explanation      blue bibcodes open ADS page with paths to full text
Author name code: carlsson
ADS astronomy entries on 2022-09-14
author:"Carlsson, Mats" 

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Title: Quiet Sun Center to Limb Variation of the Linear Polarization
    Observed by CLASP2 Across the Mg II h and k Lines
Authors: Rachmeler, L. A.; Bueno, J. Trujillo; McKenzie, D. E.;
   Ishikawa, R.; Auchère, F.; Kobayashi, K.; Kano, R.; Okamoto,
   T. J.; Bethge, C. W.; Song, D.; Ballester, E. Alsina; Belluzzi,
   L.; Pino Alemán, T. del; Ramos, A. Asensio; Yoshida, M.; Shimizu,
   T.; Winebarger, A.; Kobelski, A. R.; Vigil, G. D.; Pontieu, B. De;
   Narukage, N.; Kubo, M.; Sakao, T.; Hara, H.; Suematsu, Y.; Štěpán,
   J.; Carlsson, M.; Leenaarts, J.
2022ApJ...936...67R    Altcode: 2022arXiv220701788R
  The CLASP2 (Chromospheric LAyer Spectro-Polarimeter 2) sounding rocket
  mission was launched on 2019 April 11. CLASP2 measured the four Stokes
  parameters of the Mg II h and k spectral region around 2800 Å along a
  200″ slit at three locations on the solar disk, achieving the first
  spatially and spectrally resolved observations of the solar polarization
  in this near-ultraviolet region. The focus of the work presented here
  is the center-to-limb variation of the linear polarization across these
  resonance lines, which is produced by the scattering of anisotropic
  radiation in the solar atmosphere. The linear polarization signals of
  the Mg II h and k lines are sensitive to the magnetic field from the
  low to the upper chromosphere through the Hanle and magneto-optical
  effects. We compare the observations to theoretical predictions
  from radiative transfer calculations in unmagnetized semiempirical
  models, arguing that magnetic fields and horizontal inhomogeneities
  are needed to explain the observed polarization signals and spatial
  variations. This comparison is an important step in both validating and
  refining our understanding of the physical origin of these polarization
  signatures, and also in paving the way toward future space telescopes
  for probing the magnetic fields of the solar upper atmosphere via
  ultraviolet spectropolarimetry.

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Title: Formation and heating of chromospheric fibrils in a
    radiation-MHD simulation
Authors: Druett, M. K.; Leenaarts, J.; Carlsson, M.; Szydlarski, M.
2022A&A...665A...6D    Altcode: 2021arXiv211208245D
  <BR /> Aims: We examine the movements of mass elements within dense
  fibrils using passive tracer particles (corks) in order to understand
  the creation and destruction processes of fibrils. <BR /> Methods:
  Simulated fibrils were selected at times when they were visible in a
  Hα image proxy. The corks were selected within fibril Hα formation
  regions. From this set, we selected a cork and constructed the field
  line passing through it. Other fibrilar corks close to this field
  line were also selected and pathlines were constructed, revealing the
  locations of the mass elements forwards and backwards in time. Finally,
  we analysed the forces acting on these mass elements. <BR /> Results:
  The main process of fibrilar loading in the simulation is different
  to the mass loading scenario in which waves steepen into shocks and
  push material upwards along the field lines from locations near their
  footpoints. The twisted, low-lying field lines were destabilised
  and then they untwisted, lifting the material trapped above their
  apexes via the Lorentz force. Subsequently, the majority of the mass
  drained down the field lines towards one or both footpoints under the
  influence of gravity. Material with large horizontal velocities could
  also be elevated in rising field lines, creating somewhat parabolic
  motions, but the material was not generally moving upward along a
  stationary magnetic field line during loading. <BR /> Conclusions:
  The processes observed in the simulation are additional scenarios that
  are plausible. The criteria for observing such events are described
  in this work. We note that it is desirable for our simulations to
  also be able to form more densely packed fibrils from material fed
  from the base of field footpoints. The experimental parameters
  required to achieve this are also discussed in this paper. <P
  />Movies associated to Figs. 1, 4, 9, 14 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/202142399/olm">https://www.aanda.org</A>

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Title: Coronal oscillations in the self-consistent 3D MHD simulations
    of the solar atmosphere
Authors: Kohutova, Petra; Antolin, Patrick; Carlsson, Mats; Popovas,
   Andrius
2022cosp...44.2494K    Altcode:
  Solar coronal loops are commonly subject to oscillations. Coronal
  oscillations are typically studied using highly idealised models of
  magnetic flux-tubes. In order to improve our understanding of coronal
  oscillations, it is necessary to consider the effect of realistic
  magnetic field topology and evolution. To do this, we study excitation,
  evolution and damping of coronal oscillations in three-dimensional
  self-consistent simulations of solar atmosphere spanning from convection
  zone to solar corona using the radiation-MHD code Bifrost. We use
  forward-modelled EUV emission and three-dimensional tracing of magnetic
  field to analyse oscillatory behaviour of individual magnetic loops. We
  show that coronal loop oscillations are abundant in such models and
  the oscillation modes and characteristics match those detected in solar
  observations. Finally, we discuss the dynamics and variability of the
  oscillating loops and the implications for coronal seismology.

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Title: Acoustic-gravity wave propagation characteristics in 3D
    radiation hydrodynamic simulations of the solar atmosphere
Authors: Fleck, Bernhard; Khomenko, Elena; Carlsson, Mats; Rempel,
   Matthias; Steiner, Oskar; Riva, Fabio; Vigeesh, Gangadharan
2022cosp...44.2503F    Altcode:
  There has been tremendous progress in the degree of realism of
  three-dimensional radiation magneto-hydrodynamic simulations of the
  solar atmosphere in the past decades. Four of the most frequently
  used numerical codes are Bifrost, CO5BOLD, MANCHA3D, and MURaM. Here
  we test and compare the wave propagation characteristics in model
  runs from these four codes by measuring the dispersion relation
  of acoustic-gravity waves at various heights. We find considerable
  differences between the various models.

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Title: Stirring the Base of the Solar Wind: On Heat Transfer and
    Vortex Formation
Authors: Finley, Adam J.; Brun, Sacha A.; Carlsson, Mats; Szydlarski,
   Mikolaj; Hansteen, Viggo; Shoda, Munehito
2022arXiv220702878F    Altcode:
  Current models of the solar wind must approximate (or ignore) the
  small-scale dynamics within the solar atmosphere, however these are
  likely important in shaping the emerging wave-turbulence spectrum and
  ultimately heating/accelerating the coronal plasma. The Bifrost code
  produces realistic simulations of the solar atmosphere that facilitate
  the analysis of spatial and temporal scales which are currently at,
  or beyond, the limit of modern solar telescopes. For this study, the
  Bifrost simulation is configured to represent the solar atmosphere in
  a coronal hole region, from which the fast solar wind emerges. The
  simulation extends from the upper-convection zone (2.5 Mm below the
  photosphere) to the low-corona (14.5 Mm above the photosphere), with
  a horizontal extent of 24 Mm x 24 Mm. The twisting of the coronal
  magnetic field by photospheric flows, efficiently injects energy
  into the low-corona. Poynting fluxes of up to $2-4$ kWm$^{-2}$ are
  commonly observed inside twisted magnetic structures with diameters
  in the low-corona of 1 - 5 Mm. Torsional Alfvén waves are favourably
  transmitted along these structures, and will subsequently escape into
  the solar wind. However, reflections of these waves from the upper
  boundary condition make it difficult to unambiguously quantify the
  emerging Alfvén wave-energy flux. This study represents a first step
  in quantifying the conditions at the base of the solar wind using
  Bifrost simulations. It is shown that the coronal magnetic field is
  readily braided and twisted by photospheric flows. Temperature and
  density contrasts form between regions with active stirring motions
  and those without. Stronger whirlpool-like flows in the convection,
  concurrent with magnetic concentrations, launch torsional Alfvén waves
  up through the magnetic funnel network, which are expected to enhance
  the turbulent generation of magnetic switchbacks in the solar wind.

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Title: Abundance diagnostics in active regions with Solar
    Orbiter/SPICE
Authors: Giunta, Alessandra; Peter, Hardi; Parenti, Susanna; Buchlin,
   Eric; Thompson, William; Auchere, Frederic; Kucera, Therese; Carlsson,
   Mats; Janvier, Miho; Fludra, Andrzej; Hassler, Donald M.; Grundy,
   Timothy; Sidher, Sunil; Guest, Steve; Leeks, Sarah; Fredvik, Terje;
   Young, Peter
2022cosp...44.2583G    Altcode:
  With the launch of Solar Orbiter in February 2020, we are now able to
  fully explore the link between the solar activity on the Sun and the
  inner heliosphere. Elemental abundance measurements provide a key tracer
  to probe the source regions of the solar wind and to track it from the
  solar surface and corona to the heliosphere. Abundances of elements
  with low first ionisation potential (FIP) are enhanced in the corona
  relative to high-FIP elements, with respect to the photosphere. This is
  known as the FIP effect, which is measured as abundance bias (FIP bias)
  of low and high FIP elements. This effect is vital for understanding the
  flow of mass and energy through the solar atmosphere. The comparison
  between in-situ and remote sensing composition data, coupled with
  modelling, will allow us to trace back the source of heliospheric
  plasma. Solar Orbiter has a unique combination of in-situ and remote
  sensing instruments that will help to make such a comparison. In
  particular, the SPICE (Spectral Imaging of the Coronal Environment)
  EUV spectrometer records spectra in two wavelength bands, 70.4-79.0
  nm and 97.3-104.9 nm. SPICE is designed to provide spectroheliograms
  using a core set of emission lines arising from ions of both low-FIP
  and high-FIP elements such as C, N, O, Ne, Mg, S and Fe. These lines
  are formed over a wide range of temperatures from 20,000 K to over 1
  million K, enabling the analysis of the different layers of the solar
  atmosphere. SPICE spectroheliograms can be processed to produce FIP
  bias maps, which can be compared to in-situ measurements of the solar
  wind composition of the same elements. During the Solar Orbiter Cruise
  Phase, SPICE observed several active regions. We will present some of
  these observations and discuss the SPICE diagnostic potential to derive
  relative abundances (e.g., Mg/Ne) and the FIP bias in those regions.

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Title: The SPICE spectrograph on Solar Orbiter: an introduction and
    results from the first Orbits
Authors: Auchère, Frédéric; Peter, Hardi; Parenti, Susanna; Buchlin,
   Eric; Thompson, William; Auchere, Frederic; Teriaca, Luca; Kucera,
   Therese; Carlsson, Mats; Janvier, Miho; Fludra, Andrzej; Giunta,
   Alessandra; Schuehle, Udo; Hassler, Donald M.; Grundy, Timothy;
   Sidher, Sunil; Fredvik, Terje; Plowman, Joseph; Aznar Cuadrado, Regina
2022cosp...44.1338A    Altcode:
  The Spectral Imaging of the Coronal Environment (SPICE) instrument is
  the EUV imaging spectrometer on board the Solar Orbiter mission. With
  its ability to derive physical properties of the coronal plasma,
  SPICE is a key component of the payload to establish the connection
  between the source regions and the in-situ measurements of the solar
  wind. The spacecraft was successfully launched in February 2020 and
  completed its cruise phase in December 2021. During this period,
  the remote sensing instruments were mostly operated during limited
  periods of time for 'checkout' engineering activities and synoptic
  observations. Nonetheless, several of these periods provided enough
  opportunities already to obtain new insights on coronal physics. During
  the march 2022 perihelion - close to 0.3 AU - SPICE will provide
  its highest spatial resolution data so far. Coordinated observations
  between the remote sensing and in-situ instruments will provide the
  first opportunity to use the full potential of the Solar Orbiter
  mission. We will review the instrument characteristics and present
  initial results from the cruise phase and first close encounter.

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Title: Effects of spatial resolution on inferences of atmospheric
    quantities from simulations
Authors: Moe, Thore E.; Pereira, Tiago M. D.; Carlsson, Mats
2022A&A...662A..80M    Altcode: 2022arXiv220408849M
  Context. Small-scale processes are thought to be important for
  the dynamics of the solar atmosphere. While numerical resolution
  fundamentally limits their inclusion in magnetohydronamic (MHD)
  simulations, real observations at the same nominal resolution should
  still contain imprints of subresolution effects. This means that
  the synthetic observables from a simulation of a given resolution
  might not be directly comparable to real observables at the same
  resolution. It is thus of interest to investigate how inferences
  based on synthetic spectra from simulations with different numerical
  resolutions compare, and whether these differences persist after the
  spectra have been spatially degraded to a common resolution <BR />
  Aims: We aim to compare synthetic spectra obtained from realistic 3D
  radiative magnetohydrodynamic (rMHD) simulations run at different
  numerical resolutions from the same initial atmosphere, using very
  simple methods for inferring line-of-sight velocities and magnetic
  fields. Additionally we examine how the differing spatial resolution
  impacts the results retrieved from the STiC inversion code. <BR />
  Methods: We used the RH 1.5D code to synthesize the photospheric
  Fe I 617.33 line in local thermodynamic equilibrium (LTE), and the
  chromospheric Ca II 854.209 line in non-LTE from three MHD simulation
  snapshots of differing spatial resolution. The simulations were produced
  by the Bifrost code, using horizontal grid spacing of 6 km, 12 km, and
  23 km, respectively. They were started from the exact same atmosphere,
  and the snapshots were taken after the same exact elapsed time. The
  spectra obtained from the high-resolution snapshots were spatially
  degraded to match the lowest resolution. Simple methods, such as the
  center-of-gravity approach and the weak field approximation, were then
  used to estimate line-of-sight velocities and magnetic fields for the
  three cases after degradation. Finally, the spectra were input into
  the STiC inversion code and the retrieved line-of-sight velocities
  and magnetic field strengths, as well as the temperatures, from
  the inversions were compared. <BR /> Results: We find that while the
  simple inferences for all three simulations reveal the same large-scale
  tendencies, the higher resolutions yield more fine-grained structures
  and more extreme line-of-sight velocities and magnetic fields in
  concentrated spots even after spatial smearing. We also see indications
  that the imprints of subresolution effects on the degraded spectra
  result in systematic errors in the inversions, and that these errors
  increase with the amount of subresolution effects included. Fortunately,
  however, we find that successively including more subresolution yields
  smaller additional effects; that is to say, there is a clear trend of
  diminishing importance for progressively finer subresolution effects.

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Title: An approximate recipe of chromospheric radiative losses for
    solar flares
Authors: Hong, J.; Carlsson, M.; Ding, M. D.
2022A&A...661A..77H    Altcode: 2022arXiv220307630H
  Context. Radiative losses in the chromosphere are very important for the
  energy balance of the Sun. There have been efforts to make simple lookup
  tables for chromospheric radiative losses in the quiet Sun. During
  solar flares, the atmospheric conditions are quite different, and
  the currently available recipe is constructed from semi-empirical
  models. How these recipes work in flare conditions remains to be
  evaluated. <BR /> Aims: We aim to construct an approximate recipe
  of chromospheric radiative losses for solar flares. <BR /> Methods:
  We tabulate the optically thin radiative loss, escape probability,
  and ionization fraction using a grid of flare models from radiative
  hydrodynamic simulations as our dataset. <BR /> Results: We provide
  new lookup tables to calculate chromospheric radiative losses for
  flares. Compared with previous recipes, our recipe provides a better
  approximation of the detailed radiative losses for flares.

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Title: The Atmospheric Response to High Nonthermal Electron-beam
    Fluxes in Solar Flares. II. Hydrogen-broadening Predictions for
    Solar Flare Observations with the Daniel K. Inouye Solar Telescope
Authors: Kowalski, Adam F.; Allred, Joel C.; Carlsson, Mats; Kerr,
   Graham S.; Tremblay, Pier-Emmanuel; Namekata, Kosuke; Kuridze, David;
   Uitenbroek, Han
2022ApJ...928..190K    Altcode: 2022arXiv220113349K
  Redshifted components of chromospheric emission lines in the hard X-ray
  impulsive phase of solar flares have recently been studied through
  their 30 s evolution with the high resolution of the Interface Region
  Imaging Spectrograph. Radiative-hydrodynamic flare models show that
  these redshifts are generally reproduced by electron-beam-generated
  chromospheric condensations. The models produce large ambient electron
  densities, and the pressure broadening of the hydrogen Balmer series
  should be readily detected in observations. To accurately interpret
  the upcoming spectral data of flares with the DKIST, we incorporate
  nonideal, nonadiabatic line-broadening profiles of hydrogen into the
  RADYN code. These improvements allow time-dependent predictions for
  the extreme Balmer line wing enhancements in solar flares. We study two
  chromospheric condensation models, which cover a range of electron-beam
  fluxes (1 - 5 × 10<SUP>11</SUP> erg s<SUP>-1</SUP> cm<SUP>-2</SUP>) and
  ambient electron densities (1 - 60 × 10<SUP>13</SUP> cm<SUP>-3</SUP>)
  in the flare chromosphere. Both models produce broadening and
  redshift variations within 10 s of the onset of beam heating. In the
  chromospheric condensations, there is enhanced spectral broadening due
  to large optical depths at Hα, Hβ, and Hγ, while the much lower
  optical depth of the Balmer series H12-H16 provides a translucent
  window into the smaller electron densities in the beam-heated layers
  below the condensation. The wavelength ranges of typical DKIST/ViSP
  spectra of solar flares will be sufficient to test the predictions
  of extreme hydrogen wing broadening and accurately constrain large
  densities in chromospheric condensations.

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Title: Chromospheric emission from nanoflare heating in RADYN
    simulations
Authors: Bakke, H.; Carlsson, M.; Rouppe van der Voort, L.; Gudiksen,
   B. V.; Polito, V.; Testa, P.; De Pontieu, B.
2022A&A...659A.186B    Altcode: 2022arXiv220111961B
  Context. Heating signatures from small-scale magnetic reconnection
  events in the solar atmosphere have proven to be difficult to
  detect through observations. Numerical models that reproduce flaring
  conditions are essential in understanding how nanoflares may act as a
  heating mechanism of the corona. <BR /> Aims: We study the effects of
  non-thermal electrons in synthetic spectra from 1D hydrodynamic RADYN
  simulations of nanoflare heated loops to investigate the diagnostic
  potential of chromospheric emission from small-scale events. <BR />
  Methods: The Mg II h and k, Ca II H and K, Ca II 854.2 nm, and Hα and
  Hβ chromospheric lines were synthesised from various RADYN models of
  coronal loops subject to electron beams of nanoflare energies. The
  contribution function to the line intensity was computed to better
  understand how the atmospheric response to the non-thermal electrons
  affects the formation of spectral lines and the detailed shape of
  their spectral profiles. <BR /> Results: The spectral line signatures
  arising from the electron beams highly depend on the density of the
  loop and the lower cutoff energy of the electrons. Low-energy (5 keV)
  electrons deposit their energy in the corona and transition region,
  producing strong plasma flows that cause both redshifts and blueshifts
  of the chromospheric spectra. Higher-energy (10 and 15 keV) electrons
  deposit their energy in the lower transition region and chromosphere,
  resulting in increased emission from local heating. Our results indicate
  that effects from small-scale events can be observed with ground-based
  telescopes, expanding the list of possible diagnostics for the presence
  and properties of nanoflares.

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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
    Solar Explorer (MUSE). I. Coronal Heating
Authors: De Pontieu, Bart; Testa, Paola; Martínez-Sykora, Juan;
   Antolin, Patrick; Karampelas, Konstantinos; Hansteen, Viggo; Rempel,
   Matthias; Cheung, Mark C. M.; Reale, Fabio; Danilovic, Sanja; Pagano,
   Paolo; Polito, Vanessa; De Moortel, Ineke; Nóbrega-Siverio, Daniel;
   Van Doorsselaere, Tom; Petralia, Antonino; Asgari-Targhi, Mahboubeh;
   Boerner, Paul; Carlsson, Mats; Chintzoglou, Georgios; Daw, Adrian;
   DeLuca, Edward; Golub, Leon; Matsumoto, Takuma; Ugarte-Urra, Ignacio;
   McIntosh, Scott W.; the MUSE Team
2022ApJ...926...52D    Altcode: 2021arXiv210615584D
  The Multi-slit Solar Explorer (MUSE) is a proposed mission composed of
  a multislit extreme ultraviolet (EUV) spectrograph (in three spectral
  bands around 171 Å, 284 Å, and 108 Å) and an EUV context imager (in
  two passbands around 195 Å and 304 Å). MUSE will provide unprecedented
  spectral and imaging diagnostics of the solar corona at high spatial
  (≤0.″5) and temporal resolution (down to ~0.5 s for sit-and-stare
  observations), thanks to its innovative multislit design. By obtaining
  spectra in four bright EUV lines (Fe IX 171 Å, Fe XV 284 Å, Fe XIX-Fe
  XXI 108 Å) covering a wide range of transition regions and coronal
  temperatures along 37 slits simultaneously, MUSE will, for the first
  time, "freeze" (at a cadence as short as 10 s) with a spectroscopic
  raster the evolution of the dynamic coronal plasma over a wide range of
  scales: from the spatial scales on which energy is released (≤0.″5)
  to the large-scale (~170″ × 170″) atmospheric response. We use
  numerical modeling to showcase how MUSE will constrain the properties of
  the solar atmosphere on spatiotemporal scales (≤0.″5, ≤20 s) and
  the large field of view on which state-of-the-art models of the physical
  processes that drive coronal heating, flares, and coronal mass ejections
  (CMEs) make distinguishing and testable predictions. We describe the
  synergy between MUSE, the single-slit, high-resolution Solar-C EUVST
  spectrograph, and ground-based observatories (DKIST and others), and
  the critical role MUSE plays because of the multiscale nature of the
  physical processes involved. In this first paper, we focus on coronal
  heating mechanisms. An accompanying paper focuses on flares and CMEs.

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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
    Solar Explorer (MUSE). II. Flares and Eruptions
Authors: Cheung, Mark C. M.; Martínez-Sykora, Juan; Testa, Paola;
   De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
   Vanessa; Kerr, Graham S.; Reeves, Katharine K.; Fletcher, Lyndsay; Jin,
   Meng; Nóbrega-Siverio, Daniel; Danilovic, Sanja; Antolin, Patrick;
   Allred, Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward;
   Longcope, Dana; Takasao, Shinsuke; DeRosa, Marc L.; Boerner, Paul;
   Jaeggli, Sarah; Nitta, Nariaki V.; Daw, Adrian; Carlsson, Mats; Golub,
   Leon; The
2022ApJ...926...53C    Altcode: 2021arXiv210615591C
  Current state-of-the-art spectrographs cannot resolve the fundamental
  spatial (subarcseconds) and temporal (less than a few tens of
  seconds) scales of the coronal dynamics of solar flares and eruptive
  phenomena. The highest-resolution coronal data to date are based on
  imaging, which is blind to many of the processes that drive coronal
  energetics and dynamics. As shown by the Interface Region Imaging
  Spectrograph for the low solar atmosphere, we need high-resolution
  spectroscopic measurements with simultaneous imaging to understand the
  dominant processes. In this paper: (1) we introduce the Multi-slit Solar
  Explorer (MUSE), a spaceborne observatory to fill this observational
  gap by providing high-cadence (&lt;20 s), subarcsecond-resolution
  spectroscopic rasters over an active region size of the solar transition
  region and corona; (2) using advanced numerical models, we demonstrate
  the unique diagnostic capabilities of MUSE for exploring solar coronal
  dynamics and for constraining and discriminating models of solar flares
  and eruptions; (3) we discuss the key contributions MUSE would make
  in addressing the science objectives of the Next Generation Solar
  Physics Mission (NGSPM), and how MUSE, the high-throughput Extreme
  Ultraviolet Solar Telescope, and the Daniel K Inouye Solar Telescope
  (and other ground-based observatories) can operate as a distributed
  implementation of the NGSPM. This is a companion paper to De Pontieu
  et al., which focuses on investigating coronal heating with MUSE.

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Title: Probing the Physics of the Solar Atmosphere with the Multi-slit
Solar Explorer (MUSE): II. Flares and Eruptions
Authors: Cheung, Chun Ming Mark; Martinez-Sykora, Juan; Testa, Paola;
   De Pontieu, Bart; Chintzoglou, Georgios; Rempel, Matthias; Polito,
   Vanessa; Kerr, Graham; Reeves, Katharine; Fletcher, Lyndsay; Jin,
   Meng; Nobrega, Daniel; Danilovic, Sanja; Antolin, Patrick; Allred,
   Joel; Hansteen, Viggo; Ugarte-Urra, Ignacio; DeLuca, Edward; Longcope,
   Dana; Takasao, Shinsuke; DeRosa, Marc; Boerner, Paul; Jaeggli, Sarah;
   Nitta, Nariaki; Daw, Adrian; Carlsson, Mats; Golub, Leon
2021AGUFMSH51A..08C    Altcode:
  Current state-of-the-art spectrographs cannot resolve the fundamental
  spatial (sub-arcseconds) and temporal scales (less than a few tens
  of seconds) of the coronal dynamics of solar flares and eruptive
  phenomena. The highest resolution coronal data to date are based on
  imaging, which is blind to many of the processes that drive coronal
  energetics and dynamics. As shown by IRIS for the low solar atmosphere,
  we need high-resolution spectroscopic measurements with simultaneous
  imaging to understand the dominant processes. In this paper: (1)
  we introduce the Multi-slit Solar Explorer (MUSE), a spaceborne
  observatory to fill this observational gap by providing high-cadence
  (&lt;20 s), sub-arcsecond resolution spectroscopic rasters over an
  active region size of the solar transition region and corona; (2)
  using advanced numerical models, we demonstrate the unique diagnostic
  capabilities of MUSE for exploring solar coronal dynamics, and for
  constraining and discriminating models of solar flares and eruptions;
  (3) we discuss the key contributions MUSE would make in addressing the
  science objectives of the Next Generation Solar Physics Mission (NGSPM),
  and how MUSE, the high-throughput EUV Solar Telescope (EUVST) and the
  Daniel K Inouye Solar Telescope (and other ground-based observatories)
  can operate as a distributed implementation of the NGSPM. This is a
  companion paper to De Pontieu et al. (2021, also submitted to SH-17),
  which focuses on investigating coronal heating with MUSE.

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

---------------------------------------------------------
Title: Solar oxygen abundance
Authors: Bergemann, Maria; Hoppe, Richard; Semenova, Ekaterina;
   Carlsson, Mats; Yakovleva, Svetlana A.; Voronov, Yaroslav V.;
   Bautista, Manuel; Nemer, Ahmad; Belyaev, Andrey K.; Leenaarts, Jorrit;
   Mashonkina, Lyudmila; Reiners, Ansgar; Ellwarth, Monika
2021MNRAS.508.2236B    Altcode: 2021arXiv210901143B; 2021MNRAS.tmp.1964B
  Motivated by the controversy over the surface metallicity of the
  Sun, we present a re-analysis of the solar photospheric oxygen (O)
  abundance. New atomic models of O and Ni are used to perform non-local
  thermodynamic equilibrium (NLTE) calculations with 1D hydrostatic
  (MARCS) and 3D hydrodynamical (Stagger and Bifrost) models. The
  Bifrost 3D MHD simulations are used to quantify the influence of
  the chromosphere. We compare the 3D NLTE line profiles with new
  high-resolution, R$\approx 700\, 000$, spatially resolved spectra
  of the Sun obtained using the IAG FTS instrument. We find that the
  O I lines at 777 nm yield the abundance of log A(O) = 8.74 ± 0.03
  dex, which depends on the choice of the H-impact collisional data and
  oscillator strengths. The forbidden [O I] line at 630 nm is less model
  dependent, as it forms nearly in LTE and is only weakly sensitive to
  convection. However, the oscillator strength for this transition is more
  uncertain than for the 777 nm lines. Modelled in 3D NLTE with the Ni I
  blend, the 630 nm line yields an abundance of log A(O) = 8.77 ± 0.05
  dex. We compare our results with previous estimates in the literature
  and draw a conclusion on the most likely value of the solar photospheric
  O abundance, which we estimate at log A(O) = 8.75 ± 0.03 dex.

---------------------------------------------------------
Title: Diagnostic capabilities of spectropolarimetric observations for
    understanding solar phenomena. I. Zeeman-sensitive photospheric lines
Authors: Quintero Noda, C.; Barklem, P. S.; Gafeira, R.; Ruiz Cobo,
   B.; Collados, M.; Carlsson, M.; Martínez Pillet, V.; Orozco Suárez,
   D.; Uitenbroek, H.; Katsukawa, Y.
2021A&A...652A.161Q    Altcode: 2021arXiv210605084Q
  Future ground-based telescopes will expand our capabilities for
  simultaneous multi-line polarimetric observations in a wide range of
  wavelengths, from the near-ultraviolet to the near-infrared. This
  creates a strong demand to compare candidate spectral lines to
  establish a guideline of the lines that are most appropriate for each
  observation target. We focused in this first work on Zeeman-sensitive
  photospheric lines in the visible and infrared. We first examined their
  polarisation signals and response functions using a 1D semi-empirical
  atmosphere. Then we studied the spatial distribution of the line core
  intensity and linear and circular polarisation signals using a realistic
  3D numerical simulation. We ran inversions of synthetic profiles, and
  we compared the heights at which we obtain a high correlation between
  the input and the inferred atmosphere. We also used this opportunity
  to revisit the atomic information we have on these lines and computed
  the broadening cross-sections due to collisions with neutral hydrogen
  atoms for all the studied spectral lines. The results reveal that
  four spectral lines stand out from the rest for quiet-Sun and network
  conditions: Fe I 5250.2, 6302, 8468, and 15 648 Å. The first three
  form higher in the atmosphere, and the last line is mainly sensitive to
  the atmospheric parameters at the bottom of the photosphere. However,
  as they reach different heights, we strongly recommend using at least
  one of the first three candidates together with the Fe I 15 648 Å line
  to optimise our capabilities for inferring the thermal and magnetic
  properties of the lower atmosphere.

---------------------------------------------------------
Title: Mapping of Solar Magnetic Fields from the Photosphere to the
    Top of the Chromosphere with CLASP2
Authors: McKenzie, D.; Ishikawa, R.; Trujillo Bueno, J.; Auchere, F.;
   del Pino Aleman, T.; Okamoto, T.; Kano, R.; Song, D.; Yoshida, M.;
   Rachmeler, L.; Kobayashi, K.; Narukage, N.; Kubo, M.; Ishikawa, S.;
   Hara, H.; Suematsu, Y.; Sakao, T.; Bethge, C.; De Pontieu, B.; Vigil,
   G.; Winebarger, A.; Alsina Ballester, E.; Belluzzi, L.; Stepan, J.;
   Asensio Ramos, A.; Carlsson, M.; Leenaarts, J.
2021AAS...23810603M    Altcode:
  Coronal heating, chromospheric heating, and the heating &amp;
  acceleration of the solar wind, are well-known problems in solar
  physics. Additionally, knowledge of the magnetic energy that
  powers solar flares and coronal mass ejections, important drivers
  of space weather, is handicapped by imperfect determination of the
  magnetic field in the sun's atmosphere. Extrapolation of photospheric
  magnetic measurements into the corona is fraught with difficulties and
  uncertainties, partly due to the vastly different plasma beta between
  the photosphere and the corona. Better results in understanding
  the coronal magnetic field should be derived from measurements of
  the magnetic field in the chromosphere. To that end, we are pursuing
  quantitative determination of the magnetic field in the chromosphere,
  where plasma beta transitions from greater than unity to less than
  unity, via ultraviolet spectropolarimetry. The CLASP2 mission, flown
  on a sounding rocket in April 2019, succeeded in measuring all four
  Stokes polarization parameters in UV spectral lines formed by singly
  ionized Magnesium and neutral Manganese. Because these ions produce
  spectral lines under different conditions, CLASP2 thus was able to
  quantify the magnetic field properties at multiple heights in the
  chromosphere simultaneously, as shown in the recent paper by Ishikawa
  et al. In this presentation we will report the findings of CLASP2,
  demonstrating the variation of magnetic fields along a track on
  the solar surface and as a function of height in the chromosphere;
  and we will illustrate what is next for the CLASP missions and the
  demonstration of UV spectropolarimetry in the solar chromosphere.

---------------------------------------------------------
Title: Chromospheric Heating by Magnetohydrodynamic Waves and
    Instabilities
Authors: Srivastava, A. K.; Ballester, J. L.; Cally, P. S.; Carlsson,
   M.; Goossens, M.; Jess, D. B.; Khomenko, E.; Mathioudakis, M.;
   Murawski, K.; Zaqarashvili, T. V.
2021JGRA..12629097S    Altcode: 2021arXiv210402010S
  The importance of the chromosphere in the mass and energy transport
  within the solar atmosphere is now widely recognized. This review
  discusses the physics of magnetohydrodynamic waves and instabilities
  in large-scale chromospheric structures as well as in magnetic flux
  tubes. We highlight a number of key observational aspects that have
  helped our understanding of the role of the solar chromosphere
  in various dynamic processes and wave phenomena, and the heating
  scenario of the solar chromosphere is also discussed. The review
  focuses on the physics of waves and invokes the basics of plasma
  instabilities in the context of this important layer of the solar
  atmosphere. Potential implications, future trends and outstanding
  questions are also delineated.

---------------------------------------------------------
Title: A New View of the Solar Interface Region from the Interface
    Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, Bart; Polito, Vanessa; Hansteen, Viggo; Testa,
   Paola; Reeves, Katharine K.; Antolin, Patrick; Nóbrega-Siverio,
   Daniel Elias; Kowalski, Adam F.; Martinez-Sykora, Juan; Carlsson,
   Mats; McIntosh, Scott W.; Liu, Wei; Daw, Adrian; Kankelborg, Charles C.
2021SoPh..296...84D    Altcode: 2021arXiv210316109D
  The Interface Region Imaging Spectrograph (IRIS) has been obtaining
  near- and far-ultraviolet images and spectra of the solar atmosphere
  since July 2013. IRIS is the highest resolution observatory to provide
  seamless coverage of spectra and images from the photosphere into the
  low corona. The unique combination of near- and far-ultraviolet spectra
  and images at sub-arcsecond resolution and high cadence allows the
  tracing of mass and energy through the critical interface between the
  surface and the corona or solar wind. IRIS has enabled research into the
  fundamental physical processes thought to play a role in the low solar
  atmosphere such as ion-neutral interactions, magnetic reconnection, the
  generation, propagation, and dissipation of waves, the acceleration of
  non-thermal particles, and various small-scale instabilities. IRIS has
  provided insights into a wide range of phenomena including the discovery
  of non-thermal particles in coronal nano-flares, the formation and
  impact of spicules and other jets, resonant absorption and dissipation
  of Alfvénic waves, energy release and jet-like dynamics associated
  with braiding of magnetic-field lines, the role of turbulence and the
  tearing-mode instability in reconnection, the contribution of waves,
  turbulence, and non-thermal particles in the energy deposition during
  flares and smaller-scale events such as UV bursts, and the role of flux
  ropes and various other mechanisms in triggering and driving CMEs. IRIS
  observations have also been used to elucidate the physical mechanisms
  driving the solar irradiance that impacts Earth's upper atmosphere,
  and the connections between solar and stellar physics. Advances in
  numerical modeling, inversion codes, and machine-learning techniques
  have played a key role. With the advent of exciting new instrumentation
  both on the ground, e.g. the Daniel K. Inouye Solar Telescope (DKIST)
  and the Atacama Large Millimeter/submillimeter Array (ALMA), and
  space-based, e.g. the Parker Solar Probe and the Solar Orbiter, we aim
  to review new insights based on IRIS observations or related modeling,
  and highlight some of the outstanding challenges.

---------------------------------------------------------
Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
    (DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
   Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
   Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
   Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
   Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
   Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
   Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
   Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
   Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
   Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
   Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
   Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
   Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
   Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
   Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
   Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
   Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
   E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
   Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
   Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
   Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
   Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
   A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
   Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
   Instrument Scientists; DKIST Science Working Group; DKIST Critical
   Science Plan Community
2021SoPh..296...70R    Altcode: 2020arXiv200808203R
  The National Science Foundation's Daniel K. Inouye Solar Telescope
  (DKIST) will revolutionize our ability to measure, understand,
  and model the basic physical processes that control the structure
  and dynamics of the Sun and its atmosphere. The first-light DKIST
  images, released publicly on 29 January 2020, only hint at the
  extraordinary capabilities that will accompany full commissioning of
  the five facility instruments. With this Critical Science Plan (CSP)
  we attempt to anticipate some of what those capabilities will enable,
  providing a snapshot of some of the scientific pursuits that the DKIST
  hopes to engage as start-of-operations nears. The work builds on the
  combined contributions of the DKIST Science Working Group (SWG) and
  CSP Community members, who generously shared their experiences, plans,
  knowledge, and dreams. Discussion is primarily focused on those issues
  to which DKIST will uniquely contribute.

---------------------------------------------------------
Title: Mapping solar magnetic fields from the photosphere to the
    base of the corona
Authors: Ishikawa, Ryohko; Bueno, Javier Trujillo; del Pino Alemán,
   Tanausú; Okamoto, Takenori J.; McKenzie, David E.; Auchère,
   Frédéric; Kano, Ryouhei; Song, Donguk; Yoshida, Masaki; Rachmeler,
   Laurel A.; Kobayashi, Ken; Hara, Hirohisa; Kubo, Masahito; Narukage,
   Noriyuki; Sakao, Taro; Shimizu, Toshifumi; Suematsu, Yoshinori; Bethge,
   Christian; De Pontieu, Bart; Dalda, Alberto Sainz; Vigil, Genevieve D.;
   Winebarger, Amy; Ballester, Ernest Alsina; Belluzzi, Luca; Štěpán,
   Jiří; Ramos, Andrés Asensio; Carlsson, Mats; Leenaarts, Jorrit
2021SciA....7.8406I    Altcode: 2021arXiv210301583I
  Routine ultraviolet imaging of the Sun's upper atmosphere shows the
  spectacular manifestation of solar activity; yet we remain blind to
  its main driver, the magnetic field. Here we report unprecedented
  spectropolarimetric observations of an active region plage and
  its surrounding enhanced network, showing circular polarization in
  ultraviolet (Mg II $h$ &amp; $k$ and Mn I) and visible (Fe I) lines. We
  infer the longitudinal magnetic field from the photosphere to the
  very upper chromosphere. At the top of the plage chromosphere the
  field strengths reach more than 300 gauss, strongly correlated with
  the Mg II $k$ line core intensity and the electron pressure. This
  unique mapping shows how the magnetic field couples the different
  atmospheric layers and reveals the magnetic origin of the heating in
  the plage chromosphere.

---------------------------------------------------------
Title: Acoustic-gravity wave propagation characteristics in
    three-dimensional radiation hydrodynamic simulations of the solar
    atmosphere
Authors: Fleck, B.; Carlsson, M.; Khomenko, E.; Rempel, M.; Steiner,
   O.; Vigeesh, G.
2021RSPTA.37900170F    Altcode: 2020arXiv200705847F
  There has been tremendous progress in the degree of realism of
  three-dimensional radiation magneto-hydrodynamic simulations of the
  solar atmosphere in the past decades. Four of the most frequently
  used numerical codes are Bifrost, CO5BOLD, MANCHA3D and MURaM. Here
  we test and compare the wave propagation characteristics in model
  runs from these four codes by measuring the dispersion relation of
  acoustic-gravity waves at various heights. We find considerable
  differences between the various models. The height dependence of
  wave power, in particular of high-frequency waves, varies by up to
  two orders of magnitude between the models, and the phase difference
  spectra of several models show unexpected features, including ±180°
  phase jumps. <P />This article is part of the Theo Murphy meeting issue
  `High-resolution wave dynamics in the lower solar atmosphere'.

---------------------------------------------------------
Title: Characterization of shock wave signatures at millimetre
    wavelengths from Bifrost simulations
Authors: Eklund, Henrik; Wedemeyer, Sven; Snow, Ben; Jess, David B.;
   Jafarzadeh, Shahin; Grant, Samuel D. T.; Carlsson, Mats; Szydlarski,
   Mikołaj
2021RSPTA.37900185E    Altcode: 2020arXiv200805324E
  Observations at millimetre wavelengths provide a valuable tool to study
  the small-scale dynamics in the solar chromosphere. We evaluate the
  physical conditions of the atmosphere in the presence of a propagating
  shock wave and link that to the observable signatures in mm-wavelength
  radiation, providing valuable insights into the underlying physics
  of mm-wavelength observations. A realistic numerical simulation from
  the three-dimensional radiative magnetohydrodynamic code Bifrost
  is used to interpret changes in the atmosphere caused by shock wave
  propagation. High-cadence (1 s) time series of brightness temperature
  (T<SUB>b</SUB>) maps are calculated with the Advanced Radiative Transfer
  code at the wavelengths 1.309 mm and 1.204 mm, which represents opposite
  sides of spectral band 6 of the Atacama Large Millimeter/submillimeter
  Array (ALMA). An example of shock wave propagation is presented. The
  brightness temperatures show a strong shock wave signature with large
  variation in formation height between approximately 0.7 and 1.4 Mm. The
  results demonstrate that millimetre brightness temperatures efficiently
  track upwardly propagating shock waves in the middle chromosphere. In
  addition, we show that the gradient of the brightness temperature
  between wavelengths within ALMA band 6 can potentially be used as
  a diagnostics tool in understanding the small-scale dynamics at the
  sampled layers. <P />This article is part of the Theo Murphy meeting
  issue `High-resolution wave dynamics in the lower solar atmosphere'.

---------------------------------------------------------
Title: Relative coronal abundance diagnostics with Solar Orbiter/SPICE
Authors: Zambrana Prado, N.; Buchlin, E.; Peter, H.; Young, P. R.;
   Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Aznar Cuadrado,
   R.; Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra,
   L.; Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller,
   D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Sidher, S.; Teriaca,
   L.; Thompson, W. T.; Williams, D.
2020AGUFMSH038..09Z    Altcode:
  Linking solar activity on the surface and in the corona to the inner
  heliosphere is one of Solar Orbiter's main goals. Its UV spectrometer
  SPICE (SPectral Imaging of the Coronal Environment) will provide
  relative abundance measurements which will be key in this quest
  as different structures on the Sun have different abundances as a
  consequence of the FIP (First Ionization Potential) effect. Solar
  Orbiter's unique combination of remote sensing and in-situ instruments
  coupled with observation from other missions such as Parker Solar
  Probe will allow us to compare in-situ and remote sensing composition
  data. With the addition of modeling, these new results will allow us
  to trace back the source of heliospheric plasma. As high telemetry
  will not always be available with SPICE, we have developed a method
  for measuring relative abundances that is both telemetry efficient
  and reliable. Unlike methods based on Differential Emission Measure
  (DEM) inversion, the Linear Combination Ratio (LCR) method does not
  require a large number of spectral lines. This new method is based
  on linear combinations of UV spectral lines. The coefficients of
  the combinations are optimized such that the ratio of two linear
  combinations of radiances would yield the relative abundance of two
  elements. We present some abundance diagnostics tested on different
  combinations of spectral lines observable by SPICE.

---------------------------------------------------------
Title: Dynamics and thermal structure in the quiet Sun seen by SPICE
Authors: Peter, H.; Aznar Cuadrado, R.; Schühle, U.; Teriaca, L.;
   Auchere, F.; Carlsson, M.; Fludra, A.; Hassler, D.; Buchlin, E.;
   Caminade, S.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
   Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
   Parenti, S.; Schmutz, W. K.; Sidher, S.; Thompson, W. T.; Williams,
   D.; Young, P. R.
2020AGUFMSH038..03P    Altcode:
  We will present some of the early data of the Spectral Imaging of the
  Coronal Environment (SPICE) instrument on Solar Orbiter. One of the
  unique features of SPICE is its capability to record a wide range of
  wavelengths in the extreme UV with the possibility to record spectral
  lines giving access to a continuous plasma temperature range from 10.000
  K to well above 1 MK. The data taken so far were for commissioning
  purposes and they can be used for a preliminary evaluation of the
  science performance of the instrument. Here we will concentrate on
  sample spectra covering the whole wavelength region and on the early
  raster maps acquired in bright lines in the quiet Sun close to disk
  center. Looking at different quiet Sun features we investigate the
  thermal structure of the atmosphere and flow structures. For this
  we apply fits to the spectral profiles and check the performance in
  terms of Doppler shifts and line widths to retrieve the structure of
  the network in terms of dynamics. While the amount of data available
  so far is limited, we will have a first look on how quiet Sun plasma
  responds to heating events. For this, we will compare spectral lines
  forming at different temperatures recorded at strictly the same time.

---------------------------------------------------------
Title: A Journey of Exploration to the Polar Regions of a Star:
    Probing the Solar Poles and the Heliosphere from High Helio-Latitude
Authors: Finsterle, W.; Harra, L.; Andretta, V.; Appourchaux, T.;
   Baudin, F.; Bellot Rubio, L.; Birch, A.; Boumier, P.; Cameron, R. H.;
   Carlsson, M.; Corbard, T.; Davies, J. A.; Fazakerley, A. N.; Fineschi,
   S.; Gizon, L. C.; Harrison, R. A.; Hassler, D.; Leibacher, J. W.;
   Liewer, P. C.; Macdonald, M.; Maksimovic, M.; Murphy, N.; Naletto, G.;
   Nigro, G.; Owen, C. J.; Martinez-Pillet, V.; Rochus, P. L.; Romoli,
   M.; Sekii, T.; Spadaro, D.; Veronig, A.
2020AGUFMSH0110005F    Altcode:
  A mission to view the solar poles from high helio-latitudes (above
  60°) will build on the experience of Solar Orbiter as well as a long
  heritage of successful solar missions and instrumentation (e.g. SOHO,
  STEREO, Hinode, SDO), but will focus for the first time on the solar
  poles, enabling scientific investigations that cannot be done by
  any other mission. One of the major mysteries of the Sun is the solar
  cycle. The activity cycle of the Sun drives the structure and behaviour
  of the heliosphere and is, of course, the driver of space weather. In
  addition, solar activity and variability provides fluctuating input
  into the Earth climate models, and these same physical processes
  are applicable to stellar systems hosting exoplanets. One of the
  main obstructions to understanding the solar cycle, and hence all
  solar activity, is our current lack of understanding of the polar
  regions. We describe a mission concept that aims to address this
  fundamental issue. In parallel, we recognise that viewing the Sun
  from above the polar regions enables further scientific advantages,
  beyond those related to the solar cycle, such as unique and powerful
  studies of coronal mass ejection processes, from a global perspective,
  and studies of coronal structure and activity in polar regions. Not
  only will these provide important scientific advances for fundamental
  stellar physics research, they will feed into our understanding of
  impacts on the Earth and other planets' space environment.

---------------------------------------------------------
Title: First Results From SPICE EUV Spectrometer on Solar Orbiter
Authors: Fludra, A.; Caldwell, M.; Giunta, A. S.; Grundy, T.; Guest,
   S.; Sidher, S.; Auchere, F.; Carlsson, M.; Hassler, D.; Peter, H.;
   Aznar Cuadrado, R.; Buchlin, E.; Caminade, S.; DeForest, C.; Fredvik,
   T.; Harra, L. K.; Janvier, M.; Kucera, T. A.; Leeks, S.; Mueller,
   D.; Parenti, S.; Schmutz, W. K.; Schühle, U.; Teriaca, L.; Thompson,
   W. T.; Tustain, S.; Williams, D.; Young, P. R.
2020AGUFMSH038..02F    Altcode:
  SPICE (Spectral Imaging of Coronal Environment) is one of the remote
  sensing instruments onboard Solar Orbiter. It is an EUV imaging
  spectrometer observing the Sun in two wavelength bands: 69.6-79.4 nm
  and 96.6-105.1 nm. SPICE is capable of recording full spectra in these
  bands with exposures as short as 1s. SPICE is the only Solar Orbiter
  instrument that can measure EUV spectra from the disk and low corona
  of the Sun and record all spectral lines simultaneously. SPICE uses
  one of three narrow slits, 2"x11', 4”x11', 6”x11', or a wide slit
  30”x14'. The primary mirror can be scanned in a direction perpendicular
  to the slit, allowing raster images of up to 16' in size. <P />We
  present an overview of the first SPICE data taken on several days
  during the instrument commissioning carried out by the RAL Space team
  between 2020 April 21 and 2020 June 14. We also include results from
  SPICE observations at the first Solar Orbiter perihelion at 0.52AU,
  taken between June 16-21<SUP>st</SUP>. We give examples of full spectra
  from the quiet Sun near disk centre and provide a list of key spectral
  lines emitted in a range of temperatures between 10,000 K and over 1
  million K, from neutral hydrogen and ions of carbon, oxygen, nitrogen,
  neon, sulphur and magnesium. We show examples of first raster images
  in several strong lines, obtained with different slits and a range
  of exposure times between 5s and 180s. We describe the temperature
  coverage and density diagnostics, determination of plasma flows, and
  discuss possible applications to studies of the elemental abundances
  in the corona. We also show the first off-limb measurements with SPICE,
  as obtained when the spacecraft pointed at the limb.

---------------------------------------------------------
Title: Calibrating optical distortions in the Solar Orbiter SPICE
    spectrograph
Authors: Thompson, W. T.; Schühle, U.; Young, P. R.; Auchere, F.;
   Carlsson, M.; Fludra, A.; Hassler, D.; Peter, H.; Aznar Cuadrado, R.;
   Buchlin, E.; Caldwell, M.; DeForest, C.; Fredvik, T.; Harra, L. K.;
   Janvier, M.; Kucera, T. A.; Giunta, A. S.; Grundy, T.; Müller, D.;
   Parenti, S.; Caminade, S.; Schmutz, W. K.; Teriaca, L.; Williams,
   D.; Sidher, S.
2020AGUFMSH0360029T    Altcode:
  The Spectral Imaging of the Coronal Environment (SPICE) instrument on
  Solar Orbiter is a high-resolution imaging spectrometer operating
  at extreme ultraviolet (EUV) wavelengths from 70.4-79.0 nm and
  97.3-104.9 nm. A single-mirror off-axis paraboloid focuses the solar
  image onto the entrance slit of the spectrometer section. A Toroidal
  Variable Line Space (TVLS) grating images the entrance slit onto a
  pair of MCP-intensified APS detectors. Ray-tracing analysis prior
  to launch showed that the instrument was subject to a number of
  small image distortions which need to be corrected in the final data
  product. We compare the ray tracing results with measurements made in
  flight. Co-alignment with other telescopes on Solar Orbiter will also
  be examined.

---------------------------------------------------------
Title: First results from the EUI and SPICE observations of Alpha
    Leo near Solar Orbiter first perihelion
Authors: Buchlin, E.; Teriaca, L.; Giunta, A. S.; Grundy, T.; Andretta,
   V.; Auchere, F.; Peter, H.; Berghmans, D.; Carlsson, M.; Fludra, A.;
   Harra, L.; Hassler, D.; Long, D.; Rochus, P. L.; Schühle, U.; Aznar
   Cuadrado, R.; Caldwell, M.; Caminade, S.; DeForest, C.; Fredvik, T.;
   Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp, E.; Kucera, T. A.;
   Müller, D.; Parenti, S.; Schmutz, W. K.; Sidher, S.; Smith, P.;
   Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
2020AGUFMSH0360024B    Altcode:
  On June 16th 2020 Solar Orbiter made a dedicated observing campaign
  where the spacecraft pointed to the solar limb to allow some of the
  high resolution instruments to observe the ingress (at the east limb)
  and later the egress (west limb) of the occultation of the star Alpha
  Leonis by the solar disk. The star was chosen because its luminosity and
  early spectral type ensure high and stable flux at wavelengths between
  100 and 122 nanometers, a range observed by the High Resolution EUI
  Lyman alpha telescope (HRI-LYA) and by the long wavelength channel
  of the SPICE spectrograph. Star observations, when feasible, allow
  to gather a great deal of information on the instrument performances,
  such as the radiometric performance and the instrument optical point
  spread function (PSF). <P />We report here the first results from the
  above campaign for the two instruments.

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

---------------------------------------------------------
Title: First results from combined EUI and SPICE observations of
    Lyman lines of Hydrogen and He II
Authors: Teriaca, L.; Aznar Cuadrado, R.; Giunta, A. S.; Grundy, T.;
   Parenti, S.; Auchere, F.; Vial, J. C.; Fludra, A.; Berghmans, D.;
   Carlsson, M.; Harra, L.; Hassler, D.; Long, D.; Peter, H.; Rochus,
   P. L.; Schühle, U.; Buchlin, E.; Caldwell, M.; Caminade, S.; DeForest,
   C.; Fredvik, T.; Gissot, S.; Heerlein, K.; Janvier, M.; Kraaikamp,
   E.; Kucera, T. A.; Mueller, D.; Schmutz, W. K.; Sidher, S.; Smith, P.;
   Stegen, K.; Thompson, W. T.; Verbeeck, C.; Williams, D.; Young, P. R.
2020AGUFMSH0360003T    Altcode:
  The Solar Orbiter spacecraft carries a powerful set of remote
  sensing instruments that allow studying the solar atmosphere with
  unprecedented diagnostic capabilities. Many such diagnostics require
  the simultaneous usage of more than one instrument. One example of that
  is the capability, for the first time, to obtain (near) simultaneous
  spatially resolved observations of the emission from the first three
  lines of the Lyman series of hydrogen and of He II Lyman alpha. In fact,
  the SPectral Imaging of the Coronal Environment (SPICE) spectrometer
  can observe the Lyman beta and gamma lines in its long wavelength
  (SPICE-LW) channel, the High Resolution Lyman Alpha (HRI-LYA) telescope
  of the Extreme Ultraviolet Imager (EUI) acquires narrow band images in
  the Lyman alpha line while the Full Disk Imager (FSI) of EUI can take
  images dominated by the Lyman alpha line of ionized Helium at 30.4 nm
  (FSI-304). Being hydrogen and helium the main components of our star,
  these very bright transitions play an important role in the energy
  budget of the outer atmosphere via radiative losses and the measurement
  of their profiles and radiance ratios is a fundamental constraint to
  any comprehensive modelization effort of the upper solar chromosphere
  and transition region. Additionally, monitoring their average ratios
  can serve as a check out for the relative radiometric performance of
  the two instruments throughout the mission. Although the engineering
  data acquired so far are far from ideal in terms of time simultaneity
  (often only within about 1 h) and line coverage (often only Lyman beta
  was acquired by SPICE and not always near simultaneous images from all
  three telescopes are available) the analysis we present here still
  offers a great opportunity to have a first look at the potential of
  this diagnostic from the two instruments. In fact, we have identified
  a series of datasets obtained at disk center and at various positions
  at the solar limb that allow studying the Lyman alpha to beta radiance
  ratio and their relation to He II 30.4 as a function of the position
  on the Sun (disk center versus limb and quiet Sun versus coronal holes).

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

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

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

---------------------------------------------------------
Title: On the Formation of Lyman β and the O I 1027 and 1028 Å
    Spectral Lines
Authors: Hasegawa, Takahiro; Noda, Carlos Quintero; Shimizu, Toshifumi;
   Carlsson, Mats
2020ApJ...900...34H    Altcode: 2020arXiv200812556H
  We study the potential of Lyman β and the O I 1027 and 1028
  Å spectral lines to help in understanding the properties of the
  chromosphere and transition region (TR). The oxygen transitions are
  located in the wing of Lyman β, which is a candidate spectral line
  for the solar missions Solar Orbiter/Spectral Imaging of the Coronal
  Environment and Solar-C (EUVST). We examine the general spectroscopic
  properties of the three transitions in the quiet Sun by synthesizing
  them assuming nonlocal thermal equilibrium and taking into account
  partial redistribution effects. We estimate the heights where the
  spectral lines are sensitive to the physical parameters, computing the
  response functions to temperature and velocity using a 1D semiempirical
  atmospheric model. We also synthesize the intensity spectrum using the
  3D enhanced network simulation computed with the BIFROST code. The
  results indicate that Lyman β is sensitive to the temperature from
  the middle chromosphere to the TR, while it is mainly sensitive to
  the line-of-sight (LOS) velocity at the lower atmospheric layers,
  around 2000 km above the optical surface. The O I lines form lower
  in the middle chromosphere, being sensitive to the LOS velocities at
  heights lower than those covered by Lyman β. The spatial distribution
  of the intensity signals computed with the BIFROST atmosphere, as
  well as the inferred velocities from the line core Doppler shift,
  confirms the previous results. Therefore, these results indicate that
  the spectral window at 1025 Å contains several spectral lines that
  complement each other to seamlessly trace the thermal structure and
  gas dynamics from the middle chromosphere to the lower TR.

---------------------------------------------------------
Title: High-resolution observations of the solar photosphere,
    chromosphere, and transition region. A database of coordinated IRIS
    and SST observations
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Carlsson,
   M.; de la Cruz Rodríguez, J.; Bose, S.; Chintzoglou, G.; Drews, A.;
   Froment, C.; Gošić, M.; Graham, D. R.; Hansteen, V. H.; Henriques,
   V. M. J.; Jafarzadeh, S.; Joshi, J.; Kleint, L.; Kohutova, P.;
   Leifsen, T.; Martínez-Sykora, J.; Nóbrega-Siverio, D.; Ortiz, A.;
   Pereira, T. M. D.; Popovas, A.; Quintero Noda, C.; Sainz Dalda, A.;
   Scharmer, G. B.; Schmit, D.; Scullion, E.; Skogsrud, H.; Szydlarski,
   M.; Timmons, R.; Vissers, G. J. M.; Woods, M. M.; Zacharias, P.
2020A&A...641A.146R    Altcode: 2020arXiv200514175R
  NASA's Interface Region Imaging Spectrograph (IRIS) provides
  high-resolution observations of the solar atmosphere through ultraviolet
  spectroscopy and imaging. Since the launch of IRIS in June 2013, we
  have conducted systematic observation campaigns in coordination with
  the Swedish 1 m Solar Telescope (SST) on La Palma. The SST provides
  complementary high-resolution observations of the photosphere and
  chromosphere. The SST observations include spectropolarimetric imaging
  in photospheric Fe I lines and spectrally resolved imaging in the
  chromospheric Ca II 8542 Å, Hα, and Ca II K lines. We present
  a database of co-aligned IRIS and SST datasets that is open for
  analysis to the scientific community. The database covers a variety
  of targets including active regions, sunspots, plages, the quiet Sun,
  and coronal holes.

---------------------------------------------------------
Title: Ambipolar diffusion in the Bifrost code
Authors: Nóbrega-Siverio, D.; Martínez-Sykora, J.; Moreno-Insertis,
   F.; Carlsson, M.
2020A&A...638A..79N    Altcode: 2020arXiv200411927N
  Context. Ambipolar diffusion is a physical mechanism related to the
  drift between charged and neutral particles in a partially ionized
  plasma that is key to many different astrophysical systems. However,
  understanding its effects is challenging due to basic uncertainties
  concerning relevant microphysical aspects and the strong constraints it
  imposes on the numerical modeling. <BR /> Aims: Our aim is to introduce
  a numerical tool that allows us to address complex problems involving
  ambipolar diffusion in which, additionally, departures from ionization
  equilibrium are important or high resolution is needed. The primary
  application of this tool is for solar atmosphere calculations, but the
  methods and results presented here may also have a potential impact
  on other astrophysical systems. <BR /> Methods: We have developed a
  new module for the stellar atmosphere Bifrost code that improves its
  computational capabilities of the ambipolar diffusion term in the
  generalized Ohm's law. This module includes, among other things,
  collision terms adequate to processes in the coolest regions in
  the solar chromosphere. As the main feature of the module, we have
  implemented the super time stepping (STS) technique, which allows an
  important acceleration of the calculations. We have also introduced
  hyperdiffusion terms to guarantee the stability of the code. <BR />
  Results: We show that to have an accurate value for the ambipolar
  diffusion coefficient in the solar atmosphere it is necessary to
  include as atomic elements in the equation of state not only hydrogen
  and helium, but also the main electron donors like sodium, silicon,
  and potassium. In addition, we establish a range of criteria to set
  up an automatic selection of the free parameters of the STS method
  that guarantees the best performance, optimizing the stability and
  speed for the ambipolar diffusion calculations. We validate the STS
  implementation by comparison with a self-similar analytical solution.

---------------------------------------------------------
Title: Chromospheric Bubbles in Solar Flares
Authors: Reid, A.; Zhigulin, B.; Carlsson, M.; Mathioudakis, M.
2020ApJ...894L..21R    Altcode: 2020arXiv200510586R
  We analyze a grid of radiative hydrodynamic simulations of solar flares
  to study the energy balance and response of the atmosphere to nonthermal
  electron beam heating. The appearance of chromospheric bubbles is one
  of the most notable features that we find in the simulations. These
  pockets of chromospheric plasma get trapped between the transition
  region and the lower atmosphere as it is superheated by the particle
  beam. The chromospheric bubbles are seen in the synthetic spectra,
  appearing as an additional component to Balmer line profiles with high
  Doppler velocities as high as 200 km s<SUP>-1</SUP>. Their signatures
  are also visible in the wings of Ca II 8542 Å line profiles. These
  bubbles of chromospheric plasma are driven upward by a wave front that
  is induced by the shock of energy deposition, and require a specific
  heating rate and atmospheric location to manifest.

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Title: The Sun at millimeter wavelengths. I. Introduction to ALMA
    Band 3 observations
Authors: Wedemeyer, Sven; Szydlarski, Mikolaj; Jafarzadeh, Shahin;
   Eklund, Henrik; Guevara Gomez, Juan Camilo; Bastian, Tim; Fleck,
   Bernhard; de la Cruz Rodriguez, Jaime; Rodger, Andrew; Carlsson, Mats
2020A&A...635A..71W    Altcode: 2020arXiv200102185W
  Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started
  regular observations of the Sun in 2016, first offering receiver Band
  3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around
  1.25 mm (239 GHz). <BR /> Aims: Here we present an initial study
  of one of the first ALMA Band 3 observations of the Sun. Our aim is
  to characterise the diagnostic potential of brightness temperatures
  measured with ALMA on the Sun. <BR /> Methods: The observation covers
  a duration of 48 min at a cadence of 2 s targeting a quiet Sun region
  at disc-centre. Corresponding time series of brightness temperature
  maps are constructed with the first version of the Solar ALMA Pipeline
  and compared to simultaneous observations with the Solar Dynamics
  Observatory (SDO). <BR /> Results: The angular resolution of the
  observations is set by the synthesised beam, an elliptical Gaussian
  that is approximately 1.4″ × 2.1″ in size. The ALMA maps exhibit
  network patches, internetwork regions, and elongated thin features
  that are connected to large-scale magnetic loops, as confirmed by a
  comparison with SDO maps. The ALMA Band 3 maps correlate best with
  the SDO/AIA 171 Å, 131 Å, and 304 Å channels in that they exhibit
  network features and, although very weak in the ALMA maps, imprints
  of large-scale loops. A group of compact magnetic loops is very
  clearly visible in ALMA Band 3. The brightness temperatures in the
  loop tops reach values of about 8000-9000 K and in extreme moments
  up to 10 000 K. <BR /> Conclusions: ALMA Band 3 interferometric
  observations from early observing cycles already reveal temperature
  differences in the solar chromosphere. The weak imprint of magnetic
  loops and the correlation with the 171, 131, and 304 SDO channels
  suggests, however, that the radiation mapped in ALMA Band 3 might
  have contributions from a wider range of atmospheric heights than
  previously assumed, but the exact formation height of Band 3 needs to
  be investigated in more detail. The absolute brightness temperature
  scale as set by total power measurements remains less certain and
  must be improved in the future. Despite these complications and the
  limited angular resolution, ALMA Band 3 observations have a large
  potential for quantitative studies of the small-scale structure and
  dynamics of the solar chromosphere. <P />Movies are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201937122/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Observational constraints on the origin of the elements. II. 3D
    non-LTE formation of Ba II lines in the solar atmosphere
Authors: Gallagher, A. J.; Bergemann, M.; Collet, R.; Plez, B.;
   Leenaarts, J.; Carlsson, M.; Yakovleva, S. A.; Belyaev, A. K.
2020A&A...634A..55G    Altcode: 2019arXiv191003898G
  Context. The pursuit of more realistic spectroscopic modelling
  and consistent abundances has led us to begin a new series of
  papers designed to improve current solar and stellar abundances of
  various atomic species. To achieve this, we have begun updating the
  three-dimensional (3D) non-local thermodynamic equilibrium (non-LTE)
  radiative transfer code, MULTI3D, and the equivalent one-dimensional
  (1D) non-LTE radiative transfer code, MULTI 2.3. <BR /> Aims: We
  examine our improvements to these codes by redetermining the solar
  barium abundance. Barium was chosen for this test as it is an important
  diagnostic element of the s-process in the context of galactic chemical
  evolution. New Ba II + H collisional data for excitation and charge
  exchange reactions computed from first principles had recently become
  available and were included in the model atom. The atom also includes
  the effects of isotopic line shifts and hyperfine splitting. <BR />
  Methods: A grid of 1D LTE barium lines were constructed with MULTI 2.3
  and fit to the four Ba II lines available to us in the optical region
  of the solar spectrum. Abundance corrections were then determined in
  1D non-LTE, 3D LTE, and 3D non-LTE. A new 3D non-LTE solar barium
  abundance was computed from these corrections. <BR /> Results: We
  present for the first time the full 3D non-LTE barium abundance of
  A(Ba) = 2.27 ± 0.02 ± 0.01, which was derived from four individual
  fully consistent barium lines. Errors here represent the systematic
  and random errors, respectively.

---------------------------------------------------------
Title: Ion-neutral Interactions and Nonequilibrium Ionization in
    the Solar Chromosphere
Authors: Martínez-Sykora, Juan; Leenaarts, Jorrit; De Pontieu,
   Bart; Nóbrega-Siverio, Daniel; Hansteen, Viggo H.; Carlsson, Mats;
   Szydlarski, Mikolaj
2020ApJ...889...95M    Altcode: 2019arXiv191206682M
  The thermal structure of the chromosphere is regulated through a
  complex interaction of various heating processes, radiative cooling,
  and the ionization degree of the plasma. Here, we study the impact on
  the thermal properties of the chromosphere when including the combined
  action of nonequilibrium ionization (NEI) of hydrogen and helium and
  ion-neutral interaction effects. We have performed a 2.5D radiative
  magnetohydrodynamic simulation using the Bifrost code. This model
  includes ion-neutral interaction effects by solving the generalized
  Ohm' s law (GOL) as well as NEI for hydrogen and helium. The GOL
  equation includes ambipolar diffusion and the Hall term. We compare
  this simulation with another simulation that computes the ionization in
  local thermodynamic equilibrium (LTE) including ion-neutral interaction
  effects. Our numerical models reveal substantial thermal differences
  in magneto-acoustic shocks, the wake behind the shocks, spicules,
  low-lying magnetic loops, and the transition region. In particular,
  we find that heating through ambipolar diffusion in shock wakes is
  substantially less efficient, while in the shock fronts themselves it
  is more efficient, under NEI conditions than when assuming LTE.

