explanation      blue bibcodes open ADS page with paths to full text
Author name code: warren
ADS astronomy entries on 2022-09-14
author:"Warren, Harry P." 

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Title: A Publicly Available Multiobservatory Data Set of an Enhanced
    Network Patch from the Photosphere to the Corona
Authors: Kobelski, Adam R.; Tarr, Lucas A.; Jaeggli, Sarah A.; Luber,
   Nicholas; Warren, Harry P.; Savage, Sabrina
2022ApJS..261...15K    Altcode: 2022arXiv220501766K
  New instruments sensitive to chromospheric radiation at X-ray, UV,
  visible, IR, and submillimeter wavelengths have become available that
  significantly enhance our ability to understand the bidirectional
  flow of energy through the chromosphere. We describe the calibration,
  coalignment, initial results, and public release of a new data set
  combining a large number of these instruments to obtain multiwavelength
  photospheric, chromospheric, and coronal observations capable of
  improving our understanding of the connectivity between the photosphere
  and the corona via transient brightenings and wave signatures. The
  observations center on a bipolar region of enhanced-network
  magnetic flux near disk center on SOL2017-03-17T14:00-17:00. The
  comprehensive data set provides one of the most complete views to
  date of chromospheric activity related to small-scale brightenings
  in the corona and chromosphere. Our initial analysis shows a strong
  spatial correspondence between the areas of broadest width of the
  hydrogen-α spectral line and the hottest temperatures observed in
  Atacama Large Millimeter/submillimeter Array (ALMA) Band 3 radio
  data, with a linear coefficient of 6.12 × 10<SUP>-5</SUP>Å/K. The
  correspondence persists for the duration of cotemporal observations
  (≍60 m). Numerous transient brightenings were observed in multiple
  data series. We highlight a single, well-observed transient brightening
  in a set of thin filamentary features with a duration of 20 minutes. The
  timing of the peak intensity transitions from the cooler (ALMA, 7000 K)
  to the hotter (XRT, 3 MK) data series.

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Title: Parallel Plasma Loops and the Energization of the Solar Corona
Authors: Peter, Hardi; Chitta, Lakshmi Pradeep; Chen, Feng; Pontin,
   David I.; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
   Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
   Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
   Testa, Paola; Tiwari, Sanjiv K.; Walsh, Robert W.; Warren, Harry P.
2022ApJ...933..153P    Altcode: 2022arXiv220515919P
  The outer atmosphere of the Sun is composed of plasma heated to
  temperatures well in excess of the visible surface. We investigate
  short cool and warm (&lt;1 MK) loops seen in the core of an active
  region to address the role of field-line braiding in energizing these
  structures. We report observations from the High-resolution Coronal
  imager (Hi-C) that have been acquired in a coordinated campaign with
  the Interface Region Imaging Spectrograph (IRIS). In the core of the
  active region, the 172 Å band of Hi-C and the 1400 Å channel of IRIS
  show plasma loops at different temperatures that run in parallel. There
  is a small but detectable spatial offset of less than 1″ between
  the loops seen in the two bands. Most importantly, we do not see
  observational signatures that these loops might be twisted around each
  other. Considering the scenario of magnetic braiding, our observations
  of parallel loops imply that the stresses put into the magnetic field
  have to relax while the braiding is applied: the magnetic field never
  reaches a highly braided state on these length scales comparable to
  the separation of the loops. This supports recent numerical 3D models
  of loop braiding in which the effective dissipation is sufficiently
  large that it keeps the magnetic field from getting highly twisted
  within a loop.

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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: Constraining Global Coronal Models with Multiple Independent
    Observables
Authors: Badman, Samuel T.; Brooks, David H.; Poirier, Nicolas;
   Warren, Harry P.; Petrie, Gordon; Rouillard, Alexis P.; Nick Arge,
   C.; Bale, Stuart D.; de Pablos Agüero, Diego; Harra, Louise; Jones,
   Shaela I.; Kouloumvakos, Athanasios; Riley, Pete; Panasenco, Olga;
   Velli, Marco; Wallace, Samantha
2022ApJ...932..135B    Altcode: 2022arXiv220111818B
  Global coronal models seek to produce an accurate physical
  representation of the Sun's atmosphere that can be used, for example, to
  drive space-weather models. Assessing their accuracy is a complex task,
  and there are multiple observational pathways to provide constraints
  and tune model parameters. Here, we combine several such independent
  constraints, defining a model-agnostic framework for standardized
  comparison. We require models to predict the distribution of coronal
  holes at the photosphere, and neutral line topology at the model's outer
  boundary. We compare these predictions to extreme-ultraviolet (EUV)
  observations of coronal hole locations, white-light Carrington maps of
  the streamer belt, and the magnetic sector structure measured in situ
  by Parker Solar Probe and 1 au spacecraft. We study these metrics for
  potential field source surface (PFSS) models as a function of source
  surface height and magnetogram choice, as well as comparing to the more
  physical Wang-Sheeley-Arge (WSA) and the Magnetohydrodynamic Algorithm
  outside a Sphere (MAS) models. We find that simultaneous optimization
  of PFSS models to all three metrics is not currently possible, implying
  a trade-off between the quality of representation of coronal holes
  and streamer belt topology. WSA and MAS results show the additional
  physics that they include address this by flattening the streamer belt
  while maintaining coronal hole sizes, with MAS also improving coronal
  hole representation relative to WSA. We conclude that this framework
  is highly useful for inter- and intra-model comparisons. Integral to
  the framework is the standardization of observables required of each
  model, evaluating different model aspects.

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Title: Detection of Stellar-like Abundance Anomalies in the Slow
    Solar Wind
Authors: Brooks, David H.; Baker, Deborah; van Driel-Gesztelyi, Lidia;
   Warren, Harry P.; Yardley, Stephanie L.
2022ApJ...930L..10B    Altcode: 2022arXiv220409332B
  The elemental composition of the Sun's hot atmosphere, the corona,
  shows a distinctive pattern that is different from the underlying
  surface or photosphere. Elements that are easy to ionize in the
  chromosphere are enhanced in abundance in the corona compared to
  their photospheric values. A similar pattern of behavior is often
  observed in the slow-speed (&lt;500 km s<SUP>-1</SUP>) solar wind
  and in solar-like stellar coronae, while a reversed effect is seen
  in M dwarfs. Studies of the inverse effect have been hampered in the
  past because only unresolved (point-source) spectroscopic data were
  available for these stellar targets. Here we report the discovery of
  several inverse events observed in situ in the slow solar wind using
  particle-counting techniques. These very rare events all occur during
  periods of high solar activity that mimic conditions more widespread
  on M dwarfs. The detections allow a new way of connecting the slow
  wind to its solar source and are broadly consistent with theoretical
  models of abundance variations due to chromospheric fast-mode waves
  with amplitudes of 8-10 km s<SUP>-1</SUP>, sufficient to accelerate
  the solar wind. The results imply that M-dwarf winds are dominated
  by plasma depleted in easily ionized elements and lend credence to
  previous spectroscopic measurements.

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Title: Solar Flare Irradiance: Observations and Physical Modeling
Authors: Reep, Jeffrey W.; Siskind, David E.; Warren, Harry P.
2022ApJ...927..103R    Altcode: 2021arXiv211006310R
  We examine Solar Dynamics Observatory (SDO)/EUV Variability Experiment
  (EVE) data to better understand solar flare irradiance, and how that
  irradiance may vary for large events. We measure scaling laws relating
  Geostationary Orbital Environmental Satellites (GOES) flare classes
  to irradiance in 21 lines measured with SDO/EVE, formed across a
  wide range of temperatures, and find that this scaling depends on the
  line-formation temperature. We extrapolate these irradiance values to
  large events, exceeding X10. In order to create full spectra, however,
  we need a physical model of the irradiance. We present the first
  results of a new physical model of solar flare irradiance, NRLFLARE,
  that sums together a series of flare loops to calculate the spectral
  irradiance ranging from the X-rays through the far-UV (≍0 to 1250
  Å), constrained only by GOES/X-ray Sensors observations. We test
  this model against SDO/EVE data. The model spectra and time evolution
  compares well in high-temperature emission, but cooler lines show
  large discrepancies. We speculate that the discrepancies are likely
  due to both a nonuniform cross-section of the flaring loops as well as
  opacity effects. We then show that allowing the cross-sectional area to
  vary with height significantly improves agreement with observations,
  and is therefore a crucial parameter needed to accurately model the
  intensity of spectral lines, particularly in the transition region
  from $4.7\lesssim \mathrm{log}T\lesssim 6$ .

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Title: The EUV High-Throughput Spectroscopic Telescope (EUVST)
Authors: Warren, Harry
2021AGUFMSH51A..07W    Altcode:
  The EUV High-Throughput Spectroscopic Telescope (Solar-C/EUVST) is an
  international mission to understand the origins of solar activity by
  observing fundamental physical processes in the solar atmosphere. EUVST
  is a next generation spectrometer and slit-jaw imaging system that will
  provide seamless spectroscopic coverage of the chromosphere, transition
  region, corona, and flare plasma at very high temporal resolution
  and high spatial resolution (0.4 arcsec or 300 km). This project is
  led by Japan with contributions from the United States and European
  partners. Launch is currently scheduled for late 2026. Understanding
  the release of energy during solar flares is one of the EUVST science
  objectives. EUVST observations of flare ribbons will achieve cadences
  below 500 ms. We use hydrodynamic simulations to show that observations
  of chromospheric and transition region emission lines at these time
  scales will be able to differentiate among different energy transport
  mechanisms.

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Title: NRLFLARE: A physical model of solar flare irradiance
Authors: Reep, Jeffrey; Siskind, David; Warren, Harry
2021AGUFMSH43A..07R    Altcode:
  We introduce the NRLFLARE model, a physically-derived model of solar
  flare irradiance. The model constrains energy release and volume of
  a flare using soft X-ray observations, with which it drives a series
  of hydrodynamic simulations to construct a flare arcade. From these
  simulations, we have synthesized the irradiance from the chromosphere
  through the corona, from the X-rays through near ultraviolet, at high
  cadence and spectral resolution. To test the model, we compare to
  irradiance observations of X-, M-, and C-class flares measured with
  the Extreme Ultraviolet Variability Experiment (EVE) onboard the
  Solar Dynamics Observatory (SDO), as well as to the predictions of
  the empirical FISM2 model. We find good agreement in spectral lines
  formed at high temperatures (&gt; few x 106 K), but find the model
  significantly over-estimates intensities of transition region lines
  (105 K &lt; T &lt; 106 K). Finally, we scale the heating rates and
  volumes up to extrapolate to flares exceeding X50 in class to predict
  spectra for such unobserved flare scales.

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Title: Observations and Modeling of Long, Cool, and Overdense Loops
    in Active Region 11575
Authors: Barnes, Will; Warren, Harry
2021AGUFMSH15E2066B    Altcode:
  Long coronal loops at the periphery of active regions have been
  observed to be steady over intervals greater than a radiative
  cooling time, overdense, near-isothermal at approximately 1.5 MK,
  and have flat filter ratios. These relatively steady, high-density
  structures cannot be explained by either hydrostatic equilibrium or
  simple post-nanoflare radiative cooling and thus pose a challenge
  to current models of quiescent active region heating. To address
  these ambiguities, we analyze observations of active region 11575 as
  observed on 29 September 2012 by the Atmospheric Imaging Assembly
  (AIA) onboard the Solar Dynamics Observatory (SDO) and the Extreme
  Ultraviolet Imaging Spectrometer (EIS) onboard the Hinode spacecraft. We
  manually isolate a single long loop near the periphery of the active
  region in SDO/AIA 171 A and calculate the density, emission measure
  distribution, and filter ratio. Additionally, we analyze the time
  variability of this structure in the EUV channels of AIA over a 12
  h interval and compute cross-correlations between these channels. We
  then model the hydrodynamic evolution of this loop structure using the
  field-aligned Hydrodynamics and Radiation (HYDRAD) model for several
  different heating scenarios, including steady uniform heating as well as
  steady and time-dependent stratified footpoint heating. From our model
  results, we derive density and temperature diagnostics, emission measure
  distributions, and cross-correlations between synthetic SDO/AIA light
  curves in order to compare with our observations and thus constrain
  the parameter space of feasible heating models. While stratified,
  fully-asymmetric footpoint heating greatly increases the density of
  a 1.5 MK loop over hydrostatic equilibrium, we find that the modeled
  densities for all heating scenarios are significantly lower than those
  we derive from the EIS observations. Furthermore, we find that impulsive
  heating as well as thermal non-equilibrium, as induced by symmetric
  stratified footpoint heating, lead to emission measure distributions
  that are much broader than the observed distributions.

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Title: Preliminary Results from the Marshall Grazing Incidence X-ray
    Spectrometer (MaGIXS)
Authors: Winebarger, Amy; Savage, Sabrina; Kobayashi, Ken; Champey,
   Patrick; Golub, Leon; Walsh, Robert; Athiray, P. S.; Bradshaw, Stephen;
   Cheimets, Peter; Cirtain, Jonathan; DeLuca, Edward; Del Zanna, Giulio;
   Mason, Helen; McKenzie, David; Ramsey, Brian; Reeves, Katharine;
   Testa, Paola; Vigil, Genevieve; Warren, Harry
2021AGUFMSH51A..06W    Altcode:
  Coronal heating mechanisms are notoriously difficult to constrain with
  current observations. We present new observations from an instrument
  designed to measure a critical diagnostic of the frequency heating
  events in active regions. The Marshall Grazing Incidence X-ray
  Spectrometer (MaGIXS) is a sounding rocket mission that aims to
  observe the soft x-ray solar spectrum (0.6 2.5 nm) with both spatial
  and spectral resolution. This wavelength range has several high
  temperature and abundance diagnostics that can be used to infer the
  coronal heating frequency. MaGIXS will observe the Sun through a 12
  x 33 slot, producing “overlappograms, where the spatial and spectral
  information are overlapped and must be unfolded. In this presentation,
  I will report on the MaGIXS launch and data collection and provide
  preliminary analysis of MaGIXS observations.

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Title: A Multicomponent Magnetic Proxy for Solar Activity
Authors: Warren, Harry P.; Floyd, Linton E.; Upton, Lisa A.
2021SpWea..1902860W    Altcode:
  We present a new, multicomponent magnetic proxy for solar
  activity derived from full disk magnetograms that can be used in
  the specification and forecasting of the Sun's radiative output. To
  compute this proxy we project Carrington maps, such as the synchronic
  Carrington maps computed with the Advective Flux Transport (AFT)
  surface flux transport model, to heliographic cartesian coordinates and
  determine the total unsigned flux as a function of absolute magnetic
  flux density. Performing this calculation for each day produces
  an array of time series, one for each flux density interval. Since
  many of these time series are strongly correlated, we use principal
  component analysis to reduce them to a smaller number of uncorrelated
  time series. We show that the first few principal components accurately
  reproduce widely used proxies for solar activity, such the the 10.7
  cm radio flux and the Mg core-to-wing ratio. This suggests that these
  magnetic time series can be used as a proxy for irradiance variability
  for emission formed over a wide range of temperatures.

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Title: The Formation and Lifetime of Outflows in a Solar Active Region
Authors: Brooks, David H.; Harra, Louise; Bale, Stuart D.; Barczynski,
   Krzysztof; Mandrini, Cristina; Polito, Vanessa; Warren, Harry P.
2021ApJ...917...25B    Altcode: 2021arXiv210603318B
  Active regions are thought to be one contributor to the slow solar
  wind. Upflows in EUV coronal spectral lines are routinely observed at
  their boundaries, and provide the most direct way for upflowing material
  to escape into the heliosphere. The mechanisms that form and drive these
  upflows, however, remain to be fully characterized. It is unclear how
  quickly they form, or how long they exist during their lifetimes. They
  could be initiated low in the atmosphere during magnetic flux emergence,
  or as a response to processes occurring high in the corona when the
  active region is fully developed. On 2019 March 31 a simple bipolar
  active region (AR 12737) emerged and upflows developed on each side. We
  used observations from Hinode, SDO, IRIS, and Parker Solar Probe (PSP)
  to investigate the formation and development of the upflows from the
  eastern side. We used the spectroscopic data to detect the upflow,
  and then used the imaging data to try to trace its signature back to
  earlier in the active region emergence phase. We find that the upflow
  forms quickly, low down in the atmosphere, and that its initiation
  appears associated with a small field-opening eruption and the onset
  of a radio noise storm detected by PSP. We also confirmed that the
  upflows existed for the vast majority of the time the active region
  was observed. These results suggest that the contribution to the solar
  wind occurs even when the region is small, and continues for most of
  its lifetime.

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Title: Measurements of Coronal Magnetic Field Strengths in Solar
    Active Region Loops
Authors: Brooks, David H.; Warren, Harry P.; Landi, Enrico
2021ApJ...915L..24B    Altcode: 2021arXiv210610884B
  The characteristic electron densities, temperatures, and thermal
  distributions of 1 MK active region loops are now fairly well
  established, but their coronal magnetic field strengths remain
  undetermined. Here we present measurements from a sample of coronal
  loops observed by the Extreme-ultraviolet Imaging Spectrometer on
  Hinode. We use a recently developed diagnostic technique that involves
  atomic radiation modeling of the contribution of a magnetically
  induced transition to the Fe X 257.262 Å spectral line intensity. We
  find coronal magnetic field strengths in the range of 60-150 G. We
  discuss some aspects of these new results in the context of previous
  measurements using different spectropolarimetric techniques, and their
  influence on the derived Alfvén speeds and plasma β in coronal loops.

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Title: The CubeSat Imaging X-ray Solar Spectrometer (CubIXSS)
Authors: Caspi, A.; Shih, A. Y.; Panchapakesan, S.; Warren, H. P.;
   Woods, T. N.; Cheung, M.; DeForest, C. E.; Klimchuk, J. A.; Laurent,
   G. T.; Mason, J. P.; Palo, S. E.; Seaton, D. B.; Steslicki, M.;
   Gburek, S.; Sylwester, J.; Mrozek, T.; Kowaliński, M.; Schattenburg,
   M.; The CubIXSS Team
2021AAS...23821609C    Altcode:
  The CubeSat Imaging X-ray Solar Spectrometer (CubIXSS) is a 6U
  CubeSat proposed to NASA H-FORT. CubIXSS is motivated by a compelling
  overarching science question: what are the origins of hot plasma in
  solar flares and active regions? Elemental abundances are a unique
  diagnostic of how mass and energy flow into and within the corona,
  and CubIXSS addresses its science question through sensitive, precise
  measurements of abundances of key trace ion species, whose spectral
  signatures reveal the chromospheric or coronal origins of heated plasma
  across the entire temperature range from ~1 to &gt;30 MK. CubIXSS
  measurements of the coronal temperature distribution and elemental
  abundances directly address longstanding inconsistencies from prior
  studies using instruments with limited, differing temperature and
  composition sensitivities. <P />CubIXSS comprises two co-optimized
  and cross-calibrated instruments that fill a critical observational
  gap: <P />MOXSI, a novel diffractive spectral imager using a pinhole
  camera and X-ray transmission diffraction grating for spectroscopy of
  flares and active regions from 1 to 55 Å, with spectral and spatial
  resolutions of 0.28-0.37 Å and 29-39 arcsec FWHM, respectively;
  and <P />SASS, a suite of four spatially-integrated off-the-shelf
  spectrometers for high-cadence, high-sensitivity X-ray spectra from
  0.5 to 50 keV, with spectral resolution of 0.06-0.5 keV FWHM across
  that range. <P />If selected for implementation, CubIXSS will launch
  in late 2023 to mid-2024 to observe intense solar flares and active
  regions during the rising phase and peak of the solar cycle. Its 1-year
  prime mission is well timed with perihelia of Parker Solar Probe and
  Solar Orbiter, and with the launches of complementary missions such
  as the PUNCH Small Explorer. CubIXSS is a pathfinder for the next
  generation of Explorer-class missions with improved capabilities for
  SXR imaging spectroscopy. We present the CubIXSS motivating science
  background, its suite of instruments and expected performances, and
  other highlights from the completed Concept Study Report, including
  novel analysis techniques to fully exploit the rich data set of CubIXSS
  spectral observations.

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Title: Understanding Heating Properties in Hot and Warm Active Region
    Loops through Hydrodynamics and Forward Modeling
Authors: Barnes, W.; Warren, H.; Reep, J. W.
2020AGUFMSH0370003B    Altcode:
  While it is generally agreed that the energy to power the
  multi-million-degree corona is contained in the complex solar
  magnetic field, the processes behind how this energy is transferred
  from the stressed magnetic field to the coronal plasma remain
  poorly understood. Active region observations from a number of solar
  observatories have shown that short, compact loops near the center of
  the active region are "hot," sometimes exceeding temperatures of 4 MK,
  and are consistent with steady heating, while long loops closer to the
  periphery of the active region are significantly cooler (around 1 MK)
  and may be powered by more intermittent heating. In this poster, we
  use a field-aligned hydrodynamic model, combined with loop properties
  constrained from observations and forward modeling, to better understand
  the heating properties across the active region. Specifically,
  we use the HYDRAD code to survey an array of heating parameters,
  from impulsive heating to thermal non-equilibrium induced by
  highly-stratified, localized foot point heating for a selection of loop
  geometries derived from field extrapolations. We then forward model
  spectroscopic observations from the EUV Imaging Spectrometer instrument
  onboard Hinode as well as narrow-band imaging observations from the
  Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory,
  in order to make comparisons between observed loops and our models and
  thus constrain the parameter space of heating scenarios. In doing so,
  we gain insight into both how different types of loops are heated and
  how heating properties vary across the active region.

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Title: The CubeSat Imaging X-ray Solar Spectrometer (CubIXSS)
Authors: Caspi, A.; Shih, A. Y.; Warren, H.; Winebarger, A. R.; Woods,
   T. N.; Cheung, C. M. M.; DeForest, C.; Klimchuk, J. A.; Laurent,
   G. T.; Mason, J. P.; Palo, S. E.; Schwartz, R.; Seaton, D. B.;
   Steslicki, M.; Gburek, S.; Sylwester, J.; Mrozek, T.; Kowaliński,
   M.; Schattenburg, M.
2020AGUFMSH0480007C    Altcode:
  The CubeSat Imaging X-ray Solar Spectrometer (CubIXSS) is a 6U
  CubeSat currently in a formulation phase under the 2019 NASA H-FORT
  program. CubIXSS is motivated by a compelling overarching science
  question: what are the origins of hot plasma in solar flares and active
  regions? Elemental abundances are a unique diagnostic of how mass
  and energy flow into and within the corona, and CubIXSS addresses
  its science question through sensitive, precise measurements of
  abundances of key trace ion species, whose spectral signatures reveal
  the chromospheric or coronal origins of heated plasma across the
  entire range of coronal temperatures, from ~1 to &gt;30 MK. CubIXSS
  measurements of the coronal temperature distribution and elemental
  abundances directly address longstanding inconsistencies from prior
  studies using instruments with limited, differing temperature and
  composition sensitivities. <P />CubIXSS comprises two co-optimized and
  cross-calibrated instruments that fill a critical observational gap:
  <P />MOXSI, a novel diffractive spectral imager using a pinhole camera
  and X-ray transmission diffraction grating to achieve spectroscopy of
  flares and active regions from 1 to 55 Å, with spectral resolution of
  0.24 Å FWHM and a spatial resolution of 25 arcsec FWHM; and <P />SASS,
  a suite of four spatially-integrated off-the-shelf spectrometers for
  high-cadence, high-sensitivity measurements of soft and hard X-rays,
  from 0.5 to 50 keV, with spectral resolution from 0.06 to 0.5 keV
  FWHM. <P />If selected for implementation, CubIXSS will launch in
  mid-2023 to observe intense solar flares and active regions during
  the rising phase of the solar cycle. Its nominal 1-year mission is
  well timed with perihelia of Parker Solar Probe and Solar Orbiter,
  and with the launches of complementary missions such as the PUNCH
  Small Explorer. CubIXSS is also a pathfinder for the next generation
  of Explorer-class missions with improved capabilities for SXR imaging
  spectroscopy. We present the CubIXSS motivating science background, its
  suite of instruments and expected performances, and other highlights
  from the completed Concept Study Report, including novel analysis
  techniques to fully exploit the rich data set of CubIXSS spectral
  observations.

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Title: Constraining Global Coronal Models with Multiple Independent
    Observables
Authors: Badman, S. T.; Brooks, D.; Petrie, G. J. D.; Poirier, N.;
   Warren, H.; Bale, S. D.; de Pablos, D.; Harra, L.; Rouillard, A. P.;
   Panasenco, O.; Velli, M. C. M.
2020AGUFMSH032..08B    Altcode:
  Global coronal models seek to produce an accurate physical
  representation of the Sun's atmosphere which can be used to probe
  the dominant plasma physics processes, to connect remote and in situ
  observations and operationally to predict space weather events which
  can impact the Earth. Assessing their accuracy and usefulness is a
  complex task and there are multiple observational pathways to provide
  constraints on such models and tune their input parameters. In this
  work, we aim to combine several such independent constraints in
  a systematic fashion on coronal models. We study the intervals of
  Parker Solar Probe's early solar encounters to leverage the unique in
  situ observations taken close to the Sun, and the wealth of supporting
  observations and prior work analyzing these time intervals. We require
  our coronal models to predict the distribution of coronal holes on
  the solar surface, and the neutral line topology. We compare these
  predictions to (1) direct Extreme Ultraviolet (EUV) observations
  of coronal hole locations, (2) white light Carrington maps of the
  probable neutral line location at a few solar radii, (3) the magnetic
  sector structure measured in situ by Parker Solar Probe as well as
  1AU assets. For each of these constraints we compute a simple metric
  to evaluate model agreement and compare and contrast these metrics
  to evaluate and rank the overall accuracy of the models over a range
  of input parameters. Initial results using the coronal hole metric
  to analyze Potential Field Source Surface (PFSS) models indicate the
  optimum source surface height (Rss) parameter varied from encounter to
  encounter. Rss = 1.5 - 2.0 R_sun is shown to work best for Encounters
  1 and 3, but higher (2.0-2.5 R_sun) for encounter 2, in agreement with
  the magnetic sector structure metric and previous work (e.g. Panasenco
  et al. 2020). We discuss the extension of these results to all three
  metrics, assess differences in model accuracy among input photospheric
  boundary conditions and investigate models with more physics than PFSS.

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

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Title: Current Status of the Solar-C_EUVST Mission
Authors: Imada, S.; Shimizu, T.; Kawate, T.; Toriumi, S.; Katsukawa,
   Y.; Kubo, M.; Hara, H.; Suematsu, Y.; Ichimoto, K.; Watanabe, T.;
   Watanabe, K.; Yokoyama, T.; Warren, H.; Long, D.; Harra, L. K.;
   Teriaca, L.
2020AGUFMSH056..05I    Altcode:
  Solar-C_EUVST (EUV High-Throughput Spectroscopic Telescope) is designed
  to comprehensively understand the energy and mass transfer from the
  solar surface to the solar corona and interplanetary space, and to
  investigate the elementary processes that take place universally
  in cosmic plasmas. As a fundamental step towards answering how the
  plasma universe is created and evolves, and how the Sun influences
  the Earth and other planets in our solar system, the proposed mission
  is designed to comprehensively understand how mass and energy are
  transferred throughout the solar atmosphere. Understanding the solar
  atmosphere, which connects to the heliosphere via radiation, the solar
  wind and coronal mass ejections, and energetic particles is pivotal
  for establishing the conditions for life and habitability in the solar
  system. <P />The two primary science objectives for Solar-C_EUVST are :
  I) Understand how fundamental processes lead to the formation of the
  solar atmosphere and the solar wind, II) Understand how the solar
  atmosphere becomes unstable, releasing the energy that drives solar
  flares and eruptions. Solar-C_EUVST will, A) seamlessly observe all
  the temperature regimes of the solar atmosphere from the chromosphere
  to the corona at the same time, B) resolve elemental structures of the
  solar atmosphere with high spatial resolution and cadence to track their
  evolution, and C) obtain spectroscopic information on the dynamics of
  elementary processes taking place in the solar atmosphere. <P />In this
  talk, we will first discuss the science target of the Solar-C_EUVST,
  and then discuss the current status of the Solar-C_EUVST mission.

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Title: A sensitivity analysis of the updated optical design for
    EUVST on the Solar-C mission
Authors: Kawate, Tomoko; Tsuzuki, Toshihiro; Shimizu, Toshifumi;
   Imada, Shinsuke; Katsukawa, Yukio; Hara, Hirohisa; Suematsu, Yoshinori;
   Ichimoto, Kiyoshi; Hattori, Tomoya; Narasaki, Shota; Warren, Harry P.;
   Teriaca, Luca; Korendyke, Clarence M.; Brown, Charles M.; Auchere,
   Frederic
2020SPIE11444E..3JK    Altcode:
  The EUV high-throughput spectroscopic telescope (EUVST) onboard the
  Solar-C mission has the high spatial (0.4”) resolution over a wide
  wavelength range in the vacuum ultraviolet. To achieve high spatial
  resolution under a design constraint given by the JAXA Epsilon launch
  vehicle, we further update the optical design to secure margins
  needed to realize 0.4” spatial resolution over a field of view of
  100”×100”. To estimate the error budgets of spatial and spectral
  resolutions due to installation and fabrication errors, we perform a
  sensitivity analysis for the position and orientation of each optical
  element and for the grating parameters by ray tracing with the Zemax
  software. We obtain point spread functions (PSF) for rays from 9
  fields and at 9 wavelengths on each detector by changing each parameter
  slightly. A full width at half maximum (FWHM) of the PSF is derived at
  each field and wavelength position as a function of the perturbation
  of each optical parameter. Assuming a mount system of each optical
  element and an error of each optical parameter, we estimate spatial
  and spectral resolutions by taking installation and fabrication errors
  into account. The results of the sensitivity analysis suggest that
  budgets of the total of optical design and the assembly errors account
  for 15% and 5.8% of our budgets of the spatial resolution in the long
  wavelength and short wavelength bands, respectively. On the other hand,
  the grating fabrication errors give a large degradation of spatial and
  spectral resolutions, and investigations of compensators are needed
  to relax the fabrication tolerance of the grating surface parameters.

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Title: MinXSS-2 CubeSat mission overview: Improvements from the
    successful MinXSS-1 mission
Authors: Mason, James Paul; Woods, Thomas N.; Chamberlin, Phillip
   C.; Jones, Andrew; Kohnert, Rick; Schwab, Bennet; Sewell, Robert;
   Caspi, Amir; Moore, Christopher S.; Palo, Scott; Solomon, Stanley C.;
   Warren, Harry
2020AdSpR..66....3M    Altcode: 2019arXiv190501345M
  The second Miniature X-ray Solar Spectrometer (MinXSS-2) CubeSat, which
  begins its flight in late 2018, builds on the success of MinXSS-1,
  which flew from 2016-05-16 to 2017-05-06. The science instrument is
  more advanced - now capable of greater dynamic range with higher
  energy resolution. More data will be captured on the ground than
  was possible with MinXSS-1 thanks to a sun-synchronous, polar orbit
  and technical improvements to both the spacecraft and the ground
  network. Additionally, a new open-source beacon decoder for amateur
  radio operators is available that can automatically forward any captured
  MinXSS data to the operations and science team. While MinXSS-1 was only
  able to downlink about 1 MB of data per day corresponding to a data
  capture rate of about 1%, MinXSS-2 will increase that by at least a
  factor of 6. This increase of data capture rate in combination with
  the mission's longer orbital lifetime will be used to address new
  science questions focused on how coronal soft X-rays vary over solar
  cycle timescales and what impact those variations have on the earth's
  upper atmosphere.

---------------------------------------------------------
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: The Drivers of Active Region Outflows into the Slow Solar Wind
Authors: Brooks, David H.; Winebarger, Amy R.; Savage, Sabrina; Warren,
   Harry P.; De Pontieu, Bart; Peter, Hardi; Cirtain, Jonathan W.; Golub,
   Leon; Kobayashi, Ken; McIntosh, Scott W.; McKenzie, David; Morton,
   Richard; Rachmeler, Laurel; Testa, Paola; Tiwari, Sanjiv; Walsh, Robert
2020ApJ...894..144B    Altcode: 2020arXiv200407461B
  Plasma outflows from the edges of active regions have been suggested as
  a possible source of the slow solar wind. Spectroscopic measurements
  show that these outflows have an enhanced elemental composition,
  which is a distinct signature of the slow wind. Current spectroscopic
  observations, however, do not have sufficient spatial resolution to
  distinguish what structures are being measured or determine the driver
  of the outflows. The High-resolution Coronal Imager (Hi-C) flew on a
  sounding rocket in 2018 May and observed areas of active region outflow
  at the highest spatial resolution ever achieved (250 km). Here we use
  the Hi-C data to disentangle the outflow composition signatures observed
  with the Hinode satellite during the flight. We show that there are
  two components to the outflow emission: a substantial contribution
  from expanded plasma that appears to have been expelled from closed
  loops in the active region core and a second contribution from dynamic
  activity in active region plage, with a composition signature that
  reflects solar photospheric abundances. The two competing drivers of the
  outflows may explain the variable composition of the slow solar wind.

---------------------------------------------------------
Title: Simulating Solar Flare Irradiance with Multithreaded Models
    of Flare Arcades
Authors: Reep, Jeffrey W.; Warren, Harry P.; Moore, Christopher S.;
   Suarez, Crisel; Hayes, Laura A.
2020ApJ...895...30R    Altcode: 2020arXiv200310505R
  Understanding how energy is released in flares is one of the
  central problems of solar and stellar astrophysics. Observations of
  high-temperature flare plasma hold many potential clues as to the
  nature of this energy release. It is clear, however, that flares are
  not composed of a few impulsively heated loops, but are the result
  of heating on many small-scale threads that are energized over time,
  making it difficult to compare observations and numerical simulations
  in detail. Several previous studies have shown that it is possible
  to reproduce some aspects of the observed emission by considering the
  flare as a sequence of independently heated loops, but these studies
  generally focus on small-scale features while ignoring the global
  features of the flare. In this paper, we develop a multithreaded model
  that encompasses the time-varying geometry and heating rate for a
  series of successively heated loops composing an arcade. To validate,
  we compare with spectral observations of five flares made with the
  MinXSS CubeSat, as well as light curves measured with GOES/XRS and
  SDO/AIA. We show that this model can successfully reproduce the light
  curves and quasi-periodic pulsations in GOES/XRS, the soft X-ray spectra
  seen with MinXSS, and the light curves in various AIA passbands. The
  AIA light curves are most consistent with long-duration heating, but
  elemental abundances cannot be constrained with the model. Finally, we
  show how this model can be used to extrapolate to spectra of extreme
  events that can predict irradiance across a wide wavelength range,
  including unobserved wavelengths.

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Title: Is the High-Resolution Coronal Imager Resolving Coronal
    Strands? Results from AR 12712
Authors: Williams, Thomas; Walsh, Robert W.; Winebarger, Amy R.;
   Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; Golub,
   Leon; Kobayashi, Ken; McKenzie, David E.; Morton, Richard J.; Peter,
   Hardi; Rachmeler, Laurel A.; Savage, Sabrina L.; Testa, Paola; Tiwari,
   Sanjiv K.; Warren, Harry P.; Watkinson, Benjamin J.
2020ApJ...892..134W    Altcode: 2020arXiv200111254W
  Following the success of the first mission, the High-Resolution
  Coronal Imager (Hi-C) was launched for a third time (Hi-C 2.1)
  on 2018 May 29 from the White Sands Missile Range, NM, USA. On this
  occasion, 329 s of 17.2 nm data of target active region AR 12712 were
  captured with a cadence of ≈4 s, and a plate scale of 0.129 arcsec
  pixel<SUP>-1</SUP>. Using data captured by Hi-C 2.1 and co-aligned
  observations from SDO/AIA 17.1 nm, we investigate the widths of 49
  coronal strands. We search for evidence of substructure within the
  strands that is not detected by AIA, and further consider whether these
  strands are fully resolved by Hi-C 2.1. With the aid of multi-scale
  Gaussian normalization, strands from a region of low emission that can
  only be visualized against the contrast of the darker, underlying moss
  are studied. A comparison is made between these low-emission strands
  and those from regions of higher emission within the target active
  region. It is found that Hi-C 2.1 can resolve individual strands as
  small as ≈202 km, though the more typical strand widths seen are
  ≈513 km. For coronal strands within the region of low emission, the
  most likely width is significantly narrower than the high-emission
  strands at ≈388 km. This places the low-emission coronal strands
  beneath the resolving capabilities of SDO/AIA, highlighting the need
  for a permanent solar observatory with the resolving power of Hi-C.

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

---------------------------------------------------------
Title: The Solar Wind Speed Expansion Factor [v -f<SUB>s</SUB>]
    Relationship at the Inner Boundary (18 <SUB>R⊙</SUB>) of the
    Heliosphere
Authors: Wu, Chin-Chun; Liou, Kan; Warren, Harry
2020SoPh..295...25W    Altcode:
  The accuracy of data-driven magnetohydrodynamics (MHD) models
  depends on accurate boundary conditions specified at the inner
  heliosphere. However, not all of the MHD parameters [B ,v ,ρ ,T ]
  are measurable close to the Sun at the present time, except the vector
  magnetic field [B ] at the photosphere. The solar wind speed [v ], which
  is probably most relevant to space-weather forecasting, is often modeled
  by the standard Wang-Sheeley (WS) formula, which is based on an inverse
  relationship between the solar wind speed [v ] at 1 AU and the expansion
  factor [f<SUB>s</SUB>] estimated at 2.5 solar radii [R⊙], with the
  following generic form: v =v<SUB>1</SUB>+v<SUB>2</SUB>f<SUB>s−α</SUB>
  (where v is the solar wind speed at 18 R⊙, f<SUB>s</SUB> is the
  magnetic-field expansion factor, and v<SUB>1</SUB>, v<SUB>2</SUB>, and
  α are three free parameters to be determined). While the WS formula
  uses "source projection" to determine the solar wind source, it does
  not treat the solar wind as plasma because it uses the solar wind
  speed observed at 1 AU to derive the empirical relationship. Thus, the
  resulting formula ignores the transport and acceleration of the solar
  wind as it propagates out into the heliosphere. The purpose of this
  study is to rectify this omission by using a numerical MHD simulation
  to find the optimal set of free parameters that relate the magnetic
  properties at the source surface to the plasma parameters at 1 AU. In
  addition to the expansion factor, conservation of mass [ρ v ], magnetic
  flux [r<SUP>2</SUP>B ], and total pressure along the stream line are
  assumed to obtain the solar wind mass density, magnetic field, and
  temperature at 18 R⊙. These parameters are used as the inner boundary
  conditions of our global three-dimensional MHD (G3DMHD) code to simulate
  solar wind plasma and field parameters out to ≈1 AU. The simulation
  results are compared with the in-situ data from Wind to assess the
  accuracy. Such a procedure is repeated (880 times) to cover the three
  parameter regimes (100 &lt;v<SUB>1</SUB>&lt;350kms−<SUP>1</SUP>; 250
  &lt;v<SUB>2</SUB>&lt;700 kms−<SUP>1</SUP>; and 0.2 &lt;α &lt;0.9 )
  to find the optimal set. The simulation is performed for the period of
  CR2082 [30 March 2019 to 27 April 2009]. It is found that v =189 +679
  f<SUB>s−0.7</SUB> is the best formula to relate the solar wind speed
  at 18 <SUB>R⊙</SUB> to the expansion factor. Strictly speaking, this
  formula is most applicable for solar equatorial regions and near the
  times of solar minimum when there are few coronal mass ejection events.

---------------------------------------------------------
Title: RHESSI - GOES Comparisons of Soft X-ray Emission from Solar
    Flares, 2002 - 2017
Authors: McTiernan, J. M.; Caspi, A.; Warren, H.
2019AGUFMSH13D3427M    Altcode:
  This work is a comparison of the low energy (3 to 20 keV) response
  of the 9 detectors on-board the Reuven Ramaty High Energy Solar
  Spectroscopic Imager (RHESSI) with the X-Ray sensors on-board the
  series of Geostationary Operational Environmental Satellites (GOES),
  for the duration of the RHESSI mission. The purpose is to estimate
  the loss of sensitivity for each RHESSI detector during the mission,
  relative to GOES detectors which are expected to be more consistent over
  time. Comparisons are made during the decay phase of large solar flares,
  where non-thermal emission from accelerated electrons is expected
  to be unimportant; these large (GOES class M and X) solar flares are
  present in the RHESSI database from February 2002 through September
  2017. Calculations are done for each of the (3) different RHESSI
  attenuator states. The possibility for detection of an energy dependent
  time variation in the RHESSI detectors will also be investigated.

---------------------------------------------------------
Title: Comparing Coronal Hole Wave Properties and Density Profiles
    Derived from Indirect and Direct Observations
Authors: Weberg, M. J.; Ko, Y. K.; Laming, J. M.; Warren, H.
2019AGUFMSH53B3368W    Altcode:
  Transverse (or "Alfvénic") waves are commonly invoked by theories and
  models to explain coronal heating and solar wind acceleration. However,
  direct measurements are sparse and most of what we know about wave
  activity in the corona is derived from indirect proxies. Furthermore,
  previous studies using direct observations have revealed systematic
  discrepancies between the wave properties and energy values reported
  by indirect and direct methods. <P />In this study we examine the root
  causes and contributing factors of this discrepancy in wave properties
  by analyzing the same coronal hole using both indirect and direct
  methodologies. In the former case, we apply standard, spectrographic
  methods to data from Hinode / EIS to obtain an electron density profile
  (using line intensity ratios) and average wave velocity amplitudes
  (using measurements of non-thermal line widths). Direct measurements
  are made by identifying and tracking transverse motions in SDO / AIA
  images using the Northumbria University Wave Tracking (NUWT) code, which
  provides more detailed wave parameters as well as a relative density
  profile. While the two methodologies produce results with similar
  trends, we find that part of the discrepancy stems from the fact
  that the two methods measure complementary, rather than identical,
  structures and wave motions. We also investigate the latitudinal
  variation of wave parameters within a coronal hole and consider the
  total wave energy flux using a wider spectrum of wave frequencies than
  previously used. This study helps improve our understanding of existing
  analysis methods and builds confidence in promising new techniques.

---------------------------------------------------------
Title: Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar
    Magnetic Network Lanes
Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.;
   Winebarger, Amy R.; Tiwari, Sanjiv K.; Savage, Sabrina L.; Golub, Leon
   E.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain,
   Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.;
   Peter, Hardi; Testa, Paola; Walsh, Robert W.; Warren, Harry P.
2019ApJ...887L...8P    Altcode: 2019arXiv191102331P
  We present high-resolution, high-cadence observations of six,
  fine-scale, on-disk jet-like events observed by the High-resolution
  Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We
  combine the Hi-C 2.1 images with images from the Solar Dynamics
  Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface
  Region Imaging Spectrograph (IRIS), and investigate each event’s
  magnetic setting with co-aligned line-of-sight magnetograms from the
  SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six
  events are jetlet-like (having apparent properties of jetlets), (ii)
  all six are rooted at edges of magnetic network lanes, (iii) four of
  the jetlet-like events stem from sites of flux cancelation between
  majority-polarity network flux and merging minority-polarity flux, and
  (iv) four of the jetlet-like events show brightenings at their bases
  reminiscent of the base brightenings in coronal jets. The average
  spire length of the six jetlet-like events (9000 ± 3000 km) is three
  times shorter than that for IRIS jetlets (27,000 ± 8000 km). While
  not ruling out other generation mechanisms, the observations suggest
  that at least four of these events may be miniature versions of both
  larger-scale coronal jets that are driven by minifilament eruptions
  and still-larger-scale solar eruptions that are driven by filament
  eruptions. Therefore, we propose that our Hi-C events are driven by
  the eruption of a tiny sheared-field flux rope, and that the flux rope
  field is built and triggered to erupt by flux cancelation.

---------------------------------------------------------
Title: The solar wind speed - expansion factor (v - f<SUB>s</SUB>)
    relationship at the inner boundary (18 R<SUB>⊙</SUB>) of the
    heliosphere
Authors: Liou, K.; Wu, C. C.; Warren, H.
2019AGUFMSH41F3329L    Altcode:
  The accuracy of data-driven magnetohydrodynamics (MHD) models
  depends on accurate boundary conditions specified at the inner
  heliosphere. However, all of the MHD parameters (B, v, ρ, T)
  close to the Sun are not measurable at the present time,except the
  total magnetic field (|B|) at the photosphere. The solar wind speed
  (v), which is probably most relevant to space weather forecasting,
  is often modeled by the standard Wang-Sheely-Arge (WSA) empirical
  formula. The WSA formula is based on an inverse relationship
  between the solar wind speed measured at 1 AU and the magnetic field
  expansion factor estimated at 2.5 solar radii (R<SUB>⊙</SUB> ),
  with the following generic form: v = v<SUB>1</SUB> +v<SUB>2</SUB>
  f<SUB>s</SUB> <SUP>-</SUP><SUP>α</SUP> (where v is the solar wind
  speed at 18 R<SUB>⊙</SUB> , f<SUB>s</SUB> is the magnetic field
  expansion factor, and v<SUB>1</SUB>, v<SUB>2</SUB>, and α are three
  free parameters to be determined). Because it uses the solar wind
  speed at 1 AU, the formula ignores the transport of solar wind in the
  heliosphere. While the WSA formula uses "source projection" to account
  for the transport of the solar wind, it does not treat the solar wind
  as plasma. The purpose of this study is to rectify this omission by
  using numerical MHD simulations to find the optimal set of the free
  parameters that relate the magnetic properties at the source surface
  to the plasma parameters at 1 AU. In addition to the expansion factor,
  conservation of mass (ρv), magnetic flux (r<SUP>2</SUP>B), and total
  pressure along the stream line are assumed to obtain a complete set
  of MHD parameters at 18 R<SUB>⊙</SUB> . These parameters are used
  as the inner boundary conditions of our global three-dimensional MHD
  (G3DMHD) code to simulate solar wind plasma and field parameters out
  to ~1 AU. The simulation results are compared with the in situ data
  from Wind to assess the accuracy. Such a procedure is repeated (880
  times) to cover the three parameter regimes (100 &lt; v<SUB>1</SUB>
  &lt; 350 km/s; 250 &lt; v<SUB>2</SUB> &lt; 700 km/s; and 0.2 &lt; α
  &lt; 0.9) to find the optimal set. The simulation is performed for
  the period of CR2082. It is found that v = 189 + 679 f<SUB>s</SUB>
  <SUP>-0.7</SUP> is the best formula to relate the solar wind speed
  at 18 R<SUB>⊙</SUB> to the expansion factor. Strictly speaking,
  this formula applies only to periods around solar minimum. <P />*
  Work of CCW was partially supported by the Chief of Naval Research.

---------------------------------------------------------
Title: Fine-scale Explosive Energy Release at Sites of Prospective
    Magnetic Flux Cancellation in the Core of the Solar Active Region
    Observed by Hi-C 2.1, IRIS, and SDO
Authors: Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.;
   De Pontieu, Bart; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.;
   Rachmeler, Laurel A.; Kobayashi, Ken; Testa, Paola; Warren, Harry P.;
   Brooks, David H.; Cirtain, Jonathan W.; McKenzie, David E.; Morton,
   Richard J.; Peter, Hardi; Walsh, Robert W.
2019ApJ...887...56T    Altcode: 2019arXiv191101424T
  The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial
  and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X
  emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56
  UT. Three morphologically different types (I: dot-like; II: loop-like;
  III: surge/jet-like) of fine-scale sudden-brightening events (tiny
  microflares) are seen within and at the ends of an arch filament system
  in the core of the AR. Although type Is (not reported before) resemble
  IRIS bombs (in size, and brightness with respect to surroundings),
  our dot-like events are apparently much hotter and shorter in span
  (70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI
  magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw
  images to examine, at the sites of these events, brightenings and
  flows in the transition region and corona and evolution of magnetic
  flux in the photosphere. Most, if not all, of the events are seated
  at sites of opposite-polarity magnetic flux convergence (sometimes
  driven by adjacent flux emergence), implying likely flux cancellation
  at the microflare’s polarity inversion line. In the IRIS spectra
  and images, we find confirming evidence of field-aligned outflow from
  brightenings at the ends of loops of the arch filament system. In types
  I and II the explosion is confined, while in type III the explosion
  is ejective and drives jet-like outflow. The light curves from Hi-C,
  AIA, and IRIS peak nearly simultaneously for many of these events,
  and none of the events display a systematic cooling sequence as seen in
  typical coronal flares, suggesting that these tiny brightening events
  have chromospheric/transition region origin.

---------------------------------------------------------
Title: The High-Resolution Coronal Imager, Flight 2.1
Authors: Rachmeler, Laurel A.; Winebarger, Amy R.; Savage, Sabrina L.;
   Golub, Leon; Kobayashi, Ken; Vigil, Genevieve D.; Brooks, David H.;
   Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton,
   Richard J.; Peter, Hardi; Testa, Paola; Tiwari, Sanjiv K.; Walsh,
   Robert W.; Warren, Harry P.; Alexander, Caroline; Ansell, Darren;
   Beabout, Brent L.; Beabout, Dyana L.; Bethge, Christian W.; Champey,
   Patrick R.; Cheimets, Peter N.; Cooper, Mark A.; Creel, Helen K.;
   Gates, Richard; Gomez, Carlos; Guillory, Anthony; Haight, Harlan;
   Hogue, William D.; Holloway, Todd; Hyde, David W.; Kenyon, Richard;
   Marshall, Joseph N.; McCracken, Jeff E.; McCracken, Kenneth; Mitchell,
   Karen O.; Ordway, Mark; Owen, Tim; Ranganathan, Jagan; Robertson,
   Bryan A.; Payne, M. Janie; Podgorski, William; Pryor, Jonathan; Samra,
   Jenna; Sloan, Mark D.; Soohoo, Howard A.; Steele, D. Brandon; Thompson,
   Furman V.; Thornton, Gary S.; Watkinson, Benjamin; Windt, David
2019SoPh..294..174R    Altcode: 2019arXiv190905942R
  The third flight of the High-Resolution Coronal Imager (Hi-C 2.1)
  occurred on May 29, 2018; the Sounding Rocket was launched from White
  Sands Missile Range in New Mexico. The instrument has been modified
  from its original configuration (Hi-C 1) to observe the solar corona
  in a passband that peaks near 172 Å, and uses a new, custom-built
  low-noise camera. The instrument targeted Active Region 12712, and
  captured 78 images at a cadence of 4.4 s (18:56:22 - 19:01:57 UT; 5
  min and 35 s observing time). The image spatial resolution varies due
  to quasi-periodic motion blur from the rocket; sharp images contain
  resolved features of at least 0.47 arcsec. There are coordinated
  observations from multiple ground- and space-based telescopes providing
  an unprecedented opportunity to observe the mass and energy coupling
  between the chromosphere and the corona. Details of the instrument
  and the data set are presented in this paper.

---------------------------------------------------------
Title: Model studies of photoionization and photoelectron production
    in response to solar flares
Authors: Samaddar, S.; Siskind, D. E.; Bailey, S. M.; Reep, J. W.;
   Warren, H.
2019AGUFMSA11B3222S    Altcode:
  The solar flux, shortward of 102.6 nm deposits energy into
  the Earth's thermosphere and initiates chemical processes that
  affect the composition and structure of the ionospheric D and E
  regions. One of the primary processes is the photoionization of
  the major neutral constituents N<SUB>2</SUB>, O<SUB>2</SUB> and
  O. The photoionization of the major species leads to the formation
  of energetic photoelectrons. These primary photoelectrons create
  secondary electrons that can cause further ionization, dissociation,
  and excitation of particles. We use a photoelectron model to study
  the effects of variability of the solar flux in the production of the
  primary and secondary photoelectrons in the D and E regions of the
  thermosphere. Using a detailed hydrodynamic model of a solar flare
  arcade, we have synthesized the spectral irradiance from a large solar
  flare, extending to energies in the hard X-rays. We use this synthetic
  spectrum to study the effects of solar flares at altitudes lower than
  90 km, i.e. the D region. We have also revised the ionization and
  absorption cross-sections of the neutral species, including wavelengths
  based on new laboratory data. The new cross-sections are significantly
  different in the neighborhood of the Lyman beta emission. In this
  presentation, we examine the role of ionization by both photons
  and photoelectrons due to Lyman beta in the context of the revised
  cross sections. <P />The improved cross-sections and extension of the
  input solar flux to higher energies and therefore to lower altitudes,
  give us a better understanding of the effects of solar flares on the
  Earth's ionosphere.

---------------------------------------------------------
Title: A Next Generation Spectrometer: The EUV High-Throughput
    Spectroscopic Telescope (EUVST)
Authors: Warren, H. P.
2019AGUFMSH31C3319W    Altcode:
  An advanced spectrometer and slit-jaw imaging system has been proposed
  by an international team to JAXA's competitively selected M-class
  missions science program. The main scientific goal of the proposed
  instrument, the EUV High-Throughput Spectroscopic Telescope (EUVST),
  is to understand the transfer of mass and energy from the solar surface
  to the solar corona and interplanetary space by observing fundamental
  processes occurring in the solar atmosphere. The mission has two
  specific scientific objectives: (I) to understand how fundamental
  processes lead to the formation of the solar atmosphere and the solar
  wind, and (II) to understand how the solar atmosphere becomes unstable,
  releasing the energy that drives solar flares and eruptions. EUVST
  will make major advances by combining a seamless temperature coverage
  of the solar photosphere, chromosphere, transition region, and corona
  with very high spatial resolution (0.4ʺ or 300km) and unprecedented
  cadence (as high as 0.1s). This instrument will complement new solar
  observatories such as DKIST, the Parker Solar Probe, and Solar Orbiter
  that will be operational during the proposed mission.

---------------------------------------------------------
Title: Global Energetics of Solar Flares and Coronal Mass Ejections
Authors: Aschwanden, Markus J.; Caspi, Amir; Cohen, Christina M. S.;
   Holman, Gordon; Jing, Ju; Kretzschmar, Matthieu; Kontar, Eduard
   P.; McTiernan, James M.; Mewaldt, Richard A.; O'Flannagain, Aidan;
   Richardson, Ian G.; Ryan, Daniel; Warren, Harry P.; Xu, Yan
2019JPhCS1332a2002A    Altcode:
  We investigate the global energetics and energy closure of various
  physical processes that are energetically important in solar flares
  and coronal mass ejections (CMEs), which includes: magnetic energies,
  thermal energies, nonthermal energies (particle acceleration),
  direct and indirect plasma heating processes, kinetic CME energies,
  gravitational CME energies, aerodynamic drag of CMEs, solar
  energetic particle events, EUV and soft X-ray radiation, white-light,
  and bolometric energies. Statistics on these forms of energies is
  obtained from 400 GOES M- and X-class events during the first 3.5
  years of the Solar Dynamics Observatory (SDO) mission. A primary
  test addressed in this study is the closure of the various energies,
  such as the equivalence of the dissipated magnetic energies and the
  primary dissipated are energies (accelerated particles, direct heating,
  CME acceleration), which faciliate the energy of secondary processes
  (plasma heating, shock acceleration) and interactions with the solar
  wind (aerodynamic drag). Our study demonstrates energy closure in the
  statistical average, while individual events may have considerable
  uncertainties, requiring improved nonlinear force-free field models,
  and particle acceleration models with observationally constrained
  low-energy cutoffs.

---------------------------------------------------------
Title: Solar Active Region Heating Diagnostics from High-temperature
    Emission Using the MaGIXS
Authors: Athiray, P. S.; Winebarger, Amy R.; Barnes, Will T.; Bradshaw,
   Stephen J.; Savage, Sabrina; Warren, Harry P.; Kobayashi, Ken; Champey,
   Patrick; Golub, Leon; Glesener, Lindsay
2019ApJ...884...24A    Altcode: 2019arXiv190902541A
  The relative amount of high-temperature plasma has been found to be
  a useful diagnostic to determine the frequency of coronal heating on
  sub-resolution structures. When the loops are infrequently heated,
  a broad emission measure (EM) over a wider range of temperatures
  is expected. A narrower EM is expected for high-frequency heating
  where the loops are closer to equilibrium. The soft X-ray spectrum
  contains many spectral lines that provide high-temperature diagnostics,
  including lines from Fe XVII-XIX. This region of the solar spectrum
  will be observed by the Marshall Grazing Incidence Spectrometer (MaGIXS)
  in 2020. In this paper, we derive the expected spectral line intensity
  in MaGIXS to varying amounts of high-temperature plasma to demonstrate
  that a simple line ratio provides a powerful diagnostic to determine
  the heating frequency. Similarly, we examine ratios of AIA channel
  intensities, filter ratios from a XRT, and energy bands from the FOXSI
  sounding rocket to determine their sensitivity to this parameter. We
  find that both FOXSI and MaGIXS provide good diagnostic capabilities
  for high-temperature plasma. We then compare the predicted line ratios
  to the output of a numerical model and confirm that the MaGIXS ratios
  provide an excellent diagnostic for heating frequency.

