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Author name code: tripathi
ADS astronomy entries on 2022-09-14
author:"Tripathi, Durgesh" 

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Title: On the formation solar wind, switchbacks and Quiet Sun heating
Authors: Upendran, Vishal; Tripathi, Durgesh
2022cosp...44.1355U    Altcode:
  Coronal holes (CHs) are regions with reduced intensity and enhanced
  blueshifts over Quiet Sun (QS) regions in the corona. These differences
  are seen in the transition region (TR) seen only for regions with
  similar photospheric magnetic flux density (|B|). This work studies
  the chromospheric Mg II h&k, the C II 1334 Å, and TR Si IV line in
  CHs and QS as a function of |B|. We find all lines to show an increase
  of intensities and velocities with |B|. The chromospheric lines show
  reduced intensity, excess blueshifts, and excess redshifts in CHs
  over QS for regions with similar |B|. In the TR line, CHs show excess
  blueshifts and reduced intensity and redshift. Cross-correlation
  of chromospheric and TR velocities shows that flows in the same
  direction are tightly correlated in both regions. In contrast, only the
  chromospheric downflows are correlated with TR upflows in the opposite
  sense of direction. The TR downflows (upflows) are preferentially
  larger in QS (CHs) for similar chromospheric flows. These results may be
  explained through impulsive heating in a stratified atmosphere causing
  larger downflow (upflow) deceleration (acceleration) in QS (CHs),
  which form due to bidirectional flows generated by impulsive events. The
  observed flows and intensities may be explained by invoking interchange
  (closed-loop) reconnection in CHs (QS). An interesting possibility
  of such a model is constraining the formation of switchbacks in the
  lower atmosphere through our observations. Thus, we provide evidence
  on solar wind formation in the chromosphere and further hint towards
  a unified heating scenario in QS and CHs.

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Title: Science from Aditya-L1 mission of the Indian Space Research
    Organization
Authors: Tripathi, Durgesh
2022cosp...44.1354T    Altcode:
  The Aditya-L1 is the first observatory of the Indian Space Research
  Organization (ISRO) in space dedicated to solar observations. The
  spacecraft will carry 7 payloads providing uninterrupted observations
  of the Sun using remote sensing as well as in-situ measurements from
  the first Lagrangian point. There are four remote sensing instruments
  namely a coronagraph, an NUV imager, full-sun integrated soft X-ray and
  hard X-ray spectrometers. In addition, there are three instruments for
  in-situ measurements including a magnetometer to study the magnetic
  field variations during energetic events. I will high-light some of
  the salient feature for the mission and the important roles it will
  play in enhancing our knowledge in the science of the solar atmosphere
  and inner solar corona.

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Title: Synchronization of Small-scale Magnetic Features, Blinkers,
    and Coronal Bright Points
Authors: Shokri, Zahra; Alipour, Nasibe; Safari, Hossein; Kayshap,
   Pradeep; Podladchikova, Olena; Nigro, Giuseppina; Tripathi, Durgesh
2022ApJ...926...42S    Altcode: 2022arXiv220104459S
  We investigate the relationship between different transients such
  as blinkers detected in images taken at 304 Å, extreme ultraviolet
  coronal bright points (ECBPs) at 193 Å, X-ray coronal bright points
  (XCBPs) at 94 Å on the Atmospheric Imaging Assembly, and magnetic
  features observed by the Helioseismic and Magnetic Imager during 10
  yr of solar cycle 24. An automatic identification method is applied
  to detect transients, and the YAFTA algorithm is used to extract the
  magnetic features. Using 10 yr of data, we detect in total 7,483,827
  blinkers, 2,082,162 ECBPs, and 1,188,839 XCBPs, respectively, with
  their birth rate of about 1.1 × 10<SUP>-18</SUP> m<SUP>-2</SUP>
  s<SUP>-1</SUP>, 3.8 × 10<SUP>-19</SUP> m<SUP>-2</SUP> s<SUP>-1</SUP>,
  and 1.5 × 10<SUP>-19</SUP> m<SUP>-2</SUP> s<SUP>-1</SUP>. We find that
  about 80% of blinkers are observed at the boundaries of supergranules,
  and 57% (34%) are associated with ECBPs (XCBPs). We further find that
  about 61%-80% of transients are associated with the isolated magnetic
  poles in the quiet Sun and that the normalized maximum intensities of
  the transients are correlated with the photospheric magnetic flux of
  poles via a power law. These results conspicuously show that these
  transients have a magnetic origin and their synchronized behavior
  provides further clues toward the understanding of the coupling among
  the different layers of the solar atmosphere. Our study further reveals
  that the appearance of these transients is strongly anticorrelated
  with the sunspots' cycle. This finding can be relevant for a better
  understanding of solar dynamo and magnetic structures at different
  scales during the solar cycle.

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Title: On the Formation of Solar Wind and Switchbacks, and Quiet
    Sun Heating
Authors: Upendran, Vishal; Tripathi, Durgesh
2022ApJ...926..138U    Altcode: 2021arXiv211111668U
  The solar coronal heating in quiet Sun (QS) and coronal holes (CHs),
  including solar wind formation, are intimately tied by magnetic field
  dynamics. Thus, a detailed comparative study of these regions is
  needed to understand the underlying physical processes. CHs are known
  to have subdued intensity and larger blueshifts in the corona. This
  work investigates the similarities and differences between CHs and QS
  in the chromosphere using the Mg II h and k, C II line, and transition
  region using Si IV line, for regions with identical absolute magnetic
  flux density (∣B∣). We find CHs to have subdued intensity in all of
  the lines, with the difference increasing with line formation height and
  ∣B∣. The chromospheric lines show excess upflows and downflows in
  CH, while Si IV shows excess upflows (downflows) in CHs (QS), where the
  flows increase with ∣B∣. We further demonstrate that the upflows
  (downflows) in Si IV are correlated with both upflows and downflows
  (only downflows) in the chromospheric lines. CHs (QS) show larger
  Si IV upflows (downflows) for similar flows in the chromosphere,
  suggesting a common origin to these flows. These observations may
  be explained due to impulsive heating via interchange (closed-loop)
  reconnection in CHs (QS), resulting in bidirectional flows at different
  heights, due to differences in magnetic field topologies. Finally,
  the kinked field lines from interchange reconnection may be carried
  away as magnetic field rotations and observed as switchbacks. Thus,
  our results suggest a unified picture of solar wind emergence, coronal
  heating, and near-Sun switchback formation.

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Title: Flows in Enthalpy-based Thermal Evolution of Loops
Authors: Rajhans, Abhishek; Tripathi, Durgesh; Bradshaw, Stephen J.;
   Kashyap, Vinay L.; Klimchuk, James A.
2022ApJ...924...13R    Altcode: 2021arXiv211003204R
  Plasma-filled loop structures are common in the solar corona. Because
  detailed modeling of the dynamical evolution of these structures is
  computationally costly, an efficient method for computing approximate
  but quick physics-based solutions is to rely on space-integrated 0D
  simulations. The enthalpy-based thermal evolution of loops (EBTEL)
  framework is a commonly used method to study the exchange of mass
  and energy between the corona and transition region. EBTEL solves for
  density, temperature, and pressure, averaged over the coronal part of
  the loop, velocity at coronal base, and the instantaneous differential
  emission measure distribution in the transition region. The current
  single-fluid version of the code, EBTEL2, assumes that at all stages the
  flows are subsonic. However, sometimes the solutions show the presence
  of supersonic flows during the impulsive phase of heat input. It is thus
  necessary to account for this effect. Here, we upgrade EBTEL2 to EBTEL3
  by including the kinetic energy term in the Navier-Stokes equation. We
  compare the solutions from EBTEL3 with those obtained using EBTEL2, as
  well as the state-of-the-art field-aligned hydrodynamics code HYDRAD. We
  find that the match in pressure between EBTEL3 and HYDRAD is better than
  that between EBTEL2 and HYDRAD. Additionally, the velocities predicted
  by EBTEL3 are in close agreement with those obtained with HYDRAD when
  the flows are subsonic. However, EBTEL3 solutions deviate substantially
  from HYDRAD's when the latter predicts supersonic flows. Using the
  mismatches in the solution, we propose a criterion to determine the
  conditions under which EBTEL can be used to study flows in the system.

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Title: Machine learning inference of statistical signatures of
    heating events
Authors: Upendran, Vishal; Tripathi, Durgesh
2021AGUFMSH15D2058U    Altcode:
  The solar corona consists of a million degree Kelvin plasma. Quiet
  Sun regions (QS), which form a background over which large, dynamic
  events occur, must be studied well to understand the presence of
  this million degree plasma. In this work, we assume an impulsive
  heating forward model with the flaring frequency, flaring timescale
  and power-law slope as free parameters. We develop an inversion code
  using a Convolutional neural network to infer these free parameters
  and their associated uncertainties for coronal light curves. We apply
  this inversion scheme on light curves from each pixel in the 171, 193
  and 211 A to infer the free parameters, and find impulsive events to
  be a viable source of generating intensity. We find the correlations
  between free parameters to be explained by the domination of conduction
  losses and the existence of an energy reservoir. We further apply this
  scheme on full disc integrated, and flux-calibrated light curves from
  X-ray Solar Monitor onboard Chandrayaan-2, and put lower bounds on
  the energy flux in QS. These findings give us a deeper understanding
  of the viability of impulsive events in heating up the solar corona,
  and the advantages offered by data-driven machine learning algorithms
  in accelerating science.

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Title: Properties of the C II 1334 Å Line in Coronal Hole and Quiet
    Sun as Observed by IRIS
Authors: Upendran, Vishal; Tripathi, Durgesh
2021ApJ...922..112U    Altcode: 2021arXiv210904287U
  Coronal holes (CHs) have subdued intensity and net blueshifts
  when compared to the quiet Sun (QS) at coronal temperatures. At
  transition region temperatures, such differences are obtained for
  regions with identical absolute photospheric magnetic flux density
  (∣B∣). In this work, we use spectroscopic measurements of the C II
  1334 Å line from the Interface Region Imaging Spectrograph, formed at
  chromospheric temperatures, to investigate the intensity, Doppler shift,
  line width, skew, and excess kurtosis variations with ∣B∣. We
  find the intensity, Doppler shift, and linewidths to increase with
  ∣B∣ for CHs and QS. The CHs show deficit in intensity and excess
  total widths over QS for regions with identical ∣B∣. For pixels
  with only upflows, CHs show excess upflows over QS, while for pixels
  with only downflows, CHs show excess downflows over QS that cease to
  exist at ∣B∣ ≤ 40. Finally, the spectral profiles are found to
  be more skewed and flatter than a Gaussian, with no difference between
  CHs and QS. These results are important in understanding the heating
  of the atmosphere in CH and QS, including solar wind formation, and
  provide further constraints on the modeling of the solar atmosphere.

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Title: Multi-Stranded Simulations Mimicking FOXSI and AIA Observations
: A Single Power-Law Distribution for Transients and Steady Background
Authors: Rajhans, Abhishek; Tripathi, Durgesh; Kashyap, Vinay; Athiray,
   P. S.; Upendran, Vishal
2021AGUFMSH15E2063R    Altcode:
  Solar Coronal Heating, which Maintains the Corona at 1 MK can be
  attributed to uniform steady background heating and transients like
  impulsive flaring events. Here we explore the possibility that the
  steady heating is attributable to a large swarm of small impulsive
  events with a single power law distribution of flare energies. We
  perform a realistic simulation of multi-stranded system of loops,
  mimicking data obtained from Atmospheric Imaging Assembly (AIA)
  and Focusing Optics X-ray Solar Imager (FOXSI) for an isolated loop
  complex. We use 0D description of coronal loops (Enthalpy Based Thermal
  Evolution of Loops) for performing simulations. The loop is modelled to
  have 100 strands, based on constraints provided by Hi-C on the cross
  sectional radii of strands. 10 30 ergs is deposited in the loop over
  10,000 seconds of simulations in accordance with observed radiation
  flux. We simulate a large number of cases, uniquely determined by
  the slope of the power law distribution, along with the maximum and
  minimum energies that can be dissipated in an event. Preliminary results
  indicate that the observed light curve including the background and
  impulsive events can be best explained by a power law index of -1.8
  and maximum and minimum energies differing by more than 7-8 orders of
  magnitudes. We discuss the implications of these results and possible
  extensions.

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Title: Solar wind signatures in the chromosphere
Authors: Upendran, Vishal; Tripathi, Durgesh
2021AGUFMSH32B..05U    Altcode:
  Coronal holes (CHs) are regions with reduced intensity and enhanced
  blueshifts when compared to Quiet Sun (QS) regions at coronal
  temperatures. However, such differences are seen in transition region
  temperatures only for regions with similar magnetic flux density
  (|B|). In this work, we study the chromospheric Mg II h&amp;k, the C
  II doublet lines and transition region Si IV line in CHs and QS as a
  function of |B|. We find the intensities, velocities and the C II line
  widths to increase with increasing |B|. For both the chromospheric
  lines, we find reduced intensity, excess blueshifts as well as excess
  redshifts in CHs over QS for regions with similar |B|. Moreover,
  CHs show larger line width in CII than QS for regions with similar
  |B|. When synergy between the velocities of C II, Mg II and Si IV
  lines is investigated, we find: (a). Upflows, downflows in all the
  lines are tightly correlated. (b). Upflows in Mg II and C II have no
  correlation with downflows observed in Si IV. (c). Downflows of Mg II,
  C II are correlated with upflows of Si IV, with correlation values
  increasing from Mg II h2 to C II. These results may be explained if
  (a). Upflows in Mg II are accelerated till Si IV. (b), Downflows in Si
  IV are decelerated toward Mg II. (c). Bi-directional flows give rise to
  correlated transition region upflows and chromospheric downflows. Such
  bi-directional flows may occur due to impulsive events occurring between
  the formation height of Mg II/ C II and Si IV . The patterns of observed
  flows in CHs and QS may be explained by invoking impulsive heating in
  topologically different regions. These results provide evidence on the
  formation of solar wind in the chromosphere and further hints towards
  the unified heating scenario of the solar corona in the QS and CHs.

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Title: Characterizing the Spectral Profiles of Mg II, C II and Si
    IV in Solar Flares
Authors: Roy, Soumya; Tripathi, Durgesh; Young, Peter
2021AGUFMSH25E2128R    Altcode:
  Solar flares are the most energetic phenomena in the solar atmosphere
  with consequences for space weather through the generation of
  solar energetic particles and/or CMEs. Despite tremendous advances
  in understanding their characteristics, the complete physics of
  their origin and response to plasma in various layers of the solar
  atmosphere is not fully developed. Here, we study the characteristics
  of the spectral line profiles during different stages of flares as
  a function of photospheric magnetic flux density and compare those
  with the characteristics observed in quiescent active regions and
  quiet sun. For this purpose, we use archival observations from the
  Interface Region Imaging Spectrograph (IRIS). For context purposes,
  we used full-disk observations from the Atmospheric Imaging Assembly
  (AIA). We use the line-of-sight (LOS) magnetograms obtained by
  the Helioseismic and Magnetic Imager (HMI). We characterize the
  self-absorption observed and optical depth from the line intensities
  as a function of the magnetic flux density, which shows a signature
  of precipitation. We also see the Mg II triplets going into emission
  co-spatially in the regions where flare ribbons appear later. We use
  the 2791.6 A line to localize the regions where the triplet lines are
  observed. These results are important for the physics of flares and
  can be useful in predicting the location of a flare kernel.

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Title: Hydrodynamics of Small Transient Brightenings in the Solar
    Corona
Authors: Rajhans, Abhishek; Tripathi, Durgesh; Kashyap, Vinay L.
2021ApJ...917...29R    Altcode: 2021arXiv210508800R
  Small scale transients occur in the solar corona at much higher
  frequencies than flares and play a significant role in coronal
  dynamics. Here we study three well-identified transients discovered by
  Hi-C and also detected by the EUV channels of the Atmospheric Imaging
  Assembly (AIA) on board the Solar Dynamics Observatory. We use 0D
  enthalpy-based hydrodynamical simulations and produce synthetic
  light curves to compare with AIA observations. We have modeled
  these transients as loops of ~1.0 Mm length depositing energies
  ~10<SUP>23</SUP> erg in ~50 s. The simulated synthetic light curves
  show reasonable agreement with the observed light curves. During the
  initial phase, conduction flux from the corona dominates over the
  radiation, like impulsive flaring events. Our results further show
  that the time-integrated net enthalpy flux is positive, hence into
  the corona. The fact that we can model the observed light curves of
  these transients reasonably well by using the same physics as those
  for nanoflares, microflares, and large flares, suggests that these
  transients may have a common origin.

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Title: On the Impulsive Heating of Quiet Solar Corona
Authors: Upendran, Vishal; Tripathi, Durgesh
2021ApJ...916...59U    Altcode: 2021arXiv210316824U
  The solar corona consists of a million degree Kelvin plasma. A complete
  understanding of this phenomenon demands the study of quiet Sun (QS)
  regions. In this work, we study QS regions in the 171 Å, 193 Å, and
  211 Å passbands of the Atmospheric Imaging Assembly (AIA) on board the
  Solar Dynamics Observatory, by combining the empirical impulsive heating
  forward model of Pauluhn &amp; Solanki with a machine-learning inversion
  model that allows uncertainty quantification. We find that there are
  &amp;approx;2-3 impulsive events per minute, with a lifetime of about
  10-20 minutes. Moreover, for all the three passbands, the distribution
  of power-law slope α peaks above 2. Our exploration of correlations
  among the frequency of impulsive events and their timescales and peak
  energy suggests that conduction losses dominate over radiative cooling
  losses. All these findings suggest that impulsive heating is a viable
  heating mechanism in QS corona.

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Title: Nonthermal Velocity in the Transition Region of Active Regions
    and Its Center-to-limb Variation
Authors: Ghosh, Avyarthana; Tripathi, Durgesh; Klimchuk, James A.
2021ApJ...913..151G    Altcode: 2021arXiv210315081G
  We derive the nonthermal velocities (NTVs) in the transition region
  of an active region using the Si IV 1393.78 Å line observed by
  the Interface Region Imaging Spectrograph and compare them with the
  line-of-sight photospheric magnetic fields obtained by the Helioseismic
  and Magnetic Imager on board the Solar Dynamics Observatory. The active
  region consists of two strong field regions with opposite polarity,
  separated by a weak field corridor that widened as the active region
  evolved. The means of the NTV distributions in strong field regions
  (weak field corridors) range between ∼18-20 (16-18) km s<SUP>-1</SUP>,
  albeit the NTV maps show a much larger range. In addition, we identify
  a narrow lane in the middle of the corridor with significantly reduced
  NTV. The NTVs do not show a strong center-to-limb variation, albeit
  they show somewhat larger values near the disk center. The NTVs are
  well correlated with redshifts as well as line intensities. The results
  obtained here and those presented in our companion paper on Doppler
  shifts suggest two populations of plasma in the active region emitting
  in Si IV. The first population exists in the strong field regions and
  extends partway into the weak field corridor between them. We attribute
  this plasma to spicules heated to ∼0.1 MK (often called type II
  spicules). They have a range of inclinations relative to vertical. The
  second population exists in the center of the corridor, is relatively
  faint, and has smaller velocities, likely horizontal. These results
  provide further insights into the heating of the transition region.

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Title: Thermodynamic evolution of a sigmoidal active region with
    associated flares
Authors: Mulay, Sargam M.; Tripathi, Durgesh; Mason, Helen
2021MNRAS.504.1201M    Altcode: 2021MNRAS.tmp..832M; 2021arXiv210309561M
  Active regions often show S-shaped structures in the corona called
  sigmoids. These are highly sheared and twisted loops formed along
  the polarity inversion line. They are considered to be one of the best
  pre-eruption signatures for CMEs. Here, we investigate the thermodynamic
  evolution of an on-disc sigmoid observed during 2015 December 24-28. For
  this purpose, we have employed Emission Measure (EM) and filter-ratio
  techniques on the observations recorded by the Atmospheric Imaging
  Assembly (AIA) on-board the Solar Dynamics Observatory (SDO) and X-ray
  Telescope (XRT) on-board Hinode. The EM analysis showed multithermal
  plasma along the sigmoid and provided a peak temperature of ~10-12.5
  MK for all observed flares. The sigmoidal structure showed emission
  from Fe XVIII (93.93 Å) and Fe XXI (128.75 Å) lines in the AIA 94 and
  131 Å channels, respectively. Our results show that the hot plasma is
  often confined to very hot strands. The temperature obtained from the
  EM analysis was found to be in good agreement with that obtained using
  the XRT, AIA, and GOES filter-ratio methods. These results provide
  important constraints for the thermodynamic modelling of sigmoidal
  structures in the core of active regions. Moreover, this study also
  benchmarks different techniques available for temperature estimation
  in solar coronal structures.

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Title: Transient Formation of Loops in the Core of an Active Region
Authors: Tripathi, Durgesh
2021ApJ...909..105T    Altcode: 2021arXiv210106622T
  We study the formation of transient loops in the core of the AR
  11890. For this purpose, we have used the observations recorded by the
  Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging
  Spectrograph (IRIS). For photospheric field configuration, we have used
  the line-of-sight (LOS) magnetograms obtained from the Helioseismic and
  Magnetic Imager. The transient is simultaneously observed in all the
  UV and EUV channels of AIA and the three slit-jaw images from IRIS. The
  coexistence of the transient in all AIA and IRIS SJI channels suggests
  the transient's multithermal nature. The transient consists of short
  loops located at the base of the transient, as well as long loops. A
  differential emission measure analysis shows that the transient has a
  clumpy structure. The highest emission observed at the base is within
  the temperature bin of $\mathrm{log}T=6.65\mbox{--}6.95$ . We observe
  the longer loops at a similar temperature, albeit very feeble. Using
  LOS magnetograms, we conclude that the magnetic reconnection may have
  caused the transient. Our observations further suggest that the physics
  of the formation of such transients may be similar to those of typical
  coronal jets, albeit in different topological configurations. Such
  multiwavelength observations shed light on the formation of hot
  plasma in the solar corona and provide further essential constraints
  on modeling the thermodynamics of such transients.

