Author name code: pevtsov ADS astronomy entries on 2022-09-14 author:"Pevtsov, A." ------------------------------------------------------------------------ Title: Modeling FETCH Observations of 2005 May 13 CME Authors: Jensen, Elizabeth A.; Manchester, Ward B., IV; Wexler, David B.; Kooi, Jason E.; Nieves-Chinchilla, Teresa; Jian, Lan K.; Pevtsov, Alexei; Fung, Shing Bibcode: 2022arXiv220903350J Altcode: This paper evaluates the quality of CME analysis that has been undertaken with the rare Faraday rotation observation of an eruption. Exploring the capability of the FETCH instrument hosted on the MOST mission, a four-satellite Faraday rotation radio sounding instrument deployed between the Earth and the Sun, we discuss the opportunities and challenges to improving the current analysis approaches. 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: Reconstructing solar magnetic fields from historical observations. VIII. AIA 1600 Å contrast as a proxy of solar magnetic fields Authors: Tähtinen, I.; Virtanen, I. I.; Pevtsov, A. A.; Mursula, K. Bibcode: 2022A&A...664A...2T Altcode: 2022arXiv220413944T Context. The bright regions in the solar chromosphere and temperature minimum have a good spatial correspondence with regions of intense photospheric magnetic field. Bright regions are visible in different emission lines and parts of the continuum. Their observation started more than a hundred years ago with the invention of the spectroheliograph. While the historical spectroheliograms are essential for studying the long-term variability of the Sun, the modern satellite-borne observations can help us reveal the nature of chromospheric brightenings in previously unattainable detail.
Aims: Our aim is to improve the understanding of the relation between magnetic fields and radiative structures byf studying modern seeing-free observations of far-ultraviolet (FUV) radiation around 1600 Å and photospheric magnetic fields.
Methods: We used Helioseismic and Magnetic Imager (HMI) observations of photospheric magnetic fields and Atmospheric Imaging Assembly (AIA) observations of FUV contrast around 1600 Å. We developed a robust method to find contrast thresholds defining bright and dark AIA 1600 Å pixels, and we combine them to bright and dark clusters. We investigate the relation of magnetic fields and AIA 1600 Å radiation in bright and dark clusters.
Results: We find that the percentage of bright pixels (ranging from 2% to 10%) almost entirely explains the observed variability of 1600 Å emission. We developed a multilinear regression model based on the percentages of bright and dark pixels, which can reliably predict the magnitude of the disk-averaged unsigned magnetic field. We find that bright and dark clusters closely correspond respectively to the populations of moderate (B > 55 G) and strong (B > 1365 G) magnetic field HMI clusters. The largest bright clusters have a constant mean unsigned magnetic field, as found previously for Ca II K plages. However, the magnetic field strength of bright clusters is 254.7 ± 0.1 G, which is roughly 100 G larger than found earlier for Ca II K plages. Title: Long-Term Solar Variability and Solar Cycle Predictions: Current State of Understanding Authors: Nandi, Dibyendu; Usoskin, Ilya; Pevtsov, Alexei Bibcode: 2022cosp...44.3520N Altcode: The Sun's activity varies over timescales ranging from the very short to the very long. Long-term solar activity variations impact the Earth's atmosphere and climate and have implications for space mission planning and life-time estimates. This variability across different scales is driven by solar magnetic fields which originate in the deep convection zone, emerge through the surface and evolve. Understanding the physical basis for long-term variability over decadal scales and longer is important for developing predictive models for sunspot cycle which is an outstanding challenge. Concurrently, exploring the basis of fluctuations that lead to extreme episodes such as grand maxima in solar activity remains an important exercise with no clear indication that such episodes are predictable. We shall review here the current state of our understanding of long-term solar variability, and identify challenges that are expected to spur future developments in this field. Title: The Solar Activity Monitor Network - SAMNet Authors: Erdélyi, Robertus; Korsós, Marianna B.; Huang, Xin; Yang, Yong; Pizzey, Danielle; Wrathmall, Steven A.; Hughes, Ifan G.; Dyer, Martin J.; Dhillon, Vikram S.; Belucz, Bernadett; Brajša, Roman; Chatterjee, Piyali; Cheng, Xuewu; Deng, Yuanyong; Domínguez, Santiago Vargas; Joya, Raúl; Gömöry, Peter; Gyenge, Norbert G.; Hanslmeier, Arnold; Kucera, Ales; Kuridze, David; Li, Faquan; Liu, Zhong; Xu, Long; Mathioudakis, Mihalis; Matthews, Sarah; McAteer, James R. T.; Pevtsov, Alexei A.; Pötzi, Werner; Romano, Paolo; Shen, Jinhua; Temesváry, János; Tlatov, Andrey G.; Triana, Charles; Utz, Dominik; Veronig, Astrid M.; Wang, Yuming; Yan, Yihua; Zaqarashvili, Teimuraz; Zuccarello, Francesca Bibcode: 2022JSWSC..12....2E Altcode: The Solar Activity Magnetic Monitor (SAMM) Network (SAMNet) is a future UK-led international network of ground-based solar telescope stations. SAMNet, at its full capacity, will continuously monitor the Sun's intensity, magnetic, and Doppler velocity fields at multiple heights in the solar atmosphere (from photosphere to upper chromosphere). Each SAMM sentinel will be equipped with a cluster of identical telescopes each with a different magneto-optical filter (MOFs) to take observations in K I, Na D, and Ca I spectral bands. A subset of SAMM stations will have white-light coronagraphs and emission line coronal spectropolarimeters. The objectives of SAMNet are to provide observational data for space weather research and forecast. The goal is to achieve an operationally sufficient lead time of e.g., flare warning of 2-8 h and provide many sought-after continuous synoptic maps (e.g., LoS magnetic and velocity fields, intensity) of the lower solar atmosphere with a spatial resolution limited only by seeing or diffraction limit, and with a cadence of 10 min. The individual SAMM sentinels will be connected to their master HQ hub where data received from all the slave stations will be automatically processed and flare warning issued up to 26 h in advance. Title: Modern Faraday Rotation Studies to Probe the Solar Wind Authors: Kooi, Jason E.; Wexler, David B.; Jensen, Elizabeth A.; Kenny, Megan N.; Nieves-Chinchilla, Teresa; Wilson, Lynn B., III; Wood, Brian E.; Jian, Lan K.; Fung, Shing F.; Pevtsov, Alexei; Gopalswamy, Nat; Manchester, Ward B. Bibcode: 2022FrASS...941866K Altcode: For decades, observations of Faraday rotation have provided unique insights into the plasma density and magnetic field structure of the solar wind. Faraday rotation (FR) is the rotation of the plane of polarization when linearly polarized radiation propagates through a magnetized plasma, such as the solar corona, coronal mass ejection (CME), or stream interaction region. FR measurements are very versatile: they provide a deeper understanding of the large-scale coronal magnetic field over a range of heliocentric distances (especially ≈1.5 to 20 R⊙) not typically accessible to in situ spacecraft observations; detection of small-timescale variations in FR can provide information on magnetic field fluctuations and magnetohydrodynamic wave activity; and measurement of differential FR can be used to detect electric currents. FR depends on the integrated product of the plasma density and the magnetic field component along the line of sight to the observer; historically, models have been used to distinguish between their contributions to FR. In the last two decades, though, new methods have been developed to complement FR observations with independent measurements of the plasma density based on the choice of background radio source: calculation of the dispersion measure (pulsars), measurement of Thomson scattering brightness (radio galaxies), and application of radio ranging and apparent-Doppler tracking (spacecraft). New methods and new technology now make it possible for FR observations of solar wind structures to return not only the magnitude of the magnetic field, but also the full vector orientation. In the case of a CME, discerning the internal magnetic flux rope structure is critical for space weather applications. Title: On the Application of the Equal-contrast Technique to Ca-K Data from Kodaikanal and Other Observatories Authors: Singh, Jagdev; Priyal, Muthu; Ravindra, Belur; Bertello, Luca; Pevtsov, Alexei A. Bibcode: 2022ApJ...927..154S Altcode: The "equal-contrast technique" (ECT) methodology, developed by Singh et al. to generate uniform long time series of Ca-K images obtained during the 20th century from the Kodaikanal Observatory (KO), improved the correlation between the plage area and sunspot parameters. The same methodology can also be used on other observatory data taken with different instruments. We can combine such ECT-corrected images to reduce the gaps in the observations and make a long uniform data set to study short- and long-term variations. We apply this procedure to Mount Wilson Observatory (MWO) historical Ca-K data and recent Ca-K filtergrams obtained using narrowband filters at KO and the Mauna Loa Solar Observatory (MLSO). To determine the success of this method, the results of the analysis of the ECT images obtained from KO, MWO, and MLSO are compared. A comparison of the plage and active areas derived from KO and MWO images before and after the ECT procedure indicates an improvement in the correlation coefficients (CCs) between all the data sets after the ECT application. The CC for the combined monthly mean Ca-K plage area derived from the KO, MWO, and Precision Solar Photometric Telescope (at the MLSO) data with sunspot numbers is 0.96 for the period 1905-2015. The paper demonstrates that the time series of Ca-K data obtained from different instruments after applying the ECT procedure becomes uniform in contrast. The combined time series of KO and MWO spectroheliograms has 12 hr intervals compared to the ≍24 hr gap for a time series from a single observatory. Title: AWSoM Magnetohydrodynamic Simulation of a Solar Active Region with Realistic Spectral Synthesis Authors: Shi, Tong; Manchester, Ward, IV; Landi, Enrico; van der Holst, Bart; Szente, Judit; Chen, Yuxi; Tóth, Gábor; Bertello, Luca; Pevtsov, Alexander Bibcode: 2022ApJ...928...34S Altcode: For the first time, we simulate the detailed spectral line emission from a solar active region (AR) with the Alfvén Wave Solar Model (AWSoM). We select an AR appearing near disk center on 2018 July 13 and use the National Solar Observatory's Helioseismic and Magnetic Imager synoptic magnetogram to specify the magnetic field at the model's inner boundary. To resolve small-scale magnetic features, we apply adaptive mesh refinement with a horizontal spatial resolution of 0°.35 (4.5 Mm), four times higher than the background corona. We then apply the SPECTRUM code, using CHIANTI spectral emissivities, to calculate spectral lines forming at temperatures ranging from 0.5 to 3 MK. Comparisons are made between the simulated line intensities and those observed by Hinode/Extreme-ultraviolet Imaging Spectrometer where we find close agreement across a wide range of loop sizes and temperatures (about 20% relative error for both the loop top and footpoints at a temperature of about 1.5 MK). We also simulate and compare Doppler velocities and find that simulated flow patterns are of comparable magnitude to what is observed. Our results demonstrate the broad applicability of the low-frequency AWSoM for explaining the heating of coronal loops. Title: Measurements of the Multi-Height Solar Vector Magnetic Field Authors: Bertello, L.; Pevtsov, A.; Pevtsov, A. A. Bibcode: 2022heli.conf.4011B Altcode: The development of sophisticated numerical models of the heliosphere have made measurements of the solar vector magnetic field extremely relevant today. These measurements and a newly proposed ground-based global network will be discussed. Title: Improving the Understanding of Subsurface Structure and Dynamics of Solar Active Regions Authors: Tripathy, S. C.; Jain, K.; Kholikov, S.; Pevtsov, A. Bibcode: 2022heli.conf.4017T Altcode: NSO and HAO are promoting the design of a new global ground-based network. Here we describe additional science goals that could be addressed by this new network through multi-height observations of the solar atmosphere. Title: Analysis of Solar Hemispheric Chromosphere Properties using the Kodaikanal Observatory Ca-K Index Authors: Chowdhury, Partha; Belur, Ravindra; Bertello, Luca; Pevtsov, Alexei A. Bibcode: 2022ApJ...925...81C Altcode: The Kodaikanal Observatory has provided long-term synoptic observations of chromospheric activities in the Ca II K line (393.34 nm) since 1907. This article investigates temporal and periodic variations of the hemispheric Ca-K-index time series in the low-latitude zone (±40°), utilizing the recently digitized photographic plates of Ca-K images from the Kodaikanal Observatory for the period of 1907-1980. We find that the temporal evolution of the Ca-K index differs from one hemisphere to another, with the solar cycle peaking at different times in the opposite hemisphere, except for cycles 14, 15, and 21, when the phase difference between the two hemispheres was not significant. The monthly averaged data show a higher activity in the northern hemisphere during solar cycles 15, 16, 18, 19, and 20, and in the southern hemisphere during cycles 14, 17, and 21. We notice an exponentially decaying distribution for each hemisphere's Ca-K index and the whole solar disk. We explored different midterm periodicities of the measured Ca-K index using the wavelet technique, including Rieger-type and quasi-biennial oscillations on different timescales present in the time series. We find a clear manifestation of the Waldmeier effect (stronger cycles rise faster than the weaker ones) in both the hemispheres separately and the whole disk in the data. Finally, we have found the presence of the Gnevyshev gap (time interval between two cycle maxmima) in both the hemispheric data during cycles 15 to 20. Possible interpretations of our findings are discussed with the help of existing theoretical models and observations. Title: AWSoM MHD simulation of a solar active region with realistic spectral synthesis Authors: Manchester, Ward; Shi, Tong; Landi, Enrico; Szente, Judit; van der Holst, Bart; Chen, Yuxi; Toth, Gabor; Bertello, Luca; Pevtsov, Alexander Bibcode: 2021AGUFMSH12B..02M Altcode: For the first time, we simulate the detailed spectral line emission from a solar active region (AR) with the Alfven Wave Solar Model (AWSoM). We select an active region appearing near disk center on 2018 July 13 and use an NSO-HMI synoptic magnetogram to specify the magnetic field at the model's inner boundary. To resolve smaller-scale magnetic features, we apply adaptive mesh refinement to resolve the AR with a spatial resolution of 0.37 degrees, four times higher than the background corona. We then apply the SPECTRUM code informed with Chianti spectral emissivities to calculate more than a dozen spectral lines forming at temperatures ranging from 0.5 to 3+ MK. Comparisons are made between these simulated line profiles and those observed by the Hinode/EIS instrument where we find close agreement (within a 20% margin of error of peak intensity) across a wide range of loop sizes and temperatures. We also compare the differential emission measure calculated from both the simulation and EIS observation to further show the model's ability to capture the plasma temperature and density. Finally, we simulate and compare Doppler velocities and find that simulated flow patterns to be of comparable magnitude to what is observed. Our results demonstrate the broad applicability of the low-frequency Alfven wave balanced turbulence theory for explaining the heating of coronal loops. Title: Novel Magnetic Field and Electron Density Measurements of CMEs (within AU) with the Proposed Multiview Observatory for Solar Terrestrial Science (MOST) Mission Authors: Jensen, P. E., C. S. P., Elizabeth; Manchester, Ward; Fung, Shing; Gopalswamy, Nat; Jian, Lan; Kenny, Megan; Kooi, Jason; Lazio, Joseph; Li, Lihua; Nieves-Chinchilla, Teresa; Pevtsov, Alexei; Wexler, David; Wilson, Lynn; Wood, Brian; Bale, Stuart; Bastian, Tim Bibcode: 2021AGUFMSH33A..08J Altcode: The Multiview Observatory for Solar Terrestrial Science (MOST) mission concept will be the most advanced solar observatory to date (Gopalswamy et al, SH0001, 2021). Comprising four spacecraft, two located in the L4 and ahead of L4 position and two located in the L5 and behind of the L5 position, the four lines-of-sight (LOSs) form the basis for the unique Faraday Effect Tracker of Coronal and Heliospheric Structures (FETCH) instrument (Wexler et al, SH0019, 2021). We report on our modeling into the expected Faraday rotation (FR) caused by an Earth-directed CME crossing the MOST/FETCH radio-sensing paths using a heliospheric 3-D MHD model to obtain the necessary LOS data on electron density and magnetic field components (see example image). Specifically, we utilized simulation data of the 2005 May 13 CME (Manchester IV et al., 2014, Plasma Phys. Control. Fusion), which erupted from the north-south polarity inversion line of AR 10759 at 16:03 UT, reaching speeds around 2000 km/s in the corona. The trajectory of the CME at an acute angle to the Earth-Sun line crosses each FETCH LOS at a different time. Two LOSs are at different viewing angles with little overlap between the CME sheath and magnetic flux rope core. A blind test fitting of the Faraday rotation functions (Figures 6 and 7 in Jensen et al., 2010, Sol. Phys.) to the simulated FETCH observations reproduced the orientation of the CME for its handedness as well as its associated complementary degenerate solution. In conclusion, one of the four LOSs will be more sensitive to observing CME flux rope structure of Earthward CMEs, depending on their trajectory. We find that two of the four LOSs enable analyzing CME evolution, whereas the other two LOSs enable analyzing the average magnetic field vector in the corresponding high density regions dominating the measurements at that time. For example, the average sheath magnetic field vector can be partially measured in the plane of the ecliptic due to the angular differences between 2 LOSs. We discuss future work as this effort develops. Title: FETCH Concept: Investigating Quiescent and Transient Magnetic Structures in the Inner Heliosphere using Faraday Rotation of Spacecraft Radio Signals Authors: Wexler, David; Jensen, Elizabeth; Gopalswamy, Nat; Wilson, Lynn; Fung, Shing; Nieves-Chinchilla, Teresa; Jian, Lan; Bastian, Tim; Pevtsov, Alexei; Manchester, Ward; Kenny, Megan; Lazio, Joseph; Wood, Brian; Kooi, Jason Bibcode: 2021AGUFMSH31A..05W Altcode: The Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH) is a new instrument concept being developed to probe coronal and interplanetary magnetic field structures in the ambient solar wind, corotating interaction regions and coronal mass ejections (CMEs) as they evolve in the inner heliosphere. FETCH is one of the instruments that constitute the Multiview Observatory for Solar Terrestrial (MOST) science mission. FETCH will measure Faraday rotation (FR) of linearly polarized spacecraft radio signals transmitted along four lines of sight provided by the four MOST spacecraft: two large spacecraft deployed at Sun-Earth Lagrange points 4 and 5 and two smaller spacecraft, one ahead of L4 and the other behind L5. FETCH will transmit and receive at selected radio frequencies in the 1-100 MHz range for lines of sight with solar impact parameters < 0.5 AU. FR yields the line-of-sight (LOS) integrated product of electron number density and LOS-projected magnetic field strengths. The FR measurements will be obtained from the Stokes polarization parameters while additional plasma parameters, such as electron column density, will be extracted from other signal diagnostics. The multifrequency FR data and four lines-of-sight will be used to constrain the magnetic field topology and dynamics of interplanetary plasma structures upstream from Earth. Unique to this FR experiment, the FETCH transmitter-receiver instrumentation is positioned such that the entire sensing path remains in interplanetary space, thus avoiding the complications of trans-ionospheric FR observations. The FETCH key science objectives include: (1) characterizing CME magnetic field structure and flux rope orientation, (2) tracking CME propagation and shock signatures, (3) understanding the magnetic field features of corotating interaction regions in the extended corona and inner heliosphere, and (4) determination of large-scale MHD wave organization in regions of developed ambient solar wind and its evolution during perturbed flows. The MOST mission will build upon the achievements of the Solar Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations Observatory (STEREO) missions during the last couple of decades. FETCH will help fill the long-standing measurement gap of magnetic field data in the inner heliosphere. 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 Next Generation GONG (ngGONG) Project: Ground-based Synoptic Studies of the Sun Authors: Pillet, Valentin; Gilbert, Holly; Pevtsov, Alexei; de Wijn, Alfred Bibcode: 2021AGUFMSH45E2406P Altcode: Ground-based synoptic solar observations provide crucial contextual data used to model the large-scale state of the heliosphere. Existing ground-based synoptic programs are aging rapidly and are used in ways that differ from their original objectives. Most prominently, GONG was designed for helioseismology but is most demanded today as a provider of the magnetic boundary conditions for solar wind models. A wealth of theoretical knowledge about the connectivity between the Sun and the planets has emerged in recent years. NSO and HAO (and other international partners) are collaborating in defining a next-generation GONG (ngGONG) network that incorporates this knowledge. This contribution describes current and future contextual synoptic observations needed to fully exploit our new understanding of the underlying microphysics that leads to magnetic linkages between the Earth and the Sun. This combination of a better understanding of small-scale processes and the appropriate global context will enable a physics-based approach to Space Weather comparable to Terrestrial Weather forecasting. Title: A Comparative Study of Measurements of the Suns Axisymmetric Flows: A COFFIES Effort Authors: Upton, Lisa; Jain, Kiran; Komm, Rudolf; Mahajan, Sushant; Pevtsov, Alexei; Roudier, Thierry; Tripathy, Sushanta; Ulrich, Roger; Zhao, Junwei; Basu, Sarbani; Chen, Ruizhu; DeRosa, Marc; Hess Webber, Shea; Hoeksema, J. Bibcode: 2021AGUFMSH55D1871U Altcode: Consequence Of Fields and Flows in the Interior and Exterior of the Sun (COFFIES) is a Phase-1 NASA DRIVE Science Center (DSC), with the primary objective of developing a data driven model of solar activity. One of COFFIES five primary science questions is What drives varying large-scale motions in the Sun? To address this question, we are developing a comprehensive catalog of the variable differential rotation and meridional circulation flow patterns. This catalog includes measurements of these flows as obtained by several measurement techniques: Doppler imaging, granule tracking, magnetic pattern tracking, magnetic feature tracking, as well as both time distance and ring diagram helioseismology. We show a comparison of these flows across these varied techniques, with a particular focus on the MDI/HMI/GONG/Mount Wilson overlap period (May-July 2010). We investigate the uncertainties and attempt to reconcile any discrepancies (e.g., due to flow depth or systematics associated with the different measurement techniques). This analysis will pave the way toward accurately determining the global patterns of axisymmetric flows and their regular and irregular variations during the cycle. Title: Continuous Solar Observations from the Ground-Assessing Duty Cycle from GONG Observations Authors: Jain, Kiran; Tripathy, Sushanta C.; Hill, Frank; Pevtsov, Alexei A. Bibcode: 2021PASP..133j5001J Altcode: 2021arXiv211006319J Continuous observations play an important role in the studies of solar variability. While such observations can be achieved from space with an almost 100% duty cycle, it is difficult to accomplish a very high duty cycle from the ground. In this context, we assess the duty cycle that has been achieved from the ground by analyzing the observations of a six station network of identical instruments, the Global Oscillation Network Group (GONG). We provide a detailed analysis of the duty cycle using GONG observations spanning over 18 yr. We also discuss the duty cycle of individual sites and point out various factors that may impact individual site or network duty cycles. The mean duty cycle of the network is 93%, however it reduces by about 5% after all images pass through the stringent quality-control checks. The standard deviations in monthly and yearly duty cycle values are found to be 1.9% and 2.2%, respectively. These results provide a baseline that can be used in the planning of future ground-based networks. Title: Reconstructing solar magnetic fields from historical observations. VII. Far-side activity in surface flux transport simulations Authors: Virtanen, I. O. I.; Pevtsov, A. A.; Virtanen, I. I.; Mursula, K. Bibcode: 2021A&A...652A..79V Altcode: Context. The evolution of the photospheric magnetic field can be simulated with surface flux transport (SFT) simulations, which allow for the study of the evolution of the entire field, including polar fields, solely using observations of the active regions. However, because only one side of the Sun is visible at a time, active regions that emerge and decay on the far-side are not observed and not included in the simulations. As a result, some flux is missed.
Aims: We construct additional active regions and apply them to the far-side of the Sun in an SFT simulation to assess the possible effects and the magnitude of error that the missing far-side flux causes. We estimate how taking the missing far-side flux into account affects long-term SFT simulations.
Methods: We identified active regions from synoptic maps of the photospheric magnetic field between 1975 and 2019. We divided them into solar cycle wings and determined their lifetimes. Using the properties of observed active regions with sufficiently short lifetimes, we constructed additional active regions and inserted them into an SFT simulation.
