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Author name code: lites
ADS astronomy entries on 2022-09-14
author:"Lites, Bruce William"
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Title: Measurements of Photospheric and Chromospheric Magnetic Fields
Authors: Lagg, Andreas; Lites, Bruce; Harvey, Jack; Gosain, Sanjay;
Centeno, Rebecca
2018smf..book...37L Altcode:
No abstract at ADS
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Title: Measurements of Photospheric and Chromospheric Magnetic Fields
Authors: Lagg, Andreas; Lites, Bruce; Harvey, Jack; Gosain, Sanjay;
Centeno, Rebecca
2017SSRv..210...37L Altcode: 2015arXiv151006865L; 2015SSRv..tmp..115L
The Sun is replete with magnetic fields, with sunspots, pores
and plage regions being their most prominent representatives on
the solar surface. But even far away from these active regions,
magnetic fields are ubiquitous. To a large extent, their importance
for the thermodynamics in the solar photosphere is determined by the
total magnetic flux. Whereas in low-flux quiet Sun regions, magnetic
structures are shuffled around by the motion of granules, the high-flux
areas like sunspots or pores effectively suppress convection, leading
to a temperature decrease of up to 3000 K. The importance of magnetic
fields to the conditions in higher atmospheric layers, the chromosphere
and corona, is indisputable. Magnetic fields in both active and
quiet regions are the main coupling agent between the outer layers
of the solar atmosphere, and are therefore not only involved in the
structuring of these layers, but also for the transport of energy from
the solar surface through the corona to the interplanetary space. <P
/>Consequently, inference of magnetic fields in the photosphere, and
especially in the chromosphere, is crucial to deepen our understanding
not only for solar phenomena such as chromospheric and coronal
heating, flares or coronal mass ejections, but also for fundamental
physical topics like dynamo theory or atomic physics. In this review,
we present an overview of significant advances during the last decades
in measurement techniques, analysis methods, and the availability of
observatories, together with some selected results. We discuss the
problems of determining magnetic fields at smallest spatial scales,
connected with increasing demands on polarimetric sensitivity and
temporal resolution, and highlight some promising future developments
for their solution.
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Title: Are Internetwork Magnetic Fields in the Solar Photosphere
Horizontal or Vertical?
Authors: Lites, B. W.; Rempel, M.; Borrero, J. M.; Danilovic, S.
2017ApJ...835...14L Altcode:
Using many observations obtained during 2007 with the
Spectro-Polarimeter of the Hinode Solar Optical Telescope, we explore
the angular distribution of magnetic fields in the quiet internetwork
regions of the solar photosphere. Our work follows from the insight of
Stenflo, who examined only linear polarization signals in photospheric
lines, thereby avoiding complications of the analysis arising from the
differing responses to linear and circular polarization. We identify
and isolate regions of a strong polarization signal that occupy only
a few percent of the observed quiet Sun area yet contribute most to
the net linear polarization signal. The center-to-limb variation of
the orientation of linear polarization in these strong signal regions
indicates that the associated magnetic fields have a dominant vertical
orientation. In contrast, the great majority of the solar disk is
occupied by much weaker linear polarization signals. The orientation of
the linear polarization in these regions demonstrates that the field
orientation is dominantly horizontal throughout the photosphere. We
also apply our analysis to Stokes profiles synthesized from the
numerical MHD simulations of Rempel as viewed at various oblique
angles. The analysis of the synthetic data closely follows that of
the observations, lending confidence to using the simulations as a
guide for understanding the physical origins of the center-to-limb
variation of linear polarization in the quiet Sun area.
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Title: Do the quiet sun magnetic fields vary with the solar cycle?
Authors: Faurobert, Marianne; Ricort, Gilbert; Lites, Bruce
2015IAUS..305...22F Altcode:
The quiet Sun observed in polarized light exhibits a rich and
complex magnetic structuring which is still not fully resolved nor
understood. The present work is intended to contribute to the debate
about the origin of the quiet sun magnetic fields, in relation or
not to the global solar dynamo. We present analysis of center-to-limb
polarization measurements obtained with the SOT/SP spectropolarimeter
onboard the Hinode satellite outside active regions, in 2007 and 2013,
i.e. at a minimum and a maximum of the solar cycle, respectively. We
compare the spatial fluctuation Fourier spectra of unsigned circular and
linear polarization images after corrections for polarization bias and
focus variations between the two data sets. The decay of active regions
is clearly a source of magnetic fields in the quiet Sun. It leads to
a global increase of the polarization fluctuation power spectrum in
2013 in the network. In the internetwork, we observe no variation of
the polarization fluctuation power at mesogranular and granular scales,
whereas it increases at sub-granular scales. We interpret these results
in the following way. At the mesogranular and granular scales very
efficient mechanisms of magnetic field removal are operating in the
internetwork, that leads to a dissipation or a concentration of magnetic
fields on smaller scales. So the cycle-invariant magnetic signal that
we detect at mesogranular and granular scales must be continuously
created by a dynamo mechanism which is independent of the solar cycle.
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Title: Comparison of inversion codes for polarized line formation
in MHD simulations. I. Milne-Eddington codes
Authors: Borrero, J. M.; Lites, B. W.; Lagg, A.; Rezaei, R.; Rempel, M.
2014A&A...572A..54B Altcode: 2014arXiv1409.3376B
Milne-Eddington (M-E) inversion codes for the radiative transfer
equation are the most widely used tools to infer the magnetic field
from observations of the polarization signals in photospheric and
chromospheric spectral lines. Unfortunately, a comprehensive comparison
between the different M-E codes available to the solar physics
community is still missing, and so is a physical interpretation of their
inferences. In this contribution we offer a comparison between three
of those codes (VFISV, ASP/HAO, and HeLIx<SUP>+</SUP>). These codes are
used to invert synthetic Stokes profiles that were previously obtained
from realistic non-grey three-dimensional magnetohydrodynamical (3D MHD)
simulations. The results of the inversion are compared with each other
and with those from the MHD simulations. In the first case, the M-E
codes retrieve values for the magnetic field strength, inclination and
line-of-sight velocity that agree with each other within σ<SUB>B</SUB>
≤ 35 (Gauss), σ<SUB>γ</SUB> ≤ 1.2°, and σ<SUB>v</SUB> ≤
10 m s<SUP>-1</SUP>, respectively. Additionally, M-E inversion codes
agree with the numerical simulations, when compared at a fixed optical
depth, within σ<SUB>B</SUB> ≤ 130 (Gauss), σ<SUB>γ</SUB> ≤ 5°,
and σ<SUB>v</SUB> ≤ 320 m s<SUP>-1</SUP>. Finally, we show that
employing generalized response functions to determine the height at
which M-E codes measure physical parameters is more meaningful than
comparing at a fixed geometrical height or optical depth. In this case
the differences between M-E inferences and the 3D MHD simulations
decrease to σ<SUB>B</SUB> ≤ 90 (Gauss), σ<SUB>γ</SUB> ≤ 3°,
and σ<SUB>v</SUB> ≤ 90 m s<SUP>-1</SUP>.
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Title: High-speed photospheric material flow observed at the polarity
inversion line of a δ-type sunspot producing an X5.4 flare on 2012
March 7
Authors: Shimizu, Toshifumi; Lites, Bruce W.; Bamba, Yumi
2014PASJ...66S..14S Altcode: 2014arXiv1406.1617S; 2014PASJ..tmp..101S
Solar flares abruptly release the free energy stored as a non-potential
magnetic field in the corona and may be accompanied by eruptions
of the coronal plasma. Formation of a non-potential magnetic field
and the mechanisms for triggering the onset of flares are still
poorly understood. In particular, photospheric dynamics observed
near those polarity inversion lines that are sites of major flare
production have not been well observed with high spatial resolution
spectro-polarimetry. This paper reports on a remarkable high-speed
material flow observed along the polarity inversion line located between
flare ribbons at the main energy release side of an X5.4 flare on 2012
March 7. Observations were carried out by the spectro-polarimeter of
the Solar Optical Telescope on board Hinode. The high-speed material
flow was observed in the horizontally oriented magnetic field formed
nearly parallel to the polarity inversion line. This flow persisted from
at least six hours before the onset of the flare, and continued for at
least several hours after the onset of the flare. Observations suggest
that the observed material flow represents neither the emergence nor
convergence of the magnetic flux. Rather, it may be considered to be
material flow working both to increase the magnetic shear along the
polarity inversion line and to develop magnetic structures favorable
for the onset of the eruptive flare.
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Title: The solar cycle dependence of the weak internetwork flux
Authors: Lites, Bruce W.; Centeno, Rebecca; McIntosh, Scott W.
2014PASJ...66S...4L Altcode: 2014PASJ..tmp..109L
We examine data from the Hinode Observing Program 79 (the "HOP 79"
irradiance program) as observed using the Hinode Solar Optical
Telescope Spectro-Polarimeter for systematic changes in the weakest
observable magnetic flux during the period 2008-2013. At moderate
latitudes we find no evidence for systematic changes as a function
of time and solar latitude in either the unsigned line-of-sight flux
or in the measures of the transverse flux. However, in the polar
regions, changes are apparent in the measure of signed magnetic flux
corresponding to reversal of the polarity of the poles, changes that
persist even for the weakest observed flux. Also evident in measures
of the weakest signed flux are preferences for positive (negative)
polarity at mid-north (mid-south) latitudes (20°-60°). Center-limb
variations in various measures of the weak flux appear to be independent
of the solar cycle. The results are consistent with the operation of
a small-scale solar dynamo operating within and just below the solar
photosphere, but the measures of the weakest signed flux still contain
small signatures of the global solar cycle.
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Title: Unresolved Mixed Polarity Magnetic Fields at Flux Cancellation
Site in Solar Photosphere at 0.”3 Spatial Resolution
Authors: Kubo, Masahito; Chye Low, Boon; Lites, Bruce W.
2014ApJ...793L...9K Altcode: 2014arXiv1408.5796K
This is a follow-up investigation of a magnetic flux cancellation
event at a polarity inversion line (PIL) on the Sun observed with the
spectropolarimeter on board Hinode. Anomalous circular polarization
(Stokes V) profiles are observed in the photosphere along the PIL
at the cancellation sites. Kubo et al. previously reported that
the theoretically expected horizontal fields between the canceling
opposite-polarity magnetic elements in this event are not detected at
granular scales. We show that the observed anomalous Stokes V profiles
are reproduced successfully by adding the nearly symmetric Stokes
V profiles observed at pixels immediately adjacent to the PIL. This
result suggests that these observed anomalous Stokes V profiles are not
indications of a flux removal process, but are the result of either
a mixture of unresolved, opposite-polarity magnetic elements or the
unresolved width of the PIL, at an estimated resolution element of
about 0.”3. The hitherto undetected flux removal process accounting
for the larger-scale disappearance of magnetic flux during the observing
period is likely to also fall below resolution.
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Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Kushner, G. D.;
Akin, D. J.; Allard, B.; Berger, T.; Boerner, P.; Cheung, M.; Chou,
C.; Drake, J. F.; Duncan, D. W.; Freeland, S.; Heyman, G. F.; Hoffman,
C.; Hurlburt, N. E.; Lindgren, R. W.; Mathur, D.; Rehse, R.; Sabolish,
D.; Seguin, R.; Schrijver, C. J.; Tarbell, T. D.; Wülser, J. -P.;
Wolfson, C. J.; Yanari, C.; Mudge, J.; Nguyen-Phuc, N.; Timmons,
R.; van Bezooijen, R.; Weingrod, I.; Brookner, R.; Butcher, G.;
Dougherty, B.; Eder, J.; Knagenhjelm, V.; Larsen, S.; Mansir, D.;
Phan, L.; Boyle, P.; Cheimets, P. N.; DeLuca, E. E.; Golub, L.;
Gates, R.; Hertz, E.; McKillop, S.; Park, S.; Perry, T.; Podgorski,
W. A.; Reeves, K.; Saar, S.; Testa, P.; Tian, H.; Weber, M.; Dunn, C.;
Eccles, S.; Jaeggli, S. A.; Kankelborg, C. C.; Mashburn, K.; Pust, N.;
Springer, L.; Carvalho, R.; Kleint, L.; Marmie, J.; Mazmanian, E.;
Pereira, T. M. D.; Sawyer, S.; Strong, J.; Worden, S. P.; Carlsson,
M.; Hansteen, V. H.; Leenaarts, J.; Wiesmann, M.; Aloise, J.; Chu,
K. -C.; Bush, R. I.; Scherrer, P. H.; Brekke, P.; Martinez-Sykora,
J.; Lites, B. W.; McIntosh, S. W.; Uitenbroek, H.; Okamoto, T. J.;
Gummin, M. A.; Auker, G.; Jerram, P.; Pool, P.; Waltham, N.
2014SoPh..289.2733D Altcode: 2014arXiv1401.2491D; 2014SoPh..tmp...25D
The Interface Region Imaging Spectrograph (IRIS) small explorer
spacecraft provides simultaneous spectra and images of the photosphere,
chromosphere, transition region, and corona with 0.33 - 0.4 arcsec
spatial resolution, two-second temporal resolution, and 1 km
s<SUP>−1</SUP> velocity resolution over a field-of-view of up to
175 arcsec × 175 arcsec. IRIS was launched into a Sun-synchronous
orbit on 27 June 2013 using a Pegasus-XL rocket and consists of a
19-cm UV telescope that feeds a slit-based dual-bandpass imaging
spectrograph. IRIS obtains spectra in passbands from 1332 - 1358 Å,
1389 - 1407 Å, and 2783 - 2834 Å, including bright spectral lines
formed in the chromosphere (Mg II h 2803 Å and Mg II k 2796 Å) and
transition region (C II 1334/1335 Å and Si IV 1394/1403 Å). Slit-jaw
images in four different passbands (C II 1330, Si IV 1400, Mg II k
2796, and Mg II wing 2830 Å) can be taken simultaneously with spectral
rasters that sample regions up to 130 arcsec × 175 arcsec at a variety
of spatial samplings (from 0.33 arcsec and up). IRIS is sensitive to
emission from plasma at temperatures between 5000 K and 10 MK and will
advance our understanding of the flow of mass and energy through an
interface region, formed by the chromosphere and transition region,
between the photosphere and corona. This highly structured and dynamic
region not only acts as the conduit of all mass and energy feeding
into the corona and solar wind, it also requires an order of magnitude
more energy to heat than the corona and solar wind combined. The
IRIS investigation includes a strong numerical modeling component
based on advanced radiative-MHD codes to facilitate interpretation of
observations of this complex region. Approximately eight Gbytes of data
(after compression) are acquired by IRIS each day and made available
for unrestricted use within a few days of the observation.
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Title: The inference of the magnetic field vector in prominences
Authors: Lites, Bruce W.
2014IAUS..300..101L Altcode:
Prominences owe their existence to the presence of magnetic fields
in the solar corona. The magnetic field determines their geometry
and is crucial to their stability, energetics, and dynamics. This
review summarizes techniques for measurement of the magnetic field
vector in prominences. New techniques for inversions of full Stokes
spectro-polarimetry, incorporating both the Zeeman and Hanle mechanisms
for generation and modification of polarization, are now at the
forefront. Also reviewed are measurements of the magnetic fields in
the photosphere below prominences, and how they may be used to infer
the field geometry in and surrounding the prominence itself.
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Title: Improved Search of Principal Component Analysis Databases
for Spectro-polarimetric Inversion
Authors: Casini, R.; Asensio Ramos, A.; Lites, B. W.; López Ariste, A.
2013ApJ...773..180C Altcode: 2013arXiv1307.0061C
We describe a simple technique for the acceleration of
spectro-polarimetric inversions based on principal component analysis
(PCA) of Stokes profiles. This technique involves the indexing of the
database models based on the sign of the projections (PCA coefficients)
of the first few relevant orders of principal components of the
four Stokes parameters. In this way, each model in the database can
be attributed a distinctive binary number of 2<SUP>4n </SUP> bits,
where n is the number of PCA orders used for the indexing. Each of
these binary numbers (indices) identifies a group of "compatible"
models for the inversion of a given set of observed Stokes profiles
sharing the same index. The complete set of the binary numbers so
constructed evidently determines a partition of the database. The
search of the database for the PCA inversion of spectro-polarimetric
data can profit greatly from this indexing. In practical cases it
becomes possible to approach the ideal acceleration factor of 2<SUP>4n
</SUP> as compared to the systematic search of a non-indexed database
for a traditional PCA inversion. This indexing method relies on the
existence of a physical meaning in the sign of the PCA coefficients
of a model. For this reason, the presence of model ambiguities and of
spectro-polarimetric noise in the observations limits in practice the
number n of relevant PCA orders that can be used for the indexing.
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Title: The SP_PREP Data Preparation Package for the Hinode
Spectro-Polarimeter
Authors: Lites, B. W.; Ichimoto, K.
2013SoPh..283..601L Altcode:
The Hinode/Spectro-Polarimeter (SP) is the first space-borne precision
spectro-polarimeter for the study of solar phenomena. It is primarily
intended for measuring the solar photospheric vector magnetic field at
high spatial and spectral resolution. This objective requires that the
data are calibrated and conditioned to a high degree of precision. We
describe how the calibration package SP_PREP for the SP operates.
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Title: The Hinode Spectro-Polarimeter
Authors: Lites, B. W.; Akin, D. L.; Card, G.; Cruz, T.; Duncan, D. W.;
Edwards, C. G.; Elmore, D. F.; Hoffmann, C.; Katsukawa, Y.; Katz, N.;
Kubo, M.; Ichimoto, K.; Shimizu, T.; Shine, R. A.; Streander, K. V.;
Suematsu, A.; Tarbell, T. D.; Title, A. M.; Tsuneta, S.
2013SoPh..283..579L Altcode:
The joint Japan/US/UK Hinode mission includes the first large-aperture
visible-light solar telescope flown in space. One component of the
Focal Plane Package of that telescope is a precision spectro-polarimeter
designed to measure full Stokes spectra with the intent of using those
spectra to infer the magnetic-field vector at high precision in the
solar photosphere. This article describes the characteristics of the
flight hardware of the HinodeSpectro-Polarimeter, and summarizes its
in-flight performance.
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Title: Granular-Scale Magnetic Flux Cancellations in the Photosphere
Authors: Kubo, M.; Low, B. C.; Lites, B. W.
2012ASPC..454...41K Altcode:
We find the unresolved flux removal process at the polarity inversion
line formed by canceling opposite-polarity magnetic elements. Further
details and results of this work can be seen in Kubo et al. (2010).
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Title: Is There Observational Evidence Indicating a Small-Scale
Solar Dynamo?
Authors: Lites, B. W.
2012ASPC..455....3L Altcode:
Observations from the Hinode/SOT spectro-polarimeter are examined
with the aim of identifying diagnostics for the presence (or absence)
of a self-sustained small-scale turbulent dynamo in the upper solar
convection zone. We examine 45 Hinode data sets obtained during
2007. We find much smaller net flux imbalance within regions of the
quiet Sun having very weak flux compared to the imbalance averaged
over each data set. Further, there is no correlation of the average
net unsigned flux of regions having very weak flux relative to the
average unsigned flux of the entire region. If internetwork fields
were to arise from dispersal of flux from active regions, one would
expect both measures to show significant correlation, so this analysis
strongly supports the small-scale dynamo scenario. We also find that the
average of the longitudinal apparent flux density increases slightly
toward the limb for the very weakest observed flux elements. This
behavior is likely the result of the dominance of horizontal fields
higher in the photosphere. From data with very high signal-to-noise
ratio, the distribution of magnetic field strength indicates that the
magnetic energy of the quiet Sun is dominated by the small fraction
of field elements having kG strengths. These strong-field elements
are responsible for most of the imbalance of magnetic flux measured
in each region, so it is suggested that they arise primarily from
dispersal of flux from active regions, not from a small-scale dynamo.
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Title: Emergence of Twisted Flux in Prominence Observations
Authors: Okamoto, T. J.; Tsuneta, S.; Berger, T. E.; Lites, B. W.
2012ASPC..455..123O Altcode:
The emergence of twisted flux is a key process for supply of magnetic
flux into the corona as well as solar dynamic activities such as sunspot
formation and trigger of coronal mass ejections. In particular, there
are numerous discussions about the role and necessity of twisted flux
emergence for origin of prominences. However, the difficulty to measure
vector magnetic fields has not allowed us to investigate the detailed
relationship between emerging twisted flux and prominence. Hinode has
changed the situation. The Spectro-Polarimeter aboard Hinode has high
sensitivity to weaker magnetic fields of fine structures, and provides
opportunities to detect weak horizontal magnetic fields. As a result,
we have obtained signatures of twisted flux emergence associated with
prominences: The observational features are "broadening and narrowing
of a region dominated by horizontal magnetic field" and "rotating
direction of horizontal field" on the photosphere. Moreover, the data
show the interaction between the emerging twisted flux and granules,
and that the flux rope has high intrinsic strength 650 G, while the
flux density is as low as 100 G. Theoretical research with numerical
simulation on the basis of these results is active. In addition, we
investigate activities of a coronal cavity overlying a prominence on
the limb, and suggest the existence of twisted flux rope to explain the
activities of prominence and the coronal cavity comprehensively. Here
we introduce both these observational and theoretical results, and
discuss the details about emerging twisted flux.
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Title: Hinode Observations Suggesting the Presence of a Local
Small-scale Turbulent Dynamo
Authors: Lites, B. W.
2011ApJ...737...52L Altcode:
Analysis of observations from the Hinode/Solar Optical Telescope
spectropolarimeter (SP) yields results that are consistent with
the operation of a small-scale turbulent dynamo in the upper solar
convection zone. Examination of 45 Hinode data sets obtained in 2007
reveals only a very small correlation of the net polarity imbalance of
the regions of the quiet Sun having very weak flux, relative to the
polarity imbalance averaged over each data set. Further, there is no
correlation of the average net unsigned flux of those regions of weakest
flux with the average unsigned flux of each region studied. Positive
correlations, especially of the net unsigned flux, should exist if
the internetwork fields were to arise from dispersal of flux from
active regions, so the absence of significant correlations supports
the small-scale dynamo (SSD) scenario. Considering only regions of
weakest flux, the net longitudinal flux increases slightly toward the
limb, probably as the result of the dominance of horizontal fields
higher in the photosphere. Inferred distributions of magnetic field
strength as derived from inversions of Stokes profiles indicate that
the magnetic energy of the quiet Sun observed at the resolution of
the Hinode SP is dominated by the small fraction of field elements
having kilo-Gauss strengths. Because these strong-field elements carry
most of the imbalance of magnetic flux measured in each region, they
likely arise primarily from dispersal of flux from active regions,
rather than from an SSD.
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Title: Temporal Relation Between the Disappearance of Penumbral
Fine-scale Structure and Evershed Flow
Authors: Kubo, M.; Ichimoto, K.; Lites, B. W.; Shine, R. A.
2011ApJ...731...84K Altcode: 2011arXiv1102.1137K
We investigate the temporal relation between the Evershed flow,
dot-like bright features (penumbral grain), the complex magnetic
field structure, and dark lanes (dark core) along bright filaments in
a sunspot penumbra. We use a time series of high spatial resolution
photospheric intensity, vector magnetic field maps, and Doppler velocity
maps obtained with the Solar Optical Telescope aboard the Hinode
spacecraft. We conclude that the appearance and disappearance of the
Evershed flow and penumbra grains occur at nearly the same time and are
associated with changes of the inclination angle of the magnetic field
from vertical to more horizontal. This supports the idea that Evershed
flow is a result of thermal convection in the inclined field lines. The
dark core of the bright penumbral filament also appears coincidental
with the Evershed flow. However, the dark-cored bright filament
survives at least for 10-20 minutes after the disappearance of the
Evershed flow. The heat input into the bright filament continues even
after the end of heat transfer by the Evershed flow. This suggests that
local heating along the bright filament is important for maintaining
its brightness, in addition to heat transfer by the Evershed flow.
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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.
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Title: Observations of solar scattering polarization at high spatial
resolution
Authors: Snik, F.; de Wijn, A. G.; Ichimoto, K.; Fischer, C. E.;
Keller, C. U.; Lites, B. W.
2010A&A...519A..18S Altcode: 2010arXiv1005.5042S
Context. The weak, turbulent magnetic fields that supposedly
permeate most of the solar photosphere are difficult to observe,
because the Zeeman effect is virtually blind to them. The Hanle
effect, acting on the scattering polarization in suitable lines,
can in principle be used as a diagnostic for these fields. However,
the prediction that the majority of the weak, turbulent field resides
in intergranular lanes also poses significant challenges to scattering
polarization observations because high spatial resolution is usually
difficult to attain. <BR /> Aims: We aim to measure the difference
in scattering polarization between granules and intergranules. We
present the respective center-to-limb variations, which may serve as
input for future models. <BR /> Methods: We perform full Stokes filter
polarimetry at different solar limb positions with the CN band filter
of the Hinode-SOT Broadband Filter Imager, which represents the first
scattering polarization observations with sufficient spatial resolution
to discern the granulation. Hinode-SOT offers unprecedented spatial
resolution in combination with high polarimetric sensitivity. The CN
band is known to have a significant scattering polarization signal,
and is sensitive to the Hanle effect. We extend the instrumental
polarization calibration routine to the observing wavelength,
and correct for various systematic effects. <BR /> Results: The
scattering polarization for granules (i.e., regions brighter than
the median intensity of non-magnetic pixels) is significantly larger
than for intergranules. We derive that the intergranules (i.e., the
remaining non-magnetic pixels) exhibit (9.8±3.0)% less scattering
polarization for 0.2 < μ ≤ 0.3, although systematic effects cannot
be completely excluded. <BR /> Conclusions: These observations constrain
MHD models in combination with (polarized) radiative transfer in terms
of CN band line formation, radiation anisotropy, and magnetic fields.
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Title: Emergence of Helical Flux and the Formation of an Active
Region Filament Channel
Authors: Lites, B. W.; Kubo, M.; Berger, T.; Frank, Z.; Shine, R.;
Tarbell, T.; Title, A.; Okamoto, T. J.; Otsuji, K.
2010ApJ...718..474L Altcode:
We present comprehensive observations of the formation and evolution
of a filament channel within NOAA Active Region (AR) 10978 from
Hinode/Solar Optical Telescope and TRACE. We employ sequences
of Hinode spectro-polarimeter maps of the AR, accompanying Hinode
Narrowband Filter Instrument magnetograms in the Na I D1 line, Hinode
Broadband Filter Instrument filtergrams in the Ca II H line and G-band,
Hinode X-ray telescope X-ray images, and TRACE Fe IX 171 Å image
sequences. The development of the channel resembles qualitatively
that presented by Okamoto et al. in that many indicators point to
the emergence of a pre-existing sub-surface magnetic flux rope. The
consolidation of the filament channel into a coherent structure takes
place rapidly during the course of a few hours, and the filament form
then gradually shrinks in width over the following two days. Particular
to this filament channel is the observation of a segment along its
length of horizontal, weak (500 G) flux that, unlike the rest of the
filament channel, is not immediately flanked by strong vertical plage
fields of opposite polarity on each side of the filament. Because this
isolated horizontal field is observed in photospheric lines, we infer
that it is unlikely that the channel formed as a result of reconnection
in the corona, but the low values of inferred magnetic fill fraction
along the entire length of the filament channel suggest that the bulk
of the field resides somewhat above the low photosphere. Correlation
tracking of granulation in the G band presents no evidence for either
systematic flows toward the channel or systematic shear flows along
it. The absence of these flows, along with other indications of these
data from multiple sources, reinforces (but does not conclusively
demonstrate) the picture of an emerging flux rope as the origin of
this AR filament channel.
---------------------------------------------------------
Title: Quiescent Prominence Dynamics Observed with the Hinode Solar
Optical Telescope. I. Turbulent Upflow Plumes
Authors: Berger, Thomas E.; Slater, Gregory; Hurlburt, Neal; Shine,
Richard; Tarbell, Theodore; Title, Alan; Lites, Bruce W.; Okamoto,
Takenori J.; Ichimoto, Kiyoshi; Katsukawa, Yukio; Magara, Tetsuya;
Suematsu, Yoshinori; Shimizu, Toshifumi
2010ApJ...716.1288B Altcode:
Hinode/Solar Optical Telescope (SOT) observations reveal two new
dynamic modes in quiescent solar prominences: large-scale (20-50 Mm)
"arches" or "bubbles" that "inflate" from below into prominences, and
smaller-scale (2-6 Mm) dark turbulent upflows. These novel dynamics are
related in that they are always dark in visible-light spectral bands,
they rise through the bright prominence emission with approximately
constant speeds, and the small-scale upflows are sometimes observed to
emanate from the top of the larger bubbles. Here we present detailed
kinematic measurements of the small-scale turbulent upflows seen in
several prominences in the SOT database. The dark upflows typically
initiate vertically from 5 to 10 Mm wide dark cavities between the
bottom of the prominence and the top of the chromospheric spicule
layer. Small perturbations on the order of 1 Mm or less in size
grow on the upper boundaries of cavities to generate plumes up to
4-6 Mm across at their largest widths. All plumes develop highly
turbulent profiles, including occasional Kelvin-Helmholtz vortex
"roll-up" of the leading edge. The flows typically rise 10-15 Mm before
decelerating to equilibrium. We measure the flowfield characteristics
with a manual tracing method and with the Nonlinear Affine Velocity
Estimator (NAVE) "optical flow" code to derive velocity, acceleration,
lifetime, and height data for several representative plumes. Maximum
initial speeds are in the range of 20-30 km s<SUP>-1</SUP>, which
is supersonic for a ~10,000 K plasma. The plumes decelerate in the
final few Mm of their trajectories resulting in mean ascent speeds
of 13-17 km s<SUP>-1</SUP>. Typical lifetimes range from 300 to 1000
s (~5-15 minutes). The area growth rate of the plumes (observed as
two-dimensional objects in the plane of the sky) is initially linear
and ranges from 20,000 to 30,000 km<SUP>2</SUP> s<SUP>-1</SUP> reaching
maximum projected areas from 2 to 15 Mm<SUP>2</SUP>. Maximum contrast of
the dark flows relative to the bright prominence plasma in SOT images
is negative and ranges from -10% for smaller flows to -50% for larger
flows. Passive scalar "cork movies" derived from NAVE measurements show
that prominence plasma is entrained by the upflows, helping to counter
the ubiquitous downflow streams in the prominence. Plume formation
shows no clear temporal periodicity. However, it is common to find
"active cavities" beneath prominences that can spawn many upflows in
succession before going dormant. The mean flow recurrence time in these
active locations is roughly 300-500 s (5-8 minutes). Locations remain
active on timescales of tens of minutes up to several hours. Using a
column density ratio measurement and reasonable assumptions on plume
and prominence geometries, we estimate that the mass density in the
dark cavities is at most 20% of the visible prominence density, implying
that a single large plume could supply up to 1% of the mass of a typical
quiescent prominence. We hypothesize that the plumes are generated from
a Rayleigh-Taylor instability taking place on the boundary between
the buoyant cavities and the overlying prominence. Characteristics,
such as plume size and frequency, may be modulated by the strength
and direction of the cavity magnetic field relative to the prominence
magnetic field. We conclude that buoyant plumes are a source of
quiescent prominence mass as well as a mechanism by which prominence
plasma is advected upward, countering constant gravitational drainage.
---------------------------------------------------------
Title: Granular-scale Magnetic Flux Cancellations in the Photosphere
Authors: Kubo, M.; Low, B. C.; Lites, B. W.
2010ApJ...712.1321K Altcode: 2010arXiv1003.2863K
We investigate the evolution of five granular-scale magnetic flux
cancellations just outside the moat region of a sunspot by using
accurate spectropolarimetric measurements and G-band images with the
Solar Optical Telescope (SOT) aboard Hinode. The opposite-polarity
magnetic elements approach a junction of the intergranular lanes and
then collide with each other there. The intergranular junction has
strong redshifts, darker intensities than the regular intergranular
lanes, and surface converging flows. This clearly confirms that
the converging and downward convective motions are essential for the
approaching process of the opposite-polarity magnetic elements. However,
the motion of the approaching magnetic elements does not always match
with their surrounding surface flow patterns in our observations. This
suggests that, in addition to the surface flows, subsurface downward
convective motions and subsurface magnetic connectivities are important
for understanding the approach and collision of the opposite-polarity
elements observed in the photosphere. We find that the horizontal
magnetic field appears between the canceling opposite-polarity
elements in only one event. The horizontal fields are observed along
the intergranular lanes with Doppler redshifts. This cancellation is
most probably a result of the submergence (retraction) of low-lying
photospheric magnetic flux. In the other four events, the horizontal
field is not observed between the opposite-polarity elements at any time
when they approach and cancel each other. These approaching magnetic
elements are more concentrated rather than gradually diffused, and
they have nearly vertical fields even while they are in contact each
other. We thus infer that the actual flux cancellations are highly
time-dependent events at scales less than a pixel of Hinode SOT (about
200 km) near the solar surface.
---------------------------------------------------------
Title: Scattering Polarization in the Fe I 630 nm Emission Lines at
the Extreme Limb of the Sun
Authors: Lites, B. W.; Casini, R.; Manso Sainz, R.; Jurčák, J.;
Ichimoto, K.; Ishikawa, R.; Okamoto, T. J.; Tsuneta, S.; Bellot
Rubio, L.
2010ApJ...713..450L Altcode:
Spectro-polarimetric observations with the Solar Optical Telescope
onboard Hinode reveal the emission spectrum of the Fe I 630 nm lines
at the solar limb. The emission shell extends for less than 1” thereby
making it extremely difficult to detect from ground-based observatories
viewing the limb through the Earth's atmosphere. The linear polarization
signal is clearly due to scattering and it is predominantly oriented
in the radial direction. Using a comprehensive atomic model of
iron, we are able to interpret qualitatively the observed signals,
including the radial orientation of the linear polarization. The Hanle
effect causes the linear polarization of the Fe I 630 nm lines to be
sensitive to magnetic fields between ~0.1 G and ~40 G, and also to
be sensitive to the field's topology for stronger fields. The overall
degree of observed polarization can be reproduced by randomly oriented
horizontal magnetic fields of strength ≈2 G. The discovery of their
scattering polarization signals thus opens a new diagnostic opportunity
for these lines.
---------------------------------------------------------
Title: Emerging flux as the source of downflows in the chromosphere
Authors: Lites, B. W.
2010MmSAI..81..792L Altcode:
Downward flowing plasma is a common signature of Doppler diagnostics
in spectral lines forming in the chromosphere. Examples of such are the
foot points of arch filament systems associated with emerging flux and
the inverse Evershed flow in and around the penumbrae of sunspots. This
contribution puts forth the hypothesis that these downward flows,
at least those occurring in and around active regions, trace their
origin to the ubiquitous emergence of magnetic flux. In this scenario,
the buoyantly rising, emerging flux carries mass upward from lower
levels, then drains downward along magnetic lines of force to produce
the observed downflow signatures in the chromosphere and below. The
hypothesis is discussed and illustrated by chromospheric observations
of sunspots and filaments.
---------------------------------------------------------
Title: Granular scale magnetic flux cancellations .
Authors: Kubo, M.; Low, B. C.; Lites, B. W.
2010MmSAI..81..790K Altcode:
We summarize the evolution of granular-scale “magnetic-flux
cancellation” as observed with Hinode/SOT. Further details and results
of this work are given in \citet{Kubo2009}.
---------------------------------------------------------
Title: Unresolved Magnetic Flux Removal Process in the Photosphere
Authors: Kubo, Masahito; Chye Low, Boon; Lites, Bruce
2010cosp...38.2828K Altcode: 2010cosp.meet.2828K
The mutual loss of magnetic flux due to the apparent collision
of opposite-polarity magnetic elements is called "magnetic flux
cancellation" as a descriptive term. The flux cancellation is
essential to understand the dissipation of magnetic flux from the
solar surface. An Ω-loop submerging below the surface or a U-loop
rising through the photosphere is the usual idea to explain the
magnetic flux cancellation. Magnetic reconnection may be crucial for
the forma-tion of these loops, especially for the submerging -loop. In
fact, chromospheric and coronal activities are often observed at the
cancellation sites. We investigate the evolution of 5 cancel-lation
events of the opposite-polarity magnetic elements at granular scales by
using accurate spectropolarimetric measurements with the Solar Optical
Telescope aboard Hinode. We find that the horizontal magnetic field,
which is expected in both submerging Ω-loop model and emerging U-loop
model, does not appear between the canceling magnetic elements in 4
of the 5 events. The approaching magnetic elements in these events are
more concentrated rather than gradually diffused, and they have nearly
vertical fields even while they are in contact each other. We thus imply
that the actual flux cancellation is highly time dependent event near
the solar surface at scales less than a pixel of Hinode/SOT (about 200
km). At the polarity inversion line formed by the canceling magnetic
elements, highly asymmetric Stokes-V profiles are observed. We confirm
that such asymmetric profile can be made by the sum of the profiles at
the opposite-polarity magnetic elements next to the polarity inversion
line. This means that the approaching bipolar flux tubes still keep
their nature within the pixel where they come in contact with each
other, and thus supports the unresolved flux removal process within
the pixel at the polarity inversion line.
---------------------------------------------------------
Title: Hinode's SP and G-band Co-Alignment
Authors: Centeno, R.; Lites, B.; de Wijn, A. G.; Elmore, D.
2009ASPC..415..323C Altcode: 2009arXiv0902.0027C
We analyze the co-alignment between Hinode's BFI-Gband images and
simultaneous SP maps with the aim of characterizing the general off-sets
between them and the second order non-linear effects in SP's slit
scanning mechanism. We provide calibration functions and parameters
to correct for the nominal pixel scales and positioning
---------------------------------------------------------
Title: Statistics of Convective Collapse Events in the Photosphere
and Chromosphere Observed with the HINODE SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
Keller, C. U.
2009ASPC..415..127F Altcode:
Convective collapse, a theoretically predicted process that
intensifies existing weak magnetic fields in the solar atmosphere,
was first directly observed in a single event by Nagata et al. (2008)
using the high resolution Solar Optical Telescope (SOT) of the Hinode
satellite. Using the same space telescope, we observed 49 such events
and present a statistical analysis of convective collapse events. Our
data sets consist of high resolution time series of polarimetric
spectral scans of two iron lines formed in the lower photosphere and
filter images in Mg I b<SUB>2</SUB> and Ca II H. We were thus able
to study the implication of convective collapse events on the high
photospheric and the chromospheric layers. The physical parameters from
the full Stokes profiles were obtained with the MERLIN Milne-Eddington
inversion code. For each of the 49 events we determined the duration,
maximum photospheric downflow, and field strength increase. We found
event durations of about 10 minutes and field strengths of up to
1.65 kG.
---------------------------------------------------------
Title: Magnetic Flux Budget in a Decaying Active Region
Authors: Kubo, M.; Lites, B. W.; Shimizu, T.; Ichimoto, K.
2009ASPC..415..359K Altcode:
We investigate the sunspot decay process in terms of the magnetic flux
budget of a decaying sunspot. This article is based on results in Kubo
et al. 2008. Please see this paper for further details.
---------------------------------------------------------
Title: Is Flux Submergence an Essential Aspect of Flux Emergence?
Authors: Lites, B. W.; Frank, Z.; Shine, R. A.; Title, A. M.;
Ichimoto, K.
2009ASPC..415..172L Altcode:
High resolution Hinode Spectro-Polarimeter observations permit one
to examine the detailed structure of the magnetic field vector in
emerging flux regions. We find the field to have a concave-upward
geometry on the smallest scales observed (0.3 arcsec), indicating the
presence of U-loops at the sites of approaching and canceling opposite
polarities. This structure suggests that reconnection is taking place
at or below the surface, allowing the emerging flux to rid itself of
its considerable mass burden. Supersonic down flows are often observed
adjacent to, but not coincident with, the sites of canceling flux. We
propose that these are the sites that drain the mass contained in the
buoyantly-rising flux elements. The observations then suggest a process
of sub-surface reconnection producing O-loops that then are forced to
descend with the intergranular convective down flows, thus making flux
submergence important to the larger scale flux emergence process.
---------------------------------------------------------
Title: The Second Hinode Science Meeting: Beyond Discovery-Toward
Understanding
Authors: Lites, B.; Cheung, M.; Magara, T.; Mariska, J.; Reeves, K.
2009ASPC..415.....L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Granular Scale Magnetic Flux Cancellations as Observed with
the Hinode/SOT
Authors: Kubo, M.; Low, B.; Lites, B. W.
2009AGUFMSH53B..05K Altcode:
The mutual loss of magnetic flux due to the apparent collision
of opposite-polarity magnetic elements is called “magnetic flux
cancellation” as a descriptive term. The flux cancellation is
essential to understand the dissipation of magnetic flux from the
solar surface. We investigate the evolution of 5 granular-scale flux
cancellations just outside the moat region of a sunspot by using
accurate spectropolarimetric measurements with the Solar Optical
Telescope aboard Hinode. We find that the opposite-polarity magnetic
elements approach a junction of the intergranular lanes and then they
collide with each other there. The intergranular junction has Doppler
red shifts, darker intensities than the regular intergranular lanes,
and surface converging flows. We also find that the horizontal magnetic
field appears between the canceling elements in only one event. The
horizontal fields are observed along the intergranular lanes with red
shifts. This cancellation is most probably a result of the submergence
of low-lying photospheric magnetic flux. In the other 4 events, the
horizontal field is not observed between the opposite-polarity magnetic
elements at any time when they approach and cancel each other. These
canceling elements have nearly vertical fields even while they are
in contact each other. These events are more interesting because
in the usual idea of the submergence of a low lying Ω-loop or the
buoyant rise of a U-loop, the appearance of a horizontal field is the
observational signature of the loop top (or bottom) passing across
the photosphere. Our observational results suggest the possibility
that the actual flux cancellation is highly time dependent events near
the solar surface at scales less than a pixel of Hinode/SOT (about 200
km). Observations with a spatial resolution higher than Hinode/SOT are
essential to reveal physical process of the dissipation of magnetic
flux on the Sun.
---------------------------------------------------------
Title: A new perspective on quiet Sun magnetism
Authors: Lites, Bruce William
2009ScChG..52.1660L Altcode:
The Hinode mission has provided us with a new, quantitative view of the
magnetism of the quiet Sun. It has revealed that the quiet internetwork
areas are blanketed by horizontal fields that appear at first sight
to have more flux than the vertical fields resolved on the same
0.3″ size scale. These measurements point to the possibility that
the horizontal fields might be the primary source of the “hidden
turbulent flux” of the quiet Sun anticipated from Hanle effect
depolarization. In this paper, evidence is presented suggesting that
the “seething” horizontal fields observed by Harvey in 2007 and the
horizontal fields revealed by Hinode are the same phenomenon. Because
the seething fields appear to be of uniform fluctuation over the whole
disk, the phenomenon is most likely not associated with the dynamo
source of solar activity. Thus, the small-scale “hidden turbulent
flux” lends support to the notion of a local solar dynamo acting on
granular sizes and time scales.
---------------------------------------------------------
Title: Statistics of convective collapse events in the photosphere
and chromosphere observed with the Hinode SOT
Authors: Fischer, C. E.; de Wijn, A. G.; Centeno, R.; Lites, B. W.;
Keller, C. U.
2009A&A...504..583F Altcode: 2009arXiv0906.2308F
Convective collapse, a theoretically predicted process that intensifies
existing weak magnetic fields in the solar atmosphere, was first
directly observed in a single event by Nagata et al. (2008, ApJ,
677, L145) using the high resolution Solar Optical Telescope (SOT)
of the Hinode satellite. Using the same space telescope, we observed
49 such events and present a statistical analysis of convective
collapse events. Our data sets consist of high resolution time series
of polarimetric spectral scans of two iron lines formed in the lower
photosphere and filter images in Mg I b{2} and Ca II H, spectral lines
that are formed in the high photosphere and the lower chromosphere,
respectively. We were thus able to study the implication of convective
collapse events on the high photospheric and the chromospheric
layers. We found that in all cases, the event was accompanied by a
continuum bright point and nearly always by a brightening in the Ca
II H images. The magnesium dopplergram exhibits a strong downflow in
about three quarters of the events that took place within the field
of view of the magnesium dopplergram. The physical parameters from
the full Stokes profiles were obtained with the MERLIN Milne-Eddington
inversion code. For each of the 49 events we determined the duration,
maximum photospheric downflow, field strength increase and size. We
found event durations of about 10 min, magnetic element radii of about
0.43 arcsec and 0.35 arcsec, before and after the event, respectively,
and field strengths of up to 1.65 kG.
