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Author name code: ugarte-urra
ADS astronomy entries on 2022-09-14
author:Ugarte-Urra, I.

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Title: Properties of EUV Imaging Spectrometer (EIS) Slot Observations
Authors: Young, Peter R.; Ugarte-Urra, Ignacio
2022SoPh..297...87Y    Altcode: 2022arXiv220314161Y
  The Extreme ultraviolet Imaging Spectrometer (EIS) on board the Hinode
  spacecraft has been operating since 2006, returning high-resolution data
  in the 170 - 212 and 246 - 292 Å wavelength regions. EIS has four slit
  options, with the narrow 1<SUP>”</SUP> and 2<SUP>”</SUP> slits used
  for spectroscopy and the wide 40<SUP>”</SUP> and 266<SUP>”</SUP>
  slits used for monochromatic imaging. In this article several
  properties of the 40<SUP>”</SUP> slit (or slot) are measured using
  the Fe XII 195.12 Å line, which is formed at 1.5 MK. The projected
  width of the slot on the detector shows a small variation along the
  slit with an average value of 40.949<SUP>”</SUP>. The slot image is
  tilted on the detector and a quadratic formula is provided to describe
  the tilt. The tilt corresponds to four pixels on the detector and the
  slot centroid is offset mostly to the right (longer wavelengths) of the
  1<SUP>”</SUP> slit by up to four pixels. Measurement of the intensity
  decrease at the edge of the slot leads to an estimate of the spatial
  resolution of the images in the x -direction. The resolution varies
  quadratically along the slot, with a minimum value of 2.9<SUP>”</SUP>
  close to the detector center. Intensities measured from the slot
  images are found to be on average 14% higher than those measured
  from the 1<SUP>”</SUP> slit at the same spatial location. Background
  subtraction is necessary to derive accurate intensities in quiet-Sun
  and coronal-hole regions. Prescriptions for deriving accurate slot
  intensities for different types of slot datasets are presented.

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Title: Geometric Assumptions in Hydrodynamic Modeling of Coronal
    and Flaring Loops
Authors: Reep, Jeffrey W.; Ugarte-Urra, Ignacio; Warren, Harry P.;
   Barnes, Will T.
2022ApJ...933..106R    Altcode: 2022arXiv220304385R
  In coronal loop modeling, it is commonly assumed that the loops
  are semicircular with a uniform cross-sectional area. However,
  observed loops are rarely semicircular, and extrapolations of the
  magnetic field show that the field strength decreases with height,
  implying that the cross-sectional area expands with height. We examine
  these two assumptions directly, to understand how they affect the
  hydrodynamic and radiative response of short, hot loops to strong,
  impulsive electron beam heating events. Both the magnitude and rate
  of area expansion impact the dynamics directly, and an expanding cross
  section significantly lengthens the time for a loop to cool and drain,
  increases upflow durations, and suppresses sound waves. The standard
  T ~ n <SUP>2</SUP> relation for radiative cooling does not hold
  with expanding loops, which cool with relatively little draining. An
  increase in the eccentricity of loops, on the other hand, only increases
  the draining timescale, and is a minor effect in general. Spectral
  line intensities are also strongly impacted by the variation in the
  cross-sectional area because they depend on both the volume of the
  emitting region as well as the density and ionization state. With a
  larger expansion, the density is reduced, so the lines at all heights
  are relatively reduced in intensity, and because of the increase of
  cooling times, the hottest lines remain bright for significantly
  longer. Area expansion is critical to accurate modeling of the
  hydrodynamics and radiation, and observations are needed to constrain
  the magnitude, rate, and location of the expansion-or lack thereof.

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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). 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, 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: Energetics and 3D Structure of Elementary Events in Solar
    Coronal Heating
Authors: Einaudi, G.; Dahlburg, R. B.; Ugarte-Urra, I.; Reep, J. W.;
   Rappazzo, A. F.; Velli, M.
2021ApJ...910...84E    Altcode: 2021arXiv210313499E
  Parker first proposed (1972) that coronal heating was the necessary
  outcome of an energy flux caused by the tangling of coronal magnetic
  field lines by photospheric flows. In this paper we discuss how
  this model has been modified by subsequent numerical simulations
  outlining in particular the substantial differences between the
  "nanoflares" introduced by Parker and "elementary events," defined
  here as small-scale spatially and temporally isolated heating
  events resulting from the continuous formation and dissipation
  of field-aligned current sheets within a coronal loop. We present
  numerical simulations of the compressible 3D MHD equations using the
  HYPERION code. We use two clustering algorithms to investigate the
  properties of the simulated elementary events: an IDL implementation of
  a density-based spatial clustering of applications with noise technique,
  and our own physical distance clustering algorithm. We identify and
  track elementary heating events in time, both in temperature and in
  Joule heating space. For every event we characterize properties such
  as density, temperature, volume, aspect ratio, length, thickness,
  duration, and energy. The energies of the events are in the range
  of 10<SUP>18</SUP>-10<SUP>21</SUP> erg, with durations shorter
  than 100 s. A few events last up to 200 s and release energies
  up to 10<SUP>23</SUP> erg. While high temperatures are typically
  located at the flux tube apex, the currents extend all the way to
  the footpoints. Hence, a single elementary event cannot at present
  be detected. The observed emission is due to the superposition of
  many elementary events distributed randomly in space and time within
  the loop.

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Title: Analysis of a long-duration AR throughout five solar rotations:
    Magnetic properties and ejective events
Authors: Iglesias, Francisco; Mandrini, Cristina H.; Lopez Fuentes,
   Marcelo; Cremades, Hebe; Lopez, Fernando M.; Merenda, Luciano A.;
   Ugarte-Urra, Ignacio
2021cosp...43E1757I    Altcode:
  Coronal mass ejections (CMEs), which are among the most magnificent
  solar eruptions, are a major driver of space weather and can thus affect
  diverse human technologies. Different processes have been proposed to
  explain the initiation and release of CMEs from solar active regions
  (ARs), without reaching consensus on which is the predominant scenario,
  and thus rendering impossible to accurately predict when a CME is going
  to erupt from a given AR. To investigate AR magnetic properties that
  favor CMEs production, we employ multi-spacecraft data to analyze a
  long duration AR (NOAA 11089, 11100, 11106, 11112 and 11121) throughout
  its complete lifetime, spanning five Carrington rotations from July
  to November 2010. We use data from the Solar Dynamics Observatory
  to study the evolution of the AR magnetic properties during the five
  near-side passages, and a proxy to follow the magnetic flux changes
  when no magnetograms are available, i.e. during far-side transits. The
  ejectivity is studied by characterizing the angular widths, speeds
  and masses of 108 CMEs that we associated to the AR, when examining
  a 124-day period. Such an ejectivity tracking was possible thanks
  to the multi-viewpoint images provided by the Solar-Terrestrial
  Relations Observatory and Solar and Heliospheric Observatory in a
  quasi-quadrature configuration. We also inspected the X-ray flares
  registered by the GOES satellite and found 162 to be associated to
  the AR under study. Given the substantial number of ejections studied,
  we use a statistical approach instead of a single-event analysis. We
  found three well defined periods of very high CMEs activity and two
  periods with no mass ejections that are preceded or accompanied by
  characteristic changes in the AR magnetic flux, free magnetic energy
  and/or presence of electric currents. Our large sample of CMEs and
  long term study of a single AR, provide further evidence relating AR
  magnetic activity to CME and Flare production.

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Title: Observation and Modeling of High-temperature Solar Active
    Region Emission during the High-resolution Coronal Imager Flight of
    2018 May 29
Authors: Warren, Harry P.; Reep, Jeffrey W.; Crump, Nicholas A.;
   Ugarte-Urra, Ignacio; Brooks, David H.; Winebarger, Amy R.; Savage,
   Sabrina; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
   Leon; Kobayashi, Ken; McKenzie, David; Morton, Richard; Rachmeler,
   Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
2020ApJ...896...51W    Altcode:
  Excellent coordinated observations of NOAA active region 12712 were
  obtained during the flight of the High-resolution Coronal Imager (Hi-C)
  sounding rocket on 2018 May 29. This region displayed a typical active
  region core structure with relatively short, high-temperature loops
  crossing the polarity inversion line and bright "moss" located at the
  footpoints of these loops. The differential emission measure (DEM) in
  the active region core is very sharply peaked at about 4 MK. Further,
  there is little evidence for impulsive heating events in the moss, even
  at the high spatial resolution and cadence of Hi-C. This suggests that
  active region core heating is occurring at a high frequency and keeping
  the loops close to equilibrium. To create a time-dependent simulation of
  the active region core, we combine nonlinear force-free extrapolations
  of the measured magnetic field with a heating rate that is dependent
  on the field strength and loop length and has a Poisson waiting time
  distribution. We use the approximate solutions to the hydrodynamic
  loop equations to simulate the full ensemble of active region core
  loops for a range of heating parameters. In all cases, we find that
  high-frequency heating provides the best match to the observed DEM. For
  selected field lines, we solve the full hydrodynamic loop equations,
  including radiative transfer in the chromosphere, to simulate transition
  region and chromospheric emission. We find that for heating scenarios
  consistent with the DEM, classical signatures of energy release,
  such as transition region brightenings and chromospheric evaporation,
  are weak, suggesting that they would be difficult to detect.

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Title: Solar physics in the 2020s: DKIST, parker solar probe, and
    solar orbiter as a multi-messenger constellation
Authors: Martinez Pillet, V.; Tritschler, A.; Harra, L.; Andretta, V.;
   Vourlidas, A.; Raouafi, N.; Alterman, B. L.; Bellot Rubio, L.; Cauzzi,
   G.; Cranmer, S. R.; Gibson, S.; Habbal, S.; Ko, Y. K.; Lepri, S. T.;
   Linker, J.; Malaspina, D. M.; Matthews, S.; Parenti, S.; Petrie, G.;
   Spadaro, D.; Ugarte-Urra, I.; Warren, H.; Winslow, R.
2020arXiv200408632M    Altcode:
  The National Science Foundation (NSF) Daniel K. Inouye Solar Telescope
  (DKIST) is about to start operations at the summit of Haleakala
  (Hawaii). DKIST will join the early science phases of the NASA
  and ESA Parker Solar Probe and Solar Orbiter encounter missions. By
  combining in-situ measurements of the near-sun plasma environment and
  detail remote observations of multiple layers of the Sun, the three
  observatories form an unprecedented multi-messenger constellation to
  study the magnetic connectivity inside the solar system. This white
  paper outlines the synergistic science that this multi-messenger
  suite enables.

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Title: Analysis of a long-duration AR throughout five solar rotations:
    Magnetic properties and ejective events
Authors: Iglesias, Francisco A.; Cremades, Hebe; Merenda, Luciano A.;
   Mandrini, Cristina H.; López, Fernando M.; López Fuentes, Marcelo
   C.; Ugarte-Urra, Ignacio
2020AdSpR..65.1641I    Altcode: 2019arXiv191101265I
  Coronal mass ejections (CMEs), which are among the most magnificent
  solar eruptions, are a major driver of space weather and can thus affect
  diverse human technologies. Different processes have been proposed to
  explain the initiation and release of CMEs from solar active regions
  (ARs), without reaching consensus on which is the predominant scenario,
  and thus rendering impossible to accurately predict when a CME is going
  to erupt from a given AR. To investigate AR magnetic properties that
  favor CMEs production, we employ multi-spacecraft data to analyze a
  long duration AR (NOAA 11089, 11100, 11106, 11112 and 11121) throughout
  its complete lifetime, spanning five Carrington rotations from July
  to November 2010. We use data from the Solar Dynamics Observatory
  to study the evolution of the AR magnetic properties during the five
  near-side passages, and a proxy to follow the magnetic flux changes
  when no magnetograms are available, i.e. during far-side transits. The
  ejectivity is studied by characterizing the angular widths, speeds
  and masses of 108 CMEs that we associated to the AR, when examining
  a 124-day period. Such an ejectivity tracking was possible thanks
  to the multi-viewpoint images provided by the Solar-Terrestrial
  Relations Observatory and Solar and Heliospheric Observatory in a
  quasi-quadrature configuration. We also inspected the X-ray flares
  registered by the GOES satellite and found 162 to be associated to
  the AR under study. Given the substantial number of ejections studied,
  we use a statistical approach instead of a single-event analysis. We
  found three well defined periods of very high CMEs activity and two
  periods with no mass ejections that are preceded or accompanied by
  characteristic changes in the AR magnetic flux, free magnetic energy
  and/or presence of electric currents. Our large sample of CMEs and
  long term study of a single AR, provide further evidence relating AR
  magnetic activity to CME and Flare production.

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Title: Further Evidence for Looplike Fine Structure inside
    “Unipolar” Active Region Plages
Authors: Wang, Y. -M.; Ugarte-Urra, I.; Reep, J. W.
2019ApJ...885...34W    Altcode: 2021arXiv210406633W
  Earlier studies using extreme-ultraviolet images and line-of-sight
  magnetograms from the Solar Dynamics Observatory (SDO) have suggested
  that active region (AR) plages and strong network concentrations
  often have small, looplike features embedded within them, even
  though no minority-polarity flux is visible in the corresponding
  magnetograms. Because of the unexpected nature of these findings, we
  have searched the SDO database for examples of inverted-Y structures
  rooted inside “unipolar” plages, with such jetlike structures
  being interpreted as evidence for magnetic reconnection between small
  bipoles and the dominant-polarity field. Several illustrative cases are
  presented from the period of 2013-2015, all of which are associated with
  transient outflows from AR “moss.” The triangular or dome-shaped
  bases have horizontal dimensions of ∼2-4 Mm, corresponding to ∼1-3
  granular diameters. We also note that the spongy-textured Fe IX 17.1 nm
  moss is not confined to plages, but may extend into regions where the
  photospheric field is relatively weak or even has mixed polarity. We
  again find a tendency for bright coronal loops seen in the 17.1,
  19.3, and 21.1 nm passbands to show looplike fine structure and
  compact brightenings at their footpoints. These observations provide
  further confirmation that present-day magnetograms are significantly
  underrepresenting the amount of minority-polarity flux inside AR plages
  and again suggest that footpoint reconnection and small-scale flux
  cancellation may play a major role in coronal heating, both inside
  and outside ARs.

