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Author name code: gosain
ADS astronomy entries on 2022-09-14
author:"Gosain, Sanjay"

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Title: Multi-height Measurements Of The Solar Vector Magnetic Field:
    A White Paper Submitted To The Decadal Survey For Solar And Space
    Physics (Heliophysics) 2024-2033
Authors: Bertello, L.; Arge, N.; De Wijn, A. G.; Gosain, S.; Henney,
   C.; Leka, K. D.; Linker, J.; Liu, Y.; Luhmann, J.; Macniece, P. J.;
   Petrie, G.; Pevtsov, A.; Pevtsov, A. A.
2022arXiv220904453B    Altcode:
  This white paper advocates the importance of multi-height measurements
  of the vector magnetic field in the solar atmosphere. As briefly
  described in this document, these measurements are critical for
  addressing some of the most fundamental questions in solar and
  heliospheric physics today, including: (1) What is the origin
  of the magnetic field observed in the solar atmosphere? (2) What
  is the coupling between magnetic fields and flows throughout the
  solar atmosphere? Accurate measurements of the photospheric and
  chromospheric three-dimensional magnetic fields are required for
  a precise determination of the emergence and evolution of active
  regions. Newly emerging magnetic flux in pre-existing magnetic regions
  causes an increase in the topological complexity of the magnetic field,
  which leads to flares and coronal mass ejections. Measurements of the
  vector magnetic field constitute also the primary product for space
  weather operations, research, and modeling of the solar atmosphere
  and heliosphere. The proposed next generation Ground-based solar
  Observing Network Group (ngGONG), a coordinated system of multi-platform
  instruments, will address these questions and provide large datasets
  for statistical investigations of solar feature behavior and evolution
  and continuity in monitoring for space-weather focused endeavors
  both research and operational. It will also enable sun-as-a-star
  investigations, crucial as we look toward understanding other
  planet-hosting stars.

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Title: A Compact Full-disk Solar Magnetograph based on miniaturization
    of GONG instrument
Authors: Gosain, Sanjay; Harvey, Jack; Martinez-Pillet, Valentin;
   Woods, Tom; Hill, Frank
2022arXiv220707728G    Altcode:
  Designing compact instruments is the key for the scientific exploration
  by smaller spacecrafts such as cubesats or by deep space missions. Such
  missions require compact instrument designs to have minimal instrument
  mass. Here we present a proof of concept for miniaturization of the
  Global Oscillation Network Group GONG instrument. GONG instrument
  routinely obtains solar full disk Doppler and magnetic field maps of
  the solar photosphere using Ni 676 nm absorption line. A key concept
  for miniaturization of GONG optical design is to replace the bulky
  Lyot filter with a narrow-band interference filter and reduce the
  length of feed telescope. We present validation of the concept via
  numerical modeling as well as by proof of concept observations.

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Title: Estimation of projection effects in the solar polar magnetic
    flux measurements from an ecliptic view.
Authors: Gosain, Sanjay; Uitenbroek, Han
2021AGUFMSH34D..04G    Altcode:
  The distribution and evolution of the magnetic field at the solar poles
  through a solar cycle is an important parameter in understanding the
  solar dynamo. The accurate observations of the polar magnetic flux is
  very challenging from the ecliptic view, mainly due to (a) geometric
  foreshortening which limits the spatial resolution, and (b) the oblique
  view of predominantly vertical magnetic flux elements, which presents
  rather small line-of-sight component of the magnetic field towards
  the ecliptic. Due to these effects the polar magnetic flux is poorly
  measured. Depending upon the measurement technique, longitudinal versus
  full vector field measurement, where the latter is extremely sesnitive
  to the SNR and azimuth disamiguation problem, the polar magnetic flux
  measurements could be underestimated or overestimated. To estimate the
  extent of systematic errors in magetic flux measurements at the solar
  poles due to aforementioned projection effects we use MHD simulations of
  quiet sun network as a reference solar atmosphere. Using the numerical
  model of the solar atmosphere we simulate the observations from the
  ecliptic as well as from out-of-ecliptic vantage points, such as from
  a solar polar orbit at various heliographic latitudes. Using these
  simulated observations we make an assessment of the systematic errors
  in our measurements of the magnetic flux due to projection effects
  and the extent of under- or over estimation.

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Title: The Multiview Observatory for Solar Terrestrial Science (MOST)
Authors: Gopalswamy, Nat; Kucera, Therese; Leake, James; MacDowall,
   Robert; Wilson, Lynn; Kanekal, Shrikanth; Shih, Albert; Christe,
   Steven; Gong, Qian; Viall, Nicholeen; Tadikonda, Sivakumar; Fung,
   Shing; Yashiro, Seiji; Makela, Pertti; Golub, Leon; DeLuca, Edward;
   Reeves, Katharine; Seaton, Daniel; Savage, Sabrina; Winebarger, Amy;
   DeForest, Craig; Desai, Mihir; Bastian, Tim; Lazio, Joseph; Jensen,
   P. E., C. S. P., Elizabeth; Manchester, Ward; Wood, Brian; Kooi,
   Jason; Wexler, David; Bale, Stuart; Krucker, Sam; Hurlburt, Neal;
   DeRosa, Marc; Pevtsov, Alexei; Tripathy, Sushanta; Jain, Kiran;
   Gosain, Sanjay; Petrie, Gordon; Kholikov, Shukirjon; Zhao, Junwei;
   Scherrer, Philip; Woods, Thomas; Chamberlin, Philip; Kenny, Megan
2021AGUFMSH12A..07G    Altcode:
  The Multiview Observatory for Solar Terrestrial Science (MOST) is a
  comprehensive mission concept targeting the magnetic coupling between
  the solar interior and the heliosphere. The wide-ranging imagery and
  time series data from MOST will help understand the solar drivers and
  the heliospheric responses as a system, discerning and tracking 3D
  magnetic field structures, both transient and quiescent in the inner
  heliosphere. MOST will have seven remote-sensing and three in-situ
  instruments: (1) Magnetic and Doppler Imager (MaDI) to investigate
  surface and subsurface magnetism by exploiting the combination of
  helioseismic and magnetic-field measurements in the photosphere; (2)
  Inner Coronal Imager in EUV (ICIE) to study large-scale structures
  such as active regions, coronal holes and eruptive structures by
  capturing the magnetic connection between the photosphere and the
  corona to about 3 solar radii; (3) Hard X-ray Imager (HXI) to image
  the non-thermal flare structure; (4) White-light Coronagraph (WCOR) to
  seamlessly study transient and quiescent large-scale coronal structures
  extending from the ICIE field of view (FOV); (5) Faraday Effect
  Tracker of Coronal and Heliospheric structures (FETCH), a novel radio
  package to determine the magnetic field structure and plasma column
  density, and their evolution within 0.5 au; (6) Heliospheric Imager
  with Polarization (HIP) to track solar features beyond the WCOR FOV,
  study their impact on Earth, and provide important context for FETCH;
  (7) Radio and Plasma Wave instrument (M/WAVES) to study electron beams
  and shocks propagating into the heliosphere via passive radio emission;
  (8) Solar High-energy Ion Velocity Analyzer (SHIVA) to determine spectra
  of electrons, and ions from H to Fe at multiple spatial locations
  and use energetic particles as tracers of magnetic connectivity; (9)
  Solar Wind Magnetometer (MAG) to characterize magnetic structures at
  1 au; (10) Solar Wind Plasma Instrument (SWPI) to characterize plasma
  structures at 1 au. MOST will have two large spacecraft with identical
  payloads deployed at L4 and L5 and two smaller spacecraft ahead of L4
  and behind L5 to carry additional FETCH elements. MOST will build upon
  SOHO and STEREO achievements to expand the multiview observational
  approach into the first half of the 21st Century.

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Title: The Solaris Solar Polar Mission: Exploring one of the last
    Unexplored Regions of the Solar System
Authors: Hassler, D.; Newmark, J. S.; Gibson, S. E.; Duncan, N. A.;
   Gosain, S.; Harvey, J. W.; Wuelser, J. P.; Woods, T. N.
2020AGUFMSH0110003H    Altcode:
  The solar poles are one of the last unexplored regions of the solar
  system. Although Ulysses flew over the poles in the 1990s, it did
  not have remote sensing instruments onboard to probe the Sun's polar
  magnetic field or surface/sub-surface flows. I will discuss Solaris,
  a proposed Solar Polar MIDEX mission to fly over the solar poles at 75
  degrees inclination to address key outstanding, breakthrough problems
  in solar physics, & fill holes in our scientific understanding
  that will not be addressed by current or planned future missions. Such
  a small, focused, "paradigm-breaking" mission is achievable now with
  existing launchers and technology, & is enabled by miniaturized
  instrument technology such as the Compact Doppler Magnetograph (CDM),
  developed for Solaris to provide magnetic field & Doppler velocity
  measurements in a small (15kg) package. Solaris will also provide
  enabling observations for space weather research & stimulate future
  research through new unanticipated discoveries.

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Title: The Solaris Solar Polar Mission
Authors: Hassler, Donald M.; Newmark, Jeff; Gibson, Sarah; Harra,
   Louise; Appourchaux, Thierry; Auchere, Frederic; Berghmans, David;
   Colaninno, Robin; Fineschi, Silvano; Gizon, Laurent; Gosain, Sanjay;
   Hoeksema, Todd; Kintziger, Christian; Linker, John; Rochus, Pierre;
   Schou, Jesper; Viall, Nicholeen; West, Matt; Woods, Tom; Wuelser,
   Jean-Pierre
2020EGUGA..2217703H    Altcode:
  The solar poles are one of the last unexplored regions of the solar
  system. Although Ulysses flew over the poles in the 1990s, it did
  not have remote sensing instruments onboard to probe the Sun's polar
  magnetic field or surface/sub-surface flows.We will discuss Solaris,
  a proposed Solar Polar MIDEX mission to revolutionize our understanding
  of the Sun by addressing fundamental questions that can only be answered
  from a polar vantage point. Solaris uses a Jupiter gravity assist to
  escape the ecliptic plane and fly over both poles of the Sun to >75
  deg. inclination, obtaining the first high-latitude, multi-month-long,
  continuous remote-sensing solar observations. Solaris will address key
  outstanding, breakthrough problems in solar physics and fill holes in
  our scientific understanding that will not be addressed by current
  missions.With focused science and a simple, elegant mission design,
  Solaris will also provide enabling observations for space weather
  research (e.g. polar view of CMEs), and stimulate future research
  through new unanticipated discoveries.

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Title: Acceleration of Coronal Mass Ejection Plasma in the Low Corona
    as Measured by the Citizen CATE Experiment
Authors: Penn, Matthew J.; Baer, Robert; Walter, Donald; Pierce,
   Michael; Gelderman, Richard; Ursache, Andrei; Elmore, David; Mitchell,
   Adrianna; Kovac, Sarah; Hare, Honor; McKay, Myles; Jensen, Logan;
   Watson, Zachary; Conley, Mike; Powers, Lynn; Lazarova, Marianna;
   Wright, Joseph; Young, David; Isberner, Fred; Hart, C. Alexandra;
   Sheeley, N. R., Jr.; Penn, Debbie; Allen-Penn, Kate; Alder, Bruce;
   Alder, Ryan; Hall-Conley, Geri; Gerdes, David; Weber, Katherine;
   Johnson, Jeffrey; Matzek, Gerald; Somes, Steven; Sobnosky, Rob;
   McGowen, Robert; Meo, Michael; Proctor, Damani; Wessinger, Charlie;
   Schilling, Jeannine; Kerr, Jay; Beltzer-Sweeney, Alexander; Falatoun,
   Alex; Higgins, David; Boyce, Grady; Hettick, Jared; Blanco, Philip;
   Dixon, Scott; Ardebilianfard, Sepehr; Boyce, Pat; Lighthill, Richard;
   Lighthill, Denese; Anderson, David; Anderson, Mine; Schad, Thomas;
   Smith, Sonna; Jensen, Declan; Allen, Anthony; Smith, Donavan; Brandon,
   Gage; Earp, Joe; Earp, Jane; Blair, Bob; Claver, Chuck F.; Claver,
   Jennifer A.; Claver, Ryan H.; Hoops, Danielle; Rivera, Esteban;
   Gibson, Llanee; Hiner, Martin; Lann, Rein; Miller, Shaedyn; Briggs,
   Burton; Davis, Karan; Jackson, Brian; Kautzsch, Kaleb; Sandidge,
   Wesley; Lucas, Russell; Gregg, Duane; Kamenetzky, Julia; Rivera,
   Tiffany; Shaw, Joe; Scherrer, Bryan; Sandbak, Dylan; McFate, Richard;
   Harris, Wilson; Brasier, Zachery; McNeil, Stephen; Jensen, Jack;
   Jensen, Makai; Moore, Mason; Temple, Alexandria; Vanderhorst, Thomas;
   Kautz, Richard; Bellorado, Orion; Jenkins, LaVor R.; Pantuso, Corey;
   Carey, Marley; Byrnes, Josh; Scholtens, Kyle; Web, Julian; Baker,
   Brain; Barngrover, Katie; Hathaway, Drew; Smith, Kallen; Chandler,
   Kellyn; Hinkle, Lydia; Chandler, Ione; Gisler, Galen; Benner, Jack;
   Mas, Madison; Rogers, Maya; Moore, Prescott; Pelofske, Elijah;
   Gulley, Stephen; Short, Beth; Crooker, Isabel; Hammock, Jennifer;
   Cardenas, Katsina; Cardenas, Kateri; Wellman, Jennifer; Roy, Mark;
   Meyer, Joe; Brough, Jalynne; Brough, Kameron; Nelson, Tim; Nelson,
   Zack; Russell, Caleb; Bautz, Theresa; Weitzel, Eric; Team; Wistisen,
   Michele; Aagard, Shae; Whipps, Zachary; Neuroth, Logan; Poste, Dawson;
   Worthen, Connor; Gosain, Sanjay; Steward, Mark; Gosain, Vanshita;
   Gosain, Ruchi; Jorgensen, Janet; Doucette, Eleanor; Doucette, Reba;
   Iwen, Elliott; Cochran, Alexus; Stith, James; Scribner, Doug; Kenney,
   Austen; Pisciotti, Kolby; Pease, Irene; Cynamon, Samuel; Cynamon,
   Charles; Cynamon, Dawn; Tolbert, Bart; Dupree, Jean A.; Weremeichik,
   Jeremy; Pindell, Nathan; Stives, Kristen; Simacek, Thomas K.; Simacek,
   Yolanta G.; Simacek, Anne L.; Boeck, Wayne; Boeck, Andreea; Ryan,
   Austin; Wierzorec, Gabriel; Klebe, Dimitri; Costanza, Bryan; Cerny,
   Arnie; Schmale, Trevor; Hoffman, Tessa; Streeter, Sam; Erickson,
   Jack; McClellan, Michele; Erickson, Ella; Brettell, Brynn; Shoffner,
   Savannah; McClellan, Emilie; VanVoorhis, Julie; Bramhall, Cole; Stelly,
   Daniel; Bee, Bentley; Acevedo, Bruno; Kroeger, Madison; Trumpenski,
   Ben; Sump, Nolan; Brook, Liam; Ernzen, Jagert; Lewis, Jessica;
   Maderak, Ryan; Kennedy, Charles; Dembinski, David; Wright, Rita;
   Foster, Michael; Ahmadbasir, Mohammad; Laycox, Monty; Foster, James;
   Orr, Ethan; Staab, Ashley; Speck, Angela; Baldridge, Sean; Kegley,
   Lucy; Bavlnka, Jordan; Ballew, Thomas; Callen, Bruce; Ojakangas,
   Gregory; Bremer, Mark; Angliongto, Maryanne; Redecker, Mark; Bremer,
   Chris; Hill, Peggy; Rodgers, Michael; Duncan, Jordan; Fincher, Sam;
   Nielsen, Ben; Hasler, Samantha; Shivelbine, Taylor; Howard, Tyler;
   Midden, Chris; Patrick, Sean; Glenn, Kerry; Mandrell, Chris; Dawson,
   Kyle; Cortez, Margaret; Levsky, Alyssa; Gallaba, Dinuka; Perrone,
   Mason; Taylor, Jasmyn; Yanamandra-Fisher, Padma A.; Harper, Howard;
   Adams, Lindsay; Springer, Michaela; Menard, BillyJoe; Boggs, Dylan;
   Lynch, Caitlin; Watson, Jacob; York, Andi; Matthews, David; Brown,
   Kiley; Garrison, Dylan; Mangin, Jonathan; Mangin, Isaac; Birriel,
   Jennifer; Birriel, Ignacio; Yess, Capp; Anderson, Jesse; Caudill,
   Ethan; Smith, Allyn; Buckner, Spencer; Longhurst, Russ; Fagan, Ben;
   Nations, Christian; DiMatties, Jeffrey; Thompson, Patricia; Garrison,
   David; Garrison, Thomas; Garrison, William; Kidd, Mary; Baker, Maria;
   Ledford, Mary-Beth; Winebarger, Amy; Freed, Michael; Church, Morgyn;
   Dickens, Jim; Anderson, Bob; Smith, Ned; Dorsey, Lynne; Justice, Doug;
   Zavala, Daniel; Stockbridge, Zach; Brittain, Sean; Jensen, Stanley;
   Leiendecker, Harrison; Thompson, Erin; Deady, Michelle; Quinn-Hughes,
   Kelly; Slimmer, David; Granger, Valerie; LaRoche, Michael; Hill
   LaRoche, Serena; Manspeaker, Rachel; Nguyen, Peter; Smith, Daniel;
   Payne, Jim; Zissett, Jerry; Roberts, Arianna M.; Roberts, Gabrielle
   W.; Roberts, Harrison; Riddle, Amy; Ursache, Corina; Ursache, Elena
2020PASP..132a4201P    Altcode:
  The citizen Continental-America Telescopic Eclipse (CATE) Experiment
  was a new type of citizen science experiment designed to capture a time
  sequence of white-light coronal observations during totality from 17:16
  to 18:48 UT on 2017 August 21. Using identical instruments the CATE
  group imaged the inner corona from 1 to 2.1 RSun with 1.″43 pixels
  at a cadence of 2.1 s. A slow coronal mass ejection (CME) started on
  the SW limb of the Sun before the total eclipse began. An analysis
  of CATE data from 17:22 to 17:39 UT maps the spatial distribution of
  coronal flow velocities from about 1.2 to 2.1 RSun, and shows the CME
  material accelerates from about 0 to 200 km s<SUP>-1</SUP> across this
  part of the corona. This CME is observed by LASCO C2 at 3.1-13 RSun
  with a constant speed of 254 km s<SUP>-1</SUP>. The CATE and LASCO
  observations are not fit by either constant acceleration nor spatially
  uniform velocity change, and so the CME acceleration mechanism must
  produce variable acceleration in this region of the corona.