---------------------------------------------------------
Title: Cosmic ray interactions in the solar atmosphere
Authors: Hudson, Hugh S.; MacKinnon, Alec; Szydlarski, Mikolaj;
   Carlsson, Mats
2020MNRAS.491.4852H    Altcode: 2019arXiv191001186H; 2019MNRAS.tmp.3116H
  High-energy particles enter the solar atmosphere from Galactic or
  solar coronal sources, and produce 'albedo' emission from the quiet
  Sun that is now observable across a wide range of photon energies. The
  interaction of high-energy particles in a stellar atmosphere depends
  essentially upon the joint variation of the magnetic field and plasma
  density, which heretofore has been characterized parametrically as
  P ∝ B<SUP>α</SUP> with P the gas pressure and B the magnitude of
  the magnetic field. We re-examine that parametrization by using a
  self-consistent 3D MHD model (Bifrost) and show that this relationship
  tends to P ∝ B<SUP>3.5 ± 0.1</SUP> based on the visible portions
  of the sample of open-field flux tubes in such a model, but with large
  variations from point to point. This scatter corresponds to the strong
  meandering of the open-field flux tubes in the lower atmosphere, which
  will have a strong effect on the prediction of the emission anisotropy
  (limb brightening). The simulations show that much of the open flux
  in coronal holes originates in weak-field regions within the granular
  pattern of the convective motions seen in the simulations.

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Title: Capabilities of bisector analysis of the Si I 10 827 Å line
    for estimating line-of-sight velocities in the quiet Sun
Authors: González Manrique, S. J.; Quintero Noda, C.; Kuckein, C.;
   Ruiz Cobo, B.; Carlsson, M.
2020A&A...634A..19G    Altcode: 2020arXiv200100508G
  We examine the capabilities of a fast and simple method to infer
  line-of-sight (LOS) velocities from observations of the photospheric
  Si I 10 827 Å line. This spectral line is routinely observed together
  with the chromospheric He I 10 830 Å triplet as it helps to constrain
  the atmospheric parameters. We study the accuracy of bisector analysis
  and a line core fit of Si I 10 827 Å. We employ synthetic profiles
  starting from the Bifrost enhanced network simulation. The profiles are
  computed solving the radiative transfer equation, including non-local
  thermodynamic equilibrium effects on the determination of the atomic
  level populations of Si I. We found a good correlation between the
  inferred velocities from bisectors taken at different line profile
  intensities and the original simulation velocity at given optical
  depths. This good correlation means that we can associate bisectors
  taken at different line-profile percentages with atmospheric layers
  that linearly increase as we scan lower spectral line intensities. We
  also determined that a fit to the line-core intensity is robust and
  reliable, providing information about atmospheric layers that are
  above those accessible through bisectors. Therefore, by combining
  both methods on the Si I 10 827 Å line, we can seamlessly trace the
  quiet-Sun LOS velocity stratification from the deep photosphere to
  higher layers until around logτ = -3.5 in a fast and straightforward
  way. This method is ideal for generating quick-look reference images
  for future missions like the Daniel K. Inoue Solar Telescope and the
  European Solar Telescope, for example.

---------------------------------------------------------
Title: Nonequilibrium ionization and ambipolar diffusion in solar
    magnetic flux emergence processes
Authors: Nóbrega-Siverio, D.; Moreno-Insertis, F.; Martínez-Sykora,
   J.; Carlsson, M.; Szydlarski, M.
2020A&A...633A..66N    Altcode: 2019arXiv191201015N
  Context. Magnetic flux emergence from the solar interior has
  been shown to be a key mechanism for unleashing a wide variety of
  phenomena. However, there are still open questions concerning the
  rise of the magnetized plasma through the atmosphere, mainly in
  the chromosphere, where the plasma departs from local thermodynamic
  equilibrium (LTE) and is partially ionized. <BR /> Aims: We aim to
  investigate the impact of the nonequilibrium (NEQ) ionization and
  recombination and molecule formation of hydrogen, as well as ambipolar
  diffusion, on the dynamics and thermodynamics of the flux emergence
  process. <BR /> Methods: Using the radiation-magnetohydrodynamic
  Bifrost code, we performed 2.5D numerical experiments of magnetic flux
  emergence from the convection zone up to the corona. The experiments
  include the NEQ ionization and recombination of atomic hydrogen, the NEQ
  formation and dissociation of H<SUB>2</SUB> molecules, and the ambipolar
  diffusion term of the generalized Ohm's law. <BR /> Results: Our
  experiments show that the LTE assumption substantially underestimates
  the ionization fraction in most of the emerged region, leading to an
  artificial increase in the ambipolar diffusion and, therefore, in the
  heating and temperatures as compared to those found when taking the
  NEQ effects on the hydrogen ion population into account. We see that
  LTE also overestimates the number density of H<SUB>2</SUB> molecules
  within the emerged region, thus mistakenly magnifying the exothermic
  contribution of the H<SUB>2</SUB> molecule formation to the thermal
  energy during the flux emergence process. We find that the ambipolar
  diffusion does not significantly affect the amount of total unsigned
  emerged magnetic flux, but it is important in the shocks that cross
  the emerged region, heating the plasma on characteristic times ranging
  from 0.1 to 100 s. We also briefly discuss the importance of including
  elements heavier than hydrogen in the equation of state so as not to
  overestimate the role of ambipolar diffusion in the atmosphere. <P
  />Movies associated to Figs. 2-5, 8, 9, and A.1 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936944/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: The SPICE (Spectral Imaging of the Coronal Environment)
    Ultraviolet Imaging Spectrograph Investigation
Authors: Hassler, D.; Auchere, F.; Carlsson, M.; Fludra, A.; Giunta,
   A. S.; Mueller, D.; Peter, H.; Parenti, S.; Teriaca, L.; Fredvik, T.
2019AGUFMSH24A..02H    Altcode:
  One of the primary objectives of the Solar Orbiter mission is to link
  remote sensing observations of the solar surface structures with in-situ
  observations of solar wind streams. The SPICE (Spectral Imaging of the
  Coronal Environment) instrument will characterize the plasma properties
  of regions near the Sun to directly compare with in-situ measurements
  from both Solar Orbiter &amp; Parker Solar Probe. Specifically, SPICE
  will map outflow velocities of surface features to solar wind structures
  with similar composition (FIP, M/q) measured in-situ by the SWA/HIS
  instrument on Solar Orbiter. These observations will help discriminate
  models of solar wind origin by matching composition signatures in
  solar wind streams to surface feature composition, and discriminate
  physical processes that inject material from closed structures into
  solar wind streams. <P />This presentation will provide an overview of
  the SPICE investigation, including science &amp; measurement objective,
  instrument design, capabilities and performance as measured during
  calibration prior to delivery to the Solar Orbiter spacecraft. The
  presentation will also provide a description of the operations concept
  and data processing during the mission.

---------------------------------------------------------
Title: Science Requirement Document (SRD) for the European Solar
    Telescope (EST) (2nd edition, December 2019)
Authors: Schlichenmaier, R.; Bellot Rubio, L. R.; Collados, M.;
   Erdelyi, R.; Feller, A.; Fletcher, L.; Jurcak, J.; Khomenko, E.;
   Leenaarts, J.; Matthews, S.; Belluzzi, L.; Carlsson, M.; Dalmasse,
   K.; Danilovic, S.; Gömöry, P.; Kuckein, C.; Manso Sainz, R.;
   Martinez Gonzalez, M.; Mathioudakis, M.; Ortiz, A.; Riethmüller,
   T. L.; Rouppe van der Voort, L.; Simoes, P. J. A.; Trujillo Bueno,
   J.; Utz, D.; Zuccarello, F.
2019arXiv191208650S    Altcode:
  The European Solar Telescope (EST) is a research infrastructure
  for solar physics. It is planned to be an on-axis solar telescope
  with an aperture of 4 m and equipped with an innovative suite of
  spectro-polarimetric and imaging post-focus instrumentation. The EST
  project was initiated and is driven by EAST, the European Association
  for Solar Telescopes. EAST was founded in 2006 as an association
  of 14 European countries. Today, as of December 2019, EAST consists
  of 26 European research institutes from 18 European countries. The
  Preliminary Design Phase of EST was accomplished between 2008 and
  2011. During this phase, in 2010, the first version of the EST Science
  Requirement Document (SRD) was published. After EST became a project
  on the ESFRI roadmap 2016, the preparatory phase started. The goal
  of the preparatory phase is to accomplish a final design for the
  telescope and the legal governance structure of EST. A major milestone
  on this path is to revisit and update the Science Requirement Document
  (SRD). The EST Science Advisory Group (SAG) has been constituted by
  EAST and the Board of the PRE-EST EU project in November 2017 and has
  been charged with the task of providing with a final statement on the
  science requirements for EST. Based on the conceptual design, the SRD
  update takes into account recent technical and scientific developments,
  to ensure that EST provides significant advancement beyond the current
  state-of-the-art. The present update of the EST SRD has been developed
  and discussed during a series of EST SAG meetings. The SRD develops
  the top-level science objectives of EST into individual science
  cases. Identifying critical science requirements is one of its main
  goals. Those requirements will define the capabilities of EST and the
  post-focus instrument suite. The technical requirements for the final
  design of EST will be derived from the SRD.

---------------------------------------------------------
Title: Cosmic Rays Across the Rainbow Bridge: Particle Interactions
    in a Magnetized Plasma Atmosphere
Authors: Hudson, H. S.; MacKinnon, A.; Szydlarski, M.; Carlsson, M.
2019AGUFMSH21B..02H    Altcode:
  High-energy particles enter the solar atmosphere from Galactic or solar
  sources, producing gamma-ray "albedo” radiations. These emissions come
  from the quiet Sun and from the large-scale corona, as well as from
  the vicinity of flares, and have been observed across a wide range of
  photon energies (MeV to GeV). The interaction of high-energy particles
  in the solar atmosphere depends essentially upon the joint variation of
  the magnetic field and the gas, and this has heretofore generally been
  characterized parametrically as P ~ B<SUP>alpha</SUP> (Zweibel &amp;
  Haber 1983), with P the gas pressure and B the magnitude of the magnetic
  field. We have checked this relationship with a Bifrost 3D MHD model,
  approximating the particle transport as a guiding-center motion along
  "open” (large-scale) fieldlines. We find alpha ~ 2.2 in the strongest
  (kG) fields in the simulation, but individual field structures have
  widely disparate relationships. The scatter corresponds to the strong
  meandering of the open-field flux tubes in the lower atmosphere and
  to their incessant dynamics. We discuss this and other aspects of
  the interactions of high-energy particles with the Sun (the "solar
  Størmer problem”).

---------------------------------------------------------
Title: Co-spatial velocity and magnetic swirls in the simulated
    solar photosphere
Authors: Liu, Jiajia; Carlsson, Mats; Nelson, Chris J.; Erdélyi,
   Robert
2019A&A...632A..97L    Altcode: 2019arXiv191110923L
  Context. Velocity or intensity swirls have now been shown to be
  widely present throughout the photosphere and chromosphere. It has
  been suggested that these events could contribute to the heating
  of the upper solar atmosphere, via exciting Alfvén pulses, which
  could carry significant amounts of energy. However, the conjectured
  necessary physical conditions for their excitation, that the magnetic
  field rotates co-spatially and co-temporally with the velocity field,
  has not been verified. <BR /> Aims: We aim to understand whether
  photospheric velocity swirls exist co-spatially and co-temporally with
  photospheric magnetic swirls, in order to demonstrate the link between
  swirls and pulses. <BR /> Methods: The automated swirl detection
  algorithm (ASDA) is applied to the photospheric horizontal velocity
  and vertical magnetic fields obtained from a series of realistic
  numerical simulations using the radiative magnetohydrodynamics (RMHD)
  code Bifrost. The spatial relationship between the detected velocity
  and magnetic swirls is further investigated via a well-defined
  correlation index (CI) study. <BR /> Results: On average, there are
  ∼63 short-lived photospheric velocity swirls (with lifetimes mostly
  less than 20 s, and average radius of ∼37 km and rotating speeds of
  ∼2.5 km s<SUP>-1</SUP>) detected in a field of view (FOV) of 6 ×
  6 Mm<SUP>-2</SUP>, implying a total population of velocity swirls of
  ∼1.06 × 10<SUP>7</SUP> in the solar photosphere. More than 80% of the
  detected velocity swirls are found to be accompanied by local magnetic
  concentrations in intergranular lanes. On average, ∼71% of the
  detected velocity swirls have been found to co-exist with photospheric
  magnetic swirls with the same rotating direction. <BR /> Conclusions:
  The co-temporal and co-spatial rotation in the photospheric velocity
  and magnetic fields provide evidence that the conjectured condition for
  the excitation of Alfvén pulses by photospheric swirls is fulfilled.

---------------------------------------------------------
Title: Modeling Mg II during Solar Flares. II. Nonequilibrium Effects
Authors: Kerr, Graham S.; Carlsson, Mats; Allred, Joel C.
2019ApJ...885..119K    Altcode: 2019arXiv190913300K
  To extract the information that the Mg II NUV spectra (observed by the
  Interface Region Imaging Spectrograph) carry about the chromosphere
  during solar flares, and to validate models of energy transport via
  model-data comparison, forward modeling is required. The assumption
  of statistical equilibrium (SE) is typically used to obtain the
  atomic level populations from snapshots of flare atmospheres, due
  to computational necessity. However, it is possible that relying
  on SE could lead to spurious results. We compare solving the atomic
  level populations via SE versus a nonequilibrium (NEQ) time-dependent
  approach. This was achieved using flare simulations from RADYN alongside
  the minority species version MS_RADYN from which the time-dependent
  Mg II atomic level populations and radiation transfer were computed in
  complete frequency redistribution. The impacts on the emergent profiles,
  lightcurves, line ratios, and formation heights are discussed. In
  summary we note that NEQ effects during flares are typically important
  only in the initial stages and for a short period following the
  cessation of the energy injection. An analysis of the timescales of
  ionization equilibrium reveals that for most of the duration of the
  flare, when the temperatures and densities are sufficiently enhanced,
  the relaxation timescales are short (τ <SUB>relax</SUB> &lt; 0.1 s),
  so that the equilibrium solution is an adequate approximation. These
  effects vary with the size of the flare, however. In weaker flares,
  effects can be more pronounced. We recommend that NEQ effects be
  considered when possible but that SE is sufficient at most stages of
  the flare.

---------------------------------------------------------
Title: Observational constraints on the origin of the elements. I. 3D
    NLTE formation of Mn lines in late-type stars
Authors: Bergemann, Maria; Gallagher, Andrew J.; Eitner, Philipp;
   Bautista, Manuel; Collet, Remo; Yakovleva, Svetlana A.; Mayriedl,
   Anja; Plez, Bertrand; Carlsson, Mats; Leenaarts, Jorrit; Belyaev,
   Andrey K.; Hansen, Camilla
2019A&A...631A..80B    Altcode: 2019arXiv190505200B
  Manganese (Mn) is a key Fe-group element, commonly employed in
  stellar population and nucleosynthesis studies to explore the role
  of SN Ia. We have developed a new non-local thermodynamic equilibrium
  (NLTE) model of Mn, including new photo-ionisation cross-sections and
  new transition rates caused by collisions with H and H<SUP>-</SUP>
  atoms. We applied the model in combination with one-dimensional (1D)
  LTE model atmospheres and 3D hydrodynamical simulations of stellar
  convection to quantify the impact of NLTE and convection on the line
  formation. We show that the effects of NLTE are present in Mn I and, to
  a lesser degree, in Mn II lines, and these increase with metallicity and
  with the effective temperature of a model. Employing 3D NLTE radiative
  transfer, we derive a new abundance of Mn in the Sun, A(Mn) = 5.52 ±
  0.03 dex, consistent with the element abundance in C I meteorites. We
  also applied our methods to the analysis of three metal-poor benchmark
  stars. We find that 3D NLTE abundances are significantly higher than 1D
  LTE. For dwarfs, the differences between 1D NLTE and 3D NLTE abundances
  are typically within 0.15 dex, however, the effects are much larger in
  the atmospheres of giants owing to their more vigorous convection. We
  show that 3D NLTE successfully solves the ionisation and excitation
  balance for the RGB star HD 122563 that cannot be achieved by 1D LTE or
  1D NLTE modelling. For HD 84937 and HD 140283, the ionisation balance is
  satisfied, however, the resonance Mn I triplet lines still show somewhat
  lower abundances compared to the high-excitation lines. Our results for
  the benchmark stars confirm that 1D LTE modelling leads to significant
  systematic biases in Mn abundances across the full wavelength range
  from the blue to the IR. We also produce a list of Mn lines that are
  not significantly biased by 3D and can be reliably, within the 0.1 dex
  uncertainty, modelled in 1D NLTE. <P />The new cross-sections and rate
  coefficients are only available at the CDS via anonymous ftp to <A
  href="http://cdsarc.u-strasbg.fr">http://cdsarc.u-strasbg.fr</A>
  (ftp://130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/631/A80">http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/631/A80</A>The
  atomic model is available at <A
  href="https://keeper.mpdl.mpg.de/f/1ce2a838074b49fc9424/?dl=1">https://keeper.mpdl.mpg.de/f/1ce2a838074b49fc9424/?dl=1</A>

---------------------------------------------------------
Title: A comprehensive three-dimensional radiative magnetohydrodynamic
    simulation of a solar flare
Authors: Cheung, M. C. M.; Rempel, M.; Chintzoglou, G.; Chen, F.;
   Testa, P.; Martínez-Sykora, J.; Sainz Dalda, A.; DeRosa, M. L.;
   Malanushenko, A.; Hansteen, V.; De Pontieu, B.; Carlsson, M.; Gudiksen,
   B.; McIntosh, S. W.
2019NatAs...3..160C    Altcode: 2018NatAs...3..160C
  Solar and stellar flares are the most intense emitters of X-rays and
  extreme ultraviolet radiation in planetary systems<SUP>1,2</SUP>. On
  the Sun, strong flares are usually found in newly emerging sunspot
  regions<SUP>3</SUP>. The emergence of these magnetic sunspot groups
  leads to the accumulation of magnetic energy in the corona. When
  the magnetic field undergoes abrupt relaxation, the energy released
  powers coronal mass ejections as well as heating plasma to temperatures
  beyond tens of millions of kelvins. While recent work has shed light
  on how magnetic energy and twist accumulate in the corona<SUP>4</SUP>
  and on how three-dimensional magnetic reconnection allows for rapid
  energy release<SUP>5,6</SUP>, a self-consistent model capturing how
  such magnetic changes translate into observable diagnostics has remained
  elusive. Here, we present a comprehensive radiative magnetohydrodynamics
  simulation of a solar flare capturing the process from emergence to
  eruption. The simulation has sufficient realism for the synthesis of
  remote sensing measurements to compare with observations at visible,
  ultraviolet and X-ray wavelengths. This unifying model allows us to
  explain a number of well-known features of solar flares<SUP>7</SUP>,
  including the time profile of the X-ray flux during flares, origin
  and temporal evolution of chromospheric evaporation and condensation,
  and sweeping of flare ribbons in the lower atmosphere. Furthermore,
  the model reproduces the apparent non-thermal shape of coronal X-ray
  spectra, which is the result of the superposition of multi-component
  super-hot plasmas<SUP>8</SUP> up to and beyond 100 million K.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Mn lines 3D NLTE formation in
    late-type stars (Bergemann+, 2019)
Authors: Bergemann, M.; Gallagher, A. G.; Eitner, P.; Bautista, M.;
   Collet, R.; Yakovleva, S.; Mayriedl, A.; Plez, B.; Carlsson, M.;
   Leenaarts, J.; Belyaev, A. K.; Hansen, C.
2019yCat..36310080B    Altcode:
  Model rate coefficients in cm<SUP>3</SUP>/s for neutralization and
  de-exci processes in collisions of MnI+H and MnII+H<SUP>-</SUP>, as
  well as MnII+H and MnIII+H<SUP>-</SUP> for temperatures from T=1000K to
  T=10000K. <P />Total photoionization cross section for MnI levels. <P
  />(24 data files).

---------------------------------------------------------
Title: Modeling Mg II During Solar Flares. I. Partial Frequency
    Redistribution, Opacity, and Coronal Irradiation
Authors: Kerr, Graham S.; Allred, Joel C.; Carlsson, Mats
2019ApJ...883...57K    Altcode: 2019arXiv190805329K
  The Interface Region Imaging Spectrograph has routinely observed the
  flaring Mg II near-ultraviolet (NUV) spectrum, offering excellent
  diagnostic potential and a window into the location of energy
  deposition. A number of studies have forward-modeled both the general
  properties of these lines and specific flare observations. Generally
  these have forward-modeled radiation via post-processing of snapshots
  from hydrodynamic flare simulations through radiation transfer
  codes. There has, however, not been a study of how the physics
  included in these radiation transport codes affects the solution. A
  baseline setup for forward-modeling Mg II in flares is presented and
  contrasted with approaches that add or remove complexity. It is shown
  for Mg II that (1) partial frequency distribution (PRD) is still
  required during flare simulations despite the increased densities;
  (2) using full angle-dependent PRD affects the solution but takes
  significantly longer to process a snapshot; (3) including Mg I in
  non-LTE (NLTE) results in negligible differences to the Mg II lines
  but does affect the NUV quasi-continuum; (4) only hydrogen and Mg II
  need to be included in NLTE; (5) ideally the nonequilibrium hydrogen
  populations, with nonthermal collisional rates, should be used rather
  than the statistical equilibrium populations; (6) an atom consisting
  of only the ground state, h and k upper levels, and continuum level
  is insufficient to model the resonance lines; and (7) irradiation from
  a hot, dense flaring transition region can affect the formation of Mg
  II. We discuss modifications to the RH code allowing straightforward
  inclusion of the transition region and coronal irradiation in flares.

---------------------------------------------------------
Title: New View of the Solar Chromosphere
Authors: Carlsson, Mats; De Pontieu, Bart; Hansteen, Viggo H.
2019ARA&A..57..189C    Altcode:
  The solar chromosphere forms a crucial, yet complex and until recently
  poorly understood, interface between the solar photosphere and the
  heliosphere. Advances in high-resolution instrumentation, adaptive
  optics, image reconstruction techniques, and space-based observatories
  allow unprecedented high-resolution views of the finely structured and
  highly dynamic chromosphere. Dramatic progress in numerical computations
  allows 3D radiative magnetohydrodynamic forward models to take the place
  of the previous generation of 1D semiempirical atmosphere models. These
  new models provide deep insight into complex nonlocal thermodynamic
  equilibrium chromospheric diagnostics and enable physics-based
  interpretations of observations. This combination of modeling and
  observations has led to new insights into the role of shock waves,
  transverse magnetic waves, magnetic reconnection and flux emergence
  in the chromospheric energy balance, the formation of spicules,
  the impact of ion-neutral interactions, and the connectivity between
  chromosphere and transition region. During the next few years, the
  advent of new instrumentation (integral-field-unit spectropolarimetry)
  and observatories (ALMA, DKIST), coupled with novel inversion codes and
  expansion of existing numerical models to deal with ever more complex
  physical processes (including multifluid approaches), is expected to
  lead to major new insights into the dominant heating processes in the
  chromosphere and beyond.

---------------------------------------------------------
Title: Modelling of Flare Processes: A Comparison of the Two RHD
    Codes FLARIX and RADYN
Authors: Kašparová, Jana; Carlsson, Mats; Heinzel, Petr; Varady,
   Michal
2019ASPC..519..141K    Altcode:
  We present a comparison of two autonomous, methodologically different
  radiation hydrodynamic codes, FLARIX and RADYN, and their use to model
  the solar flare processes. Both codes can model the time evolution
  of a 1D atmosphere heated by a specified process, e.g. by electron
  beams propagating from the injection site in the corona down to the
  lower atmosphere. In such a scenario time scales can be rather short
  and lead to fast heating on even sub-second time scales. Our aim is
  to compare the FLARIX and RADYN codes using exactly the same setup
  and model conditions. Although such a comparison has never been done
  successfully before for this type of codes, we will present a close
  agreement between the time evolution of the modelled atmospheric
  structure for a test case of electron beam heating.

---------------------------------------------------------
Title: Modeling Mg II h, k and Triplet Lines at Solar Flare Ribbons
Authors: Zhu, Yingjie; Kowalski, Adam F.; Tian, Hui; Uitenbroek, Han;
   Carlsson, Mats; Allred, Joel C.
2019ApJ...879...19Z    Altcode: 2019arXiv190412285Z
  Observations from the Interface Region Imaging Spectrograph often
  reveal significantly broadened and non-reversed profiles of the Mg II
  h, k and triplet lines at flare ribbons. To understand the formation
  of these optically thick Mg II lines, we perform plane-parallel
  radiative hydrodynamics modeling with the RADYN code, and then
  recalculate the Mg II line profiles from RADYN atmosphere snapshots
  using the radiative transfer code RH. We find that the current RH
  code significantly underestimates the Mg II h and k Stark widths. By
  implementing semiclassical perturbation approximation results of
  quadratic Stark broadening from the STARK-B database in the RH code,
  the Stark broadenings are found to be one order of magnitude larger
  than those calculated from the current RH code. However, the improved
  Stark widths are still too small, and another factor of 30 has to be
  multiplied to reproduce the significantly broadened lines and adjacent
  continuum seen in observations. Nonthermal electrons, magnetic fields,
  three-dimensional effects, or electron density effects may account
  for this factor. Without modifying the RADYN atmosphere, we have also
  reproduced non-reversed Mg II h and k profiles, which appear when the
  electron beam energy flux is decreasing. These profiles are formed at
  an electron density of ∼8 × 10<SUP>14</SUP> cm<SUP>-3</SUP> and a
  temperature of ∼1.4 × 10<SUP>4</SUP> K, where the source function
  slightly deviates from the Planck function. Our investigation also
  demonstrates that at flare ribbons the triplet lines are formed in the
  upper chromosphere, close to the formation heights of the h and k lines.

---------------------------------------------------------
Title: The Response of the Lyα Line in Different Flare Heating Models
Authors: Hong, Jie; Li, Ying; Ding, M. D.; Carlsson, Mats
2019ApJ...879..128H    Altcode: 2019arXiv190513356H
  The solar Lyα line is the strongest line in the ultraviolet waveband,
  and is greatly enhanced during solar flares. Here we present
  radiative hydrodynamic simulations of solar flares under different
  heating models, and calculate the response of this line taking into
  account nonequilibrium ionization of hydrogen and partial frequency
  redistribution. We find that in nonthermal heating models, the Lyα line
  can show a red or blue asymmetry corresponding to the chromospheric
  evaporation or condensation, respectively. The asymmetry may change
  from red to blue if the electron beam flux is large enough to produce
  a significant chromospheric condensation region. In the Lyα intensity
  light curve, a dip appears when the change of asymmetry occurs. In
  thermal models, the Lyα line intensity peaks quickly and then falls,
  and the profile has an overall red asymmetry, which is similar to the
  profiles from heating by a soft electron beam. The Lyα profile shows
  a single red peak at the end of thermal heating, and the whole line
  is formed in a very small height range.

---------------------------------------------------------
Title: Chromospheric polarimetry through multiline observations of
the 850 nm spectral region III: Chromospheric jets driven by twisted
    magnetic fields
Authors: Quintero Noda, C.; Iijima, H.; Katsukawa, Y.; Shimizu,
   T.; Carlsson, M.; de la Cruz Rodríguez, J.; Ruiz Cobo, B.; Orozco
   Suárez, D.; Oba, T.; Anan, T.; Kubo, M.; Kawabata, Y.; Ichimoto,
   K.; Suematsu, Y.
2019MNRAS.486.4203Q    Altcode: 2019MNRAS.tmp.1081N; 2019arXiv190409151Q
  We investigate the diagnostic potential of the spectral lines at 850
  nm for understanding the magnetism of the lower atmosphere. For that
  purpose, we use a newly developed 3D simulation of a chromospheric
  jet to check the sensitivity of the spectral lines to this phenomenon
  as well as our ability to infer the atmospheric information through
  spectropolarimetric inversions of noisy synthetic data. We start
  comparing the benefits of inverting the entire spectrum at 850 nm versus
  only the Ca II 8542 Å spectral line. We found a better match of the
  input atmosphere for the former case, mainly at lower heights. However,
  the results at higher layers were not accurate. After several tests,
  we determined that we need to weight more the chromospheric lines
  than the photospheric ones in the computation of the goodness of the
  fit. The new inversion configuration allows us to obtain better fits and
  consequently more accurate physical parameters. Therefore, to extract
  the most from multiline inversions, a proper set of weights needs to
  be estimated. Besides that, we conclude again that the lines at 850
  nm, or a similar arrangement with Ca II 8542 Å plus Zeeman-sensitive
  photospheric lines, pose the best-observing configuration for examining
  the thermal and magnetic properties of the lower solar atmosphere.

---------------------------------------------------------
Title: Dissecting bombs and bursts: non-LTE inversions of
    low-atmosphere reconnection in SST and IRIS observations
Authors: Vissers, G. J. M.; de la Cruz Rodríguez, J.; Libbrecht,
   T.; Rouppe van der Voort, L. H. M.; Scharmer, G. B.; Carlsson, M.
2019A&A...627A.101V    Altcode: 2019arXiv190502035V
  Ellerman bombs and UV bursts are transient brightenings that are
  ubiquitously observed in the lower atmospheres of active and emerging
  flux regions. As they are believed to pinpoint sites of magnetic
  reconnection in reconfiguring fields, understanding their occurrence
  and detailed evolution may provide useful insight into the overall
  evolution of active regions. Here we present results from inversions
  of SST/CRISP and CHROMIS, as well as IRIS data of such transient
  events. Combining information from the Mg II h &amp; k, Si IV, and Ca
  II 8542 Å and Ca II H &amp; K lines, we aim to characterise their
  temperature and velocity stratification, as well as their magnetic
  field configuration. We find average temperature enhancements of
  a few thousand kelvin, close to the classical temperature minimum
  and similar to previous studies, but localised peak temperatures
  of up to 10 000-15 000 K from Ca II inversions. Including Mg II
  appears to generally dampen these temperature enhancements to below
  8000 K, while Si IV requires temperatures in excess of 10 000 K at
  low heights, but may also be reproduced with secondary temperature
  enhancements of 35 000-60 000 K higher up. However, reproducing Si
  IV comes at the expense of overestimating the Mg II emission. The
  line-of-sight velocity maps show clear bi-directional jet signatures
  for some events and strong correlation with substructure in the
  intensity images in general. Absolute line-of-sight velocities range
  between 5 and 20 km s<SUP>-1</SUP> on average, with slightly larger
  velocities towards, rather than away from, the observer. The inverted
  magnetic field parameters show an enhancement of the horizontal
  field co-located with the brightenings at heights similar to that of
  the temperature increase. We are thus able to largely reproduce the
  observational properties of Ellerman bombs with the UV burst signature
  (e.g. intensities, profile asymmetries, morphology, and bi-directional
  jet signatures), with temperature stratifications peaking close
  to the classical temperature minimum. Correctly modelling the Si
  IV emission in agreement with all other diagnostics is however an
  outstanding issue and remains paramount in explaining its apparent
  coincidence with Hα emission. Fine-tuning the approach (accounting for
  resolution differences, fitting localised temperature enhancements,
  and/or performing spatially coupled inversions) is likely necessary
  in order to obtain better agreement between all considered diagnostics.

---------------------------------------------------------
Title: Radiative MHD Simulation of a Solar Flare
Authors: Cheung, Mark; Rempel, Matthias D.; Chintzoglou, Georgios;
   Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
   DeRosa, Marc L.; Malanushenko, Anna; Hansteen, Viggo; Carlsson, Mats;
   De Pontieu, Bart; Gudiksen, Boris; McIntosh, Scott W.
2019AAS...23431005C    Altcode:
  We present a radiative MHD simulation of a solar flare. The
  computational domain captures the near-surface layers of the convection
  zone and overlying atmosphere. Inspired by the observed evolution of
  NOAA Active Region (AR) 12017, a parasitic bipolar region is imposed
  to emerge in the vicinity of a pre-existing sunspot. The emergence of
  twisted magnetic flux generates shear flows that create a pre-existing
  flux rope underneath the canopy field of the sunspot. Following erosion
  of the overlying bootstrapping field, the flux rope erupts. Rapid
  release of magnetic energy results in multi-wavelength synthetic
  observables (including X-ray spectra, narrowband EUV images, Doppler
  shifts of EUV lines) that are consistent with flare observations. This
  works suggests the super-position of multi-thermal, superhot (up
  to 100 MK) plasma may be partially responsible for the apparent
  non-thermal shape of coronal X-ray sources in flares. Implications
  for remote sensing observations of other astrophysical objects is also
  discussed. This work is an important stepping stone toward high-fidelity
  data-driven MHD models.

---------------------------------------------------------
Title: Ellerman bombs and UV bursts: transient events in chromospheric
    current sheets
Authors: Hansteen, V.; Ortiz, A.; Archontis, V.; Carlsson, M.; Pereira,
   T. M. D.; Bjørgen, J. P.
2019A&A...626A..33H    Altcode: 2019arXiv190411524H
  Context. Ellerman bombs (EBs), observed in the photospheric wings
  of the Hα line, and UV bursts, observed in the transition region Si
  IV line, are both brightenings related to flux emergence regions and
  specifically to magnetic flux of opposite polarity that meet in the
  photosphere. These two reconnection-related phenomena, nominally formed
  far apart, occasionally occur in the same location and at the same
  time, thus challenging our understanding of reconnection and heating
  of the lower solar atmosphere. <BR /> Aims: We consider the formation
  of an active region, including long fibrils and hot and dense coronal
  plasma. The emergence of a untwisted magnetic flux sheet, injected 2.5
  Mm below the photosphere, is studied as it pierces the photosphere
  and interacts with the preexisting ambient field. Specifically, we
  aim to study whether EBs and UV bursts are generated as a result of
  such flux emergence and examine their physical relationship. <BR />
  Methods: The Bifrost radiative magnetohydrodynamics code was used
  to model flux emerging into a model atmosphere that contained a
  fairly strong ambient field, constraining the emerging field to
  a limited volume wherein multiple reconnection events occur as
  the field breaks through the photosphere and expands into the outer
  atmosphere. Synthetic spectra of the different reconnection events were
  computed using the 1.5D RH code and the fully 3D MULTI3D code. <BR
  /> Results: The formation of UV bursts and EBs at intensities and
  with line profiles that are highly reminiscent of observed spectra
  are understood to be a result of the reconnection of emerging flux
  with itself in a long-lasting current sheet that extends over several
  scale heights through the chromosphere. Synthetic spectra in the Hα
  and Si IV 139.376 nm lines both show characteristics that are typical
  of the observations. These synthetic diagnostics suggest that there
  are no compelling reasons to assume that UV bursts occur in the
  photosphere. Instead, EBs and UV bursts are occasionally formed at
  opposite ends of a long current sheet that resides in an extended bubble
  of cool gas. <P />The movie associated to Fig. 3 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201935376/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: On the Origin of the Magnetic Energy in the Quiet Solar
    Chromosphere
Authors: Martínez-Sykora, Juan; Hansteen, Viggo H.; Gudiksen, Boris;
   Carlsson, Mats; De Pontieu, Bart; Gošić, Milan
2019ApJ...878...40M    Altcode: 2019arXiv190404464M
  The presence of magnetic field is crucial in the transport of energy
  through the solar atmosphere. Recent ground-based and space-borne
  observations of the quiet Sun have revealed that magnetic field
  accumulates at photospheric heights, via a local dynamo or from
  small-scale flux emergence events. However, most of this small-scale
  magnetic field may not expand into the chromosphere due to the entropy
  drop with height at the photosphere. Here we present a study that uses
  a high-resolution 3D radiative MHD simulation of the solar atmosphere
  with non-gray and non-LTE radiative transfer and thermal conduction
  along the magnetic field to reveal that (1) the net magnetic flux
  from the simulated quiet photosphere is not sufficient to maintain a
  chromospheric magnetic field (on average), (2) processes in the lower
  chromosphere, in the region dominated by magnetoacoustic shocks,
  are able to convert kinetic energy into magnetic energy, (3) the
  magnetic energy in the chromosphere increases linearly in time until
  the rms of the magnetic field strength saturates at roughly 4-30 G
  (horizontal average) due to conversion from kinetic energy, (4) and
  that the magnetic features formed in the chromosphere are localized
  to this region.

---------------------------------------------------------
Title: Mg II NUV Spectra in Solar Flares: Modelling approaches and
    Velocity Diagnostics
Authors: Kerr, Graham S.; Allred, Joel C.; Carlsson, Mats
2019AAS...23420413K    Altcode:
  The Interface Region Imaging Spectrograph (IRIS) has observed the Mg II
  NUV spectrum (the h &amp; k resonance and the subordinate triplet), in
  hundreds of solar flares. These lines form throughout the chromosphere,
  offering excellent diagnostic potential and a window into the location
  of flare energy deposition. A number of studies have attempted to
  forward model both the general properties of these lines in flares,
  and specific flare observations. Generally, these investigations have
  post-processed snapshots of solar atmospheres from hydrodynamic or
  radiation hydrodynamic flare simulations through advanced radiation
  transport codes. There has, however, not been a survey of how the
  physics included in these radiation transport codes affects the
  solution. We present here a detailed study showing what physics must
  be included when forward modelling these lines, including the use
  of partial redistribution (PRD), the specific treatment of (PRD),
  the need for a sufficiently large model atom, the inclusion of Mg
  I in NLTE, the inclusion of other species in NLTE, and the impact
  of using non-equilibrium hydrogen populations. Futher, we contrast
  Mg II computed in statistical equilibrium with a computation that
  includes non-equilibrium effects. Finally, we apply commonly used
  observational metrics for inferring Doppler speeds to the synthetic
  spectra, demonstrating that optical depth and radiation transfer
  effects can confuse the interpretation of those measurements.

---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: McKenzie, D. E.; Ishikawa, R.; Trujillo Bueno, J.; Auchére,
   F.; Rachmeler, L. A.; Kubo, M.; Kobayashi, K.; Winebarger, A. R.;
   Bethge, C. W.; Narukage, N.; Kano, R.; Ishikawa, S.; de Pontieu,
   B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Štěpán, J.; del Pino
   Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
2019ASPC..526..361M    Altcode:
  The hydrogen Lyman-α line at 121.6 nm and the Mg k line at 279.5
  nm are especially relevant for deciphering the magnetic structure
  of the chromosphere since their line-center signals are formed in
  the chromosphere and transition region, with unique sensitivities to
  magnetic fields. We propose the Chromospheric LAyer Spectro-Polarimeter
  (CLASP2), to build upon the success of the first CLASP flight, which
  measured the linear polarization in H I Lyman-α. The existing CLASP
  instrument will be refitted to measure all four Stokes parameters in
  the 280 nm range, including variations due to the anisotropic radiation
  pumping, the Hanle effect, and the Zeeman effect.

---------------------------------------------------------
Title: Comparison of Scattering Polarization Signals Observed by
CLASP: Possible Indication of the Hanle Effect
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
   Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
   Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
   Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
   Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
   Sainz, R.; De Pomtieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
2019ASPC..526..305I    Altcode:
  The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP; Kano et
  al. 2012; Kobayashi et al. 2012; Kubo et al. 2014) observed, for the
  first time, the linear polarization produced by scattering processes
  in the hydrogen Lyman-α (121.57 nm) and Si III (120.56 nm) lines of
  the solar disk radiation. The complexity of the observed scattering
  polarization (i.e., conspicuous spatial variations in Q/I and U/I
  at spatial scales of 10″-20″ and the absence of center-to- limb
  variation at the Lyman-α center; see Kano et al. 2017) motivated us
  to search for possible hints of the operation of the Hanle effect by
  comparing: (a) the Lyman-α line center signal, for which the critical
  field strength (B<SUB>H</SUB>) for the onset of the Hanle effect is
  53 G, (b) the Lyman-α wing, which is insensitive to the Hanle effect,
  and (c) the Si III line, whose B<SUB>H</SUB> = 290 G. We focus on four
  regions with different total unsigned photospheric magnetic fluxes
  (estimated from SDO/HMI observations), and compare the corresponding
  U/I spatial variations in the Lyman-α wing, Lyman-α center, and Si III
  line. The U/I signal in the Lyman-α wing shows an antisymmetric spatial
  distribution, which is caused by the presence of a bright structure in
  all the selected regions, regardless of the total unsigned photospheric
  magnetic flux. In an internetwork region, the Lyman-α center shows an
  antisymmetric spatial variation across the selected bright structure,
  but it does not show it in other more magnetized regions. In the Si III
  line, the spatial variation of U/I deviates from the above-mentioned
  antisymmetric shape as the total unsigned photospheric magnetic flux
  increases. We argue that a plausible explanation of this differential
  behavior is the operation of the Hanle effect. <P />This work, presented
  in an oral contribution at this Workshop, has been published on The
  Astrophysical Journal (Ishikawa et al. 2017).

---------------------------------------------------------
Title: The solar chromosphere at millimetre and ultraviolet
    wavelengths. I. Radiation temperatures and a detailed comparison
Authors: Jafarzadeh, S.; Wedemeyer, S.; Szydlarski, M.; De Pontieu,
   B.; Rezaei, R.; Carlsson, M.
2019A&A...622A.150J    Altcode: 2019arXiv190105763J
  Solar observations with the Atacama Large Millimeter/submillimeter
  Array (ALMA) provide us with direct measurements of the brightness
  temperature in the solar chromosphere. We study the temperature
  distributions obtained with ALMA Band 6 (in four sub-bands at 1.21,
  1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of,
  a sunspot, comprising quasi-quiet and active regions with different
  amounts of underlying magnetic fields. We compare these temperatures
  with those obtained at near- and far-ultraviolet (UV) wavelengths
  (and with the line-core intensities of the optically-thin far-UV
  spectra), co-observed with the Interface Region Imaging Spectrograph
  (IRIS) explorer. These include the emission peaks and cores of the Mg
  II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores
  of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the
  mid-to-high chromosphere and the low transition region. Splitting the
  ALMA sub-bands resulted in an slight increase of spatial resolution in
  individual temperature maps, thus, resolving smaller-scale structures
  compared to those produced with the standard averaging routines. We
  find that the radiation temperatures have different, though somewhat
  overlapping, distributions in different wavelengths and in the various
  magnetic regions. Comparison of the ALMA temperatures with those of
  the UV diagnostics should, however, be interpreted with great caution,
  the former is formed under the local thermodynamic equilibrium (LTE)
  conditions, the latter under non-LTE. The mean radiation temperature
  of the ALMA Band 6 is similar to that extracted from the IRIS C II
  line in all areas with exception of the sunspot and pores where the C
  II poses higher radiation temperatures. In all magnetic regions, the
  Mg II lines associate with the lowest mean radiation temperatures in
  our sample. These will provide constraints for future numerical models.

---------------------------------------------------------
Title: SI IV Resonance Line Emission during Solar Flares: Non-LTE,
    Nonequilibrium, Radiation Transfer Simulations
Authors: Kerr, Graham S.; Carlsson, Mats; Allred, Joel C.; Young,
   Peter R.; Daw, Adrian N.
2019ApJ...871...23K    Altcode: 2018arXiv181111075K
  The Interface Region Imaging Spectrograph routinely observes the Si
  IV resonance lines. When analyzing quiescent observations of these
  lines, it has typically been assumed that they form under optically
  thin conditions. This is likely valid for the quiescent Sun, but
  this assumption has also been applied to the more extreme flaring
  scenario. We used 36 electron-beam-driven radiation hydrodynamic
  solar flare simulations, computed using the RADYN code, to probe
  the validity of this assumption. Using these simulated atmospheres,
  we solved the radiation transfer equations to obtain the non-LTE,
  nonequilibrium populations, line profiles, and opacities for a model
  silicon atom, including charge exchange processes. This was achieved
  using the “minority species” version of RADYN. The inclusion of
  charge exchange resulted in a substantial fraction of Si IV at cooler
  temperatures than those predicted by ionization equilibrium. All
  simulations with an injected energy flux F&gt; 5× {10}<SUP>10</SUP>
  erg cm<SUP>-2</SUP> s<SUP>-1</SUP> resulted in optical depth effects on
  the Si IV emission, with differences in both intensity and line shape
  compared to the optically thin calculation. Weaker flares (down to F ≈
  5 × 10<SUP>9</SUP> erg cm<SUP>-2</SUP> s<SUP>-1</SUP>) also resulted
  in Si IV emission forming under optically thick conditions, depending on
  the other beam parameters. When opacity was significant, the atmospheres
  generally had column masses in excess of 5 × 10<SUP>-6</SUP> g
  cm<SUP>-2</SUP> over the temperature range 40-100 kK, and the Si IV
  formation temperatures were between 30 and 60 kK. We urge caution
  when analyzing Si IV flare observations, or when computing synthetic
  emission without performing a full radiation transfer calculation.

---------------------------------------------------------
Title: Observationally Based Models of Penumbral Microjets
Authors: Esteban Pozuelo, S.; de la Cruz Rodríguez, J.; Drews, A.;
   Rouppe van der Voort, L.; Scharmer, G. B.; Carlsson, M.
2019ApJ...870...88E    Altcode: 2018arXiv181107881E
  We study the polarization signals and physical parameters of penumbral
  microjets (PMJs) by using high spatial resolution data taken in the
  Fe I 630 nm pair, Ca II 854.2 nm, and Ca II K lines with the CRISP
  and CHROMIS instruments at the Swedish 1 m Solar Telescope. We
  infer their physical parameters, such as physical observables in
  the photosphere and chromospheric velocity diagnostics, by different
  methods, including inversions of the observed Stokes profiles with
  the STiC code. PMJs harbor overall brighter Ca II K line profiles
  and conspicuous polarization signals in Ca II 854.2 nm, specifically
  in circular polarization that often shows multiple lobes mainly due
  to the shape of Stokes I. They usually overlap photospheric regions
  with a sheared magnetic field configuration, suggesting that magnetic
  reconnections could play an important role in the origin of PMJs. The
  discrepancy between their low LOS velocities and the high apparent
  speeds reported on earlier, as well as the existence of different
  vertical velocity gradients in the chromosphere, indicate that PMJs
  might not be entirely related to mass motions. Instead, PMJs could
  be due to perturbation fronts induced by magnetic reconnections
  occurring in the deep photosphere that propagate through the
  chromosphere. This reconnection may be associated with current heating
  that produces temperature enhancements from the temperature minimum
  region. Furthermore, enhanced collisions with electrons could also
  increase the coupling to the local conditions at higher layers during
  the PMJ phase, giving a possible explanation for the enhanced emission
  in the overall Ca II K profiles emerging from these transients.

---------------------------------------------------------
Title: Study of the polarization produced by the Zeeman effect in
    the solar Mg I b lines
Authors: Quintero Noda, C.; Uitenbroek, H.; Carlsson, M.; Orozco
   Suárez, D.; Katsukawa, Y.; Shimizu, T.; Ruiz Cobo, B.; Kubo, M.; Oba,
   T.; Kawabata, Y.; Hasegawa, T.; Ichimoto, K.; Anan, T.; Suematsu, Y.
2018MNRAS.481.5675Q    Altcode: 2018arXiv181001067Q; 2018MNRAS.tmp.2566Q
  The next generation of solar observatories aim to understand the
  magnetism of the solar chromosphere. Therefore, it is crucial to
  understand the polarimetric signatures of chromospheric spectral
  lines. For this purpose, we here examine the suitability of the three
  Fraunhofer Mg I b<SUB>1</SUB>, b<SUB>2</SUB>, and b<SUB>4</SUB> lines
  at 5183.6, 5172.7, and 5167.3 Å, respectively. We start by describing
  a simplified atomic model of only six levels and three line transitions
  for computing the atomic populations of the 3p-4s (multiplet number
  2) levels involved in the Mg I b line transitions assuming non-local
  thermodynamic conditions and considering only the Zeeman effect using
  the field-free approximation. We test this simplified atom against
  more complex ones finding that, although there are differences in the
  computed profiles, they are small compared with the advantages provided
  by the simple atom in terms of speed and robustness. After comparing
  the three Mg I lines, we conclude that the most capable one is the
  b<SUB>2</SUB> line as b<SUB>1</SUB> forms at similar heights and always
  shows weaker polarization signals, while b<SUB>4</SUB> is severely
  blended with photospheric lines. We also compare Mg I b<SUB>2</SUB>
  with the K I D<SUB>1</SUB> and Ca II 8542 Å lines finding that the
  former is sensitive to the atmospheric parameters at heights that
  are in between those covered by the latter two lines. This makes Mg I
  b<SUB>2</SUB> an excellent candidate for future multiline observations
  that aim to seamlessly infer the thermal and magnetic properties of
  different features in the lower solar atmosphere.

---------------------------------------------------------
Title: CLASP Constraints on the Magnetization and Geometrical
    Complexity of the Chromosphere-Corona Transition Region
Authors: Trujillo Bueno, J.; Štěpán, J.; Belluzzi, L.; Asensio
   Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Ishikawa,
   R.; Kano, R.; Winebarger, A.; Auchère, F.; Narukage, N.; Kobayashi,
   K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
   H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
   Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
2018ApJ...866L..15T    Altcode: 2018arXiv180908865T
  The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a
  suborbital rocket experiment that on 2015 September 3 measured
  the linear polarization produced by scattering processes in the
  hydrogen Lyα line of the solar disk radiation. The line-center
  photons of this spectral line radiation mostly stem from the
  chromosphere-corona transition region (TR). These unprecedented
  spectropolarimetric observations revealed an interesting surprise,
  namely that there is practically no center-to-limb variation (CLV) in
  the Q/I line-center signals. Using an analytical model, we first show
  that the geometric complexity of the corrugated surface that delineates
  the TR has a crucial impact on the CLV of the Q/I and U/I line-center
  signals. Second, we introduce a statistical description of the solar
  atmosphere based on a 3D model derived from a state-of-the-art radiation
  magnetohydrodynamic simulation. Each realization of the statistical
  ensemble is a 3D model characterized by a given degree of magnetization
  and corrugation of the TR, and for each such realization we solve the
  full 3D radiative transfer problem taking into account the impact
  of the CLASP instrument degradation on the calculated polarization
  signals. Finally, we apply the statistical inference method presented
  in a previous paper to show that the TR of the 3D model that produces
  the best agreement with the CLASP observations has a relatively weak
  magnetic field and a relatively high degree of corrugation. We emphasize
  that a suitable way to validate or refute numerical models of the upper
  solar chromosphere is by confronting calculations and observations
  of the scattering polarization in ultraviolet lines sensitive to the
  Hanle effect.

---------------------------------------------------------
Title: A Statistical Inference Method for Interpreting the CLASP
    Observations
Authors: Štěpán, J.; Trujillo Bueno, J.; Belluzzi, L.; Asensio
   Ramos, A.; Manso Sainz, R.; del Pino Alemán, T.; Casini, R.; Kano, R.;
   Winebarger, A.; Auchère, F.; Ishikawa, R.; Narukage, N.; Kobayashi,
   K.; Bando, T.; Katsukawa, Y.; Kubo, M.; Ishikawa, S.; Giono, G.; Hara,
   H.; Suematsu, Y.; Shimizu, T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.;
   Cirtain, J.; Champey, P.; De Pontieu, B.; Carlsson, M.
2018ApJ...865...48S    Altcode: 2018arXiv180802725S
  On 2015 September 3, the Chromospheric Lyman-Alpha SpectroPolarimeter
  (CLASP) successfully measured the linear polarization produced by
  scattering processes in the hydrogen Lyα line of the solar disk
  radiation, revealing conspicuous spatial variations in the Q/I and U/I
  signals. Via the Hanle effect, the line-center Q/I and U/I amplitudes
  encode information on the magnetic field of the chromosphere-corona
  transition region, but they are also sensitive to the three-dimensional
  structure of this corrugated interface region. With the help of a simple
  line-formation model, here we propose a statistical inference method
  for interpreting the Lyα line-center polarization observed by CLASP.

---------------------------------------------------------
Title: Current State of UV Spectro-Polarimetry and its Future
    Direction
Authors: Ishikawa, Ryohko; Sakao, Taro; Katsukawa, Yukio; Hara,
   Hirohisa; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Kubo, Masahito;
   Auchere, Frederic; De Pontieu, Bart; Winebarger, Amy; Kobayashi,
   . Ken; Kano, Ryouhei; Narukage, Noriyuki; Trujillo Bueno, Javier;
   Song, Dong-uk; Manso Sainz, Rafael; Asensio Ramos, Andres; Leenaarts,
   Jorritt; Carlsson, Mats; Bando, Takamasa; Ishikawa, Shin-nosuke;
   Tsuneta, Saku; Belluzzi, Luca; Suematsu, Yoshinori; Giono, Gabriel;
   Yoshida, Masaki; Goto, Motoshi; Del Pino Aleman, Tanausu; Stepan,
   Jiri; Okamoto, Joten; Tsuzuki, Toshihiro; Uraguchi, Fumihiro; Champey,
   Patrick; Alsina Ballester, Ernest; Casini, Roberto; McKenzie, David;
   Rachmeler, Laurel; Bethge, Christian
2018cosp...42E1564I    Altcode:
  To obtain quantitative information on the magnetic field in low beta
  regions (i.e., upper chromosphere and above) has been increasingly
  important to understand the energetic phenomena of the outer
  solar atmosphere such as flare, coronal heating, and the solar wind
  acceleration. In the UV range, there are abundant spectral lines that
  originate in the upper chromosphere and transition region. However,
  the Zeeman effect in these spectral lines does not give rise to easily
  measurable polarization signals because of the weak magnetic field
  strength and the larger Doppler broadening compared with the Zeeman
  effect. Instead, the Hanle effect in UV lines is expected to be a
  suitable diagnostic tool of the magnetic field in the upper atmospheric
  layers. To investigate the validity of UV spectro-polarimetry and
  the Hanle effect, the Chromospheric Lyman-Alpha Spectro-Polarimeter
  (CLASP), which is a NASA sounding- rocket experiment, was launched at
  White Sands in US on September 3, 2015. During its 5 minutes ballistic
  flight, it successfully performed spectro-polarimetric observations
  of the hydrogen Lyman-alpha line (121.57 nm) with an unprecedentedly
  high polarization sensitivity of 0.1% in this wavelength range. CLASP
  observed the linear polarization produced by scattering process in VUV
  lines for the first time and detected the polarization signals which
  indicate the operation of the Hanle effect. Following the success
  of CLASP, we are confident that UV spectro-polarimetry is the way
  to proceed, and we are planning the second flight of CLASP (CLASP2:
  Chromospheric LAyer SpectroPolarimeter 2). For this second flight we
  will carry out spectro-polarimetry in the Mg II h and k lines around
  280 nm, with minimum modifications of the CLASP1 instrument. The linear
  polarization in the Mg II k line is induced by scattering processes and
  the Hanle effect, being sensitive to magnetic field strengths of 5 to 50
  G. In addition, the circular polarizations in the Mg II h and k lines
  induced by the Zeeman effect can be measurable in at least plage and
  active regions. The combination of the Hanle and Zeeman effects could
  help us to more reliably infer the magnetic fields of the upper solar
  chromosphere. CLASP2 was selected for flight and is being developed for
  launch in the spring of 2019.Based on these sounding rocket experiments
  (CLASP1 and 2), we aim at establishing the strategy and refining the
  instrument concept for future space missions to explore the enigmatic
  atmospheric layers via UV spectro-polarimetry.

---------------------------------------------------------
Title: Impact of Type II Spicules in the Corona: Simulations and
    Synthetic Observables
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; De Moortel, Ineke;
   Hansteen, Viggo H.; Carlsson, Mats
2018ApJ...860..116M    Altcode: 2018arXiv180506475M
  The role of type II spicules in the corona has been a much debated topic
  in recent years. This paper aims to shed light on the impact of type
  II spicules in the corona using novel 2.5D radiative MHD simulations,
  including ion-neutral interaction effects with the Bifrost code. We
  find that the formation of simulated type II spicules, driven by
  the release of magnetic tension, impacts the corona in various
  manners. Associated with the formation of spicules, the corona
  exhibits (1) magneto-acoustic shocks and flows, which supply mass
  to coronal loops, and (2) transversal magnetic waves and electric
  currents that propagate at Alfvén speeds. The transversal waves and
  electric currents, generated by the spicule’s driver and lasting
  for many minutes, are dissipated and heat the associated loop. These
  complex interactions in the corona can be connected with blueshifted
  secondary components in coronal spectral lines (red-blue asymmetries)
  observed with Hinode/EIS and SOHO/SUMER, as well as the EUV counterpart
  of type II spicules and propagating coronal disturbances observed with
  the 171 Å and 193 Å SDO/AIA channels.

---------------------------------------------------------
Title: Disentangling flows in the solar transition region
Authors: Zacharias, P.; Hansteen, V. H.; Leenaarts, J.; Carlsson,
   M.; Gudiksen, B. V.
2018A&A...614A.110Z    Altcode: 2018arXiv180407513Z
  Context. The measured average velocities in solar and stellar spectral
  lines formed at transition region temperatures have been difficult
  to interpret. The dominant redshifts observed in the lower transition
  region naturally leads to the question of how the upper layers of the
  solar (and stellar) atmosphere can be maintained. Likewise, no ready
  explanation has been made for the average blueshifts often found in
  upper transition region lines. However, realistic three-dimensional
  radiation magnetohydrodynamics (3D rMHD) models of the solar atmosphere
  are able to reproduce the observed dominant line shifts and may thus
  hold the key to resolve these issues. <BR /> Aims: These new 3D rMHD
  simulations aim to shed light on how mass flows between the chromosphere
  and corona and on how the coronal mass is maintained. These simulations
  give new insights into the coupling of various atmospheric layers
  and the origin of Doppler shifts in the solar transition region and
  corona. <BR /> Methods: The passive tracer particles, so-called corks,
  allow the tracking of parcels of plasma over time and thus the study of
  changes in plasma temperature and velocity not only locally, but also
  in a co-moving frame. By following the trajectories of the corks, we
  can investigate mass and energy flows and understand the composition
  of the observed velocities. <BR /> Results: Our findings show that
  most of the transition region mass is cooling. The preponderance of
  transition region redshifts in the model can be explained by the higher
  percentage of downflowing mass in the lower and middle transition
  region. The average upflows in the upper transition region can be
  explained by a combination of both stronger upflows than downflows
  and a higher percentage of upflowing mass. The most common combination
  at lower and middle transition region temperatures are corks that are
  cooling and traveling downward. For these corks, a strong correlation
  between the pressure gradient along the magnetic field line and the
  velocity along the magnetic field line has been observed, indicating a
  formation mechanism that is related to downward propagating pressure
  disturbances. Corks at upper transition region temperatures are
  subject to a rather slow and highly variable but continuous heating
  process. <BR /> Conclusions: Corks are shown to be an essential tool
  in 3D rMHD models in order to study mass and energy flows. We have
  shown that most transition region plasma is cooling after having been
  heated slowly to upper transition region temperatures several minutes
  before. Downward propagating pressure disturbances are identified as
  one of the main mechanisms responsible for the observed redshifts at
  transition region temperatures. <P />The movie associated to Fig. 3
  is available at <A href="https://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Spectropolarimetric Inversions of the Ca II 8542 Å Line in
    an M-class Solar Flare
Authors: Kuridze, D.; Henriques, V. M. J.; Mathioudakis, M.; Rouppe
   van der Voort, L.; de la Cruz Rodríguez, J.; Carlsson, M.
2018ApJ...860...10K    Altcode: 2018arXiv180500487K
  We study the M1.9-class solar flare SOL2015-09-27T10:40 UT using
  high-resolution full Stokes imaging spectropolarimetry of the Ca II
  8542 Å line obtained with the CRISP imaging spectropolarimeter at the
  Swedish 1-m Solar Telescope. Spectropolarimetric inversions using the
  non-LTE code NICOLE are used to construct semiempirical models of the
  flaring atmosphere to investigate the structure and evolution of the
  flare temperature and magnetic field. A comparison of the temperature
  stratification in flaring and nonflaring areas reveals strong heating
  of the flare ribbon during the flare peak. The polarization signals
  of the ribbon in the chromosphere during the flare maximum become
  stronger when compared to its surroundings and to pre- and post-flare
  profiles. Furthermore, a comparison of the response functions to
  perturbations in the line-of-sight magnetic field and temperature in
  flaring and nonflaring atmospheres shows that during the flare, the
  Ca II 8542 Å line is more sensitive to the lower atmosphere where the
  magnetic field is expected to be stronger. The chromospheric magnetic
  field was also determined with the weak-field approximation, which
  led to results similar to those obtained with the NICOLE inversions.

---------------------------------------------------------
Title: Chromospheric Heating due to Cancellation of Quiet Sun
    Internetwork Fields
Authors: Gošić, M.; de la Cruz Rodríguez, J.; De Pontieu, B.; Bellot
   Rubio, L. R.; Carlsson, M.; Esteban Pozuelo, S.; Ortiz, A.; Polito, V.
2018ApJ...857...48G    Altcode: 2018arXiv180207392G
  The heating of the solar chromosphere remains one of the most
  important questions in solar physics. Our current understanding is that
  small-scale internetwork (IN) magnetic fields play an important role
  as a heating agent. Indeed, cancellations of IN magnetic elements in
  the photosphere can produce transient brightenings in the chromosphere
  and transition region. These bright structures might be the signature
  of energy release and plasma heating, probably driven by the magnetic
  reconnection of IN field lines. Although single events are not expected
  to release large amounts of energy, their global contribution to the
  chromosphere may be significant due to their ubiquitous presence
  in quiet Sun regions. In this paper, we study cancellations of IN
  elements and analyze their impact on the energetics and dynamics of
  the quiet Sun atmosphere. We use high-resolution, multiwavelength,
  coordinated observations obtained with the Interface Region Imaging
  Spectrograph and the Swedish 1 m Solar Telescope (SST) to identify
  cancellations of IN magnetic flux patches and follow their evolution. We
  find that, on average, these events live for ∼3 minutes in the
  photosphere and ∼12 minutes in the chromosphere and/or transition
  region. Employing multi-line inversions of the Mg II h and k lines,
  we show that cancellations produce clear signatures of heating in the
  upper atmospheric layers. However, at the resolution and sensitivity
  accessible to the SST, their number density still seems to be one
  order of magnitude too low to explain the global chromospheric heating.

---------------------------------------------------------
Title: Chromospheric heating during flux emergence in the solar
    atmosphere
Authors: Leenaarts, Jorrit; de la Cruz Rodríguez, Jaime; Danilovic,
   Sanja; Scharmer, Göran; Carlsson, Mats
2018A&A...612A..28L    Altcode: 2017arXiv171200474L
  Context. The radiative losses in the solar chromosphere vary from
  4 kW m<SUP>-2</SUP> in the quiet Sun, to 20 kW m<SUP>-2</SUP> in
  active regions. The mechanisms that transport non-thermal energy to
  and deposit it in the chromosphere are still not understood. Aim. We
  aim to investigate the atmospheric structure and heating of the solar
  chromosphere in an emerging flux region. <BR /> Methods: We have used
  observations taken with the CHROMIS and CRISP instruments on the
  Swedish 1-m Solar Telescope in the Ca II K , Ca II 854.2 nm, Hα,
  and Fe I 630.1 nm and 630.2 nm lines. We analysed the various line
  profiles and in addition perform multi-line, multi-species, non-local
  thermodynamic equilibrium (non-LTE) inversions to estimate the spatial
  and temporal variation of the chromospheric structure. <BR /> Results:
  We investigate which spectral features of Ca II K contribute to the
  frequency-integrated Ca II K brightness, which we use as a tracer
  of chromospheric radiative losses. The majority of the radiative
  losses are not associated with localised high-Ca II K-brightness
  events, but instead with a more gentle, spatially extended, and
  persistent heating. The frequency-integrated Ca II K brightness
  correlates strongly with the total linear polarization in the Ca II
  854.2 nm, while the Ca II K profile shapes indicate that the bulk
  of the radiative losses occur in the lower chromosphere. Non-LTE
  inversions indicate a transition from heating concentrated around
  photospheric magnetic elements below log τ<SUB>500</SUB> = -3 to a more
  space-filling and time-persistent heating above log τ<SUB>500</SUB>
  = -4. The inferred gas temperature at log τ<SUB>500</SUB> = -3.8
  correlates strongly with the total linear polarization in the Ca
  II 854.2 nm line, suggesting that that the heating rate correlates
  with the strength of the horizontal magnetic field in the low
  chromosphere. <P />Movies attached to Figs. 1 and 4 are available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201732027/olm">https://www.aanda.org/</A>

---------------------------------------------------------
Title: Non-LTE Calculations of the Fe I 6173 Å Line in a Flaring
    Atmosphere
Authors: Hong, Jie; Ding, M. D.; Li, Ying; Carlsson, Mats
2018ApJ...857L...2H    Altcode: 2018arXiv180309912H
  The Fe I 6173 Å line is widely used in the measurements of vector
  magnetic fields by instruments including the Helioseismic and
  Magnetic Imager (HMI). We perform non-local thermodynamic equilibrium
  calculations of this line based on radiative hydrodynamic simulations
  in a flaring atmosphere. We employ both a quiet-Sun atmosphere and
  a penumbral atmosphere as the initial one in our simulations. We find
  that, in the quiet-Sun atmosphere, the line center is obviously enhanced
  during an intermediate flare. The enhanced emission is contributed from
  both radiative backwarming in the photosphere and particle beam heating
  in the lower chromosphere. A blue asymmetry of the line profile also
  appears due to an upward mass motion in the lower chromosphere. If we
  take a penumbral atmosphere as the initial atmosphere, the line has
  a more significant response to the flare heating, showing a central
  emission and an obvious asymmetry. The low spectral resolution of
  HMI would indicate some loss of information, but the enhancement
  and line asymmetry are still kept. By calculating polarized line
  profiles, we find that the Stokes I and V profiles can be altered
  as a result of flare heating. Thus the distortion of this line has
  a crucial influence on the magnetic field measured from this line,
  and one should be cautious in interpreting the magnetic transients
  observed frequently in solar flares.

