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.
Bibcode: 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.
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
Bibcode: 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.
Title: Estimation of projection effects in the solar polar magnetic
flux measurements from an ecliptic view.
Authors: Gosain, Sanjay; Uitenbroek, Han
Bibcode: 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.
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
Bibcode: 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.
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.
Bibcode: 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.
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
Bibcode: 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.
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
Bibcode: 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-1 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-1. 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.
Title: Kinetic Helicity and Lifetime of Activity Complexes During
Solar Cycle 24
Authors: Komm, R.; Gosain, S.
Bibcode: 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.
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.
Bibcode: 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.
Title: Spectral Magnetic Helicity of Solar Active Regions between
2006 and 2017
Authors: Gosain, Sanjay; Brandenburg, Axel
Bibcode: 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}.
Title: Fast Inversion of Solar Ca II Spectra in Non-local
Thermodynamic Equilibrium
Authors: Beck, C.; Gosain, S.; Kiessner, C.
Bibcode: 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.
Title: Long-Lived Activity Complexes, their Kinetic Helicity,
Lifetime, and Flare Activity
Authors: Komm, Rudolf W.; Gosain, Sanjay
Bibcode: 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.
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
Bibcode: 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.
Title: Kinetic and Current Helicity of Long-Lived Activity Complexes
During Solar Cycle 24
Authors: Komm, Rudolf; Gosain, Sanjay
Bibcode: 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.
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.
Bibcode: 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.
Title: Synoptic Magnetic Fields Measurements of the Solar Chromosphere
from SOLIS/VSM at NSO
Authors: Gosain, Sanjay; SOLIS Team
Bibcode: 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.
Bibcode: 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″×100″
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
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
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
Bibcode: 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
Bibcode: 2017psio.confE..50G
Altcode:
No abstract at ADS
Title: Current trends in ground based solar magnetometry
Authors: Gosain, Sanjay
Bibcode: 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
Bibcode: 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
Bibcode: 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 & 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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}⊙ ,
where its rise speed reached ∼14 km s-1 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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 z ) and the
geomagnetic activity index A p 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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, jz
, using vector magnetograms from the Hinode Solar Optical Telescope
(SOT). The spatial distribution of jz 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
jz 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 jz 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
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.
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 Efree =
Enlfff - Epot, 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).
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.
Bibcode: 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,
hz. 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.
Bibcode: 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.
Bibcode: 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, Hc ,
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., Hc 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°
<= θ <= 30°) separately for weak (100 G < |Br |
< 500 G) and strong (|Br | > 1000 G) radial magnetic
fields. We find that while the current helicity of strong fields follows
the well-known hemispheric rule (i.e., θ · Hc < 0),
Hc of weak fields exhibits an inverse hemispheric behavior
(i.e., θ · Hc > 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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
Bibcode: 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 ⊙-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.
Bibcode: 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 0) is ~28.2 minutes and the damping time (τ
D ) ~ 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-1 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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=<Jz/Bz>), 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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 (>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 g and spatially averaged signed
shear angle (SASSA). It is found that for the sunspot studied here
these parameters are α g = -3.5 ± 0.37(×10-9
m-1) and SASSA = -1.68 ± 0fdg014. This suggests that the
SASSA is a less dispersed non-potentiality parameter as compared to
α g . 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
g 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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
Bibcode: 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.
Bibcode: 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−1
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
Bibcode: 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 10-3
of the continuum intensity (I c ) 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Bibcode: 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.
Title: Hα Observations of 8 June, 2004 Venus Transit
Authors: Ambastha, Ashok; Ravindra, B.; Gosain, Sanjay
Bibcode: 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 Hα
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
Hα. We report that the "black-drop" effect is present in
Hα 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 Hα
images with the multi-wavelength data obtained from the TRACE satellite.
Title: Preliminary Results of Venus Transit of June 8, 2004 Observed
in Hα 6563 Å
Authors: Ravindra, B.; Ambastha, Ashok; Gosain, Sanjay
Bibcode: 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.
Title: Design of Instrument Control Software for Solar Vector
Magnetograph at Udaipur Solar Observatory
Authors: Gosain, Sanjay; Venkatakrishnan, P.; Venugopalan, K.
Bibcode: 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.
Title: Simultaneous Stokes-V diagnostic of a Sunspot using Mg b and
Fe I lines
Authors: Gosain, Sanjay; Prasad Choudhary, Debi
Bibcode: 2003SoPh..217..119G
Altcode:
Simultaneous observations of Stokes profiles in photospheric Fei
(630.15 nm and 630.25 nm) and chromospheric Mgi b1
and b2 (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.
Title: White Light and Emission Line Polarization of Solar Corona
during TSE of June 21, 2001
Authors: Ambastha, Ashok; Gosain, Sanjay
Bibcode: 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.
Title: Magnetic and velocity fields of active regions
Authors: Choudhary, D. P.; Gosain, S.
Bibcode: 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.
Title: Study of bright points in the off-band Hα filtergrams of
active regions
Authors: Choudhary, D. P.; Gosain, S.
Bibcode: 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.
Title: The Source of a coronal mass ejection in a decayed solar
active region
Authors: Prasad Choudhary, Debi; Srivastava, Nandita; Gosain, Sanjay
Bibcode: 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 Halpha 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.
Title: On Magnetic Flux Imbalance in Solar Active Regions
Authors: Choudhary, Debi Prasad; Venkatakrishnan, P.; Gosain, Sanjay
Bibcode: 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.
Title: Comparative Study of LiNbO3 and Servo Controlled
Air Gap Fabry-Perot Etalons for Solar Application
Authors: Debi Prasad, Choudhary; Gosain, Sanjay
Bibcode: 2002ExA....13..153D
Altcode:
In this note, we compare the LiNbO3 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 LiNbO3 etalons have advantageof wider acceptance angle.