; Uitenbroeck, H.
1991A&A...250..220S Altcode:
Ca II K line calculations for a 5-level atom and partial frequency
redistribution along multiple rays passing through 2D MHD models of
magnetic flux tubes in the solar atmosphere are presented. Temperature
stratifications corresponding to various empirical chromospheric
models are incorporated into the models. The influence of a number
of model parameters on individual and spatially averaged line
profiles is considered in detail. The profiles are also compared
with observations. It is found that the present models can, at
least qualitatively, reproduce a wide variety of observations if the
temperature within the magnetic component lies between that of model
F of Vernazza et al. (1981) and of model VALP of Ayres et al. (1986)
and if the temperature in the nonmagnetic part of the atmosphere
corresponds to that of the COOLC model of Ayres et al. Observations
that are consistent with this model are presented.

---------------------------------------------------------
Title: The effect of non-linear oscillations in magnetic flux tubes
on Stokes V asymmetry
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
1991A&A...249..239G Altcode:
The present knowledge on, and interpretation of, the asymmetry of
Stokes V of spectral lines thought to be formed in and around magnetic
flux tubes is reviewed. Crude models of nonlinear oscillations in the
flux tube were investigated in order to explain the observed values
of Stokes V amplitude and area asymmetry. It was found that flux tube
models with quasi-oscillatory motions, consisting of a slow upflow
and a rapid downflow in the magnetic region, as well as a downflow
in the nonmagnetic surroundings, may reproduce the observations,
both asymmetries and zero-crossing shift of Stokes V.

---------------------------------------------------------
Title: Flux tube diagnostics based on the Stokes V profiles of
infrared H-band lines.
Authors: Muglach, K.; Solanki, S. K.
1991sopo.work..489M Altcode:
Stokes V profiles of the unblended Fe I lines in the wavelength range
1.5 - 1.8 μ (H-band) observed in the solar network are analysed. The
data are consistent with an absence of stationary flows larger than
0.3 km s-1. The infrared Stokes V profiles are asymmetric
in the same sense as lines in the visible, but tend to be of smaller
magnitude, in particular the area asymmetry. The widths of the Stokes
V profiles are consistent with kG field strengths. Finally, model
calculations allow an upper limit of 2 to be set on the continuum
intensity of small magnetic features relative to the quiet Sun.

---------------------------------------------------------
Title: Stokes profile formation heights in solar magnetic flux tubes.
Authors: Larson, B.; Solanki, S. K.; Grossmann-Doerth, U.
1991sopo.work..479L Altcode:
The formation heights of magnetically split lines in small solar
magnetic flux tubes are investigated. In particular, the authors
are interested in how the heights of formation depend on different
flux tube parameters, like magnetic field strength, temperature and
temperature gradient, as well as on line parameters, such as line
strength, excitation potential and ionization stage.

---------------------------------------------------------
Title: Filigree and flux tube physics.
Authors: Spruit, H. C.; Schuessler, M.; Solanki, S. K.
1991sia..book..890S Altcode:
This review covers the properties of the small-scale (outside
sunspots) magnetic field from observational and theoretical points
of view. Special emphasis is put on the physics of small isolated
magnetic concentrations (flux tubes). Topics discussed include the
basic observational properties, the origin and disappearance of the
small-scale field, the properties of individual magnetic elements,
their influence on the solar irradiance and their interaction with
solar oscillations.

---------------------------------------------------------
Title: Inversion of Stokes V profiles: The structure of solar magnetic
fluxtubes and its dependence on the filling factor.
Authors: Keller, C. U.; Solanki, S. K.; Stenflo, J. O.; Zayer, I.
1991sopo.work..387K Altcode:
The authors present results from an inversion procedure that derive the
temperature stratification, the turbulent velocity, and the magnetic
field strength of the photospheric layers of magnetic fluxtubes from
observed Stokes V spectra near disk center. In a first step the
inversion has been applied to 10 Fe I and Fe II Stokes V profiles
of a plage and a network region to obtain reliable models of the
fluxtubes. In a second step the dependence of the fluxtube structure
on the filling factor has been studied with spectra of 3 Fe I lines
from 23 different regions based on the models derived in the first step.

---------------------------------------------------------
Title: Center-to-limb variation of the Stokes V asymmetry in solar
magnetic flux tubes.
Authors: Bünte, M.; Steiner, O.; Solanki, S. K.
1991sopo.work..468B Altcode:
The center-to-limb-variation of synthetic Stokes V line profiles
of the spectral line Fe I 5250.22 Å is presented and compared with
observations. These synthetic profiles are calculated using models
that contain the main features of the current basic pictures of small
scale magnetic fields on the Sun.

---------------------------------------------------------
Title: Magnetic Field Measurements on Cool Stars.
Authors: Solanki, S. K.
1991RvMA....4..208S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Dependence of the properties of solar magnetic flux tubes on
filling factor. II - Results of an inversion approach
Authors: Zayer, I.; Stenflo, J. O.; Keller, C. U.; Solanki, S. K.
1990A&A...239..356Z Altcode:
The dependence of the properties of solar magnetic elements on the
magnetic filling factor is studied using Stokes V spectra of three
lines observed near the center of the solar disk. The inversion
technique developed by Keller et al. (1990) is applied to three
neighboring spectral lines, and the average temperature difference,
the magnetic field strength, and the nonstationary velocity in the
relevant line-forming layers are quantitatively determined. Quantitative
evidence is provided for the dependence of the temperature within
flux tubes on the amount of magnetic flux. The flux tubes are found
to become cooler and their field strengths, at a given optical depth,
to become larger as the filling factor increases. The presence of
kilogauss field strengths within flux tubes is reconfirmed.