---------------------------------------------------------
Title: Investigating the Response of Loop Plasma to Nanoflare Heating
    Using RADYN Simulations
Authors: Polito, V.; Testa, P.; Allred, J.; De Pontieu, B.; Carlsson,
   M.; Pereira, T. M. D.; Gošić, Milan; Reale, Fabio
2018ApJ...856..178P    Altcode: 2018arXiv180405970P
  We present the results of 1D hydrodynamic simulations of coronal
  loops that are subject to nanoflares, caused by either in situ
  thermal heating or nonthermal electron (NTE) beams. The synthesized
  intensity and Doppler shifts can be directly compared with Interface
  Region Imaging Spectrograph (IRIS) and Atmospheric Imaging Assembly
  (AIA) observations of rapid variability in the transition region (TR)
  of coronal loops, associated with transient coronal heating. We find
  that NTEs with high enough low-energy cutoff ({E}<SUB>{{C</SUB>}})
  deposit energy in the lower TR and chromosphere, causing blueshifts
  (up to ∼20 km s<SUP>-1</SUP>) in the IRIS Si IV lines, which
  thermal conduction cannot reproduce. The {E}<SUB>{{C</SUB>}} threshold
  value for the blueshifts depends on the total energy of the events
  (≈5 keV for 10<SUP>24</SUP> erg, up to 15 keV for 10<SUP>25</SUP>
  erg). The observed footpoint emission intensity and flows, combined
  with the simulations, can provide constraints on both the energy of the
  heating event and {E}<SUB>{{C</SUB>}}. The response of the loop plasma
  to nanoflares depends crucially on the electron density: significant
  Si IV intensity enhancements and flows are observed only for initially
  low-density loops (&lt;10<SUP>9</SUP> cm<SUP>-3</SUP>). This provides
  a possible explanation of the relative scarcity of observations of
  significant moss variability. While the TR response to single heating
  episodes can be clearly observed, the predicted coronal emission (AIA
  94 Å) for single strands is below current detectability and can only
  be observed when several strands are heated closely in time. Finally,
  we show that the analysis of the IRIS Mg II chromospheric lines can
  help further constrain the properties of the heating mechanisms.

---------------------------------------------------------
Title: Three-dimensional modeling of the Ca II H and K lines in the
    solar atmosphere
Authors: Bjørgen, Johan P.; Sukhorukov, Andrii V.; Leenaarts, Jorrit;
   Carlsson, Mats; de la Cruz Rodríguez, Jaime; Scharmer, Göran B.;
   Hansteen, Viggo H.
2018A&A...611A..62B    Altcode: 2017arXiv171201045B
  Context. CHROMIS, a new imaging spectrometer at the Swedish 1-m Solar
  Telescope (SST), can observe the chromosphere in the H and K lines of
  Ca II at high spatial and spectral resolution. Accurate modeling as
  well as an understanding of the formation of these lines are needed to
  interpret the SST/CHROMIS observations. Such modeling is computationally
  challenging because these lines are influenced by strong departures from
  local thermodynamic equilibrium, three-dimensional radiative transfer,
  and partially coherent resonance scattering of photons. Aim. We aim to
  model the Ca II H and K lines in 3D model atmospheres to understand
  their formation and to investigate their diagnostic potential for
  probing the chromosphere. <BR /> Methods: We model the synthetic
  spectrum of Ca II using the radiative transfer code Multi3D in three
  different radiation-magnetohydrodynamic model atmospheres computed with
  the Bifrost code. We classify synthetic intensity profiles according
  to their shapes and study how their features are related to the
  physical properties in the model atmospheres. We investigate whether
  the synthetic data reproduce the observed spatially-averaged line
  shapes, center-to-limb variation and compare this data with SST/CHROMIS
  images. <BR /> Results: The spatially-averaged synthetic line profiles
  show too low central emission peaks, and too small separation between
  the peaks. The trends of the observed center-to-limb variation of
  the profiles properties are reproduced by the models. The Ca II H and
  K line profiles provide a temperature diagnostic of the temperature
  minimum and the temperature at the formation height of the emission
  peaks. The Doppler shift of the central depression is an excellent
  probe of the velocity in the upper chromosphere.

---------------------------------------------------------
Title: Hα and Hβ emission in a C3.3 solar flare: comparison between
    observations and simulations
Authors: Zuccarello, F.; Simoes, P. J. D. A.; Capparelli, V.; Fletcher,
   L.; Romano, P.; Mathioudakis, M.; Cauzzi, G.; Carlsson, M.; Kuridze,
   D.; Keys, P.
2017AGUFMSH41A2742Z    Altcode:
  This work is based on the analysis of an extremely rare set of
  simultaneous observations of a C3.3 solar flare in the Hα and Hβ lines
  at high spatial and temporal resolution, which were acquired at the
  Dunn Solar Telescope. Images of the C3.3 flare (SOL2014-04-22T15:22)
  made at various wavelengths along the Hα line profile by the
  Interferometric Bidimensional Spectrometer (IBIS) and in the Hβ
  with the Rapid Oscillations in the Solar Atmosphere (ROSA) broadband
  imager are analyzed to obtain the intensity evolution. The analysis
  shows that Hα and Hβ intensity excesses in three identified flare
  footpoints are well correlated in time. In the stronger footpoints,
  the typical value of the the Hα/Hβ intensity ratio observed is ∼
  0.4 - 0.5, in broad agreement with values obtained from a RADYN non-LTE
  simulation driven by an electron beam with parameters constrained by
  observations. The weaker footpoint has a larger Hα/Hβ ratio, again
  consistent with a RADYN simulation but with a smaller energy flux.

---------------------------------------------------------
Title: An IRIS Optically Thin View of the Dynamics of the Solar
    Chromosphere
Authors: Carlsson, M.
2017AGUFMSH41C..04C    Altcode:
  We analyze the formation of the O I 1356 and Cl I 1351 lines and
  show that they are formed in the mid-chromosphere and are optically
  thin. Their non-thermal line-widths are thus a direct measure of the
  velocity field along the line of sight. We use this insight to analyze a
  large set of observations from the Interface Region Imaging Spectrograph
  (IRIS) to study the dynamics of the Solar Chromosphere.

---------------------------------------------------------
Title: Constraints on active region coronal heating properties
    from observations and modeling of chromospheric, transition region,
    and coronal emission
Authors: Testa, P.; Polito, V.; De Pontieu, B.; Carlsson, M.; Reale,
   F.; Allred, J. C.; Hansteen, V. H.
2017AGUFMSH43A2804T    Altcode:
  We investigate coronal heating properties in active region cores in
  non-flaring conditions, using high spatial, spectral, and temporal
  resolution chromospheric/transition region/coronal observations coupled
  with detailed modeling. We will focus, in particular, on observations
  with the Interface Region Imaging Spectrograph (IRIS), joint with
  observations with Hinode (XRT and EIS) and SDO/AIA. We will discuss
  how these observations and models (1D HD and 3D MHD, with the RADYN
  and Bifrost codes) provide useful diagnostics of the coronal heating
  processes and mechanisms of energy transport.

---------------------------------------------------------
Title: Intermittent Reconnection and Plasmoids in UV Bursts in the
    Low Solar Atmosphere
Authors: Rouppe van der Voort, L.; De Pontieu, B.; Scharmer, G. B.;
   de la Cruz Rodríguez, J.; Martínez-Sykora, J.; Nóbrega-Siverio,
   D.; Guo, L. J.; Jafarzadeh, S.; Pereira, T. M. D.; Hansteen, V. H.;
   Carlsson, M.; Vissers, G.
2017ApJ...851L...6R    Altcode: 2017arXiv171104581R
  Magnetic reconnection is thought to drive a wide variety of dynamic
  phenomena in the solar atmosphere. Yet, the detailed physical mechanisms
  driving reconnection are difficult to discern in the remote sensing
  observations that are used to study the solar atmosphere. In this
  Letter, we exploit the high-resolution instruments Interface Region
  Imaging Spectrograph and the new CHROMIS Fabry-Pérot instrument at
  the Swedish 1-m Solar Telescope (SST) to identify the intermittency
  of magnetic reconnection and its association with the formation of
  plasmoids in so-called UV bursts in the low solar atmosphere. The Si IV
  1403 Å UV burst spectra from the transition region show evidence of
  highly broadened line profiles with often non-Gaussian and triangular
  shapes, in addition to signatures of bidirectional flows. Such profiles
  had previously been linked, in idealized numerical simulations, to
  magnetic reconnection driven by the plasmoid instability. Simultaneous
  CHROMIS images in the chromospheric Ca II K 3934 Å line now provide
  compelling evidence for the presence of plasmoids by revealing highly
  dynamic and rapidly moving brightenings that are smaller than 0.″2 and
  that evolve on timescales of the order of seconds. Our interpretation
  of the observations is supported by detailed comparisons with synthetic
  observables from advanced numerical simulations of magnetic reconnection
  and associated plasmoids in the chromosphere. Our results highlight
  how subarcsecond imaging spectroscopy sensitive to a wide range of
  temperatures combined with advanced numerical simulations that are
  realistic enough to compare with observations can directly reveal the
  small-scale physical processes that drive the wide range of phenomena
  in the solar atmosphere.

---------------------------------------------------------
Title: Chromospheric polarimetry through multiline observations of
    the 850-nm spectral region - II. A magnetic flux tube scenario
Authors: Quintero Noda, C.; Kato, Y.; Katsukawa, Y.; Oba, T.; de la
   Cruz Rodríguez, J.; Carlsson, M.; Shimizu, T.; Orozco Suárez, D.;
   Ruiz Cobo, B.; Kubo, M.; Anan, T.; Ichimoto, K.; Suematsu, Y.
2017MNRAS.472..727Q    Altcode: 2017arXiv170801333Q
  In this publication, we continue the work started in Quintero Noda et
  al., examining this time a numerical simulation of a magnetic flux
  tube concentration. Our goal is to study if the physical phenomena
  that take place in it, in particular, the magnetic pumping, leaves
  a specific imprint on the examined spectral lines. We find that the
  profiles from the interior of the flux tube are periodically doppler
  shifted following an oscillation pattern that is also reflected in
  the amplitude of the circular polarization signals. In addition, we
  analyse the properties of the Stokes profiles at the edges of the flux
  tube discovering the presence of linear polarization signals for the Ca
  II lines, although they are weak with an amplitude around 0.5 per cent
  of the continuum intensity. Finally, we compute the response functions
  to perturbations in the longitudinal field, and we estimate the field
  strength using the weak-field approximation. Our results indicate
  that the height of formation of the spectral lines changes during the
  magnetic pumping process, which makes the interpretation of the inferred
  magnetic field strength and its evolution more difficult. These results
  complement those from previous works, demonstrating the capabilities and
  limitations of the 850-nm spectrum for chromospheric Zeeman polarimetry
  in a very dynamic and complex atmosphere.

---------------------------------------------------------
Title: Hα and Hβ Emission in a C3.3 Solar Flare: Comparison between
    Observations and Simulations
Authors: Capparelli, Vincenzo; Zuccarello, Francesca; Romano, Paolo;
   Simões, Paulo J. A.; Fletcher, Lyndsay; Kuridze, David; Mathioudakis,
   Mihalis; Keys, Peter H.; Cauzzi, Gianna; Carlsson, Mats
2017ApJ...850...36C    Altcode: 2017arXiv171004067C
  The hydrogen Balmer series is a basic radiative loss channel from
  the flaring solar chromosphere. We report here on the analysis of an
  extremely rare set of simultaneous observations of a solar flare in the
  {{H}}α and {{H}}β lines, at high spatial and temporal resolutions,
  that were acquired at the Dunn Solar Telescope. Images of the C3.3 flare
  (SOL2014-04-22T15:22) made at various wavelengths along the {{H}}α line
  profile by the Interferometric Bidimensional Spectrometer (IBIS) and in
  the {{H}}β with the Rapid Oscillations in the Solar Atmosphere (ROSA)
  broadband imager are analyzed to obtain the intensity evolution. The
  {{H}}α and {{H}}β intensity excesses in three identified flare
  footpoints are well-correlated in time. We examine the ratio of {{H}}α
  to {{H}}β flare excess, which was proposed by previous authors as
  a possible diagnostic of the level of electron-beam energy input. In
  the stronger footpoints, the typical value of the the {{H}}α /H β
  intensity ratio observed is ∼0.4-0.5, in broad agreement with values
  obtained from a RADYN non-LTE simulation driven by an electron beam
  with parameters constrained (as far as possible) by observation. The
  weaker footpoint has a larger {{H}}α /H β ratio, again consistent
  with a RADYN simulation, but with a smaller energy flux. The {{H}}α
  line profiles observed have a less prominent central reversal than is
  predicted by the RADYN results, but can be brought into agreement if
  the {{H}}α -emitting material has a filling factor of around 0.2-0.3.

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. IX. The Formation of the
    C I 135.58 NM Line in the Solar Atmosphere
Authors: Lin, Hsiao-Hsuan; Carlsson, Mats; Leenaarts, Jorrit
2017ApJ...846...40L    Altcode: 2017arXiv170809426L
  The C I 135.58 nm line is located in the wavelength range of NASA’s
  Interface Region Imaging Spectrograph (IRIS) small explorer mission. We
  study the formation and diagnostic potential of this line by means of
  non local-thermodynamic-equilibrium modeling, employing both 1D and 3D
  radiation-magnetohydrodynamic models. The C I/C II ionization balance is
  strongly influenced by photoionization by Lyα emission. The emission
  in the C I 135.58 nm line is dominated by a recombination cascade and
  the line forming region is optically thick. The Doppler shift of the
  line correlates strongly with the vertical velocity in its line forming
  region, which is typically located at 1.5 Mm height. With IRIS, the C
  I 135.58 nm line is usually observed together with the O I 135.56 nm
  line, and from the Doppler shift of both lines, we obtain the velocity
  difference between the line forming regions of the two lines. From
  the ratio of the C I/O I line core intensity, we can determine the
  distance between the C I and the O I forming layers. Combined with the
  velocity difference, the velocity gradient at mid-chromospheric heights
  can be derived. The C I/O I total intensity line ratio is correlated
  with the inverse of the electron density in the mid-chromosphere. We
  conclude that the C I 135.58 nm line is an excellent probe of the
  middle chromosphere by itself, and together with the O I 135.56 nm
  line the two lines provide even more information, which complements
  other powerful chromospheric diagnostics of IRIS such as the Mg II h
  and k lines and the C II lines around 133.5 nm.

---------------------------------------------------------
Title: Solar polarimetry through the K I lines at 770 nm
Authors: Quintero Noda, C.; Uitenbroek, H.; Katsukawa, Y.; Shimizu,
   T.; Oba, T.; Carlsson, M.; Orozco Suárez, D.; Ruiz Cobo, B.; Kubo,
   M.; Anan, T.; Ichimoto, K.; Suematsu, Y.
2017MNRAS.470.1453Q    Altcode: 2017arXiv170510002Q
  We characterize the K I D<SUB>1</SUB> &amp; D<SUB>2</SUB> lines in
  order to determine whether they could complement the 850 nm window,
  containing the Ca II infrared triplet lines and several Zeeman sensitive
  photospheric lines, that was studied previously. We investigate the
  effect of partial redistribution on the intensity profiles, their
  sensitivity to changes in different atmospheric parameters, and
  the spatial distribution of Zeeman polarization signals employing a
  realistic magnetohydrodynamic simulation. The results show that these
  lines form in the upper photosphere at around 500 km, and that they
  are sensitive to the line-of-sight velocity and magnetic field strength
  at heights where neither the photospheric lines nor the Ca II infrared
  lines are. However, at the same time, we found that their sensitivity
  to the temperature essentially comes from the photosphere. Then, we
  conclude that the K I lines provide a complement to the lines in the
  850 nm window for the determination of atmospheric parameters in the
  upper photosphere, especially for the line-of-sight velocity and the
  magnetic field.

---------------------------------------------------------
Title: Two-dimensional Radiative Magnetohydrodynamic Simulations of
    Partial Ionization in the Chromosphere. II. Dynamics and Energetics
    of the Low Solar Atmosphere
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Carlsson, Mats;
   Hansteen, Viggo H.; Nóbrega-Siverio, Daniel; Gudiksen, Boris V.
2017ApJ...847...36M    Altcode: 2017arXiv170806781M
  We investigate the effects of interactions between ions and
  neutrals on the chromosphere and overlying corona using 2.5D
  radiative MHD simulations with the Bifrost code. We have extended
  the code capabilities implementing ion-neutral interaction effects
  using the generalized Ohm’s law, I.e., we include the Hall term
  and the ambipolar diffusion (Pedersen dissipation) in the induction
  equation. Our models span from the upper convection zone to the corona,
  with the photosphere, chromosphere, and transition region partially
  ionized. Our simulations reveal that the interactions between ionized
  particles and neutral particles have important consequences for the
  magnetothermodynamics of these modeled layers: (1) ambipolar diffusion
  increases the temperature in the chromosphere; (2) sporadically the
  horizontal magnetic field in the photosphere is diffused into the
  chromosphere, due to the large ambipolar diffusion; (3) ambipolar
  diffusion concentrates electrical currents, leading to more violent
  jets and reconnection processes, resulting in (3a) the formation of
  longer and faster spicules, (3b) heating of plasma during the spicule
  evolution, and (3c) decoupling of the plasma and magnetic field in
  spicules. Our results indicate that ambipolar diffusion is a critical
  ingredient for understanding the magnetothermodynamic properties in the
  chromosphere and transition region. The numerical simulations have been
  made publicly available, similar to previous Bifrost simulations. This
  will allow the community to study realistic numerical simulations with
  a wider range of magnetic field configurations and physics modules
  than previously possible.

---------------------------------------------------------
Title: Impact of Type II Spicules into the Corona
Authors: Martinez-Sykora, Juan; De Pontieu, Bart; Carlsson, Mats;
   Hansteen, Viggo H.; Pereira, Tiago M. D.
2017SPD....4810403M    Altcode:
  In the lower solar atmosphere, the chromosphere is permeated by jets,
  in which plasma is propelled at speeds of 50-150 km/s into the Sun’s
  atmosphere or corona. Although these spicules may play a role in heating
  the million-degree corona and are associated with Alfvén waves that
  help drive the solar wind, their generation remains mysterious. We
  implemented in the radiative MHD Bifrost code the effects of partial
  ionization using the generalized Ohm’s law. This code also solves
  the full MHD equations with non-grey and non-LTE radiative transfer
  and thermal conduction along magnetic field lines. The ion-neutral
  collision frequency is computed using recent studies that improved the
  estimation of the cross sections under chromospheric conditions (Vranjes
  &amp; Krstic 2013). Self-consistently driven jets (spicules type II)
  in magnetohydrodynamic simulations occur ubiquitously when magnetic
  tension is confined and transported upwards through interactions
  between ions and neutrals, and impulsively released to drive flows,
  heat plasma, generate Alfvén waves, and may play an important role in
  maintaining the substructure of loop fans. This mechanism explains how
  spicular plasma can be heated to millions of degrees and how Alfvén
  waves are generated in the chromosphere.

---------------------------------------------------------
Title: Realistic radiative MHD simulation of a solar flare
Authors: Rempel, Matthias D.; Cheung, Mark; Chintzoglou, Georgios;
   Chen, Feng; Testa, Paola; Martinez-Sykora, Juan; Sainz Dalda, Alberto;
   DeRosa, Marc L.; Viktorovna Malanushenko, Anna; Hansteen, Viggo H.;
   De Pontieu, Bart; Carlsson, Mats; Gudiksen, Boris; McIntosh, Scott W.
2017SPD....4840001R    Altcode:
  We present a recently developed version of the MURaM radiative
  MHD code that includes coronal physics in terms of optically thin
  radiative loss and field aligned heat conduction. The code employs
  the "Boris correction" (semi-relativistic MHD with a reduced speed
  of light) and a hyperbolic treatment of heat conduction, which allow
  for efficient simulations of the photosphere/corona system by avoiding
  the severe time-step constraints arising from Alfven wave propagation
  and heat conduction. We demonstrate that this approach can be used
  even in dynamic phases such as a flare. We consider a setup in which
  a flare is triggered by flux emergence into a pre-existing bipolar
  active region. After the coronal energy release, efficient transport
  of energy along field lines leads to the formation of flare ribbons
  within seconds. In the flare ribbons we find downflows for temperatures
  lower than ~5 MK and upflows at higher temperatures. The resulting
  soft X-ray emission shows a fast rise and slow decay, reaching a peak
  corresponding to a mid C-class flare. The post reconnection energy
  release in the corona leads to average particle energies reaching 50
  keV (500 MK under the assumption of a thermal plasma). We show that
  hard X-ray emission from the corona computed under the assumption of
  thermal bremsstrahlung can produce a power-law spectrum due to the
  multi-thermal nature of the plasma. The electron energy flux into the
  flare ribbons (classic heat conduction with free streaming limit) is
  highly inhomogeneous and reaches peak values of about 3x10<SUP>11</SUP>
  erg/cm<SUP>2</SUP>/s in a small fraction of the ribbons, indicating
  regions that could potentially produce hard X-ray footpoint sources. We
  demonstrate that these findings are robust by comparing simulations
  computed with different values of the saturation heat flux as well as
  the "reduced speed of light".

---------------------------------------------------------
Title: RADYN Simulations of Non-thermal and Thermal Models of
    Ellerman Bombs
Authors: Hong, Jie; Carlsson, Mats; Ding, M. D.
2017ApJ...845..144H    Altcode: 2017arXiv170705514H
  Ellerman bombs (EBs) are brightenings in the Hα line wings that
  are believed to be caused by magnetic reconnection in the lower
  atmosphere. To study the response and evolution of the chromospheric
  line profiles, we perform radiative hydrodynamic simulations of EBs
  using both non-thermal and thermal models. Overall, these models can
  generate line profiles that are similar to observations. However, in
  non-thermal models we find dimming in the Hα line wings and continuum
  when the heating begins, while for the thermal models dimming occurs
  only in the Hα line core, and with a longer lifetime. This difference
  in line profiles can be used to determine whether an EB is dominated by
  non-thermal heating or thermal heating. In our simulations, if a higher
  heating rate is applied, then the Hα line will be unrealistically
  strong and there are still no clear UV burst signatures.

---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel; E McKenzie, David; Ishikawa, Ryohko;
   Trujillo Bueno, Javier; Auchère, Frédéric; Kobayashi, Ken;
   Winebarger, Amy; Bethge, Christian; Kano, Ryouhei; Kubo, Masahito;
   Song, Donguk; Narukage, Noriyuki; Ishikawa, Shin-nosuke; De Pontieu,
   Bart; Carlsson, Mats; Yoshida, Masaki; Belluzzi, Luca; Stepan, Jiri;
   del Pino Alemná, Tanausú; Ballester, Ernest Alsina; Asensio Ramos,
   Andres
2017SPD....4811010R    Altcode:
  We present the instrument, science case, and timeline of the CLASP2
  sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
  Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
  the first-ever linear polarization measurements of solar hydrogen
  Lyman-alpha line, which is sensitive to the Hanle effect and can be used
  to constrain the magnetic field and geometric complexity of the upper
  chromosphere. Ly-alpha is one of several upper chromospheric lines that
  contain magnetic information. In the spring of 2019, we will re-fly
  the modified CLASP telescope to measure the full Stokes profile of Mg
  II h &amp; k near 280 nm. This set of lines is sensitive to the upper
  chromospheric magnetic field via both the Hanle and the Zeeman effects.

---------------------------------------------------------
Title: CLASP2: The Chromospheric LAyer Spectro-Polarimeter
Authors: Rachmeler, Laurel A.; McKenzie, D. E.; Ishikawa, R.;
   Trujillo-Bueno, J.; Auchere, F.; Kobayashi, K.; Winebarger, A.;
   Bethge, C.; Kano, R.; Kubo, M.; Song, D.; Narukage, N.; Ishikawa, S.;
   De Pontieu, B.; Carlsson, M.; Yoshida, M.; Belluzzi, L.; Stepan, J.;
   del Pino Alemán, T.; Alsina Ballester, E.; Asensio Ramos, A.
2017shin.confE..79R    Altcode:
  We present the instrument, science case, and timeline of the CLASP2
  sounding rocket mission. The successful CLASP (Chromospheric Lyman-Alpha
  Spectro-Polarimeter) sounding rocket flight in 2015 resulted in
  the first-ever linear polarization measurements of solar hydrogen
  Lyman-alpha line, which is sensitive to the Hanle effect and can be used
  to constrain the magnetic field and geometric complexity of the upper
  chromosphere. Ly-alpha is one of several upper chromospheric lines that
  contain magnetic information. In the spring of 2019, we will re-fly
  the modified CLASP telescope to measure the full Stokes profile of Mg
  II h &amp; k near 280 nm. This set of lines is sensitive to the upper
  chromospheric magnetic field via both the Hanle and the Zeeman effects.

---------------------------------------------------------
Title: On the generation of solar spicules and Alfvénic waves
Authors: Martínez-Sykora, J.; De Pontieu, B.; Hansteen, V. H.;
   Rouppe van der Voort, L.; Carlsson, M.; Pereira, T. M. D.
2017Sci...356.1269M    Altcode: 2017arXiv171007559M
  In the lower solar atmosphere, the chromosphere is permeated by jets
  known as spicules, in which plasma is propelled at speeds of 50 to
  150 kilometers per second into the corona. The origin of the spicules
  is poorly understood, although they are expected to play a role in
  heating the million-degree corona and are associated with Alfvénic
  waves that help drive the solar wind. We compare magnetohydrodynamic
  simulations of spicules with observations from the Interface Region
  Imaging Spectrograph and the Swedish 1-m Solar Telescope. Spicules
  are shown to occur when magnetic tension is amplified and transported
  upward through interactions between ions and neutrals or ambipolar
  diffusion. The tension is impulsively released to drive flows, heat
  plasma (through ambipolar diffusion), and generate Alfvénic waves.

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

---------------------------------------------------------
Title: Indication of the Hanle Effect by Comparing the Scattering
    Polarization Observed by CLASP in the Lyα and Si III 120.65 nm Lines
Authors: Ishikawa, R.; Trujillo Bueno, J.; Uitenbroek, H.; Kubo, M.;
   Tsuneta, S.; Goto, M.; Kano, R.; Narukage, N.; Bando, T.; Katsukawa,
   Y.; Ishikawa, S.; Giono, G.; Suematsu, Y.; Hara, H.; Shimizu, T.;
   Sakao, T.; Winebarger, A.; Kobayashi, K.; Cirtain, J.; Champey, P.;
   Auchère, F.; Štěpán, J.; Belluzzi, L.; Asensio Ramos, A.; Manso
   Sainz, R.; De Pontieu, B.; Ichimoto, K.; Carlsson, M.; Casini, R.
2017ApJ...841...31I    Altcode:
  The Chromospheric Lyman-Alpha Spectro-Polarimeter is a sounding
  rocket experiment that has provided the first successful measurement
  of the linear polarization produced by scattering processes in
  the hydrogen Lyα line (121.57 nm) radiation of the solar disk. In
  this paper, we report that the Si III line at 120.65 nm also shows
  scattering polarization and we compare the scattering polarization
  signals observed in the Lyα and Si III lines in order to search for
  observational signatures of the Hanle effect. We focus on four selected
  bright structures and investigate how the U/I spatial variations vary
  between the Lyα wing, the Lyα core, and the Si III line as a function
  of the total unsigned photospheric magnetic flux estimated from Solar
  Dynamics Observatory/Helioseismic and Magnetic Imager observations. In
  an internetwork region, the Lyα core shows an antisymmetric spatial
  variation across the selected bright structure, but it does not show
  it in other more magnetized regions. In the Si III line, the spatial
  variation of U/I deviates from the above-mentioned antisymmetric
  shape as the total unsigned photospheric magnetic flux increases. A
  plausible explanation of this difference is the operation of the Hanle
  effect. We argue that diagnostic techniques based on the scattering
  polarization observed simultaneously in two spectral lines with very
  different sensitivities to the Hanle effect, like Lyα and Si III,
  are of great potential interest for exploring the magnetism of the
  upper solar chromosphere and transition region.

---------------------------------------------------------
Title: Bombs and Flares at the Surface and Lower Atmosphere of the Sun
Authors: Hansteen, V. H.; Archontis, V.; Pereira, T. M. D.; Carlsson,
   M.; Rouppe van der Voort, L.; Leenaarts, J.
2017ApJ...839...22H    Altcode: 2017arXiv170402872H
  A spectacular manifestation of solar activity is the appearance of
  transient brightenings in the far wings of the Hα line, known as
  Ellerman bombs (EBs). Recent observations obtained by the Interface
  Region Imaging Spectrograph have revealed another type of plasma
  “bombs” (UV bursts) with high temperatures of perhaps up to 8 ×
  10<SUP>4</SUP> K within the cooler lower solar atmosphere. Realistic
  numerical modeling showing such events is needed to explain
  their nature. Here, we report on 3D radiative magnetohydrodynamic
  simulations of magnetic flux emergence in the solar atmosphere. We
  find that ubiquitous reconnection between emerging bipolar magnetic
  fields can trigger EBs in the photosphere, UV bursts in the mid/low
  chromosphere and small (nano-/micro-) flares (10<SUP>6</SUP> K) in
  the upper chromosphere. These results provide new insights into the
  emergence and build up of the coronal magnetic field and the dynamics
  and heating of the solar surface and lower atmosphere.

---------------------------------------------------------
Title: Polarization Calibration of the Chromospheric Lyman-Alpha
    SpectroPolarimeter for a 0.1% Polarization Sensitivity in the VUV
Range. Part II: In-Flight Calibration
Authors: Giono, G.; Ishikawa, R.; Narukage, N.; Kano, R.; Katsukawa,
   Y.; Kubo, M.; Ishikawa, S.; Bando, T.; Hara, H.; Suematsu, Y.;
   Winebarger, A.; Kobayashi, K.; Auchère, F.; Trujillo Bueno, J.;
   Tsuneta, S.; Shimizu, T.; Sakao, T.; Cirtain, J.; Champey, P.; Asensio
   Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
   B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
2017SoPh..292...57G    Altcode:
  The Chromospheric Lyman-Alpha SpectroPolarimeter is a sounding
  rocket instrument designed to measure for the first time the linear
  polarization of the hydrogen Lyman-α line (121.6 nm). The instrument
  was successfully launched on 3 September 2015 and observations were
  conducted at the solar disc center and close to the limb during the
  five-minutes flight. In this article, the disc center observations are
  used to provide an in-flight calibration of the instrument spurious
  polarization. The derived in-flight spurious polarization is consistent
  with the spurious polarization levels determined during the pre-flight
  calibration and a statistical analysis of the polarization fluctuations
  from solar origin is conducted to ensure a 0.014% precision on the
  spurious polarization. The combination of the pre-flight and the
  in-flight polarization calibrations provides a complete picture of
  the instrument response matrix, and a proper error transfer method
  is used to confirm the achieved polarization accuracy. As a result,
  the unprecedented 0.1% polarization accuracy of the instrument in the
  vacuum ultraviolet is ensured by the polarization calibration.

---------------------------------------------------------
Title: Discovery of Scattering Polarization in the Hydrogen Lyα
    Line of the Solar Disk Radiation
Authors: Kano, R.; Trujillo Bueno, J.; Winebarger, A.; Auchère, F.;
   Narukage, N.; Ishikawa, R.; Kobayashi, K.; Bando, T.; Katsukawa, Y.;
   Kubo, M.; Ishikawa, S.; Giono, G.; Hara, H.; Suematsu, Y.; Shimizu,
   T.; Sakao, T.; Tsuneta, S.; Ichimoto, K.; Goto, M.; Belluzzi, L.;
   Štěpán, J.; Asensio Ramos, A.; Manso Sainz, R.; Champey, P.;
   Cirtain, J.; De Pontieu, B.; Casini, R.; Carlsson, M.
2017ApJ...839L..10K    Altcode: 2017arXiv170403228K
  There is a thin transition region (TR) in the solar atmosphere where
  the temperature rises from 10,000 K in the chromosphere to millions
  of degrees in the corona. Little is known about the mechanisms that
  dominate this enigmatic region other than the magnetic field plays a
  key role. The magnetism of the TR can only be detected by polarimetric
  measurements of a few ultraviolet (UV) spectral lines, the Lyα line
  of neutral hydrogen at 121.6 nm (the strongest line of the solar UV
  spectrum) being of particular interest given its sensitivity to the
  Hanle effect (the magnetic-field-induced modification of the scattering
  line polarization). We report the discovery of linear polarization
  produced by scattering processes in the Lyα line, obtained with
  the Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) rocket
  experiment. The Stokes profiles observed by CLASP in quiet regions of
  the solar disk show that the Q/I and U/I linear polarization signals are
  of the order of 0.1% in the line core and up to a few percent in the
  nearby wings, and that both have conspicuous spatial variations with
  scales of ∼10 arcsec. These observations help constrain theoretical
  models of the chromosphere-corona TR and extrapolations of the
  magnetic field from photospheric magnetograms. In fact, the observed
  spatial variation from disk to limb of polarization at the line core
  and wings already challenge the predictions from three-dimensional
  magnetohydrodynamical models of the upper solar chromosphere.

---------------------------------------------------------
Title: Hydrogen Balmer Line Broadening in Solar and Stellar Flares
Authors: Kowalski, Adam F.; Allred, Joel C.; Uitenbroek, Han; Tremblay,
   Pier-Emmanuel; Brown, Stephen; Carlsson, Mats; Osten, Rachel A.;
   Wisniewski, John P.; Hawley, Suzanne L.
2017ApJ...837..125K    Altcode: 2017arXiv170203321K
  The broadening of the hydrogen lines during flares is thought to
  result from increased charge (electron, proton) density in the flare
  chromosphere. However, disagreements between theory and modeling
  prescriptions have precluded an accurate diagnostic of the degree
  of ionization and compression resulting from flare heating in the
  chromosphere. To resolve this issue, we have incorporated the unified
  theory of electric pressure broadening of the hydrogen lines into
  the non-LTE radiative-transfer code RH. This broadening prescription
  produces a much more realistic spectrum of the quiescent, A0 star Vega
  compared to the analytic approximations used as a damping parameter
  in the Voigt profiles. We test recent radiative-hydrodynamic (RHD)
  simulations of the atmospheric response to high nonthermal electron
  beam fluxes with the new broadening prescription and find that
  the Balmer lines are overbroadened at the densest times in the
  simulations. Adding many simultaneously heated and cooling model
  loops as a “multithread” model improves the agreement with the
  observations. We revisit the three-component phenomenological flare
  model of the YZ CMi Megaflare using recent and new RHD models. The
  evolution of the broadening, line flux ratios, and continuum flux
  ratios are well-reproduced by a multithread model with high-flux
  nonthermal electron beam heating, an extended decay phase model, and a
  “hot spot” atmosphere heated by an ultrarelativistic electron beam
  with reasonable filling factors: ∼0.1%, 1%, and 0.1% of the visible
  stellar hemisphere, respectively. The new modeling motivates future
  work to understand the origin of the extended gradual phase emission.

---------------------------------------------------------
Title: Chromospheric polarimetry through multiline observations of
    the 850-nm spectral region
Authors: Quintero Noda, C.; Shimizu, T.; Katsukawa, Y.; de la Cruz
   Rodríguez, J.; Carlsson, M.; Anan, T.; Oba, T.; Ichimoto, K.;
   Suematsu, Y.
2017MNRAS.464.4534Q    Altcode: 2016arXiv161006651Q
  Future solar missions and ground-based telescopes aim to understand the
  magnetism of the solar chromosphere. We performed a supporting study in
  Quintero Noda et al. focused on the infrared Ca II 8542 Å line and we
  concluded that it is one of the best candidates because it is sensitive
  to a large range of atmospheric heights, from the photosphere to the
  middle chromosphere. However, we believe that it is worth trying to
  improve the results produced by this line observing additional spectral
  lines. In that regard, we examined the neighbourhood solar spectrum
  looking for spectral lines which could increase the sensitivity to
  the atmospheric parameters. Interestingly, we discovered several
  photospheric lines which greatly improve the photospheric sensitivity
  to the magnetic field vector. Moreover, they are located close to a
  second chromospheric line which also belongs to the Ca II infrared
  triplet, I.e. the Ca II 8498 Å line, and enhances the sensitivity to
  the atmospheric parameters at chromospheric layers. We conclude that the
  lines in the vicinity of the Ca II 8542 Å line not only increase its
  sensitivity to the atmospheric parameters at all layers, but also they
  constitute an excellent spectral window for chromospheric polarimetry.

---------------------------------------------------------
Title: The Atmospheric Response to High Nonthermal Electron Beam
    Fluxes in Solar Flares. I. Modeling the Brightest NUV Footpoints in
    the X1 Solar Flare of 2014 March 29
Authors: Kowalski, Adam F.; Allred, Joel C.; Daw, Adrian; Cauzzi,
   Gianna; Carlsson, Mats
2017ApJ...836...12K    Altcode: 2016arXiv160907390K
  The 2014 March 29 X1 solar flare (SOL20140329T17:48) produced bright
  continuum emission in the far- and near-ultraviolet (NUV) and highly
  asymmetric chromospheric emission lines, providing long-sought
  constraints on the heating mechanisms of the lower atmosphere in
  solar flares. We analyze the continuum and emission line data from
  the Interface Region Imaging Spectrograph (IRIS) of the brightest
  flaring magnetic footpoints in this flare. We compare the NUV spectra
  of the brightest pixels to new radiative-hydrodynamic predictions
  calculated with the RADYN code using constraints on a nonthermal
  electron beam inferred from the collisional thick-target modeling of
  hard X-ray data from Reuven Ramaty High Energy Solar Spectroscopic
  Imager. We show that the atmospheric response to a high beam flux
  density satisfactorily achieves the observed continuum brightness
  in the NUV. The NUV continuum emission in this flare is consistent
  with hydrogen (Balmer) recombination radiation that originates from
  low optical depth in a dense chromospheric condensation and from the
  stationary beam-heated layers just below the condensation. A model
  producing two flaring regions (a condensation and stationary layers)
  in the lower atmosphere is also consistent with the asymmetric Fe II
  chromospheric emission line profiles observed in the impulsive phase.

---------------------------------------------------------
Title: On the generation of solar spicules and Alfvén waves
Authors: Carlsson, Mats
2017psio.confE..46C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Formation of the helium extreme-UV resonance lines
Authors: Golding, T. P.; Leenaarts, J.; Carlsson, M.
2017A&A...597A.102G    Altcode: 2016arXiv161000352G
  Context. While classical models successfully reproduce intensities
  of many transition region lines, they predict helium extreme-UV
  (EUV) line intensities roughly an order of magnitude lower than the
  observed value. <BR /> Aims: Our aim is to determine the relevant
  formation mechanism(s) of the helium EUV resonance lines capable of
  explaining the high intensities under quiet Sun conditions. <BR />
  Methods: We synthesised and studied the emergent spectra from a 3D
  radiation-magnetohydrodynamics simulation model. The effects of coronal
  illumination and non-equilibrium ionisation of hydrogen and helium
  are included self-consistently in the numerical simulation. <BR />
  Results: Radiative transfer calculations result in helium EUV line
  intensities that are an order of magnitude larger than the intensities
  calculated under the classical assumptions. The enhanced intensity
  of He Iλ584 is primarily caused by He II recombination cascades. The
  enhanced intensity of He IIλ304 and He IIλ256 is caused primarily by
  non-equilibrium helium ionisation. <BR /> Conclusions: The analysis
  shows that the long standing problem of the high helium EUV line
  intensities disappears when taking into account optically thick
  radiative transfer and non-equilibrium ionisation effects.

---------------------------------------------------------
Title: A Chromospheric Flare Model Consisting of Two Dynamical Layers:
    Critical Tests from IRIS Data of Solar Flares
Authors: Kowalski, Adam; Allred, Joel C.; Daw, Adrian N.; Cauzzi,
   Gianna; Carlsson, Mats; Inglis, Andrew; O'Neill, Aaron; Mathioudakis,
   Mihalis; Uitenbroek, Han
2017AAS...22933902K    Altcode:
  Recent 1D radiative-hydrodynamic simulations of flares have shown that
  a heated, chromospheric compression layer and a stationary layer, just
  below the compression, are produced in response to high flux electron
  beam heating. The hot blackbody-like continuum and redshifted intensity
  in singly ionized chromospheric lines in these model predictions are
  generally consistent with broad wavelength coverage spectra of M dwarf
  flares and with high spectral resolution observations of solar flares,
  respectively. We critically test this two-component chromospheric
  flare model against the Fe II profiles and NUV continuum brightness
  for several X-class solar flares observed with the Interface Region
  Imaging Spectrograph (IRIS). We present several new predictions for
  the Daniel K. Inoue Solar Telescope (DKIST).

---------------------------------------------------------
Title: SOLARNET WP 100: Access to Science Data Centres. Space missions
Authors: Carlsson, Mats
2017psio.confE.101C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Discovery of Ubiquitous Fast-Propagating Intensity Disturbances
    by the Chromospheric Lyman Alpha Spectropolarimeter (CLASP)
Authors: Kubo, M.; Katsukawa, Y.; Suematsu, Y.; Kano, R.; Bando,
   T.; Narukage, N.; Ishikawa, R.; Hara, H.; Giono, G.; Tsuneta, S.;
   Ishikawa, S.; Shimizu, T.; Sakao, T.; Winebarger, A.; Kobayashi, K.;
   Cirtain, J.; Champey, P.; Auchère, F.; Trujillo Bueno, J.; Asensio
   Ramos, A.; Štěpán, J.; Belluzzi, L.; Manso Sainz, R.; De Pontieu,
   B.; Ichimoto, K.; Carlsson, M.; Casini, R.; Goto, M.
2016ApJ...832..141K    Altcode:
  High-cadence observations by the slit-jaw (SJ) optics system of the
  sounding rocket experiment known as the Chromospheric Lyman Alpha
  Spectropolarimeter (CLASP) reveal ubiquitous intensity disturbances
  that recurrently propagate in either the chromosphere or the transition
  region or both at a speed much higher than the speed of sound. The
  CLASP/SJ instrument provides a time series of two-dimensional images
  taken with broadband filters centered on the Lyα line at a 0.6 s
  cadence. The multiple fast-propagating intensity disturbances appear in
  the quiet Sun and in an active region, and they are clearly detected in
  at least 20 areas in a field of view of 527″ × 527″ during the 5
  minute observing time. The apparent speeds of the intensity disturbances
  range from 150 to 350 km s<SUP>-1</SUP>, and they are comparable
  to the local Alfvén speed in the transition region. The intensity
  disturbances tend to propagate along bright elongated structures away
  from areas with strong photospheric magnetic fields. This suggests
  that the observed fast-propagating intensity disturbances are related
  to the magnetic canopy structures. The maximum distance traveled by
  the intensity disturbances is about 10″, and the widths are a few
  arcseconds, which are almost determined by a pixel size of 1.″03. The
  timescale of each intensity pulse is shorter than 30 s. One possible
  explanation for the fast-propagating intensity disturbances observed
  by CLASP is magnetohydrodynamic fast-mode waves.

---------------------------------------------------------
Title: On the Misalignment between Chromospheric Features and the
    Magnetic Field on the Sun
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Carlsson, Mats;
   Hansteen, Viggo
2016ApJ...831L...1M    Altcode: 2016arXiv160702551M
  Observations of the upper chromosphere show an enormous amount of
  intricate fine structure. Much of this comes in the form of linear
  features, which are most often assumed to be well aligned with the
  direction of the magnetic field in the low plasma β regime that is
  thought to dominate the upper chromosphere. We use advanced radiative
  magnetohydrodynamic simulations, including the effects of ion-neutral
  interactions (using the generalized Ohm’s law) in the partially
  ionized chromosphere, to show that the magnetic field is often not well
  aligned with chromospheric features. This occurs where the ambipolar
  diffusion is large, I.e., ions and neutral populations decouple as
  the ion-neutral collision frequency drops, allowing the field to
  slip through the neutral population; where currents perpendicular to
  the field are strong; and where thermodynamic timescales are longer
  than or similar to those of ambipolar diffusion. We find this often
  happens in dynamic spicule or fibril-like features at the top of the
  chromosphere. This has important consequences for field extrapolation
  methods, which increasingly use such upper chromospheric features
  to help constrain the chromospheric magnetic field: our results
  invalidate the underlying assumption that these features are aligned
  with the field. In addition, our results cast doubt on results from
  1D hydrodynamic models, which assume that plasma remains on the same
  field lines. Finally, our simulations show that ambipolar diffusion
  significantly alters the amount of free energy available in the coronal
  part of our simulated volume, which is likely to have consequences
  for studies of flare initiation.

---------------------------------------------------------
Title: The cause of spatial structure in solar He I 1083 nm multiplet
    images
Authors: Leenaarts, Jorrit; Golding, Thomas; Carlsson, Mats; Libbrecht,
   Tine; Joshi, Jayant
2016A&A...594A.104L    Altcode: 2016arXiv160800838L
  Context. The He I 1083 nm is a powerful diagnostic for inferring
  properties of the upper solar chromosphere, in particular for the
  magnetic field. The basic formation of the line in one-dimensional
  models is well understood, but the influence of the complex
  three-dimensional structure of the chromosphere and corona has however
  never been investigated. This structure must play an essential role
  because images taken in He I 1083 nm show structures with widths
  down to 100 km. <BR /> Aims: We aim to understand the effect of
  the three-dimensional temperature and density structure in the
  solar atmosphere on the formation of the He I 1083 nm line. <BR />
  Methods: We solved the non-LTE radiative transfer problem assuming
  statistical equilibrium for a simple nine-level helium atom that
  nevertheless captures all essential physics. As a model atmosphere we
  used a snapshot from a 3D radiation-MHD simulation computed with the
  Bifrost code. Ionising radiation from the corona was self-consistently
  taken into account. <BR /> Results: The emergent intensity in the He
  I 1083 nm is set by the source function and the opacity in the upper
  chromosphere. The former is dominated by scattering of photospheric
  radiation and does not vary much with spatial location. The latter
  is determined by the photonionisation rate in the He I ground state
  continuum, as well as the electron density in the chromosphere. The
  spatial variation of the flux of ionising radiation is caused
  by the spatially-structured emissivity of the ionising photons
  from material at T ≈ 100 kK in the transition region. The hotter
  coronal material produces more ionising photons, but the resulting
  radiation field is smooth and does not lead to small-scale variation
  of the UV flux. The corrugation of the transition region further
  increases the spatial variation of the amount of UV radiation in the
  chromosphere. Finally we find that variations in the chromospheric
  electron density also cause strong variation in He I 1083 nm
  opacity. We compare our findings to observations using SST, IRIS and
  SDO/AIA data. <P />A movie associated to Fig. 4 is available at <A
  href="http://www.aanda.org/10.1051/0004-6361/201628490/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: Chromospheric and Coronal Wave Generation in a Magnetic
    Flux Sheath
Authors: Kato, Yoshiaki; Steiner, Oskar; Hansteen, Viggo; Gudiksen,
   Boris; Wedemeyer, Sven; Carlsson, Mats
2016ApJ...827....7K    Altcode: 2016arXiv160608826K
  Using radiation magnetohydrodynamic simulations of the solar
  atmospheric layers from the upper convection zone to the lower corona,
  we investigate the self-consistent excitation of slow magneto-acoustic
  body waves (slow modes) in a magnetic flux concentration. We
  find that the convective downdrafts in the close surroundings of
  a two-dimensional flux slab “pump” the plasma inside it in
  the downward direction. This action produces a downflow inside the
  flux slab, which encompasses ever higher layers, causing an upwardly
  propagating rarefaction wave. The slow mode, excited by the adiabatic
  compression of the downflow near the optical surface, travels along the
  magnetic field in the upward direction at the tube speed. It develops
  into a shock wave at chromospheric heights, where it dissipates,
  lifts the transition region, and produces an offspring in the form
  of a compressive wave that propagates further into the corona. In the
  wake of downflows and propagating shock waves, the atmosphere inside
  the flux slab in the chromosphere and higher tends to oscillate with a
  period of ν ≈ 4 mHz. We conclude that this process of “magnetic
  pumping” is a most plausible mechanism for the direct generation
  of longitudinal chromospheric and coronal compressive waves within
  magnetic flux concentrations, and it may provide an important heat
  source in the chromosphere. It may also be responsible for certain
  types of dynamic fibrils.

---------------------------------------------------------
Title: The SPICE Spectral Imager on Solar Orbiter: Linking the Sun
    to the Heliosphere
Authors: Fludra, Andrzej; Haberreiter, Margit; Peter, Hardi; Vial,
   Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
   Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson,
   William; Gabriel, Alan; Morris, Nigel; Caldwell, Martin; Auchere,
   Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.; DeForest,
   Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne; Janvier, Miho;
   Wimmer-Schweingruber, Robert; Griffin, Douglas; Davila, Joseph; Giunta,
   Alessandra; Waltham, Nick; Eccleston, Paul; Gottwald, Alexander;
   Klein, Roman; Hanley, John; Walls, Buddy; Howe, Chris; Schuehle, Udo
2016cosp...41E.607F    Altcode:
  The SPICE (Spectral Imaging of the Coronal Environment) instrument is
  one of the key remote sensing instruments onboard the upcoming Solar
  Orbiter Mission. SPICE has been designed to contribute to the science
  goals of the mission by investigating the source regions of outflows
  and ejection processes which link the solar surface and corona to the
  heliosphere. In particular, SPICE will provide quantitative information
  on the physical state and composition of the solar atmosphere
  plasma. For example, SPICE will access relative abundances of ions to
  study the origin and the spatial/temporal variations of the 'First
  Ionization Potential effect', which are key signatures to trace the
  solar wind and plasma ejections paths within the heliosphere. Here we
  will present the instrument and its performance capability to attain the
  scientific requirements. We will also discuss how different observation
  modes can be chosen to obtain the best science results during the
  different orbits of the mission. To maximize the scientific return of
  the instrument, the SPICE team is working to optimize the instrument
  operations, and to facilitate the data access and their exploitation.

---------------------------------------------------------
Title: Solar abundances with the SPICE spectral imager on Solar
    Orbiter
Authors: Giunta, Alessandra; Haberreiter, Margit; Peter, Hardi;
   Vial, Jean-Claude; Harrison, Richard; Parenti, Susanna; Innes, Davina;
   Schmutz, Werner; Buchlin, Eric; Chamberlin, Phillip; Thompson, William;
   Bocchialini, Karine; Gabriel, Alan; Morris, Nigel; Caldwell, Martin;
   Auchere, Frederic; Curdt, Werner; Teriaca, Luca; Hassler, Donald M.;
   DeForest, Craig; Hansteen, Viggo; Carlsson, Mats; Philippon, Anne;
   Janvier, Miho; Wimmer-Schweingruber, Robert; Griffin, Douglas; Baudin,
   Frederic; Davila, Joseph; Fludra, Andrzej; Waltham, Nick; Eccleston,
   Paul; Gottwald, Alexander; Klein, Roman; Hanley, John; Walls, Buddy;
   Howe, Chris; Schuehle, Udo; Gyo, Manfred; Pfiffner, Dany
2016cosp...41E.681G    Altcode:
  Elemental composition of the solar atmosphere and in particular
  abundance bias of low and high First Ionization Potential (FIP)
  elements are a key tracer of the source regions of the solar wind. These
  abundances and their spatio-temporal variations, as well as the other
  plasma parameters , will be derived by the SPICE (Spectral Imaging
  of the Coronal Environment) EUV spectral imager on the upcoming
  Solar Orbiter mission. SPICE is designed to provide spectroheliograms
  (spectral images) using a core set of emission lines arising from ions
  of both low-FIP and high-FIP elements. These lines are formed over
  a wide range of temperatures, enabling the analysis of the different
  layers of the solar atmosphere. SPICE will use these spectroheliograms
  to produce dynamic composition maps of the solar atmosphere to be
  compared to in-situ measurements of the solar wind composition of
  the same elements (i.e. O, Ne, Mg, Fe). This will provide a tool to
  study the connectivity between the spacecraft (the Heliosphere) and
  the Sun. We will discuss the SPICE capabilities for such composition
  measurements.

---------------------------------------------------------
Title: Emergence of Granular-sized Magnetic Bubbles Through the
    Solar Atmosphere. III. The Path to the Transition Region
Authors: Ortiz, Ada; Hansteen, Viggo H.; Bellot Rubio, Luis Ramón;
   de la Cruz Rodríguez, Jaime; De Pontieu, Bart; Carlsson, Mats;
   Rouppe van der Voort, Luc
2016ApJ...825...93O    Altcode: 2016arXiv160400302O
  We study, for the first time, the ascent of granular-sized magnetic
  bubbles from the solar photosphere through the chromosphere into the
  transition region and above. Such events occurred in a flux emerging
  region in NOAA 11850 on 2013 September 25. During that time, the
  first co-observing campaign between the Swedish 1-m Solar Telescope
  (SST) and the Interface Region Imaging Spectrograph (IRIS) spacecraft
  was carried out. Simultaneous observations of the chromospheric Hα
  656.28 nm and Ca II 854.2 nm lines, plus the photospheric Fe I 630.25
  nm line, were made with the CRISP spectropolarimeter at the Spitzer
  Space Telescope (SST) reaching a spatial resolution of 0.″14. At
  the same time, IRIS was performing a four-step dense raster of the
  emerging flux region, taking slit jaw images at 133 (C II, transition
  region), 140 (Si IV, transition region), 279.6 (Mg II k, core, upper
  chromosphere), and 283.2 nm (Mg II k, wing, photosphere). Spectroscopy
  of several lines was performed by the IRIS spectrograph in the far-
  and near-ultraviolet, of which we have used the Si IV 140.3 and the
  Mg II k 279.6 nm lines. Coronal images from the Atmospheric Imaging
  Assembly of the Solar Dynamics Observatory were used to investigate
  the possible coronal signatures of the flux emergence events. The
  photospheric and chromospheric properties of small-scale emerging
  magnetic bubbles have been described in detail in Ortiz et al. Here
  we are able to follow such structures up to the transition region. We
  describe the properties, including temporal delays, of the observed
  flux emergence in all layers. We believe this may be an important
  mechanism of transporting energy and magnetic flux from subsurface
  layers to the transition region and corona.

---------------------------------------------------------
Title: The Appearance of Spicules in High Resolution Observations
    of Ca II H and Hα
Authors: Pereira, Tiago M. D.; Rouppe van der Voort, Luc; Carlsson,
   Mats
2016ApJ...824...65P    Altcode: 2016arXiv160403116P
  Solar spicules are chromospheric fibrils that appear everywhere on
  the Sun, yet their origin is not understood. Using high resolution
  observations of spicules obtained with the Swedish 1 m Solar
  Telescope, we aim to understand how spicules appear in filtergrams
  and Dopplergrams, how they compare in Ca II H and Hα filtergrams,
  and what can make them appear and disappear. We find that spicules
  display a rich and detailed spatial structure, and show a distribution
  of transverse velocities that, when aligned with the line of sight,
  can make them appear at different Hα wing positions. They become more
  abundant at positions closer to the line core, reflecting a distribution
  of Doppler shifts and widths. In Hα width maps they stand out as
  bright features both on disk and off limb, reflecting their large
  Doppler motions and possibly higher temperatures than in the typical
  Hα formation region. Spicule lifetimes measured from narrowband images
  at only a few positions will be an underestimate because Doppler shifts
  can make them disappear prematurely from such images; for such cases,
  width maps are a more robust tool. In Hα and Ca II H filtergrams,
  off-limb spicules essentially have the same properties, appearance,
  and evolution. We find that the sudden appearance of spicules can be
  explained by Doppler shifts from their transverse motions, and does
  not require other convoluted explanations.

---------------------------------------------------------
Title: Physics &amp; Diagnostics of the Drivers of Solar Eruptions
Authors: Cheung, Mark; Rempel, Matthias D.; Martinez-Sykora, Juan;
   Testa, Paola; Hansteen, Viggo H.; Viktorovna Malanushenko, Anna;
   Sainz Dalda, Alberto; DeRosa, Marc L.; De Pontieu, Bart; Carlsson,
   Mats; Chen, Feng; McIntosh, Scott W.; Gudiksen, Boris
2016SPD....47.0607C    Altcode:
  We provide an update on our NASA Heliophysics Grand Challenges Research
  (HGCR) project on the ‘Physics &amp; Diagnostics of the Drivers of
  Solar Eruptions’. This presentation will focus on results from a
  data-inspired, 3D radiative MHD model of a solar flare. The model
  flare results from the interaction of newly emerging flux with a
  pre-existing active region. Synthetic observables from the model
  reproduce observational features compatible with actual flares. These
  include signatures of coronal magnetic reconnection, chromospheric
  evaporation, EUV flare arcades, sweeping motion of flare ribbons
  and sunquakes.

---------------------------------------------------------
Title: Spectro-polarimetric observation in UV with CLASP to probe
    the chromosphere and transition region
Authors: Kano, Ryouhei; Ishikawa, Ryohko; Winebarger, Amy R.; Auchère,
   Frédéric; Trujillo Bueno, Javier; Narukage, Noriyuki; Kobayashi,
   Ken; Bando, Takamasa; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
   Shin-Nosuke; Giono, Gabriel; Hara, Hirohisa; Suematsu, Yoshinori;
   Shimizu, Toshifumi; Sakao, Taro; Tsuneta, Saku; Ichimoto, Kiyoshi;
   Goto, Motoshi; Cirtain, Jonathan W.; De Pontieu, Bart; Casini, Roberto;
   Manso Sainz, Rafael; Asensio Ramos, Andres; Stepan, Jiri; Belluzzi,
   Luca; Carlsson, Mats
2016SPD....4710107K    Altcode:
  The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a NASA
  sounding-rocket experiment that was performed in White Sands in
  the US on September 3, 2015. During its 5-minute ballistic flight,
  CLASP successfully made the first spectro-polarimetric observation in
  the Lyman-alpha line (121.57 nm) originating in the chromosphere and
  transition region. Since the Lyman-alpha polarization is sensitive
  to magnetic field of 10-100 G by the Hanle effect, we aim to infer
  the magnetic field information in such upper solar atmosphere with
  this experiment.The obtained CLASP data showed that the Lyman-alpha
  scattering polarization is about a few percent in the wings and
  the order of 0.1% in the core near the solar limb, as it had been
  theoretically predicted, and that both polarization signals have a
  conspicuous spatio-temporal variability. CLASP also observed another
  upper-chromospheric line, Si III (120.65 nm), whose critical field
  strength for the Hanle effect is 290 G, and showed a measurable
  scattering polarization of a few % in this line. The polarization
  properties of the Si III line could facilitate the interpretation of
  the scattering polarization observed in the Lyman-alpha line.In this
  presentation, we would like to show how the upper chromosphere and
  transition region are seen in the polarization of these UV lines and
  discuss the possible source of these complicated polarization signals.

---------------------------------------------------------
Title: Division G Commission 36: Theory of Stellar Atmospheres
Authors: Puls, Joachim; Hubeny, Ivan; Asplund, Martin; Allard, France;
   Allende Prieto, Carlos; Ayres, Thomas R.; Carlsson, Mats; Gustafsson,
   Bengt; Kudritzki, Rolf-Peter; Ryabchikova, Tatiana A.
2016IAUTA..29..453P    Altcode:
  Different from previous triennial reports, this report covers the
  activities of IAU Commission 36 `Theory of Stellar Atmospheres'
  over the past six years†, and will be the last report from the
  `old' Commission 36. After the General Assembly in Honolulu (August
  2015), a new Commission `Stellar and Planetary Atmospheres' (C.G5,
  under Division G, `Stars and Stellar Physics') has come into life,
  and will continue our work devoted to the outer envelopes of stars,
  as well as extend it to the atmospheres of planets (see Sect. 4).

---------------------------------------------------------
Title: Modeling Repeatedly Flaring δ Sunspots
Authors: Chatterjee, Piyali; Hansteen, Viggo; Carlsson, Mats
2016PhRvL.116j1101C    Altcode: 2016arXiv160100749C
  Active regions (ARs) appearing on the surface of the Sun are classified
  into α , β , γ , and δ by the rules of the Mount Wilson Observatory,
  California on the basis of their topological complexity. Amongst these,
  the δ sunspots are known to be superactive and produce the most
  x-ray flares. Here, we present results from a simulation of the Sun
  by mimicking the upper layers and the corona, but starting at a more
  primitive stage than any earlier treatment. We find that this initial
  state consisting of only a thin subphotospheric magnetic sheet breaks
  into multiple flux tubes which evolve into a colliding-merging system
  of spots of opposite polarity upon surface emergence, similar to those
  often seen on the Sun. The simulation goes on to produce many exotic δ
  sunspot associated phenomena: repeated flaring in the range of typical
  solar flare energy release and ejective helical flux ropes with embedded
  cool-dense plasma filaments resembling solar coronal mass ejections.

---------------------------------------------------------
Title: Non-equilibrium Helium Ionization in an MHD Simulation of
    the Solar Atmosphere
Authors: Golding, Thomas Peter; Leenaarts, Jorrit; Carlsson, Mats
2016ApJ...817..125G    Altcode: 2015arXiv151204738G
  The ionization state of the gas in the dynamic solar chromosphere can
  depart strongly from the instantaneous statistical equilibrium commonly
  assumed in numerical modeling. We improve on earlier simulations of
  the solar atmosphere that only included non-equilibrium hydrogen
  ionization by performing a 2D radiation-magnetohydrodynamics
  simulation featuring non-equilibrium ionization of both hydrogen
  and helium. The simulation includes the effect of hydrogen Lyα and
  the EUV radiation from the corona on the ionization and heating
  of the atmosphere. Details on code implementation are given. We
  obtain helium ion fractions that are far from their equilibrium
  values. Comparison with models with local thermodynamic equilibrium
  (LTE) ionization shows that non-equilibrium helium ionization leads to
  higher temperatures in wavefronts and lower temperatures in the gas
  between shocks. Assuming LTE ionization results in a thermostat-like
  behavior with matter accumulating around the temperatures where the
  LTE ionization fractions change rapidly. Comparison of DEM curves
  computed from our models shows that non-equilibrium ionization leads
  to more radiating material in the temperature range 11-18 kK, compared
  to models with LTE helium ionization. We conclude that non-equilibrium
  helium ionization is important for the dynamics and thermal structure
  of the upper chromosphere and transition region. It might also help
  resolve the problem that intensities of chromospheric lines computed
  from current models are smaller than those observed.

---------------------------------------------------------
Title: A publicly available simulation of an enhanced network region
    of the Sun
Authors: Carlsson, Mats; Hansteen, Viggo H.; Gudiksen, Boris V.;
   Leenaarts, Jorrit; De Pontieu, Bart
2016A&A...585A...4C    Altcode: 2015arXiv151007581C
  Context. The solar chromosphere is the interface between the
  solar surface and the solar corona. Modelling of this region is
  difficult because it represents the transition from optically
  thick to thin radiation escape, from gas-pressure domination to
  magnetic-pressure domination, from a neutral to an ionised state,
  from MHD to plasma physics, and from near-equilibrium (LTE) to
  non-equilibrium conditions. <BR /> Aims: Our aim is to provide the
  community with realistic simulations of the magnetic solar outer
  atmosphere. This will enable detailed comparison of existing and
  upcoming observations with synthetic observables from the simulations,
  thereby elucidating the complex interactions of magnetic fields and
  plasma that are crucial for our understanding of the dynamic outer
  atmosphere. <BR /> Methods: We used the radiation magnetohydrodynamics
  code Bifrost to perform simulations of a computational volume
  with a magnetic field topology similar to an enhanced network
  area on the Sun. <BR /> Results: The full simulation cubes are
  made available from the Hinode Science Data Centre Europe. The
  general properties of the simulation are discussed, and limitations
  are discussed. <P />The Hinode Science Data Centre Europe (<A
  href="http://www.sdc.uio.no/search/simulations">http://www.sdc.uio.no/search/simulations</A>).

---------------------------------------------------------
Title: ALMA Observations of the Sun in Cycle 4 and Beyond
Authors: Wedemeyer, S.; Fleck, B.; Battaglia, M.; Labrosse, N.;
   Fleishman, G.; Hudson, H.; Antolin, P.; Alissandrakis, C.; Ayres, T.;
   Ballester, J.; Bastian, T.; Black, J.; Benz, A.; Brajsa, R.; Carlsson,
   M.; Costa, J.; DePontieu, B.; Doyle, G.; Gimenez de Castro, G.;
   Gunár, S.; Harper, G.; Jafarzadeh, S.; Loukitcheva, M.; Nakariakov,
   V.; Oliver, R.; Schmieder, B.; Selhorst, C.; Shimojo, M.; Simões,
   P.; Soler, R.; Temmer, M.; Tiwari, S.; Van Doorsselaere, T.; Veronig,
   A.; White, S.; Yagoubov, P.; Zaqarashvili, T.
2016arXiv160100587W    Altcode:
  This document was created by the Solar Simulations for the Atacama
  Large Millimeter Observatory Network (SSALMON) in preparation of
  the first regular observations of the Sun with the Atacama Large
  Millimeter/submillimeter Array (ALMA), which are anticipated to start
  in ALMA Cycle 4 in October 2016. The science cases presented here
  demonstrate that a large number of scientifically highly interesting
  observations could be made already with the still limited solar
  observing modes foreseen for Cycle 4 and that ALMA has the potential
  to make important contributions to answering long-standing scientific
  questions in solar physics. With the proposal deadline for ALMA Cycle
  4 in April 2016 and the Commissioning and Science Verification campaign
  in December 2015 in sight, several of the SSALMON Expert Teams composed
  strategic documents in which they outlined potential solar observations
  that could be feasible given the anticipated technical capabilities
  in Cycle 4. These documents have been combined and supplemented
  with an analysis, resulting in recommendations for solar observing
  with ALMA in Cycle 4. In addition, the detailed science cases also
  demonstrate the scientific priorities of the solar physics community
  and which capabilities are wanted for the next observing cycles. The
  work on this White Paper effort was coordinated in close cooperation
  with the two international solar ALMA development studies led by
  T. Bastian (NRAO, USA) and R. Brajsa, (ESO). This document will be
  further updated until the beginning of Cycle 4 in October 2016. In
  particular, we plan to adjust the technical capabilities of the solar
  observing modes once finally decided and to further demonstrate the
  feasibility and scientific potential of the included science cases by
  means of numerical simulations of the solar atmosphere and corresponding
  simulated ALMA observations.