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

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Title: Space Climate Studies with the Solar Ultraviolet Imaging
    Telescope on board Aditya-L1 mission
Authors: Tripathi, Durgesh
2021cosp...43E.917T    Altcode:
  The Solar Ultraviolet Imaging Telescope (SUIT) is an instrument on-board
  Aditya-L1. It will measure and monitor the solar radiation in the
  wavelength range 200-400 nm, which is central to our understanding of
  Sun-climate relationship. SUIT will provide full disk images using
  11 filters (3 broadband and eight narrowband) allowing us, for the
  first time, to measure and monitor spatially resolved solar spectral
  irradiance that governs the chemistry of oxygen and ozone in the
  stratosphere of the Earth's atmosphere.

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Title: Heliophysics Public Outreach in India
Authors: Tripathi, Durgesh
2021cosp...43E2437T    Altcode:
  In the era of growing technological dependence, space weather has
  a vital role to play in developing countries like India. Various
  funding agencies have recognized this in the country, including the
  Indian Space Research Organization. Several programmes have been
  running, both on core academic level as well as public outreach for
  the capacity building in Heliophysics. In this talk, I shall highlight
  some of the steps taken within the country with a focus on those taken
  by the SciPop centre of IUCAA.

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Title: Dynamics of Sunspot Shock Waves in the Chromosphere and
    Transition Region
Authors: Kayshap, Pradeep; Tripathi, Durgesh; Jelínek, P.
2021ApJ...906..121K    Altcode: 2020arXiv201110192K
  We study the dynamics of shock waves observed in the umbra of a sunspot
  using the spectroscopic observations from the Interface Region Imaging
  Spectrograph. The presence of a shock significantly deforms the shape
  of the spectral lines of Mg II, C II, and Si IV. We found that C II
  1335.71 Å and Si IV 1393.75 Å show double-peaked profiles that change
  to a single peak later on. However, the Mg II h 2803.53 Å line first
  shows flat-top profiles that change into double peaks followed by the
  single peak. To study the shock dynamics, we isolate the shock component
  from the spectra by fitting two Gaussians. We find that the lifetime
  of the shock is largest in the Mg II h 2803.53 Å line. Moreover,
  the plasma motion shows both the acceleration and deceleration phases
  of the shock. Yet, in C II 1335.71 Å and Si IV 1393.75 Å, only
  the deceleration phase is observed. We observe a strong correlation
  between the largest blueshift of the shock and deceleration for all
  three spectral lines. We find a positive (negative) correlation between
  intensities contributed by the shocks in Mg II and C II (Si IV). This
  suggests that the shocks are first amplified in C II, followed by a
  decline in the height range corresponding to Si IV. These results may
  indicate the dissipation of shocks above the formation height of C II,
  and the shocks may have important roles in the dynamics of the upper
  chromosphere and transition region above sunspots.

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Title: ISRO's First Solar Observatory in Space: Aditya-L1 Mission
Authors: Tripathi, D.
2020AGUFMSH056..01T    Altcode:
  The dynamic and magnetically coupled atmosphere of the Sun presents
  several puzzling physical phenomena of great importance. For
  example, the existence of hotter chromosphere and corona above the
  photosphere. Due to these high-temperature layers, Sun radiates
  in UV and X-rays, which play a crucial role in the dynamics of the
  Earth's atmosphere. Similarly, the occurrence of highly energetic solar
  eruptions such as flares and coronal mass ejections, which has direct
  consequences on space weather and geo-space climate, has proven to be
  highly challenging to comprehend. The Aditya-L1 mission of the Indian
  Space Research Organization (ISRO) will help us study the dynamic
  coupling of the solar atmosphere as well as to measure and monitor the
  spatially resolved solar spectral irradiance in the near-ultraviolet
  band, which is central to the Earth's climate. The spacecraft will
  be located at the first Lagrangian Point and carry seven payloads --
  four remote-sensing and three in-situ. Combining all the instruments,
  Aditya-L1 shall cover the wavelength range from Hard X-rays to infrared
  for remote sensing. Out of three in-situ payloads, two will provide
  measurements of the charged particles. The third is a magnetometer to
  assess the interplanetary magnetic field. I shall discuss the salient
  features of the experiments onboard Aditya-L1 mission.

---------------------------------------------------------
Title: Formation and dynamics of transequatorial loops
Authors: Ghosh, Avyarthana; Tripathi, Durgesh
2020A&A...640A...3G    Altcode: 2020arXiv200512839G
  <BR /> Aims: We aim to study the dynamical evolution of transequatorial
  loops (TELs) using imaging techniques and spectroscopy. <BR />
  Methods: We used the images recorded by the Atmospheric Imaging
  Assembly and the Helioseismic Magnetic Imager on board the Solar
  Dynamics Observatory together with spectroscopic observations taken
  from the Extreme-Ultraviolet Imaging Spectrometer on board Hinode. <BR
  /> Results: The data from the AIA 193 Å channel show that TELs are
  formed between AR 12230 and a newly emerging AR 12234, evolving between
  10 and 14 December 2014. The xt-plots for 12 December 2014, obtained
  using AIA 193 Å data, reveal signatures of inflow and outflow towards
  an X-region. High-cadence AIA images also show recurrent intensity
  enhancements in close proximity to the X-region (P2), which is observed
  to have higher intensities for spectral lines that are formed at
  log T[K] = 6.20 and voids at other higher temperatures. The electron
  densities and temperatures in the X-region (and P2) are maintained
  steadily at log N<SUB>e</SUB>= 8.5-8.7 cm<SUP>-3</SUP> and log T[K] =
  6.20, respectively. Doppler velocities in the X-region show predominant
  redshifts by about 5-8 km s<SUP>-1</SUP> when they are closer to the
  disk center but blueshifts (along with some zero-velocity pixels)
  when away from the center. The full-width-half-maximum maps reveal
  non-thermal velocities of about 27-30 km s<SUP>-1</SUP> for Fe XII,
  Fe XIII, and Fe XV lines. However, the brightest pixels have nonthermal
  velocities ∼62 km s<SUP>-1</SUP> for Fe XII and Fe XIII lines. On the
  contrary, the dark X-region for Fe XV line have the highest non-thermal
  velocity (∼115 km s<SUP>-1</SUP>). <BR /> Conclusions: We conclude
  that the TELs are formed due to magnetic reconnection. We further note
  that the TELs themselves undergo magnetic reconnection, which leads to
  the re-formation of loops among individual ARs. Moreover, this study,
  for the first time, provides measurements of plasma parameters in
  X-regions, thereby providing essential constraints for theoretical
  studies. <P />The movie associated to Fig. 3 is available at <A
  href="https://www.aanda.org/10.1051/0004-6361/201936681/olm">https://www.aanda.org</A>

---------------------------------------------------------
Title: Wave amplitude modulation in fan loops as observed by AIA/SDO
Authors: Sharma, Aishawnnya; Tripathi, Durgesh; Erdélyi, Robertus;
   Gupta, Girjesh R.; Ahmed, Gazi A.
2020A&A...638A...6S    Altcode: 2020arXiv200405797S
  <BR /> Aims: We perform a detailed analysis to understand the evolution
  and dynamics of propagating intensity disturbances observed in a fan
  loop system. <BR /> Methods: We performed multiwavelength time-distance
  analysis of a fan loop system anchored in an isolated sunspot region
  (AR 12553). The active region was observed by the Atmospheric Imaging
  Assembly on board the Solar Dynamics Observatory. We measured
  the phase speeds of the propagating intensity disturbances by
  employing cross-correlation analysis, and by obtaining the slopes
  in xt-plots. We obtained original and detrended light curves at
  different heights of the time-distance maps and characterised them
  by performing Fourier and wavelet analysis, respectively. <BR />
  Results: The time-distance maps reveal clear propagation of intensity
  oscillations in all the coronal extreme ultraviolet (EUV) channels
  except AIA 94 and 335 Å. We determine the nature of the intensity
  disturbances as slow magneto-acoustic waves by measuring their phase
  speeds. The time-distance maps, as well as the detrended light curves,
  show an increase and decrease in the amplitude of propagating 3 min
  oscillations over time. The amplitude variations appear most prominently
  in AIA 171 Å, though other EUV channels also show such signatures. The
  Fourier power spectrum yields the presence of significant powers with
  several nearby frequencies in the range of 2-3 min (5-8 mHz), along
  with many other smaller peaks between 2-4 min. Wavelet analysis shows
  an increase and decrease of oscillating power around 3 min simultaneous
  to the amplitude variations. We obtain the modulation period to be in
  the range of 20-30 min. <BR /> Conclusions: Our results provide the
  viability of occurrence of phenomenon like "Beat" among the nearby
  frequencies giving rise to the observed amplitude modulation. However,
  we cannot at this stage rule out the possibility that the modulation
  may be driven by variability in an underlying unknown source.

---------------------------------------------------------
Title: Signatures of Untwisting Magnetic Field in a Small Emerging
    Bipole in the Solar Photosphere
Authors: Sangeetha, C. R.; Tripathi, Durgesh; Rajaguru, S. P.
2020ApJ...895...67S    Altcode: 2020arXiv200405615S
  We perform a study of fluid motions and its temporal evolution in and
  around a small bipolar emerging flux region using observations made
  by the Helioseismic and Magnetic Imager on board the Solar Dynamics
  Observatory. We employ local correlation tracking of the Doppler
  observations to follow horizontal fluid motions and line-of-sight
  magnetograms to follow the flux emergence. Changes in vertical
  vorticity and horizontal divergence are used to derive signatures of
  evolving twists in the magnetic field. Our analysis reveals that the
  two polarities of the magnetic flux swirl in opposite directions in
  the early stages of flux emergence indicating an unwinding of the
  pre-emergence twists in the magnetic field. We further find that
  during the emergence, there is an increase in swirly motions in the
  neighboring nonmagnetic regions. We estimate the magnetic and kinetic
  energies and find that magnetic energy is about a factor of 10 larger
  than the kinetic energy. During the evolution, when the magnetic energy
  decreases, an increase in the kinetic energy is observed indicating
  transfer of energy from the unwinding of the magnetic flux tube to the
  surrounding fluid motions. Our results thus demonstrate the presence of
  pre-emergence twists in an emerging magnetic field that is important
  in the context of the hemispheric helicity rule warranting a detailed
  statistical study in this context. Further, our observations point to
  a possible widespread generation of torsional waves in emerging flux
  regions due to the untwisting magnetic field with implications for
  upward energy transport to the corona.

---------------------------------------------------------
Title: On the Ratios of Si IV Lines (λ1394/λ1403) in an Emerging
    Flux Region
Authors: Tripathi, Durgesh; Nived, V. N.; Isobe, Hiroaki; Doyle,
   G. Gerard
2020ApJ...894..128T    Altcode: 2020arXiv200404530T
  The resonance lines of Si IV formed at λ1394 and 1403 Å are the
  most critical for the diagnostics of the solar transition region
  in the observations of the Interface Region Imaging Spectrograph
  (IRIS). Studying the intensity ratios of these lines (1394 Å/1403 Å),
  which under optically thin conditions is predicted to be two, helps us
  to diagnose the optical thickness of the plasma being observed. Here
  we study the evolution of the distribution of intensity ratios in 31
  IRIS rasters recorded for four days during the emergence of an active
  region. We found that during the early phase of the development, the
  majority of the pixels show intensity ratios smaller than two. However,
  as the active region evolves, more and more pixels show the ratios
  closer to two. Besides, there are a substantial number of pixels with
  ratio values larger than 2. At the evolved stage of the active region,
  the pixels with ratios smaller than two were located on the periphery,
  whereas those with values larger than 2 were in the core. However,
  for quiet Sun regions, the obtained intensity ratios were close to
  two irrespective of the location on the disk. Our findings suggest
  that the Si IV lines observed in active regions are affected by the
  opacity during the early phase of the flux emergence. The results
  obtained here could have important implications for the modeling of
  the solar atmosphere, including the initial stage of the emergence of
  an active region as well as the quiet Sun.

---------------------------------------------------------
Title: On Doppler Shift and Its Center-to-limb Variation in Active
    Regions in the Transition Region
Authors: Ghosh, Avyarthana; Klimchuk, James A.; Tripathi, Durgesh
2019ApJ...886...46G    Altcode: 2019arXiv191012033G
  A comprehensive understanding of the structure of Doppler motions
  in the transition region including the center-to-limb variation and
  its relationship with the magnetic field structure is vital for the
  understanding of mass and energy transfer in the solar atmosphere. In
  this paper, we have performed such a study in an active region using
  the Si IV 1394 Å emission line recorded by the Interface Region Imaging
  Spectrograph and the line-of-sight photospheric magnetic field obtained
  by the Helioseismic and Magnetic Imager onboard the Solar Dynamics
  Observatory. The active region has two opposite polarity strong field
  regions separated by a weak field corridor, which widened as the active
  region evolved. On average, the strong field regions (corridor) show(s)
  redshifts of 5-10 (3-9) km s<SUP>-1</SUP> (depending on the date of
  observation). There is, however, a narrow lane in the middle of the
  corridor with near-zero Doppler shifts at all disk positions, suggesting
  that any flows there are very slow. The Doppler velocity distributions
  in the corridor seem to have two components—a low velocity component
  centered near 0 km s<SUP>-1</SUP> and a high-velocity component centered
  near 10 km s<SUP>-1</SUP>. The high-velocity component is similar to
  the velocity distributions in the strong field regions, which have just
  one component. Both exhibit a small center-to-limb variation and seem
  to come from the same population of flows. To explain these results,
  we suggest that the emission from the lower transition region comes
  primarily from warm type II spicules, and we introduce the idea of a
  “chromospheric wall”—associated with classical cold spicules—to
  account for a diminished center-to-limb variation.

---------------------------------------------------------
Title: ICSF: Intensity Conserving Spectral Fitting
Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh
2019ascl.soft03007K    Altcode:
  ICSF (Intensity Conserving Spectral Fitting) "corrects" (x,y) data in
  which the ordinate represents the average of a quantity over a finite
  interval in the abscissa. A typical example is spectral data, where
  the average intensity over a wavelength bin (the measured quantity)
  is assigned to the center of the bin. If the profile is curved, the
  average will be different from the discrete value at the bin center
  location. ICSF, written in IDL and available separately and as part of
  SolarSoft (ascl:1208.013), corrects the intensity using an iterative
  procedure and cubic spline. The corrected intensity equals the "true"
  intensity at bin center, rather than the average over the bin. Unlike
  other methods that are restricted to a single fitting function,
  typically a spline, ICSF can be used with any function, such as a
  cubic spline or a Gaussian, with slight changes to the code.

---------------------------------------------------------
Title: Magnetic Fields and the Supply of Low-frequency Acoustic Wave
    Energy to the Solar Chromosphere
Authors: Rajaguru, S. P.; Sangeetha, C. R.; Tripathi, Durgesh
2019ApJ...871..155R    Altcode:
  The problem of solar chromospheric heating remains a challenging
  one with wider implications for stellar physics. Several studies in
  the recent past have shown that small-scale inclined magnetic field
  elements channel copious energetic low-frequency acoustic waves, which
  are normally trapped below the photosphere. These magnetoacoustic
  waves are expected to shock at chromospheric heights, contributing
  to chromospheric heating. In this work, exploiting simultaneous
  observations of photospheric vector magnetic field, Doppler, continuum,
  and line-core intensity (of Fe I 6173 Å) from the Helioseismic and
  Magnetic Imager and lower-atmospheric UV emission maps in the 1700 and
  1600 Å channels of the Atmospheric Imaging Assembly, both on board
  the Solar Dynamics Observatory of NASA, we revisit the relationships
  between magnetic field properties (inclination and strength) and the
  propagation of acoustic waves (phase travel time). We find that the
  flux of acoustic energy, in the 2-5 mHz frequency range, between the
  upper photosphere and lower chromosphere is in the range of 2.25-2.6
  kW m<SUP>-2</SUP>, which is about twice the previous estimates. We
  identify that the relatively less inclined magnetic field elements
  in the quiet Sun channel a significant amount of waves of frequency
  lower than the theoretical minimum acoustic cutoff frequency due to
  magnetic inclination. We also derive indications that these waves
  steepen and start to dissipate within the height ranges probed, while
  those let out due to inclined magnetic fields pass through. We explore
  connections with existing theoretical and numerical results that could
  explain the origin of these waves.

---------------------------------------------------------
Title: Magnetic fields and low-frequency acoustic wave-energy supply
    to the solar chromosphere
Authors: Rajaguru, S. P.; Sangeetha, C. R.; Tripathi, Durgesh
2018arXiv181205322R    Altcode:
  The problem of solar chromospheric heating remains a challenging one
  with wider implications for stellar physics. Several studies in the
  recent past have shown that small-scale inclined magnetic field elements
  channel copious amount of energetic low-frequency acoustic waves, that
  are normally trapped below the photosphere. These magneto-acoustic
  waves are expected to shock at chromospheric heights contributing
  to chromospheric heating. In this work, exploiting simultaneous
  photospheric vector magnetic field, Doppler, continuum and line-core
  intensity (of FeI 6173 Å) observations from the Helioseismic and
  Magnetic Imager (HMI) and lower-atmospheric UV emission maps in the
  1700 Å and 1600 Å channels of the Atmospheric Imaging Assembly (AIA),
  both onboard the Solar Dynamics Observatory (SDO) of NASA, we revisit
  the relationships between magnetic field properties (inclination and
  strength) and the acoustic wave propagation (phase travel time). We
  find that the flux of acoustic energy, in the 2 - 5 mHz frequency range,
  between the upper photosphere and lower chromosphere is in the range of
  2.25 - 2.6 kW m$^{-2}$, which is about twice the previous estimates. We
  identify that the relatively less-inclined magnetic field elements
  in the quiet-Sun channel a significant amount of waves of frequency
  lower than the theoretical minimum for acoustic cut-off frequency
  due to magnetic inclination. We also derive indications that these
  waves steepen and start to dissipate within the heights ranges probed,
  while those let out due to inclined magnetic fields pass through. We
  explore connections with existing theoretical and numerical results
  that could explain the origin of these waves.

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

---------------------------------------------------------
Title: Energetics of Hi-C EUV brightenings
Authors: Subramanian, Srividya; Kashyap, Vinay L.; Tripathi, Durgesh;
   Madjarska, Maria S.; Doyle, John G.
2018A&A...615A..47S    Altcode: 2018arXiv180309505S
  We study the thermal structure and energetics of the point-like extreme
  ultraviolet (EUV) brightenings within a system of fan loops observed
  in the active region AR 11520. These brightenings were simultaneously
  observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager
  and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
  Observatory (SDO). We identified 27 brightenings by automatically
  determining intensity enhancements in both Hi-C and AIA 193 Å light
  curves. The energetics of these brightenings were studied using the
  Differential Emission Measure (DEM) diagnostics. The DEM weighted
  temperatures of these transients are in the range log T(K) = 6.2-6.6
  with radiative energies ≈10<SUP>24-25</SUP> ergs and densities
  approximately equal to a few times 10<SUP>9</SUP> cm<SUP>-3</SUP>. To
  the best of our knowledge, these are the smallest brightenings in
  EUV ever detected. We used these results to determine the mechanism
  of energy loss in these brightenings. Our analysis reveals that the
  dominant mechanism of energy loss for all the identified brightenings
  is conduction rather than radiation.

---------------------------------------------------------
Title: Observation and Modeling of Chromospheric Evaporation in a
    Coronal Loop Related to Active Region Transient Brightening
Authors: Gupta, G. R.; Sarkar, Aveek; Tripathi, Durgesh
2018ApJ...857..137G    Altcode: 2018arXiv180311172G
  Using the observations recorded by the Atmospheric Imaging Assembly
  (AIA) on board the Solar Dynamics Observatory and the Interface
  Region Imaging Spectrograph (IRIS) and the Extreme-ultraviolet
  Imaging Spectrometer and X-Ray Telescope both on board Hinode, we
  present evidence of chromospheric evaporation in a coronal loop after
  the occurrence of two active region transient brightenings (ARTBs)
  at the two footpoints. The chromospheric evaporation started nearly
  simultaneously in all of the three hot channels of AIA 131, 94, and 335
  Å and was observed to be temperature dependent, being fastest in the
  highest temperature channel. The whole loop became fully brightened
  following the ARTBs after ≈25 s in 131 Å, ≈40 s in 94 Å, and
  ≈6.5 minutes in 335 Å. The differential emission measurements at
  the two footpoints (i.e., of two ARTBs) and at the loop top suggest
  that the plasma attained a maximum temperature of ∼10 MK at all
  these locations. The spectroscopic observations from IRIS revealed the
  presence of redshifted emission of ∼20 km s<SUP>-1</SUP> in cooler
  lines like C II and Si IV during the ARTBs that was cotemporal with
  the evaporation flow at the footpoint of the loop. During the ARTBs,
  the line width of C II and Si IV increased nearly by a factor of two
  during the peak emission. Moreover, enhancement in the line width
  preceded that in the Doppler shift, which again preceded enhancement
  in the intensity. The observed results were qualitatively reproduced
  by 1D hydrodynamic simulations, where energy was deposited at both of
  the footpoints of a monolithic coronal loop that mimicked the ARTBs
  identified in the observations.

---------------------------------------------------------
Title: Direct Observations of Different Sunspot Waves Influenced by
    Umbral Flashes
Authors: Sharma, Aishawnnya; Gupta, G. R.; Tripathi, Durgesh; Kashyap,
   V.; Pathak, Amit
2017ApJ...850..206S    Altcode: 2017arXiv171008438S
  We report the simultaneous presence of chromospheric umbral flashes
  and associated umbral waves, and propagating coronal disturbances, in a
  sunspot and related active region. We have analyzed time-distance maps
  obtained using the observations from the Atmospheric Imaging Assembly on
  board the Solar Dynamics Observatory. These maps show the simultaneous
  occurrence of different sunspot oscillations and waves such as umbral
  flashes, umbral waves, and coronal waves. Analysis of the original light
  curves, i.e., without implementing any Fourier filtering on them, shows
  that the amplitudes of different sunspot waves observed at different
  atmospheric layers change in synchronization with the light curves
  obtained from the umbral flash region, thus demonstrating that these
  oscillations are modulated by umbral flashes. This study provides the
  first observational evidence of the influence of sunspot oscillations
  within the umbra on other sunspot waves extending up to the corona. The
  properties of these waves and oscillations can be utilized to study
  the inherent magnetic coupling among different layers of the solar
  atmosphere above sunspots.