Results: We find that adding active regions with short lifetimes to the far-side of the Sun results in significantly stronger polar fields in minimum times and slightly delayed polarity reversals. These results partly remedy the earlier results, which show overly weak polar fields and polarity reversals that are slightly too early when far-side emergence is not taken into account. The far-side active regions do not significantly affect poleward flux surges, which are mostly caused by larger long-living active regions. The far-side emergence leads to a weak continuous flow of flux, which affects polar fields over long periods of time. Title: The Intensity and Evolution of the Extreme Solar and Geomagnetic Storms in 1938 January Authors: Hayakawa, Hisashi; Hattori, Kentaro; Pevtsov, Alexei A.; Ebihara, Yusuke; Shea, Margaret A.; McCracken, Ken G.; Daglis, Ioannis A.; Bhaskar, Ankush T.; Ribeiro, Paulo; Knipp, Delores J. Bibcode: 2021ApJ...909..197H Altcode: 2020arXiv201015762H Major solar eruptions occasionally direct interplanetary coronal mass ejections (ICMEs) to Earth and cause significant geomagnetic storms and low-latitude aurorae. While individual extreme storms are significant threats to modern civilization, storms occasionally appear in sequence, acting synergistically, and cause "perfect storms" on Earth. The stormy interval in 1938 January was one of such cases. Here, we analyze the contemporary records to reveal its time series on their source active regions, solar eruptions, ICMEs, geomagnetic storms, low-latitude aurorae, and cosmic-ray (CR) variations. Geomagnetic records show that three storms occurred successively on January 17/18 (Dcx ≍ -171 nT), January 21/22 (Dcx ≍ -328 nT), and January 25/26 (Dcx ≍ -336 nT). The amplitudes of the CR variations and storm sudden commencements (SSCs) show the impact of the first ICME as the largest (≍6% decrease in CR and 72 nT in SSC) and the ICMEs associated with the storms that followed as more moderate (≍3% decrease in CR and 63 nT in SSC; ≍2% decrease in CR and 63 nT in SSC). Interestingly, a significant solar proton event occurred on January 16/17 and the Cheltenham ionization chamber showed a possible ground-level enhancement. During the first storm, aurorae were less visible at midlatitudes, whereas, during the second and third storms, the equatorward boundaries of the auroral oval were extended down to 40.3° and 40.0° in invariant latitude. This contrast shows that the initial ICME was probably faster, with a higher total magnitude but a smaller southward component. Title: Tilt angle and lifetime of sunspot groups Authors: Nagovitsyn, Yury A.; Osipova, Aleksandra A.; Pevtsov, Alexei A. Bibcode: 2021MNRAS.501.2782N Altcode: 2020MNRAS.tmp.3619N We use the Catalogue of Solar Activity (CSA) to study the latitudinal variations of tilt of solar active regions. The tilt angles β are computed taking into account changes of the heliographic grid with latitude φ. We show that when sunspot groups of different sizes and lifetimes are included, a classical representation of the Joy's law as a linear function of latitude (β ∝ φ) is only the first approximation valid within a limited range of latitudes (-25° ≤ φ ≤ +25°). Outside this range, the functional dependence β = f(φ) becomes non-linear. Separating the data set on large long-living groups (LLG) and small short-living groups (SSG) reveals two quite different dependencies in β = f(φ): non-linearity in tilt is only present in LLGs and the steepness of linear section of β = f(φ) fit is higher for LLGs. This suggests a difference in the physical properties of two populations of solar groups, which could be hypothesized as an indication of different localization of subsurface zones of their formation in the framework of a distributed dynamo. However, since CSA contains the coordinates of sunspots averaged over the lifetime (or disc passage) of each group, one cannot rule out that the difference in tilts of SSG and LLG groups may be affected by the evolution of tilt angles during the lifetime/disc passage of the groups. Title: The Sunspot Drawing Collection of the National Solar Observatory at Sacramento Peak (1947-2004) Authors: Carrasco, V. M. S.; Pevtsov, A. A.; Nogales, J. M.; Vaquero, J. M. Bibcode: 2021SoPh..296....3C Altcode: A complete dataset of sunspot drawings recorded at Sacramento Peak Observatory (SPO) from late 1947 till mid-2004 has been digitized. We present the history of the observations and describe the data included in the drawings. We compare the sunspot number index calculated from the SPO data and the International Sunspot Number (SNv2), and we find that both series exhibit a similar behavior. The ratio of two sunspot numbers is relatively constant at about 1.2 - 1.3 during 1955-1995, with larger variations present at the beginning of the time series. This work represents the first step for the publication of the SPO sunspot catalogue in digital format. More information, such as positions and areas of sunspots, will be included in the next versions in order to provide the space weather and climate community a more complete sunspot catalogue with good quality observations. Title: International Space Weather Action Team (ISWAT) S1: Long-term Solar Variability Authors: Nandi, Dibyendu; Usoskin, Ilya; Pevtsov, Alexei Bibcode: 2021cosp...43E2412N Altcode: The COSPAR International Space Weather Action Team (ISWAT) is a global hub for space weather community efforts toward the realization of the International Living With a Star-COSPAR Space Weather Roadmap goals. The community provides an inclusive environment for collaborative research efforts, information sharing and capacity building in the space weather sciences with a specific focus on enabling prediction and applications. Action teams within ISWAT address a specific focussed topic around which the team expertise is built. In this poster presentation we highlight the ISWAT Action Team S1 (Long term solar variability). The team is motivated towards understanding solar drivers of long term variability in the heliospheric space environment, its impact on geospace and other planets. This ISWAT Team is moderated by Dibyendu Nandi, Ilya Usoskin and Alexei Pevtsov. Interested scientists can join the team through the ISWAT website at: https://iswat-cospar.org/. Title: Activities related to the COSPAR ISWAT Cluster: Ambient Solar Magnetic Field, Heating and Spectral Irradiance Authors: Reiss, Martin; Pevtsov, Alexei; Linker, Jon; Pinto, Rui; Arge, Charles; Muglach, Karin; Henney, Carl J. Bibcode: 2021cosp...43E2413R Altcode: The understanding of the magnetic field configuration in the solar atmosphere is of crucial importance for improving the modelling and ultimately the prediction of space weather from Sun to Earth. The magnetic field provides the energy source that heats the solar corona and accelerates the solar wind, and it also defines the structure of the heliosphere. However, many related unresolved questions require an interdisciplinary strategy and the coordinated cooperation of international partners. Here we present the activities of the 'Ambient Solar Magnetic Field, Heating and Spectral Irradiance' cluster embedded in the COSPAR ISWAT initiative. The action teams in this cluster will focus on critical scientific challenges in the space weather community related to the construction of global solar magnetic field maps, use of vector field synoptic maps for applied space weather modelling and research, magnetic connectivity from the surface of the Sun to any point in interplanetary space, magnetic topology of open field lines along which solar wind flows accelerate to supersonic speeds, and the solar spectral irradiance driving ionization and heating in the Earth's upper atmosphere. We will outline the objectives of the individual action teams and present the current status and roadmaps. To encourage the formation of new action teams, we will also discuss additional challenges that should be addressed by the space weather community. Title: On a limitation of Zeeman polarimetry and imperfect instrumentation in representing solar magnetic fields with weaker polarization signal Authors: Pevtsov, A. A.; Liu, Y.; Virtanen, I.; Bertello, L.; Mursula, K.; Leka, K. D.; Hughes, A. L. H. Bibcode: 2021JSWSC..11...14P Altcode: 2021arXiv210107204P Full disk vector magnetic fields are used widely for developing better understanding of large-scale structure, morphology, and patterns of the solar magnetic field. The data are also important for modeling various solar phenomena. However, observations of vector magnetic fields have one important limitation that may affect the determination of the true magnetic field orientation. This limitation stems from our ability to interpret the differing character of the Zeeman polarization signals which arise from the photospheric line-of-sight vs. the transverse components of the solar vector magnetic field, and is likely exacerbated by unresolved structure (non-unity fill fraction) as well as the disambiguation of the 180° degeneracy in the transverse-field azimuth. Here we provide a description of this phenomenon, and discuss issues, which require additional investigation. Title: Bi-lognormal Distribution of Sunspot Group Areas Authors: Nagovitsyn, Yury A.; Pevtsov, Alexei A. Bibcode: 2021ApJ...906...27N Altcode: We use daily observations from the Royal Greenwich Observatory and Kislovodsk Mountain Astronomical Station of Pulkovo Observatory to study the distribution properties of sunspot areas. To mitigate the poor statistics in the distribution of small areas, we introduce a "precision randomization" approach based on the assumption that all measured areas have a random component within the measurement uncertainty of 1 millionth of the solar hemisphere (M.S.H.). We confirm the presence of two distinct components in the distribution of sunspots previously reported by several authors, and show that the area distribution is described by the sum of two lognormal distributions responsible for small and large groups (sunspots), respectively. We also demonstrate that the area of the main spots in the groups correlates well with the total area of the group, and, thus, the findings derived for the total group areas are equally applicable to the main spots of groups. Title: Long-term studies of photospheric magnetic fields on the Sun Authors: Pevtsov, Alexei A.; Bertello, Luca; Nagovitsyn, Yury A.; Tlatov, Andrey G.; Pipin, Valery V. Bibcode: 2021JSWSC..11....4P Altcode: We briefly review the history of observations of magnetic fields on the Sun, and describe early magnetograps for full disk measurements. Changes in instruments and detectors, the cohort of observers, the knowledge base etc may result in non-uniformity of the long-term synoptic datasets. Still, such data are critical for detecting and understanding the long-term trends in solar activity. We demonstrate the value of historical data using studies of active region tilt (Joy's law) and the evolution of polar field and its reversal. Using the longest dataset of sunspot field strength measurements from Mount Wilson Observatory (1917-present) supplemented by shorter datasets from Pulkovo (1956-1997) and Crimean (1956-present) observatories we demonstrate that the magnetic properties of sunspots did not change over the last hundred years. We also show that the relationship between the sunspot area and its magnetic flux can be used to extend the studies of magnetic field in sunspots to periods with no direct magnetic field measurements. Finally, we show how more recent full disk observations of the vector magnetic field can be used to study the long-term (solar cycle) variations in magnetic helicity on the Sun. Title: COSPAR International Space Weather Action Teams: Addressing Challenges Across the Field of Space Weather. Authors: Kuznetsova, M. M.; Belehaki, A.; Bisi, M. M.; Bruinsma, S.; Fung, S. F.; Glover, A.; Grande, M.; Guo, J.; Jun, I.; Linker, J.; Mann, I. R.; Masson, A.; Mendoza, A. M. M.; Murray, S. A.; Nandy, D.; Opgenoorth, H. J.; Pevtsov, A. A.; Plainaki, C.; Reiss, M.; Sutton, E. K.; Temmer, M.; Usoskin, I. G.; Yao, Z.; Yardley, S.; Zheng, Y. Bibcode: 2020AGUFMSH0030022K Altcode: Advanced predictions of space weather impacts require improved understanding and modeling capabilities of coupled chains of space environment processes. It is necessary to assemble parts of the source-to-impact puzzle by identifying, addressing and solving problems focused on specific physical domains, and then to connect all validated solutions from space weather origins on the sun to impacts on coupled geospace system, humans and technologies. To address the need for multi-disciplinary international space weather research community connecting experts in space weather phenomena across all domains and experts in space environment impact, the COSPAR Panel on Space Weather facilitated establishment of a network of International Space Weather Action Teams (ISWAT, https://www.iswat-cospar.org, @IswatCosparOrg). ISWAT serves as a global hub for community coordinated topical collaborations focused on different aspects of space weather including advancing understanding, assessment and improvement of modeling capabilities, transitioning advances in research to operations, optimized utilization of available observations, and generating inputs to future instrumentation deployment. Action teams are building blocks of ISWAT initiative. ISWAT action teams are organized into domain-based ISWAT clusters. Action teams are working in coordinated effort across physical domain and across borders. The primary ISWAT goal is to advance space weather predictive capabilities based on best science available. The ISWAT currently includes more than 250 active participants and more than 50 action teams. The presentation will overview the outcome from the COSPAR ISWAT Inaugural Working Meeting in February 2020, highlight recent progress in advancing physics-based predictive capabilities and discuss plans for transforming COSPAR space weather Roadmap into a living document maintained by the community. Title: Intensity and time series of extreme solar-terrestrial storm in 1946 March Authors: Hayakawa, Hisashi; Ebihara, Yusuke; Pevtsov, Alexei A.; Bhaskar, Ankush; Karachik, Nina; Oliveira, Denny M. Bibcode: 2020MNRAS.497.5507H Altcode: 2020MNRAS.tmp.1670H Major solar eruptions occasionally cause magnetic superstorms on the Earth. Despite their serious consequences, the low frequency of their occurrence provides us with only limited cases through modern instrumental observations, and the intensities of historical storms before the coverage of the Dst index have been only sporadically estimated. Herein, we examine a solar-terrestrial storm that occurred in 1946 March and quantitatively evaluate its parameters. During the ascending phase of Solar Cycle 18, two moderate sunspot groups caused a major flare. The H α flaring area was recorded to be ≥600-1200 millionths of solar hemisphere, suggesting that this was an M- or X-class flare in soft X-ray intensity. Upon this eruption, a rapid interplanetary coronal mass ejection (ICME) with an average speed of ≍1590 km s-1 was launched. Based on measurements in four known mid-latitude and relatively complete magnetograms, the arrival of this extreme ICME caused a magnetic superstorm, which caused an initial phase with the H-component amplitude of ≥80 nT, followed by a main phase whose intensity was reconstructed as ≤-512 nT using most negative Dst* estimates. Meanwhile, the equatorial boundary of the auroral oval extended down to ≤41 ${^{\circ}_{.}}$ 8 in invariant latitude and formed a corona aurora in Watheroo, Australia. Interestingly, during this magnetic superstorm, larger magnetic disturbances were recorded at dusk and near the dip equator on the dayside. Its cause may be associated with a strong westward equatorial electrojet and field-aligned current, in addition to the contribution from the storm-time ring current. Title: 70 Years of Chromospheric Solar Activity and Dynamics Authors: Bertello, Luca; Pevtsov, Alexei A.; Ulrich, Roger K. Bibcode: 2020ApJ...897..181B Altcode: From 1915 to 1985 the monitoring program of the Mount Wilson Observatory, one of the Observatories of the Carnegie Institution of Washington, has taken over 35,000 daily images (spectroheliograms) of the Sun in the chromospheric resonance line of Ca II K. This important database constitutes a unique resource for a variety of retrospective analyses of the state of solar magnetism on multidecadal timescales. These observations may also hold the key for untangling some of the mysteries behind the solar dynamo, which in turn could result in a better predictive capability for current dynamo models. We describe here a procedure to calibrate and rescale these images so that homogeneous Carrington synoptic maps can be derived for the whole period covered by these observations. Temporal variations in full-disk chromospheric activity clearly show the signature of the 11 yr solar cycle, but no evidence is found for a statistically significant north/south hemispheric asymmetry. Using a feature-tracking technique we were also able to obtain the average solar rotation profile. We find no indication of any detectable periodicity in the temporal behavior of the orthogonalized rotation rate coefficients, suggesting the global chromospheric dynamics has not changed during the 70 years investigated in this work. We found also no significant evidence in our analysis for a hemispheric asymmetry in rotation rates. Title: Effect of Additional Magnetograph Observations From Different Lagrangian Points in Sun-Earth System on Predicted Properties of Quasi-Steady Solar Wind at 1 AU Authors: Pevtsov, A. A.; Petrie, G.; MacNeice, P.; Virtanen, I. I. Bibcode: 2020SpWea..1802448P Altcode: Modeling the space weather conditions for a near-Earth environment depends on a proper representation of magnetic fields on the Sun. There are discussions in the community with respect to the value of observations taken at several Lagrangian points (L1-L5) in the Sun-Earth system. Observations from a single (e.g., Earth/L1) vantage point are insufficient to characterize rapid changes in magnetic field on the far side of the Sun. Nor can they represent well the magnetic fields near the solar poles. However, if the changes in sunspot activity were moderate, how well would our predictions of the solar wind based on a single viewing point work? How much improvement could we see by adding magnetograph observations from L5, L4, and even L3? Here, we present the results of our recent modeling, which shows the level of improvement in forecasting the properties of the solar wind at Earth made possible by using additional observations from different vantage points during a period of moderate evolution of sunspot activity. As an example, we also show the improvements to the solar wind forecast from adding a single observation of the southern polar area from out-of-ecliptic spacecraft at -30° heliographic latitude vantage point. Title: Formation of Two Homologous Transequatorial Loops Authors: Chen, Jie; Pevtsov, Alexei A.; Su, Jiangtao; Erdélyi, Robertus; Deng, Yuanyong; Yang, Shangbin; Song, Yongliang Bibcode: 2020SoPh..295...59C Altcode: The formation mechanism of two homologous transequatorial loops (TLs) of July 7-8, 1999 (SOL1999-07-07) is studied. The TLs connected active region AR 8614 from the northern hemisphere to AR 8626 in the southern hemisphere. The first TL appeared as a distinct structure at 12:49 UT on July 7, the second TL appeared at 06:21 UT, on July 8. Important results are obtained in this analysis: (i) The configuration of the two TLs is similar in X-rays. (ii) The sizes of the two active regions related to the TLs increased before and during the formation of the two TLs, this induced the expansion of their coronal loops. (iii) Both TLs formed globally on a time scale shorter than 110 min (time resolution of observations). (iv) An X-shaped coronal structure was observed. This observational evidence suggests that the two TLs formed by the same physical mechanism, magnetic reconnection, between the two expanding magnetic configurations of the two ARs. Title: Monitoring solar activity with PEPSI Authors: Dineva, Ekaterina; Denker, Carsten; Strassmeier, Klaus G.; Ilyin, Ilya; Pevtsov, Alexei A. Bibcode: 2020IAUGA..30..351D Altcode: Synoptic Sun-as-a-star observations are carried out with the Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI), which receives light from the Solar Disk-Integration (SDI) telescope. Daily spectra are produced with a high signal-to-noise ratio, providing access to unprecedented quasi-continuous, long-term, disk-integrated spectra of the Sun with high spectral and temporal resolution. We developed tools to monitor and study solar activity on different time-scales ranging from daily changes, over periods related to solar rotation, to annual and decadal trends. Strong chromospheric absorption lines, such as the Ca ii H & K λ3934 & 3968 Å lines, are powerful diagnostic tools for solar activity studies, since they trace the variations of the solar magnetic field. Other lines, such as Hα λ6563 Å line and the near-infrared (NIR) Ca ii λ8542 Å line, provide additional information on the physical properties in this highly complex and dynamic atmospheric layer. Currently, we work on a data pipeline for extraction, calibration, and analysis of the PEPSI/SDI data. We compare the SDI data with daily spectra from the Integrated Sunlight Spectrometer (ISS), which is part of the Synoptic Long-Term Investigation of the Sun (SOLIS) facility operated by the U.S. National Solar Observatory (NSO). This facilitates cross-calibration and validation of the SDI data. Title: Duffing Oscillator Model of Solar Cycles Authors: Nagovitsyn, Yury A.; Pevtsov, Alexei A. Bibcode: 2020ApJ...888L..26N Altcode: We propose that the solar cycle variability could be described in the framework of an external quasi-sinusoidal influence on an oscillator with cubic nonlinearity and linear damping (Duffing oscillator). To demonstrate this, we compare the empirical amplitude-frequency dependence with the theoretical one obtained by the Krylov-Bogolyubov averaging method. The empirical data are a composite time series of 2.0 version of sunspot number series, which starts in 1700, and the sunspot group number series by Svalgaard & Schatten, scaled to sunspot number, for 1610-1699 interval. We find that while this interpretation of solar cycle is a mathematical approximation, it explains several properties of solar cycle variability. Title: Solar Cycle-Related Variability of Sun-as-a-Star Spectral Line Profiles Authors: Kalscheur, M.; Criscuoli, S.; Bertello, L.; Pevtsov, A. A. Bibcode: 2019AGUFMSH11D3390K Altcode: We use daily observations of the Sun-as-a-star by the high resolution Integrated Sunlight Spectrometer (ISS), one of three instruments which comprise the Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility, to investigate solar cycle-related variability in line profiles from three ISS spectral bands. Preliminary results show an anti-correlation between the magnitude of the CN band-head jump and total unsigned magnetic flux through the decline phase of Solar Cycle 23 and the rise and fall of Solar Cycle 24, consistent with magnetohydrodynamic simulations. Additional line parameters (core intensity, full width at half maximum and equivalent width) show correlations with the solar cycle, but may require correction for stray light. We investigate two such corrections. Varied line parameter responses to thermodynamic and magnetic structures in the solar atmosphere may provide a means of disentangling thermal and magnetic effects in disk-integrated solar spectra. These line parameter responses could in turn inform spectroscopic observations of other stars. Ultimately, this work is a step towards a better understanding of magnetic activity cycles in other Sun-like stars. Title: Reconstructing solar magnetic fields from historical observations. VI. Axial dipole moments of solar active regions in cycles 21-24 Authors: Virtanen, I. O. I.; Virtanen, I. I.; Pevtsov, A. A.; Mursula, K. Bibcode: 2019A&A...632A..39V Altcode: Context. The axial dipole moments of emerging active regions control the evolution of the axial dipole moment of the whole photospheric magnetic field and the strength of polar fields. Hale's and Joy's laws of polarity and tilt orientation affect the sign of the axial dipole moment of an active region. If both laws are valid (or both violated), the sign of the axial moment is normal. However, for some active regions, only one of the two laws is violated, and the signs of these axial dipole moments are the opposite of normal. Those opposite-sign active regions can have a significant effect, for example, on the development of polar fields.
Aims: Our aim is to determine the axial dipole moments of active regions identified from magnetographic observations and study how the axial dipole moments of normal and opposite signs are distributed in time and latitude in solar cycles 21-24.
Methods: We identified active regions in the synoptic maps of the photospheric magnetic field measured at the National Solar Observatory (NSO) Kitt Peak (KP) observatory, the Synoptic Optical Long term Investigations of the Sun (SOLIS) vector spectromagnetograph (VSM), and the Helioseismic and Magnetic Imager (HMI) aboard the Solar Dynamics Observatory (SDO), and determined their axial dipole moments.
Results: We find that, typically, some 30% of active regions have opposite-sign axial moments in every cycle, often making more than 20% of the total axial dipole moment. Most opposite-signed moments are small, but occasional large moments, which can affect the evolution of polar fields on their own, are observed. Active regions with such a large opposite-sign moment may include only a moderate amount of total magnetic flux. We find that in cycles 21-23 the northern hemisphere activates first and shows emergence of magnetic flux over a wider latitude range, while the southern hemisphere activates later, and emergence is concentrated to lower latitudes. Cycle 24 differs from cycles 21-23 in many ways. Cycle 24 is the only cycle where the northern butterfly wing includes more active regions than the southern wing, and where axial dipole moment of normal sign emerges on average later than opposite-signed axial dipole moment. The total axial dipole moment and even the average axial moment of active regions is smaller in cycle 24 than in previous cycles. Title: The effect of telescope aperture, scattered light and human vision on early measurements of sunspot and group numbers Authors: Karachik, Nina V.; Pevtsov, Alexei A.; Nagovitsyn, Yury A. Bibcode: 2019MNRAS.488.3804K Altcode: 2019arXiv190704932K Early telescopic observations of sunspots were conducted with instruments of relatively small aperture. These instruments also suffered from a higher level of scattered light, and the human eye served as a `detector'. The eye's ability to resolve small details depends on image contrast, and on average intensity variations smaller than ≈3 per cent contrast relative to background are not detected even if they are resolved by the telescope. Here we study the effect of these three parameters (telescope aperture, scattered light and detection threshold of human vision) on sunspot number, group number and area of sunspots. As an `ideal' dataset, we employ white-light (pseudo-continuum) observations from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory, and we model the appearance of sunspots by degrading the HMI images to corresponding telescope apertures with added scattered light. We discuss the effects of different parameters on sunspot counts and derive functional dependences, which could be used to normalize historical observations of sunspot counts to a common denominator. Title: Preservation of Our Astronomical Heritage Authors: Lattis, James; Osborn, Wayne; Bartlett, Jennifer Lynn; Griffin, Elizabeth; Hockey, Thomas; McCluskey, Stephen; Oswalt, Terry; Pevtsov, Alexei A.; Schechner, Sara; Trimble, Virginia Bibcode: 2019BAAS...51g..21L Altcode: 2019arXiv190710686L; 2019astro2020U..21L We argue that it is essential that the Astro2020 survey of the present state of American astronomy and the recommendations for the next decade address the issue of ensuring preservation of, and making more discoverable and accessible, the field’s rich legacy materials. Title: Research scientists in support of facilities and missions: Facility support and research as an interlocked pair Authors: Soderblom, David; Wilkes, Belinda; Saha, Abhijit; Hall, Jeff; Chené, André-Nicolas; Pevtsov, Alexei; Peterson, Bradley M. Bibcode: 2019BAAS...51g.116S Altcode: 2019astro2020U.116S Scientists who themselves depend on the facilities that they support have a much deeper knowledge of the facilities, leading to better user support, new modes, more efficient telescope use, and overall more and better scientific output. This white paper supports the value of research scientists at facilities and missions. Title: Reconstructing solar magnetic fields from historical observations. V. Sunspot magnetic field measurements at Mount Wilson Observatory Authors: Pevtsov, Alexei A.; Tlatova, Kseniya A.; Pevtsov, Alexander A.; Heikkinen, Elina; Virtanen, Ilpo; Karachik, Nina V.; Bertello, Luca; Tlatov, Andrey G.; Ulrich, Roger; Mursula, Kalevi Bibcode: 2019A&A...628A.103P Altcode: 2019arXiv190706492P Context. Systematic observations of magnetic field strength and polarity in sunspots began at Mount Wilson Observatory (MWO), USA in early 1917. Except for a few brief interruptions, this historical dataset has continued until the present.
Aims: Sunspot field strength and polarity observations are critical in our project of reconstructing the solar magnetic field over the last hundred years. We provide a detailed description of the newly digitized dataset of drawings of sunspot magnetic field observations.
Methods: The digitization of MWO drawings is based on a software package that we developed. It includes a semiautomatic selection of solar limbs and other features of the drawing, and a manual entry of the time of observations, measured field strength, and other notes handwritten on each drawing. The data are preserved in an MySQL database.
Results: We provide a brief history of the project and describe the results from digitizing this historical dataset. We also provide a summary of the final dataset and describe its known limitations. Finally, we compare the sunspot magnetic field measurements with those from other instruments, and demonstrate that, if needed, the dataset could be continued using modern observations such as, for example, the Vector Stokes Magnetograph on the Synoptic Optical Long-term Investigations of the Sun platform.

The digitized drawings are also available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A103 Title: VizieR Online Data Catalog: Mt Wilson sunspot magnetic field measurements (Pevtsov+, 2019) Authors: Pevtsov, A. A.; Tlatova, K. A.; Pevtsov, A. A.; Heikkinen, E.; Virtanen, I.; Karachik, N. V.; Bertello, L.; Tlatov, A. G.; Ulrich, R.; Mursula, K. Bibcode: 2019yCat..36280103P Altcode: MOUNT WILSON OBSERVATORY 150-foot solar tower, SUNSPOT DRAWINGS, 1917-2016.

File: figs3_5.dat (Contains data shown in Figures 3-5). Three columns contain information on date of observations (Years), measured Field strength (gauss), and radius of solar disk on drawings (pixels). For measurements on drawings that only have information about polarity, but not amplitude, we assigned a fixed value of "4900".

Files: fig6a.dat and fig6b.dat (Contain data shown in Figure 6). Entries correspond to same-day measurements of field strengths (in units of Hundreds of gauss) at Mount Wilson Observatory (MWO, left column) and Crimean Astrophysical Observatory (CrAO, right column). In Figure 6, observations from 1994-2003 are shown by black squares, and data for 2004-2014 are shown as filled red circles.

File: fig7.dat (Contain data for Figure 7). Field strengths of 50 sunspots observed at Mount Wilson Observatory (MWO) and and by Vector Stokes Magnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) platform. SOLIS/VSM data are derived using SOLIS Zeemanfit code.

(5 data files). Title: Reconstructing solar magnetic fields from historical observations. IV. Testing the reconstruction method Authors: Virtanen, I. O. I.; Virtanen, I. I.; Pevtsov, A. A.; Bertello, L.; Yeates, A.; Mursula, K. Bibcode: 2019A&A...627A..11V Altcode:
Aims: The evolution of the photospheric magnetic field has only been regularly observed since the 1970s. The absence of earlier observations severely limits our ability to understand the long-term evolution of solar magnetic fields, especially the polar fields that are important drivers of space weather. Here, we test the possibility to reconstruct the large-scale solar magnetic fields from Ca II K line observations and sunspot magnetic field observations, and to create synoptic maps of the photospheric magnetic field for times before modern-time magnetographic observations.
Methods: We reconstructed active regions from Ca II K line synoptic maps and assigned them magnetic polarities using sunspot magnetic field observations. We used the reconstructed active regions as input in a surface flux transport simulation to produce synoptic maps of the photospheric magnetic field. We compared the simulated field with the observed field in 1975-1985 in order to test and validate our method.