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Title: Kinetic Helicity and Lifetime of Activity Complexes During
    Solar Cycle 24
Authors: Komm, R.; Gosain, S.
2019ApJ...887..192K    Altcode:
  We study magnetic features on the solar surface that exist for
  several rotations during solar cycle 24. To identify them, we average
  synoptic maps over a range in latitude and stack the resulting
  longitudinal strips in time. We use synoptic maps of magnetograms
  obtained with the NSO/Synoptic Optical Long-term Investigations of
  the Sun instrument and create synoptic maps of the kinetic helicity
  of subsurface flows integrated over 2.0-7.1 Mm based on Solar
  Dynamics Observatory/Helioseismic and Magnetic Imager Dopplergrams. To
  distinguish between active and quiet regions, we sort the grid points of
  the synoptic maps by their activity level and divide the data into four
  subsets with 25% of activity each and into two subsets with the highest
  or lowest 12.5% of activity values. The kinetic helicity of these
  six subsets follows the hemispheric helicity rule with, on average,
  positive values in the southern and negative values in the northern
  hemisphere. However, the helicity of the subset with the highest
  activity is about four times higher than that of the other subsets,
  and the mid-quartile subsets show the weakest hemispheric helicity
  rule. We define the lifetime of complexes in each subset and find
  that for the high-activity subset, the amplitude of magnetic activity
  and kinetic helicity increases almost linearly with the lifetime of
  complexes. The distribution of flares closely resembles that of the
  high-activity subset. The flare-productive locations in long-lived
  complexes produce, on average, the same number of flares as those of
  short-lived complexes. However, long-lived complexes have a higher
  fractional number of these locations than the short-lived complexes
  and thus produce more flares not just because they live longer.

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Title: ngGONG: The Next Generation GONG - A New Solar Synoptic
    Observational Network
Authors: Hill, Frank; Hammel, Heidi; Martinez-Pillet, Valentin; de
   Wijn, A.; Gosain, S.; Burkepile, J.; Henney, C. J.; McAteer, J.; Bain,
   H. M.; Manchester, W.; Lin, H.; Roth, M.; Ichimoto, K.; Suematsu, Y.
2019BAAS...51g..74H    Altcode: 2019astro2020U..74H
  The white paper describes a next-generation GONG, a ground-based
  geographically distributed network of instrumentation to continually
  observe the Sun. This would provide data for solar magnetic field
  research and space weather forecasting, and would extend the time
  coverage of helioseismology.

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Title: Spectral Magnetic Helicity of Solar Active Regions between
    2006 and 2017
Authors: Gosain, Sanjay; Brandenburg, Axel
2019ApJ...882...80G    Altcode: 2019arXiv190211273G
  We compute magnetic helicity and energy spectra from about 2485 patches
  of about 100 Mm side length on the solar surface using data from
  Hinode during 2006-2017. An extensive database is assembled where we
  list the magnetic energy and helicity, large- and small-scale magnetic
  helicity, mean current helicity density, fractional magnetic helicity,
  and correlation length along with the Hinode map identification number
  (MapID), as well as the Carrington latitude and longitude for each
  MapID. While there are departures from the hemispheric sign rule
  for magnetic and current helicities, the weak trend reported here
  is in agreement with the previous results. This is argued to be a
  physical effect associated with the dominance of individual active
  regions that contribute more strongly in the better-resolved Hinode
  maps. In comparison with earlier work, the typical correlation length
  is found to be 6-8 {Mm}, while the length scale relating the magnetic
  and current helicities to each other is around 1.4 {Mm}.

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Title: Fast Inversion of Solar Ca II Spectra in Non-local
    Thermodynamic Equilibrium
Authors: Beck, C.; Gosain, S.; Kiessner, C.
2019ApJ...878...60B    Altcode: 2019arXiv190411843B
  Present-day solar imaging spectrometers typically yield a few hundred
  million spectra in one hour of observing time. This number will increase
  by an order of magnitude for future instruments with larger 4k ×
  4k sensors, such as those planned to be used for the upcoming Daniel
  K. Inouye Solar Telescope. A fast quantitative analysis of such huge
  data volumes can be done by comparing the observations to an archive of
  pre-calculated synthetic spectra to infer the thermodynamic properties
  of the atmosphere. To analyze intensity spectra of the Ca II IR line at
  854 nm in the solar atmosphere, we generated an archive with 2,000,000
  spectra under the assumption of non-local thermodynamic equilibrium
  (NLTE) with the NICOLE code. We tested its performance by inverting 60
  spectral scans of Ca II IR at 854 nm in the magnetically quiet Sun with
  700,000 profiles each. Based on the inversion results obtained using
  the full archive, we constructed a smaller archive by keeping only
  the 70,000 archive profiles that were actually used. We can reproduce
  the observed intensity spectra to within a few percent using either
  the full or the small archive. For spectra with 30 wavelength points,
  this NLTE inversion approach takes 0.02 (0.35) s per profile to obtain a
  temperature stratification when using the small (full) archive, i.e.,
  it can invert a single spectral scan in about 4 (68) hr. The code
  is able to simultaneously deal with an arbitrary number of spectral
  lines. This makes it a promising tool for deriving thermodynamic
  properties of the solar atmosphere from current or future solar
  high-resolution observations of photospheric and chromospheric lines.

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Title: Long-Lived Activity Complexes, their Kinetic Helicity,
    Lifetime, and Flare Activity
Authors: Komm, Rudolf W.; Gosain, Sanjay
2019shin.confE..53K    Altcode:
  We study long-lived activity complexes using stackplots of magnetic
  activity derived from NSO/SOLIS synoptic magnetograms. We focus on
  the kinetic helicity below the surface determined with ring-diagram
  analysis applied to full-disk Dopplergrams from SDO/HMI during
  Solar Cycle 24. The kinetic helicity of activity complexes follows
  the hemispheric helicity rule with mainly positive values in the
  southern hemisphere and negative ones in the northern hemisphere. To
  distinguish between active and quiet regions, we divide the data into
  subsets with high and low levels of activity and create stackplots of
  surface magnetic activity and subsurface kinetic helicity for each
  subset. The distribution of flares in a stackplot resembles closely
  that of the high-activity subset. The flare-productive locations in
  long-lived complexes produce, on average, the same number of flares
  as those of short-lived ones. However, long-lived complexes have a
  larger number of these locations and thus a higher flare-production
  rate than short-lived ones. We will present the latest results.

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Title: Synoptic Studies of the Sun as a Key to Understanding Stellar
    Astrospheres
Authors: Martinez Pillet, Valentin; Hill, Frank; Hammel, Heidi B.;
   de Wijn, Alfred G.; Gosain, Sanjay; Burkepile, Joan; Henney, Carl;
   McAteer, R. T. James; Bain, Hazel; Manchester, Ward; Lin, Haosheng;
   Roth, Markus; Ichimoto, Kiyoshi; Suematsu, Yoshinori
2019BAAS...51c.110M    Altcode: 2019astro2020T.110M; 2019arXiv190306944M
  Ground-based solar observations provide key contextual data (i.e., the
  "big picture") to produce a complete description of the only astrosphere
  we can study in situ: our Sun's heliosphere. This white paper outlines
  the current paradigm for ground-based solar synoptic observations,
  and indicates those areas that will benefit from focused attention.

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Title: Kinetic and Current Helicity of Long-Lived Activity Complexes
    During Solar Cycle 24
Authors: Komm, Rudolf; Gosain, Sanjay
2018csc..confE...6K    Altcode:
  We study long-lived activity complexes during Solar Cycle 24. We focus
  on the kinetic helicity below the surface determined with ring-diagram
  analysis applied to full-disk Dopplergrams from SDO/HMI. In addition,
  we study the current helicity at the solar surface of these activity
  complexes determined from synoptic vector magnetograms. Current and
  kinetic helicity of activity complexes follow the hemispheric helicity
  rule with mainly positive values in the southern hemisphere and negative
  ones in the northern hemisphere. The locations with the dominant sign of
  kinetic helicity are more organized than those of secondary sign even
  if they are not part of an activity complex, while locations with the
  secondary sign are more fragmented. We will present the latest results.

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Title: Design of a next generation synoptic solar observing network:
    solar physics research integrated network group (SPRING)
Authors: Gosain, Sanjay; Roth, Markus; Hill, Frank; Pevtsov, Alexei;
   Martinez Pillet, Valentin; Thompson, Michael J.
2018SPIE10702E..4HG    Altcode:
  Long-term synoptic observations of the Sun in different wavelength
  regions are essential to understand its secular behavior. Such
  observations have proven very important for discovery of 11 year
  solar activity cycle, 22 year magnetic cycle, polar field reversals,
  Hale's polarity law, Joy's law, that helped Babcock and Leighton
  to propose famous solar dynamo model. In more recent decades, the
  societal impact of the secular changes in Sun's output has been felt in
  terms of solar inputs to terrestrial climate-change and space-weather
  hazards. Further, it has been realized that to better understand the
  activity phenomena such as flares and coronal mass ejections (CMEs)
  one needs synoptic observations in multiple spectral lines to enable
  tomographic inference of physical parameters. Currently, there are
  both space and ground based synoptic observatories. However, given
  the requirements for the long-term stability and reliability of such
  synoptic datasets, ground-based facilities are more preferable. Also,
  the ground based observatories are easy to maintain or upgrade while
  detailed and frequent calibrations are easily possible. The only
  ground-based facility that currently provides full-disk velocity and
  magnetic field maps of the Sun around the clock and at good cadence,
  is the Global Oscillations Network Group (GONG) network of National
  Solar Observatory (NSO) which is operational since the mid 90s. Due
  to its aging instrumentation, operating for nearly three decades, and
  new requirements to obtain multiwavelength observations, a need is felt
  in the solar community to build a next generation synoptic observatory
  network. A group of international observatories have come together under
  the auspices of SOLARNET program, funded by European Union (EU), to
  carryout a preliminary design study of such a synoptic solar observing
  facility called "SPRING", which stands for Solar Physics Research
  Integrated Network Group. In this article we will present concept of
  SPRING and the optical design concept of its major instruments.ts.

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Title: Synoptic Magnetic Fields Measurements of the Solar Chromosphere
    from SOLIS/VSM at NSO
Authors: Gosain, Sanjay; SOLIS Team
2018IAUS..340...91G    Altcode:
  Full disk magnetic field measurements of the photosphere and
  chromosphere have been performed at National Solar Observatory (NSO),
  USA for many decades. Here we briefly describe recent upgrades made to
  this synoptic observing program. In particular, we present the full
  Stokes polarimetry observations made using the chromospheric Ca II
  854.2 nm spectral line. These new observations have the potential to
  probe vector nature of magnetic field in the chromosphere above the
  active regions and provide improved estimates of magnetic free-energy,
  which is released during flares and coronal mass ejections (CMEs). We
  emphasize that these observations could improve estimates of polar
  fields, as compared to photospheric observations, due to magnetic
  field expansion in higher layers and perspective effect near the
  polar regions. The global coronal potential field models and solar
  wind speed estimates depend critically on polar field measurements.

---------------------------------------------------------
Title: High-resolution Observations of Hα Spectra with a Subtractive
    Double Pass
Authors: Beck, C.; Rezaei, R.; Choudhary, D. P.; Gosain, S.;
   Tritschler, A.; Louis, R. E.
2018SoPh..293...36B    Altcode: 2017arXiv171207077B
  High-resolution imaging spectroscopy in solar physics has relied on
  Fabry-Pérot interferometers (FPIs) in recent years. FPI systems,
  however, become technically challenging and expensive for telescopes
  larger than the 1 m class. A conventional slit spectrograph with a
  diffraction-limited performance over a large field of view (FOV) can
  be built at much lower cost and effort. It can be converted into an
  imaging spectro(polari)meter using the concept of a subtractive double
  pass (SDP). We demonstrate that an SDP system can reach a similar
  performance as FPI-based systems with a high spatial and moderate
  spectral resolution across a FOV of 100<SUP>″</SUP>×100<SUP>″</SUP>
  with a spectral coverage of 1 nm. We use Hα spectra taken with an SDP
  system at the Dunn Solar Telescope and complementary full-disc data to
  infer the properties of small-scale superpenumbral filaments. We find
  that the majority of all filaments end in patches of opposite-polarity
  fields. The internal fine-structure in the line-core intensity of Hα
  at spatial scales of about 0.″5 exceeds that in other parameters
  such as the line width, indicating small-scale opacity effects in a
  larger-scale structure with common properties. We conclude that SDP
  systems in combination with (multi-conjugate) adaptive optics are a
  valid alternative to FPI systems when high spatial resolution and a
  large FOV are required. They can also reach a cadence that is comparable
  to that of FPI systems, while providing a much larger spectral range
  and a simultaneous multi-line capability.