---------------------------------------------------------
Title: The Variability of Solar Coronal Abundances in Active Regions
    and the Quiet Sun
Authors: Doschek, G. A.; Warren, H. P.
2019ApJ...884..158D    Altcode:
  Measurements of elemental abundances hold important clues to how mass
  and energy flow through the solar atmosphere. Variations in abundances
  are organized by an element’s first ionization potential (FIP),
  and many previous studies have assumed that low FIP (less than 10 eV)
  elements are enriched by a factor of 3-4 in the corona. In this paper,
  we use spatially resolved observations from the Extreme-ultraviolet
  Imaging Telescope on board the Hinode spacecraft to examine the spatial
  variability of elemental abundance in and around active regions. We find
  substantial variations within some active regions. In general, however,
  we find that the enrichment of low FIP elements is limited to bright,
  active region structures. In faint active region structures and in the
  dark, quiet regions around active regions, the measured abundances are
  close to photospheric. These measurements use the ratio of low FIP
  Si to high FIP S. Similar conclusions concerning quiet Sun regions
  have been reached recently by Del Zanna using full-Sun spectra. He
  has found that the coronal quiet Sun (at temperatures greater than
  1 MK) has photospheric abundances. Transition region abundances (at
  temperatures less than 1 MK in the solar atmosphere) have been found
  to be photospheric. These results and results from this paper suggest
  that a coronal composition is not a general property of million-degree
  plasma, but is limited to bright active region loops, and is variable.

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

---------------------------------------------------------
Title: Concept study of Solar-C_EUVST optical design
Authors: Kawate, Tomoko; Shimizu, Toshifumi; Imada, Shinsuke; Tsuzuki,
   Toshihiro; Katsukawa, Yukio; Hara, Hirohisa; Suematsu, Yoshinori;
   Ichimoto, Kiyoshi; Warren, Harry; Teriaca, Luca; Korendyke, Clarence
   M.; Brown, Charles
2019SPIE11118E..1NK    Altcode:
  The main characteristics of Solar-C_EUVST are the high temporal and
  high spatial resolutions over a wide temperature coverage. In order
  to realize the instrument for meeting these scientific requirements
  under size constraints given by the JAXA Epsilon vehicle, we examined
  four-dimensional optical parameter space of possible solutions of
  geometrical optical parameters such as mirror diameter, focal length,
  grating magnification, and so on. As a result, we have identified
  the solution space that meets the EUVST science objectives and rocket
  envelope requirements. A single solution was selected and used to define
  the initial optical parameters for the concept study of the baseline
  architecture for defining the mission concept. For this solution, we
  optimized the grating and geometrical parameters by ray tracing of the
  Zemax software. Consequently, we found an optics system that fulfills
  the requirement for a 0.4" angular resolution over a field of view of
  100" (including margins) covering spectral ranges of 170-215, 463-542,
  557-637, 690-850, 925-1085, and 1115-1275 A. This design achieves an
  effective area 10 times larger than the Extreme-ultraviolet Imaging
  Spectrometer onboard the Hinode satellite, and will provide seamless
  observations of 4.2-7.2 log(K) plasmas for the first time. Tolerance
  analyses were performed based on the optical design, and the moving
  range and step resolution of focus mechanisms were identified. In
  the presentation, we describe the derivation of the solution space,
  optimization of the optical parameters, and show the results of ray
  tracing and tolerance analyses.

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

---------------------------------------------------------
Title: The Multi-instrument (EVE-RHESSI) DEM for Solar Flares,
    and Implications for Nonthermal Emission
Authors: McTiernan, James M.; Caspi, Amir; Warren, Harry P.
2019ApJ...881..161M    Altcode: 2018arXiv180512285M
  Solar flare X-ray spectra are typically dominated by thermal
  bremsstrahlung emission in the soft X-ray (≲10 keV) energy range;
  for hard X-ray energies (≳30 keV), emission is typically nonthermal
  from beams of electrons. The low-energy extent of nonthermal emission
  has only been loosely quantified. It has been difficult to obtain
  a lower limit for a possible nonthermal cutoff energy due to the
  significantly dominant thermal emission. Here we use solar flare data
  from the extreme ultraviolet Variability Experiment on board the Solar
  Dynamics Observatory and X-ray data from the Reuven Ramaty High Energy
  Spectroscopic Imager to calculate the Differential Emission Measure
  (DEM). This improvement over the isothermal approximation and any
  single-instrument DEM helps to resolve ambiguities in the range where
  thermal and nonthermal emission overlap, and to provide constraints
  on the low-energy cutoff. In the model, thermal emission is from a
  DEM that is parameterized as multiple Gaussians in Log(T). Nonthermal
  emission results from a photon spectrum obtained using a thick-target
  emission model. Spectra for both instruments are fit simultaneously
  in a self-consistent manner. Our results have been obtained using a
  sample of 52 large (Geostationary Operational Environmental Satellite
  X- and M-class) solar flares observed between 2011 and 2013. It turns
  out that it is often possible to determine low-energy cutoffs early
  (in the first two minutes) during large flares. Cutoff energies at
  these times are typically low, less than 10 keV, when assuming coronal
  abundances. With photospheric abundances, cutoff energies are typically
  ∼10 keV higher, in the ∼17-25 keV range.

---------------------------------------------------------
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>}.

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

---------------------------------------------------------
Title: Comprehensive Determination of the Hinode/EIS Roll Angle
Authors: Pelouze, Gabriel; Auchère, Frédéric; Bocchialini, Karine;
   Harra, Louise; Baker, Deborah; Warren, Harry P.; Brooks, David H.;
   Mariska, John T.
2019SoPh..294...59P    Altcode: 2019arXiv190311923P
  We present a new coalignment method for the EUV Imaging Spectrometer
  (EIS) on board the Hinode spacecraft. In addition to the pointing
  offset and spacecraft jitter, this method determines the roll angle
  of the instrument, which has never been systematically measured, and
  which is therefore usually not corrected. The optimal pointing for EIS
  is computed by maximizing the cross-correlations of the Fe XII 195.119
  Å line with images from the 193 Å band of the Atmospheric Imaging
  Assembly (AIA) on board the Solar Dynamics Observatory (SDO). By
  coaligning 3336 rasters with high signal-to-noise ratio, we estimate
  the rotation angle between EIS and AIA and explore the distribution
  of its values. We report an average value of (−0.387<SUP>±0.007 )
  ∘</SUP>. We also provide a software implementation of this method
  that can be used to coalign any EIS raster.

---------------------------------------------------------
Title: Efficient Calculation of Non-local Thermodynamic Equilibrium
    Effects in Multithreaded Hydrodynamic Simulations of Solar Flares
Authors: Reep, Jeffrey W.; Bradshaw, Stephen J.; Crump, Nicholas A.;
   Warren, Harry P.
2019ApJ...871...18R    Altcode: 2018arXiv180609574R
  Understanding the dynamics of the chromosphere is crucial to
  understanding energy transport across the solar atmosphere. The
  chromosphere is optically thick at many wavelengths and described by
  non-local thermodynamic equilibrium (NLTE), making it difficult to
  interpret observations. Furthermore, there is considerable evidence
  that the atmosphere is filamented, and that current instruments do not
  resolve small-scale features. In flares, it is likely that multithreaded
  models are required to describe the heating. The combination of NLTE
  effects and multithreaded modeling requires computationally demanding
  calculations, which has motivated the development of a model that can
  efficiently treat both. We describe the implementation of a solver in a
  hydrodynamic code for the hydrogen level populations that approximates
  the NLTE solutions. We derive an accurate electron density across the
  atmosphere that includes the effects of nonequilibrium ionization for
  helium and metals. We show the effects on hydrodynamic simulations,
  which are used to synthesize light curves using a postprocessing
  radiative transfer code. We demonstrate the utility of this model on
  IRIS observations of a small flare. We show that the Doppler shifts
  in Mg II, C II, and O I can be explained with a multithreaded model
  of loops subjected to electron beam heating, so long as NLTE effects
  are treated. The intensities, however, do not match the observed values
  very well, which is due to assumptions about the initial atmosphere. We
  briefly show how altering the initial atmosphere can drastically alter
  line profiles and derived quantities and suggest that it should be
  tuned to preflare observations.

---------------------------------------------------------
Title: First high-resolution look at the quiet Sun with ALMA at 3mm
Authors: Nindos, A.; Alissandrakis, C. E.; Bastian, T. S.; Patsourakos,
   S.; De Pontieu, B.; Warren, H.; Ayres, T.; Hudson, H. S.; Shimizu,
   T.; Vial, J. -C.; Wedemeyer, S.; Yurchyshyn, V.
2018A&A...619L...6N    Altcode: 2018arXiv181005223N
  We present an overview of high-resolution quiet Sun observations,
  from disk center to the limb, obtained with the Atacama Large
  millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun
  regions were observed at a resolution of up to 2.5″ by 4.5″. We
  produced both average and snapshot images by self-calibrating the ALMA
  visibilities and combining the interferometric images with full-disk
  solar images. The images show well the chromospheric network, which,
  based on the unique segregation method we used, is brighter than the
  average over the fields of view of the observed regions by ∼305
  K while the intranetwork is less bright by ∼280 K, with a slight
  decrease of the network/intranetwork contrast toward the limb. At 3
  mm the network is very similar to the 1600 Å images, with somewhat
  larger size. We detect, for the first time, spicular structures,
  rising up to 15″ above the limb with a width down to the image
  resolution and brightness temperature of ∼1800 K above the local
  background. No trace of spicules, either in emission or absorption,
  is found on the disk. Our results highlight the potential of ALMA for
  the study of the quiet chromosphere.

---------------------------------------------------------
Title: Incorporating Uncertainties in Atomic Data into the Analysis
of Solar and Stellar Observations: A Case Study in Fe XIII
Authors: Yu, Xixi; Del Zanna, Giulio; Stenning, David C.;
   Cisewski-Kehe, Jessi; Kashyap, Vinay L.; Stein, Nathan; van Dyk,
   David A.; Warren, Harry P.; Weber, Mark A.
2018ApJ...866..146Y    Altcode: 2018arXiv180906173Y
  Information about the physical properties of astrophysical objects
  cannot be measured directly but is inferred by interpreting
  spectroscopic observations in the context of atomic physics
  calculations. Ratios of emission lines, for example, can be used
  to infer the electron density of the emitting plasma. Similarly,
  the relative intensities of emission lines formed over a wide range
  of temperatures yield information on the temperature structure. A
  critical component of this analysis is understanding how uncertainties
  in the underlying atomic physics propagate to the uncertainties in
  the inferred plasma parameters. At present, however, atomic physics
  databases do not include uncertainties on the atomic parameters and
  there is no established methodology for using them even if they
  did. In this paper we develop simple models for uncertainties in
  the collision strengths and decay rates for Fe XIII and apply them
  to the interpretation of density-sensitive lines observed with the
  EUV (extreme ultraviolet) Imagining spectrometer (EIS) on Hinode. We
  incorporate these uncertainties in a Bayesian framework. We consider
  both a pragmatic Bayesian method where the atomic physics information is
  unaffected by the observed data, and a fully Bayesian method where the
  data can be used to probe the physics. The former generally increases
  the uncertainty in the inferred density by about a factor of 5 compared
  with models that incorporate only statistical uncertainties. The latter
  reduces the uncertainties on the inferred densities, but identifies
  areas of possible systematic problems with either the atomic physics
  or the observed intensities.

---------------------------------------------------------
Title: Probing the evolution of a coronal cavity within a solar
    coronal mass ejection.
Authors: Harra, Louise K.; Doschek, G. A.; Hara, Hirohisa; Long,
   David; Warren, Harry; Matthews, Sarah; Lee, Kyoung-Sun; Jenkins, Jack
2018cosp...42E1381H    Altcode:
  On the 10 September 2017, an X-class solar flare erupted at the solar
  limb. The associated coronal mass ejection (CME) had the classic three
  part structure with a bright core surrounded by a dark cavity. This
  event was captured perfectly by the Hinode EUV imaging spectrometer
  (EIS). The EIS instrument captured spectroscopically the flaring
  loops, the current sheet and the cavity for the first time. In the
  'standard flare model', magnetic reconnection of coronal loops occurs
  following the eruption of a magnetic flux rope. The flux rope is a key
  element of the flare process and eruption but is inherently difficult
  to observe. Dark cavities observed within a CME are assumed to be
  flux ropes. The observations we describe here, provide an insight
  into the characteristics of a cavity, and how the rapid injection of
  energy from the flare underneath forces the rapid expansion of the
  flux rope resulting in the eruption. Doppler shifts of over 200 km/s
  are measured at either end of the cavity. There is mixed temperature
  plasma - cool material in the centre that also has strong flows, and
  hot FeXXIV emission being observed. SDO Atmospheric Imaging Assembly
  (AIA) data shows that the cavity erupts rapidly, and is being driven
  by the non-thermal energy input from the flare below as measured from
  Fermi data.

---------------------------------------------------------
Title: A Chandra/LETGS Survey of Main-sequence Stars
Authors: Wood, Brian E.; Laming, J. Martin; Warren, Harry P.;
   Poppenhaeger, Katja
2018ApJ...862...66W    Altcode: 2018arXiv180605111W
  We analyze the X-ray spectra of 19 main-sequence stars observed
  by Chandra using its LETGS configuration. Emission measure (EM)
  distributions are computed based on emission line measurements, an
  analysis that also yields evaluations of coronal abundances. The
  use of newer atomic physics data results in significant changes
  compared to past published analyses. The stellar EM distributions
  correlate with surface X-ray flux (F <SUB>X</SUB>) in a predictable
  way, regardless of spectral type. Thus, we provide EM distributions
  as a function of F <SUB>X</SUB>, which can be used to estimate the
  EM distribution of any main-sequence star with a measured broadband
  X-ray luminosity. Comparisons are made with solar EM distributions,
  both full-disk distributions and spatially resolved ones from active
  regions (ARs), flares, and the quiet Sun. For moderately active stars,
  the slopes and magnitudes of the EM distributions are in excellent
  agreement with those of solar ARs for {log}T&lt; 6.6, suggesting that
  such stars have surfaces completely filled with solar-like ARs. A
  stellar surface covered with solar X-class flares yields a reasonable
  approximation for the EM distributions of the most active stars. Unlike
  the EM distributions, coronal abundances are strongly dependent on
  spectral type, and we provide relations with surface temperature
  for both relative and absolute abundances. Finally, the coronal
  abundances of the exoplanet host star τ Boo A (F7 V) are anomalous,
  and we propose that this is due to the presence of the exoplanet.

---------------------------------------------------------
Title: New solar diagnostics enabled by novel soft x-ray imaging
    spectroscopy, and future missions
Authors: Caspi, Amir; Sylwester, Janusz; Gburek, Szymon; Crowley,
   Geoff; Woods, Thomas; Shih, Albert Y.; DeForest, Craig; Steslicki,
   Marek; Warren, Harry; Mason, James
2018cosp...42E.525C    Altcode:
  Solar soft X-ray (SXR) observations provide unique diagnostics of
  plasma heating, during solar flares and quiescent times. Spectrally-
  and temporally-resolved measurements are crucial for understanding the
  dynamics and evolution of these energetic processes; spatially-resolved
  measurements are essential for understanding energy transport. A
  critical observational gap exists from ∼0.2 to ∼3 keV (∼4-60
  Å), where spectrally-resolved stellar observations are plentiful
  but have not been routinely made for the Sun in many decades. This
  energy range includes spectral lines from highly-ionized atoms with
  both low and high first ionization potential (FIP), as well as thermal
  free-free (bremsstrahlung) and free-bound (radiative recombination)
  continua. These SXR emissions provide crucial diagnostics of plasma
  temperature distributions, as well as elemental abundances that
  probe plasma origins over a wide range of temperatures, that are
  not available from observations at other wavelengths. A better
  understanding of thermal plasma also informs our interpretation of
  hard X-ray (HXR) observations of nonthermal particles, improving our
  understanding of the relationships between particle acceleration,
  plasma heating, and the underlying release of magnetic energy during
  reconnection.We discuss a proposed small satellite pathfinder mission,
  the CubeSat Imaging X-ray Solar Spectrometer (CubIXSS), to measure
  spectrally- and spatially-resolved SXRs from the quiescent and
  flaring Sun from a 6U CubeSat platform in low-Earth orbit during
  a nominal 1-year mission. CubIXSS includes the Amptek X123-FastSDD
  silicon drift detector, a low-noise, commercial off-the-shelf (COTS)
  instrument enabling full-Sun SXR spectroscopy from ∼0.5 to ∼20
  keV with ∼0.15 keV FWHM spectral resolution with low power, mass,
  and volume requirements. Multiple detectors and tailored apertures
  provide sensitivity to SXR emission from deep solar minimum to &gt;X5
  flares. An X123-CdTe cadmium-telluride detector is also included for
  ∼5-50 keV HXR spectroscopy with ∼0.5 keV FWHM resolution. The
  precise spectra from these instruments will provide detailed
  measurements of the coronal temperature distribution and elemental
  abundances during flares and quiescent times, and, for large flares,
  context information of flare-accelerated electrons.CubIXSS also
  includes a novel spectro-spatial imager - the first ever solar imager
  on a CubeSat - utilizing a custom pinhole camera and Chandra-heritage
  X-ray transmission diffraction grating to provide spatially- resolved,
  full-Sun imaging spectroscopy from ∼0.2 to ∼10 keV (∼1-60
  Å), with ∼25 arcsec and ∼0.25 Å FWHM spatial and spectral
  resolutions, respectively. Additional pinholes with tailored filters
  provide non-dispersed images with coarse spectral information to seed
  analysis of the dispersed spectro-spatial images and for improved
  sensitivity to quiescent conditions. MOXSI's unique capabilities
  enable SXR spectroscopy and corresponding temperature and elemental
  abundance diagnostics of individual flares and active regions over a
  spectral range never before accessed by any prior solar mission.CubIXSS
  is a pathfinder for larger satellites with improved resolution and
  sensitivity. Through these groundbreaking new measurements, CubIXSS
  and future missions will improve our physical understanding of thermal
  plasma processes and impulsive energy release in the solar corona,
  from quiet Sun to solar flares.

---------------------------------------------------------
Title: Solar Cycle Observations of the Neon Abundance in the
    Sun-as-a-star
Authors: Brooks, David H.; Baker, Deborah; van Driel-Gesztelyi, Lidia;
   Warren, Harry P.
2018ApJ...861...42B    Altcode: 2018arXiv180507032B
  Properties of the Sun’s interior can be determined accurately
  from helioseismological measurements of solar oscillations. These
  measurements, however, are in conflict with photospheric elemental
  abundances derived using 3D hydrodynamic models of the solar
  atmosphere. This divergence of theory and helioseismology is known as
  the “solar modeling problem.” One possible solution is that the
  photospheric neon abundance, which is deduced indirectly by combining
  the coronal Ne/O ratio with the photospheric O abundance, is larger
  than generally accepted. There is some support for this idea from
  observations of cool stars. The Ne/O abundance ratio has also been
  found to vary with the solar cycle in the slowest solar wind streams
  and coronal streamers, and the variation from solar maximum to minimum
  in streamers (∼0.1-0.25) is large enough to potentially bring some
  of the solar models into agreement with the seismic data. Here we use
  daily sampled observations from the EUV Variability Experiment on the
  Solar Dynamics Observatory taken in 2010-2014, to investigate whether
  the coronal Ne/O abundance ratio shows a variation with the solar cycle
  when the Sun is viewed as a star. We find only a weak dependence on,
  and moderate anti-correlation with, the solar cycle with the ratio
  measured around 0.2-0.3 MK falling from 0.17 at solar minimum to
  0.11 at solar maximum. The effect is amplified at higher temperatures
  (0.3-0.6 MK) with a stronger anti-correlation and the ratio falling
  from 0.16 at solar minimum to 0.08 at solar maximum. The values we
  find at solar minimum are too low to solve the solar modeling problem.

---------------------------------------------------------
Title: On the Synthesis of GOES Light Curves from Numerical Models
Authors: Reep, Jeffrey W.; Warren, Harry P.
2018RNAAS...2...48R    Altcode: 2018RNAAS...2b..48R
  No abstract at ADS

---------------------------------------------------------
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: A Next Generation Spectrometer: The EUV High-Throughput
    Spectroscopic Telescope (EUVST)
Authors: Warren, Harry
2018tess.conf41003W    Altcode:
  &lt;span class="s1" In response to the Next Generation Solar Physics
  Mission report, an advanced spectrometer has been proposed to JAXA's
  competitively selected M-class missions science program. The main
  scientific goal of the proposed instrument, the EUV High-Throughput
  Spectroscopic Telescope (EUVST), is to understand the transfer
  of mass and energy from the solar surface to the solar corona and
  interplanetary space by observing fundamental processes occurring in the
  solar atmosphere. The mission has two specific scientific objectives:
  (I) to understand how fundamental processes lead to the formation
  of the solar atmosphere and the solar wind, and (II) to understand
  how the solar atmosphere becomes unstable, releasing the energy that
  drives solar flares and eruptions. EUVST will make major advances by
  combining a seamless temperature coverage of the solar chromosphere,
  transition region, and corona with very high spatial resolution
  (0.4ʺ or 300km) and unprecedented cadence (as high as 0.2s). This
  instrument will complement new solar observatories such as DKIST,
  the Parker Solar Probe, and Solar Orbiter that will be operational
  during the proposed mission.

---------------------------------------------------------
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: A Novel Soft X-ray Slitless Imaging Spectrograph for Unique
    Diagnostics of Hot Coronal Plasma
Authors: Caspi, Amir; Shh, Albert Y.; Warren, Harry; Woods, Thomas
   N.; Mason, James Paul; Steslicki, MArek; Gburek, Szymon; Sylwester,
   Janusz; DeForest, Craig; Schwartz, Richard; Crowley, Geoff
2018tess.conf41006C    Altcode:
  Solar soft X-ray (SXR) observations from ∼0.2 to ∼3 keV
  (∼4-60 Å), during both solar flares and quiescent times, provide
  crucial diagnostics that are not available from observations at other
  wavelengths. Specifically, SXRs reveal plasma temperature distributions,
  as well as elemental abundances that probe plasma origins over a wide
  range of temperatures. Spectrally- and temporally-resolved measurements
  are essential for understanding the dynamics and evolution of these
  energetic processes; spatially-resolved measurements are essential
  for understanding energy transport. The NGSPM study calls out an X-ray
  spectroscopic imager (T-10) as a high-priority instrument, in particular
  with a spectral resolution of better than 100 eV for SXR emission
  lines. <P />We describe a novel approach for a spectro-spatial imager
  - combining a pinhole camera with a X-ray transmission diffraction
  grating - that can achieve the required combination of spectral and
  angular resolutions at SXR energies. Such an instrument has already
  been demonstrated as a protoype on a sounding-rocket flight and can be
  proven thoroughly on a small satellite, specifically as part of the
  instrument complement of the proposed CubeSat Imaging X-ray Solar
  Spectrometer (CubIXSS) mission. CubIXSS will measure spectrally-
  and spatially-resolved SXRs from ~1 to 60 Å (~0.2-10 keV) with ~0.25
  Å and ~25 arcsec FWHM resolutions, respectively, from the quiescent
  and flaring Sun from a 6U CubeSat platform in low-Earth orbit during
  a nominal 1-year mission. Accordingly, CubIXSS is a pathfinder for
  larger satellites with improved resolution (&lt;0.1 Å, ~few arcsec)
  and sensitivity, that could be integrated with focusing optics if
  desired. Through these groundbreaking new measurements, CubIXSS and
  future missions will improve our physical understanding of thermal
  plasma processes and impulsive energy release in the solar corona,
  from quiet Sun to solar flares.

---------------------------------------------------------
Title: The Duration of Energy Deposition on Unresolved Flaring Loops
    in the Solar Corona
Authors: Reep, Jeffrey W.; Polito, Vanessa; Warren, Harry P.; Crump,
   Nicholas A.
2018ApJ...856..149R    Altcode: 2018arXiv180208884R
  Solar flares form and release energy across a large number of magnetic
  loops. The global parameters of flares, such as the total energy
  released, duration, physical size, etc., are routinely measured, and the
  hydrodynamics of a coronal loop subjected to intense heating have been
  extensively studied. It is not clear, however, how many loops comprise
  a flare, nor how the total energy is partitioned between them. In
  this work, we employ a hydrodynamic model to better understand the
  energy partition by synthesizing Si IV and Fe XXI line emission and
  comparing to observations of these lines with the Interface Region
  Imaging Spectrograph (IRIS). We find that the observed temporal
  evolution of the Doppler shifts holds important information on the
  heating duration. To demonstrate this, we first examine a single loop
  model, and find that the properties of chromospheric evaporation seen
  in Fe XXI can be reproduced by loops heated for long durations, while
  persistent redshifts seen in Si IV cannot be reproduced by any single
  loop model. We then examine a multithreaded model, assuming both a
  fixed heating duration on all loops and a distribution of heating
  durations. For a fixed heating duration, we find that durations of
  100-200 s do a fair job of reproducing both the red- and blueshifts,
  while a distribution of durations, with a median of about 50-100 s,
  does a better job. Finally, we compare our simulations directly to
  observations of an M-class flare seen by IRIS, and find good agreement
  between the modeled and observed values given these constraints.

---------------------------------------------------------
Title: Plasma Evolution within an Erupting Coronal Cavity
Authors: Long, David M.; Harra, Louise K.; Matthews, Sarah A.; Warren,
   Harry P.; Lee, Kyoung-Sun; Doschek, George A.; Hara, Hirohisa; Jenkins,
   Jack M.
2018ApJ...855...74L    Altcode: 2018arXiv180201391L
  Coronal cavities have previously been observed to be associated
  with long-lived quiescent filaments and are thought to correspond
  to the associated magnetic flux rope. Although the standard flare
  model predicts a coronal cavity corresponding to the erupting flux
  rope, these have only been observed using broadband imaging data,
  restricting an analysis to the plane-of-sky. We present a unique set of
  spectroscopic observations of an active region filament seen erupting
  at the solar limb in the extreme ultraviolet. The cavity erupted and
  expanded rapidly, with the change in rise phase contemporaneous with an
  increase in nonthermal electron energy flux of the associated flare. Hot
  and cool filamentary material was observed to rise with the erupting
  flux rope, disappearing suddenly as the cavity appeared. Although
  strongly blueshifted plasma continued to be observed flowing from
  the apex of the erupting flux rope, this outflow soon ceased. These
  results indicate that the sudden injection of energy from the flare
  beneath forced the rapid eruption and expansion of the flux rope,
  driving strong plasma flows, which resulted in the eruption of an
  under-dense filamentary flux rope.

---------------------------------------------------------
Title: Coronal Elemental Abundances in Solar Emerging Flux Regions
Authors: Baker, Deborah; Brooks, David H.; van Driel-Gesztelyi,
   Lidia; James, Alexander W.; Démoulin, Pascal; Long, David M.; Warren,
   Harry P.; Williams, David R.
2018ApJ...856...71B    Altcode: 2018arXiv180108424B
  The chemical composition of solar and stellar atmospheres differs from
  the composition of their photospheres. Abundances of elements with low
  first ionization potential (FIP) are enhanced in the corona relative
  to high-FIP elements with respect to the photosphere. This is known as
  the FIP effect and it is important for understanding the flow of mass
  and energy through solar and stellar atmospheres. We used spectroscopic
  observations from the Extreme-ultraviolet Imaging Spectrometer on board
  the Hinode observatory to investigate the spatial distribution and
  temporal evolution of coronal plasma composition within solar emerging
  flux regions inside a coronal hole. Plasma evolved to values exceeding
  those of the quiet-Sun corona during the emergence/early-decay phase
  at a similar rate for two orders of magnitude in magnetic flux, a rate
  comparable to that observed in large active regions (ARs) containing
  an order of magnitude more flux. During the late-decay phase, the rate
  of change was significantly faster than what is observed in large,
  decaying ARs. Our results suggest that the rate of increase during the
  emergence/early-decay phase is linked to the fractionation mechanism
  that leads to the FIP effect, whereas the rate of decrease during
  the later decay phase depends on the rate of reconnection with the
  surrounding magnetic field and its plasma composition.

---------------------------------------------------------
Title: Photospheric and Coronal Abundances in an X8.3 Class Limb Flare
Authors: Doschek, G. A.; Warren, H. P.; Harra, L. K.; Culhane, J. L.;
   Watanabe, T.; Hara, H.
2018ApJ...853..178D    Altcode:
  We analyze solar elemental abundances in coronal post-flare
  loops of an X8.3 flare (SOL2017-09-10T16:06) observed on the west
  limb on 2017 September 10 near 18 UT using spectra recorded by
  the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft. The abundances in the corona can differ from photospheric
  abundances due to the first ionization potential (FIP) effect. In
  some loops of this flare, we find that the abundances appear to be
  coronal at the loop apices or cusps, but steadily transform from
  coronal to photospheric as the loop footpoint is approached. This
  result is found from the intensity ratio of a low-FIP ion spectral
  line (Ca XIV) to a high-FIP ion spectral line (Ar XIV) formed at
  about the same temperature (4-5 MK). Both lines are observed close in
  wavelength. Temperature, which could alter the interpretation, does
  not appear to be a factor based on intensity ratios of Ca XV lines
  to a Ca XIV line. We discuss the abundance result in terms of the
  Laming model of the FIP effect, which is explained by the action of
  the ponderomotive force in magnetohydrodynamic (MHD) waves in coronal
  loops and in the underlying chromosphere.

---------------------------------------------------------
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: The Marshall Grazing Incidence X-ray Spectrometer (MaGIXS)
Authors: Winebarger, A. R.; Savage, S. L.; Kobayashi, K.; Champey,
   P. R.; McKenzie, D. E.; Golub, L.; Testa, P.; Reeves, K.; Cheimets,
   P.; Cirtain, J. W.; Walsh, R. W.; Bradshaw, S. J.; Warren, H.; Mason,
   H. E.; Del Zanna, G.
2017AGUFMSH44A..06W    Altcode:
  For over four decades, X-ray, EUV, and UV spectral observations have
  been used to measure physical properties of the solar atmosphere. At
  wavelengths below 10 nm, however, observations of the solar corona
  with simultaneous spatial and spectral resolution are limited,
  and not since the late 1970's have spatially resolved solar X-ray
  spectra been measured. Because the soft X-ray regime is dominated
  by emission lines formed at high temperatures, X-ray spectroscopic
  techniques yield insights to fundamental physical processes that are
  not accessible by any other means. Using a novel implementation of
  corrective optics, the Marshall Grazing Incidence X-ray Spectrometer
  (MaGIXS) will measure, for the first time, the solar spectrum from 0.6-
  2.4 nm with a 6 arcsec resolution over an 8 arcmin slit. The MaGIXS
  mission will address on of the fundamental problems of coronal physics:
  the nature of coronal heating. There are several observables in the
  MaGIXS wavelength range that will constrain the heating frequency and
  hence discriminate between competing coronal heating theories. In this
  presentation, we will present the MaGIXS scientific motivation and
  provide an update on instrument development. MaGIXS will be launched
  from White Sands Missile Range in the summer of 2019.

---------------------------------------------------------
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: Sunspots, Starspots, and Elemental Abundances
Authors: Doschek, George A.; Warren, Harry P.
2017SPD....4810601D    Altcode:
  The composition of plasma in solar and stellar atmospheres is not fixed,
  but varies from feature to feature. These variations are organized by
  the First Ionization Potential (FIP) of the element. Solar measurements
  often indicate that low FIP elements (&lt; 10eV, such as Fe, Si, Mg)
  are enriched by factors of 3-4 in the corona relative to high FIP
  elements (&gt;10 eV, such as C, N, O, Ar, He) compared to abundances
  in the photosphere. Stellar observations have also shown similar
  enrichments. An inverse FIP effect, where the low FIP elements are
  depleted, has been observed in stellar coronae of stars believed
  to have large starspots in their photospheres. The abundances are
  important for determining radiative loss rates in models, tracing the
  origin of the slow solar wind, and for understanding wave propagation
  in the chromosphere and corona. Recently, inverse FIP effects have
  been discovered in the Sun (Doschek, Warren, &amp; Feldman 2015, ApJ,
  808, L7) from spectra obtained by the Extreme-ultraviolet Imaging
  Spectrometer (EIS) on the Hinode spacecraft. The inverse FIP regions
  seem always to be near sunspots and cover only a very small area
  (characteristic length = a few arcseconds). However, in pursuing the
  search for inverse FIP regions, we have found that in some sunspot
  groups the coronal abundance at a temperature of 3-4 MK can be near
  photospheric over much larger areas of the sun near the sunspots (e.g.,
  6,000 arcsec<SUP>2</SUP>). Also, sometimes the abundances at 3-4 MK
  are in between coronal and photospheric values. This can occur in small
  areas of an active region. It is predicted (Laming 2015, Sol. Phys., 12,
  2) that the FIP effect should be highly variable in the corona. Several
  examples of coronal abundance variations are presented. Our work
  indicates that a comprehensive re-investigation of solar abundances
  is highly desirable. This work is supported by a NASA Hinode grant.

---------------------------------------------------------
Title: A Solar cycle correlation of coronal element abundances in
    Sun-as-a-star observations
Authors: Brooks, David H.; Baker, Deborah; van Driel-Gesztelyi, Lidia;
   Warren, Harry P.
2017NatCo...8..183B    Altcode: 2018arXiv180200563B
  The elemental composition in the coronae of low-activity solar-like
  stars appears to be related to fundamental stellar properties such as
  rotation, surface gravity, and spectral type. Here we use full-Sun
  observations from the Solar Dynamics Observatory, to show that when
  the Sun is observed as a star, the variation of coronal composition
  is highly correlated with a proxy for solar activity, the F10.7 cm
  radio flux, and therefore with the solar cycle phase. Similar cyclic
  variations should therefore be detectable spectroscopically in X-ray
  observations of solar analogs. The plasma composition in full-disk
  observations of the Sun is related to the evolution of coronal magnetic
  field activity. Our observations therefore introduce an uncertainty
  into the nature of any relationship between coronal composition and
  fixed stellar properties. The results highlight the importance of
  systematic full-cycle observations for understanding the elemental
  composition of solar-like stellar coronae.

---------------------------------------------------------
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: The CubeSat Imaging X-ray Solar Spectrometer (CubIXSS)
    Mission Concept
Authors: Caspi, Amir; Shih, Albert Y.; Warren, Harry; DeForest,
   Craig; Laurent, Glenn Thomas; Schwartz, Richard A.; Woods, Thomas
   N.; Mason, James; Palo, Scott; Steslicki, Marek; Sylwester, Janusz;
   Gburek, Szymon; Mrozek, Tomasz; Kowalinski, Miroslaw; Torre, Gabriele;
   Crowley, Geoffrey; Schattenburg, Mark
2017SPD....4830503C    Altcode:
  Solar soft X-ray (SXR) observations provide important diagnostics of
  plasma heating, during solar flares and quiescent times. Spectrally-
  and temporally-resolved measurements are crucial for understanding
  the dynamics, origins, and evolution of these energetic processes,
  providing probes both into the temperature distributions and elemental
  compositions of hot plasmas; spatially-resolved measurements are
  critical for understanding energy transport and mass flow. A better
  understanding of the thermal plasma improves our understanding of the
  relationships between particle acceleration, plasma heating, and the
  underlying release of magnetic energy during reconnection. We introduce
  a new proposed small satellite mission, the CubeSat Imaging X-ray Solar
  Spectrometer (CubIXSS), to measure spectrally- and spatially-resolved
  SXRs from the quiescent and flaring Sun from a 6U CubeSat platform in
  low-Earth orbit during a nominal 1-year mission. CubIXSS includes the
  Amptek X123-FastSDD silicon drift detector, a low-noise, commercial
  off-the-shelf (COTS) instrument enabling solar SXR spectroscopy from
  ~0.5 to ~30 keV with ~0.15 keV FWHM spectral resolution with low
  power, mass, and volume requirements. Multiple detectors and tailored
  apertures provide sensitivity to a wide range of solar conditions,
  optimized for a launch during solar minimum. The precise spectra
  from these instruments will provide detailed measurements of the
  coronal temperature distribution and elemental abundances from the
  quiet Sun to active regions and flares. CubIXSS also includes a
  novel spectro-spatial imager -- the first ever solar imager on a
  CubeSat -- utilizing a custom pinhole camera and Chandra-heritage
  X-ray transmission diffraction grating to provide spatially- resolved,
  full-Sun imaging spectroscopy from ~0.1 to ~10 keV, with ~25 arcsec and
  ~0.1 Å FWHM spatial and spectral resolutions, respectively. MOXSI’s
  unique capabilities enable SXR spectroscopy and temperature diagnostics
  of individual active regions and flares. Through its groundbreaking
  new measurements, CubIXSS will improve our physical understanding of
  thermal plasma processes and impulsive energy release in the solar
  corona, from quiet Sun to solar flares.

---------------------------------------------------------
Title: Sunspots, Starspots, and Elemental Abundances
Authors: Doschek, G. A.; Warren, H. P.
2017ApJ...844...52D    Altcode:
  Element abundances in the solar photosphere, chromosphere, transition
  region, and corona are key parameters for investigating sources of
  the solar wind and for estimating radiative losses in the quiet corona
  and in dynamical events such as solar flares. Abundances in the solar
  corona and photosphere differ from each other depending on the first
  ionization potential (FIP) of the element. Normally, abundances with
  FIP values less than about 10 eV are about 3-4 times more abundant in
  the corona than in the photosphere. However, recently, an inverse FIP
  effect was found in small regions near sunspots where elements with
  FIP less than 10 eV are less abundant relative to high FIP elements
  (≥slant 10 eV) than they are in the photosphere. This is similar to
  fully convective stars with large starspots. The inverse FIP effect
  is predicted to occur in the vicinity of sunspots/starspots. Up to
  now, the solar anomalous abundances have only been found in very
  spatially small areas. In this paper, we show that in the vicinity of
  sunspots there can be substantially larger areas with abundances that
  are between coronal and photospheric abundances and sometimes just
  photospheric abundances. In some cases, the FIP effect tends to shut
  down near sunspots. We examine several active regions with relatively
  large sunspots that were observed with the Extreme-ultraviolet Imaging
  Spectrometer on the Hinode spacecraft in cycle 24.

---------------------------------------------------------
Title: Measuring Velocities in the Early Stage of an Eruption:
    Using “Overlappogram” Data from Hinode EIS
Authors: Harra, Louise K.; Hara, Hirohisa; Doschek, George A.;
   Matthews, Sarah; Warren, Harry; Culhane, J. Leonard; Woods, Magnus M.
2017ApJ...842...58H    Altcode:
  In order to understand the onset phase of a solar eruption, plasma
  parameter measurements in the early phases are key to constraining
  models. There are two current instrument types that allow us to make
  such measurements: narrow-band imagers and spectrometers. In the
  former case, even narrow-band filters contain multiple emission lines,
  creating some temperature confusion. With imagers, however, rapid
  cadences are achievable and the field of view can be large. Velocities
  of the erupting structures can be measured by feature tracking. In the
  spectrometer case, slit spectrometers can provide spectrally pure images
  by “rastering” the slit to build up an image. This method provides
  limited temporal resolution, but the plasma parameters can be accurately
  measured, including velocities along the line of sight. Both methods
  have benefits and are often used in tandem. In this paper we demonstrate
  for the first time that data from the wide slot on the Hinode EUV
  Imaging Spectrometer, along with imaging data from AIA, can be used to
  deconvolve velocity information at the start of an eruption, providing
  line-of-sight velocities across an extended field of view. Using He
  II 256 Å slot data at flare onset, we observe broadening or shift(s)
  of the emission line of up to ±280 km s<SUP>-1</SUP>. These are seen at
  different locations—the redshifted plasma is seen where the hard X-ray
  source is later seen (energy deposition site). In addition, blueshifted
  plasma shows the very early onset of the fast rise of the filament.

---------------------------------------------------------
Title: Tracking the Magnetic Flux in and around Sunspots
Authors: Sheeley, N. R., Jr.; Stauffer, J. R.; Thomassie, J. C.;
   Warren, H. P.
2017ApJ...836..144S    Altcode:
  We have developed a procedure for tracking sunspots observed by the
  Helioseismic and Magnetic Imager on the Solar Dynamics Observatory
  and for making curvature-corrected space/time maps of the associated
  line-of-sight magnetic field and continuum intensity. We apply
  this procedure to 36 sunspots, each observed continuously for nine
  days around its central meridian passage time, and find that the
  proper motions separate into two distinct components depending on
  their speeds. Fast (∼3-5 km s<SUP>-1</SUP>) motions, comparable
  to Evershed flows, are produced by weak vertical fluctuations of the
  horizontal canopy field and recur on a timescale of 12-20 min. Slow
  (∼0.3-0.5 km s<SUP>-1</SUP>) motions diverge from a sunspot-centered
  ring whose location depends on the size of the sunspot, occurring in the
  mid-penumbra for large sunspots and at the outer edge of the penumbra
  for small sunspots. The slow ingoing features are contracting spokes of
  a quasi-vertical field of umbral polarity. These inflows disappear when
  the sunspot loses its penumbra, and may be related to inward-moving
  penumbral grain. The slow outgoing features may have either polarity
  depending on whether they originate from quasi-vertical fields of umbral
  polarity or from the outer edge of the canopy. When a sunspot decays,
  the penumbra and canopy disappear, and the moat becomes filled with
  slow outflows of umbral polarity. We apply our procedure to decaying
  sunspots, to long-lived sunspots, and to numerical simulations of a
  long-lived sunspot by Rempel.

---------------------------------------------------------
Title: Sparse Bayesian Inference and the Temperature Structure of
    the Solar Corona
Authors: Warren, Harry P.; Byers, Jeff M.; Crump, Nicholas A.
2017ApJ...836..215W    Altcode: 2016arXiv161005972W
  Measuring the temperature structure of the solar atmosphere is critical
  to understanding how it is heated to high temperatures. Unfortunately,
  the temperature of the upper atmosphere cannot be observed directly,
  but must be inferred from spectrally resolved observations of
  individual emission lines that span a wide range of temperatures. Such
  observations are “inverted” to determine the distribution of plasma
  temperatures along the line of sight. This inversion is ill posed and,
  in the absence of regularization, tends to produce wildly oscillatory
  solutions. We introduce the application of sparse Bayesian inference
  to the problem of inferring the temperature structure of the solar
  corona. Within a Bayesian framework a preference for solutions that
  utilize a minimum number of basis functions can be encoded into the
  prior and many ad hoc assumptions can be avoided. We demonstrate the
  efficacy of the Bayesian approach by considering a test library of 40
  assumed temperature distributions.

---------------------------------------------------------
Title: Global Energetics of Solar Flares. V. Energy Closure in Flares
    and Coronal Mass Ejections
Authors: Aschwanden, Markus J.; Caspi, Amir; Cohen, Christina M. S.;
   Holman, Gordon; Jing, Ju; Kretzschmar, Matthieu; Kontar, Eduard
   P.; McTiernan, James M.; Mewaldt, Richard A.; O'Flannagain, Aidan;
   Richardson, Ian G.; Ryan, Daniel; Warren, Harry P.; Xu, Yan
2017ApJ...836...17A    Altcode: 2017arXiv170101176A
  In this study we synthesize the results of four previous studies
  on the global energetics of solar flares and associated coronal
  mass ejections (CMEs), which include magnetic, thermal, nonthermal,
  and CME energies in 399 solar M- and X-class flare events observed
  during the first 3.5 yr of the Solar Dynamics Observatory (SDO)
  mission. Our findings are as follows. (1) The sum of the mean
  nonthermal energy of flare-accelerated particles ({E}<SUB>{nt</SUB>}),
  the energy of direct heating ({E}<SUB>{dir</SUB>}), and the
  energy in CMEs ({E}<SUB>{CME</SUB>}), which are the primary
  energy dissipation processes in a flare, is found to have a ratio of
  ({E}<SUB>{nt</SUB>}+{E}<SUB>{dir</SUB>}+{E}<SUB>{CME</SUB>})/{E}<SUB>{mag</SUB>}=0.87+/-
  0.18, compared with the dissipated magnetic free energy
  {E}<SUB>{mag</SUB>}, which confirms energy closure within the
  measurement uncertainties and corroborates the magnetic origin of
  flares and CMEs. (2) The energy partition of the dissipated magnetic
  free energy is: 0.51 ± 0.17 in nonthermal energy of ≥slant 6 {keV}
  electrons, 0.17 ± 0.17 in nonthermal ≥slant 1 {MeV} ions, 0.07 ±
  0.14 in CMEs, and 0.07 ± 0.17 in direct heating. (3) The thermal
  energy is almost always less than the nonthermal energy, which is
  consistent with the thick-target model. (4) The bolometric luminosity
  in white-light flares is comparable to the thermal energy in soft
  X-rays (SXR). (5) Solar energetic particle events carry a fraction
  ≈ 0.03 of the CME energy, which is consistent with CME-driven shock
  acceleration. (6) The warm-target model predicts a lower limit of the
  low-energy cutoff at {e}<SUB>c</SUB>≈ 6 {keV}, based on the mean peak
  temperature of the differential emission measure of T <SUB>e</SUB> =
  8.6 MK during flares. This work represents the first statistical study
  that establishes energy closure in solar flare/CME events.

---------------------------------------------------------
Title: Science Objective: Understanding Energy Transport by Alfvénic
    Waves in Solar Flares
Authors: Reep, Jeffrey W.; Warren, Harry P.; Leake, James E.; Tarr,
   Lucas A.; Russell, Alexander J. B.; Kerr, Graham S.; Hudson, Hugh S.
2017arXiv170201667R    Altcode:
  Solar flares are driven by the release of magnetic energy from
  reconnection events in the solar corona, whereafter energy is
  transported to the chromosphere, heating the plasma and causing the
  characteristic radiative losses. In the collisional thick-target model,
  electrons accelerated to energies exceeding 10 keV traverse the corona
  and impact the chromosphere, where they deposit their energy through
  collisions with the much denser plasma in the lower atmosphere. While
  there are undoubtedly high energy non-thermal electrons accelerated
  in flares, it is unclear whether these electron beams are the sole
  mechanism of energy transport, or whether they only dominate in certain
  phases of the flare's evolution. Alfvénic waves are generated during
  the post-reconnection relaxation of magnetic field lines, so it is
  important to examine their role in energy transport.

---------------------------------------------------------
Title: Diagnosing Coronal Heating Processes with Spectrally Resolved
    Soft X-ray Measurements
Authors: Caspi, Amir; Shih, Albert Y.; Warren, Harry P.; Stęślicki,
   Marek; Sylwester, Janusz
2017arXiv170100619C    Altcode:
  Decades of astrophysical observations have convincingly shown that
  soft X-ray (SXR; ~0.1--10 keV) emission provides unique diagnostics
  for the high temperature plasmas observed in solar flares and active
  regions. SXR observations critical for constraining models of energy
  release in these phenomena can be provided using instruments that
  have already been flown on sounding rockets and CubeSats, including
  miniaturized high-resolution photon-counting spectrometers and a
  novel diffractive spectral imager. These instruments have relatively
  low cost and high TRL, and would complement a wide range of mission
  concepts. In this white paper, we detail the scientific background and
  open questions motivating these instruments, the measurements required,
  and the instruments themselves that will make groundbreaking progress
  in answering these questions.

---------------------------------------------------------
Title: Propagation of atmospheric density errors to satellite orbits
Authors: Emmert, J. T.; Warren, H. P.; Segerman, A. M.; Byers, J. M.;
   Picone, J. M.
2017AdSpR..59..147E    Altcode:
  We develop and test approximate analytic expressions relating
  time-dependent atmospheric density errors to errors in the mean motion
  and mean anomaly orbital elements. The mean motion and mean anomaly
  errors are proportional to the first and second integrals, respectively,
  of the density error. This means that the mean anomaly (and hence the
  in-track position) error variance grows with time as t<SUP>3</SUP>
  for a white noise density error process and as t<SUP>5</SUP> for a
  Brownian motion density error process. Our approximate expressions
  are accurate over a wide range of orbital configurations, provided
  the perigee altitude change is less than ∼0.2 atmospheric scale
  heights. For orbit prediction, density forecasts are driven in large
  part by forecasts of solar extreme ultraviolet (EUV) irradiance; we
  show that errors in EUV ten-day forecasts (and consequently in the
  density forecasts) approximately follow a Brownian motion process.

---------------------------------------------------------
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: Combining MinXSS and RHESSI X-ray Spectra for a Comprehensive
    View of the Temperature Distribution in Solar Flares
Authors: Caspi, A.; McTiernan, J. M.; Mason, J. P.; Moore, C. S.;
   Shih, A. Y.; Warren, H.; Woods, T. N.
2016AGUFMSH13A2288C    Altcode:
  Solar flares explosively release large amounts of magnetic energy,
  a significant fraction of which goes into transient heating of coronal
  plasma to temperatures up to tens of MK. Decades of observations have
  shown that flares are multi-thermal, exhibiting broad temperature
  distributions or "differential emission measures" (DEMs). Recent
  studies suggest that the hottest parts of the DEM evolve differently
  from, and are heated by a different physical mechanism than, the
  DEM bulk. For example, the peak temperature of the hot, likely
  in-situ-heated plasma observed by RHESSI correlates significantly
  differently with flare intensity (GOES class) than does the cooler,
  likely chromospherically evaporated plasma observed by GOES XRS
  and/or Yohkoh BCS. These studies, however, used discrete (iso-/bi-)
  thermal approximations, in part because temperature determinations
  by the ratio of 2-channel GOES photometer data or selected BCS lines
  necessitated such methods. Consequently, the exact DEM profile, its
  evolution, and how these correlate with other flare parameters, remain
  poorly known. The MinXSS CubeSat deployed from the ISS in May 2016,
  and since June has observed (at least) 7 M-class and over 40 C-class
  flares. MinXSS's X123 spectrometer measures solar soft X-rays (SXRs)
  from 0.5 to 30 keV with 0.15 keV FWHM resolution; this energy range
  entirely covers both GOES XRS passbands, and overlaps with and extends
  the RHESSI observing range with 5x better resolution. It includes the
  thermal continuum emission from plasmas with temperatures down to 2 MK,
  as well as a number of mid- and high-temperature spectral lines from
  various low- and high-FIP ion species, providing critical temperature
  diagnostics for studying flare DEMs with far greater fidelity than is
  possible with GOES, or using RHESSI alone. We present spectral analyses
  of several flares observed simultaneously by MinXSS and RHESSI. We
  compare and contrast the observations of each instrument separately, and
  present the results of a joint-instrument DEM analysis that forward-fits
  a parametrized DEM model - including variable elemental abundances -
  to the combined spectra of both instruments simultaneously. We discuss
  the DEM evolution and its correlation with other flare parameters,
  and discuss the implications for plasma heating in solar flares.

---------------------------------------------------------
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: Linear and Non-Linear Forecasts of Solar Activity
Authors: Warren, H.
2016AGUFMSH11C2237W    Altcode:
  Variations in thermospheric density play a major role in perturbing the
  orbits of objects in low Earth orbit. These variations are strongly
  influenced by changes in the solar irradiance at extreme ultraviolet
  (EUV) wavelengths that are ultimately driven by changing levels of
  solar magnetic activity. Thus predicting the conjunction of operational
  satellites with orbital debris requires accurate forecasts of solar
  activity. Current operational models rely on forecasts of proxies
  for solar activity based on simple linear extrapolation methods. In
  this poster we present a systematic study of these methods applied
  to the 10.7 cm solar radio flux, a composite Mg core-to-wing ratio,
  the total unsigned solar magnetic flux, and the He II 304 irradiance
  observed by the EVE instrument on the Solar Dynamics Observatory. We
  find that although RMS errors in these forecasts appear to be small,
  the corresponding errors in very simple models, such as the persistence
  of the last measurement, are also small, and the formal skill scores
  are relatively modest. The use of these proxies and measurements in
  non-linear methods, such Gaussian process regression and recurrent
  neural networks, will also be discussed.

---------------------------------------------------------
Title: The importance of high-resolution observations of the solar
    corona
Authors: Winebarger, A. R.; Cirtain, J. W.; Golub, L.; Walsh, R. W.;
   De Pontieu, B.; Savage, S. L.; Rachmeler, L.; Kobayashi, K.; Testa,
   P.; Brooks, D.; Warren, H.; Mcintosh, S. W.; Peter, H.; Morton, R. J.;
   Alexander, C. E.; Tiwari, S. K.
2016AGUFMSH31B2577W    Altcode:
  The spatial and temporal resolutions of the available coronal
  observatories are inadequate to resolve the signatures of coronal
  heating. High-resolution and high-cadence observations available with
  the Interface Region Imaging Spectrograph (IRIS) and the High-resolution
  Coronal Imager (Hi-C) instrument hint that 0.3 arcsec resolution images
  and &lt; 10 s cadence provide the necessary resolution to detect
  heating events. Hi-C was launched from White Sands Missile Range on
  July 11, 2012 (before the launch with IRIS) and obtained images of
  a solar active region in the 19.3 nm passband. In this presentation,
  I will discuss the potential of combining a flight in Hi-C with a 17.1
  nm passband, in conjunction with IRIS. This combination will provide,
  for the first time, a definitive method of tracing the energy flow
  between the chromosphere and corona and vice versa.

---------------------------------------------------------
Title: Solar Soft X-ray Spectral Measurements and the Temperature
    Structure of Active Regions and Flares
Authors: Warren, H.
2016AGUFMSH11D..01W    Altcode: 2016AGUFMSH11D..01C
  How solar and stellar atmospheres are heated to millions of degrees
  is a fundamental problem in astrophysics. The Parker nanoflare model,
  in which the topological complexity created by turbulent photospheric
  motions is dissipated by magnetic reconnection, is perhaps the most
  widely studied theory of coronal heating. Although this model is
  conceptually similar to our understanding of how large flares work,
  recent results suggest that they may be fundamentally different. Large
  flares, for example, have a peak in the emission measure distribution
  near 10 MK, while active regions appear to have relatively little
  plasma at that temperature. For large flares, several studies have
  indicated a composition close to that of the photosphere, while
  active region structures show a clear enhancement in elements with
  low first ionization potential. These results rely on observations
  at extreme ultraviolet wavelengths, which do not provide the rich
  array of temperature and abundance diagnostics that are available
  at soft X-ray wavelengths. In this talk we will review these recent
  results and explore the potential for observations from new soft X-ray
  instrumentation such as MinXSS to advance our understanding of coronal
  heating mechanisms.

---------------------------------------------------------
Title: The EVE plus RHESSI DEM for Solar Flares, and Implications
    for Residual Non-Thermal Soft X-Ray Emission
Authors: McTiernan, J. M.; Caspi, A.; Warren, H.
2016AGUFMSH13A2289M    Altcode:
  We combine observations of solar flares from the EUV Variability
  Experiment (EVE) on-board the Solar Dynamics Observatory (SDO) with
  X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager
  (RHESSI) to calculate the Differential Emission Measure (DEM). This
  improvement over the isothermal approximation is intended to help
  to resolve ambiguities in the range where thermal and non-thermal
  emission overlap. For this current project we are interested in
  constraining cutoffs in the "residual" non-thermal spectrum; i.e.,
  the RHESSI spectrum that is left over after the DEM has accounted
  for the bulk of the soft X-ray emission. (Previous work by Caspi
  et.al. 2014ApJ...788L..31C concentrated on obtaining DEM models that
  fit both instruments' observations well). Solar flare spectra are
  typically dominated by thermal bremsstrahlung emission in the soft
  X-ray (&lt; 10 keV) energy range; at higher hard X-ray energies (&gt;
  30 keV) the emission is non-thermal from beams of electrons. The low
  energy extent of non-thermal emission can typically only be loosely
  quantified. In particular, it is difficult to obtain a lower limit
  for any possible non-thermal cutoff energy due to the larger amount of
  thermal emission. In this model, thermal emission is due to a DEM that
  is parametrized as multiple gaussians in Log(T). Non-thermal emission
  is modeled as a photon spectrum obtained using thin and thick-target
  emission models. Spectra for both instruments are fit simultaneously
  in a self-consistent manner. Preliminary results have been obtained
  using a sample of 102 large (GOES X and M class) solar flares observed
  between February 2011 and February 2013. These results show that it
  is possible to determine low energy cutoffs and breaks early during
  large flares, and to get good values for the low energy limit to the
  non-thermal cutoff.

---------------------------------------------------------
Title: The Electron Density in Explosive Transition Region Events
    Observed by IRIS
Authors: Doschek, G. A.; Warren, H. P.; Young, P. R.
2016ApJ...832...77D    Altcode:
  We discuss the intensity ratio of the O IV line at 1401.16 Å to the
  Si IV line at 1402.77 Å in Interface Region Imaging Spectrograph
  (IRIS) spectra. This intensity ratio is important if it can be used
  to measure high electron densities that cannot be measured using line
  intensity ratios of two different O IV lines from the multiplet within
  the IRIS wavelength range. Our discussion is in terms of considerably
  earlier observations made from the Skylab manned space station and
  other spectrometers on orbiting spacecraft. The earlier data on the O
  IV and Si IV ratio and other intersystem line ratios not available to
  IRIS are complementary to IRIS data. In this paper, we adopt a simple
  interpretation based on electron density. We adopt a set of assumptions
  and calculate the electron density as a function of velocity in the Si
  IV line profiles of two explosive events. At zero velocity the densities
  are about 2-3 × 10<SUP>11</SUP> cm<SUP>-3</SUP>, and near 200 km
  s<SUP>-1</SUP> outflow speed the densities are about 10<SUP>12</SUP>
  cm<SUP>-3</SUP>. The densities increase with outflow speed up to
  about 150 km s<SUP>-1</SUP> after which they level off. Because of the
  difference in the temperature of formation of the two lines and other
  possible effects such as non-ionization equilibrium, these density
  measurements do not have the precision that would be available if
  there were some additional lines near the formation temperature of O IV.