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

---------------------------------------------------------
Title: New Insights into White-Light Flare Emission from
    Radiative-Hydrodynamic Modeling of a Chromospheric Condensation
Authors: Kowalski, Adam F.; Hawley, S. L.; Carlsson, M.; Allred,
   J. C.; Uitenbroek, H.; Osten, R. A.; Holman, G.
2015SoPh..290.3487K    Altcode: 2015SoPh..tmp...61K; 2015arXiv150307057K
  The heating mechanism at high densities during M-dwarf flares is
  poorly understood. Spectra of M-dwarf flares in the optical and
  near-ultraviolet wavelength regimes have revealed three continuum
  components during the impulsive phase: 1) an energetically dominant
  blackbody component with a color temperature of T ≈10<SUP>4</SUP>K
  in the blue-optical, 2) a smaller amount of Balmer continuum emission
  in the near-ultraviolet at λ ≤3 646 Å, and 3) an apparent
  pseudo-continuum of blended high-order Balmer lines between λ =3
  646 Å and λ ≈3 900 Å. These properties are not reproduced by
  models that employ a typical "solar-type" flare heating level of
  ≤10<SUP>11</SUP>ergcm−<SUP>2</SUP>s−<SUP>1</SUP> in nonthermal
  electrons, and therefore our understanding of these spectra is
  limited to a phenomenological three-component interpretation. We
  present a new 1D radiative-hydrodynamic model of an M-dwarf flare
  from precipitating nonthermal electrons with a high energy flux of
  10<SUP>13</SUP>ergcm−<SUP>2</SUP>s−<SUP>1</SUP>. The simulation
  produces bright near-ultraviolet and optical continuum emission from a
  dense (n &gt;10<SUP>15</SUP>cm−<SUP>3</SUP>), hot (T ≈12 000 -13 500
  K) chromospheric condensation. For the first time, the observed color
  temperature and Balmer jump ratio are produced self-consistently in a
  radiative-hydrodynamic flare model. We find that a T ≈10<SUP>4</SUP>K
  blackbody-like continuum component and a low Balmer jump ratio result
  from optically thick Balmer (∞ →n =2 ) and Paschen recombination
  (∞ →n =3 ) radiation, and thus the properties of the flux spectrum
  are caused by blue (λ ≈4 300 Å) light escaping over a larger
  physical depth range than by red (λ ≈6 700 Å) and near-ultraviolet
  (λ ≈3 500 Å) light. To model the near-ultraviolet pseudo-continuum
  previously attributed to overlapping Balmer lines, we include the
  extra Balmer continuum opacity from Landau-Zener transitions that
  result from merged, high-order energy levels of hydrogen in a dense,
  partially ionized atmosphere. This reveals a new diagnostic of ambient
  charge density in the densest regions of the atmosphere that are heated
  during dMe and solar flares.

---------------------------------------------------------
Title: Heating of the Solar Chromosphere and Connections to the
    Transition Region and Corona
Authors: Carlsson, M.
2015AGUFMSH23D..01C    Altcode:
  We present observations of the chromosphere and transition region
  from IRIS and the SST. These observations are interpreted using 1D
  semi-empirical numerical experiments, 1D radiaton-MHD simulations and 3D
  "realistic" radiation-MHD simulations spanning the solar atmosphere
  from the convection zone to the corona. A picture is emerging of
  the energy balance in the solar chromosphere and connections to the
  transition region and corona.

---------------------------------------------------------
Title: Impact of the Ion-Neutral Interaction Effects in the Solar
    Chromosphere
Authors: Martínez-Sykora, J.; De Pontieu, B.; Hansteen, V. H.;
   Carlsson, M.
2015AGUFMSH31B2411M    Altcode:
  The complexity of the chromosphere is due to various regime changes
  that take place across it. Consequently, the interpretation of
  chromospheric observations is a challenging task. It is thus crucial
  to combine these observations with advanced radiative-MHD numerical
  modeling. Because the photosphere, chromosphere and transition region
  are partially ionized, the interaction between ionized and neutral
  particles has important consequences on the magneto-thermodynamics
  of these regions. We implemented the effects of partial ionization
  using generalized Ohm's law in the Bifrost code (Gudiksen et al. 2011)
  which solves the full MHD equations with non-grey and non-LTE radiative
  transfer and thermal conduction along magnetic field lines. We perform
  2.5D simulations which combines large and small scales structures. This
  leads to a highly dynamic chromosphere with large variety of physical
  processes which have not been reproduced with smaller simulations. The
  implementation of partial ionization effects impact our modeled
  radiative-MHD atmosphere, such as producing chromospheric heating and
  diffusion of photospheric magnetic field into the upper-chromosphere. We
  will also focus on which observables of these processes can be revealed
  with chromospheric observations.

---------------------------------------------------------
Title: Hα Line Profile Asymmetries and the Chromospheric Flare
    Velocity Field
Authors: Kuridze, D.; Mathioudakis, M.; Simões, P. J. A.; Rouppe van
   der Voort, L.; Carlsson, M.; Jafarzadeh, S.; Allred, J. C.; Kowalski,
   A. F.; Kennedy, M.; Fletcher, L.; Graham, D.; Keenan, F. P.
2015ApJ...813..125K    Altcode: 2015arXiv151001877K
  The asymmetries observed in the line profiles of solar flares can
  provide important diagnostics of the properties and dynamics of the
  flaring atmosphere. In this paper the evolution of the Hα and Ca ii
  λ8542 lines are studied using high spatial, temporal, and spectral
  resolution ground-based observations of an M1.1 flare obtained with
  the Swedish 1 m Solar Telescope. The temporal evolution of the Hα
  line profiles from the flare kernel shows excess emission in the red
  wing (red asymmetry) before flare maximum and excess in the blue wing
  (blue asymmetry) after maximum. However, the Ca ii λ8542 line does
  not follow the same pattern, showing only a weak red asymmetry during
  the flare. RADYN simulations are used to synthesize spectral line
  profiles for the flaring atmosphere, and good agreement is found
  with the observations. We show that the red asymmetry observed in
  Hα is not necessarily associated with plasma downflows, and the blue
  asymmetry may not be related to plasma upflows. Indeed, we conclude
  that the steep velocity gradients in the flaring chromosphere modify
  the wavelength of the central reversal in the Hα line profile. The
  shift in the wavelength of maximum opacity to shorter and longer
  wavelengths generates the red and blue asymmetries, respectively.

---------------------------------------------------------
Title: The Formation of Iris Diagnostics. VIII. Iris Observations
    in the C II 133.5 nm Multiplet.
Authors: Rathore, Bhavna; Pereira, Tiago M. D.; Carlsson, Mats;
   De Pontieu, Bart
2015ApJ...814...70R    Altcode: 2015arXiv151004845R
  The C ii 133.5 nm multiplet has been observed by NASA’s Interface
  Region Imaging Spectrograph (IRIS) in unprecedented spatial
  resolution. The aims of this work are to characterize these new
  observations of the C ii lines, place them in context with previous
  work, and to identify any additional value the C ii lines bring when
  compared with other spectral lines. We make use of wide, long exposure
  IRIS rasters covering the quiet Sun and an active region. Line
  properties such as velocity shift and width are extracted from
  individual spectra and analyzed. The lines have a variety of shapes
  (mostly single-peak or double-peak), are strongest in active regions
  and weaker in the quiet Sun. The ratio between the 133.4 and 133.5 nm
  components is always less than 1.8, indicating that their radiation
  is optically thick in all locations. Maps of the C ii line widths are
  a powerful new diagnostic of chromospheric structures, and their line
  shifts are a robust velocity diagnostic. Compared with earlier quiet Sun
  observations, we find similar absolute intensities and mean line widths,
  but smaller redshifts; this difference can perhaps be attributed to
  differences in spectral resolution and spatial coverage. The C ii
  intensity maps are somewhat similar to those of transition region
  lines, but also share some features with chromospheric maps such as
  those from the Mg ii k line, indicating that they are formed between
  the upper chromosphere and transition region. C ii intensity, width,
  and velocity maps can therefore be used to gather additional information
  about the upper chromosphere.

---------------------------------------------------------
Title: Combined Modeling of Acceleration, Transport, and Hydrodynamic
    Response in Solar Flares. II. Inclusion of Radiative Transfer
    with RADYN
Authors: Rubio da Costa, Fatima; Liu, Wei; Petrosian, Vahé; Carlsson,
   Mats
2015ApJ...813..133R    Altcode: 2015arXiv150501549R
  Solar flares involve complex processes that are coupled and span a
  wide range of temporal, spatial, and energy scales. Modeling such
  processes self-consistently has been a challenge in the past. Here we
  present results from simulations that couple particle kinetics with
  hydrodynamics (HD) of the atmospheric plasma. We combine the Stanford
  unified Fokker-Planck code that models particle acceleration and
  transport with the RADYN HD code that models the atmospheric response
  to collisional heating by accelerated electrons through detailed
  radiative transfer calculations. We perform simulations using two
  different electron spectra, one an ad hoc power law and the other
  predicted by the model of stochastic acceleration by turbulence or
  plasma waves. Surprisingly, the later model, even with energy flux \ll
  {10}<SUP>10</SUP> {erg} {{{s}}}<SUP>-1</SUP> {{cm}}<SUP>-2</SUP>, can
  cause “explosive” chromospheric evaporation and drive stronger
  up- and downflows (and HD shocks). This is partly because our
  acceleration model, like many others, produces a spectrum consisting
  of a quasi-thermal component plus a power-law tail. We synthesize
  emission-line profiles covering different heights in the lower
  atmosphere, including Hα 6563 Å, He ii 304 Å, Ca ii K 3934 Å, and
  Si iv 1393 Å. One interesting result is the unusual high temperature
  (up to a few times 10<SUP>5</SUP> K) of the formation site of He ii
  304 Å, which is expected owing to photoionization-recombination under
  flare conditions, compared to those in the quiet Sun dominated by
  collisional excitation. When compared with observations, our results
  can constrain the properties of nonthermal electrons and thus the
  poorly understood particle acceleration mechanism.

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. VII. The Formation of the
    OI 135.56 NM Line in the Solar Atmosphere
Authors: Lin, Hsiao-Hsuan; Carlsson, Mats
2015ApJ...813...34L    Altcode: 2015arXiv150906605L
  The O i 135.56 nm line is covered by NASA's Interface Region Imaging
  Spectrograph (IRIS) small explorer mission which studies how the
  solar atmosphere is energized. We study here the formation and
  diagnostic potential of this line by means of non-local thermodynamic
  equilibrium modeling employing both 1D semi-empirical and 3D radiation
  magnetohydrodynamic models. We study the basic formation mechanisms
  and derive a quintessential model atom that incorporates essential
  atomic physics for the formation of the O i 135.56 nm line. This
  atomic model has 16 levels and describes recombination cascades
  through highly excited levels by effective recombination rates. The
  ionization balance O i/O ii is set by the hydrogen ionization balance
  through charge exchange reactions. The emission in the O i 135.56 nm
  line is dominated by a recombination cascade and the line is optically
  thin. The Doppler shift of the maximum emission correlates strongly with
  the vertical velocity in its line forming region, which is typically
  located at 1.0-1.5 Mm height. The total intensity of the line emission
  is correlated with the square of the electron density. Since the O i
  135.56 nm line is optically thin, the width of the emission line is a
  very good diagnostic of non-thermal velocities. We conclude that the
  O i 135.56 nm line is an excellent probe of the middle chromosphere,
  and compliments other powerful chromospheric diagnostics of IRIS such
  as the Mg ii h &amp; k lines and the C ii lines around 133.5 nm.

---------------------------------------------------------
Title: Evidence for a Transition Region Response to Penumbral
    Microjets in Sunspots
Authors: Vissers, G. J. M.; Rouppe van der Voort, L. H. M.; Carlsson,
   M.
2015ApJ...811L..33V    Altcode: 2015arXiv150901402V
  Penumbral microjets (PMJs) are short-lived, fine-structured, and
  bright jets that are generally observed in chromospheric imaging of the
  penumbra of sunspots. Here we investigate their potential transition
  region signature by combining observations with the Swedish 1-m Solar
  Telescope in the Ca ii H and Ca ii 8542 Å lines with ultraviolet
  imaging and spectroscopy obtained with the Interface Region Imaging
  Spectrograph (IRIS), which includes the C ii 1334/1335 Å, Si iv
  1394/1403 Å, and Mg ii h &amp; k 2803/2796 Å lines. We find a clear
  corresponding signal in the IRIS Mg ii k, C ii, and Si iv slit-jaw
  images, typically offset spatially from the Ca ii signature in the
  direction along the jets: from base to top, the PMJs are predominantly
  visible in Ca ii, Mg ii k, and C ii/Si iv, suggesting progressive
  heating to transition region temperatures along the jet extent. Hence,
  these results support the suggestion from earlier studies that PMJs
  may heat to transition region temperatures.

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. VI. The Diagnostic Potential
    of the C II Lines at 133.5 nm in the Solar Atmosphere
Authors: Rathore, Bhavna; Carlsson, Mats; Leenaarts, Jorrit; De
   Pontieu, Bart
2015ApJ...811...81R    Altcode: 2015arXiv150804423R
  We use 3D radiation magnetohydrodynamic models to investigate how the
  thermodynamic quantities in the simulation are encoded in observable
  quantities, thus exploring the diagnostic potential of the C ii 133.5
  nm lines. We find that the line core intensity is correlated with the
  temperature at the formation height but the correlation is rather weak,
  especially when the lines are strong. The line core Doppler shift is a
  good measure of the line-of-sight velocity at the formation height. The
  line width is both dependent on the width of the absorption profile
  (thermal and non-thermal width) and an opacity broadening factor of
  1.2-4 due to the optically thick line formation with a larger broadening
  for double peak profiles. The C ii 133.5 nm lines can be formed both
  higher and lower than the core of the Mg ii k line depending on the
  amount of plasma in the 14-50 kK temperature range. More plasma in
  this temperature range gives a higher C ii 133.5 nm formation height
  relative to the Mg ii k line core. The synthetic line profiles have been
  compared with Interface Region Imaging Spectrograph observations. The
  derived parameters from the simulated line profiles cover the parameter
  range seen in observations but, on average, the synthetic profiles are
  too narrow. We interpret this discrepancy as a combination of a lack
  of plasma at chromospheric temperatures in the simulation box and too
  small non-thermal velocities. The large differences in the distribution
  of properties between the synthetic profiles and the observed ones
  show that the C ii 133.5 nm lines are powerful diagnostics of the
  upper chromosphere and lower transition region.

---------------------------------------------------------
Title: Numerical Simulations of Coronal Heating through Footpoint
    Braiding
Authors: Hansteen, V.; Guerreiro, N.; De Pontieu, B.; Carlsson, M.
2015ApJ...811..106H    Altcode: 2015arXiv150807234H
  Advanced three-dimensional (3D) radiative MHD simulations now reproduce
  many properties of the outer solar atmosphere. When including a domain
  from the convection zone into the corona, a hot chromosphere and corona
  are self-consistently maintained. Here we study two realistic models,
  with different simulated areas, magnetic field strength and topology,
  and numerical resolution. These are compared in order to characterize
  the heating in the 3D-MHD simulations which self-consistently
  maintains the structure of the atmosphere. We analyze the heating
  at both large and small scales and find that heating is episodic and
  highly structured in space, but occurs along loop-shaped structures,
  and moves along with the magnetic field. On large scales we find that
  the heating per particle is maximal near the transition region and that
  widely distributed opposite-polarity field in the photosphere leads
  to a greater heating scale height in the corona. On smaller scales,
  heating is concentrated in current sheets, the thicknesses of which are
  set by the numerical resolution. Some current sheets fragment in time,
  this process occurring more readily in the higher-resolution model
  leading to spatially highly intermittent heating. The large-scale
  heating structures are found to fade in less than about five minutes,
  while the smaller, local, heating shows timescales of the order of two
  minutes in one model and one minutes in the other, higher-resolution,
  model.

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. V. A Quintessential Model
    Atom of C II and General Formation Properties of the C II Lines at
    133.5 nm
Authors: Rathore, Bhavna; Carlsson, Mats
2015ApJ...811...80R    Altcode: 2015arXiv150804365R
  The C ii 133.5 {nm} lines are important observables for the NASA/SMEX
  mission Interface Region Imaging Spectrograph. To make three-dimensional
  (3D) non-LTE radiative transfer computationally feasible, it is crucial
  to have a model atom with as few levels as possible while retaining
  the main physical processes. We here develop such a model atom and we
  study the general formation properties of the C ii lines. We find that a
  nine-level model atom of C i-C iii with the transitions treated assuming
  complete frequency redistribution (CRD) suffices to describe the C ii
  133.5 {nm} lines. 3D scattering effects are important for the intensity
  in the core of the line. The lines are formed in the optically thick
  regime. The core intensity is formed in layers where the temperature is
  about 10 kK at the base of the transition region. The lines are 1.2-4
  times wider than the atomic absorption profile due to the formation in
  the optically thick regime. The smaller opacity broadening happens for
  single peak intensity profiles where the chromospheric temperature is
  low with a steep source function increase into the transition region,
  the larger broadening happens when there is a temperature increase
  from the photosphere to the low chromosphere leading to a local source
  function maximum and a double peak intensity profile with a central
  reversal. Assuming optically thin formation with the standard coronal
  approximation leads to several errors: neglecting photoionization
  severly underestimates the amount of C ii at temperatures below 16 kK,
  erroneously shifts the formation from 10 kK to 25 kK, and leads to
  too low intensities.

---------------------------------------------------------
Title: Ellerman Bombs at High Resolution. III. Simultaneous
    Observations with IRIS and SST
Authors: Vissers, G. J. M.; Rouppe van der Voort, L. H. M.; Rutten,
   R. J.; Carlsson, M.; De Pontieu, B.
2015ApJ...812...11V    Altcode: 2015arXiv150700435V
  Ellerman bombs (EBs) are transient brightenings of the extended wings
  of the solar Balmer lines in emerging active regions. We describe
  their properties in the ultraviolet lines sampled by the Interface
  Region Imaging Spectrograph (IRIS), using simultaneous imaging
  spectroscopy in Hα with the Swedish 1-m Solar Telescope (SST) and
  ultraviolet images from the Solar Dynamics Observatory for Ellerman
  bomb detection and identification. We select multiple co-observed
  EBs for detailed analysis. The IRIS spectra strengthen the view that
  EBs mark reconnection between bipolar kilogauss fluxtubes with the
  reconnection and the resulting bi-directional jet located within the
  solar photosphere and shielded by overlying chromospheric fibrils in
  the cores of strong lines. The spectra suggest that the reconnecting
  photospheric gas underneath is heated sufficiently to momentarily reach
  stages of ionization normally assigned to the transition region and the
  corona. We also analyze similar outburst phenomena that we classify as
  small flaring arch filaments and ascribe to reconnection at a higher
  location. They have different morphologies and produce hot arches in
  million-Kelvin diagnostics.

---------------------------------------------------------
Title: Observed Variability of the Solar Mg II h Spectral Line
Authors: Schmit, D.; Bryans, P.; De Pontieu, B.; McIntosh, S.;
   Leenaarts, J.; Carlsson, M.
2015ApJ...811..127S    Altcode: 2015arXiv150804714S
  The Mg ii h&amp;k doublet are two of the primary spectral lines observed
  by the Sun-pointing Interface Region Imaging Spectrograph (IRIS). These
  lines are tracers of the magnetic and thermal environment that spans
  from the photosphere to the upper chromosphere. We use a double-Gaussian
  model to fit the Mg ii h profile for a full-Sun mosaic data set taken
  on 2014 August 24. We use the ensemble of high-quality profile fits to
  conduct a statistical study on the variability of the line profile as
  it relates the magnetic structure, dynamics, and center-to-limb viewing
  angle. The average internetwork profile contains a deeply reversed
  core and is weakly asymmetric at h2. In the internetwork, we find a
  strong correlation between h3 wavelength and profile asymmetry as well
  as h1 width and h2 width. The average reversal depth of the h3 core
  is inversely related to the magnetic field. Plage and sunspots exhibit
  many profiles that do not contain a reversal. These profiles also occur
  infrequently in the internetwork. We see indications of magnetically
  aligned structures in plage and network in statistics associated with
  the line core, but these structures are not clear or extended in the
  internetwork. The center-to-limb variations are compared to predictions
  of semi-empirical model atmospheres. We measure a pronounced limb
  darkening in the line core that is not predicted by the model. The
  aim of this work is to provide a comprehensive measurement baseline
  and preliminary analysis on the observed structure and formation of
  the Mg ii profiles observed by IRIS.

---------------------------------------------------------
Title: Numerical Modeling of the Solar Chromosphere and Corona:
    What Has Been Done? What Should Be Done?
Authors: Hansteen, V.; Carlsson, M.; Gudiksen, B.
2015ASPC..498..141H    Altcode:
  A number of increasingly sophisticated numerical simulations spanning
  the solar atmosphere from below the photosphere in the convection
  zone to far above in the corona have shed considerable insight into
  the role of the magnetic field in the structure and energetics of the
  Sun's outer layers. This development is strengthened by the wealth of
  observational data now coming on-line from both ground and space based
  observatories. In this talk we will concentrate on the successes and
  failures of the modeling effort thus far and discuss the inclusion of
  various effects not traditionally considered in the MHD description
  such as time dependent ionization, non-LTE radiative transfer, and
  generalized Ohm's law.

---------------------------------------------------------
Title: What Do IRIS Observations of Mg II k Tell Us about the Solar
    Plage Chromosphere?
Authors: Carlsson, Mats; Leenaarts, Jorrit; De Pontieu, Bart
2015ApJ...809L..30C    Altcode: 2015arXiv150804888C
  We analyze observations from the Interface Region Imaging Spectrograph
  of the Mg ii k line, the Mg ii UV subordinate lines, and the O i
  135.6 {nm} line to better understand the solar plage chromosphere. We
  also make comparisons with observations from the Swedish 1-m Solar
  Telescope of the Hα line, the Ca ii 8542 line, and Solar Dynamics
  Observatory/Atmospheric Imaging Assembly observations of the coronal
  19.3 {nm} line. To understand the observed Mg ii profiles, we compare
  these observations to the results of numerical experiments. The
  single-peaked or flat-topped Mg ii k profiles found in plage imply a
  transition region at a high column mass and a hot and dense chromosphere
  of about 6500 K. This scenario is supported by the observed large-scale
  correlation between moss brightness and filled-in profiles with very
  little or absent self-reversal. The large wing width found in plage
  also implies a hot and dense chromosphere with a steep chromospheric
  temperature rise. The absence of emission in the Mg ii subordinate
  lines constrain the chromospheric temperature and the height of the
  temperature rise while the width of the O i 135.6 {nm} line sets a
  limit to the non-thermal velocities to around 7 km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: A Unified Computational Model for Solar and Stellar Flares
Authors: Allred, Joel C.; Kowalski, Adam F.; Carlsson, Mats
2015ApJ...809..104A    Altcode: 2015arXiv150704375A
  We present a unified computational framework that can be used to
  describe impulsive flares on the Sun and on dMe stars. The models
  assume that the flare impulsive phase is caused by a beam of charged
  particles that is accelerated in the corona and propagates downward
  depositing energy and momentum along the way. This rapidly heats
  the lower stellar atmosphere causing it to explosively expand and
  dramatically brighten. Our models consist of flux tubes that extend from
  the sub-photosphere into the corona. We simulate how flare-accelerated
  charged particles propagate down one-dimensional flux tubes and heat the
  stellar atmosphere using the Fokker-Planck kinetic theory. Detailed
  radiative transfer is included so that model predictions can be
  directly compared with observations. The flux of flare-accelerated
  particles drives return currents which additionally heat the stellar
  atmosphere. These effects are also included in our models. We examine
  the impact of the flare-accelerated particle beams on model solar and
  dMe stellar atmospheres and perform parameter studies varying the
  injected particle energy spectra. We find the atmospheric response
  is strongly dependent on the accelerated particle cutoff energy and
  spectral index.

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. IV. The Mg II Triplet
    Lines as a New Diagnostic for Lower Chromospheric Heating
Authors: Pereira, Tiago M. D.; Carlsson, Mats; De Pontieu, Bart;
   Hansteen, Viggo
2015ApJ...806...14P    Altcode: 2015arXiv150401733P
  A triplet of subordinate lines of Mg ii exists in the region around
  the h&amp;k lines. In solar spectra these lines are seen mostly
  in absorption, but in some cases can become emission lines. The
  aim of this work is to study the formation of this triplet, and
  investigate any diagnostic value they can bring. Using 3D radiative
  magnetohydrodynamic simulations of quiet Sun and flaring flux emergence,
  we synthesize spectra and investigate how spectral features respond
  to the underlying atmosphere. We find that emission in the lines
  is rare and is typically caused by a steep temperature increase in
  the lower chromosphere (above 1500 K, with electron densities above
  10<SUP>17</SUP> m<SUP>-3</SUP>). In both simulations the lines are
  sensitive to temperature increases taking place at column masses ≳5
  · 10<SUP>-4</SUP> g cm<SUP>-2</SUP>. Additional information can
  also be inferred from the peak-to-wing ratio and shape of the line
  profiles. Using observations from NASA's Interface Region Imaging
  Spectrograph we find both absorption and emission line profiles with
  similar shapes to the synthetic spectra, which suggests that these lines
  represent a useful diagnostic that complements the Mg ii h&amp;k lines.

---------------------------------------------------------
Title: IRIS observations and 3D `realistic' MHD models of the solar
    chromosphere
Authors: Hansteen, V.; Carlsson, M.; Gudiksen, B.
2015hsa8.conf...19H    Altcode:
  The Interface Region Imaging Spectrograph (IRIS) is a NASA “Small
  Explorer” mission. It was launched in late June 2013 and since then
  it has obtained spectra and images from the outer solar atmosphere at
  unprecedented spatial and temporal resolution. Its primary goal is to
  probe the photosphere-corona interface: the source region of outer
  atmosphere heating and dynamics and a region that has an extremely
  complicated interplay between plasma, radiation and magnetic field. The
  scientific justification for IRIS hinges on the capabilities of 3D
  magnetohydrodynamic models to allow the confident interpretation of
  observed data. The interplay between observations and modeling is
  discussed, illustrated with examples from recent IRIS observations.

---------------------------------------------------------
Title: First High-resolution Spectroscopic Observations of an Erupting
    Prominence Within a Coronal Mass Ejection by the Interface Region
    Imaging Spectrograph (IRIS)
Authors: Liu, Wei; De Pontieu, Bart; Vial, Jean-Claude; Title, Alan
   M.; Carlsson, Mats; Uitenbroek, Han; Okamoto, Takenori J.; Berger,
   Thomas E.; Antolin, Patrick
2015ApJ...803...85L    Altcode: 2015arXiv150204738L
  Spectroscopic observations of prominence eruptions associated with
  coronal mass ejections (CMEs), although relatively rare, can provide
  valuable plasma and three-dimensional geometry diagnostics. We report
  the first observations by the Interface Region Imaging Spectrograph
  mission of a spectacular fast CME/prominence eruption associated with
  an equivalent X1.6 flare on 2014 May 9. The maximum plane-of-sky and
  Doppler velocities of the eruption are 1200 and 460 km s<SUP>-1</SUP>,
  respectively. There are two eruption components separated by ∼200
  km s<SUP>-1</SUP> in Doppler velocity: a primary, bright component
  and a secondary, faint component, suggesting a hollow, rather than
  solid, cone-shaped distribution of material. The eruption involves
  a left-handed helical structure undergoing counterclockwise (viewed
  top-down) unwinding motion. There is a temporal evolution from upward
  eruption to downward fallback with less-than-free-fall speeds and
  decreasing nonthermal line widths. We find a wide range of Mg ii k/h
  line intensity ratios (less than ∼2 expected for optically-thin
  thermal emission): the lowest ever reported median value of 1.17
  found in the fallback material, a comparably high value of 1.63 in
  nearby coronal rain, and intermediate values of 1.53 and 1.41 in
  the two eruption components. The fallback material exhibits a strong
  (\gt 5σ ) linear correlation between the k/h ratio and the Doppler
  velocity as well as the line intensity. We demonstrate that Doppler
  dimming of scattered chromospheric emission by the erupted material
  can potentially explain such characteristics.

---------------------------------------------------------
Title: Three-dimensional Radiative Transfer Simulations of
    the Scattering Polarization of the Hydrogen Lyα Line in a
    Magnetohydrodynamic Model of the Chromosphere-Corona Transition Region
Authors: Štěpán, J.; Trujillo Bueno, J.; Leenaarts, J.; Carlsson, M.
2015ApJ...803...65S    Altcode: 2015arXiv150106382S
  Probing the magnetism of the upper solar chromosphere requires measuring
  and modeling the scattering polarization produced by anisotropic
  radiation pumping in UV spectral lines. Here we apply PORTA (a novel
  radiative transfer code) to investigate the hydrogen Lyα line in
  a three-dimensional model of the solar atmosphere resulting from a
  state of the art magnetohydrodynamic (MHD) simulation. At full spatial
  resolution the linear polarization signals are very significant all
  over the solar disk, with a large fraction of the field of view (FOV)
  showing line-center amplitudes well above the 1% level. Via the Hanle
  effect the line-center polarization signals are sensitive to the
  magnetic field of the model's transition region, even when its mean
  field strength is only 15 G. The breaking of the axial symmetry of the
  radiation field produces significant forward-scattering polarization
  in Lyα, without the need of an inclined magnetic field. Interestingly,
  the Hanle effect tends to decrease such forward-scattering polarization
  signals in most of the points of the FOV. When the spatial resolution is
  degraded, the line-center polarization of Lyα drops below the 1% level,
  reaching values similar to those previously found in one-dimensional
  (1D) semi-empirical models (i.e., up to about 0.5 %). The center to
  limb variation (CLV) of the spatially averaged polarization signals
  is qualitatively similar to that found in 1D models, with the largest
  line-center amplitudes at μ =cos θ ≈ 0.4 (θ being the heliocentric
  angle). These results are important, both for designing the needed
  space-based instrumentation and for a reliable interpretation of future
  observations of the Lyα polarization.

---------------------------------------------------------
Title: The role of partial ionization effects in the chromosphere
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo;
   Carlsson, Mats
2015RSPTA.37340268M    Altcode: 2015arXiv150302723M
  The energy for the coronal heating must be provided from the
  convection zone. However, the amount and the method by which this
  energy is transferred into the corona depend on the properties of the
  lower atmosphere and the corona itself. We review: (i) how the energy
  could be built in the lower solar atmosphere, (ii) how this energy is
  transferred through the solar atmosphere, and (iii) how the energy is
  finally dissipated in the chromosphere and/or corona. Any mechanism of
  energy transport has to deal with the various physical processes in the
  lower atmosphere. We will focus on a physical process that seems to
  be highly important in the chromosphere and not deeply studied until
  recently: the ion-neutral interaction effects in the chromosphere. We
  review the relevance and the role of the partial ionization in the
  chromosphere and show that this process actually impacts considerably
  the outer solar atmosphere. We include analysis of our 2.5D radiative
  magnetohydrodynamic simulations with the Bifrost code (Gudiksen et
  al. 2011 Astron. Astrophys. 531, A154 (doi:10.1051/0004-6361/201116520))
  including the partial ionization effects on the chromosphere
  and corona and thermal conduction along magnetic field lines. The
  photosphere, chromosphere and transition region are partially ionized
  and the interaction between ionized particles and neutral particles
  has important consequences on the magneto-thermodynamics of these
  layers. The partial ionization effects are treated using generalized
  Ohm's law, i.e. we consider the Hall term and the ambipolar diffusion
  (Pedersen dissipation) in the induction equation. The interaction
  between the different species affects the modelled atmosphere as
  follows: (i) the ambipolar diffusion dissipates magnetic energy and
  increases the minimum temperature in the chromosphere and (ii) the
  upper chromosphere may get heated and expanded over a greater range
  of heights. These processes reveal appreciable differences between
  the modelled atmospheres of simulations with and without ion-neutral
  interaction effects.

---------------------------------------------------------
Title: On Fibrils and Field Lines: the Nature of Hα Fibrils in the
    Solar Chromosphere
Authors: Leenaarts, Jorrit; Carlsson, Mats; Rouppe van der Voort, Luc
2015ApJ...802..136L    Altcode: 2015arXiv150200295L
  Observations of the solar chromosphere in the line core of the Hα
  line show dark elongated structures called fibrils that show swaying
  motion. We performed a three-dimensional radiation-MHD simulation of a
  network region and computed synthetic Hα images from this simulation
  to investigate the relation between fibrils and the magnetic field
  lines in the chromosphere. The periods, amplitudes, and phase speeds
  of the simulated fibrils are consistent with observations. We find that
  some fibrils trace out the same field line along the fibril’s length,
  while other fibrils sample different field lines at different locations
  along their length. Fibrils sample the same field lines on a timescale
  of ∼200 s. This is shorter than their own lifetime. Fibril-threading
  field lines carry slow-mode waves, as well as transverse waves
  propagating with the Alfvén speed. Transverse waves propagating
  in opposite directions cause an interference pattern with complex
  apparent phase speeds. The relationship between fibrils and field lines
  is governed by constant migration and swaying of the field lines,
  their mass loading and draining, and their visibility in Hα. Field
  lines are visible where they lie close to the optical depth unity
  surface. The location of the latter is at a height at which the column
  mass reaches a certain fixed value. The visibility of the field line
  is thus determined by its own mass density and by the mass density of
  the material above it. Using the swaying motion of fibrils as a tracer
  of chromospheric transverse oscillations must be done with caution.

---------------------------------------------------------
Title: Internetwork Chromospheric Bright Grains Observed With IRIS
    and SST
Authors: Martínez-Sykora, Juan; Rouppe van der Voort, Luc; Carlsson,
   Mats; De Pontieu, Bart; Pereira, Tiago M. D.; Boerner, Paul; Hurlburt,
   Neal; Kleint, Lucia; Lemen, James; Tarbell, Ted D.; Title, Alan;
   Wuelser, Jean-Pierre; Hansteen, Viggo H.; Golub, Leon; McKillop, Sean;
   Reeves, Kathy K.; Saar, Steven; Testa, Paola; Tian, Hui; Jaeggli,
   Sarah; Kankelborg, Charles
2015ApJ...803...44M    Altcode: 2015arXiv150203490M
  The Interface Region Imaging Spectrograph (IRIS) reveals small-scale
  rapid brightenings in the form of bright grains all over coronal holes
  and the quiet Sun. These bright grains are seen with the IRIS 1330,
  1400, and 2796 Å slit-jaw filters. We combine coordinated observations
  with IRIS and from the ground with the Swedish 1 m Solar Telescope
  (SST) which allows us to have chromospheric (Ca ii 8542 Å, Ca ii H
  3968 Å, Hα, and Mg ii k 2796 Å) and transition region (C ii 1334 Å,
  Si iv 1403 Å) spectral imaging, and single-wavelength Stokes maps
  in Fe i 6302 Å at high spatial (0\buildrel{\prime\prime}\over{.}
  33), temporal, and spectral resolution. We conclude that the IRIS
  slit-jaw grains are the counterpart of so-called acoustic grains,
  i.e., resulting from chromospheric acoustic waves in a non-magnetic
  environment. We compare slit-jaw images (SJIs) with spectra from the
  IRIS spectrograph. We conclude that the grain intensity in the 2796
  Å slit-jaw filter comes from both the Mg ii k core and wings. The
  signal in the C ii and Si iv lines is too weak to explain the presence
  of grains in the 1300 and 1400 Å SJIs and we conclude that the grain
  signal in these passbands comes mostly from the continuum. Although
  weak, the characteristic shock signatures of acoustic grains can often
  be detected in IRIS C ii spectra. For some grains, a spectral signature
  can be found in IRIS Si iv. This suggests that upward propagating
  acoustic waves sometimes reach all the way up to the transition region.

---------------------------------------------------------
Title: A Unified Computational Model for Solar and Stellar Flares
Authors: Allred, Joel; Kowalski, Adam; Carlsson, Mats
2015TESS....130207A    Altcode:
  We describe a unified computational framework which can be used to model
  impulsive flares on the Sun and on dMe stars. The models are constructed
  assuming that the flare impulsive phase is caused by a beam of charged
  particles (primarily electrons and protons) that is accelerated in the
  corona and propagates downward depositing energy and momentum along
  the way. This rapidly heats the lower stellar atmosphere causing it to
  explosively expand and emission to dramatically brighten. Our models
  consist of flux tubes that extend from the sub-photosphere into the
  corona. We simulate how these flare-accelerated particles propagate
  down one dimensional flux tubes and heat the stellar atmosphere
  using Fokker-Planck kinetic theory. Detailed radiative transfer is
  included so that model predictions can be directly compared with
  observations. The flux of flare-accelerated particles drives return
  currents which additionally heat the stellar atmosphere, and these
  effects are also included in our models. We examine the impact of
  the flare-accelerated particle beams on model solar and dMe stellar
  atmospheres and perform parameter studies varying the injected particle
  energy spectra. We find the atmospheric response is strongly dependent
  on the accelerated particle cutoff energy and spectral index.

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

---------------------------------------------------------
Title: Homologous Helical Jets: Observations By IRIS, SDO, and Hinode
    and Magnetic Modeling With Data-Driven Simulations
Authors: Cheung, Mark C. M.; De Pontieu, B.; Tarbell, T. D.; Fu, Y.;
   Tian, H.; Testa, P.; Reeves, K. K.; Martínez-Sykora, J.; Boerner,
   P.; Wülser, J. P.; Lemen, J.; Title, A. M.; Hurlburt, N.; Kleint,
   L.; Kankelborg, C.; Jaeggli, S.; Golub, L.; McKillop, S.; Saar, S.;
   Carlsson, M.; Hansteen, V.
2015ApJ...801...83C    Altcode: 2015arXiv150101593C
  We report on observations of recurrent jets by instruments on board
  the Interface Region Imaging Spectrograph, Solar Dynamics Observatory
  (SDO), and Hinode spacecraft. Over a 4 hr period on 2013 July 21,
  recurrent coronal jets were observed to emanate from NOAA Active Region
  11793. Far-ultraviolet spectra probing plasma at transition region
  temperatures show evidence of oppositely directed flows with components
  reaching Doppler velocities of ±100 km s<SUP>-1</SUP>. Raster Doppler
  maps using a Si iv transition region line show all four jets to have
  helical motion of the same sense. Simultaneous observations of the
  region by SDO and Hinode show that the jets emanate from a source
  region comprising a pore embedded in the interior of a supergranule. The
  parasitic pore has opposite polarity flux compared to the surrounding
  network field. This leads to a spine-fan magnetic topology in the
  coronal field that is amenable to jet formation. Time-dependent
  data-driven simulations are used to investigate the underlying drivers
  for the jets. These numerical experiments show that the emergence of
  current-carrying magnetic field in the vicinity of the pore supplies
  the magnetic twist needed for recurrent helical jet formation.

---------------------------------------------------------
Title: Heating Signatures in the Disk Counterparts of Solar Spicules
    in Interface Region Imaging Spectrograph Observations
Authors: Rouppe van der Voort, L.; De Pontieu, B.; Pereira, T. M. D.;
   Carlsson, M.; Hansteen, V.
2015ApJ...799L...3R    Altcode: 2014arXiv1412.4531R
  We use coordinated observations with the Interface Region Imaging
  Spectrograph (IRIS) and the Swedish 1 m Solar Telescope to identify
  the disk counterpart of type II spicules in upper-chromospheric and
  transition region (TR) diagnostics. These disk counterparts were
  earlier identified through short-lived asymmetries in chromospheric
  spectral lines: rapid blue- or red-shifted excursions (RBEs or RREs). We
  find clear signatures of RBEs and RREs in Mg II h &amp; k, often with
  excursions of the central h3 and k3 absorption features in concert with
  asymmetries in co-temporal and co-spatial Hα spectral profiles. We find
  spectral signatures for RBEs and RREs in C II 1335 and 1336 Å and Si
  IV 1394 and 1403 Å spectral lines and interpret this as a sign that
  type II spicules are heated to at least TR temperatures, supporting
  other recent work. These C II and Si IV spectral signals are weaker
  for a smaller network region than for more extended network regions in
  our data. A number of bright features around extended network regions
  observed in IRIS slit-jaw imagery SJI 1330 and 1400, recently identified
  as network jets, can be clearly connected to Hα RBEs and/or RREs in
  our coordinated data. We speculate that at least part of the diffuse
  halo around network regions in the IRIS SJI 1330 and 1400 images can
  be attributed to type II spicules with insufficient opacity in the C
  II and Si IV lines to stand out as single features in these passbands.

---------------------------------------------------------
Title: IRIS diagnostics of non-thermal particles in coronal loops
    heated by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J. C.; Carlsson, M.;
   Reale, F.; Daw, A. N.
2014AGUFMSH53D..08T    Altcode:
  The variability of emission of the "moss", i.e., the upper transition
  region (TR) layer of high pressure loops in active regions, provides
  stringent constraints on the characteristics of heating events. We
  will discuss the new coronal heating diagnostics provided by the
  Interface Region Imaging Spectrograph (IRIS) together with SDO/AIA. IRIS
  provides imaging and spectral observations of the solar chromosphere
  and transition region, at high spatial (0.166 arcsec/pix) and temporal
  (down to ~1s) resolution at FUV and NUV wavelengths. We discuss how
  simultaneous IRIS and AIA observations, together with loop modeling
  (with the RADYN code) including chromosphere, transition region and
  corona, allow us to study impulsive heating events (nanoflares) and the
  energy transport mechanism between the corona and the lower atmospheric
  layers (thermal conduction vs. beams of non-thermal particles). We will
  show how the modeling of rapid moss brightenings provides diagnostics
  for the presence and properties of non-thermal particles in nanoflares,
  which are below the detectability threshold of hard X-ray observations.

---------------------------------------------------------
Title: Observables of Ion-Neutral Interaction Effects in the Solar
    Chromosphere
Authors: Martínez-Sykora, J.; De Pontieu, B.; Hansteen, V. H.;
   Pereira, T. M. D.; Leenaarts, J.; Carlsson, M.
2014AGUFMSH51C4176M    Altcode:
  The chromosphere and transition region constitute the interface
  between the solar surface and the corona and modulate the flow of
  mass and energy into the upper atmosphere. IRIS was launched in 2013
  to study the chromosphere and transition region. The complexity of the
  chromosphere is due to various regime changes that take place across it,
  like: Hydrogen goes from predominantly neutral to predominantly ionized;
  the plasma behavior changes from collisional to collision-less; it goes
  from gas-pressure dominated to magnetically driven, etc. Consequently,
  the interpretation of chromospheric observations in general and those
  from IRIS, in particular, is a challenging task. It is thus crucial
  to combine IRIS observations with advanced radiative-MHD numerical
  modeling. Because the photosphere, chromosphere and transition region
  are partially ionized, the interaction between ionized and neutral
  particles has important consequences on the magneto-thermodynamics of
  these regions. We implemented the effects of partial ionization using
  generalized Ohm's law in the Bifrost code (Gudiksen et al. 2011) which
  solves the full MHD equations with non-grey and non-LTE radiative
  transfer and thermal conduction along magnetic field lines. The
  implementation of partial ionization effects impact our modeled
  radiative-MHD atmosphere, such as producing chromospheric heating and
  diffusion of photospheric magnetic field into the upper-chromosphere. We
  will focus on which observables of these processes can be revealed
  with IRIS.

---------------------------------------------------------
Title: Probing the solar interface region
Authors: De Pontieu, Bart; Title, Alan; Carlsson, Mats
2014Sci...346..315D    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Hot explosions in the cool atmosphere of the Sun
Authors: Peter, H.; Tian, H.; Curdt, W.; Schmit, D.; Innes, D.;
   De Pontieu, B.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
   Tarbell, T. D.; Wuelser, J. P.; Martínez-Sykora, Juan; Kleint,
   L.; Golub, L.; McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.;
   Kankelborg, C.; Jaeggli, S.; Carlsson, M.; Hansteen, V.
2014Sci...346C.315P    Altcode: 2014arXiv1410.5842P
  The solar atmosphere was traditionally represented with a simple
  one-dimensional model. Over the past few decades, this paradigm shifted
  for the chromosphere and corona that constitute the outer atmosphere,
  which is now considered a dynamic structured envelope. Recent
  observations by the Interface Region Imaging Spectrograph (IRIS) reveal
  that it is difficult to determine what is up and down, even in the cool
  6000-kelvin photosphere just above the solar surface: This region hosts
  pockets of hot plasma transiently heated to almost 100,000 kelvin. The
  energy to heat and accelerate the plasma requires a considerable
  fraction of the energy from flares, the largest solar disruptions. These
  IRIS observations not only confirm that the photosphere is more complex
  than conventionally thought, but also provide insight into the energy
  conversion in the process of magnetic reconnection.

---------------------------------------------------------
Title: A Sounding Rocket Experiment for the Chromospheric Lyman-Alpha
    Spectro-Polarimeter (CLASP)
Authors: Kubo, M.; Kano, R.; Kobayashi, K.; Bando, T.; Narukage, N.;
   Ishikawa, R.; Tsuneta, S.; Katsukawa, Y.; Ishikawa, S.; Suematsu, Y.;
   Hara, H.; Shimizu, T.; Sakao, T.; Ichimoto, K.; Goto, M.; Holloway,
   T.; Winebarger, A.; Cirtain, J.; De Pontieu, B.; Casini, R.; Auchère,
   F.; Trujillo Bueno, J.; Manso Sainz, R.; Belluzzi, L.; Asensio Ramos,
   A.; Štěpán, J.; Carlsson, M.
2014ASPC..489..307K    Altcode:
  A sounding-rocket experiment called the Chromospheric Lyman-Alpha
  Spectro-Polarimeter (CLASP) is presently under development to measure
  the linear polarization profiles in the hydrogen Lyman-alpha (Lyα)
  line at 121.567 nm. CLASP is a vacuum-UV (VUV) spectropolarimeter to aim
  for first detection of the linear polarizations caused by scattering
  processes and the Hanle effect in the Lyα line with high accuracy
  (0.1%). This is a fist step for exploration of magnetic fields in
  the upper chromosphere and transition region of the Sun. Accurate
  measurements of the linear polarization signals caused by scattering
  processes and the Hanle effect in strong UV lines like Lyα are
  essential to explore with future solar telescopes the strength
  and structures of the magnetic field in the upper chromosphere and
  transition region of the Sun. The CLASP proposal has been accepted by
  NASA in 2012, and the flight is planned in 2015.

---------------------------------------------------------
Title: The unresolved fine structure resolved: IRIS observations of
    the solar transition region
Authors: Hansteen, V.; De Pontieu, B.; Carlsson, M.; Lemen, J.; Title,
   A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.; Pereira,
   T. M. D.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
   S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
   Martínez-Sykora, J.
2014Sci...346E.315H    Altcode: 2014arXiv1412.3611H
  The heating of the outer solar atmospheric layers, i.e., the transition
  region and corona, to high temperatures is a long-standing problem
  in solar (and stellar) physics. Solutions have been hampered by an
  incomplete understanding of the magnetically controlled structure of
  these regions. The high spatial and temporal resolution observations
  with the Interface Region Imaging Spectrograph (IRIS) at the solar
  limb reveal a plethora of short, low-lying loops or loop segments
  at transition-region temperatures that vary rapidly, on the time
  scales of minutes. We argue that the existence of these loops solves
  a long-standing observational mystery. At the same time, based on
  comparison with numerical models, this detection sheds light on a
  critical piece of the coronal heating puzzle.

---------------------------------------------------------
Title: Evidence of nonthermal particles in coronal loops heated
    impulsively by nanoflares
Authors: Testa, P.; De Pontieu, B.; Allred, J.; Carlsson, M.; Reale,
   F.; Daw, A.; Hansteen, V.; Martinez-Sykora, J.; Liu, W.; DeLuca, E. E.;
   Golub, L.; McKillop, S.; Reeves, K.; Saar, S.; Tian, H.; Lemen, J.;
   Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
   Kleint, L.; Kankelborg, C.; Jaeggli, S.
2014Sci...346B.315T    Altcode: 2014arXiv1410.6130T
  The physical processes causing energy exchange between the Sun’s
  hot corona and its cool lower atmosphere remain poorly understood. The
  chromosphere and transition region (TR) form an interface region between
  the surface and the corona that is highly sensitive to the coronal
  heating mechanism. High-resolution observations with the Interface
  Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to
  60 seconds) of intensity and velocity on small spatial scales (≲500
  kilometers) at the footpoints of hot and dynamic coronal loops. The
  observations are consistent with numerical simulations of heating by
  beams of nonthermal electrons, which are generated in small impulsive
  (≲30 seconds) heating events called “coronal nanoflares.” The
  accelerated electrons deposit a sizable fraction of their energy
  (≲10<SUP>25 </SUP>erg) in the chromosphere and TR. Our analysis
  provides tight constraints on the properties of such electron beams
  and new diagnostics for their presence in the nonflaring corona.

---------------------------------------------------------
Title: Prevalence of small-scale jets from the networks of the solar
    transition region and chromosphere
Authors: Tian, H.; DeLuca, E. E.; Cranmer, S. R.; De Pontieu, B.;
   Peter, H.; Martínez-Sykora, J.; Golub, L.; McKillop, S.; Reeves,
   K. K.; Miralles, M. P.; McCauley, P.; Saar, S.; Testa, P.; Weber,
   M.; Murphy, N.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt, N.;
   Tarbell, T. D.; Wuelser, J. P.; Kleint, L.; Kankelborg, C.; Jaeggli,
   S.; Carlsson, M.; Hansteen, V.; McIntosh, S. W.
2014Sci...346A.315T    Altcode: 2014arXiv1410.6143T
  As the interface between the Sun’s photosphere and corona, the
  chromosphere and transition region play a key role in the formation and
  acceleration of the solar wind. Observations from the Interface Region
  Imaging Spectrograph reveal the prevalence of intermittent small-scale
  jets with speeds of 80 to 250 kilometers per second from the narrow
  bright network lanes of this interface region. These jets have lifetimes
  of 20 to 80 seconds and widths of ≤300 kilometers. They originate from
  small-scale bright regions, often preceded by footpoint brightenings
  and accompanied by transverse waves with amplitudes of ~20 kilometers
  per second. Many jets reach temperatures of at least ~10<SUP>5</SUP>
  kelvin and constitute an important element of the transition region
  structures. They are likely an intermittent but persistent source of
  mass and energy for the solar wind.

---------------------------------------------------------
Title: On the prevalence of small-scale twist in the solar
    chromosphere and transition region
Authors: De Pontieu, B.; Rouppe van der Voort, L.; McIntosh, S. W.;
   Pereira, T. M. D.; Carlsson, M.; Hansteen, V.; Skogsrud, H.; Lemen,
   J.; Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser,
   J. P.; De Luca, E. E.; Golub, L.; McKillop, S.; Reeves, K.; Saar,
   S.; Testa, P.; Tian, H.; Kankelborg, C.; Jaeggli, S.; Kleint, L.;
   Martinez-Sykora, J.
2014Sci...346D.315D    Altcode: 2014arXiv1410.6862D
  The solar chromosphere and transition region (TR) form an interface
  between the Sun’s surface and its hot outer atmosphere. There,
  most of the nonthermal energy that powers the solar atmosphere
  is transformed into heat, although the detailed mechanism remains
  elusive. High-resolution (0.33-arc second) observations with NASA’s
  Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere
  and TR that are replete with twist or torsional motions on sub-arc
  second scales, occurring in active regions, quiet Sun regions, and
  coronal holes alike. We coordinated observations with the Swedish
  1-meter Solar Telescope (SST) to quantify these twisting motions and
  their association with rapid heating to at least TR temperatures. This
  view of the interface region provides insight into what heats the low
  solar atmosphere.

---------------------------------------------------------
Title: An Interface Region Imaging Spectrograph First View on Solar
    Spicules
Authors: Pereira, T. M. D.; De Pontieu, B.; Carlsson, M.; Hansteen,
   V.; Tarbell, T. D.; Lemen, J.; Title, A.; Boerner, P.; Hurlburt,
   N.; Wülser, J. P.; Martínez-Sykora, J.; Kleint, L.; Golub, L.;
   McKillop, S.; Reeves, K. K.; Saar, S.; Testa, P.; Tian, H.; Jaeggli,
   S.; Kankelborg, C.
2014ApJ...792L..15P    Altcode: 2014arXiv1407.6360P
  Solar spicules have eluded modelers and observers for decades. Since
  the discovery of the more energetic type II, spicules have become
  a heated topic but their contribution to the energy balance of the
  low solar atmosphere remains unknown. Here we give a first glimpse of
  what quiet-Sun spicules look like when observed with NASA's recently
  launched Interface Region Imaging Spectrograph (IRIS). Using IRIS
  spectra and filtergrams that sample the chromosphere and transition
  region, we compare the properties and evolution of spicules as
  observed in a coordinated campaign with Hinode and the Atmospheric
  Imaging Assembly. Our IRIS observations allow us to follow the thermal
  evolution of type II spicules and finally confirm that the fading
  of Ca II H spicules appears to be caused by rapid heating to higher
  temperatures. The IRIS spicules do not fade but continue evolving,
  reaching higher and falling back down after 500-800 s. Ca II H type
  II spicules are thus the initial stages of violent and hotter events
  that mostly remain invisible in Ca II H filtergrams. These events
  have very different properties from type I spicules, which show lower
  velocities and no fading from chromospheric passbands. The IRIS spectra
  of spicules show the same signature as their proposed disk counterparts,
  reinforcing earlier work. Spectroheliograms from spectral rasters also
  confirm that quiet-Sun spicules originate in bushes from the magnetic
  network. Our results suggest that type II spicules are indeed the
  site of vigorous heating (to at least transition region temperatures)
  along extensive parts of the upward moving spicular plasma.

---------------------------------------------------------
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.

---------------------------------------------------------
Title: Detection of Supersonic Downflows and Associated Heating
    Events in the Transition Region above Sunspots
Authors: Kleint, L.; Antolin, P.; Tian, H.; Judge, P.; Testa, P.;
   De Pontieu, B.; Martínez-Sykora, J.; Reeves, K. K.; Wuelser, J. P.;
   McKillop, S.; Saar, S.; Carlsson, M.; Boerner, P.; Hurlburt, N.; Lemen,
   J.; Tarbell, T. D.; Title, A.; Golub, L.; Hansteen, V.; Jaeggli, S.;
   Kankelborg, C.
2014ApJ...789L..42K    Altcode: 2014arXiv1406.6816K
  Interface Region Imaging Spectrograph data allow us to study the solar
  transition region (TR) with an unprecedented spatial resolution of
  0.”33. On 2013 August 30, we observed bursts of high Doppler shifts
  suggesting strong supersonic downflows of up to 200 km s<SUP>-1</SUP>
  and weaker, slightly slower upflows in the spectral lines Mg II h
  and k, C II 1336, Si IV 1394 Å, and 1403 Å, that are correlated
  with brightenings in the slitjaw images (SJIs). The bursty behavior
  lasts throughout the 2 hr observation, with average burst durations
  of about 20 s. The locations of these short-lived events appear to
  be the umbral and penumbral footpoints of EUV loops. Fast apparent
  downflows are observed along these loops in the SJIs and in the
  Atmospheric Imaging Assembly, suggesting that the loops are thermally
  unstable. We interpret the observations as cool material falling
  from coronal heights, and especially coronal rain produced along the
  thermally unstable loops, which leads to an increase of intensity
  at the loop footpoints, probably indicating an increase of density
  and temperature in the TR. The rain speeds are on the higher end of
  previously reported speeds for this phenomenon, and possibly higher
  than the free-fall velocity along the loops. On other observing days,
  similar bright dots are sometimes aligned into ribbons, resembling
  small flare ribbons. These observations provide a first insight into
  small-scale heating events in sunspots in the TR.

---------------------------------------------------------
Title: F-CHROMA.Flare Chromospheres: Observations, Models and Archives
Authors: Cauzzi, Gianna; Fletcher, Lyndsay; Mathioudakis, Mihalis;
   Carlsson, Mats; Heinzel, Petr; Berlicki, Arek; Zuccarello, Francesca
2014AAS...22412339C    Altcode:
  F-CHROMA is a collaborative project newly funded under the EU-Framework
  Programme 7 "FP7-SPACE-2013-1", involving seven different European
  research Institutes and Universities. The goal of F-CHROMA is to
  substantially advance our understanding of the physics of energy
  dissipation and radiation in the flaring solar atmosphere, with a
  particular focus on the flares' chromosphere. A major outcome of the
  F-CHROMA project will be the creation of an archive of chromospheric
  flare observations and models to be made available to the community
  for further research.In this poster we describe the structure and
  milestones of the project, the different activities planned, as well
  as early results. Emphasis will be given to the dissemination efforts
  of the project to make results of these activities available to and
  usable by the community.

---------------------------------------------------------
Title: IRIS Observations of Twist in the Low Solar Atmosphere
Authors: De Pontieu, Bart; Rouppe van der Voort, Luc; Pereira,
   Tiago M. D.; Skogsrud, Haakon; McIntosh, Scott W.; Carlsson, Mats;
   Hansteen, Viggo
2014AAS...22431302D    Altcode:
  The Interface Region Imaging Spectrograph (IRIS) small explorer
  was launched in June 2013. IRIS’s high-resolution (0.33 arcsec),
  high-cadence (2s) images and spectra reveal a solar chromosphere and
  transition region that is riddled with twist. This is evidenced by the
  presence of ubiquitous torsional motions on very small (subarcsec)
  spatial scales. These motions occur in active regions, quiet Sun
  and coronal holes on a variety of structures such as spicules at
  the limb, rapid-blue/red-shifted events (RBEs and RREs) as well as
  low-lying loops. We use IRIS data and observations from the Swedish
  Solar Telescope (SST) in La Palma, Spain to describe these motions
  quantitatively, study their propagation, and illustrate how such
  strong twisting motions are often associated with significant and
  rapid heating to at least transition region temperatures.

---------------------------------------------------------
Title: Diagnostics of coronal heating and mechanisms of energy
    transport from IRIS and AIA observations of active region moss
Authors: Testa, Paola; De Pontieu, Bart; Allred, Joel C.; Carlsson,
   Mats; Reale, Fabio; Daw, Adrian N.; Hansteen, Viggo
2014AAS...22431305T    Altcode:
  The variability of emission of the "moss", i.e., the upper transition
  region (TR) layer of high pressure loops in active regions provides
  stringent constraints on the characteristics of heating events. The
  Interface Region Imaging Spectrograph (IRIS), launched in June
  2013, provides imaging and spectral observations at high spatial
  (0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV
  and NUV wavelengths, and together with the high spatial and temporal
  resolution observations of SDO/AIA, can provide important insights
  into the coronal heating mechanisms. We present here an analysis of
  the temporal variability properties of moss regions at the footpoints
  of hot active region core loops undergoing heating, as observed by IRIS
  and AIA, covering emission from the corona to the transition region and
  the chromosphere. We model the observations using dynamic loop models
  (the Palermo-Harvard code, and RADYN, which also includes the effects of
  non-thermal particles) and discuss the implications on energy transport
  mechanisms (thermal conduction vs beams of non-thermal particles).

---------------------------------------------------------
Title: IRIS observations of the transition region above sunspots:
    oscillations and moving penumbral dots
Authors: Tian, Hui; DeLuca, Ed; Weber, Mark A.; McKillop, Sean;
   Reeves, Kathy; Kleint, Lucia; Martinez-Sykora, Juan; De Pontieu,
   Bart; Carlsson, Mats
2014AAS...22431306T    Altcode:
  NASA's IRIS mission is providing high-cadence and high-resolution
  observations of the solar transition region and chromosphere. We
  present results from IRIS observation of the transition region above
  sunspots. The major findings can be summarized as following: (1) The C
  II and Mg II line profiles are almost Gaussian in the sunspot umbra and
  clearly exhibit a deep reversal at the line center in the plage region,
  suggesting a greatly reduced opacity in the sunspot atmosphere. (2)
  Strongly nonlinear sunspot oscillations can be clearly identified
  in not only the slit jaw images of 2796Å, 1400Å and 1330Å, but
  also in spectra of the bright Mg II, C II and Si IV lines. The Si
  iv oscillation lags those of C ii and Mg ii by 3 and 12 seconds,
  respectively. The temporal evolution of the line core is dominated by
  the following behavior: a rapid excursion to the blue side, accompanied
  by an intensity increase, followed by a linear decrease of the velocity
  to the red side. The maximum intensity slightly lags the maximum blue
  shift in Si iv , whereas the intensity enhancement slightly precedes the
  maximum blue shift in Mg ii . We find a positive correlation between
  the maximum velocity and deceleration. These results are consistent
  with numerical simulations of upward propagating magneto-acoustic
  shock waves. We also demonstrate that the strongly nonlinear line
  width oscillation, reported both previously and here, is spurious. (3)
  Many small-scale bright dots are present in the penumbral filaments and
  light bridges in SJI 1330Å and 1400Å images obtained in high-cadence
  observations. They are usually smaller than 1" and often just a couple
  of pixels wide. Some bright dots show apparent movement with a speed of
  20-60 km/s(either outward or inward). The lifetime of these penumbral
  dots is mostly less than 1 min. The most obvious feature of the Si IV
  profiles in the bright dots is the enhanced line width. Besides that,
  the profile looks normal and no obvious fast flows are detected. The
  bright dots in the light bridges even show oscillation patterns. It's
  not clear whether these oscillations are triggered by the umbral
  oscillations or not.

---------------------------------------------------------
Title: Hybrid Kinetic and Radiative Hydrodynamic Simulations of
    Solar Flares and Comparison With Multiwavelength Observations
Authors: Rubio Da Costa, Fatima; Petrosian, Vahe; Liu, Wei; Carlsson,
   Mats; Kleint, Lucia
2014AAS...22440906R    Altcode:
  We present a unified simulation which combines two physical processes:
  how the particles are accelerated and the energy is transported along
  a coronal loop, and how the atmosphere responds. The “flare”
  code from Stanford University (Petrosian et al, 2001) models the
  stochastic acceleration and transport of particles and radiation of
  solar flares. It includes pitch angle diffusion and energy loss, and
  computes collisional heating to the background plasma and bremsstrahlung
  emission along the loop. The radiative hydrodynamic RADYN Code
  (Carlsson et al, 1992, 1996; Allred et al, 2005) computes the energy
  transport by the injected non-thermal electrons at the top of a 1D
  coronal loop. Recently, we have combined the two codes by updating the
  non-thermal heating in the RADYN code from the "flare" code, allowing us
  to develop a self-consistent simulation. In addition, we can now model
  more realistically the multi-wavelength emission of solar flares and
  compare it with observations, e.g., at optical wavelengths from IBIS at
  the Dunn Solar Telescope and in X-rays from RHESSI. The high resolution
  UV observations from the recently launched IRIS imaging spectrograph
  will be particularly useful in this regard. These will allow us to
  compare numerically modeled and observed emissions of solar flares in
  several lines using more robust simulations than possible before.

---------------------------------------------------------
Title: High-resolution Observations of the Shock Wave Behavior for
    Sunspot Oscillations with the Interface Region Imaging Spectrograph
Authors: Tian, H.; DeLuca, E.; Reeves, K. K.; McKillop, S.; De Pontieu,
   B.; Martínez-Sykora, J.; Carlsson, M.; Hansteen, V.; Kleint, L.;
   Cheung, M.; Golub, L.; Saar, S.; Testa, P.; Weber, M.; Lemen, J.;
   Title, A.; Boerner, P.; Hurlburt, N.; Tarbell, T. D.; Wuelser, J. P.;
   Kankelborg, C.; Jaeggli, S.; McIntosh, S. W.
2014ApJ...786..137T    Altcode: 2014arXiv1404.6291T
  We present the first results of sunspot oscillations from observations
  by the Interface Region Imaging Spectrograph. The strongly nonlinear
  oscillation is identified in both the slit-jaw images and the
  spectra of several emission lines formed in the transition region and
  chromosphere. We first apply a single Gaussian fit to the profiles of
  the Mg II 2796.35 Å, C II 1335.71 Å, and Si IV 1393.76 Å lines in the
  sunspot. The intensity change is ~30%. The Doppler shift oscillation
  reveals a sawtooth pattern with an amplitude of ~10 km s<SUP>-1</SUP>
  in Si IV. The Si IV oscillation lags those of C II and Mg II by ~3 and
  ~12 s, respectively. The line width suddenly increases as the Doppler
  shift changes from redshift to blueshift. However, we demonstrate
  that this increase is caused by the superposition of two emission
  components. We then perform detailed analysis of the line profiles at
  a few selected locations on the slit. The temporal evolution of the
  line core is dominated by the following behavior: a rapid excursion
  to the blue side, accompanied by an intensity increase, followed by a
  linear decrease of the velocity to the red side. The maximum intensity
  slightly lags the maximum blueshift in Si IV, whereas the intensity
  enhancement slightly precedes the maximum blueshift in Mg II. We find
  a positive correlation between the maximum velocity and deceleration,
  a result that is consistent with numerical simulations of upward
  propagating magnetoacoustic shock waves.

---------------------------------------------------------
Title: Detailed and Simplified Nonequilibrium Helium Ionization in
    the Solar Atmosphere
Authors: Golding, Thomas Peter; Carlsson, Mats; Leenaarts, Jorrit
2014ApJ...784...30G    Altcode: 2014arXiv1401.7562G
  Helium ionization plays an important role in the energy balance of the
  upper chromosphere and transition region. Helium spectral lines are also
  often used as diagnostics of these regions. We carry out one-dimensional
  radiation-hydrodynamics simulations of the solar atmosphere and
  find that the helium ionization is set mostly by photoionization and
  direct collisional ionization, counteracted by radiative recombination
  cascades. By introducing an additional recombination rate mimicking
  the recombination cascades, we construct a simplified three-level
  helium model atom consisting of only the ground states. This model
  atom is suitable for modeling nonequilibrium helium ionization in
  three-dimensional numerical models. We perform a brief investigation of
  the formation of the He I 10830 and He II 304 spectral lines. Both lines
  show nonequilibrium features that are not recovered with statistical
  equilibrium models, and caution should therefore be exercised when
  such models are used as a basis for interpretating observations.

---------------------------------------------------------
Title: The Effect of Isotopic Splitting on the Bisector and Inversions
    of the Solar Ca II 854.2 nm Line
Authors: Leenaarts, Jorrit; de la Cruz Rodríguez, Jaime; Kochukhov,
   Oleg; Carlsson, Mats
2014ApJ...784L..17L    Altcode: 2014arXiv1401.5019L
  The Ca II 854.2 nm spectral line is a common diagnostic of the solar
  chromosphere. The average line profile shows an asymmetric core,
  and its bisector shows a characteristic inverse-C shape. The line
  actually consists of six components with slightly different wavelengths
  depending on the isotope of calcium. This isotopic splitting of the
  line has been taken into account in studies of non-solar stars, but
  never for the Sun. We performed non-LTE radiative transfer computations
  from three models of the solar atmosphere and show that the line-core
  asymmetry and inverse C-shape of the bisector of the 854.2 nm line
  can be explained by isotopic splitting. We confirm this finding by
  analyzing observations and showing that the line asymmetry is present
  irrespective of conditions in the solar atmosphere. Finally, we show
  that inversions based on the Ca II 854.2 nm line should take the
  isotopic splitting into account, otherwise the inferred atmospheres
  will contain erroneous velocity gradients and temperatures.