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

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Title: The Magnetic Properties of Heating Events on High-temperature
    Active-region Loops
Authors: Ugarte-Urra, Ignacio; Crump, Nicholas A.; Warren, Harry P.;
   Wiegelmann, Thomas
2019ApJ...877..129U    Altcode: 2019arXiv190411976U
  Understanding the relationship between the magnetic field and coronal
  heating is one of the central problems of solar physics. However,
  studies of the magnetic properties of impulsively heated loops have
  been rare. We present results from a study of 34 evolving coronal loops
  observed in the Fe XVIII line component of 94 Å filter images obtained
  by the Atmospheric Imaging Assembly (AIA)/Solar Dynamics Observatory
  (SDO) from three active regions with different magnetic conditions. We
  show that the peak intensity per unit cross section of the loops depends
  on their individual magnetic and geometric properties. The intensity
  scales proportionally to the average field strength along the loop (B
  <SUB>avg</SUB>) and inversely with the loop length (L) for a combined
  dependence of {({B}<SUB>avg</SUB>}/L)}<SUP>0.52+/- 0.13</SUP>. These
  loop properties are inferred from magnetic extrapolations of the
  photospheric Helioseismic and Magnetic Imager (HMI)/SDO line-of-sight
  and vector magnetic field in three approximations: potential and two
  nonlinear force-free (NLFF) methods. Through hydrodynamic modeling
  (enthalpy-based thermal evolution loop (EBTEL) model) we show that
  this behavior is compatible with impulsively heated loops with a
  volumetric heating rate that scales as {ɛ }<SUB>{{H</SUB>}}∼
  {B}<SUB>avg</SUB>}<SUP>0.3+/- 0.2</SUP>/{L}<SUP>0.2{+/-
  </SUP><SUB>0.1</SUB><SUP>0.2</SUP>}.

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Title: Advancing the Advective Flux Transport Model
Authors: Upton, Lisa; Ugarte-Urra, Ignacio; Warren, Harry
2019AAS...23411802U    Altcode:
  The Advective Flux Transport (AFT) model has proven to be a reliable
  surface flux transport model for describing the evolution of the global
  magnetic field, accurately reproducing the evolution of the polar
  field. AFT has also been shown to accurately (within a factor of 2)
  reproduce the evolution of the total unsigned flux of simple active
  regions over the course of their lifetimes. Here we will discuss the
  work being done to validate and advance the AFT model. We will discuss
  the ability of AFT to reproduce other active region properties, such
  as tilt angles, polarity separation, area expansion and magnetic
  elements size distribution, for simple and more complex active
  regions. Currently, AFT uses data assimilation to incorporate the
  magnetic field from magnetograms from the Earth's vantage point. We will
  also discuss the work that is being done to develop an automated process
  for adding in far-side active regions observed by STEREO in 304 Å.

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Title: Dependence of Coronal Loop Temperature on Loop Length and
    Magnetic Field Strength
Authors: Dahlburg, R. B.; Einaudi, G.; Ugarte-Urra, I.; Rappazzo,
   A. F.; Velli, M.
2018ApJ...868..116D    Altcode:
  The temperature characteristics of solar coronal loops over a wide
  range of lengths and magnetic field strengths are investigated by
  means of numerical simulations. A very high correlation between
  magnetic field strength (B <SUB>0</SUB>) and maximum temperature
  (T <SUB>max</SUB>) is found. Shorter loops rooted at stronger fields
  are those that reach higher maximum temperatures. High temperatures
  constitute a small part of the loop volume. For loops of equal length,
  those with stronger magnetic fields have broader emission measure
  distributions. The conditions underlying the variety of loops observed
  in the solar corona are discussed, an explanation of why both cold
  and hot loops exist is provided, and suggestions are given as to
  what observations need to be made to confirm the results. Data in
  the analysis are provided by numerical simulations using HYPERION,
  an explicit massively parallel Fourier collocation-finite-difference
  code. In the simulations footpoints are convected with a randomized
  large-scale flow. This produces a Poynting flux which leads to the
  buildup of magnetic energy in the loop. The magnetic energy is then
  transformed into thermal energy by a magnetic reconnection process
  occurring within current sheets formed locally by an energy cascade
  toward small scales.

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Title: Toward a Quantitative Comparison of Magnetic Field
    Extrapolations and Observed Coronal Loops
Authors: Warren, Harry P.; Crump, Nicholas A.; Ugarte-Urra, Ignacio;
   Sun, Xudong; Aschwanden, Markus J.; Wiegelmann, Thomas
2018ApJ...860...46W    Altcode: 2018arXiv180500281W
  It is widely believed that loops observed in the solar atmosphere
  trace out magnetic field lines. However, the degree to which magnetic
  field extrapolations yield field lines that actually do follow loops
  has yet to be studied systematically. In this paper, we apply three
  different extrapolation techniques—a simple potential model, a
  nonlinear force-free (NLFF) model based on photospheric vector data,
  and an NLFF model based on forward fitting magnetic sources with
  vertical currents—to 15 active regions that span a wide range of
  magnetic conditions. We use a distance metric to assess how well each
  of these models is able to match field lines to the 12202 loops traced
  in coronal images. These distances are typically 1″-2″. We also
  compute the misalignment angle between each traced loop and the local
  magnetic field vector, and find values of 5°-12°. We find that the
  NLFF models generally outperform the potential extrapolation on these
  metrics, although the differences between the different extrapolations
  are relatively small. The methodology that we employ for this study
  suggests a number of ways that both the extrapolations and loop
  identification can be improved.

---------------------------------------------------------
Title: The Magnetic Properties of High-Temperature Active Region Loops
Authors: Ugarte-Urra, Ignacio; Crump, Nicholas A.; Warren, Harry
2018tess.conf22206U    Altcode:
  Understanding the relationship between the magnetic field and coronal
  heating is one of the central problems of solar physics. However,
  studies of the magnetic properties of impulsively heated loops have
  been rare. We present results from a study of 34 coronal loops observed
  in the in the Fe XVIII line component of AIA/SDO 94 Å filter images
  from three active regions with different magnetic conditions. We
  show that the peak radiance per unit volume of the Fe XVIII loops is
  correlated to their individual magnetic and geometric properties, namely
  field strength (B) and length (L). These are inferred from magnetic
  extrapolations of the photospheric field, in three approximations
  (potential and two NLFF methods), thus providing an uncertainty in
  our estimate of those quantities. Our results provide support, for
  the first time at the scale of individual loops, to the B/L scaling
  in the heating that has been successful in modeling full active regions.

---------------------------------------------------------
Title: Spectroscopic Observations of Current Sheet Formation and
    Evolution
Authors: Warren, Harry; Brooks, David; Ugarte-Urra, Ignacio; Crump,
   Nicholas A.; Doschek, George A.; Stenborg, Guillermo; Reep, Jeffrey W.
2018tess.conf31904W    Altcode:
  &lt;span class="s1" We report on the structure and evolution of
  a current sheet that formed in the wake of an eruptive X8.3 flare
  observed at the west limb of the Sun on September 10, 2017. Using
  observations from the Hinode/EIS and SDO/AIA, we find that plasma
  in the current sheet reaches temperatures of about 20MK and that the
  range of temperatures is relatively narrow. The highest temperatures
  occur at the base of the current sheet, in the region near the top
  of the post-flare loop arcade. The broadest high temperature line
  profiles, in contrast, occur at the largest observed heights. Further,
  line broadening is strong very early in the flare and diminishes over
  time. The current sheet can be observed in the AIA 211 and 171 channels,
  which have a considerable contribution from thermal bremsstrahlung
  at flare temperatures. Comparisons of the emission measure in these
  channels with other EIS wavelengths and AIA channels dominated by
  Fe line emission indicate a coronal composition and suggest that
  the current sheet is formed by the heating of plasma already in the
  corona. Finally, we also investigate the structure in the current sheet
  as imaged by AIA and find clear evidence for collapsing loops. Taken
  together, these observations suggest that some flare heating occurs
  in the current sheet while additional energy is released as newly
  reconnected field lines relax and become more dipolar.

---------------------------------------------------------
Title: Spectroscopic Observations of Current Sheet Formation and
    Evolution
Authors: Warren, Harry P.; Brooks, David H.; Ugarte-Urra, Ignacio;
   Reep, Jeffrey W.; Crump, Nicholas A.; Doschek, George A.
2018ApJ...854..122W    Altcode: 2017arXiv171110826W
  We report on the structure and evolution of a current sheet that formed
  in the wake of an eruptive X8.3 flare observed at the west limb of
  the Sun on 2017 September 10. Using observations from the EUV Imaging
  Spectrometer (EIS) on Hinode and the Atmospheric Imaging Assembly
  (AIA) on the Solar Dynamics Observatory, we find that plasma in the
  current sheet reaches temperatures of about 20 MK and that the range
  of temperatures is relatively narrow. The highest temperatures occur
  at the base of the current sheet, in the region near the top of the
  post-flare loop arcade. The broadest high temperature line profiles,
  in contrast, occur at the largest observed heights. Furthermore,
  line broadening is strong very early in the flare and diminishes over
  time. The current sheet can be observed in the AIA 211 and 171 channels,
  which have a considerable contribution from thermal bremsstrahlung
  at flare temperatures. Comparisons of the emission measure in these
  channels with other EIS wavelengths and AIA channels dominated by
  Fe line emission indicate a coronal composition and suggest that
  the current sheet is formed by the heating of plasma already in the
  corona. Taken together, these observations suggest that some flare
  heating occurs in the current sheet, while additional energy is released
  as newly reconnected field lines relax and become more dipolar.

---------------------------------------------------------
Title: Signatures Of Coronal Heating Driven By Footpoint Shuffling:
    Closed and Open Structures.
Authors: Velli, M. C. M.; Rappazzo, A. F.; Dahlburg, R. B.; Einaudi,
   G.; Ugarte-Urra, I.
2017AGUFMSH41D..01V    Altcode:
  We have previously described the characteristic state of the confined
  coronal magnetic field as a special case of magnetically dominated
  magnetohydrodynamic (MHD) turbulence, where the free energy in
  the transverse magnetic field is continuously cascaded to small
  scales, even though the overall kinetic energy is small. This coronal
  turbulence problem is defined by the photospheric boundary conditions:
  here we discuss recent numerical simulations of the fully compressible
  3D MHD equations using the HYPERION code. Loops are forced at their
  footpoints by random photospheric motions, energizing the field to
  a state with continuous formation and dissipation of field-aligned
  current sheets: energy is deposited at small scales where heating
  occurs. Only a fraction of the coronal mass and volume gets heated
  at any time. Temperature and density are highly structured at scales
  that, in the solar corona, remain observationally unresolved: the
  plasma of simulated loops is multithermal, where highly dynamical
  hotter and cooler plasma strands are scattered throughout the loop at
  sub-observational scales. We will also compare Reduced MHD simulations
  with fully compressible simulations and photospheric forcings with
  different time-scales compared to the Alfv'en transit time. Finally,
  we will discuss the differences between the closed field and open field
  (solar wind) turbulence heating problem, leading to observational
  consequences that may be amenable to Parker Solar Probe and Solar
  Orbiter.

---------------------------------------------------------
Title: Modeling Coronal Response in Decaying Active Regions with
    Magnetic Flux Transport and Steady Heating
Authors: Ugarte-Urra, Ignacio; Warren, Harry P.; Upton, Lisa A.;
   Young, Peter R.
2017ApJ...846..165U    Altcode: 2017arXiv170804324U
  We present new measurements of the dependence of the extreme ultraviolet
  (EUV) radiance on the total magnetic flux in active regions as obtained
  from the Atmospheric Imaging Assembly (AIA) and the Helioseismic
  and Magnetic Imager on board the Solar Dynamics Observatory. Using
  observations of nine active regions tracked along different stages of
  evolution, we extend the known radiance—magnetic flux power-law
  relationship (I\propto {{{Φ }}}<SUP>α </SUP>) to the AIA 335
  Å passband, and the Fe xviii 93.93 Å spectral line in the 94 Å
  passband. We find that the total unsigned magnetic flux divided by the
  polarity separation ({{Φ }}/D) is a better indicator of radiance for
  the Fe xviii line with a slope of α =3.22+/- 0.03. We then use these
  results to test our current understanding of magnetic flux evolution
  and coronal heating. We use magnetograms from the simulated decay of
  these active regions produced by the Advective Flux Transport model
  as boundary conditions for potential extrapolations of the magnetic
  field in the corona. We then model the hydrodynamics of each individual
  field line with the Enthalpy-based Thermal Evolution of Loops model with
  steady heating scaled as the ratio of the average field strength and the
  length (\bar{B}/L) and render the Fe xviii and 335 Å emission. We find
  that steady heating is able to partially reproduce the magnitudes and
  slopes of the EUV radiance—magnetic flux relationships and discuss
  how impulsive heating can help reconcile the discrepancies. This
  study demonstrates that combined models of magnetic flux transport,
  magnetic topology, and heating can yield realistic estimates for the
  decay of active region radiances with time.