---------------------------------------------------------
Title: Measurements of Photospheric and Chromospheric Magnetic Fields
Authors: Lagg, Andreas; Lites, Bruce; Harvey, Jack; Gosain, Sanjay;
   Centeno, Rebecca
2018smf..book...37L    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Search for a Signature of Twist-removal in the Magnetic Field
    of Sunspots in Relation with Major Flares
Authors: Burtseva, Olga; Gosain, Sanjay; Pevtsov, Alexei A.
2017ApJ...849..103B    Altcode: 2017arXiv171102166B
  We investigate the restructuring of the magnetic field in sunspots
  associated with two flares: the X6.5 flare on 2006 December 6 and the
  X2.2 flare on 2011 February 15. The observed changes were evaluated
  with respect to the so-called twist-removal model, in which helicity
  (twist) is removed from the corona as the result of an eruption. Since
  no vector magnetograms were available for the X6.5 flare, we applied the
  azimuthal symmetry approach to line-of-sight magnetograms to reconstruct
  the pseudo-vector magnetic field and investigate the changes in average
  twist and inclination of magnetic field in the sunspot around the
  time of the flare. For the X2.2 flare, results from the full vector
  magnetograms were compared with the pseudo-vector field data. For
  both flares, the data show changes consistent with the twist-removal
  scenario. We also evaluate the validity of the azimuthal symmetry
  approach on simple isolated round sunspots. In general, the derivations
  based on the azimuthal symmetry approach agree with true-vector field
  data though we find that even for symmetric sunspots the distribution of
  the magnetic field may deviate from an axially symmetric distribution.

---------------------------------------------------------
Title: Measurements of Photospheric and Chromospheric Magnetic Fields
Authors: Lagg, Andreas; Lites, Bruce; Harvey, Jack; Gosain, Sanjay;
   Centeno, Rebecca
2017SSRv..210...37L    Altcode: 2015arXiv151006865L; 2015SSRv..tmp..115L
  The Sun is replete with magnetic fields, with sunspots, pores
  and plage regions being their most prominent representatives on
  the solar surface. But even far away from these active regions,
  magnetic fields are ubiquitous. To a large extent, their importance
  for the thermodynamics in the solar photosphere is determined by the
  total magnetic flux. Whereas in low-flux quiet Sun regions, magnetic
  structures are shuffled around by the motion of granules, the high-flux
  areas like sunspots or pores effectively suppress convection, leading
  to a temperature decrease of up to 3000 K. The importance of magnetic
  fields to the conditions in higher atmospheric layers, the chromosphere
  and corona, is indisputable. Magnetic fields in both active and
  quiet regions are the main coupling agent between the outer layers
  of the solar atmosphere, and are therefore not only involved in the
  structuring of these layers, but also for the transport of energy from
  the solar surface through the corona to the interplanetary space. <P
  />Consequently, inference of magnetic fields in the photosphere, and
  especially in the chromosphere, is crucial to deepen our understanding
  not only for solar phenomena such as chromospheric and coronal
  heating, flares or coronal mass ejections, but also for fundamental
  physical topics like dynamo theory or atomic physics. In this review,
  we present an overview of significant advances during the last decades
  in measurement techniques, analysis methods, and the availability of
  observatories, together with some selected results. We discuss the
  problems of determining magnetic fields at smallest spatial scales,
  connected with increasing demands on polarimetric sensitivity and
  temporal resolution, and highlight some promising future developments
  for their solution.

---------------------------------------------------------
Title: The Importance of Long-Term Synoptic Observations and Data
    Sets for Solar Physics and Helioseismology
Authors: Elsworth, Yvonne; Broomhall, Anne-Marie; Gosain, Sanjay;
   Roth, Markus; Jefferies, Stuart M.; Hill, Frank
2017hdsi.book..143E    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Structure of chromospheric magnetic field in solar active
regions: results from SOLIS/VSM Ca II 854.2 nm observations
Authors: Gosain, Sanjay
2017psio.confE..50G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Current trends in ground based solar magnetometry
Authors: Gosain, Sanjay
2016AsJPh..25..221G    Altcode:
  Continuous observations of the sun, over more than a century, have
  led to several important discoveries in solar astronomy. These include
  the discovery of the solar magnetism and its cyclic modulation, active
  region formation and decay and their role in energetic phenomena such
  as fares and coronal mass ejections (CMEs), fine structure and dynamics
  of the sunspots and small-scale organization of the magnetic flux in
  the form of flux tubes and so forth. In this article we give a brief
  overview of advancements in solar observational techniques in recent
  decades and the results obtained from the such observations. These
  include techniques to achieve high angular resolution, high spectral and
  polarimetric sensitivity and innovative new detectors. A wide range of
  spatial, temporal and spectral domains exploited by solar astronomers
  to understand the solar phenomena are discussed. Many new upcoming
  telescopes and instruments that are designed to address different
  aspects of solar physics problems are briefly described. Finally,
  we discuss the advantages of observing from the ground and how they
  can complement space-based observations.

---------------------------------------------------------
Title: Full-Disk Chromospheric Vector Magnetograms with Ca II 854.2
nm line: Some Promising Applications
Authors: Gosain, Sanjay; Harvey, J. W.; Harker, Brian; Pillet, V. M.;
   Pevtsov, Alexei A.; Marble, Andrew R.; Bertello, Luca; + SOLIS-Team
2016SPD....47.0103G    Altcode:
  Over the last decade, the focus of solar magnetometry has shifted
  outward from the photosphere to the chromospheric layers. The reasons
  for this are many. With regards to instrumentation faster detectors
  with more sensitivity have become available, as have fast electro-optic
  modulators. Also, there are several potential benefits of observing
  vector fields in the chromospheric layer as the magnetic field is
  more force-free in this layer as compared to the photosphere. Coronal
  force-free field extrapolations are more reliable using chromospheric
  fields as the lower boundary condition and free magnetic energy is
  readily computed using the magnetic virial theorem. Recently, a full
  Stokes polarimeter for the chromospheric Ca II 854.2 nm spectral line
  was developed and installed in the Vector Spectromagnetograph (VSM)
  instrument on the Synoptic Optical Long-term Investigations of the
  Sun (SOLIS) telescope. We present details of this new polarimeter,
  full disk spectropolarimetric observations and vector magnetograms
  of the chromosphere, and examples of some promising applications
  (e.g., maps of normal component of electric current density in the
  chromosphere, free magnetic energy estimated using virial theorem,
  and non-potentiality parameter magnetic shear angle).This work
  utilizes SOLIS data obtained by the NSO Integrated Synoptic Program
  (NISP), managed by the National Solar Observatory, which is operated
  by the Association of Universities for Research in Astronomy (AURA),
  Inc. under a cooperative agreement with the National Science Foundation

---------------------------------------------------------
Title: Current Status of the SOLIS Program: Improved and New Data
    Products
Authors: Bertello, Luca; Britanik, John; Callahan, Lorraine; Gosain,
   Sanjay; Harker, Brian; Harvey, J. W.; Hughes, A.; Marble, A.; Pevtsov,
   Alexei A.; Wentzel, Thomas
2016SPD....47.1002B    Altcode:
  Over the past year the Synoptic Optical Long-term Investigations of the
  Sun (SOLIS) team has made significant improvements to the data products
  provided to the solar and heliospheric community. In particular,
  a considerable effort has been dedicated to reprocess the archive of
  vector and longitudinal photospheric magnetograms, from 2003 to present,
  using the latest production code. This endeavor is now near completion
  and will assure that all derived magnetic products, such as synoptic
  maps and flux time series, are consistently calibrated. In addition,
  new products have been recently developed. For example, time series of
  daily averages of the Sun's polar magnetic field derived from full-disk
  photospheric FeI 630.15 nm longitudinal magnetograms are now available
  from the SOLIS website at solis.nso.edu/0/vsm/vsm_plrfield.html.New
  intensity calibration of high resolution Ca II K &amp; H spectra from
  the Integrated Sunlight Spectrometer (ISS) led to significant reduction
  in daily variations of parameters derived from these spectra. The
  SOLIS team will soon also release Carrington synoptic maps for the
  three components of the photospheric magnetic field derived from vector
  measurements taken in the Fe I 630.15 nm spectral line. The addition,
  in late 2015, of a new Ca II 854.2 nm full-Stokes polarimeter into
  the SOLIS core program of magnetic observations will make available to
  the community daily chromospheric measurements of the complete Stokes
  polarization vector.We present here a summary of these improvements,
  with particular emphasis on the new products that can be accessed
  from the SOLIS data page at solis.nso.edu/0/solis_data.html. For
  a description of the diagnostic capability of the new Ca II 854.2
  nm spectro-polarimeter and preliminary results we refer to other
  presentations by SOLIS team members at this meeting.This work utilizes
  SOLIS data obtained by the NSO Integrated Synoptic Program (NISP),
  managed by the National Solar Observatory, which is operated by
  the Association of Universities for Research in Astronomy (AURA),
  Inc. under a cooperative agreement with the National Science Foundation.

---------------------------------------------------------
Title: Ca II 854.2 nm Spectromagnetograms: A Powerful Chromospheric
    Diagnostic
Authors: Harvey, J. W.; Bertello, Luca; Branston, D.; Britanik, J.;
   Bulau, S.; Cole, L.; Gosain, Sanjay; Harker, Brian; Jones, Harrison P.;
   Marble, A.; Martinez Pillet, V.; Pevtsov, A.; Schramm, K.; Streander,
   Kim; Villegas, H.
2016SPD....4710106H    Altcode:
  The transition from physical dominance by plasma flows in the
  photosphere to magnetic pressure in the solar chromosphere motivates
  as many diagnostic observations as possible across this important
  region. Among the few ground-accessible spectral lines formed within
  the chromosphere, the Ca II 854.2 nm line has the desirable properties
  of presence everywhere on the solar disk, Zeeman sensitivity, and
  narrow line width. Mapped observations of circular polarization within
  this line (spectromagnetograms) have been made at NSO infrequently
  since 1974, with regular daily full-disk observations starting in
  August 1996. Full-disk spectral observations of the complete Stokes
  polarization vector are now being made regularly since November
  2015. It is not easy to estimate chromospheric magnetic field
  properties from the 854.2 nm line profile polarization. To provide
  rough quick-look vector field maps we found that the weak-field
  approximation provides a fair first estimate of the line-of-sight
  component but appears to be too simple to interpret the transverse
  magnetic field from frequently asymmetric, linearly-polarized line
  profiles. More realistic estimates of the chromospheric vector field,
  short of extremely lengthy, full 3D, non-local radiative transfer
  inversions, are being investigated. We briefly introduce recent
  instrumental modifications and observational characteristics, sample
  observations, and results concerning the expansion of the chromospheric
  field with increasing height, the presence of large areas of weak,
  nearly horizontal fields, and field estimates in plages, sunspots,
  flares, filaments, and filament channels. The Stokes spectra will be
  freely available to the community.This work utilizes SOLIS data obtained
  by the NSO Integrated Synoptic Program (NISP), managed by the National
  Solar Observatory, which is operated by the Association of Universities
  for Research in Astronomy (AURA), Inc. under a cooperative agreement
  with the National Science Foundation.

---------------------------------------------------------
Title: HMI Vector and Uncertainty Carrington Synoptic Maps
Authors: Bertello, Luca; Hughes, A.; Gosain, Sanjay; Harker, Brian;
   Harvey, J. W.; Marble, Andrew R.; Pevtsov, Alexei A.
2016SPD....47.1001B    Altcode:
  Based on our experience with data from the Vector Spectromagnetograph
  (VSM) instrument, which is part of the Synoptic Optical Long-term
  Investigations of the Sun (SOLIS)facility, we have produced HMI vector
  and uncertainty synoptic maps for all Carrington rotations from May
  2010 through December 2015. HMI observations provide 12-minute cadence
  magnetograms, both for longitudinal and full-Stokes measurements. For
  this investigation we have used only two magnetograms per day, 12
  hours apart, which are sufficient to produce accurate maps in the
  longitude-sine(latitude) projection with 1x1 square-degree resolution
  at the equator. From both the HMI longitudinal and vector magnetograms
  we have computed radial-flux and spatial-variance synoptic maps. For
  the longitudinal data, we have included pole-filled radial-flux maps,
  and for the vector data, we have included synoptic maps of the poloidal
  and toroidal magnetic flux.We describe here the procedure to generate
  those maps and discuss some of their main features. A comparison with
  similar products from the SOLIS/VSM is also addressed. The HMI data
  used are courtesy of NASA/SDO and HMI science teams.

---------------------------------------------------------
Title: Flare-related changes in pseudo-vector magnetic field derived
    from line-of-sight magnetograms
Authors: Burtseva, Olga; Gosain, Sanjay; Pevtsov, Alexei A.
2016SPD....47.0637B    Altcode:
  Longitudinal field is a projection of full vector field to
  the line-of-sight direction. Thus, it is possible to derive some
  information about the vector field from line-of-sight data in round
  sunspots, assuming that average properties of vector magnetic field in
  these sunspots depend mostly on distance from center of sunspot. Under
  this assumption, one can reconstruct vertical, radial, and tangential
  components of vector magnetic field using azimuthal averaging. This
  technique can be useful for investigation of twist and inclination in
  magnetic field in particular in flaring regions when vector data are
  not available. In this study we validate the cylindrical symmetry
  technique on example of a simple round sunspot. Then we attempt
  to study changes in (pseudo-vector) magnetic fields in isolated and
  round sunspots associated with flare events using SDO/HMI longitudinal
  magnetograms. We compare the pseudo-vector results with vector data.

---------------------------------------------------------
Title: Interrupted Eruption of Large Quiescent Filament Associated
    with a Halo CME
Authors: Gosain, S.; Filippov, Boris; Ajor Maurya, Ram; Chandra, Ramesh
2016ApJ...821...85G    Altcode:
  We analyze the observations of an eruptive quiescent filament associated
  with a halo Coronal Mass Ejection (CME). We use observations from
  the Atmospheric Imaging Assembly (AIA) instrument onboard the Solar
  Dynamics Observatory (SDO), Solar and Heliospheric Observatory
  (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO), and the
  Solar Terrestrial Relations Observatory (STEREO A/B) satellites. The
  filament exhibits a slow-rise phase followed by a gradual acceleration
  and then completely disappears. The filament could be traced in STEREO
  observations up to an altitude of about 1.44 {R}<SUB>⊙ </SUB>,
  where its rise speed reached ∼14 km s<SUP>-1</SUP> and disappeared
  completely at about 10:32 UT on 2011 October 21. The CME associated
  with the filament eruption and two bright ribbons in the chromosphere
  both appeared at about 01:30 UT on October 22, I.e., 15 hr after the
  filament eruption was seen in He II 304 Å filtergrams. We show that
  this delay is abnormally large even if the slow rise speed and slow
  acceleration of the filament are taken into account. To understand the
  cause of this delay, we compute the decay index (n) of the overlying
  coronal magnetic field. The height distribution of the decay index, n,
  suggests that the zone of instability (n \gt 1) at a lower altitude,
  144-480 Mm, is followed by a zone of stability (n \lt 1) between 540
  and 660 Mm. We interpret the observed delay to be due to the presence
  of the latter zone, I.e., the zone of stability, which could provide a
  second quasi-equilibrium state to the filament until it finally erupts.