---------------------------------------------------------
Title: Diagnostics of coronal heating and mechanisms of energy
    transport from IRIS and AIA observations of active region moss
Authors: Testa, Paola; Reale, Fabio; De Pontieu, Bart; Hansteen,
   Viggo; Carlsson, Mats; Allred, Joel; Daw, Adrian
2014cosp...40E3323T    Altcode:
  The variability of emission of the "moss", i.e., the upper transition
  region (TR) layer of high pressure loops in active regions provides
  stringent constraints on the characteristics of heating events. The
  Interface Region Imaging Spectrograph (IRIS), launched in June
  2013, provides imaging and spectral observations at high spatial
  (0.166 arcsec/pix), and temporal (down to ~1s) resolution at FUV
  and NUV wavelengths, and together with the high spatial and temporal
  resolution observations of SDO/AIA, can provide important insights
  into the coronal heating mechanisms. We present here an analysis of
  the temporal variability properties of moss regions at the footpoints
  of hot active region core loops undergoing heating, as observed by IRIS
  and AIA, covering emission from the corona to the transition region and
  the chromosphere. We model the observations using dynamic loop models
  (the Palermo-Harvard code, and RADYN, which also includes the effects of
  non-thermal particles) and discuss the implications on energy transport
  mechanisms (thermal conduction vs beams of non-thermal particles).

---------------------------------------------------------
Title: Measuring energy flux of magneto-acoustic wave in the magnetic
    elements by using IRIS
Authors: Kato, Yoshiaki; De Pontieu, Bart; Martinez-Sykora, Juan;
   Hansteen, Viggo; Pereira, Tiago; Leenaarts, Jorritt; Carlsson, Mats
2014cosp...40E1423K    Altcode:
  NASA's Interface Region Imaging Spectrograph (IRIS) has opened a new
  window to explore the chromospheric/coronal waves that potentially
  energize the solar atmosphere. By using an imaging spectrograph covering
  the Si IV and Mg II h&amp;k lines as well as a slit-jaw imager centered
  at Si IV and Mg II k onboard IRIS, we can determine the nature of
  propagating magneto-acoustic waves just below and in the transition
  region. In this study, we compute the vertically emergent intensity of
  the Si IV and Mg II h&amp;k lines from a time series of snapshots of
  a magnetic element in a two-dimensional Radiative MHD simulation from
  the Bifrost code. We investigate the synthetic line profiles to detect
  the slow magneto-acoustic body wave (slow mode) which becomes a slow
  shock at the lower chromosphere in the magnetic element. We find that
  the Doppler shift of the line core gives the velocity amplitude of the
  longitudinal magneto-acoustic body wave. The contribution function of
  the line core indicates that the formation of Mg II h&amp;k lines is
  associated with the propagating shocks and therefore the time evolution
  of the line core intensity represents the propagating shocks projected
  on the optical surface. We will report on measurement of the energy
  flux of slow modes in the magnetic elements by using IRIS observations.

---------------------------------------------------------
Title: The Atmospheric Response to High Fluxes of Nonthermal Electrons
    during M Dwarf Flares
Authors: Kowalski, Adam; Allred, J. C.; Carlsson, M.; Hawley, S. L.;
   Holman, G. D.; Mathioudakis, M.; Osten, R. A.; Uitenbroek, H.
2014AAS...22315117K    Altcode:
  Flares are thought to be the result of magnetic fields in the stellar
  corona that undergo reconnection and accelerate charged particles
  into the lower atmosphere. Spectra of M dwarf flares in the optical
  and near-ultraviolet wavelength regimes can be used to constrain the
  heating mechanism of the lower stellar atmosphere. These observations
  show several ubiquitous properties of the continuum emission, which
  is not reproduced by models that use typical “solar-type” heating
  functions. We present results from a grid of new flare models using the
  RADYN code, which simultaneously calculates the radiative transfer and
  hydrodynamics on short timescales. We explore the atmospheric response
  to a short ~2 second burst of a very high heating rate from nonthermal
  electrons using a solar-type heating function, and we propose a new
  “M dwarf-type” heating variation that explains a range of observed
  spectral properties, such as ~10,000 K blackbody emission and a smooth
  continuum across the Balmer jump wavelength (3646A).

---------------------------------------------------------
Title: Comparison between IRIS Data and Numerical Models
Authors: Carlsson, Mats; De Pontieu, Bart; Hansteen, Viggo; Pereira,
   Tiago; Leenaarts, Jorritt
2014cosp...40E.458C    Altcode:
  The enigmatic chromosphere is the transition between the solar surface
  and the eruptive outer solar atmosphere. The chromosphere harbours
  and constrains the mass and energy loading processes that define the
  heating of the corona, the acceleration and the composition of the solar
  wind, and the energetics and triggering of solar outbursts (filament
  eruptions, flares, coronal mass ejections). The chromosphere is arguably
  the most difficult and least understood domain of solar physics. All
  at once it represents the transition from optically thick to thin
  radiation escape, from gas-pressure domination to magnetic-pressure
  domination, from neutral to ionised state, from MHD to plasma physics,
  and from near-equilibrium ("LTE") to non-equilibrium conditions. IRIS
  provides a leap in observational capability of the chromospheric
  plasma with an unprecedented combination of high spatial, temporal
  and spectral resolution in lines with diagnostic information all the
  way from the photosphere to the upper transition region. To fully
  extract this information it is necessary to combine the observations
  with numerical simulations that include a realistic description of the
  complicated physics of the chromosphere. In this talk, we will present
  such realistic simulations, spanning the solar atmosphere from the
  convection zone to the corona, and synthetic observations calculated
  from the simulations. These synthetic observations are compared with
  observations from IRIS.

---------------------------------------------------------
Title: Impact of the Partial Ionization in the solar atmosphere
    using 2.5D Radiative MHD Simulations
Authors: Martinez-Sykora, Juan; De Pontieu, Bart; Hansteen, Viggo;
   Carlsson, Mats
2014cosp...40E2019M    Altcode:
  The chromosphere/transition region constitute the interface between
  the solar surface and the corona and modulate the flow of mass and
  energy into the upper atmosphere. IRIS was launched in 2013 to study the
  chromosphere and transition region. The complexity of the chromosphere
  is due to various regime changes that take place across it, like:
  Hydrogen goes from predominantly neutral to predominantly ionized;
  the plasma behavior changes from collisional to collision-less; it goes
  from gas-pressure dominated to magnetically driven, etc. Consequently,
  the interpretation of chromospheric observations in general and those
  from IRIS, in particular, is a challenging task. It is thus crucial
  to combine IRIS observations with advanced radiative-MHD numerical
  modeling. Because the photosphere, chromosphere and transition region
  are partially ionized, the interaction between ionized and neutral
  particles has important consequences on the magneto-thermodynamics
  of these regions. We implemented the effects of partial ionization
  using generalized Ohm's law in the Bifrost code (Gudiksen et al. 2011)
  which includes full MHD equations with non-grey and non-LTE radiative
  transfer and thermal conduction along magnetic field lines. I will
  describe the importance and impact of taking into account partial
  ionization effects in the modeled radiative-MHD atmosphere, such as
  chromospheric heating, photospheric magnetic field diffused into the
  upper-chromosphere which expands into the upper atmosphere filling
  the corona with mass, magnetic flux, energy and current, etc.

---------------------------------------------------------
Title: Effects of flux emergence in the outer solar
    atmosphere. Observational advances
Authors: Ortiz Carbonell, Ada; De Pontieu, Bart; Bellot Rubio, L. R.;
   Hansteen, Viggo; Rouppe van der Voort, Luc; Carlsson, Mats
2014cosp...40E2387O    Altcode:
  We study granular sized magnetic flux emergence events that occur in
  a flux emergence region in NOAA 11850 on September 25, 2013. During
  that time, the first co-observing campaign between the Swedish 1 m
  Solar Telescope and the IRIS spacecraft was carried out. Simultaneous
  observations of the Halpha 656.28 nm and Ca II 854.2 nm chromospheric
  lines, and the Fe I 630.25 nm photospheric line, were made with
  the CRISP/SST spectropolarimeter reaching a spatial resolution of
  0."14. At the same time, IRIS was performing a four-step dense raster
  of the said emerging flux region, taking slit-jaw images at 133 (C II
  transiti on region), 140 (Si IV, transition region), 279.6 (Mg II k,
  core, upper chromosphere), and 283.2 nm (Mg II k, wing, photosphere),
  obtaining thus the highest resolution images ever taken of the upper
  chromosphere and transition region. The photospheric and chromospheric
  properties of the emerging magnetic flux bubbles have been described
  in detail in Ortiz et al. (2014). However, in the current work we are
  able to follow such lower atmosphere observations of flux emergence
  up to the transition region with unprecedented spatial and temporal
  resolution. We describe the properties (size, time delays, lifetime,
  velocities, temperature) of the observed signatures of flux emergence
  in the transition region. We believe this may be an important mechanism
  of transporting energy and magnetic flux to the upper layers of the
  solar atmosphere, namely the transition region and corona, at least
  in cases when active regions are formed by flux emerging through the
  photosphere. * Ortiz et al. (2014) ApJ 781, 126

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. III. Near-ultraviolet
    Spectra and Images
Authors: Pereira, T. M. D.; Leenaarts, J.; De Pontieu, B.; Carlsson,
   M.; Uitenbroek, H.
2013ApJ...778..143P    Altcode: 2013arXiv1310.1926P
  The Mg II h&amp;k lines are the prime chromospheric diagnostics
  of NASA's Interface Region Imaging Spectrograph (IRIS). In the
  previous papers of this series, we used a realistic three-dimensional
  radiative magnetohydrodynamics model to calculate the h&amp;k lines
  in detail and investigated how their spectral features relate to the
  underlying atmosphere. In this work, we employ the same approach to
  investigate how the h&amp;k diagnostics fare when taking into account
  the finite resolution of IRIS and different noise levels. In addition,
  we investigate the diagnostic potential of several other photospheric
  lines and near-continuum regions present in the near-ultraviolet
  (NUV) window of IRIS and study the formation of the NUV slit-jaw
  images. We find that the instrumental resolution of IRIS has a small
  effect on the quality of the h&amp;k diagnostics; the relations
  between the spectral features and atmospheric properties are mostly
  unchanged. The peak separation is the most affected diagnostic, but
  mainly due to limitations of the simulation. The effects of noise
  start to be noticeable at a signal-to-noise ratio (S/N) of 20, but we
  show that with noise filtering one can obtain reliable diagnostics at
  least down to a S/N of 5. The many photospheric lines present in the
  NUV window provide velocity information for at least eight distinct
  photospheric heights. Using line-free regions in the h&amp;k far wings,
  we derive good estimates of photospheric temperature for at least
  three heights. Both of these diagnostics, in particular the latter,
  can be obtained even at S/Ns as low as 5.

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. II. The Formation of the
    Mg II h&amp;k Lines in the Solar Atmosphere
Authors: Leenaarts, J.; Pereira, T. M. D.; Carlsson, M.; Uitenbroek,
   H.; De Pontieu, B.
2013ApJ...772...90L    Altcode: 2013arXiv1306.0671L
  NASA's Interface Region Imaging Spectrograph (IRIS) small explorer
  mission will study how the solar atmosphere is energized. IRIS
  contains an imaging spectrograph that covers the Mg II h&amp;k lines
  as well as a slit-jaw imager centered at Mg II k. Understanding
  the observations requires forward modeling of Mg II h&amp;k line
  formation from three-dimensional (3D) radiation-magnetohydrodynamic
  (RMHD) models. This paper is the second in a series where we undertake
  this modeling. We compute the vertically emergent h&amp;k intensity
  from a snapshot of a dynamic 3D RMHD model of the solar atmosphere,
  and investigate which diagnostic information about the atmosphere is
  contained in the synthetic line profiles. We find that the Doppler
  shift of the central line depression correlates strongly with the
  vertical velocity at optical depth unity, which is typically located
  less than 200 km below the transition region (TR). By combining the
  Doppler shifts of the h and k lines we can retrieve the sign of the
  velocity gradient just below the TR. The intensity in the central line
  depression is anti-correlated with the formation height, especially
  in subfields of a few square Mm. This intensity could thus be used to
  measure the spatial variation of the height of the TR. The intensity
  in the line-core emission peaks correlates with the temperature at
  its formation height, especially for strong emission peaks. The peaks
  can thus be exploited as a temperature diagnostic. The wavelength
  difference between the blue and red peaks provides a diagnostic of the
  velocity gradients in the upper chromosphere. The intensity ratio of
  the blue and red peaks correlates strongly with the average velocity
  in the upper chromosphere. We conclude that the Mg II h&amp;k lines
  are excellent probes of the very upper chromosphere just below the
  TR, a height regime that is impossible to probe with other spectral
  lines. They also provide decent temperature and velocity diagnostics
  of the middle chromosphere.

---------------------------------------------------------
Title: The Formation of IRIS Diagnostics. I. A Quintessential
    Model Atom of Mg II and General Formation Properties of the Mg II
    h&amp;k Lines
Authors: Leenaarts, J.; Pereira, T. M. D.; Carlsson, M.; Uitenbroek,
   H.; De Pontieu, B.
2013ApJ...772...89L    Altcode: 2013arXiv1306.0668L
  NASA's Interface Region Imaging Spectrograph (IRIS) space mission will
  study how the solar atmosphere is energized. IRIS contains an imaging
  spectrograph that covers the Mg II h&amp;k lines as well as a slit-jaw
  imager centered at Mg II k. Understanding the observations will require
  forward modeling of Mg II h&amp;k line formation from three-dimensional
  (3D) radiation-MHD models. This paper is the first in a series where we
  undertake this forward modeling. We discuss the atomic physics pertinent
  to h&amp;k line formation, present a quintessential model atom that can
  be used in radiative transfer computations, and discuss the effect of
  partial redistribution (PRD) and 3D radiative transfer on the emergent
  line profiles. We conclude that Mg II h&amp;k can be modeled accurately
  with a four-level plus continuum Mg II model atom. Ideally radiative
  transfer computations should be done in 3D including PRD effects. In
  practice this is currently not possible. A reasonable compromise is to
  use one-dimensional PRD computations to model the line profile up to
  and including the central emission peaks, and use 3D transfer assuming
  complete redistribution to model the central depression.

---------------------------------------------------------
Title: Chromospheric Lyman Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, Ken; Kano, R.; Trujillo Bueno, J.; Winebarger,
   A. R.; Cirtain, J. W.; Bando, T.; De Pontieu, B.; Ishikawa, R.;
   Katsukawa, Y.; Kubo, M.; Narukage, N.; Sakao, T.; Tsuneta, S.;
   Auchère, F.; Asensio Ramos, A.; Belluzzi, L.; Carlsson, M.; Casini,
   R.; Hara, H.; Ichimoto, K.; Manso Sainz, R.; Shimizu, T.; Stepan,
   J.; Suematsu, Y.; Holloway, T.
2013SPD....44..142K    Altcode:
  The Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP) is a VUV
  spectropolarimeter optimized for measuring the linear polarization of
  the Lyman-alpha line (121.6 nm). The Lyman-alpha line is predicted to
  show linear polarization caused by atomic scattering in the chromosphere
  and modified by the magnetic field through the Hanle effect. The
  Hanle effect is sensitive to weaker magnetic fields than Zeeman
  effect, and is not canceled by opposing fields, making it sensitive
  to tangled or unresolved magnetic field structures. These factors make
  the Hanle effect a valuable tool for probing the magnetic field in the
  chromosphere above the quiet sun. To meet this goal, CLASP is designed
  to measure linear polarization with 0.1% polarization sensitivity
  at 0.01 nm spectral resolution and 10" spatial resolution. CLASP is
  scheduled to be launched in 2015.

---------------------------------------------------------
Title: A Detailed Comparison between the Observed and Synthesized
    Properties of a Simulated Type II Spicule
Authors: Martínez-Sykora, Juan; De Pontieu, Bart; Leenaarts, Jorrit;
   Pereira, Tiago M. D.; Carlsson, Mats; Hansteen, Viggo; Stern, Julie
   V.; Tian, Hui; McIntosh, Scott W.; Rouppe van der Voort, Luc
2013ApJ...771...66M    Altcode: 2013arXiv1305.2397M
  We have performed a three-dimensional radiative MHD simulation of the
  solar atmosphere. This simulation shows a jet-like feature that shows
  similarities to the type II spicules observed for the first time with
  Hinode's Solar Optical Telescope. Rapid blueshifted events (RBEs) on the
  solar disk are associated with these spicules. Observational results
  suggest they may contribute significantly in supplying the corona
  with hot plasma. We perform a detailed comparison of the properties
  of the simulated jet with those of type II spicules (observed with
  Hinode) and RBEs (with ground-based instruments). We analyze a wide
  variety of synthetic emission and absorption lines from the simulations
  including chromospheric (Ca II 8542 Å, Ca II H, and Hα) to transition
  region and coronal temperatures (10,000 K to several million K). We
  compare their synthetic intensities, line profiles, Doppler shifts,
  line widths, and asymmetries with observations from Hinode/SOT and
  EIS, SOHO/SUMER, the Swedish 1 m Solar Telescope, and SDO/AIA. Many
  properties of the synthetic observables resemble the observations,
  and we describe in detail the physical processes that lead to these
  observables. Detailed analysis of the synthetic observables provides
  insight into how observations should be analyzed to derive information
  about physical variables in such a dynamic event. For example, we
  find that line-of-sight superposition in the optically thin atmosphere
  requires the combination of Doppler shifts and spectral line asymmetry
  to determine the velocity in the jet. In our simulated type II spicule,
  the lifetime of the asymmetry of the transition region lines is shorter
  than that of the coronal lines. Other properties differ from the
  observations, especially in the chromospheric lines. The mass density
  of the part of the spicule with a chromospheric temperature is too low
  to produce significant opacity in chromospheric lines. The synthetic
  Ca II 8542 Å and Hα profiles therefore do not show signal resembling
  RBEs. These and other discrepancies are described in detail, and we
  discuss which mechanisms and physical processes may need to be included
  in the MHD simulations to mimic the thermodynamic processes of the
  chromosphere and corona, in particular to reproduce type II spicules.

---------------------------------------------------------
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, Bart; Title, A. M.; Lemen, J.; Wuelser, J.;
   Tarbell, T. D.; Schrijver, C. J.; Golub, L.; Kankelborg, C.; Carlsson,
   M.; Hansteen, V. H.; Worden, S.; IRIS Team
2013SPD....44...03D    Altcode:
  The solar chromosphere and transition region (TR) form a highly
  structured and dynamic interface region between the photosphere and
  the corona. This 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. Nevertheless,
  the chromosphere remains poorly understood, because of the complexity
  of the required observational and analytical tools: the interface
  region is highly complex with transitions from optically thick to
  optically thin radiation, from pressure to magnetic field domination,
  and large density and temperature contrasts on small spatial scales. The
  Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
  SMEX mission in 2009 and is scheduled to launch on 26-June-2013 (with
  first light scheduled for mid July). IRIS addresses critical questions:
  (1) Which types of non-thermal energy dominate in the chromosphere and
  beyond? (2) How does the chromosphere regulate mass and energy supply
  to the corona and heliosphere? (3) How do magnetic flux and matter
  rise through the lower atmosphere, and what role does flux emergence
  play in flares and mass ejections? These questions are addressed with
  a high-resolution near and far UV imaging spectrometer sensitive to
  emission from plasma at temperatures between 5,000 K and 10 MK. IRIS
  has a field-of-view of 120 arcsec, a spatial resolution of 0.4 arcsec,
  and velocity resolution of 0.5 km/s. The IRIS investigation includes
  a strong numerical modeling component based on advanced radiative MHD
  codes to facilitate interpretation of observations. We describe the
  IRIS instrumentation and numerical modeling, and present the plans for
  observations, calibration and data distribution. We will highlight some
  of the issues that IRIS observations can help resolve. More information
  can be found at http://iris.lmsal.com

---------------------------------------------------------
Title: A new approach to model particle acceleration and energy
    transfer in solar flares
Authors: Rubio Da Costa, Fatima; Zuccarello, F.; Fletcher, L.;
   Labrosse, N.; Kasparova, J.; Prosecký, T.; Carlsson, M.; Petrosian,
   V.; Liu, W.
2013SPD....4440401R    Altcode:
  Motivated by available observations of two different flares in Lyα and
  Hα, we model the conditions of the solar atmosphere using a radiation
  hydrodynamics code (RADYN, Carlsson &amp; Stein, 1992) and analyze the
  energy transport carried by a beam of non-thermal electrons injected
  at the top of a 1D coronal loop. The numerical Lyα and Hα intensities
  match with the observations. The electron energy distribution is assumed
  to follow a power law of the form (E/E<SUP>c</SUP> )<SUB>-δ</SUB> for
  energies greater than a cutoff value of E<SUP>c</SUP>. Abbett &amp;
  Hawley (1999) and Allred et al. (2005) assumed that the non-thermal
  electrons flux injected at the top of a flaring loop, the cut-off energy
  and the power law index are constant over time. An improvement was
  achieved by Allred &amp; Hawley (2006), who modified the RADYN code
  in such a way that the input parameters were time dependent. Their
  inputs were based on observations of a flare obtained with RHESSI. By
  combining RADYN with the “flare” code from Stanford University
  which models the acceleration and transport of particles and radiation
  of solar flares in non-LTE regime, we can calculate the non-thermal
  electrons flux, the cut-off energy and the power law index at every
  simulated time step. The atmospheric parameters calculated by RADYN
  could in turn be used as updated inputs for "flare", providing several
  advantages over the results from Liu et al. (2009), who combined the
  particle acceleration code with a 1-D hydrodynamic code, improving
  the atmospheric conditions.

---------------------------------------------------------
Title: Numerical Simulations of Spicule Acceleration
Authors: Guerreiro, N.; Carlsson, M.; Hansteen, V.
2013ApJ...766..128G    Altcode:
  Observations in the Hα line of hydrogen and the H and K lines of singly
  ionized calcium on the solar limb reveal the existence of structures
  with jet-like behavior, usually designated as spicules. The driving
  mechanism for such structures remains poorly understood. Sterling
  et al. shed some light on the problem mimicking reconnection events
  in the chromosphere with a one-dimensional code by injecting energy
  with different spatial and temporal distributions and tracing the
  thermodynamic evolution of the upper chromospheric plasma. They found
  three different classes of jets resulting from these injections. We
  follow their approach but improve the physical description by including
  non-LTE cooling in strong spectral lines and non-equilibrium hydrogen
  ionization. Increased cooling and conversion of injected energy into
  hydrogen ionization energy instead of thermal energy both lead to weaker
  jets and smaller final extent of the spicules compared with Sterling
  et al. In our simulations we find different behavior depending on
  the timescale for hydrogen ionization/recombination. Radiation-driven
  ionization fronts also form.

---------------------------------------------------------
Title: Heating of the Magnetic Chromosphere: Observational Constraints
    from Ca II λ8542 Spectra
Authors: de la Cruz Rodríguez, J.; De Pontieu, B.; Carlsson, M.;
   Rouppe van der Voort, L. H. M.
2013ApJ...764L..11D    Altcode: 2013arXiv1301.3141D
  The heating of the Sun's chromosphere remains poorly understood. While
  progress has been made on understanding what drives the quiet-Sun
  internetwork chromosphere, chromospheric heating in strong magnetic
  field regions continues to present a difficult challenge, mostly
  because of a lack of observational constraints. We use high-resolution
  spectropolarimetric data from the Swedish 1 m Solar Telescope to
  identify the location and spatio-temporal properties of heating in
  the magnetic chromosphere. In particular, we report the existence of
  raised-core spectral line profiles in the Ca II λ8542 line. These
  profiles are characterized by the absence of an absorption line
  core, showing a quasi-flat profile between λ ≈ ±0.5 Å, and are
  abundant close to magnetic bright points and plage. Comparison with
  three-dimensional MHD simulations indicates that such profiles occur
  when the line of sight goes through an "elevated temperature canopy"
  associated with the expansion with height of the magnetic field of
  flux concentrations. This temperature canopy in the simulations is
  caused by ohmic dissipation where there are strong magnetic field
  gradients. The raised-core profiles are thus indicators of locations
  of increased chromospheric heating. We characterize the location and
  temporal and spatial properties of such profiles in our observations,
  thus providing much stricter constraints on theoretical models of
  chromospheric heating mechanisms than before.

---------------------------------------------------------
Title: The Effects of Spatio-temporal Resolution on Deduced Spicule
    Properties
Authors: Pereira, Tiago M. D.; De Pontieu, Bart; Carlsson, Mats
2013ApJ...764...69P    Altcode: 2012arXiv1212.2969P
  Spicules have been observed on the Sun for more than a century,
  typically in chromospheric lines such as Hα and Ca II H. Recent
  work has shown that so-called "type II" spicules may have a role in
  providing mass to the corona and the solar wind. In chromospheric
  filtergrams these spicules are not seen to fall back down, and they
  are shorter lived and more dynamic than the spicules that have been
  classically reported in ground-based observations. Observations of
  type II spicules with Hinode show fundamentally different properties
  from what was previously measured. In earlier work we showed that these
  dynamic type II spicules are the most common type, a view that was not
  properly identified by early observations. The aim of this work is to
  investigate the effects of spatio-temporal resolution in the classical
  spicule measurements. Making use of Hinode data degraded to match
  the observing conditions of older ground-based studies, we measure
  the properties of spicules with a semi-automated algorithm. These
  results are then compared to measurements using the original Hinode
  data. We find that degrading the data has a significant effect on the
  measured properties of spicules. Most importantly, the results from
  the degraded data agree well with older studies (e.g., mean spicule
  duration more than 5 minutes, and upward apparent velocities of about
  25 km s<SUP>-1</SUP>). These results illustrate how the combination
  of spicule superposition, low spatial resolution and cadence affect
  the measured properties of spicules, and that previous measurements
  can be misleading.

---------------------------------------------------------
Title: The Interface Region Imaging Spectrograph (IRIS)
Authors: De Pontieu, B.; Title, A. M.; Lemen, J. R.; Wuelser, J.;
   Tarbell, T. D.; Schrijver, C.; Golub, L.; Kankelborg, C. C.; Hansteen,
   V. H.; Carlsson, M.
2012AGUFMSH33D2256D    Altcode:
  The solar chromosphere and transition region (TR) form a highly
  structured and dynamic interface region between the photosphere and
  the corona. This 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. Nevertheless,
  the chromosphere remains poorly understood, because of the complexity
  of the required observational and analytical tools: the interface
  region is highly complex with transitions from optically thick to
  optically thin radiation, from pressure to magnetic field domination,
  and large density and temperature contrasts on small spatial scales. The
  Interface Region Imaging Spectrograph (IRIS) was selected for a NASA
  SMEX mission in 2009 and is scheduled to launch in early 2013. IRIS
  addresses critical questions: (1) Which types of non-thermal energy
  dominate in the chromosphere and beyond? (2) How does the chromosphere
  regulate mass and energy supply to the corona and heliosphere? (3)
  How do magnetic flux and matter rise through the lower atmosphere, and
  what role does flux emergence play in flares and mass ejections? These
  questions are addressed with a high-resolution near and far UV imaging
  spectrometer sensitive to emission from plasma at temperatures between
  5,000 K and 10 MK. IRIS has a field-of-view of 120 arcsec, a spatial
  resolution of 0.4 arcsec, and velocity resolution of 0.5 km/s. The
  IRIS investigation includes a strong numerical modeling component
  based on advanced radiative MHD codes to facilitate interpretation of
  observations. We will describe the IRIS instrumentation and numerical
  modeling, and present the status of the IRIS observatory development. We
  will highlight some of the issues that IRIS observations can help
  resolve.

---------------------------------------------------------
Title: Chromospheric Magnetic Fields: Observations, Simulations and
    their Interpretation
Authors: de la Cruz Rodríguez, J.; Socas-Navarro, H.; Carlsson, M.;
   Leenaarts, J.
2012ASPC..463...15D    Altcode: 2012arXiv1203.4577D
  The magnetic field of the quiet-Sun chromosphere remains a mystery
  for solar physicists. The reduced number of chromospheric lines are
  intrinsically hard to model and only a few of them are magnetically
  sensitive. In this work, we use a 3D numerical simulation of the outer
  layers of the solar atmosphere, to asses the reliability of non-LTE
  inversions, in this case applied to the Ca II λ8542 Å line. We show
  that NLTE inversions provide realistic estimates of physical quantities
  from synthetic observations.

---------------------------------------------------------
Title: 2nd ATST-EAST Workshop in Solar Physics: Magnetic Fields from
    the Photosphere to the Corona
Authors: Rimmele, T. R.; Tritschler, A.; Wöger, F.; Collados Vera,
   M.; Socas-Navarro, H.; Schlichenmaier, R.; Carlsson, M.; Berger, T.;
   Cadavid, A.; Gilbert, P. R.; Goode, P. R.; Knölker, M.
2012ASPC..463.....R    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Quantifying Spicules
Authors: Pereira, Tiago M. D.; De Pontieu, Bart; Carlsson, Mats
2012ApJ...759...18P    Altcode: 2012arXiv1208.4404P
  Understanding the dynamic solar chromosphere is fundamental in solar
  physics. Spicules are an important feature of the chromosphere,
  connecting the photosphere to the corona, potentially mediating
  the transfer of energy and mass. The aim of this work is to study
  the properties of spicules over different regions of the Sun. Our
  goal is to investigate if there is more than one type of spicule,
  and how spicules behave in the quiet Sun, coronal holes, and active
  regions. We make use of high cadence and high spatial resolution Ca
  II H observations taken by Hinode/Solar Optical Telescope. Making use
  of a semi-automated detection algorithm, we self-consistently track
  and measure the properties of 519 spicules over different regions. We
  find clear evidence of two types of spicules. Type I spicules show
  a rise and fall and have typical lifetimes of 150-400 s and maximum
  ascending velocities of 15-40 km s<SUP>-1</SUP>, while type II spicules
  have shorter lifetimes of 50-150 s, faster velocities of 30-110 km
  s<SUP>-1</SUP>, and are not seen to fall down, but rather fade at
  around their maximum length. Type II spicules are the most common, seen
  in the quiet Sun and coronal holes. Type I spicules are seen mostly
  in active regions. There are regional differences between quiet-Sun
  and coronal hole spicules, likely attributable to the different field
  configurations. The properties of type II spicules are consistent with
  published results of rapid blueshifted events (RBEs), supporting the
  hypothesis that RBEs are their disk counterparts. For type I spicules
  we find the relations between their properties to be consistent with
  a magnetoacoustic shock wave driver, and with dynamic fibrils as their
  disk counterpart. The driver of type II spicules remains unclear from
  limb observations.

---------------------------------------------------------
Title: Investigating the Reliability of Coronal Emission Measure
    Distribution Diagnostics using Three-dimensional Radiative
    Magnetohydrodynamic Simulations
Authors: Testa, Paola; De Pontieu, Bart; Martínez-Sykora, Juan;
   Hansteen, Viggo; Carlsson, Mats
2012ApJ...758...54T    Altcode: 2012arXiv1208.4286T
  Determining the temperature distribution of coronal plasmas can provide
  stringent constraints on coronal heating. Current observations with
  the Extreme ultraviolet Imaging Spectrograph (EIS) on board Hinode
  and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
  Observatory provide diagnostics of the emission measure distribution
  (EMD) of the coronal plasma. Here we test the reliability of temperature
  diagnostics using three-dimensional radiative MHD simulations. We
  produce synthetic observables from the models and apply the Monte
  Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with
  the "true" distributions from the model, we assess the limitations
  of the diagnostics as a function of the plasma parameters and the
  signal-to-noise ratio of the data. We find that EMDs derived from
  EIS synthetic data reproduce some general characteristics of the true
  distributions, but usually show differences from the true EMDs that
  are much larger than the estimated uncertainties suggest, especially
  when structures with significantly different density overlap along
  the line of sight. When using AIA synthetic data the derived EMDs
  reproduce the true EMDs much less accurately, especially for broad
  EMDs. The differences between the two instruments are due to the:
  (1) smaller number of constraints provided by AIA data and (2) broad
  temperature response function of the AIA channels which provide looser
  constraints to the temperature distribution. Our results suggest that
  EMDs derived from current observatories may often show significant
  discrepancies from the true EMDs, rendering their interpretation
  fraught with uncertainty. These inherent limitations to the method
  should be carefully considered when using these distributions to
  constrain coronal heating.

---------------------------------------------------------
Title: The Hanle Effect of Lyα in a Magnetohydrodynamic Model of
    the Solar Transition Region
Authors: Štěpán, J.; Trujillo Bueno, J.; Carlsson, M.; Leenaarts, J.
2012ApJ...758L..43S    Altcode: 2012arXiv1208.4929S
  In order to understand the heating of the solar corona it is crucial
  to obtain empirical information on the magnetic field in its lower
  boundary (the transition region). To this end, we need to measure
  and model the linear polarization produced by scattering processes in
  strong UV lines, such as the hydrogen Lyα line. The interpretation
  of the observed Stokes profiles will require taking into account that
  the outer solar atmosphere is highly structured and dynamic, and that
  the height of the transition region may well vary from one place in
  the atmosphere to another. Here, we report on the Lyα scattering
  polarization signals we have calculated in a realistic model of an
  enhanced network region, resulting from a state-of-the-art radiation
  magnetohydrodynamic simulation. This model is characterized by spatially
  complex variations of the physical quantities at transition region
  heights. The results of our investigation lead us to emphasize that
  scattering processes in the upper solar chromosphere should indeed
  produce measurable linear polarization in Lyα. More importantly,
  we show that via the Hanle effect the model's magnetic field produces
  significant changes in the emergent Q/I and U/I profiles. Therefore, we
  argue that by measuring the polarization signals produced by scattering
  processes and the Hanle effect in Lyα and contrasting them with those
  computed in increasingly realistic atmospheric models, we should be
  able to decipher the magnetic, thermal, and dynamic structure of the
  upper chromosphere and transition region of the Sun.

---------------------------------------------------------
Title: Chromospheric Lyman-alpha spectro-polarimeter (CLASP)
Authors: Kano, Ryouhei; Bando, Takamasa; Narukage, Noriyuki; Ishikawa,
   Ryoko; Tsuneta, Saku; Katsukawa, Yukio; Kubo, Masahito; Ishikawa,
   Shin-nosuke; Hara, Hirohisa; Shimizu, Toshifumi; Suematsu, Yoshinori;
   Ichimoto, Kiyoshi; Sakao, Taro; Goto, Motoshi; Kato, Yoshiaki; Imada,
   Shinsuke; Kobayashi, Ken; Holloway, Todd; Winebarger, Amy; Cirtain,
   Jonathan; De Pontieu, Bart; Casini, Roberto; Trujillo Bueno, Javier;
   Štepán, Jiří; Manso Sainz, Rafael; Belluzzi, Luca; Asensio Ramos,
   Andres; Auchère, Frédéric; Carlsson, Mats
2012SPIE.8443E..4FK    Altcode:
  One of the biggest challenges in heliophysics is to decipher the
  magnetic structure of the solar chromosphere. The importance of
  measuring the chromospheric magnetic field is due to both the key role
  the chromosphere plays in energizing and structuring the outer solar
  atmosphere and the inability of extrapolation of photospheric fields to
  adequately describe this key boundary region. Over the last few years,
  significant progress has been made in the spectral line formation
  of UV lines as well as the MHD modeling of the solar atmosphere. It
  is found that the Hanle effect in the Lyman-alpha line (121.567 nm)
  is a most promising diagnostic tool for weaker magnetic fields in
  the chromosphere and transition region. Based on this groundbreaking
  research, we propose the Chromospheric Lyman-Alpha Spectro-Polarimeter
  (CLASP) to NASA as a sounding rocket experiment, for making the first
  measurement of the linear polarization produced by scattering processes
  and the Hanle effect in the Lyman-alpha line (121.567 nm), and making
  the first exploration of the magnetic field in the upper chromosphere
  and transition region of the Sun. The CLASP instrument consists
  of a Cassegrain telescope, a rotating 1/2-wave plate, a dual-beam
  spectrograph assembly with a grating working as a beam splitter, and
  an identical pair of reflective polarization analyzers each equipped
  with a CCD camera. We propose to launch CLASP in December 2014.

---------------------------------------------------------
Title: Implications for Coronal Heating from Coronal Rain
Authors: Antolin, P.; Shibata, K.; Carlsson, M.; Rouppe van der Voort,
   L.; Vissers, G.; Hansteen, V.
2012ASPC..454..171A    Altcode:
  Coronal rain is a phenomenon above active regions in which cool plasma
  condensations fall down from coronal heights. Numerical simulations of
  loops have shown that such condensations can naturally form in the case
  of footpoint concentrated heating through the “catastrophic cooling”
  mechanism. In this work we analize high resolution limb observations in
  Ca II H and Hα of coronal rain performed by Hinode/SOT and by Crisp of
  SST and derive statistical properties. We further investigate the link
  between coronal rain and the coronal heating mechanisms by performing
  1.5-D MHD simulations of a loop subject to footpoint heating and to
  Alfvén waves generated in the photosphere. It is found that if a loop
  is heated predominantly from Alfvén waves coronal rain is inhibited
  due to the characteristic uniform heating they produce. Hence coronal
  rain can point both to the spatial distribution of the heating and to
  the agent of the heating itself, thus acting as a marker for coronal
  heating mechanisms.

---------------------------------------------------------
Title: Non-local thermodynamic equilibrium inversions from a 3D
    magnetohydrodynamic chromospheric model
Authors: de la Cruz Rodríguez, J.; Socas-Navarro, H.; Carlsson, M.;
   Leenaarts, J.
2012A&A...543A..34D    Altcode: 2012arXiv1205.3171D
  Context. The structure of the solar chromosphere is believed to
  be governed by magnetic fields, even in quiet-Sun regions that
  have a relatively weak photospheric field. During the past decade
  inversion methods have emerged as powerful tools for analyzing the
  chromosphere of active regions. The applicability of inversions to
  infer the stratification of the physical conditions in a dynamic 3D
  solar chromosphere has not yet been studied in detail. <BR /> Aims:
  This study aims to establish the diagnostic capabilities of non-local
  thermodynamical equilibrium (NLTE) inversion techniques of Stokes
  profiles induced by the Zeeman effect in the Ca ii λ8542 Å line. <BR
  /> Methods: We computed the Ca ii atomic level populations in a snapshot
  from a 3D radiation-MHD simulation of the quiet solar atmosphere in
  non-LTE using the 3D radiative transfer code Multi3d. These populations
  were used to compute synthetic full-Stokes profiles in the Ca ii
  λ8542 Å line using 1.5D radiative transfer and the inversion code
  Nicole. The profiles were then spectrally degraded to account for
  finite filter width, and Gaussian noise was added to account for
  finite photon flux. These profiles were inverted using Nicole and
  the results were compared with the original model atmosphere. <BR />
  Results: Our NLTE inversions applied to quiet-Sun synthetic observations
  provide reasonably good estimates of the chromospheric magnetic field,
  line-of-sight velocities and somewhat less accurate, but still very
  useful, estimates of the temperature. Three-dimensional scattering
  of photons cause cool pockets in the chromosphere to be invisible in
  the line profile and consequently they are also not recovered by the
  inversions. To successfully detect Stokes linear polarization in this
  quiet snapshot, a noise level below 10<SUP>-3.5</SUP> is necessary.

---------------------------------------------------------
Title: Ubiquitous Torsional Motions in Type II Spicules
Authors: De Pontieu, B.; Carlsson, M.; Rouppe van der Voort, L. H. M.;
   Rutten, R. J.; Hansteen, V. H.; Watanabe, H.
2012ApJ...752L..12D    Altcode: 2012arXiv1205.5006D
  Spicules are long, thin, highly dynamic features that jut out
  ubiquitously from the solar limb. They dominate the interface between
  the chromosphere and corona and may provide significant mass and energy
  to the corona. We use high-quality observations with the Swedish 1
  m Solar Telescope to establish that so-called type II spicules are
  characterized by the simultaneous action of three different types of
  motion: (1) field-aligned flows of order 50-100 km s<SUP>-1</SUP>,
  (2) swaying motions of order 15-20 km s<SUP>-1</SUP>, and (3) torsional
  motions of order 25-30 km s<SUP>-1</SUP>. The first two modes have been
  studied in detail before, but not the torsional motions. Our analysis
  of many near-limb and off-limb spectra and narrowband images using
  multiple spectral lines yields strong evidence that most, if not all,
  type II spicules undergo large torsional modulation and that these
  motions, like spicule swaying, represent Alfvénic waves propagating
  outward at several hundred km s<SUP>-1</SUP>. The combined action
  of the different motions explains the similar morphology of spicule
  bushes in the outer red and blue wings of chromospheric lines, and
  needs to be taken into account when interpreting Doppler motions to
  derive estimates for field-aligned flows in spicules and determining
  the Alfvénic wave energy in the solar atmosphere. Our results also
  suggest that large torsional motion is an ingredient in the production
  of type II spicules and that spicules play an important role in the
  transport of helicity through the solar atmosphere.

---------------------------------------------------------
Title: A Sharp Look at Coronal Rain with Hinode/SOT and SST/CRISP
Authors: Antolin, P.; Carlsson, M.; Rouppe van der Voort, L.;
   Verwichte, E.; Vissers, G.
2012ASPC..455..253A    Altcode: 2012arXiv1202.0787A
  The tropical wisdom that when it is hot and dense we can expect
  rain might also apply to the Sun. Indeed, observations and numerical
  simulations have showed that strong heating at footpoints of loops,
  as is the case for active regions, puts their coronae out of thermal
  equilibrium, which can lead to a phenomenon known as catastrophic
  cooling. Following local pressure loss in the corona, hot plasma
  locally condenses in these loops and dramatically cools down to
  chromospheric temperatures. These blobs become bright in Hα and
  Ca ii H in time scales of minutes, and their dynamics seem to be
  subject more to internal pressure changes in the loop rather than to
  gravity. They thus become trackers of the magnetic field, which results
  in the spectacular coronal rain that is observed falling down coronal
  loops. In this work we report on high resolution observations of coronal
  rain with the Solar Optical Telescope (SOT) on Hinode and CRISP at
  the Swedish Solar Telescope (SST). A statistical study is performed in
  which properties such as velocities and accelerations of coronal rain
  are derived. We show how this phenomenon can constitute a diagnostic
  tool for the internal physical conditions inside loops. Furthermore, we
  analyze transverse oscillations of strand-like condensations composing
  coronal rain falling in a loop, and discuss the possible nature of the
  wave. This points to the important role that coronal rain can play in
  the fields of coronal heating and coronal seismology.

---------------------------------------------------------
Title: 4th Hinode Science Meeting: Unsolved Problems and Recent
    Insights
Authors: Bellot Rubio, L.; Reale, F.; Carlsson, M.
2012ASPC..455.....B    Altcode: 2012ASPC..455.....R
  No abstract at ADS

---------------------------------------------------------
Title: The Chromospheric Lyman-Alpha SpectroPolarimeter: CLASP
Authors: Kobayashi, K.; Kano, R.; Trujillo-Bueno, J.; Asensio Ramos,
   A.; Bando, T.; Belluzzi, L.; Carlsson, M.; De Pontieu, R. C. B.; Hara,
   H.; Ichimoto, K.; Ishikawa, R.; Katsukawa, Y.; Kubo, M.; Manso Sainz,
   R.; Narukage, N.; Sakao, T.; Stepan, J.; Suematsu, Y.; Tsuneta, S.;
   Watanabe, H.; Winebarger, A.
2012ASPC..456..233K    Altcode:
  The magnetic field plays a crucial role in the chromosphere and the
  transition region, and our poor empirical knowledge of the magnetic
  field in the upper chromosphere and transition region is a major
  impediment to advancing the understanding of the solar atmosphere. The
  Hanle effect promises to be a valuable alternative to Zeeman effect
  as a method of measuring the magnetic field in the chromosphere and
  transition region; it is sensitive to weaker magnetic fields, and
  also sensitive to tangled, unresolved field structures. <P />CLASP
  is a sounding rocket experiment that aims to observe the Hanle effect
  polarization of the Lyman α (1215.67Å) line in the solar chromosphere
  and transition region, and prove the usefulness of this technique in
  placing constraints on the magnetic field strength and orientation
  in the low plasma-β region of the solar atmosphere. The Ly-α line
  has been chosen because it is a chromospheric/transition-region line,
  and because the Hanle effect polarization of this line is predicted to
  be sensitive to 10-250 Gauss, encompassing the range of interest. The
  CLASP instrument is designed to measure linear polarization in the
  Ly-α line with a polarization sensitivity of 0.1%. The instrument is
  currently funded for development. The optical design of the instrument
  has been finalized, and an extensive series of component-level tests
  are underway to validate the design.

---------------------------------------------------------
Title: How Low-Quality Observations Affect Spicule Properties
Authors: Pereira, Tiago M. D.; De Pontieu, B.; Carlsson, M.
2012AAS...22020306P    Altcode:
  Spicules have been observed on the sun for more than 80 years, in
  several chromospheric lines such as H-alpha and Ca II H. Recent work
  has shown that spicules have the potential to drive the solar wind
  and heat the chromosphere, making them a hotly contested topic in
  solar physics. Despite the wealth of observations available, their
  properties are still a matter of debate. Difficulties in measuring
  their properties arise because spicules occur on short spatial and
  temporal scales, and are very abundant (superimposed) at the limb. Most
  of the older observations lacked either the spatial resolution or
  cadence necessary to measure spicules. This changed with Hinode/SOT,
  which has provided seeing-free observations with high cadence and
  spatial resolution. Using SOT observations, we find that in the
  quiet sun most spicules are shorter lived and can move much faster
  than previously measured. In this work we try to reconcile the recent
  results with results from older observations. We degrade SOT data to
  match the cadence and resolution of older data sets, and apply the same
  semi-automated method to detect and measure the properties of spicules
  to both the original and degraded data. We find that degrading the data
  has a significant effect on the measured properties of spicules. Most
  importantly, the results from the degraded data agree very well
  with older studies (e.g. mean spicule duration more than 5 minutes,
  and upward velocities of about 25 km/s). These results illustrate how
  the combination of spicule superposition, low spatial resolution, and
  cadence affect the measured properties of spicules, and that previous
  measurements can thus be unreliable.

---------------------------------------------------------
Title: The Formation of the Hα Line in the Solar Chromosphere
Authors: Leenaarts, J.; Carlsson, M.; Rouppe van der Voort, L.
2012ApJ...749..136L    Altcode: 2012arXiv1202.1926L
  We use state-of-the-art radiation-MHD simulations and three-dimensional
  (3D) non-LTE radiative transfer computations to investigate Hα
  line formation in the solar chromosphere and apply the results of
  this investigation to develop the potential of Hα as a diagnostic
  of the chromosphere. We show that one can accurately model Hα line
  formation assuming statistical equilibrium and complete frequency
  redistribution provided the computation of the model atmosphere
  included non-equilibrium ionization of hydrogen and the Lyα and
  Lyβ line profiles are described by Doppler profiles. We find that
  3D radiative transfer is essential in modeling hydrogen lines due
  to the low photon destruction probability in Hα. The Hα opacity
  in the upper chromosphere is mainly sensitive to the mass density
  and only weakly sensitive to the temperature. We find that the Hα
  line-core intensity is correlated with the average formation height:
  The larger the average formation height is, the lower the intensity
  will be. The line-core width is a measure of the gas temperature
  in the line-forming region. The fibril-like dark structures seen in
  Hα line-core images computed from our model atmosphere are tracing
  magnetic field lines. These structures are caused by field-aligned
  ridges of enhanced chromospheric mass density that raise their average
  formation height, and therefore make them appear dark against their
  deeper-formed surroundings. We compare with observations, and find that
  the simulated line-core widths are very similar to the observed ones,
  without the need for additional microturbulence.

---------------------------------------------------------
Title: State-of-the-art of non-LTE diagnostics: observations and
    simulations
Authors: Carlsson, Mats
2012decs.confE..32C    Altcode:
  Advanced MHD simulations combined with non-LTE diagnostics are
  revolutionizing our view of chromospheric dynamics and heating. We will
  discuss how well synthetic observables compare with observations,
  how diagnostic codes can be used to derive physical information
  about the atmosphere, what is missing in current calculations and the
  consequences of current assumptions. Examples will focus on often used
  or to-be-used diagnostics of chromospheric lines, such as Ca II 8542,
  H-alpha and Mg II h/k.

---------------------------------------------------------
Title: Using 3D MHD realistic simulations of the solar corona to
    test plasma diagnostics
Authors: Testa, P.; De Pontieu, B.; Martinez-Sykora, J.; Hansteen,
   V.; Carlsson, M.
2012decs.confE..27T    Altcode:
  We synthesize coronal images and spectra from advanced 3D MHD
  simulations obtained from the state-of-the art Bifrost code, and
  explore how well they reproduce coronal observations with SDO/AIA and
  Hinode/EIS. We apply standard diagnostic techniques (e.g., density, and
  temperature diagnostics) to the synthetic observations and investigate
  how accurately the derived physical information matches the plasma
  parameters of the model. We discuss the limitations of the diagnostics
  and their implications.

---------------------------------------------------------
Title: NLTE inversions from a 3D MHD Chromospheric simulation
Authors: de la Cruz Rodriguez, J.; Socas-Navarro, H.; Carlsson, M.;
   Leenaarts, J.
2012decs.confE..80D    Altcode:
  The structure of the solar chromosphere is believed to be governed
  by magnetic fields, even in quiet Sun regions with a relatively weak
  field. Measuring the magnetic field of the solar chromosphere is an
  outstanding challenge for observers. Inversion codes allow for detailed
  interpretation of full-Stokes data from spectral lines formed in the
  chromosphere. However, the applicability of non-LTE inversions to infer
  physical conditions in the dynamic 3D solar chromosphere, has not yet
  been studied in detail. In this study, we use a snapshot from a 3D MHD
  simulation of quiet-sun, extending from the photosphere to the corona,
  to asses the reliability of non-LTE inversions to infer chromospheric
  quantities, especially the magnetic field.

---------------------------------------------------------
Title: The formation of the Halpha line in the solar chromosphere
Authors: Leenaarts, J.; Carlsson; M.; Rouppe van der Voort, Rouppe, L.
2012decs.confE..14L    Altcode:
  We use state-of-the-art radiation-MHD simulations and 3D non-LTE
  radiative transfer computations to investigate Halpha line formation
  in the solar chromosphere. We find that 3D radiative transfer is
  essential in modeling hydrogen lines due to the low photon destruction
  probability in Halpha. The Halpha opacity in the upper chromosphere
  is mainly sensitive to the mass density and only weakly sensitive to
  temperature. We find that the Halpha line-core intensity is correlated
  with the average formation height: the lower the intensity, the larger
  the average formation height. The line-core width is a measure of
  the gas temperature in the line-forming region. The fibril-like dark
  structures seen in Halpha line-core images computed from our model
  atmosphere are tracing magnetic field lines. These structures are
  caused by field-aligned ridges of enhanced chromospheric mass density
  that raise their average formation height, and therefore makes them
  appear dark against their deeper-formed surroundings.

---------------------------------------------------------
Title: Potential for diagnostics with IRIS and Mg II lines
Authors: Pereira, Tiago M. D.; Carlsson, Mats; Leenaarts, Jorrit;
   Uitenbroek, Han; De Pontieu, Bart; Martinez-Sykora, Juan
2012decs.confE..13P    Altcode:
  The IRIS mission will open up a new window into the solar chromosphere
  and transition region. An important diagnostic that IRIS will bring
  is the Mg II H and K lines. Radiation from these lines is believed
  to be come from a wide range of formation depths, from the higher
  photosphere to the onset of the transition region. With a complex
  formation mechanism, Mg II H and K suffer from departures from LTE
  and partial redistribution (PRD). In this preliminary analysis we will
  look into the potential for diagnostics of Mg II H and K. Using a new
  parallel version of the RH code we synthesised Mg II H and K spectra
  from 3D rMHD simulations of the solar atmosphere. We will discuss
  the relevance of several approximations on the final observables,
  and will compare the Mg II H and K filtergrams with those of Ca II H,
  a robust chromospheric diagnostic line widely used with Hinode/SOT/BFI.

---------------------------------------------------------
Title: The generation of shock waves traveling from the photosphere
    to the transition region within network magnetic elements
Authors: Kato, Y.; Hansteen, V.; Steiner, O.; Carlsson, M.
2012decs.confE..54K    Altcode:
  We investigate the generation of shock waves near the photosphere by
  convective downdrafts in the immediate surroundings of the magnetic
  flux concentration, using radiation magnetohydrodynamic (RMHD) 2D
  simulations of the solar atmosphere. The simulations comprise the layers
  from the upper convection zone to the lower corona. We call this the
  "magnetic pumping process". We find that the generated slow modes via
  magnetic pumping travel upward along the magnetic flux concentration,
  developing into a shock wave in chromospheric heights. The waves
  continue to propagate further up through the transition region and into
  the corona. In the course of propagation through the transition layer,
  a small fraction of the longitudinal slow mode is converted into a
  transverse wave mode. We report on how much energy is deposited by
  propagating shock waves through the transition region and we discuss
  the the dissipation process above the photosphere within the magnetic
  flux concentration..

---------------------------------------------------------
Title: Approximations for radiative cooling and heating in the
    solar chromosphere
Authors: Carlsson, M.; Leenaarts, J.
2012A&A...539A..39C    Altcode: 2012arXiv1202.2996C
  Context. The radiative energy balance in the solar chromosphere is
  dominated by strong spectral lines that are formed out of LTE. It
  is computationally prohibitive to solve the full equations of
  radiative transfer and statistical equilibrium in 3D time dependent
  MHD simulations. <BR /> Aims: We look for simple recipes to compute
  the radiative energy balance in the dominant lines under solar
  chromospheric conditions. <BR /> Methods: We use detailed calculations
  in time-dependent and 2D MHD snapshots to derive empirical formulae
  for the radiative cooling and heating. <BR /> Results: The radiative
  cooling in neutral hydrogen lines and the Lyman continuum, the H
  and K and intrared triplet lines of singly ionized calcium and the h
  and k lines of singly ionized magnesium can be written as a product
  of an optically thin emission (dependent on temperature), an escape
  probability (dependent on column mass) and an ionization fraction
  (dependent on temperature). In the cool pockets of the chromosphere
  the same transitions contribute to the heating of the gas and similar
  formulae can be derived for these processes. We finally derive a simple
  recipe for the radiative heating of the chromosphere from incoming
  coronal radiation. We compare our recipes with the detailed results
  and comment on the accuracy and applicability of the recipes.

---------------------------------------------------------
Title: The Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP)j
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Bando, T.;
   Belluzzi, L.; Casini, R.; Carlsson, M.; Cirtain, J. W.; De Pontieu,
   B.; Hara, H.; Ichimoto, K.; Ishikawa, R.; Kano, R.; Katsukawa, Y.;
   Kim, T.; Kubo, M.; Manso Sainz, R.; Narukage, N.; Asensio Ramos,
   A.; Robinson, B.; Sakao, T.; Shimizu, T.; Stepan, J.; Suematsu, Y.;
   Watanabe, H.; West, E.; Winebarger, A. R.
2011AGUFM.P14C..05K    Altcode:
  We present an overview of the Chromospheric Lyman-Alpha
  SpectroPolarimeter (CLASP) program. CLASP is a proposed sounding rocket
  experiment currently under development as collaboration between Japan,
  USA and Spain. The aim is to achieve the first measurement of magnetic
  field in the upper chromosphere and transition region of the Sun
  through the detection and measurement of Hanle effect polarization
  of the Lyman alpha line. The Hanle effect (i.e. the magnetic field
  induced modification of the linear polarization due to scattering
  processes in spectral lines) is believed to be a powerful tool for
  measuring the magnetic field in the upper chromosphere, as it is more
  sensitive to weaker magnetic fields than the Zeeman effect, and also
  sensitive to magnetic fields tangled at spatial scales too small to be
  resolved. The Lyman-alpha (121.567 nm) line has been chosen because
  it is a chromospheric/transition-region line, and because the Hanle
  effect polarization of the Lyman-alpha line is predicted to be sensitive
  to 10-250 Gauss, encompassing the range of interest. Hanle effect is
  predicted to be observable as linear polarization or depolarization,
  depending on the geometry, with a fractional polarization amplitude
  varying between 0.1% and 1% depending on the strength and orientation of
  the magnetic field. This quantification of the chromospheric magnetic
  field requires a highly sensitive polarization measurement. The
  CLASP instrument consists of a large aperture (287 mm) Cassegrain
  telescope mated to a polarizing beamsplitter and a matched pair
  of grating spectrographs. The polarizing beamsplitter consists
  of a continuously rotating waveplate and a linear beamsplitter,
  allowing simultaneous measurement of orthogonal polarizations and
  in-flight self-calibration. Development of the instrument is underway,
  and prototypes of all optical components have been tested using a
  synchrotron beamline. The experiment is proposed for flight in 2014.

---------------------------------------------------------
Title: Quantifying spicules
Authors: Pereira, T. M.; De Pontieu, B.; Carlsson, M.
2011AGUFMSH34B..01P    Altcode:
  Understanding the dynamic solar chromosphere is of paramount importance
  in solar physics. Spicules are an important feature of the chromosphere,
  connecting the photosphere to the corona, potentially mediating the
  transfer of energy and mass. While it is generally accepted that
  there is more than one type of spicule, their quick motions, small
  spatial scales, and short lifetimes have prevented a systematic study
  of their properties over different solar regions. In the present work
  we undertake such a study, using Ca H filtergrams from Hinode/SOT and
  a semi-automated method to detect and track the spicules. Looking at
  different magnetic field configurations (quiet Sun, coronal holes,
  active regions), we discuss how the properties of the spicules change,
  how the two spicule populations (type I and type II) are connected,
  and how spicules are related to other chromospheric phenomena such as
  dynamic fibrils.

---------------------------------------------------------
Title: Wave Propagation and Jet Formation in the Chromosphere
Authors: Heggland, L.; Hansteen, V. H.; De Pontieu, B.; Carlsson, M.
2011ApJ...743..142H    Altcode: 2011arXiv1112.0037H
  We present the results of numerical simulations of wave propagation
  and jet formation in solar atmosphere models with different magnetic
  field configurations. The presence in the chromosphere of waves with
  periods longer than the acoustic cutoff period has been ascribed to
  either strong inclined magnetic fields, or changes in the radiative
  relaxation time. Our simulations include a sophisticated treatment
  of radiative losses, as well as fields with different strengths
  and inclinations. Using Fourier and wavelet analysis techniques,
  we investigate the periodicity of the waves that travel through the
  chromosphere. We find that the velocity signal is dominated by waves
  with periods around 5 minutes in regions of strong, inclined field,
  including at the edges of strong flux tubes where the field expands,
  whereas 3 minute waves dominate in regions of weak or vertically
  oriented fields. Our results show that the field inclination is very
  important for long-period wave propagation, whereas variations in the
  radiative relaxation time have little effect. Furthermore, we find
  that atmospheric conditions can vary significantly on timescales of
  a few minutes, meaning that a Fourier analysis of wave propagation
  can be misleading. Wavelet techniques take variations with time into
  account and are more suitable analysis tools. Finally, we investigate
  the properties of jets formed by the propagating waves once they reach
  the transition region, and find systematic differences between the
  jets in inclined-field regions and those in vertical field regions,
  in agreement with observations of dynamic fibrils.

---------------------------------------------------------
Title: Generation and propagation of Alfvenic waves in spicules
Authors: De Pontieu, B.; Okamoto, T. J.; Rouppe van der Voort, L.;
   Hansteen, V. H.; Carlsson, M.
2011AGUFMSH13B1956D    Altcode:
  Both spicules and Alfven waves have recently been implicated in
  playing a role in the heating of the outer atmosphere. Yet we do
  not know how spicules or Alfven waves are generated. Here we focus
  on the properties of Alfvenic waves in spicules and their role in
  forming spicules. We use high-resolution observations taken with the
  Solar Optical Telescope onboard Hinode, and with the CRISP Fabry-Perot
  Interferometer at the Swedish Solar Telescope (SST) in La Palma to study
  the generation and propagation of Alfvenic waves in spicules and their
  disk counterparts. Using automated detection algorithms to identify
  propagating waves in limb spicules, we find evidence for both up-
  and downward propagating as well as standing waves. Our data suggests
  significant reflection of waves in and around spicules and provides
  constraints for theoretical models of spicules and wave propagation
  through the chromosphere. We also show observational evidence (using
  SST data) of the generation of Alfven waves and the role they play in
  forming spicules.

---------------------------------------------------------
Title: Testing coronal plasma diagnostics using 3D MHD models of
    the solar atmosphere
Authors: Testa, P.; Martinez-Sykora, J.; Hansteen, V. H.; De Pontieu,
   B.; Carlsson, M.
2011AGUFMSH53C..06T    Altcode:
  We synthesize coronal images and spectra from advanced 3D radiative
  MHD simulations obtained from the state-of-the-art Bifrost code, and
  explore how well they reproduce coronal observations with SDO/AIA
  and Hinode/EIS and XRT. We apply standard diagnostic techniques
  (e.g., density, temperature, abundance diagnostics) to the synthetic
  observations and investigate how accurately the derived physical
  information matches the plasma parameters of the model. We discuss
  the limitations of the diagnostics and their implications.

---------------------------------------------------------
Title: Overview of Chromospheric Lyman-Alpha SpectroPolarimeter
    (CLASP)
Authors: Narukage, Noriyuki; Tsuneta, Saku; Bando, Takamasa; Kano,
   Ryouhei; Kubo, Masahito; Ishikawa, Ryoko; Hara, Hirohisa; Suematsu,
   Yoshinori; Katsukawa, Yukio; Watanabe, Hiroko; Ichimoto, Kiyoshi;
   Sakao, Taro; Shimizu, Toshifumi; Kobayashi, Ken; Robinson, Brian; Kim,
   Tony; Winebarger, Amy; West, Edward; Cirtain, Jonathan; De Pontieu,
   Bart; Casini, Roberto; Trujillo Bueno, Javier; Stepan, Jiri; Manso
   Sainz, Rafael; Belluzzi, Luca; Asensio Ramos, Andres; Carlsson, Mats
2011SPIE.8148E..0HN    Altcode: 2011SPIE.8148E..16N
  The solar chromosphere is an important boundary, through which all of
  the plasma, magnetic fields and energy in the corona and solar wind
  are supplied. Since the Zeeman splitting is typically smaller than
  the Doppler line broadening in the chromosphere and transition region,
  it is not effective to explore weak magnetic fields. However, this is
  not the case for the Hanle effect, when we have an instrument with
  high polarization sensitivity (~ 0.1%). "Chromospheric Lyman- Alpha
  SpectroPolarimeter (CLASP)" is the sounding rocket experiment to detect
  linear polarization produced by the Hanle effect in Lyman-alpha line
  (121.567 nm) and to make the first direct measurement of magnetic
  fields in the upper chromosphere and lower transition region. To
  achieve the high sensitivity of ~ 0.1% within a rocket flight (5
  minutes) in Lyman-alpha line, which is easily absorbed by materials,
  we design the optical system mainly with reflections. The CLASP
  consists of a classical Cassegrain telescope, a polarimeter and a
  spectrometer. The polarimeter consists of a rotating 1/2-wave plate
  and two reflecting polarization analyzers. One of the analyzer also
  works as a polarization beam splitter to give us two orthogonal linear
  polarizations simultaneously. The CLASP is planned to be launched in
  2014 summer.

---------------------------------------------------------
Title: Alfvénic waves with sufficient energy to power the quiet
    solar corona and fast solar wind
Authors: McIntosh, Scott W.; de Pontieu, Bart; Carlsson, Mats;
   Hansteen, Viggo; Boerner, Paul; Goossens, Marcel
2011Natur.475..477M    Altcode:
  Energy is required to heat the outer solar atmosphere to millions of
  degrees (refs 1, 2) and to accelerate the solar wind to hundreds of
  kilometres per second (refs 2-6). Alfvén waves (travelling oscillations
  of ions and magnetic field) have been invoked as a possible mechanism
  to transport magneto-convective energy upwards along the Sun's magnetic
  field lines into the corona. Previous observations of Alfvénic waves
  in the corona revealed amplitudes far too small (0.5kms<SUP>-1</SUP>)
  to supply the energy flux (100-200Wm<SUP>-2</SUP>) required to
  drive the fast solar wind or balance the radiative losses of the
  quiet corona. Here we report observations of the transition region
  (between the chromosphere and the corona) and of the corona that
  reveal how Alfvénic motions permeate the dynamic and finely structured
  outer solar atmosphere. The ubiquitous outward-propagating Alfvénic
  motions observed have amplitudes of the order of 20kms<SUP>-1</SUP> and
  periods of the order of 100-500s throughout the quiescent atmosphere
  (compatible with recent investigations), and are energetic enough to
  accelerate the fast solar wind and heat the quiet corona.

---------------------------------------------------------
Title: Quiet-Sun imaging asymmetries in Na I D<SUB>1</SUB> compared
    with other strong Fraunhofer lines
Authors: Rutten, R. J.; Leenaarts, J.; Rouppe van der Voort, L. H. M.;
   de Wijn, A. G.; Carlsson, M.; Hansteen, V.
2011A&A...531A..17R    Altcode: 2011arXiv1104.4307R
  Imaging spectroscopy of the solar atmosphere using the Na I
  D<SUB>1</SUB> line yields marked asymmetry between the blue and
  red line wings: sampling a quiet-Sun area in the blue wing displays
  reversed granulation, whereas sampling in the red wing displays normal
  granulation. The Mg I b<SUB>2</SUB> line of comparable strength does
  not show this asymmetry, nor does the stronger Ca II 8542 Å line. We
  demonstrate the phenomenon with near-simultaneous spectral images in
  Na I D<SUB>1</SUB>, Mg I b<SUB>2</SUB>, and Ca II 8542 Å from the
  Swedish 1-m Solar Telescope. We then explain it with line-formation
  insights from classical 1D modeling and with a 3D magnetohydrodynamical
  simulation combined with NLTE spectral line synthesis that permits
  detailed comparison with the observations in a common format. The
  cause of the imaging asymmetry is the combination of correlations
  between intensity and Dopplershift modulation in granular overshoot
  and the sensitivity to these of the steep profile flanks of the Na
  I D<SUB>1</SUB> line. The Mg I b<SUB>2</SUB> line has similar core
  formation but much wider wings due to larger opacity buildup and
  damping in the photosphere. Both lines obtain marked core asymmetry
  from photospheric shocks in or near strong magnetic concentrations,
  less from higher-up internetwork shocks that produce similar asymmetry
  in the spatially averaged Ca II 8542 Å profile.