---------------------------------------------------------
Title: The influence of vertical magnetic field gradients on the
measured field strength and filling factor in late-type stars.
Authors: Grossmann-Doerth, U.; Solanki, S. K.
1990A&A...238..279G Altcode:
The influence of a vertical gradient of the magnetic field in late type
stars on the measurement of magnetic field strengths and filling factors
is studied. Line profiles and contribution functions of spectral lines
with large Lande factors are calculated in model stellar atmospheres in
the presence of a magnetic field with a vertical gradient. It is found
that the four lines, which have often been used to measure solar and
stellar magnetic fields in the past, are formed at heights sufficiently
different to account for differences in apparent field strength of up
to 1000 G if the fields are assumed to be similarly structured as in
the sun. Thus it is concluded that the vertical gradient of the field
may contribute to a good part of the discrepancy between different
published measurements of field strength and filling factor in the K2
dwarf Epsilon-Eri.

---------------------------------------------------------
Title: Solar magnetic field strength determinations from high spatial
resolution filtergrams
Authors: Keller, C. U.; Stenflo, J. O.; Solanki, S. K.; Tarbell,
T. D.; Title, A. M.
1990A&A...236..250K Altcode:
Circularly polarized images with high spatial resolution (better than 1
arcsec) of a solar active region, obtained with a tunable filter in the
wings of Fe I 5247.1 A and Fe I 5250.2 A, have been analyzed in terms of
the magnetic line ratio technique introduced by Stenflo (1973). Whenever
a measurable amount of polarization is present, the distribution of
the observed magnetic-line ratio is compatible with a unique value,
which is randomly blurred by noise due to the photon statistics,
the CCD camera, and atmospheric distortions. There is no need for a
distribution of field strengths to explain the observed distribution of
the magnetic line ratio. Consequently, the observations are compatible
with a unique magnetic field strength in solar small-scale magnetic
elements of about 1000 G at the level of line formation. For a thin
flux tube, this corresponds to a field strength of approximately 2000
G at the level of continuum formation, which is in excellent agreement
with previous field strength determinations from low spatial resolution
spectra (4-10 arcsec).

---------------------------------------------------------
Title: How magnetic is the solar chromosphere?
Authors: Solanki, S. K.; Steiner, O.
1990A&A...234..519S Altcode:
The lower solar chromosphere is thought to have a very inhomogeneous
temperature structure, with hot magnetic flux tubes surrounded by cool
(T less than 4000 K) nonmagnetic gas (Ayres et al., 1986). The effect
of such a thermally bifurcated atmosphere on the structure of the
magnetic field in the chromosphere is considered. It is shown that
magnetic flux tubes expand much more rapidly if the atmosphere is
thermally bifurcated than if it is homogeneous. They merge and form a
magnetic canopy with an almost horizontal base which does not exceed
approximately 800-1000 km above tau = 1, irrespective of the magnetic
filling factor. Hence the middle and upper chromosphere is filled with
a magnetic field almost everywhere on the sun. The consequences of this
result both for the sun and for other late type stars are discussed.

---------------------------------------------------------
Title: Structure of solar magnetic fluxtubes from the inversion of
Stokes spectra at disk center
Authors: Keller, C. U.; Steiner, O.; Stenflo, J. O.; Solanki, S. K.
1990A&A...233..583K Altcode:
The paper presents an inversion procedure that derives the temperature
stratification, the turbulent velocity, and the magnetic field strength
of the photospheric layers of small-scale magnetic fields from observed
Stokes V spectra and the continuum intensity. The inversion is based
on the determination of a small number of model flux parameters by a
nonlinear least squares fitting algorithm. The minimization of the sum
of the squared differences between observed and synthetic observables
makes it possible to determine the temperature stratification and the
magnetic field strength.

---------------------------------------------------------
Title: Solar line asymmetries and the magnetic filling factor
Authors: Brandt, P. N.; Solanki, S. K.
1990A&A...231..221B Altcode:
Results are presented of an analysis of high-quality Fourier transform
spectrometer spectra obtained in facular regions near solar disk center
having different amounts of magnetic flux or, equivalently, different
filling factors, alpha. The line parameters (width, equivalent width,
depth, bisector shape, and wavelength) of 32 spectral lines and their
variation with alpha are studied. Line depth is seen to decrease with
increasing filling factor for all the observed lines, while the line
width increases, even after compensation has been made for the Zeeman
broadening. For strong or temperature-insensitive lines the equivalent
width stays practically unchanged, but decreases for weak lines. The
findings are qualitatively explained by a decrease in the contrast
between the upflow and downflow components of the nonmagnetic part
of the atmosphere in active regions (abnormal granulation) coupled to
either a decrease in the average temperature of the nonmagnetic part
or a significant increase in small-scale velocity.