---------------------------------------------------------
Title: Magnetic Flux Budget of a Decaying Sunspot
Authors: Kubo, Masahito; Lites, Bruce W.; Shimizu, Toshifumi;
Ichimoto, Kiyoshi
2009shin.confE...9K Altcode:
Numerous small magnetic elements called moving magnetic features (MMFs)
are generally observed in the moat region that surrounds a sunspot. We
attempt to address a basic question how much magnetic flux is carried
away from a sunspot by MMFs and is subsequently removed from the
photosphere. This is essential for understanding decay of sunspots
and distribution of magnetic flux on the Sun. We estimate the magnetic
flux budget in a decaying sunspot and its surrounding moat region by
using a time series of the spatial distribution of vector magnetic
fields in the photosphere. Spectropolarimetric measurements with the
Solar Optical Telescope aboard the Hinode satellite allow us, for
the first time, to know an accurate flux change without any effects
of atmospheric seeing. The amount of magnetic flux that decreases
in the sunspot and (inner) moat region is very similar to magnetic
flux transported to the outer boundary of the moat region. The flux
loss rates of magnetic elements with positive and negative polarities
balance each other around the outer boundary of the moat region. These
results suggest that most of the magnetic flux in the sunspot is
transported to the outer boundary of the moat region as MMFs, and
then the transported flux is removed from the photosphere by apparent
collisions of opposite-polarity magnetic elements (called
---------------------------------------------------------
Title: A New View of Fine Scale Dynamics and Magnetism of Sunspots
Revealed by Hinode/SOT
Authors: Ichimoto, K.; Suematsu, Y.; Katsukawa, Y.; Tsuneta, S.;
Shimojo, M.; Shimizu, T.; Shine, R. A.; Tarbell, T. D.; Berger, T.;
Title, A. M.; Lites, B. W.; Kubo, M.; Yokoyama, T.; Nagata, S.
2009ASPC..405..167I Altcode:
The Solar Optical Telescope on-board Hinode is providing a new view of
the fine scale dynamics in sunspots with its high spatial resolution and
unprecedented image stability. We present three features related to the
Evershed flow each of which raises a new puzzle in sunspot dynamics;
i.e., twisting appearance of penumbral filaments, the source and sink
of individual Evershed flow channels, and the net circular polarization
in penumbrae with its spatial relation to the Evershed flow channels.
---------------------------------------------------------
Title: Has Hinode Revealed the Missing Turbulent Flux of the
Quiet Sun?
Authors: Lites, B. W.; Kubo, M.; Socas-Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A. M.; Ichimoto, K.; Katsukawa,
Y.; Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2009ASPC..405..173L Altcode:
The Hinode Spectro-Polarimeter has revealed the presence of surprisingly
strong horizontal magnetic fields nearly everywhere in the quiet
solar atmosphere. These horizontal fields, along with measures of the
vertical fields, may be the signature of the “hidden turbulent flux”
of the quiet Sun. The measured horizontal fields average at least to
55 Gauss: nearly 5 times that of the measured longitudinal apparent
flux density. The nature of these fields are reviewed, and discussed
in the light of recent magneto-convection numerical simulations of
the quiet Sun.
---------------------------------------------------------
Title: Nonlinear Force-Free Magnetic Field Modeling of AR 10953:
A Critical Assessment
Authors: De Rosa, Marc L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; Amari, T.; Canou, A.; McTiernan,
J. M.; Régnier, S.; Thalmann, J. K.; Valori, G.; Wheatland, M. S.;
Wiegelmann, T.; Cheung, M. C. M.; Conlon, P. A.; Fuhrmann, M.;
Inhester, B.; Tadesse, T.
2009SPD....40.3102D Altcode:
Nonlinear force-free field (NLFFF) modeling seeks to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have failed to arrive at consistent solutions when
applied to (thus far, two) cases using the highest-available-resolution
vector magnetogram data from Hinode/SOT-SP (in the region of the
modeling area of interest) and line-of-sight magnetograms from
SOHO/MDI (where vector data were not available). One issue is that
NLFFF models require consistent, force-free vector magnetic boundary
data, and vector magnetogram data sampling the photosphere do not
satisfy this requirement. Consequently, several problems have arisen
that are believed to affect such modeling efforts. We use AR 10953
to illustrate these problems, namely: (1) some of the far-reaching,
current-carrying connections are exterior to the observational field
of view, (2) the solution algorithms do not (yet) incorporate the
measurement uncertainties in the vector magnetogram data, and/or (3)
a better way is needed to account for the Lorentz forces within the
layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.
---------------------------------------------------------
Title: Hinode Observation of the Magnetic Fields in a Sunspot Light
Bridge Accompanied by Long-Lasting Chromospheric Plasma Ejections
Authors: Shimizu, Toshifumi; Katsukawa, Yukio; Kubo, Masahito; Lites,
Bruce W.; Ichimoto, Kiyoshi; Suematsu, Yoshinori; Tsuneta, Saku;
Nagata, Shin'ichi; Shine, Richard A.; Tarbell, Theodore D.
2009ApJ...696L..66S Altcode:
We present high-resolution magnetic field measurements of a sunspot
light bridge (LB) that produced chromospheric plasma ejections
intermittently and recurrently for more than 1 day. The observations
were carried out with the Hinode Solar Optical Telescope on 2007
April 29 and 30. The spectro-polarimeter reveals obliquely oriented
magnetic fields with vertical electric current density higher than
100 mA m<SUP>-2</SUP> along the LB. The observations suggest that
current-carrying highly twisted magnetic flux tubes are trapped below
a cusp-shaped magnetic structure along the LB. The presence of trapped
current-carrying flux tubes is essential for causing long-lasting
chromospheric plasma ejections at the interface with pre-existing
vertically oriented umbral fields. A bidirectional jet was clearly
detected, suggesting magnetic reconnections occurring at very low
altitudes, slightly above the height where the vector magnetic fields
are measured. Moreover, we found another strong vertical electric
current on the interface between the current-carrying flux tube
and pre-existing umbral field, which might be a direct detection
of the currents flowing in the current sheet formed at the magnetic
reconnection sites.
---------------------------------------------------------
Title: A Critical Assessment of Nonlinear Force-Free Field Modeling
of the Solar Corona for Active Region 10953
Authors: De Rosa, Marc L.; Schrijver, Carolus J.; Barnes, Graham;
Leka, K. D.; Lites, Bruce W.; Aschwanden, Markus J.; Amari, Tahar;
Canou, Aurélien; McTiernan, James M.; Régnier, Stéphane; Thalmann,
Julia K.; Valori, Gherardo; Wheatland, Michael S.; Wiegelmann, Thomas;
Cheung, Mark C. M.; Conlon, Paul A.; Fuhrmann, Marcel; Inhester,
Bernd; Tadesse, Tilaye
2009ApJ...696.1780D Altcode: 2009arXiv0902.1007D
Nonlinear force-free field (NLFFF) models are thought to be viable
tools for investigating the structure, dynamics, and evolution of
the coronae of solar active regions. In a series of NLFFF modeling
studies, we have found that NLFFF models are successful in application
to analytic test cases, and relatively successful when applied
to numerically constructed Sun-like test cases, but they are less
successful in application to real solar data. Different NLFFF models
have been found to have markedly different field line configurations
and to provide widely varying estimates of the magnetic free energy in
the coronal volume, when applied to solar data. NLFFF models require
consistent, force-free vector magnetic boundary data. However,
vector magnetogram observations sampling the photosphere, which is
dynamic and contains significant Lorentz and buoyancy forces, do not
satisfy this requirement, thus creating several major problems for
force-free coronal modeling efforts. In this paper, we discuss NLFFF
modeling of NOAA Active Region 10953 using Hinode/SOT-SP, Hinode/XRT,
STEREO/SECCHI-EUVI, and SOHO/MDI observations, and in the process
illustrate three such issues we judge to be critical to the success of
NLFFF modeling: (1) vector magnetic field data covering larger areas
are needed so that more electric currents associated with the full
active regions of interest are measured, (2) the modeling algorithms
need a way to accommodate the various uncertainties in the boundary
data, and (3) a more realistic physical model is needed to approximate
the photosphere-to-corona interface in order to better transform the
forced photospheric magnetograms into adequate approximations of nearly
force-free fields at the base of the corona. We make recommendations
for future modeling efforts to overcome these as yet unsolved problems.
---------------------------------------------------------
Title: Magnetic Flux Budget of a Decaying Sunspot
Authors: Kubo, Masahito; Lites, B. W.; Shimizu, T.; Ichimoto, K.
2009SPD....40.0905K Altcode:
We estimate how much magnetic flux is lost in a decaying sunspot
and how much magnetic flux is carried away from the sunspot through
its surrounding moat region. A time series of spectropolarimetric
measurements with the Solar Optical Telescope aboard Hinode allows us,
for the first time, to investigate an accurate flux change without
any effects of atmospheric seeing. The amount of magnetic flux that
decreases in the sunspot and moat region is almost equal to that of
magnetic flux transported to the outer boundary of the moat region. The
flux loss rates of magnetic elements with positive and negative
polarities are balanced each other around the outer boundary of the
moat region. These results suggest that most of the magnetic flux in
the sunspot is transported to the outer boundary of the moat region
as moving magnetic features, and then removed from the photosphere by
flux cancellation around the moat boundary.
---------------------------------------------------------
Title: Direct Imaging of Fine Structure in the Chromosphere of a
Sunspot Umbra
Authors: Socas-Navarro, H.; McIntosh, S. W.; Centeno, R.; de Wijn,
A. G.; Lites, B. W.
2009ApJ...696.1683S Altcode: 2008arXiv0810.0597S
High-resolution imaging observations from the Hinode spacecraft in the
Ca II H line are employed to study the dynamics of the chromosphere
above a sunspot. We find that umbral flashes and other brightenings
produced by the oscillation are extremely rich in fine structure,
even beyond the resolving limit of our observations (0farcs22). The
umbra is tremendously dynamic to the point that our time cadence of
20 s does not suffice to resolve the fast lateral (probably apparent)
motion of the emission source. Some bright elements in our data set
move with horizontal propagation speeds of 30 km s<SUP>-1</SUP>. We have
detected filamentary structures inside the umbra (some of which have a
horizontal extension of ~1500 km) which, to our best knowledge, had not
been reported before. The power spectra of the intensity fluctuations
reveal a few distinct areas with different properties within the umbra
that seem to correspond with the umbral cores that form it. Inside
each one of these areas the dominant frequencies of the oscillation
are coherent, but they vary considerably from one core to another.
---------------------------------------------------------
Title: Prominence Formation Associated with an Emerging Helical
Flux Rope
Authors: Okamoto, Takenori J.; Tsuneta, Saku; Lites, Bruce W.; Kubo,
Masahito; Yokoyama, Takaaki; Berger, Thomas E.; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Nagata, Shin'ichi; Shibata, Kazunari; Shimizu,
Toshifumi; Shine, Richard A.; Suematsu, Yoshinori; Tarbell, Theodore
D.; Title, Alan M.
2009ApJ...697..913O Altcode: 2009arXiv0904.0007O
The formation and evolution process and magnetic configuration of
solar prominences remain unclear. In order to study the formation
process of prominences, we examine continuous observations of a
prominence in NOAA AR 10953 with the Solar Optical Telescope on
the Hinode satellite. As reported in our previous Letter, we find
a signature suggesting that a helical flux rope emerges from below
the photosphere under a pre-existing prominence. Here we investigate
more detailed properties and photospheric indications of the emerging
helical flux rope, and discuss their relationship to the formation of
the prominence. Our main conclusions are: (1) a dark region with absence
of strong vertical magnetic fields broadens and then narrows in Ca II
H-line filtergrams. This phenomenon is consistent with the emergence
of the helical flux rope as photospheric counterparts. The size of the
flux rope is roughly 30,000 km long and 10,000 km wide. The width is
larger than that of the prominence. (2) No shear motion or converging
flows are detected, but we find diverging flows such as mesogranules
along the polarity inversion line. The presence of mesogranules may
be related to the emergence of the helical flux rope. (3) The emerging
helical flux rope reconnects with magnetic fields of the pre-existing
prominence to stabilize the prominence for the next several days. We
thus conjecture that prominence coronal magnetic fields emerge in
the form of helical flux ropes that contribute to the formation and
maintenance of the prominence.
---------------------------------------------------------
Title: Emergence of Helical Flux and the Formation of an Active
Region Filament Channel
Authors: Lites, Bruce W.
2009SPD....40.0910L Altcode:
We present comprehensive observations from Hinode/SOT and TRACE of the
formation and evolution of a filament channel within NOAA Active Region
10978. We employ sequences of Hinode spectro-polarimeter maps of the
active region, accompaning Hinode NFI magnetograms in the Na I D1 line,
Hinode BFI filtergrams in the Ca II H-line and G-band, and TRACE Fe IX
171 [[Unable to Display Character: &#506]] image sequences. The
development of the channel resembles qualitatively that presented
by Okamoto et al. (2008,2009) in that many indicators that point to
the emergence of a pre-existing sub-surface flux rope. The formation
takes place rapidly in the course of a few hours, and the filament
channel gradually shrinks over the following two days. Particular to
this filament channel is the observation of a segment of horizontal,
weak (500 Gauss) flux that is not flanked by stronger field, opposite
polarity flux. Because this isolated horizontal field is observed in
photospheric lines, we infer that it is unlikely that the channel
formed as a result of reconnection in the higher layers of the
atmosphere. Furthermore, correlation tracking of granulation in the
G-band presents no evidence for either systematic flows toward the
channel or systematic shear flows along it. The absence of these flows
reinforces the picture of an emerging flux rope as the origin of this
filament channel.
---------------------------------------------------------
Title: The Topology and Behavior of Magnetic Fields Emerging at the
Solar Photosphere
Authors: Lites, B. W.
2009SSRv..144..197L Altcode: 2008SSRv..tmp..156L
The nature of flux emerging through the surface layers of the Sun is
examined in the light of new high-resolution magnetic field observations
from the Hinode space mission. The combination of vector magnetic
field data and visible-light imaging from Hinode support the hypothesis
that active region filaments are created as a result of an emerging,
twisted flux system. The observations do not present strong evidence
for an alternate hypothesis: that the filaments form as a result of
localized shear flows at the photospheric level. Examination of the
vector magnetic field at very small scales in emerging flux regions
suggests that reconnection at the photospheric level and below,
followed by submergence of flux, is a likely and essential part of
the flux emergence process. The reconnection and flux submergence are
driven by granular convection.
---------------------------------------------------------
Title: The Topology and Behavior of Magnetic Fields Emerging at the
Solar Photosphere
Authors: Lites, B. W.
2009odsm.book..197L Altcode:
The nature of flux emerging through the surface layers of the Sun is
examined in the light of new high-resolution magnetic field observations
from the Hinode space mission. The combination of vector magnetic
field data and visible-light imaging from Hinode support the hypothesis
that active region filaments are created as a result of an emerging,
twisted flux system. The observations do not present strong evidence
for an alternate hypothesis: that the filaments form as a result of
localized shear flows at the photospheric level. Examination of the
vector magnetic field at very small scales in emerging flux regions
suggests that reconnection at the photospheric level and below,
followed by submergence of flux, is a likely and essential part of
the flux emergence process. The reconnection and flux submergence are
driven by granular convection.
---------------------------------------------------------
Title: Observations and Nonlinear Force-Free Field Modeling of Active
Region 10953
Authors: Su, Yingna; van Ballegooijen, Adriaan; Lites, Bruce W.;
Deluca, Edward E.; Golub, Leon; Grigis, Paolo C.; Huang, Guangli;
Ji, Haisheng
2009ApJ...691..105S Altcode:
We present multiwavelength observations of a simple bipolar active
region (NOAA 10953), which produced several small flares (mostly B class
and one C8.5 class) and filament activations from April 30 to May 3 in
2007. We also explore nonlinear force-free field (NLFFF) modeling of
this region prior to the C8.5 flare on May 2, using magnetograph data
from SOHO/MDI and Hinode/SOT. A series of NLFFF models are constructed
using the flux-rope insertion method. By comparing the modeled field
lines with multiple X-ray loops observed by Hinode/XRT, we find that
the axial flux of the flux rope in the best-fit models is (7± 2)×
10<SUP>20</SUP> Mx, while the poloidal flux has a wider range of
(0.1-10)× 10<SUP>10</SUP> Mx cm<SUP>-1</SUP>. The axial flux in the
best-fit model is well below the upper limit (~15× 10<SUP>20</SUP>
Mx) for stable force-free configurations, which is consistent with the
fact that no successful full filament eruption occurred in this active
region. From multiwavelength observations of the C8.5 flare, we find
that the X-ray brightenings (in both RHESSI and XRT) appeared about 20
minutes earlier than the EUV brightenings seen in TRACE 171 Å images
and filament activations seen in MLSO Hα images. This is interpreted as
an indication that the X-ray emission may be caused by direct coronal
heating due to reconnection, and the energy transported down to the
chromosphere may be too low to produce EUV brightenings. This flare
started from nearly unsheared flare loop, unlike most two-ribbon flares
that begin with highly sheared footpoint brightenings. By comparing
with our NLFFF model, we find that the early flare loop is located
above the flux rope that has a sharp boundary. We suggest that this
flare started near the outer edge of the flux rope, not at the inner
side or at the bottom as in the standard two-ribbon flare model.
---------------------------------------------------------
Title: The Scientific Ballooning Program
Authors: Israel, Martin; Boggs, Steven; Cherry, Michael; Devlin,
Mark; Grindlay, Jonathan; Lites, Bruce; Ormes, Jonathan; Young, Eliot;
Tueller, Jack; Mitchell, John
2009astro2010P..24I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonlinear Force-Free Magnetic Field Modeling of the Solar
Corona: A Critical Assessment
Authors: De Rosa, M. L.; Schrijver, C. J.; Barnes, G.; Leka, K. D.;
Lites, B. W.; Aschwanden, M. J.; McTiernan, J. M.; Régnier, S.;
Thalmann, J.; Valori, G.; Wheatland, M. S.; Wiegelmann, T.; Cheung,
M.; Conlon, P. A.; Fuhrmann, M.; Inhester, B.; Tadesse, T.
2008AGUFMSH41A1604D Altcode:
Nonlinear force-free field (NLFFF) modeling promises to provide accurate
representations of the structure of the magnetic field above solar
active regions, from which estimates of physical quantities of interest
(e.g., free energy and helicity) can be made. However, the suite of
NLFFF algorithms have so far failed to arrive at consistent solutions
when applied to cases using the highest-available-resolution vector
magnetogram data from Hinode/SOT-SP (in the region of the modeling
area of interest) and line-of-sight magnetograms from SOHO/MDI (where
vector data were not been available). It is our view that the lack of
robust results indicates an endemic problem with the NLFFF modeling
process, and that this process will likely continue to fail until (1)
more of the far-reaching, current-carrying connections are within the
observational field of view, (2) the solution algorithms incorporate
the measurement uncertainties in the vector magnetogram data, and/or
(3) a better way is found to account for the Lorentz forces within
the layer between the photosphere and coronal base. In light of these
issues, we conclude that it remains difficult to derive useful and
significant estimates of physical quantities from NLFFF models.
---------------------------------------------------------
Title: Erratum: "Magnetic Flux Loss and Flux Transport in a Decaying
Active Region" (ApJ, 686, 1447 [2008])
Authors: Kubo, M.; Lites, B. W.; Shimizu, T.; Ichimoto, K.
2008ApJ...689.1456K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Magnetic Landscape of the Sun's Polar Region
Authors: Tsuneta, S.; Ichimoto, K.; Katsukawa, Y.; Lites, B. W.;
Matsuzaki, K.; Nagata, S.; Orozco Suárez, D.; Shimizu, T.; Shimojo,
M.; Shine, R. A.; Suematsu, Y.; Suzuki, T. K.; Tarbell, T. D.; Title,
A. M.
2008ApJ...688.1374T Altcode: 2008arXiv0807.4631T
We present observations of the magnetic landscape of the polar region
of the Sun that are unprecedented in terms of spatial resolution,
field of view, and polarimetric precision. They were carried out with
the Solar Optical Telescope aboard Hinode. Using a Milne-Eddington
inversion, we find many vertically oriented magnetic flux tubes
with field strengths as strong as 1 kG scattered in latitude between
70° and 90°. They all have the same polarity, consistent with the
global polarity of the polar region. The field vectors are observed to
diverge from the centers of the flux elements, consistent with a view
of magnetic fields that are expanding and fanning out with height. The
polar region is also found to have ubiquitous horizontal fields. The
polar regions are the source of the fast solar wind, which is channeled
along unipolar coronal magnetic fields whose photospheric source is
evidently rooted in the strong-field, vertical patches of flux. We
conjecture that vertical flux tubes with large expansion around the
photospheric-coronal boundary serve as efficient chimneys for Alfvén
waves that accelerate the solar wind.
---------------------------------------------------------
Title: Magnetic Flux Loss and Flux Transport in a Decaying Active
Region
Authors: Kubo, M.; Lites, B. W.; Shimizu, T.; Ichimoto, K.
2008ApJ...686.1447K Altcode: 2008arXiv0807.4340K
We estimate the temporal change of magnetic flux normal to the solar
surface in a decaying active region by using a time series of the
spatial distribution of vector magnetic fields in the photosphere. The
vector magnetic fields are derived from full spectropolarimetric
measurements with the Solar Optical Telescope aboard Hinode. We compare
a magnetic flux loss rate to a flux transport rate in a decaying sunspot
and its surrounding moat region. The amount of magnetic flux that
decreases in the sunspot and moat region is very similar to magnetic
flux transported to the outer boundary of the moat region. The flux
loss rates [(dF/dt)<SUB>loss</SUB>] of magnetic elements with positive
and negative polarities balance each other around the outer boundary of
the moat region. These results suggest that most of the magnetic flux
in the sunspot is transported to the outer boundary of the moat region
as moving magnetic features, and then removed from the photosphere by
flux cancellation around the outer boundary of the moat region.
---------------------------------------------------------
Title: Magnetic Fields of the Quiet Sun: A New Quantitative
Perspective From Hinode
Authors: Lites, B. W.; Kubo, M.; Socas-Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Katsukawa, Y.;
Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2008ASPC..397...17L Altcode:
This article summarizes results of studies presented in two papers
already published: Lites et al. (2007a); Lites et al. (2007b). Please
see these for further details.
---------------------------------------------------------
Title: On-orbit Performance of the Solar Optical Telescope aboard
Hinode
Authors: Ichimoto, K.; Katsukawa, Y.; Tarbell, T.; Shine, R. A.;
Hoffmann, C.; Berger, T.; Cruz, T.; Suematsu, Y.; Tsuneta, S.; Shimizu,
T.; Lites, B. W.
2008ASPC..397....5I Altcode: 2008arXiv0804.3248I
On-orbit performance of the Solar Optical Telescope (SOT) aboard Hinode
is described with some attention to its unpredicted aspects. In general,
SOT reveals an excellent performance and has been providing outstanding
data. Some unexpected features exist, however, in behaviours of the
focus position, throughput and structural stability. Most of them are
recovered by the daily operation i.e., frequent focus adjustment,
careful heater setting and corrections in data analysis. The
tunable filter contains air bubbles which degrade the data quality
significantly. Schemes for tuning the filter without disturbing the
bubbles have been developed and tested, and some useful procedures
to obtain Dopplergrams and magnetograms are now available. October
and March, when the orbit of satellite becomes nearly perpendicular
to the direction towards the Sun, provide a favourable condition for
continuous runs of the narrow-band filter imager.
---------------------------------------------------------
Title: Evolution of Magnetic Fields at the Boundary of the Penumbra
Authors: Kubo, M.; Ichimoto, K.; Shimizu, T.; Lites, B. W.; Tsuneta,
S.; Suematsu, Y.; Katsukawa, Y.; Nagata, S.; Tarbell, T.; Shine,
R. A.; Title, A. M.
2008ASPC..397...79K Altcode:
The formation of moving magnetic features (MMFs) separating from the
penumbra were successfully observed with the Solar Optical Telescope
(SOT) aboard the Hinode satellite. We find that bright features in
the outer penumbra are located at the penumbral spines, which have
magnetic fields more vertical than the surroundings, or located at the
MMFs separating from the spines. This suggests that convection in the
outer penumbra is related to the disintegration of the sunspot.
---------------------------------------------------------
Title: Hinode Observations of Magnetic Elements in Internetwork Areas
Authors: de Wijn, A. G.; Lites, B. W.; Berger, T. E.; Frank, Z. A.;
Tarbell, T. D.; Ishikawa, R.
2008ApJ...684.1469D Altcode: 2008arXiv0806.0345D
We use sequences of images and magnetograms from Hinode to
study magnetic elements in internetwork parts of the quiet solar
photosphere. Visual inspection shows the existence of many long-lived
(several hours) structures that interact frequently and may migrate
over distances of ~7 Mm over a period of a few hours. About a fifth
of the elements have an associated bright point in G-band or Ca
II H intensity. We apply a hysteresis-based algorithm to identify
elements. The algorithm is able to track elements for about 10 minutes
on average. Elements intermittently drop below the detection limit,
although the associated flux apparently persists and often reappears
some time later. We infer proper motions of elements from their
successive positions and find that they obey a Gaussian distribution
with an rms of 1.57 +/- 0.08 km s<SUP>-1</SUP>. The apparent flows
indicate a bias of about 0.2 km s<SUP>-1</SUP> toward the network
boundary. Elements of negative polarity show a higher bias than elements
of positive polarity, perhaps as a result of the dominant positive
polarity of the network in the field of view or because of increased
mobility due to their smaller size. A preference for motions in X is
likely explained by higher supergranular flow in that direction. We
search for emerging bipoles by grouping elements of opposite polarity
that appear close together in space and time. We find no evidence
supporting Joy's law at arcsecond scales.
---------------------------------------------------------
Title: Erratum: The Analysis of Penumbral Fine Structure Using an
Advanced Inversion Technique
Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi;
Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta,
Saku
2008PASJ...60..933J Altcode:
In the article [PASJ 59, S601-S606 (2007)], the word ”CSIC” was
omitted from the affiliation of Dr. Luis Bellot Rubio. The correct
affiliation is : <SUP>2</SUP>Instituto de Astrofísica de Andalucía
(CSIC), Apdo. de Correos 3004, 18080 Granada, Spain
---------------------------------------------------------
Title: Disintegration of Magnetic Flux in Decaying Sunspots as
Observed with the Hinode SOT
Authors: Kubo, M.; Lites, B. W.; Ichimoto, K.; Shimizu, T.; Suematsu,
Y.; Katsukawa, Y.; Tarbell, T. D.; Shine, R. A.; Title, A. M.; Nagata,
S.; Tsuneta, S.
2008ApJ...681.1677K Altcode: 2008arXiv0806.0415K
Continuous observations of sunspot penumbrae with the Solar Optical
Telescope aboard Hinode clearly show that the outer boundary of the
penumbra fluctuates around its averaged position. The penumbral outer
boundary moves inward when granules appear in the outer penumbra. We
discover that such granules appear one after another while moving
magnetic features (MMFs) are separating from the penumbral "spines"
(penumbral features that have fields that are stronger and more vertical
than those of their surroundings). These granules that appear in the
outer penumbra often merge with bright features inside the penumbra
that move with the spines as they elongate toward the moat region. This
suggests that convective motions around the penumbral outer boundary are
related to the disintegration of magnetic flux in the sunspot. We also
find that dark penumbral filaments frequently elongate into the moat
region in the vicinity of MMFs that detach from penumbral spines. Such
elongating dark penumbral filaments correspond to nearly horizontal
fields extending from the penumbra. Pairs of MMFs with positive and
negative polarities are sometimes observed along the elongating dark
penumbral filaments. This strongly supports the notion that such
elongating dark penumbral filaments have magnetic fields with a "sea
serpent"-like structure. Evershed flows, which are associated with the
penumbral horizontal fields, may be related to the detachment of the
MMFs from the penumbral spines, as well as to the formation of the MMFs
along the dark penumbral filaments that elongate into the moat region.
---------------------------------------------------------
Title: Polarization Calibration of the Solar Optical Telescope
onboard Hinode
Authors: Ichimoto, K.; Lites, B.; Elmore, D.; Suematsu, Y.; Tsuneta,
S.; Katsukawa, Y.; Shimizu, T.; Shine, R.; Tarbell, T.; Title, A.;
Kiyohara, J.; Shinoda, K.; Card, G.; Lecinski, A.; Streander, K.;
Nakagiri, M.; Miyashita, M.; Noguchi, M.; Hoffmann, C.; Cruz, T.
2008SoPh..249..233I Altcode: 2008SoPh..tmp...69I
The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector
magnetic fields on the Sun through precise spectropolarimetry of
solar spectral lines with a spatial resolution of 0.2 - 0.3 arcsec. A
photometric accuracy of 10<SUP>−3</SUP> is achieved and, after the
polarization calibration, any artificial polarization from crosstalk
among Stokes parameters is required to be suppressed below the level
of the statistical noise over the SOT's field of view. This goal was
achieved by the highly optimized design of the SOT as a polarimeter,
extensive analyses and testing of optical elements, and an end-to-end
calibration test of the entire system. In this paper we review both
the approach adopted to realize the high-precision polarimeter of the
SOT and its final polarization characteristics.
---------------------------------------------------------
Title: The Solar Optical Telescope for the Hinode Mission: An Overview
Authors: Tsuneta, S.; Ichimoto, K.; Katsukawa, Y.; Nagata, S.; Otsubo,
M.; Shimizu, T.; Suematsu, Y.; Nakagiri, M.; Noguchi, M.; Tarbell,
T.; Title, A.; Shine, R.; Rosenberg, W.; Hoffmann, C.; Jurcevich,
B.; Kushner, G.; Levay, M.; Lites, B.; Elmore, D.; Matsushita, T.;
Kawaguchi, N.; Saito, H.; Mikami, I.; Hill, L. D.; Owens, J. K.
2008SoPh..249..167T Altcode: 2008SoPh..tmp...74T; 2007arXiv0711.1715T
The Solar Optical Telescope (SOT) aboard the Hinode satellite
(formerly called Solar-B) consists of the Optical Telescope Assembly
(OTA) and the Focal Plane Package (FPP). The OTA is a 50-cm
diffraction-limited Gregorian telescope, and the FPP includes the
narrowband filtergraph (NFI) and the broadband filtergraph (BFI), plus
the Stokes Spectro-Polarimeter (SP). The SOT provides unprecedented
high-resolution photometric and vector magnetic images of the
photosphere and chromosphere with a very stable point spread function
and is equipped with an image-stabilization system with performance
better than 0.01 arcsec rms. Together with the other two instruments
on Hinode (the X-Ray Telescope (XRT) and the EUV Imaging Spectrometer
(EIS)), the SOT is poised to address many fundamental questions about
solar magnetohydrodynamics. This paper provides an overview; the
details of the instrument are presented in a series of companion papers.
---------------------------------------------------------
Title: Frequent Occurrence of High-Speed Local Mass Downflows on
the Solar Surface
Authors: Shimizu, T.; Lites, B. W.; Katsukawa, Y.; Ichimoto, K.;
Suematsu, Y.; Tsuneta, S.; Nagata, S.; Kubo, M.; Shine, R. A.; Tarbell,
T. D.
2008ApJ...680.1467S Altcode: 2008arXiv0804.1167S
We report on new spectropolarimetric measurements with simultaneous
filter imaging observation, revealing the frequent appearance of
polarization signals indicating high-speed, probably supersonic,
downflows that are associated with at least three different
configurations of magnetic fields in the solar photosphere. The
observations were carried out with the Solar Optical Telescope on
board the Hinode satellite. High-speed downflows are excited when a
moving magnetic feature is newly formed near the penumbral boundary of
sunspots. Also, a new type of downflows is identified at the edge of
sunspot umbra that lack accompanying penumbral structures. These may
be triggered by the interaction of magnetic fields swept by convection
with well-concentrated magnetic flux. Another class of high-speed
downflows are observed in quiet Sun and sunspot moat regions. These are
closely related to the formation of small concentrated magnetic flux
patches. High-speed downflows of all types are transient time-dependent
mass motions. These findings suggest that the excitation of supersonic
mass flows are one of the key observational features of the dynamical
evolution occurring in magnetic-field fine structures on the solar
surface.
---------------------------------------------------------
Title: Cooperative Observation of Ellerman Bombs between the Solar
Optical Telescope aboard Hinode and Hida/Domeless Solar Telescope
Authors: Matsumoto, Takuma; Kitai, Reizaburo; Shibata, Kazunari;
Nagata, Shin'ichi; Otsuji, Kenichi; Nakamura, Tahei; Watanabe, Hiroko;
Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Shimizu,
Toshifumi; Katsukawa, Yukio; Tarbell, Theodore D.; Lites, Bruce W.;
Shine, Richard A.; Title, Alan M.
2008PASJ...60..577M Altcode:
High-resolution CaIIH broad-band filter images of NOAA10933 on 2007
January 5 were obtained by the Solar Optical Telescope aboard the Hinode
satellite. Many small-scale (∼1") bright points were observed outside
the sunspot and inside the emerging flux region. We identified some of
these bright points with Ellerman bombs (EBs) by using Hα images taken
by the Domeless Solar Telescope at Hida observatory. The sub-arcsec
structures of two EBs seen in CaIIH were studied in detail. Our
observation showed the following two aspects: (1) The CaIIH bright
points identified with EBs were associated with the bipolar magnetic
field structures, as reported by previous studies. (2)The structure
of the CaIIH bright points turned out to consist of the following two
parts: a central elongated bright core (0.7" × 0.5") located along
the magnetic neutral line and a diffuse halo (1.2"×1.8").
---------------------------------------------------------
Title: Emergence of a helical flux rope and prominence formation
Authors: Okamoto, T. J.; Tsuneta, S.; Lites, B. W.; Kubo, M.; Yokoyama,
T.; Berger, T. E.; Ichimoto, K.; Katsukawa, Y.; Nagata, S.; Shibata,
K.; Shimizu, T.; Shine, R. A.; Suematsu, Y.; Tarbell, T. D.; Title,
A. M.
2008AGUSMSP43B..06O Altcode:
We report a discovery about emergence of a helical flux rope. The
episode may be related to the formation and evolution of an active
region prominence. Statistical studies by previous authors indicate that
numerous prominences have the inverse-polarity configuration suggesting
the helical magnetic configurations. There are two theoretical
models about formation of such a coronal helical magnetic field in
association with prominences: flux rope model and sheared-arcade
model. We have so far no clear observational evidence to support
either model. In order to find a clue about the formation of the
prominence, we had continuous observations of NOAA AR 10953 with the
SOT during 2007 April 28 to May 9. A prominence was located over the
polarity inversion line in the south-east of the main sunspot. These
observations provided us with a time series of vector magnetic fields
on the photosphere under the prominence. We found four new features:
(1) The abutting opposite-polarity regions on the two sides along
the polarity inversion line first grew laterally in size and then
narrowed. (2) These abutting regions contained vertically-weak,
but horizontally-strong magnetic fields. (3) The orientations of
the horizontal magnetic fields along the polarity inversion line on
the photosphere gradually changed with time from a normal- polarity
configuration to an inverse-polarity one. (4) The horizontal-magnetic
field region was blueshifted. These indicate that helical flux rope
emerges from below the photosphere into the corona along the polarity
inversion line under the prominence. We suggest that this supply of a
helical magnetic flux possibly into the corona is related to formation
and maintenance of active-region prominences.
---------------------------------------------------------
Title: Photospheric Signature of Penumbral Microjets
Authors: Katsukawa, Y.; Jurcak, J.; Ichimoto, K.; Suemtasu, Y.;
Tsuneta, S.; Shimizu, T.; Berger, T. E.; Shine, R. A.; Tarbell, T. D.;
Lites, B. W.
2008AGUSMSP53A..03K Altcode:
HINODE Solar Optical Telescope (SOT) discovered ubiquitous occurrence
of fine-scale jetlike activities in penumbral chromospheres, which
are referred to as penumbral microjets. The microjets' small width
of 400 km and short duration of less than 1 min make them difficult
to identify in existing ground-based observations. The apparent
rise velocity is faster than 50km/s and is roughly comparable to
the Alfven speed in the sunspot chromosphere. These properties of
penumbral microjets suggest that magnetic reconnection in uncombed
magnetic field configuration is the most possible cause of penumbral
microjets. In order to understand magnetic configuration associated with
penumbral microjets and prove the chromospheric magnetic reconnection
hypothesis, we investigated relationship between penumbral microjets
seen in CaIIH images and photospheric magnetic fields measured by
the HINODE spectro-polarimeter. We found the inclination angles of
penumbral microjets measured in CaII H images are roughly consistent
with inclination angles of relatively vertical magnetic field
component in uncombed magnetic field configuration. In addition,
strong and transient downflows are observed in the photosphere near
the boundary of a horizontal flux tube associated with a penumbral
microjet. The size of the downflow region is about 300km, which is
close to the width of penumbral microjets seen in CaII H images. The
downflow velocity of several km/s might be a result of an outflow of
chromospheric magnetic reconnection and suffer deceleration due to
the higher density in the photosphere.
---------------------------------------------------------
Title: Non-Linear Force-Free Field Modeling of a Solar Active Region
Around the Time of a Major Flare and Coronal Mass Ejection
Authors: De Rosa, M. L.; Schrijver, C. J.; Metcalf, T. R.; Barnes,
G.; Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann,
T.; Wheatland, M.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
M.; Kusano, K.; Régnier, S.; Thalmann, J.
2008AGUSMSP31A..06D Altcode:
Solar flares and coronal mass ejections are associated with rapid
changes in coronal magnetic field connectivity and are powered by
the partial dissipation of electrical currents that run through
the solar corona. A critical unanswered question is whether the
currents involved are induced by the advection along the photosphere
of pre-existing atmospheric magnetic flux, or whether these currents
are associated with newly emergent flux. We address this problem by
applying nonlinear force-free field (NLFFF) modeling to the highest
resolution and quality vector-magnetographic data observed by the
recently launched Hinode satellite on NOAA Active Region 10930 around
the time of a powerful X3.4 flare in December 2006. We compute 14
NLFFF models using 4 different codes having a variety of boundary
conditions. We find that the model fields differ markedly in geometry,
energy content, and force-freeness. We do find agreement of the best-fit
model field with the observed coronal configuration, and argue (1)
that strong electrical currents emerge together with magnetic flux
preceding the flare, (2) that these currents are carried in an ensemble
of thin strands, (3) that the global pattern of these currents and
of field lines are compatible with a large-scale twisted flux rope
topology, and (4) that the ~1032~erg change in energy associated with
the coronal electrical currents suffices to power the flare and its
associated coronal mass ejection. We discuss the relative merits of
these models in a general critique of our present abilities to model
the coronal magnetic field based on surface vector field measurements.
---------------------------------------------------------
Title: Evershed Flows as an Integral Part of Penumbral Formation
and its Fine Structure
Authors: Ryutova, M.; Berger, T.; Lites, B.; Title, A.; Frank, Z.
2008AGUSMSP41B..07R Altcode:
Observations of Evershed flows with the Solar Optical Telescope (SOT)
on Hinode (Ichimito, Shine, Lites, et al. 2008, PASJ, 59, S593) showed
that penumbral flows have small scale structures and much more complex
properties than those of a simple outflow of material with unique
direction and appearence. We address this problem and show that the
flow properties are directly connected to the observed properties of
penumbral filaments and are an integral part of penumbral development
during sunspot formation. In our recent model (Ryutova, Berger, &
Title, 2008, ApJ, 676, April), based on the observations that sunspot
has a filamentary structure and consists of a dense conglomerate of
non-collinear interlaced flux tubes, the penumbra is formed due to
an on-going reconnection processes that leads to branching out of the
peripheral flux tubes from the "trunk". As flux tubes have different
parameters, branching occurs at different heights and with different
inclinations, thus forming an "uncombed" penumbra. Each elemental act
of reconnection generates an inevitable twist in the post-reconnection
filaments that acquire a screw pinch configuration. This explains
the remarkable dynamic stability of penumbral filaments and their
observed properties, such as presence of dark cores, wrapping and
spinning of filaments around each other, bright footpoints, etc. Here
we show that propagation of twist along current carrying helical flux
tubes is accompanied by plasma flows that may have diverse properties
depending on the location of interacting flux tubes, their inclination
and pitch. We apply the model to observations taken with the SOT
instrument, which includes spectro-polarimetric data, and perform
quantitative analysis.
---------------------------------------------------------
Title: Sources and Sinks of the Evershed Flow
Authors: Shine, R. A.; Title, A. M.; Ichimoto, K.; Lites, B.
2008AGUSMSP31A..01S Altcode:
Extending the work of Ichimoto et al (2007), we investigate the sources
and sinks of the Evershed flow in sunspot penumbra using data from the
Solar Optical Telescope (SOT) instruments on the Hinode satellite. We
use spectral maps taken with the Spectro-Polarimeter (SP) that provide
detailed snapshots of the large sunspot in AR 10930 over a range
of viewing angles as it rotated across the solar disk in December
2006. These are supplemented by images taken with the Filtergraph
(FG) instrument that show the dynamics of the structures. AR 10930 has
some large sunspots showing sources and sinks within the penumbra as
well as near the inner and outer boundaries. There are also regions
of contact between penumbra of two sunspots (of opposite magnetic
polarity) that show stronger horizontal flows and downdrafts than seen
elsewhere in the penumbras. The relationship between Evershed "clouds"
showing quasi-periodic variations in the spatially averaged Evershed
flow and the penumbral fine structures is also investigated. This work
was supported by NASA contract NNM07AA01C.
---------------------------------------------------------
Title: Disintegration of Magnetic Flux in Decaying Sunspots as
Observed with the Hinode/SOT
Authors: Kubo, M.; Lites, B. W.; Ichimoto, K.; Shimizu, T.; Suematsu,
Y.; Katsukawa, Y.; Tarbell, T. D.; Shine, R. A.; Title, A. M.; Nagata,
S.; Tsuneta, S.
2008AGUSMSP31B..01K Altcode:
Continuous observations of sunspot penumbrae with the Solar Optical
Telescope aboard Hinode clearly show that the outer boundary of the
penumbra fluctuates around its averaged position. The penumbral outer
boundary moves inward when granules appear in the outer penumbra. We
discover that such granules appear one after another while moving
magnetic features (MMFs) are separating from the penumbral "spines"
(penumbral features having fields that are stronger and more vertical
than their surroundings). These granules that appear in the outer
penumbra often merge with bright features inside the penumbra that move
with spines as they elongate toward the moat region. This suggests that
convective motions around the penumbral outer boundary are related to
disintegration of magnetic flux in the sunspot. We also find that dark
penumbral filaments frequently elongate into the moat region in the
vicinity of MMFs that detach from penumbral spines. Such elongating
dark penumbral filaments correspond to nearly horizontal fields
extending from the penumbra. Pairs of MMFs with positive and negative
polarities are sometimes observed along the elongating dark penumbral
filaments. This strongly supports the notion that such elongating dark
penumbral filaments have magnetic fields with a "sea serpent"-like
structure. Evershed flows, which are associated with the penumbral
horizontal fields, may be related to detachment of the MMFs from the
penumbral spines, as well as to the formation of the MMFs along the
dark penumbral filaments that elongate into the moat region.
---------------------------------------------------------
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: Formation of Solar Magnetic Flux Tubes with Kilogauss Field
Strength Induced by Convective Instability
Authors: Nagata, Shin'ichi; Tsuneta, Saku; Suematsu, Yoshinori;
Ichimoto, Kiyoshi; Katsukawa, Yukio; Shimizu, Toshifumi; Yokoyama,
Takaaki; Tarbell, Theodore D.; Lites, Bruce W.; Shine, Richard A.;
Berger, Thomas E.; Title, Alan M.; Bellot Rubio, Luis R.; Orozco
Suárez, David
2008ApJ...677L.145N Altcode:
Convective instability has been a mechanism used to explain
the formation of solar photospheric flux tubes with kG field
strength. However, the turbulence of the Earth's atmosphere has
prevented ground-based observers from examining the hypothesis
with precise polarimetric measurement on the subarcsecond scale
flux tubes. Here we discuss observational evidence of this scenario
based on observations with the Solar Optical Telescope (SOT) aboard
Hinode. The cooling of an equipartition field strength flux tube
precedes a transient downflow reaching 6 km s<SUP>-1</SUP> and the
intensification of the field strength to 2 kG. These observations
agree very well with the theoretical predictions.
---------------------------------------------------------
Title: Transient horizontal magnetic fields in solar plage regions
Authors: Ishikawa, R.; Tsuneta, S.; Ichimoto, K.; Isobe, H.; Katsukawa,
Y.; Lites, B. W.; Nagata, S.; Shimizu, T.; Shine, R. A.; Suematsu,
Y.; Tarbell, T. D.; Title, A. M.
2008A&A...481L..25I Altcode: 2008arXiv0802.1769I
Aims:We report the discovery of isolated, small-scale emerging
magnetic fields in a plage region with the Solar Optical Telescope
aboard Hinode. <BR />Methods: Spectro-polarimetric observations were
carried out with a cadence of 34 s for the plage region located near
disc center. The vector magnetic fields are inferred by Milne-Eddington
inversion. <BR />Results: The observations reveal widespread occurrence
of transient, spatially isolated horizontal magnetic fields. The
lateral extent of the horizontal magnetic fields is comparable to
the size of photospheric granules. These horizontal magnetic fields
seem to be tossed about by upflows and downflows of the granular
convection. We also report an event that appears to be driven by the
magnetic buoyancy instability. We refer to buoyancy-driven emergence
as type 1 and convection-driven emergence as type 2. Although both
events have magnetic field strengths of about 600 G, the filling
factor of type 1 is a factor of two larger than that of type 2. <BR
/>Conclusions: Our finding suggests that the granular convection in
the plage regions is characterized by a high rate of occurrence of
granular-sized transient horizontal fields.