---------------------------------------------------------
Title: The stellar atmosphere simulation code Bifrost. Code
    description and validation
Authors: Gudiksen, B. V.; Carlsson, M.; Hansteen, V. H.; Hayek, W.;
   Leenaarts, J.; Martínez-Sykora, J.
2011A&A...531A.154G    Altcode: 2011arXiv1105.6306G
  Context. Numerical simulations of stellar convection and photospheres
  have been developed to the point where detailed shapes of observed
  spectral lines can be explained. Stellar atmospheres are very complex,
  and very different physical regimes are present in the convection zone,
  photosphere, chromosphere, transition region and corona. To understand
  the details of the atmosphere it is necessary to simulate the whole
  atmosphere since the different layers interact strongly. These physical
  regimes are very diverse and it takes a highly efficient massively
  parallel numerical code to solve the associated equations. <BR /> Aims:
  The design, implementation and validation of the massively parallel
  numerical code Bifrost for simulating stellar atmospheres from the
  convection zone to the corona. <BR /> Methods: The code is subjected
  to a number of validation tests, among them the Sod shock tube test,
  the Orzag-Tang colliding shock test, boundary condition tests and
  tests of how the code treats magnetic field advection, chromospheric
  radiation, radiative transfer in an isothermal scattering atmosphere,
  hydrogen ionization and thermal conduction. Results.Bifrost completes
  the tests with good results and shows near linear efficiency scaling
  to thousands of computing cores.

---------------------------------------------------------
Title: On the minimum temperature of the quiet solar chromosphere
Authors: Leenaarts, J.; Carlsson, M.; Hansteen, V.; Gudiksen, B. V.
2011A&A...530A.124L    Altcode: 2011arXiv1104.5081L
  <BR /> Aims: We aim to provide an estimate of the minimum temperature
  of the quiet solar chromosphere. <BR /> Methods: We perform a 2D
  radiation-MHD simulation spanning the upper convection zone to the
  lower corona. The simulation includes non-LTE radiative transfer
  and an equation-of-state that includes non-equilibrium ionization
  of hydrogen and non-equilibrium H<SUB>2</SUB> molecule formation. We
  analyze the reliability of the various assumptions made in our model
  in order to assess the realism of the simulation. <BR /> Results:
  Our simulation contains pockets of cool gas with down to 1660 K from
  1 Mm up to 3.2 Mm height. It overestimates the radiative heating,
  and contains non-physical heating below 1660 K. Therefore we conclude
  that cool pockets in the quiet solar chromosphere might have even
  lower temperatures than in the simulation, provided that there exist
  areas in the chromosphere without significant magnetic heating. We
  suggest off-limb molecular spectroscopy to look for such cool pockets
  and 3D simulations including a local dynamo and a magnetic carpet to
  investigate Joule heating in the quiet chromosphere.

---------------------------------------------------------
Title: Helioseismic Studies With Multi-wavelength Data From HMI And
    AIA Onboard SDO
Authors: Hill, Frank; Jain, K.; Tripathy, S.; Kholikov, S.; Gonzalez
   Hernandez, I.; Leibacher, J.; Howe, R.; Baudin, F.; Carlsson, M.;
   Chaplin, W.; Tarbell, T.
2011SPD....42.2111H    Altcode: 2011BAAS..43S.2111H
  The successful launch of the Solar Dynamics Observatory (SDO) in
  February 2010 opens important, new possibilities for helioseismic
  exploration of the solar interior and atmosphere using multi-wavelength
  observations from multiple instruments. In order to better understand
  the solar interior and atmosphere, as well as the physics of the
  helioseismic modes and waves themselves, we exploit the potential of
  the Atmospheric Imaging Assembly (AIA) 1600 and 1700 Angstrom continuum
  measurements and the contemporaneous Helioseismic and Magnetic Imager
  (HMI) Fe I 6173.3 Angstrom velocity and intensity observations. Standard
  techniques of helioseismology e.g Sun-as-a-star, spherical harmonic
  analysis, ring diagrams, and time- distance analysis are applied to
  obtain acoustic mode parameters and other characteristics. Here we
  present our preliminary results, and interpret these in the context
  of the differences in the heights of formation of the lines.

---------------------------------------------------------
Title: A Sounding Rocket Experiment for Spectropolarimetric
    Observations with the Ly<SUB>α</SUB> Line at 121.6 nm (CLASP)
Authors: Ishikawa, R.; Bando, T.; Fujimura, D.; Hara, H.; Kano,
   R.; Kobiki, T.; Narukage, N.; Tsuneta, S.; Ueda, K.; Wantanabe,
   H.; Kobayashi, K.; Trujillo Bueno, J.; Manso Sainz, R.; Stepan, J.;
   de Pontieu, B.; Carlsson, M.; Casini, R.
2011ASPC..437..287I    Altcode:
  A team consisting of Japan, USA, Spain, and Norway is developing a
  high-throughput Chromospheric Lyman-Alpha SpectroPolarimeter (CLASP),
  which is proposed to fly with a NASA sounding rocket in 2014. CLASP will
  explore the magnetism of the upper solar chromosphere and transition
  region via the Hanle effect of the Ly<SUB>α</SUB> line for the first
  time. This experiment requires spectropolarimetric observations with
  high polarimetric sensitivity (∼0.1%) and wavelength resolution
  (0.1 Å). The final spatial resolution (slit width) is being discussed
  taking into account the required high signal-to-noise ratio. We have
  demonstrated the performance of the Ly<SUB>α</SUB> polarimeter by
  extensively using the Ultraviolet Synchrotron ORbital Radiation Facility
  (UVSOR) at the Institute for Molecular Sciences. In this contribution,
  we report these measurements at UVSOR together with the current status
  of the CLASP project.

---------------------------------------------------------
Title: Non-equilibrium calcium ionisation in the solar atmosphere
Authors: Wedemeyer-Böhm, S.; Carlsson, M.
2011A&A...528A...1W    Altcode: 2011arXiv1101.2211W
  Context. The chromosphere of the Sun is a temporally and spatially
  very varying medium for which the assumption of ionisation equilibrium
  is questionable. <BR /> Aims: Our aim is to determine the dominant
  processes and timescales for the ionisation equilibrium of calcium under
  solar chromospheric conditions. <BR /> Methods: The study is based on
  numerical simulations with the RADYN code, which combines hydrodynamics
  with a detailed solution of the radiative transfer equation. The
  calculations include a detailed non-equilibrium treatment of hydrogen,
  calcium, and helium. Next to an hour long simulation sequence,
  additional simulations are produced, for which the stratification is
  slightly perturbed so that a ionisation relaxation timescale can be
  determined. The simulations are characterised by upwards propagating
  shock waves, which cause strong temperature fluctuations and variations
  of the (non-equilibrium) ionisation degree of calcium. <BR /> Results:
  The passage of a hot shock front leads to a strong net ionisation
  of Ca II, rapidly followed by net recombination. The relaxation
  timescale of the calcium ionisation state is found to be of the
  order of a few seconds at the top of the photosphere and 10 to 30 s
  in the upper chromosphere. At heights around 1 Mm, we find typical
  values around 60 s and in extreme cases up to ~150 s. Generally,
  the timescales are significantly reduced in the wakes of ubiquitous
  hot shock fronts. The timescales can be reliably determined from a
  simple analysis of the eigenvalues of the transition rate matrix. The
  timescales are dominated by the radiative recombination from Ca III
  into the metastable Ca II energy levels of the 4d <SUP>2</SUP>D
  term. These transitions depend strongly on the density of free
  electrons and therefore on the (non-equilibrium) ionisation degree of
  hydrogen, which is the main electron donor. <BR /> Conclusions: The
  ionisation/recombination timescales derived here are too long for the
  assumption of an instantaneous ionisation equilibrium to be valid and,
  on the other hand, are not long enough to warrant an assumption of a
  constant ionisation fraction. Fortunately, the ionisation degree of Ca
  ii remains small in the height range, where the cores of the H, K, and
  the infrared triplet lines are formed. We conclude that the difference
  due to a detailed treatment of Ca ionisation has only negligible impact
  on the modelling of spectral lines of Ca ii and the plasma properties
  under the conditions in the quiet solar chromosphere.

---------------------------------------------------------
Title: Solar velocity references from 3D HD photospheric models
Authors: de la Cruz Rodríguez, J.; Kiselman, D.; Carlsson, M.
2011A&A...528A.113D    Altcode: 2011arXiv1101.2671D
  Context. The measurement of Doppler velocities in spectroscopic solar
  observations requires a reference for the local frame of rest. The
  rotational and radial velocities of the Earth and the rotation of
  the Sun introduce velocity offsets in the observations. Normally,
  good references for velocities are missing (e.g. telluric lines),
  especially in filter-based spectropolarimetric observations. <BR />
  Aims: We determine an absolute reference for line-of-sight velocities
  measured from solar observations for any heliocentric angle, calibrating
  the convective line shift of spatially-averaged profiles on quiet sun
  from a 3D hydrodynamical simulation. This method works whenever there
  is quiet sun in the field-of-view, and it has the advantage of being
  relatively insensitive to uncertainties in the atomic data. <BR />
  Methods: We carry out radiative transfer computations in LTE for
  selected C i and Fe i lines, whereas the Ca ii infrared lines are
  synthesized in non-LTE. Radiative transfer calculations are done with
  a modified version of Multi, using the snapshots of a non-magnetic
  3D hydrodynamical simulation of the photosphere. <BR /> Results:
  The resulting synthetic profiles show the expected C-shaped bisector
  at disk center. The degree of asymmetry and the line shifts, however,
  show a clear dependence on the heliocentric angle and the properties of
  the lines. The profiles at μ = 1 are compared with observed profiles
  to prove their reliability, and they are tested against errors induced
  by the LTE calculations, inaccuracies in the atomic data and the 3D
  simulation. <BR /> Conclusions: Theoretical quiet-sun profiles of lines
  commonly used by solar observers are provided to the community. Those
  can be used as absolute references for line-of-sight velocities. The
  limb effect is produced by the projection of the 3D atmosphere along the
  line of sight. Non-LTE effects on Fe i lines are found to have a small
  impact on the convective shifts of the lines, reinforcing the usability
  of the LTE approximation in this case. We estimate the precision of the
  disk-center line shifts to be approximately 50 m s<SUP>-1</SUP>, but
  the off-center profiles remain to be tested against observations. <P
  />The spectral profiles are only available in electronic form at the
  CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via <A
  href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A113">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/528/A113</A>

---------------------------------------------------------
Title: VizieR Online Data Catalog: Synthetic lines in the Sun (de
    la Cruz Rodríguez+, 2011)
Authors: de la Cruz Rodríguez, J.; Kiselman, D.; Carlsson, M.
2011yCat..35289113D    Altcode:
  We have computed synthetic spectra from a realistic 3D numerical
  simulation of the solar photosphere. We provide the spatially
  averaged spectra for selected lines that are commonly used on solar
  applications. These data can be used to calibrate Doppler velocity
  measurements in the solar photosphere. The calculations are carried
  out along the solar disk from heliocentric angle mu=1.0 to mu=0.3. <P
  />(11 data files).

---------------------------------------------------------
Title: The Origins of Hot Plasma in the Solar Corona
Authors: De Pontieu, B.; McIntosh, S. W.; Carlsson, M.; Hansteen,
   V. H.; Tarbell, T. D.; Boerner, P.; Martinez-Sykora, J.; Schrijver,
   C. J.; Title, A. M.
2011Sci...331...55D    Altcode:
  The Sun's outer atmosphere, or corona, is heated to millions of degrees,
  considerably hotter than its surface or photosphere. Explanations for
  this enigma typically invoke the deposition in the corona of nonthermal
  energy generated by magnetoconvection. However, the coronal heating
  mechanism remains unknown. We used observations from the Solar Dynamics
  Observatory and the Hinode solar physics mission to reveal a ubiquitous
  coronal mass supply in which chromospheric plasma in fountainlike jets
  or spicules is accelerated upward into the corona, with much of the
  plasma heated to temperatures between ~0.02 and 0.1 million kelvin (MK)
  and a small but sufficient fraction to temperatures above 1 MK. These
  observations provide constraints on the coronal heating mechanism(s)
  and highlight the importance of the interface region between photosphere
  and corona.

---------------------------------------------------------
Title: Ubiquitous Alfvenic Motions in Quiet Sun, Coronal Hole and
    Active Region Corona
Authors: McIntosh, S. W.; de Pontieu, B.; Carlsson, M.; Hansteen,
   V. H.; Sdo/Aia Mission Team
2010AGUFMSH14A..01M    Altcode:
  We use observations with AIA onboard SDO and report the discovery of
  ubiquitous Alfvenic oscillations in the corona of quiet Sun, active
  regions and coronal holes. These Alfvenic oscillations have significant
  power, and seem to be connected to the chromospheric Alfvenic
  oscillations previously reported with Hinode. We use Monte Carlo
  simulations to determine the strength and periods of the waves. Using
  unique joint observations of Hinode, the Solar Dynamics Observatory, and
  HAO's CoMP instrument we study the excitation of transverse oscillations
  as a function of space, time, and temperature. We will discuss the
  energetic impact and diagnostic capabilities of this ever-present
  process and how it can be used to build a more self-consistent picture
  of energy transport into the inner heliosphere. Transverse Oscillations
  Observed Above the Solar North Pole in the He II 304Å (bottom) and Fe
  IX 171Å (top) channels. Studying the progression of such points with
  altitude yields important information about wave propagation into the
  magnetically open corona.

---------------------------------------------------------
Title: The Chromospheric Lyman Alpha SpectroPolarimeter (CLASP)
Authors: Kobayashi, K.; Tsuneta, S.; Trujillo Bueno, J.; Cirtain,
   J. W.; Bando, T.; Kano, R.; Hara, H.; Fujimura, D.; Ueda, K.; Ishikawa,
   R.; Watanabe, H.; Ichimoto, K.; Sakao, T.; de Pontieu, B.; Carlsson,
   M.; Casini, R.
2010AGUFMSH11B1632K    Altcode:
  Magnetic fields in the solar chromosphere play a key role in the
  energy transfer and dynamics of the solar atmosphere. Yet a direct
  observation of the chromospheric magnetic field remains one of the
  greatest challenges in solar physics. While some advances have been
  made for observing the Zeeman effect in strong chromospheric lines,
  the effect is small and difficult to detect outside sunspots. The
  Hanle effect offers a promising alternative; it is sensitive to weaker
  magnetic fields (e.g., 5-500 G for Ly-Alpha), and while its magnitude
  saturates at stronger magnetic fields, the linear polarization signals
  remain sensitive to the magnetic field orientation. The Hanle effect
  is not only limited to off-limb observations. Because the chromosphere
  is illuminated by an anisotropic radiation field, the Ly-Alpha line is
  predicted to show linear polarization for on-disk, near-limb regions,
  and magnetic field is predicted to cause a measurable depolarization. At
  disk center, the Ly-Alpha radiation is predicted to be negligible
  in the absence of magnetic field, and linearly polarized to an order
  of 0.3% in the presence of an inclined magnetic field. The proposed
  CLASP sounding rocket instrument is designed to detect 0.3% linear
  polarization of the Ly-Alpha line at 1.5 arcsecond spatial resolution
  (0.7’’ pixel size) and 10 pm spectral resolution. The instrument
  consists of a 30 cm aperture Cassegrain telescope and a dual-beam
  spectropolarimeter. The telescope employs a “cold mirror’’ design
  that uses multilayer coatings to reflect only the target wavelength
  range into the spectropolarimeter. The polarization analyzer consists of
  a rotating waveplate and a polarizing beamsplitter that comprises MgF2
  plates placed at Brewster’s Angle. Each output beam of the polarizing
  beamsplitter, representing two orthogonal linear polarizations, is
  dispersed and focused using a separate spherical varied-line-space
  grating, and imaged with a separate 512x512 CCD camera. Prototypes
  of key optical components have been fabricated and tested. Instrument
  design is being finalized, and the experiment will be proposed for a
  2014 flight aboard a NASA sounding rocket.

---------------------------------------------------------
Title: The role of the chromosphere in filling the corona with hot
    plasma (Invited)
Authors: de Pontieu, B.; McIntosh, S. W.; Carlsson, M.; Hansteen,
   V. H.; Tarbell, T. D.; Boerner, P.; Martinez-Sykora, J.; Schrijver,
   C. J.; Title, A. M.
2010AGUFMSH21C..03D    Altcode:
  We use coordinated observations from the Solar Dynamics Observatory
  (SDO), Hinode and the Swedish Solar Telescope (SST) to show how
  plasma is heated to coronal temperatures from its source in the
  chromosphere. Our observations reveal a ubiquitous mass supply
  for the solar corona in which chromospheric plasma is accelerated
  upward into the corona with much of the plasma heated to transition
  region temperatures, and a small, but significant fraction heated
  to temperatures in excess of 1 million K. Our observations show,
  for the first time, how chromospheric spicules, fountain-like jets
  that have long been considered potential candidates for coronal
  heating, are directly associated with heating of plasma to coronal
  temperatures. These results provide strong physical constraints on
  the mechanism(s) responsible for coronal heating and do not seem
  compatible with current models. The association with chromospheric
  spicules highlights the importance of the interface region between
  the photosphere and corona to gain a full understanding of the coronal
  heating problem.

---------------------------------------------------------
Title: Radiative Hydrodynamic Simulations of Acoustic Waves in
    Sunspots
Authors: Bard, S.; Carlsson, M.
2010ApJ...722..888B    Altcode:
  We investigate the formation and evolution of the Ca II H line in a
  sunspot. The aim of our study is to establish the mechanisms underlying
  the formation of the frequently observed brightenings of small regions
  of sunspot umbrae known as "umbral flashes." We perform fully consistent
  NLTE radiation hydrodynamic simulations of the propagation of acoustic
  waves in sunspot umbrae and conclude that umbral flashes result from
  increased emission of the local solar material during the passage
  of acoustic waves originating in the photosphere and steepening to
  shock in the chromosphere. To quantify the significance of possible
  physical mechanisms that contribute to the formation of umbral flashes,
  we perform a set of simulations on a grid formed by different wave
  power spectra, different inbound coronal radiation, and different
  parameterized chromospheric heating. Our simulations show that the
  waves with frequencies in the range 4.5-7.0 mHz are critical to the
  formation of the observed blueshifts of umbral flashes while waves with
  frequencies below 4.5 mHz do not play a role despite their dominance
  in the photosphere. The observed emission in the Ca II H core between
  flashes only occurs in the simulations that include significant inbound
  coronal radiation and/or extra non-radiative chromospheric heating in
  addition to shock dissipation.

---------------------------------------------------------
Title: On Redshifts and Blueshifts in the Transition Region and Corona
Authors: Hansteen, V. H.; Hara, H.; De Pontieu, B.; Carlsson, M.
2010ApJ...718.1070H    Altcode: 2010arXiv1001.4769H
  Emission lines formed in the transition region (TR) of the Sun have long
  been known to show pervasive redshifts. Despite a variety of proposed
  explanations, these TR downflows (and the slight upflows in the low
  corona) remain poorly understood. We present results from comprehensive
  three-dimensional MHD models that span the upper convection zone up to
  the corona, 15 Mm above the photosphere. The TR and coronal heating
  in these models is caused by the stressing of the magnetic field by
  photospheric and convection "zone dynamics," but also in some models by
  the injection of emerging magnetic flux. We show that rapid, episodic
  heating, at low heights of the upper chromospheric plasma to coronal
  temperatures naturally produces downflows in TR lines, and slight
  upflows in low coronal lines, with similar amplitudes to those observed
  with EUV/UV spectrographs. We find that TR redshifts naturally arise
  in episodically heated models where the average volumetric heating
  scale height lies between that of the chromospheric pressure scale
  height of 200 km and the coronal scale height of 50 Mm.

---------------------------------------------------------
Title: On the Solar Chromosphere Observed at the LIMB with Hinode
Authors: Judge, Philip G.; Carlsson, Mats
2010ApJ...719..469J    Altcode: 2010arXiv1004.1398J
  Broadband images in the Ca II H line, from the Broadband Filter Imager
  (BFI) instrument on the Hinode spacecraft, show emission from spicules
  emerging from and visible right down to the observed limb. Surprisingly,
  little absorption of spicule light is seen along their lengths. We
  present formal solutions to the transfer equation for given (ad hoc)
  source functions, including a stratified chromosphere from which
  spicules emanate. The model parameters are broadly compatible with
  earlier studies of spicules. The visibility of Ca II spicules down
  to the limb in Hinode data seems to require that spicule emission
  be Doppler shifted relative to the stratified atmosphere, either by
  supersonic turbulent or organized spicular motion. The non-spicule
  component of the chromosphere is almost invisible in the broadband BFI
  data, but we predict that it will be clearly visible in high spectral
  resolution data. Broadband Ca II H limb images give the false impression
  that the chromosphere is dominated by spicules. Our analysis serves
  as a reminder that the absence of a signature can be as significant
  as its presence.

---------------------------------------------------------
Title: Radiative transfer with scattering for domain-decomposed 3D
    MHD simulations of cool stellar atmospheres. Numerical methods and
    application to the quiet, non-magnetic, surface of a solar-type star
Authors: Hayek, W.; Asplund, M.; Carlsson, M.; Trampedach, R.; Collet,
   R.; Gudiksen, B. V.; Hansteen, V. H.; Leenaarts, J.
2010A&A...517A..49H    Altcode: 2010arXiv1007.2760H
  <BR /> Aims: We present the implementation of a radiative
  transfer solver with coherent scattering in the new BIFROST
  code for radiative magneto-hydrodynamical (MHD) simulations of
  stellar surface convection. The code is fully parallelized using
  MPI domain decomposition, which allows for large grid sizes and
  improved resolution of hydrodynamical structures. We apply the code
  to simulate the surface granulation in a solar-type star, ignoring
  magnetic fields, and investigate the importance of coherent scattering
  for the atmospheric structure. <BR /> Methods: A scattering term
  is added to the radiative transfer equation, requiring an iterative
  computation of the radiation field. We use a short-characteristics-based
  Gauss-Seidel acceleration scheme to compute radiative flux divergences
  for the energy equation. The effects of coherent scattering are
  tested by comparing the temperature stratification of three 3D
  time-dependent hydrodynamical atmosphere models of a solar-type star:
  without scattering, with continuum scattering only, and with both
  continuum and line scattering. <BR /> Results: We show that continuum
  scattering does not have a significant impact on the photospheric
  temperature structure for a star like the Sun. Including scattering in
  line-blanketing, however, leads to a decrease of temperatures by about
  350 K below log<SUB>10</SUB> τ<SUB>5000</SUB> ⪉ -4. The effect is
  opposite to that of 1D hydrostatic models in radiative equilibrium,
  where scattering reduces the cooling effect of strong LTE lines in
  the higher layers of the photosphere. Coherent line scattering also
  changes the temperature distribution in the high atmosphere, where
  we observe stronger fluctuations compared to a treatment of lines as
  true absorbers.

---------------------------------------------------------
Title: On the Origin of High-Frequency "Acoustic” Power in
    Photospheric and Chromospheric Velocity Power Spectra
Authors: Fleck, Bernard; Straus, T.; Carlsson, M.; Jefferies, S. M.;
   Severino, G.; Tarbell, T. D.
2010AAS...21640309F    Altcode: 2010BAAS...41..879F
  In a recent paper (Fleck et al., 2010) we compared observed Dopplergram
  time series from Hinode with results from 3-D numerical simulations
  based on the Oslo "Stagger” and CO5BOLD codes. Given the rapid falloff
  of atmospheric modulation transfer functions at high frequencies due
  to the extended widths of typical velocity response functions, one
  would expect the high-frequency tail of Doppler power spectra to drop
  significantly below those of actual velocities at the corresponding
  heights in the simulations. Surprisingly, our analysis of power spectra
  of Doppler shifts of simulated line profiles did not reveal such a
  steep falloff at high frequencies. Instead, they are comparable to
  (and in some cases even larger than) those of the actual velocities,
  making estimates of the energy flux of high frequency acoustic
  waves questionable, in particular those that apply atmospheric MTF
  corrections. In this work we study the cause of this unexpected
  behavior in detail, with particular emphasis on the role of rapidly
  changing velocity response functions in a dynamic atmosphere with
  strong vertical velocity gradients.

---------------------------------------------------------
Title: New Frontiers in Solar Chromospheric Physics
Authors: Carlsson, Mats P. O.
2010AAS...21620701C    Altcode:
  The enigmatic chromosphere is the transition between the solar surface
  and the eruptive outer solar atmosphere. The chromosphere harbours
  and constrains the mass and energy loading processes that define the
  heating of the corona, the acceleration and the composition of the solar
  wind, and the energetics and triggering of solar outbursts (filament
  eruptions, flares, coronal mass ejections). <P />Magnetic fields
  break through the solar surface in a hierarchy of magnetic elements
  ranging from Earth-sized sunspots down to tiny concentrations that are
  barely resolved in the highest-resolution photospheric images. In the
  chromosphere they combine in intricate, highly dynamic, and continuously
  evolving fibrilar patterns. Movements of the photospheric field-line
  footpoints drive, guide, and control the flows of energy and mass
  into the corona, and trigger energy-releasing magnetic reconnection
  through relentless topological rearrangement. The conversion from
  convectively driven footpoint motion to outer-atmosphere outflows and
  loading takes place in the dynamic, fine-structured chromosphere. <P
  />The chromosphere is arguably the most difficult and least understood
  domain of solar physics. All at once it represents the transition from
  optically thick to thin radiation escape, from gas-pressure domination
  to magnetic-pressure domination, from neutral to ionised state, from MHD
  to plasma physics, and from near-equilibrium ("LTE") to non-equilibrium
  conditions. <P />A number of important facilities for observing the
  solar chromosphere have recently come on line (e.g. the Hinode satellite
  and ground-based Fabry-Perot interferometers) or will become operational
  in the near future (e.g. SDO and IRIS). The overwhelming complexity of
  the chromosphere makes it necessary to have numerical simulations for
  the interpretation of the observations. Such realistic simulations,
  spanning the solar atmosphere from the convection zone to the corona,
  are now becoming feasible. <P />This presentation will introduce the
  fascinating aspects of chromospheric physics and review recent results
  from both observations and numerical simulations.

---------------------------------------------------------
Title: Radiative Hydrodynamic Simulation of the Continuum Emission
    in Solar White-Light Flares
Authors: Cheng, J. X.; Ding, M. D.; Carlsson, Mats
2010ApJ...711..185C    Altcode:
  It is believed that solar white-light flares (WLFs) originate in the
  lower chromosphere and upper photosphere. In particular, some recently
  observed WLFs show a large continuum enhancement at 1.56 μm where the
  opacity reaches its minimum. Therefore, it is important to clarify
  how the energy is transferred to the lower layers responsible for
  the production of WLFs. Based on radiative hydrodynamic simulations,
  we study the role of non-thermal electron beams in increasing the
  continuum emission. We vary the parameters of the electron beam and
  disk positions and compare the results with observations. The electron
  beam heated model can explain most of the observational white-light
  enhancements. For the most energetic WLFs observed so far, however, a
  very large electron beam flux and a high low-energy cutoff, which are
  possibly beyond the parameter space in our simulations, are required
  in order to reproduce the observed white-light emission.

---------------------------------------------------------
Title: The Quiet Solar Atmosphere Observed and Simulated in Na
    I D<SUB>1</SUB>
Authors: Leenaarts, J.; Rutten, R. J.; Reardon, K.; Carlsson, M.;
   Hansteen, V.
2010ApJ...709.1362L    Altcode: 2009arXiv0912.2206L
  The Na I D<SUB>1</SUB> line in the solar spectrum is sometimes
  attributed to the solar chromosphere. We study its formation in
  quiet-Sun network and internetwork. We first present high-resolution
  profile-resolved images taken in this line with the imaging
  spectrometer Interferometric Bidimensional Spectrometer at the Dunn
  Solar Telescope and compare these to simultaneous chromospheric images
  taken in Ca II 8542 Å and Hα. We then model Na I D<SUB>1</SUB>
  formation by performing three-dimensional (3D) non-local
  thermodynamic equilibrium profile synthesis for a snapshot from a
  3D radiation-magnetohydrodynamics simulation. We find that most Na I
  D<SUB>1</SUB> brightness is not chromospheric but samples the magnetic
  concentrations that make up the quiet-Sun network in the photosphere,
  well below the height where they merge into chromospheric canopies,
  with aureoles from 3D resonance scattering. The line core is sensitive
  to magneto-acoustic shocks in and near magnetic concentrations, where
  shocks occur deeper than elsewhere, and may provide evidence of heating
  deep within magnetic concentrations.

---------------------------------------------------------
Title: On red-shifts in the transition region and corona .
Authors: Hansteen, V. H.; Hara, H.; de Pontieu, B.; Carlsson, M.
2010MmSAI..81..729H    Altcode:
  We present evidence that transition region red-shifts are naturally
  produced in episodically heated models where the average volumetric
  heating scale height lies between that of the chromospheric
  pressure scale height of 200 km and the coronal scale height of
  50 Mm. In order to do so we present results from 3d MHD models
  spanning the upper convection zone up to the corona, 15 Mm above the
  photosphere. Transition region and coronal heating in these models
  is due both the stressing of the magnetic field by photospheric and
  convection `zone dynamics, but also in some models by the injection
  of emerging magnetic flux.

---------------------------------------------------------
Title: High frequency waves in the solar atmosphere?.
Authors: Fleck, B.; Straus, T.; Carlsson, M.; Jefferies, S. M.;
   Severino, G.; Tarbell, T. D.
2010MmSAI..81..777F    Altcode: 2010arXiv1002.3285F
  The present study addresses the following questions: How representative
  of the actual velocities in the solar atmosphere are the Doppler
  shifts of spectral lines? How reliable is the velocity signal derived
  from narrowband filtergrams? How well defined is the height of the
  measured Doppler signal? Why do phase difference spectra always pull
  to 0<SUP>o</SUP> phase lag at high frequencies? Can we actually observe
  high frequency waves (P&lt; 70 s)? What is the atmospheric MTF of high
  frequency waves? How reliably can we determine the energy flux of high
  frequency waves? We address these questions by comparing observations
  obtained with Hinode/NFI with results from two 3D numerical simulations
  (Oslo Stagger and CO<SUP>5</SUP>BOLD). Our results suggest that the
  observed high frequency Doppler velocity signal is caused by rapid
  height variations of the velocity response function in an atmosphere
  with strong velocity gradients and cannot be interpreted as evidence of
  propagating high frequency acoustic waves. Estimates of the energy flux
  of high frequency waves should be treated with caution, in particular
  those that apply atmospheric MTF corrections.

---------------------------------------------------------
Title: On the detection of fast moving upflows in the quiet solar
    photosphere.
Authors: Straus, Th.; Fleck, B.; Jefferies, S. M.; Carlsson, M.;
   Tarbell, T. D.
2010MmSAI..81..751S    Altcode: 2010arXiv1002.3305S
  In our studies of the dynamics and energetics of the solar atmosphere,
  we have detected, in high-quality observations from Hinode SOT/NFI,
  ubiquitous small-scale upflows which move horizontally with supersonic
  velocities in the quiet Sun. We present the properties of these fast
  moving upflows (FMUs) and discuss different interpretations.

---------------------------------------------------------
Title: Chromospheric heating and structure as determined from high
    resolution 3D simulations .
Authors: Carlsson, M.; Hansteen, V. H.; Gudiksen, B. V.
2010MmSAI..81..582C    Altcode: 2010arXiv1001.1546C
  We have performed 3D radiation MHD simulations extending from the
  convection zone to the corona covering a box 16 Mm<SUP>3</SUP> at 32
  km spatial resolution. The simulations show very fine structure in
  the chromosphere with acoustic shocks interacting with the magnetic
  field. Magnetic flux concentrations have a temperature lower than the
  surroundings in the photosphere but higher in the low chromosphere. The
  heating is there mostly through ohmic dissipation preferentially at
  the edges of the flux concentrations. The magnetic field is often
  wound up around the flux concentrations. When acoustic waves travel
  up along the field this topology leads to swirling motions seen in
  chromospheric diagnostic lines such as the calcium infrared triplet.

---------------------------------------------------------
Title: The Interface Region Imaging Spectrograph (IRIS) Small Explorer
Authors: de Pontieu, B.; Title, A. M.; Schryver, C. J.; Lemen, J. R.;
   Golub, L.; Kankelborg, C. C.; Carlsson, M.
2009AGUFMSH33B1499D    Altcode:
  The Interface Region Imaging Spectrograph (IRIS) was recently selected
  as a small explorer mission by NASA. The primary goal of IRIS is to
  understand how the solar atmosphere is energized. The IRIS investigation
  combines advanced numerical modeling with a high resolution 20 cm UV
  imaging spectrograph that will obtain spectra covering temperatures
  from 4,500 to 10 MK in three wavelength ranges (1332-1358 Angstrom,
  1390-1406 Angstrom and 2785-2835 Angstrom) and simultaneous images
  covering temperatures from 4,500 K to 65,000 K. IRIS will obtain UV
  spectra and images with high resolution in space (1/3 arcsec) and time
  (1s) focused on the chromosphere and transition region of the Sun, a
  complex dynamic interface region between the photosphere and corona. In
  this region, all but a few percent of the non-radiative energy leaving
  the Sun is converted into heat and radiation. IRIS fills a crucial gap
  in our ability to advance Sun-Earth connection studies by tracing the
  flow of energy and plasma through this foundation of the corona and
  heliosphere. The IRIS investigation is led by PI Alan Title (LMSAL)
  with major participation by the Harvard Smithsonian Astrophysical
  Observatory, Montana State University, NASA Ames Research Center,
  Stanford University and the University of Oslo (Norway). IRIS is
  scheduled for launch in late 2012, and will have a nominal two year
  mission lifetime.

---------------------------------------------------------
Title: MULTI3D: A Domain-Decomposed 3D Radiative Transfer Code
Authors: Leenaarts, J.; Carlsson, M.
2009ASPC..415...87L    Altcode:
  We present MULTI3D, a 3D radiative transfer code currently under
  development. It is optimized for computing NLTE problems based on
  (radiation-)MHD models of stellar atmospheres. MULTI3D is based on
  MULTI and includes most of the physics present in that code. MULTI3D was
  first written as a serial code by Botnen (1997) and has recently been
  upgraded to an MPI-parallelized, domain-decomposed version. The code
  has so far successfully been run on up to 64 processors, solving the
  NLTE radiative transfer for a six-level Ca II atom with 400 frequency
  points in an atmosphere of 256 × 128 × 108 grid points.

---------------------------------------------------------
Title: On-disk Counterparts of Type II Spicules in the Ca II 854.2
    nm and Hα Lines
Authors: Rouppe van der Voort, L.; Leenaarts, J.; de Pontieu, B.;
   Carlsson, M.; Vissers, G.
2009ApJ...705..272R    Altcode: 2009arXiv0909.2115R
  Recently, a second type of spicules was discovered at the solar
  limb with the Solar Optical Telescope onboard the Japanese Hinode
  spacecraft. These previously unrecognized type II spicules are thin
  chromospheric jets that are shorter lived (10-60 s) and that show much
  higher apparent upward velocities (of order 50-100 km s<SUP>-1</SUP>)
  than the classical spicules. Since they have been implicated in
  providing hot plasma to coronal loops, their formation, evolution,
  and properties are important ingredients for a better understanding
  of the mass and energy balance of the low solar atmosphere. Here, we
  report on the discovery of the disk counterparts of type II spicules
  using spectral imaging data in the Ca II 854.2 nm and Hα lines with
  the CRisp Imaging SpectroPolarimeter at the Swedish Solar Telescope in
  La Palma. We find rapid blueward excursions in the line profiles of
  both chromospheric lines that correspond to thin, jet-like features
  that show apparent velocities of order 50 km s<SUP>-1</SUP>. These
  blueward excursions seem to form a separate absorbing component with
  Doppler shifts of order 20 and 50 km s<SUP>-1</SUP> for the Ca II 854.2
  nm and Hα line, respectively. We show that the appearance, lifetimes,
  longitudinal and transverse velocities, and occurrence rate of these
  rapid blue excursions on the disk are very similar to those of the type
  II spicules at the limb. A detailed study of the spectral line profiles
  in these events suggests that plasma is accelerated along the jet,
  and plasma is being heated throughout the short lifetime of the event.

---------------------------------------------------------
Title: Twisted Flux Tube Emergence from the Convection Zone to the
    Corona. II. Later States
Authors: Martínez-Sykora, Juan; Hansteen, Viggo; Carlsson, Mats
2009ApJ...702..129M    Altcode: 2009arXiv0906.5464M
  Three-dimensional numerical simulations of magnetic flux emergence
  are carried out in a computational domain spanning the upper layers
  of the convection zone to the lower corona. We use the Oslo Staggered
  Code to solve the full magnetohydrodynamic equations with non-gray
  and non-local thermodynamic equilibrium radiative transfer and thermal
  conduction along the magnetic field lines. In this paper, we concentrate
  on the later stages of the simulations and study the evolution of the
  structure of the rising flux in the upper chromosphere and corona, the
  interaction between the emerging flux and the weak coronal magnetic
  field initially present, and the associated dynamics. The flux tube
  injected at the bottom boundary rises to the photosphere where it
  largely remains. However, some parts of the flux tube become unstable
  and expand in patches into the upper chromosphere. The flux rapidly
  expands toward the corona, pushing the coronal and transition region
  material aside, and lifting and maintaining the transition region at
  heights greater than 5 Mm above the photosphere for extensive periods
  of time. The pre-existing magnetic field in the corona and transition
  region is perturbed by the incoming flux and reoriented by a series of
  high Joule heating events. Low-density structures form in the corona,
  while at later times a high-density filamentary structure appears in
  the lower part of the expanding flux. The dynamics of these and other
  structures is discussed. While Joule heating due to the expanding flux
  is episodic, it increases in relative strength as fresh magnetic field
  rises and becomes energetically important in the upper chromosphere and
  corona at later times. Chromospheric, transition region, and coronal
  lines are computed and their response to the perturbation caused by
  the expanding emerging flux is discussed.

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Title: Spicule-Like Structures Observed in Three-Dimensional Realistic
    Magnetohydrodynamic Simulations
Authors: Martínez-Sykora, Juan; Hansteen, Viggo; De Pontieu, Bart;
   Carlsson, Mats
2009ApJ...701.1569M    Altcode: 2009arXiv0906.4446M
  We analyze features that resemble type I spicules in two different
  three-dimensional numerical simulations in which we include horizontal
  magnetic flux emergence in a computational domain spanning the
  upper layers of the convection zone to the lower corona. The two
  simulations differ mainly in the pre-existing ambient magnetic field
  strength and in the properties of the inserted flux tube. We use the
  Oslo Staggered Code to solve the full magnetohydrodynamic equations
  with nongray and non-LTE radiative transfer and thermal conduction
  along the magnetic field lines. We find a multitude of features that
  show a spatiotemporal evolution that is similar to that observed in
  type I spicules, which are characterized by parabolic height versus
  time profiles, and are dominated by rapid upward motion at speeds
  of 10-30 km s<SUP>-1</SUP>, followed by downward motion at similar
  velocities. We measured the parameters of the parabolic profile of the
  spicules and find similar correlations between the parameters as those
  found in observations. The values for height (or length) and duration
  of the spicules found in the simulations are more limited in range than
  those in the observations. The spicules found in the simulation with
  higher pre-existing ambient field have shorter length and smaller
  velocities. From the simulations, it appears that these kinds of
  spicules can, in principle, be driven by a variety of mechanisms that
  include p-modes, collapsing granules, magnetic energy release in the
  photosphere and lower chromosphere, and convective buffeting of flux
  concentrations.

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Title: Neutral oxygen spectral line formation revisited with new
collisional data: large departures from LTE at low metallicity
Authors: Fabbian, D.; Asplund, M.; Barklem, P. S.; Carlsson, M.;
   Kiselman, D.
2009A&A...500.1221F    Altcode: 2009arXiv0902.4472F
  Aims: A detailed study is presented, including estimates of the
  impact on elemental abundance analysis, of the non-local thermodynamic
  equilibrium (non-LTE) formation of the high-excitation neutral oxygen
  777 nm triplet in model atmospheres representative of stars with
  spectral types F to K. <BR />Methods: We have applied the statistical
  equilibrium code MULTI to a number of plane-parallel MARCS atmospheric
  models covering late-type stars (4500 ≤ T_eff ≤ 6500 K, 2 ≤ log
  g ≤ 5 [cgs], and -3.5 ≤ [Fe/H] ≤ 0). The atomic model employed
  includes, in particular, recent quantum-mechanical electron collision
  data. <BR />Results: We confirm that the O i triplet lines form under
  non-LTE conditions in late-type stars, suffering negative abundance
  corrections with respect to LTE. At solar metallicity, the non-LTE
  effect, mainly attributed in previous studies to photon losses in the
  triplet itself, is also driven by an additional significant contribution
  from line opacity. At low metallicity, the very pronounced departures
  from LTE are due to overpopulation of the lower level (3s ^5S^o) of the
  transition. Large line opacity stems from triplet-quintet intersystem
  electron collisions, a form of coupling previously not considered or
  seriously underestimated. The non-LTE effects generally become severe
  for models (both giants and dwarfs) with higher T_eff. Interestingly,
  in metal-poor turn-off stars, the negative non-LTE abundance corrections
  tend to rapidly become more severe towards lower metallicity. When
  neglecting H collisions, they amount to as much as |Δlog ɛ_O|
  ~ 0.9 dex and ~1.2 dex, respectively at [Fe/H] = -3 and [Fe/H]
  = -3.5. Even when such collisions are included, the LTE abundance
  remains a serious overestimate, correspondingly by |Δlog ɛ_O| ~ 0.5
  dex and ~0.9 dex at such low metallicities. Although the poorly known
  inelastic hydrogen collisions thus remain an important uncertainty,
  the large metallicity-dependent non-LTE effects seem to point to
  a resulting “low” (compared to LTE) [O/Fe] in metal-poor halo
  stars. <BR />Conclusions: Our results may be important in solving
  the long-standing [O/Fe] debate. When applying the derived non-LTE
  corrections, the LTE oxygen abundance inferred from the 777 nm permitted
  triplet will be decreased substantially at low metallicity. If the
  classical Drawin formula is employed for O+H collisions, the derived
  [O/Fe] trend becomes almost flat below [Fe/H] ~ -1, in better agreement
  with recent literature estimates generally obtained from other oxygen
  abundance indicators. A value of [O/Fe] ⪉ +0.5 may therefore be
  appropriate, as suggested by standard theoretical models of type II
  supernovae nucleosynthetic yields. If neglecting impacts with H atoms
  instead, [O/Fe] decreases towards lower [Fe/H], which would open new
  questions. Our tests using ATLAS model atmospheres show that, though
  non-LTE corrections for metal-poor dwarfs are smaller (by ~0.2 dex
  when adopting efficient H collisions) than in the MARCS case, our
  main conclusions are preserved, and that the LTE approach tends to
  seriously overestimate the O abundance at low metallicity. However,
  in order to finally reach consistency between oxygen abundances from
  the different available spectral features, it is of high priority to
  reduce the large uncertainty regarding H collisions, to undertake a
  full investigation of the interplay of non-LTE and 3D effects, and to
  clarify the issue of the temperature scale at low metallicity.

---------------------------------------------------------
Title: The Temperature Diagnostic Properties of the Mg I 457.1 nm Line
Authors: Langangen, Øystein; Carlsson, Mats
2009ApJ...696.1892L    Altcode: 2009arXiv0903.1492L
  We analyze the important formation processes for the Mg I 457.1 nm
  line. This line is an intercombination line and the source function
  is close to the local thermodynamic equilibrium (LTE) value. The
  strong coupling to the local temperature and the relatively high
  population of the lower level (the ground state of Mg I) makes this
  line an ideal candidate for temperature diagnostics in the lower
  chromosphere/temperature minimum region. Linking the temperature probed
  to an absolute physical height is nontrivial because of non-LTE (NLTE)
  ionization. We analyze the NLTE effects and find that photoionization
  from the lower energy levels together with cascading collisional
  recombination dominates the ionization balance. Taking properly into
  account the line blanketing in the UV is essential for obtaining the
  right photoionization rates. The identification of the main NLTE effects
  in the line allows us to construct a "quintessential" model atom, ideal
  for computationally demanding tasks, e.g., full three-dimensional
  and/or time-dependent radiative transfer. Furthermore, we analyze
  the diagnostic potential to temperature of this line in solarlike
  atmospheres, by synthesizing the line from a series of parameterized
  atmospheric models. These models have been constructed with fixed
  effective temperature, but with a variable heat term in the energy
  equation to obtain a chromospheric temperature rise at different
  heights. We conclude that the line has a significant potential in
  the diagnostics of the lower chromosphere temperature structure,
  especially for cooler atmospheres, such as sunspots.

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Title: Three-Dimensional Non-LTE Radiative Transfer Computation of
    the CA 8542 Infrared Line From a Radiation-MHD Simulation
Authors: Leenaarts, J.; Carlsson, M.; Hansteen, V.; Rouppe van der
   Voort, L.
2009ApJ...694L.128L    Altcode: 2009arXiv0903.0791L
  The interpretation of imagery of the solar chromosphere in the
  widely used Ca II 854.2 nm infrared line is hampered by its complex,
  three-dimensional, and non-LTE formation. Forward modeling is
  required to aid understanding. We use a three-dimensional non-LTE
  radiative transfer code to compute synthetic Ca II 854.2 nm images
  from a radiation-MHD simulation of the solar atmosphere spanning
  from the convection zone to the corona. We compare the simulation
  with observations obtained with the CRISP filter at the Swedish 1 m
  Solar Telescope. We find that the simulation reproduces dark patches
  in the blue line wing caused by Doppler shifts, brightenings in the
  line core caused by upward-propagating shocks, and thin dark elongated
  structures in the line core that form the interface between upward and
  downward gas motion in the chromosphere. The synthetic line core is
  narrower than the observed one, indicating that the Sun exhibits both
  more vigorous large-scale dynamics as well as small scale motions that
  are not resolved within the simulation, presumably owing to a lack of
  spatial resolution.

---------------------------------------------------------
Title: Hydrodynamics and radiative transfer of 3D model atmospheres.
    Current status, limitations, and how to make headway
Authors: Carlsson, Mats
2009MmSAI..80..606C    Altcode:
  3D MHD models are important tools for advancing our understanding of
  stellar atmospheres. A major computational challenge is the treatment
  of radiative transfer; both to get a realistic treatment of the
  energy transfer in the 3D modelling and for the diagnostic problem of
  calculating the emergent spectrum in more detail from such models. The
  current status, limitations and future directions of 3D MHD atmospheric
  modelling and the treatment of radiative transfer are here discussed.

---------------------------------------------------------
Title: Advancing our understanding of the chromosphere
Authors: Hansteen, V. H.; Carlsson, M.; de Pontieu, B.
2008AGUFMSH51C..01H    Altcode:
  Recent progress has shown the solar chromosphere to be fundamentally
  dynamic, where non-linear techniques must be used to understand
  its nature. It is also the region where the magnetic field grows
  to dominate the plasma and where the coupling between radiation and
  matter becomes becomes quite tenuous. Understanding the workings of the
  chromosphere is vital if one is to understand the flow of energy between
  the solar surface and its outer atmosphere and wind. Recent numerical
  developments have shown that it is feasible to model the chromosphere,
  even to the extent that newly available high resolution observations
  sometimes can be reproduced in detail. We will discuss the challenges
  facing numerical chromospheric models and the observations needed to
  validate or refute them.

---------------------------------------------------------
Title: Dynamics of the upper chromosphere
Authors: de Pontieu, B.; Carlsson, M.; McIntosh, S.; Hansteen, V.;
   Tarbell, T.
2008AGUFMSH51C..05D    Altcode:
  In the past few years, high-resolution observations with ground-based
  telescopes and the Broadband Filter Imager (BFI) and Narrowband
  Filter Imager (NFI) of the Solar Optical Telescope onboard Hinode
  have revolutionized our view of the dynamics and energetics of
  the chromosphere. We review some of these results, including the
  discovery of two different types of spicules and the finding that the
  chromosphere is riddled with strong Alfvenic waves. We describe how
  these observations, when combined with advanced numerical simulations,
  can help address important unresolved issues regarding the connection
  between the photosphere and corona, such as the role of waves and
  of reconnection in driving the dynamics and energetics of the upper
  chromosphere, and how chromospheric dynamics impact the transition
  region and corona.

---------------------------------------------------------
Title: 3D radiative transfer in stellar atmospheres
Authors: Carlsson, M.
2008PhST..133a4012C    Altcode:
  Three-dimensional (3D) radiative transfer in stellar atmospheres is
  reviewed with special emphasis on the atmospheres of cool stars and
  applications. A short review of methods in 3D radiative transfer shows
  that mature methods exist, both for taking into account radiation as an
  energy transport mechanism in 3D (magneto-) hydrodynamical simulations
  of stellar atmospheres and for the diagnostic problem of calculating the
  emergent spectrum in more detail from such models, both assuming local
  thermodynamic equilibrium (LTE) and in non-LTE. Such methods have been
  implemented in several codes, and examples of applications are given.

---------------------------------------------------------
Title: What do Spicules Tell us About the Chromosphere?
Authors: de Pontieu, B.; Carlsson, M.; McIntosh, S.; Hansteen, V.;
   Tarbell, T.
2008ESPM...12.2.15D    Altcode:
  In the past few years, high-resolution observations with ground-based
  telescopes and the Broadband Filter Imager (BFI) and Narrowband
  Filter Imager (NFI) of the Solar Optical Telescope onboard
  Hinode have revolutionized our view of spicules and their role in
  the chromosphere. We review some of these results, including the
  discovery of two different types of spicules with different dynamics
  and formation mechanisms, as well as the finding that the chromosphere
  is riddled with strong Alfvenic waves. <P />In an effort to determine
  the formation mechanism of spicules and their impact on the outer
  atmosphere, we further focus on the thermal evolution and velocities
  developed by spicules. We use Dopplergrams made in the Na D 589.6 nm,
  H-alpha 656.3 nm and Mg B 517.3 nm passbands, as well as filtergrams in
  the Ca H 396.8 nm passband to study the spatio-temporal relationship
  between the various spicular features. We compare those findings with
  synthesized images based on line profiles computed from high-resolution
  3D MHD numerical simulations from the University of Oslo. We also use
  the Dopplergram data to investigate the velocities that develop in
  the two types of spicules that were reported previously. We perform
  statistical analysis of apparent velocities in the plane of the sky
  and line-of-sight velocities derived from Dopplergrams to disentangle
  the superposition of Alfvenic wave amplitudes and field-aligned
  flows. We study these properties for a variety of magnetic field
  configurations (coronal holes, quiet Sun, active region). Finally,
  we focus on the formation mechanism of spicules by analyzing spicular
  features in Dopplergrams on the disk that were taken simultaneously
  with SP magnetograms.

---------------------------------------------------------
Title: Constructing Computationally Tractable Models of Si I for
    the 1082.7 nm Transition
Authors: Bard, S.; Carlsson, M.
2008ApJ...682.1376B    Altcode:
  The Si I 1082.7 nm line is often observed together with the He
  I 1083.0 nm. The silicon line is assumed to give a measure of the
  photospheric driver of the chromospheric dynamics observed in the He
  I 1083.0 nm line. To exploit the diagnostic potential of the silicon
  line it is of interest to study its line formation. We here analyze
  physical processes in the formation of the Si I 1082.7 nm line and
  find that it is formed in non-LTE (NLTE). Its line core intensity is
  lower than the corresponding LTE value because the source function is
  below the Planck function due to photon losses in the line itself. In
  order to make possible full NLTE dynamic calculations of this line
  we develop a general method for reducing the size of atomic models
  used in NLTE calculations by representing several physically similar
  energy levels as one mean level. Our procedure preserves all the
  important physical properties of the atom that have a bearing on the
  observable spectrographic properties of the line under study. We
  apply our procedure to the Si I atom for the 1082.7 nm transition
  under solar conditions, and we are able to reduce the size of the
  atomic model from 238 levels and 3152 transitions to 23 levels and
  171 transitions with no significant change in the calculated emergent
  intensity of the 1082.7 nm line. We calculate the response functions
  for the Si I 1082.7 nm line both in the quiet Sun and above sunspot
  umbrae. We find that the line-center Doppler shift has a mean response
  height to velocity perturbations of 541 km in a quiet-Sun atmosphere
  and 308 km in a sunspot atmosphere. These numbers depend on the model
  atmosphere employed.

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Title: Search for High Velocities in the Disk Counterpart of Type
    II Spicules
Authors: Langangen, Ø.; De Pontieu, B.; Carlsson, M.; Hansteen,
   V. H.; Cauzzi, G.; Reardon, K.
2008ApJ...679L.167L    Altcode: 2008arXiv0804.3256L
  Recently, De Pontieu and coworkers discovered a class of spicules
  that evolve more rapidly than previously known spicules, with rapid
  apparent motions of 50-150 km s<SUP>-1</SUP>, thickness of a few 100
  km, and lifetimes of order 10-60 s. These so-called type II spicules
  have been difficult to study because of limited spatiotemporal and
  thermal resolution. Here we use the IBIS instrument to search for the
  high velocities in the disk counterpart of type II spicules. We have
  detected rapidly evolving events, with lifetimes that are less than a
  minute and often equal to the cadence of the instrument (19 s). These
  events are characterized by a Doppler shift that only appears in the
  blue wing of the Ca II IR line. Furthermore, the spatial extent,
  lifetime, and location near network all suggest a link to type II
  spicules. However, the magnitude of the measured Doppler velocity is
  significantly lower than the apparent motions seen at the limb. We
  use Monte Carlo simulations to show that this discrepancy can be
  explained by a forward model in which the visibility on the disk of
  the high-velocity flows in these events is limited by a combination
  of line-of-sight projection and reduced opacity in upward propelled
  plasma, especially in reconnection driven jets that are powered by a
  roughly constant energy supply.

---------------------------------------------------------
Title: Twisted Flux Tube Emergence From the Convection Zone to
    the Corona
Authors: Martínez-Sykora, Juan; Hansteen, Viggo; Carlsson, Mats
2008ApJ...679..871M    Altcode: 2007arXiv0712.3854M
  Three-dimensional numerical simulations of a horizontal magnetic flux
  tube emergence with different twist are carried out in a computational
  domain spanning the upper layers of the convection zone to the lower
  corona. We use the Oslo Stagger Code to solve the full MHD equations
  with non-gray, non-LTE radiative transfer and thermal conduction along
  the magnetic lines. A magnetic flux tube is input at the bottom boundary
  into a weakly magnetized atmosphere. The photospheric and chromospheric
  response is described with magnetograms and synthetic continuum as
  well as Ca II H line images and velocity field distributions. In the
  photosphere the granular size increases when the flux tube approaches
  from below, as has been reported previously in the literature. In
  the convective overshoot region, some 200 km above the photosphere,
  adiabatic expansion produces cooling, darker regions with the structure
  of granulation cells. We also find evidence of collapsed granulation
  at the boundaries of the rising flux tube. Once the flux tube has
  crossed the photosphere, bright points related to concentrated magnetic
  field, vorticity, high vertical velocities, and heating by compressed
  material are found at heights up to 500 km above the photosphere. At
  greater heights, in the magnetized chromosphere, the rising flux tube
  produces a large, cool, magnetized bubble that tends to expel the
  usual chromospheric oscillations. In addition, the rising flux tube
  dramatically increases the chromospheric scale height, pushing the
  transition region and corona aside, such that the chromosphere extends
  up to 6 Mm above the photosphere. We find flux tube emergence through
  the photosphere to the lower corona to be a relatively slow process,
  taking of order 1 hr.

---------------------------------------------------------
Title: Velocities and thermal evolution of chromospheric spicules
Authors: de Pontieu, B.; McIntosh, S. W.; Tarbell, T.; Carlsson,
   M. P.; Hansteen, V. H.
2008AGUSMSP53A..06D    Altcode:
  We use the Broadband Filter Imager (BFI) and Narrowband Filter
  Imager (NFI) of the Solar Optical Telescope on Hinode to study the
  thermal evolution and velocities developed by chromospheric plasma in
  spicules. We use Dopplergrams made in the Na D 589.6 nm, Hα 656.3 nm
  and Mg B 517.3 nm passbands, as well as filtergrams in the Ca H 396.8 nm
  passband to study the spatio-temporal relationship between the various
  spicular features. We compare those findings with synthesized images
  based on line profiles computed from high-resolution 3D MHD numerical
  simulations from the University of Oslo. We also use the Dopplergram
  data to investigate the velocities that develop in the two types of
  spicules that were reported previously. We perform statistical analysis
  of apparent velocities in the plane of the sky and line-of-sight
  velocities derived from Dopplergrams to disentangle the superposition
  of Alfvenic wave amplitudes and field-aligned flows. We study these
  properties for a variety of magnetic field configurations (coronal
  holes, quiet Sun, active region). Finally, we focus on the formation
  mechanism of spicules by analyzing spicular features in Dopplergrams
  on the disk that were taken simultaneously with SP magnetograms. This
  work was supported by NASA contract NNM07AA01C. The Hinode mission is
  operated by ISAS/JAXA, NAOJ, NASA, STFC, ESA and NSC.

---------------------------------------------------------
Title: Chromospheric Flows in the Vicinity of Magnetic Features in
    the Quiet Sun Observed with Hinode SOT
Authors: Tarbell, T.; de Pontieu, B.; Carlsson, M.; Hansteen, V.;
   McIntosh, S.; Ichimoto, K.
2008AGUSMSP41B..02T    Altcode:
  The Narrowband Filter Imager of the Solar Optical Telescope on Hinode
  can measure Doppler shifts and line-of- sight magnetic fields in two
  lines with contributions from the low chromosphere: Na D 589.6 nm and
  Mg b 517.3 nm. The SOT Spectro-Polarimeter also measures very accurate
  vector magnetic fields and Doppler velocities in the photosphere. These
  observations have diffraction-limited spatial resolution and superb
  stability. We present examples of these measurements in quiet sun
  at various disk positions. In addition to the expected granulation
  and f- and p-modes, conspicuous longer-lived downflows are seen near
  strong network flux elements. Transient upflows are also detected,
  presumably the base of flows seen in spicules at the limb and H-alpha
  mottles on the disk. Velocity features associated with emerging and
  cancelling magnetic features are also described. The observations are
  compared with synthesized images made from line profiles computed from
  the University of Oslo 3-D MHD simulations. This work was supported by
  NASA contract NNM07AA01C. The Hinode mission is operated by ISAS/JAXA,
  NAOJ, NASA, STFC, ESA and NSC.

---------------------------------------------------------
Title: Spectroscopic Measurements of Dynamic Fibrils in the Ca II
    λ8662 Line
Authors: Langangen, Øystein; Carlsson, Mats; Rouppe van der Voort,
   Luc; Hansteen, Viggo; De Pontieu, Bart
2008ApJ...673.1194L    Altcode: 2007arXiv0710.0247L
  We present high spatial resolution spectroscopic measurements of dynamic
  fibrils (DFs) in the Ca II λ8662 line. These data show clear Doppler
  shifts in the identified DFs, which demonstrates that at least a subset
  of DFs are actual mass motions in the chromosphere. A statistical
  analysis of 26 DFs reveals a strong and statistically significant
  correlation between the maximal velocity and the deceleration. The
  range of the velocities and the decelerations are substantially lower,
  about a factor 2, in our spectroscopic observations compared to the
  earlier results based on proper motion in narrowband images. There
  are fundamental differences in the different observational methods;
  when DFs are observed spectroscopically, the measured Doppler shifts
  are a result of the atmospheric velocity, weighted with the response
  function to velocity over an extended height. When the proper motion
  of DFs is observed in narrowband images, the movement of the top
  of the DF is observed. This point is sharply defined because of the
  high contrast between the DF and the surroundings. The observational
  differences between the two methods are examined by several numerical
  experiments using both numerical simulations and a time series of
  narrowband Hα images. With basis in the simulations we conclude that
  the lower maximal velocity is explained by the low formation height of
  the Ca IR line. We conclude that the present observations support the
  earlier result that DFs are driven by magnetoacoustic shocks excited
  by convective flows and p-modes.

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Title: Chromospheric Alfvénic Waves Strong Enough to Power the
    Solar Wind
Authors: De Pontieu, B.; McIntosh, S. W.; Carlsson, M.; Hansteen,
   V. H.; Tarbell, T. D.; Schrijver, C. J.; Title, A. M.; Shine, R. A.;
   Tsuneta, S.; Katsukawa, Y.; Ichimoto, K.; Suematsu, Y.; Shimizu, T.;
   Nagata, S.
2007Sci...318.1574D    Altcode:
  Alfvén waves have been invoked as a possible mechanism for the heating
  of the Sun's outer atmosphere, or corona, to millions of degrees and
  for the acceleration of the solar wind to hundreds of kilometers per
  second. However, Alfvén waves of sufficient strength have not been
  unambiguously observed in the solar atmosphere. We used images of
  high temporal and spatial resolution obtained with the Solar Optical
  Telescope onboard the Japanese Hinode satellite to reveal that the
  chromosphere, the region sandwiched between the solar surface and
  the corona, is permeated by Alfvén waves with strong amplitudes on
  the order of 10 to 25 kilometers per second and periods of 100 to
  500 seconds. Estimates of the energy flux carried by these waves and
  comparisons with advanced radiative magnetohydrodynamic simulations
  indicate that such Alfvén waves are energetic enough to accelerate
  the solar wind and possibly to heat the quiet corona.

---------------------------------------------------------
Title: Hinode and the Corona's Lower Boundary: Spicules and Alfven
    Waves
Authors: de Pontieu, B.; McIntosh, S. W.; Hansteen, V.; Carlsson, M. P.
2007AGUFMSH52C..08D    Altcode:
  The lower boundary of the corona, or chromosphere, requires of order
  100 times more energy than the corona itself, and provides the mass
  to fill coronal loops. Yet the chromosphere and its coupling to the
  corona is often overlooked. Recently, observations with the Solar
  Optical Telescope (SOT) onboard Hinode and ground-based telescopes
  combined with advanced numerical simulations have provided us with
  unprecedented views and a better understanding of the (spicular)
  dynamics of the chromosphere and how the lower boundary couples to
  the corona and solar wind. We analyze high-resolution, high-cadence
  Ca II and Hα observations of the solar chromosphere and find that the
  dynamics of the magnetized chromosphere are dominated by at least two
  different types of spicules. We show that the first type involves up-
  and downward motion that is driven by shock waves that form when global
  oscillations and convective flows leak into the chromosphere along
  magnetic field lines on on 3-7 minute timescales. The second type of
  spicules is much more dynamic: they form rapidly (in ~10s), are very
  thin (&lt;200km wide), have lifetimes of 10-150s (at any one height) and
  seem to be rapidly heated to (at least) transition region temperatures,
  sending material through the chromosphere at speeds of order 50-150
  km/s. The properties of Type II spicules suggest a formation process
  that is a consequence of magnetic reconnection. We discuss the impact of
  both spicules types on the coronal mass and energy balance. Our analysis
  of Hinode data also indicates that the chromosphere is permeated by
  strong Alfvén waves. Both types of spicules are observed to carry
  these Alfvén waves, which have significant amplitudes of order 20 km/s,
  transverse displacements of order 500-1,000 km and periods of 150-400
  s. Estimates of the energy flux carried by these Alfvén waves and
  comparisons to advanced radiative MHD simulations indicate that these
  waves most likely play a significant role in the acceleration of the
  solar wind, and possibly the heating of the quiet Sun corona. We will
  discuss the implications of these waves on the energy balance of the
  lower atmosphere.

---------------------------------------------------------
Title: On Connecting the Dynamics of the Chromosphere and Transition
    Region with Hinode SOT and EIS
Authors: Hansteen, Viggo H.; de Pontieu, Bart; Carlsson, Mats;
   McIntosh, Scott; Watanabe, Tetsuya; Warren, Harry P.; Harra, Louise K.;
   Hara, Hirohisa; Tarbell, Theodore D.; Shine, Dick; Title, Alan M.;
   Schrijver, Carolus J.; Tsuneta, Saku; Katsukawa, Yukio; Ichimoto,
   Kiyoshi; Suematsu, Yoshinori; Shimizu, Toshifumi
2007PASJ...59S.699H    Altcode: 2007arXiv0711.0487H
  We use coordinated Hinode SOT/EIS observations that include
  high-resolution magnetograms, chromospheric, and transition region
  (TR) imaging, and TR/coronal spectra in a first test to study how
  the dynamics of the TR are driven by the highly dynamic photospheric
  magnetic fields and the ubiquitous chromospheric waves. Initial
  analysis shows that these connections are quite subtle and require a
  combination of techniques including magnetic field extrapolations,
  frequency-filtered time-series, and comparisons with synthetic
  chromospheric and TR images from advanced 3D numerical simulations. As a
  first result, we find signatures of magnetic flux emergence as well as
  3 and 5mHz wave power above regions of enhanced photospheric magnetic
  field in both chromospheric, transition region, and coronal emission.

---------------------------------------------------------
Title: Can High Frequency Acoustic Waves Heat the Quiet Sun
    Chromosphere?
Authors: Carlsson, Mats; Hansteen, Viggo H.; de Pontieu, Bart;
   McIntosh, Scott; Tarbell, Theodore D.; Shine, Dick; Tsuneta, Saku;
   Katsukawa, Yukio; Ichimoto, Kiyoshi; Suematsu, Yoshinori; Shimizu,
   Toshifumi; Nagata, Shin'ichi
2007PASJ...59S.663C    Altcode: 2007arXiv0709.3462C
  We use Hinode/SOT Ca II H-line and blue continuum broadband observations
  to study the presence and power of high frequency acoustic waves at
  high spatial resolution. We find that there is no dominant power at
  small spatial scales; the integrated power using the full resolution of
  Hinode (0.05” pixels, 0.16” resolution) is larger than the power in
  the data degraded to 0.5” pixels (TRACE pixel size) by only a factor
  of 1.2. At 20 mHz the ratio is 1.6. Combining this result with the
  estimates of the acoustic flux based on TRACE data of Fossum &amp;
  Carlsson (2006), we conclude that the total energy flux in acoustic
  waves of frequency 5-40 mHz entering the internetwork chromosphere of
  the quiet Sun is less than 800 W m$^{-2}$, inadequate to balance the
  radiative losses in a static chromosphere by a factor of five.

---------------------------------------------------------
Title: A Tale of Two Spicules: The Impact of Spicules on the Magnetic
    Chromosphere
Authors: de Pontieu, Bart; McIntosh, Scott; Hansteen, Viggo H.;
   Carlsson, Mats; Schrijver, Carolus J.; Tarbell, Theodore D.; Title,
   Alan M.; Shine, Richard A.; Suematsu, Yoshinori; Tsuneta, Saku;
   Katsukawa, Yukio; Ichimoto, Kiyoshi; Shimizu, Toshifumi; Nagata,
   Shin'ichi
2007PASJ...59S.655D    Altcode: 2007arXiv0710.2934D
  We use high-resolution observations of the Sun in CaIIH (3968Å)
  from the Solar Optical Telescope on Hinode to show that there are
  at least two types of spicules that dominate the structure of the
  magnetic solar chromosphere. Both types are tied to the relentless
  magnetoconvective driving in the photosphere, but have very different
  dynamic properties. “Type-I” spicules are driven by shock waves
  that form when global oscillations and convective flows leak into
  the upper atmosphere along magnetic field lines on 3--7minute
  timescales. “Type-II” spicules are much more dynamic: they form
  rapidly (in ∼ 10s), are very thin (≤ 200 km wide), have lifetimes
  of 10-150s (at any one height), and seem to be rapidly heated to
  (at least) transition region temperatures, sending material through
  the chromosphere at speeds of order 50--150kms<SUP>-1</SUP>. The
  properties of Type II spicules suggest a formation process that is
  a consequence of magnetic reconnection, typically in the vicinity
  of magnetic flux concentrations in plage and network. Both types of
  spicules are observed to carry Alfvén waves with significant amplitudes
  of order 20kms<SUP>-1</SUP>.