---------------------------------------------------------
Title: Modeling Active Region Evolution - at the Sun’s Surface
    and into the Corona
Authors: Upton, Lisa; Ugarte-Urra, Ignacio; Warren, Harry; Young,
   Peter R.
2017SPD....4840502U    Altcode:
  The STEREO mission provides the first opportunity to track the long-term
  evolution of Active Regions over multiple rotations. The Advective Flux
  Transport (AFT) model is a state of the art Surface Flux Transport
  model, which simulates the observed near-surface flows to model
  the transport of magnetic flux over the entire Sun. Combining STEREO
  observations with AFT has allowed us to characterize the flux-luminosity
  relationship for He 304 Å and to validate the far-side evolution of
  individual active regions produced with AFT. Here, we present recent
  results in which we extend this radiance - magnetic flux power-law
  relationship to the AIA 335 Å passband, and the Fe XVIII 93.93 Å
  spectral line in the 94 Å passband. We use these results to test
  our current understanding of magnetic flux evolution and coronal
  heating by modeling the hydrodynamics of individual field lines with
  the Enthalpy-based Thermal Evolution of Loops (EBTEL) model including
  steady heating scaled as the ratio of the average field strength and
  the length (B/L). We find that steady heating is able to partially
  reproduce the EUV radiance - magnetic flux relationships and their
  observed temporal evolution. We also discuss how time-dependent
  heating may be able to explain the remaining discrepancies. This
  study demonstrates that combined models of magnetic flux transport,
  magnetic topology and heating can yield realistic estimates for the
  decay of active region radiances with time.

---------------------------------------------------------
Title: A study of the long term evolution in active region upflows
Authors: Harra, Louise K.; Ugarte-Urra, Ignacio; De Rosa, Marc;
   Mandrini, Cristina; van Driel-Gesztelyi, Lidia; Baker, Deborah;
   Culhane, J. Leonard; Démoulin, Pascal
2017PASJ...69...47H    Altcode:
  Since their discovery, upflows at the edges of active regions have
  attracted a lot of interest, primarily as they could potentially
  contribute to the slow solar wind. One aspect that has not been studied
  yet is how the long term evolution of active regions impacts the
  upflows. In this work, we analyze one active region that survives three
  solar rotations. We track how the flows change with time. We use local
  and global modeling of the decaying active region to determine how the
  age of the active region will impact the extent of the open magnetic
  fields, and then how some of the upflows could become outflows. We
  finish with a discussion of how these results, set in a broader context,
  can be further developed with the Solar Orbiter mission.

---------------------------------------------------------
Title: Advancing our Understanding of Active Region Evolution and
    Surface Flux Transport Using Far Side Imaging from STEREO 304
Authors: Upton, L.; Ugarte-Urra, I.; Warren, H. P.; Hathaway, D. H.
2016AGUFMSH42B..02U    Altcode:
  The STEREO mission, combined with SDO, provides a unique opportunity
  to view the solar surface continuously. These continuous observations
  provide the first opportunity to track the long-term evolution of Active
  Regions over multiple rotations. We present recent results in which we
  illustrate how He 304 Å images can be used as a proxies for magnetic
  flux measurements. We will present the long-term evolution of select
  isolated Active Regions as seen in He 304 Å. These data are then
  used to validate the far-side evolution of individual active regions
  produced with our Advective Flux Transport model - AFT. The AFT model
  is a state of the art Surface Flux Transport model, which simulates
  the observed near-surface flows (including an evolving convective flow
  velocity field) to model the transport of magnetic flux over the entire
  Sun. Finally, we will show that when new flux emergence occurs on the
  far-side of the Sun, 304 Å images can provide sufficient information
  about the active region to predict its evolution. These far-side Active
  Regions have a substantial impact on the coronal and interplanetary
  field configuration used for space weather predictions.

---------------------------------------------------------
Title: Observational Signatures of Coronal Heating
Authors: Dahlburg, R. B.; Einaudi, G.; Ugarte-Urra, I.; Warren, H. P.;
   Rappazzo, A. F.; Velli, M.; Taylor, B.
2016AGUFMSH42A..06D    Altcode:
  Recent research on observational signatures of turbulent heating of
  a coronal loop will be discussed. The evolution of the loop is is
  studied by means of numericalsimulations of the fully compressible
  three-dimensionalmagnetohydrodynamic equations using the HYPERION
  code. HYPERION calculates the full energy cycle involving footpoint
  convection, magnetic reconnection,nonlinear thermal conduction and
  optically thin radiation.The footpoints of the loop magnetic field
  are convected by random photospheric motions. As a consequence
  the magnetic field in the loop is energized and develops turbulent
  nonlinear dynamics characterized by the continuous formation and
  dissipation of field-aligned current sheets: energy is deposited
  at small scales where heating occurs. Dissipation is non-uniformly
  distributed so that only a fraction of thecoronal mass and volume gets
  heated at any time. Temperature and density are highly structured at
  scales which, in the solar corona, remain observationally unresolved:
  the plasma of the simulated loop is multi-thermal, where highly
  dynamical hotter and cooler plasma strands arescattered throughout
  the loop at sub-observational scales. Typical simulated coronal loops
  are 50000 km length and have axial magnetic field intensities ranging
  from 0.01 to 0.04 Tesla.To connect these simulations to observations
  the computed numberdensities and temperatures are used to synthesize
  the intensities expected inemission lines typically observed with
  the Extreme ultraviolet Imaging Spectrometer(EIS) on Hinode. These
  intensities are then employed to compute differentialemission measure
  distributions, which are found to be very similar to those derivedfrom
  observations of solar active regions.

---------------------------------------------------------
Title: Using STEREO/SECCHI EUV Far Side Solar Images as Proxies of
    Magnetic Fields
Authors: Ugarte-Urra, I.
2016AGUFMSH43A2552U    Altcode:
  In a recent study we showed that 304 A images can be used as a proxy of
  the total magnetic flux when magnetic field data is not available. We
  took advantage of our ability to obtain 360 degree EUV maps of the Sun,
  resulting from a combination of the multiple perspectives of SDO/AIA and
  STEREO EUVI A and B images, and tracked active regions over long periods
  of time that we then compared to a magnetic flux transport model. Here
  we simplify the scenario to show how to use single perspective far
  side 304 images to extract magnetic field information of active regions.

---------------------------------------------------------
Title: Correlation of Coronal Plasma Properties and Solar Magnetic
    Field in a Decaying Active Region
Authors: Ko, Yuan-Kuen; Young, Peter R.; Muglach, Karin; Warren,
   Harry P.; Ugarte-Urra, Ignacio
2016ApJ...826..126K    Altcode:
  We present the analysis of a decaying active region observed by
  the EUV Imaging Spectrometer on Hinode during 2009 December 7-11. We
  investigated the temporal evolution of its structure exhibited by plasma
  at temperatures from 300,000 to 2.8 million degrees, and derived the
  electron density, differential emission measure, effective electron
  temperature, and elemental abundance ratios of Si/S and Fe/S (as a
  measure of the First Ionization Potential (FIP) Effect). We compared
  these coronal properties to the temporal evolution of the photospheric
  magnetic field strength obtained from the Solar and Heliospheric
  Observatory Michelson Doppler Imager magnetograms. We find that, while
  these coronal properties all decreased with time during this decay
  phase, the largest change was at plasma above 1.5 million degrees. The
  photospheric magnetic field strength also decreased with time but
  mainly for field strengths lower than about 70 Gauss. The effective
  electron temperature and the FIP bias seem to reach a “basal” state
  (at 1.5 × 10<SUP>6</SUP> K and 1.5, respectively) into the quiet Sun
  when the mean photospheric magnetic field (excluding all areas &lt;10 G)
  weakened to below 35 G, while the electron density continued to decrease
  with the weakening field. These physical properties are all positively
  correlated with each other and the correlation is the strongest in
  the high-temperature plasma. Such correlation properties should be
  considered in the quest for our understanding of how the corona is
  heated. The variations in the elemental abundance should especially
  be considered together with the electron temperature and density.

---------------------------------------------------------
Title: Numerical Simulation of DC Coronal Heating
Authors: Dahlburg, Russell B.; Einaudi, G.; Taylor, Brian D.;
   Ugarte-Urra, Ignacio; Warren, Harry; Rappazzo, A. F.; Velli, Marco
2016SPD....47.0305D    Altcode:
  Recent research on observational signatures of turbulent heating of
  a coronal loop will be discussed. The evolution of the loop is is
  studied by means of numerical simulations of the fully compressible
  three-dimensional magnetohydrodynamic equations using the HYPERION
  code. HYPERION calculates the full energy cycle involving footpoint
  convection, magnetic reconnection, nonlinear thermal conduction
  and optically thin radiation. The footpoints of the loop magnetic
  field are convected by random photospheric motions. As a consequence
  the magnetic field in the loop is energized and develops turbulent
  nonlinear dynamics characterized by the continuous formation and
  dissipation of field-aligned current sheets: energy is deposited
  at small scales where heating occurs. Dissipation is non-uniformly
  distributed so that only a fraction of thecoronal mass and volume gets
  heated at any time. Temperature and density are highly structured at
  scales which, in the solar corona, remain observationally unresolved:
  the plasma of the simulated loop is multi thermal, where highly
  dynamical hotter and cooler plasma strands are scattered throughout
  the loop at sub-observational scales. Typical simulated coronal loops
  are 50000 km length and have axial magnetic field intensities ranging
  from 0.01 to 0.04 Tesla. To connect these simulations to observations
  the computed number densities and temperatures are used to synthesize
  the intensities expected in emission lines typically observed with
  the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. These
  intensities are then employed to compute differential emission measure
  distributions, which are found to be very similar to those derived
  from observations of solar active regions.

---------------------------------------------------------
Title: Observational Signatures of Coronal Loop Heating and Cooling
    Driven by Footpoint Shuffling
Authors: Dahlburg, R. B.; Einaudi, G.; Taylor, B. D.; Ugarte-Urra,
   I.; Warren, H. P.; Rappazzo, A. F.; Velli, M.
2016ApJ...817...47D    Altcode: 2015arXiv151203079D
  The evolution of a coronal loop is studied by means of
  numerical simulations of the fully compressible three-dimensional
  magnetohydrodynamic equations using the HYPERION code. The footpoints
  of the loop magnetic field are advected by random motions. As a
  consequence, the magnetic field in the loop is energized and develops
  turbulent nonlinear dynamics characterized by the continuous formation
  and dissipation of field-aligned current sheets: energy is deposited
  at small scales where heating occurs. Dissipation is nonuniformly
  distributed so that only a fraction of the coronal mass and volume gets
  heated at any time. Temperature and density are highly structured at
  scales that, in the solar corona, remain observationally unresolved:
  the plasma of our simulated loop is multithermal, where highly dynamical
  hotter and cooler plasma strands are scattered throughout the loop at
  sub-observational scales. Numerical simulations of coronal loops of
  50,000 km length and axial magnetic field intensities ranging from 0.01
  to 0.04 T are presented. To connect these simulations to observations,
  we use the computed number densities and temperatures to synthesize
  the intensities expected in emission lines typically observed with the
  Extreme Ultraviolet Imaging Spectrometer on Hinode. These intensities
  are used to compute differential emission measure distributions using
  the Monte Carlo Markov Chain code, which are very similar to those
  derived from observations of solar active regions. We conclude that
  coronal heating is found to be strongly intermittent in space and time,
  with only small portions of the coronal loop being heated: in fact,
  at any given time, most of the corona is cooling down.

---------------------------------------------------------
Title: Magnetic Flux Transport and the Long-term Evolution of Solar
    Active Regions
Authors: Ugarte-Urra, Ignacio; Upton, Lisa; Warren, Harry P.; Hathaway,
   David H.
2015ApJ...815...90U    Altcode: 2015arXiv151104030U
  With multiple vantage points around the Sun, Solar Terrestrial Relations
  Observatory (STEREO) and Solar Dynamics Observatory imaging observations
  provide a unique opportunity to view the solar surface continuously. We
  use He ii 304 Å data from these observatories to isolate and track
  ten active regions and study their long-term evolution. We find
  that active regions typically follow a standard pattern of emergence
  over several days followed by a slower decay that is proportional in
  time to the peak intensity in the region. Since STEREO does not make
  direct observations of the magnetic field, we employ a flux-luminosity
  relationship to infer the total unsigned magnetic flux evolution. To
  investigate this magnetic flux decay over several rotations we use
  a surface flux transport model, the Advective Flux Transport model,
  that simulates convective flows using a time-varying velocity field
  and find that the model provides realistic predictions when information
  about the active region's magnetic field strength and distribution at
  peak flux is available. Finally, we illustrate how 304 Å images can
  be used as a proxy for magnetic flux measurements when magnetic field
  data is not accessible.

---------------------------------------------------------
Title: On the long-term evolution of solar active regions from full
    Sun observations, magnetic flux transport and hydrodynamic modeling
Authors: Ugarte-Urra, Ignacio; Upton, Lisa; Warren, Harry; Hathaway,
   David H.
2015TESS....120104U    Altcode:
  With their multiple vantage points around the Sun, STEREO and SDO
  observations provide a unique opportunity to view the solar surface
  continuously. We use data from these observatories to study the
  long-term evolution of solar active regions in He II 304 A. We
  show that active regions follow a universal pattern of emergence
  over several days followed by a decay that is proportional to the
  peak intensity in the region. We find that magnetic surface flux
  transport simulations are able to reproduce this evolution. Since
  STEREO does not make direct observations of the magnetic field, we use
  the flux-luminosity relationship to infer the total unsigned magnetic
  flux from the He 304 A images. We also illustrate the use of far-side
  imaging to introduce solar active regions into magnetic surface flux
  transport simulations. We finally show how these models can be used to
  determine the long-term coronal emission evolution in active regions
  by coupling extrapolations of the magnetic flux transport simulations
  field with EBTEL solutions to the hydrodynamic loop equations.

---------------------------------------------------------
Title: Full-Sun observations for identifying the source of the slow
    solar wind
Authors: Brooks, David H.; Ugarte-Urra, Ignacio; Warren, Harry P.
2015NatCo...6.5947B    Altcode: 2016arXiv160509514B; 2015NatCo...6E5947B
  Fast (&gt;700 km s<SUP>-1</SUP>) and slow
  (~400 km s<SUP>-1</SUP>) winds stream from the Sun, permeate
  the heliosphere and influence the near-Earth environment. While the
  fast wind is known to emanate primarily from polar coronal holes,
  the source of the slow wind remains unknown. Here we identify possible
  sites of origin using a slow solar wind source map of the entire Sun,
  which we construct from specially designed, full-disk observations
  from the Hinode satellite, and a magnetic field model. Our map
  provides a full-Sun observation that combines three key ingredients
  for identifying the sources: velocity, plasma composition and magnetic
  topology and shows them as solar wind composition plasma outflowing on
  open magnetic field lines. The area coverage of the identified sources
  is large enough that the sum of their mass contributions can explain
  a significant fraction of the mass loss rate of the solar wind.