---------------------------------------------------------
Title: Interesting lines in the infrared solar spectrum between 1.49
and 1.8 microns
Authors: Solanki, S. K.; Biemont, E.; Muerset, U.
1990A&AS...83..307S Altcode:
Lists are presented of two groups of spectral lines interesting for the
study of solar and stellar magnetic fields, convection and atmospheric
structure and appearing in the IR solar spectrum between 1.49 and
1.8 microns. The first group contains 130 spectral lines judged to be
relatively unblended from a visual inspection of the spectra, while the
second is composed of 30 lines exhibiting large Stokes V amplitudes
in a quiet network, region. Some interesting aspects of these lines
are discussed. In particular, it is pointed out that blending due
to magnetically unsplit spectral lines, such as telluric lines, can
seriously affect all four Stokes parameters.

---------------------------------------------------------
Title: Flux tube diagnostics based on infrared H-band lines.
Authors: Muglach, K.; Solanki, S. K.
1990AGAb....5...45M Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Empirical Models of Photospheric Flux Tubes
Authors: Solanki, S. K.
1990IAUS..138..103S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The Observational Signature of Flux Tube Waves and an Upper
Limit on the Energy Flux Transported by Them
Authors: Solanki, S. K.; Roberts, B.
1990IAUS..138..259S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Waves in solar photospheric flux tubes and their influence
on the observable spectrum
Authors: Solanki, S. K.; Roberts, B.
1990GMS....58..181S Altcode:
Linear calculations of undamped magnetoacoustic waves in thin solar
magnetic flux tubes are presented and their influence on the Stokes
V profiles of various iron lines is studied. This is a necessary
first step for the diagnostics of the properties of flux tube waves,
in particular the amount of energy transported by them into the upper
atmosphere. It is shown that, with sufficiently high spatial resolution,
observations can distinguish between standing and propagating waves
on the basis of line parameters of photospheric spectral lines
alone. Particular attention is given to exploring quantitative
diagnostics for the wave amplitude, since it is currently the most
important unknown parameter determining the energy flux carried by
the waves. It is found that although this parameter can be derived
relatively simply if the thermal fluctuations produced by the wave
are ignored (i.e., for an isothermal wave), the task becomes much
more complex for the more realistic case of a coupled variation of
temperature and velocity.

---------------------------------------------------------
Title: Quantitative explanation of Stokes V asymmetry in solar
magnetic flux tubes
Authors: Solanki, S. K.
1990GMS....58..185S Altcode:
A 2D flux-tube model of a solar magnetic element is presently used
to calculate Stokes profiles of four spectral lines with various
properties. This model, which uses empirically-derived temperature and
magnetic field strength values, is able to reproduce the asymmetry
between the blue and red Stokes V wings in addition to other line
parameters observed near the disk center in solar active-region
plages. The Stokes V symmetry is a straightforward consequence of
the current view of magnetic elements that are embedded in cool,
downflowing intergranular lanes, in the presence of large-amplitude
nonstationary mass motions within magnetic elements.

---------------------------------------------------------
Title: At what heights are spectral lines formed in solar magnetic
flux tubes?
Authors: Larsson, B.; Solanki, S.; Grossmann-Doerth, U.
1990nba..meet..169L Altcode: 1990taco.conf..169L
Illustrative examples, taken from a study of the formation of
magnetically split lines in solar magnetic flux tubes, are presented. A
particular interest is: in how the heights of formation depend on
different flux tube parameters, like the magnetic field strength, the
temperature and temperature gradient, as well as on line parameters,
such as line strength, excitation potential and ionization stage. The
result should help to improve the construction of empirical models
of magnetic features and provide a new understanding of the spectral
diagnostics used in the study of the solar magnetic field.

---------------------------------------------------------
Title: The origin and the diagnostic capabilities of the Stokes V
asymmetry observed in solar faculae and the network
Authors: Solanki, S. K.
1989A&A...224..225S Altcode:
The origin of the Stokes V asymmetry observed near disk center
in solar active regions and in the quiet network is studied with
the help of a two-dimensional flux tube model of solar magnetic
elements. It is shown that the observed relative area and amplitude
asymmetry, the zero-crossing wavelengths, and the width of four Fe
I and II Stokes V profiles belonging to lines with widely different
properties can be reproduced relatively well within the framework
of the model incorporating certain features. The sensitivity of the
Stokes V asymmetry to the thermal and velocity structure in and around
solar magnetic elements is also demonstrated. It is the Stokes V line
parameter most sensitive to the atmosphere in the vicinity of magnetic
elements, and can also become a powerful diagnostic of the mass motions
inside the magnetic elements. Values of the temperature and velocity
in the immediate surroundings of these elements at the height of line
formation are derived for the first time.

---------------------------------------------------------
Title: Stokes V asymmetry and shift of spectral lines
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
1989A&A...221..338G Altcode:
Further evidence is given for the interpretation of the observed
unshifted and asymmetric Stokes V profiles in the solar atmosphere
in terms of a magnetic flux concentration expanding with height and
surrounded by a downflow. A general proof is given that a V profile
originating in an atmosphere in which magnetic field and flow are
spatially separated along the line of sight has a zero-crossing
wavelength which is unshifted with respect to the rest wavelength of
the line center. Heuristic considerations for the dependence of the
asymmetry of Stokes V on Zeeman shift, Doppler shift, line width,
and strength are described and confirmed by exploratory calculations.