---------------------------------------------------------
Title: Non-equilibrium hydrogen ionization in 2D simulations of the
    solar atmosphere
Authors: Leenaarts, J.; Carlsson, M.; Hansteen, V.; Rutten, R. J.
2007A&A...473..625L    Altcode: 2007arXiv0709.3751L
  Context: The ionization of hydrogen in the solar chromosphere and
  transition region does not obey LTE or instantaneous statistical
  equilibrium because the timescale is long compared with important
  hydrodynamical timescales, especially of magneto-acoustic shocks. Since
  the pressure, temperature, and electron density depend sensitively on
  hydrogen ionization, numerical simulation of the solar atmosphere
  requires non-equilibrium treatment of all pertinent hydrogen
  transitions. The same holds for any diagnostic application employing
  hydrogen lines. <BR />Aims: To demonstrate the importance and to
  quantify the effects of non-equilibrium hydrogen ionization, both
  on the dynamical structure of the solar atmosphere and on hydrogen
  line formation, in particular Hα. <BR />Methods: We implement an
  algorithm to compute non-equilibrium hydrogen ionization and its
  coupling into the MHD equations within an existing radiation MHD code,
  and perform a two-dimensional simulation of the solar atmosphere from
  the convection zone to the corona. <BR />Results: Analysis of the
  simulation results and comparison to a companion simulation assuming
  LTE shows that: a) non-equilibrium computation delivers much smaller
  variations of the chromospheric hydrogen ionization than for LTE. The
  ionization is smaller within shocks but subsequently remains high in
  the cool intershock phases. As a result, the chromospheric temperature
  variations are much larger than for LTE because in non-equilibrium,
  hydrogen ionization is a less effective internal energy buffer. The
  actual shock temperatures are therefore higher and the intershock
  temperatures lower. b) The chromospheric populations of the hydrogen
  n = 2 level, which governs the opacity of Hα, are coupled to the
  ion populations. They are set by the high temperature in shocks
  and subsequently remain high in the cool intershock phases. c)
  The temperature structure and the hydrogen level populations differ
  much between the chromosphere above photospheric magnetic elements
  and above quiet internetwork. d) The hydrogen n = 2 population and
  column density are persistently high in dynamic fibrils, suggesting
  that these obtain their visibility from being optically thick in Hα
  also at low temperature. <P />Movie and Appendix A are only available
  in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: High-Resolution Observations and Numerical Simulations of
    Chromospheric Fibrils and Mottles
Authors: de Pontieu, B.; Hansteen, V. H.; Rouppe van der Voort, L.;
   van Noort, M.; Carlsson, M.
2007ASPC..368...65D    Altcode:
  With the recent advent of the Swedish 1-m Solar Telescope (SST),
  advanced image processing techniques, as well as numerical simulations
  that provide a more realistic view of the chromosphere, a comprehensive
  understanding of chromospheric jets such as spicules, mottles and
  fibrils is now within reach. In this paper, we briefly summarize results
  from a recent analysis of dynamic fibrils, short-lived jet-like features
  that dominate the chromosphere (as imaged in Hα) above and about active
  region plage. Using extremely high-resolution observations obtained
  at the SST, and advanced numerical 2D radiative MHD simulations, we
  show that fibrils are most likely formed by chromospheric shock waves
  that occur when convective flows and global oscillations leak into the
  chromosphere along the field lines of magnetic flux concentrations. <P
  />In addition, we present some preliminary observations of quiet Sun
  jets or mottles. We find that the mechanism that produces fibrils
  in active regions is most likely also at work in quiet Sun regions,
  although it is modified by the weaker magnetic field and the presence of
  more mixed-polarity. A comparison with numerical simulations suggests
  that the weaker magnetic field in quiet Sun allows for significantly
  stronger (than in active regions) transverse motions that are
  superposed on the field-aligned, shock-driven motions. This leads
  to a more dynamic, and much more complex environment than in active
  region plage. In addition, our observations of the mixed polarity
  environment in quiet Sun regions suggest that other mechanisms, such
  as reconnection, may well play a significant role in the formation of
  some quiet Sun jets. Simultaneous high-resolution magnetograms (such
  as those provided by Hinode), as well as numerical simulations that
  take into account a whole variety of different magnetic configurations,
  will be necessary to determine the relative importance in quiet Sun of,
  respectively, the fibril-mechanism and reconnection.

---------------------------------------------------------
Title: Non-equilibrium Hydrogen Ionization in the Solar Atmosphere
Authors: Leenaarts, J.; Wedemeyer-Böhm, S.; Carlsson, M.; Hansteen,
   V. H.
2007ASPC..368..103L    Altcode:
  The assumption of statistical equilibrium for atomic level populations
  of hydrogen does not hold under the conditions of the chromosphere
  due to the low density and the short dynamic timescale. In order to
  calculate the hydrogen ionization balance and the electron density one
  has to solve the time-dependent rate equations. We present results
  from 2D and 3D radiation-magneto-hydrodynamics simulations of the
  solar atmosphere incorporating the time-dependent rate equations
  for hydrogen. Both the hydrogen ionization degree and the electron
  density in our models are much more constant than LTE and statistical
  equilibrium theory predict. These simulations provide multi-dimensional
  model atmospheres with realistic electron densities and hydrogen level
  populations that can be used in detailed radiative transfer modeling.

---------------------------------------------------------
Title: Chromospheric Spectrometry at High Spatial Resolution
Authors: Langangen, Ø.; Carlsson, M.; Rouppe van der Voort, L.;
   Hansteen, V. H.; de Pontieu, B.
2007ASPC..368..145L    Altcode:
  In this summary we present spectrograms and images of the
  chromosphere obtained in a co-observation campaign with the SST and
  the DOT. The data are used to identify and measure the Doppler shifts
  of dynamic fibrils. Quantitative comparison with the results of <P
  />\citep{ol-2006ApJ...647L..73H} requires compensation for several
  observational issues.

---------------------------------------------------------
Title: 3D Numerical Models of the Chromosphere, Transition Region,
    and Corona
Authors: Hansteen, V. H.; Carlsson, M.; Gudiksen, B.
2007ASPC..368..107H    Altcode: 2007arXiv0704.1511H
  A major goal in solar physics has during the last five decades
  been to find how energy flux generated in the solar convection zone
  is transported and dissipated in the outer solar layers. Progress
  in this field has been slow and painstaking. However, advances in
  computer hardware and numerical methods, vastly increased observational
  capabilities and growing physical insight seem finally to be leading
  towards understanding. Here we present exploratory numerical MHD models
  that span the entire solar atmosphere from the upper convection zone
  to the lower corona. These models include non-grey, non-LTE radiative
  transport in the photosphere and chromosphere, optically thin radiative
  losses as well as magnetic field-aligned heat conduction in the
  transition region and corona.

---------------------------------------------------------
Title: Modeling the Solar Chromosphere
Authors: Carlsson, M.
2007ASPC..368...49C    Altcode: 2007arXiv0704.1509C
  Spectral diagnostic features formed in the solar chromosphere are few
  and difficult to interpret --- they are neither formed in the optically
  thin regime nor in local thermodynamic equilibrium (LTE). <P />To probe
  the state of the chromosphere, both from observations and theory, it
  is therefore necessary with modeling. <P />I discuss both traditional
  semi-empirical modeling, numerical experiments illustrating important
  ingredients necessary for a self-consistent theoretical modeling of
  the solar chromosphere and the first results of such models.

---------------------------------------------------------
Title: Observational Evidence For The Ubiquity Of Strong Alfven
    Waves In The Magnetized Chromosphere
Authors: De Pontieu, Bart; McIntosh, S. W.; Carlsson, M.; Hansteen,
   V. H.; Schrijver, C. J.; Tarbell, T. D.; Title, A.; SOT Team
2007AAS...210.9415D    Altcode: 2007BAAS...39R.219D
  Hinode/SOT Ca II broadband observations show that Alfven waves with
  significant amplitudes of order 10-20 km/s and periods of 150-300 s are
  extremely ubiquitous in the magnetized middle to upper chromosphere. Our
  observations focus on spicules at the limb, and straw-like features
  associated with network and plage on the disk. We find that the
  weak straw-like features and most spicules all undergo significant
  transverse motions that are driven by Alfven waves. These waves are
  seen to propagate both up- and downward, and may carry an energy flux
  that is significant compared to both the local, coronal and solar wind
  energy balance. We will provide estimates of the energy flux carried
  by these waves, and will compare our observations with Alfven waves
  that are observed in 3D numerical simulations that include advanced
  radiative transfer treatment for the chromosphere. <P />This work was
  supported by NASA contract NNM07AA01C.

---------------------------------------------------------
Title: Connecting The Dynamics Of The Chromosphere And Transition
    Region With Hinode/sot And Eis
Authors: Hansteen, Viggo H.; McIntosh, S.; De Pontieu, B.; Carlsson,
   M.; SOT Team
2007AAS...210.9430H    Altcode: 2007BAAS...39..222H
  We will use coordinated Hinode SOT/EIS observations that include
  high-resolution magnetograms, chromospheric and TR imaging and
  TR/coronal spectra to study how the dynamics of the TR are driven by
  the higly dynamic photospheric magnetic fields and the ubiquitous
  chromospheric waves. Using travel time analysis, magnetic field
  extrapolations, frequency filtered timeseries and comparisons with
  synthetic chromospheric and TR images from advanced 3D numerical
  simulations, we will study and establish how the dynamics of the
  photosphere, chromosphere and TR are connected.

---------------------------------------------------------
Title: Magnetoacoustic Shocks as a Driver of Quiet-Sun Mottles
Authors: Rouppe van der Voort, L. H. M.; De Pontieu, B.; Hansteen,
   V. H.; Carlsson, M.; van Noort, M.
2007ApJ...660L.169R    Altcode: 2007astro.ph..3535R
  We present high spatial and high temporal resolution observations of
  the quiet Sun in Hα obtained with the Swedish 1-m Solar Telescope on
  La Palma. We observe that many mottles, jetlike features in the quiet
  Sun, display clear up- and downward motions along their main axis. In
  addition, many mottles show vigorous transverse displacements. Unique
  identification of the mottles throughout their lifetime is much harder
  than for their active region counterpart, dynamic fibrils. This is
  because many seem to lack a sharply defined edge at their top, and
  significant fading often occurs throughout their lifetime. For those
  mottles that can be reliably tracked, we find that the mottle tops
  often undergo parabolic paths. We find a linear correlation between
  the deceleration these mottles undergo and the maximum velocity they
  reach, similar to what was found earlier for dynamic fibrils. Combined
  with an analysis of oscillatory properties, we conclude that at least
  part of the quiet-Sun mottles are driven by magnetoacoustic shocks. In
  addition, the mixed-polarity environment and vigorous dynamics suggest
  that reconnection may play a significant role in the formation of some
  quiet-Sun jets.

---------------------------------------------------------
Title: A Tale of Two Spicules
Authors: McIntosh, Scott W.; De Pontieu, B.; Carlsson, M.; Hansteen,
   V. H.; Schrijver, C. J.; Tarbell, T. D.; Title, A. M.; SOT Team
2007AAS...210.9414M    Altcode: 2007BAAS...39..219M
  Hinode/SOT Ca II broadband images and movies show that there are
  several different types of spicules at the limb. These different
  types are distinguished by dynamics on different timescales. The
  first type involves up- and downward motion on timescales of 3-5
  minutes. The dynamics of these spicules are very similar to those of
  fibrils and mottles as observed on the disk. Recent work suggests that
  these are driven by slow-mode magnetoacoustic shocks that form when
  convective flows and global oscillations leak into the chromosphere
  along magnetic flux tubes. The second type is much more dynamic with
  typical lifetimes of 10-60 s. These spicules are characterized by
  sudden appearance and disappearance that may be indicative of rapid
  heating to TR temperatures. We will describe the properties of these
  spicules in various magnetic environments (coronal hole, quiet Sun,
  active region) and study the possible role of reconnection in driving
  the second type of spicules. In addition, we will perform detailed
  comparisons of these different types of jets with synthetic Ca images
  derived from advanced 3D numerical simulations that encompass the
  convection zone up through the corona.

---------------------------------------------------------
Title: Can High Frequency Acoustic Waves Heat the Quiet Sun
    Chromosphere?
Authors: Carlsson, Mats P. O.; De Pontieu, B.; Tarbell, T.; Hansteen,
   V. H.; McIntosh, S.; SOT Team
2007AAS...210.6306C    Altcode: 2007BAAS...39..172C
  We use Hinode/SOT Ca II, G-band and blue continuum broadband
  observations to study the presence and power of high frequency acoustic
  waves at high spatial resolution. Previous observations with TRACE,
  which were limited by the 1 arcsec resolution, and 1D numerical
  simulations (Fossum &amp; Carlsson, 2005) have been used to constrain
  the possible role of high frequency waves in the heating of the quiet
  Sun chromosphere. We will use the higher spatial resolution Hinode
  data and comparisons with both 1D and 3D numerical models to study
  the amount of high frequency power at smaller scales, and whether that
  power is sufficient to heat the quiet Sun chromosphere.

---------------------------------------------------------
Title: Observations and Simulations of Fibrils and Mottles
Authors: De Pontieu, Bart; Hansteen, Viggo H.; Rouppe van der Voort,
   Luc; van Noort, Michiel; Carlsson, Mats
2007astro.ph..2081D    Altcode:
  With the recent advent of the Swedish 1-m Solar Telescope (SST),
  advanced image processing techniques, as well as numerical simulations
  that provide a more realistic view of the chromosphere, a comprehensive
  understanding of chromospheric jets such as spicules, mottles and
  fibrils is now within reach. In this paper, we briefly summarize
  results from a recent analysis of dynamic fibrils, short-lived
  jet-like features that dominate the chromosphere (as imaged in
  H-alpha) above and about active region plage. Using extremely
  high-resolution observations obtained at the SST, and advanced
  numerical 2D radiative MHD simulations, we show that fibrils are most
  likely formed by chromospheric shock waves that occur when convective
  flows and global oscillations leak into the chromosphere along the
  field lines of magnetic flux concentrations. In addition, we present
  some preliminary observations of quiet Sun jets or mottles. We find
  that the mechanism that produces fibrils in active regions is most
  likely also at work in quiet Sun regions, although it is modified by
  the weaker magnetic field and the presence of more mixed-polarity. A
  comparison with numerical simulations suggests that the weaker magnetic
  field in quiet Sun allows for significantly stronger (than in active
  regions) transverse motions that are superposed on the field-aligned,
  shock-driven motions. This leads to a more dynamic, and much more
  complex environment than in active region plage. In addition, our
  observations of the mixed polarity environment in quiet Sun regions
  suggest that other mechanisms, such as reconnection, may well play a
  significant role in the formation of some quiet Sun jets.

---------------------------------------------------------
Title: Velocities Measured in Small-Scale Solar Magnetic Elements
Authors: Langangen, Øystein; Carlsson, Mats; Rouppe van der Voort,
   Luc; Stein, R. F.
2007ApJ...655..615L    Altcode: 2006astro.ph.11741L
  We have obtained high-resolution spectrograms of small-scale magnetic
  structures with the Swedish 1-m Solar Telescope. We present Doppler
  measurements at 0.2" spatial resolution of bright points, ribbons,
  and flowers, and their immediate surroundings, in the C I λ5380.3 line
  (formed in the deep photosphere) and the two Fe I lines at 5379.6 and
  5386.3 Å. The velocity inside the flowers and ribbons are measured to
  be almost zero, while we observe downflows at the edges. These downflows
  are increasing with decreasing height. We also analyze realistic
  magnetoconvective simulations to obtain a better understanding of the
  interpretation of the observed signal. We calculate how the Doppler
  signal depends on the velocity field in various structures. Both the
  smearing effect of the nonnegligible width of this velocity response
  function along the line of sight and of the smearing from the telescope
  and atmospheric point-spread function are discussed. These studies lead
  us to the conclusion that the velocity inside the magnetic elements
  is really upflow of order 1-2 km s<SUP>-1</SUP>, while the downflows
  at the edges really are much stronger than observed, of order 1.5-3.3
  km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: High-Resolution Observations and Modeling of Dynamic Fibrils
Authors: De Pontieu, B.; Hansteen, V. H.; Rouppe van der Voort, L.;
   van Noort, M.; Carlsson, M.
2007ApJ...655..624D    Altcode: 2007astro.ph..1786D
  We present unprecedented high-resolution Hα observations, obtained
  with the Swedish 1 m Solar Telescope, that, for the first time,
  spatially and temporally resolve dynamic fibrils in active regions on
  the Sun. These jetlike features are similar to mottles or spicules in
  quiet Sun. We find that most of these fibrils follow almost perfect
  parabolic paths in their ascent and descent. We measure the properties
  of the parabolic paths taken by 257 fibrils and present an overview
  of the deceleration, maximum velocity, maximum length, and duration,
  as well as their widths and the thickness of a bright ring that often
  occurs above dynamic fibrils. We find that the observed deceleration
  of the projected path is typically only a fraction of solar gravity
  and incompatible with a ballistic path at solar gravity. We report on
  significant differences of fibril properties between those occurring
  above a dense plage region and those above a less dense plage region
  where the magnetic field seems more inclined from the vertical. We
  compare these findings to advanced numerical two-dimensional radiative
  MHD simulations and find that fibrils are most likely formed by
  chromospheric shock waves that occur when convective flows and global
  oscillations leak into the chromosphere along the field lines of
  magnetic flux concentrations. Detailed comparison of observed and
  simulated fibril properties shows striking similarities of the values
  for deceleration, maximum velocity, maximum length, and duration. We
  compare our results with observations of mottles and find that a
  similar mechanism is most likely at work in the quiet Sun.

---------------------------------------------------------
Title: High Spatial Resolution Observations of Solar Magnetic
    Structures
Authors: Rouppe van der Voort, L.; van Noort, M.; Carlsson, M.;
   Hansteen, V.
2006ASPC..354...37R    Altcode:
  We present observations of the dynamic evolution of photospheric
  magnetic structures in the G-band, continuum, magnetograms and
  Dopplergrams. The observations were obtained with the Swedish one-m
  Solar Telescope on La Palma. Using adaptive optics and the Multi-Object
  Multi-Frame Blind Deconvolution image restoration technique, we obtained
  several datasets at close to the diffraction limit of the telescope
  (0.1 arcsec) over long periods of time. We show examples of the
  dynamical evolution of different magnetic structures: the advection
  of individual bright points by the granular flow, the formation and
  fragmentation of flux sheets, and the continuous transition between
  micro-pores, elongated ribbons and more circular “flowers”. Narrow
  sheets with downdrafts are found right at the edges of magnetic field
  concentrations.

---------------------------------------------------------
Title: Dynamic Fibrils Are Driven by Magnetoacoustic Shocks
Authors: de Pontieu, B.; Hansteen, V. H.; Rouppe van der Voort, L.;
   van Noort, M.; Carlsson, M.
2006AGUFMSH23B0359D    Altcode:
  With the recent advent of the Swedish 1-m Solar Telescope (SST),
  advanced image processing techniques, as well as numerical simulations
  that provide a more realistic view of the chromosphere, a comprehensive
  understanding of chromospheric jets such as spicules, mottles and
  fibrils is now within reach. We will present results from a recent
  analysis of dynamic fibrils, short-lived jet-like features that
  dominate the chromosphere (as imaged in Hα) above and about active
  region plage. These jets are similar to mottles and spicules in quiet
  Sun. Our analysis is based on a time series of extremely high-resolution
  (120 km) images taken in Hα linecenter at 1 second cadence, obtained by
  the Oslo group at the SST in October 2005. The 78 min long time series
  for the first time, spatially and temporally resolves dynamic fibrils
  in active regions. Our analysis shows that most of the fibrils follow
  almost perfect parabolic paths in their ascent and descent. We measure
  the properties of the parabolic paths taken by 257 different dynamic
  fibrils, and find that the observed deceleration of the projected
  path is typically only a fraction of solar gravity, and incompatible
  with a ballistic path at solar gravity. We report on significant
  differences of measured fibril properties between those occurring in
  association with a dense plage region, and those above a less dense
  plage region where the magnetic field seems more inclined away from
  the vertical. We compare these observational findings to advanced
  numerical 2D radiative MHD simulations, and find that fibrils are most
  likely formed by chromospheric shock waves that occur when convective
  flows and global oscillations leak into the chromosphere along the
  field lines of magnetic flux concentrations. Detailed comparison
  of the properties of fibrils found in our observations and those in
  our numerical simulations shows striking similarities of the values
  for deceleration, maximum velocity, maximum length and duration. The
  numerical simulations also reproduce the correlations we observe between
  various fibrils properties, as well as the regional differences, taking
  into account the different magnetic configuration for the various
  regions. We compare our results with observations of mottles and find
  that a similar mechanism is most likely at work in the quiet Sun.

---------------------------------------------------------
Title: Chromospheric Modeling
Authors: Carlsson, M.
2006ASPC..354..291C    Altcode:
  We discuss chromospheric modeling -- both semi-empirical models and
  theoretical models. The development of new computational schemes,
  new approximate treatments of time dependent hydrogen ionization and
  more powerful computers have paved the way for comprehensive models in
  three dimensions extending from the convection zone to the corona. The
  first results of such models have just appeared.

---------------------------------------------------------
Title: The non-LTE line formation of neutral carbon in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
2006A&A...458..899F    Altcode: 2006astro.ph..8284F
  Aims.We investigate the non-Local Thermodynamic Equilibrium (non-LTE)
  line formation of neutral carbon in late-type stars in order to remove
  some of the potential systematic errors in stellar abundance analyses
  employing C i features.<BR /> Methods: .The statistical equilibrium
  code MULTI was used on a grid of plane-parallel 1D MARCS atmospheric
  models.<BR /> Results: .Within the parameter space explored, the
  high-excitation C i lines studied are stronger in non-LTE due to
  the combined effect of line source function drop and increased line
  opacity due to overpopulation of the lower level for the transitions
  considered; the relative importance of the two effects depends on
  the particular combination of T<SUB>{eff</SUB>}, log g, [Fe/H] and
  [C/Fe] and on the analysed C i line. As a consequence, the non-LTE
  abundance corrections are negative and can be substantially so,
  for example ∼ -0.4 dex in halo turn-off stars at [Fe/H]∼ -3. The
  magnitude of the non-LTE corrections is rather insensitive to whether
  inelastic H collisions are included or not.<BR /> Conclusions: .Our
  results have implications on studies of nucleosynthetic processes and
  on Galactic chemical evolution models. When applying our calculated
  corrections to recent observational data, the upturn in [C/O] at low
  metallicity might still be present (thus apparently still necessitating
  contributions from massive Pop. III stars for the carbon production),
  but at a lower level and possibly with a rather shallow trend of ∼
  -0.2 dex/dex below [O/H]∼ -1.

---------------------------------------------------------
Title: Rapid Temporal Variability of Faculae: High-Resolution
    Observations and Modeling
Authors: De Pontieu, B.; Carlsson, M.; Stein, R.; Rouppe van der Voort,
   L.; Löfdahl, M.; van Noort, M.; Nordlund, Å.; Scharmer, G.
2006ApJ...646.1405D    Altcode:
  We present high-resolution G-band observations (obtained with the
  Swedish 1 m Solar Telescope) of the rapid temporal variability of
  faculae, which occurs on granular timescales. By combining these
  observations with magnetoconvection simulations of a plage region, we
  show that much of this variability is not intrinsic to the magnetic
  field concentrations that are associated with faculae, but rather
  a phenomenon associated with the normal evolution and splitting of
  granules. We also show examples of facular variability caused by
  changes in the magnetic field, with movies of dynamic behavior of
  the striations that dominate much of the facular appearance at 0.1"
  resolution. Examples of these dynamics include merging, splitting,
  rapid motion, apparent fluting, and possibly swaying.

---------------------------------------------------------
Title: Dynamic Fibrils Are Driven by Magnetoacoustic Shocks
Authors: Hansteen, V. H.; De Pontieu, B.; Rouppe van der Voort, L.;
   van Noort, M.; Carlsson, M.
2006ApJ...647L..73H    Altcode: 2006astro.ph..7332H
  The formation of jets such as dynamic fibrils, mottles, and spicules
  in the solar chromosphere is one of the most important, but also
  most poorly understood, phenomena of the Sun's magnetized outer
  atmosphere. We use extremely high resolution observations from the
  Swedish 1 m Solar Telescope combined with advanced numerical modeling
  to show that in active regions these jets are a natural consequence of
  upwardly propagating slow-mode magnetoacoustic shocks. These shocks
  form when waves generated by convective flows and global p-mode
  oscillations in the lower lying photosphere leak upward into the
  magnetized chromosphere. We find excellent agreement between observed
  and simulated jet velocities, decelerations, lifetimes, and lengths. Our
  findings suggest that previous observations of quiet-Sun spicules and
  mottles may also be interpreted in light of a shock-driven mechanism.

---------------------------------------------------------
Title: Determination of the Acoustic Wave Flux in the Lower Solar
    Chromosphere
Authors: Fossum, Astrid; Carlsson, Mats
2006ApJ...646..579F    Altcode:
  High-cadence observations of the quiet Sun have been obtained with
  the Transition Region And Coronal Explorer (TRACE) satellite in two
  UV passbands around 1600 and 1700 Å. The observational program has
  been optimized for the detection of high-frequency acoustic waves:
  the cadence is strictly regular, there is no data compression, and the
  exposure time is optimized for quiet-Sun regions. Significant intensity
  variations are detected up to 40 mHz frequency. Non-LTE radiation
  hydrodynamics simulations are performed in order to calculate the
  acoustic energy flux that the observed intensity variations correspond
  to. The derived acoustic energy flux spectrum at the formation height
  of the UV continua (about 400 km) is decreasing with frequency. For
  frequencies above 40 mHz we derive an upper limit. The integrated
  acoustic energy flux is 255 W m<SUP>-2</SUP> in the frequency range
  5-50 mHz. This is lower than what is needed to balance the radiative
  losses from the quiet-Sun chromosphere by at least a factor of 10. The
  major uncertainty in the analysis is the possibility of high-frequency
  power with spatial scales smaller than the resolution element of
  TRACE. We make estimates of this effect and find it unlikely that
  it is larger than a factor of 2. In the convection zone, where the
  waves are generated, the energy spectrum is rather flat and may have
  a peak at high frequencies. We also show that the sensitivity of the
  observations to high-frequency waves is directly given by the Fourier
  transform of the response function.

---------------------------------------------------------
Title: Radiative Hydrodynamic Models of Optical and Ultraviolet
    Emission from M Dwarf Flares
Authors: Allred, Joel C.; Hawley, Suzanne L.; Abbett, William P.;
   Carlsson, Mats
2006ApJ...644..484A    Altcode: 2006astro.ph..3195A
  We report on radiative hydrodynamic simulations of M dwarf stellar
  flares and compare the model predictions to observations of several
  flares. The flares were simulated by calculating the hydrodynamic
  response of a model M dwarf atmosphere to a beam of nonthermal
  electrons. Radiative back-warming through numerous soft X-ray,
  extreme-ultraviolet, and ultraviolet transitions are also included. The
  equations of radiative transfer and statistical equilibrium are treated
  in non-LTE for many transitions of hydrogen, helium, and the Ca II
  ion, allowing the calculation of detailed line profiles and continuum
  radiation. Two simulations were carried out, with electron beam fluxes
  corresponding to moderate and strong beam heating. In both cases we
  find that the dynamics can be naturally divided into two phases: an
  initial gentle phase in which hydrogen and helium radiate away much
  of the beam energy and an explosive phase characterized by large
  hydrodynamic waves. During the initial phase, lower chromospheric
  material is evaporated into higher regions of the atmosphere, causing
  many lines and continua to brighten dramatically. The He II 304 line
  is especially enhanced, becoming the brightest line in the flaring
  spectrum. The hydrogen Balmer lines also become much brighter and show
  very broad line widths, in agreement with observations. We compare
  our predicted Balmer decrements to decrements calculated for several
  flare observations and find the predictions to be in general agreement
  with the observations. During the explosive phase both condensation and
  evaporation waves are produced. The moderate flare simulation predicts
  a peak evaporation wave of ~130 km s<SUP>-1</SUP> and a condensation
  wave of ~30 km s<SUP>-1</SUP>. The velocity of the condensation wave
  matches velocities observed in several transition region lines. The
  optical continuum also greatly intensifies, reaching a peak increase
  of 130% (at 6000 Å) for the strong flare, but does not match observed
  white-light spectra.

---------------------------------------------------------
Title: A comparison of solar proxy-magnetometry diagnostics
Authors: Leenaarts, J.; Rutten, R. J.; Carlsson, M.; Uitenbroek, H.
2006A&A...452L..15L    Altcode:
  Aims.We test various proxy-magnetometry diagnostics, i.e., brightness
  signatures of small-scale magnetic elements, for studying magnetic
  field structures in the solar photosphere.<BR /> Methods: .Images are
  numerically synthesized from a 3D solar magneto-convection simulation
  for, respectively, the G band at 430.5 nm, the CN band at 388.3 nm,
  and the blue wings of the H α, H β, Ca ii H, and Ca ii 854.2 nm
  lines.<BR /> Results: .Both visual comparison and scatter diagrams of
  the computed intensity versus the magnetic field strength show that,
  in particular for somewhat spatially extended magnetic elements, the
  blue H α wing presents the best proxy-magnetometry diagnostic, followed
  by the blue wing of H β. The latter yields higher diffraction-limit
  resolution.<BR /> Conclusions: .We recommend using the blue H α wing
  to locate and track small-scale photospheric magnetic elements through
  their brightness appearance.

---------------------------------------------------------
Title: Simulation of Quiet-Sun Waves in the Ca II Infrared Triplet
Authors: Pietarila, A.; Socas-Navarro, H.; Bogdan, T.; Carlsson, M.;
   Stein, R. F.
2006ApJ...640.1142P    Altcode: 2005astro.ph.10744P
  The Ca II infrared triplet lines around 8540 Å are good candidates
  for observing chromospheric magnetism. Model spectra of these lines
  are obtained by combining a radiation hydrodynamic simulation with a
  Stokes synthesis code. The simulation shows interesting time-varying
  behavior of the Stokes V profiles as waves propagate through the
  formation region of the lines. Disappearing and reappearing lobes
  in the Stokes V profiles as well as profile asymmetries are closely
  related to the atmospheric velocity gradients.

---------------------------------------------------------
Title: DOT tomography of the solar atmosphere. VI. Magnetic elements
    as bright points in the blue wing of Hα
Authors: Leenaarts, J.; Rutten, R. J.; Sütterlin, P.; Carlsson, M.;
   Uitenbroek, H.
2006A&A...449.1209L    Altcode:
  High-resolution solar images taken in the blue wing of the Balmer H
  α line with the Dutch Open Telescope show intergranular magnetic
  elements as strikingly bright features, similar to, but with
  appreciably larger contrast over the surrounding granulation than
  their more familiar manifestation as G-band bright points. Part of
  this prominent appearance is due to low granular contrast, without
  granule/lane brightness reversal as, e.g., in the wings of Ca II H
  &amp; K. We use 1D and 2D radiative transfer modeling and 3D solar
  convection and magnetoconvection simulations to reproduce and explain
  the H α wing images. We find that the blue H α wing obeys near-LTE
  line formation. It appears particularly bright in magnetic elements
  through low temperature gradients. The granulation observed in the blue
  wing of H α has low contrast because of the lack of H α opacity in the
  upper photosphere, Doppler cancellation, and large opacity sensitivity
  to temperature working against source function sensitivity. We conclude
  that the blue H α wing represents a promising proxy magnetometer to
  locate and track isolated intermittent magnetic elements, a better one
  than the G band and the wings of Ca II H &amp; K although less sharp
  at given aperture.

---------------------------------------------------------
Title: Numerical modelling of MHD waves in the solar chromosphere
Authors: Carlsson, Mats; Bogdan, Thomas J.
2006RSPTA.364..395C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Ci Non-LTE Spectral Line Formation in Late-Type Stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.
2006cams.book...52F    Altcode:
  We present the results from our non-LTE investigation for neutral
  carbon, which was carried out to remove potential systematic errors
  in stellar abundance analyses. The calculations were performed for
  late-type stars and give substantial negative non-LTE abundance
  corrections. When applied to observations of extremely metal-poor
  stars, which within the LTE framework seem to suggest a possible [C/O]
  uprise at low metallicities (Akerman et al. 2004), these improvements
  will have important implications, enabling us to understand if the
  standard chemical evolution model is adequate, with no need to invoke
  signatures by Pop. III stars for the carbon nucleosynthesis.

---------------------------------------------------------
Title: Simulated Solar Plages
Authors: Stein, R. F.; Carlsson, M.; de Pontieu, B.; Scharmer, G.;
   Nordlund, Å.; Benson, D.
2006apri.meet...30S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Are High Frequency Acoustic Waves Sufficient to Heat the
    Solar Chromosphere?
Authors: Fossum, A.; Carlsson, M.
2005ESASP.600E..17F    Altcode: 2005ESPM...11...17F; 2005dysu.confE..17F
  No abstract at ADS

---------------------------------------------------------
Title: The Diagnostic Potential of the MG i 4571.1 Å Line
Authors: Langangen, Ø.; Carlsson, M.; Rouppe van der Voort, L.
2005ESASP.600E..65L    Altcode: 2005ESPM...11...65L; 2005dysu.confE..65L
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric Waves
Authors: Carlsson, M.; Hansteen, V.
2005ESASP.600E..16C    Altcode: 2005dysu.confE..16C; 2005ESPM...11...16C
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric Waves
Authors: Carlsson, M.; Hansteen, V.
2005ESASP.596E..39C    Altcode: 2005ccmf.confE..39C
  No abstract at ADS

---------------------------------------------------------
Title: Small Scale Magnetic Elements as Bright Points in the Blue
    Hα Wing
Authors: Leenaarts, J.; Sütterlin, P.; Rutten, R. J.; Carlsson, M.;
   Uitenbroek, H.
2005ESASP.596E..15L    Altcode: 2005ccmf.confE..15L
  No abstract at ADS

---------------------------------------------------------
Title: Radiative Hydrodynamic Models of the Optical and Ultraviolet
    Emission from Solar Flares
Authors: Allred, Joel C.; Hawley, Suzanne L.; Abbett, William P.;
   Carlsson, Mats
2005ApJ...630..573A    Altcode: 2005astro.ph..7335A
  We report on radiative hydrodynamic simulations of moderate and strong
  solar flares. The flares were simulated by calculating the atmospheric
  response to a beam of nonthermal electrons injected at the apex of a
  one-dimensional closed coronal loop and include heating from thermal
  soft X-ray, extreme ultraviolet, and ultraviolet (XEUV) emission. The
  equations of radiative transfer and statistical equilibrium were
  treated in non-LTE and solved for numerous transitions of hydrogen,
  helium, and Ca II, allowing the calculation of detailed line profiles
  and continuum emission. This work improves on previous simulations
  by incorporating more realistic nonthermal electron beam models and
  includes a more rigorous model of thermal XEUV heating. We find that
  XEUV back-warming contributes less than 10% of the heating, even in
  strong flares. The simulations show elevated coronal and transition
  region densities resulting in dramatic increases in line and continuum
  emission in both the UV and optical regions. The optical continuum
  reaches a peak increase of several percent, which is consistent with
  enhancements observed in solar white-light flares. For a moderate flare
  (~M class), the dynamics are characterized by a long gentle phase of
  near balance between flare heating and radiative cooling, followed
  by an explosive phase with beam heating dominating over cooling and
  characterized by strong hydrodynamic waves. For a strong flare (~X
  class), the gentle phase is much shorter, and we speculate that for even
  stronger flares the gentle phase may be essentially nonexistent. During
  the explosive phase, synthetic profiles for lines formed in the upper
  chromosphere and transition region show blueshifts corresponding to
  a plasma velocity of ~120 km s<SUP>-1</SUP>, and lines formed in the
  lower chromosphere show redshifts of ~40 km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: High-frequency acoustic waves are not sufficient to heat the
    solar chromosphere
Authors: Fossum, Astrid; Carlsson, Mats
2005Natur.435..919F    Altcode:
  One of the main unanswered questions in solar physics is why the Sun's
  outer atmosphere is hotter than its surface. Theory predicts abundant
  production of high-frequency (10-50mHz) acoustic waves in subsurface
  layers of the Sun, and such waves are believed by many to constitute the
  dominant heating mechanism of the chromosphere (the lower part of the
  outer solar atmosphere) in non-magnetic regions. Such high-frequency
  waves are difficult to detect because of high-frequency disturbances
  in Earth's atmosphere (seeing) and other factors. Here we report the
  detection of high-frequency waves, and we use numerical simulations
  to show that the acoustic energy flux of these waves is too low, by a
  factor of at least ten, to balance the radiative losses in the solar
  chromosphere. Acoustic waves therefore cannot constitute the dominant
  heating mechanism of the solar chromosphere.

---------------------------------------------------------
Title: Response Functions of the Ultraviolet Filters of TRACE and
    the Detectability of High-Frequency Acoustic Waves
Authors: Fossum, Astrid; Carlsson, Mats
2005ApJ...625..556F    Altcode:
  We have used detailed non-LTE radiation hydrodynamic simulations to
  investigate the detectability of high-frequency acoustic waves with
  the Transition Region And Coronal Explorer (TRACE). A broad spectrum
  of acoustic waves are fed into the computational domain at the lower
  boundary of the model atmosphere, and TRACE UV continuum intensities
  are calculated by folding the derived intensities with the TRACE filter
  transmission functions for the 1700 and 1600 filters. Power spectra,
  phase diagrams, and intensity response functions are calculated, and
  intensity formation heights are derived. The simulations show that the
  average response height of the 1700 and 1600 passbands are 360 and 430
  km, with widths of 325 and 185 km. The width of the TRACE intensity
  response functions reduces the power of the intensity oscillations
  considerably, but if waves are present with power enough to be of
  importance for the energy balance of the chromosphere, they should be
  detectable at least up to 40 mHz in the absence of instrumental noise,
  especially in the 1600 passband. The phase difference between the
  synthesized 1600 and 1700 TRACE intensities follows the curve expected
  for propagating acoustic waves up to 15 mHz. For higher frequencies
  the phase difference decreases and approaches zero before the coherence
  drops down, similar to the observed behavior. This is explained by the
  double-peaked nature of the response function for the 1700 intensities.

---------------------------------------------------------
Title: Multi-dimensional Radiation MHD as a Tool to Understanding
    Waves in Realistic Magnetic Topologies of the Solar Chromosphere
Authors: Carlsson, M.
2005AGUSMSH12A..01C    Altcode:
  Advances in computing capabilities have made it possible to perform
  multi-dimensional radiation MHD simulations with a realistic description
  of the physics in the photosphere. In the chromosphere non-LTE becomes
  important and the choice is between realistic physics in one dimension
  and approximations to the non-local radiation in multi-dimensions. We
  will here discuss such simulations from a methodological vantage
  point. We will discuss how we can make such simulations to study how
  waves are excited in the solar convection zone, how they propagate
  through the chromosphere and transition region and undergo mode
  conversion, refraction and reflection in various magnetic field
  topologies. We will also discuss the limitations of observational
  diagnostics with respect to wide response functions, non-locality and
  non-equilibrium effects.

---------------------------------------------------------
Title: Solar magnetic elements at 0.1 arcsec resolution. II. Dynamical
    evolution
Authors: Rouppe van der Voort, L. H. M.; Hansteen, V. H.; Carlsson,
   M.; Fossum, A.; Marthinussen, E.; van Noort, M. J.; Berger, T. E.
2005A&A...435..327R    Altcode:
  Small magnetic structures can be seen in G-band filtergrams as isolated
  bright points, strings of bright points and dark micro-pores. At a
  resolution of 0.1 arcsec, new forms of magnetic structures are found
  in strong field areas: elongated “ribbons” and more circular
  “flowers”. In this paper we study the temporal evolution of
  these small scale magnetic structures. In strong-field regions the
  time-evolution is more that of a magnetic fluid than that of collections
  of flux-tubes that keep their identity. We find that the granular flow
  concentrates the magnetic field into flux sheets that are visible as
  thin bright features in the filtergrams. Weak upflows are found in
  the flux sheets and downflows in the immediate surroundings. The flux
  sheets often become unstable to a fluting instability and the edges
  buckle. The sheets tend to break up into strings of bright points,
  still with weak upflows in the magnetic elements and zero velocity or
  downflows between them. Where there are larger flux concentrations
  we find ribbons, flowers and micro-pores. There is a continuous
  transition between these forms and they evolve from one form to
  another. The appearance is mostly determined by the horizontal size
  - larger structures are dark (micro-pores), narrower structures are
  ribbon shaped and the flowers are the smallest in extent. All these
  structures have darker inner parts and a bright edge. The plasma is
  found to be at rest in the ribbons, with small concentrations of weak
  upflow sites. Narrow sheets with downdrafts are found right at the
  edges of the magnetic field concentrations.

---------------------------------------------------------
Title: Detectability of high frequency acoustic waves with TRACE
Authors: Fossum, A.; Carlsson, M.
2005ASSL..320..239F    Altcode: 2005smp..conf..239F
  No abstract at ADS

---------------------------------------------------------
Title: CI non LTE spectral line formation in late-type stars
Authors: Fabbian, D.; Asplund, M.; Carlsson, M.; Kiselman, D.
2005IAUS..228..255F    Altcode: 2005astro.ph..8063F
  We present non-Local Thermodynamic Equilibrium (non-LTE) calculations
  for neutral carbon spectral line formation, carried out for a grid
  of model atmospheres covering the range of late-type stars. The
  results of our detailed calculations suggest that the carbon
  non-LTE corrections in these stars are higher than usually adopted,
  remaining substantial even at low metallicity. For the most metal-poor
  stars in the sample of Akerman et al (2004), the effects are of the
  order of Δlogɛ<SUB>C</SUB> ≃ -0.35ldots-0.45 (when neglecting H
  collisions). Applying our results to those observations, the apparent
  [C/O] upturn seen in their LTE analysis is no longer present, thus
  revealing no need to invoke contributions from Pop. III stars to the
  carbon nucleosynthesis.

---------------------------------------------------------
Title: Chromospheric Heating and Dynamics
Authors: Carlsson, M.; Stein, R. F.
2004ASPC..325..243C    Altcode:
  We review observations of the dynamics and energetics of the solar
  chromosphere. The observations are interpreted with the help of
  detailed radiation hydrodynamic modelling. It is concluded that
  acoustic waves play an important role for the dynamics and energetics
  of the chromosphere but additional heating is necessary, even for the
  internetwork regions. This additional heating is strongly correlated
  with the observed magnetic field strength.

---------------------------------------------------------
Title: Solar magnetic elements at 0.1 arcsec resolution. General
    appearance and magnetic structure
Authors: Berger, T. E.; Rouppe van der Voort, L. H. M.; Löfdahl,
   M. G.; Carlsson, M.; Fossum, A.; Hansteen, V. H.; Marthinussen, E.;
   Title, A.; Scharmer, G.
2004A&A...428..613B    Altcode:
  New observations of solar magnetic elements in a remnant active region
  plage near disk center are presented. The observations were obtained at
  the recently commissioned Swedish 1-m Solar Telescope on La Palma. We
  examine a single 430.5 nm G-band filtergram that resolves ∼70 km
  (0.1 arcsec) structures and find new forms of magnetic structures
  in this particular region. A cotemporal Ca II H-line image is used
  to examine the low-chromosphere of network elements. A cotemporal Fe
  I 630.25 nm magnetogram that resolves structures as small as 120 km
  (0.18 arcsec) FWHM with a flux sensitivity of approximately 130 Mx
  cm<SUP>-2</SUP> quantifies the magnetic structure of the region. A
  Ni I 676.8 nm Dopplergram establishes relative velocity patterns
  associated with the network features with an accuracy of about 300 m
  s<SUP>-1</SUP>. We find that magnetic flux in this region as seen in
  both the magnetogram and the G-band image is typically structured into
  larger, amorphous, “ribbons” which are not resolved into individual
  flux tubes. The measured magnetic flux density in the ribbon structures
  ranges from 300 to 1500 Mx cm<SUP>-2</SUP>, the higher values occurring
  at localized concentrations embedded within the ribbons. The Dopplergram
  indicates relative downflows associated with all magnetic elements
  with some indication that higher downflows occur adjacent to the peak
  magnetic flux location. The mean absolute magnetic flux density of the
  remnant plage network is about 130 Mx cm<SUP>-2</SUP>; in the lowest
  flux regions of the field-of-view, the mean absolute flux density is
  approximately 60 Mx cm<SUP>-2</SUP>. Within these quiet regions we do
  not find evidence of pervasive kilo-gauss strength magnetic elements
  as seen in recent high resolution internetwork studies. In general,
  the observations confirm recent 3-dimensional numerical simulations
  which show that the magnetic field in high-density regions such as
  plage is concentrated in complex structures that are not generally
  composed of discrete magnetic flux tubes. <P />Appendices are only
  available in electronic form at http://www.edpsciences.org

---------------------------------------------------------
Title: Mode Conversion in Magneto-Atmospheres
Authors: Bogdan, T. J.; Carlsson, M.; Hansteen, V.; Heggland, L.;
   Leer, E.; McMurry, A. D.; Stein, R. F.
2004AGUFMSH13A1162B    Altcode:
  Numerical simulations of wave propagation in a simple magneto-atmosphere
  are employed to illustrate the complex nature of wave transformation
  and conversion taking place in solar and stellar atmospheres. An
  isothermal atmosphere threaded by a potential poloidal magnetic
  field, and a superposed uniform toroidal field, is treated in a local
  cartesian approximation. Spatial variations are restricted to the
  two poloidal dimensions, but the toroidal field ensures that all
  three MHD waves are present in the simulation. As in our previous
  purely two-dimensional simulations (Bogdan et al. ApJ 599, 626-60,
  2003), mode mixing and transformation take place at surfaces where
  the magnetic and thermal pressures are equal. In the present case,
  the upward propagating acoustic-gravity (MAG) wave is converted into
  roughly equal parts transmitted fast, intermediate (Alfven), and
  slow magneto-acoustic-gravity waves in passing through this mixing
  layer. Unlike the fast and slow waves, the Alfven wave is weakly
  damped, and is able to deposit its energy and momentum in the upper
  chromosphere and corona. The fast and slow MAG waves are decoupled
  on either side of mixing layer owing to their disparate propagation
  speeds. Under certain fortuitous circumstances, the Alfven wave also
  decouples from the fast and slow MAG waves.

---------------------------------------------------------
Title: Observational Manifestations of Solar Magnetoconvection:
    Center-to-Limb Variation
Authors: Carlsson, Mats; Stein, Robert F.; Nordlund, Åke; Scharmer,
   Göran B.
2004ApJ...610L.137C    Altcode: 2004astro.ph..6160C
  We present the first center-to-limb G-band images synthesized from
  high-resolution simulations of solar magnetoconvection. Toward the
  limb the simulations show “hilly” granulation with dark bands on
  the far side, bright granulation walls, and striated faculae, similar
  to observations. At disk center G-band bright points are flanked
  by dark lanes. The increased brightness in magnetic elements is due
  to their lower density compared with the surrounding intergranular
  medium. One thus sees deeper layers where the temperature is higher. At
  a given geometric height, the magnetic elements are cooler than the
  surrounding medium. In the G band, the contrast is further increased
  by the destruction of CH in the low-density magnetic elements. The
  optical depth unity surface is very corrugated. Bright granules have
  their continuum optical depth unity 80 km above the mean surface,
  the magnetic elements 200-300 km below. The horizontal temperature
  gradient is especially large next to flux concentrations. When viewed
  at an angle, the deep magnetic elements' optical surface is hidden by
  the granules and the bright points are no longer visible, except where
  the “magnetic valleys” are aligned with the line of sight. Toward
  the limb, the low density in the strong magnetic elements causes unit
  line-of-sight optical depth to occur deeper in the granule walls behind
  than for rays not going through magnetic elements, and variations
  in the field strength produce a striated appearance in the bright
  granule walls.

---------------------------------------------------------
Title: A Comparison of the Outer Atmosphere of the “Flat Activity”
    Star τ Ceti (G8 V) with the Sun (G2 V) and α Centauri A (G2 V)
Authors: Judge, Philip G.; Saar, Steven H.; Carlsson, Mats; Ayres,
   Thomas R.
2004ApJ...609..392J    Altcode:
  Driven by the desire to understand the roles of acoustic and
  magnetic mechanisms in heating the outer atmospheres of Sun-like
  stars, we compare solar UV spectra with archival STIS spectra from
  the Hubble Space Telescope of α Cen A (G2 V) and new STIS spectra
  of the extremely inactive dwarf star τ Cet (G8 V, V=3.5). The
  activity of τ Cet shows occasional rotational modulations but no
  long-term cyclic variation. It may be in a phase analogous to the
  solar Maunder minimum. Solar disk center intensities from both the
  HRTS instrument and the SUMER instrument on SOHO were converted to
  Sun-as-a-star fluxes by using center-to-limb data from Dammasch and
  colleagues. The derived solar flux spectrum represents conditions
  near the minimum of the solar magnetic activity cycle. We find that
  the τ Cet line profiles differ systematically from those of the Sun
  and α Cen A. While lines formed in the middle chromospheres appear
  similar, the entire emission from the upper chromosphere to the middle
  transition region of τ Cet has lower flux densities by factors of
  ~2, the line widths are significantly narrower, and, uniquely, the
  transition region lines are not significantly redshifted. The soft
  X-ray surface flux of τ Cet, measured between 0.1 and 2.4 keV, is
  ~9×10<SUP>3</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>, several times
  smaller than the median solar value. We also find that the UV spectrum
  of α Cen serves as a proxy for a Sun-as-a-star spectrum when the Sun
  is in an intermediate phase of its activity cycle but that its coronal
  emission may be somewhat smaller. We discuss the implications of these
  results for magnetic fields and heating mechanisms in the stars and
  speculate that τ Cet's UV spectrum might represent the solar spectrum
  during a grand minimum phase.

---------------------------------------------------------
Title: Solar Physics at Evergreen
Authors: Zita, E. J.; Bogdan, T. J.; Carlsson, M.; Judge, P.; Heller,
   N.; Johnson, M.; Petty, S.
2004APS..NWS.C1005Z    Altcode:
  We have recently established a solar physics research program at
  The Evergreen State College. Famed for its cloudy skies, the Pacific
  Northwest is an ideal location for solar physics research activities
  that do not require local observations. Collaborators from the High
  Altitude Observatory (HAO) at the National Center for Atmospheric
  Research have shared solar data from satellite-borne instruments such
  as TRACE and SUMER. HAO colleagues also share data from computer
  simulations of magneto-hydrodynamics (MHD) in the chromosphere,
  generated by the Institute for Theoretical Astrophysics (ITA) at
  the University of Oslo. Evergreen students and faculty learned to
  analyze data from satellites and simulations, in Boulder and Oslo, and
  established an infrastructure for continuing our analyses in Olympia. We
  are investigating the role of magnetic waves in heating the solar
  atmosphere. Comparing data from satellites and simulations shows that
  acoustic oscillations from the photosphere cannot effectively propagate
  into the chromosphere, but that magnetic waves can carry energy up
  toward the hot, thin corona. We find that acoustic waves can change into
  magnetic waves, especially near the magnetic "canopy," a region where
  the sound speed is comparable to magnetic wave speeds. Understanding
  MHD wave transformations and their role in energy transport can help
  answer outstanding questions about the anomalous heating of the solar
  atmosphere. Ref: Waves in the magnetized solar atmosphere II: Waves
  from localized sources in magnetic flux concentrations. Bogdan et al.,
  2003, ApJ 597

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

---------------------------------------------------------
Title: G-band Images from MHD Convection Simulations
Authors: Stein, R. F.; Carlsson, M.; Nordlund, A.; Scharmer, G.
2004AAS...204.8804S    Altcode: 2004BAAS...36..820S
  High resolution magneto-convection simulations are used to calculate
  G-band and G-continuum images at various angles. Towards the limb
  the simulations show "hilly" granulation, bright granulation walls,
  intergranular striations and "sticking out" G-band bright features
  similar to observations. The increased brightness in magnetic
  elements is due to their lower density compared with the surrounding
  intergranular medium, so that one sees deeper layers where the
  temperature is higher. At a given geometric height, the magnetic
  elements are not hotter than the surrounding medium. In the G-band,
  the contrast is further increased by the destruction of CH in the
  low density magnetic elements. The optical depth unity surface is
  very corrugated. Bright granules have their continuum optical depth
  unity 80 km above the mean surface, the magnetic elements 200-300 km
  below. At large angles, the deep lying magnetic elements are hidden
  by the granules and the bright points are no longer visible. Where
  the "magnetic valleys" are aligned with the line of sight, they are
  visible as elongated structures seemingly "sticking out". Even when
  the deep hot surface is hidden, the low density in the strong magnetic
  elements causes unit line-of-sight optical depth to occur deeper in
  the granule walls behind then for rays not going through magnetic
  elements. Flux concentrations in intergranular lanes therefore cause
  a striped intensity pattern. This work is funded by NSF grants AST
  0205500 and ATM 99881112 and NASA grants NAG 5 12450 and NNGO4GB92G.

---------------------------------------------------------
Title: Observations of solar magnetic elements with 0.1" resolution
Authors: Berger, T. E.; Rouppe van der Voort, L. H. M.; Lofdahl,
   M. G.; Carlsson, M.; Fossum, A.; Hansteen, V. H.; Marthinussen, E.;
   Title, A. M.; Scharmer, G.
2004AAS...204.2005B    Altcode: 2004BAAS...36..686B
  New observations of solar magnetic elements in a remnant active region
  plage near disk center are presented. The observations were taken with
  the Swedish 1-meter Solar Telescope on La Palma. We examine a single
  430.5 nm G-band filtergram that resolves ∼70 km (0.”1) structures
  and find new forms of magnetic structures in this particular region. A
  simultaneous Ca II H-line image is used to examine the low-chromosphere
  of network elements. A simultaneous Fe I 630.25 nm magnetogram
  that resolves structures as small as 120 km (0.”18) FWHM with a
  flux sensitivity of approximately 130 Mx cm<SUP>-2</SUP> quantifies
  the magnetic structure of the region. A Ni I 676.8 nm Dopplergram
  establishes relative velocity patterns associated with the network
  features with an accuracy of about 300 m s<SUP>-1</SUP>. Magnetic flux
  in this region as seen in both the magnetogram and the G-band image
  is typically structured into larger, amorphous, “ribbons” with a
  wide range of flux density values, rather than isolated kilogauss
  flux tubes. We also present filtergrams and magnetograms of magnetic
  elements at the solar limb showing that solar faculae are resolved
  into bright granular walls that appear to project 350 to 500 km above
  the photosphere.

---------------------------------------------------------
Title: Detectability of High Frequency Acoustic Waves with TRACE
Authors: Fossum, A.; Carlsson, M.
2004ESASP.547..125F    Altcode: 2004soho...13..125F
  High frequency acoustic waves have been proposed as a mechanism to heat
  the Solar chromosphere in internetwork regions. Such waves are difficult
  to detect using ground based observations because of seeing. Space
  based Solar observatories like SOHO and TRACE are not hampered by such
  high frequency disturbances caused by the Earth's atmosphere. We have
  used detailed NLTE radiation hydrodynamic simulations to investigate
  the detectability of high frequency acoustic waves with TRACE. A broad
  spectrum of acoustic waves are fed into the computational domain at
  the lower boundary of the model atmosphere and TRACE UV continuum
  intensities are calculated by folding the derived intensities with the
  TRACE filter functions for the 1600 and 1700 filters. Power spectra,
  phase diagrams and intensity response functions are calculated and
  intensity formation heights are derived. The simulations show that
  the width of the TRACE intensity response functions sets an upper
  frequency limit of 40 mHz for the detection of high frequency waves
  even in the absence of instrumental noise. Furthermore, Poisson noise
  for typical TRACE exposure times in a 30 minute time-series limits
  the detectability to below 25 mHz.

---------------------------------------------------------
Title: Observations at 0{.  ^{primeprime}}1 Resolution of the Dynamic
    Evolution of Magnetic Elements
Authors: Carlsson, Mats; Rouppe van der Voort, Luc; Hansteen, Viggo
2004IAUS..223..207C    Altcode: 2005IAUS..223..207C
  We present observations of the dynamic evolution of photospheric
  magnetic elements in the G-band, magnetograms and Dopplergrams. The
  observations were obtained with the Swedish 1m Solar Telescope on La
  Palma at close to the diffraction limit of 0{. ^{primeprime}}1. In
  the most quiet regions we observe individual bright points in the
  G-band with corresponding magnetic signal in the magnetograms. Where
  the filling factor of the magnetic field is larger, the bright points
  interact when advected by the granular and super-granular flow-fields,
  flux sheets form and fragment. The plage region of the decaying active
  region is filled with more complex topologies like ribbon structures
  with darker interior and bright, knotted edges. These change into
  flower-like shape when small in extent and into micro-pores when
  the flux region is larger in extent. The magnetic elements in the
  plage region are associated with upflows with strong downflows in the
  immediate vicinity in the low-field region.

---------------------------------------------------------
Title: Radiative hydrodynamic simulations of acoustic waves in
    sunspots
Authors: Bard, S.; Carlsson, M.
2004IAUS..223..445B    Altcode: 2005IAUS..223..445B
  We describe fully consistent NLTE radiation hydrodynamic simulations
  of the propagation of acoustic waves in sunspot umbrae. In contrast
  to the case of the quiet internetwork Sun, we find that the observed
  behavior of the resonance lines of singly ionized calcium (H and K
  lines) cannot be explained without adding non-acoustic heating. The
  best agreement with observations is obtained with an extra heating
  term as a function of height that is constant per volume.

---------------------------------------------------------
Title: High resolution limb images synthesized from 3D MHD simulations
Authors: Carlsson, Mats; Stein, Robert F.; Nordlund, Åke; Scharmer,
   Göran B.
2004IAUS..223..233C    Altcode: 2005IAUS..223..233C
  We present the first center-to-limb G-band images synthesized from
  high resolution simulations of solar magneto-convection. Towards the
  limb the simulations show "hilly" granulation with dark bands on the
  far side, bright granulation walls and striated faculae, similar
  to observations. At disk center G-band bright points are flanked
  by dark lanes. The increased brightness in magnetic elements is due
  to their lower density compared with the surrounding intergranular
  medium. One thus sees deeper layers where the temperature is higher. At
  a given geometric height, the magnetic elements are cooler than the
  surrounding medium. In the G-band, the contrast is further increased
  by the destruction of CH in the low density magnetic elements. The
  optical depth unity surface is very corrugated. Bright granules have
  their continuum optical depth unity 80 km above the mean surface,
  the magnetic elements 200-300 km below. The horizontal temperature
  gradient is especially large next to flux concentrations. When viewed
  at an angle, the deep magnetic elements optical surface is hidden by
  the granules and the bright points are no longer visible, except where
  the "magnetic valleys" are aligned with the line of sight. Towards
  the limb, the low density in the strong magnetic elements causes
  unit line-of-sight optical depth to occur deeper in the granule
  walls behind than for rays not going through magnetic elements and
  variations in the field strength produce a striated appearance in the
  bright granule walls.

---------------------------------------------------------
Title: Theory and Simulations of Solar Atmosphere Dynamics
Authors: Stein, R. F.; Bogdan, T. J.; Carlsson, M.; Hansteen, V.;
   McMurry, A.; Rosenthal, C. S.; Nordlund, Å.
2004ESASP.547...93S    Altcode: 2004soho...13...93S
  Numerical simulations are used to study the generation and propagation
  of waves in the solar atmosphere. Solar p-mode oscillations are excited
  by turbulent pressure work and entropy fluctuations (non-adiabatic gas
  pressure work) near the solar surface. Interactions between short and
  long period waves and radiative energy transfer control the formation of
  shocks. The magnetic structure of the atmosphere induces coupling among
  various MHD wave modes, with intense coupling and wave transformation
  at the beta equal one surface, which likely is the location of the
  so-called "magnetic canopy".

---------------------------------------------------------
Title: Waves in the Magnetized Solar Atmosphere. II. Waves from
    Localized Sources in Magnetic Flux Concentrations
Authors: Bogdan, T. J.; Carlsson, M.; Hansteen, V. H.; McMurry, A.;
   Rosenthal, C. S.; Johnson, M.; Petty-Powell, S.; Zita, E. J.; Stein,
   R. F.; McIntosh, S. W.; Nordlund, Å.
2003ApJ...599..626B    Altcode:
  Numerical simulations of wave propagation in a two-dimensional
  stratified magneto-atmosphere are presented for conditions that
  are representative of the solar photosphere and chromosphere. Both
  the emergent magnetic flux and the extent of the wave source are
  spatially localized at the lower photospheric boundary of the
  simulation. The calculations show that the coupling between the
  fast and slow magneto-acoustic-gravity (MAG) waves is confined to
  thin quasi-one-dimensional atmospheric layers where the sound speed
  and the Alfvén velocity are comparable in magnitude. Away from this
  wave conversion zone, which we call the magnetic canopy, the two MAG
  waves are effectively decoupled because either the magnetic pressure
  (B<SUP>2</SUP>/8π) or the plasma pressure (p=Nk<SUB>B</SUB>T)
  dominates over the other. The character of the fluctuations observed
  in the magneto-atmosphere depend sensitively on the relative location
  and orientation of the magnetic canopy with respect to the wave source
  and the observation point. Several distinct wave trains may converge
  on and simultaneously pass through a given location. Their coherent
  superposition presents a bewildering variety of Doppler and intensity
  time series because (1) some waves come directly from the source while
  others emerge from the magnetic canopy following mode conversion, (2)
  the propagation directions of the individual wave trains are neither
  co-aligned with each other nor with the observer's line of sight, and
  (3) the wave trains may be either fast or slow MAG waves that exhibit
  different characteristics depending on whether they are observed in
  high-β or low-β plasmas (β≡8πp/B<SUP>2</SUP>). Through the
  analysis of four numerical experiments a coherent and physically
  intuitive picture emerges of how fast and slow MAG waves interact
  within two-dimensional magneto-atmospheres.

---------------------------------------------------------
Title: MHD Waves in Magnetic Flux Concentrations
Authors: Bogdan, T. J.; Carlsson, M.; Hansteen, V.; Zita, E. J.;
   Stein, R. F.; McIntosh, S. W.
2003AGUFMSH42B0535B    Altcode:
  Results from 2D MHD simulations of waves in a stratified isothermal
  atmosphere will be presented and analyzed. The waves are generated
  by a localized piston source situated on the lower, photospheric,
  boundary of the computational domain. A combination of fast and slow
  magneto-atmospheric waves propagates with little mutual interaction
  until they encounter the surface where the sound speed and the Alfven
  speed are comparable in magnitude. The waves couple strongly in this
  region and emerge with different amplitudes and phases. Owing to
  this mode mixing and the large variation in the Alfven speed in the
  magneto-atmosphere, the fluctuations observed at a given location are
  often a superposition of both fast and slow waves which have traversed
  different paths and have undergone different transformations during
  their journies.

---------------------------------------------------------
Title: On the Origin of the Basal Emission from Stellar Atmospheres:
    Analysis of Solar C II Lines
Authors: Judge, Philip G.; Carlsson, Mats; Stein, Robert F.
2003ApJ...597.1158J    Altcode:
  Combining a variety of data with radiation hydrodynamic simulations,
  we examine the heating of the Sun's internetwork chromosphere
  and the hypothesis that the chromospheric “basal” emission
  arises because of acoustic wave dissipation. We focus on the
  2s2p<SUP>2</SUP><SUP>2</SUP>D-2s<SUP>2</SUP>2p<SUP>2</SUP>P<SUP>o</SUP>
  multiplet of C II near 1335 Å, whose basal level of chromospheric
  emission has been reliably determined for stars and the Sun by
  Schrijver and colleagues. By accounting for center-to-limb variations
  and the different spectral bandpasses of the instruments used, we find
  that Schrijver's C II solar basal intensity substantially exceeds
  stellar values, and that it can be identified with intensities seen
  in typical internetwork regions with the SUMER instrument on the SOHO
  spacecraft. Some time-series data sets of internetwork regions are
  then examined and compared with simulations made specifically for a
  typical observational data set, with vertical velocities at the lower
  boundaries fixed from observations with the MDI instrument on SOHO. The
  simulations can qualitatively account for the observed internetwork UV
  continuum fluctuations seen with SUMER, formed 0.6-0.85 Mm above the
  photosphere. However, they fail to capture almost any property of the
  observed internetwork C II multiplet, which is formed substantially
  higher. The time-averaged simulations can account for between 1/7
  and 1/4 of the C II basal intensities; they predict oscillatory power
  between 5 and 10 mHz, whereas internetwork observations are dominated by
  low-frequency (&lt;2 mHz) power of solar origin. The average simulated
  C II intensities, which have a large contribution from the transition
  region heated by conduction down from a coronal upper boundary,
  fall short even of the smaller stellar basal intensities by a factor
  of &gt;=2. Together with known properties of weak, internetwork
  photospheric magnetic fields, we conclude that the internetwork
  upper chromosphere is probably dominated by magnetic heating. Thus,
  the solar basal (and internetwork) intensities of the C II 1335 Å
  multiplet originate from magnetic, and not acoustic, mechanisms,
  in contradiction to the commonly accepted picture

---------------------------------------------------------
Title: Dynamic Modelling of the Outer Atmosphere of α Tau
Authors: McMurry, A. D.; Carlsson, M.; Stein, R. F.
2003csss...12..323M    Altcode:
  Using one-dimensional radiation-hydrodynamics simulations a model of
  the outer atmosphere of α Tau is created. The reaction of the model
  to acoustic waves is explored. It is found that high frequency waves
  are radiatively damped out in the photosphere. The lower frequency
  waves above the Hydrodynamic acoustic cutoff frequency do produce some
  chromospheric heating.