Results: The reconstruction very accurately reproduces the long-term evolution of the large-scale field, including the poleward flux surges and the strength of polar fields. The reconstruction has slightly less emerging flux because a few weak active regions are missing, but it includes the large active regions that are the most important for the large-scale evolution of the field. Although our reconstruction method is very robust, individual reconstructed active regions may be slightly inaccurate in terms of area, total flux, or polarity, which leads to some uncertainty in the simulation. However, due to the randomness of these inaccuracies and the lack of long-term memory in the simulation, these problems do not significantly affect the long-term evolution of the large-scale field. Title: Evolution of Magnetic Helicity in Solar Cycle 24 Authors: Pipin, Valery V.; Pevtsov, Alexei A.; Liu, Yang; Kosovichev, Alexander G. Bibcode: 2019ApJ...877L..36P Altcode: 2019arXiv190500772P We propose a novel approach to reconstruct the surface magnetic helicity density on the Sun or Sun-like stars. The magnetic vector potential is determined via decomposition of vector magnetic-field measurements into toroidal and poloidal components. The method is verified using data from a non-axisymmetric dynamo model. We apply the method to vector field synoptic maps from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory to study the evolution of the magnetic helicity density during solar cycle 24. It is found that the mean helicity density of the non-axisymmetric magnetic field of the Sun evolves in a way similar to that reported for the current helicity density of the solar active regions. It predominantly has a negative sign in the northern hemisphere, while it is mainly positive in the southern hemisphere. Also, the hemispheric helicity rule for the non-axisymmetric magnetic field showed the sign inversion at the end of cycle 24. The evolution of the magnetic helicity density of a large-scale axisymmetric magnetic field is different from what is predicted by dynamo theory. On one hand, the mean large- and small-scale components of magnetic helicity density display the hemispheric helicity rule of opposite signs at the beginning of cycle 24. However, later in the cycle, the two helicities exhibit the same sign, in contrast with theoretical expectations. Title: Historical astronomical data: urgent need for preservation, digitization enabling scientific exploration Authors: Pevtsov, Alexei; Griffin, Elizabeth; Grindlay, Jonathan; Kafka, Stella; Bartlett, Jennifer; Usoskin, Ilya; Mursula, Kalevi; Gibson, Sarah; Pillet, Valentín; Burkepile, Joan; Webb, David; Clette, Frédéric; Hesser, James; Stetson, Peter; Muñoz-Jaramillo, Andres; Hill, Frank; Bogart, Rick; Osborn, Wayne; Longcope, Dana Bibcode: 2019BAAS...51c.190P Altcode: 2019arXiv190304839P; 2019astro2020T.190P This white paper emphasizes critical importance of preservation, digitization and scientific exploration of historical astronomical data. It outlines the rationale, provides examples of new science with such data, and reviews the potential losses to science if nothing it done. Title: Reconstructing Extreme Space Weather From Planet Hosting Stars Authors: Airapetian, Vladimir; Adibekyan, V.; Ansdell, M.; Alexander, D.; Barklay, T.; Bastian, T.; Boro Saikia, S.; Cohen, O.; Cuntz, M.; Danchi, W.; Davenport, J.; DeNolfo, G.; DeVore, R.; Dong, C. F.; Drake, J. J.; France, K.; Fraschetti, F.; Herbst, K.; Garcia-Sage, K.; Gillon, M.; Glocer, A.; Grenfell, J. L.; Gronoff, G.; Gopalswamy, N.; Guedel, M.; Hartnett, H.; Harutyunyan, H.; Hinkel, N. R.; Jensen, A. G.; Jin, M.; Johnstone, C.; Kahler, S.; Kalas, P.; Kane, S. R.; Kay, C.; Kitiashvili, I. N.; Kochukhov, O.; Kondrashov, D.; Lazio, J.; Leake, J.; Li, G.; Linsky, J.; Lueftinger, T.; Lynch, B.; Lyra, W.; Mandell, A. M.; Mandt, K. E.; Maehara, H.; Miesch, M. S.; Mickaelian, A. M.; Mouschou, S.; Notsu, Y.; Ofman, L.; Oman, L. D.; Osten, R. A.; Oran, R.; Petre, R.; Ramirez, R. M.; Rau, G.; Redfield, S.; Réville, V.; Rugheimer, S.; Scheucher, M.; Schlieder, J. E.; Shibata, K.; Schnittman, J. D.; Soderblom, David; Strugarek, A.; Turner, J. D.; Usmanov, A.; Van Der Holst, B.; Vidotto, A.; Vourlidas, A.; Way, M. J.; Wolk, Scott J.; Zank, G. P.; Zarka, P.; Kopparapu, R.; Babakhanova, S.; Pevtsov, A. A.; Lee, Y.; Henning, W.; Colón, K. D.; Wolf, E. T. Bibcode: 2019BAAS...51c.564A Altcode: 2019astro2020T.564A; 2019arXiv190306853A The goal of this white paper is to identify and describe promising key research goals to aid the theoretical characterization and observational detection of ionizing radiation from quiescent and flaring upper atmospheres of planet hosts as well as properties of stellar coronal mass ejections (CMEs) and stellar energetic particle (SEP) events. Title: Structure and evolution of the photospheric magnetic field in 2010-2017: comparison of SOLIS/VSM vector field and BLOS potential field Authors: Virtanen, Ilpo I.; Pevtsov, Alexei A.; Mursula, Kalevi Bibcode: 2019A&A...624A..73V Altcode: 2019arXiv190410740V Context. The line-of-sight (LOS) component of the large-scale photospheric magnetic field has been observed since the 1950s, but the daily full-disk observations of the full vector magnetic field started only in 2010 using the SOLIS Vector Stokes Magnetograph (VSM) and the SDO helioseismic and magnetic imager (HMI). Traditionally, potential field extrapolations are based on the assumption that the magnetic field in the photosphere is approximately radial. The validity of this assumption has not been tested yet.
Aims: We investigate here the structure and evolution of the three components of the solar large-scale magnetic field in 2010-2017, covering the ascending to mid-declining phase of solar cycle 24, using SOLIS/VSM vector synoptic maps of the photospheric magnetic field.
Methods: We compare the observed VSM vector magnetic field to the potential vector field derived using the VSM LOS magnetic field observations as an input. The new vector field data allow us to derive the meridional inclination and the azimuth angle of the magnetic field and to investigate their solar cycle evolution and latitudinal profile of these quantities.
Results: SOLIS/VSM vector data show that the photospheric magnetic field is in general fairly non-radial. In the meridional plane the field is inclined toward the equator, reflecting the dipolar structure of the solar magnetic field. Rotationally averaged meridional inclination does not have significant solar cycle variation. While the vector radial component Br and the potential radial component BPFSSr are fairly similar, the meridional and zonal components do not agree very well. We find that SOLIS/VSM vector observations are noisy at high latitudes and suffer from the vantage point effect more than LOS observations. This is due to different noise properties in the LOS and transverse components of the magnetic field, which needs to be addressed in future studies. Title: Extended statistical analysis of emerging solar active regions Authors: Kutsenko, Alexander S.; Abramenko, Valentina I.; Pevtsov, Alexei A. Bibcode: 2019MNRAS.484.4393K Altcode: 2019MNRAS.tmp..310K; 2018arXiv181112089K We use observations of line-of-sight magnetograms from Helioseismic and Magnetic Imager onboard of Solar Dynamics Observatory to investigate polarity separation, magnetic flux, flux emergence rate, twist and tilt of solar emerging active regions. Functional dependence of polarity separation and maximum magnetic flux of an active region is in agreement with a simple model of flux emergence as the result of buoyancy forces. Our investigation did not reveal any strong dependence of emergence rate on twist properties of active regions. Title: VizieR Online Data Catalog: 24 years monitoring of Sun and Sun-like stars (Radick+, 2018) Authors: Radick, R. R.; Lockwood, G. W.; Henry, G. W.; Hall, J. C.; Pevtsov, A. A. Bibcode: 2019yCat..18550075R Altcode: Starting in the late 1970s, variations in total solar irradiance (TSI) have been monitored by radiometers aboard a series of spacecraft, including the Total Irradiance Monitor (TIM) instrument on the SOlar Radiation and Climate Experiment (SORCE) satellite from 2003 to the present.

Observations to monitor relatively bright stars very similar to the Sun have been made with the Solar-Stellar Spectrograph (SSS) at Lowell Observatory and automatic photometric telescopes (APTs) at Fairborn Observatory beginning in 1992 and 1993, respectively. In all, 72 stars, including 18 from the broader R98-L07 (1998ApJS..118..239R and 2007ApJS..171..260L) sample, have been observed at both locations, some for as long as 24 seasons. These joint observations provide the primary stellar data for this paper.

(3 data files). Title: Some Features of the Two Sunspot Group Populations' Properties Authors: Nagovitsyn, Yu. A.; Pevtsov, A. A.; Osipova, A. A.; Ivanov, V. G. Bibcode: 2018Ge&Ae..58.1170N Altcode: This paper describes some features of the two sunspot group populations' properties: Large Long-living Groups, LLG, and Small Short-living, SSG (each distributed lognormally), divided by the lifetime of the group (less and strictly more than 5 days). It is shown that the relative fraction of LLG varies with the latitude from 0.45 at mid-latitudes to 0.25-0.30 at low and high latitudes. The SSG has a wider spread in latitude than the LLG. It is shown that the N-S asymmetry is an overall global process to which both the LLG and the SSG are exposed. At the same time, the asymmetry of LLG shows a slightly higher dispersion of oscillations than the asymmetry of SSG. Other properties of sunspot groups in the context of the two separate populations existence are considered. Title: The magnetic field vector of the Sun-as-a-star - II. Evolution of the large-scale vector field through activity cycle 24 Authors: Vidotto, A. A.; Lehmann, L. T.; Jardine, M.; Pevtsov, A. A. Bibcode: 2018MNRAS.480..477V Altcode: 2018MNRAS.tmp.1832V; 2018arXiv180706334V In this work, we investigate how the large-scale magnetic field of the Sun, in its three vector components, has evolved during most of cycle 24, from 2010 January to 2018 April. To filter out the small-scale field of the Sun, present in high-resolution synoptic maps, we use a spherical harmonic decomposition method, which decomposes the solar field in multipoles with different ℓ degrees. By summing together the low-ℓ multipoles, we reconstruct the large-scale field at a resolution similar to observed stellar magnetic fields, which allows the direct comparison between solar and stellar magnetic maps. During cycle 24, the `Sun-as-a-star' magnetic field shows a polarity reversal in the radial and meridional components, but not in the azimuthal component. The large-scale solar field remains mainly poloidal with {≳ } 70{{ per cent}} of its energy contained in the poloidal component. During its evolution, the large-scale field is more axisymmetric and more poloidal when near minima in sunspot numbers, and with a larger intensity near maximum. There is a correlation between toroidal energy and sunspot number, which indicates that spot fields are major contributors to the toroidal large-scale energy of the Sun. The solar large-scale magnetic properties fit smoothly with observational trends of stellar magnetism reported in See et al. The toroidal (< B_tor^2 >) and poloidal (< B_pol^2 >) energies are related as < B_tor^2 > ∝ < B_pol^2 > ^{1.38± 0.04}. Similar to the stellar sample, the large-scale field of the Sun shows a lack of toroidal non-axisymmetric field. Title: Roadmap for Reliable Ensemble Forecasting of the Sun-Earth System Authors: Nita, Gelu; Angryk, Rafal; Aydin, Berkay; Banda, Juan; Bastian, Tim; Berger, Tom; Bindi, Veronica; Boucheron, Laura; Cao, Wenda; Christian, Eric; de Nolfo, Georgia; DeLuca, Edward; DeRosa, Marc; Downs, Cooper; Fleishman, Gregory; Fuentes, Olac; Gary, Dale; Hill, Frank; Hoeksema, Todd; Hu, Qiang; Ilie, Raluca; Ireland, Jack; Kamalabadi, Farzad; Korreck, Kelly; Kosovichev, Alexander; Lin, Jessica; Lugaz, Noe; Mannucci, Anthony; Mansour, Nagi; Martens, Petrus; Mays, Leila; McAteer, James; McIntosh, Scott W.; Oria, Vincent; Pan, David; Panesi, Marco; Pesnell, W. Dean; Pevtsov, Alexei; Pillet, Valentin; Rachmeler, Laurel; Ridley, Aaron; Scherliess, Ludger; Toth, Gabor; Velli, Marco; White, Stephen; Zhang, Jie; Zou, Shasha Bibcode: 2018arXiv181008728N Altcode: The authors of this report met on 28-30 March 2018 at the New Jersey Institute of Technology, Newark, New Jersey, for a 3-day workshop that brought together a group of data providers, expert modelers, and computer and data scientists, in the solar discipline. Their objective was to identify challenges in the path towards building an effective framework to achieve transformative advances in the understanding and forecasting of the Sun-Earth system from the upper convection zone of the Sun to the Earth's magnetosphere. The workshop aimed to develop a research roadmap that targets the scientific challenge of coupling observations and modeling with emerging data-science research to extract knowledge from the large volumes of data (observed and simulated) while stimulating computer science with new research applications. The desire among the attendees was to promote future trans-disciplinary collaborations and identify areas of convergence across disciplines. The workshop combined a set of plenary sessions featuring invited introductory talks and workshop progress reports, interleaved with a set of breakout sessions focused on specific topics of interest. Each breakout group generated short documents, listing the challenges identified during their discussions in addition to possible ways of attacking them collectively. These documents were combined into this report-wherein a list of prioritized activities have been collated, shared and endorsed. Title: Reconstructing solar magnetic fields from historical observations. III. Activity in one hemisphere is sufficient to cause polar field reversals in both hemispheres Authors: Virtanen, I. O. I.; Virtanen, I. I.; Pevtsov, A. A.; Mursula, K. Bibcode: 2018A&A...616A.134V Altcode:
Aims: Sunspot activity is often hemispherically asymmetric, and during the Maunder minimum, activity was almost completely limited to one hemisphere. In this work, we use surface flux simulation to study how magnetic activity limited only to the southern hemisphere affects the long-term evolution of the photospheric magnetic field in both hemispheres. The key question is whether sunspot activity in one hemisphere is enough to reverse the polarity of polar fields in both hemispheres.
Methods: We simulated the evolution of the photospheric magnetic field from 1978 to 2016 using the observed active regions of the southern hemisphere as input. We studied the flow of magnetic flux across the equator and its subsequent motion towards the northern pole. We also tested how the simulated magnetic field is changed when the activity of the southern hemisphere is reduced.
Results: We find that activity in the southern hemisphere is enough to reverse the polarity of polar fields in both hemispheres by the cross-equatorial transport of magnetic flux. About 1% of the flux emerging in the southern hemisphere is transported across the equator, but only 0.1%-0.2% reaches high latitudes to reverse and regenerate a weak polar field in the northern hemisphere. The polarity reversals in the northern hemisphere are delayed compared to the southern hemisphere, leading to a quadrupole Sun lasting for several years. Title: Tilt of Sunspot Bipoles in Solar Cycles 15 to 24 Authors: Tlatova, Ksenia; Tlatov, Andrey; Pevtsov, Alexei; Mursula, Kalevi; Vasil'eva, Valeria; Heikkinen, Elina; Bertello, Luca; Pevtsov, Alexander; Virtanen, Ilpo; Karachik, Nina Bibcode: 2018SoPh..293..118T Altcode: 2018arXiv180707913T We use recently digitized sunspot drawings from Mount Wilson Observatory to investigate the latitudinal dependence of tilt angles of active regions and its change with solar cycle. The drawings cover the period from 1917 to present and contain information as regards polarity and strength of magnetic field in sunspots. We identified clusters of sunspots of same polarity, and used these clusters to form "bipole pairs". The orientation of these bipole pairs was used to measure their tilts. We find that the latitudinal profile of tilts does not monotonically increase with latitude as most previous studies assumed, but instead, it shows a clear maximum at about 25 - 30 degree latitudes. Functional dependence of tilt (γ ) on latitude (φ ) was found to be γ =(0.20 ±0.08 )sin(2.80 φ )+(−0.00 ±0.06 ). We also find that latitudinal dependence of tilts varies from one solar cycle to another, but larger tilts do not seem to result in stronger solar cycles. Finally, we find the presence of a systematic offset in tilt of active regions (non-zero tilts at the equator), with odd cycles exhibiting negative offset and even cycles showing the positive offset. Title: Current Efforts to Preserve Mt. Wilson Historical Observations Authors: Pevtsov, Alexander; Pevtsov, Alexei; Virtanen, Ilpo; Bertello, Luca Bibcode: 2018cosp...42E2653P Altcode: Mount Wilson Observatory (MWO) located in the San Gabriel Mountains near Pasadena, California, has been taking solar observations since the early 1900s. The earliest of which include the nearly unbroken record of daily sunspot activity from 1917 through the present day. Full disk spectroheliograms in Ca K spectral line were taken from 1915 through 1985. Starting from the 1950s synoptic magnetograms were also taken utilizing the full disk longitudinal magnetograph at MWO. However, working with historical long-term dataset presents unique challenges. To be useful, data from hand drawings needed to be digitized. Furthermore, data server failures in the past have led to a loss of public access to parts of these historical data sets. Over the past several years we have worked to process and extract metadata from MWO sunspot drawings. Recently, a new project on the preservation of historical magnetograms has been started. These efforts have provided insight into dealing with issues presented by historical datasets. In this presentation we provide an overview of current efforts in preserving the historical (solar) datasets from MWO. We discuss some of these issues and the application of these insights with regard to the recovery and processing of early magnetogram data along with the current plans to transfer this data to the public domain. 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: Modeling the Global Coronal Field with Simulated Synoptic Magnetograms from Earth and the Lagrange Points L3, L4, and L5 Authors: Petrie, Gordon; Pevtsov, Alexei; Schwarz, Andrew; DeRosa, Marc Bibcode: 2018SoPh..293...88P Altcode: The solar photospheric magnetic flux distribution is key to structuring the global solar corona and heliosphere. Regular full-disk photospheric magnetogram data are therefore essential to our ability to model and forecast heliospheric phenomena such as space weather. However, our spatio-temporal coverage of the photospheric field is currently limited by our single vantage point at/near Earth. In particular, the polar fields play a leading role in structuring the large-scale corona and heliosphere, but each pole is unobservable for >6 months per year. Here we model the possible effect of full-disk magnetogram data from the Lagrange points L4 and L5, each extending longitude coverage by 60∘. Adding data also from the more distant point L3 extends the longitudinal coverage much further. The additional vantage points also improve the visibility of the globally influential polar fields. Using a flux-transport model for the solar photospheric field, we model full-disk observations from Earth/L1, L3, L4, and L5 over a solar cycle, construct synoptic maps using a novel weighting scheme adapted for merging magnetogram data from multiple viewpoints, and compute potential-field models for the global coronal field. Each additional viewpoint brings the maps and models into closer agreement with the reference field from the flux-transport simulation, with particular improvement at polar latitudes, the main source of the fast solar wind. Title: Composite Photospheric Synoptic Magnetic Maps Authors: Bertello, Luca; Pevtsov, Alexei A.; Petrie, Gordon J. D. Bibcode: 2018tess.conf11502B Altcode: Photospheric synoptic maps of the Sun's magnetic field are the primary drivers of both coronal and heliospheric Title: Modeling the Global Coronal Field with Simulated Synoptic Magnetograms from Earth and the Lagrange points L3, L4 and L5 Authors: Petrie, Gordon J. D.; Pevtsov, Alexei A.; Schwarz, Andrew Michael; DeRosa, Marc Bibcode: 2018tess.conf40132P Altcode: The solar photospheric magnetic flux distribution determines the global structure of the solar corona and heliosphere. Regular full-disk photospheric magnetogram data are therefore essential to our ability to model and forecast heliospheric phenomena such as space weather. However, our spatio-temporal coverage of the photospheric field is currently limited by our single vantage point at/near Earth. In particular, the polar fields define the large-scale structure of the corona and heliosphere but each pole is unobservable for > 6 months per year. Here we model the possible effect of full-disk magnetogram data from the Lagrange points L4 and L5, each extending longitude coverage by 60 degrees. Adding data also from the more distant point L3 extends longitudinal coverage much further. The additional vantage points also improve the visibility of the globally influential polar fields. Using a flux-transport model for the solar photospheric field we model full-disk observations from Earth/L1, L3, L4 and L5 over a solar cycle, construct synoptic maps using a novel weighting scheme adapted for merging magnetogram data from multiple viewpoints, and compute potential-field models for the global coronal field. Each additional viewpoint significantly improves the performance of the maps and models with particular improvement at polar latitudes, the main source of the fast solar wind. Title: Is activity in one hemisphere enough to maintain the magnetic cycle? Authors: Virtanen, Iiro; Virtanen, Ilpo; Pevtsov, Alexei; Mursula, Kalevi Bibcode: 2018EGUGA..2018095V Altcode: Sunspot activity is often hemispherically asymmetric, and during the Maunder minimum activity was almost completely limited to one hemisphere. We use surface flux simulations to study how magnetic activity limited only to the southern hemisphere affects the long-term evolution of the photospheric magnetic field in both hemispheres. The key question is whether activity in one hemisphere is enough to maintain the magnetic cycle of polar areas in both hemispheres. We simulate the evolution of the field from 1978 to 2016 using the observed active regions of the southern hemisphere as input. We study the flow of magnetic flux across the equator and its subsequent motion towards the northern pole. We find that activity in the southern hemisphere is enough to maintain the magnetic cycle in both hemispheres by the cross-equatorial flow of magnetic flux. About one percent of the flux emerging in the southern hemisphere is transported across the equator, but only 0.1%-0.2% reaches high latitudes to reverse and regenerate a weak polar field in the northern hemisphere. The magnetic cycle of the northern hemisphere is delayed compared to the southern hemisphere, leading to a quadrupole Sun lasting for several years. Title: Reconstructing Solar Magnetic Field Evolution Over the Past Century Authors: Pevtsov, Alexei Bibcode: 2018EGUGA..2013274P Altcode: This talk will review the current state of long- term synoptic programs and present results of several recent projects aimed at reconstructing a more detailed picture of solar activity over the last century. In particular, we will present the recent findings and discuss open questions of research projects by international team 420 supported by the International Space Science Institute (Bern, Switzerland, see http://www.issibern.ch/teams/solheliomagnet/#). The team aims at developing methods to study the evolution of magnetic activity prior to modern age of solar magnetography using historical data from Kodaikanal (India) and Mount Wilson (USA) observatories and modern surface flux transport models. Title: Electric Currents in the Solar Atmosphere Authors: Fleishman, Gregory D.; Pevtsov, Alexei A. Bibcode: 2018GMS...235...43F Altcode: No abstract at ADS Title: Patterns of Variation for the Sun and Sun-like Stars Authors: Radick, Richard R.; Lockwood, G. Wesley; Henry, Gregory W.; Hall, Jeffrey C.; Pevtsov, Alexei A. Bibcode: 2018ApJ...855...75R Altcode: We compare patterns of variation for the Sun and 72 Sun-like stars by combining total and spectral solar irradiance measurements between 2003 and 2017 from the SORCE satellite, Strömgren b, y stellar photometry between 1993 and 2017 from Fairborn Observatory, and solar and stellar chromospheric Ca II H+K emission observations between 1992 and 2016 from Lowell Observatory. The new data and their analysis strengthen the relationships found previously between chromospheric and brightness variability on the decadal timescale of the solar activity cycle. Both chromospheric H+K and photometric b, y variability among Sun-like stars are related to average chromospheric activity by power laws on this timescale. Young active stars become fainter as their H+K emission increases, and older, less active, more Sun-age stars tend to show a pattern of direct correlation between photometric and chromospheric emission variations. The directly correlated pattern between total solar irradiance and chromospheric Ca II emission variations shown by the Sun appears to extend also to variations in the Strömgren b, y portion of the solar spectrum. Although the Sun does not differ strongly from its stellar age and spectral class mates in the activity and variability characteristics that we have now studied for over three decades, it may be somewhat unusual in two respects: (1) its comparatively smooth, regular activity cycle, and (2) its rather low photometric brightness variation relative to its chromospheric activity level and variation, perhaps indicating that facular emission and sunspot darkening are especially well-balanced on the Sun. Title: Two Populations of Sunspots: Differential Rotation Authors: Nagovitsyn, Yu. A.; Pevtsov, A. A.; Osipova, A. A. Bibcode: 2018AstL...44..202N Altcode: To investigate the differential rotation of sunspot groups using the Greenwich data, we propose an approach based on a statistical analysis of the histograms of particular longitudinal velocities in different latitude intervals. The general statistical velocity distributions for all such intervals are shown to be described by two rather than one normal distribution, so that two fundamental rotation modes exist simultaneously: fast and slow. The differentiality of rotation for the modes is the same: the coefficient at sin2 in Faye's law is 2.87-2.88 deg/day, while the equatorial rotation rates differ significantly, 0.27 deg/day. On the other hand, an analysis of the longitudinal velocities for the previously revealed two differing populations of sunspot groups has shown that small short-lived groups (SSGs) are associated with the fast rotation mode, while large long-lived groups (LLGs) are associated with both fast and slow modes. The results obtained not only suggest a real physical difference between the two populations of sunspots but also give new empirical data for the development of a dynamo theory, in particular, for the theory of a spatially distributed dynamo. Title: Space Weather Forecasting and Supporting Research in the USA Authors: Pevtsov, A. A. Bibcode: 2017Ge&Ae..57..769P Altcode: 2016arXiv161102652P In the United State, scientific research in space weather is funded by several Government Agencies including the National Science Foundation (NSF) and the National Aeronautics and Space Agency (NASA). For civilian and commercial purposes, space weather forecast is done by the Space Weather Prediction Center (SWPC) of the National Oceanic and Atmospheric Administration (NOAA). Observational data for modeling come from the network of groundbased observatories funded via various sources, as well as from the instruments on spacecraft. Numerical models used in forecast are developed in framework of individual research projects. The article provides a brief review of current state of space weather-related research and forecasting in the USA. 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: On the timing of the next great solar activity minimum Authors: Tlatov, A. G.; Pevtsov, A. A. Bibcode: 2017AdSpR..60.1108T Altcode: The long-term variations in solar activity are studied using the dataset comprised of sunspot number and 14C radioisotope timeseries. We use a novel S200 index to identify possible past Grand Minima (GM). The Maunder, Oort, Wolf and Spörer Minima fall in phase with the minimum of S200 index. We also show GM develop in clusters, with a separation of about 400-600 years between individual GM. Extending these found similarities to modern solar activity, it is predicted that next grand solar minimum may occur in about ∼ 2090 ± 20 . Title: VizieR Online Data Catalog: Calibrated solar S-index time series (Egeland+, 2017) Authors: Egeland, R.; Soon, W.; Baliunas, S.; Hall, J. C.; Pevtsov, A. A.; Bertello, L. Bibcode: 2017yCat..18350025E Altcode: The Mount Wilson HK Program observed the Moon with both the HKP-1 and HKP-2 instruments. After removing 11 obvious outliers, there are 162 HKP-1 observations taken from 1966 September 2 to 1977 June 4 with the Mount Wilson 100 inch reflector, covering the maximum of cycle 20 and the cycle 20-21 minimum. As mentioned in Baliunas+ (1995ApJ...438..269B), observations of the Moon resumed in 1993 with the HKP-2 instrument. After removing 10 obvious outliers, there are 75 HKP-2 observations taken from 1994 March 27 to 2002 November 23 with the Mount Wilson 60 inch reflector, covering the end of cycle 22 and the cycle 23 minimum, extending just past the cycle 23 maximum. The end of observations coincides with the unfortunate termination of the HK Project in 2003.