---------------------------------------------------------
Title: The VAULT2.0 Observing Campaign: A Comprehensive Investigation
    of the Chromosphere-Corona Interface at Sub-arcsecond scales
Authors: Vourlidas, A.; Korendyke, C.; Tun-Beltran, S. D.; Ugarte-Urra,
   I.; Morrill, J. S.; Warren, H. P.; Young, P.; De Pontieu, B.; Gauzzi,
   G.; Reardon, K.
2014AGUFMSH41C4155V    Altcode:
  We report the first results from an observing campaign in support of
  the VAULT2.0 sounding rocket launch on September 30, 2014. VAULT2.0
  is a Lya (1216Å) spectroheliograph capable of 0.3" (~250 km) spatial
  resolution. The objective of the VAULT2.0 project is the study of
  the chromosphere-corona interface. This interface has acquired renewed
  emphasis over the last few years, thanks to high-resolution observations
  from Hinode/SOT and EIS instruments and the Lya imaging from the two
  VAULT flights. The observations have shown that the upper chromosphere
  may play a more important role in heating the corona and in affecting
  EUV observations that previously thought: (1) by supplying the mass
  via Type-II spicules and, (2) by absorbing coronal emission. Many of
  the required clues for further progress are located in sub-arcsecond
  structures with temperatures between 10000 and 50000 K, a regime not
  accessible by Hinode or SDO. Lyman-alpha observations are, therefore,
  ideal, for filling in this gap. The observing campaign in support of
  the VAULT2.0 is closely coordinated with the Hinode and IRIS missions
  to study the mass/energy flow from the chromosphere to the corona with
  joint observations of type-II spicules, and the magnetic connectivity
  of coronal loops using the full imaging and spectral capabilities of
  IRIS, Hinode and SDO. Several ground-based observatories also provide
  important observations (IBIS, BBSO, SOLIS). The VAULT2.0 project is
  funded by the NASA LCAS program.

---------------------------------------------------------
Title: VizieR Online Data Catalog: UV spectrum of the quiet Sun
    above the limb (Warren+, 2014)
Authors: Warren, H. P.; Ugarte-Urra, I.; Landi, E.
2014yCat..22130011W    Altcode:
  First, we compare full-disk mosaics constructed by scanning the EIS slot
  over the Sun with irradiance observations made by the EUV Variability
  Experiment (EVE; Woods et al. 2012SoPh..275..115W) on the Solar
  Dynamics Observatory (SDO) mission. These comparisons provide a means
  of establishing the absolute calibration for EIS. Second, we combine
  extended EIS observations from above the limb in the quiet Sun with a
  simple temperature model to simultaneously determine the differential
  emission measure (DEM) distribution and the time-dependent changes
  to the effective areas that best fit all of the available spectral
  lines. <P />In Figure 2 we show the average spectrum from an observation
  of seven consecutive runs of EL<SUB>FULL</SUB>CCD<SUB>W</SUB>SUMER. The
  observations began on 2007 November 4 19:12 and ended on the same date
  at 23:51 UT. The EIS field of view was centered at (990", -50") about
  22" above the limb of the Sun. The central 129 pixels along the slit
  have been averaged over 38 exposures (11 exposures were corrupted in
  transmission to the ground) for a total of 4902 intensity measurements
  at each wavelength. Since each exposure is 300s, the spectrum represents
  1470600 pixels of effective exposure time and allows weak lines at
  the ends of the detector to be measured. <P />(1 data file).

---------------------------------------------------------
Title: The Absolute Calibration of the EUV Imaging Spectrometer
    on Hinode
Authors: Warren, Harry P.; Ugarte-Urra, Ignacio; Landi, Enrico
2014ApJS..213...11W    Altcode: 2013arXiv1310.5324W
  We investigate the absolute calibration of the EUV Imaging Spectrometer
  (EIS) on Hinode by comparing EIS full-disk mosaics with irradiance
  observations from the EUV Variability Experiment on the Solar Dynamics
  Observatory. We also use extended observations of the quiet corona above
  the limb combined with a simple differential emission measure model
  to establish new effective area curves that incorporate information
  from the most recent atomic physics calculations. We find that changes
  to the EIS instrument sensitivity are a complex function of both time
  and wavelength. We find that the sensitivity is decaying exponentially
  with time and that the decay constants vary with wavelength. The EIS
  short wavelength channel shows significantly longer decay times than
  the long wavelength channel.

---------------------------------------------------------
Title: The Hydrodynamics of High Temperature Plasma: Reproducing
    the Properties of High Temperature Emission in Solar Active Regions
Authors: Ugarte-Urra, Ignacio; Warren, Harry
2014AAS...22431205U    Altcode:
  The launch of Hinode and SDO have revolutionized our ability to
  measure the plasma properties of the solar corona. Many studies have
  documented both the temperature structure of the corona as well as
  its temporal variability. Of particular interest is the behavior
  of high temperature loops that are typically found in the core of
  an active region. Temperature distributions in these regions are
  often sharply peaked near 4 MK but rapidly evolving loops are also
  observed. In this talk we will present results from our effort to
  perform hydrodynamic simulations of 15 solar active regions that cover
  a wide range of solar conditions and to reconcile these simulations
  with observations. In this work we have coupled non-linear force
  free extrapolations with solutions to the hydrodynamic loop equations
  approximated by EBTEL. Using relatively simple heating scenarios we are
  able to reproduce three important properties of the observations: the
  dependance of the observed intensity on magnetic flux, the sharply
  peaked emission measure distributions for large regions, and the
  general frequency distribution of the observed events. Our current
  simulations, however, suggest much stronger 1MK emission near the
  neutral line than is observed, indicating the heating of small loops
  is not well understood. We also do not properly reproduce the relative
  distribution of large and small events in these active regions.

---------------------------------------------------------
Title: Determining Heating Timescales in Solar Active Region Cores
    from AIA/SDO Fe XVIII Images
Authors: Ugarte-Urra, Ignacio; Warren, Harry P.
2014ApJ...783...12U    Altcode: 2013arXiv1311.6346U
  We present a study of the frequency of transient brightenings in the
  core of solar active regions as observed in the Fe XVIII line component
  of AIA/SDO 94 Å filter images. The Fe XVIII emission is isolated using
  an empirical correction to remove the contribution of "warm" emission to
  this channel. Comparing with simultaneous observations from EIS/Hinode,
  we find that the variability observed in Fe XVIII is strongly correlated
  with the emission from lines formed at similar temperatures. We examine
  the evolution of loops in the cores of active regions at various stages
  of evolution. Using a newly developed event detection algorithm,
  we characterize the distribution of event frequency, duration, and
  magnitude in these active regions. These distributions are similar for
  regions of similar age and show a consistent pattern as the regions
  age. This suggests that these characteristics are important constraints
  for models of solar active regions. We find that the typical frequency
  of the intensity fluctuations is about 1400 s for any given line of
  sight, i.e., about two to three events per hour. Using the EBTEL 0D
  hydrodynamic model, however, we show that this only sets a lower limit
  on the heating frequency along that line of sight.

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Title: High Spatial Resolution Observations of Loops in the Solar
    Corona
Authors: Brooks, David H.; Warren, Harry P.; Ugarte-Urra, Ignacio;
   Winebarger, Amy R.
2013ApJ...772L..19B    Altcode: 2013arXiv1305.2246B
  Understanding how the solar corona is structured is of fundamental
  importance to determine how the Sun's upper atmosphere is heated to
  high temperatures. Recent spectroscopic studies have suggested that an
  instrument with a spatial resolution of 200 km or better is necessary
  to resolve coronal loops. The High Resolution Coronal Imager (Hi-C)
  achieved this performance on a rocket flight in 2012 July. We use Hi-C
  data to measure the Gaussian widths of 91 loops observed in the solar
  corona and find a distribution that peaks at about 270 km. We also
  use Atmospheric Imaging Assembly data for a subset of these loops and
  find temperature distributions that are generally very narrow. These
  observations provide further evidence that loops in the solar corona
  are often structured at a scale of several hundred kilometers, well
  above the spatial scale of many proposed physical mechanisms.

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Title: Heating Frequency in the core of Active Regions
Authors: Ugarte-Urra, Ignacio; Warren, H.
2013SPD....4430502U    Altcode:
  We present a study of the frequency and duration of brightenings in the
  core of solar active regions as observed in the Fe XVIII line component
  of AIA/SDO 94 A filter images. The Fe XVIII emission was isolated by
  removing the "warm" emission contribution using as proxy the emission
  from the AIA 193 and 171 channels. We examined the evolution of loop
  in cores of several active regions that span a wide range of total
  magnetic field strengths and at various stages of evolution. Using
  a newly developed event detector algorithm we find that the typical
  frequency of occurrence of detectable brightness enhancements is in
  the order of 20 minutes. Using EBTEL, a 0D hydrodynamical model, we
  show that a single loop heated a that frequency would be experiencing
  effectively steady heating. Then we evaluate different heating scenarios
  with multiple loops along the line-of-sight. Finally, we report on our
  preliminary efforts to reproduce those characteristic timescales on
  full active region models where field lines from a non-linear force
  free extrapolation are populated with EBTEL solutions.

---------------------------------------------------------
Title: Heating frequency in active region cores as observed in AIA
    Fe XVIII images
Authors: Ugarte-Urra, I.; Warren, H. P.
2013enss.confE..85U    Altcode:
  We present a study of the frequency and duration of brightenings in the
  core of solar active regions as observed in the Fe XVIII line component
  of AIA/SDO 94 A filter images. The Fe XVIII emission was isolated by
  removing the "warm" emission contribution using as proxy the emission
  from the AIA 193 and 171 channels. We examined the evolution of loop
  in cores of several active regions that span a wide range of total
  magnetic field strengths and at various stages of evolution. Using
  a newly developed event detector algorithm we find that the typical
  frequency of occurrence of brightness enhancements is in the order
  of tens of minutes. We then use those values to evaluate different
  scenarios of heating frequency using 1D hydrodynamical models of loops.

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Title: Is Active Region Core Variability Age Dependent?
Authors: Ugarte-Urra, Ignacio; Warren, Harry P.
2012ApJ...761...21U    Altcode:
  The presence of both steady and transient loops in active region cores
  has been reported from soft X-ray and extreme-ultraviolet observations
  of the solar corona. The relationship between the different loop
  populations, however, remains an open question. We present an
  investigation of the short-term variability of loops in the core of
  two active regions in the context of their long-term evolution. We
  take advantage of the nearly full Sun observations of STEREO and Solar
  Dynamics Observatory spacecraft to track these active regions as they
  rotate around the Sun multiple times. We then diagnose the variability
  of the active region cores at several instances of their lifetime
  using EIS/Hinode spectral capabilities. We inspect a broad range of
  temperatures, including for the first time spatially and temporally
  resolved images of Ca XIV and Ca XV lines. We find that the active
  region cores become fainter and steadier with time. The significant
  emission measure at high temperatures that is not correlated with a
  comparable increase at low temperatures suggests that high-frequency
  heating is viable. The presence, however, during the early stages,
  of an enhanced emission measure in the "hot" (3.0-4.5 MK) and "cool"
  (0.6-0.9 MK) components suggests that low-frequency heating also plays
  a significant role. Our results explain why there have been recent
  studies supporting both heating scenarios.

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Title: Solar Coronal Loops Resolved by Hinode and the Solar Dynamics
    Observatory
Authors: Brooks, David H.; Warren, Harry P.; Ugarte-Urra, Ignacio
2012ApJ...755L..33B    Altcode:
  Despite decades of studying the Sun, the coronal heating problem remains
  unsolved. One fundamental issue is that we do not know the spatial scale
  of the coronal heating mechanism. At a spatial resolution of 1000 km or
  more, it is likely that most observations represent superpositions of
  multiple unresolved structures. In this Letter, we use a combination
  of spectroscopic data from the Hinode EUV Imaging Spectrometer and
  high-resolution images from the Atmospheric Imaging Assembly on the
  Solar Dynamics Observatory to determine the spatial scales of coronal
  loops. We use density measurements to construct multi-thread models of
  the observed loops and confirm these models using the higher spatial
  resolution imaging data. The results allow us to set constraints on the
  number of threads needed to reproduce a particular loop structure. We
  demonstrate that in several cases million degree loops are revealed to
  be single monolithic structures that are fully spatially resolved by
  current instruments. The majority of loops, however, must be composed
  of a number of finer, unresolved threads, but the models suggest that
  even for these loops the number of threads could be small, implying
  that they are also close to being resolved. These results challenge
  heating models of loops based on the reconnection of braided magnetic
  fields in the corona.

---------------------------------------------------------
Title: Solar Coronal Loops Resolved by Hinode and SDO
Authors: Brooks, David H.; Warren, Harry P.; Ugarte-Urra, Ignacio
2012arXiv1205.5814B    Altcode:
  Despite decades of studying the Sun, the coronal heating problem remains
  unsolved. One fundamental issue is that we do not know the spatial scale
  of the coronal heating mechanism. At a spatial resolution of 1000 km or
  more it is likely that most observations represent superpositions of
  multiple unresolved structures. In this letter, we use a combination
  of spectroscopic data from the Hinode EUV Imaging Spectrometer (EIS)
  and high resolution images from the Atmospheric Imaging Assembly
  (AIA) on the Solar Dynamics Observatory to determine the spatial
  scales of coronal loops. We use density measurements to construct
  multi-thread models of the observed loops and confirm these models
  using the higher spatial resolution imaging data. The results allow
  us to set constraints on the number of threads needed to reproduce
  a particular loop structure. We demonstrate that in several cases
  million degree loops are revealed to be single monolithic structures
  that are fully spatially resolved by current instruments. The majority
  of loops, however, must be composed of a number of finer, unresolved
  threads; but the models suggest that even for these loops the number
  of threads could be small, implying that they are also close to being
  resolved. These results challenge heating models of loops based on
  the reconnection of braided magnetic fields in the corona.