---------------------------------------------------------
Title: Net circular polarization of sunspots in high spatial
resolution
Authors: Ichimoto, K.; Tsuneta, S.; Suematsu, Y.; Katsukawa, Y.;
Shimizu, T.; Lites, B. W.; Kubo, M.; Tarbell, T. D.; Shine, R. A.;
Title, A. M.; Nagata, S.
2008A&A...481L...9I Altcode:
Context: Net circular polarization (NCP) of spectral lines in
sunspots has been most successfully explained by the presense of
discontinuities in the magnetic field inclination and flow velocity
along the line-of-sight in the geometry of the embedded flux tube model
of penumbrae (Δγ-effect). <BR />Aims: The fine scale structure of
NCP in a sunspot is examined with special attention paid to spatial
relations of the Evershed flow to confirm the validity of the present
interpretation of the NCP of sunspots. <BR />Methods: High resolution
spectro-polarimetric data of a positive-polarity sunspot obtained
by the Solar Optical Telescope aboard Hinode are analysed. <BR
/>Results: A positive NCP is associated with the Evershed flow
channels in both limb-side and disk center-side penumbrae and with
upflows in the penumbra at disk center. The negative NCP in the disk
center-side penumbra is generated in inter-Evershed flow channels. <BR
/>Conclusions: The first result is apparently inconsistent with the
current explanation of NCP with the Δγ-effect but rather suggests a
positive correlation between the magnetic field strength and the flow
velocity as the cause of the NCP. The second result serves as strong
evidence for the presence of gas flows in inter-Evershed flow channels.
---------------------------------------------------------
Title: Nonlinear Force-free Field Modeling of a Solar Active Region
around the Time of a Major Flare and Coronal Mass Ejection
Authors: Schrijver, C. J.; DeRosa, M. L.; Metcalf, T.; Barnes, G.;
Lites, B.; Tarbell, T.; McTiernan, J.; Valori, G.; Wiegelmann, T.;
Wheatland, M. S.; Amari, T.; Aulanier, G.; Démoulin, P.; Fuhrmann,
M.; Kusano, K.; Régnier, S.; Thalmann, J. K.
2008ApJ...675.1637S Altcode: 2007arXiv0712.0023S
Solar flares and coronal mass ejections are associated with rapid
changes in field connectivity and are powered by the partial dissipation
of electrical currents in the solar atmosphere. A critical unanswered
question is whether the currents involved are induced by the motion of
preexisting atmospheric magnetic flux subject to surface plasma flows or
whether these currents are associated with the emergence of flux from
within the solar convective zone. We address this problem by applying
state-of-the-art nonlinear force-free field (NLFFF) modeling to the
highest resolution and quality vector-magnetographic data observed
by the recently launched Hinode satellite on NOAA AR 10930 around
the time of a powerful X3.4 flare. We compute 14 NLFFF models with
four different codes and a variety of boundary conditions. We find
that the model fields differ markedly in geometry, energy content,
and force-freeness. We discuss the relative merits of these models in
a general critique of present abilities to model the coronal magnetic
field based on surface vector field measurements. For our application
in particular, we find a fair agreement of the best-fit model field
with the observed coronal configuration, and argue (1) that strong
electrical currents emerge together with magnetic flux preceding the
flare, (2) that these currents are carried in an ensemble of thin
strands, (3) that the global pattern of these currents and of field
lines are compatible with a large-scale twisted flux rope topology,
and (4) that the ~10<SUP>32</SUP> erg change in energy associated with
the coronal electrical currents suffices to power the flare and its
associated coronal mass ejection.
---------------------------------------------------------
Title: Hinode SOT Observations of Solar Quiescent Prominence Dynamics
Authors: Berger, Thomas E.; Shine, Richard A.; Slater, Gregory L.;
Tarbell, Theodore D.; Title, Alan M.; Okamoto, Takenori J.; Ichimoto,
Kiyoshi; Katsukawa, Yukio; Suematsu, Yoshinori; Tsuneta, Saku; Lites,
Bruce W.; Shimizu, Toshifumi
2008ApJ...676L..89B Altcode:
We report findings from multihour 0.2” resolution movies of
solar quiescent prominences (QPs) observed with the Solar Optical
Telescope (SOT) on the Hinode satellite. The observations verify
previous findings of filamentary downflows and vortices in QPs. SOT
observations also verify large-scale transverse oscillations in QPs,
with periods of 20-40 minutes and amplitudes of 2-5 Mm. The upward
propagation speed of several waves is found to be ~10 km s<SUP>-1</SUP>,
comparable to the sound speed of a 10,000 K plasma, implying that
the waves are magnetoacoustic in origin. Most significantly, Hinode
SOT observations reveal that dark, episodic upflows are common in
QPs. The upflows are 170-700 km in width, exhibit turbulent flow,
and rise with approximately constant speeds of ~20 km s<SUP>-1</SUP>
from the base of the prominence to heights of ~10-20 Mm. The upflows
are visible in both the Ca II H-line and Hα bandpasses of SOT. The new
flows are seen in about half of the QPs observed by SOT to date. The
dark upflows resemble buoyant starting plumes in both their velocity
profile and flow structure. We discuss thermal and magnetic mechanisms
as possible causes of the plumes.
---------------------------------------------------------
Title: Emergence of a Helical Flux Rope under an Active Region
Prominence
Authors: Okamoto, Takenori J.; Tsuneta, Saku; Lites, Bruce W.; Kubo,
Masahito; Yokoyama, Takaaki; Berger, Thomas E.; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Nagata, Shin'ichi; Shibata, Kazunari; Shimizu,
Toshifumi; Shine, Richard A.; Suematsu, Yoshinori; Tarbell, Theodore
D.; Title, Alan M.
2008ApJ...673L.215O Altcode: 2008arXiv0801.1956O
Continuous observations were obtained of NOAA AR 10953 with the Solar
Optical Telescope (SOT) on board the Hinode satellite from 2007 April
28 to May 9. A prominence was located over the polarity inversion
line (PIL) to the southeast of the main sunspot. These observations
provided us with a time series of vector magnetic fields on the
photosphere under the prominence. We found four features: (1) The
abutting opposite-polarity regions on the two sides along the PIL first
grew laterally in size and then narrowed. (2) These abutting regions
contained vertically weak but horizontally strong magnetic fields. (3)
The orientations of the horizontal magnetic fields along the PIL on
the photosphere gradually changed with time from a normal-polarity
configuration to an inverse-polarity one. (4) The horizontal magnetic
field region was blueshifted. These indicate that helical flux rope
was emerging from below the photosphere into the corona along the PIL
under the preexisting prominence. We suggest that this supply of a
helical magnetic flux to the corona is associated with evolution and
maintenance of active region prominences.
---------------------------------------------------------
Title: The Horizontal Magnetic Flux of the Quiet-Sun Internetwork
as Observed with the Hinode Spectro-Polarimeter
Authors: Lites, B. W.; Kubo, M.; Socas-Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Katsukawa, Y.;
Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2008ApJ...672.1237L Altcode:
Observations of very quiet Sun using the Solar Optical
Telescope/Spectro-Polarimeter (SOT/SP) aboard the Hinode spacecraft
reveal that the quiet internetwork regions are pervaded by horizontal
magnetic flux. The spatial average horizontal apparent flux density
derived from wavelength-integrated measures of Zeeman-induced linear
polarization is B<SUP>T</SUP><SUB>app</SUB> = 55 Mx cm <SUP>-2</SUP>, as
compared to the corresponding average vertical apparent flux density of
| B<SUP>L</SUP><SUB>app</SUB>| = 11 Mx cm <SUP>-2</SUP>. Distributions
of apparent flux density are presented. Magnetic fields are organized on
mesogranular scales, with both horizontal and vertical fields showing
"voids" of reduced flux density of a few granules spatial extent. The
vertical fields are concentrated in the intergranular lanes, whereas the
stronger horizontal fields are somewhat separated spatially from the
vertical fields and occur most commonly at the edges of the bright
granules. High-S/N observations from disk center to the limb help
to constrain possible causes of the apparent imbalance between |
B<SUP>L</SUP><SUB>app</SUB>| and B<SUP>T</SUP><SUB>app</SUB>, with
unresolved structures of linear dimension on the surface smaller by at
least a factor of 2 relative to the SOT/SP angular resolution being one
likely cause of this discrepancy. Other scenarios for explaining this
imbalance are discussed. The horizontal fields are likely the source of
the "seething" fields of the quiet Sun discovered by Harvey et al. The
horizontal fields may also contribute to the "hidden" turbulent flux
suggested by studies involving Hanle effect depolarization of scattered
radiation.
---------------------------------------------------------
Title: Hinode Observations of Flux Emergence in Quiet and Active
Regions
Authors: Lites, B. W.; Centeno, R.; Kubo, M.; Socas-Navarro, H. Berger,
T.; Frank, Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.;
Katsukawa, Y.; Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2008ASPC..383...71L Altcode:
We review briefly the observational understanding of emergence of
flux in both the quiet Sun and active regions in the light of first
results from the joint Japan/US/UK Hinode mission. That spacecraft
is now providing us with our first continuous, high resolution
measurements of the photospheric vector magnetic field, along with
high resolution observations of the thermal and dynamic properties
of the chromosphere and corona. This review is intended to present a
few very early results and to highlight the potential for discovery
offered by this extraordinary new mission. The discovery of ubiquitous
horizontal magnetic flux in the quiet internetwork regions is presented.
---------------------------------------------------------
Title: Mangetic field properties at the footpoints of solar
microflares (active-region transient brightenings)
Authors: Shimizu, T.; Kano, R.; Katsukawa, Y.; Kubo, M.; Deluca, E.;
Ichimoto, K.; Lites, B.; Nagata, S.; Sakao, T.; Shine, R.; Suematsu,
Y.; Tarbell, T.; Title, A.; Tsuneta, S.
2007AGUFMSH52C..06S Altcode:
Solar active regions produce numerous numbers of small-scale explosive
energy releases, i.e., microflares, which are captured by imaging
observations in soft X-rays as transient brightenings of small-scale
coronal loops. Thanks to advanced performance of X-Ray Telescope (XRT)
onboard the Hinode satellite, we can investigate finer structure
of the brightening X-ray sources in more details than we did with
Yohkoh data. One of important questions on microflares is what causes
microflares. The simultaneous visible-light observations by the Solar
Optical Telescope (SOT) allow us to explore magnetic activities
and magnetic field configuration at the photospheric footpoints
of brightening loops, giving key observations to investigate the
question. For our investigations of corona-photosphere magnetic
coupling, we have established co-alignment between SOT and XRT
with accuracy better than 1 arcsec (Shimizu et al. 2007, PASJ in
press). It turns out that Ca II H observations are very useful
to identify the exact positions of footpoints of X-ray transient
brightening loops. Small "Kernels" are sometimes observed in Ca II H
and they may be signature of highly accelerated non-thermal particles
impinging on chromosphere. As already shown in Shimizu et al.(2002),
frequent transient brightenings are observed at the locations where
emerging activities are on going. However, another type of brightening
triggering mechanism should exist to explain some observed multiple-loop
brightenings. In the multiple-loop brightenings, multiple loops are
magnetically in parallel with each other and no apparent magnetic
activities, such as emerging and canceling, are observed at and near
the footpoints. This paper will present SOT observations of some
microflares observed with XRT.
---------------------------------------------------------
Title: Small-Scale Jetlike Features in Penumbral Chromospheres
Authors: Katsukawa, Y.; Berger, T. E.; Ichimoto, K.; Lites, B. W.;
Nagata, S.; Shimizu, T.; Shine, R. A.; Suematsu, Y.; Tarbell, T. D.;
Title, A. M.; Tsuneta, S.
2007Sci...318.1594K Altcode:
We observed fine-scale jetlike features, referred to as penumbral
microjets, in chromospheres of sunspot penumbrae. The microjets
were identified in image sequences of a sunspot taken through a Ca II
H-line filter on the Solar Optical Telescope on board the Japanese solar
physics satellite Hinode. The microjets’ small width of 400 kilometers
and short duration of less than 1 minute make them difficult to identify
in existing observations. The microjets are possibly caused by magnetic
reconnection in the complex magnetic configuration in penumbrae and
have the potential to heat the corona above a sunspot.
---------------------------------------------------------
Title: Magnetic and Doppler Observations of the Photosphere and Low
Chromosphere with the Solar Optical Telescope on Hinode
Authors: Tarbell, T. D.; Lites, B. W.; Shine, R. A.; Ichimoto, K.
2007AGUFMSH53A1064T Altcode:
We present magnetic field and Doppler shift measurements in the Mg
I b line at 517.3 nm obtained with the Solar Optical Telescope's
Narrowband Filter Imager on Hinode. The line core forms in the low
chromosphere, and the wings where the measurements are made probably
form around the temperature minimum. Stokes IQUV images in the red and
blue wings are combined to make movies of longitudinal magnetograms
and Dopplergrams. The direction of the transverse field component is
also measurable in strong field concentrations. These are compared
with very accurate photospheric magnetic measurements in Fe I 630.2 nm
from the Spectro-Polarimeter. This comparison calibrates the filter
longitudinal magnetograms in flux density and shows changes in field
geometry with height. The Doppler measurements are calibrated using
wavelength scans through the Mg line profile. A number of emerging and
canceling magnetic features were observed in AR 10961 during its disk
passage in late June and early July. Since these were made during the
Hinode eclipse season, the observations have somewhat lower spatial
resolution than usual (0.32 arcsecond pixels), but the uniformity
and sensitivity are excellent. Intermittent upflows seen between
canceling magnetic features are interpreted in terms of reconnection
outflows. Strong, persistent downflows are seen adjacent to but not
on flux concentrations outside of sunspots and pores. In the sunspot,
running penumbral waves are clearly visible, and steady downflows are
observed over the light bridges. Hinode is a Japanese mission developed
and launched by ISAS/ JAXA, with NAOJ as domestic partner and NASA and
STFC (UK) as international partners. It is operated by these agencies
in cooperation with ESA and NSC (Norway).
---------------------------------------------------------
Title: Chromospheric Anemone Jets as Evidence of Ubiquitous
Reconnection
Authors: Shibata, Kazunari; Nakamura, Tahei; Matsumoto, Takuma; Otsuji,
Kenichi; Okamoto, Takenori J.; Nishizuka, Naoto; Kawate, Tomoko;
Watanabe, Hiroko; Nagata, Shin'ichi; UeNo, Satoru; Kitai, Reizaburo;
Nozawa, Satoshi; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi;
Shimizu, Toshifumi; Katsukawa, Yukio; Tarbell, Theodore D.; Berger,
Thomas E.; Lites, Bruce W.; Shine, Richard A.; Title, Alan M.
2007Sci...318.1591S Altcode: 2008arXiv0810.3974S
The heating of the solar chromosphere and corona is a long-standing
puzzle in solar physics. Hinode observations show the ubiquitous
presence of chromospheric anemone jets outside sunspots in active
regions. They are typically 3 to 7 arc seconds = 2000 to 5000 kilometers
long and 0.2 to 0.4 arc second = 150 to 300 kilometers wide, and their
velocity is 10 to 20 kilometers per second. These small jets have an
inverted Y-shape, similar to the shape of x-ray anemone jets in the
corona. These features imply that magnetic reconnection similar to that
in the corona is occurring at a much smaller spatial scale throughout
the chromosphere and suggest that the heating of the solar chromosphere
and corona may be related to small-scale ubiquitous reconnection.
---------------------------------------------------------
Title: Twisting Motions of Sunspot Penumbral Filaments
Authors: Ichimoto, K.; Suematsu, Y.; Tsuneta, S.; Katsukawa, Y.;
Shimizu, T.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Lites, B. W.;
Kubo, M.; Nagata, S.
2007Sci...318.1597I Altcode:
The penumbra of a sunspot is composed of numerous thin, radially
extended, bright and dark filaments carrying outward gas flows
(the Evershed flow). Using high-resolution images obtained by the
Solar Optical Telescope aboard the solar physics satellite Hinode, we
discovered a number of penumbral bright filaments revealing twisting
motions about their axes. These twisting motions are observed only
in penumbrae located in the direction perpendicular to the symmetry
line connecting the sunspot center and the solar disk center, and
the direction of the twist (that is, lateral motions of intensity
fluctuation across filaments) is always from limb side to disk-center
side. Thus, the twisting feature is not an actual twist or turn of
filaments but a manifestation of dynamics of penumbral filaments with
three-dimensional radiative transfer effects.
---------------------------------------------------------
Title: Hinode observations reveal boundary layers of magnetic elements
in the solar photosphere
Authors: Rezaei, R.; Steiner, O.; Wedemeyer-Böhm, S.; Schlichenmaier,
R.; Schmidt, W.; Lites, B. W.
2007A&A...476L..33R Altcode: 2007arXiv0711.0408R
Aims:We study the structure of the magnetic elements in network-cell
interiors. <BR />Methods: A quiet Sun area close to the disc centre was
observed with the spectro-polarimeter of the Solar Optical Telescope
on board the Hinode space mission, which yielded the best spatial
resolution ever achieved in polarimetric data of the Fe I 630 nm line
pair. For comparison and interpretation, we synthesize a similar data
set from a three-dimensional magneto-hydrodynamic simulation. <BR
/>Results: We find several examples of magnetic elements, either
roundish (tube) or elongated (sheet), which show a central area of
negative Stokes-V area asymmetry framed or surrounded by a peripheral
area with larger positive asymmetry. This pattern was predicted
some eight years ago on the basis of numerical simulations. Here,
we observationally confirm its existence for the first time. <BR
/>Conclusions: We gather convincing evidence that this pattern of
Stokes-V area asymmetry is caused by the funnel-shaped boundary of
magnetic elements that separates the flux concentration from the
weak-field environment. On this basis, we conclude that electric
current sheets induced by such magnetic boundary layers are common in
the photosphere.
---------------------------------------------------------
Title: Hinode SOT observations of plume upflows and cascading
downflows in quiescent solar prominences
Authors: Berger, T.; Shine, R.; Slater, G.; Tarbell, T.; Title, A.;
Lites, B.; Tsuneta, S.; Okamoto, T. J.; Ichimoto, K.; Katsukawa, Y.;
Sekii, T.; Suematsu, Y.; Shimizu, T.
2007AGUFMSH53A1065B Altcode:
We present several Hinode SOT filtergram movies of quiescent solar
prominences that show newly discovered "plume-like" upflows and
cascading "waterfall-like" downflows that persist for the entire
multi-hour duration of the observations. The flow speeds are on the
order of 10 km/sec with typical widths of 400-700 km. Preliminary
calculations show that if the upflows are buoyancy driven, the
associated thermal perturbation is on the order of 10,000 K, sufficient
to explain the dark appearance of the upflows in the interference
filter passbands. In addition we observe rotational vortices and
body oscillations within the prominences. These new observations
challenge current magnetostatic models of solar prominences by showing
that prominence plasmas are in constant motion, often in directions
perpendicular to the magnetic field lines proposed by the models. TRACE,
Hinode/EIS, and Hinode/XRT observations are used to investigate the
differential topology of the flows across temperature regimes.
---------------------------------------------------------
Title: Coronal Transverse Magnetohydrodynamic Waves in a Solar
Prominence
Authors: Okamoto, T. J.; Tsuneta, S.; Berger, T. E.; Ichimoto, K.;
Katsukawa, Y.; Lites, B. W.; Nagata, S.; Shibata, K.; Shimizu, T.;
Shine, R. A.; Suematsu, Y.; Tarbell, T. D.; Title, A. M.
2007Sci...318.1577O Altcode: 2008arXiv0801.1958O
Solar prominences are cool 10<SUP>4</SUP> kelvin plasma clouds
supported in the surrounding 10<SUP>6</SUP> kelvin coronal plasma by
as-yet-undetermined mechanisms. Observations from Hinode show fine-scale
threadlike structures oscillating in the plane of the sky with periods
of several minutes. We suggest that these represent Alfvén waves
propagating on coronal magnetic field lines and that these may play
a role in heating the corona.
---------------------------------------------------------
Title: Quiet-Sun Internetwork Magnetic Fields from the Inversion of
Hinode Measurements
Authors: Orozco Suárez, D.; Bellot Rubio, L. R.; del Toro Iniesta,
J. C.; Tsuneta, S.; Lites, B. W.; Ichimoto, K.; Katsukawa, Y.; Nagata,
S.; Shimizu, T.; Shine, R. A.; Suematsu, Y.; Tarbell, T. D.; Title,
A. M.
2007ApJ...670L..61O Altcode: 2007arXiv0710.1405O
We analyze Fe I 630 nm observations of the quiet Sun at disk center
taken with the spectropolarimeter of the Solar Optical Telescope aboard
the Hinode satellite. A significant fraction of the scanned area,
including granules, turns out to be covered by magnetic fields. We
derive field strength and inclination probability density functions from
a Milne-Eddington inversion of the observed Stokes profiles. They show
that the internetwork consists of very inclined, hG fields. As expected,
network areas exhibit a predominance of kG field concentrations. The
high spatial resolution of Hinode's spectropolarimetric measurements
brings to an agreement the results obtained from the analysis of
visible and near-infrared lines.
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Title: Center-to-Limb Variation of Stokes V Asymmetries in Solar
Pores Observed with the Hinode Spectro-Polarimeter
Authors: Morinaga, Shuji; Nagata, Shin'ichi; Ichimoto, Kiyoshi;
Suematsu, Yoshinori; Tsuneta, Saku; Katsukawa, Yukio; Shimizu,
Toshifumi; Shine, Richard A.; Tarbell, Theodore D.; Title, Alan M.;
Lites, Bruce; Kubo, Masahito; Sakurai, Takashi
2007PASJ...59S.613M Altcode:
Here we present spectro-polarimetric measurements of several pores
and the surrounding regions taken with the Solar Optical Telescope
aboard Hinode at various viewing angles. We analyzed the Stokes V
area asymmetry, and confirmed that it is depressed at the center of
the pores, while it shows large positive values (a blue lobe larger
than a red lobe) in the surrounding area; this is consistent with a
previous report. In addition to this ring of positive asymmetry, we
found regions of alternating positive and negative area asymmetries
when weak V regions were observed near the solar limb. The positive
asymmetry occurs on the disk-center side and the negative asymmetry
on the limb side of the magnetic concentrations. These center-to-limb
variations of the Stokes V area asymmetry can be interpreted as being
a systematic inflow of plasma into the magnetic concentrations from
their surroundings.
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Title: Initial Results on Line-of-Sight Field Calibrations of SP/NFI
Data Taken by SOT/Hinode
Authors: Chae, Jongchul; Moon, Yong-Jae; Park, Young-Deuk; Ichimoto,
Kiyoshi; Sakurai, Takashi; Suematsu, Yoshinori; Tsuneta, Saku;
Katsukawa, Yukio; Shimizu, Toshifumi; Shine, Richard A.; Tarbell,
Theodore D.; Title, Alan M.; Lites, Bruce; Kubo, Masahito; Nagata,
Shin'ichi; Yokoyama, Takaaki
2007PASJ...59S.619C Altcode:
We present initial results on the line-of-sight field calibration
of the two kinds of Stokes I and V data taken by the Solar Optical
Telescope on the satellite Hinode: spectral profiles of Stokes I and V
parameters recorded on the Spectro-polarimeter (SP), and monochromatic
images of the same parameters recorded on the Narrow-band Filter Imager
(NFI). By applying the center-of-gravity method to the SP data of
AR10930 taken on 2006 December 11, we determined the line-of-sight field
at every location in the active region. As a result, we found that the
line-of-sight field strength ranges up to 2kG in plages, even without
taking into account the filling factor, and up to 3.5kG or higher values
inside the umbra of the major sunspot. We calibrated the NFI data in
reference to the field determined from the SP data. In regions outside
the sunspots and the penumbral regions, we adopted a linear relation,
B<SUB>||</SUB> = βV / I, between the circular polarization, V / I,
and the line-of-sight field strength, B<SUB>||</SUB>, and obtained β =
23.5kG in regions outside the sunspots, and β = 12.0kG in penumbral
regions. In umbral regions of sunspots, a first-order polynomial was
adopted to model the reversal of the polarization signal over the
field strength.
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Title: Response of the Solar Atmosphere to Magnetic Flux Emergence
from Hinode Observations
Authors: Li, Hui; Sakurai, Takashi; Ichimito, Kiyoshi; Suematsu,
Yoshinori; Tsuneta, Saku; Katsukawa, Yukio; Shimizu, Toshifumi; Shine,
Richard A.; Tarbell, Theodore D.; Title, Alan M.; Lites, Bruce; Kubo,
Masahito; Nagata, Shin'ichi; Kotoku, Jun; Shibasaki, Kiyoto; Saar,
Steven H.; Bobra, Monica
2007PASJ...59S.643L Altcode:
No abstract at ADS
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Title: Initial Helioseismic Observations by Hinode/SOT
Authors: Sekii, Takashi; Kosovichev, Alexander G.; Zhao, Junwei;
Tsuneta, Saku; Shibahashi, Hiromoto; Berger, Thomas E.; Ichimoto,
Kiyoshi; Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu,
Toshifumi; Shine, Richard A.; Suematsu, Yoshinori; Tarbell, Theodore
D.; Title, Alan M.
2007PASJ...59S.637S Altcode: 2007arXiv0709.1806S
Results from initial helioseismic observations by the Solar Optical
Telescope on-board Hinode are reported. It has been demonstrated
that intensity oscillation data from the Broadband Filter Imager
can be used for various helioseismic analyses. The k - ω power
spectra, as well as the corresponding time-distance cross-correlation
function, which promise high-resolution time-distance analysis below
the 6-Mm travelling distance, were obtained for G-band and CaII-H
data. Subsurface supergranular patterns were observed from our first
time-distance analysis. The results show that the solar oscillation
spectrum is extended to much higher frequencies and wavenumbers, and
the time-distance diagram is extended to much shorter travel distances
and times than were observed before, thus revealing great potential
for high-resolution helioseismic observations from Hinode.
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Title: Hinode Observations of Horizontal Quiet Sun Magnetic Flux
and the “Hidden Turbulent Magnetic Flux”
Authors: Lites, Bruce; Socas-Navarro, Hector; Kubo, Masahito; Berger,
Thomas; Frank, Zoe; Shine, Richard A.; Tarbell, Theodore D.; Title,
Alan M.; Ichimoto, Kiyoshi; Katsukawa, Yukio; Tsuneta, Saku; Suematsu,
Yoshinori; Shimizu, Toshifumi
2007PASJ...59S.571L Altcode:
We present observations of magnetic fields of the very quiet Sun
near disk center using the Spectro-Polarimeter of the Solar Optical
Telescope aboard the Hinode satellite. These observations reveal for
the first time the ubiquitous presence of horizontal magnetic fields in
the internetwork regions. The horizontal fields are spatially distinct
from the vertical fields, demonstrating that they are not arising mainly
from buffeting of vertical flux tubes by the granular convection. The
horizontal component has an average “apparent flux density” of
55Mxcm<SUP>-2</SUP> (assuming the horizontal field structures are
spatially resolved), in contrast to the average apparent vertical flux
density of 11Mxcm<SUP>-2</SUP>. The vertical fields reside mainly in
the intergranular lanes, whereas the horizontal fields occur mainly
over the bright granules, with a preference to be near the outside
edge of the bright granules. The large apparent imbalance of vertical
and horizontal flux densities is discussed, and several scenarios are
presented to explain this imbalance.
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Title: Strategy for the Inversion of Hinode Spectropolarimetric
Measurements in the Quiet Sun
Authors: Orozco Suárez, David; Bellot Rubio, Luis R.; Del Toro
Iniesta, Jose Carlos; Tsuneta, Saku; Lites, Bruce; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
Richard A.; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.
2007PASJ...59S.837O Altcode: 2007arXiv0709.2033O
In this paper we propose an inversion strategy for the analysis of
spectropolarimetric measurements taken by Hinode in the quiet Sun. The
Spectro-Polarimeter of the Solar Optical Telescope aboard Hinode records
the Stokes spectra of the FeI line pair at 630.2nm with unprecendented
angular resolution, high spectral resolution, and high sensitivity. We
discuss the need to consider a local stray-light contamination to
account for the effects of telescope diffraction. The strategy is
applied to observations of a wide quiet Sun area at disk center. Using
these data we examine the influence of noise and initial guess models
in the inversion results. Our analysis yields the distributions of
magnetic field strengths and stray-light factors. They show that quiet
Sun internetwork regions consist mainly of hG fields with stray-light
contamination of about 0.8.
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Title: Hinode Observations of a Vector Magnetic Field Change
Associated with a Flare on 2006 December 13
Authors: Kubo, Masahito; Yokoyama, Takaaki; Katsukawa, Yukio; Lites,
Bruce; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto, Kiyoshi; Shimizu,
Toshifumi; Nagata, Shin'ichi; Tarbell, Theodore D.; Shine, Richard A.;
Title, Alan M.; Elmore David
2007PASJ...59S.779K Altcode: 2007arXiv0709.2397K
Continuous observations of the flare productive active region 10930
were successfully carried out with the Solar Optical Telescope aboard
the Hinode spacecraft during 2006 December 6 to 19. We focused on the
evolution of photospheric magnetic fields in this active region, and the
magnetic field properties at the site of the X3.4 class flare, using
a time series of vector field maps with high spatial resolution. The
X3.4 class flare occurred on 2006 December 13 at the apparent
collision site between the large, opposite polarity umbrae. Elongated
magnetic structures with alternatingly positive and negative polarities
resulting from flux emergence appeared one day before the flare in the
collision site penumbra. Subsequently, the polarity inversion line
at the collision site became very complicated. The number of bright
loops in CaII H increased during the formation of these elongated
magnetic structures. Flare ribbons and bright loops evolved along
the polarity inversion line and one footpoint of the bright loop was
located in a region having a large departure of the field azimuth angle
with respect to its surroundings. SOT observations with high spatial
resolution and high polarization precision revealed temporal change in
the fine structure of magnetic fields at the flare site: some parts of
the complicated polarity inversion line then disappeared, and in those
regions the azimuth angle of the photospheric magnetic field changed by
about 90°, becoming more spatially uniform within the collision site.
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Title: The Analysis of Penumbral Fine Structure Using an Advanced
Inversion Technique
Authors: Jurcák, Jan; Bellot Rubio, Luis; Ichimoto, Kiyoshi;
Katsukawa, Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi;
Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.; Tsuneta,
Saku
2007PASJ...59S.601J Altcode: 2007arXiv0707.1560J
We present a method to study the penumbral fine structure using data
obtained by the spectropolarimeter on board Hinode. For the first
time, the penumbral filaments can be considered as being resolved in
spectropolarimetric measurements. This enables us to use inversion
codes with only one-component model atmospheres, and thus to assign
the obtained stratifications of the plasma parameters directly to the
penumbral fine structure. This approach was applied to the limb-side
part of the penumbra in the active region NOAA10923. Preliminary results
show a clear dependence of the plasma parameters on the continuum
intensity in the inner penumbra, i.e., a weaker and horizontal magnetic
field along with an increased line-of-sight velocity are found in the
low layers of the bright filaments. The results in the mid penumbra
are ambiguous, and future analyses are necessary to unveil the magnetic
field structure and other plasma parameters there.
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Title: Fine-Scale Structures of the Evershed Effect Observed by the
Solar Optical Telescope aboard Hinode
Authors: Ichimoto, Kiyoshi; Shine, Richard A.; Lites, Bruce; Kubo,
Masahito; Shimizu, Toshifumi; Suematsu, Yoshinori; Tsuneta, Saku;
Katsukawa, Yukio; Tarbell, Theodore D.; Title, Alan M.; Nagata,
Shin'ichi; Yokoyama, Takaaki; Shimojo, Masumi
2007PASJ...59S.593I Altcode:
The small-scale structure of the Evershed effect is being studied
using data obtained by the Spectropolarimeter and the Broadband Filter
Imager of the Solar Optical Telescope aboard Hinode. We find that the
Evershed flow starts at the leading edge of inwardly migrating bright
penumbral grains, and turns to nearly a horizontal flow preferentially
in the dark lanes of the penumbra. A number of small elongated regions
that have an upward motion of ∼ 1kms<SUP>-1</SUP> are found in the
deep photosphere distributed over the penumbra. They are cospatial
with bright grains and have relatively horizontal magnetic fields. A
number of patches having a strong downward motion associated with the
opposite magnetic polarity from the sunspot are also found in the mid
and outer penumbra. They could be identified as foot points of the
Evershed flow channels, though the identification of individual pairs
is not straightforward. Our results provide strong support for some
recent findings from ground-based high-resolution observations, and
are in general agreement with the well-known picture of the uncombed
structure of the penumbra, in which the penumbrae consist of rising
flux tubes carrying nearly horizontal Evershed flows embedded in more
vertical background magnetic fields.
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Title: Flare Ribbons Observed with G-band and FeI 6302Å, Filters
of the Solar Optical Telescope on Board Hinode
Authors: Isobe, Hiroaki; Kubo, Masahito; Minoshima, Takashi; Ichimoto,
Kiyoshi; Katsukawa, Yukio; Tarbell, Theodore D.; Tsuneta, Saku; Berger,
Thomas E.; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
Richard A.; Suematsu, Yoshinori; Title, Alan M.
2007PASJ...59S.807I Altcode: 2007arXiv0711.3946I
The Solar Optical Telescope (SOT) on board the Hinode satellite observed
an X3.4 class flare on 2006 December 13. A typical two-ribbon structure
was observed, not only in the chromospheric CaII H line, but also in
the G-band and FeI 6302Å line. The high-resolution, seeing-free images
achieved by SOT revealed, for the first time, sub-arcsec fine structures
of the “white light” flare. The G-band flare ribbons on sunspot
umbrae showed a sharp leading edge, followed by a diffuse inside,
as well as a previously known core-halo structure. The underlying
structures, such as umbral dots, penumbral filaments, and granules,
were visible in the flare ribbons. Assuming that the sharp leading
edge was directly heated by a particle beam and the diffuse parts were
heated by radiative back-warming, we estimated the depth of the diffuse
flare emission using an intensity profile of the flare ribbon. We found
that the depth of the diffuse emission was about 100km or less from
the height of the source of radiative back-warming. The flare ribbons
were also visible in the Stokes-V images of FeI 6302Å, as a transient
polarity reversal. This is probably related to a “magnetic transient”
reported in the literature. The intensity increase in Stokes-I images
indicates that the FeI 6302Å line was significantly deformed by the
flare, which may cause such a magnetic transient.
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Title: Small-Scale Magnetic-Flux Emergence Observed with Hinode
Solar Optical Telescope
Authors: Otsuji, Kenichi; Shibata, Kazunari; Kitai, Reizaburo; Ueno,
Satoru; Nagata, Shin'ichi; Matsumoto, Takuma; Nakamura, Tahei;
Watanabe, Hiroko; Tsuneta, Saku; Suematsu, Yoshinori; Ichimoto,
Kiyoshi; Shimizu, Toshifumi; Katsukawa, Yukio; Tarbell, Theodore D.;
Lites, Bruce; Shine, Richard A.; Title Alan M.
2007PASJ...59S.649O Altcode: 2007arXiv0709.3207O
We observed small-scale magnetic-flux emergence in a sunspot moat region
by the Solar Optical Telescope (SOT) aboard the Hinode satellite. We
analyzed filtergram images observed at wavelengths of Fe 6302Å, G band,
and CaII H. In Stokes I images of Fe 6302Å, emerging magnetic flux was
recognized as dark lanes. In the G band, they showed to be their shapes
almost the same as in Stokes I images. These magnetic fluxes appeared
as dark filaments in CaII H images. Stokes V images of Fe 6302Å showed
pairs of opposite polarities at footpoints of each filament. These
magnetic concentrations were identified to correspond to bright points
in G band/CaII H images. From an analysis of time-sliced diagrams, we
derived the following properties of emerging flux, which are consistent
with those of previous studies: (1) Two footpoints separate each other
at a speed of 4.2kms<SUP>-1</SUP> during the initial phase of evolution,
and decrease to about 1kms<SUP>-1</SUP> 10minutes later. (2) CaII H
filaments appear almost simultaneously with the formation of dark lanes
in Stokes I in an observational cadence of 2minutes. (3) The lifetime
of the dark lanes in the Stokes I and G band is 8minutes, while that
of Ca filament is 12minutes. An interesting phenomena was observed,
that an emerging flux tube expanded laterally in the photosphere with a
speed of 3.8kms<SUP>-1</SUP>. A discussion on the horizontal expansion
of the flux tube is given with refernce to previous simulation studies.
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Title: Observations of Sunspot Oscillations in G Band and CaII H
Line with Solar Optical Telescope on Hinode
Authors: Nagashima, Kaori; Sekii, Takashi; Kosovichev, Alexander G.;
Shibahashi, Hiromoto; Tsuneta, Saku; Ichimoto, Kiyoshi; Katsukawa,
Yukio; Lites, Bruce; Nagata, Shin'ichi; Shimizu, Toshifumi; Shine,
Richard A.; Suematsu, Yoshinori; Tarbell, Theodore D.; Title, Alan M.
2007PASJ...59S.631N Altcode: 2007arXiv0709.0569N
Exploiting high-resolution observations made by the Solar Optical
Telescope on board Hinode, we investigate the spatial distribution
of the power spectral density of the oscillatory signal in and around
the active region NOAA 10935. The G-band data show that in the umbra
the oscillatory power is suppressed in all frequency ranges. On
the other hand, in CaII H intensity maps oscillations in the umbra,
so-called umbral flashes, are clearly seen with the power peaking around
5.5mHz. The CaII H power distribution shows the enhanced elements with
the spatial scale of the umbral flashes over most of the umbra, but
there is a region with suppressed power at the center of the umbra. The
origin and property of this node-like feature remain unexplained.
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Title: Hinode SP Vector Magnetogram of AR10930 and Its
Cross-Comparison with MDI
Authors: Moon, Yong-Jae; Kim, Yeon-Han; Park, Young-Deuk; Ichimoto,
Kiyoshi; Sakurai, Takashi; Chae, Jongchul; Cho, Kyung Suk; Bong,
Suchan; Suematsu, Yoshinori; Tsuneta, Saku; Katsukawa, Yukio; Shimojo,
Masumi; Shimizu, Toshifumi; Shine, Richard A.; Tarbell, Theodore D.;
Title, Alan M.; Lites, Bruce; Kubo, Masahito; Nagata, Shin'ichi;
Yokoyama, Takaaki
2007PASJ...59S.625M Altcode:
We present one Hinode Spectropolarimeter (SP) magnetogram of AR 10930
that produced several major flares. The inversion from Stokes profiles
to magnetic field vectors was made using the standard Milne-Eddington
code. We successfully applied the Uniform Shear Method for resolving
the 180° ambiguity to the magnetogram. The inversion gave very strong
magnetic field strengths (near 4500 gauss) for a small portion of area
in the umbra. Considering that the observed V-profile of 6301.5Å was
well-fitted as well as a direct estimation of the Zeeman splitting
results in 4300-4600 gauss, we think that the field strengths
should not be far from the actual value. A cross-comparison of the
Hinode SP and SOHO MDI high resolution flux densities shows that the
MDI flux density could be significantly underestimated by about a
factor of two. In addition, it has a serious negative correlation
(the so-called Zeeman saturation effect) with the Hinode SP flux
density for umbral regions. Finally, we could successfully obtain
a recalibrated MDI magnetogram that has been corrected for the
Zeeman saturation effect using not only a pair of MDI intensity and
magnetogram data simultaneously observed, but also the relationship
from the cross-comparison between the Hinode SP and MDI flux densities.
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Title: Formation Process of a Light Bridge Revealed with the Hinode
Solar Optical Telescope
Authors: Katsukawa, Yukio; Yokoyama, Takaaki; Berger, Thomas E.;
Ichimoto, Kiyoshi; Kubo, Masahito; Lites, Bruce; Nagata, Shin'ichi;
Shimizu, Toshifumi; Shine, Richard A.; Suematsu, Yoshinori; Tarbell,
Theodore D.; Title, Alan M.; Tsuneta, Saku
2007PASJ...59S.577K Altcode: 2007arXiv0709.2527K
The Solar Optical Telescope (SOT) on-board Hinode successfully and
continuously observed the formation process of a light bridge in a
matured sunspot of the NOAA active region 10923 for several days with
high spatial resolution. During its formation, many umbral dots were
observed to be emerging from the leading edges of penumbral filaments,
and rapidly intruding into the umbra. The precursor of the light bridge
formation was also identified as a relatively slow inward motion of
the umbral dots, which emerged not near the penumbra, but inside the
umbra. The spectro-polarimeter on SOT provided physical conditions in
the photosphere around the umbral dots and the light bridges. We found
that the light bridges and the umbral dots had significantly weaker
magnetic fields associated with upflows relative to the core of the
umbra, which implies that there was hot gas with weak field strength
penetrating from the subphotosphere to near the visible surface inside
those structures. There needs to be a mechanism to drive the inward
motion of the hot gas along the light bridges. We suggest that the
emergence and the inward motion are triggered by a buoyant penumbral
flux tube as well as subphotospheric flow crossing the sunspot.
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Title: Umbral Fine Structures in Sunspots Observed with Hinode Solar
Optical Telescope
Authors: Kitai, Reizaburo; Watanabe, Hiroko; Nakamura, Tahei; Otsuji,
Ken-ichi; Matsumoto, Takuma; UeNo, Satoru; Nagata, Shin'ichi; Shibata,
Kazunari; Muller, Richard; Ichimoto, Kiyoshi; Tsuneta, Saku; Suematsu,
Yoshinori; Katsukawa, Yukio; Shimizu, Toshifumi; Tarbell, Theodore D.;
Shine, Richard A.; Title, Alan M.; Lites, Bruce
2007PASJ...59S.585K Altcode: 2007arXiv0711.3266K
A high resolution imaging observation of a sunspot umbra was made with
the Hinode Solar Optical Telescope. Filtergrams at wavelengths of the
blue and green continua were taken during three consecutive days. The
umbra consisted of a dark core region, several diffuse components,
and numerous umbral dots. We derived basic properties of umbral dots
(UDs), especially their temperatures, lifetimes, proper motions,
spatial distribution, and morphological evolution. The brightness
of UDs is confirmed to depend on the brightness of their surrounding
background. Several UDs show fission and fusion. Thanks to the stable
condition of the space observation, we could for the first time follow
the temporal behavior of these events. The derived properties of the
internal structure of the umbra are discussed from the viewpoint of
magnetoconvection in a strong magnetic field.
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Title: Formation of Moving Magnetic Features and Penumbral Magnetic
Fields with Hinode/SOT
Authors: Kubo, Masahito; Ichimoto, Kiyoshi; Shimizu, Toshifumi;
Tsuneta, Saku; Suematsu, Yoshinori; Katsukawa, Yukio; Nagata,
Shin'ichi; Tarbell, Theodore D.; Shine, Richard A.; Title, Alan M.;
Frank, Zoe A.; Lites, Bruce; Elmore, David
2007PASJ...59S.607K Altcode: 2007arXiv0709.1853K
Vector magnetic fields of moving magnetic features (MMFs) were well
observed with the Solar Optical Telescope (SOT) aboard the Hinode
satellite. We focused on the evolution of three MMFs with the SOT in
this study. We found that an MMF having relatively vertical fields
with the same polarity as the sunspot was detached from the penumbra
around the granules appearing in the outer penumbra. This suggests
that granular motions in the outer penumbra are responsible for
disintegration of the sunspot. Two MMFs with polarity opposite to
the sunspot are located around the outer edge of horizontal fields
extending from the penumbra. This is evidence that the MMFs with
polarity opposite to the sunspot are the prolongation of penumbral
horizontal fields. Redshifts larger than the sonic velocity in the
photosphere are detected for some of the MMFs with polarity opposite
to the sunspot.
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Title: Summary Review: Science with the SOT
Authors: Lites, B. W.
2007ASPC..369..579L Altcode:
This workshop highlights the ongoing maturation of numerical modeling
and simulations that are increasingly useful in interpretation of
observations. A few examples of presentations that underscore this
theme are briefly discussed. Next, a brief advocacy of the advantages
of close coordination of Solar-B and ground-based observations is
presented. Finally, three controversial hypotheses are presented in
order to stimulate discussion within our community.
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Title: Estimate on SOT Light Level in Flight with Throughput
Measurements in SOT Sun Tests
Authors: Shimizu, T.; Kubo, M.; Tarbell, T. D.; Berger, T. E.;
Suematsu, Y.; Ichimoto, K.; Katsukawa, Y.; Miyashita, M.; Noguchi,
M.; Nakagiri, M.; Tsuneta, S.; Elmore, D. F.; Lites, B. W.