We seek to extend our time series of solar variability beyond cycle 23 by establishing a proxy to the NSO Sacramento Peak (NSO/SP) observations taken from 1976 to 2016, covering cycles 21 to 24. The spectral intensity scale is set by integrating a 0.53Å band centered at 3934.869Å in the K-line wing and setting it to the fixed value of 0.162.

We extend the S-index record back to cycle 20 using the composite K time series of Bertello+ (2016SoPh..291.2967B). See section 3 for further explanations.

(1 data file). Title: Sub-Pixel Magnetic Field and Plasma Dynamics Derived from Photospheric Spectral Data Authors: Rasca, Anthony P.; Chen, James; Pevtsov, Alexei A. Bibcode: 2017SPD....4810104R Altcode: Current high-resolution observations of the photosphere show small dynamic features at the resolving limit during emerging flux events. However, line-of-sight (LOS) magnetogram pixels only contain the net uncanceled magnetic flux, which is expected to increase for fixed regions as resolution limits improve. Using a new method with spectrographic images, we quantify distortions in photospheric absorption (or emission) lines caused by sub-pixel magnetic field and plasma dynamics in the vicinity of active regions and emerging flux events. Absorption lines—quantified by their displacement, width, asymmetry, and peakedness—have previously been used with Stokes I images from SOLIS/VSM to relate line distortions with sub-pixel plasma dynamics driven by solar flares or small-scale flux ropes. The method is extended to include the full Stokes parameters and relate inferred sub-pixel dynamics with small-scale magnetic fields. Our analysis is performed on several sets of spectrographic images taken by SOLIS/VSM while observing eruptive and non-eruptive active regions. We discuss the results of this application and their relevance for understanding magnetic fields signatures and coupled plasma properties on sub-pixel scales. Title: Reconstructing solar magnetic fields from historical observations. II. Testing the surface flux transport model Authors: Virtanen, I. O. I.; Virtanen, I. I.; Pevtsov, A. A.; Yeates, A.; Mursula, K. Bibcode: 2017A&A...604A...8V Altcode:
Aims: We aim to use the surface flux transport model to simulate the long-term evolution of the photospheric magnetic field from historical observations. In this work we study the accuracy of the model and its sensitivity to uncertainties in its main parameters and the input data.
Methods: We tested the model by running simulations with different values of meridional circulation and supergranular diffusion parameters, and studied how the flux distribution inside active regions and the initial magnetic field affected the simulation. We compared the results to assess how sensitive the simulation is to uncertainties in meridional circulation speed, supergranular diffusion, and input data. We also compared the simulated magnetic field with observations.
Results: We find that there is generally good agreement between simulations and observations. Although the model is not capable of replicating fine details of the magnetic field, the long-term evolution of the polar field is very similar in simulations and observations. Simulations typically yield a smoother evolution of polar fields than observations, which often include artificial variations due to observational limitations. We also find that the simulated field is fairly insensitive to uncertainties in model parameters or the input data. Due to the decay term included in the model the effects of the uncertainties are somewhat minor or temporary, lasting typically one solar cycle. Title: How radial is the photospheric magnetic field? Authors: Virtanen, Ilpo; Pevtsov, Alexei; Mursula, Kalevi Bibcode: 2017shin.confE..51V Altcode: The new data set of SOLIS/VSM vector synoptic maps of photospheric magnetic fields since 2010 reveals new features about the structure and evolution of the solar magnetic field. We investigate the structure and evolution of large scale vector magnetic fields in 2010 - 2016, covering the ascending to declining phase of solar cycle 24. We compare the observed VSM vector magnetic field to the potential vector field derived using the VSM line-of-sight magnetic field observations as an input. The new data set allows to derive the inclination angle, the meridional inclination and the azimuth angle of the magnetic field and to investigate solar cycle evolution and latitudinal profile of these quantities. Title: Ca II K 1-A Emission Index Composites Authors: Bertello, Luca; Marble, Andrew R.; Pevtsov, Alexei A. Bibcode: 2017arXiv170200838B Altcode: We describe here a procedure to combine measurements in the 393.37 nm Ca II K spectral line taken at different observatories. Measurements from the National Solar Observatory (NSO) Integrated Sunlight Spectrometer (ISS) on the Synoptic Optical Long-term Investigations of the Sun (SOLIS) telescope, the NSO/Sac Peak Ca II K-Line Monitoring Program, and Ca II K filtergrams from Kodaikanal Solar Observatory (KKL) are merged together to create a pair of composites of the Ca II K 1-A emission index. These composites are publicly available from the SOLIS website at http://solis.nso.edu/0/iss/. Title: Long-term variations in sunspot magnetic field-area relation Authors: Nagovitsyn, Y. A.; Pevtsov, A. A.; Osipova, A. A. Bibcode: 2017AN....338...26N Altcode: 2016arXiv160801132N Using observations of sunspot magnetic field strengths (H) from the Crimean Astrophysical Observatory (CrAO) and area (S) of sunspots from the Kislovodsk Mountain Astronomical Station of Pulkovo Observatory, we investigate the changes in the relation between H and S over the period of about two solar cycles (1994-2013). The data were fitted by H = A + B log S, where A = (778+/-46) and B = (778+/-25). We show that the correlation between H and S varies with the phase of solar cycle, and $A$ coefficient decreases significantly after year 2001, while B coefficient does not change significantly. Furthermore, our data confirm the presence of two distinct populations in distribution of sunspots (small sunspots with weaker field strength and large sunspots with stronger field). We show that relative contribution of each component to the distribution of sunspots by their area changes with the phase of solar cycle and on longer-then-cycle periods. We interpret these changes as a signature of a long-term (centennial) variations in properties of sunspots. Title: The Mount Wilson Observatory S-index of the Sun Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Pevtsov, Alexei A.; Bertello, Luca Bibcode: 2017ApJ...835...25E Altcode: 2016arXiv161104540E The most commonly used index of stellar magnetic activity is the instrumental flux scale of singly ionized calcium H & K line core emission, S, developed by the Mount Wilson Observatory (MWO) HK Project, or the derivative index {R}{HK}\prime . Accurately placing the Sun on the S scale is important for comparing solar activity to that of the Sun-like stars. We present previously unpublished measurements of the reflected sunlight from the Moon using the second-generation MWO HK photometer during solar cycle 23 and determine cycle minimum {S}23,\min =0.1634+/- 0.0008, amplitude {{Δ }}{S}23=0.0143+/- 0.0012, and mean < {S}23> =0.1701+/- 0.0005. By establishing a proxy relationship with the closely related National Solar Observatory Sacramento Peak calcium K emission index, itself well correlated with the Kodaikanal Observatory plage index, we extend the MWO S time series to cover cycles 15-24 and find on average < {S}\min > =0.1621+/- 0.0008, < {{Δ }}{S}{cyc}> =0.0145+/- 0.0012, < {S}{cyc}> =0.1694+/- 0.0005. Our measurements represent an improvement over previous estimates that relied on stellar measurements or solar proxies with non-overlapping time series. We find good agreement from these results with measurements by the Solar-Stellar Spectrograph at Lowell Observatory, an independently calibrated instrument, which gives us additional confidence that we have accurately placed the Sun on the S-index flux scale. Title: On the Presence of Two Populations of Sunspots Authors: Nagovitsyn, Yury A.; Pevtsov, Alexei A. Bibcode: 2016ApJ...833...94N Altcode: Using historical (1894-1976) and more modern (1977-2014) observations, we investigate statistical properties of distributions of sunspot areas and their long-term variations. We confirm the presence of two populations of sunspots with smaller and larger areas, and show that sunspot/group lifetime can be used to separate the two populations on small short-lived sunspot groups (SSG) and large long-lived groups (LLG). The area properties of LLG are nearly constant over the entire period of observations, while the SSGs show significant long-term variations. Based on the presence of long-term variations in one component and the absence of those in the other, we suggest that the production of two populations of sunspots (SSG and LLG) may be affected by different processes. Title: Sub-Pixel Magnetic Field Dynamics Derived from Photospheric Spectral Line Profiles Authors: Rasca, A.; Chen, J.; Pevtsov, A. A.; Yurchyshyn, V.; Bertello, L. Bibcode: 2016AGUFMSH13C2308R Altcode: Current high-resolution observations of the photosphere show small dynamic features at the resolving limit during emerging flux events. However, line-of-sight (LOS) magnetogram pixels only contain the net uncanceled magnetic flux, which is expected to increase for fixed regions as resolution limits improve. Using a new method with spectrographic images, we quantify distortions in photospheric absorption (or emission) lines caused by sub-pixel magnetic field and plasma dynamics in the vicinity of active regions and emerging flux events. Absorption lines—quantified by their displacement, width, asymmetry, and peakedness—have previously been used with Stokes I images from SOLIS/VSM to relate line distortions with sub-pixel plasma dynamics driven by solar flares or small-scale flux ropes. The method is extended to include the full Stokes parameters and relate inferred sub-pixel dynamics with small-scale magnetic fields. Our analysis is performed on several sets of spectrographic images taken by SOLIS/VSM and NST/NIRIS while observing eruptive and non-eruptive active regions. We discuss the results of this application and their relevance for understanding magnetic fields signatures and coupled plasma properties on sub-pixel scales. Title: The vorticity of Solar photospheric flows on the scale of granulation Authors: Pevtsov, A. A. Bibcode: 2016Ge&Ae..56..972P Altcode: 2016arXiv160601390P We employ time sequences of images observed with a G-band filter (λ4305Å) by the Solar Optical Telescope (SOT) on board of Hinode spacecraft at different latitude along solar central meridian to study vorticity of granular flows in quiet Sun areas during deep minimum of solar activity. Using a feature correlation tracking (FCT) technique, we calculate the vorticity of granular-scale flows. Assuming the known pattern of vertical flows (upward in granules and downward in intergranular lanes), we infer the sign of kinetic helicity of these flows. We show that the kinetic helicity of granular flows and intergranular vortices exhibits a weak hemispheric preference, which is in agreement with the action of the Coriolis force. This slight hemispheric sign asymmetry, however, is not statistically significant given large scatter in the average vorticity. The sign of the current helicity density of network magnetic fields computed using full disk vector magnetograms from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) does not show any hemispheric preference. The combination of these two findings suggests that the photospheric dynamo operating on the scale of granular flows is non-helical in nature. Title: Modeling the Global Coronal Field with Simulated Synoptic Magnetograms from L1 and L5 Authors: Petrie, G. J. D.; Bertello, L.; Pevtsov, A. A. Bibcode: 2016AGUFMSH11C2242P Altcode: In solar physics and space weather research, full-disk photospheric magnetograms are routinely used to map the full solar surface in near-real-time, and coronal field models are extrapolated from these data. One major shortcoming of this approach is that, at present, the magnetograms can only be taken from the Earth's direction. Thus data immediately eastward of the sub-Earth point in synoptic maps are around three weeks old, missing much active-region evolution and leading to inaccuracies in the models. A new magnetograph at L5 would update the synoptic maps at this critical location east of central meridian and would provide a more accurate, up-to-date picture of the global photospheric and coronal field. We demonstrate the value of L5 observations by simulating the construction of synoptic magnetograms from both L1 and L5 directions using past near-real-time data from two observatories: the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectromagnetograph (VSM) and Global Oscillation Network Group (GONG). We extrapolate potential-field source-surface (PFSS) coronal field models and compare their open-field and streamer distributions to coronal observations from the Solar Terrestrial Relations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA). Title: Blending of Ground- and Space-Based Magnetograms: Application to L1-L5 Solar Wind and Coronal Hole Predictions Authors: Berger, T. E.; Pevtsov, A. A.; Martinez-Pillet, V.; Bertello, L.; Petrie, G. J. D.; Arge, C. N.; Henney, C. J.; Biesecker, D. A. Bibcode: 2016AGUFMSH11C2241B Altcode: We examine the effect of blending ground-based Global Oscillations Network Group (GONG) line-of-sight solar magnetic flux maps ("magnetograms") with space-based magnetograms from the Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) instrument on solar wind and coronal hole model-based forecasts. The longitudinally blended maps are used to "reforecast" solar wind conditions using the Wang-Sheeley-Arge (WSA) solar wind model during historical periods of coronal hole High Speed Streams (HSS) and Corotating Interaction Regions (CIRs) and compared to Advanced Composition Explorer (ACE) data at the L1 Lagrangian point. The same WSA runs are repeated using GONG and HMI data alone to determine the effect of data blending. The blended maps are also used to create Potential Field Source Surface (PFSS) maps of open coronal field lines and compared with historical coronal hole data from SDO Atmospheric Imaging Assembly (AIA) images. The study addresses the feasibility of combining ground- and space-based data from instruments with widely disparate and varying spatiotemporal resolution and flux sensitivity levels for use as inputs to solar wind and coronal hole forecasting models. The results are relevant to mission studies considering blended data inputs from, e.g., L5 Lagrangian point satellite instruments with ground-based measurements on the Sun-Earth line, as well as to expected magnetogram data from the Solar Orbiter Polarimetric and Helioseismic Imager (PHI) instrument. This study complements others that examine the utility of having multiple viewpoint (e.g. L1 and L5) magnetogram inputs to solar wind models by exploring data blending from disparate instruments. Title: Pixel Analysis of Photospheric Spectral Data. I. Plasma Dynamics Authors: Rasca, Anthony P.; Chen, James; Pevtsov, Alexei A. Bibcode: 2016ApJ...832...53R Altcode: Recent observations of the photosphere using high spatial and temporal resolution show small dynamic features at or below the current resolving limits. A new pixel dynamics method has been developed to analyze spectral profiles and quantify changes in line displacement, width, asymmetry, and peakedness of photospheric absorption lines. The algorithm evaluates variations of line profile properties in each pixel and determines the statistics of such fluctuations averaged over all pixels in a given region. The method has been used to derive statistical characteristics of pixel fluctuations in observed quiet-Sun regions, an active region with no eruption, and an active region with an ongoing eruption. Using Stokes I images from the Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) telescope on 2012 March 13, variations in line width and peakedness of Fe I 6301.5 Å are shown to have a distinct spatial and temporal relationship with an M7.9 X-ray flare in NOAA 11429. This relationship is observed as stationary and contiguous patches of pixels adjacent to a sunspot exhibiting intense flattening in the line profile and line-center displacement as the X-ray flare approaches peak intensity, which is not present in area scans of the non-eruptive active region. The analysis of pixel dynamics allows one to extract quantitative information on differences in plasma dynamics on sub-pixel scales in these photospheric regions. The analysis can be extended to include the Stokes parameters and study signatures of vector components of magnetic fields and coupled plasma properties. Title: Correlation Between Sunspot Number and Ca II K Emission Index Authors: Bertello, Luca; Pevtsov, Alexei; Tlatov, Andrey; Singh, Jagdev Bibcode: 2016SoPh..291.2967B Altcode: 2016arXiv160601092B; 2016SoPh..tmp..121B Long-term synoptic observations in the resonance line of Ca II K constitute a fundamental database for a variety of retrospective analyses of the state of the solar magnetism. Synoptic Ca II K observations began in late 1904 at the Kodaikanal Observatory in India. In the early 1970s, the National Solar Observatory (NSO) at Sacramento Peak (USA) started a new program of daily Sun-as-a-star observations in the Ca II K line. Today the NSO is continuing these observations through its Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility. These different data sets can be combined into a single disk-integrated Ca II K index time series that describes the average properties of the chromospheric emission over several solar cycles. We present such a Ca II K composite and discuss its correlation with the new entirely revised sunspot number data series. For this preliminary investigation, the scaling factor between pairs of time series was determined assuming a simple linear model for the relationship between the monthly mean values during the duration of overlapping observations. Title: Two populations of sunspots and secular variations of their characteristics Authors: Nagovitsyn, Yu. A.; Pevtsov, A. A.; Osipova, A. A.; Tlatov, A. G.; Miletskii, E. V.; Nagovitsyna, E. Yu. Bibcode: 2016AstL...42..703N Altcode: We investigate the magnetic fields and total areas of mid- and low-latitude sunspots based on observations at the Greenwich and Kislovodsk (sunspot areas) and Mount Wilson, Crimean, Pulkovo, Ural, IMIS, Ussuriysk, IZMIRAN, and Shemakha (magnetic fields) observatories. We show that the coefficients in the linear form of the dependence of the logarithm of the total sunspot area S on its maximum magnetic field H change with time. Two distinct populations of sunspots are identified using the twodimensional H-log S occurrence histogram: small and large, separated by the boundaries log S = 1.6 ( S = 40 MSH) and H = 2050 G. Analysis of the sunspot magnetic flux also reveals the existence of two lognormally distributed populations with the mean boundary between them Φ = 1021 Mx. At the same time, the positions of the flux occurrence maxima for the populations change on a secular time scale: by factors of 4.5 and 1.15 for small and large sunspots, respectively. We have confirmed that the sunspots form two physically distinct populations and show that the properties of these populations change noticeably with time. This finding is consistent with the hypothesis about the existence of two magnetic field generation zones on the Sun within the framework of a spatially distributed dynamo. Title: Impact of Magnetic Carrington Synoptic and Spatial Variance Maps in Modeling of the Corona and Solar Wind Authors: Bertello, Luca; Pevtsov, Alexie A.; Petrie, Gordon J. D.; Hughes, Anna L. H.; Macniece, Peter J. Bibcode: 2016usc..confE..42B Altcode: Synoptic maps derived from the measured photospheric solar longitudinal magnetic field are routinely used to drive coronal and heliospheric models. The recent development of spatial variance maps has provided an additional resource to better understanding the limitation of these models. In addition, measurements of the vector magnetic field are now available from different instruments (e.g. SDO/HMI, SOLIS/VSM) and can be used to compute synoptic maps of the true radial field. However, due to the low sensitivity of these measurements in regions of weak magnetic field, the adoption of these maps has been very limited. An effort is underway at NSO to merge both longitudinal and vector measurements together and derive more reliable synoptic maps of the radial field. An even more ambitious project is ongoing to produce also the first radial synoptic maps derived from SOLIS/VSM chromospheric measurements. Validation and diagnostic capability of these products will be discussed. Title: The Possible Impact of L5 Magnetograms on Non-potential Solar Coronal Magnetic Field Simulations Authors: Weinzierl, Marion; Mackay, Duncan H.; Yeates, Anthony R.; Pevtsov, Alexei A. Bibcode: 2016ApJ...828..102W Altcode: The proposed Carrington-L5 mission would bring instruments to the L5 Lagrange point to provide us with crucial data for space weather prediction. To assess the importance of including a magnetograph, we consider the possible differences in non-potential solar coronal magnetic field simulations when magnetograph observations are available from the L5 point, compared with an L1-based field of view (FOV). A timeseries of synoptic radial magnetic field maps is constructed to capture the emergence of two active regions from the L5 FOV. These regions are initially absent in the L1 magnetic field maps, but are included once they rotate into the L1 FOV. Non-potential simulations for these two sets of input data are compared in detail. Within the bipolar active regions themselves, differences in the magnetic field structure can exist between the two simulations once the active regions are included in both. These differences tend to reduce within 5 days of the active region being included in L1. The delayed emergence in L1 can, however, lead to significant persistent differences in long-range connectivity between the active regions and the surrounding fields, and also in the global magnetic energy. In particular, the open magnetic flux and the location of open magnetic footpoints, are sensitive to capturing the real-time of emergence. These results suggest that a magnetograph at L5 could significantly improve predictions of the non-potential corona, the interplanetary magnetic field, and of solar wind source regions on the Sun. Title: Dynamo Sensitivity In Solar Analogs With 50 Years Of Ca II H & K Activity Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016csss.confE...6E Altcode: 2016csss.confE..73E; 2016arXiv160904756E The Sun has a steady 11-year cycle in magnetic activity most well-known by the rising and falling in the occurrence of dark sunspots on the solar disk in visible bandpasses. The 11-year cycle is also manifest in the variations of emission in the Ca II H & K line cores, due to non-thermal (i.e. magnetic) heating in the lower chromosphere. The large variation in Ca II H & K emission allows for study of the patterns of long-term variability in other stars thanks to synoptic monitoring with the Mount Wilson Observatory HK photometers (1966-2003) and Lowell Observatory Solar-Stellar Spectrograph (1994-present). Overlapping measurements for a set of 27 nearby solar-analog (spectral types G0-G5) stars were used to calibrate the two instruments and construct time series of magnetic activity up to 50 years in length. Precise properties of fundamental importance to the dynamo are available from Hipparcos, the Geneva-Copenhagen Survey, and CHARA interferometry. Using these long time series and measurements of fundamental properties, we do a comparative study of stellar "twins" to explore the sensitivity of the stellar dynamo to small changes to structure, rotation, and composition. We also compare this sample to the Sun and find hints that the regular periodic variability of the solar cycle may be rare among its nearest neighbors in parameter space. Title: Solar Ca II K Observations Authors: Bertello, Luca; Pevtsov, Alexei A.; Tlatov, Andrey; Singh, Jagdev Bibcode: 2016AsJPh..25..295B Altcode: Some of the most important archives of past and current long-term solar synoptic observations in the resonance line of Ca II K are described here. These observations are very important for understanding the state of the solar magnetism on time scales up to several decades. The first observations of this kind began in 1904 at the Kodaikanal Observatory (India), followed by similar programs at different other locations. Regular full-disk Ca II K monitoring programs started in 1915 at the Mount Wilson Observatory (USA) and in 1917 at the National Solar Observatory of Japan. Beginning in 1919 and in 1926 regular observations were taken also at the Paris-Meudon Observatory (France) and at the "Donati solar tower telescope of the Arcetri Astrophysical Observatory in Italy, respectively. In 1926 the the Astronomical Observatory of the Coimbra University in Portugal started its own program of Ca II K observations. Although some of these programs have been terminated over the years, their data archives constitute a unique resource for studies of solar variability. In the early 1970s, the National Solar Observatory (NSO) at Sacramento Peak (USA) started a new program of daily Sun-as-a-star observations in the Ca II K line. Today the NSO is continuing these observations through its Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility. Title: Pixel Analysis and Plasma Dynamics Characterized by Photospheric Spectral Data Authors: Rasca, Anthony P.; Chen, James; Pevtsov, Alexei A. Bibcode: 2016shin.confE.142R Altcode: Recent observations of the photosphere using high spatial and temporal resolution show small dynamic features at or below the current resolving limits. A new pixel dynamics method has been developed to analyze spectral profiles and quantify changes in line displacement, width, asymmetry, and peakedness of photospheric absorption lines. The algorithm evaluates variations of line profile properties in each pixel and determines the statistics of such fluctuations averaged over all pixels in a given region of interest. The method has been used to derive the statistical characteristics of pixel fluctuations in observed quiet-sun regions, an active region with no eruption, and an active region with an ongoing eruption. Using Stokes I images from SOLIS/VSM on 2012 March 13, variations in line width and peakedness of Fe I 630.15 nm, are shown to have a distinct spatial and temporal relationship with an M7.9 X-ray flare in NOAA 11429. This relationship is observed as contiguous patches of pixels near a sunspot exhibiting intense flattening in the line profile and line-center displacement as the X-ray flare approaches peak intensity, which is not present in area scans of the non-eruptive active region. Furthermore, these patches of pixels remain stationary relative to the sunspot. These results connote that the analysis of pixel dynamics allows one to extract quantitative information on differences in plasma dynamics on sub-pixel scales in these regions in the photosphere. The analysis can be extended to include the Stokes parameters and study signatures of vector components of magnetic fields and coupled plasma properties. Title: The Solar Dynamo Zoo Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016csss.confE..72E Altcode: We present composite time series of Ca II H & K line core emission indices of up to 50 years in length for a set of 27 solar-analog stars (spectral types G0-G5; within 10% of the solar mass) and the Sun. These unique data are available thanks to the long-term dedicated efforts of the Mount Wilson Observatory HK project, the Lowell Observatory Solar-Stellar Spectrograph, and the National Solar Observatory/Air Force Research Laboratory/Sacramento Peak K-line monitoring program. The Ca II H & K emission originates in the lower chromosphere and is strongly correlated with the presence of magnetic plage regions in the Sun. These synoptic observations allow us to trace the patterns long-term magnetic variability and explore dynamo behavior over a wide range of rotation regimes and stellar evolution timescales.In this poster, the Ca HK observations are expressed using the Mount Wilson S-index. Each time series is accompanied by a Lomb-Scargle periodogram, fundemental stellar parameters derived from the Geneva-Copenhagen Survey, and statistics derived from the time series including the median S-index value and seasonal and long-term amplitudes. Statistically significant periodogram peaks are ranked according to a new cycle quality metric. We find that clear, simple, Sun-like cycles are the minority in this sample. Title: Solar Physics Research in the Russian Subcontinent - Current Status and Future Authors: Pevtsov, A. A.; Nagovitsyn, Yu. A.; Tlatov, A. G.; Demidov, M. L. Bibcode: 2016AsJPh..25..477P Altcode: 2016arXiv160601331P Modern research in solar physics in Russia is a multifaceted endeavor, which includes multi-wavelength observations from the ground- and space-based instruments, extensive theoretical and numerical modeling studies, new instrument development, and cross-disciplinary and international research. The research is conducted at the research organizations under the auspices of the Russian Academy of Sciences and to a lesser extent, by the research groups at Universities. Here, we review the history of solar physics research in Russia, and provide an update on recent developments. Title: Pixel Analysis and Plasma Dynamics Characterized by Photospheric Spectral Data Authors: Rasca, Anthony P.; Chen, James; Pevtsov, Alexei A. Bibcode: 2016SPD....47.1206R Altcode: Recent observations of the photosphere using high spatial and temporal resolutions show small dynamic features at the resolving limit during emerging flux events. However, line-of-sight (LOS) magnetogram pixels only contain the net uncanceled magnetic flux, which is expected to increase for fixed regions as resolution limits improve. A new pixel dynamics method uses spectrographic images to characterize photospheric absorption line profiles by variations in line displacement, width, asymmetry, and peakedness and is applied to quiet-sun regions, active regions with no eruption, and an active region with an ongoing eruption. Using Stokes I images from SOLIS/VSM on 2012 March 13, variations in line width and peakedness of Fe I 6301.5 Å are shown to have a strong spatial and temporal relationship with an M7.9 X-ray flare originating from NOAA 11429. This relationship is observed as a flattening in the line profile as the X-ray flare approaches peak intensity and was not present in area scans of a non-eruptive active region on 2011 April 14. These results are used to estimate dynamic plasma properties on sub-pixel scales and provide both spatial and temporal information of sub-pixel activity at the photosphere. The analysis can be extended to include the full Stokes parameters and study signatures of magnetic fields and coupled plasma properties. 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: HMI Synoptic Maps Produced by NSO/NISP Authors: Hughes, Anna L. H.; Bertello, Luca; Marble, Andrew R.; Oien, Niles A.; Petrie, Gordon; Pevtsov, Alexei A. Bibcode: 2016arXiv160503500H Altcode: Recently, the National Solar Observatory (NSO) Solar-atmosphere Pipeline Working Group has undertaken the production of synoptic maps from Helioseismic and Magnetic Imager (HMI) magnetograms. A set of maps has been processed spanning the data available for 2010-2015 using twice daily images (taken at UT midnight and noon) and running them through the same algorithms used to produce SOLIS/VSM 6302l mean-magnetic and spatial-variance maps. The contents of this document provide an overview of what these maps look like, and the processing steps used to generate them from the original HMI input data. Title: Dynamo Sensitivity in Solar Analogs with 50 Years of Ca II H & K Activity Authors: Egeland, Ricky; Soon, Willie H.; Baliunas, Sallie L.; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016SPD....4720307E Altcode: The Sun has a steady 11-year cycle in magnetic activity most well-known by the rising and falling in the occurrence of dark sunspots on the solar disk in visible bandpasses. The 11-year cycle is also manifest in the variations of emission in the Ca II H & K line cores, due to non-thermal (i.e. magnetic) heating in the lower chromosphere. The large variation in Ca II H & K emission allows for study of the patterns of long-term variability in other stars thanks to synoptic monitoring with the Mount Wilson Observatory HK photometers (1966-2003) and Lowell Observatory Solar-Stellar Spectrograph (1994-present). Overlapping measurements for a set of 27 nearby solar-analog (spectral types G0-G5) stars were used to calibrate the two instruments and construct time series of magnetic activity up to 50 years in length. Precise properties of fundamental importance to the dynamo are available from Hipparcos, the Geneva-Copenhagen Survey, and CHARA interferometry. Using these long time series and measurements of fundamental properties, we do a comparative study of stellar "twins" to explore the sensitivity of the stellar dynamo to small changes to structure, rotation, and composition. We also compare this sample to the Sun and find hints that the regular periodic variability of the solar cycle may be rare among its nearest neighbors in parameter space. 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: The Solar Dynamo Zoo Authors: Egeland, Ricky; Soon, Willie H.; Baliunas, Sallie L.; Hall, Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W. Bibcode: 2016SPD....47.1103E Altcode: We present composite time series of Ca II H & K line core emission indices of up to 50 years in length for a set of 27 solar-analog stars (spectral types G0-G5; within ~10% of the solar mass) and the Sun. These unique data are available thanks to the long-term dedicated efforts of the Mount Wilson Observatory HK project, the Lowell Observatory Solar-Stellar Spectrograph, and the National Solar Observatory/Air Force Research Laboratory/Sacremento Peak K-line monitoring program. The Ca II H & K emission originates in the lower chromosphere and is strongly correlated with the presence of magnetic plage regions in the Sun. These synoptic observations allow us to trace the patterns long-term magnetic variability and explore dynamo behavior over a wide range of rotation regimes and stellar evolution timescales. Title: The Need for Synoptic Solar Observations from the Ground Authors: Pevtsov, A. A. Bibcode: 2016ASPC..504...71P Altcode: Synoptic observations are indispensable in studies of long-term effects pertinent to variation in solar radiative output, space weather and space climate, as well as for understanding the physics of global processes taking place on our nearest star. Synoptic data also allow putting the Sun in the context of stellar evolution. Historically, the main-stay of such observations has been groundbased although the improving longevity of space-borne instruments puts some space missions into the category of synoptic facilities. Space- and groundbased (synoptic) observations are complementary to each other; neither is inferior or superior to the other. Groundbased facilities can have a long-term (50 years+) operations horizon, and in comparison with their spacebased counterparts, they are less expensive to operate and have fewer restrictions on international collaboration and data access. The instruments can be serviced, upgraded, and cross-calibrated to ensure the continuity and uniformity of long-term data series. New measurements could be added in response to changes in understanding the solar phenomena. Some drawbacks such as day-night cycle and the variable atmospheric seeing can be mitigated e.g., by creating global networks and by employing adaptive optics. Furthermore, the groundbased synoptic observations can serve as a backbone and a back-up to spacebased observations. Here I review some existing groundbased synoptic facilities, describe plans for future networks, and outline the current efforts in strengthening the international collaboration in synoptic solar observations from the ground. Title: Long-term Synoptic Observations of Ca II K and Magnetic Flux Authors: Bertello, L.; Pevtsov, A. A.; Tlatov, A. G. Bibcode: 2016ASPC..504..213B Altcode: Long-term synoptic observations in the resonance line of Ca II K and measurements of the solar magnetic flux over several decades constitute a fundamental database for a variety of retrospective analyzes of the state of the solar magnetism. These data archives may also hold the key for untangling some of the mysteries behind the solar dynamo, which in turn could result in a better predictive capability of current dynamo models. Synoptic Ca II K observations began in 1907 at the Kodaikanal observatory (India) and in 1915 at the Mt Wilson (California, USA) solar observatory. By the early 1970s a number of synoptic programs for solar magnetic observations were established that provided full disk magnetograms. These programs include measurements carried out at the Mt Wilson 150-foot solar tower, Wilcox observatory (California, USA), and by the National Solar Observatory (NSO, USA). Today the NSO is continuing these observations through its Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility. We will review some of these historical observations, their properties, and their importance for understanding the behavior of the solar magnetic field over multidecadal time scales. We will also show recent results about using Ca II K spectroheliograms and sunspot magnetic field measurements to reconstruct homogeneous series of pseudo-magnetograms prior the magnetograph era. Title: The reversal of the Sun's magnetic field in cycle 24 Authors: Mordvinov, Aleksandr; Pevtsov, Alexei; Bertello, Luka; Petri, Gordon Bibcode: 2016STP.....2a...3M Altcode: 2016arXiv160202460M; 2016SZF.....2a...3M Analysis of synoptic data from the Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS) and the NASA/NSO Spectromagnetograph (SPM) at the NSO/Kitt Peak Vacuum Telescope facility shows that the reversals of solar polar magnetic fields exhibit elements of a stochastic process, which may include the development of specific patterns of emerging magnetic flux, and the asymmetry in activity between northern and southern hemispheres. The presence of such irregularities makes the modeling and prediction of polar field reversals extremely hard if possible. In a classical model of solar activity cycle, the unipolar magnetic regions (UMRs) of predominantly following polarity fields are transported polewards due to meridional flows and diffusion. The UMRs gradually cancel out the polar magnetic field of the previous cycle, and rebuild the polar field of opposite polarity setting the stage for the next cycle. We show, however, that this deterministic picture can be easily altered by the developing of a strong center of activity, or by the emergence of an extremely large active region, or by a "strategically placed" coronal hole. We demonstrate that the activity occurring during the current cycle 24 may be the result of this randomness in the evolution of the solar surface magnetic field. Title: Reconstructing solar magnetic fields from historical observations. I. Renormalized Ca K spectroheliograms and pseudo-magnetograms Authors: Pevtsov, Alexei A.; Virtanen, Ilpo; Mursula, Kalevi; Tlatov, Andrey; Bertello, Luca Bibcode: 2016A&A...585A..40P Altcode:
Aims: The present work is the first in a series of articles that develop a new proxy to represent the evolution of magnetic activity in past solar cycles by combining the information from historical Ca II K line spectroheliograms and sunspot magnetic field measurements.