---------------------------------------------------------
Title: Can We Resolve Coronal Loops with Hinode and SDO?
Authors: Ugarte-Urra, Ignacio; Brooks, D. H.; Warren, H. P.
2012AAS...22030903U    Altcode:
  A combination of spectral data from the Hinode EUV Imaging Spectrometer
  (EIS) and high resolution imaging from the Solar Dynamics Observatory
  (SDO) Atmospheric Imaging Assembly (AIA) are used to investigate
  the fundamental spatial scales of coronal loops. We construct
  multi-isothermal thread models and find that we are able to successfully
  reproduce the cross-loop intensity profiles observed by EIS and AIA. The
  models allow us to set constraints on the number of threads needed to
  reproduce a particular loop structure, and the results suggest that
  although most coronal loops remain unresolved, current instruments
  are close to resolving them. We discuss implications for future high
  resolution EUV spectral imaging instruments.

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Title: Filament destabilization and CME release during a long
    duration flare
Authors: Zuccarello, F.; Contarino, L.; Farnik, F.; Karlicky, M.;
   Romano, P.; Ugarte-Urra, I.
2011A&A...533A.100Z    Altcode:
  Context. During complex and long duration solar flares, several filament
  destabilizations or eruptions can occur that are often related to
  coronal mass ejections (CMEs). <BR /> Aims: We describe the study of
  an X3.8 long duration event (LDE) that occurred in NOAA 10720 on 17
  January 2005 and was characterized by three filament destabilizations
  and two CMEs. <BR /> Methods: Using multi-wavelength data provided
  by both ground-based instruments and satellites, in addition to MDI
  magnetograms, we investigated the morphological and magnetic evolution
  of the active region before and during the LDE. <BR /> Results: Our
  analysis of H<SUB>α</SUB> and 1600 Å images showed that initially a
  two-ribbon structure developed in the central part of the active region,
  where a filament was previously observed. At a later time, two bright
  ribbons (in the most eastern side) and a strong brightness increase
  (at the western outskirt of the active region) were simultaneously
  observed. In a subsequent time interval, a new pair of ribbons was
  observed in the western side of the active region. Moreover, a linear
  force-free field extrapolation helped identify a null point in the
  central part of the active region. <BR /> Conclusions: The initial
  filament destabilization that occurred in the central part of NOAA
  10720 was probably due to magnetic flux emergence and photospheric
  shearing motions, which caused a slow tether-cutting process beneath
  the filament. The rearrangement of the magnetic field configuration,
  occurring in the same area as the location of the null point, changed
  the magnetic field connectivity in the active region, triggering two
  filament eruptions in the eastern and western part of the active region
  and two halo CMEs, in a kind of domino effect.

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Title: A Standard-to-blowout Jet
Authors: Liu, Chang; Deng, Na; Liu, Rui; Ugarte-Urra, Ignacio; Wang,
   Shuo; Wang, Haimin
2011ApJ...735L..18L    Altcode: 2011arXiv1105.3244L
  The commonly observed jets provide critical information on the
  small-scale energy release in the solar atmosphere. We report a near
  disk-center jet on 2010 July 20, observed by the Solar Dynamics
  Observatory. In this event, the standard interchange magnetic
  reconnection between an emerging flux spanning 9 × 10<SUP>3</SUP>
  km and ambient open fields is followed by a blowout-like eruption. In
  the "standard" stage, as the emerging negative element approached the
  nearby positive network fields, a jet with a dome-like base in EUV grew
  for 30 minutes before the jet spire began to migrate laterally with
  enhanced flux emergence. In the "blowout" stage, the above converging
  fields collided and the subsequent cancellation produced a UV microflare
  lasting seven minutes, in which the dome of the jet seemed to be blown
  out as (1) the spire swung faster and exhibited an unwinding motion
  before vanishing, (2) a rising loop and a blob erupted leaving behind
  cusped structures, with the blob spiraling outward in acceleration
  after the flare maximum, and (3) ejecting material with a curtain-like
  structure at chromospheric to transition-region temperatures also
  underwent a transverse motion. It is thus suggested that the flare
  reconnection rapidly removes the outer fields of the emerging flux to
  allow its twisted core field to erupt, a scenario favoring the jet-scale
  magnetic breakout model as recently advocated by Moore et al. in 2010.

---------------------------------------------------------
Title: A Standard-to-blowout Jet
Authors: Liu, Chang; Deng, N.; Liu, R.; Ugarte-Urra, I.; Wang, S.;
   Wang, H.
2011SPD....42.1734L    Altcode: 2011BAAS..43S.1734L
  The commonly observed jets provide critical information on the
  small-scale energy release in the solar atmosphere. We report a
  near disk-center jet on 2010 July 20, observed by the Solar Dynamics
  Observatory. In this jet, the standard interchange magnetic reconnection
  between an emerging flux spanning 9x10<SUP>3</SUP> km and ambient
  open fields is followed by a blowout-like eruption. In the "standard"
  stage, as the emerging negative element approached the nearby positive
  network fields, a jet with a dome-like base in EUV grew for 30 minutes
  before the jet spire began to migrate laterally with enhanced flux
  emergence. In the "blowout" stage, the above converging fields collided
  and the subsequent cancellation produced an A6 microflare visible
  in 1700 A images. In the latter stage that lasted seven minutes, the
  dome of the jet seemed to be blown out as (1) the spire swung faster
  and exhibited an unwinding motion before vanishing, (2) a rising loop
  and a blob erupted leaving behind cusped structures, with the blob
  spiraling outward in acceleration after the flare maximum, and (3)
  ejecting material that formed a curtain-like structure at chromospheric
  to transition-region temperatures also underwent a transverse motion. It
  is thus suggested that the flare reconnection rapidly removes the outer
  fields of the emerging flux to allow its twisted core field to erupt,
  a scenario favoring the jet-scale magnetic breakout model as recently
  advocated by Moore et al. in 2010.

---------------------------------------------------------
Title: Temporal Variability of Active Region Outflows
Authors: Ugarte-Urra, Ignacio; Warren, Harry P.
2011ApJ...730...37U    Altcode: 2010arXiv1008.4730U
  Recent observations from the Extreme-ultraviolet Imaging Spectrometer
  (EIS) on board Hinode have shown that low-density areas on the
  periphery of active regions are characterized by strong blueshifts in
  the emission of spectral lines formed at 1 MK. These Doppler shifts have
  been associated with outward propagating disturbances observed with
  extreme-ultraviolet and soft X-ray imagers. Since these instruments
  can have broad temperature responses, we investigate these intensity
  fluctuations using the monochromatic imaging capabilities of the EIS
  wide slit (slot) and confirm their 1 MK nature. We also look into
  their spectral temporal variability using narrow slit observations and
  present the first Doppler movies of the outflow regions. We find that
  the Fe XII 195.119 Å blueshifted spectral profiles at their footpoints
  exhibit transient blue wing enhancements on timescales as short as the 5
  minute cadence. We have also looked at the fan peripheral loops observed
  at 0.6 MK in Si VII 275.368 Å in those regions and find no sign of
  the recurrent outward propagating disturbances with velocities of
  40-130 km s<SUP>-1</SUP> seen in Fe XII. We do observe downward trends
  (15-20 km s<SUP>-1</SUP>) consistent with the characteristic redshifts
  measured at their footpoints. We, therefore, find no evidence that the
  structures at these two temperatures and the intensity fluctuations
  they exhibit are related to one another.

---------------------------------------------------------
Title: The Temperature Dependence of Solar Active Region Outflows
Authors: Warren, Harry P.; Ugarte-Urra, Ignacio; Young, Peter R.;
   Stenborg, Guillermo
2011ApJ...727...58W    Altcode: 2010arXiv1008.2696W
  Spectroscopic observations with the EUV Imaging Spectrometer (EIS)
  on Hinode have revealed large areas of high-speed outflows at the
  periphery of many solar active regions. These outflows are of interest
  because they may connect to the heliosphere and contribute to the
  solar wind. In this paper, we use slit rasters from EIS in combination
  with narrowband slot imaging to study the temperature dependence and
  morphology of an outflow region and show that it is more complicated
  than previously thought. Outflows are observed primarily in emission
  lines from Fe XI to Fe XV. Observations at lower temperatures (Si VII),
  in contrast, show bright fan-like structures that are dominated by
  inflows. These data also indicate that the morphology of the outflows
  and the fans is different, outflows are observed in regions where
  there is no emission in Si VII. This suggests that the fans, which
  are often associated with outflows in studies involving imaging data,
  are not directly related to the active region outflows.

---------------------------------------------------------
Title: Science Objectives for an X-Ray Microcalorimeter Observing
    the Sun
Authors: Laming, J. Martin; Adams, J.; Alexander, D.; Aschwanden, M;
   Bailey, C.; Bandler, S.; Bookbinder, J.; Bradshaw, S.; Brickhouse,
   N.; Chervenak, J.; Christe, S.; Cirtain, J.; Cranmer, S.; Deiker, S.;
   DeLuca, E.; Del Zanna, G.; Dennis, B.; Doschek, G.; Eckart, M.; Fludra,
   A.; Finkbeiner, F.; Grigis, P.; Harrison, R.; Ji, L.; Kankelborg,
   C.; Kashyap, V.; Kelly, D.; Kelley, R.; Kilbourne, C.; Klimchuk, J.;
   Ko, Y. -K.; Landi, E.; Linton, M.; Longcope, D.; Lukin, V.; Mariska,
   J.; Martinez-Galarce, D.; Mason, H.; McKenzie, D.; Osten, R.; Peres,
   G.; Pevtsov, A.; Porter, K. Phillips F. S.; Rabin, D.; Rakowski, C.;
   Raymond, J.; Reale, F.; Reeves, K.; Sadleir, J.; Savin, D.; Schmelz,
   J.; Smith, R. K.; Smith, S.; Stern, R.; Sylwester, J.; Tripathi, D.;
   Ugarte-Urra, I.; Young, P.; Warren, H.; Wood, B.
2010arXiv1011.4052L    Altcode:
  We present the science case for a broadband X-ray imager with
  high-resolution spectroscopy, including simulations of X-ray spectral
  diagnostics of both active regions and solar flares. This is part of
  a trilogy of white papers discussing science, instrument (Bandler et
  al. 2010), and missions (Bookbinder et al. 2010) to exploit major
  advances recently made in transition-edge sensor (TES) detector
  technology that enable resolution better than 2 eV in an array that
  can handle high count rates. Combined with a modest X-ray mirror, this
  instrument would combine arcsecondscale imaging with high-resolution
  spectra over a field of view sufficiently large for the study of
  active regions and flares, enabling a wide range of studies such as
  the detection of microheating in active regions, ion-resolved velocity
  flows, and the presence of non-thermal electrons in hot plasmas. It
  would also enable more direct comparisons between solar and stellar
  soft X-ray spectra, a waveband in which (unusually) we currently have
  much better stellar data than we do of the Sun.

---------------------------------------------------------
Title: An Argument for Two Coronal Heating Models
Authors: Winebarger, Amy R.; Warren, H. P.; Brooks, D. H.; Ugarte-Urra,
   I.
2010AAS...21630002W    Altcode:
  There are several different models for the time and spatial scale
  of the energy release in the corona. Over the past several years,
  several different attempts at reconciling model predictions with
  observations have been made with varying degrees of success. In this
  talk, we review three popular heating models and discuss the expected
  observables associated with each model. We then show observations
  and compare them to the predictions. We find that observations of
  loops with a peak temperature near 1 MK are consistent with impulsive
  heating while observations of high temperature loops rooted in the
  moss are consistent with a steady heating model. This indicates the
  time scale of the heating, and potentially the heating mechanism,
  are markedly different in the two structures.

---------------------------------------------------------
Title: Variability of Hot Plasma in Solar Active Regions.
Authors: Ugarte-Urra, Ignacio; Warren, H. P.
2010AAS...21640712U    Altcode: 2010BAAS...41..861U
  The core of a solar active region is generally dominated by hot,
  high density, slowly evolving loops that appear to be consistent with
  steady heating. However, these loops are generally studied using
  instruments with a broad temperature response, which may mask some
  of the variability. Here we investigate the evolution of coronal
  loops emitting at temperatures above 3MK in fast scans taken with
  the Extreme-ultraviolet Imaging Spectrometer on board Hinode. We show
  evidence for short term variability at these temperatures and present
  the differential emission measure changes associated with them.

---------------------------------------------------------
Title: Modeling Evolving Coronal Loops with Observations from Stereo,
    Hinode, and Trace
Authors: Warren, Harry P.; Kim, David M.; DeGiorgi, Amanda M.;
   Ugarte-Urra, Ignacio
2010ApJ...713.1095W    Altcode: 2009arXiv0904.3920W
  The high densities, long lifetimes, and narrow emission measure
  distributions observed in coronal loops with apex temperatures
  near 1 MK are difficult to reconcile with physical models of the
  solar atmosphere. It has been proposed that the observed loops are
  actually composed of sub-resolution "threads" that have been heated
  impulsively and are cooling. We apply this heating scenario to nearly
  simultaneous observations of an evolving post-flare loop arcade
  observed with EUVI/STEREO, EIS/Hinode, XRT/Hinode, and TRACE. We
  find that it is possible to reproduce the extended loop lifetime,
  high electron density, and the narrow differential emission measure
  with a multi-thread hydrodynamic model provided that the timescale
  for the energy release is sufficiently short. The model, however,
  does not reproduce the evolution of the very high temperature emission
  observed with XRT. In XRT the emission appears diffuse and it may be
  that this discrepancy is simply due to the difficulty of isolating
  individual loops at these temperatures. This discrepancy may also
  reflect fundamental problems with our understanding of post-reconnection
  dynamics during the conductive cooling phase of loop evolution.