---------------------------------------------------------
Title: The Importance of Long-Term Synoptic Observations and Data
    Sets for Solar Physics and Helioseismology
Authors: Elsworth, Yvonne; Broomhall, Anne-Marie; Gosain, Sanjay;
   Roth, Markus; Jefferies, Stuart M.; Hill, Frank
2015SSRv..196..137E    Altcode: 2015SSRv..tmp..106E
  A casual single glance at the Sun would not lead an observer to conclude
  that it varies. The discovery of the 11-year sunspot cycle was only
  made possible through systematic daily observations of the Sun over
  150 years and even today historic sunspot drawings are used to study
  the behavior of past solar cycles. The origin of solar activity is
  still poorly understood as shown by the number of different models
  that give widely different predictions for the strength and timing
  of future cycles. Our understanding of the rapid transient phenomena
  related to solar activity, such as flares and coronal mass ejections
  (CMEs) is also insufficient and making reliable predictions of these
  events, which can adversely impact technology, remains elusive. There
  is thus still much to learn about the Sun and its activity that requires
  observations over many solar cycles. In particular, modern helioseismic
  observations of the solar interior currently span only 1.5 cycles,
  which is far too short to adequately sample the characteristics of
  the plasma flows that govern the dynamo mechanism underlying solar
  activity. In this paper, we review some of the long-term solar and
  helioseismic observations and outline some future directions.

---------------------------------------------------------
Title: Cylindrical Symmetry of Sunspots as a Proxy for Flare-Related
    Changes in Pseudo-Vector Magnetic Field Derived from Line-of-Sight
    Magnetograms
Authors: Pevtsov, A. A.; Burtseva, O.; Gosain, S.
2015AGUFMSH43B2450P    Altcode:
  Large-scale changes in the magnetic field twist and inclination in
  flaring regions are often observed in vector magnetograms. When
  vector data are not available, such changes can be investigated
  using proxies for vector magnetic fields derived from line-of-sight
  magnetograms. Longitudinal field is a projection of full vector field
  to the line-of-sight direction. Thus, it is possible to derive some
  information about the vector field from line-of-sight data in round
  sunspots, assuming that average properties of vector magnetic field in
  these sunspots depend mostly on distance from center of sunspot. Under
  this assumption, one can reconstruct vertical, radial, and tangential
  components of vector magnetic field using azimuthal averaging. We
  study changes in (pseudo-vector) magnetic fields, including twist
  and inclination of the magnetic fields, in sunspots associated with
  flare events using SDO/HMI longitudinal magnetograms. We compare the
  pseudo-vector results with SDO/HMI vector data.

---------------------------------------------------------
Title: Design of a Full Stokes Polarimeter for Chromospheric
    Measurements with SOLIS/VSM
Authors: Gosain, S.; Harvey, J. W.
2015IAUS..305..186G    Altcode:
  The synoptic observations of the magnetic field of the Sun have
  continued at the National Solar Observatory (NSO) since 1970s. The
  daily full-disk maps of the longitudinal magnetic field are regularly
  combined to form Carrington maps of the photospheric magnetic flux per
  solar rotation. These maps continue to be used by the international
  research community for a variety of studies related to solar magnetism
  as well as for space weather studies. The current NSO synoptic facility
  is the Synoptic Optical Long-term Investigation of the Sun (SOLIS),
  which regularly provides photospheric vector and chromospheric
  longitudinal full-disk magnetograms, among other data products. In
  the near future, an upgrade of SOLIS to produce chromospheric vector
  magnetograms is planned. We present the design of a new polarization
  modulator package for full Stokes polarimetry of the chromospheric Ca
  II 854.2 nm spectral line.

---------------------------------------------------------
Title: Short-term periodicities in interplanetary, geomagnetic and
    solar phenomena during solar cycle 24
Authors: Chowdhury, Partha; Choudhary, D. P.; Gosain, S.; Moon, Y. -J.
2015Ap&SS.356....7C    Altcode:
  In this paper we study the quasi-periodic variations of sunspot
  area/number, 10.7 cm solar radio flux, Average Photospheric Magnetic
  Flux, interplanetary magnetic field ( B <SUB> z </SUB>) and the
  geomagnetic activity index A <SUB> p </SUB> during the ascending phase
  of the current solar cycle 24. We use both Lomb-Scargle periodogram
  and wavelet analysis technique and find evidence for a multitude of
  quasi-periodic oscillations in all the data sets. In high frequency
  range (10 days to 100 days), both methods yield similar significance
  periodicities around 20-35 days and 45-60 days in all data sets. In
  the case of intermediate range, the significant periods were around
  100-130 days, 140-170 days and 180-240 days The Morlet wavelet power
  spectrum shows that all of the above-mentioned periods are intermittent
  in nature. We find that the well-known "Rieger period" of (150-160
  days) and near Rieger periods (130-190 days) were significant in both
  solar, interplanetary magnetic field and geomagnetic activity data sets
  during cycle 24. The geomagnetic activity is the result of the solar
  wind-magnetosphere interaction. Thus the variations in the detected
  periodicity in variety of solar, interplanetary and geomagnetic indices
  could be helpful to improve our knowledge of the inter-relationship
  between various processes in the Sun-Earth-Heliosphere system.

---------------------------------------------------------
Title: Current and Kinetic Helicity of Long-lived Activity Complexes
Authors: Komm, Rudolf; Gosain, Sanjay
2015ApJ...798...20K    Altcode:
  We study long-lived activity complexes and their current helicity at
  the solar surface and their kinetic helicity below the surface. The
  current helicity has been determined from synoptic vector magnetograms
  from the NSO/SOLIS facility, and the kinetic helicity of subsurface
  flows has been determined with ring-diagram analysis applied to
  full-disk Dopplergrams from NSO/GONG and SDO/HMI. Current and kinetic
  helicity of activity complexes follow the hemispheric helicity rule
  with mainly positive values (78%; 78%, respectively, with a 95%
  confidence level of 31%) in the southern hemisphere and negative ones
  (80%; 93%, respectively, with a 95% confidence level of 22% and 14%,
  respectively) in the northern hemisphere. The locations with the
  dominant sign of kinetic helicity derived from Global Oscillation
  Network Group (GONG) and SDO/HMI data are more organized than those of
  the secondary sign even if they are not part of an activity complex,
  while locations with the secondary sign are more fragmented. This is
  the case for both hemispheres even for the northern one where it is
  not as obvious visually due to the large amount of magnetic activity
  present as compared to the southern hemisphere. The current helicity
  shows a similar behavior. The dominant sign of current helicity is
  the same as that of kinetic helicity for the majority of the activity
  complexes (83% with a 95% confidence level of 15%). During the 24
  Carrington rotations analyzed here, there is at least one longitude in
  each hemisphere where activity complexes occur repeatedly throughout
  the epoch. These "active" longitudes are identifiable as locations of
  strong current and kinetic helicity of the same sign.

---------------------------------------------------------
Title: Current and Kinetic Helicity of Long-Lived Activity Complexes
Authors: Komm, R.; Gosain, S.
2014AGUFMSH41B4137K    Altcode:
  We focus on long-lived activity complexes and their helicity below and
  above the solar surface. These locations of recurrent flux emergence
  in or close to a pre-existing active region, last for typically five
  to seven solar rotations. It is known that emergence of new magnetic
  flux in pre-existing magnetic region causes an increase in topological
  complexity of the magnetic field which leads to flares and Coronal Mass
  Ejections (CMEs). A quantitative measure of topological complexity
  of magnetic fields is given by the magnetic helicity which measures
  twisting and linking of the magnetic field. The current helicity
  determined from vector magnetograms is the equivalent of the kinetic
  helicity determined from subsurface flows. The helicity is thus an ideal
  quantity to investigate the linkage of magnetic fields in the solar
  atmosphere with flows in the upper solar convection zone. The subsurface
  flows from the surface to a depth of 16 Mm are determined with a
  ring-diagram analysis of GONG and SDO/HMI Dopplergrams and the current
  helicity density is determined from SOLIS vector magnetograms. We
  will study the kinetic and current helicity as a function of time and
  Carrington longitude, averaged over a suitable range of latitudes in
  either hemisphere. We will present the latest results.

---------------------------------------------------------
Title: Global Solar Free Magnetic Energy and Electric Current Density
    Distribution of Carrington Rotation 2124
Authors: Tadesse, Tilaye; Pevtsov, Alexei A.; Wiegelmann, T.; MacNeice,
   P. J.; Gosain, S.
2014SoPh..289.4031T    Altcode: 2013arXiv1310.5790T
  Solar eruptive phenomena, like flares and coronal mass ejections
  (CMEs), are governed by magnetic fields. To describe the structure of
  these phenomena one needs information on the magnetic flux density and
  the electric current density vector components in three dimensions
  throughout the atmosphere. However, current spectro-polarimetric
  measurements typically limit the determination of the vector magnetic
  field to only the photosphere. Therefore, there is considerable
  interest in accurate modeling of the solar coronal magnetic field
  using photospheric vector magnetograms as boundary data. In this work,
  we model the coronal magnetic field for global solar atmosphere using
  nonlinear force-free field (NLFFF) extrapolation codes implemented to
  a synoptic maps of photospheric vector magnetic field synthesized from
  the Vector Spectromagnetograph (VSM) on Synoptic Optical Long-term
  Investigations of the Sun (SOLIS) as boundary condition. Using
  the resulting three-dimensional magnetic field, we calculate the
  three-dimensional electric current density and magnetic energy
  throughout the solar atmosphere for Carrington rotation 2124 using our
  global extrapolation code. We found that spatially, the low-lying,
  current-carrying core field demonstrates a strong concentration of
  free energy in the active-region core, from the photosphere to the
  lower corona (about 70 Mm). The free energy density appears largely
  co-spatial with the electric current distribution.

---------------------------------------------------------
Title: Distribution of Electric Currents in Sunspots from Photosphere
    to Corona
Authors: Gosain, Sanjay; Démoulin, Pascal; López Fuentes, Marcelo
2014ApJ...793...15G    Altcode:
  We present a study of two regular sunspots that exhibit nearly uniform
  twist from the photosphere to the corona. We derive the twist parameter
  in the corona and in the chromosphere by minimizing the difference
  between the extrapolated linear force-free field model field lines
  and the observed intensity structures in the extreme-ultraviolet
  images of the Sun. The chromospheric structures appear more twisted
  than the coronal structures by a factor of two. Further, we derive
  the vertical component of electric current density, j<SUB>z</SUB>
  , using vector magnetograms from the Hinode Solar Optical Telescope
  (SOT). The spatial distribution of j<SUB>z</SUB> has a zebra pattern
  of strong positive and negative values owing to the penumbral fibril
  structure resolved by Hinode/SOT. This zebra pattern is due to the
  derivative of the horizontal magnetic field across the thin fibrils;
  therefore, it is strong and masks weaker currents that might be present,
  for example, as a result of the twist of the sunspot. We decompose
  j<SUB>z</SUB> into the contribution due to the derivatives along
  and across the direction of the horizontal field, which follows the
  fibril orientation closely. The map of the tangential component has
  more distributed currents that are coherent with the chromospheric
  and coronal twisted structures. Moreover, it allows us to map and
  identify the direct and return currents in the sunspots. Finally, this
  decomposition of j<SUB>z</SUB> is general and can be applied to any
  vector magnetogram in order to better identify the weaker large-scale
  currents that are associated with coronal twisted/sheared structures.

---------------------------------------------------------
Title: Hemispheric Distribution of Subsurface Kinetic Helicity and
    Its Variation with Magnetic Activity
Authors: Komm, R.; Gosain, S.; Pevtsov, A. A.
2014SoPh..289.2399K    Altcode: 2014SoPh..tmp...25K
  We study the hemispheric distribution of the kinetic helicity of
  subsurface flows in the near-surface layers of the solar convection
  zone and its variation with magnetic activity. We determine subsurface
  flows with a ring-diagram analysis applied to Global Oscillation Network
  Group (GONG) Dopplergrams and Dynamics Program data from the Michelson
  Doppler Imager (MDI) instrument onboard the Solar and Heliospheric
  Observatory (SOHO). We determine the average kinetic helicity density
  as a function of Carrington rotation and latitude. The average kinetic
  helicity density at all depths and the kinetic helicity, integrated
  over 2 - 7 Mm, follow the same hemispheric rule as the current/magnetic
  helicity proxies with predominantly positive values in the southern
  and negative ones in the northern hemisphere. This holds true for all
  levels of magnetic activity from quiet to active regions. However,
  this is a statistical result; only about 55 % of all locations follow
  the hemispheric rule. But these locations have larger helicity values
  than those that do not follow the rule. The average values of helicity
  density increase with depth for all levels of activity, which might
  reflect an increase of the characteristic size of convective motions
  with greater depth. The average helicity of subsets of high magnetic
  activity is about five times larger than that of subsets of low
  activity. The solar-cycle variation of helicity is thus mainly due to
  the presence or absence of active regions. During the rising phase of
  cycle 24, locations of high magnetic activity at low latitudes show
  a weaker hemispheric behavior compared to the rising phase of cycle 23.

---------------------------------------------------------
Title: Current and Kinetic Helicity of Long-Lived Activity Complexes
Authors: Komm, Rudolf; Gosain, S.
2014shin.confE..60K    Altcode:
  We focus on long-lived activity complexes and their helicity below and
  above the solar surface. These locations of recurrent flux emergence
  in or close to a pre-existing active region, last for typically five
  to seven solar rotations. It is known that emergence of new magnetic
  flux in pre-existing magnetic region causes an increase in topological
  complexity of the magnetic field which leads to flares and Coronal Mass
  Ejections (CMEs). A quantitative measure of topological complexity
  of magnetic fields is given by the magnetic helicity which measures
  twisting and linking of the magnetic field. The current helicity
  determined from vector magnetograms is the equivalent of the kinetic
  helicity determined from subsurface flows. The helicity is thus an ideal
  quantity to investigate the linkage of magnetic fields in the solar
  atmosphere with flows in the upper solar convection zone. The subsurface
  flows from the surface to a depth of 16 Mm are determined with a
  ring-diagram analysis of GONG and SDO/HMI Dopplergrams and the current
  helicity density is determined from SOLIS vector magnetograms. We
  will study the kinetic and current helicity as a function of time and
  Carrington longitude, averaged over a suitable range of latitudes in
  either hemisphere. We will present the latest results.

---------------------------------------------------------
Title: First use of synoptic vector magnetograms for global nonlinear,
    force-free coronal magnetic field models
Authors: Tadesse, T.; Wiegelmann, T.; Gosain, S.; MacNeice, P.;
   Pevtsov, A. A.
2014A&A...562A.105T    Altcode: 2013arXiv1309.5853T
  Context. The magnetic field permeating the solar atmosphere is
  generally thought to provide the energy for much of the activity
  seen in the solar corona, such as flares, coronal mass ejections
  (CMEs), etc. To overcome the unavailability of coronal magnetic field
  measurements, photospheric magnetic field vector data can be used to
  reconstruct the coronal field. Currently, there are several modelling
  techniques being used to calculate three-dimensional field lines into
  the solar atmosphere. <BR /> Aims: For the first time, synoptic maps
  of a photospheric-vector magnetic field synthesized from the vector
  spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations
  of the Sun (SOLIS) are used to model the coronal magnetic field and
  estimate free magnetic energy in the global scale. The free energy
  (i.e., the energy in excess of the potential field energy) is one of
  the main indicators used in space weather forecasts to predict the
  eruptivity of active regions. <BR /> Methods: We solve the nonlinear
  force-free field equations using an optimization principle in spherical
  geometry. The resulting three-dimensional magnetic fields are used
  to estimate the magnetic free energy content E<SUB>free</SUB> =
  E<SUB>nlfff</SUB> - E<SUB>pot</SUB>, which is the difference of the
  magnetic energies between the nonpotential field and the potential field
  in the global solar corona. For comparison, we overlay the extrapolated
  magnetic field lines with the extreme ultraviolet (EUV) observations
  by the atmospheric imaging assembly (AIA) on board the Solar Dynamics
  Observatory (SDO). <BR /> Results: For a single Carrington rotation
  2121, we find that the global nonlinear force-free field (NLFFF)
  magnetic energy density is 10.3% higher than the potential one. Most
  of this free energy is located in active regions.