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

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

---------------------------------------------------------
Title: MWA Observations of Solar Radio Bursts and the Quiet Sun
Authors: Cairns, I.; Oberoi, D.; Morgan, J.; Bastian, T.; Bhatnagar,
   S.; Bisi, M.; Benkevitch, L.; Bowman, J.; Donea, A.; Giersch, O.;
   Jackson, B.; Chat, G. L.; Golub, L.; Hariharan, K.; Herne, D.; Kasper,
   J.; Kennewell, J.; Lonsdale, C.; Lobzin, V.; Matthews, L.; Mohan, A.;
   Padmanabhan, J.; Pankratius, V.; Pick, M.; Subramanian, P.; Ramesh,
   R.; Raymond, J.; Reeves, K.; Rogers, A.; Sharma, R.; Tingay, S.;
   Tremblay, S.; Tripathi, D.; Webb, D.; White, S.; Abidin, Z. B. Z.
2017mwa..prop..A06C    Altcode:
  A hundred hours of observing time for solar observations is requested
  during the 2017-A observing semester. These data will be used to address
  science objectives for solar burst science (Goal A), studies of weak
  non-thermal radiation (Goal B) and quiet sun science (Goal C). Goal
  A will focus on detailed investigations of individual events seen in
  the MWA data, using the unsurpassed spectroscopic imaging ability
  of the MWA to address some key solar physics questions. Detailed
  observations of type II bursts, of which MWA has observed two, will
  be one focus, with MWA polarimetric imaging observations of type III
  bursts another focus. Goal B will address studies of the numerous
  short lived and narrow band emission features, significantly weaker
  than those seen by most other instruments revealed by the MWA. These
  emission features do not resemble any known types of solar bursts, but
  are possible signatures of "nanoflares" which have long been suspected
  to play a role in coronal heating. A large database of these events is
  needed to be able to reliably estimate their contribution to coronal
  heating. These observations will contribute to this database. Goal C
  will focus on characterizing the Sun's background thermal emission,
  their short and long term variability and looking for evidence of a
  scattering disc around the Sun.

---------------------------------------------------------
Title: The Aditya-L1 Mission of Indian Space Research Organization
Authors: Tripathi, Durgesh
2016cosp...41E1937T    Altcode:
  The Aditya-L1 is the first mission of the Indian Space Research
  Organization (ISRO) dedicated to solar observations. The spacecraft
  will be located at the first Lagrangian point and will provide
  continuous observations of the Sun using remote sensing as well as
  in-situ measurements. The spacecraft will carry 7 payloads including a
  coronagraph that will image the corona in visible and IR wavelength and
  will provide measurements of coronal magnetic field and will study the
  dynamics of coronal mass ejections; a NUV imaging telescope to study
  the coupling between solar photosphere and chromosphere and to measure
  spatially resolved solar spectral irradiance and its variation. There
  will be two payloads to study the soft X-ray and hard X-ray emission
  from the Sun, two payloads for in-situ measurements of the charged
  particles and a magnetometer to study the magnetic field variations
  during energetic events. Some of the salient features of the experiments
  on board Aditya-L1 mission will be discussed.

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

---------------------------------------------------------
Title: Multiwavelength study of 20 jets that emanate from the
    periphery of active regions
Authors: Mulay, Sargam M.; Tripathi, Durgesh; Del Zanna, Giulio;
   Mason, Helen
2016A&A...589A..79M    Altcode: 2016arXiv160200151M
  <BR /> Aims: We present a multiwavelength analysis of 20 EUV jets which
  occurred at the periphery of active regions close to sunspots. We
  discuss the physical parameters of the jets and their relation
  with other phenomena such as Hα surges, nonthermal type-III radio
  bursts and hard X-ray (HXR) emission. <BR /> Methods: These jets
  were observed between August 2010 and June 2013 by the Atmospheric
  Imaging Assembly (AIA) instrument that is onboard the Solar Dynamic
  Observatory (SDO). We selected events that were observed on the solar
  disk within +/-60° latitude. Using AIA wavelength channels that
  are sensitive to coronal temperatures, we studied the temperature
  distribution in the jets using the line of sight (LOS) differential
  emission measure (DEM) technique. We also investigated the role of the
  photospheric magnetic field using the LOS magnetogram data from the
  Helioseismic and Magnetic Imager (HMI) onboard SDO. <BR /> Results:
  It has been observed that most of the jets originated from the western
  periphery of active regions. Their lifetimes range from 5 to 39 min
  with an average of 18 min and their velocities range from 87 to 532
  km s<SUP>-1</SUP> with an average of 271 km s<SUP>-1</SUP>. All the
  jets are co-temporally associated with Hα surges. Most of the jets
  are co-temporal with nonthermal type-III radio bursts observed by the
  Wind/WAVES spacecraft in the frequency range from 20 kHz to 13 MHz. We
  confirm the source region of these bursts using the potential field
  source surface (PFSS) technique. Using Reuven Ramaty High Energy Solar
  Spectroscopic Imager (RHESSI) observations, we found that half of the
  jets produced HXR emission and they often shared the same source region
  as the HXR emission (6-12 keV). Ten out of 20 events showed that the
  jets originated in a region of flux cancellation and six jets in a
  region of flux emergence. Four events showed flux emergence and then
  cancellation during the jet evolution. DEM analyses showed that for
  most of the spires of the jets, the DEM peaked at around log T [K] =
  6.2/6.3 (~2 MK). In addition, we derived an emission measure and a lower
  limit of electron density at the location of the spire (jet 1: log EM =
  28.6, N<SUB>e</SUB> = 1.3 × 10<SUP>10</SUP> cm<SUP>-3</SUP>; jet 2:
  log EM = 28.0, N<SUB>e</SUB> = 8.6 × 10<SUP>9</SUP> cm<SUP>-3</SUP>)
  and the footpoint (jet 1 - log EM = 28.6, N<SUB>e</SUB> = 1.1 ×
  10<SUP>10</SUP> cm<SUP>-3</SUP>; jet 2: log EM = 28.1, N<SUB>e</SUB> =
  8.4 × 10<SUP>9</SUP> cm<SUP>-3</SUP>). These results are in agreement
  with those obtained earlier by studying individual active region
  jets. <BR /> Conclusions: The observation of flux cancellation, the
  association with HXR emission and emission of nonthermal type-III
  radio bursts, suggest that the initiation and therefore, heating
  is taking place at the base of the jet. This is also supported by
  the high temperature plasma revealed by the DEM analysis in the jet
  footpoint (peak in the DEM at log T [K] = 6.5). Our results provide
  substantial constraints for theoretical modeling of the jets and their
  thermodynamic nature. <P />Movies are available in electronic form at <A
  href="http://www.aanda.org/10.1051/0004-6361/201527473/olm">http://www.aanda.org</A>

---------------------------------------------------------
Title: On the Bright Loop Top Emission in Post-eruption Arcades
Authors: Sharma, Rohit; Tripathi, Durgesh; Isobe, Hiroaki; Ghosh,
   Avyarthana
2016ApJ...823...47S    Altcode: 2016arXiv160304959S
  Observations of post-eruption arcades (PEAs) in X-rays and EUV reveal
  strong localized brightenings at the loop top regions. The origins
  of these brightenings and their dynamics are not well understood
  to date. Here, we study the dynamics of PEAs using one-dimensional
  hydrodynamic modeling, focusing on understanding the formation of
  localized brightening. Our findings suggest that these brightenings are
  the result of collisions between the counter-streaming chromospheric
  evaporation from both the footpoints. We perform forward modeling
  of the emission observed in simulated results in various spectral
  lines observed by the Extreme-Ultraviolet Imaging Telescope on board
  Hinode. The forward-modeled intensities in various spectral lines are
  in close agreement with a flare observed on 2006 December 17 by EIS.

---------------------------------------------------------
Title: A Hot Flux Rope Observed by SDO/AIA
Authors: Aparna, V.; Tripathi, Durgesh
2016ApJ...819...71A    Altcode: 2016arXiv160101620A
  A filament eruption was observed on 2010 October 31 in the images
  recorded by the Atmospheric Imaging Assembly (AIA) on board the
  Solar Dynamic Observatory (SDO) in its Extreme Ultra-Violet (EUV)
  channels. The filament showed a slow-rise phase followed by a fast rise
  and was classified to be an asymmetric eruption. In addition, multiple
  localized brightenings which were spatially and temporally associated
  with the slow-rise phase were identified, leading us to believe that
  the tether-cutting mechanism initiated the eruption. An associated flux
  rope was detected in high-temperature channels of AIA, namely 94 and
  131 Å, corresponding to 7 and 11 MK plasma respectively. In addition,
  these channels are also sensitive to cooler plasma corresponding to 1-2
  MK. In this study, we have applied the algorithm devised by Warren et
  al. to remove cooler emission from the 94 Å channel to deduce only the
  high-temperature structure of the flux rope and to study its temporal
  evolution. We found that the flux rope was very clearly seen in the
  clean 94 Å channel image corresponding to Fe xviii emission, which
  corresponds to a plasma at a temperature of 7 MK. This temperature
  matched well with that obtained using Differential Emission Measure
  analysis. This study provides important constrains in the modeling of
  the thermodynamic structure of the flux ropes in coronal mass ejections.

---------------------------------------------------------
Title: Intensity Conserving Spectral Fitting
Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D.
2016SoPh..291...55K    Altcode: 2015SoPh..tmp..180K
  The detailed shapes of spectral-line profiles provide valuable
  information about the emitting plasma, especially when the plasma
  contains an unresolved mixture of velocities, temperatures, and
  densities. As a result of finite spectral resolution, the intensity
  measured by a spectrometer is the average intensity across a wavelength
  bin of non-zero size. It is assigned to the wavelength position at
  the center of the bin. However, the actual intensity at that discrete
  position will be different if the profile is curved, as it invariably
  is. Standard fitting routines (spline, Gaussian, etc.) do not account
  for this difference, and this can result in significant errors when
  making sensitive measurements. We have developed an iterative procedure
  that corrects for this effect. It converges rapidly and is very
  flexible in that it can be used with any fitting function. We present
  examples of cubic-spline and Gaussian fits and give special attention
  to measurements of blue-red asymmetries of coronal emission lines.

---------------------------------------------------------
Title: IRIS and SDO Observations of Recurrent Explosive Events
Authors: Gupta, G. R.; Tripathi, Durgesh
2015ApJ...809...82G    Altcode: 2015arXiv150605327G
  Observations of recurrent explosive events (EEs) with timescales of 3-5
  minutes are reported. These EEs have been observed with the Interface
  Region Imaging Spectrograph (IRIS) and have a spatial dimension of
  ∼ 1\buildrel{\prime\prime}\over{.} 5 along the slit. The spectral
  line profiles of C ii 1335/1336 Å and Si iv 1394/1403 Å become
  highly broadened both in red as well as blue wings. Several absorption
  lines on top of the broadened profiles were identified. In addition,
  emission lines corresponding to neutral lines such as Cl i 1351.66 Å,
  C i 1354.29 Å, and C i 1355.84 Å were identified. The C i 1354.29
  Å and C i 1355.84 Å lines were found only during the EEs, whereas
  Cl i 1351.66 Å broadens during the EEs. The estimated lower limit on
  electron number density obtained using the line ratios of Si iv and O
  iv is about {10}<SUP>13.5</SUP> cm<SUP>-3</SUP>, suggesting that the
  observed events are most likely occurring at heights corresponding
  to a lower chromosphere. To the best of our knowledge, for the first
  time we have detected short-period variability (30 s and 60-90 s)
  within the EE bursts. Observations of the photospheric magnetic fields
  underneath EEs indicate that a negative polarity field emerges in
  the neighborhood of oppositely directed positive fields that undergo
  repetitive reconnection (magnetic flux cancellation) events. The
  dynamic changes observed in AIA 1700 Å, 1600 Å, C ii 1330 Å, and Si
  iv 1400 Å intensity images corresponded very well with the emergence
  and cancellation of photospheric magnetic field (negative polarity)
  on a timescale of 3-5 minutes. The observations reported here suggest
  that these EEs are formed due to magnetic reconnection and are occurring
  in the lower chromosphere.

---------------------------------------------------------
Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool
    for Spectroscopic Analysis
Authors: Klimchuk, James A.; Patsourakos, Spiros; Tripathi, Durgesh
2015TESS....120309K    Altcode: 2015arXiv150608102K
  Spectroscopy is an extremely powerful tool for diagnosing astrophysical
  and other plasmas. For example, the shapes of line profiles provide
  valuable information on the distribution of velocities along
  an optically thin line-of-sight and across the finite area of a
  resolution element. A number of recent studies have measured the
  asymmetries of line profiles in order to detect faint high-speed
  upflows, perhaps associated with coronal nanoflares or perhaps
  associated with chromospheric nanoflares and type II spicules. Over
  most of the Sun, these asymmetries are very subtle, so great care
  must be taken. A common technique is to perform a spline fit of the
  points in the profile in order to extract information at a spectral
  resolution higher than that of the original data. However, a fundamental
  problem is that the fits do not conserve intensity. We have therefore
  developed an iterative procedure called Intensity Conserving Spline
  Interpolation that does preserve the observed intensity within each
  wavelength bin. It improves the measurement of line asymmetries and
  can also help with the determination of line blends.

---------------------------------------------------------
Title: Sunspot waves and triggering of homologous active region jets
Authors: Chandra, R.; Gupta, G. R.; Mulay, Sargam; Tripathi, Durgesh
2015MNRAS.446.3741C    Altcode: 2014arXiv1410.8315C
  We present and discuss multiwavelength observations of five homologous
  recurrent solar jets that occurred in active region NOAA 11133 on
  2010 December 11. These jets were well observed by the Solar Dynamic
  observatory (SDO) with high spatial and temporal resolution. The
  speed of the jets ranged between 86 and 267 km s<SUP>-1</SUP>. A
  type III radio burst was observed in association with all the five
  jets. The investigation of the overall evolution of magnetic field in
  the source regions suggested that the flux was continuously emerging
  on longer term. However, all the jets but J5 were triggered during
  a local dip in the magnetic flux, suggesting the launch of the jets
  during localized submergence of magnetic flux. Additionally, using the
  PFSS modelling of the photospheric magnetic field, we found that all
  the jets were ejected in the direction of open field lines. We also
  traced sunspot oscillations from the sunspot interior to foot-point
  of jets and found presence of ∼3 min oscillations in all the SDO/AIA
  (Atmospheric Imaging Assembly) passbands. The wavelet analysis revealed
  an increase in amplitude of the oscillations just before the trigger of
  the jets, that decreased after the jets were triggered. The observations
  of increased amplitude of the oscillation and its subsequent decrease
  provides evidence of wave-induced reconnection triggering the jets.

---------------------------------------------------------
Title: Spectroscopic Observations of a Coronal Loop: Basic Physical
    Plasma Parameters Along the Full Loop Length
Authors: Gupta, G. R.; Tripathi, Durgesh; Mason, Helen E.
2015ApJ...800..140G    Altcode: 2014arXiv1412.7428G
  Coronal loops are the basic structures of the solar transition
  region and corona. Understanding of the physical mechanisms behind
  the loop heating, plasma flows, and filling are still considered a
  major challenge in solar physics. The mechanism(s) should be able
  to supply mass to the corona from the chromosphere and to heat the
  plasma over 1 MK within a small distance of a few hundred kilometers
  from the chromosphere to the corona. This problem makes coronal loops
  an interesting target for detailed study. In this study, we focus on
  spectroscopic observations of a coronal loop observed in its full length
  in various spectral lines as recorded by the Extreme-ultraviolet Imaging
  Spectrometer on board Hinode. We derive physical plasma parameters such
  as electron density, temperature, pressure, column depth, and filling
  factors along the loop length from one footpoint to the another. The
  obtained parameters are used to infer whether the observed coronal loop
  is overdense or underdense with respect to gravitational stratification
  of the solar atmosphere. These new measurements of physical plasma
  parameters, from one footpoint to another, provide important constraints
  on the modeling of the mass and energy balance in coronal loops.

---------------------------------------------------------
Title: Observations and Modeling of North-South Asymmetries Using
    a Flux Transport Dynamo
Authors: Shetye, Juie; Tripathi, Durgesh; Dikpati, Mausumi
2015ApJ...799..220S    Altcode: 2014arXiv1412.3245S
  The peculiar behavior of solar cycle 23 and its prolonged minima has
  been one of the most studied problems over the past few years. In the
  present paper, we study the asymmetries in active region magnetic
  flux in the northern and southern hemispheres during the complete
  solar cycle 23 and the rising phase of solar cycle 24. During the
  declining phase of solar cycle 23, we find that the magnetic flux in
  the southern hemisphere is about 10 times stronger than that in the
  northern hemisphere; however, during the rising phase of cycle 24,
  this trend is reversed. The magnetic flux becomes about a factor
  of four stronger in the northern hemisphere than in the southern
  hemisphere. Additionally, we find that there was a significant delay
  (about five months) in change of the polarity in the southern hemisphere
  in comparison with the northern hemisphere. These results provide us
  with hints of how the toroidal fluxes have contributed to the solar
  dynamo during the prolonged minima in solar cycle 23 and in the rising
  phase of solar cycle 24. Using a solar flux-transport dynamo model, we
  demonstrate that persistently stronger sunspot cycles in one hemisphere
  could be caused by the effect of greater inflows into active region
  belts in that hemisphere. Observations indicate that greater inflows
  are associated with stronger activity. Some other change or difference
  in meridional circulation between hemispheres could cause the weaker
  hemisphere to become the stronger one.

---------------------------------------------------------
Title: The evolution of the emission measure distribution in the
    core of an active region
Authors: Del Zanna, Giulio; Tripathi, Durgesh; Mason, Helen;
   Subramanian, Srividya; O'Dwyer, Brendan
2015A&A...573A.104D    Altcode: 2014arXiv1411.0128D
  We study the spatial distribution and evolution of the slope of the
  emission measure (EM) between 1 MK and 3 MK in the core of the active
  region (AR) NOAA 11193, first when it appeared near the central meridian
  and then again when it reappeared after a solar rotation. We use
  observations recorded by the Extreme-ultraviolet Imaging Spectrometer
  (EIS) aboard Hinode, with a new radiometric calibration. We also use
  observations from the Atmospheric Imaging Assembly (AIA) aboard the
  Solar Dynamics Observatory (SDO). We present the first spatially
  resolved maps of the EM slope in the 1-3 MK range within the core
  of the AR using several methods, either from approximations or from
  the differential emission measure (DEM). A significant variation of
  the slope is found at different spatial locations within the active
  region. We selected two regions that were not greatly affected by lower
  temperature emission along the line of sight. We found that the EM
  had a power law of the form EM ∝ T<SUP>b</SUP>, with b = 4.4 ± 0.4,
  and 4.6 ± 0.4, during the first and second appearance of the active
  region, respectively. During the second rotation, line-of-sight effects
  become more important, although difficult to estimate. We found that
  the use of the ground calibration for Hinode/EIS and the approximate
  method to derive the EM, used in previous publications, produce an
  underestimation of the slopes. The EM distribution in active region
  cores is generally found to be consistent with high frequency heating,
  and does not change much during the evolution of the active region.

---------------------------------------------------------
Title: Intensity Conserving Spline Interpolation (ICSI): A New Tool
    for Spectroscopic Analysis
Authors: Klimchuk, J. A.; Patsourakos, S.; Tripathi, D.
2014AGUFMSH13B4109K    Altcode:
  Spectroscopy is an extremely powerful tool for diagnosing astrophysical
  and other plasmas. For example, the shapes of line profiles provide
  valuable information on the distribution of velocities along
  an optically thin line-of-sight and across the finite area of a
  resolution element. A number of recent studies have measured the
  asymmetries of line profiles in order to detect faint high-speed
  upflows, perhaps associated with coronal nanoflares or perhaps
  associated with chromospheric nanoflares and type II spicules. Over
  most of the Sun, these asymmetries are very subtle, so great care
  must be taken. A common technique is to perform a spline fit of the
  points in the profile in order to extract information at a spectral
  resolution higher than that of the original data. However, a fundamental
  problem is that the fits do not conserve intensity. We have therefore
  developed an iterative procedure called Intensity Conserving Spline
  Interpolation that does preserve the observed intensity within each
  wavelength bin. It improves the measurement of line asymmetries and
  can also help with the determination of line blends.

---------------------------------------------------------
Title: Emission Measure Distribution for Diffuse Regions in Solar
    Active Regions
Authors: Subramanian, Srividya; Tripathi, Durgesh; Klimchuk, James A.;
   Mason, Helen E.
2014ApJ...795...76S    Altcode: 2014arXiv1409.1447S
  Our knowledge of the diffuse emission that encompasses active regions
  is very limited. In this paper we investigate two off-limb active
  regions, namely, AR 10939 and AR 10961, to probe the underlying heating
  mechanisms. For this purpose, we have used spectral observations from
  Hinode/EIS and employed the emission measure (EM) technique to obtain
  the thermal structure of these diffuse regions. Our results show that
  the characteristic EM distributions of the diffuse emission regions peak
  at log T = 6.25 and the coolward slopes are in the range 1.4-3.3. This
  suggests that both low- as well as high-frequency nanoflare heating
  events are at work. Our results provide additional constraints on the
  properties of these diffuse emission regions and their contribution to
  the background/foreground when active region cores are observed on-disk.

---------------------------------------------------------
Title: Initiation of Coronal Mass Ejection Event Observed on 2010
November 3: Multi-wavelength Perspective
Authors: Mulay, Sargam; Subramanian, Srividya; Tripathi, Durgesh;
   Isobe, Hiroaki; Glesener, Lindsay
2014ApJ...794...78M    Altcode: 2014arXiv1407.5837M
  One of the major unsolved problems in solar physics is that of coronal
  mass ejection (CME) initiation. In this paper, we have studied the
  initiation of a flare-associated CME that occurred on 2010 November 3
  using multi-wavelength observations recorded by the Atmospheric Imaging
  Assembly on board the Solar Dynamics Observatory and the Reuven Ramaty
  High Energy Solar Spectroscopic Imager. We report an observation of
  an inflow structure initially in the 304 Å and the 1600 Å images
  a few seconds later. This inflow structure was detected as one of
  the legs of the CME. We also observed a non-thermal compact source
  concurrent and near co-spatial with the brightening and movement of the
  inflow structure. The appearance of this compact non-thermal source,
  brightening, and movement of the inflow structure and the subsequent
  outward movement of the CME structure in the corona led us to conclude
  that the CME initiation was caused by magnetic reconnection.