---------------------------------------------------------
Title: The internal magnetic field structure of solar magnetic
elements
Authors: Solanki, S.; Zayer, I.; Stenflo, J. O.
1989hsrs.conf..409S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The internal magnetic distribution and the diameters of solar
magnetic elements.
Authors: Zayer, I.; Solanki, S. K.; Stenflo, J. O.
1989A&A...211..463Z Altcode:
A diagnostic is proposed for the horizontal distribution and vertical
gradient of the magnetic field with spatially unresolved solar magnetic
elements. Radiative transfer calculations are conducted to model the
magnetic field structure, which is fitted to observational data from a
Fourier transform spectrometer. It is found that a vertical gradient
of the magnetic field strength must be present in solar magnetic
fluxtubes and that, in the lower photosphere, the field strength inside
the fluxtube must be horizontally nearly constant. The magnetic field
strengths and gradients derived at the disk center satisfy observations
near 0.6 microns, if the appropriate model fluxtube size is chosen.

---------------------------------------------------------
Title: On the Analysis of Stokes J and V Profiles in the Infrared
Authors: Solanki, S. K.
1989AGAb....3...20S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic fields in late-type dwarfs : preliminary results
from a multiline approach.
Authors: Mathys, G.; Solanki, S. K.
1989A&A...208..189M Altcode:
Preliminary results of a multiline approach to the diagnosis of magnetic
fields in late-type dwarfs are presented. The spectra of fours stars
observed with the Coude Echelle Spectrometer of the European Southern
Observatory are analyzed using the Stenflo-Lindegren technique, which
permits empirical relations to be obtained between various parameters
characterizing a statistical sample of observed line profiles and the
atomic quantities pertaining to the corresponding transitions. These
empirical relations are first tested on solar and stellar data and then
interpreted with the help of a simple model of the line formation,
and constraints on the magnetic field properties (mean strength,
filling factor, thermodynamic properties of the magnetic regions
compared to the nonmagnetic parts of the stellar surface) are derived.

---------------------------------------------------------
Title: Magnetic fields in late-type dwarfs: Preliminary results from
a multiline approach
Authors: Mathys, G.; Solanki, S. K.
1988STIN...9019928M Altcode:
Results of a multiline approach to the diagnosis of magnetic fields in
late-type dwarfs are presented. The spectra of four stars observed with
the Coude echelle spectrometer of the European Southern Observatory are
analyzed using the Stenflo-Lindegren technique, which permits empirical
relations to be obtained between various parameters characterizing a
statistical sample of observed line profiles and the atomic quantities
pertaining to the corresponding transitions. These empirical relations
are tested on solar and stellar data and interpreted with a simple model
of the line formation. Constraints on the magnetic field properties
(mean strength, filling factor, thermodynamic properties of the magnetic
regions compared to the nonmagnetic parts of the stellar surface) are
derived. In spite of the crudeness of approximations, the results are
compatible with those obtained with other methods. The advantages of
the Stenflo-Lindegren technique over other approaches are sketched.

---------------------------------------------------------
Title: Unshifted, asymmetric Stokes V-profiles - Possible solution
of a riddle
Authors: Grossmann-Doerth, U.; Schuessler, M.; Solanki, S. K.
1988A&A...206L..37G Altcode:
We show that Stokes V-profiles originating in an atmosphere
in which a magnetic field and a systematic velocity field are
spatially separated along the line of sight are asymmetric with
unshifted zero-crossings. Such a configuration is probably realized
in the peripheral parts of magnetic flux concentrations in the solar
photosphere: Since the magnetic field flares out with height, the line
of sight traverses both a static magnetic region and a downdraft in
the non-magnetic surroundings. V-profiles formed in these parts of the
flux concentation will be strongly asymmetric but unshifted while the
V-profiles from the central parts are symmetric and unshifted. The
resulting mean V-profiles show the characteristics of the observed
profiles, i.e. they are unshifted and asymmetric.

---------------------------------------------------------
Title: Interpretation of broad band circular polarization measurements
using Stokes V spectra
Authors: Muerset, U.; Stenflo, J. O.; Solanki, S. K.
1988A&A...204..279M Altcode:
The wavelength dependence and the center to limb variation of the broad
band circular polarization of solar active regions are determined by
integrating over spectra with a large wavelength range obtained with a
Fourier transform spectrometer (FTS). It is shown that the broad band
circular polarization (BBC) is due mainly to the asymmetry of the Stokes
V profiles. The approximate contributions of lines of different depths
to the total broad band signal are analyzed. The diagnostic contents
of BBC observations with low spatial resolution, such as those of
Kemp et al. (1987), are discussed. These observations are reproduced
with the help of simulated broad band polarization data obtained by
integrating FTS spectra. It is shown that the spatial distribution
of the net field on the solar surface (within a single large spatial
resolution element) can affect the measured BBC signal considerably,
and may even change its sign.