---------------------------------------------------------
Title: Transition Region and Chromospheric Signatures of Impulsive
    Heating Events. I. Observations
Authors: Warren, Harry P.; Reep, Jeffrey W.; Crump, Nicholas A.;
   Simões, Paulo J. A.
2016ApJ...829...35W    Altcode: 2016arXiv160609045W
  We exploit the high spatial resolution and high cadence of the Interface
  Region Imaging Spectrograph (IRIS) to investigate the response of
  the transition region and chromosphere to energy deposition during
  a small flare. Simultaneous observations from the Reuven Ramaty
  High Energy Solar Spectroscopic Imager provide constraints on the
  energetic electrons precipitating into the flare footpoints, while
  observations of the X-Ray Telescope, Atmospheric Imaging Assembly, and
  Extreme Ultraviolet Imaging Spectrometer (EIS) allow us to measure
  the temperatures and emission measures from the resulting flare
  loops. We find clear evidence for heating over an extended period on
  the spatial scale of a single IRIS pixel. During the impulsive phase
  of this event, the intensities in each pixel for the Si IV 1402.770 Å,
  C II 1334.535 Å, Mg II 2796.354 Å, and O I 1355.598 Å emission lines
  are characterized by numerous small-scale bursts typically lasting 60
  s or less. Redshifts are observed in Si IV, C II, and Mg II during the
  impulsive phase. Mg II shows redshifts during the bursts and stationary
  emission at other times. The Si IV and C II profiles, in contrast, are
  observed to be redshifted at all times during the impulsive phase. These
  persistent redshifts are a challenge for one-dimensional hydrodynamic
  models, which predict only short-duration downflows in response to
  impulsive heating. We conjecture that energy is being released on many
  small-scale filaments with a power-law distribution of heating rates.

---------------------------------------------------------
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: Transition Region and Chromospheric Signatures of Impulsive
    Heating Events. II. Modeling
Authors: Reep, Jeffrey W.; Warren, Harry P.; Crump, Nicholas A.;
   Simões, Paulo J. A.
2016ApJ...827..145R    Altcode: 2016arXiv160706684R
  Results from the Solar Maximum Mission showed a close connection
  between the hard X-ray (HXR) and transition region (TR) emission in
  solar flares. Analogously, the modern combination of RHESSI and IRIS
  data can inform the details of heating processes in ways that were
  never before possible. We study a small event that was observed with
  RHESSI, IRIS, SDO, and Hinode, allowing us to strongly constrain the
  heating and hydrodynamical properties of the flare, with detailed
  observations presented in a previous paper. Long duration redshifts
  of TR lines observed in this event, as well as many other events,
  are fundamentally incompatible with chromospheric condensation
  on a single loop. We combine RHESSI and IRIS data to measure the
  energy partition among the many magnetic strands that comprise the
  flare. Using that observationally determined energy partition, we show
  that a proper multithreaded model can reproduce these redshifts in
  magnitude, duration, and line intensity, while simultaneously being
  well constrained by the observed density, temperature, and emission
  measure. We comment on the implications for both RHESSI and IRIS
  observations of flares in general, namely that: (1) a single loop model
  is inconsistent with long duration redshifts, among other observables;
  (2) the average time between energization of strands is less than 10
  s, which implies that for a HXR burst lasting 10 minutes, there were
  at least 60 strands within a single IRIS pixel located on the flare
  ribbon; (3) the majority of these strands were explosively heated with
  an energy distribution well described by a power law of slope ≈ -1.6;
  (4) the multi-stranded model reproduces the observed line profiles,
  peak temperatures, differential emission measure distributions,
  and densities.

---------------------------------------------------------
Title: Properties and Modeling of Unresolved Fine Structure Loops
    Observed in the Solar Transition Region by IRIS
Authors: Brooks, David H.; Reep, Jeffrey W.; Warren, Harry P.
2016ApJ...826L..18B    Altcode: 2016arXiv160605440B
  Recent observations from the Interface Region Imaging Spectrograph
  (IRIS) have discovered a new class of numerous low-lying dynamic loop
  structures, and it has been argued that they are the long-postulated
  unresolved fine structures (UFSs) that dominate the emission of the
  solar transition region. In this letter, we combine IRIS measurements
  of the properties of a sample of 108 UFSs (intensities, lengths, widths,
  lifetimes) with one-dimensional non-equilibrium ionization simulations,
  using the HYDRAD hydrodynamic model to examine whether the UFSs are now
  truly spatially resolved in the sense of being individual structures
  rather than being composed of multiple magnetic threads. We find that
  a simulation of an impulsively heated single strand can reproduce most
  of the observed properties, suggesting that the UFSs may be resolved,
  and the distribution of UFS widths implies that they are structured on
  a spatial scale of 133 km on average. Spatial scales of a few hundred
  kilometers appear to be typical for a range of chromospheric and
  coronal structures, and we conjecture that this could be an important
  clue for understanding the coronal heating process.

---------------------------------------------------------
Title: The Mysterious Case of the Solar Argon Abundance near Sunspots
    in Flares
Authors: Doschek, G. A.; Warren, H. P.
2016ApJ...825...36D    Altcode:
  Recently we discussed an enhancement of the abundance of Ar xiv relative
  to Ca xiv near a sunspot during a flare, observed in spectra recorded
  by the Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft. The observed Ar xiv/Ca xiv ratio yields an argon/calcium
  abundance ratio seven times greater than expected from the photospheric
  abundance. Such a large abundance anomaly is unprecedented in the solar
  atmosphere. We interpreted this result as being due to an inverse first
  ionization potential (FIP) effect. In the published work, two lines of
  Ar xiv were observed, and one line was tentatively identified as an Ar
  xi line. In this paper, we report observing a similar enhancement in a
  full-CCD EIS flare spectrum in 13 argon lines that lie within the EIS
  wavelength ranges. The observed lines include two Ar xi lines, four
  Ar xiii lines, six Ar xiv lines, and one Ar xv line. The enhancement
  is far less than reported in Doschek et al. but exhibits similar
  morphology. The argon abundance is close to a photospheric abundance
  in the enhanced area, and the abundance could be photospheric. This
  enhancement occurs in association with a sunspot in a small area only
  a few arcseconds (1″ = about 700 km) in size. There is no enhancement
  effect observed in the normally high-FIP sulfur and oxygen line ratios
  relative to lines of low-FIP elements available to EIS. Calculations of
  path lengths in the strongest enhanced area in Doschek et al. indicate
  a depletion of low-FIP elements.

---------------------------------------------------------
Title: Transition Region Abundance Measurements During Impulsive
    Heating Events
Authors: Warren, Harry P.; Brooks, David H.; Doschek, George A.;
   Feldman, Uri
2016ApJ...824...56W    Altcode: 2015arXiv151204447W
  It is well established that elemental abundances vary in the solar
  atmosphere and that this variation is organized by first ionization
  potential (FIP). Previous studies have shown that in the solar corona,
  low-FIP elements such as Fe, Si, Mg, and Ca, are generally enriched
  relative to high-FIP elements such as C, N, O, Ar, and Ne. In this paper
  we report on measurements of plasma composition made during impulsive
  heating events observed at transition region temperatures with the
  Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these
  events the intensities of O IV, v, and VI emission lines are enhanced
  relative to emission lines from Mg v, VI, and vii and Si VI and vii,
  and indicate a composition close to that of the photosphere. Long-lived
  coronal fan structures, in contrast, show an enrichment of low-FIP
  elements. We conjecture that the plasma composition is an important
  signature of the coronal heating process, with impulsive heating leading
  to the evaporation of unfractionated material from the lower layers of
  the solar atmosphere and higher-frequency heating leading to long-lived
  structures and the accumulation of low-FIP elements in the corona.

---------------------------------------------------------
Title: The Light at the End of the Tunnel: Uncertainties in Atomic
    Physics, Bayesian Inference, and the Analysis of Solar and Stellar
    Observations
Authors: Warren, Harry
2016SPD....4720801W    Altcode:
  We report on the efforts of a multidisciplinary International Space
  Science Institute team that is investigating the limits of our ability
  to infer the physical properties of solar and stellar atmospheres from
  remote sensing observations. As part of this project we have estimated
  the uncertainties in the collisional cross sections and radiative
  decay rates for Fe XIII and O VII and created 1000 realizations of the
  CHIANTI atomic database. These perturbed atomic data are then used
  to analyze solar observations from the EIS spectrometer on Hinode
  and stellar observations from the LETG on Chandra within a Bayesian
  framework. For the solar case we find that the systematic errors
  from the atomic physics dominate the statistical uncertainties from
  the observations. For many cases the uncertainties are about 10 times
  larger when variations in the atomic data are included. This indicates
  the need for very accurate atomic physics. Comparisons among recent
  Fe XIII calculations suggest that for some transitions the collision
  rates are currently known well enough to measure the electron density
  and emission measure to about 15%.

---------------------------------------------------------
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: The Mysterious Case of the Solar Argon Abundance Near Sunspots
    in Flares
Authors: Doschek, George A.; Warren, Harry
2016SPD....4730207D    Altcode:
  Recently Doschek et al. (2015, ApJL, 808, L7) reported on an observation
  of an enhancement of the abundance of Ar XIV relative to Ca XIV
  of about a factor of 30 near a sunspot during a flare, observed in
  spectra recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS)
  on the Hinode spacecraft. This enhancement yields an argon/calcium
  abundance ratio 7 times greater than expected from the photospheric
  abundances. Such a large abundance anomaly is unprecedented in the
  solar atmosphere. We interpreted this result as due to an inverse
  First Ionization Potential (FIP) effect. Argon is a high-FIP element
  and calcium is a low-FIP element. In the published work two lines of
  Ar XIV were observed and one line was tentatively identified as an Ar
  XI line. The number of argon lines was limited by the limitations of
  the flare study that was executed. In this paper we report observing
  a similar enhancement in a full-CCD EIS flare spectrum in argon lines
  with reasonable statistics and lack of blending that lie within the
  EIS wavelength ranges. The observed lines include two Ar XI lines,
  four Ar XIII lines, six Ar XIV lines, and one Ar XV line. The
  enhancement is far less than reported in Doschek et al. (2015)
  but exhibits similar morphology. The argon abundance is close to a
  photospheric abundance in the enhanced area, and is only marginally
  an inverse FIP effect. However, as for the published cases, this newly
  discovered enhancement occurs in association with a sunspot in a small
  area only a few arcsec in size and therefore we feel it is produced
  by the same physics that produced the strong inverse FIP case. There
  is no enhancement effect observed in the normally high-FIP sulfur and
  oxygen line ratios relative to lines of low-FIP elements available
  to EIS. Calculations of path lengths in the strongest enhanced area
  in Doschek et al. (2015) indicate that the argon/calcium enhancement
  is due to a depletion of low-FIP elements. This work is supported by
  a NASA Hinode grant.

---------------------------------------------------------
Title: Transition Region and Chromospheric Signatures of Impulsive
    Heating Events
Authors: Warren, Harry; Reep, Jeffrey; Crump, Nicholas
2016SPD....4740303W    Altcode:
  We exploit the high spatial resolution and high cadence of the Interface
  Region Imaging Spectrograph (IRIS) to investigate the response of
  the transition region and chromosphere to energy deposition during
  several small flares. We find that during the impulsive phase of
  these events the intensities of the C II 1334.535 and Si IV 1402.770
  A emission lines are characterized by numerous, small-scale impulsive
  bursts typically lasting 60 s or less followed by a slower decay
  over several minutes. These variations in intensity are usually
  accompanied by impulsive redshifts of 20-40 km/s, although some
  blueshifted profiles are also observed. For one particularly well
  observed event we combine the IRIS observations with co-temporal
  measurements of hard X-ray emission from RHESSSI, transition region
  density from EIS, and high-temperature coronal loops with XRT and AIA
  to constrain 1D hydrodynamic models of loop evolution. Many aspects
  of the observations can be explained with simple heating scenarios,
  but some cannot. The simulated Doppler shifts, for example, show very
  short-duration redshifts during the initial phase of the heating while
  the observed redshifts persist over several minutes.

---------------------------------------------------------
Title: The EVE plus RHESSI DEM for Solar Flares, and Implications
    for Residual Non-Thermal X-Ray Emission
Authors: McTiernan, James; Caspi, Amir; Warren, Harry
2016SPD....47.0618M    Altcode:
  Solar flare spectra are typically dominated by thermal emission in the
  soft X-ray energy range. The low energy extent of non-thermal emission
  can only be loosely quantified using currently available X-ray data. To
  address this issue, we combine observations from the EUV Variability
  Experiment (EVE) on-board the Solar Dynamics Observatory (SDO) with
  X-ray data from the Reuven Ramaty High Energy Spectroscopic Imager
  (RHESSI) to calculate the Differential Emission Measure (DEM) for solar
  flares. This improvement over the isothermal approximation helps to
  resolve the ambiguity in the range where the thermal and non-thermal
  components may have similar photon fluxes. This "crossover" range can
  extend up to 30 keV.Previous work (Caspi et.al. 2014ApJ...788L..31C)
  concentrated on obtaining DEM models that fit both instruments'
  observations well. For this current project we are interested in breaks
  and cutoffs in the "residual" non-thermal spectrum; i.e., the RHESSI
  spectrum that is left over after the DEM has accounted for the bulk
  of the soft X-ray emission. As in our earlier work, thermal emission
  is modeled using a DEM that is parametrized as multiple gaussians
  in temperature. Non-thermal emission is modeled as a photon spectrum
  obtained using a thin-target emission model ('thin2' from the SolarSoft
  Xray IDL package). Spectra for both instruments are fit simultaneously
  in a self-consistent manner.For this study, we have examined the DEM
  and non-thermal resuidual emission for a sample of relatively large
  (GOES M class and above) solar flares observed from 2011 to 2014. The
  results for the DEM and non-thermal parameters found using the combined
  EVE-RHESSI data are compared with those found using only RHESSI data.

---------------------------------------------------------
Title: Science Goals and First Light Analysis from the Miniature
    X-ray Solar Spectrometer (MinXSS) CubeSat
Authors: Caspi, Amir; Woods, Thomas N.; Warren, Harry; Chamberlin,
   Phillip C.; Jones, Andrew; Mason, James; McTiernan, James; Moore,
   Christopher; Palo, Scott; Solomon, Stanley
2016SPD....47.0306C    Altcode:
  The Miniature X-ray Solar Spectrometer (MinXSS) is a 3U CubeSat with
  deployment from the ISS planned in Q2 2016. Its goal is to measure the
  solar soft X-ray (SXR) spectral irradiance, an observational signature
  of hot plasma in the solar corona. Over the last few decades, there
  have been very few spectrally resolved observations from ~0.2 to ~4 keV
  (~0.3-6 nm). This range is sensitive to high-temperature plasma and
  contains many spectral lines (e.g., Mg, Si, Fe, S, Ar), the abundances
  of which probe plasma transport and provide valuable constraints on
  plasma heating mechanisms during both flares and quiescence. This
  solar SXR emission is primarily absorbed in the E-region of Earth's
  ionosphere, and the subsequently driven dynamical processes are still
  poorly understood, in large part because the energy distribution of the
  incident SXRs is not yet well characterized.MinXSS flies a miniature
  commercial off-the-shelf soft X-ray (SXR) spectrometer, the Amptek
  X123-SDD. The silicon drift detector has 0.5 mm fully depleted thickness
  and a 25 mm^2 physical area, with a ~16 micron Be entrance window;
  with on-board thermoelectric cooling and pulse pile-up rejection,
  it is sensitive to solar SXRs from ~0.5 to 30 keV with ~0.15 keV FWHM
  resolution. MinXSS also includes a broadband SXR photometer, providing
  an integrated intensity over a similar energy range for comparison,
  cross-calibration, and additional data, especially useful during more
  intense flares at the upper end of the X123 dynamic range.We present
  the MinXSS science goals for studying hot plasma in the solar corona,
  including impulsive flare heating and quiescent coronal heating,
  and the impact of the resultant SXR emission on Earth's ionosphere,
  thermosphere, and mesosphere. We present analysis of MinXSS first
  light results (depending on deployment date from the ISS), as well as
  modeling and predictions of future observations over the MinXSS 6-12
  month mission lifetime.

---------------------------------------------------------
Title: The Rapid Acquisition Imaging Spectrograph Experiment (RAISE)
    Sounding Rocket Investigation
Authors: Laurent, Glenn T.; Hassler, Donald M.; Deforest, Craig;
   Slater, David D.; Thomas, Roger J.; Ayres, Thomas; Davis, Michael; de
   Pontieu, Bart; Diller, Jed; Graham, Roy; Michaelis, Harald; Schuele,
   Udo; Warren, Harry
2016JAI.....540006L    Altcode:
  We present a summary of the solar observing Rapid Acquisition
  Imaging Spectrograph Experiment (RAISE) sounding rocket program
  including an overview of the design and calibration of the instrument,
  flight performance, and preliminary chromospheric results from the
  successful November 2014 launch of the RAISE instrument. The RAISE
  sounding rocket payload is the fastest scanning-slit solar ultraviolet
  imaging spectrograph flown to date. RAISE is designed to observe the
  dynamics and heating of the solar chromosphere and corona on time
  scales as short as 100-200ms, with arcsecond spatial resolution and
  a velocity sensitivity of 1-2km/s. Two full spectral passbands over
  the same one-dimensional spatial field are recorded simultaneously
  with no scanning of the detectors or grating. The two different
  spectral bands (first-order 1205-1251Å and 1524-1569Å) are imaged
  onto two intensified Active Pixel Sensor (APS) detectors whose focal
  planes are individually adjusted for optimized performance. RAISE
  reads out the full field of both detectors at 5-10Hz, recording up
  to 1800 complete spectra (per detector) in a single 6-min rocket
  flight. This opens up a new domain of high time resolution spectral
  imaging and spectroscopy. RAISE is designed to observe small-scale
  multithermal dynamics in Active Region (AR) and quiet Sun loops,
  identify the strength, spectrum and location of high frequency waves
  in the solar atmosphere, and determine the nature of energy release
  in the chromospheric network.

---------------------------------------------------------
Title: Measurements of Non-thermal Line Widths in Solar Active Regions
Authors: Brooks, David H.; Warren, Harry P.
2016ApJ...820...63B    Altcode: 2015arXiv151102313B
  Spectral line widths are often observed to be larger than can be
  accounted for by thermal and instrumental broadening alone. This excess
  broadening is a key observational constraint for both nanoflare and
  wave dissipation models of coronal heating. Here we present a survey
  of non-thermal velocities measured in the high temperature loops (1-4
  MK) often found in the cores of solar active regions. This survey of
  Hinode Extreme Ultraviolet Imaging Spectrometer (EIS) observations
  covers 15 non-flaring active regions that span a wide range of solar
  conditions. We find relatively small non-thermal velocities, with a
  mean value of 17.6 ± 5.3 km s<SUP>-1</SUP>, and no significant trend
  with temperature or active region magnetic flux. These measurements
  appear to be inconsistent with those expected from reconnection jets in
  the corona, chromospheric evaporation induced by coronal nanoflares,
  and Alfvén wave turbulence models. Furthermore, because the observed
  non-thermal widths are generally small, such measurements are difficult
  and susceptible to systematic effects.

---------------------------------------------------------
Title: Converging Supergranular Flows and the Formation of Coronal
    Plumes
Authors: Wang, Y. -M.; Warren, H. P.; Muglach, K.
2016ApJ...818..203W    Altcode:
  Earlier studies have suggested that coronal plumes are energized
  by magnetic reconnection between unipolar flux concentrations and
  nearby bipoles, even though magnetograms sometimes show very little
  minority-polarity flux near the footpoints of plumes. Here we use
  high-resolution extreme-ultraviolet (EUV) images and magnetograms
  from the Solar Dynamics Observatory (SDO) to clarify the relationship
  between plume emission and the underlying photospheric field. We
  find that plumes form where unipolar network elements inside coronal
  holes converge to form dense clumps, and fade as the clumps disperse
  again. The converging flows also carry internetwork fields of both
  polarities. Although the minority-polarity flux is sometimes barely
  visible in the magnetograms, the corresponding EUV images almost
  invariably show loop-like features in the core of the plumes, with the
  fine structure changing on timescales of minutes or less. We conclude
  that the SDO observations are consistent with a model in which plume
  emission originates from interchange reconnection in converging flows,
  with the plume lifetime being determined by the ∼1 day evolutionary
  timescale of the supergranular network. Furthermore, the presence of
  large EUV bright points and/or ephemeral regions is not a necessary
  precondition for the formation of plumes, which can be energized
  even by the weak, mixed-polarity internetwork fields swept up by
  converging flows.

---------------------------------------------------------
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: New Instruments for Spectrally-Resolved Solar Soft X-ray
    Observations from CubeSats, and Larger Missions
Authors: Caspi, A.; Shih, A.; Warren, H. P.; DeForest, C. E.; Woods,
   T. N.
2015AGUFMSH13B2444C    Altcode: 2015AGUFMSH13B2444D
  Solar soft X-ray (SXR) observations provide important diagnostics of
  plasma heating, during solar flares and quiescent times. Spectrally-
  and temporally-resolved measurements are crucial for understanding the
  dynamics and evolution of these energetic processes; spatially-resolved
  measurements are critical for understanding energy transport. A better
  understanding of the thermal plasma informs our interpretation of
  hard X-ray (HXR) observations of nonthermal particles, improving our
  understanding of the relationships between particle acceleration,
  plasma heating, and the underlying release of magnetic energy during
  reconnection. We introduce a new proposed mission, the CubeSat
  Imaging X-ray Solar Spectrometer (CubIXSS), to measure spectrally-
  and spatially-resolved SXRs from the quiescent and flaring Sun from
  a 6U CubeSat platform in low-Earth orbit during a nominal 1-year
  mission. CubIXSS includes the Amptek X123-SDD silicon drift detector,
  a low-noise, commercial off-the-shelf (COTS) instrument enabling
  solar SXR spectroscopy from ~0.5 to ~30 keV with ~0.15 keV FWHM
  spectral resolution with low power, mass, and volume requirements. An
  X123-CdTe cadmium-telluride detector is also included for ~5-100
  keV HXR spectroscopy with ~0.5-1 keV FWHM resolution. CubIXSS also
  includes a novel spectro-spatial imager -- the first ever solar imager
  on a CubeSat -- utilizing a pinhole aperture and X-ray transmission
  diffraction grating to provide full-Sun imaging from ~0.1 to ~10 keV,
  with ~25 arcsec and ~0.1 Å FWHM spatial and spectral resolutions,
  respectively. We discuss scaled versions of these instruments, with
  greater sensitivity and dynamic range, and significantly improved
  spectral and spatial resolutions for the imager, for deployment on
  larger platforms such as Small Explorer missions.

---------------------------------------------------------
Title: Energy Release and Transport in Super-Hot Solar Flares
Authors: Caspi, A.; McTiernan, J. M.; Shih, A.; Martinez Oliveros,
   J. C.; Allred, J. C.; Warren, H. P.
2015AGUFMSH22A..08C    Altcode: 2015AGUFMSH22A..08M
  Solar flares efficiently convert the magnetic energy stored in the
  Sun's complex coronal magnetic field into the kinetic energies of hot
  plasma, accelerated particles, and bulk flows. In intense flares, up to
  10^32-33 ergs can go into heating plasma to tens of MK, accelerating
  electrons to hundreds of MeV and ions to tens of GeV, and ejecting
  10^9-10 kg of coronal material into the heliosphere at thousands of
  km/s. However, the exact physical mechanisms behind these phenomena are
  poorly understood. For example, while "super-hot" (T &gt; 30 MK) plasma
  temperatures appear to be common in the most intense, X-class flares,
  how that plasma is so efficiently heated remains unknown. Current
  studies favor an in situ heating process for super-hot plasma, versus
  chromospheric evaporation for cooler plasma, although the specific
  mechanism is under debate. X-class flares are also often associated
  with enhanced photospheric/chromospheric white light emission, which
  is itself poorly understood, and with fast (&gt;1000 km/s) CMEs;
  super-hot flares are more commonly observed in eruptive two-ribbon
  arcade flares than in highly-confined events. These phenomena may well
  have common underlying drivers. We discuss the current understanding of
  super-hot plasma in solar flares, its formation, and evolution, based on
  observations from RHESSI, SDO/EVE, SDO/AIA, and other instruments. We
  discuss the energetics of these events and their relationship to white
  light enhancement and fast CMEs. We explore the possibility of energy
  deposition by accelerated ions as a common driver for super-hot plasmas
  and white light enhancement, and discuss future instrumentation -- both
  for CubeSats and Explorers -- that will provide a deeper understanding
  of these phenomena and their interrelationships.

---------------------------------------------------------
Title: Modeling Chromospheric Nanoflares with HYDRAD
Authors: Reep, J. W.; Warren, H. P.
2015AGUFMSH31D..02R    Altcode:
  Observational advances with IRIS have given the ability to observe
  details of the coronal transition region (TR) with extremely high
  spatial resolution. Spectral lines formed in the TR, in particular,
  illuminate the dynamics of mass and energy flow between the chromosphere
  and corona. Using a sophisticated hydrodynamic model, we simulate
  nanoflares driven by different heating mechanisms - electron beams, in
  situ thermal heating, and Alfvenic waves. By examining the atmospheric
  response and by forward modeling of spectral lines, we can directly
  compare with observations of the TR in order to differentiate potential
  heating mechanisms. We thus present the results of a large, systematic
  investigation of the parameter space of chromospheric nanoflares. We
  discuss similarities and differences predicted by the different heating
  mechanisms, all within the context of observed quantities.

---------------------------------------------------------
Title: Active Region Soft X-Ray Spectra as Observed Using Sounding
    Rocket Measurements from the Solar Aspect Monitor (SAM), - a Modified
    SDO/EVE Instrument
Authors: Wieman, S. R.; Didkovsky, L. V.; Woods, T. N.; Jones, A. R.;
   Caspi, A.; Warren, H. P.
2015AGUFMSH23B2446W    Altcode:
  Observations of solar active regions (ARs) in the soft x-ray spectral
  range (0.5 to 3.0 nm) were made on sounding rocket flight NASA 36.290
  using a modified Solar Aspect Monitor (SAM), a pinhole camera on the
  EUV Variability Experiment (EVE) sounding rocket instrument. The suite
  of EVE rocket instruments is designed for under-flight calibrations
  of the orbital EVE on SDO. While the sounding rocket EVE instrument
  is for the most part a duplicate of the EVE on SDO, the SAM channel
  on the rocket version was modified in 2012 to include a free-standing
  transmission grating so that it could provide spectrally resolved
  images of the solar disk with the best signal to noise ratio for
  the brightest features on it, such as ARs. Calibrations of the EVE
  sounding rocket instrument at the National Institute of Standards and
  Technology Synchrotron Ultraviolet Radiation Facility (NIST SURF) have
  provided a measurement of the SAM absolute spectral response function
  and a mapping of wavelength separation in the grating diffraction
  pattern. For solar observations, this spectral separation is on a
  similar scale to the spatial size of the AR on the CCD, so dispersed
  AR images associated with emission lines of similar wavelength tend
  to overlap. Furthermore, SAM shares a CCD detector with MEGS-A, a
  separate EVE spectrometer channel, and artifacts of the MEGS-A signal
  (a set of bright spectral lines) appear in the SAM images. For these
  reasons some processing and analysis of the solar images obtained by
  SAM must be performed in order to determine spectra of the observed
  ARs. We present a method for determining AR spectra from the SAM
  rocket images and report initial soft X-ray spectra for two of the
  major active regions (AR11877 and AR11875) observed on flight 36.290
  on 21 October 2013 at about 18:30 UT. We also compare our results with
  concurrent measurements from other solar soft x-ray instrumentation.

---------------------------------------------------------
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: The Missing Solar Irradiance Spectrum: 1 to 7 nm
Authors: Sojka, J. J.; Lewis, M.; David, M.; Schunk, R. W.; Woods,
   T. N.; Eparvier, F. G.; Warren, H. P.
2015AGUFMSH32A..02S    Altcode:
  During large X-class flares the Earth's upper atmospheric
  E-region responds immediately to solar photons in the 1 to 7 nm
  range. The response can change the E-region density by factors
  approaching 10, create large changes in conductivity, and plague HF
  communications. GOES-XRS provide 0.1 to 0.8 nm and a 0.05 to 0.4 nm
  integral channels; SOHO-SEM provided a 0 to 50 nm irradiance; TIMED and
  SORCE-XPS diode measurements also integrated down to 0.1 nm; and most
  recently SDO-EVE provided a 0.1 to 7 nm irradiance. For atmospheric
  response to solar flares the cadence is also crucial. Both GOES and SDO
  provided integral measurements at 10 seconds or better. Unfortunately
  these measurements have failed to capture the 1 to 7 nm spectral
  changes that occur during flares. It is these spectral changes that
  create the major impact since the ionization cross-section of the
  dominant atmospheric species, N2 and O2, both contain step function
  changes in the cross-sections. Models of the solar irradiance over
  this critical wavelength regime have suffered from the need to model
  the spectral variability based on incomplete measurements. The most
  sophisticated empirical model FISM [Chamberlin et al., 2008] used 1
  nm spectral binning and various implementations of the above integral
  measurements to describe the 1 to 7 nm irradiance. Since excellent solar
  observations exist at other wavelengths it is possible to construct an
  empirical model of the solar atmosphere and then use this model to infer
  the spectral distribution at wavelengths below 5 nm. This differential
  emission measure approach has been used successfully in other contexts
  [e.g., Warren, 2005, Chamberlin et al., 2009]. This paper contrasts
  the broadband versus spectrally resolved descriptions of the incoming
  irradiance that affects the upper atmospheric E-layer. The results
  provide a prescription of what wavelength resolution would be needed to
  adequately measure the incoming solar irradiance in the 1 to 7 nm range.

---------------------------------------------------------
Title: Flare Footpoint Regions and a Surge Observed by Hinode/EIS,
    RHESSI, and SDO/AIA
Authors: Doschek, G. A.; Warren, H. P.; Dennis, B. R.; Reep, J. W.;
   Caspi, A.
2015ApJ...813...32D    Altcode: 2015arXiv151007088D
  The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft observed flare footpoint regions coincident with a surge
  for an M3.7 flare observed on 2011 September 25 at N12 E33 in active
  region 11302. The flare was observed in spectral lines of O vi, Fe x,
  Fe xii, Fe xiv, Fe xv, Fe xvi, Fe xvii, Fe xxiii, and Fe xxiv. The
  EIS observations were made coincident with hard X-ray bursts observed
  by RHESSI. Overlays of the RHESSI images on the EIS raster images
  at different wavelengths show a spatial coincidence of features in
  the RHESSI images with the EIS upflow and downflow regions, as well
  as loop-top or near-loop-top regions. A complex array of phenomena
  were observed, including multiple evaporation regions and the surge,
  which was also observed by the Solar Dynamics Observatory/Atmospheric
  Imaging Assembly telescopes. The slit of the EIS spectrometer covered
  several flare footpoint regions from which evaporative upflows in Fe
  xxiii and Fe xxiv lines were observed with Doppler speeds greater than
  500 km s<SUP>-1</SUP>. For ions such as Fe xv both evaporative outflows
  (∼200 km s<SUP>-1</SUP>) and downflows (∼30-50 km s<SUP>-1</SUP>)
  were observed. Nonthermal motions from 120 to 300 km s<SUP>-1</SUP>
  were measured in flare lines. In the surge, Doppler speeds are
  found from about 0 to over 250 km s<SUP>-1</SUP> in lines from ions
  such as Fe xiv. The nonthermal motions could be due to multiple
  sources slightly Doppler-shifted from each other or turbulence in
  the evaporating plasma. We estimate the energetics of the hard X-ray
  burst and obtain a total flare energy in accelerated electrons of ≥7
  × 10<SUP>28</SUP> erg. This is a lower limit because only an upper
  limit can be determined for the low-energy cutoff to the electron
  spectrum. We find that detailed modeling of this event would require
  a multithreaded model owing to its complexity.

---------------------------------------------------------
Title: Benchmark Test of Differential Emission Measure Codes and
    Multi-thermal Energies in Solar Active Regions
Authors: Aschwanden, Markus J.; Boerner, Paul; Caspi, Amir; McTiernan,
   James M.; Ryan, Daniel; Warren, Harry
2015SoPh..290.2733A    Altcode: 2015arXiv150907546A; 2015SoPh..tmp..146A
  We compare the ability of 11 differential emission measure (DEM)
  forward-fitting and inversion methods to constrain the properties
  of active regions and solar flares by simulating synthetic data
  using the instrumental response functions of the Solar Dynamics
  Observatory/Atmospheric Imaging Assembly (SDO/AIA) and EUV Variability
  Experiment (SDO/EVE), the Reuven Ramaty High Energy Solar Spectroscopic
  Imager (RHESSI), and the Geostationary Operational Environmental
  Satellite/X-ray Sensor (GOES/XRS). The codes include the single-Gaussian
  DEM, a bi-Gaussian DEM, a fixed-Gaussian DEM, a linear spline DEM,
  the spatial-synthesis DEM, the Monte-Carlo Markov Chain DEM, the
  regularized DEM inversion, the Hinode/X-Ray Telescope (XRT) method, a
  polynomial spline DEM, an EVE+GOES, and an EVE+RHESSI method. Averaging
  the results from all 11 DEM methods, we find the following accuracies
  in the inversion of physical parameters: the EM-weighted temperature
  T<SUB>w</SUB><SUP>fit</SUP>/T<SUB>w</SUB><SUP>sim</SUP>=0.9
  ±0.1 , the peak emission measure
  EM<SUB>p</SUB><SUP>fit</SUP>/EM<SUB>p</SUB><SUP>sim</SUP>=0.6
  ±0.2 , the total emission measure
  EM<SUB>t</SUB><SUP>fit</SUP>/EM<SUB>t</SUB><SUP>sim</SUP>=0.8
  ±0.3 , and the multi-thermal energies
  E<SUB>th</SUB><SUP>fit</SUP>/EM<SUB>th</SUB><SUP>approx</SUP>=1.2
  ±0.4 . We find that the AIA spatial-synthesis, the EVE+GOES, and the
  EVE+RHESSI method yield the most accurate results.

---------------------------------------------------------
Title: VizieR Online Data Catalog: Global energetics of solar
    flares. II. (Aschwanden+, 2015)
Authors: Aschwanden, M. J.; Boerner, P.; Ryan, D.; Caspi, A.;
   McTiernan, J. M.; Warren, H. P.
2015yCat..18020053A    Altcode:
  The dataset we are analyzing for this project on the global energetics
  of flares includes all M- and X-class flares observed with the Solar
  Dynamics Observatory (SDO) during the first 3.5yr of the mission
  (2010 June 1 to 2014 January 31), which amounts to 399 flare events,
  as described in Paper I (Aschwanden et al. 2014, J/ApJ/797/50). We
  attempt to calculate the thermal energies in all 399 cataloged
  events, but we encountered eight events with incomplete or corrupted
  Atmospheric Imaging Assembly (AIA) data, so that we are left with
  391 events suitable for thermal data analysis. <P />AIA provides EUV
  images corresponding to an effective spatial resolution of ~1.6". <P
  />(1 data file).

---------------------------------------------------------
Title: Anomalous Relative Ar/Ca Coronal Abundances Observed by the
    Hinode/EUV Imaging Spectrometer Near Sunspots
Authors: Doschek, G. A.; Warren, H. P.; Feldman, U.
2015ApJ...808L...7D    Altcode:
  In determining the element abundance of argon (a high first ionization
  potential; FIP element) relative to calcium (a low FIP element) in
  flares, unexpectedly high intensities of two Ar xiv lines (194.40,
  187.96 Å) relative to a Ca xiv line (193.87 Å) intensity were
  found in small (a few arcseconds) regions near sunspots in flare
  spectra recorded by the Extreme-ultraviolet Imaging Spectrometer
  on the Hinode spacecraft. In the most extreme case the Ar xiv line
  intensity relative to the Ca xiv intensity was 7 times the value
  expected from the photospheric abundance ratio, which is about 30
  times the abundance of argon relative to calcium in active regions,
  i.e., the measured Ar/Ca abundance ratio is about 10 instead of 0.37
  as in active regions. The Ar xiv and Ca xiv lines are formed near 3.4
  MK and have very similar contribution functions. This is the first
  observation of the inverse FIP effect in the Sun. Other regions show
  increases of 2-3 over photospheric abundances, or just photospheric
  abundances. This phenomenon appears to occur rarely and only over
  small areas of flares away from the regions containing multi-million
  degree plasma, but more work is needed to quantify the occurrences
  and their locations. In the bright hot regions of flares the Ar/Ca
  abundance ratio is coronal, i.e., the same as in active regions. In
  this Letter we show three examples of the inverse FIP effect.

---------------------------------------------------------
Title: Multi-thermal Energies of Solar Flares
Authors: Ryan, Daniel; Aschwanden, Markus; Boerner, Paul; Caspi,
   Amir; McTiernan, James; Warren, Harry
2015TESS....130215R    Altcode:
  Measuring energy partition in solar eruptions is key to understanding
  how different processes affect their evolution. In order to improve
  our knowledge on this topic, we are participating in a multi-study
  project to measure the energy partition of 400 M- and X-class flares
  and associated coronal mass ejections (CMEs). In this study we focus
  on the flare thermal energies of 391 of these events. We improve upon
  previous studies in the following ways: 1) We determine thermal energy
  using spatially resolved multi-thermal differential emission measures
  (DEMs) determined from AIA (Atmospheric Imaging Assembly) rather than
  relying on the isothermal assumption; 2) We determine flare volumes
  by thresholding these DEM maps rather than relying on single passband
  observations which may not show the full flare volume; 3) We analyze
  a greater number of events than previous similar studies to increase
  the statistical reliability of our results. We find that the thermal
  energies of these flares lie in the range 10^26.8—10^32 erg. These
  results are compared to those of Aschwanden et al. (2014) who examined
  a subset of these events. They determined the dissipated non-potential
  magnetic energy which is thought to be the total energy available
  to drive solar eruptions. For the 171 events common to both studies,
  we find that the ratio of flare thermal energy to dissipated magnetic
  energy ranges from 2%—40%. This is an order of magnitude higher than
  previously found by Emslie et al. (2012). This may be because Emslie et
  al. (2012) had to assume the amount of non-potential magnetic energy,
  or that they relied on the isothermal assumption to determine flare
  thermal energies. The improved results found here will help us better
  understand the role played by flare thermal processes in dissipating
  the overall energy of solar eruptions.

---------------------------------------------------------
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: Spectrally-resolved Soft X-ray Observations and the Temperature
    Structure of the Solar Corona
Authors: Caspi, Amir; Warren, Harry; McTiernan, James; Woods, Thomas N.
2015TESS....120403C    Altcode:
  Solar X-ray observations provide important diagnostics of plasma
  heating and particle acceleration, during solar flares and quiescent
  periods. How the corona is heated to its ~1-3 MK nominal temperature
  remains one of the fundamental unanswered questions of solar physics;
  heating of plasma to tens of MK during solar flares -- particularly
  to the hottest observed temperatures of up to ~50 MK -- is also still
  poorly understood. Soft X-ray emission (~0.1-10 keV; or ~0.1-10 nm)
  is particularly sensitive to hot coronal plasma and serves as a probe
  of the thermal processes driving coronal plasma heating. Spectrally-
  and temporally-resolved measurements are crucial for understanding
  these energetic processes, but there have historically been very
  few such observations. We present new solar soft X-ray spectra from
  the Amptek X123-SDD, measuring quiescent solar X-ray emission from
  ~0.5 to ~30 keV with ~0.15 keV FWHM resolution from two SDO/EVE
  calibration sounding rocket underflights in 2012 and 2013. Combined
  with observations from RHESSI, GOES/XRS, SDO/EVE, and SDO/AIA, the
  temperature distribution derived from these data suggest significant hot
  (5-10 MK) emission from active regions, and the 2013 spectra suggest a
  low-FIP enhancement of only ~1.6 relative to the photosphere, 40% of the
  usually-observed value from quiescent coronal plasma. We explore the
  implications of these findings on coronal heating. We discuss future
  missions for spectrally-resolved soft X-ray observations using the
  X123-SDD, including the upcoming MinXSS 3U CubeSat using the X123-SDD
  and scheduled for deployment in mid-2015, and the CubIXSS 6U CubeSat
  mission concept.

---------------------------------------------------------
Title: Modelling nanoflares in active regions and implications for
    coronal heating mechanisms
Authors: Cargill, P. J.; Warren, H. P.; Bradshaw, S. J.
2015RSPTA.37340260C    Altcode:
  Recent observations from the Hinode and Solar Dynamics Observatory
  spacecraft have provided major advances in understanding the heating of
  solar active regions (ARs). For ARs comprising many magnetic strands
  or sub-loops heated by small, impulsive events (nanoflares), it is
  suggested that (i) the time between individual nanoflares in a magnetic
  strand is 500-2000 s, (ii) a weak 'hot' component (more than 106.6 K)
  is present, and (iii) nanoflare energies may be as low as a few 1023
  ergs. These imply small heating events in a stressed coronal magnetic
  field, where the time between individual nanoflares on a strand is of
  order the cooling time. Modelling suggests that the observed properties
  are incompatible with nanoflare models that require long energy build-up
  (over 10 s of thousands of seconds) and with steady heating.

---------------------------------------------------------
Title: RAISE (Rapid Acquisition Imaging Spectrograph Experiment):
    Results and Instrument Status
Authors: Laurent, Glenn T.; Hassler, Donald; DeForest, Craig; Ayres,
   Tom; Davis, Michael; DePontieu, Bart; Diller, Jed; Graham, Roy;
   Schule, Udo; Warren, Harry
2015TESS....140203L    Altcode:
  We present initial results from the successful November 2014 launch of
  the RAISE (Rapid Acquisition Imaging Spectrograph Experiment) sounding
  rocket program, including intensity maps, high-speed spectroheliograms
  and dopplergrams, as well as an update on instrument status. The
  RAISE sounding rocket payload is the fastest high-speed scanning-slit
  imaging spectrograph flown to date and is designed to observe the
  dynamics and heating of the solar chromosphere and corona on time
  scales as short as 100-200ms, with arcsecond spatial resolution and a
  velocity sensitivity of 1-2 km/s. The instrument is based on a class of
  UV/EUV imaging spectrometers that use only two reflections to provide
  quasi-stigmatic performance simultaneously over multiple wavelengths
  and spatial fields. The design uses an off-axis parabolic telescope
  mirror to form a real image of the sun on the spectrometer entrance
  aperture. A slit then selects a portion of the solar image, passing its
  light onto a near-normal incidence toroidal grating, which re-images
  the spectrally dispersed radiation onto two array detectors. Two
  full spectral passbands over the same one-dimensional spatial field
  are recorded simultaneously with no scanning of the detectors or
  grating. The two different spectral bands (1st-order 1205-1243Å and
  1526-1564Å) are imaged onto two intensified Active Pixel Sensor (APS)
  detectors whose focal planes are individually adjusted for optimized
  performance. RAISE reads out the full field of both detectors at 5-10
  Hz, allowing us to record over 1,500 complete spectral observations in
  a single 5-minute rocket flight, opening up a new domain of high time
  resolution spectral imaging and spectroscopy. RAISE is designed to
  study small-scale multithermal dynamics in active region (AR) loops,
  explore the strength, spectrum and location of high frequency waves
  in the solar atmosphere, and investigate the nature of transient
  brightenings in the chromospheric network.

---------------------------------------------------------
Title: Measuring Elemental Abundances in Impulsive Heating Events
    with EIS
Authors: Warren, Harry; Doschek, George A.; Young, Peter
2015TESS....121306W    Altcode:
  It is well established that elemental abundances vary in the solar
  atmosphere and that this variation is organized by first ionization
  potential (FIP). Previous studies have indicated that in the solar
  corona low FIP elements, such as Fe, Si, and Mg, are enriched relative
  to high FIP elements, such as H, He, C, N, and O. In this paper we
  report on measurements of plasma composition made during transient
  heating events observed at transition region temperatures with the
  Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these
  events the intensities of O IV, V, and VI emission lines are enhanced
  relative to emission lines from Mg V, VI, and VII and indicate a
  composition close to that of the photosphere. Differential emission
  measure calculations show a broad distribution of temperatures in
  these events. Long-lived coronal structures, in contrast, show an
  enrichment of low FIP elements and relatively narrow temperature
  distributions. We conjecture that plasma composition is an important
  signature of the coronal heating process, with impulsive heating
  leading to the evaporation of unfractionated material from the lower
  layers of the solar atmosphere and higher frequency heating leading
  to the accumulation of low-FIP elements in the corona.

---------------------------------------------------------
Title: Magnetic and Hydrodynamic Energy Scaling Laws in Solar Flares
Authors: Aschwanden, Markus; Boerner, Paul; Xu, Yan; Ju, Jing; Ryan,
   Dan; Caspi, Amir; McTiernan, James; Warren, Harry
2015TESS....140603A    Altcode:
  We determine the dissipated non-potential magnetic energy and measure
  the multi-thermal energy in a sample of about 400 M and X-class
  flares observed with AIA and HMI during the first 4 years of the SDO
  mission. The free energy is determined with two nonlinear force-free
  field (NLFFF) models, one is based on the 3D vectorphotospheric magnetic
  field and the other uses forward-fitting of a vertical-current model to
  automatically traced coronal loops.The multi-thermal energy is measured
  with a spatial-synthesis differential emission measure (DEM) code,
  which yields a more comprehensive multi-thermal energy (being larger
  by an averagefactor of 14) than iso-thermal estimates. We show how the
  correlations and powerlaw-like size distributions of energies and other
  geometrical and physical parameters reveal magnetic and hydrodynamic
  scaling lawsthat are in agreement with recent statistical models of
  nonlinear dissipative systems governed by self-organized criticality.

---------------------------------------------------------
Title: The Multi-Instrument (EVE-RHESSI) DEM for Solar Flares,
    and Implications for Residual Non-Thermal Soft X-Ray Emission
Authors: McTiernan, James M.; Caspi, Amir; Warren, Harry
2015TESS....130210M    Altcode:
  In the soft X-ray energy range, solar flare spectra are typically
  dominated by thermal emission. The low energy extent of non-thermal
  emission can only be loosely quantified using currently available
  X-ray data. To address this issue, we combine observations from the EUV
  Variability Experiment (EVE) on-board the Solar Dynamics Observatory
  (SDO) with X-ray data from the Reuven Ramaty High Energy Spectroscopic
  Imager (RHESSI). The improvement over the isothermal approximation is
  intended to resolve the ambiguity in the range where the thermal and
  non-thermal components may have similar photon fluxes. This "crossover"
  range can extend up to 30 keV for medium to large solar flares.Previous
  work (Caspi et.al. 2014ApJ...788L..31C) has concentrated on obtaining
  DEM models that fit both instruments' observations well. Now we are
  interested in any breaks and cutoffs in the "residual" non-thermal
  spectrum; i.e., the RHESSI spectrum that is left over after the
  DEM has accounted for the bulk of the soft X-ray emission. Thermal
  emission is again modeled using a DEM that is parametrized as multiple
  gaussians in temperature; the non-thermal emission is modeled as a
  photon spectrum obtained using a thin-target emission model ('thin2'
  from the SolarSoft Xray IDL package). Spectra for both instruments
  are fit simultaneously in a self-consistent manner. The results for
  non-thermal parameters then are compared with those found using RHESSI
  data alone, with isothermal and double-thermal models.

---------------------------------------------------------
Title: Global Energetics of Solar Flares: II. Thermal Energies
Authors: Aschwanden, Markus J.; Boerner, Paul; Ryan, Daniel; Caspi,
   Amir; McTiernan, James M.; Warren, Harry P.
2015ApJ...802...53A    Altcode: 2015arXiv150205941A
  We present the second part of a project on the global energetics of
  solar flares and coronal mass ejections that includes about 400 M-
  and X-class flares observed with the Atmospheric Imaging Assembly
  (AIA) onboard the Solar Dynamics Observatory (SDO) during the
  first 3.5 yr of its mission. In this Paper II we compute the
  differential emission measure (DEM) distribution functions and
  associated multithermal energies, using a spatially-synthesized
  Gaussian DEM forward-fitting method. The multithermal DEM function
  yields a significantly higher (by an average factor of ≈14),
  but more comprehensive (multi-)thermal energy than an isothermal
  energy estimate from the same AIA data. We find a statistical
  energy ratio of {{E}<SUB>th</SUB>}/{{E}<SUB>diss</SUB>} ≈ 2-40%
  between the multithermal energy E<SUB>th</SUB> and the magnetically
  dissipated energy E<SUB>diss</SUB>, which is an order of magnitude
  higher than the estimates of Emslie et al. 2012. For the analyzed
  set of M- and X-class flares we find the following physical
  parameter ranges: L={{10}<SUP>8.2</SUP>}{{-10}<SUP>9.7</SUP>}
  cm for the length scale of the flare areas,
  {{T}<SUB>p</SUB>}={{10}<SUP>5.7</SUP>}{{-10}<SUP>7.4</SUP>}
  K for the DEM peak temperature,
  {{T}<SUB>w</SUB>}={{10}<SUP>6.8</SUP>}{{-10}<SUP>7.6</SUP>}
  K for the emission measure-weighted temperature,
  {{n}<SUB>p</SUB>}={{10}<SUP>10.3</SUP>}-{{10}<SUP>11.8</SUP>}
  cm<SUP>-3</SUP> for the average electron density,
  E{{M}<SUB>p</SUB>}={{10}<SUP>47.3</SUP>}-{{10}<SUP>50.3</SUP>}
  cm<SUP>-3</SUP> for the DEM peak emission measure, and
  {{E}<SUB>th</SUB>}={{10}<SUP>26.8</SUP>}-{{10}<SUP>32.0</SUP>} erg
  for the multithermal energies. The deduced multithermal energies
  are consistent with the RTV scaling law {{E}<SUB>th,RTV</SUB>}=7.3×
  {{10}<SUP>-10</SUP>} T<SUB>p</SUB><SUP>3</SUP>L<SUB>p</SUB><SUP>2</SUP>,
  which predicts extremal values of {{E}<SUB>th,max </SUB>}≈ 1.5×
  {{10}<SUP>33</SUP>} erg for the largest flare and {{E}<SUB>th,min
  </SUB>}≈ 1× {{10}<SUP>24</SUP>} erg for the smallest coronal
  nanoflare. The size distributions of the spatial parameters exhibit
  powerlaw tails that are consistent with the predictions of the
  fractal-diffusive self-organized criticality model combined with the
  RTV scaling law.

---------------------------------------------------------
Title: New Observations of the Solar 0.5-5 keV Soft X-Ray Spectrum
Authors: Caspi, Amir; Woods, Thomas N.; Warren, Harry P.
2015ApJ...802L...2C    Altcode: 2015arXiv150201725C
  The solar corona is orders of magnitude hotter than the underlying
  photosphere, but how the corona attains such high temperatures is
  still not understood. Soft X-ray (SXR) emission provides important
  diagnostics for thermal processes in the high-temperature corona, and
  is also an important driver of ionospheric dynamics at Earth. There is
  a crucial observational gap between ∼0.2 and ∼4 keV, outside the
  ranges of existing spectrometers. We present observations from a new
  SXR spectrometer, the Amptek X123-SDD, which measured the spatially
  integrated solar spectral irradiance from ∼0.5 to ∼5 keV, with
  ∼0.15 keV FWHM resolution, during sounding rocket flights on 2012
  June 23 and 2013 October 21. These measurements show that the highly
  variable SXR emission is orders of magnitude greater than that during
  the deep minimum of 2009, even with only weak activity. The observed
  spectra show significant high-temperature (5-10 MK) emission and are
  well fit by simple power-law temperature distributions with indices
  of ∼6, close to the predictions of nanoflare models of coronal
  heating. Observations during the more active 2013 flight indicate
  an enrichment of low first-ionization potential elements of only
  ∼1.6, below the usually observed value of ∼4, suggesting that
  abundance variations may be related to coronal heating processes. The
  XUV Photometer System Level 4 data product, a spectral irradiance
  model derived from integrated broadband measurements, significantly
  overestimates the spectra from both flights, suggesting a need for
  revision of its non-flare reference spectra, with important implications
  for studies of Earth ionospheric dynamics driven by solar SXRs.

---------------------------------------------------------
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: New Solar Soft X-ray Observations from the X123 Spectrometer
Authors: Caspi, A.; McTiernan, J. M.; Warren, H. P.; Woods, T. N.
2014AGUFMSH53B4220C    Altcode:
  The Amptek X123 is a new soft X-ray photon-counting spectrometer, based
  on a silicon drift detector with integrated thermoelectric cooler,
  vacuum housing, and multi-channel analyzer (including pulse pile-up
  rejection), capable of measuring solar line and continuum emission from
  ~0.5 to ~30 keV with ~0.15 keV FWHM resolution. It was flown on two
  recent SDO/EVE sounding rocket calibration underflights, is the primary
  science instrument on the upcoming Miniature X-ray Solar Spectrometer
  (MinXSS) NASA CubeSat, and is part of the proposed instrument payload
  for the CubeSat Imaging X-ray Solar Spectrometer (CubIXSS) mission
  concept. With the best resolution yet obtained from a broadband X-ray
  spectrometer, the X123 will enable new studies of plasma heating and
  particle acceleration, during flares and quiescent periods, and help to
  fill a crucial observational gap from ~0.2 to ~1.2 keV, not currently
  measured by existing instruments but critical for understanding
  solar-driven dynamics in Earth's upper atmosphere (ionosphere,
  thermosphere, mesosphere). We present results from a new analysis of
  X123 data obtained from the SDO/EVE rocket flights. In preparation
  for future MinXSS and CubIXSS data, we adapt a recently-developed
  technique combining EUV and X-ray spectra from SDO/EVE and RHESSI,
  respectively, to obtain a self-consistent differential emission measure
  (DEM) over the full range of coronal temperatures, ~2-50 MK. Including
  the X123 rocket X-ray spectra, we apply the adapted technique to examine
  both the coronal DEM and composition during quiescent (non-flaring)
  times with varying activity levels, obtaining constraints on the
  high-temperature extent of the quiescent DEM, the elemental abundances,
  and any potential non-thermal emission, and use the observations to
  extrapolate the spectrum to the poorly-observed ~0.2-1.2 keV band. We
  compare these results with those from a parallel technique using SDO/AIA
  imaging data. We discuss the implications for coronal plasma heating
  and the expectations for future observations from MinXSS and CubIXSS.

---------------------------------------------------------
Title: Computing Solar EUV Irradiance Variability
Authors: Warren, H. P.
2014AGUFMSH21C4130W    Altcode:
  The solar EUV irradiance plays a central role in determining the state
  of the Earth's upper atmosphere. The EUV irradiance at the shortest
  wavelengths, which is highly variable over time scales from seconds
  to decades, is particularly important for many aspects of space
  weather. Systematic spectrally resolved observations at the shortest
  EUV wavelengths, however, have been rare and there is a need to develop
  a methodology for estimating and forecasting the solar irradiance
  at all EUV wavelengths from sparse data sets. In this presentation
  we report on our efforts to use AIA DEM calculations to estimate the
  solar EUV irradiance at wavelength below 450 Å, where the emission
  is predominately optically thin. To validate our AIA DEM calculations
  we have performed extensive comparisons with simultaneous observations
  from the EVE instrument on SDO and the EIS instrument on Hinode and find
  that with the proper constraints we can generally reproduce the results
  obtained with detailed spectroscopic observations. Using a proxy for
  solar activity derived from photospheric magnetic field measurements
  we extend our model calculations to previous solar cycles and discuss
  how the model can be used to forecast EUV irradiance variability over
  short time scales. Finally, we speculate on what is needed to further
  develop semi-empirical and physical models for use in understanding
  the solar spectral irradiance at these wavelengths.

---------------------------------------------------------
Title: Using Running Difference Images to Track Proper Motions of
    XUV Coronal Intensity on the Sun
Authors: Sheeley, N. R., Jr.; Warren, H. P.; Lee, J.; Chung, S.;
   Katz, J.; Namkung, M.
2014ApJ...797..131S    Altcode:
  We have developed a procedure for observing and tracking proper
  motions of faint XUV coronal intensity on the Sun and have applied
  this procedure to study the collective motions of cellular plumes and
  the shorter-period waves in sunspots. Our space/time maps of cellular
  plumes show a series of tracks with the same 5-8 minute repetition
  times and ~100 km s<SUP>-1</SUP> sky-plane speeds found previously
  in active-region fans and in coronal hole plumes. By synchronizing
  movies and space/time maps, we find that the tracks are produced by
  elongated ejections from the unipolar flux concentrations at the bases
  of the cellular plumes and that the phases of these ejections are
  uncorrelated from cell to cell. Thus, the large-scale motion is not a
  continuous flow, but is more like a system of independent conveyor belts
  all moving in the same direction along the magnetic field. In contrast,
  the proper motions in sunspots are clearly waves resulting from periodic
  disturbances in the sunspot umbras. The periods are ~2.6 minutes, but
  the sky-plane speeds and wavelengths depend on the heights of the waves
  above the sunspot. In the chromosphere, the waves decelerate from 35-45
  km s<SUP>-1</SUP> in the umbra to 7-8 km s<SUP>-1</SUP> toward the outer
  edge of the penumbra, but in the corona, the waves accelerate to ~60-100
  km s<SUP>-1</SUP>. Because chromospheric and coronal tracks originate
  from the same space/time locations, the coronal waves must emerge from
  the same umbral flashes that produce the chromospheric waves.