---------------------------------------------------------
Title: Determination of Prominence Plasma β from the Dynamics of
    Rising Plumes
Authors: Hillier, Andrew; Hillier, Richard; Tripathi, Durgesh
2014IAUS..300...94H    Altcode:
  Observations of quiescent prominences show rising plumes, dark in
  chromospheric lines, that propagate from large bubbles. In this paper
  we present a method that may be used to determine the plasma β (ratio
  of gas pressure to magnetic pressure) from the rising plumes. Using
  the classic fluid dynamic solution for flow around a circular cylinder,
  the compression of the prominence material can be estimated. Application
  to a prominence gave an estimate of the plasma β as β=0.47-1.13 for
  a ratio of specific heats of γ=1.4-1.7.

---------------------------------------------------------
Title: SDO/AIA Observations of a Partially Erupting Prominence
Authors: Tripathi, Durgesh; Reeves, Katharine K.; Gibson, Sarah E.;
   Srivastava, Abhishek; Joshi, Navin C.
2013ApJ...778..142T    Altcode: 2013arXiv1310.0162T
  We report an observation of a partially erupting prominence and its
  associated dynamical plasma processes based on observations recorded
  by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics
  Observatory. The prominence first went through a slow rise (SR) phase
  followed by a fast rise (FR) phase. The SR phase began after a couple of
  small brightenings were seen toward the footpoints. When the prominence
  had transitioned from SR to FR, it had already become kinked. The
  prominence shows strong brightening at the central kink location during
  the start of FR. We interpret this as an internal magnetic reconnection
  occurring at a vertical current sheet forming between the two legs of
  the erupting prominence (flux rope). The brightening at the central
  kink location is seen in all EUV channels of AIA. The contributions of
  differential emission at higher temperatures are larger compared to that
  for typical coronal temperatures supporting a reconnection scenario at
  the central kink location. The plasma above the brightening location
  is ejected as a hot plasmoid-like structure embedded in a coronal
  mass ejection, and those below the brightening move down in the form
  of blobs moving toward the Sun's surface. The unique time resolution
  of the AIA has allowed these eruptive aspects, including SR-to-FR,
  kinking, central current sheet formation, plasmoid-like eruption,
  and filament "splitting," to be observed in a single event, providing
  strong and comprehensive evidence in favor of the model of partially
  erupting flux ropes.

---------------------------------------------------------
Title: Asymmetries in Coronal Spectral Lines and Emission Measure
    Distribution
Authors: Tripathi, Durgesh; Klimchuk, James A.
2013ApJ...779....1T    Altcode: 2013arXiv1310.0168T
  It has previously been argued that (1) spicules do not provide enough
  pre-heated plasma to fill the corona, and (2) even if they did,
  additional heating would be required to keep the plasma hot as it
  expands upward. Here we address whether spicules play an important
  role by injecting plasma at cooler temperatures (&lt;2 MK), which
  then gets heated to coronal values at higher altitudes. We measure
  red-blue asymmetries in line profiles formed over a wide range of
  temperatures in the bright moss areas of two active regions. We derive
  emission measure distributions from the excess wing emission. We find
  that the asymmetries and emission measures are small and conclude
  that spicules do not inject an important (dominant) mass flux into
  the cores of active regions at temperatures &gt;0.6 MK (log T &gt;
  5.8). These conclusions apply not only to spicules but also to any
  process that suddenly heats and accelerates chromospheric plasma
  (e.g., a chromospheric nanoflare). The traditional picture of coronal
  heating and chromospheric evaporation appears to remain the most likely
  explanation of the active region corona.

---------------------------------------------------------
Title: Where is Coronal Plasma Heated?
Authors: Klimchuk, James A.; Bradshaw, S.; Patsourakos, S.; Tripathi,
   D.
2013SPD....4420006K    Altcode:
  The coupling between the chromosphere and corona is a question of
  great current interest. It has long been understood that coronal mass
  originates in the chromosphere and that the energy which powers the
  corona flows up through the chromosphere. However, the details of
  how this happens are now being questioned. In the traditional view,
  “mechanical” energy flows into the corona in the form of waves
  or gradually increasing magnetic stresses. The waves and stresses
  dissipate and heat the plasma. The resulting downward thermal conduction
  flux causes material to evaporate from the chromosphere and fill
  the corona. If the heating is steady, an equilibrium is established
  whereby radiation and thermal conduction balance the energy input. If
  the heating is impulsive (a nanoflare), the evaporated plasma cools
  and drains, only to reappear during the next event. In either case,
  the heating occurs in the corona. A new idea is that the heating
  occurs instead in the chromosphere. Cold plasma is directly heated
  to coronal temperatures and then flows upward due to expansion and
  perhaps also an ejection process. The hot tips of type II spicules
  are one example, though spicules need not be involved. I will discuss
  these two fundamentally different scenarios and the observational
  predictions that they make. A comparison with actual observations
  leads to the conclusion that only a small fraction of the hot plasma
  in the corona comes from chromospheric heating. Most coronal plasma
  is a consequence of heating that occurs in the corona itself.

---------------------------------------------------------
Title: Origin of Macrospicule and Jet in Polar Corona by a Small-scale
    Kinked Flux Tube
Authors: Kayshap, P.; Srivastava, Abhishek K.; Murawski, K.; Tripathi,
   Durgesh
2013ApJ...770L...3K    Altcode: 2013arXiv1305.0338K
  We report an observation of a small-scale flux tube that undergoes
  kinking and triggers the macrospicule and a jet on 2010 November 11
  in the north polar corona. The small-scale flux tube emerged well
  before the triggering of the macrospicule and as time progresses the
  two opposite halves of this omega-shaped flux tube bent transversely
  and approach each other. After ~2 minutes, the two approaching halves
  of the kinked flux tube touch each other and an internal reconnection
  as well as an energy release takes place at the adjoining location and
  a macrospicule was launched which goes up to a height of 12 Mm. Plasma
  begins to move horizontally as well as vertically upward along with the
  onset of the macrospicule and thereafter converts into a large-scale
  jet in which the core denser plasma reaches up to ~40 Mm in the solar
  atmosphere with a projected speed of ~95 km s<SUP>-1</SUP>. The fainter
  and decelerating plasma chunks of this jet were also seen up to ~60
  Mm. We perform a two-dimensional numerical simulation by considering
  the VAL-C initial atmospheric conditions to understand the physical
  scenario of the observed macrospicule and associated jet. The simulation
  results show that reconnection-generated velocity pulse in the lower
  solar atmosphere steepens into slow shock and the cool plasma is driven
  behind it in the form of macrospicule. The horizontal surface waves
  also appeared with shock fronts at different heights, which most likely
  drove and spread the large-scale jet associated with the macrospicule.

---------------------------------------------------------
Title: Doppler Shifts in Active Region Moss Using SOHO/SUMER
Authors: Winebarger, Amy; Tripathi, Durgesh; Mason, Helen E.; Del
   Zanna, Giulio
2013ApJ...767..107W    Altcode:
  The velocity of the plasma at the footpoint of hot loops in active
  region cores can be used to discriminate between different heating
  frequencies. Velocities on the order of a few kilometers per second
  would indicate low-frequency heating on sub-resolution strands,
  while velocities close to zero would indicate high-frequency (steady)
  heating. To discriminate between these two values requires accurate
  velocity measurements; previous velocity measurements suffer from
  large uncertainties, mainly due to the lack of an absolute wavelength
  reference scale. In this paper, we determine the velocity in the loop
  footpoints using observations from Solar Ultraviolet Measurements of
  Emitted Radiation (SUMER) on Solar and Heliospheric Observatory. We
  use neutral spectral lines to determine the wavelength scale of the
  observations with an uncertainty in the absolute velocity of &lt;3.5 km
  s<SUP>-1</SUP> and co-aligned Transition Region and Coronal Explorer
  (TRACE) images to identify footpoint regions. We studied three
  different active regions and found average redshifts in the Ne VIII
  770 Å emission line (formed at 6 × 10<SUP>5</SUP> K) of 5.17 ± 5.37
  km s<SUP>-1</SUP> and average redshifts in the C IV 1548 and 1550 Å
  emission lines (formed at 1 × 10<SUP>5</SUP> K) of 13.94 ± 4.93 km
  s<SUP>-1</SUP> and 14.91 ± 6.09 km s<SUP>-1</SUP>, respectively. We
  find no correlation between the brightness in the spectral line and
  the measured velocity, nor do we find correlation between the Ne VIII
  and C IV velocities measured co-spatially and co-temporally. SUMER
  scanned two of the active regions twice; in those active regions we
  find positive correlation between the co-spatial velocities measured
  during the first and second scans. These results provide definitive
  and quantitative measurements for comparisons with simulations of
  different coronal heating mechanisms.

---------------------------------------------------------
Title: Observational Evidence of Sausage-pinch Instability in Solar
    Corona by SDO/AIA
Authors: Srivastava, A. K.; Erdélyi, R.; Tripathi, Durgesh; Fedun,
   V.; Joshi, N. C.; Kayshap, P.
2013ApJ...765L..42S    Altcode: 2013arXiv1302.1286S
  We present the first observational evidence of the evolution of
  sausage-pinch instability in active region 11295 during a prominence
  eruption using data recorded on 2011 September 12 by the Atmospheric
  Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). We
  have identified a magnetic flux tube visible in AIA 304 Å that shows
  curvatures on its surface with variable cross-sections as well as
  enhanced brightness. These curvatures evolved and thereafter smoothed
  out within a timescale of a minute. The curved locations on the flux
  tube exhibit a radial outward enhancement of the surface of about 1-2 Mm
  (a factor of two larger than the original thickness of the flux tube)
  from the equilibrium position. AIA 193 Å snapshots also show the
  formation of bright knots and narrow regions in-between at the four
  locations as that of 304 Å along the flux tube where plasma emission
  is larger compared to the background. The formation of bright knots
  over an entire flux tube as well as the narrow regions in &lt;60 s
  may be the morphological signature of the sausage instability. We
  also find the flows of confined plasma (propagation of brightness)
  in these bright knots along the field lines, which indicates the
  dynamicity of the flux tube that probably causes the dominance of the
  longitudinal field component over short temporal scales. The observed
  longitudinal motion of the plasma frozen in the magnetic field lines
  further vanishes the formed curvatures and plasma confinements as well
  as growth of instability to stabilize the flux tube.

---------------------------------------------------------
Title: Heating of active region cores: Impulsive or steady?
Authors: Tripathi, Durgesh
2013ASInC..10...73T    Altcode:
  The question of active region heating has proven to be highly
  challenging since its discovery in 1940s. The recent observational
  facilities have shed new lights towards the understanding of this
  problem. In this paper we review some of the new measurements to study
  the heating mechanisms in the hot core loops of active regions using
  the observations recorded by Solar Ultraviolet Measurements of Emitted
  Radiation (SUMER) onboard SoHO and the Extreme-ultraviolet Imaging
  Spectrometer (EIS) aboard Hinode. These new measurements show that the
  properties of hot core loops are consistent with by impulsive heating
  -- low frequency nanoflare - scenario. However, the evidences are not
  strong enough to rule-out steady heating completely. Further measurement
  using better spectral resolution and temperature coverage is required,
  which will be provided by Interface Region Imaging Spectrometer (IRIS)
  and Solar-C in near future.

---------------------------------------------------------
Title: Determination of Prominence Plasma β from the Dynamics of
    Rising Plumes
Authors: Hillier, Andrew; Hillier, Richard; Tripathi, Durgesh
2012ApJ...761..106H    Altcode: 2012arXiv1211.0742H
  Observations by the Hinode satellite show in great detail the
  dynamics of rising plumes, dark in chromospheric lines, in quiescent
  prominences that propagate from large (~10 Mm) bubbles that form at
  the base of the prominences. These plumes present a very interesting
  opportunity to study magnetohydrodynamic (MHD) phenomena in quiescent
  prominences, but obstacles still remain. One of the biggest issues is
  that of the magnetic field strength, which is not easily measurable
  in prominences. In this paper we present a method that may be
  used to determine a prominence's plasma β when rising plumes are
  observed. Using the classic fluid dynamic solution for flow around
  a circular cylinder with an MHD correction, the compression of the
  prominence material can be estimated. This has been successfully
  confirmed through simulations; application to a prominence gave an
  estimate of the plasma β as β = 0.47 ± 0.079 to 1.13 ± 0.080
  for the range γ = 1.4-1.7. Using this method it may be possible to
  estimate the plasma β of observed prominences, therefore helping our
  understanding of a prominence's dynamics in terms of MHD phenomena.

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

---------------------------------------------------------
Title: Temperature and Extreme-ultraviolet Intensity in a Coronal
    Prominence Cavity and Streamer
Authors: Kucera, T. A.; Gibson, S. E.; Schmit, D. J.; Landi, E.;
   Tripathi, D.
2012ApJ...757...73K    Altcode:
  We analyze the temperature and EUV line emission of a coronal cavity and
  surrounding streamer in terms of a morphological forward model. We use a
  series of iron line ratios observed with the Hinode Extreme-ultraviolet
  Imaging Spectrograph (EIS) on 2007 August 9 to constrain temperature
  as a function of altitude in a morphological forward model of the
  streamer and cavity. We also compare model predictions to the EIS EUV
  line intensities and polarized brightness (pB) data from the Mauna
  Loa Solar Observatory (MLSO) Mark 4 K-coronameter. This work builds
  on earlier analysis using the same model to determine geometry of
  and density in the same cavity and streamer. The fit to the data
  with altitude-dependent temperature profiles indicates that both
  the streamer and cavity have temperatures in the range 1.4-1.7
  MK. However, the cavity exhibits substantial substructure such
  that the altitude-dependent temperature profile is not sufficient to
  completely model conditions in the cavity. Coronal prominence cavities
  are structured by magnetism so clues to this structure are to be found
  in their plasma properties. These temperature substructures are likely
  related to structures in the cavity magnetic field. Furthermore,
  we find that the model overestimates the EUV line intensities by a
  factor of 4-10, without overestimating pB. We discuss this difference
  in terms of filling factors and uncertainties in density diagnostics
  and elemental abundances.

---------------------------------------------------------
Title: Active Region Moss: Doppler Shifts from
    Hinode/Extreme-ultraviolet Imaging Spectrometer Observations
Authors: Tripathi, Durgesh; Mason, Helen E.; Klimchuk, James A.
2012ApJ...753...37T    Altcode: 2012arXiv1204.6550T
  Studying the Doppler shifts and the temperature dependence of Doppler
  shifts in moss regions can help us understand the heating processes
  in the core of the active regions. In this paper, we have used an
  active region observation recorded by the Extreme-ultraviolet Imaging
  Spectrometer (EIS) on board Hinode on 2007 December 12 to measure the
  Doppler shifts in the moss regions. We have distinguished the moss
  regions from the rest of the active region by defining a low-density
  cutoff as derived by Tripathi et al. in 2010. We have carried out a
  very careful analysis of the EIS wavelength calibration based on the
  method described by Young et al. in 2012. For spectral lines having
  maximum sensitivity between log T = 5.85 and log T = 6.25 K, we find
  that the velocity distribution peaks at around 0 km s<SUP>-1</SUP>
  with an estimated error of 4-5 km s<SUP>-1</SUP>. The width of the
  distribution decreases with temperature. The mean of the distribution
  shows a blueshift which increases with increasing temperature and the
  distribution also shows asymmetries toward blueshift. Comparing these
  results with observables predicted from different coronal heating
  models, we find that these results are consistent with both steady
  and impulsive heating scenarios. However, the fact that there are a
  significant number of pixels showing velocity amplitudes that exceed
  the uncertainty of 5 km s<SUP>-1</SUP> is suggestive of impulsive
  heating. Clearly, further observational constraints are needed to
  distinguish between these two heating scenarios.

---------------------------------------------------------
Title: On the Multiple Energy Release and Filament Activation during
    M5.4 Class Flare from NOAA AR 11121 on 06 November 2010
Authors: Kayshap, Pradeep; Chandra, Ramesh; Tripathi, Durgesh;
   Srivastava, Abhishek K.; Joshi, N. C.
2012cosp...39..903K    Altcode: 2012cosp.meet..903K
  No abstract at ADS

---------------------------------------------------------
Title: Observations of Flows and Waves in Active Regions: An
    observational Overview
Authors: Tripathi, Durgesh
2012cosp...39.2002T    Altcode: 2012cosp.meet.2002T
  In order to understand one of the most intensely studies problem
  in solar physics i.e. the problem of solar coronal heating, it is
  mandatory to understand the mass and energy transport in the outer solar
  atmosphere. Doppler shift measurements in the transition and corona
  reveal an abundance of plasma flow across a range of temperature having
  different patterns in different part of the active region, suggesting
  flow of material. The high resolution imaging observations have revealed
  that there is an abundance of quasi periodic propagating features
  which are often interpreted as manifestation of slow magneto-acoustic
  waves propagating into the atmosphere guided by loop structures. In
  this talk we will review some recent highlights of the studies of
  flows and waves and their role in understanding the mass and energy
  transport in the outer atmosphere.

---------------------------------------------------------
Title: Observations of Plasma Upflow in a Warm Loop with Hinode/EIS
Authors: Tripathi, Durgesh; Mason, Helen E.; Del Zanna, Giulio;
   Bradshaw, Steven
2012ApJ...754L...4T    Altcode: 2012arXiv1206.3367T
  A complete understanding of Doppler shift in active region loops can
  help probe the basic physical mechanism involved into the heating
  of those loops. Here, we present observations of upflows in coronal
  loops detected in a range of temperatures (log T = 5.8-6.2). The loop
  was not discernible above these temperatures. The speed of upflow
  was strongest at the footpoint and decreased with height. The upflow
  speed at the footpoint was about 20 km s<SUP>-1</SUP> in Fe VIII, which
  decreased with temperature, being about 13 km s<SUP>-1</SUP> in Fe X,
  about 8 km s<SUP>-1</SUP> in Fe XII, and about 4 km s<SUP>-1</SUP> in
  Fe XIII. To the best of our knowledge, this is the first observation
  providing evidence of upflow of plasma in coronal loop structures at
  these temperatures. We interpret these observations as evidence of
  chromospheric evaporation in quasi-static coronal loops.

---------------------------------------------------------
Title: Cross-Calibration of Hinode/EIS and SDO/AIA
Authors: O'Dwyer, B.; Zanna, G. D.; Mason, H. E.; Weber, M. A.;
   Tripathi, D.
2012ASPC..455..369O    Altcode:
  We examine the contribution of spectral lines and continuum emission
  to the EUV channels of the Atmospheric Imaging Assembly (AIA) on
  the Solar Dynamics Observatory (SDO) in different regions of the
  solar atmosphere (coronal hole, quiet Sun, active region, and flare
  plasma). We highlight the contribution of particular spectral lines
  which under certain conditions can affect the interpretation of SDO
  AIA data. In addition we use simultaneous observations from the Hinode
  Extreme-ultraviolet Imaging Spectrometer (EIS) and SDO/AIA to examine
  their relative intensity calibration. Good agreement is found between
  the two instruments for an active region observation.

---------------------------------------------------------
Title: Understanding Coronal Heating with Emission Measure
    Distributions
Authors: Klimchuk, James A.; Tripathi, D.; Bradshaw, S. J.; Mason,
   H. E.
2012AAS...22042302K    Altcode:
  It is widely believed that the cross-field spatial scale of coronal
  heating is small, so that the fundamental plasma structures
  (loop strands) are spatially unresolved. We therefore must
  appeal to diagnostic techniques that are not strongly affected by
  spatial averaging. One valuable observable is the emission measure
  distribution, EM(T), which indicates how much material is present
  at each temperature. Using data from the Extreme-ultraviolet Imaging
  Spectrograph on the Hinode mission, we have determined emission measure
  distributions in the cores of two active regions. The distributions have
  power law slopes of approximately 2.4 coolward of the peak. We compare
  these slopes, as well as the amount of emission measure at very high
  temperature, with the predictions of a series of models. The models
  assume impulsive heating (nanoflares) in unresolved strands and take
  full account of nonequilibrium ionization.

---------------------------------------------------------
Title: Temperature Structure of a Coronal Cavity and Streamer
Authors: Kucera, Therese A.; Gibson, S. E.; Schmit, D. J.; Landi,
   E.; Tripathi, D.
2012AAS...22052113K    Altcode:
  We analyze the temperature and EUV line emission of a coronal cavity and
  surrounding streamer in terms of a morphological forward model. We use a
  series of iron line ratios observed with the Hinode Extreme-ultraviolet
  Imaging Spectrograph (EIS) on 2007 Aug. 9 to constrain temperature
  as a function of altitude in a morphological forward model of the
  streamer and cavity. We also compare model prediction of the EIS EUV
  line intensities and polarized brightness (pB) data from the Mauna Loa
  Solar Observatory (MLSO) MK4. This work builds on earlier analysis using
  the same model to determine geometry of and density in the same cavity
  and streamer (Gibson et al. 2010 and Schmit and Gibson 2011). The fit
  to the data with altitude dependent temperature profiles indicates that
  both the streamer and cavity have temperatures in the range 1.4-1.7
  MK. However, the cavity exhibits substantial substructure such that the
  altitude dependent temperature profile is not sufficient to completely
  model conditions in the cavity. This work is supported in part by the
  NASA SHP program

---------------------------------------------------------
Title: Spectroscopic Diagnostics and Heating of Active Region Cores
Authors: Tripathi, D.; Mason, H. E.; Klimchuk, J. A.
2012decs.confE..92T    Altcode:
  It is widely believed that we are still far from spatially resolving
  the fundamental plasma structures in solar corona. Therefore,
  we must use spectroscopic diagnostic techniques such as emission
  measure distribution (EM(T)) and Doppler shifts that are not affected
  by spatial averaging. Using observations recorded by the Extreme
  ultraviolet Imaging Spectrometer we have studies emission measure (EM)
  distribution and Doppler shift in the moss and inter-moss regions. The
  EM distributions obtained for moss regions cab be reproduced by
  considering strong coronal condensation scenario suggesting bulk
  downflow of the plasma. Doppler shift measurements for the moss regions
  show that almost all the moss regions are red-shifted with velocities
  up to 15km/s with mean velocity of 5 km/s. However, the uncertainty
  on the Doppler shift was large. The EM distributions obtained for
  inter-moss regions have power law slopes of approximately 2.4 coolward
  of the peak. We compare the EM for inter-moss region with that obtained
  from nanoflare model using EBTEL (Enthalpy-Based Thermal Evolution of
  Loops). Our results suggest that the EM distribution for both the moss
  as well as inter-moss regions and Doppler shift in the moss regions can
  be explained by nanoflare heating. IRIS will provide a better account
  of the Doppler shift in the moss regions, which will dramatically
  enhance our understanding of the heating of active region core.