---------------------------------------------------------
Title: The Temperature Structure of Active Region Loops
Authors: Warren, H. P.; Ugarte-Urra, I.; Degiorgi, A.
2009ASPC..415..303W    Altcode:
  Previous solar observations have shown that coronal loops near 1 MK
  are difficult to reconcile with simple heating models. These loops
  have lifetimes that are long relative to a radiative cooling time and
  densities that are large relative to thermodynamic equilibrium. Models
  proposed to explain these properties generally rely on the existence of
  small scale filaments that are in various stages of heating and cooling,
  suggesting a distribution of temperatures within a loop. We present
  the observation of an evolving coronal loop observed with EIS/Hinode
  and TRACE. This loop has a high density, a narrow distribution of
  temperatures, and a lifetime that is long relative to a radiative
  cooling time. These properties will be difficult to reconcile with
  physical models of coronal loops.

---------------------------------------------------------
Title: Hinode Coronal Loop Observations
Authors: Ugarte-Urra, I.; Warren, H. P.; Brooks, D. H.
2009ASPC..415..241U    Altcode:
  Coronal loops are the building blocks of the solar
  atmosphere. Understanding their mechanism of formation means
  understanding the mechanism responsible for heating the solar
  corona. The properties of coronal loops are only partially
  established. Several issues such as the relationship among structures
  seen at different temperatures, the temperature distribution of the
  emission, or the degree of filamentation within a volume remain under
  discussion. Hinode, as the new generation solar observatory, provides
  the best suited diagnostics to address some of these issues. We
  demonstrate that this is the case using a case study, AR 10978,
  and encourage systematic studies of larger samples as solar activity
  increases. Results for AR 10978 are consistent with loops rooted in
  highly dynamic unipolar magnetic field areas made of multiple strands
  that get heated to at least 2.5 MK, and cool down rather coherently
  to transition region temperatures.

---------------------------------------------------------
Title: X-Ray Jets in Coronal Holes: Numerical Simulation and Hinode
    Observations
Authors: Moreno-Insertis, F.; Galsgaard, K.; Ugarte-Urra, I.
2009ASPC..415...51M    Altcode:
  We report on our recent 3D numerical models of the launching of hot,
  high-speed jets in a coronal hole following the emergence of magnetized
  plasma from the solar interior. As part of the same research, we have
  also analyzed Hinode (EIS and XRT) and Soho-MDI observational data
  of an actual process of flux emergence followed by jet launching in
  a coronal hole. From the observations, we reconstruct the magnetic
  topology at the emergence site and calculate velocity and further
  physical properties of the observed event. The 3D model was calculated
  for realistic conditions in a coronal hole, including, in particular,
  a low-density (10<SUP>8</SUP> particles cm<SUP>-3</SUP>), high Alfven
  speed plasma prior to the emergence. After emergence, a ribbon-like
  current sheet is created at the site of collision of the emerging and
  preexisting magnetic systems. Field line reconnection ensues, which
  leads to the ejection of the X-Ray jet. We analyze the global magnetic
  topology, and the temperature, velocity and current distribution in
  the 3D experiment. The numerical results provide a good match to the
  observed features of the coronal hole jets. This is meant regarding
  both our own observational results as well as the ranges and average
  values of the statistical study by Savcheva et al. (2007).

---------------------------------------------------------
Title: Exploiting EIS/Hinode Imaging Diagnostic Capabilities
Authors: Ugarte-Urra, Ignacio; Warren, H. P.
2009SPD....40.1219U    Altcode:
  Using a wide slit, also called slot, the Extreme-ultraviolet Imaging
  Spectrometer, on-board Hinode, is capable of obtaining relatively
  fast (1-3 min) simultaneous monochromatic images of various spectral
  lines with different formation temperatures ranging 0.4-3 MK. This
  mode allows us to study morphology and dynamics of solar coronal
  and transition region structures across the temperature spectrum in
  a similar way to an EUV imager. This is achieved at the expense of
  spectral resolution. In this paper we investigate the plasma diagnostic
  capabilities of these spectrally pure images.Wide slit images can be
  interpreted as a superposition of simultaneous narrow slit spectra
  from adjacent solar positions. From the comparison of consecutive
  narrow slit rasters and wide slit images, we demonstrate that by
  making simple assumptions it is possible to extract the narrow slit
  spectra out of the slot images. This encouraging result opens up the
  door for plasma diagnostics, like electron density from spectral line
  ratios and differential emission measure analysis, for solar dynamic
  events. Various examples, as well as the limitations and validity of
  the assumptions, are discussed.

---------------------------------------------------------
Title: Active Region Transition Region Loop Populations and Their
    Relationship to the Corona
Authors: Ugarte-Urra, Ignacio; Warren, Harry P.; Brooks, David H.
2009ApJ...695..642U    Altcode: 2009arXiv0901.1075U
  The relationships among coronal loop structures at different
  temperatures are not settled. Previous studies have suggested that
  coronal loops in the core of an active region (AR) are not seen cooling
  through lower temperatures and therefore are steadily heated. If loops
  were cooling, the transition region would be an ideal temperature regime
  to look for a signature of their evolution. The Extreme-ultraviolet
  Imaging Spectrometer on Hinode provides monochromatic images of the
  solar transition region and corona at an unprecedented cadence and
  spatial resolution, making it an ideal instrument to shed light on
  this issue. Analysis of observations of AR 10978 taken in 2007 December
  8-19 indicates that there are two dominant loop populations in the AR:
  (1) core multitemperature loops that undergo a continuous process of
  heating and cooling in the full observed temperature range 0.4-2.5
  MK and even higher as shown by the X-Ray Telescope and (2) peripheral
  loops which evolve mostly in the temperature range 0.4-1.3 MK. Loops
  at transition region temperatures can reach heights of 150 Mm in the
  corona above the limb and develop downflows with velocities in the
  range of 39-105 km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: The X17.2 flare occurred in NOAA 10486: an example of filament
    destabilization caused by a domino effect
Authors: Zuccarello, F.; Romano, P.; Farnik, F.; Karlicky, M.;
   Contarino, L.; Battiato, V.; Guglielmino, S. L.; Comparato, M.;
   Ugarte-Urra, I.
2009A&A...493..629Z    Altcode:
  Context: It is now possible to distinguish between two main models
  describing the mechanisms responsible for eruptive flares : the standard
  model, which assumes that most of the energy is released, by magnetic
  reconnection, in the region hosting the core of a sheared magnetic
  field, and the breakout model, which assumes reconnection occurs
  at first in a magnetic arcade overlaying the eruptive features. <BR
  />Aims: We analyze the phenomena observed in NOAA 10486 before and
  during an X17.2 flare that occurred on 2003 October 28, to study the
  relationship between the pre-flare and flare phases and determine which
  model is the most suitable for interpreting this event. <BR />Methods:
  We performed an analysis of multiwavelength data set available for
  the event using radio data (0.8-4.5 GHz), images in the visible range
  (WL and Hα), EUV images (1600 and 195 Å), and X-ray data, as well
  as MDI longitudinal magnetograms. We determined the temporal sequence
  of events occurring before and during the X17.2 flare and the magnetic
  field configuration in the linear force-free field approximation. <BR
  />Results: The active region was characterized by a multiple arcade
  configuration and the X17.2 flare was preceded, by ~2 h, by the partial
  eruption of one filament. This eruption caused reconnection at null
  points located in the low atmosphere and a decrease in magnetic tension
  in the coronal field lines overlaying other filaments present in the
  active region. As a consequence, these filaments were destabilized and
  the X17.2 flare occurred. <BR />Conclusions: The phenomena observed
  in NOAA 10486 before and during the X17.2 flare cannot be explained
  by a simple scenario such as the standard or breakout model, but
  instead in terms of a so-called domino effect, involving a sequence
  of destabilizing processes that triggered the flare.

---------------------------------------------------------
Title: The Role of Transient Brightenings in Heating the Solar Corona
Authors: Brooks, David H.; Ugarte-Urra, Ignacio; Warren, Harry P.
2008ApJ...689L..77B    Altcode:
  Nanoflare reconnection events have been proposed as a mechanism for
  heating the corona. Parker's original suggestion was that frequent
  reconnection events occur in coronal loops due to the braiding of the
  magnetic field. Many observational studies, however, have focused on the
  properties of isolated transient brightenings unassociated with loops,
  but their cause, role, and relevance for coronal heating have not
  yet been established. Using Hinode SOT magnetograms and high-cadence
  EIS spectral data we study the relationship between chromospheric,
  transition region, and coronal emission and the evolution of the
  magnetic field. We find that hot, relatively steadily emitting coronal
  loops and isolated transient brightenings are both associated with
  magnetic flux regions that are highly dynamic. An essential difference,
  however, is that brightenings are typically found in regions of flux
  collision and cancellation whereas coronal loops are generally rooted
  in magnetic field regions that are locally unipolar with unmixed
  flux. This suggests that the type of heating (transient vs. steady) is
  related to the structure of the magnetic field, and that the heating
  in transient events may be fundamentally different than in coronal
  loops. This implies that they do not play an important role in heating
  the "quiescent" corona.

---------------------------------------------------------
Title: Observations of Active Region Loops with the EUV Imaging
    Spectrometer on Hinode
Authors: Warren, Harry P.; Ugarte-Urra, Ignacio; Doschek, George A.;
   Brooks, David H.; Williams, David R.
2008ApJ...686L.131W    Altcode: 2008arXiv0808.3227W
  Previous solar observations have shown that coronal loops near 1 MK
  are difficult to reconcile with simple heating models. These loops have
  lifetimes that are long relative to a radiative cooling time, suggesting
  quasi-steady heating. The electron densities in these loops, however,
  are too high to be consistent with thermodynamic equilibrium. Models
  proposed to explain these properties generally rely on the existence
  of smaller scale filaments within the loop that are in various stages
  of heating and cooling. Such a framework implies that there should be
  a distribution of temperatures within a coronal loop. In this paper
  we analyze new observations from the EUV Imaging Spectrometer (EIS)
  on Hinode. EIS is capable of observing active regions over a wide range
  of temperatures (Fe VIII-Fe XVII) at relatively high spatial resolution
  (1”). We find that most isolated coronal loops that are bright in Fe
  XII generally have very narrow temperature distributions (σ<SUB>T</SUB>
  lesssim 3 × 10<SUP>5</SUP> K), but are not isothermal. We also derive
  volumetric filling factors in these loops of approximately 10%. Both
  results lend support to the filament models.

---------------------------------------------------------
Title: The Role of Isolated EUV Brightenings in Heating the Corona
Authors: Brooks, D. H.; Warren, H. P.; Ugarte-Urra, I.
2008AGUSMSP43C..04B    Altcode:
  Nanoflare reconnection events have been proposed as a mechanism for
  heating the solar corona. Parker's original suggestion was that frequent
  reconnection events occur in coronal loops due to the twisting and
  braiding of the magnetic field. Many observational studies, however,
  have focused on the radiating properties of isolated brightening
  events, but their cause, role, and relevance for coronal heating
  has not yet been established. Using Hinode Solar Optical Telescope
  (SOT) magnetograms and high cadence EUV Imaging Spectrometer (EIS)
  slot rasters we study the relationship between transition region and
  coronal emission and the evolution of the magnetic field. We find that
  hot, relatively steadily emitting coronal loops are generally rooted in
  magnetic field regions that are locally unipolar yet highly dynamic,
  whereas detailed analysis shows that ubiquitous EUV brightenings are
  found in regions of magnetic flux cancellation in the photosphere. This
  suggests that the heating in transient events may be fundamentally
  different than the heating in coronal loops and that they play no
  direct role in the heating of the quiescent corona.

---------------------------------------------------------
Title: EIS: a new view of active region transition region loops
Authors: Ugarte-Urra, I.; Warren, H. P.; Brooks, D. H.
2008AGUSMSP41C..03U    Altcode:
  The EUV Imaging Spectrometer (EIS) on board Hinode is providing
  unprecedented diagnostics of solar coronal plasmas. One of its less
  exploited capabilities is the ability to make instantaneous spectrally
  pure images with the 40” slot. Simultaneous transition region (Mg
  VI, Mg VII, Si VII) and coronal (Fe XI - Fe XVI) images allow us
  to observe active region loops as we have not been able to before,
  given the spatial resolution (1arcsec pixels), cadence (70s) and,
  most importantly, the broad temperature coverage. Under this scrutiny
  two distinct populations of active region transition region loops can
  be differentiated: core loops that result from the cooling of several
  million degree plasma; and fan structures with their main contribution
  in the 0.6-1 MK temperature range. These results suggest that the cores
  of active regions are not as steady as commonly assumed and reinforce
  the idea of coexistance of differentiated loop populations within the
  active region topology. We present the properties of the loops and we
  discuss the implications that these new observations have for current
  transition region and coronal models.

---------------------------------------------------------
Title: Jets in Coronal Holes: Hinode Observations and
    Three-dimensional Computer Modeling
Authors: Moreno-Insertis, F.; Galsgaard, K.; Ugarte-Urra, I.
2008ApJ...673L.211M    Altcode: 2007arXiv0712.1059M
  Recent observations of coronal hole areas with the XRT and
  EIS instruments on board the Hinode satellite have shown with
  unprecedented detail the launching of fast, hot jets away from the
  solar surface. In some cases these events coincide with episodes
  of flux emergence from beneath the photosphere. In this Letter we
  show results of a three-dimensional numerical experiment of flux
  emergence from the solar interior into a coronal hole and compare
  them with simultaneous XRT and EIS observations of a jet-launching
  event that accompanied the appearance of a bipolar region in MDI
  magnetograms. The magnetic skeleton and topology that result in the
  experiment bear a strong resemblance to linear force-free extrapolations
  of the SOHO/MDI magnetograms. A thin current sheet is formed at the
  boundary of the emerging plasma. A jet is launched upward along the
  open reconnected field lines with values of temperature, density,
  and velocity in agreement with the XRT and EIS observations. Below the
  jet, a split-vault structure results with two chambers: a shrinking one
  containing the emerged field loops and a growing one with loops produced
  by the reconnection. The ongoing reconnection leads to a horizontal
  drift of the vault-and-jet structure. The timescales, velocities, and
  other plasma properties in the experiment are consistent with recent
  statistical studies of this type of event made with Hinode data.