---------------------------------------------------------
Title: Propagation of Forecast Errors from the Sun to LEO
Trajectories: How Does Drag Uncertainty Affect Conjunction Frequency?
Authors: Emmert, J.; Byers, J.; Warren, H.; Segerman, A.
2014amos.confE..48E    Altcode:
  Atmospheric drag is the largest source of error in the prediction
  of trajectories of most objects in low-Earth orbit, and solar
  variability is the largest source of error in upper atmospheric density
  forecasts. There is thus a need to accurately propagate solar forecast
  uncertainty to atmospheric density uncertainty and thence to satellite
  position uncertainty. Furthermore, the collective position uncertainty
  of the LEO population determines the frequency of conjunctions that must
  be assessed in order to avoid collisions. To maintain Space Situational
  Awareness of the growing LEO population, the number of conjunctions
  must be kept at a manageable level to avoid being overwhelmed by false
  alarms. This criterion can be used to define solar and atmospheric
  forecast accuracy requirements. In this paper, we examine how solar
  forecast errors grow with increasing forecast time, and how this
  uncertainty maps to atmospheric density uncertainty as a function of
  altitude. We then develop analytical approximations of the mapping from
  density uncertainty to in-track position uncertainty, as a function of
  perigee height, orbital eccentricity, ballistic coefficient, background
  atmospheric conditions, and forecast time. Finally, we estimate the
  conjunction frequency between operational LEO satellites and the entire
  LEO population (separately considering objects larger than 10 cm and
  objects larger than 1 cm), based on the statistical distributions of
  the key orbital parameters (perigee height, eccentricity, inclination
  and ballistic coefficient) and assumed solar and density forecast
  uncertainties.

---------------------------------------------------------
Title: Exploiting the Magnetic Origin of Solar Activity in Forecasting
    Thermospheric Density Variations
Authors: Warren, H.; Emmert, J.
2014amos.confE.111W    Altcode:
  A detailed understanding of solar irradiance and its variability
  at extreme ultraviolet (EUV) wavelengths is required to model
  thermospheric density and to specify and forecast satellite
  drag. Current operational models rely on forecasts of proxies for
  solar activity based on autoregression. The forecasts from these
  models generally degrade to climatology after only a few days. Solar
  magnetic fields are ultimately responsible for variations in the EUV
  irradiance. The evolution of solar magnetic fields is well understood
  and results from a combination of solar rotation, diffusion, meridional
  flow, and magnetic flux emergence. In this presentation we review the
  current state of autoregressive proxy models and compare their forecast
  skill against new activity models based on magnetic flux transport.

---------------------------------------------------------
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: Constraining Solar Flare Differential Emission Measures with
    EVE and RHESSI
Authors: Caspi, Amir; McTiernan, James M.; Warren, Harry P.
2014ApJ...788L..31C    Altcode: 2014arXiv1405.7068C
  Deriving a well-constrained differential emission measure (DEM)
  distribution for solar flares has historically been difficult,
  primarily because no single instrument is sensitive to the full range
  of coronal temperatures observed in flares, from lsim2 to gsim50
  MK. We present a new technique, combining extreme ultraviolet (EUV)
  spectra from the EUV Variability Experiment (EVE) onboard the Solar
  Dynamics Observatory with X-ray spectra from the Reuven Ramaty High
  Energy Solar Spectroscopic Imager (RHESSI), to derive, for the first
  time, a self-consistent, well-constrained DEM for jointly observed
  solar flares. EVE is sensitive to ~2-25 MK thermal plasma emission,
  and RHESSI to gsim10 MK together, the two instruments cover the full
  range of flare coronal plasma temperatures. We have validated the
  new technique on artificial test data, and apply it to two X-class
  flares from solar cycle 24 to determine the flare DEM and its temporal
  evolution; the constraints on the thermal emission derived from the EVE
  data also constrain the low energy cutoff of the non-thermal electrons,
  a crucial parameter for flare energetics. The DEM analysis can also
  be used to predict the soft X-ray flux in the poorly observed ~0.4-5
  nm range, with important applications for geospace science.

---------------------------------------------------------
Title: Absolute Abundance Measurements in Solar Flares
Authors: Warren, Harry
2014AAS...22412301W    Altcode:
  We present measurements of elemental abundances in solar flares with
  EVE/SDO and EIS/Hinode. EVE observes both high temperature Fe emission
  lines Fe XV-XXIV and continuum emission from thermal bremsstrahlung
  that is proportional to the abundance of H. By comparing the relative
  intensities of line and continuum emission it is possible to determine
  the enrichment of the flare plasma relative to the composition of
  the photosphere. This is the first ionization potential or FIP bias
  (F). Since thermal bremsstrahlung at EUV wavelengths is relatively
  insensitive to the electron temperature it is important to account for
  the distribution of electron temperatures in the emitting plasma. We
  accomplish this by using the observed spectra to infer the differential
  emission measure distribution and FIP bias simultaneously. In
  each of the 21 flares that we analyze we find that the observed
  composition is close to photospheric. The mean FIP bias in our sample
  is F=1.17+-0.22. Furthermore, we have compared the EVE measurements
  with corresponding flare observations of intermediate temperature S,
  Ar, Ca, and Fe emission lines taken with EIS. Our initial calculations
  also indicate a photospheric composition for these observations. This
  analysis suggests that the bulk of the plasma evaporated during a flare
  comes from deep in the chromosphere, below the region where elemental
  fractionation in the non-flaring corona occurs.

---------------------------------------------------------
Title: Photometric and Thermal Cross-calibration of Solar EUV
    Instruments
Authors: Boerner, P. F.; Testa, P.; Warren, H.; Weber, M. A.;
   Schrijver, C. J.
2014SoPh..289.2377B    Altcode: 2013arXiv1307.8045B
  We present an assessment of the accuracy of the calibration measurements
  and atomic physics models that go into calculating the SDO/AIA response
  as a function of wavelength and temperature. The wavelength response
  is tested by convolving SDO/EVE and Hinode/EIS spectral data with the
  AIA effective area functions and by comparing the predictions with
  AIA observations. For most channels, the AIA intensities summed over
  the disk agree with the corresponding measurements derived from the
  current version (V2) of the EVE data to within the estimated 25 %
  calibration error. This agreement indicates that the AIA effective
  areas are generally stable in time. The AIA 304 Å channel, however,
  does show degradation by a factor of almost 3 from May 2010 through
  September 2011, when the throughput apparently reached a minimum. We
  also found some inconsistencies in the 335 Å passband, possibly due to
  higher-order contamination of the EVE data. The intensities in the AIA
  193 Å channel agree to within the uncertainties with the corresponding
  measurements from EIS full CCD observations. Analysis of high-resolution
  X-ray spectra of the solar-like corona of Procyon and of EVE spectra
  allowed us to investigate the accuracy and completeness of the CHIANTI
  database in the AIA shorter wavelength passbands. We found that in
  the 94 Å channel, the spectral model significantly underestimates the
  plasma emission owing to a multitude of missing lines. We derived an
  empirical correction for the AIA temperature responses by performing
  differential emission measure (DEM) inversion on a broad set of EVE
  spectra and adjusting the AIA response functions so that the count
  rates predicted by the full-disk DEMs match the observations.

---------------------------------------------------------
Title: The Multi-Instrument, Comprehensive Differential Emission
    Measure (DEM) of the Solar Corona During Flares and Quiescent Periods
Authors: Caspi, Amir; McTiernan, James; Warren, Harry; Woods, Thomas N.
2014AAS...22412307C    Altcode:
  Thermal plasma in the solar corona, while often modeled as isothermal
  for ease of analysis, is in fact decidedly multi-thermal, ranging
  from ~1-2 MK in the quiescent corona to ~30-50 MK in intensely
  flaring loops. It has proven difficult to obtain a well-constrained
  differential emission measure (DEM) from a single instrument, as
  the wavelength ranges of individual instruments, even those with
  broadband coverage, provide sensitivity to only a limited range of
  plasma temperatures. Recently, we developed a new technique using
  combined extreme ultraviolet (EUV) and soft and hard X-ray (SXR, HXR)
  data from the EUV Variability Experiment (EVE) onboard the Solar
  Dynamics Observatory (SDO) and the Reuven Ramaty High Energy Solar
  Spectroscopic Imager (RHESSI), respectively, to obtain a self-consistent
  DEM that is strongly constrained across the full range of coronal plasma
  temperatures (&lt;2 to &gt;50 MK). An accurate, precise determination
  of the plasma temperature distribution enables not only studies of
  plasma heating and thermal plasma evolution, but can also provide
  strong constraints on the non-thermal accelerated electron population,
  including the low-energy cutoff which is typically determined only as
  a loose upper limit.We present EVE+RHESSI DEM results from selected
  intense (X-class) flares from solar cycle 24, including determining
  the non-thermal low-energy cutoff and examining how this evolves with
  the temperature distribution. We also apply this technique to combine
  EUV data from EVE with SXR data from the GOES X-ray Sensor (XRS)
  and the X123, a new SXR spectrometer flown on two recent SDO/EVE
  calibration sounding rockets, to examine the DEM during quiescent
  (non-flaring) times with varying activity levels; the X-ray data
  provide crucial constraints on the high-temperate extent of the DEM
  and any potential non-thermal emission. We compare these results with
  those from a parallel technique to derive DEMs from imaging data from
  the Atmospheric Imaging Assembly (AIA) onboard SDO, and we discuss the
  implications for plasma heating, both during flares and in the quiescent
  corona. This research is supported by NASA contracts NAS5-98033 and
  NAS5-02140, and NASA Heliophysics Guest Investigator Grant NNX12AH48G.

---------------------------------------------------------
Title: Plasma Dynamics Above Solar Flare Soft X-Ray Loop Tops
Authors: Doschek, G. A.; McKenzie, D. E.; Warren, H. P.
2014ApJ...788...26D    Altcode:
  We measure non-thermal motions in flare loop tops and above the loop
  tops using profiles of highly ionized spectral lines of Fe XXIV and Fe
  XXIII formed at multimillion-degree temperatures. Non-thermal motions
  that may be due to turbulence or multiple flow regions along the line of
  sight are extracted from the line profiles. The non-thermal motions are
  measured for four flares seen at or close to the solar limb. The profile
  data are obtained using the Extreme-ultraviolet Imaging Spectrometer on
  the Hinode spacecraft. The multimillion-degree non-thermal motions are
  between 20 and 60 km s<SUP>-1</SUP> and appear to increase with height
  above the loop tops. Motions determined from coronal lines (i.e., lines
  formed at about 1.5 MK) tend to be smaller. The multimillion-degree
  temperatures in the loop tops and above range from about 11 MK to 15 MK
  and also tend to increase with height above the bright X-ray-emitting
  loop tops. The non-thermal motions measured along the line of sight,
  as well as their apparent increase with height, are supported by
  Solar Dynamics Observatory Atmospheric Imaging Assembly measurements
  of turbulent velocities in the plane of the sky.

---------------------------------------------------------
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: Non-thermal Motions in and Above Flare Loop Tops Measured by
    the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode
Authors: Doschek, George A.; McKenzie, David Eugene; Warren, Harry P
2014AAS...22411105D    Altcode:
  The plasma volume above the soft X-ray emitting loop tops is of
  particular interest for studying the formation of flare loops. We
  present EIS observations of non-thermal motions (turbulence) determined
  from spectral line profiles of Fe XXIII and Fe XXIV ions for three
  well-observed flares near the solar limb. We compare the non-thermal
  motions at temperatures near 10 MK with the motions along the same
  lines-of-sight determined from lines of coronal ions such as Fe XII, Fe
  XIV, and Fe XV formed at 1-2 MK. The take-away is that the non-thermal
  motions obtained from Fe XXIII and Fe XXIV lines increase with height
  towards the reconnection region, up to speeds of about 50-60 km/s
  for the largest heights that we can observe. The implication is that
  considerable plasma heating occurs outside the reconnection region. In
  addition, we discuss the implications of results obtained for flares
  from earlier X-ray Yohkoh observations of line profiles of Fe XXV and
  Ca XIX on the current results from EIS and AIA. Fe XXV is formed at
  significantly higher temperatures than any strong flare EUV spectral
  line observed by EIS or by imaging telescopes such as AIA or TRACE. This
  work is supported by NASA grants.

---------------------------------------------------------
Title: Measurements of Absolute Abundances in Solar Flares
Authors: Warren, Harry P.
2014ApJ...786L...2W    Altcode: 2013arXiv1310.4765W
  We present measurements of elemental abundances in solar flares
  with the EUV Variability Experiment (EVE) on the Solar Dynamics
  Observatory. EVE observes both high temperature Fe emission lines
  (Fe XV-Fe XXIV) and continuum emission from thermal bremsstrahlung
  that is proportional to the abundance of H. By comparing the relative
  intensities of line and continuum emission it is possible to determine
  the enrichment of the flare plasma relative to the composition of
  the photosphere. This is the first ionization potential or FIP bias
  (f). Since thermal bremsstrahlung at EUV wavelengths is relatively
  insensitive to the electron temperature, it is important to account for
  the distribution of electron temperatures in the emitting plasma. We
  accomplish this by using the observed spectra to infer the differential
  emission measure distribution and FIP bias simultaneously. In each of
  the 21 flares that we analyze we find that the observed composition is
  close to photospheric. The mean FIP bias in our sample is f = 1.17 ±
  0.22. This analysis suggests that the bulk of the plasma evaporated
  during a flare comes from deep in the chromosphere, below the region
  where elemental fractionation occurs.

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

---------------------------------------------------------
Title: Using Coronal Cells to Infer the Magnetic Field Structure
    and Chirality of Filament Channels
Authors: Sheeley, N. R., Jr.; Martin, S. F.; Panasenco, O.; Warren,
   H. P.
2013ApJ...772...88S    Altcode: 2013arXiv1306.2273S
  Coronal cells are visible at temperatures of ~1.2 MK in Fe XII
  coronal images obtained from the Solar Dynamics Observatory and Solar
  Terrestrial Relations Observatory spacecraft. We show that near a
  filament channel, the plumelike tails of these cells bend horizontally
  in opposite directions on the two sides of the channel like fibrils
  in the chromosphere. Because the cells are rooted in magnetic flux
  concentrations of majority polarity, these observations can be used
  with photospheric magnetograms to infer the direction of the horizontal
  field in filament channels and the chirality of the associated magnetic
  field. This method is similar to the procedure for inferring the
  direction of the magnetic field and the chirality of the fibril pattern
  in filament channels from Hα observations. However, the coronal cell
  observations are easier to use and provide clear inferences of the
  horizontal field direction for heights up to ~50 Mm into the corona.

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

---------------------------------------------------------
Title: Turbulence in the Flare Reconnection Region
Authors: Doschek, George A.; McKenzie, D. E.; Warren, H.
2013SPD....4430401D    Altcode:
  The physical conditions such as temperature, density, and dynamical
  properties in the flare reconnection region, located above the bright
  soft X-ray loops, are basically not known although there have been
  measurements of non-thermal hard X-ray emission properties by RHESSI
  and earlier by HXT on Yohkoh. The advent of Hinode and the Solar
  Dynamics Observatory (SDO) spatially resolved observations, however,
  has changed this and it is now possible to measure in more detail some
  of the properties of the reconnection region. AIA imagery on SDO and
  the Extreme-ultraviolet Imaging Spectrometer (EIS) and X-ray Telescope
  (XRT) on Hinode allow values of non-thermal motions or turbulence in
  the reconnection region to be determined. Turbulence is predicted by
  theoretical models of magnetic reconnection in flares (e.g., see Liu et
  al. 2008, ApJ, 676, 704) and has long been inferred spectroscopically
  from non-thermal broadening of flare emission lines. Studies with
  Hinode/XRT and SDO/AIA demonstrate that two-dimensional investigations
  of flare velocity fields can be made, by imaging the plasma sheets
  above post-CME flare arcades. These measurements are made possible
  through the use of local correlation tracking (LCT), as shown by
  McKenzie (2013), ApJ, 766, 39, and reveal signatures of turbulence,
  including temporally and spatially varying vorticity. For some flares
  the AIA and XRT results can be combined with Doppler measurements of
  turbulence obtained with EIS. EIS data consist of raster scans that
  include the reconnection region for flares on the limb or near the
  limb. A set of spectral lines are observed that cover temperatures
  from 0.25 MK up to ~20 MK. A temperature in the reconnection region
  is calculated from the Fe XXIII/Fe XXIV line ratio and the thermal
  Doppler and instrumental widths are subtracted from the total line
  widths. The remainder is non-thermal motions or turbulence. We will
  present coordinated analyses of EIS and AIA observations of plasma
  sheets in post-CME flares, and demonstrate that the turbulent speeds
  found by LCT are about the same magnitude as those derived from EIS
  spectral line profiles obtained in the same or nearby locations.

---------------------------------------------------------
Title: EVE-RHESSI Observations of Thermal and Nonthermal Solar
    Flare Emission
Authors: McTiernan, James; Caspi, A.; Warren, H.
2013SPD....44...55M    Altcode:
  Solar flares accelerate electrons up to hundreds of MeV and heat plasma
  to tens of MK. In large (GOES M- and X-class) flares, in addition
  to the 10-25 MK plasma thought to be the result of chromospheric
  evaporation, even hotter plasma (up to 50 MK) may be directly heated
  in the corona. While observations of hard X-ray bremmstrahlung directly
  probe the nonthermal electron population, for large flares the spectra
  below 20-30 keV are typically dominated by thermal emission. The low
  energy extent of the nonthermal spectrum can be only loosely quantified
  by hard X-ray spectrometers, resulting in significant implications
  for calculating flare energy budgets and for constraining possible
  acceleration mechanisms. A precise characterization of the thermal
  emission is imperative. Extreme ultraviolet observations from the EUV
  Variability Experiment (EVE) on-board the Solar Dynamics Observatory
  (SDO), combined with X-ray data from the Reuven Ramaty High Energy
  Spectroscopic Imager (RHESSI), currently offer the most comprehensive
  view of the flare temperature distribution. EVE observes EUV emission
  lines with peak formation temperatures of 2-20 MK, while RHESSI observes
  the X-ray bremsstrahlung of hot, 10-50 MK plasma; combined, the two
  instruments cover the full range of flare plasma temperatures. In this
  work, we handle the EVE-RHESSI data for a few large flares in three
  steps; first we calculate differential emission measures (DEMs) using
  EVE and RHESSI independently for purposes of cross-calibration. Second,
  we create combined EVE-RHESSI DEMs, fixing the nonthermal spectral
  parameters to those found using a RHESSI-only spectral fit. The final
  step is to unconstrain the nonthermal parameters (in particular,
  the low-energy cutoff of the spectrum) and let them be fit in the same
  process as the EVE-RHESSI DEM, to obtain a fully self-consistent thermal
  plus nonthermal model. This research is supported by NASA Heliophysics
  Guest Investigator Grant NNX12AH48G.

---------------------------------------------------------
Title: Progress toward high resolution EUV spectroscopy
Authors: Korendyke, C.; Doschek, G. A.; Warren, H.; Young, P. R.;
   Chua, D.; Hassler, D. M.; Landi, E.; Davila, J. M.; Klimchuck, J.;
   Tun, S.; DeForest, C.; Mariska, J. T.; Solar C Spectroscopy Working
   Group; LEMUR; EUVST Development Team
2013SPD....44..143K    Altcode:
  HIgh resolution EUV spectroscopy is a critical instrumental technique
  to understand fundamental physical processes in the high temperature
  solar atmosphere. Spectroscopic observations are used to measure
  differential emission measure, line of sight and turbulent flows,
  plasma densities and emission measures. Spatially resolved, spectra of
  these emission lines with adequate cadence will provide the necessary
  clues linking small scale structures with large scale, energetic
  solar phenomena. The necessary observations to determine underlying
  physical processes and to provide comprehensive temperature coverage
  of the solar atmosphere above the chromosphere will be obtained by the
  proposed EUVST instrument for Solar C. This instrument and its design
  will be discussed in this paper. Progress on the VEry high Resolution
  Imaging Spectrograph (VERIS) sounding rocket instrument presently under
  development at the Naval Research Laboratory will also be discussed.

---------------------------------------------------------
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: Status of RAISE, the Rapid Acquisition Imaging Spectrograph
    Experiment
Authors: Laurent, Glenn T.; Hassler, D. M.; DeForest, C.; Ayres,
   T. R.; Davis, M.; De Pontieu, B.; Schuehle, U.; Warren, H.
2013SPD....44..145L    Altcode:
  The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) sounding
  rocket payload is a high speed scanning-slit imaging spectrograph
  designed to observe the dynamics and heating of the solar chromosphere
  and corona on time scales as short as 100 ms, with 1 arcsec spatial
  resolution and a velocity sensitivity of 1-2 km/s. The instrument is
  based on a new class of UV/EUV imaging spectrometers that use only
  two reflections to provide quasi-stigmatic performance simultaneously
  over multiple wavelengths and spatial fields. The design uses an
  off-axis parabolic telescope mirror to form a real image of the sun
  on the spectrometer entrance aperture. A slit then selects a portion
  of the solar image, passing its light onto a near-normal incidence
  toroidal grating, which re-images the spectrally dispersed radiation
  onto two array detectors. Two full spectral passbands over the same
  one-dimensional spatial field are recorded simultaneously with no
  scanning of the detectors or grating. The two different spectral
  bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two
  intensified Active Pixel Sensor (APS) detectors whose focal planes are
  individually adjusted for optimized performance. The telescope and
  grating are coated with B4C to enhance short wavelength (2nd order)
  reflectance, enabling the instrument to record the brightest lines
  between 602-622Å and 761-780Å at the same time. RAISE reads out the
  full field of both detectors at 5-10 Hz, allowing us to record over
  1,500 complete spectral observations in a single 5-minute rocket flight,
  opening up a new domain of high time resolution spectral imaging and
  spectroscopy. We present an overview of the project, a summary of the
  maiden flight results, and an update on instrument status.Abstract
  (2,250 Maximum Characters): The Rapid Acquisition Imaging Spectrograph
  Experiment (RAISE) sounding rocket payload is a high speed scanning-slit
  imaging spectrograph designed to observe the dynamics and heating of the
  solar chromosphere and corona on time scales as short as 100 ms, with 1
  arcsec spatial resolution and a velocity sensitivity of 1-2 km/s. The
  instrument is based on a new class of UV/EUV imaging spectrometers
  that use only two reflections to provide quasi-stigmatic performance
  simultaneously over multiple wavelengths and spatial fields. The design
  uses an off-axis parabolic telescope mirror to form a real image of
  the sun on the spectrometer entrance aperture. A slit then selects
  a portion of the solar image, passing its light onto a near-normal
  incidence toroidal grating, which re-images the spectrally dispersed
  radiation onto two array detectors. Two full spectral passbands over
  the same one-dimensional spatial field are recorded simultaneously with
  no scanning of the detectors or grating. The two different spectral
  bands (1st-order 1205-1243Å and 1526-1564Å) are imaged onto two
  intensified Active Pixel Sensor (APS) detectors whose focal planes are
  individually adjusted for optimized performance. The telescope and
  grating are coated with B4C to enhance short wavelength (2nd order)
  reflectance, enabling the instrument to record the brightest lines
  between 602-622Å and 761-780Å at the same time. RAISE reads out the
  full field of both detectors at 5-10 Hz, allowing us to record over
  1,500 complete spectral observations in a single 5-minute rocket flight,
  opening up a new domain of high time resolution spectral imaging and
  spectroscopy. We present an overview of the project, a summary of the
  maiden flight results, and an update on instrument status.

---------------------------------------------------------
Title: Observations of Thermal Flare Plasma with the EUV Variability
    Experiment
Authors: Warren, Harry P.; Mariska, John T.; Doschek, George A.
2013ApJ...770..116W    Altcode: 2012arXiv1211.1875W
  One of the defining characteristics of a solar flare is the impulsive
  formation of very high temperature plasma. The properties of the
  thermal emission are not well understood, however, and the analysis of
  solar flare observations is often predicated on the assumption that the
  flare plasma is isothermal. The EUV Variability Experiment (EVE) on the
  Solar Dynamics Observatory provides spectrally resolved observations of
  emission lines that span a wide range of temperatures (e.g., Fe XV-Fe
  XXIV) and allow for thermal flare plasma to be studied in detail. In
  this paper we describe a method for computing the differential emission
  measure distribution in a flare using EVE observations and apply it to
  several representative events. We find that in all phases of the flare
  the differential emission measure distribution is broad. Comparisons
  of EVE spectra with calculations based on parameters derived from
  the Geostationary Operational Environmental Satellites soft X-ray
  fluxes indicate that the isothermal approximation is generally a poor
  representation of the thermal structure of a flare.

---------------------------------------------------------
Title: Properties of a Solar Flare Kernel Observed by Hinode and SDO
Authors: Young, P. R.; Doschek, G. A.; Warren, H. P.; Hara, H.
2013ApJ...766..127Y    Altcode: 2012arXiv1212.4388Y
  Flare kernels are compact features located in the solar chromosphere
  that are the sites of rapid heating and plasma upflow during the rise
  phase of flares. An example is presented from a M1.1 class flare in
  active region AR 11158 observed on 2011 February 16 07:44 UT for which
  the location of the upflow region seen by EUV Imaging Spectrometer (EIS)
  can be precisely aligned to high spatial resolution images obtained by
  the Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic
  Imager (HMI) on board the Solar Dynamics Observatory (SDO). A string
  of bright flare kernels is found to be aligned with a ridge of strong
  magnetic field, and one kernel site is highlighted for which an upflow
  speed of ≈400 km s<SUP>-1</SUP> is measured in lines formed at 10-30
  MK. The line-of-sight magnetic field strength at this location is
  ≈1000 G. Emission over a continuous range of temperatures down to
  the chromosphere is found, and the kernels have a similar morphology
  at all temperatures and are spatially coincident with sizes at the
  resolution limit of the AIA instrument (lsim400 km). For temperatures
  of 0.3-3.0 MK the EIS emission lines show multiple velocity components,
  with the dominant component becoming more blueshifted with temperature
  from a redshift of 35 km s<SUP>-1</SUP> at 0.3 MK to a blueshift of
  60 km s<SUP>-1</SUP> at 3.0 MK. Emission lines from 1.5-3.0 MK show a
  weak redshifted component at around 60-70 km s<SUP>-1</SUP> implying
  multi-directional flows at the kernel site. Significant non-thermal
  broadening corresponding to velocities of ≈120 km s<SUP>-1</SUP> is
  found at 10-30 MK, and the electron density in the kernel, measured
  at 2 MK, is 3.4 × 10<SUP>10</SUP> cm<SUP>-3</SUP>. Finally, the Fe
  XXIV λ192.03/λ255.11 ratio suggests that the EIS calibration has
  changed since launch, with the long wavelength channel less sensitive
  than the short wavelength channel by around a factor two.

---------------------------------------------------------
Title: Chromospheric Evaporation in an M1.8 Flare Observed by the
    Extreme-ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Warren, H. P.; Young, P. R.
2013ApJ...767...55D    Altcode: 2012arXiv1212.4027D
  We discuss observations of chromospheric evaporation for a complex
  flare that occurred on 2012 March 9 near 03:30 UT obtained from the
  Extreme-ultraviolet Imaging Spectrometer (EIS) on board the Hinode
  spacecraft. This was a multiple event with a strong energy input
  that reached the M1.8 class when observed by EIS. EIS was in raster
  mode and fortunately the slit was almost at the exact location of
  a significant energy input. Also, EIS obtained a full-CCD spectrum
  of the flare, i.e., the entire CCD was readout so that data were
  obtained for about the 500 lines identified in the EIS wavelength
  ranges. Chromospheric evaporation characterized by 150-200 km
  s<SUP>-1</SUP> upflows was observed in multiple locations in
  multi-million degree spectral lines of flare ions such as Fe XXII,
  Fe XXIII, and Fe XXIV, with simultaneous 20-60 km s<SUP>-1</SUP>
  upflows in million degree coronal lines from ions such as Fe XII-Fe
  XVI. The behavior of cooler, transition region ions such as O VI, Fe
  VIII, He II, and Fe X is more complex, but upflows were also observed
  in Fe VIII and Fe X lines. At a point close to strong energy input in
  space and time, the flare ions Fe XXII, Fe XXIII, and Fe XXIV reveal
  an isothermal source with a temperature close to 14 MK and no strong
  blueshifted components. At this location there is a strong downflow
  in cooler active region lines from ions such as Fe XIII and Fe XIV,
  on the order of 200 km s<SUP>-1</SUP>. We speculate that this downflow
  may be evidence of the downward shock produced by reconnection in the
  current sheet seen in MHD simulations. A sunquake also occurred near
  this location. Electron densities were obtained from density sensitive
  lines ratios from Fe XIII and Fe XIV. Atmospheric Imaging Assembly
  (AIA) observations from the Solar Dynamics Observatory are used with
  JHelioviewer to obtain a qualitative overview of the flare. However,
  AIA data are not presented in this paper. In summary, spectroscopic data
  from EIS are presented that can be used for predictive tests of models
  of chromospheric evaporation as envisaged in the Standard Flare Model.

---------------------------------------------------------
Title: Flare Footpoint Regions Observed by the Extreme-ultraviolet
    Imaging Spectrometer (EIS) on Hinode
Authors: Doschek, G. A.; Warren, H. P.; Young, P. R.; Caspi, A.
2013enss.confE..74D    Altcode:
  The Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode has
  observed flare footpoints using a variety of studies designed to
  observe various aspects of the solar flare Standard Model. Some of
  these observations are accompanied by imaging data from RHESSI. We
  present observations of upflows in flare footpoint regions obtained
  from picket-fence raster observations of two flares that occurred
  on 24 and 25 September 2011. The observations consist of upflow and
  non-thermal speeds at various temperatures (from about 1 MK to 15
  MK) at footpoint regions as well as a limited differential emission
  measure. RHESSI observations provide constraints on the energetic
  electron precipitation into the footpoints. Electron densities are
  available from an Fe XIV ratio, and SDO AIA data are also investigated
  for context. The RHESSI energy input will be assessed in terms of 1D
  models of the footpoint regions.

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

---------------------------------------------------------
Title: Computing the Solar EUV Irradiance at Wavelengths Below 450 Å
Authors: Warren, Harry
2013enss.confE..47W    Altcode:
  The solar EUV irradiance plays a central role in determining the state
  of the Earth's upper atmosphere. The EUV irradiance at the shortest
  wavelengths, which is highly variable over time scales from seconds
  to decades, is particularly important for many aspects of space
  weather. Systematic spectrally resolved observations at the shortest
  EUV wavelengths, however, have been rare and there is a need to develop
  a methodology for estimating and forecasting the solar irradiance at
  all EUV wavelengths from sparse data sets. The AIA on SDO provides full
  Sun solar images in 7 narrow EUV wavelength ranges. These channels were
  selected to provide complete thermal coverage of the corona and allow
  for calculation of the differential emission measure distribution. In
  this presentation we report on our efforts to use AIA DEM calculations
  to estimate the solar EUV irradiance at wavelength below 450 Å, where
  the emission is predominately optically thin. To validate our AIA DEM
  calculations we have performed extensive comparisons with simultaneous
  observations from the EIS instrument on Hinode and find that with the
  proper constraints we can generally reproduce the results obtained
  with detailed spectroscopic observations using AIA. We also present
  comparisons with existing time series of QEUV, the integrated solar
  irradiance at wavelengths below 450 Å.

---------------------------------------------------------
Title: SDO and Hinode observations of coronal heating at a flare
    kernel site
Authors: Young, P. R.; Doschek, G. A.; Warren, H. P.; Hara, H.
2013enss.confE..36Y    Altcode:
  Flare kernels are compact features located in the chromosphere that
  are the sites of rapid heating and plasma upflow during the rise phase
  of flares. They provide an excellent opportunity for testing models of
  energy transport and dissipation in the solar atmosphere as they are
  very bright and emit over a wide temperature range. A M1.1 class flare
  that peaked at 07:44 UT on 2011 February 16 was observed simultaneously
  by SDO and Hinode, and one flare kernel observed prior to the flare
  peak is highlighted. It is found to emit at all temperatures from
  the chromosphere through to 30 MK, with all AIA channels brightening
  simultaneously and rise times of only 1 minute. The kernel is located on
  a ridge of strong magnetic field close to a neutral line in the active
  region. The kernel is at the resolution limit of AIA, suggesting a size
  of &lt; 0.6 arcsec. Hinode/EIS allows velocity patterns in the kernel
  to be tracked over a wide temperature range and reveals a dominant high
  speed upflow of 400 km/s at temperatures of 10-30 MK, with both down
  and upflows measured at cooler temperatures of 1.5-3.0 MK, suggesting
  unresolved structures. All emission lines show evidence of significant
  non-thermal broadening, and the electron density of the plasma is 3.4
  x 10^10 cm-3. The observations are compared to models of chromospheric
  evaporation and similarities and differences are highlighted.

---------------------------------------------------------
Title: Exploring Thermal and Non-Thermal Flare Emission with EVE
    and RHESSI
Authors: Caspi, Amir; McTiernan, James M.; Warren, Harry P.
2013enss.confE.121C    Altcode:
  Solar flares accelerate electrons up to hundreds of MeV and heat plasma
  to tens of MK, but the physical processes behind these phenomena
  remain poorly understood. In intense (GOES M- and X-class) flares,
  in addition to the common 10-25 MK plasma thought to be the result
  of chromospheric evaporation, even hotter plasma (up to 50 MK) may
  be directly heated in the corona. While observations of hard X-ray
  bremmstrahlung directly probe the non-thermal electron population, for
  large flares, the spectra below 20-30 keV are typically dominated by
  this strong thermal emission. The low-energy extent of the non-thermal
  spectrum can be only loosely quantified, resulting in significant
  implications for calculating flare energy budgets and for constraining
  possible acceleration mechanisms. A precise characterization of the
  thermal electron population is imperative, and this requires an equally
  precise characterization of the thermal emission. Extreme ultraviolet
  observations from the EUV Variability Experiment (EVE) on-board the
  Solar Dynamics Observatory (SDO), combined with X-ray data from the
  Reuven Ramaty High Energy Spectroscopic Imager (RHESSI), currently offer
  the most comprehensive view of the flare temperature distribution. EVE
  observes EUV emission lines with peak formation temperatures of 2-20
  MK, while RHESSI observes the X-ray bremsstrahlung of hot, 10-50 MK
  plasma; combined, the two instruments cover the full range of flare
  plasma temperatures. Previously, we have calculated differential
  emission measures (DEMs) using EVE and RHESSI independently, for a
  small number of flares, and showed that they tend to agree well in the
  10-20 MK region, where their responses overlap, but that, as expected,
  they disagree significantly outside this range, where the DEM is
  poorly constrained by one instrument or the other, exemplifying the
  need for a unified solution. Recently, we have developed a technique
  for determining flare DEMs using both EVE and RHESSI simultaneously,
  with each instrument constraining the other. We apply this technique
  to a number of synthetic test cases to show that it robustly recovers
  the input test DEMs, and then show results of analyzing real data from
  two intense, X-class flares. Through this technique, for the first
  time, we can determine self-consistent DEMs over the complete flare
  temperature range of 3-50 MK, and this precise determination of the
  thermal emission will later enable detailed studies of the non-thermal
  electron populations, as well.

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

---------------------------------------------------------
Title: Exploring Thermal and Non-Thermal Flare Emission with EVE
    and RHESSI
Authors: McTiernan, J. M.; Warren, H. P.; Caspi, A.
2012AGUFMSH52B..02M    Altcode:
  Solar flares accelerate electrons up to hundreds of MeV and heat plasma
  to tens of MK, but the physical processes behind these phenomena remain
  poorly understood. In large (GOES M- and X-class) flares, in addition
  to the 10-25 MK plasma thought to be the result of chromospheric
  evaporation, even hotter plasma (up to 50 MK) may be directly heated
  in the corona. While observations of hard X-ray bremmstrahlung
  directly probe the non-thermal electron population, for large flares
  the spectra below 20-30 keV are typically dominated by this strong
  thermal emission. The low energy extent of the non-thermal spectrum
  can be only loosely quantified, resulting in significant implications
  for calculating flare energy budgets and for constraining possible
  acceleration mechanisms. A precise characterization of the non-thermal
  electron population requires an equally precise characterization of
  the thermal emission. Extreme ultraviolet observations from the EUV
  Variability Experiment (EVE) on-board the Solar Dynamics Observatory
  (SDO), combined with X-ray data from the Reuven Ramaty High Energy
  Spectroscopic Imager (RHESSI), currently offer the most comprehensive
  view of the flare temperature distribution. EVE observes EUV emission
  lines with peak formation temperatures of 2-20 MK, while RHESSI observes
  the X-ray bremsstrahlung of hot, 10-50 MK plasma; combined, the two
  instruments cover the full range of flare plasma temperatures. We
  have calculated differential emission measures (DEMs), using EVE and
  RHESSI independently, for a small number of flares. In this work we
  concentrate on comparing the observed DEM functions from EVE and RHESSI
  with each other, during different phases of flares, for the purpose
  of cross-calibration of the two instruments. When cross-calibration
  is successful, we will combine the data from the two instruments to
  create a DEM function for the temperature range up to 50 MK.

---------------------------------------------------------
Title: Chromospheric Evaporation in an M1.8 Flare Observed by the
    Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode
Authors: Doschek, G. A.; Warren, H. P.
2012AGUFMSH52B..04D    Altcode:
  We discuss observations of chromospheric evaporation for a flare
  that occurred on 9 March 2012 near 03:30 UT obtained from the
  Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft. This was a multiple event with a strong energy input
  that reached the M1.8 class when observed by EIS. EIS was in raster
  mode and fortunately the slit reached almost the exact location of a
  significant energy input. Also, fortunately EIS obtained a full-CCD
  spectrum of the flare, i.e., the entire CCD was readout so that data
  were obtained for about the 500 lines identified in the EIS wavelength
  ranges. Chromospheric evaporation characterized by 150-200 km/s upflows
  was observed in several locations in multi-million degree spectral lines
  of flare ions such as Fe XXII, Fe XXIII, Fe XXIV, with simultaneous 20 -
  60 km/s upflows in a host of million degree coronal lines from ions such
  as Fe XI - Fe XVI. The behavior of cooler, transition region ions such
  as O VI, Fe VIII, He II, and Fe X is more complex. At a point close
  to strong energy input, the flare ions reveal an isothermal source
  with a temperature close to 14 MK. At this point there is a strong
  downflow in cooler active region lines from ions such as Fe XIII
  and Fe XIV. Electron densities were obtained from density sensitive
  lines ratios from Fe XIII and Fe XIV. The results to be presented
  are refined from the preliminary data given above and combined with
  context AIA observations for a comparison with predictions of models
  of chromospheric evaporation as envisaged in the Standard Flare Model.

---------------------------------------------------------
Title: A Systematic Survey of High Temperature Emission in Solar
    Active Regions
Authors: Warren, H. P.
2012AGUFMSH31B..01W    Altcode:
  The temperature structure of the solar corona holds many important
  clues as to how the solar atmosphere is heated. Recent observations
  with EIS/Hinode and AIA/SDO have shown that well constrained temperature
  measurements can be made over a wide range of solar conditions. In this
  talk I will present results from a systematic study of the differential
  emission measure distribution in 15 active region cores. We focus on
  measurements in the "inter-moss" region, that is, the region between
  the loop footpoints, where the observations are easier to interpret. To
  reduce the uncertainties at the highest temperatures we present a
  new method for isolating the Fe XVIII emission in the AIA/SDO 94
  channel. The resulting differential emission measure distributions
  show that the temperature distribution in an active region core is
  often strongly peaked near 4MK. We will compare these results to
  the analysis of evolving million degree loops, which show a similar,
  sharply peaked temperature distribution. This work was sponsored by
  the Office of Naval Research and by NASA

---------------------------------------------------------
Title: The Fundamental Structure of Coronal Loops
Authors: Winebarger, A. R.; Warren, H. P.; Cirtain, J. W.; Kobayashi,
   K.; Korreck, K. E.; Golub, L.; Kuzin, S.; Walsh, R. W.; DeForest,
   C.; De Pontieu, B.; Title, A. M.; Weber, M.
2012AGUFMSH31B..06W    Altcode:
  During the past ten years, solar physicists have attempted to infer the
  coronal heating mechanism by comparing observations of coronal loops
  with hydrodynamic model predictions. These comparisons often used
  the addition of sub-resolution strands to explain the observed loop
  properties. On July 11, 2012, the High Resolution Coronal Imager (Hi-C)
  was launched on a sounding rocket. This instrument obtained images of
  the solar corona was 0.2-0.3” resolution in a narrowband EUV filter
  centered around 193 Angstroms. In this talk, we will compare these
  high resolution images to simultaneous density measurements obtained
  with the Extreme Ultraviolet Imaging Spectrograph (EIS) on Hinode to
  determine whether the structures observed with Hi-C are resolved.

---------------------------------------------------------
Title: Computing the Solar EUV Irradiance at Wavelengths Below 450 Å
Authors: Warren, H. P.
2012AGUFMSH13C2270W    Altcode:
  The solar EUV irradiance plays a central role in determining the state
  of the Earth's upper atmosphere. The EUV irradiance at the shortest
  wavelengths, which is highly variable over time scales from seconds
  to decades, is particularly important for many aspects of space
  weather. Systematic spectrally resolved observations at the shortest
  EUV wavelengths, however, have been rare and there is a need to develop
  a methodology for estimating and forecasting the solar irradiance at
  all EUV wavelengths from sparse data sets. The AIA on SDO provides full
  Sun solar images in 7 narrow EUV wavelength ranges. These channels were
  selected to provide complete thermal coverage of the corona and allow
  for calculation of the differential emission measure distribution. In
  this presentation we report on our efforts to use AIA DEM calculations
  to estimate the solar EUV irradiance at wavelength below 450 Å,
  where the emission is predominately optically thin. To validate our
  AIA DEM calculations we have performed extensive comparisons with
  simultaneous observations from the EIS instrument on Hinode and find
  that with the proper constraints we can generally reproduce the results
  obtained with detailed spectroscopic observations using AIA. We also
  anticipate presenting comparisons with existing time series of QEUV,
  the integrated solar irradiance at wavelengths below 450 Å.

---------------------------------------------------------
Title: Hinode/EIS measurements of Abundances in Solar Active Region
    Outflows
Authors: Brooks, D.; Warren, H. P.
2012AGUFMSH52A..04B    Altcode:
  Peripheral outflows appear to be a common feature of active regions,
  and may be a significant source of the slow speed solar wind. Spectral
  line profiles from the Hinode EUV Imaging Spectrometer (EIS) show that
  the bulk outflows reach speeds of ~50km/s with a much faster component
  reaching hundreds of km/s. I will review recent measurements of the
  elemental composition of the outflows obtained by EIS, with particular
  attention paid to AR 10978 that was observed as it crossed the solar
  disk in December 2007. EIS measurements show that the temperature
  distribution of the outflows is dominated by coronal emission, and
  that plasma with a slow wind-like composition flowed from the edge of
  AR 10978 for at least five days. Furthermore, when the outflow from
  the Western side was favorably oriented in the Earth direction, the
  composition was found to match the value measured a few days later by
  ACE/SWICS. The composition of the high speed component of the outflows
  was also found to be similar to that of the slow speed wind, implying
  that it may also be a contributor. Observations and models indicate
  that it takes time for plasma to evolve to the enhanced composition
  typical of the slow wind, suggesting that the material in the outflows
  is trapped on closed loops before escaping, perhaps by interchange
  reconnection. The results, therefore, also identify the high speed
  component of the plasma as having a coronal origin. A significant
  constraint on the mechanisms that drive the outflows.

---------------------------------------------------------
Title: A Systematic Survey of High-temperature Emission in Solar
    Active Regions
Authors: Warren, Harry P.; Winebarger, Amy R.; Brooks, David H.
2012ApJ...759..141W    Altcode: 2012arXiv1204.3220W
  The recent analysis of observations taken with the EUV Imaging
  Spectrometer and X-Ray Telescope instruments on Hinode suggests that
  well-constrained measurements of the temperature distribution in solar
  active regions can finally be made. Such measurements are critical
  for constraining theories of coronal heating. Past analysis, however,
  has suffered from limited sample sizes and large uncertainties at
  temperatures between 5 and 10 MK. Here we present a systematic study
  of the differential emission measure distribution in 15 active region
  cores. We focus on measurements in the "inter-moss" region, that is, the
  region between the loop footpoints, where the observations are easier
  to interpret. To reduce the uncertainties at the highest temperatures
  we present a new method for isolating the Fe XVIII emission in the
  AIA/SDO 94 Å channel. The resulting differential emission measure
  distributions confirm our previous analysis showing that the temperature
  distribution in an active region core is often strongly peaked near 4
  MK. We characterize the properties of the emission distribution as a
  function of the total unsigned magnetic flux. We find that the amount
  of high-temperature emission in the active region core is correlated
  with the total unsigned magnetic flux, while the emission at lower
  temperatures, in contrast, is inversely related. These results provide
  compelling evidence that high-temperature active region emission is
  often close to equilibrium, although weaker active regions may be
  dominated by evolving million degree loops in the core.

---------------------------------------------------------
Title: The Coronal Source of Extreme-ultraviolet Line Profile
    Asymmetries in Solar Active Region Outflows
Authors: Brooks, David H.; Warren, Harry P.
2012ApJ...760L...5B    Altcode: 2012arXiv1210.1274B
  High-resolution spectra from the Hinode EUV Imaging Spectrometer have
  revealed that coronal spectral line profiles are sometimes asymmetric,
  with a faint enhancement in the blue wing on the order of 100 km
  s<SUP>-1</SUP>. These asymmetries could be important since they may
  be subtle yet diagnostically useful signatures of coronal heating or
  solar wind acceleration processes. It has also been suggested that
  they are signatures of chromospheric jets supplying mass and energy
  to the corona. Until now, however, there have been no studies of the
  physical properties of the plasma producing the asymmetries. Here we
  identify regions of asymmetric profiles in the outflows of AR 10978
  using an asymmetric Gaussian function and extract the intensities
  of the faint component using multiple Gaussian fits. We then derive
  the temperature structure and chemical composition of the plasma
  producing the asymmetries. We find that the asymmetries are dependent
  on temperature, and are clearer and stronger in coronal lines. The
  temperature distribution peaks around 1.4-1.8 MK with an emission
  measure at least an order of magnitude larger than that at 0.6
  MK. The first ionization potential bias is found to be 3-5, implying
  that the high-speed component of the outflows may also contribute to
  the slow-speed wind. Observations and models indicate that it takes
  time for plasma to evolve to a coronal composition, suggesting that
  the material is trapped on closed loops before escaping, perhaps by
  interchange reconnection. The results, therefore, identify the plasma
  producing the asymmetries as having a coronal origin.

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

---------------------------------------------------------
Title: Constraints on the Heating Time Scale in Active Regions
Authors: Brooks, D. H.; Warren, H. P.
2012ASPC..454..189B    Altcode:
  Understanding the heating time scale is important for constraining
  models of active region emission. Hinode observations of moss at the
  bases of high temperature active region core loops are allowing us to
  study this problem in unprecedented detail. Here we discuss some of
  our recent results studying the variability of moss properties such as
  intensity, magnetic flux, Doppler and non-thermal velocity. We find that
  most of these quantities are relatively constant. One interpretation is
  that the heating is therefore effectively steady , i.e., heating events
  occur with a rapid repetition rate. Alternatively, the heating could be
  low frequency, but only if it occurs on sub-resolution spatial scales.

---------------------------------------------------------
Title: Spectroscopic Observations of Fe XVIII in Solar Active Regions
Authors: Teriaca, Luca; Warren, Harry P.; Curdt, Werner
2012ApJ...754L..40T    Altcode: 2012arXiv1206.4228T
  The large uncertainties associated with measuring the amount of
  high temperature emission in solar active regions (ARs) represents
  a significant impediment to making progress on the coronal heating
  problem. Most current observations at temperatures of 3 MK and above
  are taken with broadband soft X-ray instruments. Such measurements
  have proven difficult to interpret unambiguously. Here, we present the
  first spectroscopic observations of the Fe XVIII 974.86 Å emission
  line in an on-disk AR taken with the SUMER instrument on SOHO. Fe
  XVIII has a peak formation temperature of 7.1 MK and provides important
  constraints on the amount of impulsive heating in the corona. Detailed
  evaluation of the spectra and comparison of the SUMER data with soft
  X-ray images from the X-Ray Telescope on Hinode confirm that this line
  is unblended. We also compare the spectroscopic data with observations
  from the Atmospheric Imaging Assembly (AIA) 94 Å channel on the Solar
  Dynamics Observatory. The AIA 94 Å channel also contains Fe XVIII, but
  is blended with emission formed at lower temperatures. We find that it
  is possible to remove the contaminating blends and form relatively pure
  Fe XVIII images that are consistent with the spectroscopic observations
  from SUMER. The observed spectra also contain the Ca XIV 943.63 Å
  line that, although a factor 2-6 weaker than the Fe XVIII 974.86 Å
  line, allows us to probe the plasma around 3.5 MK. The observed ratio
  between the two lines indicates (isothermal approximation) that most
  of the plasma in the brighter Fe XVIII AR loops is at temperatures
  between 3.5 and 4 MK.

---------------------------------------------------------
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 EUV and XUV energy input to thermosphere on solar
    rotation time scales derived from photoelectron observations.
Authors: Peterson, W. K. Bill; Solomon, Stanley; Warren, Harry;
   Fontenla, Juan; Woods, Thomas; Richards, Phil; Chamberlin, Phillip;
   Tobiska, W. Kent
2012cosp...39.1489P    Altcode: 2012cosp.meet.1489P
  Solar radiation below ~100 nm produces photoelectrons, a substantial
  portion of the F region ionization, most of the E region ionization,
  and drives chemical reactions in the thermosphere. Unquantified
  uncertainties in thermospheric models exist because of uncertainties
  in solar irradiance models used to fill spectral and temporal gaps in
  solar irradiance observations. We investigate uncertainties in solar
  energy input to the thermosphere on solar rotation time scales using
  photoelectron observations from the FAST satellite. We compare observed
  and modeled photoelectron energy spectra using two photoelectron
  production codes driven by five different solar irradiance models. We
  observe about 1.7 per cent of the ionizing solar irradiance power in the
  escaping photoelectron flux. Most of the code/model pairs used reproduce
  the average escaping photoelectron flux over a 109-day interval in
  late 2006. The code/model pairs we used do not completely reproduce
  the observed spectral and solar cycle variations in photoelectron power
  density. For the interval examined, 30 per cent of the variability in
  photoelectron power density with equivalent wavelengths between 18
  and 45 nm was not captured in the code/model pairs. For equivalent
  wavelengths below ~ 16 nm, most of the variability was missed. This
  result implies that thermospheric model runs based on the solar
  irradiance models we tested systematically underestimate the energy
  input from ionizing radiation on solar rotation time scales.

---------------------------------------------------------
Title: A Comprehensive View of the Temperature Distribution in Solar
    Flares from EVE and RHESSI
Authors: Caspi, Amir; McTiernan, J. M.; Warren, H. P.
2012AAS...22020411C    Altcode:
  Solar flares accelerate electrons up to hundreds of MeV and heat
  plasma up to tens of MK, but the physical processes behind these
  phenomena remain poorly understood. While the ubiquitous 10-25 MK
  plasma is commonly accepted to result from chromospheric evaporation,
  evidence suggests that in intense (GOES M- and X-class) flares, the
  hottest, 20-50 MK plasma is directly heated in the corona, although
  the heating mechanism and its connection to the flare-accelerated
  non-thermal electrons is not yet understood. While observations of
  hard X-ray bremmstrahlung directly probe the non-thermal electron
  population, the spectra below 20-30 keV are typically dominated by
  strong thermal emission. The low-energy extent of the non-thermal
  spectrum can thus be only loosely quantified, which has significant
  implications for calculating flare energy budgets and for constraining
  possible acceleration mechanisms. Hence, a precise characterization
  of the thermal electron population is imperative. <P />New extreme
  ultraviolet observations from the EUV Variability Experiment (EVE)
  on-board the Solar Dynamics Observatory (SDO), combined with X-ray data
  from the Reuven Ramaty High Energy Spectroscopic Imager (RHESSI), offer
  the most comprehensive view into the flare temperature distribution to
  date. EVE observes a wealth of EUV emission lines with peak formation
  temperatures of 2-20 MK, while RHESSI observes the X-ray bremsstrahlung
  of hot, 10-50 MK plasmas; combined, the two instruments have excellent
  temperature sampling and coverage over the full range of flare plasma
  temperatures. We have calculated differential emission measures
  (DEMs) using EVE and RHESSI independently, for separately observed
  events. We present a novel method of combining simultaneous EVE and
  RHESSI observations to determine the flare DEM, and its evolution,
  over the full 1-100 MK range during intense M/X flares. We present
  preliminary results from the 2011-Feb-15 X2.2 flare, and compare with
  the RHESSI non-thermal emission to discuss the implications for flare
  plasma heating.

---------------------------------------------------------
Title: Evidence of a Connection Between Active Region Outflows and
    the Solar Wind
Authors: Brooks, D. H.; Warren, H. P.
2012ASPC..455..327B    Altcode:
  We present new evidence of a connection between active region (AR)
  outflows and the slow speed solar wind from chemical composition
  measurements made by the EUV Imaging Spectrometer (EIS) on Hinode. By
  combining the differential emission measure (DEM) distribution derived
  using low First Ionization Potential (FIP) elements (Fe and Si) with
  the modeling of the high FIP element S, we are able to measure the
  degree of FIP bias in an observed region. We have applied this analysis
  to the outflow areas of AR 10978 observed in December 2007. Since the
  results of our study have already been presented by Brooks &amp; Warren
  (2011), we use this short conference proceeding to show one illustrative
  example and the methodology in detail. We focus on the western outflow
  from AR 10978 observed on December 11 and show that the FIP bias of
  3.4 matches the value of 3.5 measured in situ three days later at
  Earth by the Solar Wind Ion Composition Spectrometer (SWICS) on the
  ACE spacecraft. We consider this to be compelling evidence that the
  plasma in the outflow region really travels to the slow wind at Earth.

---------------------------------------------------------
Title: Evidence for Two Separate But Interlaced Components of the
    Chromospheric Magnetic Field
Authors: Muglach, Karin; Reardon, K.; Wang, Y.; Warren, H.
2012AAS...22012403M    Altcode:
  Chromospheric fibrils are generally thought to trace out horizontal
  magnetic fields that fan out from flux concentrations in the
  photosphere. A high-resolution (0.2") image taken in the core of the
  Ca II 854.2 nm line shows the dark fibrils within an active region
  remnant as fine, looplike features that are aligned parallel to each
  other and have lengths on the order of a supergranular diameter ( 30
  Mm). Comparison with a line-of-sight magnetogram confirms that the
  fibrils are centered above intranetwork areas, with one end rooted
  just inside <P />the neighboring plage or strong unipolar network
  but the other endpoint less clearly defined. Focusing on a particular
  arcade-like structure lying entirely on one side of a filament channel
  (large-scale polarity inversion), we find that the total amount of
  positive-polarity flux underlying this “fibril arcade” is 50 times
  greater than the total amount of negative-polarity flux. Thus, if the
  fibrils represent closed loops, they must consist of very weak fields
  (in terms of flux density), which are interpenetrated by a more vertical
  field that contains most of the flux. This surprising result suggests
  that the fibrils in unipolar regions connect the network to the nearby
  intranetwork flux, while the bulk of the network flux is diverted
  upward into the corona and connects to remote regions of the opposite
  polarity. We conclude that the chromospheric field near the edge of
  the network has an interlaced structure resembling that in sunspot
  penumbrae, with the fibrils representing the low-lying horizontal flux
  that remains trapped within the highly nonpotential chromospheric layer.

---------------------------------------------------------
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: Solar EUV and XUV energy input to thermosphere on solar
    rotation time scales derived from photoelectron observations
Authors: Peterson, W. K.; Woods, T. N.; Fontenla, J. M.; Richards,
   P. G.; Chamberlin, P. C.; Solomon, S. C.; Tobiska, W. K.; Warren, H. P.
2012JGRA..117.5320P    Altcode: 2012JGRA..11705320P
  Solar radiation below ∼100 nm produces photoelectrons, a substantial
  portion of the F region ionization, most of the E region ionization,
  and drives chemical reactions in the thermosphere. Unquantified
  uncertainties in thermospheric models exist because of uncertainties
  in solar irradiance models used to fill spectral and temporal gaps
  in solar irradiance observations. We investigate uncertainties
  in solar energy input to the thermosphere on solar rotation time
  scales using photoelectron observations from the FAST satellite. We
  compare observed and modeled photoelectron energy spectra using two
  photoelectron production codes driven by five different solar irradiance
  models. We observe about 1.7% of the ionizing solar irradiance power
  in the escaping photoelectron flux. Most of the code/model pairs
  used reproduce the average escaping photoelectron flux over a 109-day
  interval in late 2006. The code/model pairs we used do not completely
  reproduce the observed spectral and solar rotation variations in
  photoelectron power density. For the interval examined, 30% of the
  variability in photoelectron power density with equivalent wavelengths
  between 18 and 45 nm was not captured in the code/model pairs. For
  equivalent wavelengths below ∼16 nm, most of the variability was
  missed. This result implies that thermospheric model runs based on
  the solar irradiance models we tested systematically underestimate
  the energy input from ionizing radiation on solar rotation time scales.