---------------------------------------------------------
Title: Contribution and response functions for Stokes line profiles
formed in a magnetic field
Authors: Grossmann-Doerth, U.; Larsson, B.; Solanki, S. K.
1988A&A...204..266G Altcode:
Expressions defining the contribution functions of the 'line depression'
Stokes profiles formed in a general magnetic field are derived. Such
contribution functions are better suited to determining the heights at
which the bound-bound transitions responsible for spectral lines are
important than the contribution functions to the 'intensity' Stokes
parameters defined by Van Ballegooijen (1985). Expressions defining
response functions for both 'intensity' and 'line depression' Stokes
parameters are also derived for an arbitrary atmosphere and magnetic
field. A code for calculating the various Stokes contribution functions
is described and some example calculations are presented. These clearly
demonstrate the superior diagnostic value of the contribution functions
to the 'line depression' Stokes profiles.

---------------------------------------------------------
Title: Can stationary velocity fields explain the Stokes V asymmetry
observed in solar magnetic elements?
Authors: Solanki, S. K.; Pahlke, K. D.
1988A&A...201..143S Altcode:
A mechanism for producing the observed asymmetry between the amplitudes
and areas of the blue and red wings of Stokes V profiles, which
is based on velocity gradients, is explored. It is found that the
velocity gradients do not produce a Stokes V area asymmetry in very
weak lines. A stationary velocity gradient is neither able to reproduce
the observed asymmetry of lines of different strengths and excitation
potentials nor simultaneously reproduce the widths and asymmetries
of strong lines. If the asymmetries of Fe I 5250.2 A, Fe I 6301.5 A,
and Fe I 6302.5 A are reproduced, it is shown that their zero crossing
wavelengths are too strongly redshifted as compared to observations.

---------------------------------------------------------
Title: Magnetic field strength in solar flux tubes - A model
atmosphere independent determination
Authors: Sanchez Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
Solanki, S. K.
1988A&A...196..266S Altcode:
The "line ratio method" (Stenflo, 1973) has been extensively used in
the past to carry out measurements of the magnetic field strength in
spatially unresolved magnetic flux concentrations. The authors present
here a new variant of this technique, which is particularly simple as
it does not depend on any radiative transfer calculations and thus the
assumption of a model atmosphere is not required. General properties
of the transfer equation lead to a relationship between the circular
polarization generated by two lines which are identical except for
their Landé factors. This can be used to directly determine the field
strength from the measured line profiles. In order to test the method
the authors have applied it to experimental data. A comparison with
the traditional line ratio method is shown.

---------------------------------------------------------
Title: Continuum intensity of magnetic flux concentrations - Are
magnetic elements bright points?
Authors: Schuessler, M.; Solanki, S. K.
1988A&A...192..338S Altcode:
The authors use the weakening of temperature sensitive spectral
lines (Fe I λ5250.2 and λ5247.1) in a strong plage region to
derive a lower limit (≈1.4 of the quiet photospheric value) for the
continuum intensity in magnetic flux concentrations. This suggests an
identification of magnetic elements with the observed photospheric
bright points. The authors discuss the implications of this result
for the quantitative determination of magnetic flux and propose a
procedure for obtaining information on the physical structure of the
non-magnetic surroundings of flux concentrations.

---------------------------------------------------------
Title: Magnetic Field of Late-Type Stars : a New Approach
Authors: Mathys, G.; Solanki, S. K.
1988IAUS..132..325M Altcode:
Magnetic field diagnosis in three late-type stars is performed using
the multiline technique originally developed by Stenflo and Lindegren
(1977) to study spatially unresolved magnetic features on the sun.

---------------------------------------------------------
Title: A new technique for the measurement of stellar magnetic fields:
First Results
Authors: Solanki, S. K.; Mathys, G.
1988ASSL..143...39S Altcode: 1988acse.conf...39S
A technique for determining strengths and filling factors of stellar
magnetic fields is presented. It is based on a statistical analysis
of a large number of unblended Fe I lines and was first introduced
by Stenflo and Lindegren (1977). It has been tested in solar active
regions and is now applied to late type stars. First results of an
analysis of high S/N spectra of three stars are presented and compared
to previous measurements.

---------------------------------------------------------
Title: Velocity and temperature in solar magnetic fluxtubes from a
statistical centre-to-limb analysis
Authors: Pantellini, F. G. E.; Solanki, S. K.; Stenflo, J. O.
1988A&A...189..263P Altcode:
Stokes I and V profiles of a large number of unblended Fe I
lines observed at different positions on the solar disk have
been analyzed. Asymmetries in the Stokes V profile are noted. The
center-to-limb variation of the zero-crossing wavelength of the weak
and medium strong lines is found to be consistent with the absence of
stationary flows in fluxtubes. The stronger lines are shown to be more
blueshifted than the weak ones at all limb distances. The fluxtube
temperature structure is confirmed to be a function of the filling
factor. The rms velocity amplitude is found to increase somewhat when
approaching the limb, in contrast to what would be expected if the
mass motions were mostly vertical.