---------------------------------------------------------
Title: Active Regions with Superpenumbral Whirls and Their Subsurface
    Kinetic Helicity
Authors: Komm, R.; Gosain, S.; Pevtsov, A.
2014SoPh..289..475K    Altcode:
  We search for a signature of helicity flow from the solar interior
  to the photosphere and chromosphere. For this purpose, we study two
  active regions, NOAA 11084 and 11092, that show a regular pattern of
  superpenumbral whirls in chromospheric and coronal images. These two
  regions are good candidates for comparing magnetic/current helicity with
  subsurface kinetic helicity because the patterns persist throughout the
  disk passage of both regions. We use photospheric vector magnetograms
  from SOLIS/VSM and SDO/HMI to determine a magnetic helicity proxy, the
  spatially averaged signed shear angle (SASSA). The SASSA parameter
  produces consistent results leading to positive values for NOAA
  11084 and negative ones for NOAA 11092 consistent with the clockwise
  and counter-clockwise orientation of the whirls. We then derive
  the properties of the subsurface flows associated with these active
  regions. We measure subsurface flows using a ring-diagram analysis of
  GONG high-resolution Doppler data and derive their kinetic helicity,
  h<SUB>z</SUB>. Since the patterns persist throughout the disk passage,
  we analyze synoptic maps of the subsurface kinetic helicity density. The
  sign of the subsurface kinetic helicity is negative for NOAA 11084
  and positive for NOAA 11092; the sign of the kinetic helicity is
  thus anticorrelated with that of the SASSA parameter. As a control
  experiment, we study the subsurface flows of six active regions without
  a persistent whirl pattern. Four of the six regions show a mixture
  of positive and negative kinetic helicity resulting in small average
  values, while two regions are clearly dominated by kinetic helicity
  of one sign or the other, as in the case of regions with whirls. The
  regions without whirls follow overall the same hemispheric rule in
  their kinetic helicity as in their current helicity with positive
  values in the southern and negative values in the northern hemisphere.

---------------------------------------------------------
Title: Flux emergence, flux imbalance, magnetic free energy and
    solar flares
Authors: Choudhary, Debi Prasad; Gosain, Sanjay; Gopalswamy, Nat;
   Manoharan, P. K.; Chandra, R.; Uddin, W.; Srivastava, A. K.; Yashiro,
   S.; Joshi, N. C.; Kayshap, P.; Dwivedi, V. C.; Mahalakshmi, K.;
   Elamathi, E.; Norris, Max; Awasthi, A. K.; Jain, R.
2013AdSpR..52.1561C    Altcode:
  Emergence of complex magnetic flux in the solar active regions lead
  to several observational effects such as a change in sunspot area
  and flux embalance in photospheric magnetograms. The flux emergence
  also results in twisted magnetic field lines that add to free energy
  content. The magnetic field configuration of these active regions
  relax to near potential-field configuration after energy release
  through solar flares and coronal mass ejections. In this paper,
  we study the relation of flare productivity of active regions with
  their evolution of magnetic flux emergence, flux imbalance and free
  energy content. We use the sunspot area and number for flux emergence
  study as they contain most of the concentrated magnetic flux in the
  active region. The magnetic flux imbalance and the free energy are
  estimated using the HMI/SDO magnetograms and Virial theorem method. We
  find that the active regions that undergo large changes in sunspot
  area are most flare productive. The active regions become flary when
  the free energy content exceeds 50% of the total energy. Although,
  the flary active regions show magnetic flux imbalance, it is hard to
  predict flare activity based on this parameter alone.

---------------------------------------------------------
Title: First Synoptic Maps of Photospheric Vector Magnetic Field
from SOLIS/VSM: Non-radial Magnetic Fields and Hemispheric Pattern
    of Helicity
Authors: Gosain, S.; Pevtsov, A. A.; Rudenko, G. V.; Anfinogentov,
   S. A.
2013ApJ...772...52G    Altcode: 2013arXiv1305.3294G
  We use daily full-disk vector magnetograms from Vector
  Spectromagnetograph on Synoptic Optical Long-term Investigations of the
  Sun system to synthesize the first Carrington maps of the photospheric
  vector magnetic field. We describe these maps and make a comparison
  of the observed radial field with the radial field estimate from
  line-of-sight magnetograms. Furthermore, we employ these maps to study
  the hemispheric pattern of current helicity density, H<SUB>c</SUB> ,
  during the rising phase of solar cycle 24. The longitudinal average
  over the 23 consecutive solar rotations shows a clear signature of
  the hemispheric helicity rule, i.e., H<SUB>c</SUB> is predominantly
  negative in the north and positive in the south. Although our data
  include the early phase of cycle 24, there appears to be no evidence for
  a possible (systematic) reversal of the hemispheric helicity rule at the
  beginning of the cycle as predicted by some dynamo models. Furthermore,
  we compute the hemispheric pattern in active region latitudes (-30°
  &lt;= θ &lt;= 30°) separately for weak (100 G &lt; |B<SUB>r</SUB> |
  &lt; 500 G) and strong (|B<SUB>r</SUB> | &gt; 1000 G) radial magnetic
  fields. We find that while the current helicity of strong fields follows
  the well-known hemispheric rule (i.e., θ · H<SUB>c</SUB> &lt; 0),
  H<SUB>c</SUB> of weak fields exhibits an inverse hemispheric behavior
  (i.e., θ · H<SUB>c</SUB> &gt; 0), albeit with large statistical
  scatter. We discuss two plausible scenarios to explain the opposite
  hemispheric trend of helicity in weak and strong field regions.

---------------------------------------------------------
Title: Helicity of Subsurface Flows and Magnetic Activity in the
    Photosphere
Authors: Komm, Rudolf; Gosain, S.; Pevtsov, A. A.
2013shin.confE..43K    Altcode:
  Subsurface flows associated with active regions show generally
  large values of kinetic helicity density. The vertical component
  of kinetic helicity is defined as the product of the curl of the
  horizontal velocities and the vertical velocity component. It is
  thus the equivalent of current helicity determined from vector
  magnetograms. The vertical component of kinetic helicity follows
  on average the hemispheric rule established for current helicity
  with negative values in the northern hemisphere and positive values
  in the southern one. We analyze 11 years of GONG Dopplergrams and
  derive subsurface flows from the surface to a depth of 16 Mm with
  the ring-diagram technique. From these velocities, we calculate
  the kinetic helicity density and integrate it over selected depth
  ranges. We will study the kinetic helicity as a function of time and
  latitude for different levels of magnetic activity, such as active
  and quiet regions. We will present the latest results.

---------------------------------------------------------
Title: A Study of the Hemispheric Asymmetry of Sunspot Area during
    Solar Cycles 23 and 24
Authors: Chowdhury, Partha; Choudhary, D. P.; Gosain, Sanjay
2013ApJ...768..188C    Altcode:
  Solar activity indices vary over the Sun's disk, and various activity
  parameters are not considered to be symmetric between the northern
  and southern hemispheres of the Sun. The north-south asymmetry of
  different solar indices provides an important clue to understanding
  subphotospheric dynamics and solar dynamo action, especially with
  regard to nonlinear dynamo models. In the present work, we study
  the statistical significance of the north-south asymmetry of sunspot
  areas for the complete solar cycle 23 (1996-2008) and rising branch of
  cycle 24 (first 45 months). The preferred hemisphere in each year of
  cycles 23 and 24 has been identified by calculating the probability of
  hemispheric distribution of sunspot areas. The statistically significant
  intermediate-term periodicities of the north-south asymmetry of
  sunspot area data have also been investigated using Lomb-Scargle and
  wavelet techniques. A number of short- and mid-term periods including
  the best-known Rieger one (150-160 days) are detected in cycle 23 and
  near Rieger-type periods during cycle 24, and most of them are found
  to be time variable. We present our results and discuss their possible
  explanations with the help of theoretical models and observations.

---------------------------------------------------------
Title: Resolving Azimuth Ambiguity Using Vertical Nature of Solar
    Quiet-Sun Magnetic Fields
Authors: Gosain, S.; Pevtsov, A. A.
2013SoPh..283..195G    Altcode: 2012arXiv1210.6691G; 2012SoPh..tmp..243G
  The measurement of solar magnetic fields using the Zeeman effect
  diagnostics has a fundamental 180° ambiguity in the determination
  of the azimuth angle of the transverse field component. There are
  several methods that are used in the community and each one has its
  merits and demerits. Here we present a disambiguation idea that is
  based on the assumption that most of the magnetic field on the sun
  is predominantly vertical. While the method is not applicable to
  penumbra or other features harboring predominantly horizontal fields
  like the sheared neutral lines, it is useful for regions where fields
  are predominantly vertical like network and plage areas. The method is
  tested with the full-disk solar vector magnetograms observed by the
  SOLIS/VSM instrument. We find that statistically about 60 - 85 % of
  the pixels in a typical full-disk magnetogram has a field inclination
  in the range of 0 - 30° with respect to the local solar normal, and
  thus can be successfully disambiguated by the proposed method. Due to
  its non-iterative nature, the present method is extremely fast and
  therefore can be used as a good initial guess for iterative schemes
  like the non-potential field computation (NPFC) method. Furthermore,
  the method is insensitive to noisy pixels as it does not depend upon
  the neighboring pixels or derivatives.

---------------------------------------------------------
Title: A Multi-spacecraft View of a Giant Filament Eruption during
    2009 September 26/27
Authors: Gosain, Sanjay; Schmieder, Brigitte; Artzner, Guy; Bogachev,
   Sergei; Török, Tibor
2012ApJ...761...25G    Altcode: 2012arXiv1210.6686G
  We analyze multi-spacecraft observations of a giant filament eruption
  that occurred during 2009 September 26 and 27. The filament eruption was
  associated with a relatively slow coronal mass ejection. The filament
  consisted of a large and a small part, and both parts erupted nearly
  simultaneously. Here we focus on the eruption associated with the
  larger part of the filament. The STEREO satellites were separated
  by about 117° during this event, so we additionally used SoHO/EIT
  and CORONAS/TESIS observations as a third eye (Earth view) to aid our
  measurements. We measure the plane-of-sky trajectory of the filament as
  seen from STEREO-A and TESIS viewpoints. Using a simple trigonometric
  relation, we then use these measurements to estimate the true direction
  of propagation of the filament which allows us to derive the true
  R/R <SUB>⊙</SUB>-time profile of the filament apex. Furthermore, we
  develop a new tomographic method that can potentially provide a more
  robust three-dimensional (3D) reconstruction by exploiting multiple
  simultaneous views. We apply this method also to investigate the 3D
  evolution of the top part of filament. We expect this method to be
  useful when SDO and STEREO observations are combined. We then analyze
  the kinematics of the eruptive filament during its rapid acceleration
  phase by fitting different functional forms to the height-time
  data derived from the two methods. We find that for both methods an
  exponential function fits the rise profile of the filament slightly
  better than parabolic or cubic functions. Finally, we confront these
  results with the predictions of theoretical eruption models.

---------------------------------------------------------
Title: Dual Trigger of Transverse Oscillations in a Prominence by
EUV Fast and Slow Coronal Waves: SDO/AIA and STEREO/EUVI Observations
Authors: Gosain, S.; Foullon, C.
2012ApJ...761..103G    Altcode: 2012arXiv1210.6690G
  We analyze flare-associated transverse oscillations in a quiescent
  solar prominence on 2010 September 8-9. Both the flaring active region
  and the prominence were located near the west limb, with a favorable
  configuration and viewing angle. The full-disk extreme ultraviolet (EUV)
  images of the Sun obtained with high spatial and temporal resolution by
  the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory
  show flare-associated lateral oscillations of the prominence sheet. The
  STEREO-A spacecraft, 81fdg5 ahead of the Sun-Earth line, provides an
  on-disk view of the flare-associated coronal disturbances. We derive
  the temporal profile of the lateral displacement of the prominence sheet
  by using the image cross-correlation technique. The displacement curve
  was de-trended and the residual oscillatory pattern was derived. We
  fit these oscillations with a damped cosine function with a variable
  period and find that the period is increasing. The initial oscillation
  period (P <SUB>0</SUB>) is ~28.2 minutes and the damping time (τ<SUB>
  D </SUB>) ~ 44 minutes. We confirm the presence of fast and slow EUV
  wave components. Using STEREO-A observations, we derive a propagation
  speed of ~250 km s<SUP>-1</SUP> for the slow EUV wave by applying the
  time-slice technique to the running difference images. We propose that
  the prominence oscillations are excited by the fast EUV wave while the
  increase in oscillation period of the prominence is an apparent effect,
  related to a phase change due to the slow EUV wave acting as a secondary
  trigger. We discuss implications of the dual trigger effect for coronal
  prominence seismology and scaling law studies of damping mechanisms.

---------------------------------------------------------
Title: A New Technique for Solar Imaging Spectro-polarimetry using
    Shack-Hartmann and Fabry-Pérot
Authors: Gosain, S.; Sankarasubramanian, K.; Venkatakrishnan, P.;
   Raja Bayanna, A.
2012ASPC..463..301G    Altcode:
  A new technique for solar imaging spectro-polarimetry is
  presented. Using the combination of a Shack-Hartmann (SH) and
  a Fabry-Pérot (FP) interferometer, high-cadence spectroscopic
  observations can be obtained at discrete wavelength positions
  simultaneously, thereby avoiding errors due to non-simultaneity of the
  wavelength scans. A SH mask is used to generate multiple images of the
  same field-of-view (FOV). These multiple images when passed through the
  FP in a collimated-beam arrangement are shifted in wavelength due to
  the angular dependence of the FP filter transmission profile. Thus,
  by re-imaging one obtains multiple images of the FOV which are
  tuned to different wavelength points across the spectral line, in
  a single exposure. The schematic of the setup and the laboratory
  simulation of such a configuration is presented. The technique has
  an advantage of simultaneity over conventional wavelength scanning
  filtergraphs and has potential for observing highly-dynamic phenomena
  like solar flares. Also, one can exploit the method to perform
  snapshot spectropolarimetry by designing a special polarization
  modulator. The limitation of this technique is that it downgrades the
  spatial resolution due to the downsampling of the pupil into smaller
  sub-apertures. However, for large aperture telescopes like 4 meter
  class telescopes (ATST) this is not a major issue and one can still
  work at sub-arcsec resolution, though not at the diffraction limit of
  the full aperture.

---------------------------------------------------------
Title: Coherent Lateral Motion of Penumbral Filaments during the
    X-class Flare of 13 December 2006
Authors: Gosain, S.; Venkatakrishnan, P.; Tiwari, S. K.
2012ASPC..454..273G    Altcode:
  The high-resolution pictures of the solar photosphere from space
  based 50 cm Solar Optical Telescope (SOT) onboard Hinode spacecraft,
  are now routinely observed. Such images of a δ-sunspot in NOAA 10930
  were obtained by Hinode during 13 December 2006 while a X-class flare
  occurred in this active region. Two bright ribbons were visible even
  in white light and G-band images apart from chromospheric Ca II H
  images. We register the sunspot globally using cross-correlation
  technique and analyse local effects during flare interval. We find
  that during flare the penumbral filaments show lateral motion. Also,
  we locate two patches, one in either polarity, which show converging
  motion towards the polarity inversion line (PIL). In Ca II H images
  we find kernel with pre-flare brightening which lie along the PIL.

---------------------------------------------------------
Title: Reconstruction of 3D Coronal Magnetic Structures from
    THEMIS/MTR and Hinode/SOT Vector Maps
Authors: Schmieder, B.; Guo, Y.; Aulanier, G.; Démoulin, P.; Török,
   T.; Bommier, V.; Wiegelmann, T.; Gosain, S.
2012ASPC..454..363S    Altcode:
  Coordinated campaigns using THEMIS, Hinode, and other instruments have
  allowed us to study the magnetic fields of faculae, filaments, and
  active regions. In a first case, we modelled the 3D magnetic field in a
  flaring active region with a nonlinear force-free field extrapolation,
  using magnetic vectors observed by THEMIS/MTR as boundary condition. In
  order to construct a consistent bottom boundary for the model, we
  first removed the 180 degree ambiguity of the transverse fields and
  minimized the force and torque in the observed vector fields. We found
  a twisted magnetic flux rope, well aligned with the polarity inversion
  line and a part of an Hα filament, and located where a large flare is
  initiated about two hours later. In a second case, Hinode/SOT allowed
  us to detect fine flux concentrations in faculae, while MTR provided us
  with magnetic information at different levels in the atmosphere. The
  polarimetry analysis of the MTR and SOT data gave consistent results,
  using both UNNOFIT and MELANIE inversion codes.