---------------------------------------------------------
Title: Hinode/EIS Flare Spectra During RHESSI Hard X-ray Bursts
Authors: Young, Peter R.; Warren, H.; Doschek, G.
2012AAS...22020442Y    Altcode:
  The standard flare model requires a beam of non-thermal electrons
  - generated at the coronal flare site - to hit the chromosphere
  and trigger heating and chromospheric evaporation. Ultraviolet
  spectrometers allow the heated, evaporating plasma to be observed
  and its properties measured. Observations of a M3 flare observed in
  2011 September with Hinode/EIS, RHESSI and SDO/AIA will be presented,
  revealing the physical conditions in the flare ribbons at the time of
  the hard X-ray bursts. At the hottest temperatures (20 MK) upflowing
  plasma with speeds up to 500 km/s are found co-spatial with stationary
  plasma, while at cooler temperatures (0.5-2 MK) small downflows and
  large non-thermal broadening are found. These observations will be
  compared with predictions from multi-strand hydrodynamic simulations
  that take the RHESSI-derived electron beam spectrum as input.

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

---------------------------------------------------------
Title: Coronal Cells
Authors: Sheeley, N. R., Jr.; Warren, H. P.
2012ApJ...749...40S    Altcode:
  We have recently noticed cellular features in Fe XII 193 Å images of
  the 1.2 MK corona. They occur in regions bounded by a coronal hole
  and a filament channel, and are centered on flux elements of the
  photospheric magnetic network. Like their neighboring coronal holes,
  these regions have minority-polarity flux that is ~0.1-0.3 times
  their flux of majority polarity. Consequently, the minority-polarity
  flux is "grabbed" by the majority-polarity flux to form low-lying
  loops, and the remainder of the network flux escapes to connect with
  its opposite-polarity counterpart in distant active regions of the
  Sun. As these regions are carried toward the limb by solar rotation,
  the cells disappear and are replaced by linear plumes projecting toward
  the limb. In simultaneous views from the Solar Terrestrial Relations
  Observatory and Solar Dynamics Observatory spacecraft, these plumes
  project in opposite directions, extending away from the coronal hole in
  one view and toward the hole in the other view, suggesting that they are
  sky-plane projections of the same radial structures. We conclude that
  these regions are composed of closely spaced radial plumes, extending
  upward like candles on a birthday cake and visible as cells when seen
  from above. We suppose that a coronal hole has this same discrete,
  cellular magnetic structure, but that it is not seen until the
  encroachment of opposite-polarity flux closes part or all of the hole.

---------------------------------------------------------
Title: Defining the "Blind Spot" of Hinode EIS and XRT Temperature
    Measurements
Authors: Winebarger, Amy R.; Warren, Harry P.; Schmelz, Joan T.;
   Cirtain, Jonathan; Mulu-Moore, Fana; Golub, Leon; Kobayashi, Ken
2012ApJ...746L..17W    Altcode:
  Observing high-temperature, low emission measure plasma is key to
  unlocking the coronal heating problem. With current instrumentation,
  a combination of EUV spectral data from Hinode Extreme-ultraviolet
  Imaging Spectrometer (EIS; sensitive to temperatures up to 4 MK)
  and broadband filter data from Hinode X-ray Telescope (XRT; sensitive
  to higher temperatures) is typically used to diagnose the temperature
  structure of the observed plasma. In this Letter, we demonstrate that a
  "blind spot" exists in temperature-emission measure space for combined
  Hinode EIS and XRT observations. For a typical active region core with
  significant emission at 3-4 MK, Hinode EIS and XRT are insensitive
  to plasma with temperatures greater than ~6 MK and emission measures
  less than ~10<SUP>27</SUP> cm<SUP>-5</SUP>. We then demonstrate that
  the temperature and emission measure limits of this blind spot depend
  upon the temperature distribution of the plasma along the line of sight
  by considering a hypothetical emission measure distribution sharply
  peaked at 1 MK. For this emission measure distribution, we find that
  EIS and XRT are insensitive to plasma with emission measures less
  than ~10<SUP>26</SUP> cm<SUP>-5</SUP>. We suggest that a spatially and
  spectrally resolved 6-24 Å spectrum would improve the sensitivity to
  these high-temperature, low emission measure plasma.

---------------------------------------------------------
Title: Extreme Ultraviolet Variability Experiment (EVE) on the
Solar Dynamics Observatory (SDO): Overview of Science Objectives,
    Instrument Design, Data Products, and Model Developments
Authors: Woods, T. N.; Eparvier, F. G.; Hock, R.; Jones, A. R.;
   Woodraska, D.; Judge, D.; Didkovsky, L.; Lean, J.; Mariska, J.;
   Warren, H.; McMullin, D.; Chamberlin, P.; Berthiaume, G.; Bailey,
   S.; Fuller-Rowell, T.; Sojka, J.; Tobiska, W. K.; Viereck, R.
2012SoPh..275..115W    Altcode:
  The highly variable solar extreme ultraviolet (EUV) radiation is
  the major energy input to the Earth's upper atmosphere, strongly
  impacting the geospace environment, affecting satellite operations,
  communications, and navigation. The Extreme ultraviolet Variability
  Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will
  measure the solar EUV irradiance from 0.1 to 105 nm with unprecedented
  spectral resolution (0.1 nm), temporal cadence (ten seconds), and
  accuracy (20%). EVE includes several irradiance instruments: The
  Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence
  spectrograph that measures the solar EUV irradiance in the 5 to 37 nm
  range with 0.1-nm resolution, and the MEGS-B is a normal-incidence,
  dual-pass spectrograph that measures the solar EUV irradiance in the
  35 to 105 nm range with 0.1-nm resolution. To provide MEGS in-flight
  calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV
  irradiance in broadbands between 0.1 and 39 nm, and a MEGS-Photometer
  measures the Sun's bright hydrogen emission at 121.6 nm. The EVE data
  products include a near real-time space-weather product (Level 0C),
  which provides the solar EUV irradiance in specific bands and also
  spectra in 0.1-nm intervals with a cadence of one minute and with a
  time delay of less than 15 minutes. The EVE higher-level products
  are Level 2 with the solar EUV irradiance at higher time cadence
  (0.25 seconds for photometers and ten seconds for spectrographs) and
  Level 3 with averages of the solar irradiance over a day and over each
  one-hour period. The EVE team also plans to advance existing models of
  solar EUV irradiance and to operationally use the EVE measurements in
  models of Earth's ionosphere and thermosphere. Improved understanding
  of the evolution of solar flares and extending the various models to
  incorporate solar flare events are high priorities for the EVE team.

---------------------------------------------------------
Title: Plasma Diagnostics of an EIT Wave Observed by Hinode/EIS
    and SDO/AIA
Authors: Veronig, A. M.; Gömöry, P.; Kienreich, I. W.; Muhr, N.;
   Vršnak, B.; Temmer, M.; Warren, H. P.
2011ApJ...743L..10V    Altcode: 2011arXiv1111.3505V
  We present plasma diagnostics of an Extreme-Ultraviolet
  Imaging Telescope (EIT) wave observed with high cadence in
  Hinode/Extreme-Ultraviolet Imaging Spectrometer (EIS) sit-and-stare
  spectroscopy and Solar Dynamics Observatory/Atmospheric Imaging
  Assembly imagery obtained during the HOP-180 observing campaign on 2011
  February 16. At the propagating EIT wave front, we observe downward
  plasma flows in the EIS Fe XII, Fe XIII, and Fe XVI spectral lines
  (log T ≈ 6.1-6.4) with line-of-sight (LOS) velocities up to 20
  km s<SUP>-1</SUP>. These redshifts are followed by blueshifts with
  upward velocities up to -5 km s<SUP>-1</SUP> indicating relaxation
  of the plasma behind the wave front. During the wave evolution, the
  downward velocity pulse steepens from a few km s<SUP>-1</SUP> up to 20
  km s<SUP>-1</SUP> and subsequently decays, correlated with the relative
  changes of the line intensities. The expected increase of the plasma
  densities at the EIT wave front estimated from the observed intensity
  increase lies within the noise level of our density diagnostics from
  EIS Fe XIII 202/203 Å line ratios. No significant LOS plasma motions
  are observed in the He II line, suggesting that the wave pulse was not
  strong enough to perturb the underlying chromosphere. This is consistent
  with the finding that no Hα Moreton wave was associated with the
  event. The EIT wave propagating along the EIS slit reveals a strong
  deceleration of a ≈ -540 m s<SUP>-2</SUP> and a start velocity of v
  <SUB>0</SUB> ≈ 590 km s<SUP>-1</SUP>. These findings are consistent
  with the passage of a coronal fast-mode MHD wave, pushing the plasma
  downward and compressing it at the coronal base.

---------------------------------------------------------
Title: Observations of Reconnecting Flare Loops with the Atmospheric
    Imaging Assembly
Authors: Warren, Harry P.; O'Brien, Casey M.; Sheeley, Neil R., Jr.
2011ApJ...742...92W    Altcode: 2011arXiv1109.2474W
  Perhaps the most compelling evidence for the role of magnetic
  reconnection in solar flares comes from the supra-arcade downflows that
  have been observed above many post-flare loop arcades. These downflows
  are thought to be related to highly non-potential field lines that have
  reconnected and are propagating away from the current sheet. We present
  new observations of supra-arcade downflows taken with the Atmospheric
  Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). The
  morphology and dynamics of the downflows observed with AIA provide new
  evidence for the role of magnetic reconnection in solar flares. With
  these new observations we are able to measure downflows originating
  at larger heights than in previous studies. We find, however,
  that the initial velocities measured here (~144 km s<SUP>-1</SUP>)
  are well below the Alfvén speed expected in the lower corona, and
  consistent with previous results. We also find no evidence that the
  downflows brighten with time, as would be expected from chromospheric
  evaporation. These observations suggest that simple two-dimensional
  models cannot explain the detailed observations of solar flares.

---------------------------------------------------------
Title: Evidence for Two Separate but Interlaced Components of the
    Chromospheric Magnetic Field
Authors: Reardon, K. P.; Wang, Y. -M.; Muglach, K.; Warren, H. P.
2011ApJ...742..119R    Altcode:
  Chromospheric fibrils are generally thought to trace out low-lying,
  mainly horizontal magnetic fields that fan out from flux concentrations
  in the photosphere. A high-resolution (~0farcs1 pixel<SUP>-1</SUP>)
  image, taken in the core of the Ca II 854.2 nm line and covering
  an unusually large area, shows the dark fibrils within an active
  region remnant as fine, looplike features that are aligned parallel
  to each other and have lengths comparable to a supergranular
  diameter. Comparison with simultaneous line-of-sight magnetograms
  confirms that the fibrils are centered above intranetwork areas
  (supergranular cell interiors), with one end rooted just inside the
  neighboring plage or strong unipolar network but the other endpoint
  less clearly defined. Focusing on a particular arcade-like structure
  lying entirely on one side of a filament channel (large-scale polarity
  inversion), we find that the total amount of positive-polarity flux
  underlying this "fibril arcade" is ~50 times greater than the total
  amount of negative-polarity flux. Thus, if the fibrils represent closed
  loops, they must consist of very weak fields (in terms of total magnetic
  flux), which are interpenetrated by a more vertical field that contains
  most of the flux. This surprising result suggests that the fibrils in
  unipolar regions connect the network to the nearby intranetwork flux,
  while the bulk of the network flux links to remote regions of the
  opposite polarity, forming a second, higher canopy above the fibril
  canopy. The chromospheric field near the edge of the network thus has
  an interlaced structure resembling that in sunspot penumbrae.

---------------------------------------------------------
Title: Cross-Calibration and Thermal Analysis with SDO/AIA
Authors: Boerner, P.; Warren, H. P.; Testa, P.; Weber, M.; Schrijver,
   C. J.
2011AGUFMSH13B1955B    Altcode:
  The measured intensity in each pixel of the images from SDO/AIA and
  similar narrowband EUV imagers can be used to perform quantitative
  analysis of the temperature and density of the plasma along the
  line of sight. This type of analysis depends very sensitively on the
  accuracy of the instrument calibration and the atomic physics models
  used to estimate the plasma emissivity. Unfortunately, it is difficult
  to assess the accuracy of these parameters, other than by verifying
  the consistency of datasets from different instruments and analysis
  techniques. Here we use differential emission measure models of the
  plasma temperature structure constrained by spectroscopic observations
  from SDO/EVE and Hinode/EIS to assess the AIA temperature response
  functions. The response functions generated using the CHIANTI database
  underestimate the emission from the non-flaring corona in the 94 and 131
  Å channels. We find empirical corrections to the temperature response
  functions for these channels that are internally consistent and provide
  good agreement with DEMs obtained from other instruments. We present an
  assessment of the reliability of thermal analysis using AIA data based
  on the current state of the instrument calibration and spectral models.

---------------------------------------------------------
Title: Can a Long Nanoflare Storm Explain the Observed Emission
    Measure Distributions in Active Region Cores?
Authors: Mulu-Moore, Fana M.; Winebarger, Amy R.; Warren, Harry P.
2011ApJ...742L...6M    Altcode: 2012arXiv1205.5486M
  All theories that attempt to explain the heating of the high-temperature
  plasma observed in the solar corona are based on short bursts of
  energy. The intensities and velocities measured in the cores of
  quiescent active regions, however, can be steady over many hours of
  observation. One heating scenario that has been proposed to reconcile
  such observations with impulsive heating models is the "long nanoflare
  storm," where short-duration heating events occur infrequently on many
  sub-resolution strands; the emission of the strands is then averaged
  together to explain the observed steady structures. In this Letter,
  we examine the emission measure distribution predicted for such a long
  nanoflare storm by modeling an arcade of strands in an active region
  core. Comparisons of the computed emission measure distributions with
  recent observations indicate that the long nanoflare storm scenario
  implies greater than five times more 1 MK emission than is actually
  observed for all plausible combinations of loop lengths, heating rates,
  and abundances. We conjecture that if the plasma had "super coronal"
  abundances, the model may be able to match the observations at low
  temperatures.

---------------------------------------------------------
Title: Using a Differential Emission Measure and Density Measurements
    in an Active Region Core to Test a Steady Heating Model
Authors: Winebarger, Amy R.; Schmelz, Joan T.; Warren, Harry P.;
   Saar, Steve H.; Kashyap, Vinay L.
2011ApJ...740....2W    Altcode: 2011arXiv1106.5057W
  The frequency of heating events in the corona is an important
  constraint on the coronal heating mechanisms. Observations indicate
  that the intensities and velocities measured in active region cores are
  effectively steady, suggesting that heating events occur rapidly enough
  to keep high-temperature active region loops close to equilibrium. In
  this paper, we couple observations of active region (AR) 10955 made
  with the X-Ray Telescope and the EUV Imaging Spectrometer on board
  Hinode to test a simple steady heating model. First we calculate the
  differential emission measure (DEM) of the apex region of the loops in
  the active region core. We find the DEM to be broad and peaked around
  3 MK. We then determine the densities in the corresponding footpoint
  regions. Using potential field extrapolations to approximate the loop
  lengths and the density-sensitive line ratios to infer the magnitude
  of the heating, we build a steady heating model for the active region
  core and find that we can match the general properties of the observed
  DEM for the temperature range of 6.3 &lt; log T &lt; 6.7. This model,
  for the first time, accounts for the base pressure, loop length,
  and distribution of apex temperatures of the core loops. We find that
  the density-sensitive spectral line intensities and the bulk of the
  hot emission in the active region core are consistent with steady
  heating. We also find, however, that the steady heating model cannot
  address the emission observed at lower temperatures. This emission may
  be due to foreground or background structures, or may indicate that the
  heating in the core is more complicated. Different heating scenarios
  must be tested to determine if they have the same level of agreement.

---------------------------------------------------------
Title: New Solar Extreme-ultraviolet Irradiance Observations during
    Flares
Authors: Woods, Thomas N.; Hock, Rachel; Eparvier, Frank; Jones,
   Andrew R.; Chamberlin, Phillip C.; Klimchuk, James A.; Didkovsky,
   Leonid; Judge, Darrell; Mariska, John; Warren, Harry; Schrijver,
   Carolus J.; Webb, David F.; Bailey, Scott; Tobiska, W. Kent
2011ApJ...739...59W    Altcode:
  New solar extreme-ultraviolet (EUV) irradiance observations from the
  NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment provide
  full coverage in the EUV range from 0.1 to 106 nm and continuously at
  a cadence of 10 s for spectra at 0.1 nm resolution and even faster,
  0.25 s, for six EUV bands. These observations can be decomposed into
  four distinct characteristics during flares. First, the emissions
  that dominate during the flare's impulsive phase are the transition
  region emissions, such as the He II 30.4 nm. Second, the hot coronal
  emissions above 5 MK dominate during the gradual phase and are highly
  correlated with the GOES X-ray. A third flare characteristic in the
  EUV is coronal dimming, seen best in the cool corona, such as the
  Fe IX 17.1 nm. As the post-flare loops reconnect and cool, many of
  the EUV coronal emissions peak a few minutes after the GOES X-ray
  peak. One interesting variation of the post-eruptive loop reconnection
  is that warm coronal emissions (e.g., Fe XVI 33.5 nm) sometimes exhibit
  a second large peak separated from the primary flare event by many
  minutes to hours, with EUV emission originating not from the original
  flare site and its immediate vicinity, but rather from a volume of
  higher loops. We refer to this second peak as the EUV late phase. The
  characterization of many flares during the SDO mission is provided,
  including quantification of the spectral irradiance from the EUV late
  phase that cannot be inferred from GOES X-ray diagnostics.

---------------------------------------------------------
Title: Constraints on the Heating of High-temperature Active Region
Loops: Observations from Hinode and the Solar Dynamics Observatory
Authors: Warren, Harry P.; Brooks, David H.; Winebarger, Amy R.
2011ApJ...734...90W    Altcode: 2010arXiv1009.5976W
  We present observations of high-temperature emission in the core
  of a solar active region using instruments on Hinode and the Solar
  Dynamics Observatory (SDO). These multi-instrument observations allow
  us to determine the distribution of plasma temperatures and follow the
  evolution of emission at different temperatures. We find that at the
  apex of the high-temperature loops the emission measure distribution
  is strongly peaked near 4 MK and falls off sharply at both higher and
  lower temperatures. Perhaps most significantly, the emission measure at
  0.5 MK is reduced by more than two orders of magnitude from the peak at
  4 MK. We also find that the temporal evolution in broadband soft X-ray
  images is relatively constant over about 6 hr of observing. Observations
  in the cooler SDO/Atmospheric Imaging Assembly (AIA) bandpasses
  generally do not show cooling loops in the core of the active region,
  consistent with the steady emission observed at high temperatures. These
  observations suggest that the high-temperature loops observed in the
  core of an active region are close to equilibrium. We find that it is
  possible to reproduce the relative intensities of high-temperature
  emission lines with a simple, high-frequency heating scenario where
  heating events occur on timescales much less than a characteristic
  cooling time. In contrast, low-frequency heating scenarios, which are
  commonly invoked to describe nanoflare models of coronal heating, do
  not reproduce the relative intensities of high-temperature emission
  lines and predict low-temperature emission that is approximately an
  order of magnitude too large. We also present an initial look at images
  from the SDO/AIA 94 Å channel, which is sensitive to Fe XVIII.

---------------------------------------------------------
Title: Flares Observed By Hinode During 14-18 February 2011
Authors: Young, Peter R.; Doschek, G. A.; Warren, H. P.
2011SPD....42.2213Y    Altcode: 2011BAAS..43S.2213Y
  Active region AR 11158 produced an X1 flare and several M flares during
  2011 February 14-18, and yielded the best set of flare observations
  captured by the Hinode satellite in four years. Finding the mechanisms
  responsible for flares was one of the major science goals of the Hinode
  mission, and data from AR 11158 will be presented to demonstrate how
  this goal is being achieved with Hinode data. A particular focus will
  be on relating plasma flows and temperature and density changes measured
  with the EIS instrument to the magnetic field evolution observed by SOT,
  and the coronal evolution observed with SDO/AIA.

---------------------------------------------------------
Title: Determining the Structure of Solar Coronal Loops Using Their
    Evolution
Authors: Mulu-Moore, Fana M.; Winebarger, Amy R.; Warren, Harry P.;
   Aschwanden, Markus J.
2011ApJ...733...59M    Altcode:
  Despite significant progress in understanding the dynamics of the
  corona, there remain several unanswered questions about the basic
  physical properties of coronal loops. Recent observations from
  different instruments have yielded contradictory results about some
  characteristics of coronal loops, specifically as to whether the
  observed loops are spatially resolved. In this paper, we examine the
  evolution of coronal loops through two extreme-ultraviolet filters
  and determine if they evolve as a single cooling strand. We measure
  the temporal evolution of eight active region loops previously
  studied and found to be isothermal and resolved by Aschwanden &amp;
  Nightingale. All eight loops appear in "hotter" TRACE filter images
  (Fe XII 195 Å) before appearing in the "cooler" (Fe IX/Fe X 171 Å)
  TRACE filter images. We use the measured delay between the two filters
  to calculate a cooling time and then determine if that cooling time is
  consistent with the observed lifetime of the loop. We do this twice:
  once when the loop appears (rise phase) and once when it disappears
  (decay phase). We find that only one loop appears consistent with a
  single cooling strand and hence could be considered to be resolved by
  TRACE. For the remaining seven loops, their observed lifetimes are
  longer than expected for a single cooling strand. We suggest that
  these loops could be formed of multiple cooling strands, each at a
  different temperature. These findings indicate that the majority of
  loops observed by TRACE are unresolved.

---------------------------------------------------------
Title: EUV Spectral Line Formation and the Temperature Structure of
Active Region Fan Loops: Observations with Hinode/EIS and SDO/AIA
Authors: Brooks, David H.; Warren, Harry P.; Young, Peter R.
2011ApJ...730...85B    Altcode: 2011arXiv1101.5240B
  With the aim of studying active region fan loops using observations
  from the Hinode EUV Imaging Spectrometer (EIS) and Solar Dynamics
  Observatory Atmospheric Imaging Assembly (AIA), we investigate a number
  of inconsistencies in modeling the absolute intensities of Fe VIII
  and Si VII lines, and address why spectroheliograms formed from these
  lines look very similar despite the fact that ionization equilibrium
  calculations suggest that they have significantly different formation
  temperatures: log(T<SUB>e</SUB> /K) = 5.6 and 5.8, respectively. It is
  important to resolve these issues because confidence has been undermined
  in their use for differential emission measure (DEM) analysis, and
  Fe VIII is the main contributor to the AIA 131 Å channel at low
  temperatures. Furthermore, the strong Fe VIII 185.213 Å and Si VII
  275.368 Å lines are the best EIS lines to use for velocity studies
  in the transition region, and for assigning the correct temperature
  to velocity measurements in the fans. We find that the Fe VIII 185.213
  Å line is particularly sensitive to the slope of the DEM, leading to
  disproportionate changes in its effective formation temperature. If
  the DEM has a steep gradient in the log(T<SUB>e</SUB> /K) = 5.6-5.8
  temperature range, or is strongly peaked, Fe VIII 185.213 Å and Si VII
  275.368 Å will be formed at the same temperature. We show that this
  effect explains the similarity of these images in the fans. Furthermore,
  we show that the most recent ionization balance compilations resolve the
  discrepancies in absolute intensities. With these difficulties overcome,
  we combine EIS and AIA data to determine the temperature structure of
  a number of fan loops and find that they have peak temperatures of
  0.8-1.2 MK. The EIS data indicate that the temperature distribution
  has a finite (but narrow) width &lt; log (σ_{T_e}/K) = 5.5 which,
  in one detailed case, is found to broaden substantially toward the
  loop base. AIA and EIS yield similar results on the temperature,
  emission measure magnitude, and thermal distribution in the fans,
  though sometimes the AIA data suggest a relatively larger thermal
  width. The result is that both the Fe VIII 185.213 Å and Si VII
  275.368 Å lines are formed at log(T<SUB>e</SUB> /K)~ 5.9 in the fans,
  and the AIA 131 Å response also shifts to this temperature.

---------------------------------------------------------
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: Establishing a Connection Between Active Region Outflows and
the Solar Wind: Abundance Measurements with EIS/Hinode
Authors: Brooks, David H.; Warren, Harry P.
2011ApJ...727L..13B    Altcode: 2010arXiv1009.4291B
  One of the most interesting discoveries from Hinode is the presence
  of persistent high-temperature high-speed outflows from the edges
  of active regions (ARs). EUV imaging spectrometer (EIS) measurements
  indicate that the outflows reach velocities of 50 km s<SUP>-1</SUP>
  with spectral line asymmetries approaching 200 km s<SUP>-1</SUP>. It
  has been suggested that these outflows may lie on open field lines
  that connect to the heliosphere, and that they could potentially
  be a significant source of the slow speed solar wind. A direct link
  has been difficult to establish, however. We use EIS measurements of
  spectral line intensities that are sensitive to changes in the relative
  abundance of Si and S as a result of the first ionization potential
  (FIP) effect, to measure the chemical composition in the outflow
  regions of AR 10978 over a 5 day period in 2007 December. We find that
  Si is always enhanced over S by a factor of 3-4. This is generally
  consistent with the enhancement factor of low FIP elements measured
  in situ in the slow solar wind by non-spectroscopic methods. Plasma
  with a slow wind-like composition was therefore flowing from the edge
  of the AR for at least 5 days. Furthermore, on December 10 and 11,
  when the outflow from the western side was favorably oriented in the
  Earth direction, the Si/S ratio was found to match the value measured
  a few days later by the Advanced Composition Explorer/Solar Wind Ion
  Composition Spectrometer. These results provide strong observational
  evidence for a direct connection between the solar wind, and the
  coronal plasma in the outflow regions.

---------------------------------------------------------
Title: Photoelectrons as a tool to evaluate spectral and temporal
    variations of solar EUV and XUV irradiance models over solar rotation
    and solar cycle time scales
Authors: Peterson, W. K.; Woods, T. N.; Fontenla, J. M.; Richards,
   P. G.; Tobiska, W.; Solomon, S. C.; Warren, H. P.
2010AGUFMSA33B1766P    Altcode:
  Solar radiation below 50 nm produces a substantial portion of the F
  region ionization and most of the E region ionization that drives
  chemical reactions in the thermosphere. Because of a lack of high
  temporal and spectral resolution Solar EUV and XUV observations,
  particularly below 27 nm, various solar irradiance models have
  been developed. We have developed a technique to use observations of
  escaping photoelectron fluxes from the FAST satellite and two different
  photoelectron production codes driven by model solar irradiance values
  to systematically examine differences between observed and calculated
  escaping photoelectron fluxes. We have compared modeled and observed
  photoelectron fluxes from the start of TIMED/SEE data availability
  (2002) to the end of FAST photoelectron observations (2009). Solar
  irradiance inputs included TIMED/SEE data, which is derived from a model
  below 27 nm, and the FISM Version 1, the SRPM predictive model based on
  solar observation, HEUVAC, S2000, and NRL, solar irradiance models. We
  used the GLOW and FLIP photoelectron production codes. We find that
  model photoelectron spectra generated using the HEUVAC solar irradiance
  model have the best overall agreement with observations. Photoelectron
  spectra generated with the the TIMED/SEE based FISM model best agree
  with the observations on solar cycle time scales. Below ~27 nm all but
  the HEUVAC solar irradiance model produces photoelectron fluxes that are
  systematically below observations. We also noted systematic differences
  in the photoelectron energy spectra below 25 eV produced by the GLOW
  and FLIP photoelectron production codes for all solar irradiance inputs.

---------------------------------------------------------
Title: Solar flare impulsive phase observations from SDO and other
    observatories
Authors: Chamberlin, P. C.; Woods, T. N.; Schrijver, C. J.; Warren,
   H. P.; Milligan, R. O.; Christe, S.; Brosius, J. W.
2010AGUFMSH23A1832C    Altcode:
  With the start of normal operations of the Solar Dynamics Observatory
  in May 2010, the Extreme ultraviolet Variability Experiment (EVE)
  and the Atmospheric Imaging Assembly (AIA) have been returning the
  most accurate solar XUV and EUV measurements every 10 and 12 seconds,
  respectively, at almost 100% duty cycle. The focus of the presentation
  will be the solar flare impulsive phase observations provided by EVE
  and AIA and what these observations can tell us about the evolution
  of the initial phase of solar flares. Also emphasized throughout
  is how simultaneous observations with other instruments, such as
  RHESSI, SOHO-CDS, and HINODE-EIS, will help provide a more complete
  characterization of the solar flares and the evolution and energetics
  during the impulsive phase. These co-temporal observations from the
  other solar instruments can provide information such as extending
  the high temperature range spectra and images beyond that provided
  by the EUV and XUV wavelengths, provide electron density input into
  the lower atmosphere at the footpoints, and provide plasma flows of
  chromospheric evaporation, among other characteristics.

---------------------------------------------------------
Title: Physical Properties of Solar Flares: New Results from EVE/SDO
Authors: Warren, H. P.; Mariska, J. T.; Doschek, G. A.; Eve Team
2010AGUFMSH13A..06W    Altcode:
  Much of our current understanding of the temperature and density
  structure of solar flares has been derived from broad band X-ray
  instruments, such as RHESSI, GOES, and SXT/Yohkoh, or the observation
  of isolated emission lines, such as from BCS/Yohkoh. This has lead
  to uncertainties in determining the distribution of temperatures and
  densities in a flare. The EUV Variability Experiment (EVE) on the Solar
  Dynamics Observatory (SDO) provides an unprecedented opportunity to
  observe a very wide range of high-temperature emission lines at high
  cadence (10 s) and relatively high spectral resolution (1 A). The
  spectral range between 90 and 200 Angstroms is particularly rich in
  emission lines from Fe that are formed at temperatures above 7 MK
  (Fe XVIII - Fe XXIV). This range also includes one of the few density
  diagnostics (Fe XXI 145.66/128.75) that is useful in solar flare
  observations. Our initial calculations suggest very broad differential
  emission measure distributions and indicate high densities (Log Ne as
  high as 11.7), which implies a very rapid cooling of flare plasma. These
  observations are broadly consistent with flare models that allow for
  the release of energy on many independent threads and we will discuss
  these results in the context of current theories of solar flares.

---------------------------------------------------------
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: Radiative and magnetic properties of solar active
    regions. II. Spatially resolved analysis of O V 62.97 nm transition
    region emission
Authors: Fludra, A.; Warren, H.
2010A&A...523A..47F    Altcode:
  Context. Global relationships between the photospheric magnetic flux
  and the extreme ultraviolet emission integrated over active region
  area have been studied in a previous paper by Fludra &amp; Ireland
  (2008, A&amp;A, 483, 609). Spatially integrated EUV line intensities
  are tightly correlated with the total unsigned magnetic flux, and
  yet these global power laws have been shown to be insufficient for
  accurately determining the coronal heating mechanism owing to the
  mathematical ill-conditioning of the inverse problem. <BR /> Aims:
  Our aim is to establish a relationship between the EUV line intensities
  and the photospheric magnetic flux density on small spatial scales in
  active regions and investigate whether it provides a way of identifying
  the process that heats the coronal loops. <BR /> Methods: We compare
  spatially resolved EUV transition region emission and the photospheric
  magnetic flux density. This analysis is based on the O V 62.97 nm line
  recorded by the SOHO Coronal Diagnostic Spectrometer (CDS) and SOHO MDI
  magnetograms for six solar active regions. The magnetic flux density
  ϕ is converted to a simulated O V intensity using a model relationship
  I(ϕ, L) = Cϕ<SUP>δ</SUP> L<SUP>λ</SUP>, where the loop length L is
  obtained from potential magnetic field extrapolations. This simulated
  spatial distribution of O V intensities is convolved with the CDS
  instrument's point spread function and compared pixel by pixel with the
  observed O V line intensity. Parameters δ and λ are derived to give
  the best fit for the observed and simulated intensities. <BR /> Results:
  Spatially-resolved analysis of the transition region emission reveals
  the complex nature of the heating processes in active regions. In some
  active regions, particularly large, local intensity enhancements up to
  a factor of five are present. When areas with O V intensities above
  3000 erg cm<SUP>-2</SUP> s<SUP>-1</SUP> sr<SUP>-1</SUP> are ignored,
  a power law has been fitted to the relationship between the local O
  V line intensity and the photospheric magnetic flux density in each
  active region. The average power index δ from all regions is 0.4±0.1
  and λ = -0.15±0.07. However, the scatter of intensities in all
  regions is significantly greater than ±3σ from the fitted model. We
  therefore determine for the first time an empirical lower boundary for
  the I<SUB>OV</SUB>-ϕ relationship that is the same for five active
  regions. We postulate that it represents a basal heating. Because this
  boundary is present in the spatially-resolved data, this is compelling
  proof that the magnetic field is one of the major factors contributing
  to the basal component of the heating of the coronal plasma. We discuss
  the implications for the diagnostics of the coronal heating mechanism.

---------------------------------------------------------
Title: Characteristics and Evolution of the Magnetic Field and
    Chromospheric Emission in an Active Region Core Observed by Hinode
Authors: Brooks, David H.; Warren, Harry P.; Winebarger, Amy R.
2010ApJ...720.1380B    Altcode: 2010arXiv1006.5776B
  We describe the characteristics and evolution of the magnetic field and
  chromospheric emission in an active region core observed by the Solar
  Optical Telescope (SOT) on Hinode. Consistent with previous studies,
  we find that the moss is unipolar, the spatial distribution of magnetic
  flux evolves slowly, and that the magnetic field is only moderately
  inclined. We also show that the field-line inclination and horizontal
  component are coherent, and that the magnetic field is mostly sheared
  in the inter-moss regions where the highest magnetic flux variability
  is seen. Using extrapolations from spectropolarimeter magnetograms,
  we show that the magnetic connectivity in the moss is different from
  that in the quiet Sun because most of the magnetic field extends to
  significant coronal heights. The magnetic flux, field vector, and
  chromospheric emission in the moss also appear highly dynamic but
  actually show only small-scale variations in magnitude on timescales
  longer than the cooling times for hydrodynamic loops computed from
  our extrapolations, suggesting high-frequency (continuous) heating
  events. Some evidence is found for flux (Ca II intensity) changes on
  the order of 100-200 G (DN) on timescales of 20-30 minutes that could
  be taken as indicative of low-frequency heating. We find, however,
  that only a small fraction (10%) of our simulated loops would be
  expected to cool on these timescales, and we do not find clear evidence
  that the flux changes consistently produce intensity changes in the
  chromosphere. Using observations from the EUV Imaging Spectrometer
  (EIS), we also determine that the filling factor in the moss is ~16%,
  consistent with previous studies and larger than the size of an SOT
  pixel. The magnetic flux and chromospheric intensity in most individual
  SOT pixels in the moss vary by less than ~20% and ~10%, respectively,
  on loop cooling timescales. In view of the high energy requirements of
  the chromosphere, we suggest that these variations could be sufficient
  for the heating of "warm" EUV loops, but that the high basal levels
  may be more important for powering the hot core loops rooted in the
  moss. The magnetic field and chromospheric emission appear to evolve
  gradually on spatial scales comparable to the cross-field scale of
  the fundamental coronal structures inferred from EIS measurements.

---------------------------------------------------------
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: Determining the Temperature Structure of Solar Coronal Loops
    using their Temporal Evolution
Authors: Mulu, Fana; Winebarger, A. R.; Warren, H. P.; Aschwanden,
   M. J.; Klimchuk, J. A.
2010AAS...21630001M    Altcode:
  Despite much progress toward understanding the dynamics of the
  corona, the physical properties of coronal loops are not yet fully
  understood. Recent investigations and observations from different
  instruments have yielded contradictory results about the true physical
  properties of coronal loops, specifically as to whether the observed
  loops are isothermal structures or the convolution of several
  multi-thermal strands. In this talk, we introduce a new technique
  to determine if an observed loop is isothermal or multi-thermal. We
  determine the evolution of ten selected loops in multiple filter
  images from the Transition Region and Coronal Explorer (TRACE). Our
  new technique calculates the delay, calculates a cooling time,
  and determines if that cooling time is consistent with the observed
  lifetime. If the observational lifetime of the loop agrees with the
  calculated lifetime, then we can conclude that the loop is a single
  "monolithic” structure that heats and cools as a homogeneous unit,
  with isothermal temperature over the cross-section. If not, the
  loop must be a bundle of multiple multi-thermal strands, all being
  heated and cooling independently. In the second part of the talk,
  we utilize the concept of nanoflare storms to understand the reason
  behind the extended lifetimes. By simulating the observed light curves
  of the loops using EBTEL (Enthalpy-Based Thermal Evolution of Loops),
  we find that the longer observed lifetimes can be reproduced by using
  a set of small-scale impulsively heated strands.

---------------------------------------------------------
Title: Steady Heating Model of an Active Region Core
Authors: Winebarger, Amy R.; Schmelz, J. T.; Saar, S. H.; Kashyap,
   V. L.; Warren, H. P.
2010AAS...21640711W    Altcode: 2010BAAS...41R.861W
  If the heating in an active region core is steady, the base pressure of
  loop as well as its loop length determines exactly the apex temperature,
  density and required heating rate. In this research, we analyze data
  of an active region core that is observed with both Hinode XRT and
  EIS instruments. We use the density sensitve Fe XII line ratios to
  determine the base pressure of the loops and geometrical constraints
  to determine the loop lengths. We use the hotter spectral lines coupled
  with the XRT filter intensities to determine the differential emission
  measure (DEM) of the core plasma. Using the base pressures and loop
  lengths, we populate loops in a model active region to determine a
  model DEM. We then compare this emission measure distribution to the
  observed distribution.

---------------------------------------------------------
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: SDO Extreme Ultraviolet Variability Experiment (EVE):
    Instrument and First Light
Authors: Woods, Thomas N.; Eparvier, F.; Hock, R.; Jones, A.;
   Didkovsky, L.; Judge, D.; Chamberlin, P.; Lean, J.; Warren, H.;
   Mariska, J.
2010AAS...21630802W    Altcode:
  The Extreme ultraviolet Variability Experiment (EVE) aboard the
  NASA Solar Dynamics Observatory (SDO) was launched on 11 February
  2010. The EVE instruments measure the solar extreme ultraviolet
  (EUV) irradiance from 0.1 to 105 nm with unprecedented spectral
  resolution (0.1 nm), temporal cadence (10 sec minimum), and accuracy
  (20% or better). The highly variable solar EUV irradiance is a key
  measurement for the NASA Living With the Star (LWS) program as it is
  the major energy input into the Earth's upper atmosphere and thus
  impacts the geospace environment that affects satellite operations
  and communication and navigation systems. The EVE measurements, along
  with additional solar measurements from SDO and other satellite and
  ground-based instruments, will be used to advance our understanding of
  the solar EUV irradiance variability. For short time scales, EVE will
  make detailed observations on the evolution of flare events that are
  an important interest for space weather research and operations. For
  longer time scales, EVE measurements will be compared to other solar
  EUV irradiance measurements to help establish a composite time series
  of the solar EUV irradiance. The EVE instrument will be described, and
  first light results from EVE during the rise of solar cycle 24 will be
  presented. The EVE instrument team is supported by the NASA SDO Project.

---------------------------------------------------------
Title: The Observation and Modeling of High Temperature Active Region
    Emission with Hinode
Authors: Warren, Harry; Brooks, D. H.; Winebarger, A. R.
2010AAS...21640709W    Altcode: 2010BAAS...41Q.861W
  The high temperature emission that is present in the core of an active
  region is generally unresolved by current solar instrumentation. This
  makes it difficult to isolate and study individual loops. One way
  to circumvent this problem is to study the moss, which is the bright
  emission from the footpoints of hot active region loops seen in many
  solar EUV images. Moss observations are particularly useful because
  they provide boundary conditions for physical models of coronal loops
  without the need to know the loop geometry. With their high spatial and
  temporal resolution and broad array of diagnostics, the instruments
  on Hinode have provided many new insights into the properties of
  the moss. These observations appear to be generally consistent with
  steady heating in high temperature active region loops. Fast scans
  with EIS, for example, show that the moss intensities, Doppler shifts,
  and nonthermal velocities are constant over many hours. Our initial
  analysis of SOT Ca data from the moss also shows remarkably constant
  emission even at this very high spatial resolution. Steady heating
  models are consistent with the intensities observed with EIS. In this
  talk we review Hinode observations and modeling of the moss emission
  and extend these models to simulations of entire active regions.

---------------------------------------------------------
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: Evidence for Steady Heating: Observations of an Active Region
    Core with Hinode and TRACE
Authors: Warren, Harry P.; Winebarger, Amy R.; Brooks, David H.
2010ApJ...711..228W    Altcode: 2009arXiv0910.0458W
  The timescale for energy release is an important parameter for
  constraining the coronal heating mechanism. Observations of "warm"
  coronal loops (~1 MK) have indicated that the heating is impulsive and
  that coronal plasma is far from equilibrium. In contrast, observations
  at higher temperatures (~3 MK) have generally been consistent with
  steady heating models. Previous observations, however, have not been
  able to exclude the possibility that the high temperature loops are
  actually composed of many small-scale threads that are in various stages
  of heating and cooling and only appear to be in equilibrium. With new
  observations from the EUV Imaging Spectrometer and X-ray Telescope
  (XRT) on Hinode we have the ability to investigate the properties of
  high temperature coronal plasma in extraordinary detail. We examine
  the emission in the core of an active region and find three independent
  lines of evidence for steady heating. We find that the emission observed
  in XRT is generally steady for hours, with a fluctuation level of
  approximately 15% in an individual pixel. Short-lived impulsive heating
  events are observed, but they appear to be unrelated to the steady
  emission that dominates the active region. Furthermore, we find no
  evidence for warm emission that is spatially correlated with the hot
  emission, as would be expected if the high temperature loops are the
  result of impulsive heating. Finally, we also find that intensities in
  the "moss," the footpoints of high temperature loops, are consistent
  with steady heating models provided that we account for the local
  expansion of the loop from the base of the transition region to the
  corona. In combination, these results provide strong evidence that
  the heating in the core of an active region is effectively steady,
  that is, the time between heating events is short relative to the
  relevant radiative and conductive cooling times.

---------------------------------------------------------
Title: Bright Points and Jets in Polar Coronal Holes Observed by
    the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Landi, E.; Warren, H. P.; Harra, L. K.
2010ApJ...710.1806D    Altcode:
  We present observations of polar coronal hole bright points (BPs)
  made with the Extreme-ultraviolet Imaging Spectrometer (EIS) on the
  Hinode spacecraft. The data consist of raster images of BPs in multiple
  spectral lines from mostly coronal ions, e.g., Fe X-Fe XV. The BPs
  are observed for short intervals and thus the data are snapshots of
  the BPs obtained during their evolution. The images reveal a complex
  unresolved temperature structure (EIS resolution is about 2”), with the
  highest temperature being about 2 × 10<SUP>6</SUP> K. Some BPs appear
  as small loops with temperatures that are highest near the top. But
  others are more point-like with surrounding structures. However, the
  thermal time evolution of the BPs is an important factor in their
  appearance. A BP may appear quite different at different times. We
  discuss one BP with an associated jet that is bright enough to allow
  statistically meaningful measurements. The jet Doppler speed along the
  line of sight is about 15-20 km s<SUP>-1</SUP>. Electron densities of
  the BPs and the jet are typically near 10<SUP>9</SUP> cm<SUP>-3</SUP>,
  which implies path lengths along the line of sight on the order of a
  few arcsec. We also construct differential emission measure curves for
  two of the best observed BPs. High spatial resolution (significantly
  better than 1”) is required to fully resolve the BP structures.

---------------------------------------------------------
Title: Nitric oxide density enhancements due to solar flares
Authors: Rodgers, E. M.; Bailey, S. M.; Warren, H. P.; Woods, T. N.;
   Eparvier, F. G.
2010AdSpR..45...28R    Altcode:
  A differential emission measure technique is used to determine flare
  spectra using solar observations from the soft X-ray instruments aboard
  the Thermosphere Ionosphere Mesosphere Energetics Dynamics and Solar
  Radiation and Climate Experiment satellites. We examine the effect
  of the solar flare soft X-ray energy input on the nitric oxide (NO)
  density in the lower thermosphere. The retrieved spectrum of the 28
  October 2003 X18 flare is input to a photochemical thermospheric NO
  model to calculate the predicted flare NO enhancements. Model results
  are compared to Student Nitric Oxide Explorer Ultraviolet Spectrometer
  observations of this flare. We present results of this comparison and
  show that the model and data are in agreement. In addition, the NO
  density enhancements due to several flares are studied. We present
  results that show large solar flares can deposit the same amount of
  0.1-2 and 0.1-7 nm energy to the thermosphere during a relatively
  short time as the Sun normally deposits in one day. The NO column
  density nearly doubles when the daily integrated energy above 5 J
  m<SUP>-2</SUP> is doubled.

---------------------------------------------------------
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: Ultra-Hot Plasma in Active Regions Observed by the
    Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Ko, Y. -K.; Doschek, G. A.; Warren, H. P.; Yount, P. R.
2009ASPC..415..275K    Altcode:
  We present a specific algorithm to extract the Ca XVII λ192.858
  line from the blending with two Fe XI and six O V lines in the
  Hinode/EIS data. This is a review of the work to be published by Ko et
  al. (2009). We demonstrate that the Ca XVII line can be satisfactorily
  extracted from the blend if the Ca XVII emission contributes to at
  least 10% of the blend. This Ca XVII line, with formation temperature
  at 6 million degrees, is thus a viable line in the EIS data to probe the
  thermal structure in non-flaring active regions at its high temperature
  end and provides valuable constraints for coronal heating models.

---------------------------------------------------------
Title: Hinode/Extreme-Ultraviolet Imaging Spectrometer Observations
    of the Temperature Structure of the Quiet Corona
Authors: Brooks, David H.; Warren, Harry P.; Williams, David R.;
   Watanabe, Tetsuya
2009ApJ...705.1522B    Altcode: 2009arXiv0905.3603B
  We present a differential emission measure (DEM) analysis of the quiet
  solar corona on disk using data obtained by the Extreme-ultraviolet
  Imaging Spectrometer (EIS) on Hinode. We show that the expected
  quiet-Sun DEM distribution can be recovered from judiciously selected
  lines, and that their average intensities can be reproduced to
  within 30%. We present a subset of these selected lines spanning the
  temperature range log T = 5.6-6.4 K that can be used to derive the DEM
  distribution reliably, including a subset of iron lines that can be used
  to derive the DEM distribution free of the possibility of uncertainties
  in the elemental abundances. The subset can be used without the need for
  extensive measurements, and the observed intensities can be reproduced
  to within the estimated uncertainty in the pre-launch calibration
  of EIS. Furthermore, using this subset, we also demonstrate that
  the quiet coronal DEM distribution can be recovered on size scales
  down to the spatial resolution of the instrument (1” pixels). The
  subset will therefore be useful for studies of small-scale spatial
  inhomogeneities in the coronal temperature structure, for example,
  in addition to studies requiring multiple DEM derivations in space or
  time. We apply the subset to 45 quiet-Sun data sets taken in the period
  2007 January to April, and show that although the absolute magnitude
  of the coronal DEM may scale with the amount of released energy, the
  shape of the distribution is very similar up to at least log T ~ 6.2 K
  in all cases. This result is consistent with the view that the shape of
  the quiet-Sun DEM is mainly a function of the radiating and conducting
  properties of the plasma and is fairly insensitive to the location and
  rate of energy deposition. This universal DEM may be sensitive to other
  factors such as loop geometry, flows, and the heating mechanism, but
  if so they cannot vary significantly from quiet-Sun region to region.

---------------------------------------------------------
Title: Flows and Motions in Moss in the Core of a Flaring Active
Region: Evidence for Steady Heating
Authors: Brooks, David H.; Warren, Harry P.
2009ApJ...703L..10B    Altcode: 2009arXiv0905.3462B
  We present new measurements of the time variability of intensity,
  Doppler, and nonthermal velocities in moss in an active region core
  observed by the EUV Imaging Spectrometer on Hinode in 2007 June. The
  measurements are derived from spectral profiles of the Fe XII 195
  Å line. Using the 2” slit, we repeatedly scanned 150” by 150”
  in a few minutes. This is the first time it has been possible to
  make such velocity measurements in the moss, and the data presented
  are the highest cadence spatially resolved maps of moss Doppler and
  nonthermal velocities ever obtained in the corona. The observed region
  produced numerous C- and M-class flares with several occurring in
  the core close to the moss. The magnetic field was therefore clearly
  changing in the active region core, so we ought to be able to detect
  dynamic signatures in the moss if they exist. Our measurements of
  moss intensities agree with previous studies in that a less than 15%
  variability is seen over a period of 16 hr. Our new measurements of
  Doppler and nonthermal velocities reveal no strong flows or motions
  in the moss, nor any significant variability in these quantities. The
  results confirm that moss at the bases of high temperature coronal loops
  is heated quasi-steadily. They also show that quasi-steady heating
  can contribute significantly even in the core of a flare productive
  active region. Such heating may be impulsive at high frequency, but
  if so it does not give rise to large flows or motions.

---------------------------------------------------------
Title: The Temperature and Density Structure of the Solar
    Corona. I. Observations of the Quiet Sun with the EUV Imaging
    Spectrometer on Hinode
Authors: Warren, Harry P.; Brooks, David H.
2009ApJ...700..762W    Altcode: 2009arXiv0901.1621W
  Measurements of the temperature and density structure of the
  solar corona provide critical constraints on theories of coronal
  heating. Unfortunately, the complexity of the solar atmosphere,
  observational uncertainties, and the limitations of current atomic
  calculations, particularly those for Fe, all conspire to make this
  task very difficult. A critical assessment of plasma diagnostics in
  the corona is essential to making progress on the coronal heating
  problem. In this paper, we present an analysis of temperature and
  density measurements above the limb in the quiet corona using new
  observations from the EUV Imaging Spectrometer (EIS) on Hinode. By
  comparing the Si and Fe emission observed with EIS we are able to
  identify emission lines that yield consistent emission measure
  distributions. With these data we find that the distribution of
  temperatures in the quiet corona above the limb is strongly peaked
  near 1 MK, consistent with previous studies. We also find, however,
  that there is a tail in the emission measure distribution that extends
  to higher temperatures. EIS density measurements from several density
  sensitive line ratios are found to be generally consistent with
  each other and with previous measurements in the quiet corona. Our
  analysis, however, also indicates that a significant fraction of the
  weaker emission lines observed in the EIS wavelength ranges cannot be
  understood with current atomic data.

---------------------------------------------------------
Title: Hot Plasma in Nonflaring Active Regions Observed by the
    Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Ko, Yuan-Kuen; Doschek, George A.; Warren, Harry P.; Young,
   Peter R.
2009ApJ...697.1956K    Altcode: 2009arXiv0903.3029K
  The Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft obtains high-resolution spectra of the solar atmosphere
  in two wavelength ranges: 170-210 and 250-290 Å. These wavelength
  regions contain a wealth of emission lines covering temperature regions
  from the chromosphere/transition region (e.g., He II, Si VII) up to
  flare temperatures (Fe XXIII, Fe XXIV). Of particular interest for
  understanding coronal heating is a line of Ca XVII at 192.858 Å,
  formed near a temperature of 6 × 10<SUP>6</SUP> K. However, this
  line is blended with two Fe XI and six O V lines. In this paper we
  discuss a specific procedure to extract the Ca XVII line from the
  blend. We have performed this procedure on the raster data of five
  active regions (ARs) and a limb flare, and demonstrated that the Ca
  XVII line can be satisfactorily extracted from the blend if the Ca XVII
  flux contributes to at least ~10% of the blend. We show examples of the
  high-temperature corona depicted by the Ca XVII emission and find that
  the Ca XVII emission has three morphological features in these ARs: (1)
  "fat" medium-sized loops confined in a smaller space than the 1 million
  degree corona, (2) weaker, diffuse emission surrounding these loops that
  spread over the core of the AR, and (3) the locations of the strong Ca
  XVII loops are often weak in line emission formed from the 1 million
  degree plasma. We find that the emission measure ratio of the 6 million
  degree plasma relative to the cooler 1 million degree plasma in the
  core of the ARs, using the Ca XVII to Fe XI line intensity ratio as a
  proxy, can be as high as 10. Outside of the AR core where the 1 million
  degree loops are abundant, the ratio has an upper limit of about 0.5.

---------------------------------------------------------
Title: Diagnostics of High Temperature Active Region Plasma with
    EIS/Hinode
Authors: Warren, Harry; Ko, Y.; Doschek, G.
2009SPD....40.1212W    Altcode:
  Solar active region loops at different temperatures appear to have very
  different properties. Coronal loops with apex temperatures near 1 MK
  have high densities and lifetimes long relative to a characteristic
  cooling time. The properties of these loops are generally consistent
  with impulsive heating models. Higher temperature coronal emission,
  in contrast, is generally consistent with steady heating models. This
  conclusion is largely based on the analysis of broad-band observations
  from the SXT on Yohkoh, which had modest spatial resolution and
  temperature discrimination. Because of these diagnostic limitations the
  time scale for the heating in the core of an active region is still
  an open question. The high resolution EIS spectrometer on Hinode
  provides new spectroscopic diagnostics of high temperature plasma
  in active region cores through the observation of Ca XIV, XV, XVI,
  and XVII emission lines. An initial survey of active regions cores
  indicates that the emission measure at high temperatures ( 3 MK) is
  uncorrelated with the emission measure at lower temperatures ( 1 MK),
  suggesting that these loops are not fully cooling. These results will
  be discussed in the context of hydrodynamic models.

---------------------------------------------------------
Title: The Relationship Between Cooling Time and Equilibrium Density
    and Temperature
Authors: Winebarger, Amy R.; Warren, H. P.; Mulu-Moore, F. M.
2009SPD....40.1210W    Altcode:
  There now exists significant evidence that the overdense, 1-2 MK
  active regions loops observed at EUV wavelengths are cooling. One
  heating model for these loops is that they are impulsively heated and
  then cool with no additional energy input. At some point in the loop's
  evolution before it reaches 1-2 MK, the density and temperature at the
  apex of the loop will resemble the expected density and temperature for
  a steady, uniformly heated loop; we term this the loop's equilibrium
  time. In our previous work, we have determined that the equilibrium
  conditions of a loop are related to the total amount of energy released
  in the loop. In this poster, we investigate the relationship between
  the cooling time measured at 1.5 MK and the equilibrium density and
  temperature in hopes to relate the observed cooling time with the
  total energy released in the loop. To do this, we calculate a grid of
  solutions to the one-dimensional hydrodynamic equations and develop
  an empirical relationship between the cooling time and equilibrium
  density and temperature. We then discuss the ability to further relate
  these values to the total energy released in the loop.

---------------------------------------------------------
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: Classifying Coronal Loops as Isothermal or Multi-thermal
    Using the Loops' Evolution
Authors: Mulu, Fana; Winebarger, A. R.; Warren, H. P.; Aschwanden,
   M. J.
2009SPD....40.1218M    Altcode:
  Despite much progress toward understanding the dynamics of the
  corona, the physical properties of coronal loops are not yet fully
  understood. Recent investigations and observations from different
  instruments have yielded contradictory results about the true
  physical properties of coronal loops, specifically as to whether the
  observed loops are isothermal structures or the convolution of several
  multi-thermal strands. In this poster, we introduce a new technique
  to determine if an observed loop is isothermal or multi-thermal. We
  will determine the evolution of loops in multiple filter images from
  the Transition Region and Coronal Explorer (TRACE). Our new technique
  will calculate the delay of the loop between different filter images,
  calculate a cooling time, and determine if that cooling time is
  consistent with the observed lifetime. We will present preliminary
  results that show if the temperature structure across coronal loops
  is isothermal or multi-thermal.

---------------------------------------------------------
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: Can the Composition of the Solar Corona Be Derived from
    Hinode/Extreme-Ultraviolet Imaging Spectrometer Spectra?
Authors: Feldman, U.; Warren, H. P.; Brown, C. M.; Doschek, G. A.
2009ApJ...695...36F    Altcode:
  Elemental abundances appear to be the same everywhere in the
  photosphere, but in the solar corona they vary in different
  regions. Abundances in quiet Sun (closed) flux tubes are different from
  those in coronal hole (CH, open) magnetic field regions, and therefore
  abundance variations might possibly be used to determine locations of
  slow and fast solar wind in the corona. In active regions, abundances
  can change from region to region and can vary with the age of the
  region. In the present paper, we evaluate the feasibility of determining
  relative elemental abundances in the corona using spectra acquired by
  the Extreme-ultraviolet Imaging Spectrometer (EIS) on Hinode. As test
  cases, we attempt to evaluate the coronal composition above the limb
  in an equatorial quiet region and in a polar CH. We also determine
  the elemental composition of coronal regions with moderate activity on
  the disk and at the limb. To estimate the accuracy of the instrumental
  calibration and the atomic physics used in the calculations, we compare
  the derived composition with earlier derivations from spectra recorded
  by the Solar Ultraviolet Measurements of Emitted Radiation spectrometer
  in similar regions. We find that EIS can be used to determine relative
  abundance variations in the inner solar corona. The determination of
  absolute abundances can also be attempted after additional calibrations
  in space are accomplished.