---------------------------------------------------------
Title: Observations of Transient Active Region Heating with Hinode
Authors: Warren, Harry P.; Ugarte-Urra, Ignacio; Brooks, David H.;
   Cirtain, Jonathan W.; Williams, David R.; Hara, Hirohisa
2007PASJ...59S.675W    Altcode: 2007arXiv0711.0357W
  We present observations of transient active region heating events
  observed with the Extreme Ultraviolet Imaging Spectrometer (EIS) and
  X-ray Telescope (XRT) on Hinode. This initial investigation focuses
  on NOAA active region 10940 as observed by Hinode on 2007 February 1
  between 12 and 19UT. In these observations we find numerous examples
  of transient heating events within the active region. The high spatial
  resolution and broad temperature coverage of these instruments allows
  us to track the evolution of coronal plasma. The evolution of the
  emission observed with XRT and EIS during these events is generally
  consistent with loops that have been heated and are cooling. We have
  analyzed the most energetic heating event observed during this period,
  a small GOES B-class flare, in some detail and present some of the
  spectral signatures of the event, such as relative Doppler shifts at
  one of the loop footpoints and enhanced line widths during the rise
  phase of the event. While the analysis of these transient events has
  the potential to yield insights into the coronal heating mechanism,
  these observations do not rule out the possibility that there is a
  strong steady heating level in the active region. Detailed statistical
  analysis will be required to address this question definitively.

---------------------------------------------------------
Title: Hinode EUV Imaging Spectrometer Observations of Solar Active
    Region Dynamics
Authors: Mariska, John T.; Warren, Harry P.; Ugarte-Urra, Ignacio;
   Brooks, David H.; Williams, David R.; Hara, Hirohisa
2007PASJ...59S.713M    Altcode: 2007arXiv0708.4309M
  The EUV Imaging Spectrometer (EIS) on the Hinode satellite is capable of
  measuring emission line center positions for Gaussian line profiles to a
  fraction of a spectral pixel, resulting in relative solar Doppler-shift
  measurements with an accuracy of a less than a km s<SUP>-1</SUP> for
  strong lines. We show an example of the application of that capability
  to an active region sit-and-stare observation in which the EIS slit
  is placed at one location on the Sun and many exposures are taken
  while the spacecraft tracking keeps the same solar location within
  the slit. For the active region examined (NOAA10930), we find that
  significant intensity and Doppler-shift fluctuations as a function of
  time are present at a number of locations. These fluctuations appear
  to be similar to those observed in high-temperature emission lines
  with other space-borne spectroscopic instruments. With its increased
  sensitivity over earlier spectrometers and its ability to image many
  emission lines simultaneously, EIS should provide significant new
  constraints on Doppler-shift oscillations in the corona.

---------------------------------------------------------
Title: Hinode EUV Imaging Spectrometer Observations of Active Region
Loop Morphology: Implications for Static Heating Models of Coronal
    Emission
Authors: Brooks, David H.; Warren, Harry P.; Ugarte-Urra, Ignacio;
   Matsuzaki, Keiichi; Williams, David R.
2007PASJ...59S.691B    Altcode:
  Theoretically, magnetic fields are expected to expand as they rise
  above the photosphere and into the corona, so the apparent uniform
  cross-sections of active region loops are difficult to understand. There
  has been some debate as to whether coronal loops really have constant
  cross-sections, or are actually unresolved and composed of expanding
  threads within the constant cross-section envelopes. Furthermore, loop
  expansion is critical to the success or failure of hydrostatic models
  in reproducing the intensities and morphology of observed emission. We
  analyze Hinode EIS (EUV Imaging Spectrometer) observations of loops
  in active region 10953 and detect only moderate apex width expansion
  over a broad range of temperatures from log T<SUB>e</SUB> / K = 5.6
  to 6.25. The expansion is less than required by steady-state heating
  models of coronal emission suggesting that such models will have
  difficulty reproducing both low and high temperature loop emission
  simultaneously. At higher temperatures (&gt; log T<SUB>e</SUB> /
  K = 6.3) the apex widths increase substantially, but the emission
  at these temperatures likely comes from a combination of multiple
  loops. These observations demonstrate the advantage of EIS over previous
  instruments. For the first time, active region loops can be examined
  over a broad temperature range with high temperature fidelity and the
  same spatial resolution. The results therefore provide further clues
  to the coronal heating timescale and thus have implications for the
  direction of future modeling efforts.

---------------------------------------------------------
Title: The Magnetic Topology of Coronal Mass Ejection Sources
Authors: Ugarte-Urra, Ignacio; Warren, Harry P.; Winebarger, Amy R.
2007ApJ...662.1293U    Altcode: 2007astro.ph..3049U
  In an attempt to test current initiation models of coronal mass
  ejections (CMEs), with an emphasis on the magnetic breakout model, we
  inspect the magnetic topology of the sources of 26 CME events in the
  context of their chromospheric and coronal response in an interval
  of approximately 9 hr around the eruption onset. First we perform
  current-free (potential) extrapolations of photospheric magnetograms
  to retrieve the key topological ingredients, such as coronal magnetic
  null points. Then we compare the reconnection signatures observed in
  the high-cadence and high spatial resolution Transition Region and
  Coronal Explorer (TRACE) images with the location of the relevant
  topological features. The comparison reveals that only seven events
  can be interpreted in terms of the breakout model, which requires
  a multipolar topology with preeruption reconnection at a coronal
  null. We find, however, that a larger number of events (12) cannot
  be interpreted in those terms. No magnetic null is found in six of
  them. Seven other cases remain difficult to interpret. We also show
  that there are no systematic differences between the CME speed and
  flare energies of events under different interpretations.

---------------------------------------------------------
Title: EIS/Hinode Look At Active Region Dynamics
Authors: Ugarte-Urra, Ignacio; Warren, H. P.; Brooks, D. H.; Williams,
   D. R.; Cirtain, J. W.; McKenzie, D. E.; Weber, M.; Hara, H.; Harra,
   L. K.
2007AAS...210.9429U    Altcode: 2007BAAS...39..222U
  We present some initial results from the Hinode EUV Imaging Spectrometer
  (EIS) on the heating and cooling of active region loops. The events
  we observe are part of the short term active region evolution within
  the span of 50 hours of sit-and-stare observations. We investigate
  the temporal evolution of the intensity and Doppler shift of spectral
  lines formed at different temperatures. We then determine time lags
  and cooling times at various temperature regimes and discuss the
  results in the context of previous results provided by earlier space
  missions. This effort is considered a first step into the hydrodynamic
  modeling of the loop structures. The morphology of the structures is
  obtained from X-Ray Telescope (XRT) and TRACE images.

---------------------------------------------------------
Title: Determining the Chirality Of Filaments Associated with CMEs
Authors: Mulu, Fana; Winebarger, A.; Ugarte-Urra, I.; Warren, H.
2007AAS...210.2914M    Altcode: 2007BAAS...39..139M
  There is currently much debate over the initiation mechanism of coronal
  mass ejections. One distinction in the various models is the degree
  of magnetic complexity in the pre-CME active region. For instance,
  the magnetic breakout model requires a null point in the coronal
  field and for reconnection to occur at that null point. Recently,
  Ugarta-Urra et al. (2007) investigated the magnetic topology of the
  sources of 26 CME events using extrapolations of photospheric fields to
  find the location of coronal magnetic null points, if any, and hence
  test the validity of the breakout model. Seven of the 26 CMEs studied
  supported the breakout model, 12 did not support the model, and 7 were
  difficult to interpret. In this poster, we present preliminary results
  from a continuing investigation these 26 events. First we determine
  if an Halpha filament was associated with the eruption. If a filament
  was present, we find the chirality (handedness) of the filaments using
  the method described by Martin (1998). We will categorize the filament
  properties in terms of Ugarte-Urra's findings to determine if certain
  filament properties are associated with a breakout or non-breakout CMEs.

---------------------------------------------------------
Title: An Investigation into the Variability of Heating in a Solar
    Active Region
Authors: Ugarte-Urra, Ignacio; Winebarger, Amy R.; Warren, Harry P.
2006ApJ...643.1245U    Altcode:
  Previous studies have indicated that both steady and impulsive heating
  mechanisms play a role in active region heating. In this paper,
  we present a study of 20 hours of soft X-ray and EUV observations
  of solar active region NOAA AR 8731. We examine the evolution of six
  representative loop structures that brighten and fade first from X-ray
  images and subsequently from the EUV images. We determine their lifetime
  and the delay between their appearance in the different filters. We
  find that the lifetime in the EUV filters is much longer than expected
  for a single cooling loop. We also notice that the delay in the loops'
  appearance in the X-ray and EUV filters is proportional to the loop
  length. We model one of the loops using a hydrodynamic model with both
  impulsive and quasi-steady heating functions and find that neither of
  these simple heating functions can well reproduce the observed loop
  characteristics in both the X-ray and EUV images. Hence, although this
  active region is dominated by variable emission and the characteristics
  of the observed loops are qualitatively consistent with a cooling loop,
  the timescale of the heating in this active region remains unknown.

---------------------------------------------------------
Title: The Magnetic Topology of Coronal Mass Ejection Sources
Authors: Ugarte-Urra, Ignacio; Warren, H. P.
2006SPD....37.2205U    Altcode: 2006BAAS...38..249U
  We present results from the study of the sources of 15 coronal mass
  ejections (CME) observed with TRACE. These events are a subset of
  the preliminary 48 catalogued CME events with sources that fall
  within ±400 arcsec of disk center and were observed with TRACE, in
  any of its UV or EUV bandpasses, during the period 1998--2003. The
  evolution of the eruptions is analyzed in the context of the magnetic
  topology given by a potential field extrapolation of a photospheric
  magnetogram. The extrapolations are used to determine the presence of
  nulls and quasi-separatrix layers. We discuss the results in the context
  of the current CME models and their observational predictions. The
  breakout model for CMEs, for example, requires the presence of a null
  encompassing the sheared neutral line. Pre-eruption reconnection is
  expected to take place at the null. We find magnetic nulls in many
  of the events. For most of them, however, we do not see compelling
  evidence for pre-eruption reconnection.This research was supported by
  the NASA Living With a Star Program.

---------------------------------------------------------
Title: Optical and EUV observations of solar flare kernels
Authors: García-Alvarez, D.; Johns-Krull, C. M.; Doyle, J. G.;
   Ugarte-Urra, I.; Madjarska, M. S.; Butler, C. J.
2005A&A...444..593G    Altcode:
  We present high-resolution spectral observations, covering the entire
  optical region (3800-9000 Å), of a solar flare observed during
  a multi-wavelength campaign. The flare, recorded on 2002 January
  11, was a medium solar flare event (GOES class C7.5). The spectral
  observations were carried out using the Hamilton echelle spectrograph on
  the coudé auxiliary telescope at Lick Observatory and with the Coronal
  Diagnostic Spectrometer (CDS) on board SoHO. The high signal-to-noise
  optical spectra are analysed using the same techniques as we applied to
  stellar flare data. Hα images obtained at Big Bear Solar Observatory
  (BBSO), plus magnetograms obtained with the Michelson Doppler Imager
  (MDI) on board SoHO and Transition Region And Coronal Explorer (TRACE)
  1600 Å were used in the flare analysis. We observe stellar-like
  behaviour in the main solar chromospheric activity indicators, which
  show either filling-in or emission during the flare. We find that the
  Balmer and Ca II lines show asymmetric profiles, with red-shifted
  wings and blue-shifted cores. This behaviour could be explained by
  material expanding. During the flare, the Mg i and Fe i lines show
  a filling-in of the line profile indicating that the flare affected
  the lower atmosphere. There is some evidence for pre-flare heating
  as seen in Fe xix 592 Å. Furthermore, O v 629 Å shows an increase
  in flux some 10 min. before the coronal lines, perhaps indicating
  particle beam heating in the initial stages of the flare. We have
  also determined the main physical parameters at flare maximum. The
  electron densities and electron temperatures found for the flare imply
  that the Balmer emitting plasma originates in the chromosphere. The
  physical parameters obtained for the modelled flare are consistent
  with previously derived values for solar flares.

---------------------------------------------------------
Title: Evidence for explosive event activity originating in the
    chromosphere
Authors: Doyle, J. G.; Ishak, B.; Ugarte-Urra, I.; Bryans, P.; Summers,
   H. P.
2005A&A...439.1183D    Altcode:
  We report on a joint SUMER, CDS, TRACE study, concentrating on
  a region which shows prolonged EUV explosive event (EE) activity
  in the transition region line N v 1238 Å, yet little evidence of
  such activity in another transition region line O v 629 Å (formed
  at a similar temperature) which was observed simultaneously. A
  possible explanation for the lack of major activity in the O v line
  in several explosive events could be that they originate in the lower
  chromosphere. This is consistent with the enhancements in the C i 1249
  Å line and with the findings of another study which reported time
  delays between the chromospheric and transition region lines in some
  EE's using high cadence observations (10 s exposure time) obtained
  with the SUMER spectrometer in H i Ly 6 (20 000 K) and S vi (200 000
  K). Using the generalized collisional-radiative picture, including
  the population of metastable levels, we derive the density dependent
  contribution function for both N v 1238 and O v 629 for four values
  of the electron density; 10<SUP>6</SUP> cm<SUP>-3</SUP> representing
  the low density limit, 10<SUP>9</SUP> cm<SUP>-3</SUP> for a typical
  quiet Sun electron density plus 10<SUP>11</SUP> cm<SUP>-3</SUP> and
  10<SUP>12</SUP> cm<SUP>-3</SUP> for an active region. These calculations
  show that with increasing electron density, both lines shift to slightly
  lower temperatures. However, the major difference is in the relative
  increase in the line flux with increasing density. For N v, increasing
  the density to 10<SUP>11</SUP> cm<SUP>-3</SUP> results in a 60%
  increase in the line flux, while O v shows a 30% decrease. Increasing
  the electron density to 10<SUP>12</SUP> cm<SUP>-3</SUP> results in a
  factor of two decrease in the O v flux, thus making it difficult to
  detect explosive event activity in this line if the event is formed
  in the chromosphere. Other explosive events which show simultaneous
  activity in both lines are probably formed in the transition region. In
  one such event, activity is observed in both N v and O v, yet nothing
  in C i. In this event we also observe an increase in the TRACE 173
  emission, delayed by ≈40 s compared to the transition region lines.