---------------------------------------------------------
Title: Rotation of an erupting filament observed by STEREO EUVI and
    COR1 instruments (Corrigendum)
Authors: Bemporad, A.; Mierla, M.; Tripathi, D.
2012A&A...537C...1B    Altcode:
  Present Address: inter-University Centre for Astronomy and Astrophysics,
  Post Bag 4, Ganeshkhind, 411007 Pune, India.

---------------------------------------------------------
Title: Understanding Coronal Heating with Emission Measure
    Distributions
Authors: Klimchuk, J. A.; Tripathi, D.; Bradshaw, S. J.; Mason, H. E.
2011AGUFMSH43F..03K    Altcode:
  It is widely believed that the cross-field spatial scale of coronal
  heating is small, so that the fundamental plasma structures
  (loop strands) are spatially unresolved. We therefore must
  appeal to diagnostic techniques that are not strongly affected by
  spatial averaging. One valuable observable is the emission measure
  distribution, EM(T), which indicates how much material is present
  at each temperature. Using data from the Extreme-ultraviolet Imaging
  Spectrograph on the Hinode mission, we have determined emission measure
  distributions in the cores of two active regions. The distributions
  have power law slopes of approximately 2.4 coolward of the peak. We
  compare these slopes, as well as the amount of emission measure at
  very high temperature, with the predictions of a series of models. The
  models assume impulsive heating (nanoflares) in unresolved strands and
  take full account of nonequilibrium ionization. A variety of nanoflare
  properties and initial conditions are considered. We also comment on the
  selection of spectral lines for upcoming missions like Solar Orbiter.

---------------------------------------------------------
Title: Emission Measure Distribution and Heating of Two Active
    Region Cores
Authors: Tripathi, Durgesh; Klimchuk, James A.; Mason, Helen E.
2011ApJ...740..111T    Altcode: 2011arXiv1107.4480T
  Using data from the Extreme-ultraviolet Imaging Spectrometer aboard
  Hinode, we have studied the coronal plasma in the core of two active
  regions. Concentrating on the area between opposite polarity moss, we
  found emission measure distributions having an approximate power-law
  form EMvpropT <SUP>2.4</SUP> from log T = 5.5 up to a peak at log T
  = 6.55. We show that the observations compare very favorably with
  a simple model of nanoflare-heated loop strands. They also appear
  to be consistent with more sophisticated nanoflare models. However,
  in the absence of additional constraints, steady heating is also a
  viable explanation.

---------------------------------------------------------
Title: Rotation of an erupting filament observed by the STEREO EUVI
    and COR1 instruments
Authors: Bemporad, A.; Mierla, M.; Tripathi, D.
2011A&A...531A.147B    Altcode:
  On August 31, 2007, a prominence eruption was observed by the Solar
  TErrestrial RElations Observatory (STEREO) in the Extreme-UltraViolet
  Imager (EUVI) 304 images and later on, as the core of a three-part
  coronal mass ejection (CME) in images acquired by the inner STEREO
  coronagraph (COR1). Because they were covered by both STEREO
  spacecraft from right vantage points, these observations provide an
  excellent opportunity to perform a three-dimensional (3D) prominence
  reconstruction and study its evolution. We employed the tie-pointing
  technique to reconstruct the 3D shape and trajectory of the prominence,
  which has been followed from an heliocentric distance of ~1.3 up to ~2.4
  R<SUB>⊙</SUB> during the first 1.3 h of eruption. Data show evidence
  for a progressive clockwise prominence rotation by ~90° occurring
  not only in the early phase of the eruption sampled by EUVI, but also
  at larger heliocentric distances as seen by COR1. Interestingly,
  a counter-clockwise rotation of the filament was observed in Hα
  images in the week before the eruption; the filament does not show a
  twisted shape. In the same period, the potential field extrapolated at
  different times shows a clockwise rotation of closed lines overlying the
  filament. This suggests that a magnetic helicity storage occurred not in
  the filament itself, but in the global magnetic field configuration
  of the surrounding corona. Moreover, close inspection to the
  high-resolution EUVI images revealed a small scale helical feature along
  the erupting prominence. The sense of rotation of this helix agrees with
  the observed prominence rotation, providing evidence for the conversion
  of twist into writhe. The observed rotation of an erupting prominence,
  if representative of the flux rope rotation, may have a strong impact
  on the definition of geo-effectiveness of CMEs for space weather
  forecasting purposes. <P />Two movies are available in electronic form
  at <A href="http://www.aanda.org">http://www.aanda.org</A>

---------------------------------------------------------
Title: Solar plasma spectroscopy: achievements and future challenges
Authors: Del Zanna, Giulio; Tripathi, Durgesh; Young, Peter
2011A&G....52b..17D    Altcode:
  MEETING REPORT Giulio Del Zanna, Durgesh Tripathi and Peter Young
  report on a meeting to celebrate the career of Helen Mason - and the
  development of an important field in solar physics.

---------------------------------------------------------
Title: Hinode extreme-ultraviolet imaging spectrometer observations
    of a limb active region
Authors: O'Dwyer, B.; Del Zanna, G.; Mason, H. E.; Sterling, A. C.;
   Tripathi, D.; Young, P. R.
2011A&A...525A.137O    Altcode:
  <BR /> Aims: We investigate the electron density and temperature
  structure of a limb active region. <BR /> Methods: We have carried out
  a study of an active region close to the solar limb using observations
  from the Extreme-ultraviolet Imaging Spectrometer (EIS) and the X-ray
  telescope (XRT) on board Hinode. The electron density and temperature
  distributions of the coronal emission have been determined using
  emission line intensity ratios. Differential emission measure (DEM)
  analysis and the emission measure (EM) loci technique were used to
  examine the thermal structure of the emitting plasma as a function
  of distance from the limb. <BR /> Results: The highest temperature
  and electron density values are found to be located in the core of
  the active region, with a peak electron number density value of 1.9
  × 10<SUP>10</SUP> cm<SUP>-3</SUP> measured using the Fe XII 186.887
  Å to 192.394 Å line intensity ratio. The plasma along the line of
  sight in the active region was found to be multi-thermal at different
  distances from the limb. The EIS and XRT DEM analyses appear to be
  in agreement in the temperature interval from log T = 6.5-6.7. <BR />
  Conclusions: Our results provide new constraints for models of coronal
  heating in active regions.

---------------------------------------------------------
Title: Three-dimensional morphology of a coronal prominence cavity
Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de
   Toma, G.; Hao, J.; Hill, S. M.; Hudson, H. S.; Marque, C.; McIntosh,
   P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.;
   Sterling, A.; Tripathi, D.; Williams, D. R.; Zhang, M.
2010AGUFMSH51A1667G    Altcode:
  We present a three-dimensional density model of coronal prominence
  cavities, and a morphological fit that has been tightly constrained
  by a uniquely well-observed cavity. Observations were obtained as part
  of an International Heliophysical Year campaign by instruments from a
  variety of space- and ground-based observatories, spanning wavelengths
  from radio to soft-X-ray to integrated white light. From these data
  it is clear that the prominence cavity is the limb manifestation of
  a longitudinally-extended polar-crown filament channel, and that
  the cavity is a region of low density relative to the surrounding
  corona. As a first step towards quantifying density and temperature
  from campaign spectroscopic data, we establish the three-dimensional
  morphology of the cavity. This is critical for taking line-of-sight
  projection effects into account, since cavities are not localized in the
  plane of the sky and the corona is optically thin. We have augmented
  a global coronal streamer model to include a tunnel-like cavity with
  elliptical cross-section and a Gaussian variation of height along
  the tunnel length. We have developed a semi-automated routine that
  fits ellipses to cross-sections of the cavity as it rotates past the
  solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI)
  observations from the two Solar Terrestrial Relations Observatory
  (STEREO) spacecraft. This defines the morphological parameters of our
  model, from which we reproduce forward-modeled cavity observables. We
  find that cavity morphology and orientation, in combination with the
  viewpoints of the observing spacecraft, explains the observed variation
  in cavity visibility for the east vs. west limbs.

---------------------------------------------------------
Title: Three-dimensional Morphology of a Coronal Prominence Cavity
Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de
   Toma, G.; Hao, J.; Hill, S.; Hudson, H. S.; Marqué, C.; McIntosh,
   P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.;
   Seaton, D. B.; Sterling, A. C.; Tripathi, D.; Williams, D. R.;
   Zhang, M.
2010ApJ...724.1133G    Altcode:
  We present a three-dimensional density model of coronal prominence
  cavities, and a morphological fit that has been tightly constrained
  by a uniquely well-observed cavity. Observations were obtained as part
  of an International Heliophysical Year campaign by instruments from a
  variety of space- and ground-based observatories, spanning wavelengths
  from radio to soft X-ray to integrated white light. From these data
  it is clear that the prominence cavity is the limb manifestation of
  a longitudinally extended polar-crown filament channel, and that the
  cavity is a region of low density relative to the surrounding corona. As
  a first step toward quantifying density and temperature from campaign
  spectroscopic data, we establish the three-dimensional morphology
  of the cavity. This is critical for taking line-of-sight projection
  effects into account, since cavities are not localized in the plane of
  the sky and the corona is optically thin. We have augmented a global
  coronal streamer model to include a tunnel-like cavity with elliptical
  cross-section and a Gaussian variation of height along the tunnel
  length. We have developed a semi-automated routine that fits ellipses
  to cross-sections of the cavity as it rotates past the solar limb, and
  have applied it to Extreme Ultraviolet Imager observations from the
  two Solar Terrestrial Relations Observatory spacecraft. This defines
  the morphological parameters of our model, from which we reproduce
  forward-modeled cavity observables. We find that cavity morphology
  and orientation, in combination with the viewpoints of the observing
  spacecraft, explain the observed variation in cavity visibility for
  the east versus west limbs.

---------------------------------------------------------
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: Evidence of Impulsive Heating in Active Region Core Loops
Authors: Tripathi, Durgesh; Mason, Helen E.; Klimchuk, James A.
2010ApJ...723..713T    Altcode: 2010arXiv1009.0663T
  Using a full spectral scan of an active region from the
  Extreme-Ultraviolet Imaging Spectrometer (EIS) we have obtained emission
  measure EM(T) distributions in two different moss regions within the
  same active region. We have compared these with theoretical transition
  region EMs derived for three limiting cases, namely, static equilibrium,
  strong condensation, and strong evaporation from Klimchuk et al. The
  EM distributions in both the moss regions are strikingly similar and
  show a monotonically increasing trend from log T[K] = 5.15-6.3. Using
  photospheric abundances, we obtain a consistent EM distribution for
  all ions. Comparing the observed and theoretical EM distributions,
  we find that the observed EM distribution is best explained by the
  strong condensation case (EM<SUB>con</SUB>), suggesting that a downward
  enthalpy flux plays an important and possibly dominant role in powering
  the transition region moss emission. The downflows could be due to
  unresolved coronal plasma that is cooling and draining after having
  been impulsively heated. This supports the idea that the hot loops
  (with temperatures of 3-5 MK) seen in the core of active regions are
  heated by nanoflares.

---------------------------------------------------------
Title: SDO/AIA response to coronal hole, quiet Sun, active region,
    and flare plasma
Authors: O'Dwyer, B.; Del Zanna, G.; Mason, H. E.; Weber, M. A.;
   Tripathi, D.
2010A&A...521A..21O    Altcode:
  <BR /> Aims: We examine the contribution of spectral lines and continuum
  emission to the EUV channels of the Atmospheric Imaging Assembly (AIA)
  on the Solar Dynamics Observatory (SDO) in different regions of the
  solar atmosphere. <BR /> Methods: Synthetic spectra were obtained using
  the CHIANTI atomic database and sample differential emission measures
  for coronal hole, quiet Sun, active region and flare plasma. These
  synthetic spectra were convolved with the effective area of each
  channel, in order to determine the dominant contribution in different
  regions of the solar atmosphere. <BR /> Results: We highlight the
  contribution of particular spectral lines which under certain conditions
  can affect the interpretation of SDO/AIA data.

---------------------------------------------------------
Title: Active region moss. Basic physical parameters and their
    temporal variation
Authors: Tripathi, D.; Mason, H. E.; Del Zanna, G.; Young, P. R.
2010A&A...518A..42T    Altcode: 2010arXiv1005.2220T
  Context. Active region moss are transition region phenomena, first noted
  in the images recorded by the Transition Region and Coronal Explorer
  (TRACE) in λ171. Moss regions are thought to be the footpoints of
  hot loops (3-5 MK) seen in the core of active regions. These hot
  loops appear “fuzzy” (unresolved). Therefore, it is difficult to
  study the physical plasma parameters in individual hot core loops and
  hence their heating mechanisms. Moss regions provide an excellent
  opportunity to study the physics of hot loops. In addition, they
  allow us to study the transition region dynamics in the footpoint
  regions. <BR /> Aims: To derive the physical plasma parameters such as
  temperature, electron density, and filling factors in moss regions and
  to study their variation over a short (an hour) and a long time period
  (5 consecutive days). <BR /> Methods: Primarily, we have analyzed
  spectroscopic observations recorded by the Extreme-ultraviolet Imaging
  Spectrometer (EIS) aboard Hinode. In addition we have used supplementary
  observations taken from TRACE and the X-Ray Telescope (XRT) aboard
  Hinode. <BR /> Results: The moss emission is strongest in the Fe XII
  and Fe XIII lines. Based on analyses using line ratios and emission
  measure we found that moss regions have a characteristic temperature
  of log T[K] = 6.2. The temperature structure in moss region remains
  almost identical from one region to another and it does not change
  with time. The electron densities measured at different locations in
  the moss regions using Fe XII ratios are about 1-3 × 10<SUP>10</SUP>
  cm<SUP>-3</SUP> and about 2-4 × 10<SUP>9</SUP> cm<SUP>-3</SUP> using
  Fe XIII and Fe XIV. The densities in the moss regions are similar in
  different places and show very little variation over short and long
  time scales. The derived electron density substantially increased (by
  a factor of about 3-4 or even more in some cases) when a background
  subtraction was performed. The filling factor of the moss plasma
  can vary between 0.1-1 and the path length along which the emission
  originates is from a few 100 to a few 1000 kms long. By combining the
  observations recorded by TRACE, EIS and XRT, we find that the moss
  regions correspond to the footpoints of both hot and warm loops.

---------------------------------------------------------
Title: Thermal Properties of Coronal Cavities as Observed by the
    X-Ray Telescope on Hinode
Authors: Reeves, Kathy; Gibson, S. E.; Kucera, T. A.; Hudson, H. S.;
   Tripathi, D.
2010AAS...21640511R    Altcode: 2010BAAS...41..891R
  Coronal cavities are voids in coronal emission often observed above
  high latitude filament channels. Sometimes, these cavities have
  areas of bright X-ray emission in their centers (i.e. Hudson et al
  <P />1999). In this study, we use data from the X-ray Telescope (XRT)
  on Hinode to examine the thermal emission properties of two kinds of
  coronal cavities, those with and without enhanced emission at their
  centers. For cavities with bright X-ray emission in their centers,
  we find evidence for elevated temperatures in the cavity center. We
  find no obvious correlation between the presence of <P />bright cavity
  cores and filament presence or eruption. <P />This work is part of the
  effort of the International Space Science Institute International Team
  on Prominence Cavities

---------------------------------------------------------
Title: Relationship Between Earth-Directed Solar Eruptions and
Magnetic Clouds at 1 AU: A Brief Review
Authors: Yurchyshyn, Vasyl; Tripathi, Durgesh
2010aogs...21...51Y    Altcode: 2009arXiv0904.2366Y
  We review relationships between coronal mass ejections (CMEs), EIT
  post eruption arcades, and the coronal neutral line associated with
  global magnetic field and magnetic clouds near the Earth. Our previous
  findings indicate that the orientation of a halo CME elongation may
  correspond to the orientation of the underlying flux rope. Here we
  revisit these preliminary reports by comparing orientation angles
  of elongated LASCO CMEs, both full and partial halos, to the post
  eruption arcades. Based on 100 analysed events, it was found that the
  overwhelming majority of halo CMEs are elongated in the direction of
  the axial field of the post eruption arcades. Moreover, this conclusion
  also holds for partial halo CMEs as well as for events that originate
  further from the disk center. This suggests that the projection effect
  does not drastically change the appearance of full and partial halos
  and their images still bear reliable information about the underlying
  magnetic fields. We also compared orientations of the erupted fields
  near the Sun and in the interplanetary space and found that the local
  tilt of the coronal neutral line at 2.5 solar radii is well correlated
  with the magnetic cloud axis measured near the Earth. We suggest that
  the heliospheric magnetic fields significantly affect the propagating
  ejecta. Sometimes, the ejecta may even rotate so that its axis locally
  aligns itself with the heliospheric current sheet.

---------------------------------------------------------
Title: Geometric Model of a Coronal Cavity
Authors: Kucera, Therese A.; Gibson, S. E.; Rastawicki, D.; Dove, J.;
   de Toma, G.; Hao, J.; Hudson, H. S.; Marque, C.; McIntosh, P. S.;
   Reeves, K. K.; Schmidt, D. J.; Sterling, A. C.; Tripathi, D. K.;
   Williams, D. R.; Zhang, M.
2010AAS...21640510K    Altcode: 2010BAAS...41..890K
  We observed a coronal cavity from August 8-18 2007 during a
  multi-instrument observing campaign organized under the auspices of
  the International Heliophysical Year (IHY). Here we present initial
  efforts to model the cavity with a geometrical streamer-cavity
  model. The model is based the white-light streamer model of Gibson et
  al. (2003), which has been enhanced by the addition of a cavity and
  the capability to model EUV and X-ray emission. The cavity is modeled
  with an elliptical cross-section and Gaussian fall-off in length and
  width inside the streamer. Density and temperature can be varied in the
  streamer and cavity and constrained via comparison with data. Although
  this model is purely morphological, it allows for three-dimensional,
  multi-temperature analysis and characterization of the data, which
  can then provide constraints for future physical modeling. Initial
  comparisons to STEREO/EUVI images of the cavity and streamer show that
  the model can provide a good fit to the data. This work is part of the
  effort of the International Space Science Institute International Team
  on Prominence Cavities.

---------------------------------------------------------
Title: Diagnostics of Active Region Loops Observed with Hinode/EIS
Authors: Tripathi, D.; Mason, H. E.; Dwivedi, B. N.; Del Zanna, G.
2009ASPC..415..260T    Altcode:
  The Extreme Ultraviolet Imaging Spectrometer (EIS) on board Hinode
  provides us with an excellent opportunity to study the physical
  parameters in spatially resolved coronal structures. In this paper
  we have carried out a study of active region loops using observations
  from the EIS. The active region was observed on 2007 Ma 19 using the
  1 arcsec slit of EIS. At coronal temperatures, we find that electron
  densities measured from Fe XII and Si X line ratios decrease along
  the loop length, being ≈10<SUP>10</SUP>0 cm<SUP>-3</SUP> at foot
  point and ≈10<SUP>8.5</SUP> cm<SUP>-3</SUP> at a height of about 75
  Mm. However, the electron densities measured from the Mg VII line ratios
  (at a transition region temperature) show significantly lower values
  at the foot point. The electron temperature along the loop increases
  with height from ≈0.8 MK (at foot point) to ≈1.5 MK (at a height
  of 75 Mm). The temperature diagnostics using EM-loci at different
  locations along the loop show that the loop is “nearly isothermal”
  or “mildly multi-thermal” along the LOS. These measurements provide
  important constraints on the theoretical modelling of coronal loops.

---------------------------------------------------------
Title: Large Amplitude Oscillations in Prominences
Authors: Tripathi, D.; Isobe, H.; Jain, R.
2009SSRv..149..283T    Altcode: 2009arXiv0910.4059T
  Since the first reports of oscillations in prominences in the 1930s,
  there have been major theoretical and observational developments to
  understand the nature of these oscillatory phenomena, leading to the
  whole new field of the so-called “prominence seismology”. There
  are two types of oscillatory phenomena observed in prominences;
  “small-amplitude oscillations” (2-3 km s<SUP>-1</SUP>), which
  are quite common, and “large-amplitude oscillations” (&gt;20 km
  s<SUP>-1</SUP>) for which observations are scarce. Large-amplitude
  oscillations have been found as “winking filament” in H α as
  well as motion in the plane-of-sky in H α, EUV, micro-wave and
  He 10830 observations. Historically, it has been suggested that
  the large-amplitude oscillations in prominences were triggered by
  disturbances such as fast-mode MHD waves (Moreton wave) produced by
  remote flares. Recent observations show, in addition, that near-by
  flares or jets can also create such large-amplitude oscillations in
  prominences. Large-amplitude oscillations, which are observed both in
  transverse as well as longitudinal direction, have a range of periods
  varying from tens of minutes to a few hours. Using the observed period
  of oscillation and simple theoretical models, the obtained magnetic
  field in prominences has shown quite a good agreement with directly
  measured one and, therefore, justifies prominence seismology as a
  powerful diagnostic tool. On rare occasions, when the large-amplitude
  oscillations have been observed before or during the eruption, the
  oscillations may be applied to diagnose the stability and the eruption
  mechanism. Here we review the recent developments and understanding
  in the observational properties of large-amplitude oscillations and
  their trigger mechanisms and stability in the context of prominence
  seismology.

---------------------------------------------------------
Title: Rotation of White-light Coronal Mass Ejection Structures as
    Inferred from LASCO Coronagraph
Authors: Yurchyshyn, Vasyl; Abramenko, Valentyna; Tripathi, Durgesh
2009ApJ...705..426Y    Altcode:
  Understanding the connection between the magnetic configurations of a
  coronal mass ejection (CME) and their counterpart in the interplanetary
  medium is very important in terms of space weather predictions. Our
  previous findings indicate that the orientation of a halo CME elongation
  may correspond to the orientation of the underlying flux rope. Here
  we further explore these preliminary results by comparing orientation
  angles of elongated LASCO CMEs, both full and partial halos, to the
  EUV Imaging Telescope post-eruption arcades (PEAs). By analyzing a
  sample of 100 events, we found that the overwhelming majority of CMEs
  are elongated in the direction of the axial field of PEAs. During their
  evolution, CMEs appear to rotate by about 10° for most of the events
  (70%) with about 30°-50° for some events, and the corresponding time
  profiles display regular and gradual changes. It seems that there is
  a slight preference for the CMEs to rotate toward the solar equator
  and heliospheric current sheet (59% of the cases). We suggest that the
  rotation of the ejecta may be due to the presence of a heliospheric
  magnetic field, and it could shed light on the problems related to
  connecting solar surface phenomena to their interplanetary counterparts.