---------------------------------------------------------
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: Modeling of the Extreme-Ultraviolet and Soft X-Ray Emission
    in a Solar Coronal Bright Point
Authors: Brooks, David H.; Warren, Harry P.
2008ApJ...687.1363B    Altcode:
  Previous studies have been able to reproduce both the observed
  intensities and the morphology of high-temperature solar plasma
  using steady state heating models. These models, however, have
  been unable to reproduce the lower temperature emission observed in
  active regions. Here we present results from numerical simulations
  of a coronal bright point. We use potential field extrapolations of a
  Kitt Peak magnetogram to compute the coronal field lines and populate
  them with solutions to the hydrostatic loop equations based on a
  volumetric heating function that scales as bar B/L, where bar B is the
  magnetic field strength averaged along a field line and L is the loop
  length. We consider the effects of altering the magnitude and scale
  height of the energy deposition and the effect of allowing the loop
  cross sections to expand proportionally to 1/bar B. We then use the
  computed densities and temperatures to calculate average intensities
  and simulated EUV and soft X-ray images and compared them to Yohkoh
  and SOHO observations. We find that our best-case model (apex heating
  of expanding loops) can reproduce the high-temperature emission, the
  general morphology of the lower temperature emission, and the majority
  of the average intensities of reliable lines over a wide range of
  temperatures to within ~20%. The morphology in the EUV visualizations,
  however, shows some differences from the observations. These results
  suggest the role of nonpotential or evolving magnetic fields, or
  dynamic processes, but indicate that departures from the potential
  field hydrostatic case may not be too large.

---------------------------------------------------------
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: Solar Observations of High-Temperature Emission with the
    Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Warren, Harry P.; Feldman, Uri; Brown, Charles M.
2008ApJ...685.1277W    Altcode:
  We present an analysis of solar coronal emission lines formed above 2.5
  MK observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode
  during a small flare. Our main purpose is to evaluate the internal
  consistency of the atomic data available for the observed emission. We
  find that the observed emission from high-temperature Ca lines (Ca XIV,
  XV, XVI, and XVII) is generally consistent with the available atomic
  data. The observed Fe XVII emission at these wavelengths, in contrast,
  is more difficult to reconcile with current atomic calculations. The
  energy levels tabulated in the CHIANTI atomic physics database generally
  do not correspond to the observed wavelengths. After associating the
  calculated emissivities with the observed emission by hand, we find
  that the observed intensities are roughly consistent with what is
  predicted. However, the intensity of the strongest unblended line, Fe
  XVII 254.87 Å, is not consistent with the intensities of the other Fe
  XVII lines at these wavelengths. Several of the Ca XV emission lines,
  which are formed at about 4 MK, form density-sensitive line ratios in
  the range log n<SUB>e</SUB> = 9-11 cm<SUP>-3</SUP>. Density measurements
  at these temperatures are potentially important for understanding
  the coronal heating mechanism. Our initial analysis suggests that
  high-temperature active region plasma is underdense relative to the
  predictions of steady heating models.

---------------------------------------------------------
Title: Flows and Nonthermal Velocities in Solar Active Regions
Observed with the EUV Imaging Spectrometer on Hinode: A Tracer of
    Active Region Sources of Heliospheric Magnetic Fields?
Authors: Doschek, G. A.; Warren, H. P.; Mariska, J. T.; Muglach, K.;
   Culhane, J. L.; Hara, H.; Watanabe, T.
2008ApJ...686.1362D    Altcode: 2008arXiv0807.2860D
  From Doppler velocity maps of active regions constructed from spectra
  obtained by the EUV Imaging Spectrometer (EIS) on the Hinode spacecraft
  we observe large areas of outflow (20-50 km s<SUP>-1</SUP>) that can
  persist for at least a day. These outflows occur in areas of active
  regions that are faint in coronal spectral lines formed at typical
  quiet-Sun and active region temperatures. The outflows are positively
  correlated with nonthermal velocities in coronal plasmas. The bulk
  mass motions and nonthermal velocities are derived from spectral line
  centroids and line widths, mostly from a strong line of Fe XII at
  195.12 Å. The electron temperature of the outflow regions estimated
  from an Fe XIII to Fe XII line intensity ratio is about (1.2-1.4) ×
  10<SUP>6</SUP> K. The electron density of the outflow regions derived
  from a density-sensitive intensity ratio of Fe XII lines is rather low
  for an active region. Most regions average around 7 × 10<SUP>8</SUP>
  cm<SUP>-3</SUP>, but there are variations on pixel spatial scales
  of about a factor of 4. We discuss results in detail for two active
  regions observed by EIS. Images of active regions in line intensity,
  line width, and line centroid are obtained by rastering the regions. We
  also discuss data from the active regions obtained from other orbiting
  spacecraft that support the conclusions obtained from analysis of the
  EIS spectra. The locations of the flows in the active regions with
  respect to the longitudinal photospheric magnetic fields suggest that
  these regions might be tracers of long loops and/or open magnetic
  fields that extend into the heliosphere, and thus the flows could
  possibly contribute significantly to the solar wind.

---------------------------------------------------------
Title: Observations of Doppler Shift Oscillations with the EUV
    Imaging Spectrometer on Hinode
Authors: Mariska, John T.; Warren, Harry P.; Williams, David R.;
   Watanabe, Tetsuya
2008ApJ...681L..41M    Altcode: 2008arXiv0806.0265M
  Damped Doppler shift oscillations have been observed in emission lines
  from ions formed at flare temperatures with the Solar Ultraviolet
  Measurements of Emitted Radiation spectrometer on the Solar and
  Heliospheric Observatory and with the Bragg Crystal Spectrometer
  on Yohkoh. This Letter reports the detection of low-amplitude damped
  oscillations in coronal emission lines formed at much lower temperatures
  observed with the EUV Imaging Spectrometer on the Hinode satellite. The
  oscillations have an amplitude of about 2 km s<SUP>-1</SUP> and a
  period of around 35 minutes. The decay times show some evidence for
  a temperature dependence with the lowest temperature of formation
  emission line (Fe XII 195.12 Å) exhibiting a decay time of about 43
  minutes, while the highest temperature of formation emission line (Fe XV
  284.16 Å) shows no evidence for decay over more than two periods of the
  oscillation. The data appear to be consistent with slow magnetoacoustic
  standing waves, but may be inconsistent with conductive damping.

---------------------------------------------------------
Title: Observations of Doppler Shift Oscillations With the EUV
    Imaging Spectrometer on Hinode
Authors: Mariska, J. T.; Warren, H. P.; Williams, D. R.; Watanabe, T.
2008AGUSMSP31A..04M    Altcode:
  Damped Doppler shift oscillations have been observed in emission lines
  from ions formed at flare temperatures with the Solar Ultraviolet
  Measurements of Emitted Radiation spectrometer on SOHO and the Bragg
  Crystal Spectrometer on Yohkoh. We report the detection of similar
  oscillations in coronal emission lines observed with the EUV Imaging
  Spectrometer on the Hinode satellite. The oscillations, which are
  present in emission lines formed at lower temperatures than seen with
  the instruments listed above, have an amplitude of about 2 km s- 1,
  and a period of around 35 min. The decay times show some evidence
  for a temperature dependence with the lowest temperature of formation
  emission line (Fe~XII 195.12 Å) exhibiting a decay time of about 43
  min, while the highest temperature of formation emission line (Fe~XV
  284.16 Å) shows no evidence for decay over more than two periods of the
  oscillation. The data appear to be consistent with slow magnetoacoustic
  standing waves.

---------------------------------------------------------
Title: Comparison of One-dimensional Hydrodynamic Codes and Analytical
    Models for Time- Dependent Heating
Authors: Mulu-Moore, F.; Winebarger, A. R.; Warren, H. P.
2008AGUSMSP31C..07M    Altcode:
  Numerous coronal heating theories have suggested that the heating in
  the corona is highly dynamic and strongly time-dependent. One method of
  investigating the coronal heating problem is to compare observations
  to solutions of the one-dimensional hydrodynamic equations. Because
  the numerical simulations are computationally intensive, there are
  also analytical models that describe the evolution of the plasma that
  has been heated dynamically. In this poster, we present a comparison
  of numerical simulations and analytical models for a limited number
  of dynamic heating functions.

---------------------------------------------------------
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: Electron Densities in Active Region Loops Observed with
    Hinode/EIS
Authors: Warren, H. P.; Winebarger, A. R.; Brooks, D. H.
2008AGUSMSP41C..02W    Altcode:
  Active region observations with the Transition Region and Coronal
  Explorer (TRACE) showed that loops near 1 MK appear to have high
  densities relative to the predictions of scaling laws based on steady
  heating. These loops also persist much longer than a radiative cooling
  time. This lead to the formation of models based on the impulsive
  heating of small scale filaments. With the launch of the EUV Imaging
  Spectrometer (EIS) on Hinode we now have a much more detailed view of
  coronal loops at these temperatures. We find that the temperatures,
  densities, and filling factors inferred from the new spectroscopic
  data are largely consistent with our interpretation of the earlier
  TRACE observations. The impulsive heating models also predict low
  densities relative to the steady heating models at high temperatures,
  and we will discuss the EIS evidence for hot, underdense loops in
  solar active regions.

---------------------------------------------------------
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: Ultra-Hot Plasma in Active Regions Observed by the
    Extreme-ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Warren, H. P.; Feldman, U.
2008AGUSMSP43C..01D    Altcode:
  The Extreme-ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft obtains high resolution spectra of the solar atmosphere in
  two wavelength ranges: 170 - 210 and 250 — 290 Angstroms. These
  wavelength regions contain a wealth of emission lines covering
  temperature regions from the chromosphere/transition region (e.g.,
  He II, Si VII) up to soft X-ray flare temperatures (Fe XXIII,
  Fe XXIV). EIS can obtain line profiles and intensities for the
  spectral lines in these wavelength regions. Of particular interest
  for understanding coronal heating is a line of Ca XVII, formed near
  a temperature of 6 MK. This line is blended with lines of Fe XI and O
  V. However, by using unblended lines of these ions, the Ca XVII line
  can be deconvolved from the blended emission. EIS has obtained many
  raster observations of active regions by stepping the slit in small
  increments across the active region, producing monochromatic images
  of the active region. The Ca XVII blend has been included in many of
  these rasters. In this paper we discuss the appearance and frequency
  of 6 MK plasma in active regions in the absence of strong flaring
  activity. This temperature region is not well-observed by normal
  incidence imaging spectrometers and therefore the EIS data shed light
  on higher temperature areas of active regions than normally available
  from imaging instruments alone. We discuss how to deconvolve the blend
  and show examples of 6 MK plasma emission in several active regions.

---------------------------------------------------------
Title: Observation and Modeling of Coronal "Moss" With the EUV
    Imaging Spectrometer on Hinode
Authors: Warren, Harry P.; Winebarger, Amy R.; Mariska, John T.;
   Doschek, George A.; Hara, Hirohisa
2008ApJ...677.1395W    Altcode: 2007arXiv0709.0396W
  Observations of transition region emission in solar active regions
  represent a powerful tool for determining the properties of hot coronal
  loops. We present the analysis of new observations of active region
  moss taken with the Extreme Ultraviolet Imaging Spectrometer (EIS)
  on the Hinode satellite. EIS observations of a density sensitive Fe
  XII line ratio suggest moss densities of approximately 10<SUP>10</SUP>
  cm<SUP>-3</SUP> and pressures of 3 × 10<SUP>16</SUP> cm<SUP>-3</SUP>
  K. We find that the moss intensities predicted by steady, uniformly
  heated loop models are too intense relative to the observations,
  consistent with previous work. To bring the steady heating model into
  agreement with the observations a filling factor is required. Our
  analysis indicates that the filling factor in the moss is nonuniform
  and varies inversely with the loop pressure. The intensities predicted
  by steady uniform heating are generally consistent with the EIS moss
  observations. There are, however, significant discrepancies for the
  coolest emission line available in the data we analyze.

---------------------------------------------------------
Title: Modeling X-Ray Loops and EUV "Moss" in an Active Region Core
Authors: Winebarger, Amy R.; Warren, Harry P.; Falconer, David A.
2008ApJ...676..672W    Altcode: 2007arXiv0712.0756W
  The soft X-ray intensity of loops in active region cores and the
  corresponding footpoint, or moss, intensity observed in the EUV remain
  steady for several hours of observation. The steadiness of the emission
  has prompted many to suggest that the heating in these loops must also
  be steady, although no direct comparison between the observed X-ray and
  EUV intensities and the steady heating solutions of the hydrodynamic
  equations has yet been made. In this paper we perform these simulations
  and simultaneously model the X-ray and EUV moss intensities in one
  active region core with steady uniform heating. To perform this task,
  we introduce a new technique to constrain the model parameters using
  the measured EUV footpoint intensity to infer a heating rate. Using an
  ensemble of loop structures derived from magnetic field extrapolation
  of photospheric field, we associate each field line with an EUV moss
  intensity, then determine the steady uniform heating rate on that
  field line that reproduces the observed EUV intensity within 5% for
  a specific cross-sectional area, or filling factor. We then calculate
  the total X-ray filter intensities from all loops in the ensemble and
  compare this to the observed X-ray intensities. We complete this task
  iteratively to determine the filling factor that returns the best match
  to the observed X-ray intensities. We find that a filling factor of 8%
  and loops that expand with height provides the best agreement with
  the intensity in two X-ray filters, although the simulated SXT Al12
  intensity is 147% the observed intensity and the SXT AlMg intensity is
  80% the observed intensity. From this solution we determine the required
  heating rate scales as bar B<SUP>0.29</SUP>L<SUP>-0.95</SUP>. Finally,
  we discuss the future potential of this type of modeling, such as the
  ability to use density measurements to fully constrain filling factor,
  and its shortcomings, such as the requirement to use potential field
  extrapolations to approximate the coronal field.

---------------------------------------------------------
Title: Solar Flare Soft X-ray Irradiance and its Impact on the
    Earth's Upper Atmosphere
Authors: Rodgers, Erica; Bailey, Scott; Warren, Harry; Woods, Thomas;
   Eparvier, Francis
2008cosp...37.2627R    Altcode: 2008cosp.meet.2627R
  Solar flares dramatically enhance the soft X-ray region of the
  solar spectrum. A differential emission measure technique is used
  to determine flare spectra from Thermosphere Ionosphere Mesosphere
  Energetics Dynamics (TIMED) and Solar Radiation and Climate Experiment
  (SORCE) solar observations. Results show that flares primarily enhance
  the soft X-ray irradiance in the 0.1-2 nm range, and rapidly modify
  the energy input to the lower thermosphere. Most of the excess flare
  0.1-2 nm irradiance comes from 1-2 nm, thus flares deposit a large
  amount of their energy between 100-110 km. One of the key effects of
  this energy deposition is to modify nitric oxide (NO), which plays an
  important role in the energy balance of the thermosphere as it is a
  source of radiative cooling through infrared emissions. The density of
  NO is highly variable as a function of time and latitude, and reaches
  a maximum in the same altitude region where the flare irradiance
  is absorbed. Valid comparisons between Student Nitric Oxide Explorer
  (SNOE) satellite NO observations and those predicted by a photochemical
  thermospheric model provide a better understanding of low latitude flare
  enhanced NO density. Results show that large flares can deposit the
  same amount of 0.1-2 nm energy to the thermosphere during a relatively
  short time as the Sun normally deposits in one day, thus doubling the
  energy, which doubles the NO density.

---------------------------------------------------------
Title: A Streamer Ejection with Reconnection Close to the Sun
Authors: Sheeley, N. R., Jr.; Warren, H. P.; Wang, Y. -M.
2007ApJ...671..926S    Altcode:
  We previously described coronal events that expand gradually outward
  over an interval of 1-2 days and then suddenly tear apart in the
  coronagraph's 2-6 R<SUB>solar</SUB> field of view to form an outgoing
  flux rope and an inward system of collapsing loops. Now, we combine
  LASCO white-light images of the outer corona with spectrally resolved
  EIT images of the inner corona to describe a similar event for which the
  separation occurs closer to the Sun. The evolution of this 2006 July
  1-2 event had four phases: (1) an expansion phase in which magnetic
  loops rise slowly upward and increase the amount of open flux in the
  adjacent polar coronal hole and in the low-latitude hole of opposite
  polarity; (2) a stretching phase in which the legs of the rising
  loops pinch together to form a current sheet; (3) a transition phase
  in which field line reconnection produces an outgoing flux rope and a
  hot cusp of new loops; and (4) an end phase in which the reconnected
  loops become visible at lower temperatures, and the outgoing flux rope
  plows through the slow material ahead of it to form a traveling bow
  wave. During this time, the photospheric field was relatively weak and
  unchanging, as if the eruption had a nonmagnetic origin. We suppose
  that coronal heating gradually overpowers magnetic tension and causes
  the streamer to separate into a system of collapsing loops and a flux
  rope that is carried outward in the solar wind.

---------------------------------------------------------
Title: Benchmarking 1D Hydrodynamic Codes for Steady State Solutions
Authors: Mulu-Moore, F.; Winebarger, A.; Warren, H.
2007AGUFMSH33A1097M    Altcode:
  Recent studies that investigate the coronal heating problem use
  numerical codes to solve the 1D hydrodynamic equations. Many different
  numerical solutions are involved for solving the equations, however,
  only a few comparison have been made between the different numerical
  results. In this study, we begin a benchmarking process by comparing
  steady state solutions from the NRL Solar Flux Tube Model(SOLFTM), AAD's
  code and Serio's Scaling Law by calculating percentage differences in
  their simulated temperatures and densities.

---------------------------------------------------------
Title: Using Hinode Data to Explicitly Model Active Regions Cores
Authors: Winebarger, A. R.; Warren, H. P.
2007AGUFMSH52C..01W    Altcode:
  There have been many recent studies that have modeled active regions
  as an ensemble of steadily heated loops. One limitation of these
  studies is that they required a series of assumptions, such as how
  the heating rate scales with the magnetic field strength, loop length,
  and filling factor. We have developed a new technique that allows us
  to infer the heating rate directly from the observations. Our method
  uses observations of density sensitive line ratios in the "moss"
  (or footpoints) of active regions cores to infer both the heating rate
  and the filling factor. In this talk we will present the application
  of our modeling technique to new observations from the EIS and XRT
  instruments on Hinode.

---------------------------------------------------------
Title: The Temperature and Density Structure of an Active Region
    Observed with the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, George A.; Mariska, John T.; Warren, Harry P.;
   Culhane, Len; Watanabe, Tetsuya; Young, Peter R.; Mason, Helen E.;
   Dere, Kenneth P.
2007PASJ...59S.707D    Altcode:
  The Extreme-Ultraviolet Imaging Spectrometer (EIS) on Hinode
  produces high resolution spectra that can be combined via rasters
  into monochromatic images of solar structures, such as active
  regions. Electron temperature and density maps of the structures can
  be obtained by imaging the structures in different spectral lines with
  ratios sensitive to either temperature or density. Doppler maps and
  ion temperature maps can be made from spectral line wavelengths and
  profiles, respectively. In this paper we discuss coronal temperature
  and density distributions within an active region, illustrating the
  power of EIS for solar plasma diagnostics.

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

---------------------------------------------------------
Title: 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: Velocity Structure of Jets in a Coronal Hole
Authors: Kamio, Suguru; Hara, Hirohisa; Watanabe, Tetsuya; Matsuzaki,
   Keiichi; Shibata, Kazunari; Culhane, Len; Warren, Harry P.
2007PASJ...59S.757K    Altcode: 2007arXiv0711.2848K
  The velocity structures of jets in a coronal hole have been derived
  for the first time. Hinode observations revealed the existence
  of many bright points in coronal holes. They are loop-shaped and
  sometimes associated with coronal jets. Spectra obtained with the
  Extreme-ultraviolet Imaging Spectrometer aboard Hinode were analyzed
  to infer the Doppler velocity of bright loops and jets in a coronal
  hole of the north polar region. Elongated jets above bright loops are
  found to be blue-shifted by 30kms<SUP>-1</SUP> at maximum, while foot
  points of bright loops are red-shifted. Blue-shifts detected in coronal
  jets are interpreted as being upflows produced by magnetic reconnection
  between emerging flux and the ambient field in the coronal hole.

---------------------------------------------------------
Title: Theoretical Predictions of X-Ray and Extreme-UV Flare Emissions
    Using a Loss-of-Equilibrium Model of Solar Eruptions
Authors: Reeves, Katharine K.; Warren, Harry P.; Forbes, Terry G.
2007ApJ...668.1210R    Altcode:
  In this paper, we present numerical simulations of solar flares that
  couple a loss-of-equilibrium solar eruption model with a one-dimensional
  hydrodynamic model. In these calculations, the eruption is initiated by
  footpoint motions that disrupt the balance of forces acting on a flux
  rope. After the eruption begins, a current sheet forms and an arcade
  of flare loops is created by reconnecting magnetic fields. Thermal
  energy input into the flare loops is found by assuming the complete
  thermalization of the Poynting flux swept into the current sheet. This
  thermal energy is input into a one-dimensional hydrodynamic code for
  each loop formed in the multithreaded flare arcade. We find that a
  density enhancement occurs at the loop top when the two evaporating
  plasma fronts in each leg of the loop collide there. Simulated flare
  images show that these loop-top density enhancements produce “bars”
  of bright emission similar to those observed in the Transition Region
  and Coronal Explorer (TRACE) 195 Å bandpass and loop-top “knots” of
  bright emission seen in flare observations by the Soft X-Ray Telescope
  (SXT) on Yohkoh. We also simulate flare spectra from the Bragg Crystal
  Spectrometer (BCS) on Yohkoh. We find that during the early stages of
  flare initiation, there are significant blueshifts in the Ca XIX line,
  but the intensities are too faint to be observed with BCS. In general,
  the results of this model simulate observed flare emissions quite well,
  indicating that the reconnection model of solar flares is energetically
  consistent with observations.

---------------------------------------------------------
Title: Nonthermal Velocities in Solar Active Regions Observed with
    the Extreme-Ultraviolet Imaging Spectrometer on Hinode
Authors: Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Brown, C. M.;
   Culhane, J. L.; Hara, H.; Watanabe, T.; Young, P. R.; Mason, H. E.
2007ApJ...667L.109D    Altcode:
  We discuss nonthermal velocities in an active region as revealed
  by the Extreme-Ultraviolet Imaging Spectrometer (EIS) on the Hinode
  spacecraft. The velocities are derived from spectral line profiles in
  the extreme-ultraviolet (EUV) from a strong line of Fe XII at 195.12 Å
  by fitting each line profile to a Gaussian function. We compare maps
  of the full width at half-maximum values, the Fe XII spectral line
  intensity, the Fe XII Doppler shift, the electron temperature, and
  electron density. We find that the largest widths in the active region
  do not occur in the most intense regions, but seem to concentrate in
  less intense regions, some of which are directly adjacent to coronal
  loops, and some of which concentrate in regions which also exhibit
  relative Doppler outflows. The increased widths can also occur over
  extended parts of the active region.

---------------------------------------------------------
Title: Static and Dynamic Modeling of a Solar Active Region
Authors: Warren, Harry P.; Winebarger, Amy R.
2007ApJ...666.1245W    Altcode: 2006astro.ph..9023W
  Recent hydrostatic simulations of solar active regions have shown
  that it is possible to reproduce both the total intensity and the
  general morphology of the high-temperature emission observed at soft
  X-ray wavelengths using static heating models. These static models,
  however, cannot account for the lower temperature emission. In addition,
  there is ample observational evidence that the solar corona is highly
  variable, indicating a significant role for dynamical processes
  in coronal heating. Because they are computationally demanding,
  full hydrodynamic simulations of solar active regions have not been
  considered previously. In this paper we make first application of an
  impulsive heating model to the simulation of an entire active region,
  AR 8156 observed on 1998 February 16. We model this region by coupling
  potential field extrapolations to full solutions of the time-dependent
  hydrodynamic loop equations. To make the problem more tractable
  we begin with a static heating model that reproduces the emission
  observed in four different Yohkoh Soft X-Ray Telescope (SXT) filters
  and consider impulsive heating scenarios that yield time-averaged SXT
  intensities that are consistent with the static case. We find that
  it is possible to reproduce the total observed soft X-ray emission in
  all of the SXT filters with a dynamical heating model, indicating that
  nanoflare heating is consistent with the observational properties of
  the high-temperature solar corona. At EUV wavelengths the simulated
  emission shows more coronal loops, but the agreement between the
  simulation and the observation is still not acceptable.

---------------------------------------------------------
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: Impact of Flare Radiation on the Ionosphere
Authors: Slinker, S.; Krall, J.; Huba, J. D.; Warren, H.; Joyce, G.
2007AGUSMSA33A..03S    Altcode:
  We study the impact of the solar flare radiation on the low- to
  mid-latitude ionosphere for a number of flares: 28 Oct 2003, 29 Oct
  2003, 4 Nov 2004, and 7 Sept 2005. We use the solar EUV spectrum from
  the Flare Irradiance Spectral Model (FISM)1; the spectrum considers
  10Å bins from 10 -- 1050 Å and a one minute cadence. We use this
  spectrum in the NRL three-dimensional ionosphere model SAMI3 to
  obtain the global impact of the flare on the mid- to low-latitude
  ionosphere. We find that the TEC can increase by ~ 10% which can be
  as high as ~ 25 TECU. Finally, we compare our results to GPS data and
  discuss improvements to the model. 1 Chamberlin, P.C., T.N. Woods,
  and F.G. Eparvier, ILWS Workshop Proc., GOA, 2006. Research supported
  by ONR.

---------------------------------------------------------
Title: Hinode EIS Observations of Solar Active Regions
Authors: Mariska, John T.; Doschek, G. A.; Warren, H. P.; Brooks,
   D. H.; Young, P. R.; Watanabe, T.; Culhane, J. L.
2007AAS...210.7202M    Altcode: 2007BAAS...39R.178M
  The EUV Imaging Spectrometer (EIS) on the Hinode satellite provides
  high spatial and spectral resolution data along a 512 arcsec slit in
  two wavelength ranges, 170--210 Angstroms and 250--290 Angstroms. These
  wavelengths mostly contain emission lines from upper transition region
  and coronal plasmas. Emission from these wavelengths is routinely
  imaged using instruments such as the EIT on SOHO and TRACE, but there
  are few high-resolution spectra to aid in more deeply understanding
  the physical conditions and dynamics associated with the intensity
  variations seen in the images. In this presentation, we show some
  initial results from EIS active region studies aimed at mapping the
  density, temperature, nonthermal broadening, and Doppler shifts in
  active regions. This presentation focusses on spectroheliograms of
  active regions in diagnostically interesting spectral lines. These
  show the overall active region morphology and the behavior of Doppler
  shifts, nonthermal velocities, and densities as a function of position,
  but at the expense of high time resolution. Other presentations will
  focus on how the observed physical parameters vary with time.

---------------------------------------------------------
Title: Intercalibration of the X-ray Telescope and the EUV Imaging
    Spectrometer on Hinode
Authors: Golub, Leon; Cirtain, J.; DeLuca, E. E.; Hara, H.; Warren,
   H.; Weber, M.
2007AAS...210.9418G    Altcode: 2007BAAS...39..220G
  The X-Ray Telescope and the Extreme-Ultra Violet Imaging Spectrometer
  on Hinode are designed to measure the emission of excited ions formed
  at temperatures ranging from 10<SUP>4</SUP>-10<SUP>8</SUP> K. The
  temperature overlap of these two telescope is from 0.7 to 20 MK, and
  an on-orbit calibration of the sensitivity of the two instruments
  to solar features will provide a basis for future observational
  comparisons. Using calibrated samples of data from each instrument,
  and relying to a great extent on the CHIANTI spectral code, we have
  derived an estimate of the inter-calibration of the two telescope
  for a variety of different solar features and conditions. This is a
  major step in enhancing our ability to use the instruments together
  for providing quantitative diagnostics of the solar plasma.

---------------------------------------------------------
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: Static and Dynamic Simulations of a Solar Active Region
Authors: Warren, Harry; Winebarger, A. R.
2007AAS...210.9104W    Altcode: 2007BAAS...39R.204W
  Most previous work on the coronal heating problem has focused on the
  observation and simulation of individual loops. The recent proliferation
  of high speed, multi-processor computers has made it possible to
  simulate large ensembles of loops and consider the emission from entire
  active regions using both steady and impulsive heating models. In this
  paper we present simulations of AR8156, which was observed by SXT and
  EIT in many filters. We model this region by coupling potential field
  extrapolations to full solutions of the 1D hydrodynamic loop equations
  using both steady and impulsive heating scenarios. The steady heating
  model is able to reproduce the total intensity and general morphology
  of the soft X-ray emission observed in four SXT filters. The steady
  models, however, cannot reproduce the loop emission observed at lower
  temperatures. Using the steady heating rate for each field line as the
  basis for an impulsive heating scenario we find that the time-dependent
  modeling is able to reproduce both the high temperature emission and
  many, but not all, features of the emission at lower temperatures. We
  will also discuss how new observations from Hinode will greatly improve
  the observational constraints on the coronal heating problem.

---------------------------------------------------------
Title: Post-CME Reconnection and the Generation of Descending Solar
    Coronal Voids
Authors: Linton, Mark; Longcope, D.; Warren, H.
2007AAS...210.2903L    Altcode: 2007BAAS...39R.137L
  Observations of solar coronal flares occurring behind coronal mass
  ejections (CME's) have shown downflowing voids in the corona, which are
  believed to be the signatures of descending magnetic flux tubes. We are
  studying the hypothesis that these flux tubes have reconnected in the
  current sheet which forms behind the CME in the high corona. We will
  present three dimensional MHD simulations of a localized reconnection
  event in a Y-type post-CME current sheet. The reconnected field
  creates a downflow which rapidly decelerates as it hits the Y-line
  and the magnetic loops below it. We will compare this deceleration
  with the observed deceleration of coronal voids when they hit coronal
  arcades. We will also present studies of the 3D tearing mode in this
  current sheet. This tearing generates numerous localized reconnection
  patches, and a cascade of reconnected fluxtubes. We will compare this
  cascade with the the cascades of descending voids and coronal loops
  which are seen following a CME event, providing further evidence that
  the observed voids are reconnected flux tubes. <P />This research was
  supported by grants from NASA and ONR.

---------------------------------------------------------
Title: Initial Results On Active Region Loop Morphology From Hinode
    EIS And XRT.
Authors: Brooks, David; Warren, H.; Young, P.; Matsuzaki, K.;
   Williams, D.
2007AAS...210.6307B    Altcode: 2007BAAS...39Q.172B
  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 coronal loops are difficult to
  understand. There has been some debate in the community as to whether
  coronal loops really have constant cross-sections (as suggested by
  TRACE and SXT), 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 observed intensities and morphology in
  active region loops, bright points, and the full Sun. Hinode EIS and
  XRT provide unprecedented spatial resolution at high temperatures
  that can be used to reexamine the morphology of active region loops
  and provide new insights. Here we present initial results from our
  study of active region loop widths with EIS and XRT.

---------------------------------------------------------
Title: Atomic oxygen photoionization rates computed with high
    resolution cross sections and solar fluxes
Authors: Meier, R. R.; McLaughlin, Brendan M.; Warren, H. P.;
   Bishop, James
2007GeoRL..34.1104M    Altcode:
  Accurate knowledge of photoionization rates is fundamental for the
  study and understanding of gases in the solar system. Past calculations
  of the photoionization rates of atmospheric gases lack the spectral
  resolution to accommodate highly structured autoionization features in
  the photoionization cross section. A new theoretical model of the atomic
  oxygen photoionization cross section combined with a new solar minimum
  spectral irradiance model enables calculations at very high spectral
  resolution (0.001 nm). Our analysis of unattenuated photoionization
  rates reveals no strong coincidences among myriad bright solar emission
  lines and autoionization lines in the cross section. However, deeper
  in the terrestrial atmosphere, opacity effects are significant and the
  need for high spectral accuracy becomes increasingly important. In
  our solar minimum example, factor of 3 errors occur when the lower
  thermospheric photoionization rate of atomic oxygen is computed at 1
  nm spectral resolution for both the cross section and solar flux.

---------------------------------------------------------
Title: Soft X-ray irradiances during solar flares observed by
    TIMED-SEE
Authors: Rodgers, E. M.; Bailey, S. M.; Warren, H. P.; Woods, T. N.;
   Eparvier, F. G.
2006JGRA..11110S13R    Altcode:
  Observations from the Thermosphere Ionosphere Mesosphere Energetics
  Dynamics-Solar Extreme Ultraviolet Experiment (TIMED-SEE) are
  analyzed to determine the solar soft X-ray energy emission during a
  solar flare. The TIMED-SEE X-ray ultraviolet Photometer System (XPS)
  detectors utilize broadband photodiodes that observe from 0.1 to 27
  nm. The XPS observed 29 flares of various strengths over a 6-month
  period in 2002. We describe an emission measure technique to interpret
  the broadband observations and determine a best fit flare spectrum. This
  technique is applied to the 29 flares observed by the XPS. Our results
  show that most of the enhancement in the solar spectrum during a
  flare comes from the 0-2 nm wavelength range. We also show that the XPS
  calculated 0.1-0.8 nm irradiance for brighter M-class and X-class flares
  is in good agreement with the Geostationary Operational Environmental
  Satellites (GOES) observed 0.1-0.8 nm irradiance. Also, the XPS 0-7
  nm flare irradiance is well correlated with the 0.1-0.8 nm irradiance
  observed by GOES. We show that the total 0-7 nm irradiance of smaller
  X-class flares (X1-X5) calculated at the time of the XPS observation
  provides 2-3 times the energy of the quiet Sun 0-7 nm irradiance.

---------------------------------------------------------
Title: Using a Loss-of-Equilibrium CME Model to Predict X-Ray and
    EUV Emissions Resulting From Solar Flares
Authors: Reeves, K. K.; Warren, H. P.; Forbes, T. G.
2006IAUJD...3E..68R    Altcode:
  In this study, we use a loss-of-equilibrium model for solar eruptions
  to calculate the thermal energy input into a system of flare loops. In
  this model, the flare consists of a system of reconnecting loops
  below a current sheet that connects the flare to an erupting flux
  rope. The thermal energy is calculated by assuming that all of the
  Poynting flux into the current sheet is thermalized. The density,
  temperature and velocity of the plasma in each reconnected loop
  are then calculated using a 1D hydrodynamic code. These parameters
  are coupled with the instrument response functions of various solar
  instruments to calculate flare emissions. We simulate spectra from the
  Bragg Crystal Spectrometer (BCS) on Yohkoh, and find that the strong
  blueshifts that should be present due to chromospheric evaporation
  during flare initiation are difficult to observe with BCS, but may be
  better observed with a more sensitive instrument. We also find that a
  density enhancement occurs at the top of a loop when evaporating plasma
  fronts in each loop leg collide there. This enhancement gives rise to
  bright loop-top intensities in simulated Transition Region and Coronal
  Explorer (TRACE) and Yohkoh Soft X-ray Telescope (SXT) images. These
  loop-top features have been observed in TRACE and SXT images, and are
  not explained by single-loop flare models. The Atmospheric Imaging
  Assembly (AIA) on the Solar Dynamics Observatory should be able to
  observe these features in detail, and we will use this model to help
  develop flare observing programs for AIA.

---------------------------------------------------------
Title: Heating of the Solar Corona: Modeling the EUV/X-ray Emission
Authors: Brooks, D. H.; Warren, H. P.
2006ESASP.617E..11B    Altcode: 2006soho...17E..11B
  No abstract at ADS

---------------------------------------------------------
Title: Hydrostatic Modeling of the Integrated Soft X-Ray and Extreme
    Ultraviolet Emission in Solar Active Regions
Authors: Warren, Harry P.; Winebarger, Amy R.
2006ApJ...645..711W    Altcode: 2006astro.ph..2052W
  Many studies of the solar corona have shown that the observed X-ray
  luminosity is well correlated with the total unsigned magnetic flux. In
  this paper we present results from the extensive numerical modeling of
  active regions observed with the Solar and Heliospheric Observatory
  (SOHO) EUV Imaging Telescope (EIT), the Yohkoh Soft X-Ray Telescope
  (SXT), and the SOHO Michelson Doppler Imager (MDI). We use potential
  field extrapolations to compute magnetic field lines and populate
  these field lines with solutions to the hydrostatic loop equations
  assuming steady, uniform heating. Our volumetric heating rates are of
  the form ɛ<SUB>H</SUB>~B¯<SUP>α</SUP>/L<SUP>β</SUP>, where B¯ is
  the magnetic field strength averaged along a field line and L is the
  loop length. Comparisons between the observed and simulated emission
  for 26 active regions suggest that coronal heating models that scale
  as ɛ<SUB>H</SUB>~B¯/L are in the closest agreement with the observed
  emission at high temperatures. The field-braiding reconnection model
  of Parker, for example, is consistent with our results. We find,
  however, that the integrated intensities alone are insufficient to
  uniquely determine the parameterization of the volumetric heating
  rate. Visualizations of the emission are also needed. We also find
  that there are significant discrepancies between our simulation results
  and the lower temperature emission observed in the EIT channels.

---------------------------------------------------------
Title: 3D Reconnection Simulations of Descending Coronal Voids
Authors: Linton, Mark; Longcope, D.; Warren, H.; McKenzie, D.
2006SPD....37.0123L    Altcode: 2006BAAS...38R.219L
  We will present simulations of a highly localized, finite durationburst
  of 3D reconnection in a post-CME current sheet. Suchreconnection forms
  a pair of 3D reconnected flux tubes piercing thecurrent sheet. These
  tubes retract from the reconnection region,pushing their way through
  the surrounding magnetic field to form apost-reconnection arcade below
  the reconnection region. We willdiscuss how the evolution of these
  reconnected flux tubes can formthe descending, post-eruption voids
  which have been seen in thehigh corona by the Yohkoh, TRACE and LASCO
  instruments. Wewill compare the velocities and deceleration profiles of
  theobserved voids with those of the simulated reconnected flux tubes.We
  will also show how the presence of multiple reconnectionregions in a
  single current sheet affects the dynamics of thereconnected tubes.

---------------------------------------------------------
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: Using X-ray and EUV Active Region Observations to Constrain
    the CoronalHeating Rate
Authors: Winebarger, Amy R.; Warren, H. P.
2006SPD....37.1702W    Altcode: 2006BAAS...38..245W
  One constraint on the coronal heating mechanism may come from the
  observation that X-ray and EUV intensities of solar active regions
  are well correlated with the total unsigned magnetic flux. In this
  presentation, we discuss an extensive modeling effort using 26 active
  regions observed with EIT, SXT, and MDI. For each active region, we use
  potential field extrapolations of the photospheric field to estimate
  the coronal field. We then populate the resulting field lines with
  solutions to the hydrostatic loop equations assuming steady, uniform
  heating rates of the form E B^alpha/L^beta. We compare the resulting
  relationship between the simulated X-ray and EUV intensities and total
  unsigned flux with the observed relationship. We find that solutions
  with E B/L are the most consistent with the X-ray observations as well
  as the EUV "moss" intensities, but no heating function well matches
  the EUV loop intensities. Because static models are unable to address
  the extended emission at lower (1-2 MK) temperatures, we suggest that
  dynamical processes play a significant role in active region heating.

---------------------------------------------------------
Title: Modeling High Resolution Flare Spectra Using Hydrodynamic
    Simulations
Authors: Warren, Harry; Doschek, G.
2006SPD....37.2702W    Altcode: 2006BAAS...38..253W
  Understanding the hydrodynamic response of the solar atmosphere to
  the release of energy during a flare has been a long standing problem
  in solar physics. Early time-dependent hydrodynamic simulations were
  able to reproduce the high temperatures and densities observed in solar
  flares, but were not able to model the observations in any detail. For
  example, these simulations could not account for the relatively slow
  decay of the observed emission or the absence of blueshifts in high
  spectral resolution line profiles at flare onset. We have found that by
  representing the flare as a succession of independently heated filaments
  it is possible to reproduce both the evolution of line intensity and
  the shape of the line profile using hydrodynamic simulations. Here
  we present detailed comparisons between our simulation results and
  several flares observed with the Yohkoh Bragg Crystal Spectrometer
  (BCS). Comparisons with 3D MHD simulations will also be discussed.

---------------------------------------------------------
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: Modeling of the EUV/Soft X-ray Emission in a Large Coronal
    Bright Point
Authors: Brooks, David; Warren, H.
2006SPD....37.0126B    Altcode: 2006BAAS...38R.219B
  We use potential field extrapolations of SOHO/MDI and Kitt Peak Vacuum
  Telescope high resolution magnetograms to model the magnetic field line
  distribution in a large coronal bright point. We populate the field
  lines with solutions to the hydrostatic loop equations and simulate the
  emission observed at EUV and soft X-ray wavelengths. The results are
  compared in detail to observations obtained by Yohkoh/SXT, SOHO/EIT,
  and SOHO/CDS. Previous similar studies of larger active regions have
  shown that relatively good agreement is obtained between the simulated
  and observed soft X-ray images. The simulations, however, fail to
  correctly model the loop emission and integrated intensities at EUV
  wavelengths simultaneously. Our results support these conclusions; the
  SXT images and integrated intensities agree well with the observations,
  but the spatial distributions of the EUV line intensities are incorrect
  even when the integrated intensities are correct. We further extend the
  analysis to lines formed in the transition region. Here the simulated
  intensities are too large by factors of 2--4 and there are differences
  in the morphology of the network emission. We explore the consequences
  for these comparisons of using loop expansion and different forms of
  the heating function in the models. The techniques are also applied
  to model the on-disk and off-limb intensities in the quiet corona.This
  research was supported by the NASA Guest Investigator Program and the
  Office of Naval Research.

---------------------------------------------------------
Title: The Intercalibration of SOHO EIT, CDS-NIS, and TRACE
Authors: Brooks, David H.; Warren, Harry P.
2006ApJS..164..202B    Altcode:
  Using coordinated observations of a quiet coronal region, we study the
  intercalibration of the CDS and EIT instruments on board the Solar and
  Heliospheric Observatory (SOHO) and the Transition Region and Coronal
  Explorer (TRACE). We derive the differential emission measure (DEM)
  distribution from CDS spectral line intensities and convolve it with
  EIT and TRACE temperature response functions, calculated with the
  latest atomic data from the CHIANTI database, to predict count rates
  in their observing channels. We examine different analysis methods and
  briefly discuss some more advanced aspects of atomic modeling such as
  the density dependence of the ionization fractions. We investigate the
  implications for our study using data from the ADAS database. We find
  that our CDS DEM can predict the TRACE and EIT 171 and 195 Å channel
  count rates to within 25%. However, the accuracy of the predictions
  depends on the ionization fractions and elemental abundances used. The
  TRACE 284 Å and EIT 284 and 304 Å filter predictions do not agree
  well with the observations, even after taking the contribution from
  the optically thick He II 304 Å line to the TRACE 284 Å channel into
  account. The different CDS DEM solutions we derive using different
  ionization fractions produce fairly similar results: the majority of
  the CDS line intensities used are reproduced to within 20% with only
  around one-fifth reproduced to worse than 50%. However, the comparison
  provides us with further clues with which to explain the discrepancies
  found for some lines, and highlights the need for accurate equilibrium
  ionization balance calculations even at low density.

---------------------------------------------------------
Title: Photoionization Rate of Atomic Oxygen
Authors: Meier, R. R.; McLaughlin, B. M.; Warren, H. P.; Bishop, J.
2006AGUSMSA23B..01M    Altcode:
  Accurate knowledge of the photoionization rate of atomic oxygen
  is important for the study and understanding of the ionospheres
  and emission processes of terrestrial, planetary, and cometary
  atmospheres. Past calculations of the photoionization rate have
  been carried out at various spectral resolutions, but none were at
  sufficiently high resolution to accommodate accidental resonances
  between solar emission lines and highly structured auto-ionization
  features in the photoionization cross section. A new version of the
  NRLEUV solar spectral irradiance model (at solar minimum) and a new
  model of the O photoionization cross section enable calculations at
  very high spectral resolution. We find unattenuated photoionization
  rates computed at 0.001 nm resolution are larger than those at moderate
  resolution (0.1 nm) by amounts approaching 20%. Allowing for attenuation
  in the terrestrial atmosphere, we find differences in photoionization
  rates computed at high and moderate resolution to vary with altitude,
  especially below 200 km where deviations of plus or minus 20% occur
  between the two cases.

---------------------------------------------------------
Title: Solar Flare Soft X-ray Irradiance and its Impact on the
    Earth's Upper Atmosphere
Authors: Rodgers, E. M.; Bailey, S. M.; Warren, H. P.; Woods, T. N.;
   Eparvier, F. G.
2006AGUSMSA23B..03R    Altcode:
  Solar flare soft X-ray irradiance provides a highly variable energy
  source to the lower thermosphere. Observations from three NASA
  satellite missions, the Thermosphere, Ionosphere, Mesosphere,
  Energetics and Dynamics - Solar Extreme Ultraviolet Experiment
  (TIMED-SEE), the Solar Radiation and Climate Experiment (SORCE) and
  the Student Nitric Oxide Explorer (SNOE) are analyzed to determine
  how solar soft X-ray irradiance varies during a solar flare and
  how this irradiance affects the Earth's lower thermosphere. Solar
  soft X-rays are one of the principal energy sources that lead to the
  production of thermospheric nitric oxide (NO) through the dissociation
  of odd-nitrogen. NO is an important source of radiative cooling in the
  thermosphere and therefore performs an important role in the energy
  balance. The XUV Photometer System (XPS) aboard TIMED-SEE and the XPS
  aboard SORCE both include a suite of photodiode detectors that measure
  the solar soft X-ray irradiance in broadband channels from 0.1 to 27
  nm. The TIMED-SEE XPS observed 29 flares of various strengths over
  a six month period in 2002 and the SORCE XPS observed several large
  flares during the fall of 2003. An emission measure technique is used
  to interpret the broadband observations and determine a solar flare
  spectrum with a model that calculates theoretical spectra for input
  differential emission measures (DEM). The DEMs are iterated until
  the resulting spectrum reproduces the XPS observations. These solar
  flare spectra are used to determine the soft X-ray energy input to
  the Earth's lower thermosphere. Most of the solar flare soft X-ray
  irradiance comes from the 1 - 2 nm range and is deposited near 106
  km. The abundance of NO peaks near 106 km and responds dramatically to
  energy deposited in the upper atmosphere. SNOE observed a significant
  increase in thermospheric NO following the X17 solar flare on 28 October
  2003. Analysis of solar flare NO density enhancements and a comparison
  to results from a photochemical model will be presented along with a
  description of the solar flare spectral analysis.

---------------------------------------------------------
Title: Carrington Maps of the Upper Photosphere
Authors: Sheeley, N. R., Jr.; Warren, H. P.
2006ApJ...641..611S    Altcode:
  We have used images of the Sun's disk, obtained in the 6767 Å
  continuum with the Michelson Doppler Interferometer (MDI) on the
  Solar and Heliospheric Observatory (SOHO), to make Carrington
  maps of the upper photosphere during the years 1996-2005. Each map
  is constructed from observations near the limb where the continuum
  radiation originates relatively high in the photosphere and faculae have
  their greatest visibility. Consequently, the Carrington maps resemble
  spectroheliograms in temperature-sensitive photospheric lines and show
  the global distribution of faculae and all but the smallest sunspots
  (which are obscured by overlying faculae). A time-lapse sequence of the
  combined east-limb and west-limb maps shows the emergence of active
  regions and the evolution of large-scale patterns of faculae with an
  average temporal resolution of 14 days during the sunspot cycle. Also,
  a longitudinally averaged butterfly diagram of these maps shows that in
  each hemisphere there is a facula-free zone separating the old-cycle
  polar field from trailing-polarity flux that is migrating poleward
  from the sunspot belts. These facula-free zones coincide with the
  neutral zones of the axisymmetric component of photospheric magnetic
  field and their arrival at the poles in 2001 marks the reversal of the
  polar fields. We think that this mapmaking technique can be applied
  to white-light images obtained daily at the Mount Wilson Observatory
  since 1905 and that the resulting Carrington maps will provide details
  about the polar-field reversal process during past sunspot cycles when
  high-quality magnetograms were unavailable.

---------------------------------------------------------
Title: Multithread Hydrodynamic Modeling of a Solar Flare
Authors: Warren, Harry P.
2006ApJ...637..522W    Altcode: 2005astro.ph..7328W
  Past hydrodynamic simulations have been able to reproduce the high
  temperatures and densities characteristic of solar flares. These
  simulations, however, have not been able to account for the slow
  decay of the observed flare emission or the absence of blueshifts
  in high spectral resolution line profiles. Recent work has suggested
  that modeling a flare as a sequence of independently heated threads
  instead of as a single loop may resolve the discrepancies between
  the simulations and observations. In this paper, we present a method
  for computing multithread, time-dependent hydrodynamic simulations
  of solar flares and apply it to observations of the Masuda flare of
  1992 January 13. We show that it is possible to reproduce the temporal
  evolution of high temperature thermal flare plasma observed with the
  instruments on the GOES and Yohkoh satellites. The results from these
  simulations suggest that the heating timescale for a individual thread
  is on the order of 200 s. Significantly shorter heating timescales
  (20 s) lead to very high temperatures and are inconsistent with the
  emission observed by Yohkoh.

---------------------------------------------------------
Title: NRLEUV 2: A new model of solar EUV irradiance variability
Authors: Warren, Harry P.
2006AdSpR..37..359W    Altcode:
  NRLEUV represents an independent approach to modeling the Sun's
  EUV irradiance and its variability. Instead of relying on existing
  irradiance observations, our model utilizes differential emission
  measure distributions derived from spatially and spectrally resolved
  solar observations, full-disk solar images, and a database of atomic
  physics parameters to calculate the solar EUV irradiance. Recent
  updates to the model include the calculation of a new quiet Sun
  differential emission measure distribution using data from the CDS and
  SUMER spectrometers on SOHO and the use of a more extensive database
  of atomic physics parameters. Here, we present comparisons between
  the NRLEUV quiet Sun reference spectrum and solar minimum irradiance
  observations. Although there are many areas of agreement between
  the modeled spectrum and the observations, there are some major
  disagreements. The computed spectra cannot reproduce the observed
  irradiances at wavelengths below about 160 Å. The observed irradiances
  appear to overstate the magnitude of the EUV continua. We also present
  some initial comparisons between the NRLEUV irradiance variability model
  and TIMED/SEE data. We find that the NRLEUV model tends to overpredict
  the absolute magnitude of the irradiance at many wavelengths. The
  model also appears to underpredict the magnitude of the solar-cycle
  and solar rotational variation in transition region emission lines.

---------------------------------------------------------
Title: Observing the Solar atmosphere with the Extreme Ultraviolet
    Imaging Spectrometer on Solar B
Authors: Korendyke, C. M.; Brown, C.; Dere, K.; Doschek, G.; Klimchuk,
   J.; Landi, E.; Mariska, J.; Warren, H.; Lang, J.
2005AGUFMSH41B1124K    Altcode:
  The Extreme Ultraviolet Imaging Spectrometer (EIS) is part of the
  instrument complement on the Solar B satellite, scheduled for launch
  in the summer of 2006. The instrument has been calibrated and is
  presently mounted on the spacecraft. EIS is the most sensitive EUV
  solar spectrometer to be flown. The instrument is the first of a new
  generation of two optical element, solar spectrographs. Preliminary
  results from the laboratory focussing and calibration of the
  instrument will be shown. The instrument wavelength coverage includes
  reasonably bright spectral lines emitted by plasmas from 0.1 to 20 MK
  in temperature. The wavelength range also provides coronal density
  diagnostics. Temperature, density and velocity diagnostics will be
  discussed. An example observing program for exploring active region
  evolution and dynamics will be discussed.

---------------------------------------------------------
Title: Chromospheric Evaporation in Solar Flares Revisited
Authors: Doschek, G. A.; Warren, H. P.
2005ApJ...629.1150D    Altcode:
  We investigate the initial stage of chromospheric evaporation in flares
  using soft X-ray spectra obtained by the Bragg Crystal Spectrometer
  (BCS) experiment on Yohkoh. We find that the centroid wavelength
  of the Ca XIX line in spectra with the first detectable emission is
  within about 8.5×10<SUP>-4</SUP> Å of the rest wavelength, which
  corresponds to a Doppler shift of no more than 80 km s<SUP>-1</SUP>. We
  also determine the minimum detectable soft X-ray flare volume emission
  measure from BCS Ca XIX flare spectra. We find that the minimum
  detectable emission measured by BCS is produced by an X-ray flux
  that is about equal to the peak intensity of a class A6 flare. These
  results are difficult to reconcile with one-dimensional hydrodynamic
  simulations of an impulsively heated flare loop, which predict large
  Doppler shifts during the initial stage of the heating. Furthermore,
  inspection of high spatial resolution TRACE images of flare plasma
  indicate significant differences between the observed morphology and
  the predictions of hydrodynamic models. The evolution of the intensity
  and the Doppler shifts are more consistent with models that assume the
  sequential heating of small-scale threads rather than the heating of an
  individual loop. However, the bright knots of emission and asymmetrical
  intensity distributions seen in flare images cannot be explained by
  current numerical models of chromospheric evaporation.

---------------------------------------------------------
Title: Global response of the low-latitude to midlatitude ionosphere
    due to the Bastille Day flare
Authors: Huba, J. D.; Warren, H. P.; Joyce, G.; Pi, X.; Iijima, B.;
   Coker, C.
2005GeoRL..3215103H    Altcode:
  The first global simulation study and comparison to data of the
  ionospheric effects associated with the enhanced EUV irradiance of
  the Bastille Day flare are presented. This is done by incorporating a
  time-dependent EUV spectrum, based on data and hydrodynamic modeling,
  into the NRL ionosphere model SAMI3. The simulation results indicate
  that the total electron content (TEC) increases to over 7 TEC units in
  the daytime, low-latitude ionosphere. In addition, it is predicted that
  the maximum density in the F-layer (NmF2) increases by $\lesssim$20%
  and that the height of the maximum electron density (HmF2) decreases by
  $\lesssim$20%. These results are explained by the increased ionization
  at altitudes &lt;400 km which increases TEC and NmF2 while decreasing
  HmF2. The results are in reasonably good agreement with data obtained
  from GPS satellites and the TOPEX satellite.

---------------------------------------------------------
Title: Cooling Active Region Loops Observed with SXT and TRACE
Authors: Winebarger, Amy R.; Warren, Harry P.
2005ApJ...626..543W    Altcode: 2005astro.ph..2270W
  An impulsive heating multiple strand (IHMS) model is able to
  reproduce the observational characteristics of EUV (~1 MK) active
  region loops. This model implies that some of the loops must reach
  temperatures where X-ray filters are sensitive (&gt;2.5 MK) before
  they cool to EUV temperatures. Hence, some bright EUV loops must be
  preceded by bright X-ray loops. Previous analyses of X-ray and EUV
  active region observations, however, have concluded that EUV loops
  are not the result of cooling X-ray loops. In this paper, we examine
  two active regions observed in both X-ray and EUV filters and analyze
  the evolution of five loops over several hours. These loops first
  appear bright in the X-ray images and later appear bright in the EUV
  images. The delay between the appearance of the loops in the X-ray and
  EUV filters is as little as 1 hr and as much as 3 hr. All five loops
  appear as single “monolithic” structures in the X-ray images but
  are resolved into many smaller structures in the (higher resolution)
  EUV images. The positions of the loops appear to shift during cooling,
  implying that the magnetic field is changing as the loops evolve. There
  is no correlation between the brightness of the loop in the X-ray and
  EUV filters, meaning that a bright X-ray loop does not necessarily
  cool to a bright EUV loop, and vice versa. The progression of the
  loops from X-ray images to EUV images and the observed substructure
  is qualitatively consistent with the IHMS model.

---------------------------------------------------------
Title: Reconciling Hydrodynamic Simulations With Yohkoh and RHESSI
    Observations of Solar Flares
Authors: Warren, H. P.
2005AGUSMSP23B..07W    Altcode:
  High spatial resolution TRACE observations provide compelling
  observational evidence for small-scale filamentation in solar flares. In
  this poster we present results from time-dependent hydrodynamic
  simulations that treat a flare as a succession of <P />independently
  heated filaments. The energy deposited onto each filament and the
  volume of each filament are derived from the observed GOES soft X-ray
  fluxes. These numerical simulations are able to reproduce both the
  evolution of the line intensity and the shape of the line profile
  for the Yohkoh BCS Ca XIX and S XV lines. Of particular significance
  is the fact that the simulated line profiles are always dominated
  by the stationary component, consistent with observations. In this
  model the strongly blueshifted emission evident during the initial
  heating of a thread is largely masked by emission from threads that
  have been heated previously and do not show bulk motions. In addition
  to comparisons with Yohkoh we will also present detailed comparisons
  between simulation results and RHESSI flare observations.

---------------------------------------------------------
Title: Chromospheric Evaporation in Solar Flares Revisited
Authors: Doschek, G. A.; Warren, H. P.
2005AGUSMSP52A..05D    Altcode:
  We investigate the initial stage of chromospheric evaporation in
  flares using soft X-ray flare spectra obtained by the Bragg Crystal
  Spectrometer (BCS) experiment on Yohkoh. We determine the minimum
  detectable soft X-ray flare volume emission measure from BCS Ca XIX
  flare spectra. We find that the minimum detectable emission measure
  by BCS is produced by an X-ray flux that is about equal to the peak
  intensity of a class A5 flare. We also find that the centroid wavelength
  of the Ca XIX line in spectra with the first detectable emission is
  within about 8.5E-4 Angstroms of the rest wavelength, which is 80
  km/s in terms of a Doppler shift. We interpret our results assuming
  sequential chromospheric evaporation into a multi-threaded flare loop
  envelop. Under this assumption, by comparing the BCS results with
  images of flares from the Soft X-ray Telescope (SXT) on Yohkoh and
  from TRACE, we have determined the minimum energy and electron density
  of multi-million degree soft X-ray plasma that can be detected using
  presently available spectroscopic X-ray data. In addition we consider
  the implications of a multi-thread loop model on TRACE and Yohkoh flare
  images, and the differences between the images and the multi-thread
  predictions. We find that the multi-million degree flare plasma in TRACE
  images frequently exhibits structures that do not resemble the images
  of loops expected from the numerical simulations of evaporation. Thus,
  while observational signatures of flare dynamics can be consistent
  with chromospheric evaporation simulations, problems still remain in
  understanding the loop morphology of the multi-million degree plasma.

