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