Methods: We use synoptic (Carrington) maps from 1915-1985 that were derived from daily Ca K line observations at Mount Wilson Observatory to identify the chromospheric plages and to create synoptic pseudo-magnetograms. We use historical observations of sunspot magnetic fields from 1917 to the present to assign polarity to pixels situated within plages. The original Ca K spectroheliograms are nonuniform in their brightness, and we develop a novel approach to re-normalize their intensities.
Results: We show that a homogeneous long-term series of pseudo-magnetograms can be successfully constructed by combining sunspot field measurements and plages with renormalized intensities. In our tests, about 80% of pixels situated within plages showed the same magnetic polarity as the synoptic magnetograms taken with the Kitt Peak Vacuum Telescope. Finally, we discuss possible approaches to further improve the agreement between observed and pseudo-magnetograms. Title: Pixel Analysis and Plasma Dynamics Characterized by Photospheric Spectral Data Authors: Rasca, A.; Chen, J.; Pevtsov, A. A. Bibcode: 2015AGUFMSH21C..07R Altcode: Continued advances in solar observations have led to higher-resolution magnetograms and surface (photospheric) images, revealing bipolar magnetic features operating near the resolution limit during emerging flux events and other phenomena used to predict solar eruptions responsible for geomagnetic plasma disturbances. However, line of sight (LOS) magnetogram pixels only contain the net uncanceled magnetic flux, which is expected to increase for fixed regions as resolution limits improve. A pixel dynamics model utilizing Stokes I spectral profiles was previously-used to quantify changes in the Doppler shift, width, asymmetry, and tail flatness of Fe I lines at 6301.5 and 6302.5 Å and used pixel-by-pixel line profile fluctuations to characterize quiet and active regions on the Sun. We use this pixel dynamics model with circularly polarized photospheric data (e.g., SOLIS data) to estimate plasma dynamic properties at a sub-pixel level. The analysis can be extended to include the full Stokes parameters and study signatures of magnetic fields and coupled plasma properties on sub-pixel scales. Title: Effect of uncertainties in solar synoptic magnetic flux maps in modeling of solar wind Authors: Pevtsov, Alexei A.; Bertello, Luca; MacNeice, Peter Bibcode: 2015AdSpR..56.2719P Altcode: Recently, the NSO/SOLIS team developed variance (error) maps that represent uncertainties in magnetic flux synoptic charts. These uncertainties are determined by the spatial variances of the magnetic flux distribution from full disk magnetograms that contribute to each bin in the synoptic chart. Here we present a study of the effects of variances on solar wind parameters (wind speed, density, magnetic field, and temperature) derived using the WSA-ENLIL model and ensemble modeling approach. We compare the results of the modeling with near-Earth solar wind magnetic field and plasma data as extracted from NASA/GSFC's OMNI data set. We show that analysis of uncertainties may be useful for understanding the sensitivity of the model predictions to short-term evolution of magnetic field and noise in the synoptic magnetograms. Title: H-alpha Off-limb Carrington Synoptic Charts Authors: Bertello, L.; Hughes, A.; Pevtsov, A. A. Bibcode: 2015AGUFMSH43B2459B Altcode: Observations of solar prominences (and filaments) reveal complex structures, with significant differences inmorphology, lifetime, and complexity of their magnetic field environment. Studies of thesesolar features are important for understanding not only their origin but also their role as precursors ofenergetic events such as flares and coronal mass ejections.The Global Oscillation Network Group (GONG) operated by the National Solar Observatory provides, amongother products, high-cadence broad-band intensity measurements centered in the core ofH-alpha spectral line. Prominences and filaments are quite visible in these 2Kx2K images, that havebeen obtained since 2010. We recentlystarted a project to produce an archive of H-alpha off-limb Carrington Synoptic Charts to be usedfor systematic studies of prominences. Charts are produced to show both spatial and temporal variabilityof these features in four radius zones covering 1.01 to 1.11 solar radii. Here we describe the applied methodologyand show some preliminary results. Potential applications of interest to the solar and heliospheric communitiesare also briefly discussed. Title: Long-term variations in the sunspot magnetic fields and bipole properties from 1918 to 2014 Authors: Tlatova, K. A.; Vasil'eva, V. V.; Pevtsov, A. A. Bibcode: 2015Ge&Ae..55..896T Altcode: Long-term measurements of sunspot magnetic fields have been analyzed with the use of the Mount Wilson Observatory (MWO) data based on the digitization of the magnetic field strength ( B) and umbra and pore areas from 1918 to 2014. Time variations in the magnetic field strength and the possible causes of such variations (which are related to variations in the solar activity level and instrumental effects) were considered. It was shown that artifacts related to instrumental effects exist in the measurements for small sunspots and pores. The magnetic bipole characteristics were determined for the sunspot groups. It was established that the tilt angle of the magnetic bipole axis of even cycles is larger than the tilt angle in the next odd cycles (except for the cycle pair 22-23). Title: How a Magnetograph at L5 would Improve the Space Weather Prediction Capabilities. Authors: Pevtsov, A. A. Bibcode: 2015AGUFMSH14A..01P Altcode: Knowledge of the magnetic field in solar photosphere plays essential role in modern space weather forecast. Thus, for example, synoptic maps of radial magnetic field are used as input for WSA-ENLIL model to derive the properties of solar wind near the Earth and elsewhere in the solar system. Topology of magnetic field around the source regions of flares and CMEs offers important clues about orientation of magnetic field in interplanetary magnetic clouds and ejecta, and the information about large-scale magnetic connectivity in solar corona brings better understanding of remote triggering solar eruptions. Here I will review the benefits of having magnetograph observations from two viewing points: one at Earth-viewing angle and the other at L5, and I will discuss the type of magnetographs that can be considered for a future L5 mission. 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: Digital tabulation of historical sunspot field strength measurements from the Mount Wilson Observatory Authors: Pevtsov, Alexei; Tlatov, Andrey; Bertello, Luca; Ulrich, Roger Bibcode: 2015IAUGA..2236421P Altcode: Direct (manual) measurements of magnetic fields in sunspots based on Zeeman effect represent the longest magnetic observations pertinent to the Sun. Regular (daily) observations started in about 1917 and continue till present. The data consist of daily drawings of sunspots with the corresponding field strength and polarity measurements handwritten on these drawings. All the drawings are now scanned to digital images (JPEG format). However, the lack of tabulated data severely limits the use of this unique data set. Here we report on status and the results of several recent projects aimed at the digital tabulation of MWO drawings. While the individual projects are funded independently by the American (USA) and Russian funding agencies, the groups collaborate closely with each other to achieve a common goal - creation of tabulated data set contacting magnetic field and sunspot position information derived from the drawings. The collaboration is coordinated by the IAU working group on Coordination of Synoptic Observations of the Sun. Title: Long-term Synoptic Observations of the Sun. Authors: Pevtsov, Alexei Bibcode: 2015IAUGA..2246721P Altcode: Does the solar activity vary with time, or it remains constant? How systematic or intermittent solar cycles are? Long-term observations of the Sun are the reason we know answers to these questions. Ultimately, the development of a better understanding of stellar cycles will require similar long-term observations of other sun-like stars. To facilitate international collaboration on synoptic long-term solar observations, IAU created a working group on “Coordination of Synoptic Observations of the Sun.” The working group provides a forum for discussion of all issues relevant to past, current, and future synoptic programs, preservation, calibration, and access to synoptic solar data products. This talk will provide a summary of recent activity by this IAU WG. It will also present a brief overview of recent research on sun-as-a-star conducted at the US National Solar Observatory. Title: Comparisons of Photospheric Pixel Dynamics Between Eruptive and Non-Eruptive Regions Authors: Rasca, Anthony P.; Chen, James; Pevtsov, Alexei A. Bibcode: 2015shin.confE..34R Altcode: Recent advances in solar observations have led to higher-resolution surface (photosphere) images that reveal bipolar magnetic features operating near the resolution limit during emerging flux events. Further improvements in resolution are expected to reveal even smaller dynamic features. Such photospheric features provide observable indications of what is happening before, during, and after flux emergence, eruptions in the corona, and other phenomena. Visible changes in photospheric active regions also play a major role in predicting eruptions that are responsible for geomagnetic plasma disturbances. A new method has been developed to extract physical information from photospheric data (e.g., SOLIS Stokes parameters) based on the statistics of pixel-by-pixel variations in spectral (absorption or emission) line quantities such as line profile Doppler shift, width, asymmetry, and flatness. Such properties are determined by the last interaction between detected photons and optically thick photospheric plasmas, and may contain extractable information on local plasma properties at sub-pixel scales. Applying the method to photospheric data with high spectral resolution, our pixel-by-pixel analysis is performed for various regions on the solar disk, ranging from quiet-Sun regions to active regions exhibiting eruptions, characterizing photospheric dynamics using spectral profiles. In particular, the method quantitatively characterizes the time profile of changes in spectral properties in photospheric features and provides improved physical constraints on observed quantities. Title: Hard X-Ray Emission During Flares and Photospheric Field Changes Authors: Burtseva, O.; Martínez-Oliveros, J. C.; Petrie, G. J. D.; Pevtsov, A. A. Bibcode: 2015ApJ...806..173B Altcode: 2015arXiv150500509B We study the correlation between abrupt permanent changes of magnetic field during X-class flares observed by the Global Oscillation Network Group and Helioseismic and Magnetic Imager instruments, and the hard X-ray (HXR) emission observed by RHESSI, to relate the photospheric field changes to the coronal restructuring and investigate the origin of the field changes. We find that spatially the early RHESSI emission corresponds well to locations of the strong field changes. The field changes occur predominantly in the regions of strong magnetic field near the polarity inversion line (PIL). The later RHESSI emission does not correspond to significant field changes as the flare footpoints are moving away from the PIL. Most of the field changes start before or around the start time of the detectable HXR signal, and they end at about the same time or later than the detectable HXR flare emission. Some of the field changes propagate with speed close to that of the HXR footpoint at a later phase of the flare. The propagation of the field changes often takes place after the strongest peak in the HXR signal when the footpoints start moving away from the PIL, i.e., the field changes follow the same trajectory as the HXR footpoint, but at an earlier time. Thus, the field changes and HXR emission are spatio-temporally related but not co-spatial nor simultaneous. We also find that in the strongest X-class flares the amplitudes of the field changes peak a few minutes earlier than the peak of the HXR signal. We briefly discuss this observed time delay in terms of the formation of current sheets during eruptions. Title: The Minimum of Solar Cycle 23: As Deep as It Could Be? Authors: Muñoz-Jaramillo, Andrés; Senkpeil, Ryan R.; Longcope, Dana W.; Tlatov, Andrey G.; Pevtsov, Alexei A.; Balmaceda, Laura A.; DeLuca, Edward E.; Martens, Petrus C. H. Bibcode: 2015ApJ...804...68M Altcode: 2015arXiv150801222M In this work we introduce a new way of binning sunspot group data with the purpose of better understanding the impact of the solar cycle on sunspot properties and how this defined the characteristics of the extended minimum of cycle 23. Our approach assumes that the statistical properties of sunspots are completely determined by the strength of the underlying large-scale field and have no additional time dependencies. We use the amplitude of the cycle at any given moment (something we refer to as activity level) as a proxy for the strength of this deep-seated magnetic field. We find that the sunspot size distribution is composed of two populations: one population of groups and active regions and a second population of pores and ephemeral regions. When fits are performed at periods of different activity level, only the statistical properties of the former population, the active regions, are found to vary. Finally, we study the relative contribution of each component (small-scale versus large-scale) to solar magnetism. We find that when hemispheres are treated separately, almost every one of the past 12 solar minima reaches a point where the main contribution to magnetism comes from the small-scale component. However, due to asymmetries in cycle phase, this state is very rarely reached by both hemispheres at the same time. From this we infer that even though each hemisphere did reach the magnetic baseline, from a heliospheric point of view the minimum of cycle 23 was not as deep as it could have been. Title: The Diagnostic Value of Photospheric Fraunhofer Lines in Sun-as-a-Star Observations Authors: Bertello, Luca; Pevtsov, Alexei A.; Marble, Andrew R. Bibcode: 2015TESS....140311B Altcode: The distinctive sensitivity of photospheric Fraunhofer lines to variations in the thermodynamic and magnetic structures of the solar atmosphere provides an excellent tool to investigate these variations at different time scales.We used daily Sun-as-a-star spectra taken with the Integrated Sunlight Spectrometer (ISS) and longitudinal magnetograms from the Vector SpectroMagnetograph (VSM) to study the correlation between the global magnetic flux and changes in the line shape of several photospheric spectral lines during different phases of the solar cycle. ISS and VSM are two of three instruments comprising the Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility operated by the National Solar Observatory. We find a clear signature of temporal global magnetic flux variations in several of these photospheric spectral lines, suggesting that the results of our analysis can be used to develop a better understanding of the magnetic cycle of activity in other solar-type stars. Title: The Minimum of Solar Cycle 23: As Deep as It Could Be? Authors: Munoz-Jaramillo, Andres; Senkpeil, Ryan; Longcope, Dana; Tlatov, Andrey; Pevtsov, Alexei A.; Balmaceda, Laura; DeLuca, Edward E.; Martens, Petrus C. Bibcode: 2015TESS....130803M Altcode: After a lull lasting more than 60 years of seemly uniform solar minima, the solar minimum of solar cycle 23 came as a great surprise due to its depth, duration, and record lows in a wide variety of solar activity indices and solar wind properties. One of the consequence of such an event is the revival of the interest in extreme minima, grand minima, and the identification of a solar basal state of minimum magnetic activity.In this presentation we will discuss a new way of binning sunspot group data, with the purpose of better understanding the impact of the solar cycle on sunspot properties, and how this defined the characteristics of the extended minimum of cycle 23. Our main result is centered around the fact that the sunspot size distribution is composed of two populations, a population of groups and active regions, and second of pores and ephemeral regions. We find that only the properties of the former population, the active regions, is found to vary with the solar cycle, while the propeties of pores and ephemeral regions does not.Taking advantage of our statistical characterization we probe the question of the solar baseline magnetism. We find that, when hemispheres are treated separately, almost every one of the past 12 solar minima reaches such a point. However, due to asymmetries in cycle phase, the basal state is very rarely reached by both hemispheres at the same time. From this we infer that, even though each hemisphere did reach the magnetic baseline, from a heliospheric point of view the minimum of cycle 23 was not as deep as it could have been. Title: Pixel Dynamics Analysis of Photospheric Spectral Data Authors: Rasca, Anthony P.; Chen, James; Pevtsov, Alexei A. Bibcode: 2015TESS....110301R Altcode: Recent advances in solar observations have led to higher-resolution surface (photosphere) images that reveal bipolar magnetic features operating near the resolution limit during emerging flux events. Further improvements in resolution are expected to reveal even smaller dynamic features. Such photospheric features provide observable indications of what is happening before, during, and after flux emergence, eruptions in the corona, and other phenomena. Visible changes in photospheric active regions also play a major role in predicting eruptions that are responsible for geomagnetic plasma disturbances. A new method has been developed to extract physical information from photospheric data (e.g., SOLIS Stokes parameters) based on the statistics of pixel-by-pixel variations in spectral (absorption or emission) line quantities such as line profile Doppler shift, width, asymmetry, and flatness. Such properties are determined by the last interaction between detected photons and optically thick photospheric plasmas, and may contain extractable information on local plasma properties at sub-pixel scales. Applying the method to photospheric data with high spectral resolution, our pixel-by-pixel analysis is performed for various regions on the solar disk, ranging from quiet-Sun regions to active regions exhibiting eruptions, characterizing photospheric dynamics using spectral profiles. In particular, the method quantitatively characterizes the time profile of changes in spectral properties in photospheric features and provides improved physical constraints on observed quantities. Title: Uncertainties Associated to Near Real-Time Synoptic Magnetic maps and Implications for Solar Wind Models Authors: Bertello, Luca; Pevtsov, Alexei A.; Macniece, Peter Bibcode: 2015TESS....111003B Altcode: Beginning with May 2006 data, the National Solar Observatory is providing uncertainty (spatial-variance) maps to accompany its database of magnetic flux synoptic charts. Early studies using few selected integral Carrington rotation maps have shown the impact of these uncertainty maps on the outcome numerical models of the coronal magnetic field and the solar wind (e.g., Bertello et al. 2014, Solar Physics, 289 (7), 2419). Here we discuss the evolution of solar wind parameters at Earth computed from the WSA-ENLIL model using the more suitable near real-time magnetic flux synoptic charts and their corresponding uncertainty maps. We investigated the short-term variations in these parameters during periods of low and high levels of solar activity to determine the predictive capabilities of these maps at different phases of the solar cycle. Our preliminary analysis based on integral synoptic maps suggests that during the period of low solar activity the short-term variations in solar wind parameters are within the scatter of the ensemble modeling. When the activity is high, the short-term variations in the observed parameters are larger than the scatter from the modeling. The results of this investigation will help to get a better understanding about some aspects of existing models of the solar wind that may require further improvements. Title: Application of Mutual Information Methods in Time-Distance Helioseismology Authors: Keys, Dustin; Kholikov, Shukur; Pevtsov, Alexei A. Bibcode: 2015SoPh..290..659K Altcode: 2015SoPh..tmp...15K; 2015arXiv150105597K We apply a new technique, the mutual information (MI) from information theory, to time-distance helioseismology, and demonstrate that it can successfully reproduce several classic results based on the widely used cross-covariance method. MI quantifies the deviation of two random variables from complete independence and represents a more general method for detecting dependencies in time series than the cross-covariance function, which only detects linear relationships. We briefly describe the MI-based technique and discuss the results of applying MI to derive the solar differential profile, a travel-time deviation map for a sunspot, and a time-distance diagram from quiet-Sun measurements. Title: Small-scale and Global Dynamos and the Area and Flux Distributions of Active Regions, Sunspot Groups, and Sunspots: A Multi-database Study Authors: Muñoz-Jaramillo, Andrés; Senkpeil, Ryan R.; Windmueller, John C.; Amouzou, Ernest C.; Longcope, Dana W.; Tlatov, Andrey G.; Nagovitsyn, Yury A.; Pevtsov, Alexei A.; Chapman, Gary A.; Cookson, Angela M.; Yeates, Anthony R.; Watson, Fraser T.; Balmaceda, Laura A.; DeLuca, Edward E.; Martens, Petrus C. H. Bibcode: 2015ApJ...800...48M Altcode: 2014arXiv1410.6281M In this work, we take advantage of 11 different sunspot group, sunspot, and active region databases to characterize the area and flux distributions of photospheric magnetic structures. We find that, when taken separately, different databases are better fitted by different distributions (as has been reported previously in the literature). However, we find that all our databases can be reconciled by the simple application of a proportionality constant, and that, in reality, different databases are sampling different parts of a composite distribution. This composite distribution is made up by linear combination of Weibull and log-normal distributions—where a pure Weibull (log-normal) characterizes the distribution of structures with fluxes below (above) 1021Mx (1022Mx). Additionally, we demonstrate that the Weibull distribution shows the expected linear behavior of a power-law distribution (when extended to smaller fluxes), making our results compatible with the results of Parnell et al. We propose that this is evidence of two separate mechanisms giving rise to visible structures on the photosphere: one directly connected to the global component of the dynamo (and the generation of bipolar active regions), and the other with the small-scale component of the dynamo (and the fragmentation of magnetic structures due to their interaction with turbulent convection). Title: Properties of sunspot umbrae of leading and trailing polarity in 1917-2013 Authors: Tlatov, Andrey Georgievich; Tlatova, K. A.; Vasil'eva, V. V.; Pevtsov, A. A.; Mursula, K. Bibcode: 2015AdSpR..55..835T Altcode: Using the software developed by us, we produced a digitized (tabulated) database of sunspot umbrae and pores observed at Mount Wilson Observatory (MWO) in 1917-2013. The database includes the heliographic coordinates, areas and the polarity and strength of magnetic fields of umbrae and pores in the MWO sunspot drawings. Using this database we study here the properties and long-term variation of sunspot umbrae and pores, separately for leading and trailing polarity spots. We find that the leading sunspots have tendency for larger umbrae and stronger magnetic field strength than the trailing spots. The average field strength and area of sunspot umbrae vary with sunspot cycle. Furthermore, the mean magnetic field strength in sunspot umbrae exhibits a gradual increase from early 1960s to 1990s. The nature of this increase is discussed. Title: SOLIS: Reconciling Disk-integrated and Disk-resolved Spectra from the Sun Authors: Pevtsov, Alexei A.; Bertello, Luca; Harker, Brian; Giampapa, Mark; Marble, Andrew R. Bibcode: 2015csss...18..887P Altcode: 2014arXiv1411.7266P Unlike other stars, the surface of the Sun can be spatially resolved to a high degree of detail . But the Sun can also be observed as if it was a distant star. The availability of solar disk-resolved and disk-integrated spectra offers an opportunity to devise methods to derive information about the spatial distribution of solar features from Sun-as-a-star measurements. Here, we present an update on work done at the National Solar Observatory to reconcile disk-integrated and disk-resolved solar spectra from the Synoptic Optical Long-term Investigation of the Sun (SOLIS) station. The results of this work will lead to a new approach to infer the information about the spatial distribution of features on other stars, from the overall filling factor of active regions to, possibly, the latitude/longitude distribution of features. Title: Solar Cycle Dependency of Sun-as-a-Star Photospheric Spectral Line Profiles Authors: Bertello, Luca; Pevtsov, Alexei A.; Giampapa, Mark S.; Marble, Andrew R. Bibcode: 2015csss...18..693B Altcode: We investigate solar-cycle related changes in the profile of several photospheric spectral lines taken with the Integrated Sunlight Spectrometer (ISS) operating at the National Solar Observatory at Kitt Peak (Arizona). ISS, which is one of three instruments comprising the Synoptic Optical Long-term Investigations of the Sun (SOLIS) facility, is designed to obtain high spectral resolution (R = 300,000) observations of the Sun-as-a-star in a broad range of wavelengths (350 nm - 1100 nm). Daily measurements were obtained since December 2006, covering the decline of solar cycle 23 and the rising phase of cycle 24. We present time series of line parameters and discuss their correlation to indices of solar magnetic activity. Because of their different response to variations in the thermodynamic and magnetic structures of the solar atmosphere, the measured line shape parameters provide an excellent tool for disentangling thermal and magnetic effects occurring during different phases of the solar cycle. The results of this analysis may also help with developing a better understanding of magnetic cycles of activity in other solar-like stars. Title: Magnetic Helicity, Tilt, and Twist Authors: Pevtsov, Alexei A.; Berger, Mitchell A.; Nindos, Alexander; Norton, Aimee A.; van Driel-Gesztelyi, Lidia Bibcode: 2015sac..book..285P Altcode: No abstract at ADS Title: Quantifying Photospheric Processes Using a New Pixel Dynamics Model Authors: Rasca, A.; Chen, J.; Pevtsov, A. A. Bibcode: 2014AGUFMSH41B4130R Altcode: Recent advances in solar observations have led to higher-resolution surface (photosphere) images that reveal bipolar magnetic features operating near the resolution limit during emerging flux events. Further improvements in resolution are expected to reveal even smaller dynamic features. Such photospheric features provide observable indications of what is happening before, during, and after flux emergence, eruptions in the corona, and other phenomena. Visible changes in photospheric active regions also play a major role in predicting eruptions that are responsible for geomagnetic plasma disturbances. We present a new method to extract physical information from photospheric data (e.g., SOLIS Stokes parameters) based on the statistics of pixel-by-pixel variations in spectral (absorption) line quantities such as line profile width, asymmetry, and flatness. Such properties are determined by the last interaction between detected photons and optically thick photospheric plasmas, and may contain extractable information on local plasma properties at sub-pixel scales. Applying the method to photospheric data with high spectral resolution, our pixel-by-pixel analysis is performed for various regions on the solar disk, ranging from quiet-Sun regions to active regions exhibiting eruptions, characterizing photospheric dynamics using spectral profiles. In particular, the method quantitatively characterizes the time profile of changes in spectral properties in photospheric features and provides improved physical constraints on observed quantities. Title: What SDO tells us about structure and evolution of coronal bright points Authors: Karachik, N. V.; Minenko, E.; Sattarov, I.; Pevtsov, A. A.; Sherdonov, C. T. Bibcode: 2014AN....335.1037K Altcode: Using magnetograms and coronal images from two instruments on board the Solar Dynamics Observatory (SDO), we study structure and evolution of a limited number of coronal bright points (CBPs). Our results show that the relation between CBPs and their magnetic footpoints is not simple. In some cases, CBP may appear as a bright portion of a larger loop (with clearly identifiable footpoints), and in some cases, an isolated CBP may develop between magnetic poles, which might not be the closest ones to each other or which might not be involved in the magnetic flux cancellation. We suggest that the magnetic connectivity responsible for formation of isolated coronal bright points is governed by the orientation of the large-scale magnetic field. Title: Magnetic Helicity, Tilt, and Twist Authors: Pevtsov, Alexei A.; Berger, Mitchell A.; Nindos, Alexander; Norton, Aimee A.; van Driel-Gesztelyi, Lidia Bibcode: 2014SSRv..186..285P Altcode: Since its introduction to astro- and solar physics, the concept of helicity has proven to be useful in providing critical insights into physics of various processes from astrophysical dynamos, to magnetic reconnection and eruptive phenomena. Signature of helicity was also detected in many solar features, including orientation of solar active regions, or Joy's law. Here we provide a summary of both solar phenomena and consider mutual relationship and its importance for the evolution of solar magnetic fields. 