---------------------------------------------------------
Title: Dynamics of coronal loops in NOAA 11158 during X2.2 flare
    of 15-Feb-2011
Authors: Gosain, Sanjay
2012cosp...39..699G    Altcode: 2012cosp.meet..699G
  No abstract at ADS

---------------------------------------------------------
Title: Evolution of Dip-shear and Twist-shear during X-class flare
    in NOAA 11158
Authors: Gosain, Sanjay
2012cosp...39..698G    Altcode: 2012cosp.meet..698G
  We study the evolution of dip-shear and twist shear in a region close
  to flaring site in NOAA 11158. This active region emerged as a complex
  delta active region complex with a pair of twisted rotating sunspots in
  the middle. The X-2.2 class flare took place near the Polarity Inversion
  Line (PIL). We find that after the flare there was an increase in
  twist shear and a decrease in dip-shear close to the PIL. The results
  are similar to that obtained by Gosain and Venkatakrishnan (ApJ 720,
  L137, 2010) during X-class flare in NOAA 10930 during 13 December
  2006. It seems that there is a general tendency for dip shear to
  increase before the flare and show a subsequent decrease after the
  flare and so it can be exploited as a potential flare predictor.

---------------------------------------------------------
Title: Active regions with superpenumbral whirls and their subsurface
    flow vorticity
Authors: Komm, Rudolf W.; Gosain, S.; Pevtsov, A.
2012shin.confE.119K    Altcode:
  We search for a signature of helicity flow from the solar interior to
  the photosphere and chromosphere. We study two active regions NOAA
  11084 and NOAA 11092 that show a regular pattern of superpenumbral
  whirls in H-alpha. The pattern persists throughout the disk passage
  of both regions. We use photospheric vector magnetograms from
  SOLIS/VSM to determine two helicity proxies: vertical component of
  the current helicity density (Hc_z=Jz.Bz) and the mean twist parameter
  (alpha_z=&lt;Jz/Bz&gt;), and to study their evolution. We compare the
  two proxies of magnetic helicity with the properties of the subsurface
  flows below the active regions. For this purpose, we analyze subsurface
  flows measured with a ring-diagram analysis of GONG high-resolution
  Doppler data and derive their vorticity. As a control experiment,
  we study the subsurface flows of six active regions that do not show
  a regular whirl pattern in the chromosphere.

---------------------------------------------------------
Title: Evidence for Collapsing Fields in the Corona and Photosphere
during the 2011 February 15 X2.2 Flare: SDO/AIA and HMI Observations
Authors: Gosain, S.
2012ApJ...749...85G    Altcode: 2012arXiv1202.1784G
  We use high-resolution Solar Dynamics Observatory (SDO)/Atmospheric
  Imaging Assembly observations to study the evolution of the coronal
  loops in a flaring solar active region, NOAA 11158. We identify three
  distinct phases of the coronal loop dynamics during this event:
  (1) slow-rise phase: slow rising motion of the loop-tops prior to
  the flare in response to the slow rise of the underlying flux rope;
  (2) collapse phase: sudden contraction of the loop-tops, with
  the lower loops collapsing earlier than the higher loops; and (3)
  oscillation phase: the loops exhibit global kink oscillations after
  the collapse phase at different periods, with the period decreasing
  with the decreasing height of the loops. The period of these loop
  oscillations is used to estimate the field strength in the coronal
  loops. Furthermore, we also use SDO/Helioseismic and Magnetic Imager
  (HMI) observations to study the photospheric changes close to the
  polarity inversion line (PIL). The longitudinal magnetograms show a
  stepwise permanent decrease in the magnetic flux after the flare over
  a coherent patch along the PIL. Furthermore, we examine the HMI Stokes
  I, Q, U, V profiles over this patch and find that the Stokes-V signal
  systematically decreases while the Stokes-Q and U signals increase
  after the flare. These observations suggest that close to the PIL the
  field configuration became more horizontal after the flare. We also use
  HMI vector magnetic field observations to quantify the changes in the
  field inclination angle and find an inward collapse of the field lines
  toward the PIL by ~10°. These observations are consistent with the
  "coronal implosion" scenario and its predictions about flare-related
  photospheric field changes.

---------------------------------------------------------
Title: Rapid Disappearance of Penumbra-Like Features near a Flaring
Polarity Inversion Line: The Hinode Observations
Authors: Ravindra, B.; Gosain, Sanjay
2012AdAst2012E..24R    Altcode: 2012AdAst2012E..54R; 2012arXiv1205.3254R
  We present the observations of penumbra like features (PLFs) near a
  polarity inversion line (PIL) of flaring region. The PIL is located
  at the moat boundary of active region (NOAA 10960). The PLFs appear
  similar to sunspot penumbrae in morphology but occupy small area,
  about 6$\times10^{7}$ km$^{2}$, and are not associated with sunspot or
  pore. We observed a rapid disappearance of the PLFs after a C1.7 class
  flare, which occurred close to the PIL. The local correlation tracking
  (LCT) of these features shows presence of horizontal flows directed
  away from the end-points of the PLFs, similar to the radial outward
  flow found around regular sunspots, which is also known as the moat
  flow. Hard X-ray emission, coincident with the location of the PLFs,
  is found in RHESSI observations, suggesting a spatial correlation
  between the occurrence of the flare and decay of the PLFs. Vector
  magnetic field derived from the observations obtained by Hinode
  spectro-polarimeter SOT/SP instrument, before and after the flare,
  shows a significant change in the horizontal as well as the vertical
  component of the field, after the flare. The weakening of both the
  components of the magnetic field in the flare interval suggests that
  rapid cancellation and/or submergence of the magnetic field in PLFs
  occurred during the flare interval.

---------------------------------------------------------
Title: Detecting the Large Scale Magnetic Helicity Patterns on the
    Sun using SOLIS/VSM and SDO/HMI fulldisk vector magnetograms
Authors: Gosain, S.; Pevtsov, A. A.; Rudenko, G. V.; Anfinogentov,
   S. A.
2011AGUFMSH31A1996G    Altcode:
  We use fulldisk vector magnetograms observed by the SOLIS/VSM and
  SDO/HMI instruments to compute the large scale helicity patterns on the
  sun. Such studies have been carried out in the past using the vector
  magnetograms reconstructed from temporal sequence of longitudinal
  magnetograms. These earlier results suggest the presence of a
  hemispheric pattern in the sign of current helicity density. However,
  these reconstructed vector magnetograms have their limitations as
  they are based on certain assumptions. On the other hand, the direct
  observations of the vector magnetic field of the full sun by SOLIS/VSM
  and SDO/HMI instruments can now be used to investigate the large scale
  magnetic helicity patterns on the sun. We use the newly developed
  SFQ azimuth disambiguation method in our study. This method has been
  shown to work better for fulldisk vector magnetograms as it solves
  the ambiguity in spherical geometry. We present the first results of
  current helicity computation for full disk vector magnetograms and
  compare the inferences from two instruments.

---------------------------------------------------------
Title: Evolution of twist-shear and dip-shear in flaring active
    region NOAA 10930
Authors: Gosain, Sanjay; Venkatakrishnan, P.
2011IAUS..273..212G    Altcode: 2010arXiv1010.0532G
  We study the evolution of magnetic shear angle in a flare productive
  active region NOAA 10930. The magnetic shear angle is defined as the
  deviation in the orientation of the observed magnetic field vector with
  respect to the potential field vector. The shear angle is measured in
  horizontal as well as vertical plane. The former is computed by taking
  the difference between the azimuth angles of the observed and potential
  field and is called the twist-shear, while the latter is computed by
  taking the difference between the inclination angles of the observed
  and potential field and is called the dip-shear. The evolution of the
  two shear angles is then tracked over a small region located over the
  sheared penumbra of the delta sunspot in NOAA 10930. We find that,
  while the twist-shear shows an increasing trend after the flare the
  dip-shear shows a significant drop after the flare.

---------------------------------------------------------
Title: Distribution of magnetic shear angle in an emerging flux region
Authors: Gosain, Sanjay
2011IAUS..273..347G    Altcode: 2010arXiv1010.0534G
  We study the distribution of magnetic shear in an emerging flux region
  using the high-resolution Hinode/SOT SP observations. The distribution
  of mean magnetic shear angle across the active region shows large
  values near region of flux emergence i.e., in the middle of existing
  bipolar region and decreases while approaching the periphery of the
  active region.

---------------------------------------------------------
Title: Hemispheric Trends In The Current Helicity Of The Large Scale
Solar Magnetic Fields : Vsm/solis And Hmi/sdo Observations
Authors: Gosain, Sanjay; Pevtsov, A.
2011SPD....42.1719G    Altcode: 2011BAAS..43S.1719G
  The current helicity of the large-scale magnetic fields has been
  computed in the past by using reconstructed vector magnetograms. Such
  magnetograms were derived by using sequence of line-of-sight
  magnetograms (Pevtsov A. A., and Latushko S. M.: 2000) and were
  used for studying the helicity patterns during cycle 22 and 23. The
  reconstruction method, however, made several assumptions, and the
  meridional component could not be reconstructed very well. Full disk
  vector magnetograms, which are now available from VSM/SOLIS and HMI/SDO
  are very promising to make a systematic study of large scale helicity
  patterns during cycle 24, which is in its onset phase. In this paper
  we shall discuss our preliminary results about the large-scale helicity
  patterns in the beginning of cycle 24 using VSM/SOLIS and HMI/SDO full
  disk vector magnetograms.

---------------------------------------------------------
Title: Acoustic Power Absorption and its Relation to Vector Magnetic
    Field of a Sunspot
Authors: Gosain, S.; Mathew, S. K.; Venkatakrishnan, P.
2011SoPh..268..335G    Altcode: 2010arXiv1008.1456G; 2010SoPh..tmp..163G
  The distribution of acoustic power over sunspots shows an enhanced
  absorption near the umbra - penumbra boundary. Previous studies revealed
  that the region of enhanced absorption coincides with the region of
  strongest transverse potential field. The aim of this paper is to i)
  utilize the high-resolution vector magnetograms derived using Hinode
  SOT/SP observations and study the relationship between the vector
  magnetic field and power absorption and ii) study the variation of
  power absorption in sunspot penumbrae due to the presence of spine-like
  radial structures.

---------------------------------------------------------
Title: Solar Polar Fields During Cycles 21 - 23: Correlation with
    Meridional Flows
Authors: Janardhan, P.; Bisoi, Susanta K.; Gosain, S.
2010SoPh..267..267J    Altcode: 2010arXiv1009.4299J; 2010SoPh..tmp..189J
  We have examined polar magnetic fields for the last three solar cycles,
  viz. Cycles 21, 22, and 23 using NSO/Kitt Peak synoptic magnetograms. In
  addition, we have used SOHO/MDI magnetograms to derive the polar fields
  during Cycle 23. Both Kitt Peak and MDI data at high latitudes (78° -
  90°) in both solar hemispheres show a significant drop in the absolute
  value of polar fields from the late declining phase of the Solar
  Cycle 22 to the maximum of the Solar Cycle 23. We find that long-term
  changes in the absolute value of the polar field, in Cycle 23, are
  well correlated with changes in meridional-flow speeds that have been
  reported recently. We discuss the implication of this in influencing
  the extremely prolonged minimum experienced at the start of the current
  Cycle 24 and in forecasting the behavior of future solar cycles.

---------------------------------------------------------
Title: The Evolution of the Twist Shear and Dip Shear During X-class
Flare of 2006 December 13: Hinode Observations
Authors: Gosain, Sanjay; Venkatakrishnan, P.
2010ApJ...720L.137G    Altcode: 2010arXiv1007.2702G
  The non-potentiality of solar magnetic fields is traditionally measured
  in terms of a magnetic shear angle, i.e., the angle between the observed
  and potential field azimuths. Here, we introduce another measure of the
  shear that has not been previously studied in solar active regions,
  i.e., the one that is associated with the inclination angle of the
  magnetic field. This form of the shear, which we call "dip shear,"
  can be calculated by taking the difference between the observed and the
  potential field inclination. In this Letter, we study the evolution of
  the dip shear as well as the conventional twist shear in a δ-sunspot
  using high-resolution vector magnetograms from the Hinode space
  mission. We monitor these shears in a penumbral region located close
  to a flaring site during 2006 December 12 and 13. It is found that (1)
  the penumbral area close to the flaring site shows a high value of the
  twist shear and dip shear as compared with other parts of the penumbra,
  (2) after the flare, the value of the dip shear drops in this region
  while the twist shear tends to increase, (3) the dip shear and twist
  shear are correlated such that pixels with a large twist shear also
  tend to exhibit a large dip shear, and (4) the correlation between
  the twist shear and dip shear is tighter after the flare. The present
  study suggests that monitoring the twist shear alone during the flare is
  not sufficient, but we need to monitor it together with the dip shear.

---------------------------------------------------------
Title: Magnetic Non-potentiality of Solar Active Regions and Peak
    X-ray Flux of the Associated Flares
Authors: Tiwari, Sanjiv Kumar; Venkatakrishnan, P.; Gosain, Sanjay
2010ApJ...721..622T    Altcode: 2010arXiv1007.4876T
  Predicting the severity of solar eruptive phenomena such as flares and
  coronal mass ejections remains a great challenge despite concerted
  efforts to do so over the past several decades. However, the advent
  of high-quality vector magnetograms obtained from Hinode (SOT/SP) has
  increased the possibility of meeting this challenge. In particular,
  the spatially averaged signed shear angle (SASSA) seems to be a
  unique parameter for quantifying the non-potentiality of active
  regions. We demonstrate the usefulness of the SASSA for predicting
  flare severity. For this purpose, we present case studies of the
  evolution of magnetic non-potentiality using 115 vector magnetograms of
  four active regions, namely, ARs NOAA 10930, 10960, 10961, and 10963
  during 2006 December 8-15, 2007 June 3-10, 2007 June 28-July 5, and
  2007 July 10-17, respectively. The NOAA ARs 10930 and 10960 were very
  active and produced X and M class flares, respectively, along with many
  smaller X-ray flares. On the other hand, the NOAA ARs 10961 and 10963
  were relatively less active and produced only very small (mostly A-
  and B-class) flares. For this study, we have used a large number of
  high-resolution vector magnetograms obtained from Hinode (SOT/SP). Our
  analysis shows that the peak X-ray flux of the most intense solar
  flare emanating from the active regions depends on the magnitude of
  the SASSA at the time of the flare. This finding of the existence of
  a lower limit of the SASSA for a given class of X-ray flares will be
  very useful for space weather forecasting. We have also studied another
  non-potentiality parameter called the mean weighted shear angle (MWSA)
  of the vector magnetograms along with the SASSA. We find that the MWSA
  does not show such distinction as the SASSA for upper limits of the
  GOES X-ray flux of solar flares; however, both the quantities show
  similar trends during the evolution of all active regions studied.