---------------------------------------------------------
Title: Large-Scale Flows in Prominence Cavities
Authors: Schmit, D. J.; Gibson, S. E.; Tomczyk, S.; Reeves, K. K.;
   Sterling, Alphonse C.; Brooks, D. H.; Williams, D. R.; Tripathi, D.
2009ApJ...700L..96S    Altcode:
  Regions of rarefied density often form cavities above quiescent
  prominences. We observed two different cavities with the Coronal
  Multichannel Polarimeter on 2005 April 21 and with Hinode/EIS on 2008
  November 8. Inside both of these cavities, we find coherent velocity
  structures based on spectral Doppler shifts. These flows have speeds of
  5-10 km s<SUP>-1</SUP>, occur over length scales of tens of megameters,
  and persist for at least 1 hr. Flows in cavities are an example of
  the nonstatic nature of quiescent structures in the solar atmosphere.

---------------------------------------------------------
Title: Temperature Tomography of a Coronal Sigmoid Supporting the
    Gradual Formation of a Flux Rope
Authors: Tripathi, Durgesh; Kliem, Bernhard; Mason, Helen E.; Young,
   Peter R.; Green, Lucie M.
2009ApJ...698L..27T    Altcode: 2009arXiv0904.4782T
  Multiwavelength observations of a sigmoidal (S-shaped) solar coronal
  source by the EUV Imaging Spectrometer and the X-Ray Telescope
  aboard the Hinode spacecraft and by the EUV Imager aboard STEREO are
  reported. The data reveal the coexistence of a pair of J-shaped hot
  arcs at temperatures T&gt;2 MK with an S-shaped structure at somewhat
  lower temperatures (T ≈ 1-1.3 MK). The middle section of the S-shaped
  structure runs along the polarity inversion line of the photospheric
  field, bridging the gap between the arcs. Flux cancellation occurs
  at the same location in the photosphere. The sigmoid forms in the
  gradual decay phase of the active region, which does not experience
  an eruption. These findings correspond to the expected signatures
  of a flux rope forming, or being augmented, gradually by a topology
  transformation inside a magnetic arcade. In such a transformation, the
  plasma on newly formed helical field lines in the outer flux shell of
  the rope (S-shaped in projection) is expected to enter a cooling phase
  once the reconnection of their parent field line pairs (double-J shaped
  in projection) is complete. Thus, the data support the conjecture that
  flux ropes can exist in the corona prior to eruptive activity.

---------------------------------------------------------
Title: Active Region Loops: Hinode/Extreme-Ultraviolet Imaging
    Spectrometer Observations
Authors: Tripathi, Durgesh; Mason, Helen E.; Dwivedi, Bhola N.;
   del Zanna, Giulio; Young, Peter R.
2009ApJ...694.1256T    Altcode: 2009arXiv0901.0095T
  We have carried out a study of active region loops using observations
  from the Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode
  using 1” raster data for an active region observed on 2007 May 19. We
  find that active region structures which are clearly discernible in
  cooler lines (≈1 MK) become "fuzzy" at higher temperatures (≈2
  MK). The active region was comprised of redshifted emissions (downflows)
  in the core and blueshifted emissions (upflows) at the boundary. The
  flow velocities estimated in the two regions located near the footpoints
  of coronal loop showed redshifted emission at transition region
  temperature and blueshifted emission at coronal temperature. The upflow
  speed in these regions increased with temperature. For more detailed
  study we selected one particular well-defined loop. Downward flows are
  detected along the coronal loop, being stronger in lower-temperature
  lines (rising up to 60 km s<SUP>-1</SUP> near the footpoint). The
  downflow was localized toward the footpoint in transition region lines
  (Si VII) and toward the loop top in high-temperature line (Fe XV). By
  carefully accounting for the background emission we found that the
  loop structure was close to isothermal for each position along the
  loop, with the temperature rising from around 0.8 MK to 1.5 MK from
  the close to the base to higher up toward the apex (≈75 Mm). We
  derived electron density using well-established line ratio diagnostic
  techniques. Electron densities along the active region loop were found
  to vary from 10<SUP>10</SUP> cm<SUP>-3</SUP> close to the footpoint to
  10<SUP>8.5</SUP> cm<SUP>-3</SUP> higher up. A lower electron density,
  varying from 10<SUP>9</SUP> cm<SUP>-3</SUP> close to the footpoint to
  10<SUP>8.5</SUP> cm<SUP>-3</SUP> higher up, was found for the lower
  temperature density diagnostic. Using these densities we derived filling
  factors in along the coronal loop which can be as low as 0.02 near the
  base of the loop. The filling factor increased with projected height
  of the loop. These results provide important constraints on coronal
  loop modeling.

---------------------------------------------------------
Title: Partially-erupting prominences: a comparison between
    observations and model-predicted observables
Authors: Tripathi, D.; Gibson, S. E.; Qiu, J.; Fletcher, L.; Liu,
   R.; Gilbert, H.; Mason, H. E.
2009A&A...498..295T    Altcode: 2009arXiv0902.1228T
  Aims: We investigate several partially-erupting prominences to
  study their relationship with other CME-associated phenomena and
  compare these observations with observables predicted by a model
  of partially-expelled-flux-ropes (Gibson &amp; Fan 2006a, ApJ,
  637, L65; 2006b, J. Geophys. Res., 111, 12103). <BR />Methods: We
  studied 6 selected events with partially-erupting prominences using
  multi-wavelength observations recorded by the Extreme-ultraviolet
  Imaging Telescope (EIT), Transition Region and Coronal Explorer
  (TRACE), Mauna Loa Solar Observatory (MLSO), Big Bear Solar Observatory
  (BBSO), and Soft X-ray Telescope (SXT). The observational features
  associated with partially-erupting prominences were then compared
  with the predicted observables from the model. <BR />Results: The
  partially-expelled-flux-rope (PEFR) model can explain the partial
  eruption of these prominences, and in addition predicts a variety
  of other CME-related observables that provide evidence of internal
  reconnection during eruption. We find that all of the partially-erupting
  prominences studied in this paper exhibit indirect evidence of internal
  reconnection. Moreover, all cases showed evidence of at least one
  observable unique to the PEFR model, e.g., dimmings external to the
  source region and/or a soft X-ray cusp overlying a reformed sigmoid. <BR
  />Conclusions: The PEFR model provides a plausible mechanism to explain
  the observed evolution of partially-erupting-prominence-associated
  CMEs in our study.

---------------------------------------------------------
Title: Chapter 7: Active Region Diagnostics
Authors: Mason, H. E.; Tripathi, D.
2008psa..book..127M    Altcode:
  Active regions present us with complex and dynamic structures, which
  look relatively simple, but are in fact very difficult to model and
  explain. An active region is a region on the Sun where the magnetic
  field breaks through the surface (photosphere and chromosphere) to
  form giant arches of hot plasma. The magnetic field is stronger than
  in surrounding regions and the plasma is hotter, so emits strongly
  in UV and X-ray radiation. Figures 7.1 and 7.2 show UV images of the
  Sun taken with the Transition Region and Coronal Explorer (TRACE)
  spacecraft and the Extreme Ultraviolet Imaging Telescope (EIT) aboard
  the Solar and Heliospheric Observatory (SOHO) spacecraft. The hot plasma
  (around a million degree) traces out the magnetic field structures...

---------------------------------------------------------
Title: Active Region Microflares From Hinode and RHESSI
Authors: Chifor, C.; Hannah, I. G.; Mason, H. E.; Isobe, H.; Yokoyama,
   T.; Young, P. R.; Tripathi, D.
2008ASPC..397..164C    Altcode:
  We are studying microflares (A, B-C class flares) in active regions
  using coordinated observations from Hinode and RHESSI. Hinode/EIS
  has unprecedented diagnostic power for small, transient activity
  in the solar corona, providing temperature, density, and velocity
  information. For this purpose, we designed and ran an EIS observing
  sequence to provide high-cadence data at both transition region and
  coronal temperatures. A preliminary analysis of these observations is
  reported, with one data set given as an example.

---------------------------------------------------------
Title: Source Region Evolution of the Solar Wind Disappearance Event
    of 11 May 1999
Authors: Janardhan, P.; Tripathi, D.; Mason, H. E.
2008ESPM...122.118J    Altcode:
  A recent, detailed study of the well known "solar wind disappearance
  event" of 11 May 1999 traced its origin to a coronal hole lying adjacent
  to a large active region, AR8525 <P />in Carrington rotation 1949. The
  active region was located at central meridian on 05 May 1999 when the
  flows responsible for this event began. In this paper we examine the
  evolution of the active region-coronal hole complex during 5-6 May 1999
  to study the changes that apparently played a key role in causing this
  disappearance event. To study the evolution of the solar source region
  of the disappearance event of 11 May 1999 we have used images from the
  Soft X-ray Telescope (SXT), the Extreme-ultraviolet Imaging Telescope
  (EIT) and the Michelson Doppler Imager (MDI) to examine the evolution
  of the coronal hole and active region complex at the source region of
  the disappearance event. We find a dynamic evolution taking place in
  the coronal hole-active region boundary at the source region of the
  disappearance event of 11 May 1999. Based on the combined observations
  it appears that the rapid evolution seen in the coronal hole is due to
  reconnection's taking place between the newly emerging flux and the open
  field regions from the coronal hole and the active region-coronal hole
  boundary regions. This evolution, which is found to reduce the area of
  the coronal hole, is accompanied by the formation of new loops in EUV
  images which are spatially and temporally correlated with emerging flux
  regions as seen in MDI data. <P />As opposed to the well known drivers
  of space weather phenomena like CME's or large flares, disappearance
  events are not associated with explosive solar phenomena. However, they
  do produce other observable effects that are not fully understood. In
  the period leading up to the disappearance event of 11 May 1999, our
  observations, during quiet solar conditions and in the absence of CMEs,
  provide the first clear evidence for Sun-Earth connection originating
  from an evolving active region-coronal hole region located at central
  meridian. With the exception of corotating interacting regions, these
  observations provide the first link between the Sun and space weather
  effects at 1 AU, arising from non-explosive solar events.

---------------------------------------------------------
Title: Density Structure in Active Regions from Hinode/EIS
Authors: Tripathi, D.; Mason, H. E.; Young, P. R.; Chifor, C.; Del
   Zanna, G.
2008ASPC..397...45T    Altcode:
  The Extreme-ultraviolet Imaging Spectrometer (EIS) on board Hinode
  provides an excellent opportunity to study the physical plasma
  parameters in spatially resolved coronal features. In this paper we
  present the density structure in an active region at many different
  temperatures. The active region was rastered on May 01, 2007 with the
  2^{”} slit. We find that the electron density is highest in the core
  of the active region where it exceeds log_{10} N_e = 10.5.

---------------------------------------------------------
Title: The Filament-Moreton Wave Interaction of 2006 December 6
Authors: Gilbert, Holly R.; Daou, Antoun G.; Young, Daniel; Tripathi,
   Durgesh; Alexander, David
2008ApJ...685..629G    Altcode:
  We utilize chromospheric observations obtained at MLSO of the 2006
  December 6 Moreton wave, which exhibits two distinct fronts, and
  subsequent filament activation to conduct a comprehensive analysis of
  the wave-filament interaction. By determining the period, amplitude, and
  evolution of the oscillations in the activated filament, we make certain
  inferences regarding the physical properties of both the wave and the
  filament. The large-amplitude oscillations induced in the filament by
  the wave passage last on the order of 180 minutes and demonstrate a
  complicated mixture of transverse and perpendicular motion with respect
  to the filament spine. These oscillations are predominantly along the
  filament axis, with a period of ~29 minutes and maximum line-of-sight
  velocity amplitude of ~41 km s<SUP>-1</SUP>. A careful examination of
  the complex oscillatory response of the filament elucidates some of the
  fundamental characteristics of the related Moreton wave. Specifically,
  we infer the maximum total kinetic energy involved in the interaction,
  the structure and topology of the passing wave, and discuss implications
  for the topology of the responding magnetic structure supporting the
  filament. The results of this observational study equip us with a
  better understanding of how filaments become activated and the nature
  of their responses to large propagating disturbances.

---------------------------------------------------------
Title: The solar wind disappearance event of 11 May 1999: source
    region evolution
Authors: Janardhan, P.; Tripathi, D.; Mason, H. E.
2008A&A...488L...1J    Altcode: 2008arXiv0807.2697J
  Context: A recent, detailed study of the well-known “solar wind
  disappearance event” of 11 May 1999 traced its origin to a coronal
  hole (CH) lying adjacent to a large active region (AR), AR8525 in
  Carrington rotation 1949. The AR was located at central meridian on 05
  May 1999 when the flows responsible for this event began. We examine
  the evolution of the AR-CH complex during 5-6 May 1999 to study the
  changes that apparently played a key role in causing this disappearance
  event. <BR />Aims: To study the evolution of the solar source region
  of the disappearance event of 11 May 1999. <BR />Methods: Using images
  from the Soft X-ray Telescope (SXT), the Extreme-ultraviolet Imaging
  Telescope (EIT) and the Michelson Doppler Imager (MDI) to examine
  the evolution of the CH and AR complex at the source region of the
  disappearance event. <BR />Results: We find a dynamic evolution taking
  place in the CH-AR boundary at the source region of the disappearance
  event of 11 May 1999. This evolution, which is found to reduce the
  area of the CH, is accompanied by the formation of new loops in EUV
  images that are spatially-and-temporally correlated with emerging flux
  regions as seen in MDI data. <BR />Conclusions: In the period leading
  up to the disappearance event of 11 May 1999, our observations,
  during quiet solar conditions and in the absence of CMEs, provide
  the first clear evidence for Sun-Earth connection originating from an
  evolving AR-CH region located at central meridian. With the exception
  of corotating interacting regions (CIR), these observations provide the
  first link between the Sun and space weather effects at 1 AU, arising
  from non-explosive solar events. <P />2 movies are only available in
  electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Prominence Seismology: Wavelet Analysis of Filament
    Oscillations
Authors: Pintér, Balázs; Jain, Rekha; Tripathi, Durgesh; Isobe,
   Hiroaki
2008ApJ...680.1560P    Altcode:
  The temporal and spatial behavior of a large-amplitude
  filament oscillation is investigated using wavelet analysis. The
  extreme-ultraviolet (EUV) images of the phenomenon, which occurred on
  2002 October 15, were taken from the EUV Imaging Telescope on board
  the Solar and Heliospheric Observatory (SOHO). The wavelet spectra,
  extracted from the intensity data, show that the filament oscillates
  as a rigid body, with a period of about 2.5-2.6 hr which is almost
  constant along the filament. The period slowly decreases with time
  until the filament erupts. No clear sign of the eruption is found in
  the wavelet spectrum prior to the eruption, that followed the filament
  oscillation. The axial component of the magnetic field is estimated
  between 1 and 5 G, which is believed to be reasonable for a polar
  crown filament of this kind.

---------------------------------------------------------
Title: Statistical Study of Orientations of Coronal Mass Ejections
    and EIT Flare Arcades
Authors: Yurchyshyn, V.; Tripathi, D.
2008AGUSMSH43A..01Y    Altcode:
  Coronal mass ejections (CMEs) and their interplanetary counterparts,
  interplanetary CMEs (ICMEs) usually exhibit a complex structure that
  very often includes a magnetic cloud (MC), which is thought to be
  a magnetic fluxrope. Our recent study indicates the orientation of a
  halo CME elongation may correspond to the orientation of the underlying
  flux rope. This is a continuation of the research and here we compare
  orientation angles of elongated LASCO CMEs, both halo and partial to the
  EIT post eruption arcades (PEA). Data for 100 events had been analyzed
  and er report the following: i) it is further supported that majority
  of halo CMEs are elongated in the direction of the aixial field of
  PEA arcades. This relationship is found to be weeker for partial CME
  and those events that originate further from the disk center. There
  also is an indication that events in the northern hemisphere generally
  exhibit better correlation that those in the southern hemisphere.

---------------------------------------------------------
Title: Multi-wavelength Comparison of Prominence Cavities
Authors: Schmit, D. J.; Gibson, S.; de Toma, G.; Reeves, K.; Tripathi,
   D.; Kucera, T.; Marque, C.; Tomczyk, S.
2008AGUSMSP43B..04S    Altcode:
  Recent observational campaigns have brought together a wealth of
  data specifically designed to explore the physical properties and
  dynamics of prominence cavities. In particular, STEREO and Hinode
  data have provided new perspectives on these structures. In order to
  effectively analyze the data in a cohesive manner, we produce overlays
  of several distinct and complimentary datasets including SOHO UVCS,
  CDS, and EIT, Hinode SOT and EIS, STEREO SECCHI, TRACE, and Nancay
  Radioheliograph data as well as new observations of coronal magnetic
  fields in cavities from the Coronal Multichannel Polarimeter. We are
  thus able to investigate how sensitive morphology is to the wavelength
  observed which details the nature of the plasma in the cavity.

---------------------------------------------------------
Title: Density structure of an active region and associated moss
    using Hinode/EIS
Authors: Tripathi, D.; Mason, H. E.; Young, P. R.; Del Zanna, G.
2008A&A...481L..53T    Altcode: 2008arXiv0802.3311T
  Context: Studying the problem of active region heating requires precise
  measurements of physical plasma parameters such as electron density,
  temperature, etc. It is also important to understand the relationship
  of coronal structures with the magnetic field. The Extreme-ultraviolet
  Imaging Spectrometer (EIS) aboard Hinode provides a rare opportunity to
  derive electron density simultaneously at different temperatures. <BR
  />Aims: We study the density structure and characterise plasma in
  active regions and associated moss regions. In addition, we study its
  relationship to the photospheric magnetic field. <BR />Methods: We used
  data recorded by the EIS, together with magnetic field measurements
  from the Michelson Doppler Imager (MDI) aboard SoHO and images recorded
  with the Transition Region And Coronal Explorer (TRACE) and X-Ray
  Telescope (XRT/Hinode). <BR />Results: We find that the hot core of
  the active region is densest with values as high as 10<SUP>10.5</SUP>
  cm<SUP>-3</SUP>. The electron density estimated in specific regions
  in the active region moss decreases with increasing temperature. The
  moss areas were located primarily on one side of the active region,
  and they map the positive polarity regions almost exactly. The density
  within the moss region was highest at log T=5.8{-}6.1, with a value
  around 10<SUP>10.0{-</SUP>10.5} cm<SUP>-3</SUP>. The moss densities
  were highest in the strong positive magnetic field region. However,
  there was no such correlation for the negative polarity areas, where
  there was a large sunspot.

---------------------------------------------------------
Title: An active region jet observed with Hinode
Authors: Chifor, C.; Young, P. R.; Isobe, H.; Mason, H. E.; Tripathi,
   D.; Hara, H.; Yokoyama, T.
2008A&A...481L..57C    Altcode:
  Aims:We study the physical properties of an active region (AR) jet in
  order to probe the mechanisms responsible for it. <BR />Methods: We
  report 2007 January 15/16 observations of a recurring jet situated on
  the west side of NOAA AR 10938. Multi-wavelength data from all three
  instruments onboard Hinode were analysed. This paper focuses on one
  instance of a jet observed with the Hinode/EUV Imaging Spectrometer
  (EIS). Using EIS raster data we measured the temperatures, Doppler
  shifts, density, and filling factor. <BR />Results: A strong
  blue-shifted component and an indication of a weak red-shifted
  component at the base of the jet was observed around Log T<SUB>e</SUB>
  = 6.2. The up-flow velocities exceeded 150 km s<SUP>-1</SUP>. The
  jet component was seen over a range of temperatures between 5.4 and
  6.4 in Log T_e. Using Fe XII λ186 and λ195 line ratios, we measured
  densities above Log N<SUB>e</SUB> = 11 for the high-velocity up-flow
  component. We found that the density of the high-velocity up-flow
  increases with velocity. We estimate the filling factor in the jet
  up-flow to be &lt;0.03. With the Hinode/Solar Optical Telescope (SOT),
  we observed recurrent (quasi periodic) magnetic flux cancelations just
  before the recurrent jet emission was seen in images taken with the
  X-ray Telescope (XRT). <BR />Conclusions: The high-velocity up-flows,
  together with the density dependence on velocity, support an evaporation
  scenario for the acceleration of this jet. The high density and small
  filling factor, coupled with the high Doppler velocities are strongly
  suggestive of multiple small-scale magnetic reconnection events being
  responsible for the production of both EUV and X-ray jets.

---------------------------------------------------------
Title: Relationship Between CME-Associated Waves Observed on 5
    March 2000
Authors: Raouafi, N. -E.; Tripathi, D.
2008ASPC..383..421R    Altcode: 2008arXiv0801.0766R
  We study the relationship between different wave phenomena associated
  with a coronal mass ejection (CME) observed on 05 Mar. 2000. EIT
  waves were observed in the images recorded by EIT at 195 Å. The
  white-light LASCO/C2 images show clear deflection and propagation
  of a kink along with the CME. Spectroscopic observations recorded
  by the UVCS reveals excessive line broadening in the two O VI lines
  (1032 and 1037 Å). Moreover very hot lines such as Si XII and Mg X
  were observed. Interestingly, the EIT wave, the streamer deflection
  and the intensity modulation along the slit were all propagating
  northeast. Spatial and temporal correlations show that the streamer
  deflection and spectral line broadening are highly likely to be due
  to a CME-driven shock wave and that the EIT wave is the signature of
  a CME-driven shock wave in the lower corona.