2007ASPC..369...51S Altcode:
The SOT (Solar Optical Telescope, e.g., Shimizu 2004) optical
system consists of 50cm-aperture optical telescope (OTA) and focal
plane instrument (FPP). The solar light into the telescope penetrates
through many optical elements located in OTA and FPP before illuminating
CCDs. Natural solar light was fed to the integrated SOT in sun tests for
verifying various optical aspects including the confirmation of photon
throughput. CCD exposures provide the number of photons accumulated
in an exposure duration with a clean-room test condition. To estimate
the absolute intensity of the solar light at the telescope entrance
in the clean-room test condition, we developed a pinhole-PSD sensor
for simultaneous monitoring the solar light outside the clean room
and measured the transmission of light through two flat mirrors of
the heliostat and clean-room entrance window glass as a function of
wavelength. The PSD sensor was pre-calibrated with continuous monitoring
the solar light in a day long under a clear constant sky condition,
determining the earth atmospheric attenuation and the PSD output for
the solar light on orbit. These throughput measurements have provided
an estimate on photon throughput for the SOT flight model. The results
confirm suitable number of photons without saturation for proper CCD
exposures in flight.
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Title: Performance Characteristics of the Solar-B Spectro-Polarimeter
Authors: Lites, B. W.; Elmore, D. F.; Streander, K. V.; Hoffmann,
C. M.; Tarbell, T. D.; Title, A. M.; Shine, R. A.; Ichimoto, K.;
Tsuneta, S.; Shimizu, T.; Suematsu, Y.
2007ASPC..369...55L Altcode:
The Focal Plane Package (FPP) of the Solar Optical Telescope (SOT)
includes the first precision Spectro-Polarimeter (SP) for solar space
observations. The FPP/SP will provide high precision measures of
the vector magnetic field in the solar photosphere. Here we present
some as-built performance specifications for the entire system of
telescope + polarimeter. The FPP-SP system represents significant
gains in several aspects over existing spectro-polarimetric systems;
notably, angular resolution, polarimetric accuracy, spectral purity,
and most importantly, temporal continuity of stable, high angular
resolution. In this short summary of the poster, a few of the
performance characteristics of the SP are presented.
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Title: Calibration of the SOT Polarization
Authors: Ichimoto, K.; Suematsu, Y.; Shimizu, T.; Katsukawa, Y.;
Noguchi, M.; Nakagiri, M.; Miyashita, M.; Tsuneta, S.; Tarbell, T. D.;
Shine, R. A.; Hoffmann, C. M.; Cruz, T.; Lites, B. W.; Elmore, D. F.
2007ASPC..369...39I Altcode:
Calibration of SOT polarization property was performed using natural
sunlight and well calibrated sheet polarizer (linear and circular)
placed on the entrance of the telescope. The polarimeter response
matrices were determined for the spectropolarimeter (SP) and the
narrowband filter imager (NFI), and it is shown that they are well
behave as predicted and constant over the field of view. The crosstalk
between I,Q,U,V will be suppressed to the negligible level at the
photometric accuracy of 10^{-3} after the calibration with the obtained
matrices. The sensitivity of SOT on linear and circular polarizations
at each wavelength observed by NFI are also obtained.
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Title: Vector Spectropolarimetry of Dark-cored Penumbral Filaments
with Hinode
Authors: Bellot Rubio, L. R.; Tsuneta, S.; Ichimoto, K.; Katsukawa,
Y.; Lites, B. W.; Nagata, S.; Shimizu, T.; Shine, R. A.; Suematsu,
Y.; Tarbell, T. D.; Title, A. M.; del Toro Iniesta, J. C.
2007ApJ...668L..91B Altcode: 2007arXiv0708.2791B
We present spectropolarimetric measurements of dark-cored penumbral
filaments taken with Hinode at a resolution of 0.3". Our observations
demonstrate that dark-cored filaments are more prominent in polarized
light than in continuum intensity. Far from disk center, the Stokes
profiles emerging from these structures are very asymmetric and show
evidence for magnetic fields of different inclinations along the
line of sight, together with strong Evershed flows of at least 6-7 km
s<SUP>-1</SUP>. In sunspots closer to disk center, dark-cored penumbral
filaments exhibit regular Stokes profiles with little asymmetries due
to the vanishing line-of-sight component of the horizontal Evershed
flow. An inversion of the observed spectra indicates that the magnetic
field is weaker and more inclined in the dark cores as compared with
the surrounding bright structures. This is compatible with the idea
that dark-cored filaments are the manifestation of flux tubes carrying
hot Evershed flows.
---------------------------------------------------------
Title: Emergence of Small-Scale Magnetic Loops in the Quiet-Sun
Internetwork
Authors: Centeno, R.; Socas-Navarro, H.; Lites, B.; Kubo, M.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Tsuneta, S.;
Katsukawa, Y.; Suematsu, Y.; Shimizu, T.; Nagata, S.
2007ApJ...666L.137C Altcode: 2007arXiv0708.0844C
We study the emergence of magnetic flux at very small spatial
scales (less than 2") in the quiet-Sun internetwork. To this aim,
a time series of spectropolarimetric maps was taken at disk center
using the instrument SP/SOT on board Hinode. The LTE inversion of
the full Stokes vector measured in the Fe I 6301 and 6302 Å lines
allows us to retrieve the magnetic flux and topology in the region
of study. In the example presented here, the magnetic flux emerges
within a granular structure. The horizontal magnetic field appears
prior to any significant amount of vertical field. As time goes on,
the traces of the horizontal field disappear, while the vertical dipoles
drift-carried by the plasma motions-toward the surrounding intergranular
lanes. These events take place within typical granulation timescales.
---------------------------------------------------------
Title: Variation of the Stokes-V area asymmetry across magnetic
elements
Authors: Rezaei, R.; Steiner, O.; Wedemeyer-Böhm, S.; Schlichenmaier,
R.; Lites, B. W.
2007AN....328..706R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Patches in Internetwork Quiet Sun
Authors: De Wijn, Alfred; Lites, B.; Berger, T.; Shine, R.; Title,
A.; Katsukawa, Y.; Tsuneta, S.; Suematsu, Y.; Shimizu, T.; Hinode Team
2007AAS...210.9412D Altcode: 2007BAAS...39Q.219D
We study strong flux elements in the quiet sun in the context of
the nature of quiet-sun magnetism, its coupling to chromospheric,
transition-region and coronal fields, and the nature of a local
turbulent dynamo. Strong, kilogauss flux elements show up intermittently
as small bright points in G-band and Ca II H images. Although
bright points have been extensively studied in the magnetic network,
internetwork magnetism has only come under scrutiny in recent years. A
full spectrum of field strengths seems to be ubiquitously present in
the internetwork at small spatial scales, with the stronger elements
residing in intergranular lanes. De Wijn et al. (2005) found that bright
points in quiet sun internetwork areas appear recurrently with varying
intensity and horizontal motion within long-lived patches that outline
cell patterns on mesogranular scales. They estimate that the "magnetic
patches" have a mean lifetime of nine hours, much longer than granular
timescales. We use multi-hour sequences of G-band and Ca II H images
as well as magnetograms recorded by the Hinode satellite to follow up
on their results. The larger field of view, the longer sequences, the
addition of magnetograms, and the absence of atmospheric seeing allows
us to better constrain the patch lifetime, to provide much improved
statistics on IBP lifetime, to compare IBPs to network bright points,
and to study field polarity of IBPs in patches and between nearby
patches. <P />Hinode is an international project supported by JAXA,
NASA, PPARC and ESA. We are grateful to the Hinode team for all their
efforts in the design, build and operation of the mission.
---------------------------------------------------------
Title: Hinode/SOT Observation of Fine Structure of the Evershed Flow
Authors: Ichimoto, Kiyoshi; Suematsu, Y.; Tsuneta, S.; Katsukawa, Y.;
Shimojo, M.; Kubo, M.; Shimizu, T.; Shine, R.; Tarbell, T.; Title,
A.; Lites, B.; Elmore, D.; Yokoyama, T.; Nagaka, S.
2007AAS...210.9408I Altcode: 2007BAAS...39..218I
Small scale structure of the Evershed effect was studied using the
Spectropolarimeter (SP) and Broadband Filter Imager (BFI) of SOT aboard
Hinode. SP maps and high cadence continuum images of BFI coverting
entire sunspots are used to investigate the spatial distribution of
the flow field, brightness and magnetic fields. It is revealed that the
Evershed flow starts at the front edge of inwardly migrating penumbral
grains with an upward velocity component and turns to nearly holizontal
flow preferentially in dark lanes (or dark core of filaments) of the
penumbra. Our results are in general agreement with the well known
uncombed penumbral concept in which the Evershed flow takes place
in nearly holizontal field channels. We discovered a number of tiny
elongated regions in deep photosphere in which there is an obvious
upward motion of 1-1.5km/s distributing over the penumbra. <P />They
could be identified as the 'foot points' of the individual Evershed
flow channels. Cross-correlation among the flow speed, intensity,
magnetic field strength and inclination, and distribution of string
down flows in and around the penumbra will also be discussed.
---------------------------------------------------------
Title: Magnetic Flux Emergence In The Quiet Sun Photosphere
Authors: Centeno, Rebecca; Lites, B.; Socas-Navarro, H.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Tsuneta, S.;
Katsukawa, Y.; Suematsu, Y.; Kubo, M.; Shimizu, T.
2007AAS...210.9406C Altcode: 2007BAAS...39..218C
We study the emergence of magnetic flux at very small spacial scales
(less than 1 arcsec) in the quiet Sun internetwork. To this aim, several
time series of spectropolarimetric maps were taken at disk center using
the instrument SP/SOT on board Hinode. The LTE inversion of the full
Stokes vector measured in the Fe I 6301 and 6302 lines will allow us
to retrieve the magnetic flux and topology in the region of study. We
find that the magnetic flux emerges typically within the granular
structures. In many cases, the horizontal magnetic field appears
prior to any significant amount of vertical field. As time goes on,
the traces of the horizontal field dissapear while the the vertical
dipoles drift -carried by the plasma motions- towards the surrounding
intergranular lanes. Sometimes they stay trapped there for a while
but they eventually either disappear by disgregation/cancelation
or agregate to other magnetic field concentrations giving rise to
larger flux elements. The time scale of these events is of the order
of 10-20 minutes.
---------------------------------------------------------
Title: Formation of Moving Magnetic Features and Penumbral Magnetic
Fields
Authors: Kubo, Masahito; Ichimoto, K.; Shimizu, T.; Tsuneta, S.;
Suematsu, Y.; Katsukawa, Y.; Nagata, S.; Lites, B. W.; Frank, Z.;
Tarbell, T. D.; Shine, R. A.; Title, A. M.
2007AAS...210.9410K Altcode: 2007BAAS...39..218K
We investigate the formation process of Moving Magnetic Features
(MMFs) observed with Hinode/SOT. Moving magnetic features are small
magnetic elements moving outward in the moat region surrounding
mature sunspots. We derive vector magnetic fields of MMFs around
simple sunspots near the disk center. Most of MMFs with polarity
opposite to the sunspot have large redshift around the penumbral outer
boundary. We find that some of them have Doppler velocities of about
10 km/s and such large Doppler motion is observed only in the Stokes
V profile. The Stokes Q and U profiles in the same pixel do not have
any significant Doppler motions. Horizontal magnetic fields of the
penumbra frequently extend to the moat region and the MMFs having
horizontal fields with polarity same as the sunspot are formed. The
MMFs with polarity opposite to the sunspot appear around the outer
edge of the extending penumbral fields. We also find penumbral spines,
which have more vertical magnetic fields than the surroundings, branch
off at their outer edge and MMFs having relatively vertical fields
with polarity same as the sunspot are detached from the outer edge
of the branch. The branch of penumbral spine is formed when granular
cells in the moat region go into the penumbra.
---------------------------------------------------------
Title: Ubiquitous Horizontal Magnetic Fields in the Quiet Solar
Photosphere as Revealed by HINODE Meaurements
Authors: Lites, Bruce W.; Socas Navarro, H.; Berger, T.; Frank,
Z.; Shine, R.; Tarbell, T.; Title, A.; Ichimoto, K.; Katsukawa,
Y.; Tsuneta, S.; Suematsu, Y.; Kubo, M.; Shimizu, T.; Nagata, S.;
Hinode Team
2007AAS...210.6303L Altcode: 2007BAAS...39..171L
Measurements with the HINODE Spectro-Polarimeter (SP) of the quiet
Sun allow characterization of the weak, mixed-polarity magnetic
flux at the highest angular resolution to date (0.3"), and with good
polarimetric sensitivity(0.025% relative to the continuum). The image
stabilization of the HINODE spacecraft allows long integrations with
degradation of the image quality only by the evolution of the solar
granulation. From the Stokes V profile measurements we find an average
solar "Apparent Flux Density" of 14 Mx cm-2, with significant Stokes V
signals at every position on the disk at all times. However, there are
patches of meso-granular size (5-15") where the flux is very weak. At
this high sensitivity, transverse fields produce measurable Stokes
Q,U linear polarization signals over a majority of the area, with
apparent transverse flux densities in the internetwork significantly
larger than the corresponding longitudinal flux densities. When viewed
at the center of the solar disk, the Stokes V signals (longitudinal
fields) show a preference for occurrence in the intergranular lanes,
and the Q,U signals occur preferably over the granule interiors,
but neither association is exclusive. <P />Hinode is an international
project supported by JAXA, NASA, PPARC and ESA. We are grateful to the
Hinode team for all their efforts in the design, build and operation
of the mission.
---------------------------------------------------------
Title: Attempt to detect Aflven waves with Solar Optical Telescope
aboard Hinode
Authors: Tsuneta, Saku; Suematsu, Y.; Ichimoto, K.; Katsukawa, Y.;
Shimizu, T.; Nagata, S.; Orozco Suárez, D.; Lites, B.; Shine, D.;
Tarbell, T.; Title, A.
2007AAS...210.9428T Altcode: 2007BAAS...39..222T
Flux tube on the sun may carry linear and torsional Alfven waves
generated by photospheric motion. Photospheric motion of 2 km/s would
provide magnetic fluctuation of 40G for 1KG tube and for the Alfven
speed of 50km/s. This may be close to the detection limit of the Stokes
Q and U signals for flux tubes located in the sun center. However,
for flux tubes located near the limb, the fluctuation would be seen in
the Stokes V signal, and can be detectable. <P />We also may be able
to confirm the 90 degree phase shift between magnetic fluctuation and
velocity fluctuation, which is easier to observe for flux tubes near
the limb. Detection of waves would be important in terms of coronal
heating and solar wind acceleration. An attempt to detect waves along
flux tubes will be reported.
---------------------------------------------------------
Title: Is Coronal X-ray Emission Energized By Electric Currents?
Authors: Ishibashi, Kazunori; Metcalf, T.; Lites, B.
2007AAS...210.9421I Altcode: 2007BAAS...39..220I
We examine the spatial correlation between coronal X-ray emission
observed with the Hinode X-Ray Telescope and electric currents observed
with the Hinode Solar Optical Telescope Spectro-polarimeter. We
determine to what extent the X-ray brightness is correlated with
electric current density and hence to what extent the hot corona is
energized by electric currents which flow through the photosphere. We
will also consider whether the currents reach the corona to heat the
coronal plasma or whether they predominantly close below the corona. <P
/>Hinode is an international project supported by JAXA, NASA, PPARC
and ESA. We are grateful to the Hinode team for all their efforts in
the design, development and operation of the mission.
---------------------------------------------------------
Title: Discovery Of Cool Cloud-like Structures In The Corona With
Hinode Solar Optical Telescope
Authors: Okamoto, Takenori; Tsuneta, S.; Katsukawa, Y.; Ichimoto,
K.; Suematsu, Y.; Shimizu, T.; Nagata, S.; Shibata, K.; Tarbell, T.;
Shine, R.; Berger, T.; Lites, B.; Myers, D.
2007AAS...210.9426O Altcode: 2007BAAS...39..221O
A solar observation satellite Hinode (Japanese for sun rise) was
launched in September 2006.Hinode carried 3 advanced solar telescopes,
visible light telescope, EUV imaging spectrometer, and X-ray telescope
to simultaneously observe the photosphere, chromosphere, transition
region, and corona. In the performance verification phase of the Hinode
spacecraft with its telescopes, we observed an active region AR10921
near the west limb of the solar disk on November 9 2006. At this point,
we planned to observe spicules on the limb with a broadband filter
dedicated to Ca II H line (3968A). Ca II-H emission line (3968A) comes
from plasma with temperature of approx. 10(4) K, which is much lower
than the coronal temperature of 10(6-7) K. In addition to spectacular
spicules, we find a large cloud-like structure located 10,000-20,000
km above the limb. The cloud has a very complex fine structure with
dominant horizontal thread-like structure. Some features are moving
horizontally and also have clear vertical oscillatory motions. The
periods and amplitudes of these oscillations are 130-250 seconds and
200-850 km, respectively. The vertical oscillatory motion sometimes
has a coherence length as long as 16,000 km. We conclude that from
various observational features this vertical oscillation is a signature
of Alfven waves propagating along the horizontal magnetic fields. We
will discuss their origin and implications.
---------------------------------------------------------
Title: Discovery Of Small-scale Horizontal Magnetic Structures On
The Solar Photosphere
Authors: Ishikawa, Ryohko; Tsuneta, S.; Suematsu, Y.; Ichimoto, K.;
Katsukawa, Y.; Nagata, S.; Ishobe, H.; Tarbell, T.; Lites, B. W.;
Title, A.
2007AAS...210.9404I Altcode: 2007BAAS...39..217I
We discover two different types of episodes on the appearance
of horizontal magnetic fields with Solar Optical Telescope aboard
Hinode. <P />The first episode is an emergence of strong thin horizontal
magnetic fields associated with separating vertical components on
both ends. Its size is about two granules. We also detect strong area
asymmetry of the environment Stokes Vprofile for the bout 8 minutes
before the first emergence of the horizontal component. One of the
footpoints has very strong downflows (several km/s), while the region
with strong linear polarization signal has small blue shift, indicating
an upward-moving horizontal flux. <P />The second episode appears to be
more ubiquitous. Linear polarization signals appear inside granules (not
in inter-granules). Their size is smaller than granules, and lifetime
is longer than several minutes. We will summarize the nature of the
two types of the horizontal magnetic fluxes, and discuss their origin.
---------------------------------------------------------
Title: Hinode/SOT Observations of Sunspot Penumbral Dynamics and
Evolution
Authors: Shine, Richard A.; Hagenaar, M.; Tarbell, T.; Title, A.;
Lites, B.; Ichimoto, K.; Tsuneta, S.; Katsakawa, Y.; Suematsu, Y.;
Nagata, S.; Kubo, M.; Shimizu, T.
2007AAS...210.9407S Altcode: 2007BAAS...39..218S
The Solar Optical Telescope (SOT) on the Hinode satellite (launched
October 2006) has obtained long and nearly continuous time series of
several large sunspots including those in NOAA AR's 10923, 10925,
and 10930. Here we use high resolution movies taken primarily with
the broad band Ca II (396.8nm) and G band (430.5nm) channels and
magnetograms taken with the 630.2nm narrow band channel to study
the details and short term evolution of penumbral fine structures
as well as the long term evolution of the sunspots. We compute flow
maps and use space/time slices to track motions of Evershed clouds,
penumbral grains, and visualize oscillations. The data contain examples
of penumbral formation and disintegration including "orphan" penumbra
(i.e., penumbra without an obvious umbra). There is also an interesting
instance of "colliding" penumbra in AR 10930 as two sunspots of opposite
polarity converged. The zone of apparent shear was associated with
several flares. <P />This work was supported by NASA contract NNM07AA01C
---------------------------------------------------------
Title: Magnetic Landscape Of Solar Polar Region With Solar Optical
Telescope Aboard Hinode
Authors: Tsuneta, Saku; Suematsu, Y.; Ichimoto, K.; Shimizu, T.;
Katsukawa, Y.; Nagata, S.; Orozco Suárez, D.; Lites, B.; Shine, D.;
Tarbell, T.; Title, A.
2007AAS...210.9405T Altcode: 2007BAAS...39..218T
Solar polar region is the final destination for remnant magnetic
fields due to meridional flow and granular diffusion, and is very
important for the global solar dynamo. Hinode satellite carried out
high-resolution spectro-polarimetric observations for the Northern
pole on 2006 November 22 as a part of its performance verification
program. We find ubiquitous isolated (positive and negative) patches
in the Stokes V map (i.e. fields horizontal to local surface) all over
the Arctic circle. The Q (vertical to local surface) map indicates
scattered vertical flux tubes, which have bipolar feature in the U and
V maps. This suggests canopy-like structure of the strong isolated flux
tubes. This will be compared with equatorial landscape with similar
distance from the sun center. Strong flux tube and weaker ubiquitous
horizontal fields as represented by Stokes V would have implication
to the current understanding of the global and local dynamo.
---------------------------------------------------------
Title: A suite of community tools for spectro-polarimetric analysis .
Authors: Lites, B.; Casini, R.; Garcia, J.; Socas-Navarro, H.
2007MmSAI..78..148L Altcode:
The National Center for Atmospheric Research (NCAR) has undertaken a
3-year initiative to develop the Community Spectro-polarimetric Analysis
Center (CSAC). The goal of this effort is to provide the community
with standardized tools for extracting the solar magnetic field
vector and related atmospheric parameters from spectro-polarimetric
observations. The emphasis will be to develop portable, efficient, and
well-documented procedures for analysis of data from the many new and
upcoming observational facilities, both ground- and space-based. The
initial focus of CSAC will be the development of robust methods
for inversion of Stokes spectral data, starting with a standard
Milne-Eddington inversion that has been the workhorse for analysis of
data from e.g. the Advanced Stokes Polarimeter. Upon completion of that
code, the program will move to more sophisticated methods that embrace
more realistic and detailed models of the solar atmosphere. Very
fast methods for inversion (neural networks or pattern recognition
techniques, for example) are also candidates. Finally, the CSAC is
intended to eventually provide standardized methods for resolution of
the 180-degree field azimuth ambiguity, and for visualization of the
resulting magnetic field vector maps. CSAC is formulated as a community
effort, and as such will receive guidance and input from the community.
---------------------------------------------------------
Title: Polarimetric Observations of the Formation of a G-Band
Bright Point
Authors: Beck, C.; Schmidt, W.; Bellot Rubio, L. R.; Schlichenmaier,
R.; Sütterlin, P.; Lites, B. W.
2006ASPC..358...72B Altcode:
We investigate the kinematic and magnetic properties of G-band bright
points in the moat of a regular sunspot. The analysis is based on vector
polarimetric measurements made at the German Vacuum Tower Telescope in
visible (630 nm) and infrared (1565 nm) spectral lines, complemented
by high-resolution filtergrams in the G-band at 430.6 nm and the core
of the Ca II H line at 396.7 nm from the Dutch Open Telescope. The
spectro-polarimetric data has been inverted to derive the magnetic
field properties of the observed region. We witness the formation of a
G-band bright point from a patch of diffuse flux with an initial field
strength of 0.4 kG. The magnetic field strength increases to 0.9 kG in
the course of several minutes, accompanied by a downflow of magnetized
plasma. A few minutes after the field intensification, a G-band bright
point is seen at the location of the flux concentration. The formation
of the bright point shows the signatures of convective collapse.
---------------------------------------------------------
Title: Spectral Line Selection for HMI
Authors: Norton, A. A.; Pietarila Graham, J. D.; Ulrich, R. K.;
Schou, J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; López Ariste, A.;
Bush, R. I.; Socas-Navarro, H.; Scherrer, P. H.
2006ASPC..358..193N Altcode:
We present information on two spectral lines, Fe I 6173 Å and Ni I 6768
Å, that were candidates for use in the Helioseismic and Magnetic Imager
(HMI) instrument. Both Fe I and Ni I profiles have clean continuum and
no blends that threaten performance. The higher Landé factor of Fe
I means its operational velocity range in regions of strong magnetic
field is smaller than for Ne I. Fe I performs better than Ni I for
vector magnetic field retrieval. Inversion results show that Fe I
consistently determines field strength and flux more accurately than
the Ni I line. Inversions show inclination and azimuthal errors are
recovered to ≈2° above 600 Mx/cm<SUP>2</SUP> for Fe I and above
1000 Mx/cm<SUP>2</SUP> for Ni I. The Fe I line was recommended, and
ultimately chosen, for use in HMI.
---------------------------------------------------------
Title: Spectral Line Selection for HMI: A Comparison of Fe I 6173
Å and Ni I 6768 Å
Authors: Norton, A. A.; Graham, J. Pietarila; Ulrich, R. K.; Schou,
J.; Tomczyk, S.; Liu, Y.; Lites, B. W.; Ariste, A. López; Bush,
R. I.; Socas-Navarro, H.; Scherrer, P. H.
2006SoPh..239...69N Altcode: 2006SoPh..tmp...88N; 2006astro.ph..8124N
We present a study of two spectral lines, Fe I 6173 Å and Ni I 6768 Å,
that were candidates to be used in the Helioseismic and Magnetic Imager
(HMI) for observing Doppler velocity and the vector magnetic field. The
line profiles were studied using the Mt. Wilson Observatory, the
Advanced Stokes Polarimeter and the Kitt Peak-McMath Pierce telescope
and one-meter Fourier transform spectrometer atlas. Both Fe I and Ni
I profiles have clean continua and no blends that threaten instrument
performance. The Fe I line is 2% deeper, 15% narrower, and has a 6%
smaller equivalent width than the Ni I line. The potential of each
spectral line to recover pre-assigned solar conditions is tested
using a least-squares minimization technique to fit Milne-Eddington
models to tens of thousands of line profiles that have been sampled
at five spectral positions across the line. Overall, the Fe I line
has a better performance than the Ni I line for vector-magnetic-field
retrieval. Specifically, the Fe I line is able to determine field
strength, longitudinal and transverse flux four times more accurately
than the Ni I line in active regions. Inclination and azimuthal angles
can be recovered to ≈2<SUP>°</SUP> above 600 Mx cm<SUP>−2</SUP>
for Fe I and above 1000 Mx cm<SUP>−2</SUP> for Ni I. Therefore, the
Fe I line better determines the magnetic-field orientation in plage,
whereas both lines provide good orientation determination in penumbrae
and umbrae. We selected the Fe I spectral line for use in HMI due to
its better performance for magnetic diagnostics while not sacrificing
velocity information. The one exception to the better performance of the
Fe I line arises when high field strengths combine with high velocities
to move the spectral line beyond the effective sampling range. The
higher g<SUB>eff</SUB> of Fe I means that its useful range of velocity
values in regions of strong magnetic field is smaller than Ni I.
---------------------------------------------------------
Title: Magnetic Field Diagnostic Capability of Solar-B/SOT:
Filtergraph Instrument
Authors: Ichimoto, K.; Suematsu, Y.; Shimizu, T.; Katsukawa, Y.;
Tsuneta, S.; Tarbell, T. D.; Shine, R. A.; Hoffmann, C. M.; Title,
A. M.; Lites, B. W.; Elmore, D. F.; Streander, K. V.
2006ASPC..358..189I Altcode:
The Narrowband Filter Instrument (NFI) of the Solar Optical Telescope
onboard Solar-B provides 2D magnetograms/Dopplergrams with a tunable
Lyot filter (width ∼ 0.1 Å) in 6 selected wavelength bands, and
spatial sampling of 0.08 arcsec/px. The Zeeman-effect sensitivity of
NFI and the detection limits of weak magnetic fields are evaluated for
2 photospheric and 3 chromospheric lines. Magnetic-field retrievability
from the NFI observables is studied using synthetic Stokes profiles
of Fe I 5250 Å. We find that, with optimized wavelength sampling at 4
positions, the inferred magnetic field is sufficiently accurate under
the hypothesis of constant magnetic field and velocity along the LOS.
---------------------------------------------------------
Title: Solar Polarization 4
Authors: Casini, R.; Lites, B. W.
2006ASPC..358.....C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Diffraction Limited Spectro-Polarimeter
Authors: Sankarasubramanian, K.; Lites, B.; Gullixson, C.; Elmore,
D.; Hegwer, S.; Streander, K.; Rimmele, T.; Fletcher, S.; Gregory,
S.; Sigwarth, M.
2006ASPC..358..201S Altcode:
The Diffraction Limited Spectro-Polarimeter (DLSP) is a
collaboration between the National Solar Observatory (NSO) and the
High Altitude Observatory (HAO) <P />to provide a stable instrument
for precision measurements of solar vector magnetic fields at high
angular resolution. The DLSP is integrated with the new high-order
Adaptive Optics (HOAO) system at the Dunn Solar Telescope (DST)
and provides Stokes spectra of the Fe I 630 nm lines approaching the
0.2 arcs3c diffraction limit of the DST. It is configured as a fixed,
well-calibrated instrument that may be used simultaneously with G-band
(1 nm bandpass) and a Ca K imagers (0.1 nm bandpass). The 2K×2K G-band
imager allows fast frame selection and includes a burst mode for speckle
imaging. The setup of DLSP and its imagers require only about 10 min of
preparation before start of observations. This fixed setup facilitates
standardized data reduction. The DLSP permits observations with 0.09
arcsec sampling in high resolution mode. In wide-field mode, the 0.27
arcsec sampling allows one to map regions about 3 arcmin on a side. The
achieved continuum S/N is 500 (1500) in high resolution (wide-field)
mode for a 4 s integration. It is possible to achieve higher S/N by
integrating longer. Data reduction routines are now available in IDL
for post-observation processing, and parallel analysis routines in
FORTRAN 77 are being developed to allow “on-the-fly” data reduction
and inversion.
---------------------------------------------------------
Title: An Overview of Existing Algorithms for Resolving the
180<SUP>°</SUP> Ambiguity in Vector Magnetic Fields: Quantitative
Tests with Synthetic Data
Authors: Metcalf, Thomas R.; Leka, K. D.; Barnes, Graham; Lites,
Bruce W.; Georgoulis, Manolis K.; Pevtsov, A. A.; Balasubramaniam,
K. S.; Gary, G. Allen; Jing, Ju; Li, Jing; Liu, Y.; Wang, H. N.;
Abramenko, Valentyna; Yurchyshyn, Vasyl; Moon, Y. -J.
2006SoPh..237..267M Altcode: 2006SoPh..tmp...14M
We report here on the present state-of-the-art in algorithms used
for resolving the 180° ambiguity in solar vector magnetic field
measurements. With present observations and techniques, some assumption
must be made about the solar magnetic field in order to resolve
this ambiguity. Our focus is the application of numerous existing
algorithms to test data for which the correct answer is known. In
this context, we compare the algorithms quantitatively and seek to
understand where each succeeds, where it fails, and why. We have
considered five basic approaches: comparing the observed field to a
reference field or direction, minimizing the vertical gradient of the
magnetic pressure, minimizing the vertical current density, minimizing
some approximation to the total current density, and minimizing some
approximation to the field's divergence. Of the automated methods
requiring no human intervention, those which minimize the square of
the vertical current density in conjunction with an approximation for
the vanishing divergence of the magnetic field show the most promise.
---------------------------------------------------------
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: Spectro-Polarimetric Observations and Non-Lte Modeling of
Ellerman Bombs
Authors: Socas-Navarro, Hector; Pillet, Valentín Martínez; Elmore,
David; Pietarila, Anna; Lites, Bruce W.; Sainz, Rafael Manso
2006SoPh..235...75S Altcode: 2005astro.ph..8667S
Ellerman bombs are bright emission features observed in the wings
of Hα, usually in the vicinity of magnetic concentrations. Here we
show that they can also be detected in the Ca II infrared triplet
lines, which are easier to interpret and therefore allow for more
detailed diagnostics. We present full Stokes observations of the
849.8 and 854.2 nm lines acquired with the new spectro-polarimeter
SPINOR. The data show no significant linear polarization at the level
of 3 × 10<SUP>−4</SUP>. The circular polarization profiles exhibit
measureable signals with a very intricate pattern of peaks. A non-LTE
analysis of the spectral profiles emerging from these features reveals
the presence of strong downflows (∼10 {km s<SUP>−1</SUP>}) in a
hot layer between the upper photosphere and the lower chromosphere.
---------------------------------------------------------
Title: Spinor: Visible and Infrared Spectro-Polarimetry at the
National Solar Observatory
Authors: Socas-Navarro, Hector; Elmore, David; Pietarila, Anna;
Darnell, Anthony; Lites, Bruce W.; Tomczyk, Steven; Hegwer, Steven
2006SoPh..235...55S Altcode: 2005astro.ph..8685S
The Spectro-Polarimeter for Infrared and Optical Regions (SPINOR)
is a new spectro-polarimeter that will serve as a facility instrument
for the Dunn Solar Telescope at the National Solar Observatory. This
instrument is capable of achromatic polarimetry over a very broad range
of wavelengths, from 430 to 1600 nm, allowing for the simultaneous
observation of several visible and infrared spectral regions with full
Stokes polarimetry. Another key feature of the design is its flexibility
to observe virtually any combination of spectral lines, limited only
by practical considerations (e.g., the number of detectors available,
space on the optical bench, etc.).
---------------------------------------------------------
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: A Detailed Analysis of an Ephemeral Region .
Authors: Guglielmino, S. L.; Martínez Pillet, V.; Ruiz Cobo, B.;
Zuccarello, F.; Lites, B. W.
2006MSAIS...9..103G Altcode:
In order to improve the understanding of the process of emergence of
magnetic flux on the solar surface, we studied the temporal evolution of
an ephemeral region using \emph{Advanced Stokes Polarimeter} data. We
adopted two different approaches: first, we used a Milne-Eddington
inversion to obtain mean parameters of the emerging bipole magnetic
configuration. Then, we considered the full radiative transfer
equation, and we studied the trend of all the previous parameters as
a function of the optical depth tau . We pointed out peculiar flows,
such as an initial upflow of 1.5 ;textrm {km s}<SUP>-1</SUP> where the
zenith angle is essentially horizontal, and downflows decreasing in
time in footpoints, characterized by a vertical field. These results
seem to confirm the emerging bipole topology, due to magnetic flux
tube emergence. The results obtained with this inversion confirm the
structure found with Milne-Eddington code. However we found regions
in which the presence of two distinct magnetic components is highly
significant. It also seems very interesting the trend of the temperature
with optical depth: the plasma temperature appears to grow up in the
high photosphere above the emerging bipole.
---------------------------------------------------------
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: Measurements of solar magnetic fields
Authors: Lites, B. W.
2006cosp...36.3626L Altcode: 2006cosp.meet.3626L
Over the past decade precision spectro-polarimetry of the sun has
resulted in highly quantitative measurements of the magnetic field
vector in the solar photosphere These successes have revealed new
understanding of how magnetic fields emerge and interact with convection
to produce the variability of the sun s radiation across the spectrum
and led to the development of many new observational capabilities
both ground- and space-based In anticipation of the revolutionary
data these instruments will provide this review highlights possible
scientific advances that can be anticipated within the next few years
including magneto-convection in the presence of weak and strong fields
structure and evolution of sunspots and measurement of magnetic fields
above the photosphere
---------------------------------------------------------
Title: Magnetic Flux Ropes in the Solar Photosphere: The Vector
Magnetic Field under Active Region Filaments
Authors: Lites, B. W.
2005ApJ...622.1275L Altcode:
This study is an observational search for evidence of
prominence-associated magnetic flux ropes at the photospheric level
in plage regions away from sunspots. Although there are a few cases
of supposed flux rope geometry in the photosphere of complex sunspot
regions (notably “δ sunspots”), such cases appear to be fairly rare
and therefore do not contribute significantly to the suspected emergence
of magnetic helicity in active regions leading to the common eruption
of coronal mass ejections. In the present study, the Advanced Stokes
Polarimeter (ASP) at the Dunn Solar Telescope of the National Solar
Observatory was used to measure simultaneously the evolution of the
photospheric vector magnetic field and the structure of the chromosphere
as seen in the Hα line. The high angular resolution of these vector
field measurements coupled with the high polarimetric precision of the
ASP has allowed the possible identification of flux rope (concave up)
geometry in the photosphere below some narrow (and supposedly low-lying)
active region filaments. Two cases of such occurrence are presented
in detail. These results indicate that flux ropes may be rather common
in normal (i.e., non-δ sunspot) active regions. Further observations
should shed some light on origin of these flux ropes as either emerging
from the solar interior or generated in the solar atmosphere as a
consequence of driven magnetic footpoint motion and reconnection.
---------------------------------------------------------
Title: Full Stokes Spectropolarimetry of Hα in Prominences
Authors: López Ariste, A.; Casini, R.; Paletou, F.; Tomczyk, S.;
Lites, B. W.; Semel, M.; Landi Degl'Innocenti, E.; Trujillo Bueno,
J.; Balasubramaniam, K. S.
2005ApJ...621L.145L Altcode:
We report on spectropolarimetric observations of Hα in prominences
made with the Télescope Héliographique pour l'Etude du Magnétisme et
des Instabilités Solaires and the High Altitude Observatory/Advanced
Stokes Polarimeter. Stokes Q and U show the expected profile shape from
resonance scattering polarization and the Hanle effect. In contrast,
most of the time, Stokes V does not show the antisymmetric profile shape
typical of the Zeeman effect but a profile that indicates the presence
of strong atomic orientation in the hydrogen levels, to an extent that
cannot be explained by invoking the alignment-to-orientation transfer
mechanism induced by the prominence magnetic field. We found that the
largest signal amplitudes of Stokes V (comparable to that of Stokes
Q and U) could be produced by a process of selective absorption of
circularly polarized radiation from the photosphere, which requires
that the prominence be in the vicinity of an active region. Although
recent observations of active region filaments indicate such a
selective absorption mechanism as a plausible explanation of the
anomalous signals observed, the particular set of conditions that
must be met suggest that a different explanation may be required
to explain the almost ubiquitous symmetric V signal observed in Hα
prominences. Therefore, we speculate that an alternative mechanism
inducing strong atomic orientation at the observed level could be due
to the presence of electric fields inducing an electric Hanle effect
on Hα. Although we are still working toward a careful modeling of
this effect, including both electric and magnetic fields, we present
some preliminary considerations that seem to support this possibility.
---------------------------------------------------------
Title: Wavelet Phase Coherence Analysis: Application to a Quiet-Sun
Magnetic Element
Authors: Bloomfield, D. Shaun; McAteer, R. T. James; Lites, Bruce W.;
Judge, Philip G.; Mathioudakis, Mihalis; Keenan, Francis P.
2004ApJ...617..623B Altcode:
A new application of wavelet analysis is presented that utilizes
the inherent phase information residing within the complex Morlet
transform. The technique is applied to a weak solar magnetic network
region, and the temporal variation of phase difference between TRACE
1700 Å and SOHO/SUMER C II 1037 Å intensities is shown. We present,
for the first time in an astrophysical setting, the application of
wavelet phase coherence, including a comparison between two methods
of testing real wavelet phase coherence against that of noise. The
example highlights the advantage of wavelet analysis over more
classical techniques, such as Fourier analysis, and the effectiveness
of the former to identify wave packets of similar frequencies but
with differing phase relations is emphasized. Using cotemporal,
ground-based Advanced Stokes Polarimeter measurements, changes in the
observed phase differences are shown to result from alterations in
the magnetic topology.
---------------------------------------------------------
Title: Observational Evidence for Small-Scale Mixture of Weak and
Strong Fields in the Quiet Sun
Authors: Socas-Navarro, H.; Lites, B. W.
2004ApJ...616..587S Altcode: 2004astro.ph.10562S
Three different maps of the quiet Sun, observed with the Advanced Stokes
Polarimeter (ASP) and the Diffraction-Limited Stokes Polarimeter
(DLSP), show evidence of strong (~=1700 G) and weak (<500 G)
fields coexisting within the resolution element at both network and
internetwork locations. The angular resolution of the observations
is of 1" (ASP) and 0.6" (DLSP). Even at the higher DLSP resolution,
a significant fraction of the network magnetic patches harbor a mixture
of strong and weak fields. Internetwork elements that exhibit kG fields
when analyzed with a single-component atmosphere are also shown to
harbor considerable amounts of weak fields. Only those patches for
which a single-component analysis yields weak fields do not show this
mixture of field strengths. Finally, there is a larger fractional area
of weak fields in the convective upflows than in the downflows.
---------------------------------------------------------
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: Characterization of Magnetic Flux in the Quiet Sun. II. The
Internetwork Fields at High Angular Resolution
Authors: Lites, B. W.; Socas-Navarro, H.
2004ApJ...613..600L Altcode:
This paper presents high-resolution (0.6") spectropolarimetric
observations of very quiet solar regions. We make determinations of the
magnetic flux density, intrinsic field strength, and magnetic filling
factor in these regions. Our results confirm other previous works in
that most of the internetwork flux is in the form of intrinsically
strong fields. However, in contrast to other recent observations, we
do not find a significant increase in the amount of unsigned magnetic
flux relative to that measured at an angular resolution of 1", nor do
we find that most internetwork lanes are populated by strong flux. We
discuss possible causes for this disparity. The lack of additional flux
with increased resolution may be used to set constrains on the typical
spatial scales at which mixed polarities occur (smaller than ~=0.6").
---------------------------------------------------------
Title: Magnetic Properties of the Solar Internetwork
Authors: Socas-Navarro, H.; Martínez Pillet, V.; Lites, B. W.
2004ApJ...611.1139S Altcode:
Advanced Stokes Polarimeter observations are used to study the
weakest polarization signals observed in the quiet photosphere with
flux densities in the range of 1.5-50 Mx cm<SUP>-2</SUP>, which
are found in internetwork regions. Our analysis allows us to reach
an unprecedented spectropolarimetric sensitivity at the cost of
sacrificing spatial resolution. We find evidence for intrinsically
different fields in granules and lanes and characterize the average
properties of the weakest observable flux concentrations. The magnetic
signals observed suggest a strong coupling between magnetic fields
and convective flows. Upflows bring up weak fields (equipartition or
weaker) to the surface, with stronger upflows carrying larger amounts
of flux. The circular polarization profiles observed in the granular
regions display a very strongly asymmetric shape, which contrasts with
the less asymmetric profiles observed in the downflowing regions. At
downflowing locations with speeds of 0.5 km s<SUP>-1</SUP>, both
weak and strong fields can be found. However, when the downflow speed
increases (up to about 1 km s<SUP>-1</SUP>) both the mean flux and the
intrinsic field strength show a tendency to increase. The asymmetry
of the circular polarization profiles also shows a clear trend as
a function of magnetic flux density. Low-flux regions display the
negative area asymmetry one naturally expects for field strengths
decreasing with height embedded in a downflowing environment. As we
move to stronger flux density locations, the well-known positive
area asymmetry develops and reaches even higher values than those
typically found in network regions. These results may have important
implications for our understanding of the coupling between magnetic
fields and convective processes that pervade the solar photosphere.
---------------------------------------------------------
Title: Evaluation of Seeing-Induced Cross Talk in Tip-Tilt-Corrected
Solar Polarimetry
Authors: Judge, Philip G.; Elmore, David F.; Lites, Bruce W.; Keller,
Christoph U.; Rimmele, Thomas
2004ApOpt..43.3817J Altcode:
We reanalyze the effects of atmosphere-induced image motions on the
measurement of solar polarized light using a formalism developed by
Lites. Our reanalysis is prompted by the advent of adaptive optics (AO)
systems that reduce image motion and higher-order aberrations, by the
availability of liquid crystals as modulation devices, and by the need
to understand how best to design polarimeters for future telescopes
such as the Advanced Technology Solar Telescope. In this first attempt
to understand the major issues, we analyze the influence of residual
image motion (tip-tilt) corrections of operational AO systems on the
cross talk between Stokes parameters and present results for several
polarization analysis schemes. Higher-order wave-front corrections are
left for future research. We also restrict our discussion to the solar
photosphere, which limits several important parameters of interest,
using some recent magnetoconvection simulations.
---------------------------------------------------------
Title: Three-Dimensional Structure of the Active Region Photosphere
as Revealed by High Angular Resolution
Authors: Lites, B. W.; Scharmer, G. B.; Berger, T. E.; Title, A. M.
2004SoPh..221...65L Altcode:
Blue continuum images of active regions at ∼ 60° from the center
of the solar disk obtained with the new Swedish 1-m Solar Telescope
reveal heretofore unreported structure of the magnetized solar
atmosphere. Perhaps the most striking aspect of these images is
that, at an angular resolution of 0.12″, they show clearly the
three-dimensional structure of the photosphere. In particular,
the Wilson depression of the dark floors of pores is readily
apparent. Conversely, the segmented structure of light bridges running
through sunspots and pores reveal that light bridges are raised
above the dark surroundings. The geometry of light bridges permits
estimates of the height of their central (slightly darker) ridge:
typically in the range 200-450 km. These images also clearly show
that facular brightenings outside of sunspots and pores occur on the
disk-center side of those granules just limbward of intergranular lanes
that presumably harbor the associated plage magnetic flux. In many cases
the brightening extends 0.5″ or more over those granules. Furthermore,
a very thin, darker lane is often found just centerward of the facular
brightening. We speculate that this feature is the signature of cool
down flows that surround flux tubes in dynamical models. These newly
recognized observational aspects of photospheric magnetic fields
should provide valuable constraints for MHD models of the magnetized
photosphere, and examination of those models as viewed from oblique
angles is encouraged.