---------------------------------------------------------
Title: On the Estimate of Magnetic Non-potentiality of Sunspots
Derived Using Hinode SOT/SP Observations: Effect of Polarimetric Noise
Authors: Gosain, Sanjay; Tiwari, Sanjiv Kumar; Venkatakrishnan, P.
2010ApJ...720.1281G    Altcode: 2010arXiv1007.2505G
  The accuracy of Milne-Eddington (ME) inversions, used to retrieve the
  magnetic field vector, depends upon the signal-to-noise ratio (S/N)
  of the spectro-polarimetric observations. The S/N in real observations
  varies from pixel to pixel; therefore the accuracy of the field vector
  also varies over the map. The aim of this work is to study the effect
  of polarimetric noise on the inference of the magnetic field vector
  and the magnetic non-potentiality of a real sunspot. To this end,
  we use the Hinode SOT/SP vector magnetogram of a real sunspot NOAA
  10933 as an input to generate synthetic Stokes profiles under ME model
  assumptions. We then add normally distributed polarimetric noise of
  the level 0.5% of continuum intensity to these synthetic profiles and
  invert them again using the ME code. This process is repeated 100 times
  with different realizations of noise. It is found that within most of
  the sunspot areas (&gt;90% area) the spread in the (1) field strength
  is less than 8 G, (2) field inclination is less than 1°, and (3)
  field azimuth is less than 5°. Further, we determine the uncertainty
  in the magnetic non-potentiality of a sunspot as determined by the
  force-free parameter α<SUB> g </SUB> and spatially averaged signed
  shear angle (SASSA). It is found that for the sunspot studied here
  these parameters are α<SUB> g </SUB> = -3.5 ± 0.37(×10<SUP>-9</SUP>
  m<SUP>-1</SUP>) and SASSA = -1.68 ± 0fdg014. This suggests that the
  SASSA is a less dispersed non-potentiality parameter as compared to
  α<SUB> g </SUB>. Further, we examine the effect of increasing noise
  levels, viz. 0.01%, 0.1%, 0.5%, and 1% of continuum intensity, and
  find that SASSA is less vulnerable to noise as compared to the α<SUB>
  g </SUB> parameter.

---------------------------------------------------------
Title: A Technique for Removing Background Features in SECCHI -
EUVI He II 304 Å Filtergrams: Application to the Filament Eruption
    of 22 May 2008
Authors: Artzner, G.; Gosain, S.; Schmieder, B.
2010SoPh..262..437A    Altcode: 2010SoPh..tmp...41A; 2010SoPh..tmp...53A; 2010arXiv1001.4884A
  The STEREO mission has been providing a stereoscopic view of filament
  eruptions in the EUV. The clearest view during a filament eruption
  is seen in He II 304 Å observations. One of the main problems in
  visualizing filament dynamics in He II 304 Å is the strong background
  contrast due to surface features. We present a technique that removes
  background features and leaves behind only the filamentary structure, as
  seen by STEREO-A and -B. The technique uses a pair of STEREO He II 304
  Å images observed simultaneously. The STEREO-B image is geometrically
  transformed to a STEREO-A view so that the background images appear
  similar. Filaments, being elevated structures, i.e., not lying on the
  same spherical surface as background features, do not appear similar
  in the transformed view. Thus, subtracting the two images cancels
  the background but leaves behind the filament structure. We apply this
  technique to study the dynamics of the filament-eruption event of 22 May
  2008, which was observed by STEREO and followed by several ground-based
  observatories participating in the Joint Observing Programme (JOP 178).

---------------------------------------------------------
Title: Magnetic Field Structures in a Facular Region Observed by
    THEMIS and Hinode
Authors: Guo, Y.; Schmieder, B.; Bommier, V.; Gosain, S.
2010SoPh..262...35G    Altcode: 2010SoPh..tmp...30G; 2010arXiv1002.4355G
  The main objective of this paper is to build and compare vector
  magnetic maps obtained by two spectral polarimeters, i.e. THEMIS/MTR and
  Hinode SOT/SP, using two inversion codes (UNNOFIT and MELANIE) based
  on the Milne - Eddington solar atmosphere model. To this end, we used
  observations of a facular region within active region NOAA 10996 on 23
  May 2008, and found consistent results concerning the field strength,
  azimuth and inclination distributions. Because SOT/SP is free from the
  seeing effect and has better spatial resolution, we were able to resolve
  small magnetic polarities with sizes of 1″ to 2″, and we could
  detect strong horizontal magnetic fields, which converge or diverge
  in negative or positive facular polarities. These findings support
  models which suggest the existence of small vertical flux tube bundles
  in faculae. A new method is proposed to get the relative formation
  heights of the multi-lines observed by MTR assuming the validity of
  a flux tube model for the faculae. We found that the Fe I 6302.5 Å
  line forms at a greater atmospheric height than the Fe I 5250.2 Å line.

---------------------------------------------------------
Title: Coherent Lateral Motion of Penumbral Filaments during
    X-class Flare
Authors: Gosain, S.; Venkatakrishnan, P.; Tiwari, Sanjiv Kumar
2010arXiv1002.0397G    Altcode:
  The high-resolution pictures of the solar photosphere from space
  based 50 cm Solar Optical Telescope (SOT) on-board Hinode spacecraft,
  are now routinely observed. Such images of a delta-sunspot in NOAA
  10930 were obtained by Hinode during 13 December 2006 while a X-class
  flare occurred in this active region. Two bright ribbons were visible
  even in white light and G-band images apart from chromospheric Ca II
  H images. We register the sunspot globally using cross-correlation
  technique and analyse local effects during flare interval. We find
  that during flare the penumbral filaments show lateral motion. Also,
  we locate two patches, one in either polarity, which show converging
  motion towards the polarity inversion line (PIL). In Ca II H images
  we find kernel with pre-flare brightening which lie along the PIL.

---------------------------------------------------------
Title: Estimation of width and inclination of a filament sheet using
    He II 304 Å observations by STEREO/EUVI
Authors: Gosain, S.; Schmieder, B.
2010AnGeo..28..149G    Altcode: 2010arXiv1001.3004G
  The STEREO mission has been providing stereoscopic view of the
  filament eruptions in EUV wavelengths. The most extended view during
  filament eruptions is seen in He II 304 Å observations, as the
  filament spine appears darker and sharper. The projected filament
  width appears differently when viewed from different angles by STEREO
  satellites. Here, we present a method for estimating the width and
  inclination of the filament sheet using He II 304 Å observations
  by STEREO-A and B satellites from the two viewpoints. The width of
  the filament sheet, when measured from its feet to its apex, gives
  estimate of filament height above the chromosphere.

---------------------------------------------------------
Title: Phase III of the USO Solar Vector Magnetograph
Authors: Gosain, S.; Venkatakrishnan, P.
2010ASSP...19..395G    Altcode: 2009arXiv0907.5267G; 2010mcia.conf..395G
  The solar vector magnetograph (SVM) is a modern imaging
  spectropolarimeter installed at Udaipur Solar Observatory (USO). Earlier
  phases saw the development of the instrument using off-the-shelf
  components with in-house software development. Subsequently,
  improvements were done in the opto-mechanical design of the sub-systems
  and the telescope tracking system. The third phase of the instrument
  development saw three major improvements: (1) installation of a
  web-camera-based telescope guiding system, developed in-house,
  (2) high-cadence spectropolarimetry using liquid-crystal variable
  retarders and a fast CCD camera, and (3) inclusion of the Na I D1
  line for chromospheric observations, in addition to the regularly used
  photospheric Fe I 6302 Å line.

---------------------------------------------------------
Title: A 3D view of eruptive filaments by STEREO
Authors: Gosain, Sanjay; Schmieder, Brigitte; Venkatakrishnan, P.;
   Chandra, Ramesh; Artzner, Guy
2010cosp...38.2916G    Altcode: 2010cosp.meet.2916G
  STEREO/SECHI/EUVI A and B observe different views of the eruption of a
  quiescent filament. We will concentrate on two events: (i) May 20 to 22,
  2008 event (A and B separated by 52.4 degrees from each other), and (ii)
  September 25 to 26, 2009 event (A and B more than 100 degrees from each
  other. After using different techniques of reconstruction we obtained
  a 3 dimensional view of untwisted flux ropes in He II 304 Angstrom,
  with fine structures. The entire disappearance phase lasted more than
  ten hours. The filament evolved very slowly ( 5 km/s) from a dense
  structure with a thick spine into fine threads. Individual threads are
  seen to be oscillating and rising to an altitude of about 150 Mm with
  velocities of about 100 km/s. The plasma disappears by diffusion in
  the corona. Weak CME events are recorded by LASCO at the beginning of
  the disappearance. In this paper we shall present the dynamics of the
  filament eruptions as viewed in 3D by STEREO using different methods. We
  shall explore the causes and consequences of the filament disappearance.

---------------------------------------------------------
Title: HINODE Observations of Coherent Lateral Motion of Penumbral
    Filaments During an X-Class Flare
Authors: Gosain, S.; Venkatakrishnan, P.; Tiwari, Sanjiv Kumar
2009ApJ...706L.240G    Altcode: 2009arXiv0910.5336G
  The X-3.4 class flare of 2006 December 13 was observed with a high
  cadence of 2 minutes at 0.2 arcsec resolution by HINODE/SOT FG
  instrument. The flare ribbons could be seen in G-band images also. A
  careful analysis of these observations after proper registration
  of images shows flare-related changes in penumbral filaments of the
  associated sunspot for the first time. The observations of sunspot
  deformation, decay of penumbral area, and changes in magnetic flux
  during large flares have been reported earlier in the literature. In
  this Letter, we report lateral motion of the penumbral filaments in
  a sheared region of the δ-sunspot during the X-class flare. Such
  shifts have not been seen earlier. The lateral motion occurs in two
  phases: (1) motion before the flare ribbons move across the penumbral
  filaments and (2) motion afterward. The former motion is directed away
  from expanding flare ribbons and lasts for about 4 minutes. The latter
  motion is directed in the opposite direction and lasts for more than
  40 minutes. Further, we locate a patch in adjacent opposite polarity
  spot moving in opposite direction to the penumbral filaments. Together
  these patches represent conjugate footpoints on either side of the
  polarity inversion line, moving toward each other. This converging
  motion could be interpreted as shrinkage of field lines.

---------------------------------------------------------
Title: 3D Evolution of a Filament Disappearance Event Observed
    by STEREO
Authors: Gosain, S.; Schmieder, B.; Venkatakrishnan, P.; Chandra,
   R.; Artzner, G.
2009SoPh..259...13G    Altcode: 2009arXiv0910.0786G
  A filament disappearance event was observed on 22 May 2008 during
  our recent campaign JOP 178. The filament, situated in the Southern
  Hemisphere, showed sinistral chirality consistent with the hemispheric
  rule. The event was well observed by several observatories,
  in particular by THEMIS. One day, before the disappearance, Hα
  observations showed up- and down-flows in adjacent locations along the
  filament, which suggest plasma motions along twisted flux rope. THEMIS
  and GONG observations show shearing photospheric motions leading
  to magnetic flux canceling around barbs. STEREO A, B spacecraft
  with separation angle 52.4°, showed quite different views of this
  untwisting flux rope in He II 304 Å images. Here, we reconstruct the
  three-dimensional geometry of the filament during its eruption phase
  using STEREO EUV He II 304 Å images and find that the filament was
  highly inclined to the solar normal. The He II 304 Å movies show
  individual threads, which oscillate and rise to an altitude of about
  120 Mm with apparent velocities of about 100 km s<SUP>−1</SUP>
  during the rapid evolution phase. Finally, as the flux rope expands
  into the corona, the filament disappears by becoming optically thin to
  undetectable levels. No CME was detected by STEREO, only a faint CME
  was recorded by LASCO at the beginning of the disappearance phase at
  02:00 UT, which could be due to partial filament eruption. Further,
  STEREO Fe XII 195 Å images showed bright loops beneath the filament
  prior to the disappearance phase, suggesting magnetic reconnection
  below the flux rope.

---------------------------------------------------------
Title: Effect of Polarimetric Noise on the Estimation of Twist and
    Magnetic Energy of Force-Free Fields
Authors: Tiwari, Sanjiv Kumar; Venkatakrishnan, P.; Gosain, Sanjay;
   Joshi, Jayant
2009ApJ...700..199T    Altcode: 2009arXiv0904.4594T
  The force-free parameter α, also known as helicity parameter or twist
  parameter, bears the same sign as the magnetic helicity under some
  restrictive conditions. The single global value of α for a whole active
  region gives the degree of twist per unit axial length. We investigate
  the effect of polarimetric noise on the calculation of global α value
  and magnetic energy of an analytical bipole. The analytical bipole
  has been generated using the force-free field approximation with a
  known value of constant α and magnetic energy. The magnetic parameters
  obtained from the analytical bipole are used to generate Stokes profiles
  from the Unno-Rachkovsky solutions for polarized radiative transfer
  equations. Then we add random noise of the order of 10<SUP>-3</SUP>
  of the continuum intensity (I <SUB> c </SUB>) in these profiles to
  simulate the real profiles obtained by modern spectropolarimeters such
  as Hinode (SOT/SP), SVM (USO), ASP, DLSP, POLIS, and SOLIS etc. These
  noisy profiles are then inverted using a Milne-Eddington inversion
  code to retrieve the magnetic parameters. Hundred realizations of this
  process of adding random noise and polarimetric inversion is repeated
  to study the distribution of error in global α and magnetic energy
  values. The results show that (1) the sign of α is not influenced
  by polarimetric noise and very accurate values of global twist can
  be calculated, and (2) accurate estimation of magnetic energy with
  uncertainty as low as 0.5% is possible under the force-free condition.

---------------------------------------------------------
Title: A 2-dimensional Scanning Solar Vector Magnetograph at Udaipur
    Solar Observatory
Authors: Gosain, S.; Venkatakrishnan, P.
2009ASPC..405..467G    Altcode:
  We describe a newly developed instrument used for performing filter
  based spectro-polarimetry of solar active regions. The instrument
  consists of a tunable Fabry-Perot etalon kept in collimated arrangement
  for spectroscopy in the wavelength range 550 to 700 nm. The polarimeter
  consists of two quarter wave-plates and a dual-beam calcite analyzer
  (Savart plate). We present the instrument design and the interactive
  tools for data analysis and visualization. These tools facilitate
  Milne-Eddington inversion, visualization, heliographic vector
  transformations and 180 degree ambiguity resolution. It is planned
  to upgrade the instrument to observe in chromospheric Na D2 and H-α
  lines together with photospheric Fe I 630.2 nm line pair, in near
  simultaneous mode.

---------------------------------------------------------
Title: Chapter 4: Solar Magnetism
Authors: Venkatakrishnan, P.; Gosain, Sanjay
2008psa..book...39V    Altcode:
  This chapter is basically divided into 2 parts. In the first part, the
  important properties of the solar magnetic field are summarized. The
  discussion begins with a simple introduction to solar magneto
  hydrodynamics. This introduction will be sufficient to understand
  the current status of the solar dynamo theory that follows. Some very
  curious and interesting results on force free fields are then presented
  in very basic terms. Finally, the application of this theoretical
  framework to the problems of coronal heating, solar flares and coronal
  mass ejections are developed in a simple unified scheme, based on a
  hierarchy of physical conditions. The second part consists of a tutorial
  on magnetographs. It begins with a description of polarization of light
  from very fundamental notions of coherence of light. This is followed
  by simple but comprehensive explanations of the Zeeman and Hanle effects
  along with the necessary basic ideas of quantum physics of scattering of
  light. Then the working of a few important magnetographs is outlined,
  with special emphasis on a solar vector magnetograph developed for
  USO, to provide a ”hands on" perspective. The article concludes with
  a few brief remarks on the possible future directions for research in
  the domain of solar magnetism...