---------------------------------------------------------
Title: Entropy Maximization, Cutoff Distribution, and Finite Stellar
    Masses
Authors: Dubey, Ritesh Kumar; Menon, V. J.; Pandey, M. K.; Tripathi,
   D. N.
2008AdAst2008E...3D    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Large-Amplitude Oscillation of an Erupting Filament as Seen
    in EUV, Hα, and Microwave Observations
Authors: Isobe, H.; Tripathi, D.; Asai, A.; Jain, R.
2007SoPh..246...89I    Altcode: 2007arXiv0711.3952I
  We present multiwavelength observations of a large-amplitude oscillation
  of a polar-crown filament on 15 October 2002, which has been reported by
  Isobe and Tripathi (Astron. Astrophys.449, L17, 2006). The oscillation
  occurred during the slow rise (≈1 km s<SUP>−1</SUP>) of the
  filament. It completed three cycles before sudden acceleration and
  eruption. The oscillation and following eruption were clearly seen in
  observations recorded by the Extreme-Ultraviolet Imaging Telescope (EIT)
  onboard the Solar and Heliospheric Observatory (SOHO). The oscillation
  was seen only in a part of the filament, and it appears to be a standing
  oscillation rather than a propagating wave. The amplitudes of velocity
  and spatial displacement of the oscillation in the plane of the sky were
  about 5 km s<SUP>−1</SUP> and 15 000 km, respectively. The period
  of oscillation was about two hours and did not change significantly
  during the oscillation. The oscillation was also observed in Hα by
  the Flare Monitoring Telescope at the Hida Observatory. We determine
  the three-dimensional motion of the oscillation from the Hα wing
  images. The maximum line-of-sight velocity was estimated to be a few
  tens of kilometers per second, although the uncertainty is large owing
  to the lack of line-profile information. Furthermore, we also identified
  the spatial displacement of the oscillation in 17-GHz microwave images
  from Nobeyama Radio Heliograph (NoRH). The filament oscillation seems
  to be triggered by magnetic reconnection between a filament barb and
  nearby emerging magnetic flux as was evident from the MDI magnetogram
  observations. No flare was observed to be associated with the onset
  of the oscillation. We also discuss possible implications of the
  oscillation as a diagnostic tool for the eruption mechanisms. We
  suggest that in the early phase of eruption a part of the filament
  lost its equilibrium first, while the remaining part was still in an
  equilibrium and oscillated.

---------------------------------------------------------
Title: On the relationship between coronal waves associated with a
    CME on 5 March 2000
Authors: Tripathi, D.; Raouafi, N. -E.
2007A&A...473..951T    Altcode:
  Aims:To study the relationship between coronal mass ejection (CME)
  associated waves. <BR />Methods: Analysis of CME eruption observations
  on 5 Mar. 2000 recorded by the Large Angle Spectrometric Coronagraph
  (LASCO), the Ultraviolet Coronagraph Spectrometer (UVCS), and the
  Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and
  Heliospheric Observatory (SOHO). <BR />Results: Images recorded by
  the LASCO/C2 show a clear deflection and kink in a streamer located
  eastward of the CME. The kink in the streamer propagated outwards
  along with the associated CME. No CME material was seen between the
  bright front of the CME and the streamer. UVCS spectra show large
  spectral line broadening, Doppler shifts and intensity changes in
  the O VI (λ1032 &amp; 1037) lines. Moreover, intensity enhancements
  in lines such as Si XII λ 520 and Mg X λ 625 forming at very high
  temperatures (&gt;2 MK; not often observed in the corona) were also
  observed. EIT images show the propagation of a wave from the CME source
  region. The speed of the wave was about 55 km s<SUP>-1</SUP> and it
  propagated predominantly in the North-East direction from the source
  region. Furthermore, it does not propagate through active regions and
  coronal holes. The deflection in the streamer recorded in the LASCO/C2
  was in the same direction as that of the EIT wave. <BR />Conclusions:
  Spatial and temporal correlations show that the deflection and the
  propagation of the kink in the streamer (based on the LASCO data),
  and plasma heating and spectral line broadening (based on the UVCS
  data), are basically due to a CME-driven shock wave. The spatial
  and temporal correlations between the EIT wave and the shock wave
  provide strong evidence in favor of the interpretation that the EIT
  waves are indeed the counterpart of CME-driven shock waves in the lower
  corona. Although, we cannot rule out the possibility that the EIT waves
  are just a manifestation of the stretching of the field lines due to
  the outward propagation of the CMEs. <P />The movie is only available
  in electronic form at http://www.aanda.org

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

---------------------------------------------------------
Title: X-ray precursors to flares and filament eruptions
Authors: Chifor, C.; Tripathi, D.; Mason, H. E.; Dennis, B. R.
2007A&A...472..967C    Altcode:
  Aims:To study preflare X-ray brightenings as diagnostics of the
  destabilisation of flare-associated erupting filaments/prominences. <BR
  />Methods: We combine new observations from the Transition Region
  and Coronal Explorer (TRACE) and the Reuven Ramaty High Energy Solar
  Spectroscopic Imager (RHESSI), as well as revisit events reported in the
  literature to date, in order to scrutinise the preflare activity during
  eight flare-associated filament eruptions. <BR />Results: The preflare
  activity occurs in the form of discrete, localised X-ray brightenings
  observed between 2 and 50 min before the impulsive phase of the flare
  and filament acceleration. These transient preflare brightenings are
  situated on or near (within 10{ arcsec} of) the polarity inversion
  line (PIL), coincident with emerging and/or canceling magnetic
  flux. The filaments begin to rise from the location of the preflare
  brightenings. In five out of eight events, the preflare brightenings
  were observed beneath the filament channel, close to the filament
  footpoint first observed to rise. Both thermal and nonthermal hard
  X-ray emissions during the preflare enhancement were detected with
  RHESSI, suggesting that both plasma heating and electron acceleration
  occurred at this time. The main energy release during the impulsive
  phase of the flare is observed close to (within 50{ arcsec} of) the
  preflare brightenings. The fast-rise phase of the filament eruption
  starts at the same time as the onset of the main flare or up to 5 min
  later. <BR />Conclusions: The preflare brightenings are precursors to
  the flare and filament eruption. These precursors represent distinct,
  localised instances of energy release, rather than a gradual energy
  release prior to the main flare. The X-ray precursors represent clearly
  observable signatures in the early stages of the eruption. Together with
  the timing of the filament fast-rise at or after the main flare onset,
  the X-ray precursors provide evidence for a tether-cutting mechanism
  initially manifested as localised magnetic reconnection being a common
  trigger for both flare emission and filament eruption. <P />Movies and
  Appendix A are only available in electronic form at http://www.aanda.org

---------------------------------------------------------
Title: Filament Activation Due To A Moreton Wave Observed On Dec. 6,
    2006
Authors: Gilbert, Holly; deToma, G.; Tripathi, D.
2007AAS...210.2505G    Altcode: 2007BAAS...39..131G
  Flare generated Moreton waves have been historically observed to
  activate filaments located at regions far from the flare site, causing
  them to oscillate (sometimes referred to as “winking”). A recent
  example of such an activation occurred on December 6, 2006 in which a
  large flare occurring near the east limb created a dramatic response
  in a filament located far to the south. We present an analysis of this
  filament activation using He I (1083 nm) intensity and velocity data
  taken at the Mauna Loa Solar Observatory (MLSO). The He I (1083 nm)
  line-of-sight velocity data provide a close examination of the motions
  and velocities involved in this dynamic filament response.

---------------------------------------------------------
Title: Ellerman Bombs and Jets Associated with Resistive Flux
    Emergence
Authors: Isobe, H.; Tripathi, D.; Archontis, V.
2007ApJ...657L..53I    Altcode:
  Using two-dimensional (2D) magnetohydrodynamic simulations we study
  the effects of resistive processes in the dynamics of magnetic
  flux emergence and its relation to Ellerman bombs and other dynamic
  phenomena in the Sun. The widely accepted scenario of flux emergence
  is the formation and expansion of Ω-shaped loops due to the Parker
  instability. Since the Parker instability has the largest growth rate at
  finite wavelength λ<SUB>p</SUB>~10H-20H, where H is the scale height
  (~200 km in the solar photosphere), a number of magnetic loops may
  rise from the initial flux sheet if it is sufficiently long. This
  process is shown in our numerical simulations. The multiple emerging
  loops expand in the atmosphere and interact with each other, leading
  to magnetic reconnection. At first reconnection occurs in the lower
  atmosphere, which allows the sinking part of the flux sheet to emerge
  above the photosphere. This reconnection also causes local heating
  that may account for Ellerman bombs. In the later stage, reconnection
  between the expanding loops occurs at higher levels of the atmosphere
  and creates high-temperature reconnection jets, and eventually a large
  (&gt;&gt;λ<SUB>p</SUB>) coronal loop is formed. Cool and dense plasma
  structures, which are similar to Hα surges, are also formed. This
  is not because of magnetic reconnection but due to the compression of
  the plasma in between the expanding loops.

---------------------------------------------------------
Title: Evolution of the photospheric magnetic field in the source
    regions of coronal mass ejections
Authors: Bothmer, V.; Tripathi, D.
2007msfa.conf..257B    Altcode:
  Six coronal mass ejections associated with erupting quiescent filaments
  on the visible solar disk were identified in data from SoHO (Solar
  and Heliospheric Observatory) LASCO (Large Angle and Spectrometric
  Coronagraph), EIT (Extreme ultraviolet Imaging Telescope) and MDI
  (Michelson Doppler Imager) data and ground-based Hα observations
  from Big Bear and Meudon observatories. These events were analysed to
  investigate whether their initiations could be related to changes of
  the underlying photospheric field. The results show that in five out
  of the six events, substantial changes in the photospheric magnetic
  field occurred in the source regions prior and around the CME's lift-off
  times as identified from emerging/diminishing flux detected by MDI. In
  one event large magnetic flux changes could be identified not in the
  source region itself, but in a neighbouring active region. The results
  demonstrate that new missions, such as STEREO and Hinode (Solar-B)
  in conjunction with SoHO and ground-based measurements, will provide
  joint data sets that have the potential to provide new insight into
  the physical causes of CMEs.

---------------------------------------------------------
Title: EIT and TRACE responses to flare plasma
Authors: Tripathi, D.; Del Zanna, G.; Mason, H. E.; Chifor, C.
2006A&A...460L..53T    Altcode: 2008arXiv0802.3852T
  Aims.To understand the contribution of active region and flare
  plasmas to the λ195 channels of SOHO/EIT (Extreme-ultraviolet Imaging
  Telescope) and TRACE (Transition Region and Coronal Explorer).<BR />
  Methods: .We have analysed an M8 flare simultaneously observed by
  the Coronal Diagnostic Spectrometer (CDS), EIT, TRACE and RHESSI. We
  obtained synthetic spectra for the flaring region and an outer region
  using the differential emission measures (DEM) of emitting plasma based
  on CDS and RHESSI observations and the CHIANTI atomic database. We
  then predicted the EIT and TRACE count rates.<BR /> Results: .For the
  flaring region, both EIT and TRACE images taken through the λ195
  filter are dominated by Fe XXIV (formed at about 20 MK). However,
  in the outer region, the emission was primarily due to the Fe XII,
  with substantial contributions from other lines. The average count
  rate for the outer region was within 25% the observed value for EIT,
  while for TRACE it was a factor of two higher. For the flare region,
  the predicted count rate was a factor of two (in case of EIT) and
  a factor of three (in case of TRACE) higher than the actual count
  rate.<BR /> Conclusions: .During a solar flare, both TRACE and EIT
  λ195 channels are found to be dominated by Fe XXIV emission. Reasonable
  agreement between predictions and observations is found, however some
  discrepancies need to be further investigated.

---------------------------------------------------------
Title: The early phases of a solar prominence eruption and associated
flare: a multi-wavelength analysis
Authors: Chifor, C.; Mason, H. E.; Tripathi, D.; Isobe, H.; Asai, A.
2006A&A...458..965C    Altcode:
  Aims.We aim to examine the precursor phases and early evolution of a
  prominence eruption associated with a M4-class flare and a partial
  halo coronal mass ejection (CME) observed on 2005 July 27. Our
  main goal is to investigate the precursor eruption signatures
  observed in EUV, X-ray and microwave emission and their relation
  to the prominence destabilisation. <BR /> Methods: .We perform a
  multi-wavelength study of the prominence morphology and motion using
  high-cadence and spatial resolution EUV 171 Å images from the TRACE
  satellite. The high-temperature flare radiative emission in soft
  and hard X-rays are analysed through imaging and spectral modeling
  with RHESSI. Complementary microwave images (17 GHz and 34 GHz)
  from NoRH are also investigated.<BR /> Results: .The activation
  of the filament proceeds from one anchored footpoint. We observe
  "pre-eruption" brightenings in X-ray and EUV images, close to the
  erupting footpoint of the prominence, being temporally correlated to
  the point when the prominence first enters a slow-rise phase, and then
  an accelerated fast-rise phase. The brightness temperature (T_b) of the
  prominence at 34 GHz is increasing during the eruption. We also find
  very good correlation between the prominence height-time profile and
  the spatially integrated soft X-ray (SXR) emission.<BR /> Conclusions:
  .We discuss the observed precursor brightenings with respect to possible
  mechanisms that might be responsible for the prominence destabilisation
  and acceleration. Our observations suggest that reconnection events
  localised beneath the erupting footpoint may eventually destabilise
  the entire prominence, causing the eruption.

---------------------------------------------------------
Title: EUV and Coronagraphic Observations of Coronal Mass Ejections
Authors: Tripathi, Durgesh
2006JApA...27..193T    Altcode:
  The Large Angle Spectrometric Coronagraph (LASCO) and
  Extreme-ultraviolet Imaging Telescope (EIT) onboard Solar and
  Heliospheric Observatory (SOHO) provide us with unprecedented
  multiwavelength observations helping us to understand different dynamic
  phenomena on the Sun and in the corona. In this paper we discuss
  the association between post-eruptive arcades (PEAs) detected by EIT
  and white-light coronal mass ejections (CMEs) detected by LASCO/C2
  telescope.

---------------------------------------------------------
Title: Multi-Wavelength Investigation of a Sigmoidal Active Region
Authors: Tripathi, D.; Mason, H. E.; Young, P. R.
2006ESASP.617E.148T    Altcode: 2006soho...17E.148T
  No abstract at ADS

---------------------------------------------------------
Title: Asymmetric Prominence Eruption: A "Domino Effect"?
Authors: Chifor, C.; Mason, H. E.; Tripathi, D.; Isobe, H.; Asai, A.
2006ESASP.617E.121C    Altcode: 2006soho...17E.121C
  No abstract at ADS

---------------------------------------------------------
Title: SOHO Observations of CME-Driven Shock and EIT Waves
Authors: Tripathi, D.; Raouafi, N. -E.
2006ESASP.617E.149T    Altcode: 2006soho...17E.149T
  No abstract at ADS

---------------------------------------------------------
Title: On the propagation of brightening after filament/prominence
    eruptions, as seen by SoHO-EIT
Authors: Tripathi, D.; Isobe, H.; Mason, H. E.
2006A&A...453.1111T    Altcode:
  Aims.To study the relationship between the propagation of brightening
  and erupting filaments/prominences in order to get some insight into
  the three-dimensional picture of magnetic reconnection.<BR /> Methods:
  .Analysis of the observations taken with the EIT (Extreme-ultraviolet
  Imaging Telescope) aboard SoHO (Solar and Heliospheric Observatory).<BR
  /> Results: .When the prominences/filaments erupted having one point
  fixed - asymmetric eruption - the brightening propagated along the
  neutral line together with the expansion/separation from the polarity
  inversion line (PIL) as expected from the standard models. However
  in case of symmetric eruptions, the brightening propagated towards
  both end points starting at the middle. When the prominence/filament
  erupted faster then the speed of the propagating brightening was
  faster and vice-versa.<BR /> Conclusions: .Based on these observations
  we conclude that the eruption and magnetic reconnection - propagation
  (along the PIL) and separation (away from PIL) of the brightening - are
  dynamically coupled phenomena. These observations can be explained by
  a simple extension of the 2D models illustrating eruption and magnetic
  reconnection to a 3D model.

---------------------------------------------------------
Title: Photospheric Field Evolution in the Source Regions of Coronal
    Mass Ejections
Authors: Bothmer, V.; Tripathi, D.
2006ESASP.617E..20B    Altcode: 2006soho...17E..20B
  No abstract at ADS

---------------------------------------------------------
Title: Stable galaxies of finite masses in the most probable
    distribution
Authors: Menon, V. J.; Dubey, Ritesh Kumar; Tripathi, D. N.
2006PhyA..367..269M    Altcode:
  Conventional equilibrium statistical mechanics of bound gravitational
  systems is known to suffer from the serious difficulties that galaxies
  acquire unbounded radii, become infinitely massive, and evaporate away
  continuously. We point out that these troubles disappear automatically
  if we use the exact, most probable, distribution having an inherent
  upper energy cutoff.

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

---------------------------------------------------------
Title: Large amplitude oscillation of a polar crown filament in the
    pre-eruption phase
Authors: Isobe, H.; Tripathi, D.
2006A&A...449L..17I    Altcode: 2006astro.ph..2432I
  Aims.We report observation of a large-amplitude filament oscillation
  followed by an eruption. This is used to probe the pre-eruption
  condition and the trigger mechanism of solar eruptions.Methods.We used
  the EUV images from the Extreme-Ultraviolet Imaging Telescope on board
  SOHO satellite and the Hα images from the Flare Monitoring Telescope
  at Hida Observatory. The observed event is a polar crown filament
  that erupted on 15 Oct. 2002.Results.The filament clearly exhibited
  oscillatory motion in the slow-rising, pre-eruption phase. The amplitude
  of the oscillation was larger than 20 km s<SUP>-1</SUP>, and the motion
  was predominantly horizontal. The period was about 2 h and seemed to
  increase during the oscillation, indicating weakening of restoring
  force.Conclusions.Even in the slow-rise phase before the eruption,
  the filament retained equilibrium and behaved as an oscillator, and
  the equilibrium is stable to nonlinear perturbation. The transition
  from such nonlinear stability to either instabilities or a loss of
  equilibrium that leads to the eruption occurred in the Alfvén time
  scale (~1 h). This suggests that the onset of the eruption was triggered
  by a fast magnetic reconnection that destabilized the pre-eruption
  magnetic configuration, rather than by the slow shearing motion at
  the photosphere.

---------------------------------------------------------
Title: The Pre-CME Sun
Authors: Gopalswamy, N.; Mikić, Z.; Maia, D.; Alexander, D.; Cremades,
   H.; Kaufmann, P.; Tripathi, D.; Wang, Y. -M.
2006SSRv..123..303G    Altcode: 2006SSRv..tmp...77G
  The coronal mass ejection (CME) phenomenon occurs in closed magnetic
  field regions on the Sun such as active regions, filament regions,
  transequatorial interconnection regions, and complexes involving a
  combination of these. This chapter describes the current knowledge
  on these closed field structures and how they lead to CMEs. After
  describing the specific magnetic structures observed in the CME source
  region, we compare the substructures of CMEs to what is observed before
  eruption. Evolution of the closed magnetic structures in response to
  various photospheric motions over different time scales (convection,
  differential rotation, meridional circulation) somehow leads to the
  eruption. We describe this pre-eruption evolution and attempt to link
  them to the observed features of CMEs. Small-scale energetic signatures
  in the form of electron acceleration (signified by nonthermal radio
  bursts at metric wavelengths) and plasma heating (observed as compact
  soft X-ray brightening) may be indicative of impending CMEs. We survey
  these pre-eruptive energy releases using observations taken before
  and during the eruption of several CMEs. Finally, we discuss how the
  observations can be converted into useful inputs to numerical models
  that can describe the CME initiation.

---------------------------------------------------------
Title: Coronal Observations of CMEs.  Report of Working Group A
Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.;
   Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.;
   Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.;
   Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J.
2006SSRv..123..127S    Altcode: 2006SSRv..tmp...58S
  CMEs have been observed for over 30 years with a wide variety of
  instruments. It is now possible to derive detailed and quantitative
  information on CME morphology, velocity, acceleration and mass. Flares
  associated with CMEs are observed in X-rays, and several different
  radio signatures are also seen. Optical and UV spectra of CMEs both on
  the disk and at the limb provide velocities along the line of sight
  and diagnostics for temperature, density and composition. From the
  vast quantity of data we attempt to synthesize the current state of
  knowledge of the properties of CMEs, along with some specific observed
  characteristics that illuminate the physical processes occurring during
  CME eruption. These include the common three-part structures of CMEs,
  which is generally attributed to compressed material at the leading
  edge, a low-density magnetic bubble and dense prominence gas. Signatures
  of shock waves are seen, but the location of these shocks relative
  to the other structures and the occurrence rate at the heights where
  Solar Energetic Particles are produced remains controversial. The
  relationships among CMEs, Moreton waves, EIT waves, and EUV dimming
  are also cloudy. The close connection between CMEs and flares suggests
  that magnetic reconnection plays an important role in CME eruption
  and evolution. We discuss the evidence for reconnection in current
  sheets from white-light, X-ray, radio and UV observations. Finally, we
  summarize the requirements for future instrumentation that might answer
  the outstanding questions and the opportunities that new space-based
  and ground-based observatories will provide in the future.