---------------------------------------------------------
Title: Are there two coronal heating mechanisms?
Authors: Winebarger, A. R.; Warren, H. P.
2005AGUSMSP41A..03W    Altcode:
  The source of coronal heating remains one of the most significant
  unknowns in solar physics. In this poster, we present analysis of two
  types of active region structures - relatively long loops that are
  bright in EUV images and short, hot loops that are bright in X-ray
  images. We compare the temporal evolution of these loops in multiple
  filters to the evolution derived from hydrodynamic simulations with
  various heating function to determine the most likely heating function
  for each structure.

---------------------------------------------------------
Title: A Solar Minimum Irradiance Spectrum for Wavelengths below
    1200 Å
Authors: Warren, Harry P.
2005ApJS..157..147W    Altcode:
  NRLEUV represents an independent approach to modeling the Sun's EUV
  irradiance and its variability. Our model utilizes differential emission
  measure distributions derived from spatially and spectrally resolved
  solar observations, full-disk solar images, and a database of atomic
  physics parameters to calculate the solar EUV irradiance. In this paper
  we present a new solar minimum irradiance spectrum for wavelengths
  below 1200 Å. This spectrum is based on extensive observations of
  the quiet Sun taken with the CDS and SUMER spectrometers on the Solar
  and Heliospheric Observatory (SOHO) and the most recent version of
  the CHIANTI atomic physics database. In general, we find excellent
  agreement between this new irradiance spectrum and our previous
  quiet-Sun reference spectrum derived primarily from Harvard Skylab
  observations. Our analysis does show that the quiet-Sun emission
  measure above about 1 MK declines more rapidly than in our earlier
  emission measure distribution and that the intensities of the EUV
  free-bound continua at some wavelengths are somewhat smaller than
  indicated by the Harvard observations. Our new reference spectrum is
  also generally consistent with recent irradiance observations taken
  near solar minimum. There are, however, two areas of persistent
  disagreement. Our solar spectrum indicates that the irradiance
  measurements overestimate the contribution of the EUV free-bound
  continua at some wavelengths by as much as a factor of 10. Our model
  also cannot reproduce the observed irradiances at wavelengths below
  about 150 Å. Comparisons with spectrally resolved solar and stellar
  observations indicate that only a small fraction of the emission lines
  in the 60-120 Å wavelength range are accounted for in CHIANTI.

---------------------------------------------------------
Title: Reconciling Hydrodynamic Simulations with Spectroscopic
    Observations of Solar Flares
Authors: Warren, Harry P.; Doschek, George A.
2005ApJ...618L.157W    Altcode:
  Chromospheric evaporation is a central element of current models
  of solar flares. The high-velocity upflows that should accompany
  evaporation, however, are rarely observed in high-resolution solar flare
  spectra. Thus the absence of blueshifted line profiles represents a
  significant discrepancy between the theory and observations of this
  phenomenon. In this Letter we present an algorithm for computing
  multiple-loop time-dependent hydrodynamic simulations of solar flares
  using a minimum of assumptions. We show that these simulations can
  accurately reproduce the Ca XIX and S XV line profiles observed with
  the Bragg Crystal Spectrometer on Yohkoh during the earliest stages
  of a flare. Since our model represents the flare as a succession
  of independently heated threads, the strongly blueshifted emission
  evident during the initial heating of a thread is largely masked by
  emission from threads that have been heated previously and do not show
  bulk motions.

---------------------------------------------------------
Title: Impact of the Bastille Day Solar Flare on the Low- to
    Mid-Latitude Ionosphere
Authors: Huba, J.; Warren, H.; Joyce, G.
2004AGUFMSA21B0357H    Altcode:
  We study the impact of the Bastille Day solar flare radiation on the
  low- to mid-latitude ionosphere. The methodology is as follows. We
  develop an EUV irradiance spectrum based upon observations for the
  Bastille Day flare. Since solar irradiance observations typically do not
  have the cadence necessary to follow the evolution of a flare, we have
  developed techniques for computing flare spectra from the available
  solar data. We then use this spectrum in the NRL three-dimensional
  ionosphere model SAMI3 to obtain the global impact of the flare on
  the mid- to low-latitude ionosphere. We assess the flare's impact
  by comparing simulation results with and without the solar flare
  enhanced EUV spectrum. A previous study using the NRL two dimensional
  ionosphere model SAMI2 and a more simplistic EUV spectrum of the
  Bastille Day storm found that flare radiation can increase the F-region
  ionosphere density by up to 50% [Meier et al., Geophys. Res. Lett. 29,
  10.1029/2001GL013956, 2002]. Research supported by ONR.

---------------------------------------------------------
Title: The Origin of Postflare Loops
Authors: Sheeley, N. R., Jr.; Warren, H. P.; Wang, Y. -M.
2004ApJ...616.1224S    Altcode:
  We apply a tracking technique, previously developed to study motions
  in the outer corona by Sheeley, Walters, Wang, and Howard, to 195 Å
  filtergrams obtained with the Transition Region and Coronal Explorer
  (TRACE) satellite and obtain height-time maps of the motions in the
  hot (10-20 MK) plasma clouds above postflare loop systems. These
  maps indicate the following two main characteristics. (1) Within the
  plasma cloud, the motions are downward at speeds of approximately 4
  km s<SUP>-1</SUP>. The cloud itself grows with time, its upper layers
  being replenished by the arrival and deceleration of fast inflows and
  its lower layers disappearing when they cool to form the tops of new
  postflare loops. (2) Early in these events, the inward motions are
  turbulent, showing a variety of dark elongated features resembling
  “tadpoles” and some bright features. Later, the inflows are visible
  as dark collapsing loops, changing from initially cusp-shaped features
  to rounder loops as they move inward. Their speeds initially lie in the
  range 100-600 km s<SUP>-1</SUP> but decrease to 4 km s<SUP>-1</SUP>
  in about 3 minutes, corresponding to an average deceleration ~1500 m
  s<SUP>-2</SUP>. Combining these observations with similar observations
  obtained at reconnection sites in the outer corona by the Large Angle
  Spectrometric Coronagraph (LASCO), we conclude that postflare loops are
  the end result of the formation, filling, deceleration, and cooling
  of magnetic loops produced by the reconnection of field lines blown
  open in the flare. The formation of collapsing loops occurs in the
  dark tadpoles; the filling of these initially dark loops occurs via
  chromospheric evaporation, which also contributes to the deceleration
  of the loops; and the radiative cooling ultimately resolves the loops
  into sharply defined structures.

---------------------------------------------------------
Title: Thermal and Nonthermal Emission in Solar Flares
Authors: Warren, Harry P.; Antiochos, Spiro K.
2004ApJ...611L..49W    Altcode:
  The observation that in many flares there is a linear correlation
  between the peak soft X-ray emission and the time-integrated nonthermal
  emission-the Neupert effect-indicates a strong link between particle
  acceleration and chromospheric evaporation. In this Letter we consider
  the hydrodynamic response of impulsively heated flare loops. We
  find that the peak soft X-ray flux should scale approximately as
  E<SUP>1.75</SUP>/V<SUP>0.75</SUP>L<SUP>0.25</SUP>, where E is the total
  input energy, V is the flare volume, and L is the loop length. This
  scaling is not consistent with the linear relationship implied by the
  Neupert effect unless there are additional correlations between the
  input energy and the other parameters of the flare.

---------------------------------------------------------
Title: Can TRACE Extreme-Ultraviolet Observations of Cooling Coronal
    Loops Be Used to Determine the Heating Parameters?
Authors: Winebarger, Amy R.; Warren, Harry P.
2004ApJ...610L.129W    Altcode:
  Recent analysis of relatively cool (~1 MK) active region loops observed
  with TRACE has suggested that these loops have been heated impulsively
  and are cooling through the TRACE bandpasses. In this Letter we
  explore the evolution of cooling loops to determine if the TRACE EUV
  observations can be used to determine the magnitude, duration, and
  location of the energy release. We find that the evolution of the apex
  density and temperature in an impulsively heated cooling loop depends
  only on the total energy deposited (not the magnitude, duration,
  or location of the energy deposition) after the loop cools past an
  “equilibrium point,” where the conductive and radiative cooling
  times are comparable. Hence, observations must be made early in the
  evolution of a loop to determine the heating parameters. Typical TRACE
  observations of cooling loops do not provide adequate information to
  discriminate between different heating scenarios.

---------------------------------------------------------
Title: Evidence for Small-Scale Filamentation and Dynamics in the
    Solar Corona
Authors: Warren, H.
2004AAS...204.8601W    Altcode: 2004BAAS...36..818W
  Observations with the Transition Region and Coronal Explorer (TRACE)
  have revealed that the solar corona is both highly dynamic and highly
  filamented. In this talk I will discuss how dynamics and filamentation
  play an important role in explaining some of the observational
  properties of the Sun's atmosphere. TRACE observations have shown,
  for example, that many relatively cool ( ∼1 MK), long-lived
  active region loops have density and temperature profiles that are
  difficult to reconcile with static models. By modeling these loops
  as a sequence of impulsively heated filaments, in contrast, it is
  possible to account for the high densities, flat temperature profiles,
  and the temporal evolution of these structures. A similar approach to
  modeling the evolution of flare emission yields much better agreement
  with observation than treating the flare as a single loop.

---------------------------------------------------------
Title: Impact of Solar Flare Radiation on the Ionosphere
Authors: Warren, H.; Huba, J. D.; Joyce, G.
2004AGUSMSA23A..07W    Altcode:
  We study the impact of enhanced solar flare radiation on the low-
  to mid-latitude ionosphere. The methodology is to develop an EUV
  irradiance spectrum based upon observations that can be used in
  the NRL ionosphere model SAMI3. Since solar irradiance observations
  typically do not have the cadence necessary to follow the evolution
  of a flare, we have developed techniques for computing flare spectra
  from the available solar data. The initial simulation study will
  use a generic flare radiation spectrum to test the technique and
  develop a baseline understanding of the impact of flare radiation on
  the ionosphere. Subsequent studies will ingest flare spectra based
  on actual events and model results will be compared to observations
  if available. A previous study of the Bastille Day storm found that
  flare radiation can increase the F-region ionosphere density by up
  to 50% [Meier et al., Geophys. Res. Lett. 29, 10.1029/2001GL013956,
  2002]. Research supported by ONR.

---------------------------------------------------------
Title: Thermal and Non-Thermal Emission in Two-Ribbon Flares
Authors: Warren, H.
2004AAS...204.4716W    Altcode: 2004BAAS...36..741W
  The observation that in many flares there is a good correlation between
  the soft X-ray emission and the time-integrated non-thermal emission
  --- the Neupert effect --- indicates a strong link between magnetic
  reconnection and particle acceleration. We present hydrodynamic
  simulations of flare loops heated by precipitating energetic
  electrons. Instead of representing a flare as a single loop, we model
  it as a succession of independently heated, small-scale filaments. We
  find that to reproduce the observed thermal emission the energy in
  the injected electrons must be proportional to the soft X-ray flux,
  not the derivative of the soft X-ray flux as suggested by the Neupert
  effect. Comparisons between the simulations and GOES and RHESSI
  observations indicates that there is not sufficient energy in the
  non-thermal electrons to account for the thermal emission observed
  in a large, long duration flare. This suggests that there must be in
  situ heating of coronal plasma as well as particle acceleration during
  magnetic reconnection.

---------------------------------------------------------
Title: Solar Extreme Ultraviolet and X-ray Irradiance Variations
Authors: Woods, Tom; Acton, Loren W.; Bailey, Scott; Eparvier, Frank;
   Garcia, Howard; Judge, Darrell; Lean, Judith; Mariska, John T.;
   McMullin, Don; Schmidtke, Gerhard; Solomon, Stanley C.; Tobiska,
   W. Kent; Warren, Harry P.; Viereck, Rodney
2004GMS...141..127W    Altcode:
  The solar extreme ultraviolet (EUV) radiation at wavelengths shortward
  of 120 nm is a primary energy source for planetary atmospheres and
  is also a tool for remote sensing of the planets. For such aeronomic
  studies, accurate values of the solar EUV irradiance are needed over
  time periods of minutes to decades. There has been a variety of solar
  EUV irradiance measurements since the 1960s, but most of the recent
  observations have been broadband measurements in the X-ray ultraviolet
  (XUV) at wavelengths shortward of 35 nm. A summary of the solar EUV
  irradiance measurements and their variability during the last decade is
  presented. One of the most significant new solar irradiance results is
  the possibility that the irradiance below 20 nm is as much as a factor
  of 4 higher than the reference Atmospheric Explorer E (AE-E) spectra
  established in the 1970s and 1980s. The primary short-term irradiance
  variability is caused by the solar rotation, which has a mean period
  of 27 days. The primary long-term variability is related to the solar
  dynamo and is known best by the 11-year sunspot cycle. The solar cycle
  variability as a function of wavelength can be characterized as 20% to
  70% between 120 and 65 nm and as a factor of 1.5 to 10 between 65 and 1
  nm. The variability of the total solar EUV irradiance, integrated from
  0 to 120 nm, is estimated to be 30-40% for a large 27-day rotational
  period and a factor of about 2 for the 11-year solar cycle during the
  recent, rather active, solar cycles.

---------------------------------------------------------
Title: NRLEUV 2: A New Model of Solar EUV Irradiance Variability
Authors: Warren, H.; Mariska, J.
2004cosp...35.1109W    Altcode: 2004cosp.meet.1109W
  NRLEUV represents an independent approach to modeling the Sun's
  EUV irradiance and its variability. Our model utilizes differential
  emission measure distributions derived from spatially and spectrally
  resolved solar observations, full-disk solar images, and an a database
  of atomic physics parameters to calculate the solar EUV irradiance. Our
  initial version of the model made use of Skylab spectra and a crude
  partitioning of solar features into quiet Sun, coronal hole, and active
  region components. Despite the simplicity of our initial effort, our
  model was able to reproduce the observed EUV irradiance variability
  at many wavelengths as well as most existing models based directly on
  observations. In this presentation we will discuss a revised version of
  the model that is based on extensive observations with the spectrometers
  on SOHO, utilizes a continuous distribution of emission measures, and
  includes the most comprehensive database of atomic physics parameters
  available. Comparisons between our model, other empirical irradiance
  models, and recent irradiance observations will also be discussed.

---------------------------------------------------------
Title: The Magnetic Corona: Magnetic Reconnection in Solar Flares
Authors: Warren, H. P.
2004IAUS..219...91W    Altcode: 2003IAUS..219E.149W
  No abstract at ADS

---------------------------------------------------------
Title: Density and Temperature Measurements in a Solar Active Region
Authors: Warren, Harry P.; Winebarger, Amy R.
2003ApJ...596L.113W    Altcode:
  We present electron density and temperature measurements from an
  active region observed above the limb with the Solar Ultraviolet
  Measurements of Emitted Radiation spectrometer on the Solar and
  Heliospheric Observatory. Density-sensitive line ratios from Si VIII
  and S X indicate densities greater than 10<SUP>8</SUP> cm<SUP>-3</SUP>
  as high as 200" (or 145 Mm) above the limb. At these heights, static,
  uniformly heated loop models predict densities close to 10<SUP>7</SUP>
  cm<SUP>-3</SUP>. Differential emission measure analysis shows that
  the observed plasma is nearly isothermal with a mean temperature of
  about 1.5 MK and a dispersion of about 0.2 MK. Both the differential
  emission measure and the Si XI/Si VIII line ratios indicate only
  small variations in the temperature at the heights observed. These
  measurements confirm recent observations from the Transition Region and
  Coronal Explorer of “overdense” plasma at temperatures near 1 MK in
  solar active regions. Time-dependent hydrodynamic simulations suggest
  that impulsive heating models can account for the large densities,
  but they have a difficult time reproducing the narrow range of observed
  temperatures. The observations of overdense, nearly isothermal plasma
  in the solar corona provide a significant challenge to theories of
  coronal heating.

---------------------------------------------------------
Title: Evolving Active Region Loops Observed with the Transition
    Region and Coronal Explorer. I. Observations
Authors: Winebarger, Amy R.; Warren, Harry P.; Seaton, Daniel B.
2003ApJ...593.1164W    Altcode:
  Observations made with TRACE have detected a class of persistent active
  region loops that have flat 195/171 Å filter ratios. The intensity of
  these loops implies a density that is as much as 3 orders of magnitude
  larger than the densities of static solutions to the hydrodynamic
  equations. It has recently been suggested that these loops are
  bundles of impulsively heated strands that are cooling through the
  TRACE passbands. This scenario implies that the loops would appear in
  the hotter (Fe XV 284 Å or Fe XII 195 Å) TRACE filter images before
  appearing in the cooler (Fe IX/X 171 Å) TRACE filter images. In this
  paper, we test this hypothesis by examining the temporal evolution
  of five active region loops in multiple TRACE EUV filter images. We
  find that all the loops appear in the hotter filter images before
  appearing in cooler filter images. We then use the measured delay
  to estimate a cooling time and find that four of the five loops have
  lifetimes greater than the expected lifetime of a cooling loop. These
  results are consistent with the hypothesis that each apparent loop
  is a bundle of sequentially heated strands; other explanations will
  also be discussed. To facilitate comparisons between these loops and
  hydrodynamic simulations, we use a new technique to estimate the loop
  length and geometry.

---------------------------------------------------------
Title: Evolving Active Region Loops Observed with the Transition
    Region and Coronal explorer. II. Time-dependent Hydrodynamic
    Simulations
Authors: Warren, Harry P.; Winebarger, Amy R.; Mariska, John T.
2003ApJ...593.1174W    Altcode:
  Observations with the Transition Region and Coronal Explorer (TRACE)
  have revealed a new class of active region loops. These loops have
  relatively flat filter ratios, suggesting approximately constant
  temperatures near 1 MK along much of the loop length. The observed
  apex intensities are also higher than static, uniformly heated loop
  models predict. These loops appear to persist for much longer than
  a characteristic cooling time. Recent analysis has indicated that
  these loops first appear in the hotter Fe XV 284 Å or Fe XII 195
  Å filters before they appear in the Fe IX/Fe X 171 Å filter. The
  delay between the appearance of the loops in the different filters
  suggests that the loops are impulsively heated and are cooling when
  they are imaged with TRACE. In this paper we present time-dependent
  hydrodynamic modeling of an evolving active region loop observed with
  TRACE. We find that by modeling the loop as a set of small-scale,
  impulsively heated filaments we can generally reproduce the spatial
  and temporal properties of the observed loop. These results suggest
  that both dynamics and filamentation are crucial to understanding the
  observed properties of active region loops observed with TRACE.

---------------------------------------------------------
Title: Evolving Active Region Loops Observed With TRACE
Authors: Warren, H. P.; Winebarger, A. R.; Mariska, J. T.
2003SPD....34.1007W    Altcode: 2003BAAS...35Q.826W
  Recent observations with TRACE have revealed a new class of active
  region loops with very interesting properties. These loops have
  relatively flat filter ratios, suggesting approximately constant
  temperatures along much of the loop length, and large densities relative
  to the predictions of static loop models. Recent analysis has indicated
  that these loops first appear in the hotter filters before they appear
  in the cooler filters. The delay between the appearance of the loops in
  the different filters suggests that the loops are impulsively heated and
  are cooling when they are imaged with TRACE. In this paper we present
  time-dependent hydrodynamic modeling of evolving active region loops
  observed with TRACE. We find that by modeling the loops as small-scale,
  impulsively heated filaments we can generally reproduce the spatial
  and temporal properties of the observations. These results suggest
  that both dynamics and filamentation are crucial to understanding the
  observed properties of active region loops observed with TRACE. <P
  />This research has been funded by the NASA SR&amp;T and Sun-Earth
  Connection Guest Investigator programs.

---------------------------------------------------------
Title: A New Method to Constrain the Iron Abundance from Cooling
    Delays in Coronal Loops
Authors: Aschwanden, Markus J.; Schrijver, Carolus J.; Winebarger,
   Amy R.; Warren, Harry P.
2003ApJ...588L..49A    Altcode: 2003astro.ph..9506A
  Recent observations with the Transition Region and Coronal Explorer
  reveal that the time delay between the appearance of a cooling loop in
  different EUV temperature filters is proportional to the loop length,
  Δt<SUB>12</SUB>~L. We model this cooling delay in terms of radiative
  loss and confirm this linear relationship theoretically. We derive an
  expression that can be used to constrain the coronal iron enhancement
  α<SUB>Fe</SUB>=A<SUP>cor</SUP><SUB>Fe</SUB>/A<SUP>ph</SUP><SUB>Fe</SUB>
  relative to the photospheric value as function of the cooling delay
  Δt<SUB>12</SUB>, flux F<SUB>2</SUB>, loop width w, and filling factor
  q<SUB>w</SUB>&lt;=1. With this relation, we find upper limits on
  the iron abundance enhancement of α<SUB>Fe</SUB>&lt;=4.8+/-1.7 for
  10 small-scale nanoflare loops, and α<SUB>Fe</SUB>&lt;=1.4+/-0.4
  for five large-scale loops, in the temperature range of T~1.0-1.4
  MK. This result supports the previous finding that low first ionization
  potential elements, including Fe, are enhanced in the corona. The
  same relation constitutes also a lower limit for the filling factor,
  which is q<SUB>w</SUB>&gt;=0.2+/-0.1 and q<SUB>w</SUB>&gt;=0.8+/-0.2
  for the two groups of coronal loops.

---------------------------------------------------------
Title: Observing the Dynamic Corona: Diagnostics to Determine
    Coronal Heating
Authors: Winebarger, A. R.; Warren, H. P.; Mariska, J. T.
2003SPD....34.1008W    Altcode: 2003BAAS...35R.826W
  High resolution observations made with TRACE have uncovered a dynamic
  solar corona. Many of these observations indicate that TRACE is
  imaging cooling loops (i.e., the loop appears in the TRACE filter
  sensitive to hotter plasma before it appears in the cooler TRACE
  filters.) Significant information can be garnered from the TRACE
  observations. For instance, the delay between the appearance of loop
  in different filters provides information on the cooling time of the
  plasma and, hence, the total energy deposited in the loop. The cooling
  time also indicates a density and hence can be used to determine the
  degree of filamentation within a loop. TRACE observations of cooling
  loops, however, tell us little about the spatial and temporal scales
  for energy deposition. In this talk, we will discuss other diagnostics
  necessary to pinpoint the magnitude, duration, and location of the
  heating. The purpose of this talk is to establish the criteria of the
  necessary spatial, spectral, and temperature resolution necessary to
  discriminate between the coronal heating theories.

---------------------------------------------------------
Title: A New Method to Constrain the Iron Abundance from Cooling
    Delays in Coronal Loops
Authors: Aschwanden, M. J.; Schrijver, C. J.; Winebarger, A. R.;
   Warren, H. P.
2003SPD....34.1701A    Altcode: 2003BAAS...35..837A
  Recent observations with TRACE reveal that the time delay between
  the appearance of a cooling loop in different EUV temperature
  filters is proportional to the loop length, dt<SUB>12</SUB>
  ∼ L . We model this cooling delay in terms of radiative loss
  and confirm this linear relationship theoretically. We derive an
  expression that can be used to constrain the coronal iron enhancement
  A<SUB>Fe</SUB>=A<SUB>Fe</SUB><SUP>cor</SUP>/A<SUB>Fe</SUB><SUP>Ph</SUP>
  relative to the photospheric value as function of the cooling delay
  dt<SUB>12</SUB>, flux F<SUB>2</SUB>, loop width w, and filling factor
  q<SUB>w</SUB> &lt; 1. With this relation we find upper limits on
  the iron abundance enhancement of A<SUB>Fe</SUB> &lt; 4.8 +/- 1.7
  for 10 small-scale nanoflare loops, and A<SUB>Fe</SUB> &lt; 1.4 +/-
  0.4 for 5 large-scale loops, in the temperature range of T ∼ 1.0-1.4
  MK. This result supports the previous finding that low-FIP elements,
  including Fe, are enhanced in the corona. The same relation constitutes
  also a lower limit for the filling factor, which is q<SUB>w</SUB> &gt;
  0.2 +/- 0.1 and q<SUB>w</SUB> &gt; 0.8 +/- 0.2 for the two groups of
  coronal loops.

---------------------------------------------------------
Title: Magnetic Modulation of Solar 304 Å Irradiance
Authors: Lean, J. L.; Mariska, J. T.; Warren, H. P.; Woods, T. N.;
   Eparvier, F. G.; McMullin, D. R.; Judge, D. L.; Newmark, J. S.;
   Viereck, R. A.
2003SPD....34.1902L    Altcode: 2003BAAS...35..842L
  Solar 304 Å irradiance is an important source of heating and ionization
  in the Earth's upper atmosphere. Because only intermittent observations
  exist prior to solar cycle 23, the absolute levels and solar cycle
  variability of 304 Å irradiance are uncertain by a factor of two,
  based on the range of estimates from four current EUV irradiance
  variability models. Large active regions are a significant source of
  304 Å radiation but their characteristics are not well specified,
  with contrasts reported in the range of two to ten. Statistical
  quantification of the role of small scale active regions and network
  is also lacking. During solar cycle 23, three different instruments
  are observing the Sun's 304 Å radiation concurrently. The EIT on SOHO
  records the brightness distribution on the solar disk in a 20 Å band,
  SEM on SOHO monitors the disk-integrated emission in an 80 Å band,
  and the SEE grating spectrometer on the TIMED spacecraft recently began
  observing EUV irradiance spectra with 4 Å resolution. We calculate
  daily histograms of the brightness distributions of EIT images after
  adjustments for various instrumental effects. Deconstructions of the
  histograms permit statistical characterizations of magnetic sources
  of 304 Å irradiance variability during solar cycle 23, in terms
  of fractional disk areas and contrasts. We also study center-to-limb
  variations. The calculations provide independent irradiance variability
  estimates for comparison with the SEM and SEE direct irradiance
  observations, and the models. We utilize the source characterizations
  to revise the NRLEUV model, the present version of which estimates 304
  Å emission by assuming that a bright active region has a contrast of
  ten, and that source region evolution is temporally similar to the Mg
  chromospheric irradiance index. Funded by NASA SEC GI Program.

---------------------------------------------------------
Title: Transition Region and Coronal Explorer and Soft X-Ray Telescope
Active Region Loop Observations: Comparisons with Static Solutions
    of the Hydrodynamic Equations
Authors: Winebarger, Amy R.; Warren, Harry P.; Mariska, John T.
2003ApJ...587..439W    Altcode:
  Active region coronal loop observations with broadband X-ray instruments
  have often been found to be consistent with the predictions of static
  loop models. Recent observations in the EUV, however, have discovered
  a class of active region loops that are difficult to reconcile with
  static loop models. In this paper, we take a comprehensive look at
  how coronal loops compare with static models. We select 67 loops with
  a large range of apex temperatures and half-lengths observed with
  either the Transition Region and Coronal Explorer or the Soft X-Ray
  Telescope. We compare these observations to static loop models using
  both uniform and nonuniform heating. We find that only 2 of the 67
  loops are fully consistent with static solutions with uniform heating
  and a filling factor of unity. We further find that long, cool (&lt;3
  MK) loops are as much as 2500 times “overdense,” while short, hot
  (&gt;3 MK) loops are as much as 63 times “underdense” when compared
  to the static solutions with uniform heating. We then consider the
  possibility that the disparity in the density could be due to steady,
  nonuniform heating along the loop and find that footpoint heating can
  increase densities only by a factor of 3 over density solutions with
  uniform heating while loop-top heating results in density solutions
  that are, at most, a factor of 2.5 smaller than the density solutions
  with uniform heating. Only 19 of the 67 loops in this data set could be
  fully consistent with hydrodynamic solutions with steady heating. Hence,
  we conclude that static loop models are poor representations of most
  active region loops.

---------------------------------------------------------
Title: A new model of solar EUV irradiance variability 2. Comparisons
    with empirical models and observations and implications for space
    weather
Authors: Lean, J. L.; Warren, H. P.; Mariska, J. T.; Bishop, J.
2003JGRA..108.1059L    Altcode:
  Motivated by the need for reliable specification of the Sun's
  electromagnetic radiation in the extreme ultraviolet (EUV)
  spectrum, we have developed a new model of solar EUV irradiance
  variability at wavelengths from 50 to 1200 Å. Solar images are
  used to quantify changes in the sources of EUV irradiance during the
  solar cycle. Optically thin EUV emission line fluxes are estimated
  from differential emission measures (DEMs) that characterize the
  properties of the solar atmosphere in the source regions, while fluxes
  for optically thick lines are modeled directly by specifying the source
  region contrasts. We compare the new model, NRLEUV, with three different
  empirical models of solar EUV irradiance since 1975. For solar cycles
  21 and 22, NRLEUV predicts overall lower EUV irradiances and smaller
  solar cycle variability than the empirical models. The average total
  EUV energy at wavelengths from 50 to 1050 Å is 2.9 mW m<SUP>-2</SUP>,
  smaller than the HFG, EUVAC, and SOLAR2000 models for which average
  energies are 3.7, 4.3, and 5.6 mW m<SUP>-2</SUP>, respectively. These
  differences have distinct wavelength dependencies. The solar cycle
  variation in total EUV energy is 1.9 for NRLEUV compared with 2.7, 2.9,
  and 2.3 for HFG, EUVAC, and SOLAR2000. Here, too, the differences are
  wavelength dependent. We compare both the NRLEUV and the empirically
  modeled EUV irradiances with selected wavelength bands and emission
  lines measured during 4 years in cycle 21 by Atmospheric Explorer-E
  (AE-E) and two broad bands at 170-200 and 260-340 Å measured in
  cycle 23 by the Solar X-Ray Photometer (SXP) on the Student Nitric
  Oxide Experiment (SNOE) and the Solar EUV Monitor (SEM) on the Solar
  and Heliospheric Observatory (SOHO), respectively. The NRLEUV model
  reproduces the variations observed during solar rotation better than, or
  as well as, the empirical models. Comparisons of solar cycle variations
  are more ambiguous because undetected instrumental drifts can cause
  spurious trends in the observations over these longer timescales. Drifts
  in the AE-E instruments may explain why the HFG and EUVAC models, which
  are based on parameterizations of these data, have larger solar cycle
  variations than NRLEUV. We assess the implications for space weather
  of the significant differences among the modeled EUV irradiances by
  using the Atmospheric Ultraviolet Radiance Integrated Code (AURIC)
  to quantify corresponding differences in upper atmosphere energy
  deposition and photoionization rates.

---------------------------------------------------------
Title: The Energy Release Process in Solar Flares; Constraints from
    TRACE Observations
Authors: Fletcher, L.; Warren, H. P.
2003LNP...612...58F    Altcode: 2003ecpa.conf...58F
  The Transition Region And Coronal Explorer Satellite, TRACE, launched
  in 1998, has proved a valuable tool in the study of solar flares. UV
  and EUV observations of the impulsive and gradual phases of many tens
  of flares have been made. TRACE's excellent spatial resolution and
  image cadence on the order of one second allow the rearrangement of the
  magnetic field to be tracked in some detail. The combination of these
  observations with data from other instruments, and with magnetic field
  reconstructions, have provided strong evidence for (a) UV emission as a
  beam proxy in the impulsive phase (b) long duration coronal heating in
  the gradual phase (c) very complex and varied magnetic geometries. We
  review the observational evidence for the above, discussing implications
  for energy release.

---------------------------------------------------------
Title: Extreme Ultraviolet Variability of the Large Solar Flare on
    April 21, 2002 and the Terrestrial Photoelectron Response
Authors: Eparvier, F. G.; Woods, T. N.; Bailey, S. M.; Peterson,
   W. K.; Solomon, S. C.; Garcia, H.; Lean, J. L.; Warren, H. P.; Carlson,
   C. W.; McFadden, J. P.
2002AGUFMSA21B0431E    Altcode:
  The near-simultaneous observations of the solar extreme ultraviolet
  (EUV) irradiance and terrestrial photoelectron distribution during and
  after the large solar flare on April 21, 2002 provide for a distinctive
  study of the effects that a solar flare can have on Earth's upper
  atmosphere. The solar EUV irradiance from 0.1-195 nm was measured by
  the Solar EUV Experiment (SEE) aboard the NASA Thermosphere, Ionosphere,
  Mesosphere, Energetics, and Dynamics (TIMED) satellite. The terrestrial
  photoelectron distribution from 50-1000 eV was measured by the Fast
  Auroral Snapshot (FAST) energetic electron sensor. The variations of
  the solar EUV irradiance from the X class flare at ~2 UT on April 21,
  2002 range from more than a factor of 8 for the X-ray emissions to less
  than 10% at longer EUV wavelengths. The spectral shape of this flare
  is similar to that predicted for the Bastille Day 2000 flare. Most of
  the solar irradiance variation is in the X-ray range and for coronal
  emissions. The photoelectron distribution changed by a factor of
  about 10 for the high-energy Auger electrons and by very little for the
  low-energy thermal electrons. Modeling of the photoelectron distribution
  using the measured solar EUV irradiance will also be presented.

---------------------------------------------------------
Title: Overview of the SDO Extreme ultraviolet Variability Experiment
    (EVE)
Authors: Woods, T. N.; Eparvier, F. G.; Rottman, G. J.; Judge,
   D. L.; McMullin, D. R.; Lean, J. L.; Mariska, J. T.; Warren, H. P.;
   Berthiaume, G. D.; Bailey, S. M.; Viereck, R. A.; Tobiska, W. K.;
   Fuller-Rowell, T. J.; Sojka, J. J.
2002AGUFMSH21C..02W    Altcode:
  The NASA Solar Dynamics Observatory (SDO), with its launch in 2007, is
  the first mission for the NASA Living With a Star (LWS) program. The
  SDO mission will provide measurements and modeling of the solar
  radiation and dynamics that can disturb Earth's environment. The
  Extreme ultraviolet Variability Experiment (EVE) is one of the
  three instrument suites on SDO. The EVE measures the solar extreme
  ultraviolet (EUV) irradiance with unprecedented spectral resolution,
  temporal cadence, accuracy, and precision. Furthermore, the EVE program
  will incorporate physics-based modeling to advance the understanding
  of the solar EUV irradiance variations based on the activity of solar
  magnetic features. The EVE instrument consists of three subsystems. The
  Multiple EUV Grating Spectrograph (MEGS) measures the 4-120 nm spectral
  irradiance with 0.1 nm spectral resolution. The Optics Free Spectrometer
  (OFS), being ionization cells, provides daily, in-flight calibrations
  for the MEGS channels. The EUV Spectrophotometer (ESP) completes the
  spectral coverage at 0.1-5 nm and 119-125 nm and provides additional
  MEGS calibrations. Collectively, the EVE instrument measures the
  solar EUV irradiance from 0.1 to 125 nm with 7% accuracy and 4%
  long-term precision.

---------------------------------------------------------
Title: Hydrodynamic Modeling of Active Region Loops
Authors: Warren, Harry P.; Winebarger, Amy R.; Hamilton, Paul S.
2002ApJ...579L..41W    Altcode:
  Recent observations with the Transition Region and Coronal Explorer
  (TRACE) have shown that many apparently cool (T<SUB>e</SUB>~1-1.5 MK)
  active region loops are much brighter and have flatter temperature
  profiles than static loop models predict. Observations also indicate
  that these loops can persist much longer than a characteristic cooling
  time. Using time-dependent hydrodynamic simulations, we explore the
  possibility that these active region loops are actually a collection
  of small-scale filaments that have been impulsively heated and
  are cooling through the TRACE 171 Å (Fe IX/X) and 195 Å (Fe XII)
  bandpasses. We find that an ensemble of independently heated filaments
  can be significantly brighter than a static uniformly heated loop and
  would have a flat filter ratio temperature when observed with TRACE.

---------------------------------------------------------
Title: Modeling the Cooling of Postflare Loops
Authors: Reeves, Katharine K.; Warren, Harry P.
2002ApJ...578..590R    Altcode:
  We present a model for the cooling of postflare loops. In our model, we
  form an arcade that consists of hundreds of loops with offset formation
  times to simulate a rising reconnection site. An initial temperature and
  density is assumed in each loop, and then the scaling laws of Cargill,
  Mariska, &amp; Antiochos are used to determine the evolution of the
  temperature and density in the loop. Once these quantities are found,
  they are passed through the instrument response functions for TRACE
  and the Yohkoh Soft X-Ray Telescope (SXT) to obtain intensities, which
  are integrated over the arcade to give a simulated light curve. This
  light curve is then compared to observed light curves from the 2000
  July 14 X6 flare. We find that this multiloop, multithermal approach
  to simulating the flare cooling fits the observed data much better
  than a single-loop model. There are some discrepancies between our
  simulations and the observed data in the decay phase of the flare,
  however, which may be due to residual late-phase heating. We also
  find that the temperatures calculated by using SXT filter ratios
  are generally lower than the initial loop temperatures needed in the
  simulation to give a good fit to the observed data.

---------------------------------------------------------
Title: Temperature and Density Measurements in a Quiet Coronal
    Streamer
Authors: Warren, Harry P.; Warshall, Andrew D.
2002ApJ...571..999W    Altcode:
  Many previous studies have used emission line or broadband filter
  ratios to infer the presence of temperature gradients in the quiet
  solar corona. Recently it has been suggested that these temperature
  gradients are not real, but result from the superposition of isothermal
  loops with different temperatures and density scale heights along
  the line of sight. A model describing this hydrostatic weighting
  bias has been developed by Aschwanden &amp; Acton. In this paper we
  present the application of the Aschwanden &amp; Acton differential
  emission measure model to Solar and Heliospheric Observatory Solar
  Ultraviolet Measurement of Emitted Radiation (SUMER) observations of
  a quiet coronal streamer. Simultaneous Yohkoh soft X-ray telescope
  (SXT) observations show increases in the filter ratios with height
  above the limb, indicating an increase in temperature. The application
  of the Aschwanden &amp; Acton model to these SUMER data, however, show
  that the temperature is constant with height and that the distribution
  of temperatures in the corona is much too narrow for the hydrostatic
  weighting bias to have any effect on the SXT filter ratios. We consider
  the possibility that there is a tenuous hot component (~3 MK) that
  accounts for the SXT observations. We find that a hot plasma with an
  emission measure sufficient to reproduce the observed SXT fluxes would
  also produce significant count rates in the high-temperature emission
  lines in the SUMER wavelength range. These lines are not observed,
  and we conclude that the SUMER spectra are not consistent with the SXT
  filter ratio temperatures. Calculations from a hydrodynamic loop model
  suggest that nonuniform footpoint heating may be consistent with the
  temperatures and densities observed at most heights, consistent with
  the recent analysis of relatively cool (~1 MK) active region loops. We
  also find, however, that at the lowest heights the observed densities
  are smaller than those predicted by uniform or footpoint heating.

---------------------------------------------------------
Title: TRACE Active Region Loops: Observation and Modeling
Authors: Hamilton, P. S.; Warren, H. P.; DeLuca, E. E.; Boyd, J. F.
2002AAS...200.0210H    Altcode: 2002BAAS...34..641H
  Recent Transition Region and Coronal Explorer (TRACE) observations have
  detected active region coronal loops that can not be easily modeled
  using hydrostatic models. Analysis of these loops suggests that they
  are overdense relative to the predictions of hydrodynamic models with
  uniform heating. This modeling, however, assumes that the observed
  emission is near 1 MK. Since the TRACE filter ratios are actually
  multivalued and high-temperature, uniformly heated models are difficult
  to exclude based on the TRACE data alone. Using co-aligned CDS rasters
  of overdense TRACE loops we find that these loops contain material at
  10<SUP>5.9</SUP> K to 10<SUP>6.2</SUP> K. From these rasters we perform
  a DEM analysis to constrain the input parameters to time-dependent
  hydrodynamic models of these loops. TRACE is supported by contract
  NAS5-38099 from NASA to LMATC.

---------------------------------------------------------
Title: Ionospheric and dayglow responses to the radiative phase of
    the Bastille Day flare
Authors: Meier, R. R.; Warren, H. P.; Nicholas, A. C.; Bishop, J.;
   Huba, J. D.; Drob, D. P.; Lean, J. L.; Picone, J. M.; Mariska, J. T.;
   Joyce, G.; Judge, D. L.; Thonnard, S. E.; Dymond, K. F.; Budzien, S. A.
2002GeoRL..29.1461M    Altcode: 2002GeoRL..29j..99M
  The Sun's Bastille Day flare on July 14, 2000 produced a variety of
  geoeffective events. This solar eruption consisted of an X-class flare
  followed by a coronal mass ejection that produced a major geomagnetic
  storm. We have undertaken a study of this event beginning with an
  analysis of the effects of the radiative phase of the flare on the
  dayglow and the ionosphere. The key new enabling work is a novel
  method of evaluating the X-ray and extreme ultraviolet (EUV) solar
  spectral irradiance changes associated with the flare. We find that
  the solar radiative output enhancements modeled during the flare are
  consistent with measurements of both solar EUV irradiance and far UV
  Earth thermospheric dayglow. We use the SAMI2 model to predict global
  ionospheric changes along a magnetic meridian that show significantly
  different northern and southern effects, suggesting that flares can
  be used to study ionospheric dynamics.

---------------------------------------------------------
Title: Temperature and Density Measurements in a Quiet Coronal
    Streamer
Authors: Warren, H. P.; Warshall, A. D.
2002AAS...200.1602W    Altcode: 2002BAAS...34Q.667W
  Recent observations with TRACE have revealed a new class of relatively
  cool ( ~1 MK) active region loops that have flat temperature
  profiles and are much denser than would be expected from hydrostatic
  equilibrium. Hydrodynamic loop modeling shows that non-uniform,
  footpoint heating is consistent with the observed properties of some
  of these loops. In this paper we present temperature and density
  measurements derived from SUMER/SoHO observations of a quiet coronal
  streamer. The streamer is nearly isothermal at all observed heights
  (50--200 Mm above the limb), indicating that the streamer is composed
  of loops with very flat temperature profiles. We also find that the
  densities measured at most heights are larger than would be expected
  from hydrostatic equilibrium. Loop models with non-uniform footpoint
  heating can reproduce the observed properties of this streamer at most
  heights. This work has been supported by NAG5-11625 and NAG5-10786.

---------------------------------------------------------
Title: Origins of the Solar Wind
Authors: Warren, Harry
2002STIN...0251137W    Altcode:
  This paper presented the differential emission measure analysis of SUMER
  observations of a coroner streamer. We found that: The coroner streamer
  is isothermal at all heights. This suggests that the loops comprising
  the streamer must have very flat temperature profiles. The coroner
  streamer is "overdense" relative to the predictions of hydrostatic
  equilibrium at most heights. At the lowest heights the streamer is
  actually "underdense". The SUMER temperature measurements are not
  consistent with those derived from simultaneous SXT observations. SXT
  indicates systematically higher temperatures as well as a strong
  temperature gradient. These SUMER measurements yield somewhat lower
  temperatures and no gradient in the temperature with height. Previous
  work has suggested that there may be a hot component to the streamer
  that is preferentially observed with SXT. Our analysis shows that high
  temperature emission lines would be observed with SUMER if this were
  true and thus discounts this possibility. We suggested that scattered
  light in SXT might produce spurious temperature measurements. The
  temperature and density structure of this coroner streamer are
  very similar to "TRACE" active region loops (flat temperature
  profiles, overdense relative to uniform heating, and relatively cool
  temperatures).

---------------------------------------------------------
Title: Hydrodynamic Modeling of Flare Loops
Authors: Reeves, K. K.; Warren, H. P.; DeLuca, E. E.; Boyd, J. F.;
   Arber, T. D.
2002AAS...200.6811R    Altcode: 2002BAAS...34..757R
  The study of post-flare loops is instrumental to understanding the
  energy deposition in flares. Previously we modeled the evolution of
  a flare arcade using a set of scaling laws for the conductive and
  radiative cooling of post-flare loops. We found that these simulated
  loops decrease in intensity faster than the observed loops. The scaling
  laws, however, did not allow for heating during the decay of the flare,
  or provide information on variations in temperature and density along
  the loop. In the current work, we use a full hydrodynamic simulation
  to investigate energy deposition in flaring loops. We will compare our
  simulated flare arcades to spatially and temporally resolved TRACE,
  SXT and HESSI observations. This work has been supported in part by
  the NASA Sun-Earth Connection Guest Investigator Program. TRACE is
  supported by Contract NAS5-38099 from NASA to LMATC.

---------------------------------------------------------
Title: New Determinations of Solar EUV Irradiance Variability for
    use in the NRLMSIS Atmospheric Density Specification Model
Authors: Lean, J. L.; Mariska, J. T.; Warren, H. P.; Bishop, J.;
   Picone, J. M.
2002AGUSMSH51B..03L    Altcode:
  A variety of space weather models require knowledge of the Sun' s EUV
  spectral irradiance because this radiation is the predominant source of
  upper atmosphere heating and ionization. Lacking reliable observations
  to specify the considerable variability of the EUV spectrum during the
  solar activity cycle, space weather research and operational models
  continue to use the 10.7 cm radio flux as a proxy for variations in EUV
  radiation, even though its shortcomings have been recognized for some
  time. For example, the largest source of error in special perturbations
  propagation of spacecraft orbits is the parameterization of solar
  EUV irradiance in the density models that the codes use to estimate
  drag. The strongest lines in the EUV spectrum are formed in the Sun'
  s upper chromosphere whereas the 10.7 cm flux is formed primarily in the
  hotter corona. We have recently developed a composite chromospheric EUV
  irradiance index by combining multiple space and ground-based datasets,
  and are reformulating NRL' s upper atmosphere neutral density model
  (NRLMSISE-00) to accommodate this new index. In a parallel effort
  we have developed a new physics-based irradiance variability model
  (NRLEUV) that calculates the EUV spectrum independently of direct
  spectral irradiance observations. The model utilizes solar images
  to extract information about the fraction of the solar atmosphere
  occupied by different active, network and quiet regions, and coronal
  holes. Representative differential emission measures are constructed
  for each of the features and the EUV disk-integrated spectrum is
  calculated by combining the emission measures with theoretically
  determined values of plasma emissivity. We use a parameterized
  version of the NRLEUV model that includes both chromospheric and
  coronal indices to calculate variations during past solar cycles in
  the total EUV energy incident at the top of the earth' s atmosphere,
  and at selected altitude in the range 100 to 1000 km, for use in future
  reformulations of NRLMSIS. We compare the new chromospheric index
  and the physics-based EUV irradiance model products with existing EUV
  model estimates derived from parameterizations of direct observations,
  and describe how NRLMSIS will incorporate these new determinations of
  the EUV irradiance to provide an improved density specification for
  space weather applications.

---------------------------------------------------------
Title: Spectral observations of quiescent EUV loops
Authors: Winebarger, A. R.; Mariska, J. T.; Warren, H. P.
2002AAS...200.1603W    Altcode: 2002BAAS...34R.667W
  Recent TRACE observations have detected a class of cool, quiescent
  loops that are inconsistent with hydrostatic loop models. These loops
  appear static, isothermal (1 MK), and overdense. In this talk, we
  present co-aligned TRACE, SUMER and CDS observations of several EUV
  loops. Every loop observed shows evidence of significant downflows
  along the loop. We confirm that the temperature along some of the
  observed loops is sharply peaked around 1 MK. In other loops, however,
  we find evidence for emission at hotter (2 MK) and cooler (0.2 MK)
  temperatures; this emission may be co-spatial with the loops observed
  in TRACE. These observations suggest that non-hydrostatic models are
  necessary to describe the loops.

---------------------------------------------------------
Title: The Development of a New Model of Solar EUV Irradiance
    Variability
Authors: Warren, Harry
2002STIN...0243799W    Altcode:
  The goal of this research project is the development of a new model of
  solar EUV (Extreme Ultraviolet) irradiance variability. The model is
  based on combining differential emission measure distributions derived
  from spatially and spectrally resolved observations of active regions,
  coronal holes, and the quiet Sun with full-disk solar images. An
  initial version of this model was developed with earlier funding from
  NASA. The new version of the model developed with this research grant
  will incorporate observations from SoHO as well as updated compilations
  of atomic data. These improvements will make the model calculations
  much more accurate.

---------------------------------------------------------
Title: Steady Flows Detected in Extreme-Ultraviolet Loops
Authors: Winebarger, Amy R.; Warren, Harry; van Ballegooijen, Adriaan;
   DeLuca, Edward E.; Golub, Leon
2002ApJ...567L..89W    Altcode:
  Recent Transition Region and Coronal Explorer (TRACE) observations have
  detected a class of active region loops whose physical properties are
  inconsistent with previous hydrostatic loop models. In this Letter we
  present the first co-aligned TRACE and the Solar Ultraviolet Measurement
  of Emitted Radiation (SUMER) observations of these loops. Although these
  loops appear static in the TRACE images, SUMER detects line-of-sight
  flows along the loops of up to 40 km s<SUP>-1</SUP>. The presence
  of flows could imply an asymmetric heating function; such a heating
  function would be expected for heating that is proportional to
  (often asymmetric) footpoint field strength. We compare a steady flow
  solution resulting from an asymmetric heating function to a static
  solution resulting from a uniform heating function in a hypothetical
  coronal loop. We find that the characteristics associated with the
  asymmetrically heated loop better compare with the characteristics of
  the loops observed in the TRACE data.

---------------------------------------------------------
Title: Energetics of Explosive Events Observed with SUMER
Authors: Winebarger, Amy R.; Emslie, A. Gordon; Mariska, John T.;
   Warren, Harry P.
2002ApJ...565.1298W    Altcode:
  Observations of solar chromosphere-corona transition region plasma show
  evidence of small-scale, short-lived dynamic phenomena characterized
  by significant nonthermal broadening and asymmetry in the wings
  of spectral line profiles. These impulsive mass motions (explosive
  events) are thought to be the product of magnetic reconnection and to
  be similar in driving mechanism (though larger in size) to nanoflares,
  the small-scale events proposed to heat the corona. In this paper,
  we present a statistical analysis of the energetics of explosive
  events to address the viability of the nanoflare heating theory. We
  consider high spectral, spatial, and temporal resolution spectra of the
  C III λ977, N IV λ765, O VI λ1032, and Ne VIII λ770 lines observed
  with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
  telescope and spectrometer. Each line profile exhibiting explosive event
  characteristics was analyzed using the velocity differential emission
  measure (VDEM) technique. A VDEM is a measure of the emitting power
  of the plasma as a function of its line-of-sight velocity and hence
  provides a method of accurately measuring the energy flux associated
  with an explosive event. We find that these events globally release
  ~4×10<SUP>4</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP> toward both the
  corona and chromosphere. This implies that explosive events themselves
  are not energetically significant to the solar atmosphere. However, the
  distribution of these explosive events as a function of their energy
  has a power-law spectral index of α=2.9+/-0.1 for the energy range
  10<SUP>22.7</SUP>-10<SUP>25.1</SUP> ergs. Since α is greater than 2,
  the energy content is dominated by the smallest events. Hence, if this
  distribution is representative of the size distribution down to lower
  energy ranges (~10<SUP>22</SUP> ergs), such small and (currently)
  undetectable events would release enough energy to heat the solar
  atmosphere.

---------------------------------------------------------
Title: RHESSI and TRACE Observations of an X-class Flare
Authors: Hudson, H.; Dennis, B.; Gallagher, P.; Krucker, S.; Reeves,
   K.; Warren, H.
2002cosp...34E3101H    Altcode: 2002cosp.meetE3101H
  RHESSI and TRACE both obtained excellent observations of an X1.5 flare
  on April 21, 2002. In this paper we provide an overview of the flare
  and discuss the high- energy imaging and spectra in detail. The TRACE
  images in the 195A passband (Fe XII and FeXXIV) reveal this flare to
  have a spiky arcade with post-flare flow field in the "supra-arcade
  downflow" pattern discovered by Yohkoh. Below the spikes, but above
  the FeXII loops, TRACE observes a region with complex motions and fine
  structure. We confirm with RHESSI that this region has an elevated
  temperature and discuss the transition between thermal and non-thermal
  sources. RHESSI also observes footpoint emission distributed along
  the flare ribbons.

---------------------------------------------------------
Title: Early Results from a Multi-Thermal Model for the Cooling of
    Post-Flare Loops
Authors: Reeves, K. K.; Warren, H. P.
2002mwoc.conf..275R    Altcode:
  We have developed a multi-thermal model for the cooling of post-flare
  loops. The model consists of an arcade of many nested loops that
  reconnect and begin cooling at slightly different times, and have
  different cooling profiles because of the different loop lengths across
  the arcade. Cooling due to both conductive and radiative processes is
  taken into account. The free parameters in the model include initial
  temperature and density in the loop, loop width and the initial loop
  length. The results from the model are then compared to TRACE and SXT
  observations. Our many-loop model does a much better job of predicting
  the SXT and TRACE light curves than a similar model with only one loop.

---------------------------------------------------------
Title: Observations of Preflare Activity with TRACE and Yohkoh
    [Invited]
Authors: Warren, H. P.
2002mwoc.conf..239W    Altcode:
  Despite several decades of observational and theoretical effort, a
  complete understanding of solar flares remains elusive. It has been
  especially difficult to understand how the evolution of the magnetic
  field triggers a flare and drives the release of energy. In this talk
  I will review TRACE and Yohkoh observations of pre-flare and impulsive
  phase dynamics related to nonthermal broadening, flare ribbon evolution,
  and breakout reconnection. Studies of these phenomena suggest that
  pre-flare activity is a potentially rich source of information on the
  mechanisms that power a flare. For example, Yohkoh BCS measurements of
  nonthermal broadening have shown that the largest nonthermal velocities
  can occur before the onset of significant hard X-ray emission. This
  suggests that nonthermal broadening is a signature of a turbulent
  phase of the flare, which can begin several minutes before the onset
  of the hard x-ray emission. TRACE observations have also yielded
  evidence for ribbon brightenings that precede the onset of the hard
  X-ray emission. The analysis of very high cadence TRACE data, however,
  indicates that energy release during the pre-flare and impulsive phases
  of the flare is occurring on different loops. Finally, comparisons of
  pre-flare TRACE images with potential field extrapolations have shown
  that pre-flare activity associated with a null point in the field is an
  essential component of eruptive flares. Understanding the relationships
  between these phenomena will require coordinated observations between
  many instruments. I will discuss how future observations from Yohkoh,
  TRACE, SoHO, HESSI, Stereo, Solar-B, and ground-based observatories
  will be used to advance our understanding of flare physics.

---------------------------------------------------------
Title: Ultraviolet Flare Ribbon Brightenings and the Onset of Hard
    X-Ray Emission
Authors: Warren, Harry P.; Warshall, Andrew D.
2001ApJ...560L..87W    Altcode:
  The broadband UV images taken by the Transition Region and Coronal
  Explorer (TRACE) provide a unique opportunity to observe transition
  region and chromospheric emission from flare footpoints at high spatial
  and temporal resolution. In this Letter, we present comparisons of
  UV flare footpoint evolution with hard X-ray light curves from the
  Yohkoh Hard X-Ray Telescope and the Compton Gamma Ray Observatory Burst
  and Transient Source Experiment (BATSE). The nine events analyzed in
  this Letter all show evidence for flare footpoint brightenings that
  precede the onset of the hard X-ray emission. Regression analysis
  between TRACE UV data taken at very high cadence (2-3 s) and hard
  X-ray light curves, however, shows that the initial hard X-ray burst
  is positively correlated only with footpoints that show no pre-hard
  X-ray activity. This indicates that energy release during the preflare
  and impulsive phases of the flare is occurring on different loops.

---------------------------------------------------------
Title: A new model of solar EUV irradiance variability: 1. Model
    formulation
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
2001JGR...10615745W    Altcode:
  We present a new model of solar irradiance variability at extreme
  ultraviolet wavelengths (EUV, 50-1200 Å). In this model, quiet Sun,
  coronal hole, and active region intensities for optically thin emission
  lines are computed from emission measure distributions determined
  from spectrally and spatially resolved observations. For optically
  thick emission lines and continua, empirical values are used. The
  contribution of various solar features to the spectral irradiance
  variability is determined from a simple model of limb-brightening
  and full-disk solar images taken at the Big Bear Solar Observatory
  and by the Soft X-Ray Telescope on Yohkoh. To extend our irradiance
  model beyond the time period covered by the available images, we
  use correlations with proxies for solar activity. Comparisons with
  the available irradiance data from the Atmospheric Explorer E (AE-E)
  spacecraft show that our model is capable of reproducing the rotational
  modulation of the EUV irradiance near solar maximum. The AE-E data,
  however, show systematically more solar cycle variability than our
  model estimates.