---------------------------------------------------------
Title: Diffraction Limited Spectro-Polarimetry at the Dunn Solar
Telescope
Authors: Sankarasubramanian, K.; Rimmele, T. R.; Lites, B. W.
2004AAS...204.2006S Altcode: 2004BAAS...36..686S
The Diffraction Limited Spectro-Polarimeter (DLSP) is a collaborative
project between the National Solar Observatory (NSO) and the
High-Altitude Observatory (HAO). This new instrument, along with the
high-order Adaptive Optics (AO-76) system (which is being developed
at the NSO) has been used to measure magnetic fields on the solar
photosphere at the highest spatial resolution (0.2 arcsec which is
the diffraction limit of the DST at the 630.0nm wavelength). A few
preliminary results obtained from the first observing run with this
instrument are, <P />(1) The fine structures present inside the sunspot
umbra (like the umbral dots) show upflows and reduced field strengths
compared to the surrounding umbra. <P />(2) The sizes of these umbral
fine structures goes down to the diffraction limit of the DST (about
0.2 arcsec). This result confirms that the instrument did achieve
its full capability. <P />(3) There are small-scale convective up and
down flows in the light bridges. The strength of these flow is about
a km/sec. The field strengths are smaller in these regions compared to
the surrounding umbra. At some places in the light bridges, the field
strengths are as small as half of the umbral field strength. <P />(4)
There are small-scale upflows in the inner penumbra of the observed
sunspot. These regions coincide with the inner foot-point of the bright
penumbral filaments as seen in the continuum intensity map. Some of
these upflow regions also show a reduced field strength.
---------------------------------------------------------
Title: The Diffraction Limited Spectro-Polarimeter: a new instrument
for high-resolution solar polarimetry
Authors: Sankarasubramanian, K.; Gullixson, Craig; Hegwer, Stephen;
Rimmele, Thomas R.; Gregory, Scott; Spence, Tony; Fletcher, Stephen;
Richards, Kit; Rousset, Emilie; Lites, Bruce; Elmore, David; Streander,
Kim; Sigwarth, Michael
2004SPIE.5171..207S Altcode:
The National Solar Observatory in collaboration with the High-Altitude
Observatory is developing a new solar polarimeter, the Diffraction
Limited Spectro-Polarimeter. In conjunction with a new high-order
adaptive optics system at the NSO Dunn Solar Telescope, the DLSP
design facilitates very high angular resolution observations of
solar vector magnetic fields. This project is being carried out in two
phases. As a follow-on to the successful completion of the first phase,
the ongoing DLSP Phase II implements a high QE CCD camera system,
a ferro-electric liquid crystal modulator, and a new opto-mechanical
system for polarization calibration. This paper documents in detail the
development of the modulator system and its performance, and presents
preliminary results from an engineering run carried out in combination
with the new NSO high-order AO system.
---------------------------------------------------------
Title: Oscillatory Signatures above Quiet Sun Magnetic Elements
Authors: Bloomfield, D. S.; McAteer, R. T. J.; Lites, B. W.; Judge,
P. G.; Mathioudakis, M.; Keenan, F. P.
2004ESASP.547...51B Altcode: 2004soho...13...51B
A new application of wavelet analysis is presented. The data used are
part of Joint Observing Proposal 72 between SoHO and TRACE, obtained on
1998 May 16 with accompanying groundbased data taken with the Dunn Solar
Telescope at Sacramento Peak, New Mexico. A weak magnetic network region
is studied and the temporal variation of phase difference between TRACE
1700 Å and SoHO/SUMER C II intensities is shown. The example clearly
highlights the advantages of wavelet analysis over more classical
techniques such as Fourier analysis, where the effectiveness of the
technique to identify wavepackets with differing phase difference
relations is emphasised.
---------------------------------------------------------
Title: The evoluton of vector magnetic fields in an emerging flux
region
Authors: Kubo, Masahito; Shimizu, Toshifumi; Tsuneta, Saku; Lites,
B. W.
2004naoj.book...41K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic maps of prominences
Authors: Casini, R.; Lopez Ariste, A.; Tomczyk, S.; Lites, B.
2003AGUFMSH42D..05C Altcode:
We present the first magnetic maps of a prominence obtained by applying
our PCA inversion approach to prominence spectropolarimetric data
in the He I D3 line. Our results indicate the presence of organized
structures in the prominence plasma embedded in magnetic field that are
significantly larger than average (50 G and higher). We reaffirm the
need for a Hanle-based diagnostics of prominence magnetism using full
Stokes spectropolarimetry, and the importance of improved, multi-line
observations, ideally involving both He I D3 and 10830.
---------------------------------------------------------
Title: Magnetic Maps of Prominences from Full Stokes Analysis of
the He I D3 Line
Authors: Casini, R.; López Ariste, A.; Tomczyk, S.; Lites, B. W.
2003ApJ...598L..67C Altcode:
We present the first magnetic maps of a prominence, derived from
inversion of spectropolarimetric data in He I D3 using the principal
component analysis of all four Stokes profiles. This prominence,
along with several others, was observed in 2002 May using the Dunn
Solar Telescope of the National Solar Observatory/Sacramento Peak
Observatory, equipped with the High Altitude Observatory Advanced
Stokes Polarimeter. The use of an unocculted instrument allowed us to
map the prominence magnetic fields down to the chromospheric limb. Our
analysis indicates that the average magnetic field in prominences
is mostly horizontal and varies between 10 and 20 G, thus confirming
previous findings. However, our maps show that fields significantly
stronger than average, even as large as 60 or 70 G, can often be found
in clearly organized plasma structures of the prominence.
---------------------------------------------------------
Title: The Evolution of Vector Magnetic Fields in an Emerging
Flux Region
Authors: Kubo, M.; Shimizu, T.; Lites, B. W.
2003ApJ...595..465K Altcode:
Collaborative observations of NOAA Active Region 9231 were carried out
during 9 days in 2000 November using the Advanced Stokes Polarimeter
(ASP), Yohkoh/SXT, TRACE, and SOHO/MDI, in order to record the
evolution of the photospheric magnetic field and its related coronal
response. During this period an emerging flux region (EFR) appeared in
the photosphere near the well-developed leading sunspot of this region,
and subsequently bright bundles of coronal loops formed between the
main concentrations of opposite magnetic polarity. The structure of
the photospheric field comprising the EFR is classified into three
regions: (1) the main bipolar magnetic flux of the EFR; (2) two small,
rapidly emerging bipoles within the EFR; and (3) the remainder of
the EFR excluding the other two regions. Two small, rapidly emerging
bipoles are observed within a few hours of their first appearance at
the photosphere. Examination of the vector magnetic field, its filling
factor, and Doppler motion within the EFR shows that the young emerging
magnetic field is nearly horizontal, the intrinsic field strength is
weaker than that of the surrounding magnetic field (~500 G), and the
weak field has a high filling factor (>80%) and upward motion (<1
km s<SUP>-1</SUP>). At both ends of the horizontal field structure we
find that the magnetic field strength increases to about 1500 G and
the filling factor drops to about 40% as the magnetic field becomes
vertical in orientation during its first 12 hr. This field strength
is typical of the field within the main bipolar magnetic flux, but
the filling factor increases to 80% during the following 2 days. The
process for organizing magnetic field configuration including convective
collapse and flux concentration provides one possible explanation
of the evolution of the field strength and the filling factor in the
EFR. In addition, aymmetric surface distributions of magnetic field
inclination were observed in the horizontal magnetic field area in the
EFR. These asymmetric distributions were also observed in the small,
young, emerging bipoles. This may mean that the magnetic field of the
EFR is affected by the preexisting magnetic environment surrounding
the EFR and that the emerging magnetic loops are deformed before or
at the time they reach the photospheric level.
---------------------------------------------------------
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: Weak-Field Magnetogram Calibration using Advanced Stokes
Polarimeter Flux Density Maps - II. SOHO/MDI Full-Disk Mode
Calibration
Authors: Berger, T. E.; Lites, B. W.
2003SoPh..213..213B Altcode:
Cotemporal Ni i 676.8 nm full-disk magnetograms from the Michelson
Doppler Interferometer (MDI) instrument on SOHO and the Advanced Stokes
Polarimeter (ASP) are quantitatively compared using observations
of active region AR 8218, a large negative polarity sunspot group
observed at S20 W22 on 13 May 1998. MDI produces flux density estimates
based on a polarized line center-of-gravity algorithm using moderate
spectral resolution filtergrams with approximately 4 arc sec angular
resolution. The magnetograms are formed by an on-board image processor
and sent to the ground where they are calibrated using an empirical
model to produce flux density maps. The ASP uses high spectral
resolution Stokes polarimetric observations to produce very high
precision vector magnetic field maps at angular resolution values on
the order of 1 arc sec in good seeing. We use ASP inversion results to
create a reference ASP `longitudinal magnetic flux density map' with
which to calibrate the MDI full-disk magnetograms. The magnetograms from
each instrument are scaled to a common reference frame and co-aligned
with an accuracy of about 1.6 arc sec. Regions of invalid data,
poor field-of-view overlap, and sunspots are masked out in order to
calibrate MDI predominately on the relatively vertical `weak-field'
plage magnetic elements. Pixel-to-pixel statistical comparisons are
used to determine an MDI magnetogram linear calibration relative to
reference ASP flux density values. We find that the current Level-1.5
MDI full-disk calibration gives flux density values lower on average
by a factor of 0.64±0.013 compared to the ASP reference in active
region plage. In sunspot regions (penumbra and umbra) the factor
is 0.69±0.007.
---------------------------------------------------------
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: Diffraction limited spectro-polarimeter - Phase I
Authors: Sankarasubramanian, Kasiviswanathan; Elmore, David F.; Lites,
Bruce W.; Sigwarth, Michael; Rimmele, Thomas R.; Hegwer, Steven L.;
Gregory, Scott; Streander, Kim V.; Wilkins, Lawrence M.; Richards,
K.; Berst, C.
2003SPIE.4843..414S Altcode:
A diffraction limited spectro-polarimeter is under construction at the
National Solar Observatory in collaboration with the High Altitude
Observatory. The scientific objective of the project is to measure
the magnetic fields on the Sun up to the diffraction limit of the Dunn
Solar Telescope. The same instrument would also measure the magnetic
field of large sunspots or sunspot groups with reasonable spatial
resolution. This requires a flexible image scale which cannot be
obtained with the current Advanced Stokes Polarimeter (ASP) without
loosing 50% of the light. The new spectro-polarimeter is designed
in such a way that the image scale can be changed without loosing
much light. It can work either in high-spatial resolution mode (0.09
arcsec per pixel) with a small field of view (FOV: 65 arcsec) or in
large FOV mode (163 arcsec) with low-spatial resolution (0.25 arcsec
per pixel). The phase-I of this project is to design and build the
spectrograph with flexible image scale. Using the existing modulation,
calibration optics of the ASP and the ASP control and data acquisition
system with ASP-CHILL camera, the spectrograph was tested for its
performance. This paper will concentrate on the performance of the
spectrograph and will discuss some preliminary results obtained with
the test runs.
---------------------------------------------------------
Title: POLIS: A spectropolarimeter for the VTT and for GREGOR
Authors: Schmidt, W.; Beck, C.; Kentischer, T.; Elmore, D.; Lites, B.
2003AN....324..300S Altcode:
The polarimetric Littrow Spectrograph POLIS is designed for vector
polarimetry at high angular and spectral resolution. It measures the
magnetic field simultaneously in the photosphere and the chromosphere
of the sun. Both branches of the polarimetry unit are dual beam systems
with a single rotating modulator for both wavelengths and polarizing
beam splitters in front of each CCD camera. POLIS has been installed
at the VTT on Tenerife and has seen First Light on 17 May 2002. A
modified version of POLIS will be developed for the balloon mission
Sunrise. That version will have UV capabilities down to 200 nm.
---------------------------------------------------------
Title: First Results from the HAO/NSO Diffraction-Limited
Spectro-Polarimeter
Authors: Lites, B. W.; Elmore, D. F.; Streander, K. V.;
Sankarasubramanian, K.; Rimmele, T. R.; Sigwarth, M.
2003ASPC..307..324L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Helioseismic and Magnetic Imager (HMI) on SDO: Full Vector
Magnetography with a Filtergraph Polarimeter
Authors: Graham, J. D.; Norton, A.; López Ariste, A.; Lites, B.;
Socas-Navarro, H.; Tomczyk, S.
2003ASPC..307..131G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Estimating the Effects of JPEG Compression and Radiation on
the Accuracy of Vector Magnetic Fields Measurements for Solar-B
Authors: Lites, B.; Shine, R. A.; López Ariste, A.; Tarbell, T. D.
2002AGUFMSH52A0471L Altcode:
The Japanese Solar-B satellite, currently scheduled for launch in
September 2005, includes a spectro-polarimeter (SP) to precisely measure
the full Stokes polarization vector (I,Q,U,V) in the Fe I lines at
6302Å. These will be processed to produce vector magnetograms of the
solar surface using algorithms based on those for the Advanced Stokes
Polarimeter (ASP) as described in Skumanich, et al, 1997, ApJ Suppl
110. Accumulations of the raw images into time averaged I,Q,U,V images
will be done on board and the results will be 12 bit JPEG compressed to
make the best use of the available telemetry. Hence a single radiation
hit in a raw image affects the entire time average at that point. Also,
radiation spikes affect JPEG compression performance. Because of
concerns about these effects, we simulated them separately and in
combination using ASP data and radiation level measurements from the
TRACE satellite. Like TRACE, Solar-B will fly in a high inclination,
sun synchronous orbit and be exposed to radiation from the polar
radiation belts as well as the SAA. Since the SP detector will be
better shielded than that on TRACE, we hope that these will be an over
estimate of the effects. The results from the simulations are very
encouraging. We find that for active region magnetic fields we can use
JPEG to compress the data volume by more than a factor of 10 without
compromising the accuracy of the inferred magnetic field vector. The
radiation in the polar regions has little effect and even the much
stronger SAA radiation causes average perturbations that are less than
the formal errors for sunspot fields and about twice the formal errors
for plage fields. However, very weak field measurements will benefit
from less lossy compression and periods of low radiation. Of course,
the very strong radiation hits always produce artifacts. Compression
performance is affected only slightly so it will not be necessary to
avoid observations in the SAA because of excessive telemetry usage. This
work was supported by NASA contract NAS8-01002.
---------------------------------------------------------
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.
---------------------------------------------------------
Title: Intensity tracers of the magnetic field: pitfalls and
opportunities
Authors: Lites, B. W.; Berger, T. E.
2002ESASP.505...57L Altcode: 2002solm.conf...57L; 2002IAUCo.188...57L
Magnetic fields are the main source of structuring of the solar
atmosphere. Stokes I images at various wavelengths reflect this
structure at the monochromatic heights of formation of the intensity. In
the photosphere intensity tracers identify the location and evolution
of kiloGauss flux tubes. In the chromosphere and above Stokes I images
may be used to identify the direction of the magnetic lines of force,
and may be used to establish the connectivity of the field inferred from
photospheric vector magnetograms. In some circumstances the intensity
diagnostics of the field may be misleading. Some of these "pitfalls"
are discussed.
---------------------------------------------------------
Title: Weak-Field Magnetogram Calibration using Advanced Stokes
Polarimeter Flux-Density Maps - I. Solar Optical Universal Polarimeter
Calibration
Authors: Berger, T. E.; Lites, B. W.
2002SoPh..208..181B Altcode:
Cotemporal Fe i 630.2 nm magnetograms from the Solar Optical Universal
Polarimeter (SOUP) filter and the Advanced Stokes Polarimeter (ASP) are
quantitatively compared using observations of active region AR 8218,
a large negative polarity sunspot group observed at S20 W22 on 13 May
1998. The SOUP instrument produces Stokes V/I `filter magnetograms'
with wide field of view and spatial resolution below 0.5 arc sec
in good seeing, but low spectral resolution. In contrast, the ASP
uses high spectral resolution to produce very high-precision vector
magnetic field maps at spatial resolution values on the order of 1
arc sec in good seeing. We use ASP inversion results to create an ASP
`longitudinal magnetic flux-density map' with which to calibrate the
less precise SOUP magnetograms. The magnetograms from each instrument
are co-aligned with an accuracy of about 1 arc sec. Regions of invalid
data, poor field-of-view overlap, and sunspots are masked out in order
to calibrate SOUP predominately on the relatively vertical `weak-field'
plage magnetic elements. Pixel-to-pixel statistical comparisons are
used to determine the SOUP magnetogram linear calibration constant
relative to ASP flux-density values. We compare three distinct
methods of scaling the ASP and SOUP data to a common reference
frame in order to explore filling factor effects. The recommended
SOUP calibration constant is 17 000 ± 550 Mx cm<SUP>−2</SUP> per
polarization percent in plage regions. We find a distinct polarity
asymmetry in SOUP response relative to the ASP, apparently due to a
spatial resolution effect in the ASP data: the smaller, less numerous,
minority polarity structures in the plage region are preferentially
blended with the majority polarity structures. The blending occurs to
a lesser degree in the high-resolution SOUP magnetogram thus leading
to an apparent increase in SOUP sensitivity to the minority polarity
structures relative to the ASP. One implication of this effect is
that in mixed polarity regions on the Sun, lower spatial resolution
magnetograms may significantly underestimate minority polarity flux
levels, thus leading to apparent flux imbalances in the data.
---------------------------------------------------------
Title: Converging Flows in the Penumbra of a δ Sunspot
Authors: Lites, B. W.; Socas-Navarro, H.; Skumanich, A.; Shimizu, T.
2002ApJ...575.1131L Altcode:
Doppler velocities in the penumbra of a δ-configuration sunspot
observed near the limb indicate flows that converge upon the
line separating locally positive and negative polarity magnetic
field (the polarity inversion line). These flows persist for many
hours. Observations of this region with the Advanced Stokes Polarimeter
(ASP) reveal a convex vector field geometry with magnetic lines of
force arching upward from positive polarity, then downward to negative
polarity. The straightforward interpretation of the combined Doppler
velocity and vector field information leads to an untenable physical
situation: were flows directed from both footpoints toward the tops
of arched magnetic lines of force, mass would rapidly load the tops of
the arches. However, there is no observational evidence of the dynamics
that such a loading would require. To better understand this apparent
contradiction, we perform two-component analyses of the observed Stokes
spectral profiles in the vicinity of the polarity inversion line, in
order to extract information about unresolved structure of the magnetic
field and its associated flows. Fits to the observed profiles, obtained
by use of two different inversion techniques, suggest strongly that, as
in penumbrae of simple sunspots, the field geometry in the convergence
zone is “fluted.” However, unlike in simple sunspots, which have only
an outward-directed Evershed flow in the more horizontal of the field
components, at each spatial point our analysis reveals flows in the two
components that are oppositely directed. We interpret these observations
as indicative of an interleaved system of field lines in the vicinity
of the polarity reversal, whereby the convergent streams are able to
slip past one another and return downward into the solar interior.
---------------------------------------------------------
Title: The upcoming new world of sunspot observations from space
Authors: Lites, B. W.
2002AN....323..277L Altcode:
Several space missions are in planning, or actually in preparation
for launch, that will provide tremendous advances in observational
capability for angular resolution, polarimetric precision, wavelength
coverage, and continuity of observation. These missions, including
Solar-B, Sunrise, Solar Dynamics Observatory, and Solar Orbiter, will
lay the observational framework for confronting many outstanding
questions regarding sunspots: their formation, evolution, and
dissipation; and their consequences for other solar phenomena. These
four missions are briefly reviewed in the context of their importance
to the physics of the sunspot phenomenon.
---------------------------------------------------------
Title: Characterization of Magnetic Flux in the Quiet Sun
Authors: Lites, B. W.
2002ApJ...573..431L Altcode:
Observations of the quiet Sun observed with the Advanced Stokes
Polarimeter are used to explore the distribution of apparent
flux density (B<SUB>app</SUB>) and size scales of internetwork
regions. For a typical disk-center quiet-Sun observation with
excellent seeing (at a quantifiable angular resolution of 1"), average
|B<SUB>app</SUB>| of 18.6 and 10.7 Mx cm<SUP>-2</SUP> are found for
the entire quiet region map and the internetwork region (2 σ noise
<|B<SUB>app</SUB>|<40Mxcm<SUP>-2</SUP>), respectively. The weak
internetwork flux appears to consist of two components: the spatially
concentrated “granular” internetwork fields and a more diffuse, weaker
component that has a characteristic size scale of a few arcseconds. Most
of the internetwork area is occupied by measurable fields: 69% of the
area has apparent flux density greater than 4.5 Mx cm<SUP>-2</SUP>
(3 σ), or 84% with flux density greater than 3.0 Mx cm<SUP>-2</SUP> (2
σ). If the results of Hanle depolarization measurements are accepted,
the internetwork flux detected here must be close (within a factor
of 2-3) to being spatially resolved and must be intrinsically weak
(10-30 G). Examination of Stokes polarimetry in quiet regions away
from disk center indicates that the central cores of network flux,
as indicated by high-polarization signals, do not have a high degree
of mixed polarity. In contrast, regions immediately surrounding the
network elements have stronger linear polarization than would be
expected from locally vertical fields, indicating a high degree of
mixed polarity. This mixed polarity may be the result of the continual
“sweeping” of mixed polarity internetwork flux toward the network
boundaries. When a quiet region has a significant imbalance of flux
of opposite polarities, the internetwork imbalance is of the same
sign and typically 1/3 that of the network. The smaller imbalance in
the internetwork suggests that a local dynamo produces most of the
internetwork flux.
---------------------------------------------------------
Title: The Solar Internetowrk Magnetic Fields
Authors: Socas-Navarro, H.; Lites, B. W.
2002AAS...200.5516S Altcode: 2002BAAS...34R.950S
The properties of solar photospheric inter-network fields are studied
using observations from the Advanced Stokes Polarimeter. By averaging
over large areas of the observed map we are able to bring down the
noise level to approximately 10<SUP>-5</SUP> and determine typical
magnetic properties of granules and intergranular lanes outside the
magnetic network.
---------------------------------------------------------
Title: Inference of Solar Vector Magnetic Fields with Filtergraph
Instruments
Authors: Graham, J. D.; Lites, B. W.; López Ariste, A.; Norton, A.;
Socas-Navarro, H.; Tomczyk, S.
2002AAS...200.5611G Altcode: 2002BAAS...34..736G
We investigate the diagnostic potential of polarimetric measurements
with filtergraph instruments. Numerical simulations are used to
explore the possibility of inferring the magnetic field vector, its
filling factor, and the thermodynamics of model atmospheres when
only a few wavelength measurements are available. The simulations
assume the magnetic sun to be represented by Milne-Eddington (ME)
atmospheres. The results indicate that two wavelength measurements
are insufficient to reliably determine the magnetic parameters,
regardless of whether magnetograph techniques or least-squares fitting
inversions are used. However, as few as four measurements analyzed
with the inversion technique provide enough information to retrieve the
intrinsic magnetic field with an accuracy better than 10 generated by
more general models and ASP data passed through a simulated filtergraph.
---------------------------------------------------------
Title: New Polarization Diagnostics for the Solar Atmosphere
Authors: Casini, R.; López Ariste, A.; Tomczyk, S.; Lites, B.
2002AAS...200.3403C Altcode: 2002BAAS...34..690C
We present relatively new diagnostics of “weak" magnetic fields in the
solar atmosphere. The first diagnostic is suggested by recent advances
in the inversion of Stokes profiles of lines formed by resonance
scattering in the weakly magnetized plasma of prominences (Hanle
effect and level-crossing; 0 to 100 G). Use of pattern recognition
techniques (PCA) in this field has marked a sensible progress with
respect to previous diagnostic procedures. The second diagnostic is
the modelling of hyperfine structured (HFS) lines that can be observed
in the spectrum of the quiet photosphere. This allows to investigate
relatively weak photospheric fields (200 G to 1000 G), in which regime
the HFS induces peculiar signatures in the Stokes profiles, including
the appearance of subcomponents and net circular polarization. The third
diagnostic is suggested by interesting polarization properties of the
Na I D1 line formed by resonance scattering: the atomic polarization
in the upper level of D1, which is responsible of a characteristic
antisymmetric (i.e., V-like) signature in the core of Stokes Q, is
rapidly suppressed for B > 10 G, irrespective of the magnetic field
direction. A common denominator of these three diagnostics is their
sensitivity to the actual strength of the magnetic field, instead
of the magnetic flux within the resolution element. Another common
aspect is that all require (or would profit from) high polarization
sensitivity, which will be one of the strengths of ATST. For the
diagnostics of prominence magnetic fields, the possibility of multiline
spectropolarimetry could be decisive. Simultaneous observations of
He I D3 (5876A) and 10830A, or of He I D3 and the Na I D lines (all
within a 20A spectral range!), would increase the inversion accuracy
of PCA. The high spatial resolution capabilities of ATST would be
advantageous mostly to diagnose weak photospheric fields, already at
the present time. Because of the complexity of radiative transfer in
complicated structures like prominences, high spatial resolution in
these structures is not the highest priority. However, we hope that
when ATST will become operative, this complicated problem will have
been attacked succesfully.
---------------------------------------------------------
Title: The sunrise international balloon program for high resolution
solar physics
Authors: Lites, B.
2002cosp...34E1321L Altcode: 2002cosp.meetE1321L
The Sunrise program is an international effort to fly a large aperture
(1-m) diffractionlimited solar telescope on a long-duration Antarctic
balloon in order to investigate the detailed physics of solar magnetism
and solar variability at very small scales. Instrumentation will include
imaging and spectrographic polarimeters to yield quantitative measures
of the solar vector magnetic field, and broad-band imaging down to 200
nm with the capability of post-observation phase diversity wavefront
correction to image the Sun with the highest angular resolution yet
(35 km at the solar surface). The program is a cooperation among United
States, Germany, and Spain, with the US portion funded by NASA. The
first science flight from Antarctica is expected in 2006.
---------------------------------------------------------
Title: Dynamics of the solar chromosphere. III. Ultraviolet brightness
oscillations from TRACE
Authors: Krijger, J. M.; Rutten, R. J.; Lites, B. W.; Straus, Th.;
Shine, R. A.; Tarbell, T. D.
2001A&A...379.1052K Altcode:
We analyze oscillations in the solar atmosphere using image sequences
from the Transition Region and Coronal Explorer (TRACE) in three
ultraviolet passbands which sample the upper solar photosphere and
low chromosphere. We exploit the absence of atmospheric seeing in
TRACE data to furnish comprehensive Fourier diagnostics (amplitude
maps, phase-difference spectra, spatio-temporal decomposition) for
quiet-Sun network and internetwork areas with excellent sampling
statistics. Comparison displays from the ground-based Ca Ii H
spectrometry that was numerically reproduced by Carlsson &
Stein are added to link our results to the acoustic shock dynamics
in this simulation. The TRACE image sequences confirm the dichotomy
in oscillatory behaviour between network and internetwork and show
upward propagation above the cutoff frequency, the onset of acoustic
shock formation in the upper photosphere, phase-difference contrast
between pseudo-mode ridges and the interridge background, enhanced
three-minute modulation aureoles around network patches, a persistent
low-intensity background pattern largely made up of internal gravity
waves, ubiquitous magnetic flashers, and low-lying magnetic canopies
with much low-frequency modulation. The spatio-temporal occurrence
pattern of internetwork grains is found to be dominated by acoustic
and gravity wave interference. We find no sign of the high-frequency
sound waves that have been proposed to heat the quiet chromosphere, but
such measurement is hampered by non-simultaneous imaging in different
passbands. We also find no signature of particular low-frequency
fluxtube waves that have been proposed to heat the network. However,
internal gravity waves may play a role in their excitation.
---------------------------------------------------------
Title: Precision spectro-polarimeter for high-resolution observations
of solar magnetic fields
Authors: Lites, Bruce W.; Elmore, David F.; Streander, Kim V.; Akin,
David L.; Berger, Tom; Duncan, Dexter W.; Edwards, Chris G.; Francis,
Barbara; Hoffmann, Chris; Katz, Noah; Levay, Michael; Mathur, Dnyanesh;
Rosenberg, William A.; Sleight, Ericka; Tarbell, Theodore D.; Title,
Alan M.; Torgerson, Darrel
2001SPIE.4498...73L Altcode:
As a Japanese National space mission with international collaboration,
Solar-B (2005 launch) will carry a spectro- polarimeter (SP)
to be operated in visible light to obtain the first high angular
resolution, precision measurements of solar vector magnetic fields
from space. The SP is part of the Focal Plane Package (FPP) fed by a
diffraction-limited 50-cm optical telescope. The SP will be operated
exclusively at the photospheric 630 nm Fe I lines. It features a
rotating, low-order crystalline quartz retarder for polarization
modulation and a reflecting Littrow spectrograph design that is
shortened by using diffraction from the 12micrometers wide slit to
fill the grating. Polarization analysis is accomplished by a modified
Savart plate beam splitter. A custom CCD detector with two active
areas, one for each beam from the beam splitter, allows continuous
high duty-cycle sampling of polarization. The spectrograph slit will
sample a 0.16 x 164 arcsec<SUP>2</SUP> rectangle of the solar image,
which may be scanned across the slit by up to +/- 160 arcsec in order
to build up vector magnetic field maps of the solar photosphere. Along
with simultaneous, co-spatial imaging and polarimetry with the filter
imagers of the FPP, the SP will provide a precise view of active and
quiet solar magnetic fields that control the structure, dynamics,
and energetics of the upper solar atmosphere.
---------------------------------------------------------
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: Pattern recognition techniques and the measurement of solar
magnetic fields
Authors: Lopez Ariste, Arturo; Rees, David E.; Socas-Navarro, Hector;
Lites, Bruce W.
2001SPIE.4477...96L Altcode:
Measuring vector magnetic fields in the solar atmosphere using the
profiles of the Stokes parameters of polarized spectral lines split
by the Zeeman effect is known as Stokes Inversion. This inverse
problem is usually solved by least-squares fitting of the Stokes
profiles. However least-squares inversion is too slow for the new
generation of solar instruments (THEMIS, SOLIS, Solar-B, ...) which will
produce an ever-growing flood of spectral data. The solar community
urgently requires a new approach capable of handling this information
explosion, preferably in real-time. We have successfully applied pattern
recognition and machine learning techniques to tackle this problem. For
example, we have developed PCA-inversion, a database search technique
based on Principal Component Analysis of the Stokes profiles. Search is
fast because it is carried out in low dimensional PCA feature space,
rather than the high dimensional space of the spectral signals. Such
a data compression approach has been widely used for search and
retrieval in many areas of data mining. PCA-inversion is the basis of
a new inversion code called FATIMA (Fast Analysis Technique for the
Inversion of Magnetic Atmospheres). Tests on data from HAO's Advanced
Stokes Polarimeter show that FATIMA isover two orders of magnitude
faster than least squares inversion. Initial tests on an alternative
code (DIANNE - Direct Inversion based on Artificial Neural NEtworks)
show great promise of achieving real-time performance. In this paper
we present the latest achievements of FATIMA and DIANNE, two powerful
examples of how pattern recognition techniques can revolutionize data
analysis in astronomy.
---------------------------------------------------------
Title: Visible-light observations and high-resolution polarimetry
Authors: Lites, Bruce W.
2001ESASP.493....3L Altcode: 2001sefs.work....3L
The polarimetric imager on Solar Orbiter will follow the realization
of significant space- and ground-based programs for high resolution
solar polarimetry in the coming decade. In this review I attempt to
identify the scientific potential of Solar Orbiter within the context
of anticipated observational capability and scientific understanding
ten years from now. The unique contribution of Solar Orbiter is its
high resolution imaging from an angular perspective well-removed from
that of the Earth. When combined with simultaneous high resolution
polarimetry from the perspective of the Earth, Solar Orbiter will
provide stereoscopic observations of the fine structure in the solar
photospheric magnetic field which will likely reveal the detailed
structure on a physical height scale, rather than an optical depth
scale. Furthermore, the observations will provide the velocity field
components in a plane, rather than along just one line-of-sight. These
advances promise tight observational constraints for fundamental
processes such as convective collapse, generation and propagation of
MHD waves in flux tubes, ultra fine-scale magnetic flux of the quiet
Sun internetwork. At some phase of its orbit, the Orbiter will also
provide the unique capability to follow the development of solar
activity through a large fraction of a complete solar rotation;
a capability that should illuminate the processes responsible for
active region decay. Finally, the perspective views of Solar Orbiter
may permit measurements of vector magnetic fields in the chromosphere
without resorting to linear polarimetry.
---------------------------------------------------------
Title: Sunspot Bright Rings: Evidence from Case Studies
Authors: Rast, M. P.; Meisner, R. W.; Lites, B. W.; Fox, P. A.; White,
O. R.
2001ApJ...557..864R Altcode:
We present evidence, from both the Precision Solar Photometric Telescope
and the Advanced Stokes Polarimeter, for a ring of enhanced continuum
intensity surrounding large isolated sunspots. We do not attempt to
evaluate the frequency of the phenomenon based on a large sample of
spots but instead concentrate on illustrative best-case examples. The
rings are about 0.5%-1.0% brighter in red and blue continuum (10 K
warmer) than the surrounding photosphere and extend about one sunspot
radius outward from the outer penumbral boundary. Most of the excess
radiation is not directly associated with the strongest regions of Ca II
K emission surrounding the spots or with measurable vertical magnetic
field when such measurements are available. Moreover, the temporal
evolution of the Ca II K and continuum emission in the ring differ,
with the continuum intensity evolving on a shorter timescale. This
suggests a convective origin for the bright ring, although a role
for weaker, more diffuse magnetic fields cannot be ruled out. While
we have inferred that only about 10% of the radiant energy missing
from the sunspot is emitted through the bright ring, even this small
enhancement may be significant to our understanding of subsurface
sunspot structure and energy transport.
---------------------------------------------------------
Title: Fast Inversion of Spectral Lines Using Principal Components
Analysis. II. Inversion of Real Stokes Data
Authors: Socas-Navarro, H.; López Ariste, A.; Lites, B. W.
2001ApJ...553..949S Altcode:
The principal components analysis (PCA) technique is used to develop
an extremely fast and stable Stokes inversion code, suitable for
application to large data sets from instruments that operate under
standard conditions. This paper provides some tips on reducing the
dimensionality of the problem, which are then used to develop a
practical implementation of PCA for the automatic analysis of Stokes
profiles. The resulting code is tested using real spectropolarimetric
observations of the pair of Fe I lines at 6302 Å at a sunspot.
---------------------------------------------------------
Title: Intercomparison of SOUP, ASP, LPSP, and MDI magnetograms
Authors: Berger, T.; Lites, B.; Martinez-Pillet, V.; Tarbell, T.;
Title, A.
2001AGUSM..SP51B12B Altcode:
We compare simultaneous magnetograms of a solar active region taken by
the Advanced Stokes Polarimeter (ASP) and the Solar Optical Universal
Polimeter (SOUP) in 1998. In addition we compare magnetograms taken by
the La Palma Stokes Polarimeter (LPSP), the Michelson Doppler Imager
(MDI) on SOHO, and the SOUP instrument in 2000. The SOUP instrument on
the Swedish Vacuum Solar Telescope (SVST) attains the highest spatial
resolution but has the least understood calibration; the ASP on the Dunn
Solar Telescope (DST) at Sacramento Peak attains the highest magnetic
field precision. The goal of the program is to better quantify the
SOUP magnetograms and thereby study magnetic element dynamics in the
photosphere with higher precision.
---------------------------------------------------------
Title: Optical Tomography of a Sunspot. II. Vector Magnetic Field
and Temperature Stratification
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
2001ApJ...547.1130W Altcode:
An observational determination of the three-dimensional magnetic
and thermal structure of a sunspot is presented. It has been
obtained through the application of the SIR inversion technique
(Stokes Inversion based on Response functions) on a low-noise, full
Stokes profile two-dimensional map of the sunspot as observed with
the Advanced Stokes Polarimeter. As a result of the inversion, maps
of the magnetic field strength, B, zenith angle, γ, azimuth, χ, and
temperature, T, over 25 layers at given optical depths (i.e., an optical
tomography) are obtained, of which those between logτ<SUB>5</SUB>=0 and
logτ<SUB>5</SUB>=-2.8 are considered to provide accurate information on
the physical parameters. All over the penumbra γ increases with depth,
while B is larger at the bottom layers of the inner penumbra (as in
the umbra) but larger at the top layers of the outer penumbra (as in
the canopy). The corrugation of the penumbral magnetic field already
observed by other authors has been confirmed by our different inversion
technique. Such a corrugation is especially evident in the zenith angle
maps of the intermediate layers, featuring the presence of the so-called
spines that we further characterize: spines are warmer and have a less
inclined magnetic field than the spaces between them and tend to have a
smaller gradient of γ with optical depth over the entire penumbra, but
with a field strength which is locally stronger in the middle penumbra
and locally weaker in the outer penumbra and beyond in the canopy. In
the lower layers of these external parts of the sunspot, most of the
field lines are seen to return to the solar surface, a result that is
closely connected with the Evershed effect (e.g., Westendorp et al.,
the third paper in this series). The Stokes V net area asymmetry map
as well as the average B, γ, and T radial distributions (and that
of the line-of-sight velocities; see the third paper in this series)
show a border between an inner and an outer penumbra with different
three-dimensional structure. We suggest that it is in this middle zone
where most of a new family of penumbral flux tubes (some of them with
Evershed flow) emerge interlaced (both horizontally and vertically)
among themselves and with the “background” magnetic field of the
penumbra. The interlacing along the line of sight is witnessed by
the indication of many points in the outer penumbra showing rapid
transitions with height between two structures, one with very weak
and inclined magnetic field at the bottom of the photosphere and the
other with a stronger and less inclined magnetic field. Over the whole
penumbra, and at all optical layers, a constant but weak deviation from
radiality of some 5° is detected for the azimuth of the vector magnetic
field, which may be in agreement with former detections but which is
not significantly higher than the size of the errors for this parameter.
---------------------------------------------------------
Title: An Observational Manifestation of Magnetoatmospheric Waves
in Internetwork Regions of the Chromosphere and Transition Region
Authors: McIntosh, S. W.; Bogdan, T. J.; Cally, P. S.; Carlsson, M.;
Hansteen, V. H.; Judge, P. G.; Lites, B. W.; Peter, H.; Rosenthal,
C. S.; Tarbell, T. D.
2001ApJ...548L.237M Altcode:
We discuss an observational signature of magnetoatmospheric waves in
the chromosphere and transition region away from network magnetic
fields. We demonstrate that when the observed quantity, line or
continuum emission, is formed under high-β conditions, where β is
the ratio of the plasma and magnetic pressures, we see fluctuations in
intensity and line-of-sight (LOS) Doppler velocity consistent with the
passage of the magnetoatmospheric waves. Conversely, if the observations
form under low-β conditions, the intensity fluctuation is suppressed,
but we retain the LOS Doppler velocity fluctuations. We speculate that
mode conversion in the β~1 region is responsible for this change in
the observational manifestation of the magnetoatmospheric waves.
---------------------------------------------------------
Title: Converging Flows in the Penumbra of a δ-Sunspot
Authors: Lites, B. W.; Socas-Navarro, H.; Skumanich, A.; Shimizu, T.
2001ASPC..248..143L Altcode: 2001mfah.conf..143L
No abstract at ADS
---------------------------------------------------------
Title: Convergent Flows in the Penumbra of a δ-Sunspot
Authors: Lites, B. W.; Socas-Navarro, H.
2001ASPC..236..329L Altcode: 2001aspt.conf..329L
No abstract at ADS
---------------------------------------------------------
Title: Space-Based Instrumentation for Inference of the Solar
Magnetic Field
Authors: Lites, B. W.
2001ASPC..248..553L Altcode: 2001mfah.conf..553L
No abstract at ADS
---------------------------------------------------------
Title: A new Stokes Polarimeter for the Dunn Solar Telescope
Authors: Sigwarth, M.; Berst, C.; Gregory, S.; Hegwer, S.; Richards,
K.; Rimmele, T.; Wilkins, L.; Lites, B. W.; Elmore, D. F.; Streander,
K. V.
2001ASPC..236...57S Altcode: 2001aspt.conf...57S
No abstract at ADS
---------------------------------------------------------
Title: The Solar-B Spectro-Polarimeter
Authors: Lites, B. W.; Elmore, D. F.; Streander, K. V.
2001ASPC..236...33L Altcode: 2001aspt.conf...33L
No abstract at ADS
---------------------------------------------------------
Title: POLIS: Simultaneous Measurement of Photospheric and
Chromospheric Magnetic Field
Authors: Schmidt, W.; Kentischer, T. J.; Bruls, J.; Lites, B. W.
2001ASPC..236...49S Altcode: 2001aspt.conf...49S
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: Calibration procedure for the polarimetric instrument for
Solar Eclipse-98
Authors: Elmore, David F.; Card, G. L.; Lecinski, A. R.; Lites,
Bruce W.; Streander, Kim V.; Tomczyk, Steven
2000SPIE.4139..370E Altcode:
We describe a ground-based eclipse instrument for measuring solar
coronal polarization brightness and intensity, and the calibration
procedures for this instrument. We present coronal measurements from the
February 26, 1998 total solar eclipse observed at Curacao, N.A.. The
instrument employs a liquid crystal variable retarder for analysis of
coronal broad band linear polarization and collects data on an array
detector spanning a 6.5 solar radius field of view. Polarization
calibration of the liquid crystal variable retarder utilizes the
tangential orientation of coronal polarization to calculate retardance
values.
---------------------------------------------------------
Title: Solar Magnetic Field: Inference by Polarimetry
Authors: Lites, B.
2000eaa..bookE2402L Altcode:
Most solar structure and phenomena occurring in the solar atmosphere
arise from the presence of magnetic fields. This article describes
techniques for remote sensing of the solar magnetic field, primarily
via analysis of the polarization it imparts to the radiation emitted
by the Sun....
---------------------------------------------------------
Title: The Solar-B Focal Plane Package
Authors: Berger, T. E.; Title, A. M.; Tarbell, T. D.; Lites, B. W.;
Elmore, D. F.
2000SPD....31.0292B Altcode: 2000BAAS...32..827B
Solar-B is a Japanese national space science mission of the Institute
of Space and Astronautical Sciences (ISAS) with participation from
US and UK research groups. The satellite consists of a 50-cm optical
telescope and Focal Plane Package (FPP) designed for high resolution
photospheric and chromospheric imaging and spectro-polarimetry as
well as two coronal instruments: the X-Ray Telescope (XRT) and the
Extreme-ultraviolet Imaging Spectrometer (EIS). Solar-B will be
launched into a Sun-synchronous orbit in August of 2004. A team of
Lockheed Martin Solar and Astrophysics Laboratory (LMSAL), High Altitude
Observatory, and ISAS personnel are designing the FPP instrument. It
consists of a narrow-band tunable birefringent filter system,
a wide band interference filter system, and a spectro-polarimeter
system for very high sensitivity Stokes polarimetry, all of which
will be fabricated at LMSAL. We describe the main science goals of
the FPP as well as the current instrument design and performance
characteristics. This work is supported by NASA contract NAS8-00014
(Solar-B FPP).
---------------------------------------------------------
Title: Physical Properties of the Solar Magnetic Photosphere under
the MISMA Hypothesis. II. Network and Internetwork Fields at the
Disk Center
Authors: Sánchez Almeida, J.; Lites, B. W.
2000ApJ...532.1215S Altcode:
This paper is the second in a series that models photospheric magnetic
structures in terms of atmospheres having optically thin fluctuations
of magnetic field and thermodynamic state (the MISMA hypothesis). We
apply an inversion procedure to the polarization of Fe I λ6301.5 and
Fe I λ6302.5 observed in network and internetwork regions with the
Advanced Stokes Polarimeter. Some 5200 independent spectra, comprising
mildly asymmetric to very abnormal Stokes profiles, were reproduced
by a single type of model atmosphere. It has three components, two
that are magnetized and one that is not. A large fraction among the
field strengths we measure are in the kG regime, but simulations
suggest that the polarization of the observed Fe I lines weakens
below detectable levels for fields substantially smaller than the
observed ones. Synthesis of Stokes profiles of the IR Fe I λ15648.5
line in MISMAs reveals the opposite behavior, i.e., an increase of
polarization for sub-kG fields. The highly transparent MISMAs inferred
from observations are significantly brighter in the continuum than an
unmagnetized atmosphere. The mass of the magnetic structures tends to be
at rest, although a minor fraction undergoes strong downflows. Downflows
are also present in the nonmagnetic environment. A significant number
of fitted Stokes profiles require opposite magnetic polarities within
the same resolution element. The occurrence of mixed polarities
increases with weakening degree of polarization, such that 25% of
the weakest signals require mixed polarity. The weak polarization
signals account for most of the total (unsigned) magnetic flux of the
observed region. By extrapolation, this indicates that a significant
fraction of photospheric magnetic flux remains undetected. The MISMA
framework provides a unified and physically consistent scenario for
interpretation of quiet Sun magnetism. Moreover, it is the only one
available at present that is able to fit the abnormal Stokes profiles
as revealed by the new generation of sensitive Stokes polarimeters.