---------------------------------------------------------
Title: Electron density along a coronal loop observed with CDS/SOHO
Authors: Ugarte-Urra, I.; Doyle, J. G.; Walsh, R. W.; Madjarska, M. S.
2005A&A...439..351U    Altcode:
  The analysis of a coronal loop observed by CDS and EIT on board SOHO
  is presented. The loop was situated above the North-East limb at
  a latitude of ~48°, being clearly visible in the hottest lines of
  the dataset, Fe xvi 360.76 Å, i.e. greater than 2 000 000 K. The
  cooler lines in the sample (i.e. O v 629.73 Å and He i 584.35 Å)
  showed only a brightening at the footpoints location. Based on
  the Fe xiv 353.84/334.17 line ratio, the electron density along
  the loop was determined following three different approaches for
  the background subtraction. No differences, within the error bars,
  can be found between the three methods. At the apex, the density is
  0.9×10<SUP>9</SUP> cm<SUP>-3</SUP>, while at the footpoint it is
  50% greater, i.e. 1.4×10<SUP>9</SUP> cm<SUP>-3</SUP>. The inferred
  filling factor values along the loop, at the formation temperature
  of the lines, are in the range 0.2-0.9. One dimensional hydrodynamic
  modelling of the loop along a given field line, gravity neglected,
  was performed. A minimum χ<SUP>2</SUP> analysis results in a best fit
  case where the total energy input is directed preferentially to the loop
  footpoint (the heating rate is three times larger at the base than at
  the apex). An isochoric solution can not be ruled out completely. The
  exercise illustrates the necessity of accurate spectral diagnostics
  in order to derive definite conclusions from theoretical models and
  suggests the need for simultaneous density and temperature diagnostics.

---------------------------------------------------------
Title: Comparison Between Explosive Events of Two Transition Region
    Lines of Similar Temperatures
Authors: Ishak, B.; Doyle, J. G.; Ugarte-Urra, I.
2005PADEU..15...21I    Altcode:
  We present the difference in behavior of two transition region lines at
  very close temperatures, observed with SUMER/SoHO. N v 1238.82 A shows
  a series of explosive events with broadenings mostly shifted to the
  blue. This is not seen in O v 629.73 A, the behavior of which remains
  "quiet" throughout most of the time series.

---------------------------------------------------------
Title: Electron densities in EUV coronal bright points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Del Zanna, G.
2005A&A...435.1169U    Altcode:
  Electron density measurements of six coronal bright points have been
  obtained using line ratio diagnostics of four ions in the temperature
  range 1.3-2.0 × 10<SUP>6</SUP> K. The results suggest that BP plasma
  has more similarities to active region plasma than to quiet Sun
  plasma. Nevertheless, they do not show the exact same behaviour: the
  increase of electron density at temperatures over log~T<SUB>e</SUB> ~
  6.2, observed in the core of active regions, has not been detected. The
  Fe XII results based on new atomic data, although in better agreement
  decreasing more than a factor of two the densities obtained with older
  calculations, are still in some instances higher than those from Si
  X. This could be a consequence of the inhomogeneity of the plasma in
  the observed volume. New measurements with a better constriction of
  the volumetric properties seem necessary to rule out the influence of
  other factors and confirm whether there is an inconsistency between
  the ions, perhaps due to line blending problems in the Fe XII lines.

---------------------------------------------------------
Title: Dissertation Talk: Brightness and Magnetic Evolution of Solar
    Coronal Bright Points
Authors: Ugarte-Urra, I.
2005AGUSMSP22A..01U    Altcode:
  Dissertation: A study of the brightness and magnetic evolution of
  several Extreme ultraviolet (EUV) coronal bright points (hereafter BPs)
  using CDS, EIT, MDI (onboard SOHO) and TRACE is presented. The results
  confirm that, down to 1" resolution, BPs are made of small loops with
  lengths of ~6 Mm and cross-sections of ~2 Mm. The loops are very
  dynamic, evolving in time scales as short as 1 -- 2 minutes. This
  is reflected in a highly variable EUV response with fluctuations
  highly correlated in spectral lines at transition region temperatures
  (in the range 3.2×104 -- 3.5×105 K). A wavelet analysis of the
  intensity variations reveals, for the first time, the existence of
  quasi-periodic oscillations with periods ranging 400--1000 s, in the
  range of periods characteristic of the chromospheric network. The
  link between BPs and network bright points is discussed. Co-spatial
  and co-temporal TRACE and MDI images also reveal the signature of
  heating events that produce sudden EUV brightenings simultaneous to
  magnetic flux cancellations. This is interpreted in terms of magnetic
  reconnection events.

---------------------------------------------------------
Title: Brightness and magnetic evolution of solar coronal bright
    points
Authors: Ugarte Urra, Ignacio
2005PhDT.........3U    Altcode:
  This thesis presents a study of the brightness and magnetic evolution
  of several Extreme ultraviolet (EUV) coronal bright points (hereafter
  BPs). The study was carried out using several instruments on board the
  Solar and Heliospheric Observatory, supported by the high resolution
  imaging from the Transition Region And Coronal Explorer. <P />The
  results confirm that, down to 1" resolution, BPs are made of small
  loops with lengths of [approximate]6 Mm and cross-sections of ≈2
  Mm. The loops are very dynamic, evolving in time scales as short as
  1 - 2 minutes. This is reflected in a highly variable EUV response
  with fluctuations highly correlated in spectral lines at transition
  region temperatures, but not always at coronal temperatures. A
  wavelet analysis of the intensity variations reveals the existence
  of quasi-periodic oscillations with periods ranging 400--1000s, in
  the range of periods characteristic of the chromospheric network. The
  link between BPs and network bright points is discussed, as well as
  the interpretation of the oscillations in terms of global acoustic
  modes of closed magnetic structures. <P />A comparison of the magnetic
  flux evolution of the magnetic polarities to the EUV flux changes is
  also presented. Throughout their lifetime, the intrinsic EUV emission
  of BPs is found to be dependent on the total magnetic flux of the
  polarities. In short time scales, co-spatial and co-temporal coronal
  images and magnetograms, reveal the signature of heating events
  that produce sudden EUV brightenings simultaneous to magnetic flux
  cancellations. This is interpreted in terms of magnetic reconnection
  events. <P />Finally, a electron density study of six coronal bright
  points produces values of ≈1.6×10 9 cm -3 , closer to active region
  plasma than to quiet Sun. The analysis of a large coronal loop (half
  length of 72 Mm) introduces the discussion on the prospects of future
  plasma diagnostics of BPs with forthcoming solar missions.

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Title: Joint Observing Program 166: Multi-Instrumental Study of
    Extreme-Ultraviolet Coronal Bright Points
Authors: Ugarte-Urra, I.; Doyle, J. G.
2004ESASP.575..535U    Altcode: 2004soho...15..535U
  No abstract at ADS

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Title: Determining the Temperature Profile Along a Plasma Loop Iii:
    Spectrometers Verus Imagers
Authors: Walsh, R. W.; Ugarte-Urra, I.; Doyle, J. G.; Noglik, J. B.
2004ESASP.575..567W    Altcode: 2004soho...15..567W
  No abstract at ADS

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Title: Brightness and magnetic evolution of solar coronal bright
    points
Authors: Ugarte-Urra, I.
2004PhDT.........1U    Altcode:
  This thesis presents a study of the brightness and magnetic evolution
  of several Extreme ultraviolet (EUV) coronal bright points (hereafter
  BPs). BPs are loop-like features of enhanced emission in the coronal
  EUV and X-ray images of the Sun, that are associated to the interaction
  of opposite photospheric magnetic polarities with magnetic fluxes of
  ≈10<SUP>18</SUP> - 10<SUP>19</SUP> Mx. The study was carried out using
  several instruments on board the Solar and Heliospheric Observatory
  (SOHO): the Extreme Ultraviolet Imager (EIT), the Coronal Diagnostic
  Spectrometer (CDS) and the Michelson Doppler Imager (MDI), supported
  by the high resolution imaging from the Transition Region And Coronal
  Explorer (TRACE). <P />The results confirm that, down to 1” (i.e. ~715
  km) resolution, BPs are made of small loops with lengths of ~6 Mm and
  cross-sections of ~2 Mm. The loops are very dynamic, evolving in time
  scales as short as 1 - 2 minutes. This is reflected in a highly variable
  EUV response with fluctuations highly correlated in spectral lines at
  transition region temperatures (in the range 3.2x10^4 - 3.5x10^5 K),
  but not always at coronal temperatures. A wavelet analysis of the
  intensity variations reveals, for the first time, the existence of
  quasi-periodic oscillations with periods ranging 400 -- 1000 s, in
  the range of periods characteristic of the chromospheric network. The
  link between BPs and network bright points is discussed, as well as
  the interpretation of the oscillations in terms of global acoustic
  modes of closed magnetic structures. <P />A comparison of the magnetic
  flux evolution of the magnetic polarities to the EUV flux changes is
  also presented. Throughout their lifetime, the intrinsic EUV emission
  of BPs is found to be dependent on the total magnetic flux of the
  polarities. In short time scales, co-spatial and co-temporal TRACE and
  MDI images, reveal the signature of heating events that produce sudden
  EUV brightenings simultaneous to magnetic flux cancellations. This is
  interpreted in terms of magnetic reconnection events. <P />Finally,
  a electron density study of six coronal bright points produces values
  of ~1.6x10<SUP>9</SUP> cm<SUP>-3</SUP>, closer to active region plasma
  than to quiet Sun. The analysis of a large coronal loop (half length
  of 72 Mm) introduces the discussion on the prospects of future plasma
  diagnostics of BPs with forthcoming solar missions like Solar-B.

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Title: CDS wide slit time-series of EUV coronal bright points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Nakariakov, V. M.; Foley, C. R.
2004A&A...425.1083U    Altcode:
  Wide slit (90<SUP>”</SUP>×240<SUP>”</SUP>) movies of four Extreme
  Ultraviolet coronal bright points (BPs) obtained with the Coronal
  Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric
  Observatory (SoHO) have been inspected. The wavelet analysis of the He
  I 584.34 Å, O V 629.73 Å and Mg VII/IX 368 Å time-series confirms
  the oscillating nature of the BPs, with periods ranging between
  600 and 1100 s. In one case we detect periods as short as 236 s. We
  suggest that these oscillations are the same as those seen in the
  chromospheric network and that a fraction of the network bright points
  are most likely the cool footpoints of the loops comprising coronal
  bright points. These oscillations are interpreted in terms of global
  acoustic modes of the closed magnetic structures associated with BPs.

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Title: Signature of oscillations in coronal bright points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E.
2004A&A...418..313U    Altcode:
  A detailed study of two consecutive bright points observed
  simultaneously with the Coronal Diagnostic Spectrometer (CDS),
  the Extreme ultraviolet Imaging Telescope (EIT) and the Michelson
  Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
  (SOHO) is presented. The analysis of the evolution of the photospheric
  magnetic features and their coronal counterpart shows that there is
  a linear dependence between the EIT Fe XII 195 Å flux and the total
  magnetic flux of the photospheric bipolarity. The appearance of the
  coronal emission is associated with the emergence of new magnetic
  flux and the disappearance of coronal emission is associated with
  the cancellation of one of the polarities. In one of the cases the
  disappearance takes place ∼3-4 h before the full cancellation of
  the weakest polarity. <P />The spectral data obtained with CDS show
  that one of the bright points experienced short time variations in
  the flux on a time scale of 420-650 s, correlated in the transition
  region lines (O V 629.73 Å and O III 599.60 Å) and also the He I
  584.34 Å line. The coronal line (Mg IX 368.07 Å) undergoes changes
  as well, but on a longer scale. The wavelet analysis of the temporal
  series reveals that many of these events appear in a random fashion and
  sometimes after periods of quietness. However, we have found two cases
  of an oscillatory behaviour. A sub-section of the O V temporal series
  of the second bright point shows a damped oscillation of five cycles
  peaking in the wavelet spectrum at 546 s, but showing in the latter few
  cycles a lengthening of that period. The period compares well with that
  detected in the S VI 933.40 Å oscillations seen in another bright point
  observed with the Solar Ultraviolet Measurements of Emitted Radiation
  (SUMER) spectrometer, which has a period of 491 s. The derived electron
  density in the transition region was 3×10<SUP>10</SUP> cm<SUP>-3</SUP>
  with some small variability, while the coronal electron density was
  5×10<SUP>8</SUP> cm<SUP>-3</SUP>.

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Title: Oscillations in Coronal Bright Points
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.; O'Shea, E.
2004ESASP.547..329U    Altcode: 2004soho...13..329U
  No abstract at ADS

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Title: Electron density variation in off-limb solar corona structures
Authors: Ugarte-Urra, I.; Doyle, J. G.; Madjarska, M. S.
2002ESASP.505..595U    Altcode: 2002IAUCo.188..595U; 2002solm.conf..595U
  We present a study of the electron density variation for off
  limb observations with the Coronal Diagnostic Spectrometer (CDS)
  on board SoHO using the density sensitive coronal line ratio Si X
  (356.0/347.4). The analysis is divided into three parts: the latitudinal
  variation from 1.01 &lt; r/R<SUB>solar</SUB> &lt; 1.09, the temporal
  variation in successive rasters, and the electron density along a hot
  coronal loop found in one of the rasters.