---------------------------------------------------------
Title: NLTE effects in solar magnetic fluxtubes
Authors: Solanki, S. K.; Steenbock, W.
1988A&A...189..243S Altcode:
NLTE calculations of approximately 200 Fe I and Fe II spectral lines
with a comprehensive model atom are presented for a quiet sun model
and a grid of fluxtube models. These calculations are compared with
LTE results and the departures from LTE in fluxtubes are estimated. For
all the fluxtube models tested, the departures from LTE ionization for
the Fe I lines are found to be larger than for the quiet sun. Fe II
lines show almost no difference between LTE and NLTE. The influence
of temperature gradients on the departures is also studied and
discussed. The profiles of five Fe I and one Fe II lines are analyzed
in detail and the errors in empirically determined velocities and
temperatures in fluxtubes, introduced by the assumption of LTE, are
estimated. It is found that assuming LTE has practically no effect on
the determined velocities, but that it may lead to an overestimation
of the temperature in fluxtubes at the heights at which the lines
are formed.

---------------------------------------------------------
Title: Properties of solar magnetic fluxtubes from only two spectral
lines
Authors: Solanki, S. K.; Keller, C.; Stenflo, J. O.
1987A&A...188..183S Altcode:
A method for the determination of the magnetic field strength,
velocity, and temperatures inside solar flux tubes, in addition to
their inclinations and filling factors, is presented which requires
only the Stokes V and Q profiles of the Fe I 5250.2 A and Fe I 5247.1
A spectral lines. Application of the procedure to spectra of the two
lines obtained at various distances from the solar limb shows that
considerable velocity broadening is required at all positions on the
disk in order to reproduce the polarimeter data. The center to limb
variation of the 5250/5247 Stokes V and Q line ratios is found to
contain little information on the height variation of the magnetic
field in the context of one-dimensional models.

---------------------------------------------------------
Title: The Photospheric Layers of Solar Magnetic Flux Tubes
Authors: Solanki, S. K.
1987PhDT.......251S Altcode:
This thesis is concerned with the structure and properties of magnetic
fluxtubes in the solar photosphere. After a brief introduction outlining
the importance of magnetic fields for the Sun and the stars, with
particular emphasis on the role of fluxtubes, a brief description
of polarised light, its properties, production, radiative transfer
and measurement is given. There follows an overview of spectroscopy
and polarimetry with a Fourier transform spectrometer (FTS). The data
forming the basis of the thesis, FTS spectra of Stokes I, V, and partly
also Q in the visible and the infrared (1.5-1.7μm), are described. The
analysis procedure is partly based on the weak-field approximation,
which is used to determine an approximation of the magnetically
unsplit Stokes I inside the fluxtubes. The lines to be analysed (a
set of 450 unblended Fe lines) are listed and their effective Landé
factors are determined from laboratory measurements. The line profiles
are parameterised and a statistical analysis of these parameters is
carried out. Line of sight bulk and turbulent velocities, temperatures
and the magnetic field in magnetic fluxtubes are determined, partly
directly from the measured profiles, but partly on the basis of
radiative transfer calculations in model fluxtubes. It is shown that
fluxtubes do not harbour significant net flows and that fluxtubes in
the network are on average hotter than those in plage regions. Finally,
MHD models of cylindrically symmetric fluxtubes are presented. The
effects of magnetic tension are included. A self-consistent formalism
is developed to take the influence of neighbouring fluxtubes into
account. The dependence of the merging height on various parameters
of the fluxtubes is discussed. It is shown that the thin fluxtube
approximation is quite reliable for fluxtubes with radii less than
approximately 100 km near the solar surface.

---------------------------------------------------------
Title: Diagnostics of solar magnetic fluxtubes with the infrared
line Fe I lambda 15648.54 A
Authors: Stenflo, J. O.; Solanki, S. K.; Harvey, J. W.
1987A&A...173..167S Altcode:
Fourier Transform Spectrometer recordings of May 1984 have been used to
explore the center-to-limb variation of the Stokes I, V, and Q profiles
of the solar infrared Fe I line at 15,648.54 A. The aim is to examine
the new possibilities offerred for the diagnostics of the spatially
unresolved magnetic flux tubes on the sun when lines with complete
Zeeman splitting are used. Comparison is made with the line-ratio
method, which must be used at visible wavelengths, where the splitting
is incomplete. The Stokes V asymmetries observed in the infrared line
are small or even of opposite sign as compared with the corresponding
asymmetries observed at visible wavelengths. This suggests that the
time-averaged height gradient of the Doppler velocities inside the
fluxtubes becomes small and may change its sign when moving down to
the bottom of the fluxtube photosphere.

---------------------------------------------------------
Title: The photospheric layers of solar magnetic fluxtubes
Authors: Solanki, Sami Khan
1987PhDT.......295S Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Center-to-limb variation of Stokes profiles and the diagnostics
of solar magnetic fluxtubes
Authors: Stenflo, J. O.; Solanki, S. K.; Harvey, J. W.
1987A&A...171..305S Altcode:
Simultaneous recordings of the Stokes I, Q, and V spectra have been
performed with a Fourier transform spectrometer in 10 solar regions
distributed over various center-to-limb distances, from disk center
to the extreme limb. The observational material and the recording
technique used are presented. The authors then evaluate the Stokes
profile parameters for a small selected set of spectral lines to explore
the potential of this qualitatively new data set for the diagnostics
of spatially unresolved magnetic fluxtubes.