---------------------------------------------------------
Title: Remote sensing of solar magnetic fields
Authors: Lites, Bruce W.
2000RvGeo..38....1L Altcode:
New techniques for remote sensing of solar magnetic fields now provide
measures of the magnetic field vector within the solar atmosphere with
high angular resolution and high precision. These measurements have
enabled a much improved physical understanding of magnetic processes
and phenomena in the solar atmosphere, processes that drive the
variability of the Sun's radiative and particulate output. The new
techniques are reviewed here in the context of the scientific advances
they have fostered. Emphasis is given to techniques for inferring the
field vector. The quantitative nature of the information needed to
explore the solar phenomena sharply constrains the needed precision
and angular resolution of the observations. These requirements are
reviewed here, along with an assessment of how future improvements in
observing capabilities will address these requirements. One may also
attribute much of the recent advance in our understanding of solar
magnetic fields to ongoing progress in techniques for analysis of the
polarization measurements that underlie solar magnetometry. The status
and prospects of analysis techniques are also reviewed.
---------------------------------------------------------
Title: Dynamics of polar plumes observed at the 1998 February
26 eclipse
Authors: Lites, B. W.; Card, G.; Elmore, D. F.; Holzer, T.; Lecinski,
A.; Streander, K. V.; Tomczyk, S.; Gurman, J. B.
1999SoPh..190..185L Altcode:
This paper presents first observations of dynamics of the white-light
solar corona detected during the few minutes of totality of a solar
eclipse. Perturbations of a polar plume associated with an embedded
`jet' structure observed simultaneously at 195 Å with the EUV
Imaging Telescope (EIT) aboard the SOHO spacecraft lead to estimates
of the electron density fluctuations accompanying the jet: ±15%. The
morphological behavior of the jet, its apparent upward propagation speed
of ≈200 km s<SUP>−1</SUP>, and the inferred density perturbations
suggest that the jet is led by a weak, outward-propagating shock
resulting from the injection of material at high velocity at the base of
the corona. Smaller perturbations of the white-light corona are apparent
at many other locations, sustaining hope that propagating Alfvén waves
may be measurable in the solar corona. Density perturbations associated
with the jet follow from empirical electron density models of the polar
inter-plume and plume regions, as derived from the ground-based eclipse
measurements of coronal polarization brightness. These models indicate
polar plume densities 4-6 times that of the interplume low corona.
---------------------------------------------------------
Title: Bright rings around sunspots
Authors: Rast, M. P.; Fox, P. A.; Lin, H.; Lites, B. W.; Meisner,
R. W.; White, O. R.
1999Natur.401..678R Altcode:
There are two possible explanations for why sunspots are dark: the
partial suppression by the sunspot magnetic fields of convective energy
transport from the underlying layers, or the removal of energy from
the sunspot by enhanced hydromagnetic wave radiation. Both processes
would reduce the energy emitted radiatively. The first explanation
is currently favoured, and predicts that the blocked energy should
show up as a bright ring around the spot, with the actual brightness
of the ring sensitive to details of solar convective transport and
sunspot structure. Previous searches for these bright rings were
inconclusive because of the presence of bright, vertical magnetic
flux tubes near the spots, and a lack of sufficient precision in the
observations. Here we report high-photometric-precision observations
of bright rings around eight sunspots. The rings are about 10K warmer
than the surrounding photosphere and extend at least one sunspot
radius out from the penumbra. About 10% of the radiative energy
missing from the sunspots is emitted through the bright rings. We
also report observations of a second set of sunspots, for which
simultaneous magnetic field measurements demonstrate that the rings
are not associated with vertical flux tubes.
---------------------------------------------------------
Title: Dynamics of the Solar Chromosphere. II. Ca II H<SUB>2V</SUB>
and K<SUB>2V</SUB> Grains versus Internetwork Fields
Authors: Lites, B. W.; Rutten, R. J.; Berger, T. E.
1999ApJ...517.1013L Altcode:
We use the Advanced Stokes Polarimeter at the NSO/Sacramento Peak
Vacuum Tower Telescope to search for spatio-temporal correlations
between enhanced magnetic fields in the quiet solar internetwork
photosphere and the occurrence of Ca II H<SUB>2V</SUB> grains in the
overlying chromosphere. We address the question of whether the shocks
that produce the latter are caused by magnetism-related processes,
or whether they are of purely hydrodynamic nature. The observations
presented here are the first in which sensitive Stokes polarimetry is
combined synchronously with high-resolution Ca II H spectrometry. We pay
particular attention to the nature and significance of weak polarization
signals from the internetwork domain, obtaining a robust estimate of
our magnetographic noise level at an apparent flux density of only
3 Mx cm<SUP>-2</SUP>. For the quiet Sun internetwork area analyzed
here, we find no direct correlation between the presence of magnetic
features with apparent flux density above this limit and the occurrence
of H<SUB>2V</SUB> brightenings. This result contradicts the one-to-one
correspondence claimed by Sivaraman & Livingston. We also find no
correspondence between H<SUB>2V</SUB> grains and the horizontal-field
internetwork features discovered by Lites et al.
---------------------------------------------------------
Title: The Solar-B Solar Optical Telescope Focal Plane Package
Authors: Levay, M.; Berger, T.; Rosenberg, W.; Tarbell, T.; Title,
A.; Bogdan, T.; Elmore, D.; Lites, B.
1999AAS...194.7610L Altcode: 1999BAAS...31R.957L
The primary goal of the Solar-B mission is to understand the physical
processes responsible for dynamics and heating of the outer solar
atmosphere. The Focal Plane Package (FPP) instrument for the 50-cm Solar
Optical Telescope provides precise measurements of the vector magnetic
field, vertical and horizontal flows, and thermal conditions in the
photosphere and low chromosphere with spatial resolution as high as
0.16 arcsec and a field-of-view as large as 320 x 160 arcsec. The FPP
can measure continuously and at high cadence to follow the evolution
of solar features. The FPP consists of broad ( 8 Angstroms) and narrow
( 100 m Angstroms) filters and a spectro-polarimeter that provides
precise polarimetry with high spectral resolution ( 25 m Angstroms). A
correlation tracker and tip-tilt mirror ensure that all focal planes
are stable to better than 0.01 arcsec. A major design consideration
of the FPP is cooperative science operations with the other Solar-B
instruments. Solar-B is a Japanese mission with US and UK partners;
S. Tsuneta is the PI of the Solar Optical Telescope and A. Title the
US PI of the FPP. It is scheduled to launch in Japanese FY 2004.
---------------------------------------------------------
Title: Internetwork Grains with TRACE
Authors: Rutten, R. J.; de Pontieu, B.; Lites, B.
1999ASPC..183..383R Altcode: 1999hrsp.conf..383R
No abstract at ADS
---------------------------------------------------------
Title: Dynamics of the Quiet Solar Chromosphere
Authors: Rutten, R. J.; Lites, B. W.; Berger, T. E.; Shine, R. A.
1999ASPC..158..249R Altcode: 1999ssa..conf..249R
No abstract at ADS
---------------------------------------------------------
Title: Vector magnetic fields of emerging solar flux. I. Properties
at the site of emergence
Authors: Lites, B. W.; Skumanich, A.; Martinez Pillet, V.
1998A&A...333.1053L Altcode:
Several small emerging bipolar regions have been observed with
the Advanced Stokes Polarimeter (ASP), including extensive time
series measurements of one small region. Both new and previously
recognized properties of the actual site of first emergence, where
the magnetic field is nearly horizontal to the surface, are revealed
by these observations. They provide the most complete and accurate
observational description to date of newly emerging vector magnetic
fields. We find that: 1) the strength of the magnetic field at the site
of the emergence (where the vector field is nearly parallel to the
solar surface) ranges from about 200 to 600 G, 2) as individual flux
elements migrate rapidly away from the emergence zone, they attain
kiloGauss strengths only after becoming oriented nearly vertically,
3) the emergence zone is dotted by small, transient, upward rising ( ~
1 km s(-1) ) horizontal magnetic elements as indicated by the Doppler
shift of the polarized spectral profiles, 4) the leading polarity flux
coalesces immediately into a compact region which forms a pore, but the
emerging following polarity flux is spatially much less compact, 5) some
“moving magnetic features” having the same magnetic polarity as the
growing pore, but on the opposite side of the pore from the emergence
zone, coalesce with the pore during the observation period, and 6)
the observations suggest a low canopy of weak horizontal magnetic
fields arches over the emergence zone. These observations support a
widely accepted picture of emerging bipolar flux: the buoyantly rising
flux transports mass from the photosphere into the chromosphere, where
it then may drain downward along arched magnetic loops. The observed
formation of a pore suggests that emergence of subsurface structure,
not organized flows near the surface, is largely responsible for the
apparent coalescence of sunspots from more diffuse fields viewed at
the solar surface. These observations neither confirm nor refute the
operation of convective collapse of flux tubes.
---------------------------------------------------------
Title: Velocity and Magnetic Field Fluctuations in the Photosphere
of a Sunspot
Authors: Lites, Bruce W.; Thomas, John H.; Bogdan, Thomas J.; Cally,
Paul S.
1998ApJ...497..464L Altcode:
We use a data set of exceptionally high quality to measure oscillations
of Doppler velocity, intensity, and the vector magnetic field at
photospheric heights in a sunspot. Based on the full Stokes inversion
of the line profiles of Fe I 630.15 and 630.25 nm, in the sunspot umbra
we find upper limits of 4 G (root mean square [rms]) for the amplitude
of 5 minute oscillations in magnetic field strength and 0.09d (rms)
for the corresponding oscillations of the inclination of the magnetic
field to the line of sight. Our measured magnitude of the oscillation
in magnetic field strength is considerably lower than that found in
1997 by Horn, Staude, & Landgraf. Moreover, we find it likely
that our measured magnetic field oscillation is at least partly due to
instrumental and inversion cross talk between the velocity and magnetic
signals, so that the actual magnetic field strength fluctuations are
even weaker than 4 G. In support of this we show, on the basis of the
eigenmodes of oscillation in a theoretical model of the sunspot umbra,
that magnetic field variations of at most 0.5 G are all that is to
be expected. The theoretical model also provides an explanation of
the shift of power peaks in Doppler velocity to the 3 minute band in
chromospheric umbral oscillations, as a natural consequence of the
drastic change in character of the eigenmodes of oscillation between
frequencies of about 4.5 and 5.0 mHz due to increased tunneling through
the acoustic cutoff-frequency barrier. Using measurements of the
phase of velocity oscillations above the acoustic cutoff frequency,
we determine the relative velocity response height in the umbra of
four different photospheric spectral lines from the phase differences
between velocities in these lines, assuming that the oscillations
propagate vertically at the local sound speed. In spacetime maps of
fluctuations in continuum intensity, Doppler velocity, magnetic field
strength, and field inclination, we see distinct features that migrate
radially inward from the inner penumbra all the way to the center of
the umbra, at speeds of a few tenths of a kilometer per second. These
moving features are probably a signature of the convective interchange
of magnetic flux tubes in the sunspot, although we failed to find any
strong correlation among the features in the different quantities,
indicating that these features have not been fully resolved.
---------------------------------------------------------
Title: Optical Tomography of a Sunspot. I. Comparison between Two
Inversion Techniques
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
1998ApJ...494..453W Altcode:
A quantitative comparison between the Milne-Eddington (ME) inversion
technique implemented by Skumanich & Lites and the SIR (Stokes
Inversion based on Response Functions) proposed by Ruiz Cobo &
del Toro Iniesta is presented. Numerical experiments are carried
out to explore the capabilities and limitations of both diagnostic
techniques. Such experiments consist of inversions of Stokes profiles
previously synthesized in “realistic” solar atmospheric models. The
results show that the ME inversion provides accurate, line-of-sight
(LOS) averaged values for the input stratification of the vector
magnetic field. Its greater speed compared to SIR makes it useful for
quick analysis of large quantities of data (such as those currently
provided by modern spectropolarimeters) if one is only interested
in LOS-averaged quantities. However, the higher order description
of the atmosphere used by SIR (which acknowledges variation of the
thermal, dynamic, and magnetic parameters through the photosphere)
allows retrieval of the stratification of all these parameters to good
accuracy. This is so even in the presence of discontinuities such
as those foreseen in magnetic canopies of sunspots. The trade-offs
between thermodynamic and magnetic parameters observed in some ME
inversions are reduced considerably in the case of SIR inversions
because of the more realistic treatment of the thermodynamics in this
analysis. Notably, both allow one to extract quantitative inferences of
fairly weak magnetic fields (below 500 G), even when they are applied
to Zeeman-sensitive lines in the visible spectrum; i.e., well below
the commonly accepted limit of 500 G. The thermodynamic parameters
resulting from the ME inversion are understood theoretically in terms
of the generalized response functions introduced by Ruiz Cobo &
del Toro Iniesta and through the concept of height of formation
for inferred values proposed by Sánchez Almeida, Ruiz Cobo, &
del Toro Iniesta. <P />The present comparison and verification of
the reliability of inversion methods is a natural first step toward
the ongoing analysis of the three-dimensional magnetic structure of
a sunspot. By using SIR (with ME results for initialization) on maps
of a whole sunspot observed by the Advanced Stokes Polarimeter, we
obtain maps at different optical layers (i.e., an optical tomography)
of the temperature, vector magnetic field, and LOS velocity. Such a
tomography will appear in subsequent papers of the present series. To
illustrate fits to the observed Stokes profiles, we show here actual
inversion results for three points observed within a sunspot: one
within the umbra, another from the outermost parts of the penumbra,
and a third from the magnetic canopy surrounding the sunspot.
---------------------------------------------------------
Title: The Seismology of Sunspots: A Comparison of Time-Distance
and Frequency-Wavenumber Methods
Authors: Bogdan, T. J.; Braun, D. C.; Lites, B. W.; Thomas, John H.
1998ApJ...492..379B Altcode:
A pair of formulae are developed that relate the absorption coefficient
and partial-wave phase shift concepts of frequency-wavenumber local
helioseismology to the center-annulus cross-correlation function
of time-distance helioseismology, under the general circumstances
that both induced and spontaneous sunspot oscillations may be
present. These formulae show that spontaneous emission of p-modes
by magnetic and Reynolds stresses within the spot and the mode
mixing between incoming and outgoing p-modes affect only the
outgoing center-annulus cross-correlation time τ<SUP>+</SUP>,
and they caution that real or spurious phase lags of the umbral
oscillation signal lead to differences in the incoming and outgoing
correlation times, resulting in τ<SUP>-</SUP> ≠ τ<SUP>+</SUP>. The
application of these methods to actual helioseismic data obtained
by the Global Oscillation Network Group (GONG) project is carried
out in order to provide a tangible illustration of how time-distance
and frequency-wavenumber ideas can profitably be combined to yield
deeper insight into the seismic probing of sunspots. <P />By using the
helioseismic GONG data in conjunction with concurrent observations of
Doppler velocities and vector magnetic fields obtained by the High
Altitude Observatory/National Solar Observatory (HAO/NSO) Advanced
Stokes Polarimeter (ASP) for the 1995 October disk passage of active
region NOAA 7912, we demonstrate that the inferred GONG umbral
signal actually originates from the umbra-penumbra boundary about 6
Mm distant from the center of the spot. Further, the ASP observations
show that the 5 minute oscillations at the umbra-penumbra boundary lag
behind those in the center of the umbra by approximately 1 minute,
which is precisely the difference between the incoming and outgoing
correlation times for NOAA 7912 recently determined by Braun. This
remarkable result underscores the perils of using umbral oscillations
in time-distance helioseismology, and it calls into question previous
claims that correlation time differences constitute direct evidence
for the existence of a steady downflow in and around sunspots. Taken
together, the observational and theoretical evidence suggest that
the p-mode forcing of the spot leads to the generation of upwardly
propagating slow magnetoatmospheric waves. These waves are in turn
responsible for the decreased amplitudes of the outwardly propagating
p-modes in the surrounding quiet Sun, and the dispersion in their travel
times between the hidden subsurface layer where they are forced and
the overlying level where the Doppler signals originate leads to the
observed phase lag between the umbral and penumbral oscillations and
the corresponding correlation time differences. <P />This work utilizes
data obtained by the Global Oscillations Network Group (GONG) project,
managed by the National Solar Observatory, a Division of the National
Optical Astronomy Observatories, which is operated by AURA, Inc.,
under a cooperative agreement with the National Science Foundation.
---------------------------------------------------------
Title: Vector Magnetic Fields of Emerging Solar Flux
Authors: Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
1998ESASP.417..259M Altcode: 1998cesh.conf..259M
No abstract at ADS
---------------------------------------------------------
Title: Evidence for a downward mass flux in the penumbral region of
a sunspot
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
1997Natur.389...47W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Vector Magnetic Field, Evershed Flow and Intensity in
a Sunspot
Authors: Stanchfield, D. C. H.; Thomas, J. H.; Lites, B. W.
1997ASNYN...5b..14S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flux Emergence and Prominences: a New Scenario for
3-DIMENSIONAL Field Geometry Based on Observations with the Advanced
Stokes Polarimeter
Authors: Lites, B. W.; Low, B. C.
1997SoPh..174...91L Altcode:
This paper presents an interpretation of the evolution of the vector
magnetic field at the photosphere based on measurements of the advanced
Stokes polarimeter, along with chromospheric Hα from the Lockheed
instrument operating on La Palma and X-ray images of the corona from
Yohkoh. These measurements are consistent with the emergence of a nearly
closed magnetic structure from the solar interior into the corona. The
highly non-potential field topology inferred from the data suggests
that strong field-aligned currents exist in the emergent magnetic
structure as it buoyantly rises through the photosphere. Material
trapped in this closed structure is pulled upward to later condense
into a prominence. By analogy of this small active region evolution
with the observed properties of large quiescent prominences, we
speculate that this process might also be operative on a much larger
scale. A 3-dimensional magnetostatic model is presented which has many
topological features in common with the observations.
---------------------------------------------------------
Title: The Vector Magnetic Field and Evershed Flow in a Sunspot
Authors: Stanchfield, D. C. H.; Thomas, J. H.; Lites, B. W.
1997ASNYN...5b..12S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Calibration of the Advanced Stokes Polarimeter
Authors: Skumanich, A.; Lites, B. W.; Martínez Pillet, V.;
Seagraves, P.
1997ApJS..110..357S Altcode:
We describe and apply the methods that have been developed to calibrate
the Advanced Stokes Polarimeter and to compensate for the polarization
effects introduced by the Vacuum Tower Telescope at the National Solar
Observatory/Sunspot. A seven-parameter model of the telescope is fitted
to data obtained at a variety of mirror angles using observations
of both the center of the solar disk and that point within a sunspot
umbra at which the magnetic field is oriented as close to the line of
sight as possible. The response matrix of the polarimeter itself is
determined by the use of polarizing calibration optics that modify
the polarization state of the beam exiting the telescope but before
entering the polarimeter. A global least-squares solution is obtained
simultaneously for the response matrix and the telescope parameters. A
detailed gain-correction procedure is described that reduces the
multiplicative gain errors in the spectral images to typically less
than 1%. We have successfully recovered net-linear polarization
profiles with peak amplitudes of 1 × 10<SUP>-3</SUP>I<SUB>c</SUB>
against an instrumentally produced background polarization of ~=1-5 ×
10<SUP>-2</SUP>I<SUB>c</SUB>. Net-polarization signals smaller than
~=3 × 10<SUP>-4</SUP>I<SUB>c</SUB> are lost, even with sufficient
averaging, in a background due to photometric and other calibration
errors.
---------------------------------------------------------
Title: The Solar-B Mission
Authors: Antiochos, Spiro; Acton, Loren; Canfield, Richard; Davila,
Joseph; Davis, John; Dere, Kenneth; Doschek, George; Golub, Leon;
Harvey, John; Hathaway, David; Hudson, Hugh; Moore, Ronald; Lites,
Bruce; Rust, David; Strong, Keith; Title, Alan
1997STIN...9721329A Altcode:
Solar-B, the next ISAS mission (with major NASA participation), is
designed to address the fundamental question of how magnetic fields
interact with plasma to produce solar variability. The mission has
a number of unique capabilities that will enable it to answer the
outstanding questions of solar magnetism. First, by escaping atmospheric
seeing, it will deliver continuous observations of the solar surface
with unprecedented spatial resolution. Second, Solar-B will deliver the
first accurate measurements of all three components of the photospheric
magnetic field. Solar-B will measure both the magnetic energy driving
the photosphere and simultaneously its effects in the corona. Solar-B
offers unique programmatic opportunities to NASA. It will continue an
effective collaboration with our most reliable international partner. It
will deliver images and data that will have strong public outreach
potential. Finally, the science of Solar-B is clearly related to the
themes of origins and plasma astrophysics, and contributes directly
to the national space weather and global change programs.
---------------------------------------------------------
Title: Velocity and Magnetic Field Fluctuations in the Photosphere
of a Sunspot
Authors: Thomas, J. H.; Lites, B. W.; Bogdan, T. J.
1997SPD....28.0236T Altcode: 1997BAAS...29..899T
We use a data set of exceptionally high quality, obtained with
the HAO/NSO Advanced Stokes Polarimeter, to measure oscillations
of Doppler velocity, intensity, and the vector magnetic field at
photospheric heights in a sunspot. We find an upper limit of 4 G
(rms) for 5-min oscillations in magnetic field strength in the
umbra, based on the full Stokes inversion of the line profiles of
Fe I 6301.5 and 6302.5. This magnitude of the oscillation in field
strength is considerably lower than that found recently by Horn,
Staude, and Landgraf (1997). We show, on the basis of the eigenmodes
of oscillation in a simple theoretical model of the sunspot umbra,
that magnetic field variations of order 1 G are all that is to be
expected. Using measurements of velocity oscillations above the acoustic
cutoff frequency, we determine the relative heights of formation in
the umbra of four different photospheric spectral lines from the phase
differences between velocities in these lines, assuming the oscillations
propagate vertically at the local sound speed. In space-time maps of
fluctuations in continuum intensity, Doppler velocity, magnetic field
strength, and field inclination we see distinct features that migrate
radially inward from the inner penumbra all the way to the center of the
umbra. These moving features are probably a signature of the convective
interchange of magnetic flux tubes in the sunspot, although we failed
to find any strong correlation among the features in the different
quantities, indicating that these features have not been fully resolved.
---------------------------------------------------------
Title: The Seismology of Sunspots: A Comparison of Time-Distance
and Frequency-Wavenumber Methods
Authors: Bogdan, T. J.; Braun, D. C.; Lites, B. W.; Thomas, J. H.
1997SPD....28.0210B Altcode: 1997BAAS...29..894B
A pair of formulae are developed which relate the absorption coefficient
and partial wave phase-shift concepts of frequency-wavenumber local
helioseismology to the center- annulus cross correlation function
of time-distance helioseismology, under the general circumstances
that both induced and spontaneous sunspot oscillations may be
present. These formulae caution that real or spurious phase lags of
the umbral oscillation signal lead to differences in the incoming and
outgoing correlation times for sunspots, as first observed by Duvall
et al. (1996, Nature, 379, 430) and recently confirmed by Braun (1997,
ApJ, submitted). By using helioseismic data obtained by the GONG project
in conjunction with concurrent observations of Doppler velocities and
magnetic fields obtained by the HAO/NSO Advanced Stokes Polarimeter
for the October 1995 disk passage of active region NOAA 7912, we
demonstrate that the inferred GONG umbral oscillation signal actually
originates from the umbra-penumbra boundary some 6 Mm distant from the
center of the spot. Further, the ASP observations show that the 5-min
oscillations at the umbra-penumbra boundary lag those in the center of
the umbra by approximately 1 min, which is precisely the difference
between the incoming and outgoing cross correlation times for NOAA
7912 recently determined by Braun. The evidence suggests that p-mode
forcing of the spot results in the generation of upward propagating
slow MAG waves. These waves are responsible for the absorption of
the p-modes, and the dispersion in their travel times between the
subsurface layer where they are forced and the overlying level where
the Doppler signals originate leads to the observed phase lag between
the umbral and penumbral oscillations, and the corresponding correlation
time differences.
---------------------------------------------------------
Title: The Vector Magnetic Field, Evershed Flow, and Intensity in
a Sunspot
Authors: Stanchfield, Donald C. H., II; Thomas, John H.; Lites,
Bruce W.
1997ApJ...477..485S Altcode:
We present results of simultaneous observations of the vector magnetic
field, Evershed flow, and intensity pattern in a nearly axisymmetric
sunspot, made with the Advanced Stokes Polarimeter at the Vacuum
Tower Telescope at NSO (Sacramento Peak). The vector magnetic field is
determined from the Stokes profiles of the magnetically sensitive lines
Fe I 630.15 and 630.25 nm, and Doppler velocities and intensities are
measured in several lines including the weak C I 538.03 nm line, formed
in the deepest layers of the atmosphere. The strength of the magnetic
field decreases with increasing zenith angle (angle of inclination to
the local vertical), and this decrease is nearly linear over most of the
range of values in the sunspot. Magnetic field strength and continuum
intensity are inversely related in the sunspot in a manner similar to
the characteristic nonlinear relationship found by Kopp & Rabin
in the infrared line Fe I 1564.9 nm. A different relationship is found
between magnetic field strength and core intensity (in Fe I 630.25 nm),
however, with the curve doubling back to give two distinct values of
field strength at the same core intensity in the penumbra--the higher
and lower field strengths corresponding to the inner and outer penumbra,
respectively. In the penumbra the magnetic field pattern consists
of spokelike extensions of stronger, more vertical magnetic field
separated by regions of weaker, nearly horizontal magnetic field,
as found by Degenhardt & Wiehr and Lites et al. The penumbral
magnetic field extends outward beyond the outer continuum boundary
of the sunspot, forming a canopy at the height of formation of Fe I
630.25 nm. Our results for the Evershed flow confirm the discovery
by Rimmele that this flow is generally confined to narrow, elevated
channels in the penumbra. In the Fe I 630.25 nm line and other strong
photospheric lines we see isolated, radially elongated channels of
Evershed flow crossing the outer penumbra. These flow channels lie
in regions of the penumbra where the magnetic field is very nearly
horizontal. In the weak C I 538.03 nm line (formed at a height h =
40 km) the flow pattern shows small, isolated patches of upflow, lying
at the inner end of the Fe I flow channels where the magnetic field is
more inclined to the horizontal. These patches presumably correspond to
the upstream footpoints of the arched magnetic flux tubes carrying the
Evershed flow. For some of the flow channels we find isolated patches
of strong downflow in the C I line just outside the penumbra that might
correspond to the downstream footpoints of these flux tubes. There is
a weak association between the Evershed flow channels and the dark
filaments seen in continuum intensity in the penumbra, but a much
stronger association between the flow and the dark filaments seen in
core intensity measured in the same spectral line.
---------------------------------------------------------
Title: Active Region Magnetic Fields. I. Plage Fields
Authors: Martínez Pillet, V.; Lites, B. W.; Skumanich, A.
1997ApJ...474..810M Altcode:
We present observations taken with the Advanced Stokes Polarimeter
(ASP) in active-region plages and study the frequency distribution of
the magnetic field strength (B), inclination with respect to vertical
(γ), azimuthal orientation (χ), and filling factor (f). The
most common values at disk center are B = 1400 G, γ < 10°,
no preferred east-west orientation, and f = 15%. At disk center,
there is a component of weak (<1000 G), more horizontal fields
that corresponds to arching field lines connecting footpoints of
different polarities. The center-to-limb variation (CLV) of the
field strength shows that, close to the limb (μ = 0.3), the field
strength is reduced to 800 G from its disk-center value. This can be
interpreted as a gradient of B with height in solar plages of around
-3 G km<SUP>-1</SUP>. From this CLV study, we also deduce that magnetic
field lines remain vertical for the entire range of heights involved. A
similar analysis is performed for structures found in active regions
that show a continuous distribution of azimuths (resembling sunspots)
but that do not have a darkening in continuum. These “azimuth centers”
show slightly larger values of B than normal plages, in particular
at their magnetic center. Filling factors are also larger on average
for these structures. <P />The velocities in the magnetic component
of active regions have been studied for both averaged Stokes profiles
over the entire active region and for the spatially resolved data. The
averaged profiles (more representative of high filling factor regions)
do not show any significant mean velocities. However, the spatial
average of Doppler velocities derived from the spatially resolved
profiles (i.e., unweighted by filling factor) show a net redshift at
disk center of 200 m s<SUP>-1</SUP>. The spatially resolved velocities
show a strong dependence on filling factor. Both mean velocities and
standard deviations are reduced when the filling factor increases. This
is interpreted as a reduction of the p-mode amplitude within the
magnetic component. Strong evidence for velocities transverse to the
magnetic field lines has been found. Typical rms values are between
200 and 300 m s<SUP>-1</SUP>, depending on the filling factor. The
possible importance of these transverse motions for the dynamics of
the upper atmospheric layers is discussed. <P />The asymmetries of the
Stokes profiles and their CLV have been studied. The averaged Stokes
V profiles show amplitude and area asymmetries that are positive
at disk center and become negative at the limb. Both asymmetries,
and for the two Fe I lines, are maximized away from disk center. The
spatially resolved amplitude asymmetries show a clear dependence on
filling factor: the larger the filling factor, the smaller the amplitude
asymmetry. On the other hand, the area asymmetry is almost independent
of the filling factor. The only observed dependence is the existence
of negative area-asymmetry profiles at disk center for filling factors
smaller than 0.2. Around 20% of the observed points in a given plage
have negative area asymmetry. The amplitude asymmetry of Stokes V is,
on the other hand, always positive. The amplitude asymmetries of the
linear polarization profiles are observed to have the same sign as
the Stokes V profiles. Similarly, the same CLV variation of the linear
polarization amplitude asymmetries as for Stokes V has been found. The
scenarios in which this similarity can exist are studied in some detail.
---------------------------------------------------------
Title: Inversion Techniques Applied to Sunspot Spectropolarimetric
Data
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
1997ASPC..118..197W Altcode: 1997fasp.conf..197W
Two inversion techniques are compared: the Unno-Rachkov\-sky fitting
method (UR) and the Stokes Inversion based on Response functions
(SIR). Results with synthetic profiles in sunspot model atmospheres and
real data show that whilst UR is well suited for recovering a constant
vec B, SIR enables us to know the run with depth of vec B and the line
of sight velocity together with the temperature stratification.
---------------------------------------------------------
Title: Optical Tomography of a Sunspot: Preliminary Results
Authors: Westendorp Plaza, C.; del Toro Iniesta, J. C.; Ruiz Cobo,
B.; Martinez Pillet, V.; Lites, B. W.; Skumanich, A.
1997ASPC..118..202W Altcode: 1997fasp.conf..202W
Preliminary results of the inversion of spectropolarimetric maps
of a sunspot observed with the Advanced Stokes Polarimeter (ASP) are
presented. The method used, Stokes Inversion based on Response functions
(SIR), does not assume constancy of the different parameters with
depth, thus enabling us to embark on an analysis of the information at
different layers in continuum optical depth (i.e. optical tomography),
of a sunspot's photosphere. Maps of the vector magnetic field and
other physical quantities like temperature or line-of-sight velocity at
several optical depths show a new and promising view of the structure
of a sunspot, casting light on long standing debates as those over
penumbral `corrugated' fields (spines), superpenumbral canopies,
return flux, or the nature of the Evershed effect.
---------------------------------------------------------
Title: Line Asymmetries and the Microstructure of Photospheric
Magnetic Fields
Authors: Sanchez Almeida, J.; Landi Degl'Innocenti, E.; Martinez
Pillet, V.; Lites, B. W.
1996ApJ...466..537S Altcode:
A systematic structuring of magnetic fields over scales much smaller
than the mean free path of photospheric photons may be responsible for
the observed asymmetrical Stokes profiles. We explore this possibility
by deriving the radiative transfer equation for microstructured magnetic
atmospheres (the MISMA approximation). This equation is subsequently
employed to show that very schematic MISMA scenarios for the penumbrae
of sunspots, plage and network regions, and internetwork regions produce
Stokes profiles that have the observed asymmetries. The details of
these model atmospheres are of secondary importance, but the ease of
generating the type of observed asymmetries with MISMAs is significant,
so the existence of MISMAs deserves serious consideration. Should such
microstructures exist, the techniques currently employed to infer
properties of the solar photosphere need to be revised. MISMAs are
also of concern for the physics of the photosphere itself. These two
topics are briefly discussed.
---------------------------------------------------------
Title: Magnetic Flux Emergence Observed with the Advanced Stokes
Polarimeter
Authors: Lites, B.; Martinez Pillet, V.
1996AAS...188.3313L Altcode: 1996BAAS...28Q.870L
We have carried out quantitative observations of the vector magnetic
field during the emergence of three small bipolar active regions in
June, 1992, July 1993, and September 1994 using the Advanced Stokes
Polarimeter (ASP). The region of horizontal magnetic field at the actual
site of emergence is always characterized by low magnetic field strength
(i.e. considerably less than 1000 Gauss). We find a strong relationship
between field strength and inclination in these regions. This suggests
that 1) flux emerging from below the photosphere does not coalesce
into strong flux tubes until it reaches the photosphere, becomes
nearly vertical as a result of magnetic buoyancy, and is then acted
upon by convective collapse, and 2) the field strength of flux rising
through the convection zone may be in rough equipartition with the fluid
motions. We find the flux emergence zone to be characterized by highly
variable (both spatially and temporally) fill factors for the magnetic
field, suggesting that the flux below the surface is filamentary,
that it rises rapidly through the photosphere to form a magnetic
canopy above the emergence region. Sequences of Hα on- and off-band
images obtained with the ASP reveal the accompanying development of
the arch-filament system, and suggest that the material within the
Hα structures is supplied by a siphon flow as evidenced by apparent
chromospheric red shifts on the sides of the loops closest to a large
pore, and blue shifts where the fields anchor in plage regions. Proper
motions of the magnetic flux images throughout a day's observation
indicate the presence of a persistent vortex flow on a small scale
(a few arcseconds). The National Center for Atmospheric Research is
sponsored by the National Science Foundation.
---------------------------------------------------------
Title: Vector Magnetic Fields and the Evershed Flow in Sunspots
Authors: Stanchfield, D. C. H., II; Thomas, J. H.; Lites, B. W.
1996AAS...188.3507S Altcode: 1996BAAS...28..872S
We present results of simultaneous observations of the vector magnetic
field and the Evershed effect in two sunspots, made with the Advanced
Stokes Polarimeter at the Vacuum Tower Telescope at NSO (Sacramento
Peak). The vector magnetic field is determined from the Stokes profiles
of the magnetically sensitive line Fe I 630.25, and Doppler velocities
are measured in several lines including the weak C I 538.03 line,
formed in the deepest layers of the atmosphere. In addition to maps
of the vector magnetic field and the line-of-sight Doppler velocity,
we present maps of the true flow speed assuming that the flow is
everywhere aligned with the magnetic field. The results confirm
the recent discovery by Rimmele (1995), that the Evershed flow is
generally confined to narrow, elevated channels in the penumbra. In
the Fe I 537.96 line (formed at a height of about 230 km) we see
isolated, radially elongated channels of Evershed flow in the outer
penumbra. These flow channels lie in regions of the penumbra where the
magnetic field is most nearly horizontal. In the C I line (formed at a
height of about 40 km) the flow pattern shows small, isolated patches
of upflow lying at the inner end of the Fe I flow channels, where the
magnetic field is more highly inclined to the horizontal. These patches
presumably correspond to the upstream footpoints of the arched magnetic
flux tubes carrying the Evershed flow. In some cases, along a radial
line extending outward from a flow channel, we find isolated patches
of downflow in the C I line just outside the penumbra, with magnetic
field inclination slightly beyond the horizontal (i.e., magnetic field
diving beneath the surface). These patches might well correspond to
the downstream footpoints of these flux tubes.
---------------------------------------------------------
Title: Small-Scale Horizontal Magnetic Fields in the Solar Photosphere
Authors: Lites, B. W.; Leka, K. D.; Skumanich, A.; Martinez Pillet,
V.; Shimizu, T.
1996ApJ...460.1019L Altcode:
We present recent observations of quiet regions near the center
of the solar disk using the Advanced Stokes Polarimeter. These
observations reveal a component of the solar magnetic field heretofore
unobserved: isolated, small-scale (typically 1"-2" or smaller),
predominantly horizontal magnetic flux structures in the solar
photosphere. These features occur in isolation of the well-known,
nearly vertical flux concentrations usually seen in the photospheric
"network." Hence we ascribe this horizontal flux to the photospheric
"internetwork." They reveal themselves by the distinct signature
of the Stokes Q and U polarization profiles, which are symmetric
about the line center. The polarization signals are weak, with peak
amplitudes typically ∼0.1%-0.2% of the continuum intensity in the
resolved spectral profiles, but they are well above the noise level
of these observations (≍0.05%). Such magnetic fields are weak
(significantly less than 1000 G) and largely horizontal owing to
the absence, or near absence, of accompanying Stokes V polarization
when observed at the center of the solar disk. These horizontal field
elements are often associated with blueshifted Stokes line profiles,
and they often occur between regions of opposite polarity (but weak)
Stokes V profiles. The horizontal elements are short-lived, typically
lasting ∼5 minutes. Our observations suggest that we are viewing the
emergence of small, concentrated loops of flux, carried upward either
by granular convection or magnetic buoyancy. Even though these entities
show weak field strengths, they also seem to be fairly common, implying
that they could carry the order of 10<SUP>24</SUP> Mx of magnetic flux
to the surface on a daily basis. However, further observational study
is needed to identify the specific nature of this phenomenon.
---------------------------------------------------------
Title: Performance Characteristics of the Advanced Stokes Polarimeter
Authors: Lites, B. W.
1996SoPh..163..223L Altcode:
Recently Zirin (1995) published a response to our paper of last year
(Lites, Martínez Pillet, and Skumanich, 1994), in which we quantified
some limitations of vector magnetometry by the use of a generic
filter magnetograph. Zirin's Letter makes specific reference to the
Advanced Stokes Polarimeter (ASP), and in so doing he makes incorrect
statements regarding the performance characteristics of the ASP. The
intent of this paper is to rectify those erroneous representations
and to clarify several other issues raised by Zirin which might give
the reader of his Letter an incorrect picture of the ASP.
---------------------------------------------------------
Title: SPLIT: a large spectro-polarimetric space instrument for
solar observations.
Authors: Schmidt, W.; Kentischer, T.; Title, A. M.; Lites, B. W.
1996AGAb...12...88S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Partial Redistribution in Multilevel Atoms. I. Method and
Application to the Solar Hydrogen Line Formation
Authors: Hubeny, I.; Lites, B. W.
1995ApJ...455..376H Altcode:
We present a robust method for solution of multilevel non-LTE
line transfer problems including the effects of partial frequency
redistribution (PRD). This method allows the self-consistent solution
for redistribution of scattered line photons simultaneously in multiple
transitions of a model atom, including the effects of resonant Raman
scattering ("cross-redistribution") among lines sharing common upper
levels. The method is incorporated into the framework of the widely used
non-LTE complete redistribution code MULTI. We have applied this method
to the problem of transfer in hydrogen lines in a plane-parallel solar
model atmosphere, including cross-redistribution between the Hα and
Lβ, using general redistribution functions for the Lα and Lβ lines
which are not restricted by the impact approximation. The convergence
properties of this method are demonstrated to be comparable to that of
the equivalent complete redistribution problem. In this solar model,
PRD in the Lα line produces the dominant influence on the level
populations. It changes considerably the populations of the excited
states of hydrogen, as well as the proton number density, in the
middle and upper chromosphere, owing to modification of the Lα wing
radiation. <P />The population of the hydrogen ground state undergoes
only modest changes, however. The influence of cross-redistribution
and PRD in Lβ has a much smaller influence on the level populations
but a considerable influence on the wing intensity of the Lβ line.
---------------------------------------------------------
Title: The Possible Ascent of a Closed Magnetic System through
the Photosphere
Authors: Lites, B. W.; Low, B. C.; Martinez Pillet, V.; Seagraves,
P.; Skumanich, A.; Frank, Z. A.; Shine, R. A.; Tsuneta, S.
1995ApJ...446..877L Altcode:
We present a comprehensive interpretation of the evolution of a small
magnetic region observed during its entire disk passage. The vector
magnetic field measurements from the Advanced Stokes Polarimeter,
along with Hα and magnetogram measurements from the Lockheed SOUP
instrument operating at the Swedish Solar Observatory on La Palma,
and soft X-ray images from the Yohkoh satellite support the hypothesis
that we have observed the passage of a nearly closed magnetic system
through the photosphere into the corona. The observations suggest that
as the magnetic flux begins to emerge into the photosphere it shows a
rather simple geometry, but it subsequently develops a small δ-sunspot
configuration with a highly sheared vector field along the polarity
inversion line running through it. At that stage, the vector field is
consistent with a concave upward magnetic topology, indicative of strong
electric currents above the photosphere. An Hα prominence is found
above this inversion line when the δ-sunspot is fully formed. These
observed features and the sequence of events are interpreted in terms
of a nearly closed magnetic system that rises through the photosphere
into the corona as a result of magnetic buoyancy. The magnetic system
persists in the corona well after the dark δ-sunspot has disappeared
in the photosphere We suggest that this coronal structure is in
quasi-static equilibrium with its buoyancy partially countered by
the weight of the plasma trapped at the bottom of closed magnetic
loops. The plausibility of such a scenario is demonstrated by a
three-dimensional magnetostatic model of the emergence of a closed,
spheroidal magnetic system in the corona, in which the Lorentz force
arising from cross-field currents is balanced by the gravitational
and pressure forces. This theoretical model carries many features in
common with the observed morphology of our active region.
---------------------------------------------------------
Title: Horizontal Internetwork Magnetic Fields Observed with the
Advanced Stokes Polarimeter
Authors: Lites, B. W.; Martìnez Pillet, V.
1995SPD....26..204L Altcode: 1995BAAS...27..951L
No abstract at ADS
---------------------------------------------------------
Title: Small scale horizontal magnetic fields in the solar photosphere
Authors: Leka, K. D.; Lites, B. W.; Skumanich, A.; Martínez Pillet,
V.; Shimizu, T.
1995IAUS..176P.120L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Quantitative Comparison of Vector Magnetic Field Measurement
and Analysis Techniques
Authors: Lites, B. W.; Martinez Pillet, V.; Skumanich, A.
1994SoPh..155....1L Altcode:
We make a quantitative comparison between spectral vs filter measurement
and analysis techniques for extraction of solar vector magnetic fields
from polarimetric data using as a basis the accurately calibrated,
high angular resolution Stokes profile data from the Advanced Stokes
Polarimeter. It is shown that filter-based measurements deliver
qualitative images of the field alignment for sunspots that are visually
similar to images derived from the more detailed analysis of the Stokes
profiles. However, quantitative comparison with least-squares fits
to the full Stokes profiles show that both the strength of the field
predicted by the filter-based analysis and its orientation contain
substantial errors. These errors are largest for plage regions
outside of sunspots, where the field strengths are inferred to be
only a fraction of their true values, and errors in the orientation of
40-50° are common. Within sunspots, errors of 20° are commonplace. The
greatest source of these errors is the inability of the filter-based
measurements to account for the small fill fraction of magnetic fields
or, equivalently, scattered light in the instrument, which reduce the
degree of polarization. The uncertainties of the full profile fitting
methods are also discussed, along with the errors introduced by coarser
wavelength sampling of the observed Stokes profiles. The least-squares
fitting procedure operates best when the profiles are sampled at least
as frequently as one Doppler width of the line.
---------------------------------------------------------
Title: Evidence for Supersonic Downflows in the Photosphere of a
Delta Sunspot
Authors: Martinez Pillet, V.; Lites, B. W.; Skumanich, A.; Degenhardt,
D.
1994ApJ...425L.113M Altcode: 1994ApJ...425L.113P
We present polarization profiles observed with the High Altitude
Observatory/National Solar Observatory (HAO/NSO) Advanced Stokes
Polarimeter (ASP) that demonstrate, in a model-independent way,
the presence of strong downflows close to the neutral line of a
delta sunspot (a spot with both polarities contained within the
same penumbra). The flows are as large as 14 km/s, a velocity that,
at photospheric levels, strongly suggests the presence of supersonic
compressive fluid flows in a region only 100-200 km above the visible
surface. These velocities are probably the largest ever reported at
photospheric levels. The region containing the downflows is large enough
(about 2 sec on a side) to be resolved, although it is likely to contain
fine structure at or below our spatial resolution. The origin of these
flows is discussed in terms of the funneling of material through an
isolated magnetic nozzle in an otherwise closed magnetic system which
is rising through the surface.