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: Investigation of the evolution of coronal bright points and magnetic field topology Authors: Minenko, E. P.; Karachik, N. V.; Sattarov, I.; Pevtsov, A. A. Bibcode: 2014AstL...40..510M Altcode: Our investigation has been carried using the instruments onboard the Solar Dynamics Observatory (SDO) providing a high resolution of images (AIA photographs and HMI magnetograms). We have investigated the structure and magnetic evolution of several coronal bright points and small scale N-S polarity magnetic fluxes closely associated with them. We also compare the evolution of the magnetic polarities of elementary isolated sources of positive and negative fluxes (magnetic bipoles) and coronal bright points. Tiny ("elementary") coronal bright points have been detected. A standard coronal bright point is shown to be a group of "elementary" coronal bright points that flare up sequentially. Our investigation shows that a change in the magnetic fluxes of opposite polarities is observed before the flare of a coronal bright point. We show that not all cases of the formation of coronal bright points are described by the magnetic reconnection model. This result has not been considered previously and has not been pointed out by other authors. Title: Uncertainties in Solar Synoptic Magnetic Flux Maps Authors: Bertello, L.; Pevtsov, A. A.; Petrie, G. J. D.; Keys, D. Bibcode: 2014SoPh..289.2419B Altcode: 2013arXiv1312.0509B; 2014SoPh..tmp....7B Magnetic flux synoptic charts are critical for a reliable modeling of the corona and heliosphere. Until now, however, these charts were provided without uncertainty estimates. The uncertainties are due to instrumental noise in the measurements and to the spatial variance of the magnetic flux distribution that contributes to each bin in the synoptic chart. We describe here a simple method to compute synoptic magnetic flux maps and their corresponding magnetic flux spatial variance charts that can be used to estimate the uncertainty in the results of coronal models. We have tested this approach by computing a potential-field source-surface model of the coronal field for a Monte Carlo simulation of Carrington synoptic magnetic flux maps generated from the variance map. We show that these uncertainties affect both the locations of source-surface neutral lines and the distributions of coronal holes in the models. 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: Magnetic Helicity of the Global Field in Solar Cycles 23 and 24 Authors: Pipin, V. V.; Pevtsov, A. A. Bibcode: 2014ApJ...789...21P Altcode: 2014arXiv1402.2386P For the first time we reconstruct the magnetic helicity density of the global axisymmetric field of the Sun using the method proposed by Brandenburg et al. and Pipin et al. To determine the components of the vector potential, we apply a gauge which is typically employed in mean-field dynamo models. This allows for a direct comparison of the reconstructed helicity with the predictions from the mean-field dynamo models. We apply this method to two different data sets: the synoptic maps of the line-of-sight magnetic field from the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO) and vector magnetic field measurements from the Vector Spectromagnetograph (VSM) on the Synoptic Optical Long-term Investigations of the Sun (SOLIS) system. Based on the analysis of the MDI/SOHO data, we find that in solar cycle 23 the global magnetic field had positive (negative) magnetic helicity in the northern (southern) hemisphere. This hemispheric sign asymmetry is opposite to the helicity of the solar active regions, but it is in agreement with the predictions of mean-field dynamo models. The data also suggest that the hemispheric helicity rule may have reversed its sign during the early and late phases of cycle 23. Furthermore, the data indicate an imbalance in magnetic helicity between the northern and southern hemispheres. This imbalance seems to correlate with the total level of activity in each hemisphere in cycle 23. The magnetic helicity for the rising phase of cycle 24 is derived from SOLIS/VSM data, and qualitatively its latitudinal pattern is similar to the pattern derived from SOHO/MDI data for cycle 23. Title: Effect of Uncertainties in Solar Synoptic Magnetic Flux Maps in Modeling of Solar Wind Authors: Pevtsov, Alexei; Bertello, Luca; Petrie, Gordon Bibcode: 2014shin.confE.159P Altcode: Recently, the NSO/SOLIS team developed variance (error) maps that represent uncertainties in magnetic flux synoptic charts. These uncertainties are determined by the spatial variance of the magnetic flux distribution from full disk magnetograms that contributes to each bin in the synoptic chart. The algorithm for the creation of these maps is described in Bertello, L., Pevtsov, A.A., Petrie, G.J.D., Keys, D.: 2014 Title: Temporal Variation of Photospheric Spectral Lines Profiles with the Solar Cycle of Activity Authors: Bertello, Luca; Pevtsov, Alexei A.; Marble, Andrew R. Bibcode: 2014AAS...22421831B Altcode: We investigated the variations in the sun-as-a-star profiles of several photospheric spectral lines observed during the decline of solar cycle 23 and the rising phase of cycle 24. Daily measurements were taken with the Integrated Sunlight Spectrometer (ISS) operating at the National Solar Observatory at Kitt Peak (Arizona) since December 2006. ISS, which is one of three instruments comprising the Solar Optical Investigations of the Sun (SOLIS) facility, is designed to obtain high spectral resolution (R = 300,000) observations of the Sun as a star in a broad range of wavelengths (350 nm - 1100 nm). Recent improvements in the spectral calibration of SOLIS/ISS measurements have significantly enhanced the diagnostic capabilities of these data.We will present time series of line parameters and discuss their correlation to the global magnetic flux. Because of their different response to variations in the thermodynamic and magnetic structures of the solar atmosphere, the measured line shape parameters provide an excellent tool to disentangle thermal and magnetic effects occurring during different phases of the solar cycle. The results of this analysis may also help with developing a better understanding of magnetic cycle of activity in other solar-like stars. Title: First use of synoptic vector magnetograms for global nonlinear, force-free coronal magnetic field models Authors: Asfaw, Tilaye Tadesse; Pevtsov, Alexei A.; Macneice, Peter J. Bibcode: 2014AAS...22432326A Altcode: 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. 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. 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, 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).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: Case Study of a Magnetic Transient in NOAA 11429 Observed by SDO/HMI During the M7.9 Flare on 13 March 2012 Authors: Harker, Brian; Pevtsov, Alexei A. Bibcode: 2014AAS...22412334H Altcode: NOAA 11429 was the source of an M7.9 X-ray flare at the western solar limb (N18° W63°) on 2012 March 13 at 17:12 UT. Observations of the line-of-sight magnetic flux and the Stokes I and V profiles from which it is derived were carried out by the Solar Dynamics Observatory Helioseismic and Magnetic Imager (SDO/HMI) with a 45 s cadence over the full disk, at a spatial sampling of 0.''5. During flare onset, a transient patch of negative flux can be observed in SDO/HMI magnetograms to rapidly appear within the positive polarity penumbra of NOAA 11429. We present here a detailed study of this magnetic transient and offer interpretations as to whether this highly debated phenomenon represents a "real" change in the structure of the magnetic field at the site of the flare, or is instead a product of instrumental/algorithmic artifacts related to particular SDO/HMI data reduction techniques. Title: Relating photospheric magnetic field changes and hard X-ray emission during flares Authors: Petrie, Gordon; Burtseva, Olga; Martinez Oliveros, Juan Carlos; Pevtsov, Alexei A. Bibcode: 2014AAS...22412328P Altcode: We study the correlation between abrupt permanent changes of magnetic field during strong flares observed by GONG and HMI instruments, and the location of hard X-ray (HXR) emission observed by RHESSI to relate the field changes to the reconnection processes in the corona and investigate the origin of the field changes. The chromospheric HXR emission in solar flares is generally regarded as the footprints of magnetic field lines newly reconnected in the corona. Also, the footpoint motions traveling away from the neutral lines are considered to be indicative of the reconnection occurring in arcade magnetic fields of increasing heights. Our analysis of six flares shows that the early HXR emission corresponds well to locations of the strong field changes. The later HXR emission does not correspond to significant field changes as the footpoint is moving away from the neutral line in later stages of the flare. The field changes and HXR emission are spatio-temporally related, but not simultaneous. The field changes start earlier and end later than the detectable HXR signal. The strongest X-class flares in our analysis show a well-defined peak in the field changes a few minutes earlier than the peak in the HXR emission. The timing relationship between the HXR and the largest photospheric field changes may indicate an indirect physical relationship between these phenomena. Tracing of the field changes at the footpoints’ locations shows that in most of the flares the field changes propagated at a speed similar to that of the HXR footpoint moving away from the neutral line. However most of the field changes occurred earlier in time. O.B., G.P. and A.P. are partially supported by NASA grant NNX14AE05G. Title: Bimodal Distribution of Magnetic Fields and Areas of Sunspots Authors: Tlatov, Andrey G.; Pevtsov, Alexei A. Bibcode: 2014SoPh..289.1143T Altcode: 2013arXiv1308.0535T We applied automatic identification of sunspot umbrae and penumbrae to daily observations from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to study their magnetic flux density (B) and area (A). The results confirm an already known logarithmic relationship between the area of sunspots and their maximum flux density. In addition, we find that the relation between average magnetic flux density () and sunspot area shows a bimodal distribution: for small sunspots and pores (A≤20 millionth of solar hemisphere, MSH), (gauss), and for large sunspots (A≥100 MSH), is about 600 G. For intermediate sunspots, average flux density linearly decreases from about 800 G to 600 G. A similar bimodal distribution was found in several other integral parameters of sunspots. We show that this bimodality can be related to different stages of sunspot penumbra formation and can be explained by the difference in average inclination of magnetic fields at the periphery of small and large sunspots. Title: A Comparison Between Nonlinear Force-Free Field and Potential Field Models Using Full-Disk SDO/HMI Magnetogram Authors: Tadesse, Tilaye; Wiegelmann, T.; MacNeice, P. J.; Inhester, B.; Olson, K.; Pevtsov, A. Bibcode: 2014SoPh..289..831T Altcode: 2012arXiv1212.5639T Measurements of magnetic fields and electric currents in the pre-eruptive corona are crucial to the study of solar eruptive phenomena, like flares and coronal mass ejections (CMEs). However, spectro-polarimetric measurements of certain photospheric lines permit a determination of the vector magnetic field only at 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 above multiple active regions with the help of a potential field and a nonlinear force-free field (NLFFF) extrapolation code over the full solar disk using Helioseismic and Magnetic Imager (SDO/HMI) data as boundary conditions. We compare projections of the resulting magnetic field lines with full-disk coronal images from the Atmospheric Imaging Assembly (SDO/AIA) for both models. This study has found that the NLFFF model reconstructs the magnetic configuration closer to observation than the potential field model for full-disk magnetic field extrapolation. We conclude that many of the trans-equatorial loops connecting the two solar hemispheres are current-free. Title: Properties of Magnetic Neutral Line Gradients and Formation of Filaments Authors: Karachik, Nina V.; Pevtsov, Alexei A. Bibcode: 2014SoPh..289..821K Altcode: 2013arXiv1307.3317K We investigate the gradients of magnetic fields across neutral lines (NLs) and compare their properties for NLs with and without chromospheric filaments. Our results show that there is a range of preferred magnetic field gradients where the filament formation is enhanced. On the other hand, a horizontal gradient of the magnetic field across an NL alone does not appear to be a single factor that determines if a filament will form (or not) in a given location. 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: Cyclic and Long-Term Variation of Sunspot Magnetic Fields Authors: Pevtsov, Alexei A.; Bertello, Luca; Tlatov, Andrey G.; Kilcik, Ali; Nagovitsyn, Yury A.; Cliver, Edward W. Bibcode: 2014SoPh..289..593P Altcode: 2013arXiv1301.5935P Measurements from the Mount Wilson Observatory (MWO) were used to study the long-term variations of sunspot field strengths from 1920 to 1958. Following a modified approach similar to that presented in Pevtsov et al. (Astrophys. J. Lett.742, L36, 2011), we selected the sunspot with the strongest measured field strength for each observing week and computed monthly averages of these weekly maximum field strengths. The data show the solar cycle variation of the peak field strengths with an amplitude of about 500 - 700 gauss (G), but no statistically significant long-term trends. Next, we used the sunspot observations from the Royal Greenwich Observatory (RGO) to establish a relationship between the sunspot areas and the sunspot field strengths for cycles 15 - 19. This relationship was used to create a proxy of the peak magnetic field strength based on sunspot areas from the RGO and the USAF/NOAA network for the period from 1874 to early 2012. Over this interval, the magnetic field proxy shows a clear solar cycle variation with an amplitude of 500 - 700 G and a weaker long-term trend. From 1874 to around 1920, the mean value of magnetic field proxy increases by about 300 - 350 G, and, following a broad maximum in 1920 - 1960, it decreases by about 300 G. Using the proxy for the magnetic field strength as the reference, we scaled the MWO field measurements to the measurements of the magnetic fields in Pevtsov et al. (2011) to construct a combined data set of maximum sunspot field strengths extending from 1920 to early 2012. This combined data set shows strong solar cycle variations and no significant long-term trend (the linear fit to the data yields a slope of − 0.2±0.8 G year−1). On the other hand, the peak sunspot field strengths observed at the minimum of the solar cycle show a gradual decline over the last three minima (corresponding to cycles 21 - 23) with a mean downward trend of ≈ 15 G year−1. 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: Solar Origins of Space Weather and Space Climate: Preface Authors: González Hernández, I.; Komm, R.; Pevtsov, A.; Leibacher, J. W. Bibcode: 2014SoPh..289..437G Altcode: No abstract at ADS Title: The sun-as-a-star solar spectrum Authors: Pevtsov, A. A.; Bertello, L.; Marble, A. R. Bibcode: 2014AN....335...21P Altcode: The Sun is the only star for which individual surface features can be observed directly. For other stars, the properties of starspots, stellar rotation, stellar flares, etc, are derived indirectly via variation of star-integrated spectral line profiles or their luminosity measurements. Solar disk-integrated and disk-resolved observations allow for investigations of the contribution of individual solar disk features to sun-as-a-star spectra. Here, we provide a brief overview of three sun-as-a-star programs, currently in operation, and describe recent improvements in observations and data reduction for the Integrated Sunlight Spectrometer (ISS), one of three instruments comprising the Synoptic Optical Long-term Investigations of the Sun (SOLIS) system. Next, we discuss studies employing sun-as-a-star observations (including Ca II K line as proxy for total unsigned magnetic flux and 2800 MHz radio flux) as well as the effects of flares on solar disk-integrated spectra. Title: Long-term variation of statistical properties of sunspot field strengths and their relation to the characteristics of solar cycles in 1917-2013 Authors: Tlatova, Kseniya; Pevtsov, Alexei; Tlatov, Andrey; Vasilieva, Valeria; Kalevi Mursula Bibcode: 2014cosp...40E3357T Altcode: We use the digitized sunspot daily drawings from the Mount Wilson Observatory (MWO) from 1917—2013 to study the long-term variations in sunspot magnetic fields. Tabulated data include the heliographic coordinates, area and magnetic field strength of all sunspots on solar disk. Sunspot field strengths exhibit several trends, which can be of instrumental or truly solar in its nature. For example, in depth analysis of the sunspot field strength and the sunspot areas indicates long-term changes in the observing system at the MWO, when systematically larger number of measurements in sub-features (e.g., multiple umbrae) was made beginning mid-20th century. The final data set is used to study several properties of active regions including difference (in field strength and area) between leading and following sunspots, the orientation of magnetic field in sunspots and pores relative to vertical direction, and the Hale (polarity) and Joy (tilt) laws over the period of about ten solar cycles. Title: Uncertainties in Solar Synoptic Maps and their Effect on Models. Authors: Pevtsov, Alexei; Petrie, Gordon; Bertello, Luca Bibcode: 2014cosp...40E2524P Altcode: Synoptic charts of the photospheric magnetic flux are used widely in modeling the magnetic field in the corona and the heliosphere. Recently, the National Solar Observatory began producing accompanying maps of uncertainties (http://solis.nso.edu/0/ermaps/6302l_er2138-2157.html), which can be used to estimate the uncertainty in the results of coronal models. These maps of uncertainties represent the spatial variance of the magnetic flux distribution that contributes to each bin in the synoptic chart. We will describe a method to compute synoptic magnetic flux spatial variance charts, and discuss the effects of these uncertainties on models of the coronal magnetic field and the solar wind speed. Title: Case Study of a Magnetic Transient in NOAA 11429 Observed by SDO/HMI during the M7.9 Flare on 2012 March 13 Authors: Harker, Brian J.; Pevtsov, Alexei A. Bibcode: 2013ApJ...778..175H Altcode: NOAA 11429 was the source of an M7.9 X-ray flare at the western solar limb (N18° W63°) on 2012 March 13 at 17:12 UT. Observations of the line-of-sight magnetic flux and the Stokes I and V profiles from which it is derived were carried out by the Solar Dynamics Observatory Helioseismic and Magnetic Imager (SDO/HMI) with a 45 s cadence over the full disk, at a spatial sampling of 0.''5. During flare onset, a transient patch of negative flux can be observed in SDO/HMI magnetograms to rapidly appear within the positive polarity penumbra of NOAA 11429. We present here a detailed study of this magnetic transient and offer interpretations as to whether this highly debated phenomenon represents a "real" change in the structure of the magnetic field at the site of the flare, or is instead a product of instrumental/algorithmic artifacts related to particular SDO/HMI data reduction techniques. Title: The Effect of Latitudinal Averaging of Surface Tracers on Patterns of Torsional Oscillations Authors: Tlatov, A. G.; Pevtsov, A. A. Bibcode: 2013ASPC..478..297T Altcode: Latitudinal bands of faster/slower (relative to average) rate of rotation of solar plasma (also known as the solar torsional oscillations) are considered to be a fundamental property of the Sun, and are believed to be important for the solar dynamo. Torsional oscillations are derived from the measurements of the solar rotation at the photosphere and (indirectly, via methods of helioseismology) in the convection zone. Here, we raise a possibility that the pattern of the torsional oscillations could be a spurious feature resulting from a combination of the differential rotation, the latitudinal drift of tracers, and a weighted contribution of tracers within an averaging window used to determine the solar rotation rate. This spurious feature may have an effect on both the observations taken in the solar photosphere (e.g., Doppler velocity measurements and feature tracking techniques) and the helioseismic measurements. Title: Fifty Years of Seismology of the Sun and Stars Authors: Jain, K.; Tripathy, S. C.; Hill, F.; Leibacher, J. W.; Pevtsov, A. A. Bibcode: 2013ASPC..478.....J Altcode: No abstract at ADS Title: Zeemanfit: Use and Development of the solis_vms_zeemanfit code Authors: Hughes, Anna L. H.; Harvey, Jack; Marble, Andrew R.; Pevtsov, Alexei A. Bibcode: 2013arXiv1312.2026H Altcode: The purpose of the SOLIS Zeemanfit Code is to provide a straight-forward, easily checked measure of the total magnetic-field strength in the high-strength umbral regions of the solar disk. In the highest-strength regions, the Zeeman splitting of the 6302-angstrom Fe line becomes wide enough for the triplet nature of the line to be visible by eye in non-polarized light. Therefore, a three-line fit to the spectra should, in principle, provide a fairly robust measure of the total magnetic-field strength. The code uses the Level-1.5 spec-cube data of the SOLIS VSM 6302-vector observations (specifically the Stokes-I and Stokes-V components) to fit the line profiles at each appropriate pixel and calculate the magnetic-field-strength from the line-center separation of the two fit 6302.5 sigma-components. The 6301.5-angstrom Fe line is also present and fit in the VSM 6302-vector data, but it is an anomalous-Zeeman line with a weaker response to magnetic fields. Therefore, no magnetic- field measure is derived from this portion of the spectral fit. Title: Camera Gap Removal in SOLIS/VSM Images Authors: Marble, Andrew R.; Callahan, Lorraine; Pevtsov, Alexei A. Bibcode: 2013arXiv1312.2909M Altcode: The Vector Spectromagnetograph (VSM) instrument on the Synoptic Optical Longterm Investigations of the Sun (SOLIS) telescope is capable of obtaining spectropolarimetry for the full Sun (or a select latitudinal range) with one arcsecond spatial resolution and 0.05 Angstrom spectral resolution. This is achieved by scanning the Sun in declination and building up spectral cubes for multiple polarization states, utilizing a beamsplitter and two separate 2k x 2k CCD cameras. As a result, the eastern and western hemispheres of the Sun are separated in preliminary VSM images by a vertical gap with soft edges and variable position and width. Prior to the comprehensive analysis presented in this document, a trial-and-error approach to removing the gap had yielded an algorithm that was inconsistent, undocumented, and responsible for incorrectly eliminating too many image columns. Here we describe, in detail, the basis for a new, streamlined, and properly calibrated prescription for locating and removing the gap that is correct to within approximately one arcsecond (one column). Title: Synoptic Magnetic Variance Maps and Their Effects on Field-extrapolation Coronal Models Authors: Bertello, Luca; Pevtsov, A. A.; Keys, D.; Petrie, G. Bibcode: 2013SPD....44..113B Altcode: The prediction and description of the conditions throughout the heliosphere relies today mostly on potential field source surface (PFSS) and magnetohydrodynamics coronal and heliospheric models. Carrington synoptic maps are produced from individual magnetograms and used as the primary drivers for these models. However, the uncertainties on the flux distribution across synoptic maps have never been included in the models. As the measure of uncertainties, we produced synoptic spatial variance (1-sigma standard deviation) maps derived from the distribution of pixel values in the sky magnetograms that contribute the to average flux in each bin of the final Carrington map. Each variance-map is then used to generate a series of Carrington maps where the value of each bin differs, randomly, from the original value by up to 3-sigma. We discuss here how the uncertainty in the Carrington map affects the location of neutral lines and the footpoint locations of the open-field, the model coronal holes, determined from a standard PFSS model. In this preliminary investigation we studied two distinct periods, corresponding to minimum and maximum of solar activity. We show that the variance in the derived synoptic maps does not affect significantly the shape of neutral line or general location of coronal holes. The position of neutral lines and boundaries of coronal holes can be shifted by as much as 5 degrees in some locations.Abstract (2,250 Maximum Characters): The prediction and description of the conditions throughout the heliosphere relies today mostly on potential field source surface (PFSS) and magnetohydrodynamics coronal and heliospheric models. Carrington synoptic maps are produced from individual magnetograms and used as the primary drivers for these models. However, the uncertainties on the flux distribution across synoptic maps have never been included in the models. As the measure of uncertainties, we produced synoptic spatial variance (1-sigma standard deviation) maps derived from the distribution of pixel values in the sky magnetograms that contribute the to average flux in each bin of the final