---------------------------------------------------------
Title: Magnetic fields: observations and theory.
Authors: Solanki, S. K.
1987PAICz..66...95S Altcode: 1987eram....1...95S
Theoretical model calculations of magnetic elements in the photospheric
layers of solar active regions are compared with the results of
observations.

---------------------------------------------------------
Title: Structure of Magnetic Flux tubes as derived from Observations
with Moderate Spatial Resolution
Authors: Solanki, S. K.
1987rfsm.conf...67S Altcode:
Motions with large amplitudes and probably a vertical velocity gradient
are present in the fluxtubes or their immediate surroundings. The exact
nature of such motions is unknown. Candidates are: stationary up-
and downflows in different fluxtubes, so that on the average little
vertical mass transfer takes place. Oscillations or waves in fluxtubes
are another possibility, whereby these motions are not in phase in
different fluxtubes. Finally, due to the geometry of the fluxtubes
(expansion with height), it is possible that motions in their immediate
surroundings may also affect Stokes V.

---------------------------------------------------------
Title: Intensity profiles in fluxtubes.
Authors: Sanches Almeida, J.; Collados, M.; del Toro Iniesta, J. C.;
Solanki, S. K.
1987PAICz..66..261S Altcode: 1987eram....1..261S
Spectroscopic analysis of the light coming from an atmosphere is a
powerful tool for revealing its properties. The problem when using
conventional spectroscopy for solar fluxtubes is their unresolved
character: magnetic and non-magnetic regions of a plage have to be
observed as a whole. With the aim of obtaining the true intensity
spectrum of an unresolved tube, the authors have developed a simple
method which can reconstruct the intensity generated in the magnetic
component. Only observed parameters are used: intensity and circular
polarization in the plage and intensity in the quiet photosphere.

---------------------------------------------------------
Title: FTS Measurements of Solar Line Asymmetries in Quiet and
Active Regions
Authors: Brandt, P. N.; Solanki, S. K.
1987rfsm.conf...82B Altcode:
Spatially averaged Fourier transform spectra (FTS) with their well known
high spectral resolution, their highly symmetric apparatus profile,
low scattered light and high S/N ratio can be used as a complementing
tool for the diagnosis of atmospheric parameters. The possibility to use
many lines measured strictly simultaneously and covering a wide range
of excitation potentials, heights of formation etc. represents another
advantage of the FTS and at the same time reduces possible errors due
to line blending. The main motivation for the present investigation of
plage versus quiet sun line profiles came from the exciting results
by Livingston &amp; Holweger (1982) and by Livingston (1983) on the
possible cycle dependence of line equivalent widths and asymmetries,
as measured in integrated sunlight. Preliminary results are given.

---------------------------------------------------------
Title: Some effects of finite spectral resolution on the Stokes
V profile
Authors: Solanki, S. K.; Stenflo, J. O.
1986A&A...170..120S Altcode:
The authors consider some general effects of spectral smearing on the
Stokes V profile of the Fe I 5250.2 Å line, as observed on the sun with
a Fourier transform spectrometer at a very high spectral resolution. The
effects of low spectral resolution are numerically simulated by
convoluting the observed line profiles with model instrumental
profiles. The authors also try to find some Stokes V parameters which
are insensitive to the spectral resolution. Finally, they show that
the large Stokes V zero-crossing wavelength shifts observed by Wiehr
(1985) and by Scholier and Wiehr (1985) from complete profiles, and
by Giovanelli and Slaughter (1978) with the line-centre-magnetogram
technique of Giovanelli and Ramsey (1971) are compatible with the
results of Stenflo and Harvey (1985) and Solanki (1985, 1986).

---------------------------------------------------------
Title: Velocities in solar magnetic fluxtubes.
Authors: Solanki, S. K.
1986A&A...168..311S Altcode:
Stokes V zero-crossing wavelengths and I(V) profiles of a large number
of unblended Fe I and II lines are used to study the velocities in
solar magnetic flux tubes. No net flows are seen in the photospheric
layers of flux tubes at disk center in both active region plages
and the quiet network. Stokes V zero-crossing wavelength shifts
relative to the wavelengths of the Stokes I profiles do not support
the presence of downflows inside flux tubes. One dimensional LTE model
calculations are used to show that the observed line profiles formed
inside a flux tube can only be reproduced if the model profiles are
broadened by velocity. The dependence of the total turbulent velocity
on line strength in the flux tube is found to differ strongly from
its dependence in the quiet photosphere.

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Title: Lines in the wavelength range λλ 4300 6700 Å with large
stokes V amplitudes outside sunspots
Authors: Solanki, S. K.; Pantellini, F. G. E.; Stenflo, J. O.
1986SoPh..107...57S Altcode: 1987SoPh..107...57S
A list of solar spectral lines in the wavelength λλ 4300-6700 å
exhibiting large Stokes V amplitudes in observed spectra of active
region plages and the quiet network is presented.