---------------------------------------------------------
Title: Vector spectropolarimetry with the Advanced Stokes Polarimeter
(ASP) for quantitative solar magnetometry
Authors: Skumanich, A.; Lites, B. W.; Martínez Pillet, V.
1994ASIC..433...99S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Configuration of a Short-Lived Delta SPOT
Authors: Martinez Pillet, V.; Lites, B. W.; Skumanich, A. P.;
Seagraves, P.
1994ASPC...68..244M Altcode: 1994sare.conf..244M
No abstract at ADS
---------------------------------------------------------
Title: Chromospheric oscillations
Authors: Lites, B. W.; Rutten, R. J.; Thomas, J. H.
1994ASIC..433..159L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Physical conditions in magnetic elements of different
polarities surrounding sunspots
Authors: Martínez Pillet, V.; Lites, B. W.; Skumanich, A. P.; Elmore,
D. F.; Seagraves, P.
1994smf..conf..219M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The dynamics of magnetic regions in the quiet chromosphere
Authors: Lites, B.
1994chdy.conf....1L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Material Flows in Sunspots
Authors: Degenhardt, D.; Lites, B. W.
1994smf..conf..185D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Vector field structure of a small sunspot
Authors: Skumanich, A.; Lites, B. W.
1994smf..conf..200S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The structure of umbral fluxtubes.
Authors: Degenhardt, D.; Lites, B. W.
1994IAUS..154..465D Altcode:
Subsurface filamentation of sunspot magnetic fields has been
postulated as a source of the visible small-scale structure of
sunspot umbrae. The authors examine this possibility by investigating
the magnetohydrodynamic structure of thin, vertical magnetized gas
columns embedded in sunspot umbrae. Steady-state magnetohydrodynamic
equations are solved numerically. The geometric shape of the steady
flow solution is a gas column converging with height. The authors
discuss the relationship of their results to observed properties of
umbral brightenings (umbral dots). They show that, even if there is
a large difference in magnetic field strength between the dot and the
ambient medium in deeper layers, the field strengths are nearly equal
in the observable layers, a result required by the observations. They
also show that either high temperatures at the lower boundary of the
dots or strong upflows are needed in order to produce bright continuum
structures.
---------------------------------------------------------
Title: Stokes Profile Analysis and Vector Magnetic Fields. VI. Fine
Scale Structure of a Sunspot
Authors: Lites, B. W.; Elmore, D. F.; Seagraves, P.; Skumanich, A. P.
1993ApJ...418..928L Altcode:
The vector magnetic field structure of a small, symmetric sunspot
observed very close to disk center has been explored using data
from the High Altitude Observatory/National Solar Observatory
Advanced Stokes Polarimeter (ASP). This instrument provides, for
the first time, quantitative information on sunspot photospheric
vector magnetic fields with high angular resolution, as derived from
full Stokes profiles of the Zeeman-sensitive Fe I line pair at 630
nm. We find the following. (1) The penumbra contains narrow, radial
"spines" of more intense magnetic field more vertically oriented than
their surroundings; (2) the magnetic field diverges azimuthally away
from the spine axes, as it should for a more intense intrusion of
field embedded in a gravitational stratified atmosphere; (3) there
are dark protrusions out from the umbra which traverse much of the
penumbra and which are characterized by more vertical magnetic field;
(4) the observed structure of the magnetic field in both the umbra
and penumbra is stable over the 30 minute duration of our observing
sequence; (5) we do not find a tight correlation of field inclination
with intensity in the penumbra; (6) at the outer edge of the penumbra,
the field penetrates the photosphere at an average angle of about 70°
from the vertical; (7) outside of the penumbra the sunspot field forms
a canopy which is directly observed by our technique; (8) outside of,
but close to the sunspot, there are small magnetic features of mixed
polarity that are rather highly inclined to the vertical, presumably
as influenced by the sunspot canopy; (9) away from the sunspot, the
isolated magnetic elements have nearly vertical orientation. These
observations suggest that magnetic buoyancy, in addition to thermal
buoyancy, plays an important role in maintaining the observed structure
in sunspot penumbra.
---------------------------------------------------------
Title: The Magnetohydrodynamics of Umbral Flux
Tubes. II. Spectroscopic Properties
Authors: Degenhardt, Detlev; Lites, Bruce W.
1993ApJ...416..875D Altcode:
We apply a recently developed magnetohydrodynamic model for flux
tube systems within sunspot umbrae for a range of model parameters
appropriate to umbral dots. The results are used to generate
synthetic observations of umbral dots, which we then compare to recent
observational data taken from the literature. <P />Below the umbral
surface, our umbral flux tube models are characterized by (1) reduced
(but nonzero) field strength relative to the surrounding umbra, (2)
a relative temperature enhancement, and (3) an assumed upflow which
advects heat toward the surface, thus making the dot brighter than
its surroundings. In this paper we vary the free parameters which
characterize our model to explore the range of physical conditions
within umbral dots as admitted by our model. We find that the equivalent
width of lines of Fe I and Fe ii within the umbral flux tubes, relative
to the surrounding umbra, provides specific quantitative constraints
for selection among parameters specified at the lower boundary of our
models. Available observations do not clearly delimit line strengths;
however, empirical models based on recent observations by Sobotka et
al. suggest that our models with strong upflow (15 m s<SUP>-1</SUP>)
and modest temperature enhancement relative to the surrounding umbra
at 100 km below the visible surface best characterize umbral dots. <P
/>We show that, even though the flow velocity is large well above the
photospheric surface of our model umbral flux tubes, the line-of-sight
component of velocity as inferred from the zero crossing of the Stokes V
profile is (in general) smaller than 0.5 km s<SUP>-1</SUP>. Likewise,
the amplitude asymmetry of the Stokes V profiles arising from our
models are correspondingly quite weak (<3%).
---------------------------------------------------------
Title: Dynamics of the Solar Chromosphere. I. Long-Period Network
Oscillations
Authors: Lites, B. W.; Rutten, R. J.; Kalkofen, W.
1993ApJ...414..345L Altcode:
We analyze differences in solar oscillations between the chromospheric
network and internetwork regions from a 1 hr sequence of spectrograms
of a quiet region near disk center. The spectrograms contain Ca II
H, Ca I 422.7 nm, and various Fe I blends in the Ca II H wing. They
permit vertical tracing of oscillations throughout the photosphere
and into the low chromosphere. We find that the rms amplitude of
Ca II H line center Doppler fluctuations is about 1.5 km/s for both
network and internetwork, but that the character of the oscillations
differs markedly in these two regions. Within internetwork areas the
chromospheric velocity power spectrum is dominated by oscillations
with frequencies at and above the acoustic cutoff frequency. They are
well correlated with the oscillations in the underlying photosphere,
but they are much reduced in the network. In contrast, the network Ca
II H line center velocity and intensity power spectra are dominated by
low-frequency oscillations with periods of 5-20 min. Their signature
is much clearer in our Ca II H line center measurements than in
previously used diagnostics which are contaminated by signals from
deeper layers. We find that these long-period oscillations are not
correlated with underlying photospheric disturbances, and we discuss
their nature.
---------------------------------------------------------
Title: The Morphology of Flare Phenomena, Magnetic Fields, and
Electric Currents in Active Regions. I. Introduction and Methods
Authors: Canfield, Richard C.; de La Beaujardiere, J. -F.; Fan,
Yuhong; Leka, K. D.; McClymont, A. N.; Metcalf, Thomas R.; Mickey,
Donald L.; Wuelser, Jean-Pierre; Lites, Bruce W.
1993ApJ...411..362C Altcode:
Electric current systems in solar active regions and their spatial
relationship to sites of electron precipitation and high-pressure
in flares were studied with the purpose of providing observational
evidence for or against the flare models commonly discussed in the
literature. The paper describes the instrumentation, the data used, and
the data analysis methods, as well as improvements made upon earlier
studies. Several flare models are overviewed, and the predictions
yielded by each model for the relationships of flares to the vertical
current systems are discussed.
---------------------------------------------------------
Title: A Magnetograph Comparison Workshop
Authors: Jones, H.; Bogart, R.; Canfield, R.; Chapman, G.; Henney,
C.; Kopp, G.; Lites, B.; Mickey, D.; Montgomery, R.; Pillet, V.;
Rabin, D.; Ulrich, R.; Walton, S.
1993BAAS...25.1216J Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some challenging problems of the structured and dynamical
solar atmosphere.
Authors: Lites, B. W.
1993ESASP1157...11L Altcode: 1993srfs.book...11L
Several current but long-standing problems of the solar photosphere are
briefly presented, along with some suggestions which may help resolved
them in the future. Particular emphasis is given to phenomena and
processes involving the solar magnetic field. These problems may best
be addressed in the future by means of carefully coordinated ground-
and space-based observations.
---------------------------------------------------------
Title: Intercomparison of Seven Magnetographs
Authors: Walton, S. R.; Bogart, R. S.; Chapman, G. A.; Henney, C.;
Jones, H.; Kopp, G.; Lites, B.; Mickey, D.; Montgomery, R.; Pillet,
V.; Rabin, D.
1993BAAS...25.1205W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Absorption of p-Modes by Sunspots: Variations with Degree
and Order
Authors: Bogdan, Thomas J.; Brown, Timothy M.; Lites, Bruce W.;
Thomas, John H.
1993ApJ...406..723B Altcode:
A spherical harmonic decomposition of the p-modes into inward and
outward propagating waves is employed to investigate the absorption
of solar p-modes by an isolated sunspot. The absorption coefficient
(averaged over frequency and azimuthal order) is found to increase
with increasing horizontal wavenumber k over the range 0-0.8/Mm. For
larger horizontal wavenumbers, in the range 0.8-1.5/Mm, the absorption
coefficient decreases with increasing k. The absorption along each
individual p-mode ridge tends to peak at an intermediate value of the
spherical harmonic degree in the range 200-400. The highest absorption
is found along the p(1) ridge, and the absorption decreases with
increasing radial order.
---------------------------------------------------------
Title: The polarization properties of Fe ii 614.9 nm
Authors: Lites, Bruce W.
1993SoPh..143..229L Altcode:
The anomalous Zeeman splitting of the FeII line at 614.9 nm results
in four unusual properties of the polarization signature of this
line in the presence of magnetic fields: the absence of linear
polarization, no magneto-optical effect, the independence of intensity
at line center from the inclination of the field, and a depolarizing
self-absorption. The origin of these properties is illustrated in terms
of the transfer of line radiation in an idealized solar atmosphere.
---------------------------------------------------------
Title: The Magnetohydrodynamics of Umbral Flux Tubes. I. Theoretical
Model
Authors: Degenhardt, Detlev; Lites, Bruce W.
1993ApJ...404..383D Altcode:
The MHD consequences of thin vertical gas columns embedded in sunspot
umbrae are investigated in order to elucidate the nature of umbral
fine structure, specifically, umbral dots, from a theoretical
perspective. Both these gas columns and the surrounding umbral
stratification are permeated by a magnetic field, the field strength
of the column being weaker than that of the ambient medium. The
steady-state MHD equations are solved numerically in the thin flux tube
approximation. The geometry of the flux tube, which in all cases is a
rapidly converging column with increasing height in the atmosphere,
is determined. At heights representing the observable layers of the
umbra, the strengths of the magnetic fields inside and outside of the
umbral flux tube approach a common value. It is shown that either high
temperatures at the lower boundary of the umbral flux tubes or strong
upflows are needed in order to produce bright continuum structures.
---------------------------------------------------------
Title: Early Results from HAO/NSO Advanced Stokes Polarimeter
Authors: Lites, B. W.; Elmore, D. F.; Tomczyk, S.; Seagraves, P.;
Skumanich, A.; Streander, K. V.
1993ASPC...46..173L Altcode: 1993mvfs.conf..173L; 1993IAUCo.141..173L
No abstract at ADS
---------------------------------------------------------
Title: Oscillations of the Magnetic Network
Authors: Lites, B. W.; Rutten, R. J.; Kalkofen, W.
1993ASPC...46..530L Altcode: 1993mvfs.conf..530L; 1993IAUCo.141..530L
No abstract at ADS
---------------------------------------------------------
Title: Asymmetric Stokes Q, U and V Line Profiles Observed in Sunspots
Authors: Sanchez Almeida, J.; Lites, B. W.
1993ASPC...46..177S Altcode: 1993mvfs.conf..177S; 1993IAUCo.141..177S
No abstract at ADS
---------------------------------------------------------
Title: The Advanced Stokes Polarimeter - A new instrument for solar
magnetic field research
Authors: Elmore, D. F.; Lites, B. W.; Tomczyk, S.; Skumanich,
A. P.; Dunn, R. B.; Schuenke, J. A.; Streander, K. V.; Leach, T. W.;
Chambellan, C. W.; Hull, H. K.
1992SPIE.1746...22E Altcode:
A new Stokes polarimeter for high spatial resolution quantitative
measurement of magnetic fields at multiple heights in the solar
atmosphere has been constructed by the National Center for Atmospheric
Research and the National Solar Observatory. The instrument uses
the Vacuum Tower Telescope at Sunspot, New Mexico, and its existing
horizontal spectrograph, universal birefringment filter, and image
motion stabilization system. The polarimeter uses a rotating retarder
polarization modulator with polarization calibration optics. Multiple
paired CCDs are used for detection followed by video processing to
produce spatial maps of the full state of polarization in restricted
regions of the solar spectrum. Two spectral regions encompassing
lines sensitive to the Zeeman effect, which form in the photosphere
and low chromosphere, are recorded simultaneously. Significant
developments include: construction of the new telescope post
focus optical arrangement, creation of a polarization model for the
telescope, construction of high-speed, low-noise solid state cameras,
and construction of computer hardware for receiving and processing
high-rate 12-bit digital data.
---------------------------------------------------------
Title: Observation and Interpretation of the Asymmetric Stokes Q,
U, and V Line Profiles in Sunspots
Authors: Sanchez Almeida, J.; Lites, B. W.
1992ApJ...398..359S Altcode:
We present a first approach to systematic characterization and
interpretation of observed asymmetries of Stokes profiles as a function
of spatial position within sunspots. Spatial maps of the full Stokes
profiles of Fe I 6302.5 A gathered in large sunspots using the HAO
Stokes II instrument reveal asymmetries that vary systematically across
large sunspots observed during 1980. We use the inversion technique
by Landolfi to extract the velocity gradients along the line of sight
(LOS) which give rise to these asymmetries. The gradients derived from
full Stokes profiles are in agreement with previous characterizations
of the Evershed flow derived from Stokes I profiles alone (i.e., a flow
increasing with depth in the atmosphere). By coupling this semiempirical
gradient of velocity with a magnetic field inclination varying along the
LOS, the synthesized profiles are able to mimic basic observed features
of the broad-band circular polarization present in our data and observed
previously by others. This characterization has magnetic field lines
which become progressively more horizontal with depth in the penumbra.
---------------------------------------------------------
Title: Localized Sources of Propagating Acoustic Waves in the Solar
Photosphere
Authors: Brown, Timothy M.; Bogdan, Thomas J.; Lites, Bruce W.;
Thomas, John H.
1992ApJ...394L..65B Altcode:
A time series of Doppler measurements of the solar photosphere with
moderate spatial resolution is described which covers a portion of the
solar disk surrounding a small sunspot group. At temporal frequencies
above 5.5 mHz, the Doppler field probes the spatial and temporal
distribution of regions that emit acoustic energy. In the frequency
range between 5.5 and 7.5 mHz, inclusive, a small fraction of the
surface area emits a disproportionate amount of acoustic energy. The
regions with excess emission are characterized by a patchy structure
at spatial scales of a few arcseconds and by association (but not
exact co-location) with regions having substantial magnetic field
strength. These observations bear on the conjecture that most of the
acoustic energy driving solar p-modes is created in localized regions
occupying a small fraction of the solar surface area.
---------------------------------------------------------
Title: The Advanced Stokes Polarimeter: A New Instrument for Solar
Magnetic Field Research
Authors: Tomczyk, S.; Elmore, D. F.; Lites, B. W.; Dunn, R. B.;
Skumanich, A.; Schuenke, J. A.; Streander, K. V.; Leach, T. W.;
Chambellan, C. W.; Lacey, L. B.
1992AAS...180.5108T Altcode: 1992BAAS...24..814T
A new Stokes polarimeter for high spatial resolution quantitative
measurement of magnetic fields at multiple heights in the solar
atmosphere has been constructed by the National Center for Atmospheric
Research and the National Solar Observatory. The instrument has become
operational at the Vacuum Tower Telescope at Sunspot, New Mexico
and uses its existing horizontal spectrograph, universal birefringent
filter, and image motion stabilization system. To these optical systems
we have added a rotating wave plate polarimeter and polarization
calibration optics. Multiple CCDs are used for detection followed by
video processing in order to produce polarization maps of solar regions
from several spectrum lines simultaneously. Significant developments
include: a) construction of the new VTT post focus optical arrangement,
b) creation of a polarization model for the VTT, c) construction of
high speed, low noise CCD cameras, and d) construction of computer
hardware for receiving and processing high rate 12-bit digital data.
---------------------------------------------------------
Title: Stokes Inversion in the Presence of Canopy-Like Structures
and Unresolved Flux-Tubes
Authors: Skumanich, A.; Grossmann-Doerth, U.; Lites, B. W.
1992AAS...180.1203S Altcode: 1992BAAS...24Q.748S
The issue of the Stokes polarization signature of canopy-like structures
and the inversion of the resulting Stokes profiles is considered for
a self-consistent flux tube (sheet) model. It is found that when the
`canopy' and its attendant current sheet have an optical thickness at
line center tau_0 <= 5, the intensity and net polarization profiles
become decoupled. An effective inversion strategy is to reduce or
eliminate the role of the intensity parameter. The Milne-Eddington
(ME) analytic inversion in current use is easily adapted for this
purpose. It is found that the use of a magnetic fill factor allows for
an approximate compensation for the presence of a field discontinuity
along the line of sight but a more accurate procedure is to restrict the
inversion to the net polarization profiles. In the case of sufficiently
thin canopies the ME inversion, when reduced to the Sears form, yields
fields within ~ 100 G of the true field. When the Stokes profiles
are averaged over the flux sheet to simulate the effects of limited
angular resolution, the fill factor strategy yields an accurate measure
of both the axial field and the width of the flux sheet at tau_0 =~
1 for observing angles <= 35(deg) to the normal. For larger angles,
opacity shielding occurs and reduced fields are derived.
---------------------------------------------------------
Title: Very high spatial resolution two-dimensional solar spectroscopy
with video CCDs
Authors: Johanneson, A.; Bida, T.; Lites, B.; Scharmer, G. B.
1992A&A...258..572J Altcode:
We have developed techniques for recording and reducing spectra of
solar fine structure with complete coverage of two-dimensional areas
at very high spatial resolution and with a minimum of seeing-induced
distortions. These new techniques permit one, for the first time,
to place the quantitative measures of atmospheric structure that are
afforded only by detailed spectral measurements into their proper
context. The techniques comprise the simultaneous acquisition of
digital spectra and slit-jaw images at video rates as the solar scene
sweeps rapidly by the spectrograph slit. During data processing the
slit-jaw images are used to monitor rigid and differential image motion
during the scan, allowing measured spectrum properties to be remapped
spatially. The resulting quality of maps of measured properties from
the spectra is close to that of the best filtergrams. We present the
techniques and show maps from scans over pores and small sunspots
obtained at a resolution approaching 1/3 arcsec in the spectral
region of the magnetically sensitive Fe I lines at 630.15 and 630.25
nm. The maps shown are of continuum intensity and calibrated Doppler
velocity. More extensive spectral inversion of these spectra to yield
the strength of the magnetic field and other parameters is now underway,
and the results of that analysis will be presented in a following paper.
---------------------------------------------------------
Title: First Results from the Advanced Stokes Polarimeter
Authors: Lites, B. W.; Dunn, R. B.; Elmore, D. F.; Tomczyk, S.;
Skumanich, A.; Streander, K. V.
1992AAS...180.1201L Altcode: 1992BAAS...24..747L
The Advanced Stokes Polarimeter (ASP) is a collaborative program between
the High Altitude Observatory (HAO) and the National Solar Observatory
(NSO) to investigate the physics of solar active regions though
quantitative measurements of vector magnetic fields. First scientific
results from the ASP were obtained during an observing run in March,
1992, when high resolution Stokes profile maps of active regions were
obtained under good seeing conditions. The ASP measures simultaneously
the full Stokes profiles in photospheric Fe I lines near 630 nm and in
the temperature minimum/low chromospheric Mg I b-lines at 517 nm. We
present scans of an isolated small sunspot near disk center, and we
discuss the fine structure of the vector field within this sunspot
and in the magnetic elements surrounding it. Observations of a complex
active region near the east limb will also be presented. This active
region produced a flare during the observational sequence.
---------------------------------------------------------
Title: Sunspot Oscillations - Observations and Implications
Authors: Lites, B. W.
1992ASIC..375..261L Altcode: 1992sto..work..261L
This review summarizes the current state of observational knowledge
of oscillations within sunspots. Three classes of oscillations are
discussed: (1) oscillations measured in the photosphere of sunspot
umbrae which are dominated by the apparent response of the umbral
photosphere to the 5-minute p-mode oscillations, (2) the energetic
oscillations in the umbral chromosphere, and (3) oscillations observed
in the penumbral chromosphere. Observational results are critically
examined. The theory of sunspot oscillations is discussed in light of
the observations, and new observational tests are proposed.
---------------------------------------------------------
Title: Phase Delays in the Vertical Propagation of Waves in the
Solar Atmosphere
Authors: Chipman, E. G.; Lites, B. W.
1991BAAS...23R1389C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High-Resolution Spectra of Solar Magnetic
Features. II. Magnetic Fields of Umbral Brightenings
Authors: Lites, Bruce W.; Bida, Thomas A.; Johannesson, A.; Scharmer,
G. B.
1991ApJ...373..683L Altcode:
The spectra of Fe I and Fe II Zeeman-sensitive lines enhanced by video
processing of CCD images are considered. The magnetic-field variation
within umbras is obtained from the nearly complete Zeeman splitting
of the Stokes I profile. It is shown that small brightenings within
umbrae have magnetic fields nearly equal to or slightly smaller than
that of the darker surroundings; these features are also nearly at rest
with respect to their surroundings. It is noted that the absence of
significant motions in umbral dots implies that radiation transports
most of the energy at and immediately below the surface. The small
size of the dots implies that, if convective plumes transport energy
below the surface of sunspot umbrae, they should have both a lateral
extent and a depth of their upper boundary comparable to or smaller
than the size of the dot.
---------------------------------------------------------
Title: Long-Period Oscillations of the Chromospheric Network
Authors: Lites, B. W.; Kalkofen, W.; Rutten, R. J.
1991BAAS...23.1050L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: LEST Progress
Authors: Lites, B.
1991BAAS...23.1034L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The derivation of vector magnetic fields from Stokes profiles:
derivative versus least squares fitting techniques.
Authors: Metcalf, T. R.; Canfield, R. C.; Mickey, D. L.; Lites, B. W.
1991sopo.work..376M Altcode:
The authors present a comparison of solar magnetic fields calculated
using the weak field equations of Jefferies, Lites, and Skumanich
and the least squares fitting method of Skumanich and Lites. The two
calculations used Fe I 6302 data from June, 1985, and are found to
agree quite well up to at least 1200 G.
---------------------------------------------------------
Title: Fringes in polarizing optical elements.
Authors: Lites, B. W.
1991sopo.work..166L Altcode:
A Muller Matrix description is developed for expressing the effects
of spectral fringes (channel spectra) arising from polarizing optical
elements in astronomical polarimeters. This description allows one
to derive the effects of fringes in a straightforward manner. The
formalism is applied to the case of the rotating linear retarder that
will be used in the Advanced Stokes Polarimeter (ASP). It is shown that,
through proper calibration of the ASP polarimeter on a pixel-by-pixel
basis, the effects of spectral fringing should not be troublesome,
but these effects may be more troublesome in polarimeters which demand
higher polarization accuracy.
---------------------------------------------------------
Title: Sensitivity to polarization: how can we measure weak vector
magnetic fields at high angular resolution?
Authors: Lites, B. W.
1991sopo.work..173L Altcode:
The difficulties of using ground-based instrumentation to measure
weak vector magnetic fields in the photosphere through polarization
measurements of high precision in the visible spectrum are discussed.
---------------------------------------------------------
Title: Velocity gradients across a flaring neutral line from Stokes
II measurements.
Authors: Skumanich, A.; Lites, B.
1991sopo.work..307S Altcode:
The pattern of profile reversals formed due to incomplete
cancellation of the Stokes net circular polarization parameter, V,
when the resolution element contains the magnetic neutral line (in the
observer's frame) represents a sensitive diagnostic of the line-of-sight
velocity difference between the opposite polarity regions. Typical V
profile patterns found in such circumstances with the HAO/SPO Stokes
II polarimeter are illustrated. Resulting velocity differences are
estimated both by analytic decomposition of a specific neutral line
profile and by composition of profiles from elements on opposite sides
of the neutral line. Pre- and post-flare Stokes II observations of
Hale Active Region ≠16604 are under such analysis.
---------------------------------------------------------
Title: The orbiting solar laboratory
Authors: Lites, B. W.
1991AdSpR..11e.181L Altcode: 1991AdSpR..11..181L
The Orbiting Solar Laboratory (OSL) is an unmanned NASA space mission
which will place a relatively large aperture (1.0 m) solar telescope
for optical and near-ultraviolet wavelengths into a slowly precessing
polar orbit, such that the spacecraft will see continuous illumination
by sunlight for about 260 days per year. Focal-plane instrumentation
for this telescope will produce images and spectra from 220-1000 nm
with an angular resolution of about 0.13 arcsec at 500 nm. Polarization
analysis will allow detailed studies of solar magnetic fields at high
resolution. The spacecraft will also carry co-observing instruments
to observe at ultraviolet and X-ray wavelengths with sub-arcsecond
resolution. The long duration of this mission will permit thorough study
of many solar phenomena whose physical behavior is rooted in small-scale
dynamical processes. Complemented by a new generation of ground-based
solar instrumentation, OSL will revolutionize our observational
understanding of MHD processes in the solar atmosphere. The OSL mission
now holds the position as the only 1992 new-start candidate in the
current NASA five-year strategic plan. Based on a 1992 startup, OSL is
scheduled for launch in 1997. <P />The National Center for Atmospheric
Research is sponsored by the National Science Foundation.
---------------------------------------------------------
Title: Preliminary results from the HAO/NSO Advanced Stokes
Polarimeter prototype observing run.
Authors: Lites, B. W.; Elmore, D.; Murphy, G.; Skumanich, A.; Tomczyk,
S.; Dunn, R. B.
1991sopo.work....3L Altcode:
A prototype version of the Advanced Stokes Polarimeter was operated at
the Sunspot Vacuum Tower Telescope of the National Solar Observatory
in May und June, 1990. Although the prototype instrument does not
have the capability of the final instrument to be deployed in 1991,
it nonetheless provided high spatial resolution Stokes profiles
observations of a small symmetric sunspot. Analysis of these
observations shows that the magnetic field at the outer edge of
the penumbra of this sunspot is highly inclined with respect to the
local normal (γ = 70 - 80°), in agreement with previous Stokes II
measurements of larger sunspots. In addition, the axial field and flux
distribution was found to be nearly identical to that of the previous
Stokes II measurement.
---------------------------------------------------------
Title: High-Resolution Spectra of Solar Magnetic Features. I. Analysis
of Penumbral Fine Structure
Authors: Lites, B. W.; Scharmer, G. B.; Skumanich, A.
1990ApJ...355..329L Altcode:
The Swedish Vacuum Telescope on La Palma was used to obtain spectra
of the magnetic-sensitive Fe I 630.25 nm line under conditions
of exceptional angular resolution (0.32 arcsec) and high spectral
resolution (FWHM 2.5 pm). Simultaneous 0.02 s CCD exposures of both the
spectrum and the slit-jaw image effectively 'freeze' the atmospheric
seeing motions and permit unambiguous identification of the spectra
of the various penumbral structures. These spectra reveal the magnetic
field strength in penumbral filaments through an intensity fit of the
Zeeman splitting of this line. The observations show that: (1) the field
strength varies from about 2100 G near the umbra-penumbra boundary
to about 900 G at the outer edge of the penumbra, (2) the observed
fluctuation of penumbral magnetic field is much less dramatic than the
fluctuation in intensity, (3) there is a suggestion of a rapid change
in field inclination between some light and dark filaments near the
edge of the penumbra, and (4) there is no obvious correlation between
Doppler shift (in part due to the Evershed flow) and filament intensity.
---------------------------------------------------------
Title: High Resolution Spectroscopy of Penumbral Fine Structure
Authors: Bida, T.; Lites, B. W.; Johannesson, A.; Scharmer, G.
1990BAAS...22..880B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stokes Profile Analysis and Vector Magnetic Fields. V. The
Magnetic Field Structure of Large Sunspots Observed with Stokes II
Authors: Lites, B. W.; Skumanich, A.
1990ApJ...348..747L Altcode:
Results are presented on the analysis of Stokes II polarimeter data
on four large sunspots during 1980, yielding the vector magnetic
field structure and thermodynamic parameters of these sunspots. It
is found that the magnetic field occupies significant fractions of
the area in both light and dark penumbral filaments, and that the
intrinsic field does not fall below 600 G, either in the sunspot
or in the surrounding plage areas, and is typically 700-800 G at
the outer edge of the penumbra. The radial variation of the vector
field in these sunspots does not agree with the return-flux models of
Fla et al. (1982). The variation of the poloidal field strength and
inclination with distance from the center of the symmetric sunspots
exhibits little nonpotential character and is well represented by the
potential field of a buried dipole.
---------------------------------------------------------
Title: High resolution spectra of umbral fine structure from the
Swedish solar observatory at La Palma
Authors: Lites, B. W.; Scharmer, G.
1989hsrs.conf..286L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Advanced Stokes Polarimeter
Authors: Lites, B. W.; Skumanich, A.
1989hsrs.conf..389L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transfer of Line Radiation in a Magnetic Field
Authors: Jefferies, John; Lites, Bruce W.; Skumanich, A.
1989ApJ...343..920J Altcode:
Using a classical approach, the transfer equations are derived for
spectral-line radiation in a medium which is permeated by a magnetic
field. Consideration is given to solutions of these equations for
the 'weak-field' case, when the Zeeman splitting is a fraction of
the Doppler width, and the range of validity of such solutions. Some
approximate expressions allow a simple inference of the vector-field
characteristics directly from the line profiles.
---------------------------------------------------------
Title: The HAO/NSO Advanced Stokes Polarimeter
Authors: Lites, B. W.; Elmore, D. F.
1989BAAS...21..863L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Magnetic Field Strength of Umbral Dots
Authors: Lites, B. W.; Bida, T. A.; Scharmer, G. B.
1989BAAS...21..854L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Constraints Imposed by Very High Resolution Spectra and Images
on Theoretical Simulations of Granular Convection
Authors: Lites, B. W.; Nordlund, Å.; Scharmer, G. B.
1989ASIC..263..349L Altcode: 1989ssg..conf..349L
No abstract at ADS
---------------------------------------------------------
Title: Photoelectric Observations of Chromospheric Sunspot
Oscillations. V. Penumbral Oscillations
Authors: Lites, Bruce W.
1988ApJ...334.1054L Altcode:
This paper presents a new analysis of observations of penumbral
magneto-atmospheric oscillations in which both the spatial and
temporal behavior are measured simultaneously in two spectral lines
(Fe I λ5434 and Ca II λ8498) formed at widely separated heights in
the atmosphere. The spatial distribution of the amplitude of oscillation
indicates that the velocity perturbations are aligned with the magnetic
field (1) in the inner penumbra at photospheric heights, and (2) in
the outer penumbra at chromospheric heights. In the outer penumbra,
it is found that the p-modes with their usual frequencies around
ν = 3 mHz are the dominant feature of the oscillatory spectrum at
photospheric heights, but oscillations of much lower frequencies are
dominant in the chromosphere.
---------------------------------------------------------
Title: Stokes Profile Analysis and Vector Magnetic
Fields. IV. Synthesis and Inversion of the Chromospheric MG i B Lines
Authors: Lites, B. W.; Skumanich, A.; Rees, D. E.; Murphy, G. A.
1988ApJ...330..493L Altcode:
An analytic solution to the transfer equations for polarized radiation
which allows for departures from LTE in the overall excitation of a
chromospheric line is discussed, and a method of least-squares inversion
is applied to profiles of Mg I b lines at 5172.7 and 5183.6 A observed
in December 1978. An analytic form expressing the source function
dependence on line-center optical depth leads to a generalization of
an existing least-squares procedure which is found to be effective in
recovering the magnetic field from simulated Stokes profiles under
specified conditions. Reasonable magnetic field values are obtained
if a macroturbulent profile smearing of 1-2 km/s is used and if the
profiles are corrected for scattered light.
---------------------------------------------------------
Title: High Resolution Observations of Penubral Magnetic Fields
Authors: Lites, B. W.; Scharmer, G. B.
1988BAAS...20..681L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Seismology
Authors: Thomas, J. H.; Lites, B. W.; Abdelatif, T. E.
1988IAUS..123..181T Altcode:
The 5 minute oscillations in a sunspot umbra are the response of the
sunspot to forcing by the 5 minute p-modes in the surrounding convection
zone (Thomas 1981). This interaction of solar p-modes with a sunspot
can be used to probe the structure of a sunspot beneath the visible
surface of the Sun (Thomas, Cram, and Nye 1982). Here the authors
report briefly the results of both an observational study and a simple
theoretical analysis of this interaction.
---------------------------------------------------------
Title: Stokes Profile Analysis and Vector Magnetic
Fields. I. Inversion of Photospheric Lines
Authors: Skumanich, A.; Lites, B. W.
1987ApJ...322..473S Altcode:
The authors consider improvements to the Auer, Heasley, and House
method for the analytic inversion of Stokes profiles via nonlinear
least squares. In the application of this method to actual sunspot
observations, the authors have found that its simplifications often
yield erroneous solutions or nonconvergent behavior. By including
damping wings and magneto-optical birefringence and by decoupling the
intensity profile from the three-vector polarization profile in the
analysis, the authors develop a more robust inversion method that
provides a more reliable and accurate estimate of sunspot vector
magnetic fields without significant loss of economy.
---------------------------------------------------------
Title: The Polarization Properties of Model Sunspots: The Broad-Band
Polarization Signature of the Schlueter-Temesvary Representation
Authors: Skumanich, A.; Lites, B. W.
1987ApJ...322..483S Altcode:
The properties and diagnostic content of integrated-over-wavelength
Zeeman-induced polarization in spectral lines formed in sunspots
are investigated. The net circular polarization (NCP) generated
by a continuously varying velocity field parallel to a constant
magnetic field with arbitrary inclination is shown to follow
the algebraic expression for the step-velocity model of Auer and
Heasley (1978). Although application of the analysis to parameters
representative of sunspots fails to yield the observed broadband
NCP radius pattern, the introduction of magnetic field gradients and
magnetooptical birefringence is found to result in a pattern similar
to that observed.
---------------------------------------------------------
Title: Rotating waveplates as polarization modulators for Stokes
polarimetry of the sun: evaluation of seeing-induced crosstalk errors
Authors: Lites, Bruce W.
1987ApOpt..26.3838L Altcode:
A formalism for estimating the crosstalk error among Stokes I,Q,U,V
introduced by seeing-induced image motion is presented. This formalism
is applied to several modulation schemes for polarization involving
rotating waveplates, and it is evaluated using an observed power
spectrum of image motion obtained from the Vacuum Tower Telescope at the
National Solar Observatory/Sunspot. It is shown that rotating waveplates
offer an acceptable alternative for measurements of absorption line
polarization of features observed on the solar disk, provided the
detection can be carried out at video frame rates or faster.
---------------------------------------------------------
Title: Stokes Profile Analysis and Vector Magnetic
Fields. III. Extended Temperature Minima of Sunspot Umbrae as Inferred
from Stokes Profiles of MG i lambda 4571
Authors: Lites, B. W.; Skumanich, A.; Rees, D. E.; Murphy, G. A.;
Carlsson, M.
1987ApJ...318..930L Altcode:
Observed Stokes profiles of Mg I 4571 A are analyzed as a diagnostic
of the magnetic field and thermal structure at the temperature minimum
of sunspot umbrae. Multilevel non-LTE transfer calculations of the Mg
I-II-III excitation and ionization balance in model umbral atmospheres
show: (1) Mg I to be far less ionized in sunspot umbrae than in the
quiet sun, leading to greatly enhanced opacity in 4571 A, and (2) LTE
excitation of 4571 A. Existing umbral models predict emission cores of
the Stokes I profile due to the chromospheric temperature rise. This
feature is not present in observed umbral profiles. Moreover, such
an emission reversal causes similar anomalous features in the Stokes
Q, U, V profiles, which are also not observed. Umbral atmospheres
with extended temperature minima are suggested. Implications for
chromospheric heating mechanisms and the utility of this line for
solar vector magnetic field measurements are discussed.
---------------------------------------------------------
Title: Synthesis and Inversion of the Chromospheric Mg I ????-Line
Stokes Profiles
Authors: Murphy, G. A.; Rees, D. E.; Lites, B. W.; Skumanich, A.
1987BAAS...19..938M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Vector Magnetic Field Structure of Large Sunspots Observed
with Stokes II
Authors: Lites, B. W.; Skumanich, A.; Lundgren, S.
1987BAAS...19..945L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous Measurements of Sunspot Umbral Oscillations in
the Photosphere, Chromosphere, and Transition Region
Authors: Thomas, John H.; Lites, Bruce W.; Gurman, Joseph B.; Ladd,
Edwin F.
1987ApJ...312..457T Altcode:
Measurements of umbral oscillations in a sunspot were made
simultaneously from space (with the SMM/UVSP instrument) in the
C IV transition-region line and from the ground (with the tower
telescope at NSO/sunspot) in spectral lines formed in the photosphere
and chromosphere. The power spectra of velocity and intensity
variations show multiple peaks in the 3 min band (4.5-10 mHz). A
strong oscillation at 5.5 mHz is coherent between the chromosphere
and transition region. Another strong oscillation mode at 7.5 mHz is
coherent between the photosphere and transition region and appears to
have a node in the chromosphere. The rms velocity in the 3 min band is
a little over 12 km/sec in both the chromosphere and transition region,
but the kinetic energy density is lower in the transition region (by
a factor of 10 or more) due to the lower mass density there. These
measurements of amplitude and phase of the waves at different heights
provided a new, independent method of testing or fitting models of
the vertical temperature distribution in the umbral chromosphere and
transition regions.
---------------------------------------------------------
Title: Rotating waveplates as polarization modulators for Stokes
polarimetryof the sun: evaluation of seeing-induced crosstalk errors.
Authors: Lites, B. W.
1987LFTR...23.....L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the need for a large aperture solar telescope for
quantitative studies of vector magnetic fields.
Authors: Lites, B. W.
1987LFTR...22.....L Altcode:
It is demonstrated that quantitative measures of the solar vector
magnetic field demand at once high spatial resolution, high spectral
resolution, and simultaneous wavelength coverage of line profiles. These
requirements dictate a large aperture telescope in order to achieve
the necessary photon flux.
---------------------------------------------------------
Title: The Interaction of Solar p-Modes with a
Sunspot. I. Observations
Authors: Abdelatif, Toufik E.; Lites, Bruce W.; Thomas, John H.
1986ApJ...311.1015A Altcode:
Time series of velocity maps of two isolated sunspots and their
surroundings were recorded in the Fe I line and the umbral line Ti
I. Both 3 and 5 min umbral oscillations were detected at photospheric
heights. The 5 min oscillations have reduced amplitude in the umbra,
which appears to act as a filter in transmitting selected frequencies
in the power spectrum of 5 min p-mode oscillations of the surrounding
convection zone. The k-omicron power spectrum of the umbral oscillations
shows this selective transmission and also shows a shift of power to
longer horizontal wavelengths. This behavior is exhibited by a simple
theoretical model of the interaction of p-modes with a sunspot. The
3 min umbral oscillations are concentrated in the dark central part
of the umbra. In both sunspots, the kinetic energy density of the 3
min umbral oscillation in the photosphere is much greater than the
corresponding kinetic energy density at chromospheric heights measured
in other sunspots.
---------------------------------------------------------
Title: Radiative Transfer Diagnostics: Understanding Multilevel
Transfer Calculations. I. Analysis of the Full Statistical Equilibrium
Equations
Authors: Skumanich, Andrew; Lites, Bruce W.
1986ApJ...310..419S Altcode:
The sensitivity analysis method of Skumanich and Lites (1985), which
makes it possible to decompose the equivalent two-level parameters of
a non-LTE transition problem into their most significant excitation
(source) and deexcitation (sink) terms, is reviewed and extended. In
the method, the statistical equilibrium (SE) equations are solved
numerically for the explicit upper and lower level occupations of a
particular transition under various combinations of perturbations
of atomic rates, both collisional and radiative, about an exact
numerical solution. The sensitivity analysis is applied to the
formation of the hydrogen spectrum in a representative model of
the solar atmosphere. Although the numerical method is not a means
of avoiding the direct algebraic solution of the SE equations, it
reduces the burden of identifying the most significant terms along the
(N-1)-factorial terms that occur in such a solution.
---------------------------------------------------------
Title: Sunspot Umbral Oscillations in the Photosphere, Chromosphere,
and Transition Region
Authors: Thomas, J. H.; Lites, B. W.; Gurman, J. B.; Ladd, E. F.
1986BAAS...18..678T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Extended Temperature Minima of Sunspot Umbrae
Authors: Lites, B. W.; Skumanich, A.; Rees, D. E.; Murphy, G. A.;
Carlsson, M.
1986BAAS...18..662L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Photoelectric Observations of Chromospheric Sunspot
Oscillations. IV. The CA II H Lines and He i lambda 10830
Authors: Lites, B. W.
1986ApJ...301.1005L Altcode:
Simultaneous observations of profiles of He I λ10830 and the Ca II
H line in sunspot umbrae have been made with the Tower telescope,
echelle spectrograph, and multidiode array at the National Solar
Observatory/Sunspot. These observations reveal the nature of
fluid motions in the upper chromosphere during the cycle of umbral
oscillations. Time sequences of profiles show that the chromospheric
He I line is in weak absorption during all phases of the umbral
oscillations, and that it undergoes periodic Doppler shifts of high
amplitude (up to 11 km s<SUP>-1</SUP>). The amplitudes and waveforms of
the Doppler shifts in the He I line indicate that the oscillations are
frequently nonlinear (i.e., forming shocks) and therefore contribute
to the heating of the upper umbral chromosphere.
---------------------------------------------------------
Title: Photoelectric Observations of Chromospheric Sunspot
Oscillations. III. Spatial Distribution of Power and Frequency
in Umbrae
Authors: Lites, B. W.
1986ApJ...301..992L Altcode:
On the basis of analyses of the spatial distribution of oscillation
power and frequency of data from Lites (1984), the multiple peaks
frequently observed in average power spectra are noted to be due to
the presence of cospatial modes with different frequencies. Changes
in these modes' amplitudes and frequencies with time and place within
an umbra appear to arise from an interference of modes in the driving
force in the photosphere. High oscillatory power regions in the 3-min
band are uncorrelated with high oscillatory power regions in the 5-min
band within the umbrae, suggesting that the 5-min oscillations in the
photosphere do not drive the 3-min chromospheric oscillations. These
results are used to develop a consistent view of the umbral oscillation
mechanism: attention is given to a photospheric resonator for fast
magnetoatmospheric waves, driving the chromospheric resonator through
nonlinear wave interaction.
---------------------------------------------------------
Title: The visible helium spectrum of a white-light flare.
Authors: Lites, B. W.; Meidig, D. F.; Trujillo Bueno, J.
1986lasf.conf..101L Altcode: 1986lasf.symp..101L
Emission lines of neutral and ionized helium at visible wavelengths are
measured in the white-light flare of 24 April 1981. These intensities,
along with accompanying profiles, are presented for the purpose of
providing an observational basis for future radiative transfer models
of white-light flares. Absolute intensities, both peak and integrated,
are given for 14 lines of He I, and for the He II line at 4686 Å. The
authors compare intensities of these lines in the white-light emitting
region to intensities measured in a flare kernel that does not show
significant continuum emission. From this, they infer that the white
light emission arises from material at chromospheric temperatures,
and not from temperatures greater than about 20,000K. A search for
Stark-enhanced forbidden neighbors to the allowed He I lines in this
disk flare was unsuccessful.
---------------------------------------------------------
Title: Future Directions for the Theory of Radiative Transfer in
Chromospheric Structures
Authors: Lites, B. W.
1985tphr.conf..273L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot umbral oscillations in the photosphere and low
chromosphere
Authors: Lites, B. W.; Thomas, J. H.