---------------------------------------------------------
Title: Software for interactively visualizing solar vector
    magnetograms of udaipur solar observatory
Authors: Gosain, Sanjay; Tiwari, Sanjiv; Joshi, Jayant;
   Venkatakrishnan, P.
2008JApA...29..107G    Altcode:
  No abstract at ADS

---------------------------------------------------------
Title: Evolution of Magnetic Helicity in NOAA 10923 Over Three
    Consecutive Solar Rotations
Authors: Tiwari, Sanjiv Kumar; Joshi, Jayant; Gosain, Sanjay;
   Venkatakrishnan, P.
2008ASSP...12..329T    Altcode: 2009arXiv0904.4024T; 2008tdad.conf..329T
  We have studied the evolution of magnetic helicity and chirality
  in an active region over three consecutive solar rotations. The
  region where it first appeared was named NOAA10923 and in subsequent
  rotations it was numbered NOAA 10930, 10935 and 10941. We compare the
  chirality of these regions at photospheric, chromospheric and coronal
  heights. The observations used for photospheric and chromospheric
  heights are taken from Solar Vector Magnetograph (SVM) and H-α imaging
  telescope of Udaipur Solar Observatory (USO), respectively. We discuss
  the chirality of the sunspots and associated H-α filaments in these
  regions. We find that the twistedness of superpenumbral filaments is
  maintained in the photospheric transverse field vectors also. We also
  compare the chirality at photospheric and chromospheric heights with
  the chirality of the associated coronal loops, as observed from the
  HINODE X-Ray Telescope.

---------------------------------------------------------
Title: Polarimetric Studies of the Solar Atmosphere
Authors: Gosain, Sanjay
2007PhDT........21G    Altcode:
  Solar magnetic fields play an important role in the variety of activity
  phenomena observed on the sun. They are present right from Sun's deep
  radiative interior up-to the heliopause. Their evolution, mainly
  due to photospheric dynamics and flux emergence, leads to activity
  phenomena like flares, filament eruptions, Coronal Mass Ejections
  (CMEs). These phenomena directly affect near-Earth space weather by
  the accompanying high-energy radiation and charged particles. In order
  to predict these events a detailed understanding of solar magnetic
  structures is required. Thus, task of measuring solar magnetic fields
  is of utmost importance in solar physics. However, the measurement of
  solar magnetic fields is very challenging task. The challenge comes
  mainly from the fact that the measurements need to be done remotely
  by sensing the polarization (due to Zeeman effect) of solar spectral
  lines. Also, the distortions in imaging due to atmospheric "seeing"
  leads to poor spatial resolution and effects polarization measurements
  . The focus of this thesis is on the measurement aspects of solar
  magnetic fields. A new instrument is developed for measuring the
  vector magnetic fields in the photosphere. The instrument is called
  Solar Vector Magnetograph (SVM). The key features of the instrument are
  (i) symmetric imaging optics with no oblique reflections, to minimize
  instrumental polarization, (ii) a tunable narrow-band imaging filter
  for scanning the spectral line, which is based on Fabry-Perot etalon,
  (iii) dual-beam polarization analyzer (Savart Plate), to minimize
  seeing induced spurious polarization signals, and (iv) a self-developed
  instrument control software for automated observations. Further,
  a data-reduction and analysis package with graphical user interface
  (GUI) is developed for interactive data reduction. The interpretation
  of observed polarization, i.e., Stokes profiles, in terms of magnetic
  field vector is done by fitting them with theoretical profiles under
  Milne-Eddington model atmosphere assumptions. The packages are developed
  for this purpose as well as for the analysis and visualization of vector
  magnetograms. Finally, a study of the effect of vector magnetic field
  parameters on the solar acoustic p-modes is carried out.

---------------------------------------------------------
Title: Solar Vector Magnetograph at Udaipur Solar Observatory:
    New Results (P18)
Authors: Gosain, S.
2006ihy..workE.110G    Altcode:
  A new Solar Vector Magnetograph has become operational at Udaipur
  Solar Observatory. The magnetograph is a straight telescope with no net
  instrumental polarization. The instrument consists of servo stabilized
  Fabry-Perot etalon which acts as a tunable narrow band filter. A
  dual beam polarimeter is designed to overcome seeing induced spurious
  polarization effects. The polarimeter modulator consists of two quartz
  waveplates mounted in a precision rotary mount. The polarization is
  measured at different wavelength positions across the spectral line. The
  polarized line profiles thus observed are reduced and inverted under
  Milne-Eddington inversion scheme. I would like to present the details
  of the instrument and its observational capabilities. Also, the data
  analysis and reduction software will be described.

---------------------------------------------------------
Title: Acoustic power and magnetic field orientation in a large
    sunspot
Authors: Gosain, S.; Venkatakrishnan, P.; Venugopalan, K.
2006ESASP.624E..59G    Altcode: 2006soho...18E..59G
  No abstract at ADS

---------------------------------------------------------
Title: Design and Status of Solar Vector Magnetograph (SVM-I) at
    Udaipur Solar Observatory
Authors: Gosain, Sanjay; Venkatakrishnan1, P.; Venugopalan, K.
2006JApA...27..285G    Altcode:
  We present the status of the instrument called SolarVector
  Magnetograph Phase-I (SVM-I) currently being developed at Udaipur
  Solar Observatory. SVM-I is an instrument which aims to determine the
  magnetic field vector in the solar atmosphere by measuring Zeeman
  induced polarization across the spectral line. The instrument is
  currently in a preliminary development stage, with all components
  under an evaluation process. The integration of components is being
  done. The integrated performance of the system on a tracking mount
  and its control software is being tested. Some test observations
  of sunspots has been carried out. In this paper we give a technical
  description of the hardware and software elements of the instrument
  and present the polarized images obtained during test observations.

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Title: H<SUB>α</SUB> Observations of 8 June, 2004 Venus Transit
Authors: Ambastha, Ashok; Ravindra, B.; Gosain, Sanjay
2006SoPh..233..171A    Altcode:
  The cosmic event of Venus transit across the solar disk occurred on 8
  June, 2004. The previous such event was witnessed about 122 years ago
  on 6 December, 1882. We observed this rare transit in H<SUB>α</SUB>
  6563 Å line-center from Udaipur Solar Observatory (USO) using both
  the full-disk and small field-of-view solar telescopes. In the earlier
  historical transits, a "black-drop" effect was observed in white light
  images, during the contact phases. The transit of 8 June, 2004 provided
  a unique opportunity to observe this effect, for the first time, in
  H<SUB>α</SUB>. We report that the "black-drop" effect is present in
  H<SUB>α</SUB> also, as in the white light observations made by the
  ground-based Global Oscillation Network Group (GONG) instrument and the
  space-borne Transition Region and Coronal Explorer (TRACE) satellite. We
  did not observe any noticeable "aureole" (atmospheric glow) around Venus
  during the ingress or egress phases. We have compared the H<SUB>α</SUB>
  images with the multi-wavelength data obtained from the TRACE satellite.

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Title: Preliminary Results of Venus Transit of June 8, 2004 Observed
    in Hα 6563 Å
Authors: Ravindra, B.; Ambastha, Ashok; Gosain, Sanjay
2005BASI...33..366R    Altcode:
  The rare cosmic event of Venus transit across the solar disk occurred
  on 8th June 2004, i.e. ~ 122 years after the last such event which
  occurred in observed on 6 December 1882. The event was observed
  at Udaipur Solar Observatory using full-disk, as well as, small
  field-of-view high resolution solar telescopes, and recorded in the
  nearly monochromatic light of Hα 6563 Å. High resolution solar images
  were taken at a cadence of 3 seconds during the period 05:10-05:30 UT
  which covered the Ist and IInd contacts of Venus. This was repeated
  during the period 11:10-11:30 UT covering the IIIrd and IVth contacts,
  while the images were obtained at a lower cadence between the period of
  the IInd and IIIrd contacts. Altogether, around 4000 filtergrams were
  obtained. We have compared our observations with the multi-wavelength
  data obtained from TRACE satellite. We studied the optical effects
  that cause the "black-drop" and the "atmospheric-glow" around Venus at
  the time of its I-II, and III-IV contacts. We have also compared the
  difference in contact timings observed in different wavelength bands.

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Title: Design of Instrument Control Software for Solar Vector
    Magnetograph at Udaipur Solar Observatory
Authors: Gosain, Sanjay; Venkatakrishnan, P.; Venugopalan, K.
2004ExA....18...31G    Altcode:
  A magnetograph is an instrument which makes measurement of solar
  magnetic field by measuring Zeeman induced polarization in solar
  spectral lines. In a typical filter based magnetograph there are three
  main modules namely, polarimeter, narrow-band spectrometer (filter),
  and imager(CCD camera). For a successful operation of magnetograph
  it is essential that these modules work in synchronization with each
  other. Here, we describe the design of instrument control system
  implemented for the Solar Vector Magnetograph under development at
  Udaipur Solar Observatory. The control software is written in Visual
  Basic and exploits the Component Object Model (COM) components for
  a fast and flexible application development. The user can interact
  with the instrument modules through a Graphical User Interface
  (GUI) and can program the sequence of magnetograph operations. The
  integration of Interactive Data Language (IDL) ActiveX components
  in the interface provides a powerful tool for online visualization,
  analysis and processing of images.

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Title: Simultaneous Stokes-V diagnostic of a Sunspot using Mg b and
    Fe I lines
Authors: Gosain, Sanjay; Prasad Choudhary, Debi
2003SoPh..217..119G    Altcode:
  Simultaneous observations of Stokes profiles in photospheric Fei
  (630.15 nm and 630.25 nm) and chromospheric Mgi b<SUB>1</SUB>
  and b<SUB>2</SUB> (518.4 nm and 517.3 nm) lines over a sunspot are
  presented. Observations were carried out using the Advanced Stokes
  Polarimeter of HAO/NSO, VTT, SacPeak, U.S.A. The Stokes-V amplitude
  asymmetries for these lines are analyzed. The values of amplitude
  asymmetry in Mgb lines are negative in disk-center-side penumbra while
  they are positive in limb-side penumbra. This trend is similar in nature
  to photospheric Fei line observations. Further, the spatial distribution
  of Stokes-V asymmetry is analyzed using Net Circular Polarization
  (NCP) maps. The chromospheric and photospheric NCP maps are different
  in many aspects. These observations with longitudinal magnetic field,
  estimated using weak field approximation, are discussed in this paper.

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Title: White Light and Emission Line Polarization of Solar Corona
    during TSE of June 21, 2001
Authors: Ambastha, Ashok; Gosain, Sanjay
2003BASI...31..295A    Altcode:
  Coronal intensity and polarization maps have been obtained for the total
  solar eclipse (TSE) o o of June 21, 2001, observed from Lusaka, Zambia
  (location: 28 17.5E 15 24.5S, Alt. 1300 mtr) at broadband H 6563Å
  (FWHM 80Å), as well as, around the coronal emission lines 5303Å
  (FWHM 12Å), and 6374Å (FWHM 12Å). The results are discussed.

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Title: Magnetic and velocity fields of active regions
Authors: Choudhary, D. P.; Gosain, S.
2003AN....324..362C    Altcode:
  We have observed about 15 active regions on the Sun, with the Advanced
  Stokes Polarimeter and Dick Dunn Telescope at NSO/SP to map the Stokes
  parameters in the photospheric Fe 6302.5 Å and chromospheric Mg i
  5173 Å lines, during 1999-2002. The observations are corrected for
  dark current, gain, instrumental polarization and cross-talk using
  ASP pipeline. The wavelength calibration is carried out using the O_2
  telluric line 6302 Å which is also present in the observations. The
  photospheric and chromospheric longitudinal magnetograms are made from
  the Stokes V profiles, which were inter-calibrated with the Kitt Peak
  magnetograms. The plasma motions are inferred from the line bisector
  measurements at different positions of the spectral line. In this paper
  we present the height dependence of Doppler velocity scatter plots of
  a sunspot in the photospheric Fe i 6302 Å line.

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Title: Study of bright points in the off-band Hα filtergrams of
    active regions
Authors: Choudhary, D. P.; Gosain, S.
2003AN....324..367C    Altcode:
  Hα filtergrams of selected active regions are obtained by the six inch
  refractor telescope at Udaipur Solar Observatory through a birefringent
  filter of 0.5 Å full width at half maximum. The field of view is ~
  4x5 arcmin with a spatial resolution of better than one arc sec. The
  filtergrams are obtained in the wavelength range of -1 to +1 Å centered
  at 6563 Å at steps of 0.1 Å. A complete scan takes about 5 seconds
  (occasionally longer). The images are recorded with a cooled CCD camera
  and corrected for dark current and flat field. We observe the bright
  points in the filtergrams beyond 0.5 Å off line center. In general,
  these features are located away from the strong field regions. We
  study their property with respect to the co-temporal photospheric
  magnetograms obtained with the GONG instrument at Udaipur. This might
  help in understanding their relation with the magnetic flux emergence
  and annihilation.

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Title: The Source of a coronal mass ejection in a decayed solar
    active region
Authors: Prasad Choudhary, Debi; Srivastava, Nandita; Gosain, Sanjay
2002A&A...395..257P    Altcode: 2002A&A...395..257C
  We have studied the source of a coronal mass ejection (CME), which
  occurred in a decayed active region NOAA 7978 on 19 October, 1996. The
  active region NOAA 7978 first appeared on the solar disk on 2 June,
  1996 and made more than five disk passages before it decayed. The event
  analysed in this paper was observed during fifth disk passage. We have
  attempted to identify the mechanism responsible for triggering this
  CME based on the analysis of photospheric magnetograms (MDI/SoHO),
  chromospheric filtergrams (Meudon and Big Bear Observatories) and
  coronal images (SXT/Yohkoh). We found that the emergence of new bipoles
  in the active region led to the eruption of a low-lying sheared filament
  observed in SXT images, subsequently followed by filament eruption
  observed both in H<SUB>alpha</SUB> and EUV wavelengths (EIT/SoHO). The
  study aims at chronologically investigating the occurrence of the
  events in different wavelengths, in order to have a comprehensive
  understanding of the mechanism involved in the launch of the CME.

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Title: On Magnetic Flux Imbalance in Solar Active Regions
Authors: Choudhary, Debi Prasad; Venkatakrishnan, P.; Gosain, Sanjay
2002ApJ...573..851C    Altcode:
  The magnetic flux imbalance of active regions has been studied using the
  longitudinal magnetograms obtained from the National Solar Observatory
  at Kitt Peak. The maximum and the median value of the flux imbalance in
  137 active regions situated near the disk center is found to be about
  62% and 9.5%, respectively. The detailed analysis of a few selected
  active regions shows that the local flux asymmetry is compensated on
  global scales. For example, the NOAA Active Region 7978, which appeared
  during the solar activity minimum period and evolved during five solar
  rotations (1996 July-October), shows a flux imbalance of about 9.5%,
  with an excess of following negative flux. However, on a global scale,
  the positive and negative flux in the entire solar disk was found to be
  nearly balanced during the same period. The global flux imbalance of
  the Sun during a full magnetic cycle is estimated from the Carrington
  maps. These maps are made by merging the solar images obtained during
  a complete solar rotation (about 27 days), hence each represents the
  entire surface of the Sun. The 10°-40° active latitudinal zone in the
  individual hemispheres during the solar maximum shows a flux imbalance
  of more than 20%. This is reduced to below 10% when the entire Sun
  is considered. The present study indicates that a fraction of the
  magnetic field from the localized active regions connects with far
  away locations.

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Title: Comparative Study of LiNbO<SUB>3</SUB> and Servo Controlled
    Air Gap Fabry-Perot Etalons for Solar Application
Authors: Debi Prasad, Choudhary; Gosain, Sanjay
2002ExA....13..153D    Altcode:
  In this note, we compare the LiNbO<SUB>3</SUB> and
  Piezo-Electrically(PE) servo controlled air gap Fabry-Perot etalons
  forobserving the Sun. An identical test setup was used toevaluate
  the instrumental parameters of the two etalons. It isfound that for
  the etalons with similar finesse the advantageof using PE Etalons
  is tunability over entire Free SpectralRange. On the other hand,
  the LiNbO<SUB>3</SUB> etalons have advantageof wider acceptance angle.