---------------------------------------------------------
Title: Multi-Wavelength Observations of CMEs and Associated Phenomena.
    Report of Working Group F
Authors: Pick, M.; Forbes, T. G.; Mann, G.; Cane, H. V.; Chen, J.;
   Ciaravella, A.; Cremades, H.; Howard, R. A.; Hudson, H. S.; Klassen,
   A.; Klein, K. L.; Lee, M. A.; Linker, J. A.; Maia, D.; Mikic,
   Z.; Raymond, J. C.; Reiner, M. J.; Simnett, G. M.; Srivastava, N.;
   Tripathi, D.; Vainio, R.; Vourlidas, A.; Zhang, J.; Zurbuchen, T. H.;
   Sheeley, N. R.; Marqué, C.
2006SSRv..123..341P    Altcode: 2006SSRv..tmp...60P
  This chapter reviews how our knowledge of CMEs and CME-associated
  phenomena has been improved, since the launch of the SOHO mission,
  thanks to multi-wavelength analysis. The combination of data obtained
  from space-based experiments and ground based instruments allows us
  to follow the space-time development of an event from the bottom of
  the corona to large distances in the interplanetary medium. Since CMEs
  originate in the low solar corona, understanding the physical processes
  that generate them is strongly dependant on coordinated multi-wavelength
  observations. CMEs display a large diversity in morphology and kinematic
  properties, but there is presently no statistical evidence that those
  properties may serve to group them into different classes. When a CME
  takes place, the coronal magnetic field undergoes restructuring. Much
  of the current research is focused on understanding how the corona
  sustains the stresses that allow the magnetic energy to build up and
  how, later on, this magnetic energy is released during eruptive flares
  and CMEs. Multi-wavelength observations have confirmed that reconnection
  plays a key role during the development of CMEs. Frequently, CMEs
  display a rather simple shape, exhibiting a well known three-part
  structure (bright leading edge, dark cavity and bright knot). These
  types of events have led to the proposal of the ‘`standard model’'
  of the development of a CME, a model which predicts the formation
  of current sheets. A few recent coronal observations provide some
  evidence for such sheets. Other more complex events correspond to
  multiple eruptions taking place on a time scale much shorter than the
  cadence of coronagraph instruments. They are often associated with
  large-scale dimming and coronal waves. The exact nature of these waves
  and the physical link between these different manifestations are not
  yet elucidated. We also discuss what kind of shocks are produced during
  a flare or a CME. Several questions remain unanswered. What is the
  nature of the shocks in the corona (blast-wave or piston-driven?) How
  they are related to Moreton waves seen in Hα? How they are related
  to interplanetary shocks? The last section discusses the origin of
  energetic electrons detected in the corona and in the interplanetary
  medium. “Complex type III-like events,”which are detected at
  hectometric wavelengths, high in the corona, and are associated with
  CMEs, appear to originate from electrons that have been accelerated
  lower in the corona and not at the bow shock of CMEs. Similarly,
  impulsive energetic electrons observed in the interplanetary medium
  are not the exclusive result of electron acceleration at the bow shocks
  of CMEs; rather they have a coronal origin.

---------------------------------------------------------
Title: Multi-Wavelength Observations of CMEs and Associated Phenomena
Authors: Pick, M.; Forbes, T. G.; Mann, G.; Cane, H. V.; Chen, J.;
   Ciaravella, A.; Cremades, H.; Howard, R. A.; Hudson, H. S.; Klassen,
   A.; Klein, K. L.; Lee, M. A.; Linker, J. A.; Maia, D.; Mikic,
   Z.; Raymond, J. C.; Reiner, M. J.; Simnett, G. M.; Srivastava, N.;
   Tripathi, D.; Vainio, R.; Vourlidas, A.; Zhang, J.; Zurbuchen, T. H.;
   Sheeley, N. R.; Marqué, C.
2006cme..book..341P    Altcode:
  This chapter reviews how our knowledge of CMEs and CME-associated
  phenomena has been improved, since the launch of the SOHO mission,
  thanks to multi-wavelength analysis. The combination of data obtained
  from space-based experiments and ground based instruments allows us
  to follow the space-time development of an event from the bottom of
  the corona to large distances in the interplanetary medium. Since
  CMEs originate in the low solar corona, understanding the physical
  processes that generate them is strongly dependant on coordinated
  multi-wavelength observations. CMEs display a large diversity in
  morphology and kinematic properties, but there is presently no
  statistical evidence that those properties may serve to group them
  into different classes. When a CME takes place, the coronal magnetic
  field undergoes restructuring. Much of the current research is focused
  on understanding how the corona sustains the stresses that allow the
  magnetic energy to build up and how, later on, this magnetic energy is
  released during eruptive flares and CMEs. Multiwavelength observations
  have confirmed that reconnection plays a key role during the development
  of CMEs. Frequently, CMEs display a rather simple shape, exhibiting a
  well known three-part structure (bright leading edge, dark cavity and
  bright knot). These types of events have led to the proposal of the
  "standard model" of the development of a CME, a model which predicts
  the formation current sheets. A few recent coronal observations provide
  some evidence for such sheets. Other more complex events correspond
  to multiple eruptions taking place on a time scale much shorter than
  the cadence of coronagraph instruments. They are often associated with
  large-scale dimming and coronal waves. The exact nature of these waves
  and the physical link between these different manifestations are not
  yet elucidated. We also discuss what kind of shocks are produced during
  a flare or a CME. Several questions remain unanswered. What is the
  nature of the shocks in the corona (blast-wave or piston-driven?) How
  they are related to Moreton waves seen in Hα? How they are related
  to interplanetary shocks? The last section discusses the origin of
  energetic electrons detected in the corona and in the interplanetary
  medium. "Complex type III-like events," which are detected at
  hectometric wavelengths, high in the corona, and are associated with
  CMEs, appear to originate from electrons that have been accelerated
  lower in the corona and not at the bow shock of CMEs. Similarly,
  impulsive energetic electrons observed in the interplanetary medium
  are not the exclusive result of electron acceleration at the bow shocks
  of CMEs; rather they have a coronal origin.

---------------------------------------------------------
Title: Coronal Observations of CMEs
Authors: Schwenn, R.; Raymond, J. C.; Alexander, D.; Ciaravella, A.;
   Gopalswamy, N.; Howard, R.; Hudson, H.; Kaufmann, P.; Klassen, A.;
   Maia, D.; Munoz-Martinez, G.; Pick, M.; Reiner, M.; Srivastava, N.;
   Tripathi, D.; Vourlidas, A.; Wang, Y. -M.; Zhang, J.
2006cme..book..127S    Altcode:
  CMEs have been observed for over 30 years with a wide variety of
  instruments. It is now possible to derive detailed and quantitative
  information on CME morphology, velocity, acceleration and mass. Flares
  associated with CMEs are observed in X-rays, and several different
  radio signatures are also seen. Optical and UV spectra of CMEs both on
  the disk and at the limb provide velocities along the line of sight
  and diagnostics for temperature, density and composition. From the
  vast quantity of data we attempt to synthesize the current state of
  knowledge of the properties of CMEs, along with some specific observed
  characteristics that illuminate the physical processes occurring during
  CME eruption. These include the common three-part structures of CMEs,
  which is generally attributed to compressed material at the leading
  edge, a low-density magnetic bubble and dense prominence gas. Signatures
  of shock waves are seen, but the location of these shocks relative
  to the other structures and the occurrence rate at the heights where
  Solar Energetic Particles are produced remains controversial. The
  relationships among CMEs, Moreton waves, EIT waves, and EUV dimming
  are also cloudy. The close connection between CMEs and flares suggests
  that magnetic reconnection plays an important role in CME eruption
  and evolution. We discuss the evidence for reconnection in current
  sheets from white-light, X-ray, radio and UV observations. Finally, we
  summarize the requirements for future instrumentation that might answer
  the outstanding questions and the opportunities that new space-based
  and ground-based observatories will provide in the future.

---------------------------------------------------------
Title: Properties of structured coronal mass ejections in solar
    cycle 23
Authors: Cremades, H.; Bothmer, V.; Tripathi, D.
2006AdSpR..38..461C    Altcode:
  The Solar and Heliospheric Observatory has provided to date doubtlessly
  the best dataset of coronal observations ever taken over the course
  of a solar cycle. Structured coronal mass ejections, i.e. events
  with clear white-light fine structures, have been selected from the
  dataset of the large angle spectroscopic coronagraph during the period
  1996 2002. Their source regions in the low corona and photosphere
  have been deduced by analyzing data from the Extreme-ultraviolet
  Imaging Telescope and Michelson Doppler Imager onboard the Solar and
  Heliospheric Observatory and from ground-based Hα measurements. Based
  on this subset of coronal mass ejections, originally compiled to study
  their three-dimensional configuration, we have analyzed the variation
  of their properties during the present solar cycle. These properties
  include latitude and tilt angle of source regions of coronal mass
  ejections, position angle of coronal mass ejections, and deviation
  of coronal mass ejections with respect to their corresponding source
  regions. The results show a pronounced and systematic confinement of
  position angles at equatorial latitudes and equatorward deviations
  during low solar activity. In contrast, fluctuating position angles
  and deviations in all directions were found at times of high solar
  activity. A method to explain the observed deflections is presented.

---------------------------------------------------------
Title: The Pre-CME Sun
Authors: Gopalswamy, N.; Mikić, Z.; Maia, D.; Alexander, D.; Cremades,
   H.; Kaufmann, P.; Tripathi, D.; Wang, Y. -M.
2006cme..book..303G    Altcode:
  The coronal mass ejection (CME) phenomenon occurs in closed magnetic
  field regions on the Sun such as active regions, filament regions,
  transequatorial interconnection regions, and complexes involving a
  combination of these. This chapter describes the current knowledge
  on these closed field structures and how they lead to CMEs. After
  describing the specific magnetic structures observed in the CME source
  region, we compare the substructures of CMEs to what is observed before
  eruption. Evolution of the closed magnetic structures in response to
  various photospheric motions over different time scales (convection,
  differential rotation, meridional circulation) somehow leads to the
  eruption. We describe this pre-eruption evolution and attempt to link
  them to the observed features of CMEs. Small-scale energetic signatures
  in the form of electron acceleration (signified by nonthermal radio
  bursts at metric wavelengths) and plasma heating (observed as compact
  soft X-ray brightening) may be indicative of impending CMEs. We survey
  these pre-eruptive energy releases using observations taken before
  and during the eruption of several CMEs. Finally, we discuss how the
  observations can be converted into useful inputs to numerical models
  that can describe the CME initiation.

---------------------------------------------------------
Title: On the Internal Structures of Coronal Mass Ejections
Authors: Tripathi, D.; Stenborg, G.
2005ESASP.600E.167T    Altcode: 2005dysu.confE.167T; 2005ESPM...11..167T
  No abstract at ADS

---------------------------------------------------------
Title: EUV and coronagraphic observations of coronal mass ejections
Authors: Tripathi, Durgesh
2005PhDT.........1T    Altcode:
  To identify the exact source regions of coronal mass ejections
  (CMEs) and to understand the basic physical mechanisms involved
  in their initiation are amongst the major challenges of modern
  day solar physics. The Extreme-ultraviolet Imgaing Telescope (EIT)
  and Large Angle Spectrometric COronagraph (LASCO) aboard Solar and
  Heliospheric Observatory (SoHO) provides unique opportunity to study
  CMEs from 1.1 to 30 R<SUB>⊙</SUB> since launch in December 1995. This
  thesis provides basic physical properties of EUV post-eruptive arcades
  (PEAs) observed by EIT at 195 Å and their role as tracers of source
  regions of CMEs. A detailed study of a specific EUV PEA event led to
  the discovery of a bright coronal inflow above the PEA. For specific
  PEA events line-of-sight magnetograms are analyzed to study the basic
  mechanism involved in CME initiation. Different varieties of evolutions
  in the photospheric magnetic field was detected during the time of CME
  eruption. We expect that the upcoming missions like STEREO and SOLAR-B
  will work in conjunction, helping us to understand the coupling between
  the photosphere and the corona.

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

---------------------------------------------------------
Title: EUV and coronagraphic observations of coronal mass ejections
Authors: Tripathi, Durgesh Kumar
2005PhDT.......163T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: The basic characteristics of EUV post-eruptive arcades and
    their role as tracers of coronal mass ejection source regions
Authors: Tripathi, D.; Bothmer, V.; Cremades, H.
2004A&A...422..337T    Altcode:
  The Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and
  Heliospheric Observatory (SOHO) spacecraft provides unique observations
  of dynamic processes in the low corona. The EIT 195 Å data taken from
  1997 to the end of 2002 were investigated to study the basic physical
  properties of post-eruptive arcades (PEAs) and their relationship with
  coronal mass ejections (CMEs) as detected by SOHO/LASCO (Large Angle
  Spectrometric Coronagraph). Over the investigated time period, 236 PEA
  events have been identified in total. For each PEA, its EUV lifetime
  as derived from the emission time at 195 Å, its heliographic position
  and length, and its corresponding photospheric source region inferred
  from SOHO/MDI (Michelson Doppler Imager) data has been studied, as well
  as the variation of these parameters over the investigated phase of
  solar cycle 23. An almost one to one correspondence is found between
  EUV PEAs and white-light CMEs. Based on this finding, PEAs can be
  considered as reliable tracers of CME events even without simultaneous
  coronagraph observations. A detailed comparison of the white-light,
  soft X-ray and EUV observation for some of the events shows, that PEAs
  form in the aftermath of CMEs likely in the course of the magnetic
  restructurings taking place at the coronal source sites. The average
  EUV emission life-time for the selected events ranged from 2 to 20
  h, with an average of 7 h. The heliographic length of the PEAs was
  in the range of 2 to 40 degrees, with an average of 15 degrees. The
  length increased by a factor of 3 to 4 in the latitude range of 20
  to 40 degrees in the northern and southern hemispheres, with longer
  PEAs being observed preferentially at higher latitudes. The PEAs were
  located mainly in the activity belts in both hemispheres, with the
  southern hemispheric ones being shifted by about 15 degree in latitude
  further away from the solar equator during 1997-2002. The decrease
  in latitude of the PEA positions was 10 to 15 degrees in the northern
  and southern hemispheres over this period. The axes of the PEAs were
  overlying magnetic polarity inversion lines when traced back to the
  MDI synoptic charts of the photospheric field. The magnetic polarities
  on both sides of the inversion lines agreed with the dominant magnetic
  pattern expected in cycle 23, i.e. being preferentially positive to the
  West of the PEA axes in the North and negative in the South. One third
  (31%) of the PEA events showed reversed polarities. The origin of PEAs
  is found not just in single bipolar regions (BPRs), but also in between
  pairs of neighboring BPRs. <P />Table 1 is available in electronic
  form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5)
  or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/422/337

---------------------------------------------------------
Title: VizieR Online Data Catalog: Solar EUV Post-Eruptive Arcades
    (Tripathi+, 2004)
Authors: Tripathi, D.; Bothmer, V.; Cremades, H.
2004yCat..34220337T    Altcode:
  The Extreme ultraviolet Imaging Telescope (EIT) on board the Solar and
  Heliospheric Observatory (SOHO) spacecraft provides unique observations
  of dynamic processes in the low corona. The EIT 195{AA} data taken from
  1997 to the end of 2002 were investigated to study the basic physical
  properties of post-eruptive arcades (PEAs) and their relationship with
  coronal mass ejections (CMEs) as detected by SOHO/LASCO (Large Angle
  Spectrometric Coronagraph). Over the investigated time period, 236 PEA
  events have been identified in total. For each PEA, its EUV lifetime as
  derived from the emission time at 195{AA}, its heliographic position
  and length, and its corresponding photospheric source region inferred
  from SOHO/MDI (Michelson Doppler Imager) data has been studied, as
  well as the variation of these parameters over the investigated phase
  of solar cycle 23. <P />(1 data file).

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

---------------------------------------------------------
Title: Properties of Structured Coronal Mass Ejections in Solar
    Cycle 23
Authors: Cremades, H.; Bothmer, V.; Tripathi, D.
2004cosp...35.1939C    Altcode: 2004cosp.meet.1939C
  The Solar and Heliospheric Observatory (SOHO) has provided to date the
  best dataset of coronal observations ever taken over the course of
  a solar cycle. Structured CMEs, i. e. events with clear white-light
  fine structures, have been selected from the LASCO (Large Angle
  Spectroscopic Coronagraph) dataset during the period 1996-2002. Their
  source regions (SRs) in the low corona and photosphere have been deduced
  by analyzing data from the EIT (Extreme-Ultraviolet Imaging Telescope)
  and MDI (Michelson Doppler Imager) instruments on board SOHO, and
  from ground-based Hα measurements. Based on this subset of CMEs,
  originally compiled to study the three-dimensional configuration of
  CMEs, we have analyzed the variation of their properties along the
  present solar cycle. These properties include SR latitude, tilt angle
  of CME SRs, CME position angle, and deviation of CMEs with respect to
  their corresponding SRs.

---------------------------------------------------------
Title: Evolution of the photospheric magnetic field in the source
    regions of coronal mass ejections
Authors: Tripathi, D.; Bothmer, V.; Cremades, H.
2004cosp...35.1966T    Altcode: 2004cosp.meet.1966T
  EIT (Extreme ultraviolet Imaging Telescope) and MDI (Michelson Doppler
  Imager) instruments on board SoHO (Solar and Heliospheric Observatory)
  provide an unprecedented opportunity to study the source regions of
  coronal mass ejections (CMEs) in the low corona and photosphere. Eight
  CMEs associated with filament eruptions observed by EIT near disk
  center were studied in detail. In five events new emerging magnetic
  flux occurred in spatial and temporal relationship with the instability
  sites of the filaments. In two cases field changes in nearby active
  regions seem to have triggered the filament eruptions. In one case,
  evidence for flux cancellation was found. The different possible causes
  of the eruptions are discussed in context with the related changes of
  the photospheric field.

---------------------------------------------------------
Title: Determination of the source regions, 3-D structures and
    magnetic field configurations of CMEs at the Sun and in the
    interplanetary medium
Authors: Bothmer, V.; Cremades, H.; Tripathi, D.
2004cosp...35.1976B    Altcode: 2004cosp.meet.1976B
  There are numerous unanswered questions concerning the origin, nature,
  evolution and consequences of coronal mass ejections at the Sun
  and in the interplanetary medium. STEREO will provide the first 3-D
  view of the Sun-Earth system and Solar-B will provide unprecedented
  measurements of the magnetic field structure of their photospheric
  source regions. The two NASA missions, scheduled for launch in 2006,
  will hence provide us with a new view of CMEs. In order to establish
  the scientific goals of these missions, this talk will provide: - A
  brief summary of our current understanding of the origin and evolution
  of CMEs based on the latest results obtained from SOHO, Yohkoh, TRACE,
  ACE and Wind observations. - A basic scheme explaining the 3-D structure
  and near-Sun evolution of CMEs that can be directly proven with STEREO
  and Solar-B. - An outline for joint science operations required to test
  existing models for the onset and evolution of CMEs up to Earth's orbit.

---------------------------------------------------------
Title: Stability Of Triangular Equilibrium Points In The Photo
    Gravitational Restricted Three Body Problem With Poynting-Robertson
    Drag
Authors: Ishwar, B.; Tripathi, D. K.
2004cosp...35...66I    Altcode: 2004cosp.meet...66I
  We have examined the stability of triangular equilibrium points in the
  photogravitational restricted three body problem with Poynting-Robertson
  drag. We consider both primaries as radiating. We have located
  the triangular equilibrium points of the problem, The position
  of triangular equilibrium points are affected by mass reduction
  factor and P-R drag. We have found the characteristic equation of
  the problem. We conclude that triangular equilibrium points remain
  unstable. All photogravitational and classical results of RTBP may be
  verified from this result.

---------------------------------------------------------
Title: 3D Magnetic Field Configuration and Evolution of Coronal
    Mass Ejections
Authors: Cremades, H.; Bothmer, V.; Tripathi, D.
2003EAEJA......852C    Altcode:
  Coronal Mass Ejections (CMEs) are the most energetic transient
  phenomena in the solar atmosphere. The origins of CMEs, their 3D
  structure and internal magnetic field configuration, as well as their
  evolution into interplanetary space are not well understood. Thanks
  to the high resolution telescopes of the SOHO Mission, for the first
  time magnetic fine structures can be resolved within CMEs observed
  close to the Sun. A set of CME events has been identified from a
  detailed investigation of LASCO (Large Angle Spectroscopic Coronagraph)
  observations taken since launch in 1995. This data set comprises those
  cases exhibiting white-light fine structures, from which their magnetic
  field configuration could be deduced. Since the observed white-light
  features are the result of an inherent line-of-sight integration
  projected on the plane of the sky, inferring the three-dimensional
  topology of CMEs is a challenging and complicated task. In order
  to reveal the actual 3D profile of a CME, an approach based on the
  characterization of their respective source region magnetic field
  configuration is addressed. The study indicates that many CMEs are
  comprised either of arcades of magnetic field lines or magnetic
  flux tubes which are trailed by prominence material. The analysis of
  additional coronal and magnetic field observations (EIT, MDI) shows
  that these magnetic structures seem to arise from already existing loop
  systems of much smaller scale that originate in bipolar field regions.

---------------------------------------------------------
Title: A Composite Stellar Model of Geostrophic Flows - Part Two
Authors: Singh, H. P.; Tripathi, D. D.; Singh, S. C.; Mishra, R. B.
1988Ap&SS.143...63S    Altcode:
  This paper contains a geometric study and solutions of the
  electromagneto-geostrophic flows, and spatially the geometrical
  treatments of magnetic field lines are discussed.

---------------------------------------------------------
Title: A Composite Stellar Model of Magnetofluid Continuum via
    Anholonomic Descriptions
Authors: Singh, H. P.; Tripathi, D. D.; Mishra, R. B.
1988Ap&SS.141..415S    Altcode:
  A theoretical analysis based on the equations of magnetofluid-dynamics
  is undertaken, in order to completely classify the geometry of the
  motion admitted by this pattern.

---------------------------------------------------------
Title: A Composite Stellar Model of Geostrophic Flows - Part One
Authors: Singh, H. P.; Tripathi, D. D.; Singh, S. C.; Mishra, R. B.
1987Ap&SS.139..413S    Altcode:
  This paper has been presented the geometric study and solutions of
  the electromagnetogeostrophic flows, and spatially the geometry of
  magnetic and current lines are discussed.

---------------------------------------------------------
Title: Rotational circulation-preserving magnetogeostrophic flows.
Authors: Singh, H. P.; Tripathi, D. D.; Mishra, R. B.
1987Ap&SS.138..315S    Altcode:
  It has been shown that the only steady, inviscid, magnetogeostrophic
  rotational circulation-preverving motion whose magnetic field line
  pattern is that of the irrotational motion is a complex-lamellar motion
  whose magnetic field magnitude bears a constant value on a magnetic
  field line.

---------------------------------------------------------
Title: The geometry of magnetic fieldlines in magnetogeostrophic
    flows.
Authors: Singh, S. N.; Singh, B. P.; Tripathi, D. D.
1987Ap&SS.137...23S    Altcode:
  It is proved that the only circulation preserving magnetogeostrophic
  flows whose current density is lamellar, and bears a constant on a
  current density vector have (1) a plane motion of constant current
  density (on which certain unsteady potential motions may be superposed)
  and (2) a particular circular helical motion.

---------------------------------------------------------
Title: Cross sections for ionization of ions by electron impact.
Authors: Tripathi, D. N.; Rai, D. K.
1971JQSRT..11.1665T    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Electronic ionization and recombination coefficients for
    atmospheric molecules-I. Electron impact ionization cross-sections.
Authors: Sharma, V. N.; Tripathi, D. N.; Rai, D. K.
1971JQSRT..11..283S    Altcode:
  No abstract at ADS