---------------------------------------------------------
Title: Nonequilibrium CO Chemistry in the Solar Atmosphere
Authors: Asensio Ramos, A.; Trujillo Bueno, J.; Carlsson, M.;
   Cernicharo, J.
2003ApJ...588L..61A    Altcode: 2003astro.ph..3460R; 2003astro.ph..3460A
  Investigating the reliability of the assumption of instantaneous
  chemical equilibrium (ICE) for calculating the CO number density in
  the solar atmosphere is of crucial importance for the resolution of
  the long-standing controversy over the existence of “cool clouds”
  in the chromosphere and for determining whether the cool gas owes its
  existence to CO radiative cooling or to a hydrodynamical process. Here
  we report the first results of such an investigation in which we
  have carried out time-dependent gas-phase chemistry calculations
  in radiation hydrodynamical simulations of solar chromospheric
  dynamics. We show that while the ICE approximation turns out to be
  suitable for modeling the observed infrared CO lines at the solar disk
  center, it may substantially overestimate the “heights of formation”
  of strong CO lines synthesized close to the edge of the solar disk,
  especially concerning vigorous dynamic cases resulting from relatively
  strong photospheric disturbances. This happens because during the
  cool phases of the hydrodynamical simulations, the CO number density
  in the outer atmospheric regions is smaller than what is stipulated
  by the ICE approximation, resulting in decreased CO opacity in the
  solar chromosphere. As a result, the cool CO-bearing gas that produces
  the observed molecular lines must be located at atmospheric heights
  not greater than ~700 km. We conclude that taking into account the
  nonequilibrium chemistry improves the agreement with the available
  on-disk and off-limb observations but that the hydrodynamical simulation
  model has to be even cooler than anticipated by the ICE approximation,
  and this has to be the case at the “new” (i.e., deeper) formation
  regions of the rovibrational CO lines.

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Title: Multi-level 3D non-LTE computations of lithium lines in the
    metal-poor halo stars HD 140283 and HD 84937
Authors: Asplund, M.; Carlsson, M.; Botnen, A. V.
2003A&A...399L..31A    Altcode: 2003astro.ph..2406A
  The lithium abundances in metal-poor halo stars are of importance
  for cosmology, galaxy evolution and stellar structure. In an attempt
  to study possible systematic errors in the derived Li abundances,
  the line formation of Li I lines has been investigated by means of
  realistic 3D hydrodynamical model atmospheres of halo stars and
  3D non-LTE radiative transfer calculations. These are the first
  detailed 3D non-LTE computations reported employing a multi-level
  atomic model showing that such problems are now computationally
  tractable. The detailed computations reveal that the Li I population
  has a strong influence from the radiation field rather than the local
  gas temperature, indicating that the low derived Li abundances found by
  Asplund et al. (\cite{Asplund1999}) are an artifact of their assumption
  of LTE. Relative to 3D LTE, the detailed calculations show pronounced
  over-ionization. In terms of abundances the 3D non-LTE values are
  within 0.05 dex of the 1D non-LTE results for the particular cases of
  HD 140283 and HD 84937, which is a consequence of the dominance of the
  radiation in determining the population density of Li I. Although 3D
  non-LTE can be expected to give results rather close (~+/- 0.1 dex)
  to 1D non-LTE for this reason, there may be systematic trends with
  metallicity and effective temperature.

---------------------------------------------------------
Title: 3D NLTE Radiative Transfer - Current Status and Future
    Prospects
Authors: Carlsson, M.
2003IAUS..210...51C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Towards 3D NLTE Radiation Magneto-Hydrodynamics
Authors: Carlsson, M.; Stein, R. F.
2003ASPC..288..505C    Altcode: 2003sam..conf..505C
  The problem of 3D Radiation Magneto-Hydrodynamics is too complex to
  solve numerically in the general case; approximations are needed to
  bring the numerical complexity to tractable levels. These approximations
  are problem dependent. We will use the case of the Solar chromosphere
  to illustrate these issues. The implementation of a 1D Radiation
  Hydrodynamics code with a rather detailed and realistic treatment
  of the coupling between radiation and matter is described. Scaling
  properties and parallelization issues are discussed. Various
  strategies and on-going work for the implementation of a 3D Radiation
  Magneto-Hydrodynamics code are described.

---------------------------------------------------------
Title: Modelling Acoustic Shocks in Outer Atmospheres of Cool
    Giant Stars
Authors: McMurry, A. D.; Carlsson, M.; Stein, R. F.
2003IAUS..210P..B7M    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Wave processes in the solar upper atmosphere
Authors: Carlsson, Mats; Stein, Robert F.
2002ESASP.505..293C    Altcode: 2002IAUCo.188..293C; 2002solm.conf..293C
  The existence of a wide variety of wave-like phenomena are inferred
  from observations of the solar upper atmosphere. Acoustic waves play
  an important role for the dynamics and energetics of the chromosphere
  but additional heating seems necessary even for the internetwork
  regions. We show that it is unlikely that this extra heating is due
  to high frequency acoustic waves due to the lack of their preferential
  excitation and the strong radiative damping of high frequency waves in
  the photosphere. When acoustic waves reach the height where the magnetic
  pressure equals the gas pressure they will undergo mode conversion,
  refraction and reflection. We discuss these processes and show that
  the critical quantity is the angle between the magnetic field and the
  velocity polarization; at angles smaller than 30 degrees much of the
  acoustic, fast mode from the photosphere is transmitted as an acoustic,
  slow mode propagating along the field lines. At larger angles, most of
  the energy is refracted/reflected and returns as a fast mode creating
  an interference pattern between the upward and downward propagating
  waves. In 3D, this interference between waves at small angles creates
  patterns with large horizontal phase speeds, especially close to
  magnetic field concentrations. When damping from shock dissipation and
  radiation is taken into account, the waves in the low-mid chromosphere
  have mostly the character of upward propagating acoustic waves and it
  is only close to the reflecting layer we get similar amplitudes for
  the upward propagating and refracted/reflected waves.

---------------------------------------------------------
Title: Waves in magnetic flux concentrations: The critical role of
    mode mixing and interference
Authors: Bogdan, T. J.; Rosenthal, C. S.; Carlsson, M.; Hansteen, V.;
   McMurry, A.; Zita, E. J.; Johnson, M.; Petty-Powell, S.; McIntosh,
   S. W.; Nordlund, Å.; Stein, R. F.; Dorch, S. B. F.
2002AN....323..196B    Altcode:
  Time-dependent numerical simulations of nonlinear wave propagation
  in a two-dimensional (slab) magnetic field geometry show wave mixing
  and interference to be important aspects of oscillatory phenomena in
  starspots and sunspots. Discrete sources located within the umbra
  generate both fast and slow MHD waves. The latter are compressive
  acoustic waves which are guided along the magnetic field lines and
  steepen into N-waves with increasing height in the spot atmosphere. The
  former are less compressive, and accelerate rapidly upward through the
  overlying low-beta portion of the umbral photosphere and chromosphere
  (beta equiv 8pi p/ B<SUP>2</SUP>). As the fast wave fronts impinge
  upon the beta ~ 1 penumbral “magnetic canopy" from above, they
  interfere with the outward-propagating field-guided slow waves, and
  they also mode convert to (non-magnetic) acoustic-gravity waves as
  they penetrate into the weak magnetic field region which lies between
  the penumbral canopy and the base of the surrounding photosphere. In
  a three-dimensional situation, one expects additional generation,
  mixing and interference with the remaining torsional Alfvén waves.

---------------------------------------------------------
Title: Dynamics in the solar chromosphere as a function of the
    magnetic field topology
Authors: Karlsen, N.; Carlsson, M.
2002ESASP.508..303K    Altcode: 2002soho...11..303K
  We have looked at the coupling between the magnetic field and
  chromospheric dynamics. Observations with the SUMER spectrograph of the
  continuum radiation at 1319 Å have been correlated with simultaneous
  MDI magnetograms and dopplergrams in high resolution mode. We have used
  7 different observing runs for our analysis, all from 1996. The absolute
  value of the magnetic field crossing the SUMER slit lies in the range
  0-100 gauss. We observe a correlation between continuum intensity and
  magnetic field strength all the way to the sensitivity limit of MDI
  (about 2 G as 3σ in the mean value). Relative intensity fluctuations
  at frequencies corresponding to propagating acoustic waves (&gt;4.5
  mHz) have smaller amplitudes with increasing radiation temperature
  (or magnetic field strength). The absolute intensity fluctuations show
  an increase with increasing radiation temperature. These findings are
  consistent with a picture where a basic intensity level is set by a
  magnetic heating process even in the darkest internetwork areas with
  superimposed intensity variations caused by acoustic waves.

---------------------------------------------------------
Title: Dynamic Hydrogen Ionization
Authors: Carlsson, Mats; Stein, R. F.
2002ApJ...572..626C    Altcode: 2002astro.ph..2313C
  We investigate the ionization of hydrogen in a dynamic solar
  atmosphere. The simulations include a detailed non-LTE treatment
  of hydrogen, calcium, and helium but lack other important
  elements. Furthermore, the omission of magnetic fields and the
  one-dimensional approach make the modeling unrealistic in the upper
  chromosphere and higher. We discuss these limitations and show
  that the main results remain valid for any reasonable chromospheric
  conditions. As in the static case, we find that the ionization of
  hydrogen in the chromosphere is dominated by collisional excitation in
  the Lyα transition followed by photoionization by Balmer continuum
  photons-the Lyman continuum does not play any significant role. In
  the transition region, collisional ionization from the ground
  state becomes the primary process. We show that the timescale for
  ionization/recombination can be estimated from the eigenvalues of a
  modified rate matrix where the optically thick Lyman transitions that
  are in detailed balance have been excluded. We find that the timescale
  for ionization/recombination is dominated by the slow collisional
  leakage from the ground state to the first excited state. Throughout the
  chromosphere the timescale is long (10<SUP>3</SUP>-10<SUP>5</SUP> s),
  except in shocks where the increased temperature and density shorten
  the timescale for ionization/recombination, especially in the upper
  chromosphere. Because the relaxation timescale is much longer than
  dynamic timescales, hydrogen ionization does not have time to reach
  its equilibrium value and its fluctuations are much smaller than the
  variation of its statistical equilibrium value appropriate for the
  instantaneous conditions. Because the ionization and recombination
  rates increase with increasing temperature and density, ionization
  in shocks is more rapid than recombination behind them. Therefore,
  the ionization state tends to represent the higher temperature of the
  shocks, and the mean electron density is up to a factor of 6 higher
  than the electron density calculated in statistical equilibrium from
  the mean atmosphere. The simulations show that a static picture and
  a dynamic picture of the chromosphere are fundamentally different
  and that time variations are crucial for our understanding of the
  chromosphere itself and the spectral features formed there.

---------------------------------------------------------
Title: Dynamics and energetics of the solar chromosphere
Authors: Carlsson, Mats; Stein, Robert F.
2002ESASP.508..245C    Altcode: 2002soho...11..245C
  We present a summary of results from a number of observational programs
  carried out with the SUMER instrument on board SOHO. Most datasets
  show clear quasi-periodic dynamic behavior ("grains") in contiunuum
  intensities with frequencies 3-10 mHz. Corresponding grains are seen
  in intensities and velocities in neutral lines, normally with phase
  differences consistent with upward propagating sound-waves. We compare
  the observations with 1D radiation hydrodynamic simulations using
  MDI Doppler-shifts to set the lower boundary. For continua formed in
  the mid-chromosphere we find that the simulations give a good match
  to the intensity fluctuations but that the minimum intensity is too
  low. We find that high frequency acoustic waves (missing from the
  current simulations) are unlikely to give the extra heating necessary
  because of the strong radiative damping (90-99%) of such waves in
  the photosphere. In continua formed in the low chromosphere the mean
  intensity is similar in the simulations and the observations but
  the simulated fluctuations are too large. The reported findings are
  consistent with a picture where a basic intensity level is set by a
  magnetic heating process even in the darkest internetwork areas with
  superimposed intensity variations caused by acoustic waves.

---------------------------------------------------------
Title: Waves in the Magnetized Solar Atmosphere. I. Basic Processes
    and Internetwork Oscillations
Authors: Rosenthal, C. S.; Bogdan, T. J.; Carlsson, M.; Dorch,
   S. B. F.; Hansteen, V.; McIntosh, S. W.; McMurry, A.; Nordlund, Å.;
   Stein, R. F.
2002ApJ...564..508R    Altcode:
  We have modeled numerically the propagation of waves through magnetic
  structures in a stratified atmosphere. We first simulate the propagation
  of waves through a number of simple, exemplary field geometries in
  order to obtain a better insight into the effect of differing field
  structures on the wave speeds, amplitudes, polarizations, direction
  of propagation, etc., with a view to understanding the wide variety of
  wavelike and oscillatory processes observed in the solar atmosphere. As
  a particular example, we then apply the method to oscillations in the
  chromospheric network and internetwork. We find that in regions where
  the field is significantly inclined to the vertical, refraction by
  the rapidly increasing phase speed of the fast modes results in total
  internal reflection of the waves at a surface whose altitude is highly
  variable. We conjecture a relationship between this phenomenon and the
  observed spatiotemporal intermittancy of the oscillations. By contrast,
  in regions where the field is close to vertical, the waves continue
  to propagate upward, channeled along the field lines but otherwise
  largely unaffected by the field.

---------------------------------------------------------
Title: Men-Invasion of Space
Authors: Carlsson, M. E.
2002iaf..confE.649C    Altcode:
  Last year I was given the fantastic opportunity by ESA to go to the IAF
  congress in Toulouse. This was one of the most exciting experiences of
  my life. I loved every minute of it, listening to the brilliant men from
  different areas of space research, telling us wonderfully interesting
  things about space. After a couple of sessions I understood there were
  very few women standing up there and giving presentations. Except
  of course, the Russian women translators and the students that were
  invited. This struck me and I started to think about it and wondered
  why? This encouraged me to investigate. I realized that I had to
  turn to the children, the ones that are going to take over after
  us, our new faces in space. When we were children we all wanted to
  become astronauts, both boys and girls. But after a couple of years
  it changed, why? So I started my research by asking questions to the
  children in different ages concerning their lives and upbringing. I was
  curious to find out when and how their personal goals changed in life,
  compared to the men. Could it depend on what our parents did when we
  were growing up or maybe where we were raised geographically? Perhaps
  the encouragement of our teachers in our first years in school or
  our social background, genes, manners and customs. When we have the
  answers we also must ask ourselves how we can make women choose a
  more engineering and scientific profile. Should we try to convert
  them to engineers or should we use their other special abilities and
  try to integrate them into the space program for example as medical
  doctors? I think that ESA and other space organizations should use
  their university students in a new outreach project. The students
  should visit their local schools and inform the children about space
  and the wonderful opportunities it can give us. This would give the
  boys, but mostly the girls, a chance to discover space.

---------------------------------------------------------
Title: Wave Propagation in a Magnetized Atmosphere
Authors: Bogdan, T. J.; Rosenthal, C. S.; Carlsson, M.; McIntosh,
   S.; Dorch, S.; Hansteen, V.; McMurry, A.; Nordlund, Å; Stein, R. F.
2001AGUSM..SH41A01B    Altcode:
  Numerical simulations of MHD wave propagation in plane-parallel
  atmospheres threaded by non-trivial potential magnetic fields will be
  presented, and their implications for understanding distinctions between
  intranetwork and internetwork oscillations will be discussed. Our
  findings basically confirm the conjecture of McIntosh et al. (2001,
  ApJ 548, L237), that the two-dimensional surface where the Alfvén
  and sound speeds coincide (i.e., where the plasma-β , the ratio of
  gas to magnetic pressure, is of order unity) plays a fundamental
  role in mediating the conversion between the fast-, intermediate-
  (Alfvén), and slow-Magneto-Atmospheric-Gravity (MAG) waves. For
  example, upward-propagating acoustic waves generated at the base of
  the internetwork photosphere suffer significant downward reflection
  when they encounter this β ≈ 1 surface. Close to the network, this
  surface descends from the upper chromosphere and low corona (which
  pertains in the internetwork cell interiors) down into the photosphere,
  and so chromospheric oscillation `shadows' are predicted to surround
  the network. In the network, strong vertical magnetic fields further
  depress the β ≈ 1 surface below the surface layers where the
  (magnetic field-aligned) acoustic waves (i.e., slow MAG-waves) are
  generated. For frequencies in excess of the cutoff frequency, these
  acoustic waves suffer little reflection from the overlying atmosphere
  and they steepen as they progress upward.

---------------------------------------------------------
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: Waves in the Magnetised Solar Atmosphere
Authors: Rosenthal, C. S.; Carlsson, M.; Hansteen, V.; McMurry,
   A.; Bogdan, T. J.; McIntosh, S.; Nordlund, A.; Stein, R. F.; Dorch,
   S. B. F.
2001IAUS..203..170R    Altcode:
  We have simulated the propagation of magneto-acoustic disturbances
  through various magneto-hydrostatic structures constructed to mimic
  the solar magnetic field. As waves propagate from regions of strong
  to weak magnetic field and vice-versa different types of wave modes
  (transverse and longitudinal) are coupled. In closed-field geometries
  we see the trapping of wave energy within loop-like structures. In
  open-field regions we see wave energy preferentially focussed away
  from strong-field regions. We discuss these oscillations in terms
  of various wave processes seen on the Sun - umbral oscillations,
  penumbral running waves, internetwork oscillations etc.

---------------------------------------------------------
Title: Solar Chromospheric Oscillations
Authors: Carlsson, M.
2000eaa..bookE2261C    Altcode:
  By the term solar chromospheric oscillations we here refer to any
  periodic or quasi-periodic dynamic phenomena seen in the solar
  CHROMOSPHERE. We thus include both propagating and standing waves....

---------------------------------------------------------
Title: Rapid intensity and velocity variations in solar transition
    region lines
Authors: Hansteen, V. H.; Betta, R.; Carlsson, M.
2000A&A...360..742H    Altcode:
  We have obtained short exposure (3 s) time series of strong upper
  chromospheric and transition region emission lines from the quiet Sun
  with the SUMER instrument onboard SOHO during two 1 hour periods in
  1996. With a Nyqvist frequency of 167 mHz and relatively high count
  rates the dataset is uniquely suited for searching for high frequency
  variations in intensity and Doppler velocity. From Monte-Carlo
  experiments taking into account the photon-counting statistics we
  estimate our detection limit to correspond to a wave-packet of four
  periods coherent over 3<SUP>”</SUP> with a Doppler-shift amplitude
  of 2.5km s<SUP>-1</SUP> in the darkest internetwork areas observed in
  C III. In the network the detection limit is estimated to be 1.5km
  s<SUP>-1</SUP>. Above 50 mHz we detect wave-packet amplitudes above
  3km s<SUP>-1</SUP> less than 0.5% of the time. Between 20 and 50 mHz
  we detect some wave-packets with a typical duration of four periods
  and amplitudes up to 8km s<SUP>-1</SUP>. At any given internetwork
  location these wave-packets are present 1% of the time. In the
  10-20 mHz range we see amplitudes above 3km s<SUP>-1</SUP> 12% of
  the time. At lower frequencies our dataset is consistent with other
  SUMER datasets reported in the literature. The chromospheric 3-7 mHz
  signal is discernible in the line emission. In the internetwork this
  is the dominant oscillation frequency but higher frequencies (7-10
  mHz) are often present and appear coherent in Doppler velocity over
  large spatial regions (≍ 40"). Wavelet analysis implies that these
  oscillations have typical durations of 1000s. The network emission also
  shows a 5 mHz signal but is dominated by low frequency variations (of
  &lt; 4 mHz) in both intensity and velocity. The oscillations show less
  power in intensity than in velocity. We find that while both red and
  blue shifted emission is observed, the transition region lines are on
  average red shifted between 5-10km s<SUP>-1</SUP> in the network. A net
  red shift is also found in the internetwork emission but it is smaller
  (&lt; 4km s<SUP>-1</SUP>). The line widths do not differ much between
  the internetwork and network, the non-thermal line widths increase
  with increasing temperature of line formation from 30km s<SUP>-1</SUP>
  for the C II 1334 Å line to 45km s<SUP>-1</SUP> for the O VI 1032
  Å line. By constructing scatterplots of velocity versus intensity we
  find that in the network a mean redshift is correlated with a high mean
  intensity. In the internetwork regions we do not find any correlation
  between the intensity and the Doppler velocity.

---------------------------------------------------------
Title: The Dynamic Solar Chromosphere
Authors: Carlsson, M.; Stein, R. F.
2000SPD....31.1102C    Altcode: 2000BAAS...32..843C
  The natural state of the Solar chromosphere is dynamic. Any
  photospheric disturbance will grow and naturally form shocks over
  the twenty scale-heights in density between the photosphere and
  the corona. Observations in the resonance lines from singly ionized
  calcium and in the ultraviolet region of the spectrum observed with
  the Solar and Heliospheric Observatory satellite also show a dynamic
  chromosphere. The dynamic picture is further supported by numerical
  simulations. Static and dynamic pictures of the chromosphere are
  fundamentally different. The simulations also show that time variations
  are crucial for our understanding of the chromosphere itself and for
  the spectral features formed there.

---------------------------------------------------------
Title: Chromospheric and Transition Region Internetwork Oscillations:
    A Signature of Upward-propagating Waves
Authors: Wikstøl, Ø.; Hansteen, V. H.; Carlsson, M.; Judge, P. G.
2000ApJ...531.1150W    Altcode:
  We analyze spectral time series obtained on 1997 April 25 with
  the SUMER instrument on SOHO. Line and continuum data near 1037
  Å were acquired at a cadence of 16 s. This spectral region was
  chosen because it contains strong emission lines of C II, formed
  in the upper chromosphere/lower transition region; O VI, formed
  in the upper transition region; and neighboring continuum emission
  formed in the middle chromosphere. The time series reveal oscillatory
  behavior. Subsonic (3-5 km s<SUP>-1</SUP> amplitude) Doppler velocity
  oscillations in the C II and O VI lines, with periods between 120
  and 200 s, are prominent. They are seen as large-scale coherent
  oscillations, typically of 3-7 Mm length scale, occasionally approaching
  15 Mm, visible most clearly in internetwork regions. The Doppler
  velocity oscillations are related to oscillations seen in the continuum
  intensity, which precede upward velocity in C II by 40-60 s. The C II
  Doppler shift precedes the O VI Doppler shift by 3-10 s. Oscillations
  are also present in the line intensities, but the intensity amplitudes
  associated with the oscillations are small. The continuum intensity
  precedes the C II intensity by 30-50 s. Phase difference analysis
  shows that there is a preponderance of upward-propagating waves in the
  upper chromosphere that drive an oscillation in the transition region
  plasma, thus extending the evidence for upward-propagating waves from
  the photosphere up to the base of the corona.

---------------------------------------------------------
Title: Oxygen Line Formation in 3D Hydrodynamical Model Atmospheres
Authors: Asplund, M.; Carlsson, M.; Garcia Perez, A. E.; Kiselman, D.
2000IAUJD...8E...8A    Altcode: 2000astro.ph.11043A
  The new generation of realistic 3-dimensional, time-dependent,
  hydrodynamical model atmospheres have been applied to the line
  formation of {O}{I}, [{O}{I}] and OH lines. Additionally detailed 3D
  non-LTE calculations have been performed for {O}{I} in order to study
  the influence of temperature inhomogeneities on the line formation
  process. Implications in terms of the evolution of oxygen abundance
  with metallicity will be discussed, partly based on new VLT/UVES
  observations of metal-poor stars.

---------------------------------------------------------
Title: Chromospheric Dynamics as seen by SUMER
Authors: Carlsson, M.
1999ESASP.448..183C    Altcode: 1999ESPM....9..183C; 1999mfsp.conf..183C
  No abstract at ADS

---------------------------------------------------------
Title: Transition Region Oscillations
Authors: Hansteen, V. H.; Wisktol, O.; Carlsson, M.; Judge, P. G.
1999ESASP.446..351H    Altcode: 1999soho....8..351H
  We analyze time series data obtained April 25th 1997 with the SUMER
  instrument on SOHO. Line and continuum data near 1037 were acquired at
  a cadence of 16s. This spectral region was chosen because it contains
  strong emission lines of C II, formed in the upper chromosphere/lower
  transition region, O VI, formed in the upper transition region, as well
  as neighboring continuum emission formed in the middle chromosphere. The
  dataset reveals oscillatory behavior containing valuable information
  on the physical structure of the chromosphere and transition
  region. Prominent in the data are subsonic (3-5 km/s amplitude)
  velocity oscillations with periods between 120 and 200 sec. They
  are seen as large scale coherent oscillations, typically of 3--7 Mm
  length scale but sometimes approaching 15Mm, visible most clearly
  in internetwork regions. The oscillations are present in C II and O
  VI velocities, as well as in the continuum intensity. The continuum
  intensity precedes upward velocity in the C II line by 40-60s and the C
  III velocity precedes the O VI velocity by 3-10s. The oscillations are
  also present in the intensities of the two lines, but the intensity
  amplitudes associated with the oscillations are small. We find that
  the continuum intensity precedes the C II intensity by 30-50s. These
  phase shifts indicate that there are upward propagating waves in the
  upper chromosphere that drive an oscillation in the transition region
  plasma. The oscillations seem to be present in most internetwork areas
  at any time, thus they are the dominant resolvable dynamical feature
  of the internetwork chromosphere and transition region.

---------------------------------------------------------
Title: Wave Modes in a Chromospheric Cavity
Authors: Carlsson, M.; Stein, R. S.
1999ASPC..184..206C    Altcode:
  Observations show enhanced power near 5.3 mHz and 7 mHz and phase
  jumps near 7 mHz. Interpretations have varied from standing waves,
  resonant wakes, shock merging and source interference. We investigate
  these processes using a non-LTE radiation hydrodynamics code. It
  is shown that the enhanced power at certain frequencies is caused
  by partial reflections from steep temperature gradients in the
  photosphere and the transition region. Due to a phase-speed that is
  very dependent on frequency close to the acoustic cut-off frequency,
  the lowest mode frequencies are rather insensitive to the location of
  the upper reflecting layer. Temperature jumps across shocks introduce
  additional reflection and modify the mode structure. A corrugated
  and moving transition region washes out the higher frequency modes
  but does not affect the lowest modes much. The modal structure is
  superimposed on a wave field that is dominated by propagating waves
  in the lower chromosphere.

---------------------------------------------------------
Title: The dynamic solar chromosphere and the ionization of hydrogen
Authors: Carlsson, Mats; Stein, Robert F.
1999AIPC..471...23C    Altcode: 1999sowi.conf...23C
  Basic physical considerations, observations and numerical simulations
  show that the solar chromosphere is very dynamic. The enhanced
  chromospheric emission, which corresponds to an outwardly increasing
  semiempirical temperature structure, can even be produced by wave
  motion without any increase in the mean gas temperature. Hence,
  the sun may not have a classical chromosphere in magnetic field free
  internetwork regions. This dynamic picture of the solar internetwork
  chromosphere is consistent with ground based observations of the Call
  resonance lines and with observations from the SOHO satellite. The
  simulations also show that a static picture and a dynamic picture of
  the chromosphere are fundamentally different and that time variations
  are crucial for our understanding of the chromosphere itself and
  the spectral features formed there. Whether the dynamic nature of
  the chromosphere is important for solar wind models depends on their
  sensitivity to chromospheric conditions. Contrary to some claims in
  the literature, the ionization of hydrogen in the upper chromosphere
  is dominated by collisional excitation in the Lyman line followed by
  photo-ionization by Balmer continuum photons-the Lyman continuum does
  not play any significant role. In the transition region, collisional
  ionization takes over as the major process. Ionization/recombination
  time-scales can be on the order of hundreds of seconds causing the
  ionization balance in the chromosphere to be significantly out of
  equilibrium with higher ionization than the equilibrium value. The
  hydrogen ionization zone is also considerably thicker than is claimed
  from dimension analyses; the ionization fraction goes from 1% to 40%
  over a height range of 600 km.

---------------------------------------------------------
Title: Multi3D, 3D Non-LTE Radiative Transfer
Authors: Botnen, A.; Carlsson, M.
1999ASSL..240..379B    Altcode: 1999numa.conf..379B
  No abstract at ADS

---------------------------------------------------------
Title: The new chromosphere
Authors: Carlsson, M.; Stein, R. F.
1998IAUS..185..435C    Altcode:
  Numerical simulations have shown that enhanced chromospheric emission,
  which corresponds to an outwardly increasing semiempirical temperature
  structure, can be produced by wave motion without any increase in
  the mean gas temperture. Hence, the sun may not have a classical
  chromosphere in magnetic field free internetwork regions. This dynamic
  picture of the solar internetwork chromosphere is also consistent
  with ground based observations of the CaII resonance lines and of CO
  absorption lines and with observations from the SOHO satellite. The
  simulations also show that a static picture and a dynamic picture of
  the chromosphere are fundamentally different and that time variations
  are crucial for our understanding of the chromosphere itself and for
  the spectral features formed there.

---------------------------------------------------------
Title: SUMER observations in transition region lines
Authors: Betta, R.; Hansteen, V.; Carlsson, M.; Wilhelm, K.
1998MmSAI..69..699B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Radiative Transfer and Radiation Hydrodynamics
Authors: Carlsson, Mats
1998LNP...507..163C    Altcode: 1998sspt.conf..163C
  Radiation plays an important role, firstly in determining the structure
  of stars through the dominant role radiation plays in the energy balance
  (in some objects also in the momentum balance), secondly because we
  diagnose astrophysical plasma through the emitted electromagnetic
  radiation.

---------------------------------------------------------
Title: SUMER Observations of the Quiet Solar Atmosphere: The Network
    Chromosphere and Lower Transition Region
Authors: Judge, Philip; Carlsson, Mats; Wilhelm, Klaus
1997ApJ...490L.195J    Altcode:
  We examine spectral properties of the network chromosphere and lower
  transition region from the SUMER instrument on the SOHO spacecraft,
  using time-series data sets discussed in an accompanying Letter by
  Carlsson, Judge, &amp; Wilhelm. The data were obtained early in the
  mission with no tracking of solar features and so cannot generally
  be used to examine intrinsic variations in features on timescales
  in excess of 383 s. Upon examination of the temporal variations and
  some preliminary power spectrum analysis, we find the following:
  (1) Transition region lines show more redshift in network regions
  than in internetwork regions and also a correlation between line
  intensity brightenings and increased redshift. (2) The internetwork
  “Ca II grain” phenomenon is not seen in He I λ584 or in lines
  of Si III and C III. (3) Very rapid changes are seen in the network
  for transition region lines with no obvious correspondence with the
  underlying chromosphere. (4) He I λ584 line profiles show very slow
  time variations. (5) Small-amplitude (2-5 km s<SUP>-1</SUP>) coherent
  oscillations of 5"-10" scale length and ~130 s period are seen in
  Doppler shifts of Si III between regions of bright network elements. (6)
  Essentially all blueshifts or redshifts are substantially less than line
  widths. We conclude that upward-propagating acoustic shock waves do not
  contribute significantly to the heating of the lower transition region,
  and that ionization equilibrium is likely to fail for the interpretation
  of certain emission lines. The spatial coherency of the Si III velocity
  oscillations indicates that the quiet Sun's magnetic field topology
  is more uniform than emission-line intensity data alone might suggest.

---------------------------------------------------------
Title: Dynamic Behavior of the Solar Atmosphere
Authors: Stein, R. F.; Carlsson, M.
1997ASSL..225..261S    Altcode: 1997scor.proc..261S
  We have studied the dynamics of acoustic and MHD waves in the
  solar atmosphere using a one-dimensional, non-LTE, radiation
  magneto-hydrodynamic code, with 6 level model atoms for hydrogen and
  singly ionized calcium. We drive waves by a piston through an initial
  atmosphere in radiative equilibrium. We report on the effects of
  radiative energy loss on the waves, the effects of shocks on line
  formation, and the behavior of typical diagnostics in a dynamic
  atmosphere.

---------------------------------------------------------
Title: SUMER Observations Confirm the Dynamic Nature of the Quiet
Solar Outer Atmosphere: The Internetwork Chromosphere
Authors: Carlsson, Mats; Judge, P. G.; Wilhelm, K.
1997ApJ...486L..63C    Altcode: 1997astro.ph..6226C
  On 1996 March 12, during the commissioning phase of the SOHO mission, we
  obtained observations of the quiet-Sun with the SUMER instrument. The
  observations were sequences of 15-20 s exposures of ultraviolet
  emission-line profiles and of the neighboring continua. These data
  contain signatures of the dynamics of the solar chromosphere that are
  uniquely useful because of wavelength coverage, moderate signal-to-noise
  ratios, and image stability. <P />We focus on data for the internetwork
  chromosphere. The dominant observed phenomenon is an oscillatory
  behavior that is analogous to the 3 minute oscillations seen in CaII
  lines. The oscillations appear to be coherent over 3"-8" diameter
  areas. At any time they occur over about 50% of the area studied,
  and they appear as large perturbations in the intensities of lines
  and continua. The oscillations are most clearly seen in intensity
  variations in the ultraviolet (λ &gt; 912 Å) continua, and they are
  also seen in the intensities and velocities of chromospheric lines of
  CI, NI, and OI. Intensity brightenings are accompanied by blueshifts
  of typically 5 km s<SUP>-1</SUP>. Phase differences between continuum
  and line intensities also indicate the presence of upward propagating
  waves. The detailed behavior is different between different lines,
  sometimes showing phase lags. The 3 minute intensity oscillations
  are occasionally seen in second spectra (CII λ1335) but never in
  third spectra (CIII and SiIII). Third spectra and HeI λ584 show
  oscillations in velocity that are not simply related to the 3 minute
  oscillations. The continuum intensity variations are consistent with
  recent simulations of chromospheric dynamics (Carlsson and Stein),
  while the line observations indicate that important ingredients are
  missing at higher layers in the simulations. <P />The data show that
  time variations are crucial for our understanding of the chromosphere
  itself and for the spectral features formed there--the quiet-Sun's
  chromosphere is very dynamic and not “quiet.” The implications of
  these data should be considered when planning chromospheric work with
  instruments such as those on SOHO.

---------------------------------------------------------
Title: Formation of Solar Calcium H and K Bright Grains
Authors: Carlsson, Mats; Stein, Robert F.
1997ApJ...481..500C    Altcode:
  We have simulated the generation of Ca II H<SUB>2V</SUB> bright
  grains by acoustic shocks. We employ a one-dimensional, non-LTE
  radiation-hydrodynamic code, with six-level model atoms for hydrogen
  and singly ionized calcium. We drive acoustic waves through a stratified
  radiative equilibrium atmosphere by a piston, whose velocity is chosen
  to match the Doppler shift observed in the Fe I 396.68 nm line in
  the H line wing, formed at about 260 km above τ<SUB>500</SUB> =
  1. <P />The simulations closely match the observed behavior of Ca
  II H<SUB>2V</SUB> bright grains down to the level of individual
  grains. The bright grains are produced by shocks near 1 Mm above
  τ<SUB>500</SUB> = 1. Shocks in the mid-chromosphere produce a large
  source function (and therefore high emissivity) because the density
  is high enough for collisions to couple the Ca II populations to the
  local conditions. The asymmetry of the line profile is due to velocity
  gradients near 1 Mm. Material motion Doppler-shifts the frequency at
  which atoms emit and absorb photons, so the maximum opacity is located
  at--and the absorption profile is symmetric about--the local fluid
  velocity, which is shifted to the blue behind shocks. The optical
  depth depends upon the velocity structure higher up. Shocks propagate
  generally into downflowing material, so there is little matter above
  to absorb the Doppler-shifted radiation. The corresponding red peak
  is absent because of small opacity at the source function maximum and
  large optical depth due to overlying material. The bright grains are
  produced primarily by waves from the photosphere that are slightly
  above the acoustic cutoff frequency. The precise time and strength
  of a grain depend upon the interference between these waves near the
  acoustic cutoff frequency and higher frequency waves. When waves near
  the acoustic cutoff frequency are weak, then higher frequency waves
  may produce grains. The “5 minute” trapped p-mode oscillations are
  not the source of the grains, although they can slightly modify the
  behavior of higher frequency waves.

---------------------------------------------------------
Title: Chromospheric Dynamics - What Can Be Learnt from Numerical
    Simulations
Authors: Carlsson, M.; Stein, R. F.
1997LNP...489..159C    Altcode: 1997shpp.conf..159C
  Observations of the solar chromosphere are often interpreted using
  methods derived from static modeling (e.g., the Vernazza et al. 1981
  model atmospheres and work based on such models) or linear theory
  (e.g., phase relations). Recent numerical simulations have shown that
  such an analysis can be very misleading. It is found that enhanced
  chromospheric emission, which corresponds to an outwardly increasing
  semi-empirical temperature structure, can be produced by wave motions
  without any increase in the mean gas temperature. Thus, despite
  long held beliefs, the Sun may not have a classical chromosphere
  in magnetic field free internetwork regions. This dynamic picture
  is consistent with observations in CO lines and the calcium H and
  K bright grains. More opaque lines, on the other hand, seem to show
  emission all of the time. This indicates the existence of a hotter,
  magnetic, component that increases in importance with height.

---------------------------------------------------------
Title: Shock Signature in Sunspots
Authors: Bard, S.; Carlsson, M.
1997ESASP.404..189B    Altcode: 1997cswn.conf..189B
  No abstract at ADS

---------------------------------------------------------
Title: Numerical Simulations Can Lead to New Insights
Authors: Stein, Robert F.; Carlsson, Mats; Nordlund, Ake
1997ASPC..123...72S    Altcode: 1997taca.conf...72S
  No abstract at ADS

---------------------------------------------------------
Title: The non-magnetic solar chromosphere.
Authors: Carlsson, M.; Stein, R. F.
1997smf..conf...59C    Altcode:
  The authors summarize recent results form self-consistent non-LTE
  radiation hydrodynamics simulations of the propagation of acoustic
  waves through the non-magnetic solar chromosphere. References to more
  detailed write-ups of the work are given.

---------------------------------------------------------
Title: Intensity and Velocity Variations in Transition Region Lines
    Observed with SUMER
Authors: Betta, R.; Hansteen, V.; Carlsson, M.; Wilhelm, K.
1997ESASP.404..205B    Altcode: 1997cswn.conf..205B
  No abstract at ADS

---------------------------------------------------------
Title: The NLTE formation of neutral-boron lines in cool stars.
Authors: Kiselman, D.; Carlsson, M.
1996A&A...311..680K    Altcode: 1996astro.ph..1144K
  We study the formation of BI lines in a grid of cool stellar model
  atmospheres without the assumption of local thermodynamic equilibrium
  (LTE). The non-LTE modelling includes the effect of other lines
  blending with the BI resonance lines. Except for the cases where the
  BI lines are very strong, the departures from LTE relevant for the
  resonance lines can be described as an overionisation effect and an
  optical-pumping effect. This causes the lines to be weaker than in LTE
  so that an abundance analysis assuming LTE will underestimate stellar
  boron abundances. We present non-LTE abundance corrections useful to
  improve on abundances derived from the Bi250nm and 209nm lines under
  the LTE assumption. Application of the results on literature data
  indicates that the B/Fe ratio in metal-poor stars is constant.

---------------------------------------------------------
Title: Solar chromospheric dynamics - Results from numerical
    simulations
Authors: Carlsson, M.; Stein, R. F.
1996ASPC..109..119C    Altcode: 1996csss....9..119C
  No abstract at ADS

---------------------------------------------------------
Title: Does a Nonmagnetic Solar Chromosphere Exist?
Authors: Carlsson, Mats; Stein, Robert F.
1995ApJ...440L..29C    Altcode: 1994astro.ph.11036C
  Enhanced chromospheric emission which corresponds to an outwardly
  increasing semiempirical temperature structure can be produced by
  wave motion without any increase in the mean gas temperture. Hence,
  the sun may not have a classical chromosphere in magnetic field
  free internetwork regions. Other significant differences between the
  properties of dynamic and static atmospheres should be considered when
  analyzing chromospheric observations.

---------------------------------------------------------
Title: Stellar Atmospheres
Authors: Carlsson, M.
1995fras.conf..181C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. VIII. MgI
    12μm diagnostics of sunspots.
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson,
   M.
1995A&A...293..225B    Altcode:
  Due to their large Zeeman sensitivity, the MgI lines at 12μm are
  important diagnostics of solar magnetism. The formation of their
  central emission features is now understood, enabling quantitative
  modeling and diagnostic application of these lines. We supply the
  first systematic analysis of solar MgI 12μm Stokes profiles employing
  detailed line-profile synthesis. We compute Stokes profiles of MgI
  12.32μm for the quiet Sun, for sunspot penumbrae and for the extended
  ("superpenumbral") magnetic canopies surrounding sunspots. We use these
  computations to analyze recent MgI 12μm observations by Hewagama
  et al. (1993). Our results are the following: (1) -Saha-Boltzmann
  temperature sensitivity explains that the emission peaks are stronger in
  penumbrae than in the quiet Sun, and that they disappear in umbrae. (2)
  -The formation heights of the emission features are approximately the
  same in penumbrae and in the quiet Sun, namely τ_500_=~10^-3^. (3)
  -The simple Seares formula allows relatively accurate determinations
  of field strength and magnetic inclination. (4) -The observed excess
  broadening of the σ-component peaks compared with the π component
  in penumbrae is well explained by primarily horizontal, smooth radial
  variation of the magnetic field strength. Additional small-scale
  variations are less than {DELTA}B =~200G. (5) -The vertical field
  gradients dB/dz in penumbrae range from 0.7G/km to 3G/km; the larger
  gradients occur near the umbra, the smaller ones near the outer edge of
  the penumbra. (6) -The MgI 12μm lines are well-suited to measure the
  base heights of superpenumbral magnetic canopies. These heights range
  between 300km and 500km above τ_500_=1 out to twice the sunspot radius,
  in excellent agreement with determinations from other infrared lines.

---------------------------------------------------------
Title: No Magnetic Field - No Chromosphere (Abstract only)
Authors: Carlsson, M.; Stein, R.
1995itsa.conf..325C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Non-LTE Effects on Be and B Abundance Determinations in
    Cool Stars
Authors: Kiselman, D.; Carlsson, M.
1995lea..conf..372K    Altcode: 1994astro.ph..9064K
  We discuss the nature of non-LTE effects affecting abundance analysis
  of cool stars. The departures from LTE of importance for the B I
  lines in solar-type stars are described and some new results are
  presented. Boron abundances derived under the LTE assumption have
  significant systematic errors, especially for metal-poor stars. For
  beryllium, current results suggest that departures from LTE will not
  affect abundance analysis significantly.

---------------------------------------------------------
Title: The Formation of the Solar He II 1640.4 Angstrom Emission Line
Authors: Wahlstrom, Cathrine; Carlsson, Mats
1994ApJ...433..417W    Altcode:
  We explain the formation of the solar He II 1640.4 A Balmer-alpha
  emission line. Non-LTE (non-local thermodynamic equilibrium) modeling is
  performed including the effects of an incoming coronal radiation field,
  the overlapping emission profile of He II 304 A with the He I continuum
  and the pumping effect of hydrogen Lyman-alpha. We find that the line
  is formed by the photoionization from the ground state of He II, mainly
  by the incident coronal radiation, followed by cascade recombination
  into the n = 3 levels. The peak of the contribution functions is at
  low temperatures, 7000-10,000 K, with a very small contribution from
  collisional excitation at a temperature of 70,000 K. We obtain good
  agreement with the observed line widths, the observed fine structure
  and the relative strength of the fine structure components with the
  blue peak about 10% stronger than the red peak. It is shown that these
  results are insensitive to the assumptions of geometry in the line
  forming regions and to the filling factor. The relative intensities
  only depend on an optically thin 1640.4 A line and optically thick
  He II Lyman lines. The observed asymmetry also imposes an upper limit
  to the density of 30 times the density at 8000 K in a plane parallel
  model. It is shown that the total intensity is very sensitive to the
  assumed geometry and filling factors. This sensitivity is parameterized
  in terms of a multiplicative factor to the assumed coronal radiation
  field. In a plane-parallel model the total intensity comes out a factor
  of 4 too low with the adopted coronal radiation field but already an
  enhancement factor of 2 of the incident radiation field gives a total
  intensity in agreement with observations. Note that this enhancement
  factor is only a quantification of the disagreement with observations.

---------------------------------------------------------
Title: The non-LTE formation of Li I lines in cool stars
Authors: Carlsson, M.; Rutten, R. J.; Bruls, J. H. M. J.; Shchukina,
   N. G.
1994A&A...288..860C    Altcode:
  We study the non-LTE (non local thermodynamic equilibrium)
  formation of Li I lines in the spectra of cool stars for a grid of
  radiative-equilibrium model atmospheres with variation in effective
  temperature, gravity, metallicity and lithium abundance. We analyze
  the mechanisms by which departures from LTE (local thermodynamic
  equilibrium) arise for Li I lines, first for the young sun (prior to
  its lithium depletion) and then across the cool-star grid. There are
  various mechanisms which compete in their effects on emergent Li I
  line strengths. Their neglect produces errors in lithium abundance
  determinations that vary in sign as well as size, both across the
  stellar grid and between different Li I lines (Figs). The errors are
  appreciable for all cooler stars and largest for cool lithium-rich
  metal-poor giants. They reverse sign between lithium-rich stars and
  lithium-poor stars for the λ=670.8nm resonance line, but not for the
  λ=610.4nm subordinate line. The non-LTE corrections are large enough
  that they should be taken into account in ongoing debates on lithium
  synthesis and depletion. We provide convenient numerical approximations
  of our results (Table 1) to this purpose. We end the paper with some
  examples in which non-LTE corrections change the slope of published
  relationships.

---------------------------------------------------------
Title: The Formation of Infrared Rydberg Lines
Authors: Rutten, R. J.; Carlsson, M.
1994IAUS..154..309R    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Computation of Infrared Hydrogen Lines
Authors: Carlsson, M.; Rutten, R. J.
1994IAUS..154..341C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Non-LTE Formation of Li I Lines from Cool Stars
Authors: Carlsson, M.; Rutten, R. J.; Bruls, J. H. M. J.; Shchukina,
   N. G.
1994ASPC...64..270C    Altcode: 1994csss....8..270C
  No abstract at ADS

---------------------------------------------------------
Title: Radiation shock dynamics in the solar chromosphere - results
    of numerical simulations
Authors: Carlsson, M.; Stein, R. F.
1994chdy.conf...47C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Chromospheric dynamics
Authors: Carlsson, Mats
1994chdy.conf.....C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Calcium II phase relations and chromospheric dynamics
Authors: Skartlien, R.; Carlsson, M.; Stein, R. F.
1994chdy.conf...79S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: MgI 12 μm diagnostics of sunspot penumbrae
Authors: Bruls, J. H. M. J.; Solanki, S. K.; Rutten, R. J.; Carlsson,
   M.
1994smf..conf..191B    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On i Lines in the Sun and Stars. I. Understanding the
    Resonance Lines
Authors: Carlsson, M.; Judge, P. G.
1993ApJ...402..344C    Altcode:
  The use of O I lines as spectral diagnostics of conditions in the
  chromospheres of the sun and cool stars is addressed, focusing on
  the resonance lines. The important processes influencing these lines
  are identified and an attempt it made to understand the detailed line
  transfer calculations in terms of simpler analytical models. How the
  lines respond to changes in uncertain atomic parameters is illustrated,
  and it is shown how the O I line flux densities depend simply and
  sensitively on the radiative transfer solution for hydrogen. Approximate
  analytical formulas are derived for the O I line flux densities in
  terms of the hydrogen number densities.

---------------------------------------------------------
Title: Non-LTE radiating shocks and the formation of Ca II lines in
    the solar chromosphere.
Authors: Carlsson, M.; Stein, R. F.
1993wpst.conf...21C    Altcode:
  The authors present self-consistent solutions of the time dependent
  one-dimensional equations of non-LTE radiation-hydrodynamics in solar
  chromospheric conditions. The vertical propagation of acoustic waves
  is calculated.

---------------------------------------------------------
Title: Non-LTE Radiating Acoustic Shocks and CA II K2V Bright Points
Authors: Carlsson, Mats; Stein, Robert F.
1992ApJ...397L..59C    Altcode:
  We present, for the first time, a self-consistent solution of the
  time-dependent 1D equations of non-LTE radiation hydrodynamics in
  solar chromospheric conditions. The vertical propagation of sinusoidal
  acoustic waves with periods of 30, 180, and 300 s is calculated. We
  find that departures from LTE and ionization recombination determine
  the temperature profiles of the shocks that develop. In LTE almost all
  the thermal energy goes into ionization, so the temperature rise is very
  small. In non-LTE, the finite transition rates delay the ionization to
  behind the shock front. The compression thus goes into thermal energy at
  the shock front leading to a high temperature amplitude. Further behind
  the shock front, the delayed ionization removes energy from the thermal
  pool, which reduces the temperature, producing a temperature spike. The
  180 s waves reproduce the observed temporal changes in the calcium K
  line profiles quite well. The observed wing brightening pattern, the
  violet/red peak asymmetry and the observed line center behavior are
  all well reproduced. The short-period waves and the 5 minute period
  waves fail especially in reproducing the observed behavior of the wings.

---------------------------------------------------------
Title: Solar hydrogen lines in the infrared
Authors: Carlsson, M.; Rutten, R. J.
1992A&A...259L..53C    Altcode:
  We study recently observed H I lines in the infrared solar spectrum,
  employing detailed NLTE modeling to explain their formation and to
  evaluate their diagnostic merits. The solar infrared H I lines vary much
  in character, depending on opacity and wavelength; our computations
  reproduce the observations closely. The line wings are primarily set
  by Stark broadening due to metal ions and protons; the line cores are
  sensitive to NLTE population departure divergence which is driven by
  Balmer-continuum photoionization. The formation heights of the H I
  lines range from the deep photosphere for near-infrared line wings
  to the chromosphere for line cores with wavelengths greater than 10
  microns; these features provide valuable diagnostics of the thermal
  structure of the solar atmosphere.

---------------------------------------------------------
Title: The calcium infrared triplet lines in stellar spectra.
Authors: Jorgensen, U. G.; Carlsson, M.; Johnson, H. R.
1992A&A...254..258J    Altcode:
  Observations of the infrared triplet lines of ionized calcium are often
  used as diagnostics of surface gravity among the stars contributing
  to the integrated light of distant galaxies. We have calculated the
  equivalent widths of these lines for a series of models with a broad
  range of input parameters to test their sensitivity to surface gravity,
  temperature, and calcium abundance. Over a larger range of parameter
  space than in earlier investigations, we find the sensitivity to be more
  complex than previously thought. We derive theoretical relations between
  equivalent width and log(g) for different values of T<SUB>eff</SUB> and
  metallicity and compare our results with observations. By actual NLTE
  calculations, we show that departures from LTE are small. Comparison
  of our results with observations of stars in the Galaxy suggests that
  the Ca/Fe ratio is an increasing function of metallicity.

---------------------------------------------------------
Title: The formation of the MG I emission features near 12 microns
Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G.
1992A&A...253..567C    Altcode:
  The formation of two Mg I 12-micron emission features in the
  solar spectrum, the existence of which was reported by Murcray et
  al. (1981), is explained using plane-parallel nonlocal thermodynamic
  equilibrium modeling with a radiative-equilibrium model atmosphere
  without chromosphere. It is shown that these emissions are a natural
  consequence of population depletion by line photon losses followed by
  population replenishment from the ionic reservoir in the highly excited
  levels. The results confirm the suggestion by Lemke and Holweger (1987)
  that the 12-micron lines are formed in the photosphere and disprove
  the claim by Zirin and Popp (1989) that the temperature minimum occurs
  much deeper than in standard models of the solar atmosphere.

---------------------------------------------------------
Title: Formation of the MG 112 TTM Lines
Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G.
1992ASPC...26..518C    Altcode: 1992csss....7..518C
  No abstract at ADS

---------------------------------------------------------
Title: CA II K2V Bright Grains Formed by Acoustic Waves
Authors: Carlsson, M.; Stein, R.
1992ASPC...26..515C    Altcode: 1992csss....7..515C
  No abstract at ADS

---------------------------------------------------------
Title: The MULTI Non-LTE Program (Invited Review)
Authors: Carlsson, M.
1992ASPC...26..499C    Altcode: 1992csss....7..499C
  No abstract at ADS

---------------------------------------------------------
Title: Formation of the KI 7699A Line in Sunspots
Authors: Caccin, B.; Carlsson, M.; Gomez, M. T.; Severino, G.
1991ASIC..341..415C    Altcode: 1991sabc.conf..415C
  No abstract at ADS

---------------------------------------------------------
Title: Global and Local Methods for One-Dimensional Problems -
    Implementation Aspects and Cpu-Time and Memory Scalings
Authors: Carlsson, M.
1991ASIC..341...39C    Altcode: 1991sabc.conf...39C
  No abstract at ADS

---------------------------------------------------------
Title: Shock Amplification by Radiation (With 1 Figure)
Authors: Carlsson, M.; Stein, R.
1991mcch.conf..366C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Deviation from the Wilson-Bappu relationship in faint red
    dwarf stars.
Authors: Elgaroy, O.; Engvold, O.; Carlsson, M.
1990A&A...234..308E    Altcode:
  New observations of the Mg II h and k lines on red dwarf stars have been
  carried out with the International Ultraviolet Explorer observatory. It
  is found that several of the dwarf stars in the sample have Mg II h
  and k lines which are narrower than expected from the Wilson-Bappu
  relationship, that is established for stars brighter than M(v) about
  7. The deviations may depend on the Mg II h and k line opacity. Evidence
  is presented in favor of the suggestion that the optical thickness of
  the Mg II lines in faint red dwarfs depends on the level of activity
  of the stars. Calculations based on models for the sun and YZ CMi
  (Mv = 12.3) support the observational results.

---------------------------------------------------------
Title: The Formation of the Mg I 12-Micron Emission Lines
Authors: Carlsson, M.; Rutten, R. J.; Shchukina, N. G.
1990PDHO....7..260C    Altcode: 1990dysu.conf..260C; 1990ESPM....6..260C
  Contents: The Mg I 12 μm line, LTE or NLTE, chromospheric formation,
  photospheric formation, collisional NLTE; departure diffusion.

---------------------------------------------------------
Title: Non-LTE radiative hydrodynamic interactions in the solar
    chromosphere.
Authors: Carlsson, M.; Stein, R.
1990ppst.conf..177C    Altcode:
  Strong, optically thick lines from iron and from ionized calcium and
  magnesium dominate the radiative losses of the solar chromosphere. This
  radiative loss cannot be approximated in the optically thin limit or
  by a grey approximation. In order to properly calculate the effects
  of waves in the chromosphere it is necessary to solve simultaneously
  the equations of hydrodynamics, radiative transfer and statistical
  equilibrium. Efficient methods in radiative transfer are here being
  combined with a treatment of the dynamical equations capable of
  resolving shocks. The authors present the first results showing that
  radiative hydrodynamic interactions may have a significant effect on
  the heating by acoustic waves.

---------------------------------------------------------
Title: Waves and radiation in stellar atmospheres.
Authors: Carlsson, M.
1990ppst.conf..115C    Altcode:
  The author discusses the problem of calculating the interactions between
  radiation and hydrodynamics in various density regimes. The possible
  approximations are outlined and diagnostic problems are discussed. The
  interactions between waves and radiation in the intermediate density
  regime (applicable to e.g. the solar chromosphere) are reviewed in
  some detail.

---------------------------------------------------------
Title: A 1-D code for radiation hydrodynamics problems.
Authors: Carlsson, M.
1989ftsa.conf...93C    Altcode:
  In order to properly calculate the effects of waves in the chromosphere
  it is necessary to solve simultaneously the equation of hydrodynamics,
  radiative transfer and statistical equilibrium. Efficient methods
  in radiative transfer are beeing combined with methods to treat the
  dynamical equations capable of resolving shocks. There is no complete
  code finished yet and this report is more of a progress report
  centered on methodology rather than a presentation of physically
  relevant results.

---------------------------------------------------------
Title: A Computer Program for Solving Multi-Level Non-Lte Radiative
    Transfer Problems in Moving or Static Atmospheres
Authors: Carlsson, M.
1988ASSL..138..273C    Altcode: 1988pffl.proc..273C; 1988IAUCo..94..273C
  A summary of the characteristics of a non-LTE computer program is
  presented. The code can be used to solve non-LTE radiative transfer
  problems in semi-infinite, plane-parallel one-dimensional atmospheres
  with a prescribed velocity field. The model atom can contain many
  atomic levels and several ionization stages. The lines are assumed to
  be formed with complete redistribution over the line profile which is
  assumed to be a Voigt function.

---------------------------------------------------------
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: Radiative transfer : an operator perturbation method and the
    application to mesoturbulence
Authors: Carlsson, Mats Per-Olof
1987PhDT.......250C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A New Sunspot Umbral Model and Its Variation with the Solar
    Cycle
Authors: Maltby, P.; Avrett, E. H.; Carlsson, M.; Kjeldseth-Moe, O.;
   Kurucz, R. L.; Loeser, R.
1986ApJ...306..284M    Altcode:
  Semiempirical model atmospheres are presented for the darkest parts of
  large sunspot umbrae, regions have called umbral cores. The approach is
  based on general-purpose computational procedures that are applicable
  to different types of stellar atmospheres. It is shown that recent
  umbral intensity measurements of the spectral energy distribution may
  be accounted for by an umbral core atmospheric model that varies with
  time during the solar cycle; the observed center-limb variation can be
  accounted for by the properties of the model. Three umbral core models
  are presented, corresponding to the early, middle, and late phases of
  the solar cycle. These three models also may be regarded as having the
  properties of dark, average, and bright umbral cores respectively. The
  effects of atomic, opacity, and abundance data uncertainties on
  the model calculations are briefly discussed. For comparison, a new
  reference model for the average quiet solar photosphere is given.

---------------------------------------------------------
Title: The outer atmosphere of the carbon star TX Piscium.
Authors: Eriksson, K.; Gustafsson, B.; Johnson, H. R.; Querci, F.;
   Querci, M.; Baumert, J. H.; Carlsson, M.; Olofsson, H.
1986A&A...161..305E    Altcode:
  A high-resolution LWP IUE spectrum of the bright N-type carbon star TX
  Psc demonstrates that the Mg II h and k emission profiles are strongly
  affected by absorption from Mg II, Mn I, probably Fe I, and possibly
  from molecules. The indication that the absorbing matter has a column
  density of not less than 10 to the 20th H atoms or molecules per sq
  cm is consistent with absorption in a slowly expanding envelope. The
  integrated Mg II line flux is found to be much greater than in 1981,
  and the radio CO (J = 1 - 0) line from the circumstellar shell is
  detected. Results for a column density of not larger than 10 to the 22nd
  H2 molecules/sq cm, and a radial velocity close to that of the star,
  are in agreement with those obtained from UV data. Some dust emission
  from carbon grains is suggested by the far infrared flux distribution,
  and a mass-loss rate estimation for the star of 10 to the -6th to 10
  to the -8th solar masses is obtained.

---------------------------------------------------------
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: A computer program for solving multi-level non-LTE radiative
    transferproblems in moving or static atmospheres.
Authors: Carlsson, M.
1986UppOR..33.....C    Altcode:
  A computer program for solving multi-level non-LTE radiative transfer
  problems is presented. The method used is that developed by Scharmer
  (1981) and Scharmer &amp; Carlsson (1985a, 1985b). The code can be
  used to solve non-LTE radiative transfer problems in semi-infinite,
  plane-parallel one-dimensional atmospheres with a prescribed macroscopic
  velocity field. The model atom can contain many atomic levels and
  several ionization stages. The lines are assumed to be formed with
  complete redistribution over the profile function which is assumed
  to be a Voigt function. <P />Some aspects of the numerical solution
  of radiative transfer problems are also discussed; in particular the
  choice of a starting approximation, instability problems due to the
  optically thin radiation field and the accuracy of methods for solving
  the transfer equation with a known source function.

---------------------------------------------------------
Title: Radiative Transfer and Turbulent Atmospheres
Authors: Carlsson, M.
1985tphr.conf...67C    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: A new approach to multi-level non-LTE radiative transfer
    problems.
Authors: Scharmer, G. B.; Carlsson, M.
1985JCoPh..59...56S    Altcode:
  A new approach to the numerical solution of multilevel, non-LTE
  problems is described. The standard non-LTE multilevel problem is
  formulated, and the statistical equilibrium equations and the radiative
  transfer equation are linearized. It is shown how to precondition the
  statistical equilibrium equations and the radiative transfer equation
  in a way which enables the solution of problems with strong numerical
  cancellation which arise from 'passive' scatterings at large optical
  depth. Simplifications in the numerical representation of radiative
  transfer processes are introduced which lead to rapid methods for
  setting up and solving the statistical equilibrium equations. Some
  calculations which have been made to test the convergence properties
  of the present scheme are described, and some generalizations of the
  present methods are briefly outlined.

---------------------------------------------------------
Title: A proposal for the LEST control system.
Authors: Engvold, O.; Andersen, T. E.; Carlsson, M.; Jensen, J. R.;
   Klim, K.
1985LFTR...15.....E    Altcode:
  Contents: Trends in development of computers and peripherals. Trends
  in telescope control and operation. Control system requirements for
  LEST. Proposed LEST control system. Remote control of LEST. Cost
  estimate. Estimated total cost of control and data reduction system.

---------------------------------------------------------
Title: Radiative transfer and turbulent atmospheres.
Authors: Carlsson, M.
1985MPARp.212...67C    Altcode:
  The paper is divided into two parts - in the first part some trends
  in radiative transfer methodology towards three dimensional modeling
  are reviewed. Special emphasis is given to operator perturbation
  techniques and to the impact of increased parallelism in new computer
  architecture. The second part illustrates some effects of velocity
  fields on the radiative transfer in spectral lines.

---------------------------------------------------------
Title: Effects of meso-scale velocity fields on the solar Ca II
    spectral lines.
Authors: Carlsson, M.; Scharmer, G. B.
1985cdm..proc..137C    Altcode:
  The effects of random mesoscale velocity fields on the solar Ca II
  K-line and the infrared 8542 A line are discussed, and average profiles
  and radiative cooling functions are compared with those obtained from
  a combination of microturbulence and macroturbulence. Profiles in
  the mesoscale regime could not be reproduced with any combination of
  micro- and macroturbulence owing to the fact that mesoscale velocity
  fields give core intensities that are much higher than those of static
  atmospheres. Calculations of radiative cooling in the two lines were
  different when mesoscale velocity fields were taken into account;
  this difference was due mainly to a redistribution of the radiative
  cooling between the lines.

---------------------------------------------------------
Title: A new method for solving multi-level non-LTE problems.
Authors: Scharmer, G. B.; Carlsson, M.
1985ASIC..152..189S    Altcode: 1985pssl.proc..189S
  A new scheme for solving multi-level non-LTE problems is described. This
  method uses an approximate operator for the relation between the
  intensity and the source function. This operator results in a
  matrix equation for the population numbers which has a simple and
  characteristic structure. Solutions are obtained such that the results
  are "exact", irrespective of the choice of the approximate operator.

---------------------------------------------------------
Title: The outer atmosphere of the carbon star TX Piscium.
Authors: Eriksson, K.; Gustafsson, B.; Johnson, H. R.; Querci, F.;
   Querci, M.; Baumert, J. H.; Carlsson, M.; Olofsson, H.
1985BETSP...2....5E    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The lightcurve and phase relation of the asteroid 133 Cyrene
Authors: Harris, A. W.; Carlsson, M.; Young, J. W.; Lagerkvist, C. I.
1984Icar...58..377H    Altcode:
  The asteroid 133 Cyrene was observed photometrically on 17 nights
  during oppositions in 1979 and 1980. The synodic period of rotation
  was found to be 12. <SUP>h</SUP>708 ± 0. <SUP>h</SUP>001 with an
  amplitude of ∼0. <SUP>m</SUP>30 during both oppositions. At large
  phase angles, the phase relation is quite ordinary ( β<SUB>v</SUB>
  ≈ 0.025 mag/degree); however, the low phase angle observations reveal
  a dramatic opposition brightening, ∼0.2 mag/degree near zero phase
  angle. The absolute magnitude, V(1,0), extrapolated with the above
  linear phase coefficient, is 8.40. The following color indicates were
  also measured: B- V = 0.90, U-B = 0.51.

---------------------------------------------------------
Title: Physical studies of asteroids. XI - Photoelectric observations
    of the asteroids 2, 161, 216 and 276
Authors: Carlsson, M.; Lagerkvist, C. -I.
1983A&AS...53..157C    Altcode:
  Lightcurves and UBV-colours are presented for the asteroids 2 Pallas,
  161 Athor, 216 Kleopatra and 276 Adelheid. For asteroid 216 a lightcurve
  amplitude of l<SUP>m</SUP>.1 was observed.

---------------------------------------------------------
Title: Physical studies of asteroids. IV - Photoelectric observations
    of the asteroids 47, 95, 431
Authors: Carlsson, M.; Lagerkvist, C. -I.
1981A&AS...45....1C    Altcode:
  Photoelectric lightcurves are presented. The synodic period of
  rotation of asteroid 95 was found to be 0<SUP>d</SUP>.3620 ±
  0<SUP>d</SUP>.0005. The asteroids 47 and 431 showed no significant
  brightness variation throughout the observing runs of 8 hours.

---------------------------------------------------------
Title: Physical studies of asteroids. I - Photoelectric observations
    of the asteroids 38, 218, 268, 344, 485, 683, 690 and 792
Authors: Carlsson, M.; Lagerkvist, C. -I.
1981A&AS...44...15C    Altcode:
  Lightcurves, rotation periods, maximum amplitudes, absolute magnitudes
  and UBV colours are presented. The following synodic periods of rotation
  were derived : Asteroid 218: 0<SUP>d</SUP>.268 ± 0<SUP>d</SUP>.006,
  asteroid 485: 0<SUP>d</SUP>.7331 ± 0<SUP>d</SUP>.0002, asteroid
  683: 0<SUP>d</SUP>.1801 ± 0<SUP>d</SUP>.0004, asteroid 792:
  0.<SUP>d</SUP>3823 ± 0<SUP>d</SUP>.0004.

---------------------------------------------------------
Title: Positions of asteroids obtained with the Schmidt telescope
    at the Uppsala Southern Station
Authors: Carlsson, M.; Hahn, G.; Lagerkvist, C. -I.
1980A&AS...41..117C    Altcode:
  Photographic positions of asteroids obtained at the Uppsala Southern
  Station are presented. Positions are presented for asteroids marked
  X or XX in Ephemerides of Minor Planets (1978), ordinary main-belt
  asteroids, Trojans and unnumbered asteroids. The IRIS plate measuring
  machine (Aslund et al., 1975) was used, and the means of the absolute
  differences between the catalog positions of the AGK3 stars and the
  observed positions were found to be 0.46 and 0.43 arc sec in right
  ascension (RA) and declination, respectively. For the SAO stars the
  corresponding values were 0.76 and 0.84 arc sec in RA and declination.