---------------------------------------------------------
Title: High Spatial Resolution Observations of a Hot Region in a
    Solar Flare with the Transition Region and Coronal Explorer
Authors: Warren, Harry P.; Reeves, Kathy K.
2001ApJ...554L.103W    Altcode:
  The Transition Region and Coronal Explorer (TRACE) provides some
  of the highest spatial resolution images ever taken of hot solar
  flare plasma. The TRACE 195 Å channel is particularly sensitive to
  high-temperature flare plasma because of the presence of the Fe XXIV
  λ192 resonance line in this bandpass. The TRACE 171 Å channel observes
  emission from thermal bremsstrahlung during a flare. Since this emission
  is generally weak, it is usually not possible to derive electron
  temperatures for flare plasma from TRACE observations. In this Letter,
  we present analysis of the 2000 March 24 X1.8 limb flare that produced
  high count rates in both the TRACE 195 and 171 Å channels. We find
  evidence for a small, high-temperature region near the top of the flare
  arcade. This hot region appears to lie at the base of the cusp-shaped
  structure that extends above the arcade. The TRACE observations are
  consistent with a strong enrichment of Fe over its photospheric value
  in the hot region that suggests in situ heating of this plasma. We
  also find that multithermal simulations of flare evolution reproduce
  the observations much better than an isothermal model does.

---------------------------------------------------------
Title: TRACE Observations of Flare Ribbon Evolution
Authors: Warren, H. P.
2001AGUSM..SP42A12W    Altcode:
  We present very high cadence (2--3 s) Transition Region and Coronal
  Explorer (TRACE) observations of the M1.1 flare that occurred on 2000
  March 17 at 11:10 UT. In this flare we find evidence for flare ribbon
  brightenings in TRACE broadband 1600 Å images that precede the onset
  of the hard X-ray emission measured with the Burst and Transient Source
  Experiment (BATSE) by as much as several minutes. Many of the flare
  footpoints that show pre-flare activity also brighten significantly
  during impulsive phase of the flare. Regression analysis between the
  TRACE and BATSE light curves, however, shows that hard x-ray emission
  is more strongly correlated with footpoints that show no pre-flare
  activity. This suggests that energy release during the pre-flare and
  impulsive phases of the flare may not be directly related. We discuss
  these results in the context of recent observations of strong nonthermal
  broadening that precedes the onset of hard X-ray emission.

---------------------------------------------------------
Title: The Temperature and Density Structure of the Quiet Solar Corona
Authors: Winebarger, A. R.; Warren, H. P.
2001AGUSM..SH31A02W    Altcode:
  The temperature and density structure of the quiet solar corona
  remains unclear. In this poster, we will present a preliminary
  analysis of a quiet solar coronal loop structure observed with SOHO and
  TRACE. After determining the magnetic field structure from potential
  field extrapolation, we attempt to model this loop using RTV scaling
  laws with various heating functions. This work is in preparation for
  a full-scale statistical study of SOHO/TRACE data to determine the
  structure of the quiet solar corona.

---------------------------------------------------------
Title: Observation of Large Flares and Their Evolution with the
    Transition Region and Coronal Explorer
Authors: Reeves, K. K.; Warren, H. P.
2001AGUSM..SP51A08R    Altcode:
  The Transition Region and Coronal Explorer (TRACE) provides some of
  the highest spatial resolution images ever taken of hot solar flare
  plasma. The TRACE 195 A channel is particularly sensitive to high
  temperature flare plasma because of the presence of the Fe XXIV 192
  A resonance line in this bandpass. The TRACE 171 A channel observes
  emission from thermal bremsstrahlung during a flare. Since this
  emission is generally weak compared to the background corona, it is
  difficult to derive electron temperatures for flare plasma from TRACE
  filter ratios. In this paper, we examine large flares observed by TRACE
  that have significant counts in the 171 A channel when compared to the
  background corona. The evolution of the filter ratios of these flares
  is examined over time and compared with a simple cooling model. The
  effects of non-equilibrium ionization are also examined.

---------------------------------------------------------
Title: Ionospheric and Thermospheric Effects During the Initial
    Radiative Phase of the Bastille Day Event
Authors: Meier, R. R.; Drob, D. P.; Nicholas, A. C.; Bishop, J.;
   Picone, J. M.; Thonnard, S. E.; Dymond, K. F.; Budzien, S. A.; Lean,
   J.; Mariska, J. T.; Huba, J. D.; Joyce, G.; Warren, H. P.; Judge, D. L.
2001AGUSM..SA51A08M    Altcode:
  Increases in the solar EUV and X-ray irradiance during a solar flare
  can produce enhanced ionization and heating in the terrestrial
  ionosphere. The resulting energetic photoelectrons in turn
  cause increases in the far ultraviolet (FUV) dayglow (100 - 150
  nm). Enhancements of some 50 per cent had previously been detected
  in OGO-4 nadir-viewing data [C B Opal, Space Research XIII, 797,
  1973]. Similar enhancements have now been seen in the FUV limb-viewing
  dayglow observations from the ARGOS satellite during the Bastille Day
  flare (July 14, 2000). Because extinction of the FUV dayglow by O2
  prevents seeing below 140 km tangent altitude on the limb, increases
  in the dayglow above that altitude must be caused by the component
  of the flare spectral irradiance which is deposited there, namely at
  wavelengths greater than 20 nm. This conclusion is corroborated by
  the observation of the flare at 30.3 nm made by the SEM instrument on
  the SOHO satellite. We study this solar-ionospheric connection using
  a modified version of the NRL solar spectrum as input to the SAMI2
  ionospheric model, and also calculate thermospheric heating rates for
  this event.

---------------------------------------------------------
Title: Intensity Fluctuations in the Solar Chromosphere
Authors: Kalkofen, W.; Warren, H. P.; Winebarger, A. R.; van
   Ballegooijen, A.; Avrett, E. H.
2001AGUSM..SP41C05K    Altcode:
  We examine two very different empirical models of the solar
  chromosphere. The first model implies steady heating, is hot at the
  top of the chromosphere and has temperature fluctuations of relatively
  low amplitude; the second model is heated intermittently, is cold most
  of the time and undergoes large temperature variations. Estimates of
  intensity fluctuations of chromospheric radiation are very different
  for the two models. We compare the model predictions with observations
  made by Skylab and by SUMER.

---------------------------------------------------------
Title: A correlation between erupted lava composition and degree of
    subsequent thermal metamorphism for HED-meteoritic basalts.
Authors: Warren, H. P.; Kallemeyn, W. G.
2001anme...26..154W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Northwest Africa 766: A new ferroan ureilite with variety of
    chromium-rich phases and associated Si, Al-rich glasses.
Authors: Sikirdji, M.; Warren, H. P.
2001anme...26..131S    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Time Variability of the “Quiet” Sun Observed with
    TRACE. II. Physical Parameters, Temperature Evolution, and Energetics
    of Extreme-Ultraviolet Nanoflares
Authors: Aschwanden, Markus J.; Tarbell, Ted D.; Nightingale, Richard
   W.; Schrijver, Carolus J.; Title, Alan; Kankelborg, Charles C.;
   Martens, Piet; Warren, Harry P.
2000ApJ...535.1047A    Altcode:
  We present a detailed analysis of the geometric and physical
  parameters of 281 EUV nanoflares, simultaneously detected with the
  TRACE telescope in the 171 and 195 Å wavelengths. The detection and
  discrimination of these flarelike events is detailed in the first paper
  in this series. We determine the loop length l, loop width w, emission
  measure EM, the evolution of the electron density n<SUB>e</SUB>(t) and
  temperature T<SUB>e</SUB>(t), the flare decay time τ<SUB>decay</SUB>,
  and calculate the radiative loss time τ<SUB>loss</SUB>, the conductive
  loss time τ<SUB>cond</SUB>, and the thermal energy E<SUB>th</SUB>. The
  findings are as follows: (1) EUV nanoflares in the energy range of
  10<SUP>24</SUP>-10<SUP>26</SUP> ergs represent miniature versions
  of larger flares observed in soft X-rays (SXR) and hard X-rays
  (HXR), scaled to lower temperatures (T<SUB>e</SUB>&lt;~2 MK),
  lower densities (n<SUB>e</SUB>&lt;~10<SUP>9</SUP> cm<SUP>-3</SUP>),
  and somewhat smaller spatial scales (l~2-20 Mm). (2) The cooling
  time τ<SUB>decay</SUB> is compatible with the radiative cooling
  time τ<SUB>rad</SUB>, but the conductive cooling timescale
  τ<SUB>cond</SUB> is about an order of magnitude shorter, suggesting
  repetitive heating cycles in time intervals of a few minutes. (3)
  The frequency distribution of thermal energies of EUV nanoflares,
  N(E)~10<SUP>-46</SUP>(E/10<SUP>24</SUP>)<SUP>-1.8</SUP> (s<SUP>-1</SUP>
  cm<SUP>-2</SUP> ergs<SUP>-1</SUP>) matches that of SXR microflares
  in the energy range of 10<SUP>26</SUP>-10<SUP>29</SUP>, and exceeds
  that of nonthermal energies of larger flares observed in HXR by a
  factor of 3-10 (in the energy range of 10<SUP>29</SUP>-10<SUP>32</SUP>
  ergs). Discrepancies of the power-law slope with other studies, which
  report higher values in the range of a=2.0-2.6 (Krucker &amp; Benz;
  Parnell &amp; Jupp), are attributed to methodical differences in the
  detection and discrimination of EUV microflares, as well as to different
  model assumptions in the calculation of the electron density. Besides
  the insufficient power of nanoflares to heat the corona, we find also
  other physical limits for nanoflares at energies &lt;~10<SUP>24</SUP>
  ergs, such as the area coverage limit, the heating temperature limit,
  the lower coronal density limit, and the chromospheric loop height
  limit. Based on these quantitative physical limitations, it appears
  that coronal heating requires other energy carriers that are not
  luminous in EUV, SXR, and HXR.

---------------------------------------------------------
Title: Fine Structure in Solar Flares
Authors: Warren, Harry P.
2000ApJ...536L.105W    Altcode:
  We present observations of several large two-ribbon flares observed
  with both the Transition Region and Coronal Explorer (TRACE) and the
  soft X-ray telescope on Yohkoh. The high spatial resolution TRACE
  observations show that solar flare plasma is generally not confined
  to a single loop or even a few isolated loops but to a multitude
  of fine coronal structures. These observations also suggest that the
  high-temperature flare plasma generally appears diffuse while the cooler
  (&lt;~2 MK) postflare plasma is looplike. We conjecture that the diffuse
  appearance of the high-temperature flare emission seen with TRACE is due
  to a combination of the emission measure structure of these flares and
  the instrumental temperature response and does not reflect fundamental
  differences in plasma morphology at the different temperatures.

---------------------------------------------------------
Title: The Morphology of the Solar Transition Region and Corona
Authors: Winebarger, A. R.; Warren, H. P.
2000SPD....31.0204W    Altcode: 2000BAAS...32..811W
  The solar transition region is an important boundary condition in
  the modeling of the solar corona, yet the basic geometry of the solar
  transition region, specifically the magnetic connectivity between the
  transition region and corona, has been heavily debated and remains
  poorly understood. In this poster, we will present analysis of a SUMER
  O VI (10<SUP>5.45</SUP> K) spectroheliogram, as well as several TRACE
  171 Angstroms (10<SUP>6.0</SUP> K) and 195 Angstroms (10<SUP>6.2</SUP>
  K) images. We quantify the structure size at each temperature using a
  fast Fourier transform analysis of the images. From this analysis, we
  find the typical size of the emitting structures in the O VI image and
  the 171 Angstroms images is smaller than that of the structures in the
  195 Angstroms images. We have also examined the magnetic connectivity
  of the various structures by comparing the images to co-aligned MDI
  magnetograms. Most of the structures present in the O VI image do
  not connect regions of opposite polarity network fields, while the
  structures observed in the 171 Angstroms and 195 Angstroms images do
  appear to have footpoints rooted in opposite polarity regions. From
  these observations, we conjecture that the geometry of the upper
  transition region and lower corona is dominated by spicules at O VI
  temperatures, small-scale loops at 171 Angstroms temperatures and
  large-scale loops at 195 Angstroms temperatures.

---------------------------------------------------------
Title: Small Scale Structure in the Solar Transition Region
Authors: Warren, Harry P.; Winebarger, Amy R.
2000ApJ...535L..63W    Altcode:
  We present analysis of a high spatial resolution (~1.5") O VI λ1032
  spectroheliogram taken with the Solar Ultraviolet Measurements of
  Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric
  Observatory. This image shows numerous narrow, looplike structures. The
  widths of the narrowest resolved features are at the spatial resolution
  of the SUMER spectrometer. In contrast to earlier Skylab observations,
  however, comparisons with a Michelson Doppler Imager magnetogram reveals
  that the majority of these looplike structures do not connect network
  magnetic fields. Instead, they extend from the supergranulation network
  into the cell-center regions where no magnetic fields are detected in
  these data. We conjecture that these fine structures are related to
  spicules and are highly dynamic.

---------------------------------------------------------
Title: Fine Structure in Solar Flares
Authors: Warren, H. P.
2000SPD....31.0262W    Altcode: 2000BAAS...32..822W
  The high spatial resolution (0.5 arcsec) and broad temperature response
  (10<SUP>4-10^7</SUP> K) of the Transition Region and Coronal Explorer
  (TRACE) make it a unique instrument for observing solar flares. Here
  we present analysis of several large two-ribbon flares observed with
  both TRACE and Yohkoh. The high spatial resolution TRACE observations
  show that solar flare plasma is generally not confined to a single
  loop or even a few isolated loops, but a multitude of fine coronal
  structures. These observations also suggest that the high temperature
  flare plasma generally appears diffuse while the cooler (&lt;2
  MK) post-flare plasma is loop-like. We conjecture that the diffuse
  appearance of the high temperature flare emission seen with TRACE is due
  to a combination of the emission measure structure of these flares and
  the instrumental temperature response and does not reflect fundamental
  differences in plasma morphology at the different temperatures.

---------------------------------------------------------
Title: Temperature Profiles of Super-Hot Flare Plasma using the
    Transition Region and Coronal Explorer (TRACE)
Authors: Reeves, K. K.; Warren, H. P.
2000SPD....31.0263R    Altcode: 2000BAAS...32..822R
  The Transition Region and Coronal Explorer (TRACE) provides some of
  the highest spatial resolution images ever taken of hot solar flare
  plasma. The TRACE 195 Angstroms channel is particularly sensitive
  to flare plasma because of the presence of the Fe XXIV 192 Angstroms
  resonance line in this bandpass. Using TRACE filter ratios to derive
  temperatures and emission measures during flares is often difficult,
  however, because the 171 Angstroms channel is predominately hydrogen
  continuum emission. This emission is generally weak and often hard
  to distinguish from the background corona. A very large flare,
  such as the X2 flare observed on March 24, 2000, yields high
  counts in the 171 Angstroms channel so that background emission
  becomes insignificant. Analysis of these data show steep temperature
  gradients below the brightest flare plasma in the arcade. These data
  also show large 195 Angstroms/171 Angstroms ratios above the arcade,
  suggesting localized regions of super-hot plasma. Interpretation of
  the filter ratios depends on the absolute abundance of Fe, however,
  and we re-examine past measurements of Fe abundances in flares.

---------------------------------------------------------
Title: Erratum: Morphology of the Quiet Solar Upper Atmosphere in
    the 4 W 104 &lt; Te &lt; 1.4 W 106 K Temperature Regime
Authors: Feldman, U.; Widing, K. G.; Warren, H. P.
2000ApJ...529.1145F    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: TRACE and Yohkoh Observations of High-Temperature Plasma in
    a Two-Ribbon Limb Flare
Authors: Warren, H. P.; Bookbinder, J. A.; Forbes, T. G.; Golub, L.;
   Hudson, H. S.; Reeves, K.; Warshall, A.
1999ApJ...527L.121W    Altcode:
  The ability of the Transition Region and Coronal Explorer
  (TRACE) to image solar plasma over a wide range of temperatures
  (T<SUB>e</SUB>~10<SUP>4</SUP>-10<SUP>7</SUP> K) at high spatial
  resolution (0.5" pixels) makes it a unique instrument for observing
  solar flares. We present TRACE and Yohkoh observations of an M2.4
  two-ribbon flare that began on 1999 July 25 at about 13:08 UT. We
  observe impulsive footpoint brightenings that are followed by the
  formation of high-temperature plasma (T<SUB>e</SUB>&gt;~10 MK)
  in the corona. After an interval of about 1300 s, cooler loops
  (T<SUB>e</SUB>&lt;2 MK) form below the hot plasma. Thus, the
  evolution of the event supports the qualitative aspects of the standard
  reconnection model of solar flares. The TRACE and Yohkoh data show that
  the bulk of the flare emission is at or below 10 MK. The TRACE data
  are also consistent with the Yohkoh observations of hotter plasma
  (T<SUB>e</SUB>~15-20 MK) existing at the top of the arcade. The
  cooling time inferred from these observations is consistent with a
  hybrid cooling time based on thermal conduction and radiative cooling.

---------------------------------------------------------
Title: Measuring the Physical Properties of the Solar Corona:
    Results from SUMER/SOHO and TRACE
Authors: Warren, H. P.
1999SoPh..190..363W    Altcode:
  Using SUMER observations taken above the limb of a quiet region we
  derive electron temperatures, emission measures, and absolute elemental
  abundances. This analysis, which uses recently published ionization
  balance calculations and the latest solar photospheric abundances,
  indicates that the low-FIP elements are enriched by a factor of 2.3±0.7
  in the corona, which is smaller than some previous measurements. TRACE
  observations of this region yield systematically lower temperatures
  and emission measures.

---------------------------------------------------------
Title: Analyzing the Energetics of Explosive Events Observed by
    SUMER on SOHO
Authors: Winebarger, Amy R.; Emslie, A. Gordon; Mariska, John T.;
   Warren, Harry P.
1999ApJ...526..471W    Altcode:
  The SUMER spectrometer on SOHO has obtained numerous observations of
  optically thin chromosphere-corona transition-region line profiles
  with high spatial, spectral, and temporal resolution. Many of these
  profiles exhibit asymmetries and broadenings associated with impulsive
  mass motions (explosive events) in the solar atmosphere. We present
  here a new method of analyzing non-Gaussian line profiles to calculate
  the distribution of fluid velocities and hence the associated energy
  flux. We illustrate this method through a preliminary analysis
  of explosive event line profiles observed by SUMER. We derive the
  magnitudes of the energy fluxes directed both toward and away from the
  observer, and their (“net flux”) differences. We also identify and
  quantify the various components of each (i.e., kinetic, thermal and
  nonthermal enthalpy, and the high-energy component associated with
  the skewed tail of the distribution). The global energy contribution
  of explosive events to the solar atmosphere is then estimated under
  two different “grouping” assumptions. This preliminary analysis
  reveals an average net upward energy flux over the entire Sun of
  10<SUP>4</SUP>-10<SUP>5</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>,
  up to an order of magnitude larger than previous estimates based
  on characteristic velocities of the fluid. Furthermore, the global
  estimate for the separate upward- and downward-directed energy fluxes
  is 10<SUP>5</SUP>-10<SUP>6</SUP> ergs cm<SUP>-2</SUP> s<SUP>-1</SUP>,
  which is comparable to the energy flux required for heating of the quiet
  corona and indicates that explosive events may indeed have significant
  implications for the energy balance of the chromosphere and corona.

---------------------------------------------------------
Title: Morphology of the Quiet Solar Upper Atmosphere in the
    4×10<SUP>4</SUP>&lt;T<SUB>e</SUB>&lt;1.4×10<SUP>6</SUP> K
    Temperature Regime
Authors: Feldman, U.; Widing, K. G.; Warren, H. P.
1999ApJ...522.1133F    Altcode:
  Studies on the morphology of the solar upper atmosphere began over
  three decades ago. Early models assumed that the temperature structure
  of the solar upper atmosphere was continuous with a thin transition
  region connecting the chromosphere with the corona. Over the years
  it became apparent that the original depiction of the solar upper
  atmosphere was too simplistic. In this paper we present a morphological
  study of the solar upper atmosphere over a wide range of temperatures
  (4×10<SUP>4</SUP>&lt;=T<SUB>e</SUB>&lt;=1.4×10<SUP>6</SUP> K)
  using high-resolution images (1<SUP>”</SUP>-2<SUP>”</SUP>)
  taken by TRACE, the SUMER spectrometer on SOHO, and the NRL
  spectroheliograph on Skylab. The images clearly show that the
  4×10<SUP>4</SUP>&lt;=T<SUB>e</SUB>&lt;=1.4×10<SUP>6</SUP>
  K temperature domain of the solar upper atmosphere consists
  of a hierarchy of isothermal loop structures. While at the
  T<SUB>e</SUB>&lt;8×10<SUP>5</SUP> K temperature regime the looplike
  structures are more abundant along the chromospheric network, at higher
  temperatures (T<SUB>e</SUB>&gt;9×10<SUP>5</SUP> K) no association
  between them and the chromospheric network is apparent. The hottest
  (T<SUB>e</SUB>~1.4×10<SUP>6</SUP> K), which are also the longest among
  the quiet-Sun loop structures, form a canopy over the lower temperature
  loop structures. We discuss in the paper possible relationships between
  the morphology of the solar upper atmosphere, its elemental abundance,
  and ideas regarding the origin of the slow-speed solar wind.

---------------------------------------------------------
Title: A new view of the solar outer atmosphere by the Transition
    Region and Coronal Explorer
Authors: Schrijver, C. J.; Title, A. M.; Berger, T. E.; Fletcher, L.;
   Hurlburt, N. E.; Nightingale, R. W.; Shine, R. A.; Tarbell, T. D.;
   Wolfson, J.; Golub, L.; Bookbinder, J. A.; DeLuca, E. E.; McMullen,
   R. A.; Warren, H. P.; Kankelborg, C. C.; Handy, B. N.; De Pontieu, B.
1999SoPh..187..261S    Altcode:
  The Transition Region and Coronal Explorer (TRACE) - described in the
  companion paper by Handy et al. (1999) - provides an unprecedented
  view of the solar outer atmosphere. In this overview, we discuss the
  initial impressions gained from, and interpretations of, the first
  million images taken with TRACE. We address, among other topics,
  the fine structure of the corona, the larger-scale thermal trends,
  the evolution of the corona over quiet and active regions, the high
  incidence of chromospheric material dynamically embedded in the coronal
  environment, the dynamics and structure of the conductively dominated
  transition region between chromosphere and corona, loop oscillations
  and flows, and sunspot coronal loops. With TRACE we observe a corona
  that is extremely dynamic and full of flows and wave phenomena, in
  which loops evolve rapidly in temperature, with associated changes in
  density. This dynamic nature points to a high degree of spatio-temporal
  variability even under conditions that traditionally have been referred
  to as quiescent. This variability requires that coronal heating can
  turn on and off on a time scale of minutes or less along field-line
  bundles with cross sections at or below the instrumental resolution
  of 700 km. Loops seen at 171 Å (∼1 MK) appear to meander through
  the coronal volume, but it is unclear whether this is caused by the
  evolution of the field or by the weaving of the heating through the
  coronal volume, shifting around for periods of up to a few tens of
  minutes and lighting up subsequent field lines. We discuss evidence
  that the heating occurs predominantly within the first 10 to 20 Mm
  from the loop footpoints. This causes the inner parts of active-region
  coronae to have a higher average temperature than the outer domains.

---------------------------------------------------------
Title: The transition region and coronal explorer
Authors: Handy, B. N.; Acton, L. W.; Kankelborg, C. C.; Wolfson, C. J.;
   Akin, D. J.; Bruner, M. E.; Caravalho, R.; Catura, R. C.; Chevalier,
   R.; Duncan, D. W.; Edwards, C. G.; Feinstein, C. N.; Freeland, S. L.;
   Friedlaender, F. M.; Hoffmann, C. H.; Hurlburt, N. E.; Jurcevich,
   B. K.; Katz, N. L.; Kelly, G. A.; Lemen, J. R.; Levay, M.; Lindgren,
   R. W.; Mathur, D. P.; Meyer, S. B.; Morrison, S. J.; Morrison, M. D.;
   Nightingale, R. W.; Pope, T. P.; Rehse, R. A.; Schrijver, C. J.;
   Shine, R. A.; Shing, L.; Strong, K. T.; Tarbell, T. D.; Title, A. M.;
   Torgerson, D. D.; Golub, L.; Bookbinder, J. A.; Caldwell, D.; Cheimets,
   P. N.; Davis, W. N.; Deluca, E. E.; McMullen, R. A.; Warren, H. P.;
   Amato, D.; Fisher, R.; Maldonado, H.; Parkinson, C.
1999SoPh..187..229H    Altcode:
  The Transition Region and Coronal Explorer (TRACE) satellite, launched
  2 April 1998, is a NASA Small Explorer (SMEX) that images the solar
  photosphere, transition region and corona with unprecedented spatial
  resolution and temporal continuity. To provide continuous coverage
  of solar phenomena, TRACE is located in a sun-synchronous polar
  orbit. The ∼700 Mbytes of data which are collected daily are made
  available for unrestricted use within a few days of observation. The
  instrument features a 30-cm Cassegrain telescope with a field of view
  of 8.5×.5 arc min and a spatial resolution of 1 arc sec (0.5 arc sec
  pixels). TRACE contains multilayer optics and a lumogen-coated CCD
  detector to record three EUV wavelengths and several UV wavelengths. It
  observes plasmas at selected temperatures from 6000 K to 10 MK with
  a typical temporal resolution of less than 1 min.

---------------------------------------------------------
Title: The density structure of a solar polar coronal hole
Authors: Warren, H. P.; Hassler, D. M.
1999JGR...104.9781W    Altcode:
  Electron densities derived from Si III, Ne VII, Mg VIII, Si VIII, and Mg
  IX line ratios observed above the limb of a polar coronal hole with the
  Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer
  on the Solar and Heliospheric Observatory (SoHO) are presented. The
  electron densities are consistent with a constant pressure of
  1.6×10<SUP>14</SUP>cm<SUP>-3</SUP>K (logP<SUB>e</SUB>=14.2).

---------------------------------------------------------
Title: A new view of the solar corona from the transition region
    and coronal explorer (TRACE)
Authors: Golub, L.; Bookbinder, J.; Deluca, E.; Karovska, M.; Warren,
   H.; Schrijver, C. J.; Shine, R.; Tarbell, T.; Title, A.; Wolfson,
   J.; Handy, B.; Kankelborg, C.
1999PhPl....6.2205G    Altcode:
  The TRACE Observatory is the first solar-observing satellite in the
  National Aeronautics and Space Administration's (NASA) Small Explorer
  series. Launched April 2, 1998, it is providing views of the solar
  transition region and low corona with unprecedented spatial and
  temporal resolution. The corona is now seen to be highly filamented,
  and filled with flows and other dynamic processes. Structure is seen
  down to the resolution limit of the instrument, while variability and
  motions are observed at all spatial locations in the solar atmosphere,
  and on very short time scales. Flares and shock waves are observed,
  and the formation of long-lived coronal structures, with consequent
  implications for coronal heating models, has been seen. This overview
  describes the instrument and presents some preliminary results from
  the first six months of operation.

---------------------------------------------------------
Title: Elemental Abundance Variations and the Structure of the Quiet
    Solar Corona and Transition Region
Authors: Warren, H. P.
1999AAS...19410002W    Altcode: 1999BAAS...31..996W
  Recent observations of Doppler shifts with the SUMER spectrometer
  on SoHO have shown that there is a transition from net redshifts
  (apparent inflows) to blueshifts (outflows) at approximately 630,000
  K in solar coronal holes. These outflows appear to be directly related
  to the formation of the high speed solar wind. This transition from net
  redshifts to blueshifts is significant because it supports the idea that
  much of the solar transition region is not connected to the corona,
  but is confined on small, closed loops. Measurements of elemental
  abundances hold important clues to the structure of solar corona and
  the origin of the high speed solar wind. In situ measurements of the
  high speed solar wind indicate that low first ionization potential
  elements are enriched by about a factor of two or less over their
  photospheric values. The slow speed wind, which is formed from quiet
  regions, shows much larger enrichements. Skylab-era measurements of
  emission formed in the lower transition region suggested no enrichment
  of low FIP elements at these temperatures in either the quiet Sun or
  coronal holes. In this paper we present a systematic investigation of
  abundance variations as a function of temperature in the quiet Sun and
  coronal holes using observations from the SUMER and CDS spectrometers
  on SoHO. We also discuss the relationship between abundance variations
  and the morphology of the solar atmosphere using high resolution images
  from TRACE.

---------------------------------------------------------
Title: On the Ability of an Extreme-Ultraviolet Multilayer
    Normal-Incidence Telescope to Provide Temperature Information for
    Solar Plasmas
Authors: Feldman, U.; Laming, J. M.; Doschek, G. A.; Warren, H. P.;
   Golub, L.
1999ApJ...511L..61F    Altcode:
  In recent years, multilayer-coated optics have been used in solar-soft
  X-ray and extreme-ultraviolet telescopes to record high-resolution,
  full Sun images. The multilayer coatings reflect efficiently over rather
  narrow wavelength bands that are selected to contain spectral emission
  lines considered to have plasma diagnostic importance for determining
  approximate electron temperatures. The purpose of this Letter is to
  discuss the effect of continuum emission on the response of multilayer
  passbands and the effect of this response on temperature determinations
  in the 4×10<SUP>6</SUP>-2×10<SUP>7</SUP> K range. Significant effects
  are largely confined to continuum emission from flare plasma. The
  flare free-free continuum in the EUV range is nearly temperature and
  wavelength insensitive and dominates the emission in passbands that
  are centered on quiet- to active-Sun coronal lines emitted by ions
  such as Fe IX-Fe XV.

---------------------------------------------------------
Title: Differentiation of siderophile elements in the Moon and the
    HED parent asteroid.
Authors: Warren, H. P.
1999anme...24..185W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Observations of High-Temperature Flare Plasma with Transition
    Region and Coronal Explorer (TRACE)
Authors: Reeves, K. K.; Golub, L.; Warren, H. P.
1999agu..meet..234R    Altcode:
  The so-called standard model of solar flares makes specific
  predictions concerning the amount, location, and timing of both hot
  (T<SUB>e</SUB>&gt;10 MK) and cool (T<SUB>e</SUB>&lt;2 MK) plasma in
  solar flares. The ability of the Transition Region and Coronal Explorer
  (TRACE) to image solar plasma over a wide range of temperatures
  (T<SUB>e</SUB>~10<SUP>4</SUP>-10<SUP>7</SUP> K) at high spatial
  resolution (0.5″ pixels) make it a unique instrument for observing
  solar flares and testing the model predictions. We present TRACE and
  Yohkoh observations of an M2.4 two-ribbon flare that began on 1999
  July 25 at about 13:08 UT. These observations are in qualitative
  agreement with the essential elements of the reconnection model. We
  observe impulsive footpoint brightenings that are quickly followed
  by the formation of high-temperature plasma in the corona. After an
  interval of about 1300 s cooler loops form below the hot plasma. The
  cooling time inferred from the observations suggests large densities
  (n<SUB>e</SUB>~10<SUP>11</SUP> cm<SUP>-3</SUP>) for the high temperature
  plasma so that radiative losses dominate the cooling process. The
  TRACE data are consistent with the Yohkoh observations of a “hot”
  (T<SUB>e</SUB>~15-20 MK) plasma existing at the top of the arcade.

---------------------------------------------------------
Title: High-Resolution Observations of the Solar Hydrogen Lyman
    Lines in the Quiet Sun with the SUMER Instrument on SOHO
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.
1998ApJS..119..105W    Altcode:
  We present high-resolution observations of the higher H Lyman series
  lines taken with the Solar Ultraviolet Measurements of Emitted Radiation
  (SUMER) experiment flown on the Solar and Heliospheric Observatory
  (SOHO) spacecraft. We have used systematic observations extending
  from disk center to the solar limb to compute average profiles for
  representative solar features of the quiet Sun, limb-brightening curves,
  and full-disk, quiet-Sun profiles for Lyβ through Lyλ(11) and the
  Lyman continuum. The effects of radiative transfer are apparent in
  all of the line profiles we studied. The average quiet-Sun profiles
  for Lyβ through Lyɛ are self-reversed, and the remaining lines are
  flat-topped. The characteristics of the line profiles vary markedly
  with intensity. We observe strong enhancements in the red wings of
  network profiles, while the faint cell-center profiles are nearly
  symmetric. We also find that the intensities of the H Lyman lines
  increase at the limb, although the limb brightening is weak compared
  to optically thin transition region emission lines and largely obscured
  by the intensity variations observed in the quiet Sun.

---------------------------------------------------------
Title: The Electron Pressure in the Solar Lower Transition Region
    Determined from O V and Si III Density-sensitive Line Ratios
Authors: Doschek, G. A.; Feldman, U.; Laming, J. M.; Warren, H. P.;
   Schüle, U.; Wilhelm, K.
1998ApJ...507..991D    Altcode:
  We determine the electron density at the temperatures of formation
  of O<SUP>+4</SUP> and Si<SUP>+2</SUP> ions, which are about 2.5 ×
  10<SUP>5</SUP> and 3.2 × 10<SUP>4</SUP> K in ionization equilibrium,
  respectively. These temperatures occur in the lower transition
  region of the Sun's atmosphere and allow a test of the often invoked
  assumption of constant pressure in quiet-Sun models. The O<SUP>+4</SUP>
  density is determined from a density-sensitive spectroscopic O V
  line ratio involving 2s2p<SUP>3</SUP>P-2p<SUP>2</SUP><SUP>3</SUP>P
  transitions that fall near 760 Å. The Si<SUP>+2</SUP> density is
  determined from a density-sensitive Si III line ratio within the
  3s3p<SUP>3</SUP>P-3p<SUP>2</SUP><SUP>3</SUP>P multiplet near 1300
  Å. There are few available line ratio techniques for determining
  the density and hence electron pressure in the quiet-Sun and coronal
  hole transition regions using lines emitted by the same ion, and
  determining these quantities is the principal motivation for this
  work. The spectra used in our analysis were obtained from the Solar
  Ultraviolet Measurements of Emitted Radiation (SUMER) experiment on the
  Solar and Heliospheric Observatory (SOHO). We determine the electron
  density and pressure in typical quiet-Sun/coronal hole regions, and
  densities in active region brightenings and in an explosive event. Our
  O V and Si III results indicate that constant pressure is valid or
  nearly valid in quiet-Sun lower transition regions, although there
  are complications arising from the weakness of a key Si III line in
  the quiet-Sun disk spectra. We also discuss our results in light of
  other density measurements and theories regarding the structure and
  heating of the transition region.

---------------------------------------------------------
Title: A new reference spectrum for the EUV irradiance of the quiet
    Sun 2. Comparisons with observations and previous models
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
1998JGR...10312091W    Altcode:
  In a companion paper we presented a new reference spectrum for the EUV
  irradiance of the quiet Sun based primarily on intensities calculated
  from a quiet Sun emission measure distribution and recent compilations
  of atomic data. The contributions of optically thick emission lines
  and continua were included empirically. In this paper we present
  comparisons between this reference spectrum and independently measured
  irradiance observations, previous quiet Sun reference spectra, and
  the predictions of empirical EUV irradiance models. These comparisons
  indicate relatively good agreement among fluxes of emission lines
  formed in the solar chromosphere and transition region. The fluxes for
  coronal emission lines in previous quiet Sun reference spectra, however,
  do not agree with our calculated fluxes or with a recent irradiance
  observation taken at a low level of solar activity. Coronal emission
  lines in the Atmospheric Explorer E (AE-E) quiet Sun reference spectrum
  SC21REFW have fluxes that are typically smaller than our calculated
  fluxes by factors of 2 or more. We also identify inconsistencies in the
  earlier reference spectrum of Heroux and Hinteregger [1978] (F74113),
  where the fluxes of many coronal emission lines with wavelengths below
  250 Å are inconsistent with the fluxes of coronal emission lines at
  longer wavelengths. The fluxes of EUV continua in the various reference
  spectra and irradiance observations also differ significantly.

---------------------------------------------------------
Title: A new reference spectrum for the EUV irradiance of the quiet
    Sun 1. Emission measure formulation
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
1998JGR...10312077W    Altcode:
  We present a quiet Sun irradiance spectrum from 50-1200 Å based
  primarily on intensities computed from a newly constructed quiet Sun
  emission measure distribution. We derive the emission measure from a
  spectrum of a portion of the quiet solar disk measured with the Harvard
  instrument on Skylab and recent compilations of atomic data. For
  some specific emission lines and continua which are not optically
  thin and cannot be computed using an emission measure, we either use
  intensities from the Harvard spectrum directly or infer them from
  other observations. Application of a simple center-to-limb variation
  converts the intensities to equivalent full-disk quiet Sun fluxes.

---------------------------------------------------------
Title: Empirical Models of Temperature, Densities, and Velocities
    in the Solar Corona
Authors: Fludra, A.; Strachan, L.; Alexander, D.; Bagenal, F.;
   Biesecker, D. A.; Dobrzycka, D.; Galvin, A. B.; Gibson, S.; Hassler,
   D.; Yo, Y. -K.; Panasyuk, A. V.; Thompson, B.; Warren, H.; del Zanna,
   G.; Zidowitz, S.; Antonucci, E.; Bromage, B. J. I.; Giordano, S.
1998EOSTr..79..278F    Altcode:
  We present empirical results for temperatures, densities, and outflow
  velocities of constituents of the solar corona from 1 to 3 Ro in
  polar coronal holes and an equatorial streamer. Data were obtained
  from a variety of space and ground-based instruments during August
  1996 as part of the SOHO Whole Sun Month Campaign. From white light
  data obtained with the SOHO/LASCO/C2 and HAO/Mauna Loa coronagraphs,
  we determine electron densities and compare them to those determined
  from the density-sensitive EUV line ratio of Si IX 350/342 Angstroms
  observed by the SOHO/Coronal Diagnostic Spectrometer (CDS). Moreover,
  from the white light density profiles we calculate temperature profiles
  and compare to temperature diagnostic information from EUV lines and
  soft X-ray images from Yohkoh. H I Ly alpha and O VI 1032/1037 Angstrom
  intensities from the SOHO Ultraviolet Coronagraph Spectrometer (UVCS)
  are used to estimate both the direction and magnitude of plasma outflow
  velocities in coronal holes and streamers above 1.5 Ro. The velocities
  are derived using densities from white light coronagraph data and
  coronal electron temperature estimates derived from Ulysses/SWICS
  ion composition data. Near the base of the corona we find the white
  light and spectral analysis produce consistent density and temperature
  information. In the extended corona we find results consistent with
  high outflow velocities and a superradial outflow geometry in polar
  coronal holes.

---------------------------------------------------------
Title: Petrology of unique Fe-Ni metal bearing cumulate eucrite
    EET92023.
Authors: Kaneda, K.; Warren, H. P.
1998anme...23...45K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: VDEM Analysis of Transition Region Line Profiles Observed
    with the SUMER Instrument on SoHO
Authors: Winebarger, A. R.; Warren, H. P.; Emslie, A. G.; Mariska,
   J. T.
1997AAS...191.7302W    Altcode: 1997BAAS...29.1320W
  The SUMER spectrometer has obtained numerous high spatial and spectral
  resolution observations of optically-thin transition region line
  profiles in various solar features (quiet Sun, active region, coronal
  hole, etc.). Frequently, these line profiles show evidence for both
  steady and impulsive mass motions, which can have profound implications
  for the mass and energy balance of the transition region and
  corona. These motions can be quantified using the Velocity Differential
  Emission Measure (VDEM) technique to derive the distribution of emission
  with respect to the line-of-sight velocity. This VDEM distribution
  can then be used to infer mean plasma velocities, momenta, and energy
  fluxes. We have found that representations of the energy flux by
  either the “mean flow approximation” {1 / 2}n m{bar v}(3) or by the
  “enthalpy approximation”(whether in a purely thermal form nkT {bar v}
  or incorporating nonthermal turbulence {1 / 2}n m /line {v(2}) {bar
  v}) all underestimate the true energy flux {1 / 2} n m /line{v(3})
  by up to an order of magnitude. In cases where lines formed at
  different temperatures have been observed in the SUMER spectral range
  simultaneously, we have estimated the divergence of the energy flux
  and so the energy deposition rate within the region bounded by the
  formation heights of the two spectral lines; implications for coronal
  heating are discussed. This work was supported by grants from the SoHO
  Guest Investigator Program and by the Office of Naval Research.

---------------------------------------------------------
Title: Observations of Doppler Shifts in a Solar Polar Coronal Hole
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.
1997ApJ...490L.187W    Altcode:
  Using observations from the Solar Ultraviolet Measurements of Emitted
  Radiation experiment flown on the Solar and Heliospheric Observatory
  spacecraft, we have measured Doppler wavelength shifts in the north
  polar coronal hole in the 1032 and 1038 Å emission lines of O VI and
  the 1036 and 1037 Å emission lines of C II relative to chromospheric
  emission lines. These observations were obtained on 1996 November 2
  when the north polar coronal hole boundary extended southward to about
  750<SUP>”</SUP> (cosθ=0.65). Our measurements indicate the presence
  of average net redshifts in coronal holes at temperatures of less than
  2.9×10<SUP>5</SUP> K. Measurements of systematic wavelength shifts
  in the Ne VIII resonance lines relative to the quiet Sun suggest a
  transition to average net outflows near 6.3×10<SUP>5</SUP> K in the
  coronal hole.

---------------------------------------------------------
Title: Doppler Shifts and Nonthermal Broadening in the Quiet Solar
Transition Region: O VI
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.; Lemaire, P.
1997ApJ...484L..91W    Altcode:
  Using observations from the Solar Ultraviolet Measurements of Emitted
  Radiation (SUMER) experiment flown on the Solar and Heliospheric
  Observatory (SOHO) spacecraft, we have measured Doppler wavelength
  shifts and nonthermal broadening in the 1032 and 1038 Å emission lines
  of O VI and the 1036 and 1037 Å emission lines of C II. Near Sun center
  the C II lines exhibit an average redshift of 2 +/- 3 km s<SUP>-1</SUP>,
  consistent with earlier observations in this temperature range. The
  O VI emission lines exhibit average Doppler velocities of 5 +/- 3
  km s<SUP>-1</SUP>, suggesting the presence of redshifted material at
  2.9 × 10<SUP>5</SUP> K. For the O VI lines, the average nonthermal
  component of the observed line width is 34 +/- 3 km s<SUP>-1</SUP>.

---------------------------------------------------------
Title: Electron Densities in the Solar Polar Coronal Holes from
    Density-Sensitive Line Ratios of Si VIII and S X
Authors: Doschek, G. A.; Warren, H. P.; Laming, J. M.; Mariska, J. T.;
   Wilhelm, K.; Lemaire, P.; Schühle, U.; Moran, T. G.
1997ApJ...482L.109D    Altcode:
  We derive electron densities as a function of height in the north and
  south polar coronal holes from a forbidden spectral line ratio of Si
  VIII. Si VIII is produced at about 8 × 10<SUP>5</SUP> K in ionization
  equilibrium. We also derive densities from a similar line ratio of S X
  (1.3 × 10<SUP>6</SUP> K). The spectra were obtained with the Solar
  Ultraviolet Measurements of Emitted Radiation spectrometer flown on
  the Solar and Heliospheric Observatory spacecraft. In addition to the
  primary mechanism of electron impact excitation, the derivation of
  theoretical level populations for Si VIII and S X includes both proton
  and resonance capture excitation. We compare the coronal hole results
  to quiet-Sun coronal measurements obtained outside the east and west
  limbs. We find for distances of a few arcseconds outside the solar
  limb that the average line-of-sight electron densities in the coronal
  holes are about a factor of 2 lower than in quiet-Sun regions. The
  decrease of density with height is exponential in the polar holes. We
  also confirm the result known from a variety of earlier observations
  that the temperature of most of the plasma in coronal holes does not
  exceed about 10<SUP>6</SUP> K.

---------------------------------------------------------
Title: The Electron Density, Temperature, and Si/Ne Abundance Ratio
    in Polar Coronal Holes from SUMER
Authors: Doschek, G. A.; Laming, J. M.; Warren, H. P.; Lemaire, P.;
   Wilhelm, K.
1997SPD....28.0404D    Altcode: 1997BAAS...29Q.908D
  The Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
  spectrometer flown on the Solar and Heliospheric Observatory (SOHO)
  covers a wavelength range with spectral and spatial resolution and
  sensitivity not previously obtained by any other solar spectrometer
  experiment. Consequently, new plasma diagnostic techniques have been
  used and developed to measure plasma parameters such as electron
  density. In this paper we discuss the electron density as a function
  of height above the solar surface in the polar coronal holes as
  determined from line ratios of Si VIII and S X. The densities vary
  between about 3 x 10(6) cm(-3) and 10(8) cm(-3) . We determine the
  emission measure at selected temperatures as a function of position
  above the polar limbs from lines of Mg VII, Mg VIII, Mg IX, and Mg
  X. The electron temperature is lower in the polar holes than in the
  quiet Sun. This result is also based on intensities of lines of Fe X,
  Fe XI, and Fe XII. We determine the Si/Ne abundance ratio (low/high
  first ionization potential elements) using lines of Ne VII, Ne VIII,
  Si VII, and Si VIII. The preliminary result is that the Si/Ne abundance
  ratio in interplume regions is close to photospheric. We also compare
  the coronal hole density and abundance results with similar results
  obtained for the quiet Sun in the east and west coronal streamers. We
  discuss our conclusions in light of results from previous missions.

---------------------------------------------------------
Title: Observations of Doppler Shifts and Nonthermal Broadening in
    the North Polar Coronal Hole and Adjacent Quiet Sun
Authors: Mariska, J. T.; Warren, H. P.; Wilhelm, K.; Lemaire, P.
1997SPD....28.0118M    Altcode: 1997BAAS...29..882M
  Coronal holes are thought to be the source of high-speed solar
  wind streams. It is, however, unclear at what height the outflow
  of material first becomes apparent. Using the Solar Ultraviolet
  Measurements of Emitted Radiation (SUMER) experiment on the Solar and
  Heliospheric Observatory (SOHO), we have obtained observations in the
  north polar coronal hole, its boundary region, and the adjacent quiet
  Sun at wavelengths that cover emission lines of O VI at 1032 and 1038
  Angstroms, Ne VIII at 770 Angstroms, and Mg X at 625 Angstroms. These
  lines are formed at temperatures of 0.3, 0.8, and 1.25 MK, respectively,
  and should thus help to determine the temperature at which outflows
  are first detected. For O VI and Mg X, we will report on Doppler shift
  measurements made relative to cooler chromospheric lines. Since there
  are no suitable emission lines from ions formed in the chromosphere
  for the Ne VIII line, we are only able to measure relative differences
  between the coronal hole and the adjacent quiet Sun. We will also
  report on the magnitude of the nonthermal broadening in these lines
  in the different solar regions. This work was supported by a NASA SOHO
  Guest Investigator Program grant.

---------------------------------------------------------
Title: Doppler Shifts and Nonthermal Broadening in the Quiet Solar
Transition Region: O VI
Authors: Warren, H. P.; Mariska, J. T.; Wilhelm, K.; Lemaire, P.
1997SPD....28.0117W    Altcode: 1997BAAS...29..882W
  Using observations from the Solar Ultraviolet Measurements of Emitted
  Radiation (SUMER) experiment flown on the Solar and Heliospheric
  Observatory (SOHO ) spacecraft, we have measured Doppler wavelength
  shifts and nonthermal broadening in the 1032 and 1038 Angstroms emission
  lines of Ovi and the 1036 and 1037 Angstroms emission lines of Cii. Near
  Sun center the Cii lines exhibit an average redshift of 2+/-3km s(-1)
  , consistent with earlier observations in this temperature range. The
  Ovi emission lines exhibit average Doppler velocities of 5+/-3km s(-1)
  suggesting the presence of redshifted material at 2.9*E(5) K. For the
  Ovi lines, the average nonthermal component of the observed line width
  is 34+/-3km s(-1) . These observations indicate a tendency for brighter
  regions to have larger average redshifts and line widths than faint
  features although the relationship is very weak. Preliminary analysis of
  observations at the limb suggests that the Doppler velocities for Ovi do
  not approach zero as would be expected for predominately radial motions.

---------------------------------------------------------
Title: Determination of the Formation Temperature of Si IV in the
    Solar Transition Region
Authors: Doschek, G. A.; Mariska, J. T.; Warren, H. P.; Wilhelm, K.;
   Lemaire, P.; Kucera, T.; Schühle, U.
1997ApJ...477L.119D    Altcode:
  Using spectra obtained with the Solar Ultraviolet Measurements
  of Emitted Radiation (SUMER) spectrometer flown on the Solar and
  Heliospheric Observatory spacecraft, we deduce the temperature
  of formation of the Si IV ion in the solar transition region
  from the Si IV ultraviolet spectral line intensity ratio, 3p
  <SUP>2</SUP>P<SUB>3/2</SUB>-3d <SUP>2</SUP>D<SUB>3/2,5/2</SUB>/3s
  <SUP>2</SUP>S<SUB>1/2</SUB>-3p <SUP>2</SUP>P<SUB>1/2</SUB>,
  and compare the result to the temperature predicted under the
  assumption of ionization equilibrium. The wavelengths are as
  follows: <SUP>2</SUP>D<SUB>3/2,5/2</SUB>, 1128.325, 1128.340 Å
  <SUP>2</SUP>P<SUB>1/2</SUB>, 1402.770 Å. Ratios are derived for
  typical features of the quiet Sun, such as cell center and network,
  and are systematically higher than those predicted at the 6.3 ×
  10<SUP>4</SUP> K ionization equilibrium temperature of formation
  of Si IV. For most solar features the ratios imply a temperature
  of formation of about 8.5 × 10<SUP>4</SUP> K. The ratios for the
  faintest features imply a temperature of formation of up to 1.6 ×
  10<SUP>5</SUP> K. It is not clear, however, that all the discrepancies
  between the measured and theoretical ratios are due to a temperature
  effect. Accurate temperature measurements are important since a large
  discrepancy from ionization equilibrium has significant implications
  for the physics of the transition region, such as the possible presence
  of nonthermal electrons.

---------------------------------------------------------
Title: Trace element chemistry of volcanic glasses in lunar meteorites
    Y 793274 and QUE 94281.
Authors: Arai, T.; Warren, H. P.; Papike, J. J.; Shearer, K. C.;
   Takeda, H.
1997anme...22....3A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The Yamato-793605 martian meteorite consortium.
Authors: Kojima, H.; Miyamoto, M.; Warren, H. P.
1997anme...22...91K    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Yamato-793605 and other presumed martian meteorites:
    Composition and petrogenesis.
Authors: Warren, H. P.; Kallemeyn, W. G.
1997anme...22..200W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Modeling solar extreme ultraviolet irradiance variability
    using emission measure distributions
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.; Marquette, W.;
   Johannesson, A.
1996GeoRL..23.2207W    Altcode:
  We introduce a new model of solar irradiance variability at extreme
  ultraviolet (EUV) wavelengths. The model combines a spectral emission
  line database, solar emission measure distributions, and estimates
  from ground-based solar images of the fraction of the Sun covered by
  the various types of activity to synthesize the irradiance. Using Call
  K-line images, the model can be used to estimate the irradiance from
  EUV line emission formed in the upper chromosphere and lower transition
  region. Comparisons of this new model with existing empirical models
  reveal both similarities and disagreements in the absolute magnitude,
  the amplitude of the rotational modulation, and the intermediate-term
  solar cycle variability of the predicted fluxes.

---------------------------------------------------------
Title: A New Model of Solar EUV Irradiance Variability
Authors: Warren, H. P.; Mariska, J. T.; Lean, J.
1996AAS...188.3617W    Altcode: 1996BAAS...28R.875W
  Solar soft X-ray (SXR, 1-100 Angstroms) and extreme ultraviolet (EUV,
  100--1200 Angstroms) radiation plays a central role in the energetics
  and dynamics of the Earth's upper atmosphere. Solar radiation at
  these wavelengths is strongly affected by solar magnetic activity
  and varies significantly during the solar activity cycle. Empirical
  models of solar irradiance variability essentially parameterize
  existing full-disk irradiance observations with proxies for solar
  activity. However, the limitations of existing EUV observations and
  absence of any current irradiance measurements at these wavelengths
  limits the utility of empirical irradiance modeling. Motivated by solar
  physics experiments on Yohkoh, SOHO, and TRACE we have developed a
  new, physics-based approach to modeling solar SXR and EUV irradiance
  variability. In this new model, the intensities of optically thin
  spectral lines are calculated using theoretically determined values
  of plasma emissivity coupled with emission measure distributions for
  features of the solar atmosphere: coronal holes, quiet Sun, and active
  regions. For emission lines with very complicated formation processes,
  such as the Lyman lines of hydrogen and helium, spatially and spectrally
  resolved solar observations are used in place of emission measure
  calculations. Information about the distribution of emitting regions
  on the Sun is inferred from full-disk images of the Sun, such as BBSO
  CaII k-line and Yohkoh SXT images, rather than from proxies for solar
  activity. Comparison of the model with existing empirical irradiance
  models based on F_{10.7} and other proxies for solar activity reveals
  disagreements in the absolute magnitude, the amplitude of the rotational
  modulation, and the solar cycle variability of the predicted fluxes at
  many wavelengths. This research was supported by the NASA SEE program.

---------------------------------------------------------
Title: VLT-mare glasses of probable pyroclastic origin in lunar
    meteorite breccias Yamato 793274 and QUE94281.
Authors: Arai, T.; Warren, H. P.
1996anme...21....4A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Compositional-petrologic investigation of eucrites and the
    QUE94201 Shergottite.
Authors: Warren, H. P.; Kallemeyn, W. G.; Arai, T.; Kaneda, K.
1996anme...21..195W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Consortium investigation of the Asuka-881371 angrite:
    Petrographic, electron microprobe, and ion microprobe observations.
Authors: Warren, H. P.; Davis, M. A.
1995anme...20..257W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Chemical variations of spinels in Asuka-881757.
Authors: Arai, T.; Takeda, H.; Warren, H. P.
1995anme...20....4A    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Consortium investigation of the Asuka-881371 angrite: Bulk-rock
    geochemistry and oxygen isotopes.
Authors: Warren, H. P.; Kallemeyn, W. G.; Mayeda, T.
1995anme...20..261W    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: On Arnol'd diffusion in a perturbed magnetic dipole field
Authors: Warren, Harry P.; Bhattacharjee, A.; Mauel, Michael E.
1992GeoRL..19..941W    Altcode:
  For certain initial conditions, the motion of charged particles in a
  magnetic dipole field is well described by the hierarchy of adiabatic
  invariants: the magnetic moment μ, the longitudinal invariant J, and
  the magnetic flux ψ. Electrostatic waves that break the axisymmetry
  of the dipole field and resonate with the drift motion can generate
  large-scale or so-called thick-layer chaos in ψ. This chaos will
  drive Arnol'd diffusion in μ and J, making the motion asymptotically
  unstable. Previous studies involving mappings [Tennyson et al., 1980;
  Kook and Meiss, 1989] have found the thick-layer Arnol'd diffusion
  rate to be proportional to the square of the perturbtion amplitude,
  consistent with quasilinear theory. Here we present numerical evidence
  that for many cases of physical interest, such as particle motion in
  a perturbed dipole field, the thick-layer diffusion rate is greatly
  attenuated from the quasilinear result.

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Title: Lithophile, siderophile, and volatile geochemistry (consortium
    investigations) of two mare-basaltic meteorites.
Authors: Warren, H. P.; Kallemeyn, W. G.
1992anme...17..113W    Altcode:
  No abstract at ADS

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Title: Lunar meteorites: A survey of the first eight district moon
    rocks from Antarctica.
Authors: Warren, H. P.
1990anme...15..131W    Altcode:
  No abstract at ADS

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Title: Geochemistry of lunar meteorite Yamato-86032.
Authors: Warren, H. P.; Kallemeyn, W. G.
1988anme...13...12W    Altcode:
  No abstract at ADS

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Title: Antarctic Meteorites XII. Papers presented to the 12th
    Symposium on Antarctic Meteorites, NIPR, Tokyo, 8-10 June 1987.
Authors: Jerde, A. E.; Warren, H. P.; Heiken, H. G.; Vaniman, T. D.
1987anme...12.....J    Altcode:
  No abstract at ADS

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Title: New data for the bulk compositions of four lunar meteorites,
    and for an Fe-rich basaltic clast of probable VLT-mare affinity
    from Y-791197.
Authors: Warren, H. P.; Kallemeyn, W. G.
1987anme...12...22W    Altcode:
  No abstract at ADS

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Title: Geochemistry of lunar meteorite Yamato-82192: Comparison with
    Yamato-791197, ALHA81005 and other lunar samples.
Authors: Warren, H. P.; Kallemeyn, W. G.
1986anme...11...31W    Altcode:
  No abstract at ADS

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Title: A potpourri of Apollo regolith breccias: Analogs of lunar
    meteorites.
Authors: Jerde, A. E.; Warren, H. P.; Heiken, H. G.; Vaniman, T. D.
1986anme...11..162J    Altcode:
  No abstract at ADS

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Title: Geochemistry of lunar meteorites Yamato-971197 and ALHA81005.
Authors: Warren, H. P.; Kallemeyn, W. G.
1985anme...10...90W    Altcode:
  No abstract at ADS

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Title: Submicrosecond Comparison of Intercontinental Clock
    Synchronization by VLBI and the NTS Satellite
Authors: Hurd, W. J.; Wardrip, S. C.; Bussion, J.; Oaks, J.; McCaskill,
   T.; Warren, H.; Whitworth, G.
1978DSNPR..49...64H    Altcode:
  No abstract at ADS