Carrington map. Each variance-map is then used to generate a series of Carrington maps where the value of each bin differs, randomly, from the original value by up to 3-sigma. We discuss here how the uncertainty in the Carrington map affects the location of neutral lines and the footpoint locations of the open-field, the model coronal holes, determined from a standard PFSS model. In this preliminary investigation we studied two distinct periods, corresponding to minimum and maximum of solar activity. We show that the variance in the derived synoptic maps does not affect significantly the shape of neutral line or general location of coronal holes. The position of neutral lines and boundaries of coronal holes can be shifted by as much as 5 degrees in some locations. Title: Improvements to the SOLIS Program: New Data Products and Recent Science Results Authors: Bertello, Luca; Callahan, L.; Gusain, S.; Harker, B.; Harvey, J. W.; Hughes, A.; Marble, A. R.; Pevtsov, A. A.; SOLIS Bibcode: 2013SPD....44..135B Altcode: Over the past two years the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Team made significant improvements to the data products provided to the solar and heliospheric community. Longitudinal photospheric magnetograms were consistently calibrated to form a uniform magnetic flux series from 2003-present. Improvements in image geometric corrections enabled providing the high spectral resolution spectra for each pixel in full disk images taken in Fe 630.2 nm and Ca II 854.2 nm. New treatment of high resolution spectra from the Integrated Sunlight Spectrometer (ISS), led to significant reduction in daily variations of parameters derived from these spectra. Several new data products were developed, including simultaneous photospheric and chromospheric longitudinal magnetograms derived from the core and wings of Ca II 854.2 nm line, and derivation of field strength via fitting non-polarized I-profiles of Fe I 630.2 nm. We present here a summary of recent changes to this database, with particular emphasis on chromospheric longitudinal magnetic field and intensity measurements, photospheric vector magnetic field products, and high-spectral resolution integrated sunlight data. Some significant results derived from the analysis of these data sets will also be presented, while more detailed descriptions about specific topics will be referred to other SOLIS-related studies presented at this meeting. Title: Hard X-ray emission during flares and changes in the photospheric magnetic field Authors: Burtseva, Olga; Martinez Oliveros, J.; Petrie, G.; Pevtsov, A. Bibcode: 2013SPD....44...73B Altcode: We study the relationship between the field changes in the photosphere and the reconnection processes in the corona by comparing the locations of abrupt permanent changes of the magnetic field during strong flares observed by the GONG and HMI instruments and hard X-ray (HXR) emission observed by RHESSI. The chromospheric HXR emission in solar flares is generally believed to mark the footprints of magnetic field lines newly reconnected in the corona. Also, the footpoint motions away from the neutral line are considered to be indicative of the reconnection occurring in arcade magnetic fields at different heights. Our analysis of six flares that occurred during the declining phase of cycle 23 shows that the strongest field changes are well correlated in space, with the HXR footprints moving away from the neutral line in later stages of the flare. The majority of field changes and HXR footpoints are spatio-temporally related but not simultaneous. We will also compare changes in the HMI vector magnetic field measurements with the location and evolution of flare footpoints and discuss possible implications for topology of the magnetic field at the reconnection site in the corona. Title: First Synoptic Maps of Photospheric Vector Magnetic Field from SOLIS/VSM: Non-radial Magnetic Fields and Hemispheric Pattern of Helicity Authors: Gusain, Sanjay; Pevtsov, A. A.; Rudenko, G. V.; Anfinogentov, S. A.; Pevtsov, A. A.; Rudenko, G. V.; Anfinogentov, S. A. Bibcode: 2013SPD....44..111G Altcode: We use daily full-disk vector magnetograms from Vector Spectromagnetograph (VSM) on Solar Optical Long-term Investigations of the Sun (SOLIS) system to synthesize the first Carrington maps of the photospheric vector magnetic field. We describe these maps and make a comparison of observed radial field with the radial field estimate from LOS magnetograms. Further, we employ these maps to study the hemispheric pattern of current helicity density, Hc, during the rising phase of the solar cycle 24. 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 South. The hemispheric pattern for individual Carrington rotations is statistically weak, consistent with previous studies of active regions’ helicity. Although our data include the early phase of cycle 24, there appears no evidence for a possible (systematic) reversal of the hemispheric helicity rule at the beginning of cycle as predicted by some dynamo models. Further, we compute the hemispheric pattern in active region latitudes (-30 ≤ θ ≤ 30) separately for weak (100< |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.Abstract (2,250 Maximum Characters): We use daily full-disk vector magnetograms from Vector Spectromagnetograph (VSM) on Solar Optical Long-term Investigations of the Sun (SOLIS) system to synthesize the first Carrington maps of the photospheric vector magnetic field. We describe these maps and make a comparison of observed radial field with the radial field estimate from LOS magnetograms. Further, we employ these maps to study the hemispheric pattern of current helicity density, Hc, during the rising phase of the solar cycle 24. 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 South. The hemispheric pattern for individual Carrington rotations is statistically weak, consistent with previous studies of active regions’ helicity. Although our data include the early phase of cycle 24, there appears no evidence for a possible (systematic) reversal of the hemispheric helicity rule at the beginning of cycle as predicted by some dynamo models. Further, we compute the hemispheric pattern in active region latitudes (-30 ≤ θ ≤ 30) separately for weak (100< |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. 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: New Synoptic Measurements of Umbral Magnetic Fields Authors: Harvey, J. W.; Hughes, A.; Marble, A.; Livingston, W. C.; Pevtsov, A.; SOLIS Team Bibcode: 2013SPD....44..112H Altcode: Apparent cyclic and secular changes of sunspot umbral intensities and magnetic field strengths have been reported for many decades. Monthly measurements since 1998 show changes that have been interpreted as a decline in sunspot vigor that, if continued, may lead to very few visible sunspots in forthcoming cycles (Livingston, Penn, and Svalgaard 2012, ApJ 757, L8). This dramatic notion is controversial (e.g. Nagovitsyn, Pevtsov, and Livingston 2012, ApJ 758, L20), and additional observational evidence is needed based on a minimum of interpretational steps and selection effects. The SOLIS vector spectromagnetograph has recorded photospheric spectra around 630.2 nm over the full solar disk daily since late 2003 with spatial and spectral pixel dimensions of about one arc second and 2.3 pm. We fit the unpolarized intensity spectra in sunspots with a simple Zeeman triplet model using a single field strength, which works well if the field strength exceeds about 2 kG and the individual spectra are not affected by strong Doppler and/or Zeeman variations. The derived total field strengths may be compared with independent spectrograph-based measurements from NSO, Hinode/SP, and Mt. Wilson and with filter-based measurements from SoHO/MDI and SDO/HMI. NSO plans to implement this reduction for all suitable archived SOLIS spectra and to continue daily umbral field strength measurements as cycle 24 proceeds. Preliminary comparisons show good agreements in some cases and systematic differences in others.Abstract (2,250 Maximum Characters): Apparent cyclic and secular changes of sunspot umbral intensities and magnetic field strengths have been reported for many decades. Monthly measurements since 1998 show changes that have been interpreted as a decline in sunspot vigor that, if continued, may lead to very few visible sunspots in forthcoming cycles (Livingston, Penn, and Svalgaard 2012, ApJ 757, L8). This dramatic notion is controversial (e.g. Nagovitsyn, Pevtsov, and Livingston 2012, ApJ 758, L20), and additional observational evidence is needed based on a minimum of interpretational steps and selection effects. The SOLIS vector spectromagnetograph has recorded photospheric spectra around 630.2 nm over the full solar disk daily since late 2003 with spatial and spectral pixel dimensions of about one arc second and 2.3 pm. We fit the unpolarized intensity spectra in sunspots with a simple Zeeman triplet model using a single field strength, which works well if the field strength exceeds about 2 kG and the individual spectra are not affected by strong Doppler and/or Zeeman variations. The derived total field strengths may be compared with independent spectrograph-based measurements from NSO, Hinode/SP, and Mt. Wilson and with filter-based measurements from SoHO/MDI and SDO/HMI. NSO plans to implement this reduction for all suitable archived SOLIS spectra and to continue daily umbral field strength measurements as cycle 24 proceeds. Preliminary comparisons show good agreements in some cases and systematic differences in others. 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: First Synoptic Maps of Photospheric Vector Magnetic Field from SOLIS/VSM: Non-Radial Magnetic Fields and Hemispheric Pattern of Helicity Authors: Gusain, Sanjay; Pevtsov, A. A.; Rudenko, G. V.; Anfinogentov, S. A. Bibcode: 2013shin.confE....G Altcode: We use daily full-disk vector magnetograms from Vector Spectromagnetograph (VSM) on Solar Optical Long-term Investigations of the Sun (SOLIS) system to synthesize the first Carrington maps of the photospheric vector magnetic field. We describe these maps and make a comparison of observed radial field with the radial field estimate from LOS magnetograms. Further, we employ these maps to study the hemispheric pattern of current helicity density, Hc, during the rising phase of the solar cycle 24. 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 South. The hemispheric pattern for individual Carrington rotations is statistically weak, consistent with previous studies of active regions' helicity. Although our data include the early phase of cycle 24, there appears no evidence for a possible (systematic) reversal of the hemispheric helicity rule at the beginning of cycle as predicted by some dynamo models. Further, we compute the hemispheric pattern in active region latitudes (-30°-+30°) separately for weak (100< |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., ? < 0), Hc of weak fields exhibits an inverse hemispheric behavior (i.e., ? > 0) albeit with large statistical scatter. Title: On Possible Variations of Basal Ca II K Chromospheric Line Profiles with the Solar Cycle Authors: Pevtsov, Alexei A.; Bertello, Luca; Uitenbroek, Han Bibcode: 2013ApJ...767...56P Altcode: We use daily observations of the Ca II K line profiles of the Sun-as-a-star taken with the Integrated Sunlight Spectrometer from 2006 December through 2011 July to deconvolve the contributions from the quiet (basal) chromosphere and with magnetic network/plage areas. The 0.5 Å emission index computed from basal profiles shows a significantly reduced modulation (as compared with one derived from the observed profiles) corresponding to the Sun's rotation. For basal contribution of the Ca II K line, the peak in power spectrum corresponding to solar rotation is broad and not well defined. Power spectra for the plage contribution show two narrow well-defined peaks corresponding to solar rotation at two distinct latitudes, in agreement with the latitudinal distribution of activity on the Sun at the end of Cycle 23 and beginning of Cycle 24. We use the lack of a signature of solar rotation in the basal (quiet Sun) component as an indication of a successful removal of the active Sun (plage) component. Even though the contribution from solar activity is removed from the basal line profiles, we find a weak dependency of intensity in the line core (K3) of basal profiles with the phase of the solar cycle. Such dependency could be the result of changes in thermal properties of basal chromosphere with the solar cycle. As an alternative explanation, we also discuss a possibility that the basal component does not change with the phase of the solar cycle. 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: Full-disk nonlinear force-free field extrapolation of SDO/HMI and SOLIS/VSM magnetograms Authors: Tadesse, T.; Wiegelmann, T.; Inhester, B.; MacNeice, P.; Pevtsov, A.; Sun, X. Bibcode: 2013A&A...550A..14T Altcode: 2012arXiv1210.3668T Context. The magnetic field configuration is essential for understanding solar explosive phenomena, such as flares and coronal mass ejections. To overcome the unavailability of coronal magnetic field measurements, photospheric magnetic field vector data can be used to reconstruct the coronal field. Two complications of this approach are that the measured photospheric magnetic field is not force-free and that one has to apply a preprocessing routine to achieve boundary conditions suitable for the force-free modeling. Furthermore the nonlinear force-free extrapolation code should take uncertainties into account in the photospheric field data. They occur due to noise, incomplete inversions, or azimuth ambiguity-removing techniques.
Aims: Extrapolation codes in Cartesian geometry for modeling the magnetic field in the corona do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, e.g., a single active region. Here we apply a method for nonlinear force-free coronal magnetic field modeling and preprocessing of photospheric vector magnetograms in spherical geometry using the optimization procedure to full disk vector magnetograms. We compare the analysis of the photospheric magnetic field and subsequent force-free modeling based on full-disk vector maps from Helioseismic and Magnetic Imager (HMI) onboard the solar dynamics observatory (SDO) and Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS).
Methods: We used HMI and VSM photospheric magnetic field measurements to model the force-free coronal field above multiple solar active regions, assuming magnetic forces to dominate. We solved the nonlinear force-free field equations by minimizing a functional in spherical coordinates over a full disk and excluding the poles. After searching for the optimum modeling parameters for the particular data sets, we compared the resulting nonlinear force-free model fields. We compared quantities, such as the total magnetic energy content, free magnetic energy, the longitudinal distribution of the magnetic pressure, and surface electric current density, using our spherical geometry extrapolation code.
Results: The magnetic field lines obtained from nonlinear force-free extrapolation based on HMI and VSM data show good agreement. However, the nonlinear force-free extrapolation based on HMI data contain more total magnetic energy, free magnetic energy, the longitudinal distribution of the magnetic pressure, and surface electric current density than do the VSM data. Title: Comparison of Ground-Based and Space-Based Longitudinal Magnetograms Authors: Pietarila, A.; Bertello, L.; Harvey, J. W.; Pevtsov, A. A. Bibcode: 2013SoPh..282...91P Altcode: 2012arXiv1209.6390P; 2012SoPh..tmp..274P We compare photospheric line-of-sight magnetograms from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) instrument with observations from the 150-foot Solar Tower at Mt. Wilson Observatory (MWO), the Helioseismic and Magnetic Imager (HMI) on the Solar Dynamics Observatory (SDO), and the Michelson Doppler Imager (MDI) on the Solar and Heliospheric Observatory (SOHO). We find very good agreement between VSM and the other data sources for both disk-averaged flux densities and pixel-by-pixel measurements. We show that the VSM mean flux density time series is of consistently high signal-to-noise ratio with no significant zero offsets. We discuss in detail some of the factors - spatial resolution, flux dependence, and position on the solar disk - affecting the determination of scaling between VSM and SOHO/MDI or SDO/HMI magnetograms. The VSM flux densities agree well with spatially smoothed data from MDI and HMI, although the scaling factors show a clear dependence on flux density. The factor to convert VSM to HMI increases with increasing flux density (from ≈1 to ≈1.5). The nonlinearity is smaller for the VSM vs. SOHO/MDI scaling factor (from ≈1 to ≈1.2). Title: Signature of Differential Rotation in Sun-as-a-star Ca II K Measurements Authors: Bertello, L.; Pevtsov, A. A.; Pietarila, A. Bibcode: 2012ApJ...761...11B Altcode: 2012arXiv1210.5556B The characterization of solar surface differential rotation (SDR) from disk-integrated chromospheric measurements has important implications for the study of differential rotation and dynamo processes in other stars. Some chromospheric lines, such as Ca II K, are very sensitive to the presence of activity on the disk and are an ideal choice for investigating SDR in Sun-as-a-star observations. Past studies indicate that when the activity is low, the determination of Sun's differential rotation from integrated-sunlight measurements becomes uncertain. However, our study shows that using the proper technique, SDR can be detected from these type of measurements even during periods of extended solar minima. This paper describes results from the analysis of the temporal variations of Ca II K line profiles observed by the Integrated Sunlight Spectrometer during the declining phase of Cycle 23 and the rising phase of Cycle 24, and discusses the signature of SDR in the power spectra computed from time series of parameters derived from these profiles. The methodology described is quite general, and could be applied to photometric time series of other main-sequence stars for detecting differential rotation. Title: The Build-Up to Eruptive Solar Events Viewed as the Development of Chiral Systems Authors: Martin, S. F.; Panasenco, O.; Berger, M. A.; Engvold, O.; Lin, Y.; Pevtsov, A. A.; Srivastava, N. Bibcode: 2012ASPC..463..157M Altcode: 2012arXiv1212.3646M When we examine the chirality or observed handedness of the chromospheric and coronal structures involved in the long-term build-up to eruptive events, we find that they evolve in very specific ways to form two and only two sets of large-scale chiral systems. Each system contains spatially separated components with both signs of chirality, the upper portion having negative (positive) chirality and the lower part possessing positive (negative) chirality. The components within a system are a filament channel (represented partially by sets of chromospheric fibrils), a filament (if present), a filament cavity, sometimes a sigmoid, and always an overlying arcade of coronal loops. When we view these components as parts of large-scale chiral systems, we more clearly see that it is not the individual components of chiral systems that erupt but rather it is the approximate upper parts of an entire evolving chiral system that erupts. We illustrate the typical pattern of build-up to eruptive solar events first without and then including the chirality in each stage of the build-up. We argue that a complete chiral system has one sign of handedness above the filament spine and the opposite handedness in the barbs and filament channel below the filament spine. If the spine has handedness, the observations favor its having the handedness of the filament cavity and coronal loops above. As the separate components of a chiral system form, we show that the system appears to maintain a balance of right-handed and left-handed features, thus preserving an initial near-zero net helicity. We further argue that the chiral systems allow us to identify key sites of energy transformation and stored energy later dissipated in the form of concurrent CMEs, erupting filaments and solar flares. Each individual chiral system may produce many successive eruptive events above a single filament channel. Because major eruptive events apparently do not occur independent of, or outside of, these unique chiral systems, we hypothesize that the development of chiral systems: (1) are fundamental to the occurrence of eruptive solar events and (2) preserve an approximate balance between positive and negative helicity (right and left-handed chirality) while preparing to release energy in the form of CMEs, erupting filaments, and flares. Title: Coronal Magnetic Field Structure and Evolution for Flaring AR 11117 and Its Surroundings Authors: Tadesse, Tilaye; Wiegelmann, T.; Inhester, B.; Pevtsov, A. Bibcode: 2012SoPh..281...53T Altcode: 2011arXiv1109.4889T; 2012SoPh..tmp...60T In this study, photospheric vector magnetograms obtained with the Synoptic Optical Long-term Investigations of the Sun (SOLIS) survey are used as boundary conditions to model three-dimensional nonlinear force-free (NLFF) coronal magnetic fields as a sequence of NLFF equilibria in spherical geometry. We study the coronal magnetic field structure inside an active region and its temporal evolution. We compare the magnetic field configuration obtained from NLFF extrapolation before and after the flaring event in active region (AR) 11117 and its surroundings observed on 27 October 2010, and we also compare the magnetic field topologies and the magnetic energy densities and study the connectivities between AR 11117 and its surroundings. During the investigated time period, we estimate the change in free magnetic energy from before to after the flare to be 1.74×1032 erg, which represents about 13.5 % of the NLFF magnetic energy before the flare. In this study, we find that electric currents from AR 11117 to its surroundings were disrupted after the flare. Title: On a Possible Explanation of the Long-term Decrease in Sunspot Field Strength Authors: Nagovitsyn, Yury A.; Pevtsov, Alexei A.; Livingston, William C. Bibcode: 2012ApJ...758L..20N Altcode: Recent studies revealed a controversy in long-term variations in sunspot field strengths. On one hand, the sunspot field strengths computed by averaging both large and small sunspots and pores show a gradual decrease over the declining phase of solar Cycle 23 and the rising phase of Cycle 24. On the other hand, the strongest sunspot field strengths demonstrate only solar cycle variations with no long-term decline. Here, we investigate the field strength and area properties of sunspots in an attempt to reconcile the presence of both tendencies in recent sunspot field strength measurements. First, we analyze the data set from Penn & Livingston, and we show that in addition to the previously reported long-term decline, the data show the solar cycle variation when only sunspots with the strongest magnetic fields are included. Next, we investigate the variations in the number of sunspots of different sizes, and we find a negative correlation between the numbers of small and large sunspots. Finally, we show that during the period of 1998-2011, the number of large sunspots gradually decreased, while the number of small sunspots steadily increased. We suggest that this change in the fraction of small and large sunspots (perhaps, due to changes in the solar dynamo) can explain the gradual decline in average sunspot field strength as observed by Penn & Livingston. Title: The role of helicity in solar magnetic fields Authors: Pevtsov, Alexei Bibcode: 2012cosp...39.1493P Altcode: 2012cosp.meet.1493P As the famous saying goes, the sun would be a boring star without its magnetic field. Equally, the sun's magnetic field would be a boring "element" without its topological complexity (helicity) and dynamics. Helicity protagonist would argue that it plays an important role in many processes that define creation, evolution, and disappearance of magnetic fields. The productivity of solar dynamo depends on kinetic helicity of its flows, but significant accumulation of magnetic helicity may also have a negative feed-back on dynamo. Propagation of magnetic fields through the convection zone and solar atmosphere may be affected by their helicity. Pre- and post-flare dynamics of magnetic fields and flows may reflect the transport of helicity through solar atmosphere, while helicity scale-separation could reveal itself in the interplanetary fields. But the skeptic might say that, perhaps, the role of helicity is overrated, and one does not need it at all? In this talk, I will provide a critical review of helicity concept and its role in solar magnetic fields. Title: Helicity patterns on the sun. Authors: Pevtsov, Alexei Bibcode: 2012cosp...39.1494P Altcode: 2012cosp.meet.1494P Helicity on the Sun comes on different scales and patterns. But what do these patterns tell us about the interior and outer layers of our home star? Why do we see a global (hemispheric) and large scale (complexes of activity) organization of helicity and what does it mean? Are there non-random patterns of helicity on small (granulation) scale? How helicity changes with solar cycle, and how it flows through solar atmosphere and heliosphere? In this talk, I will review the current state of helicity studies and discuss the questions posed above. 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: Magnetic Helicity of Solar Active Regions as Revealed by Vector Magnetograms and Coronal X-Ray Images Authors: Xu, Haiqing; Gao, Yu; Zhang, Hongqi; Sakurai, Takashi; Hagino, Masaoki; Sokoloff, Dmitry; Pevtsov, Alexei A. Bibcode: 2012PASJ...64...54X Altcode: We have used photospheric vector magnetograms of 15 different solar active regions to calculate the current helicity parameter, αav, and the linear force-free field (LFFF) parameter, αbest, that fits best the observed transverse field. The data were obtained with the Solar Magnetic Field Telescope at the Huairou Solar Observing Station, the National Astronomical Observatories of China, the Solar Flare Telescope of the National Astronomical Observatory of Japan, and the Haleakala Stokes Polarimeter at the Mees Solar Observatory, University of Hawaii, from 1997 to 2000. The agreement in sign of αav between three vector magnetographs is better than 90%. For αbest, the agreement is 80%-90%. The line-of-sight magnetograms observed with the Michelson-Doppler Imager (MDI) on SOHO and coronal X-ray images observed with the Soft X-ray Telescope (SXT) on Yohkoh have been used to determine the constant αc of the LFFF in the corona. The value of αc corresponds to the extrapolated coronal field whose field lines best match, by visual inspection, the structure of coronal loops in X-ray images. It is found that the sign agreement between photospheric αav or αbest and coronal αc is lower (60%-85%). We consider the differences in measurements, observing conditions, data reduction methods, and limitation in LFFF extrapolation, and discuss their contributions to the dispersions in the hemispheric sign rule of helicity. Title: Detection of Solar Differential Rotation in Disk-Integrated Ca II K Measurements Authors: Bertello, Luca; Pietarila, A.; Pevtsov, A. A. Bibcode: 2012AAS...22020311B Altcode: The characterization of solar differential rotation (SDR) from disk-integrated chromospheric measurements has important implications for the study of differential rotation and dynamo processes in other stars. Chromospheric lines, such as Ca II K, are very sensitive to the presence of activity on the disk and are an ideal choice for investigating SDR in Sun-as-a star

obervations. Here we use daily observations from the SOLIS Integrated Sunlight Spectrometer (ISS) to study the temporal variations of the Ca II K line profiles from 2006 to 2012.