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Title: Can velocity gradients explain the observed Stokes V asymmetry
in the absence of large zero-crossing shifts?
Authors: Pahlke, K. D.; Solanki, S. K.
1986MitAG..65..162P Altcode:
No abstract at ADS

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Title: Structure and merging of solar magnetic fluxtubes
Authors: Pneuman, G. W.; Solanki, S. K.; Stenflo, J. O.
1986A&A...154..231P Altcode:
In the present, expansion technique-based model of the solar
atmosphere's magnetic flux tubes, account is taken of the effects of
field line curvature, internal structural variations, and the merging
of the tube with its contiguous neighbors as it expands (through the
use of a small 'seed' magnetic field between the tubes that has no
influence on the solution in the limit of vanishing strength). For the
solutions obtained, the internal magnetic structure of the tube evolves
in height in a nonself-similar manner, although the gas pressure can
vary self-similarly for the special case in which internal temperature
is both uniform and equal to the external temperature. In the vicinity
of the merging height, the field approaches uniformity consistent with
a vertical tube with constant cross section.

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Title: High Spectral Resolution and Properties of Small Magnetic
Flux Tubes
Authors: Solanki, S. K.
1985tphr.conf..172S Altcode:
No abstract at ADS

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Title: Models of solar magnetic fluxtubes - Constraints imposed by
Fe I and II lines
Authors: Solanki, S. K.; Stenflo, J. O.
1985A&A...148..123S Altcode:
The diagnostic contents of the Stokes I and V profiles of about 50
unblended Fe II lines have been explored and used to set new constraints
on the temperature structure of magnetic fluxtubes. The simultaneous use
of Fe I and II lines makes it possible to determine the temperature in
both the upper and lower fluxtube photosphere. The Fe II lines further
make it possible to obtain model-insensitive values of the magnetic
filling factors. Empirically determined effective Lande factors of most
of the unblended iron lines in the visible part of the solar spectrum
are presented and compared with the corresponding LS coupling values.

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Title: High spectral resolution and properties of small magnetic
fluxtubes.
Authors: Solanki, S. K.
1985MPARp.212..172S Altcode:
Some empirical results pertaining to properties of small magnetic
fluxtubes are described. Using data obtained with a Fourier transform
spectrometer it has been possible to set constraints on the temperature
structure of fluxtubes, on the types of mass motions and velocities
inside them, and on the magnetic field strength near their τ = 1
level. The Stokes V asymmetries observed in fluxtube spectra are also
discussed and evidence is presented favouring the hypothesis that they
are produced by velocities.

---------------------------------------------------------
Title: Can Velocity Gradients Explain the Observed Stokes V Asymmetry
in the Absence of Large Zero-Crossing Shifts?
Authors: Pahlke, K. D.; Solanki, S. K.
1985MitAG..65..162P Altcode:
No abstract at ADS

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Title: The photospheric temperature structure of magnetic fluxtubes.
Authors: Solanki, S. K.
1984ESASP.220...63S Altcode: 1984ESPM....4...63S
The temperature stratifications of plage and network fluxtubes are
determined by comparing a large number of observed Fe I and Fe II lines
with LTE model calculations. The data are also compared with profiles
published in the literature. It is shown that in order to reproduce the
data correctly, a sharp dip in the fluxtube temperature must occur in
the photosphere, where the temperature of fluxtube and surroundings
become similar (at equal optical depth). The effects of different
pressure stratifications on the depths of the iron lines are briefly
discussed and it is shown that the pressure stratification giving the
best agreement with the data corresponds to a rapid expansion of the
fluxtube near the height at which the temperature dip occurs.

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Title: Properties of solar magnetic fluxtubes as revealed by Fe
I lines
Authors: Solanki, S. K.; Stenflo, J. O.
1984A&A...140..185S Altcode:
The information contents in the solar spectrum for modelling of magnetic
fluxtubes is explored by analysing the statistical properties of the
Stokes I and V line profiles of 400 unblended Fe I lines. Methods of
determining the temperature structure, photospheric magnetic field
strength, magnetic filling factor, and microturbulence velocity are
presented and used to provide estimates of these quantities in enhanced
network and plage regions. Analysis of the magnetic line broadening
shows that the magnetic field strength is approximately equal in network
and plage regions, consistent with previous results. On the other hand,
the temperature structures of the plage fluxtubes and the network
elements are observed to be substantially different. The variation
of the Stokes V line asymmetries with line strength are found to be
similar in the different solar regions, indicating similar velocity
structures in plages and network elements.

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Title: Diagnostics of solar magnetic fluxtubes using a Fourier
transform spectrometer
Authors: Stenflo, J. O.; Solanki, S.; Harvey, J. W.; Brault, J. W.
1984A&A...131..333S Altcode:
An overview is presented of the diagnostic contents for fluxtube
modelling of Fourier transform spectrometer recordings of the
longitudinal Zeeman effect near the solar disk center made in
April 1979. The observations and data reductions are summarized
and the application of the weak-field model to the Stokes profiles
is examined. The significance of telluric lines and blends and the
validity of LS coupling are considered. The magnetic fluxes, intrinsic
field strengths, and area factors are discussed and the thermodynamic
properties of fluxtubes are addressed. Mass motions inside the fluxtubes
and the height variation of fluxtube parameters are considered.