1985ApJ...294..682L Altcode:
In the present simultaneous measurement of sunspot umbrae velocity
oscillations in one spectral line formed in the low photosphere, and
in another formed in the low chromosphere, just above the temperature
minimum, the velocity power spectrum in each is found to exhibit both
5-min and 3-min oscillations, with the kinetic energy of the latter
being at least 5 times greater in the low photosphere than in the
low chromosphere. The 3-min umbral oscillation has the character of a
coherent, vertically standing wave in the photosphere. These results
imply a photospheric, rather than chromospheric, resonant origin for
the fundamental 3-min umbral oscillation. A negative phase difference
at frequencies around 2 mHz suggests the presence of gravity waves in
the umbra.
---------------------------------------------------------
Title: Steady flows in active regions observed with the HeI 10830
Å line
Authors: Lites, B. W.; Keil, S. L.; Scharmer, G. B.; Wyller, A. A.
1985SoPh...97...35L Altcode:
We show that the He I 10830 A line gives reliable Doppler shift
measurements in the upper chromosphere above active regions. Persistent
flow patterns in active regions observed near the solar limb show
features previously noted in Dopplergrams using the CIV transition
region ultraviolet emission line. Unlike the CIV measurements, however,
the He I absorption shows a strong correlation with the line-of-sight
velocity images in certain regions of some active regions.
---------------------------------------------------------
Title: The effect of line damping, magneto-optics and parasitic
light on the derivation of sunspot vector magnetic fields
Authors: Skumanich, A.; Lites, B. W.
1985svmf.nasa..341S Altcode:
The least square fitting of Stokes observations of sunspots using a
Milne-Eddington-Unno model appears to lead, in many circumstances,
to various inconsistencies such as anomalously large doppler widths
and, hence, small magnetic fields which are significantly below those
inferred solely from the Zeeman splitting in the intensity profile. It
is found that the introduction of additional physics into the model
such as the inclusion of damping wings and magneto-optic birefrigence
significantly improves the fit to Stokes parameters. Model fits
excluding the intensity profile, i.e., of both magnitude as well
as spectral shape of the polarization parameters alone, suggest
that parasitic light in the intensity profile may also be a source
of inconsistencies. The consequences of the physical changes on the
vector properties of the field derived from the Fe I lambda 6173 line
for the 17 November 1975 spot as well as on the thermodynamic state
are discussed. A Doppler width delta lambda (D) - 25mA is bound to
be consistent with a low spot temperature and microturbulence, and a
damping constant of a = 0.2.
---------------------------------------------------------
Title: The inference of vector magnetic fields from polarization
measurements with limited spectral resolution
Authors: Lites, B. W.; Skumanich, A.
1985svmf.nasa..342L Altcode:
A method is presented for recovery of the vector magnetic field and
thermodynamic parameters from polarization measurement of photospheric
line profiles measured with filtergraphs. The method includes
magneto-optic effects and may be utilized on data sampled at arbitrary
wavelengths within the line profile. The accuracy of this method is
explored through inversion of synthetic Stokes profiles subjected to
varying levels of random noise, instrumental wave-length resolution, and
line profile sampling. The level of error introduced by the systematic
effect of profile sampling over a finite fraction of the 5 minute
oscillation cycle is also investigated. The results presented here
are intended to guide instrumental design and observational procedure.
---------------------------------------------------------
Title: Least squares inversion of Stokes profiles in the presence
of velocity gradients
Authors: Skumanich, A.; Rees, D. E.; Lites, B. W.
1985svmf.nasa..306S Altcode:
The Auer, Heasley and House Stokes inversion procedure in use at
High Altitude Observatory is based on the analytic solution of the
equation of transfer for polarized light where the representation of
the thermodynamic and magnetic structure of the atmosphere is assumed
to have a high degree of invariance, namely, a Milne-Eddington (ME)
structure with a constant magnetic field. In the presence of invariance
breaking gradients the resultant Stokes profiles are represented
only approximately, if at all, by analytic forms. The accuracy of
the inversion parameters and their significance as measures of actual
structure are explored for the ME and the Landman-Finn sunspot models
under the effects of velocity gradients. The resulting field parameters
are good to a few percent and prove to be insensitive to the errors
committed by the use of a ME-representation, but the resulting ME
parameters yield a less precise measure of thermal structure.
---------------------------------------------------------
Title: Umbral Oscillations: Correlation of Amplitudes Between Two
Chromospheric Heights
Authors: Lites, B. W.
1985BAAS...17R.631L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sunspot Umbral Oscillations in the Photosphere and Low
Chromosphere
Authors: Thomas, J. H.; Lites, B. W.
1985BAAS...17..631T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Description and operation of CHISQMO, INVRTS, VOIGEN, VOIGTV,
SMEAR, RUFF, AND POSCAR in the Stokes Analysis Program
Authors: Lites, B. W.; Skumanich, A.
1985STIN...8530991L Altcode:
Some details of the computer program used to carry out the least-squares
inversion of polarization profiles obtained with the HAO (High Altitude
Observatory) Stokes Polarimeters I and II are documented. Improvements
to the computer code originated by Auer, Heasley, and House (1977)
include: magneto-optical effects, line damping, scattered light
correction, instrumental broadening, and allowing the line center
position to be a free parameter. The entire program has not been
documented here, since various aspects of the program are still being
revised and improved.
---------------------------------------------------------
Title: On The Broad-Band Circular Polarization Signature of Sunspots
Authors: Skumanich, A.; Lites, B. W.
1985BAAS...17R.631S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Steady flows in active regions observed with the He I 10830
Å line.
Authors: Lites, B. W.; Keil, S. L.; Scharmer, G. B.; Wyller, A. A.
1985cdm..proc..287L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Least squares inversion of Stokes profiles in the presence
of velocity gradients.
Authors: Skumanich, A.; Rees, D. E.; Lites, B. W.
1985NASCP2374..306S Altcode:
The authors study the performance of the least squares fit when
applied to theoretical profiles calculated with a realistic model of a
sunspot. The model has gradients in all physical parameters including
magnetic and velocity fields. This numerical experiment allows one
to assess the physical significance of the Milne-Eddington and mean
field parameters provided by the inversion. Observed Stokes profiles
invariably have asymmetric distortions due to velocity gradients in
the solar atmosphere. The inversion method symmetrizes the profiles
prior to fitting and it is important to know how this affects the
inference on the magnetic vector.
---------------------------------------------------------
Title: Chromospheric diagnostics and modelling; Proceedings of the
Conference, Sunspot, NM, August 13-16, 1984
Authors: Lites, B. W.
1985cdm..proc.....L Altcode:
The conference presents papers on the observed structure of the
chromosphere, recent thermal models and modeling techniques,
chromospheric magnetic field structure, chromospheric heating and
dynamics, and new and proposed observational diagnostics. Attention is
focused on HRTS observations of the solar chromosphere and transition
zone, an interpretation of H-alpha observations of chromospheric
fine structure, an inhomogeneous model of the chromosphere, Ca II K
resonance line polarization, magnetic canopies and models of the solar
chromosphere, and mechanisms for chromospheric heating. Other topics
include the dynamical behavior of a theoretical chromosphere model,
Alfvenic heating of the chromosphere and corona, cool plasma at the
base of the solar chromosphere revealed by infrared bands of carbon
monoxide, and Ayres' bifurcated solar model.
---------------------------------------------------------
Title: Radiative transfer diagnostics: Understanding multi-level
transfer calculations.
Authors: Skumanich, A.; Lites, B. W.
1985ASIC..152..175S Altcode: 1985pssl.proc..175S
The authors present a method of interpreting the solution to a
multi-level, multi-transition non-LTE transfer problem. The method
respresents the solutions in terms of equivalent two-level forms with
a scattering and a source term. The resulting individual quenching
probability, i.e. the difference of the scattering albedo from one,
and source term are then decomposed by a perturbation method into
their principal dependence on collisional and/or radiative rates. The
method is illustrated by considering the excitation and ionization of
hydrogen in the VAL 3C model of the quiet sun chromosphere.
---------------------------------------------------------
Title: The inference of vector magnetic fields from polarization
measurements with limited spectral resolution.
Authors: Lites, B. W.; Skumanich, A.
1985NASCP2374..342L Altcode:
The authors present a method for recovery of the vector magnetic
field and thermodynamic parameters from polarization measurements of
photospheric line profiles measured with filtergraphs.
---------------------------------------------------------
Title: The effect of line damping, magneto-optics and parasitic
light on thederivation of sunspot vector magnetic fields.
Authors: Skumanich, A.; Lites, B. W.
1985NASCP2374..341S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Future directions for the theory of radiative transfer in
chromospheric structures.
Authors: Lites, B. W.
1985MPARp.212..273L Altcode:
The treatment of the theory of radiative transfer as applied to both
modelling of the chromosphere and analysis of chromospheric spectra is
reviewed. Topics for continued research are discussed, with emphasis
on understanding the physics of the chromospheric phenomenon. Special
attention is paid to theoretical developments that may be clarified
by observations gathered by the Solar Optical Telescope.
---------------------------------------------------------
Title: Observational aspects of sunspot oscillations.
Authors: Lites, B. W.
1984ESASP.220..207L Altcode: 1984ESPM....4..207L
Several new observational results of oscillations in sunspots are
presented. Observations of umbral oscillations in Ca II H and He I 10830
Å show that they have high amplitude in the upper chromosphere. The
umbral oscillations have several co-spatial frequency modes.
---------------------------------------------------------
Title: The H<SUP>−</SUP> equilibrium using coupled rate
equations for H<SUP>−</SUP>, H, H<SUP>+</SUP>, H<SUB>2</SUB>,
and H<SUB>2</SUB><SUP>+</SUP>
Authors: Lites, B. W.; Mihalas, D.
1984SoPh...93...23L Altcode:
We formulate rate equations for the reaction network
coupling H, H<SUP>−</SUP>, H<SUP>+</SUP>, H<SUB>2</SUB>, and
H<SUB>2</SUB><SUP>+</SUP>. We attempt to systematize the notation,
and to write the equations in a form suitable for modern computational
methods of handling the coupled rate equations and radiative transfer
equations, for both dynamical and static atmospheres. We have accounted
for more processes than are generally considered in most current work;
some of these may have an impact on the equilibrium of H<SUP>−</SUP>
(hence its opacity) and on charge conservation (hence the proton
density) in the atmospheres of solar-type stars.
---------------------------------------------------------
Title: Photoelectric observations of chromospheric sunspot
oscillations. II - Propagation characteristics
Authors: Lites, B. W.
1984ApJ...277..874L Altcode:
Measurements of oscillations in umbrae and penumbrae using the line
pairs (Ca II lambda 8498 - lambda 8542) and (Fe I lambda 5434 - Ca
II lambda 8498) are presented for seven sunspots and 11 observing
runs. In the umbral chromosphere, the observations reported here,
taken with other measurements of umbral oscillations, suggest that
the oscillations are upward propagating acoustic (or slow mode)
disturbances, and that they become nonlinear and develop into shock
waves in the upper layers. They cause a significant increase in the
radiative output of the umbral chromosphere, indicating the possibility
of nonthermal heating at these levels. On the basis of this picture,
umbral chromospheres have a greater physical extent in height than
predicted by umbral models with coronal pressures greater than those
found in the quiet sun. Oscillations are present in the outer regions
of penumbrae with frequencies and phase relationships that suggest
the possibility of magneto-gravity waves.
---------------------------------------------------------
Title: The Color Temperature of a Sunspot Penumbra
Authors: Lites, B. W.
1984SoPh...90....1L Altcode:
The new Multi-Diode Array and the recently modified Universal
Birefringent Filter were used at the Vacuum Tower Telescope at the
Sacramento Peak National Observatory to measure the continuum color
temperature of a sunspot penumbra between 428.4 and 667.6 nm. The
results show that the color temperatures within the penumbral structures
closely follow a measure of the wavelength average of the brightness
temperature. These observations suggest that, if the dark penumbral
filaments overlie a normal quiet photosphere, they are opaque to the
radiation from below.
---------------------------------------------------------
Title: Oscillations in a Sunspot and the Surrounding Photosphere
Authors: Abdelatif, T. E.; Lites, B. W.; Thomas, J. H.
1984ssdp.conf..141A Altcode:
Velocity oscillations at photospheric heights in a sunspot and its
surroundings have been measured. The average temporal power spectrum of
oscillations in the sunspot umbra shows the five-minute oscillations
splitting into several distinct modes and also shows the existence
of the three-minute umbral oscillation at photospheric heights, with
greater kinetic energy density than in the chromosphere.
---------------------------------------------------------
Title: A Diagnostic for the Distribution of Medium to Small-Scale
Chromospheric Motions
Authors: Lites, B. W.
1984ssdp.conf..157L Altcode:
The shapes of the line cores of self-reversed optically-thick
chromospheric lines provide a sensitive measure of chromospheric macro-
and microturbulence.
---------------------------------------------------------
Title: An Estimation of the Fluctuations in the Extreme Limb of
the Sun
Authors: Lites, B. W.
1983SoPh...85..193L Altcode:
Detailed computations of synthetic solar limb curves are carried out for
the purpose of estimating the effects of inhomogeneities in the solar
atmosphere upon the observed limb position. Methods of determining
the limb position given a solar limb curve are compared. The method
of finding the locus of a fixed intensity level with respect to the
average disk-center intensity at a given wavelength seems to be the
most tractable definition to use on noise free data. It is found that
limb fluctuations due to the solar 5-min p-mode oscillations produce a
fluctuation in the limb height of about 6 km (0.008 arc sec) rms. Limb
fluctuations due to granulation and chromospheric structure are much
smaller. The wavelength dependence of the solar H<SUP>−</SUP> opacity
causes the height of the limb to increase by about 35 km between 400
and 850 nm, thus leading to a `limb reddening' at the extreme limb of
the Sun.
---------------------------------------------------------
Title: Oscillations in Sunspots and the Surrounding Photosphere
Authors: Abdelatif, T.; Lites, B. W.; Thomas, J. H.
1983BAAS...15R.719A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A model of a sunspot chromosphere based on OSO 8 observations
Authors: Lites, B. W.; Skumanich, A.
1982ApJS...49..293L Altcode:
OSO 8 spectrometer observations of the H I, Mg II, and Ca II resonance
lines of a large quiet sunspot during November 16-17, 1975, along with
a C IV line of that event obtained by a ground-based spectrometer,
are analyzed together with near-simultaneous ground-based Stokes
measurements to yield an umbral chromosphere and transition region
model. Features of this model include a chromosphere that is effectively
thin in the resonance lines of H I and Mg II, while being saturated
in Ca II, and an upper chromospheric structure similar to that of
quiet-sun models. The similarity of the upper chromosphere of the
sunspot umbra to the quiet-sun chromosphere suggests that the intense
magnetic field plays only a passive role in the chromospheric heating
mechanism, and the observations cited indicate that solar-type stars
with large areas of ordered magnetic flux would not necessarily exhibit
extremely active chromosphere.
---------------------------------------------------------
Title: The vertical propagation of waves in the solar atmosphere. II
Phase delays in the quiet chromosphere and cell-network distinctions
Authors: Lites, B. W.; Chipman, E. G.; White, O. R.
1982ApJ...253..367L Altcode:
The differences in the phase of the velocity oscillations between
a pair of chromospheric Ca II lines was measured using the Vacuum
Tower Telescope at the Sacramento Peak Observatory. The observed phase
differences indicate that the acoustic modes are trapped or envanescent,
rather than propagating, in the chromosphere. Systematic distinctions
are found in the phase delays between quiet network and cell interior
regions for both intensity and velocity oscillations in photospheric and
chromospheric lines. The theory of linear perturbations in an isothermal
atmosphere is invoked to interpret these differences. From this analysis
it is found that one or more of the following explanations is possible:
(1) the radiative damping is more effective in the network than in the
cell interior; (2) the network features exclude oscillations of large
horizontal wavenumber; or (3) the scale height of the chromosphere is
larger in the network than in the cell interior.
---------------------------------------------------------
Title: Photoelectric observations of propagating sunspot oscillations
Authors: Lites, B. W.; White, O. R.; Packman, D.
1982ApJ...253..386L Altcode:
Repeated intensity and velocity images of a large, isolated sunspot in
both the chromospheric Ca II 8542 A and photospheric Fe I 5576 line were
performed. It is shown by means of a movie of the digital data for the
chromospheric line that a relationship exists between the propagating
umbral disturbances and the running penumbral waves. Power spectra of
the oscillations show a sharp peak at a period of about 170 sec in both
the velocity and intensity signals, and the oscillations at any point
in the sunspot are found to be very regular. The phase relationship
between the velocity and the intensity of the chromospheric oscillations
contrasts with that for the quiet sun. The mechanical energy flux
carried by the observed umbral disturbances does not appear to be a
significant contributor to the overall energy budget of the sunspot
or the surrounding active region.
---------------------------------------------------------
Title: Transition-Zone Observations of Rapid Flare Events as Observed
by OSO-8
Authors: Lites, B. W.
1981SoPh...71..329L Altcode:
The rapid dissipation of flare energy has been observed in the
transition-zone line of C IV at 1548.2 Å using the University of
Colorado spectrometer aboard OSO-8. Impulsive brightenings have been
resolved with characteristic risetimes as low as 3.5 s. One event
is analyzed in detail, in which it is inferred that the electron
density is greater than 2 × 10<SUP>11</SUP> cm<SUP>−3</SUP> at T =
60 000 K, and that the flare energy is deposited at a rate of 2 ergs
cm<SUP>−3</SUP> s<SUP>−1</SUP> or greater. The temporal behavior
of the intensity at the center of the C IV line is consistent with a
non-equilibrium ionization of C III through C V. If this event is a
result of the multiple tearing mode instability as the primary energy
release mechanism, then the observations indicate a pre-flare magnetic
field of about 175 G.
---------------------------------------------------------
Title: A Search for Microwave Counterparts of Umbral Flashes
Authors: McConnell, D.; Kundu, M. R.; Schmahl, E. J.; Lites, B.
1981BAAS...13..858M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observation of Vertical Phase Delays of Chromospheric
Oscillations Above Sunspot Umbrae
Authors: Lites, B. W.
1981BAAS...13..909L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: OSO-8 Observations of the Impulsive Phase of Solar Flares in
the Transition Zone and Corona
Authors: Lites, B. W.; Bruner, E. C., Jr.; Wolfson, C. J.
1981SoPh...69..373L Altcode:
Several solar flares have been observed from their onset in C IV λ
1548.2 and 1-8 Å X-rays using instruments aboard OSO-8. In addition,
microwave and Hα flare patrol data have been obtained for this
study. The impulsive brightening in C IV is frequently accompanied
by redshifts, interpreted as downflows, of the order of 80 km
s<SUP>-1</SUP>. The maximum soft X-ray intensity usually arrives several
minutes after the maximum C IV intensity. The most energetic C IV event
studied shows a small blueshift just before reaching maximum intensity,
and estimates of the mass flux associated with this upflow through
the transition-zone are consistent with the increase of mass in the
coronal loops as observed in soft X-rays. This event had no observable
microwave burst, suggesting that electron beams did not play a major
role in the chromospheric and transition-zone excitation. Lastly, our
observations suggest that the frequent occurrence of violent dynamical
processes at the onset of the flare are associated with the initial
energy release mechanism.
---------------------------------------------------------
Title: An empirical view of the chromospheric temperature structure
above a sunspot umbra
Authors: Lites, B. W.; Skumanich, A.
1981phss.conf..152L Altcode:
OSO-8 observations of the chromospheric and transition region emission
lines are used to develop a temperature-based model of the chromosphere
above a sunspot. The data base included observations of Lyman-alpha,
Lyman-beta, the resonance lines of singly-ionized Mg, and the resonance
lines of singly-ionized Ca. Details of the line profiles are provided,
and features of the derived plateau model of the chromosphere are
discussed. Weak reversals and broad wings in the observed Ca II lines
were accounted for by assuming a 5 km/sec broadening, thus implying
greater significance for the Ca II/Mg II, K/H, and k/h intensity
ratios than details of the line profile shapes. The L-alpha and L-beta
intensities are noted to constrain the upper chromosphere and transition
region pressure to lower values than in the average quiet solar corona.
---------------------------------------------------------
Title: Steady Flows in the Chromosphere and Transition-Zone above
Active Regions as Observed by OSO-8
Authors: Lites, B. W.
1980SoPh...68..327L Altcode:
Two years of data from the University of Colorado ultraviolet
spectrometer aboard OSO-8 were searched for steady line-of-sight flows
in the chromosphere and transition-zone above active regions. The
most conspicuous pattern that emerges from this data set is that
many sunspots show persistent blueshifts of transition-zone lines
indicating velocities of about 20 km s<SUP>−1</SUP> with respect
to the surrounding plage areas. The data show much smaller shifts in
ultraviolet emission lines arising from the chromosphere: the shifts
are frequently to the blue, but sometimes redshifts do occur. Plage
areas often show a redshift of the transition-zone lines relative to
the surrounding quiet areas, and a strong gradient of the vertical
component of the velocity is evident in many plages. One area of
persistent blueshift was observed in the transition-zone above an
active region filament. The energy requirement of these steady flows
over sunspots is discussed.
---------------------------------------------------------
Title: On the formation of Fe II lines in stellar spectra. I. Solar
spatial intensity variation of lambda 3969.4.
Authors: Cram, L. E.; Rutten, R. J.; Lites, B. W.
1980ApJ...241..374C Altcode:
High-spatial-resolution solar observations of the weak Fe II lambda
3969.4 line are employed to study non-local thermodynamic equilibrium
effects in Fe II line formation. This line is superposed on the wing
of the Ca II H line, which raises its height of formation. The line
shows extraordinary spatial intensity variations, including emission
features whose contrast increases toward the limb. Observed profiles
of the Fe II resonance lines in the UV are used to define formation
parameters in a 15-level atomic model computation, which shows that Fe
II subordinate lines are generally formed out of local thermodynamic
equilibrium as a result of pumping by UV line-wing photons from the
deep photosphere. For the lambda 3969.4 line, this pumping results in
large sensitivity to the atmospheric structure in layers deeper than
the layer of formation of the H-wing background intensity. The absence
of intense emission cores in the Fe II resonance lines, the effects
of partially coherent scattering, and the effects of chromospheric and
photospheric inhomogeneities are discussed. It is found that emission
of lambda 3969.4 provides a diagnostic of the inhomogeneous structure
of the deep photosphere, for the sun and for late-type stars.
---------------------------------------------------------
Title: Photoelectric Observations of Propagating Sunspot Oscillations
Authors: Lites, B. W.; White, O. R.; Packman, D.
1980BAAS...12..897L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: OSO-8 Observations of the Sunspot Chromosphere
Authors: Skumanich, A.; Lites, B. W.
1980BAAS...12..896S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impulsive EUV bursts observed in C iv with OSO-8
Authors: Athay, R. G.; White, O. R.; Lites, B. W.; Bruner, E. C., Jr.
1980SoPh...66..357A Altcode:
Time sequences of profiles of the λ1548 line of C IV containing 51 EUV
bursts observed in or near active regions are analyzed to determine the
brightness, Doppler shift and line broadening characteristics of the
bursts. The bursts have mean lifetimes of approximately 150s, and mean
increases in brightness at burst maximum of four-fold as observed with a
field of view of 2″ × 20″. Mean burst diameters are estimated to be
3″, or smaller. All but three of the bursts show Doppler shifts with
velocities sometimes exceeding 75 km s<SUP>−1</SUP>; 31 are dominated
by red shifts and 17 are dominated by blue shifts. Approximately
half of the latter group have red-shifted precursors. We interpret
the bursts as prominence material, such as surges and coronal rain,
moving through the field of view of the spectrometer.
---------------------------------------------------------
Title: Transition-Zone Observations of Rapid Flare Events As Observed
by OSO-8
Authors: Lites, B. W.
1980BAAS...12..479L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Line formation in the solar chromosphere. II - an optically
thick region of the chromosphere-corona transition region observed
with OSO 8
Authors: Lites, B. W.; Hansen, E. R.; Shine, R. A.
1980ApJ...236..280L Altcode:
The University of Colorado ultraviolet spectrometer aboard the Orbiting
Solar Observatory 8(OSO 8) has measured self-reversed profiles of the
resonance line of C IV lamda 1548.2 at the limb passage of an active
region. The degree of the self-reversal together with the absolute
intensity of the line profile determine the electron density in the
active region at 10 to the 10th/cu cm at temperatures where the C IV
line is formed. The nonthermal component of the broadening velocity
is no more than 14km/s, and the physical thickness of an equivalent
plane-parallel slab in hydrostatic equilibrium that would give rise
to the observed line profiles is about 430 km.
---------------------------------------------------------
Title: The chromosphere and transition region
Authors: Canfield, R. C.; Brown, J. C.; Craig, I. J. D.; Brueckner,
G. E.; Cook, J. W.; Doschek, G. A.; Emslie, A. G.; Machado, M. E.;
Henoux, J. -C.; Lites, B. W.
1980sfsl.work..231C Altcode: 1980sofl.symp..231C
The physical processes occurring as a result of the transfer of
energy and momentum from the primary solar flare energy release site
in the corona to the underlying chromosphere and transition region
during the course of the flare are investigated through a comparison
of theoretical models and observational data. Static, dynamic and
hydrodynamic models of the lower-temperature chromospheric flare are
reviewed. The roles of thermal conduction, radiation, fast particles
and mass motion in chromosphere-corona interactions are analyzed on
the basis of Skylab UV, EUV and X-ray data, and empirical and synthetic
models of the chromospheric and upper photospheric responses to flares
are developed. The canonical model of chromospheric heating during
flares as a result of primary energy release elsewhere is found to be
justified in the chromosphere as a whole, although not entirely as the
temperature minimum, and a simplified model of horizontal chromospheric
flare structure based on results obtained is presented.
---------------------------------------------------------
Title: Transition region chromospheric models of 24 UMa based on
IUE ultraviolet spectrograms.
Authors: Simon, T.; Stencel, R. E.; Lites, B. W.
1980PASP...92R.550S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Diagnostic Use of Feii H and K Wing Emission Lines
Authors: Cram, L. E.; Rutten, R. J.; Lites, B. W.
1980LNP...114..102C Altcode: 1980IAUCo..51..102C; 1980sttu.coll..102C
No abstract at ADS
---------------------------------------------------------
Title: The vertical propagation of waves in the solar
atmosphere. I. Observations of phase delay.
Authors: Lites, B. W.; Chipman, E. G.
1979ApJ...231..570L Altcode:
The Sacramento Peak Observatory Tower Vacuum Telescope, echelle
spectrograph, and diode array were used to simultaneously measure
velocities and intensities in three spectral lines and the
continuum. According to our contribution function calculations,
these wavelengths are formed at heights from the low photosphere to
the chromosphere. The phase velocities of the intensity and velocity
oscillations between the various heights, and the phase relations
between intensity and velocity at one height were determined as a
function of frequency in the range 0-11.1 mHz. The oscillations are
found to be predominantly evanescent in nature for frequencies less
than 4 mHz and propagating upward at higher frequencies, with phase
velocities approaching the sound speed at approximately 6 mHz. We
calculated the upward mechanical flux in the observed waves at two
atmospheric heights by an integration in frequency, and we show that
in the chromosphere the propagated power is centered at 6 mHz but is
still much too small to heat the overlying atmosphere.
---------------------------------------------------------
Title: A semiempirical model of the upper flare chromosphere.
Authors: Lites, B. W.; Cook, J. W.
1979ApJ...228..598L Altcode:
Ultraviolet spectra of the August 9, 1973, flare taken with the NRL
S082B spectrograph aboard ATM/Skylab have been analyzed to derive
a semiempirical model of the flare chromosphere between 5500 and
100,000 K. The hydrogen radiative transfer is solved to obtain a
self-consistent set of physical conditions within the flare atmosphere,
from which line profiles and continua of the ions C I, C II, C III,
and C IV are synthesized and compared with the observations. The model
exhibits a rapid rise in the temperature at a column mass of 0.0003
g/sq cm. There is some evidence for much of the C III line emission's
arising from flare kernels not exceeding 3 arcsec in size, and the C
IV line profiles indicate the possibility of nonequilibrium excitation.
---------------------------------------------------------
Title: Frequency Shift of Solar Oscillations in a Flaring Region
Authors: Illing, R. M. E.; Lites, B. W.
1979BAAS...11..398I Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Mass motions in impulsive flarelike brightenings as observed
by OSO 8.
Authors: Bruner, E. C., Jr.; Lites, B. W.
1979ApJ...228..322B Altcode:
C IV 1548-A line profiles obtained with the University of Colorado
spectrometer aboard OSO 8 reveal transient, redshifted brightenings
in the chromosphere-corona transition region above active regions and
sunspots. In these events the intensity rises by factors of up to 5
in less than the profile sampling interval of 27 sec. These events
indicate that the emitting material is moving downward at velocities
of up to 30 km/sec. The increase in line intensity and the amount
of motion are consistent with the interpretation of these events as
pressure waves propagating down magnetic flux loops.
---------------------------------------------------------
Title: Overlapping emission peaks in the solar C I multiplet at
lambda 1560 and lambda 1657.
Authors: Shine, R. A.; Lites, B. W.; Chipman, E. G.
1978ApJ...224..247S Altcode:
Observations of the C I multiplets at 1560 and 1657 A made with the
University of Colorado spectrometer on the OSO 8 satellite are presented
and compared with computed profiles for the Vernazza-Avrett-Loeser
solar atmosphere. These are optically thick emission lines formed in
the solar chromosphere that show the central reversals typical of such
lines. In each multiplet there is an interesting case of overlapping
emission peaks which shows that such peaks do not constructively combine
but instead weaken. This behavior is easily understood and reproduced
with an optically thick, non-LTE mode of formation for these lines and
is not consistent with an optically thin mechanism. We also find that
the shapes of these blends are very sensitive to the magnitude of the
nonthermal microvelocities.
---------------------------------------------------------
Title: Line formation in the solar chromosphere. I. The C II resonance
lines observed with OSO 8.
Authors: Lites, B. W.; Shine, R. A.; Chipman, E. G.
1978ApJ...222..333L Altcode:
The temperature structure of the upper chromosphere is investigated
using center-to-limb measurements of the C II resonance lines at 1335
A from the University of Colorado spectrometer aboard OSO 8. Spectrum
synthesis of these lines shows them to be extremely sensitive to the
temperature and the physical extent of the 20,000 K plateau proposed
by Vernazza et al (1973). Hydrostatic equilibrium models of the quiet
chromosphere are computed to obtain theoretical spectra of the Lyman
lines and continuum as well as the center-to-limb behavior of the C
II lines. Good agreement is found with observations for a plateau at
16,500 K with about 25% more material than that of Vernazza et al.
---------------------------------------------------------
Title: OSO-8 Measurements of Rapid Downflow in the Transition Zone
During the Impulsive Phase of Solar Flares.
Authors: Lites, B. W.; Bruner, E. C.; Hansen, E. R.
1978BAAS...10..441L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observations of Phase Delays and the Vertical Propagation of
Waves in the Solar Atmosphere.
Authors: Lites, B. W.; Chipman, E. G.
1978BAAS...10..415L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Ultraviolet brightenings in active regions as observed
from OSO-8.
Authors: Lites, B. W.; Hansen, E. R.
1977SoPh...55..347L Altcode:
Repeated raster images of solar active regions taken at the line centers
of the Si IV and C IV resonance lines using the University of Colorado
(CU) ultraviolet spectrometer aboard OSO-8 reveal dramatic transient
brightenings of up to factors of 10. These brightenings last several
minutes and frequently show a repetitive character. Inspection of
simultaneous Hα flare patrol records show that these transition zone
events are often associated with subflare-like brightenings in the
chromosphere. These observations indicate that direct excitation or
heating of material already at transition zone temperatures caused by
non-thermal particle streams is inadequate to explain the degree of
brightening of these lines. The measurements suggest that some process
that enhances density of material at ∼10<SUP>5</SUP> K is occurring
during these events.
---------------------------------------------------------
Title: Center-to-Limb Profiles and Spatial Variations of SiII and
FeII Lines in the Solar EUV.
Authors: Shine, R. A.; Lites, B. W.
1977BAAS....9R.325S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transient Brightenings in Transition Zone Lines.
Authors: Bruner, E. C., Jr.; Lites, B. W.
1977BAAS....9Q.323B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Preliminary results from the Orbiting Solar Observatory 8:
transition-zone dynamics over a sunspot.
Authors: Bruner, E. C., Jr.; Chipman, E. G.; Lites, B. W.; Rottman,
G. J.; Shine, R. A.; Athay, R. G.; White, O. R.
1976ApJ...210L..97B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Preliminary results from the Orbiting Solar Observatory 8:
velocities in the solar chromosphere observed in the Si II lambda
1816 line.
Authors: Chipman, E. G.; Bruner, E. C., Jr.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; Athay, R. G.; White, O. R.
1976ApJ...210L.103C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Preliminary results from the Orbiting Solar Observatory 8:
observations of optically thin lines.
Authors: Shine, R. A.; Roussel-Dupre, D.; Bruner, E. C., Jr.; Chipman,
E. G.; Lites, B. W.; Rottman, G. J.; Athay, R. G.; White, O. R.
1976ApJ...210L.107S Altcode:
The University of Colorado spectrometer aboard OSO 8 has measured
the high temperature C IV resonance lines (at 1548 and 1551 A) and
the Si IV resonance lines (at 1393 and 1402 A) formed in the solar
chromosphere-corona transition region. Preliminary results include
studies of mean profiles, a comparison of cell and network profiles,
and the behavior of the lines at the extreme solar limb.
---------------------------------------------------------
Title: Preliminary results from the Orbiting Solar Observatory 8:
persistent velocity fields in the chromosphere and transition region.
Authors: Lites, B. W.; Bruner, E. C., Jr.; Chipman, E. G.; Shine,
R. A.; Rottman, G. J.; White, O. R.; Athay, R. G.
1976ApJ...210L.111L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Analysis of OSO-8 Measurements of the Center-to-Limb Behavior
of Solar CII Line Profiles.
Authors: Lites, B. W.; Shine, R. A.
1976BAAS....8..501L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Periodic Fluctuations in the Solar Transition Zone
Authors: Bruner, E. C., Jr.; Chipman, E. G.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; Orrall, F. Q.; Athay, R. G.; White, O. R.
1976BAAS....8Q.313B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Model Calculations of Chromospheric Lines Observed by OSO-8
Authors: Shine, R. A.; Lites, B. W.; Chipman, E. G.; Rousel-Dupree,
D.; Bruner, E. C., Jr.; Rottman, G. J.; Orrall, F. Q.; Athay, R. G.;
White, O. R.
1976BAAS....8..331S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Velocities in the Solar Chromosphere Observed in the CII
λ1336 Line
Authors: Chipman, E. G.; Bruner, E. C., Jr.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; Orrall, F. Q.; White, O. R.; Athay, R. G.
1976BAAS....8..312C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: OSO-8 Observations of Mean Vertical Motions in the Solar
Transition Region
Authors: Roussel-Dupree, D. C.; Shine, R. A.; Chipman, E. G.; Bruner,
E. C., Jr.; Lites, B. W.; Rottman, G. J.; Orrall, F. Q.; Athay, R. G.;
White, O. R.
1976BAAS....8..312R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Short Period Chromospheric Oscillations Observed with OSO-8
Authors: Athay, R. G.; White, O. R.; Bruner, E. C., Jr.; Chipman,
E. G.; Lites, B. W.; Shine, R. A.; Orrall, F. Q.
1976BAAS....8..312A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Supergranulation Velocity Fields Observed in the Solar
Transition Region with OSO-8
Authors: November, L. J.; Toomre, J.; Gebbie, K. B.; Simon, G. W.;
Bruner, E. C., Jr.; Chipman, E. G.; Lites, B. W.; Shine, R. A.;
Orrall, F. Q.; Athay, R. G.; White, O. R.
1976BAAS....8..311N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Repetitive Brightenings in Active Region Transition Zone
Lines as Observed with OSO-8
Authors: Lites, B. W.; Hansen, E. R.; Shine, R. A.; Chipman, E. G.;
Bruner, E. C., Jr.; Orrall, F. Q.; Athay, R. G.; White, O. R.; Rottman,
G. J.
1976BAAS....8Q.331L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High Resolution Spectroscopy From Orbiting Solar Observatory
VIII: Transition Zone Dynamics Over a Sunspot
Authors: Bruner, E. C., Jr.; Chipman, E. G.; Lites, B. W.; Rottman,
G. J.; Shine, R. A.; Athay, R. G.; White, O. R.
1975BAAS....7..522B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Persistent Velocity Fields in the Middle Chromosphere
Authors: Lites, B. W.; Bruner, E. C., Jr.; Chipman, E. G.; Shine,
R. A.; Rottman, G. J.; White, O. R.; Athay, R. G.
1975BAAS....7..522L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Velocities in the Solar Chromosphere Observed in the Si II
λ1816 Line
Authors: Chipman, E. G.; Bruner, E. C., Jr.; Shine, R. A.; Lites,
B. W.; Rottman, G. J.; White, O. R.; Athay, R. G.
1975BAAS....7..522C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: OSO-8 Observations of Optically Thin Lines
Authors: Shine, R. A.; Rousell-Dupree, D.; Bruner, E. C., Jr.; Chipman,
E. G.; Lites, B. W.; Rottman, G. J.; Athay, R. G.; White, O. R.
1975BAAS....7Q.552S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Solar Fen 2L 3969. 4 Disk Emission Line
Authors: Lites, B. W.
1974A&A....33..363L Altcode:
Summary. The recent identification by Engvold and Halvorsen (1973)
of the solar Fe II emission feature at 3969.40 is confirmed through
line profile synthesis from kinetic equilibrium computations. In
sharp contrast to the photospheric origin of the emission in rare
earth lines in the H and K line wings, the Fe ii line emission appears
to be of chromospheric origin. It is suggested that this line could
be used as another indicator of conditions in the low chromosphere,
for example in plage regions near the limb. Key words: solar emission
lines - chromosphere - solar iron
---------------------------------------------------------
Title: Fe I line formation in solar-type giants and dwarfs.
Authors: Lites, B. W.; Cowley, C. R.
1974A&A....31..361L Altcode:
Summary. The formation of Fe ilines is investigated in stellar models
of solar Teff but surface gravities ranging fr6m log g =4 to log g
=2. The results of these kinetic equilibrium computations demonstrate
that the departures from LTE in the Fe I lines generally cause only
small differences from equivalent widths computed under the LTE
assumption. Thus one does not expect large errors in iron abundance
determinations to arise in stars of these types from the neglect of
departures from LTE. The Fe I line formation in stars of extremely low
metal abundances indicates that departures from LTE in the Fe i-Fe ii
ionization balance could cause an iron abundance based upon the Saha
equilibrium to underestimate the true abundance by a maximum of about
40 %. This study provides no evidence that departures from LTE in Fe I
lines could account for the increase in measured microturbulence from
solartype dwarf to supergiant stars as determined by curveof-growth
studies. However, moderate strength Fe I lines may be strongly affected
by damping, and the failure to recognize this may lead to overestimates
in curve-of-growth microturbulences. Key words: stellar iron abundances
- line formation
---------------------------------------------------------
Title: The Influence of Blends upon the Formation of Spectral Lines
Authors: Lites, B. W.
1974A&A....30..297L Altcode:
Summary. The effect of blending of normal stellar absorption lines
is investigated in order to determine the error introduced when such
blending is neglected in line transfer calculations. Solutions of the
radiative transfer equations in some typical blended solar absorption
lines demonstrate that, in cases where the line under consideration
has only weaker blends confined to wavelengths outside the immediate
line core, the neglect of the blending in the radiative transfer
computations is indeed a valid approximation. Key words: radiative
transfer - line formation - blends
---------------------------------------------------------
Title: The Solar Neutral Iron Spectrum. II: Profile Synthesis of
Representative Fe I Fraunhofer Lines
Authors: Lites, Bruce W.
1973SoPh...32..283L Altcode:
The profiles of eighteen neutral iron lines of varying strengths were
synthesized from disk center to the limb using source functions from
detailed statistical equilibrium calculations. Emphasis is placed upon
the analysis of the strong Fe I lines between 3500 Å and 4500 Å which
are formed at and below the region of the initial temperature rise in
the chromosphere. The major results are as follows: (1) We find an
iron abundance of 1.5 × 1<SUP>−5</SUP> relative to hydrogen (7.2
on a logarithmic scale with hydrogen equal to 12) that is independent
of the assumed microturbulence model since it is based upon the far
wing profiles of the strong lines. The far wings are formed in the
photosphere where both the ionization and excitation equilibria are in
detailed balance, so this abundance is directly comparable to other LTE
abundances. (2) The strong line cores indicate that the chromospheric
electron densities in the region of the initial temperature rise are
similar to those derived by Henze (1969) from eclipse observations;
i.e. higher than the HSRA model (Gingerich et al., 1971) by factors
of two to five. We present (3) an anisotropic (angle-dependent)
microturbulent velocity model, and (4) a mean macroturbulent velocity
that aids in fitting the line cores. The formation of the two Fe I
lines λ5232.95 and λ5250.21 is also discussed.
---------------------------------------------------------
Title: The Solar Neutral Iron Spectrum. I: Measurement of Solar Fe
I Line Profiles from Center to Limb
Authors: Lites, Bruce W.; Brault, J. W.
1973SoPh...30..283L Altcode:
Mean profiles of eighteen neutral iron lines of varying strengths were
measured at selected positions from the center of the solar disk to the
limb. These profiles were obtained by rapid photoelectric scanning of
the spectrum with a double-pass spectrometer. The Fe I lines selected
are representative of most of the stronger low-lying transitions in the
neutral iron atom. In addition to the iron lines, this observational
program includes center-to-limb measurements of three Ti II lines and
of the Ca I resonance line λ4226.7. The line profiles are presented
here in graphical form after correction for instrumental effects and
normalization to the local disk center continuum.
---------------------------------------------------------
Title: F i Ionization and Excitation Equilibrium in the Solar
Atmosphere
Authors: Athay, R. Grant; Lites, B. W.
1972ApJ...176..809A Altcode:
Computations for a 15-level model Fe I atom in the solar atmosphere
indicate that many of the Fe I spectral lines are strongly influenced
by departures from LTE. The strong lines originating from the ground
term and low-lying metastable terms have a strong chromospheric
contribution. Although for many of the lines the source functions
saturate to the Planck function near the temperature minimum
(τ_5000 ≈ 10<SUP>-4</SUP>) and lower, the ionization equilibrium
does not saturate to the Saha condition until τ_5000 > 3 ×
10<SUP>-3</SUP>. The low-lying levels in Fe I reach maximum absolute
populations near τ_5000 = 3 × 10<SUP>-3</SUP>, and lines originating
from these levels tend to be formed at atmospheric depths where τ_5000;
≤ 3 × 10<SUP>-3</SUP>. For high-excitation levels in Fe I, departures
of the line source function from the Planck function extend deeper
into the photosphere and may influence abundances derived from lines
originating from these high lying levels. From the weakness of the
principal Fe II lines in the far-ultraviolet (λ2599, in particular)
relative to lines of Si II and Mg II it is suggested that the Fe II
f-values of Corliss and Bozman are too high by a factor of the order of
10+2. Fe I photoionization from the lowest levels may be a significant
source of opacity in the region 1600-2000 Å.
---------------------------------------------------------
Title: A First Order Analysis of Variations of the Limb Darkening
and the Shapes for Solar Fraunhofer Lilnes
Authors: Athay, R. G.; Lites, B. W.; White, O. R.; Brault, J. W.
1972SoPh...24...18A Altcode:
New center-to-limb measurements in FeI lines show changes in both
the line profiles and the limb darkening curves that appear to be
characteristic of many other solar lines. Here we seek the constraints
placed on the atmospheric model by these effects. We find that in
addition to a depth varying source function we must also allow the
ratio of the continuous absorption coefficient to the total absorption
coefficient to pass through a minimum in the mid-photosphere. Such an
effect is consistent with inward increases of the Doppler width and
damping constant in the upper photosphere and an inward increase of
the ionization for both iron and hydrogen in the low photosphere.
---------------------------------------------------------
Title: FeI Ionization and Excitation Equilibrium in the Solar
Atmosphere.
Authors: Lites, B. W.; Athay, R. G.
1972BAAS....4..212L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observation and Analysis of the Solar Neutral Iron Spectrum.
Authors: Lites, Bruce William
1972PhDT.........7L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Hα Doppler Brightening and Lyman-α Doppler Dimming in Moving
Hα Prominences
Authors: Hyder, Charles L.; Lites, Bruce W.
1970SoPh...14..147H Altcode:
We consider the effect that coherent motion has on the observed
brightness of moving clouds above the photosphere. We find that steady
state clouds (constant N<SUB>e</SUB> and T<SUB>e</SUB>) that are moving
perpendicular to the line of sight will appear brighter in Hα for
speeds between 8 and 100 km/sec and dimmer for speeds greater than 135
km/sec. The brightening and dimming are due to apparent Doppler shifts
of the respective Hα absorption and the Lyman-α emission profiles
`seen' by the absorption profile of the moving cloud.