We discuss the signature of SDR in the power spectra computed from time series of parameters derived from these profiles, and the implications for detecting differential rotation in other Main-Sequence stars. Title: Abrupt Changes in the Photospheric Magnetic Structures and H-alpha Chromosphere during the 2006 December 6 X6.5 Flare Authors: Petrie, Gordon; Balasubramaniam, K. S.; Burtseva, O.; Pevtsov, A. A. Bibcode: 2012AAS...22020406P Altcode: The active region NOAA 10930 produced the last X-class flares of Solar Cycle 23, including one at 18:29 UT on December 6. Here we investigate the relationships between signatures of this flare observed in the photospheric magnetic field and white light and continuum intensity, and H-alpha chromosphere. We use GONG 1-minute magnetograms and continuum intensity images and (1-minute?) ISOON white-light and H-alpha images to show that (1) the sunspot penumbral area and mean intensity decreased abruptly during the flare; (2) the magnetic field changed in large, contiguous patterns inside and immediately outside the southern and western penumbra resulting in a more vertical penumbral field on average; (3) H-alpha brightenings were observed to begin around the GOES start time, the earliest occurring near the sunspot and later brightenings progressively further north and south of the center of the active region near magnetic neutral lines; and (4) most of the detected photospheric flux cancellation (75%) occurred during the flare, and the remainder before the flare. Title: Ca II K And H Spectral Line Profiles From “Basal” And “Magnetic” Chromospheres Authors: Pevtsov, Alexei A.; Bertello, L. Bibcode: 2012AAS...22020309P Altcode: We use observations from the SOLIS’ Integrated Sunlight Spectrometer (ISS) to investigate properties of the Ca II K and H disk-integrated spectral line profiles. The ISS daily observations cover the period of declining phase of cycle 23 and rising phase of cycle 24. The contributions of “basal” and “magnetic” chromospheres were extracted from the observed profiles in order to investigate their solar-cycle dependency. Our analysis suggests that the properties of the "basal" chromosphere may change slightly with the cycle of activity. Title: Solar Cycle Variations of Sunspot Magnetic Field Strengths from the Mount Wilson Observatory Authors: Pevtsov, Alexei A.; Bertello, L.; Tlatov, A.; Nagovitsyn, Y.; Kilcik, A. Bibcode: 2012AAS...22011003P Altcode: We used historical synoptic data the Mount Wilson Observatory (MWO) to study long-term changes in sunspot magnetic field strengths over the period of 1920-1959. By selecting sunspots with the strongest field strength for each observing day, we find that the average field strengths in sunspots vary with solar cycle with amplitude of a few hundred Gauss. The data show no statistically significant long-term trend over the period of about 40 years covered by these observations. We also find that the fractional distribution of sunspots changes from cycle to cycle. From Cycle 15 to Cycle 19, MWO data show a steady increase in fraction of sunspots with weaker field strengths (<1000 G), while the fraction of sunspots with strongest field strengths (>3000 G) steadily decreases. The fraction of sunspots with field strengths between 1000-3000 Gauss does not change in any systematic way. In contract, the fractional distribution of sunspots by their area (i.e., small, intermediate, and large) taken from the Greenwich observatory data set does not change during the same period of time. The different behavior in these two fractional distributions might indicate some physical changes in the properties of sunspots (e.g., sunspots of about the same area show progressively smaller field strengths), or it could be the result of some systematic instrumental/observational effects. We discuss our findings in the framework of these two possible explanations. Title: Coronal Mass Ejections from Magnetic Systems Encompassing Filament Channels Without Filaments Authors: Pevtsov, Alexei A.; Panasenco, Olga; Martin, Sara F. Bibcode: 2012SoPh..277..185P Altcode: Well-developed filament channels may be present in the solar atmosphere even when there is no trace of filament material inside them. Such magnetic systems with filament channels without filaments can result in coronal mass ejections that might appear to have no corresponding solar surface source regions. In this case study, we analyze CMEs on 9 August 2001 and 3 March 2011 and trace their origins to magnetic systems with filament channels containing no obvious filament material on the days around the eruptions. Title: Magnetic Connectivity Between Active Regions 10987, 10988, and 10989 by Means of Nonlinear Force-Free Field Extrapolation Authors: Tadesse, Tilaye; Wiegelmann, T.; Inhester, B.; Pevtsov, A. Bibcode: 2012SoPh..277..119T Altcode: 2011SoPh..tmp..167T; 2011arXiv1104.2246T; 2011SoPh..tmp..236T; 2011SoPh..tmp..102T Extrapolation codes for modelling the magnetic field in the corona in Cartesian geometry do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, e.g., a single active region. We apply a method for nonlinear force-free coronal magnetic field modelling of photospheric vector magnetograms in spherical geometry which allows us to study the connectivity between multi-active regions. We use Vector Spectromagnetograph (VSM) data from the Synoptic Optical Long-term Investigations of the Sun (SOLIS) survey to model the coronal magnetic field, where we study three neighbouring magnetically connected active regions (ARs 10987, 10988, 10989) observed on 28, 29, and 30 March 2008, respectively. We compare the magnetic field topologies and the magnetic energy densities and study the connectivities between the active regions. We have studied the time evolution of the magnetic field over the period of three days and found no major changes in topologies, as there was no major eruption event. From this study we have concluded that active regions are much more connected magnetically than the electric current. Title: Complex Magnetic Evolution and Magnetic Helicity in the Solar Atmosphere Authors: Pevtsov, Alexei A. Bibcode: 2012ASSP...30...83P Altcode: 2012snc..book...83P; 2013arXiv1302.0414P Solar atmosphere is a single system unified by the presence of large-scale magnetic fields. Topological changes in magnetic fields that occur in one place may have consequences for coronal heating and eruptions for other, even remote locations. Coronal magnetic fields also play role in transport of magnetic helicity from Sun's subphotosphere/upper convection zone to the interplanetary space. We discuss observational evidence pertinent to some aspects of the solar corona being a global interconnected system, i.e., large-scale coronal heating due to new flux emergence, eruption of chromospheric filament resulting from changes in magnetic topology triggered by new flux emergence, sunspots rotation as manifestation of transport of helicity through the photosphere, and potential consequences of re-distribution of energy from solar luminosity to the dynamo for solar cycle variations of solar irradiance. Title: Pulsating B Stars observed by Kepler Authors: McNamara, Bernard J.; Jackiewicz, J.; McKeever, J.; McAteer, J.; Boucheron, L.; Cao, H.; Voelz, D.; DeGrave, K.; Kirk, M.; Taylor, G.; Al-Ghraibah, A.; Pevtsov, A.; Calabro, B.; Hao, Y. Bibcode: 2012AAS...21934804M Altcode: In a prior investigation using Kepler data, Balona et al. (2011) found that the measured frequency spectra of B stars differed from those obtained using ground-based observations. The low amplitude frequency spectra of these stars are quantified by analyzing a larger number of B stars. These stars are then categorized using the designations adopted in the Balona et al. study. Most of the frequencies we measure are too small to be detected using conventional ground-based observations. They are probably associated with higher order spherical harmonic modes. A plan to determine the l values of the larger amplitude B star frequencies is presented. Title: Detecting Flows, Waves and Nanoflares in the Solar Corona Authors: Calabro, Brandon; McAteer, J.; Pevtsov, A. Bibcode: 2012AAS...21914403C Altcode: Oscillations in the solar corona are studied using data from Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA). We use a wavelet analysis to search for oscillatory signals in 3D datacubes (two spatial dimensions, one temporal dimension) in each of the extreme ultraviolet passbands of AIA, and apply a pixel-grouping algorithm to enable us to study coherent patches of the solar corona. By looking at regions of the corona that oscillate at similar periodicity we are able to interpret the spatial behavior of oscillations through different heights in the solar corona and transversely across the corona. We propose a method to identify and extract flows, waves, and nanoflares and determine the contribution of each of these in heating coronal plasma. Title: Automated Classification of Flaring Behavior in Solar Active Regions: Preliminary Results Authors: Al-Ghraibah, Amani; Boucheron, L. E.; McAteer, R.; Cao, H.; Jackiewicz, J.; McNamara, B.; Voelz, D.; Calabro, B.; DeGrave, K.; Hao, Y.; Kirk, M.; Pevtsov, A.; Mckeever, J.; Taylor, G. Bibcode: 2012AAS...21914516A Altcode: Solar active events are the source of many energetic and geo-effective events such as solar flares and coronal mass ejections (CMEs). Understanding how these complex source regions evolve and produce these events is of fundamental importance, not only to solar physics but also the demands of space weather forecasting. In this poster, we present preliminary results from our analysis of the physical properties of active region magnetic fields using fractal-, gradient-, neutral line-, emerging flux-, and wavelet-based techniques. These analyses look to use the defined physical measures to form a predictive model for flaring behavior in active regions. Title: Intelligent Search of Solar Data Authors: Hao, Yifan; Cao, H.; McNamara, B.; Jackiewicz, J.; McAteer, J.; Boucheron, L.; Voelz, D.; Kirk, M.; Taylor, G.; DeGrave, K.; Al-Ghraibah, A.; Pevtsov, A.; Calabro, B. Bibcode: 2012AAS...21914411H Altcode: The enormous amount of solar data, a result of new observational missions, needs to be stored and retrieved intelligently. Existing systems (e.g., the Science Archive of the Solar and Heliospheric Observatory (SOHO); soho.nascom.nasa.go) manage solar data merely using metadata (e.g., the time that images were taken) or other programmatic information. As a result, such systems can only support very primitive queries (e.g., images taken in June 2009). From such search results, scientists have to manually select their needed data for further analysis.

On the other hand, solar data, either raw or processed, are often associated with semantic information such as the active regions in an image and corresponding text annotations. Such semantic knowledge can provide much more insights to the data and can help scientists quickly find data that are related to a specific research goal or topic (e.g., solar flares or coronal mass ejections). A solar data management system should be able to intelligently utilize such relevant semantic data to facilitate solar data retrieval, and ultimately saves investigators valuable time.

In this work, we build a prototype for the intelligent retrieval and exploration of solar data by utilizing the semantic knowledge associated with raw or processed solar data. The core of this prototype is a "query processing” component that utilizes a unified index technique to support both simple basic queries (e.g., images taken in 2007) over the metadata and intelligent topic queries (e.g., image regions related to "Solar Flares” in 2007) over other complicated contents. This component leverages different types of data (especially semantic information) to improve the search accuracy. Besides this, another facilitating component is designed to provide user-friendly result exploration functionalities when the "query processing” component returns a set of query results. Title: Coronal Loop Detection and Seismology Authors: Pevtsov, Alexander; McAteer, R. T. J.; Jackiewicz, J.; McNamara, B.; Kirk, M.; Degrave, K.; Boucheron, L.; Calabro, B. Bibcode: 2012AAS...21914405P Altcode: We study the spatial distribution and temporal evolution of coronal loops using data from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA). We apply an automated coronal loop detection algorithm that is maximized for accuracy and completeness, and reconnects orphaned segments of coronal loops, to extreme ultraviolet images of the solar corona. We quantify the loop size distribution with a scaling index in each of the SDO AIA passbands, and show how this changes with time. This provides new insights into the physical mechanisms that create coronal structure. 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: Long-term Trends in Sunspot Magnetic Fields Authors: Pevtsov, Alexei A.; Nagovitsyn, Yury A.; Tlatov, Andrey G.; Rybak, Alexey L. Bibcode: 2011ApJ...742L..36P Altcode: Recent studies indicate that a maximum field strength in sunspots shows a gradual decrease over the last several years. By extrapolating this trend, Penn & Livingston proposed that sunspots may completely disappear in the not-so-distant future. To verify these recent findings, we employ historic synoptic data sets from seven observatories in the former USSR covering the period from 1957 to 2011 (from 1998 to 2011, observations were taken at only one observatory). Our results indicate that while sunspot field strengths rise and wane with solar cycle, there is not a long-term trend that would suggest a gradual decrease in sunspot magnetic fields over the four and a half solar cycles covered by these observations. Title: Investigation of Some Problems of Moreton Wave Authors: Pevtsov, A. A.; Mamedov, S. H.; Dzhalilov, N. S.; Gulu-zadeh, J. M.; Mustafa, F. R. Bibcode: 2011AzAJ....6d..22P Altcode: In the paper we study the some problems of physics of Moreton wave. Two possible variants of explanation were considered for the observed pattern of this wave in the Hα-line: 1) using cloud model of the wave front, located in the upper chromosphere and committing a radial movement up and down, and 2) by shifting the entire absorption line Hα. It was shown that for any values of the optical parameters of clouds, namely: S- source function, τ-optical thickness, Δλd - Doppler width and Doppler shift Δλsh of the cloud within the absorption line of Hα (due to radial motions of the cloud- the wave front) is not possible to obtain the observed brightness curve of the front within Hα- absorption line. It is shown that the observed wave-front image can only and only by shifting the entire absorption line Nα. Based on this, it was concluded that the Moreton waves propagate in the formation lay of absorption lines Hα, in other words, in the photosphere and lower chromosphere. It is shown that the Moreton wave is not observed in the upper chromosphere, which also confirms the conclusion given above. Further, it is shown that this wave can not propagate in the corona, since the cooling time of the coronal gas to a temperature of 10 000 K an order of magnitude greater than the wave period. Title: The Disappearing Solar Filament of 2003 June 11: A Three-body Problem Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Cliver, E. W.; Martin, S. F.; Panasenco, O. Bibcode: 2011ApJ...743..202B Altcode: The eruption of a large quiescent filament on 2003 June 11 was preceded by the birth of a nearby active region—a common scenario. In this case, however, the filament lay near a pre-existing active region and the new active region did not destabilize the filament by direct magnetic connection. Instead it appears to have done so indirectly via magnetic coupling with the established region. Restructuring between the perturbed fields of the old region and the filament then weakened the arcade overlying the midpoint of filament, where the eruption originated. The inferred rate (~11° day-1) at which the magnetic disturbance propagates from the mature region to destabilize the filament is larger than the mean speed (~5º-6° day-1) but still within the scatter obtained for Bruzek's empirical relationship between the distance from a newly formed active region to a quiescent filament and the time from active region appearance to filament disappearance. The higher propagation speed in the 2003 June 11 case may be due to the "broadside" (versus ''end-on") angle of attack of the (effective) new flux to the coronal magnetic fields overlying a central section of the axis of the filament. Title: The Longitudinal Solar Magnetic Field Measured by SOLIS Authors: Bertello, L.; Pevtsov, A. A.; Harvey, J. W.; Pietarila, A. Bibcode: 2011AGUFMSH13B1934B Altcode: The SOLIS (Synoptic Optical Long-term Investigations of the Sun) Vector SpectroMagnetograph (VSM) instrument operating at the National Solar Observatory at Kitt Peak (Arizona) measures the full-disk longitudinal solar magnetic field in the neutral iron spectral lines at 630.15-630.25 nm (photosphere) and ionized calcium spectral line at 854.2 nm (lower chromosphere). Over the past two years a considerable effort has been made to improve the quality of the computed magnetograms. Major modifications to the original data reduction pipeline include a new determination of the instrumental magnetic bias and an improved calibration of the computed solar magnetic flux density. As a result of these changes SOLIS-VSM is now able to provide, among other products, more reliable values of the full-disk mean magnetic flux measured in the photosphere and low chromosphere. In addition, these improvements open the possibility to extend the current SOLIS-VSM catalog with new products of interest to the solar and heliospheric communities. We describe some of these changes and their impact on the quality of the derived SOLIS-VSM data. Title: Properties of Magnetic Neutral Lines and Filament Formation Authors: Karachik, N.; Pevtsov, A. A. Bibcode: 2011AGUFMSH31A1988K Altcode: Chromospheric filaments form at a boundary (neutral lines) between opposite polarity magnetic fields. Both the total length of neutral lines and the number of filaments vary with solar cycle. However, our analysis indicates that the cycle variation in filaments is not due to the change in the total length of neutral lines. It is likely due to change in magnetic properties of neutral lines. In present study we compare properties of magnetic polarity inversion lines that have filaments above them and those without filaments, and investigate how these properties change during the solar cycle. Our results show that the gradient as well as convergence/divergence of magnetic field across neutral lines are not the major factors that determine the places of filament formation. We discuss the role of canceling magnetic features in filament formation and their cycle variation. Title: 3- and 5- Minute Oscillatory Behavior in the Solar Corona Authors: Calabro, Brandon; McAteer, James; Pevtsov, Alexander Bibcode: 2011APS..4CF.F1020C Altcode: We study the spatially- and temporally-localized oscillatory behavior of the solar corona using a 6-hour sequence of narrowband 171A (extreme ultraviolet) image from the SWAP instrument onboard Proba2. We use a Morlet wavelet transform to extract oscillation parameters from the temporal evolution of emission in each pixel and study the variation in space and time of oscillatory power in the 3- and 5-minute band. We extract and compare these parameters between active Sun, quiet Sun and coronal hole regions. In each region of the corona studied the 5-minute periodicity is more prevalent than the 3-minute periodicity by a factor of 2--3. All areas of the corona exhibit a similar temporal behavior in the 5-minute band, suggesting a global driving mechanism. However, the dominance of the 5-minute periodicity is stronger in active regions than in other areas of the Sun. The 3-minute periodicity in active regions tends to be localized in the sunspot umbra, whereas the 5-minute is more prevalent in the penumbra. Title: Ground-based synoptic instrumentation for solar observations Authors: Balasubramaniam, K. S.; Pevtsov, Alexei Bibcode: 2011SPIE.8148E..09B Altcode: 2011SPIE.8148E...8B We will describe the status of current ground-based solar spectroscopic and imaging instruments used in solar observations. We will describe the advantages and disadvantages of using these two classes of instruments with examples drawn from the Improved Solar Optical Observing Network (ISOON) and Synoptic Long Term Investigations of the Sun (SOLIS) Network. Besides instrumental requirements and lessons learned from existing ground-based instruments, this talk will also focus on the future needs and requirements of ground-based solar optical observations. Title: Subsurface kinetic helicity of flows near active regions Authors: Komm, R.; Jain, K.; Petrie, G.; Pevtsov, A.; González Hernández I.; Hill, F. Bibcode: 2011sdmi.confE..68K Altcode: We study the temporal variation of subsurface flows associated with emerging and decaying active regions on the Sun. We measure the subsurface flows analyzing GONG high-resolution Doppler data with ring-diagram analysis. We can detect the emergence of magnetic flux in these flows when averaging over a sufficiently large sample. In a previous study, we have found that emerging flux has a faster rotation than the ambient fluid and pushes it up, as indicated by enhanced vertical velocity and faster-than-average zonal flow. Here, we show that the kinetic helicity density of subsurface flows increases when new flux emerges and decreases when flux decays. Title: Improvements in the Determination of ISS Ca II K Parameters Authors: Bertello, L.; Pevtsov, A. A.; Harvey, J. W.; Toussaint, R. M. Bibcode: 2011SoPh..272..229B Altcode: 2011arXiv1106.4265B Measurements of the ionized Ca II K line are one of the major resources for long-term studies of solar and stellar activity. They also play a critical role in many studies related to solar irradiance variability, particularly as a ground-based proxy to model the solar ultraviolet flux variation that may influence the Earth's climate. Full disk images of the Sun in Ca II K have been available from various observatories for more than 100 years and latter synoptic Sun-as-a-star observations in Ca II K began in the early 1970s. One of these instruments, the Integrated Sunlight Spectrometer (ISS) has been in operation at Kitt Peak (Arizona) since late 2006. The ISS takes daily observations of solar spectra in nine spectra bands, including the Ca II K and H lines. We describe recent improvements in data reduction of Ca II K observations, and present time variations of nine parameters derived from the profile of this spectral line. Title: Two types of coronal bright points their characteristics, and evolution Authors: Sattarov, Isroil; Karachik, Nina V.; Sherdanov, Chori T.; Tillaboev, Azlarxon M.; Pevtsov, Alexei A. Bibcode: 2011IAUS..273..343S Altcode: Using maximum brightness of coronal bright point's (CBP) as a criterion, we separate them on two categories: dim CBPs, associated with areas of a quiet Sun, and bright CBPs, associated with an active Sun. This study reports on characteristics of two types of CBPs and their evolution. Title: Solar Wind and Coronal Bright Points inside Coronal Holes Authors: Karachik, Nina V.; Pevtsov, Alexei A. Bibcode: 2011ApJ...735...47K Altcode: Observations of 108 coronal holes (CHs) from 1998-2008 were used to investigate the correlation between fast solar wind (SW) and several parameters of CHs. Our main goal was to establish the association between coronal bright points (CBPs; as sites of magnetic reconnection) and fast SW. Using in situ measurements of the SW, we have connected streams of the fast SW at 1 AU with their source regions, CHs. We studied a correlation between the SW speed and selected parameters of CHs: total area of the CH, total intensity inside the CH, fraction of area of the CH associated with CBPs, and their integrated brightness inside each CH. In agreement with previous studies, we found that the SW speed most strongly correlates with the total area of the CHs. The correlation is stronger for the non (de)projected areas of CHs (which are measured in image plane) suggesting that the near-equatorial parts of CHs make a larger contribution to the SW measured at near Earth orbit. This correlation varies with solar activity. It peaks for periods of moderate activity, but decreases slightly for higher or lower levels of activity. A weaker correlation between the SW speed and other studied parameters was found, but it can be explained by correlating these parameters with the CH's area. We also studied the spatial distribution of CBPs inside 10 CHs. We found that the density of CBPs is higher in the inner part of CHs. As such, results suggest that although the reconnection processes occurring in CBPs may contribute to the fast SW, they do not serve as the main mechanism of wind acceleration. Title: Subsurface kinetic helicity of flows near active regions Authors: Komm, Rudolf; Jain, K.; Petrie, G.; Pevtsov, A.; González Hernández, I.; Hill, F. Bibcode: 2011shin.confE.142K Altcode: We study the flows in the upper solar convection zone determined from GONG data using the standard dense-pack ring-diagram analysis and derive daily and synoptic maps of the velocity components. We also calculate the vorticity and the kinetic helicity density of the flows. Previous studies have shown that the vorticity is enhanced near locations of active regions and that the kinetic helicity density associated with active regions correlates well with the X-ray flare intensity of active regions. These fluid dynamics descriptors are thus promising indicators for investigating the relation between active regions and associated subsurface flows. Here, we focus on the temporal evolution of subsurface kinetic helicity density during flux emergence and decay. We will present the latest results. Title: The Pulsation Spectra of Kepler B Stars Authors: McNamara, Bernard J.; Jackiewicz, J.; McAteer, J.; Boucheron, L.; Cao, H.; Voelz, D.; Kirk, M.; Taylor, G.; DeGrave, K.; Al-Ghraibah, A.; Lovekin, C.; Pevtsov, A. Bibcode: 2011AAS...21840717M Altcode: 2011BAAS..43G40717M The Kepler satellite was designed to obtain single filter light curves of over 100,000 stars during its 3.5 year mission lifetime. The accuracy of each 30 minute measurement is about 20 parts per million for a 12 magnitude star. Although the primary objective of Kepler is to search for the signal of Earth-like planets in these light curves, dozens of pulsating B stars are included among its targets. This poster presents and overview of the techniques used to obtain the frequency spectra of these stars. A data base of stellar pulsation spectra is also presented along with the positions of these stars in the HR diagram. A major limitation of the Kepler data is that it does not allow the spherical harmonic l and m values of the pulsation modes to be determined. To do this multi-color observations or spectra are needed. A list of candidate stars for this type of effort is provided. This work is supported by the NASA Kepler Guest Observer program. Title: Ca Ii K and H Measurements from the SOLIS ISS Instrument Authors: Bertello, Luca; Pevtsov, A. A.; Pietarila, A.; Harvey, J. W.; Toussaint, R. M.; SOLIS Team Bibcode: 2011SPD....42.1744B Altcode: 2011BAAS..43S.1744B Precise measurements of the disk integrated solar Ca II K and H lines play a critical role in many investigations of solar activity and studies related to solar irradiance variability. The Integrated Sunlight Spectrometer(ISS) operating at the National Solar Observatory at Kitt Peak (Arizona) since December 2006 is designed to obtain high spectral resolution (R = 300,000) observations of the Sun as a star in a broad range of wavelengths (350 nm -1100 nm). The ISS is one of three instruments, with the Vector Spectro-Magnetograph (VSM) and the Full Disk Patrol (FDP), comprising the Synoptic Optical Long-term Investigations of the Sun (SOLIS) - a synoptic facility for solar observations operating at NSO/Kitt Peak. The ISS takes daily observations of solar spectra in nine spectral bands, including the Ca II K and H lines. We describe recent improvements in data reduction of Ca II K and H observations, and present time variations of parameters derived from the profiles of these spectral lines. Some properties of these time series are also discussed. Title: The Influence of Rotation on the Pulsation Spectra of B-stars Authors: McNamara, Bernard J.; Jackiewicz, J.; Lovekin, C.; McAteer, J.; Boucheron, L.; Cao, H.; Voelz, D.; Kirk, M.; Taylor, G.; DeGrave, K.; Al-Ghraibah, A.; Pevtsov, A. Bibcode: 2011SPD....42.1619M Altcode: 2011BAAS..43S.1619M B stars are known to oscillate in both radial and non-radial modes. Rotation may play an important role in altering the pulsation spectra of these stars. The results of 2D model calculations of rapidly rotating early B-stars is presented and used to examine the frequency spectrum of a Kepler B-star. The reduction procedure to determine stellar pulsation spectra using Kepler data sets is discussed, as well as the need for additional observational data to constrain the B-star spherical harmonic l and m values. This work is supported by the NASA Kepler Guest Observer program. Title: Properties of Magnetic Neutral Lines and Chromospheric Filaments Formation Authors: Karachik, Nina; Pevtsov, A. A. Bibcode: 2011SPD....42.1728K Altcode: 2011BAAS..43S.1728K Chromospheric filaments - large concentrations of dense and cool material held in place by magnetic fields - form at a boundary (neutral lines) between opposite polarity magnetic fields. However, not all magnetic neutral lines have filaments above them. In present research we compare properties of magnetic polarity inversion lines that have filaments above them and those without filaments, and investigate how these properties change during solar cycle. The results are used to establish the conditions at neutral lines that may lead to formation of the chromospheric filaments. Title: Solar Magnetic Fields As Observed By Solis Authors: Pietarila, Anna; Bertello, L.; Callahan, L.; Harker, B.; Harvey, J.; Marble, A.; Pevtsov, A.; Toussaint, R. Bibcode: 2011SPD....42.1746P Altcode: 2011BAAS..43S.1746P The Vector Spectromagnetograph (VSM), part of the Synoptic Optical Long-term Investigations of the Sun (SOLIS), makes spectropolarimetric observations of the full-disk of the Sun in the photospheric Fe I lines around 630 nm (Stokes I, Q, U and V) and the chromospheric Ca II 854.2 nm (Stokes I and V) line. We present some of the updated SOLIS VSM data products and show how they compare with data from other instruments, e.g., SDO/HMI and Hinode/SP. We also illustrate some of the differences between the photospheric and chromospheric magnetograms, and how they can be used to study the height variation of the magnetic field. 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: Coronal Loop detection and seismology Authors: Pevtsov, Alexander; McAteer, R. T. J.; Jackiewicz, J.; Kirk, M.; McNamara, B.; DeGrave, K.; Amani Al-Ghraibah, A.; Boucheron, L.; Voelz, D.; Cao, H.; Taylor, G. Bibcode: 2011SPD....42.1822P Altcode: 2011BAAS..43S.1822P Using a TRACE image with a bipolar active region and over one hundred distinguishable loops, we examine several current methods for automated coronal loop detection. Using the same TRACE image, several new approaches are also taken in an attempt to increase accuracy and completeness rates for the automated detection process. By means of these new methods the expectation is to achieve a higher degree of completeness while maintaining a high level of accuracy in the detection process. To increase completeness, an automated attempt for the reconnection between orphaned loop segments will also be tested. In the future, an approach to reconstruction of three-dimensional images from several two-dimensional images can be devised by using the detected coronal loops and a known 3D offset of each image. However this process heavily depends on the ability to accurately and completely detect the coronal loops. Title: Status of Synoptic Optical Long-term Investigation of the Sun (SOLIS) Project. Authors: Pevtsov, Alexei A.; Streander, K.; Harvey, J.; Bertello, L.; Branston, D.; Britanik, J.; Callahan, L.; Cole, L.; Galayda, E.; Harker, B.; Hauth, D.; Jaksha, D.; Leiker, C.; Marble, A.; Mills, N.; Pietarila, A.; Schramm, K.; Stover, E.; Suarez-Sola, I.; Toussaint, R. Bibcode: 2011SPD....42.1747P Altcode: 2011BAAS..43S.1747P Synoptic Optical Long-term Investigation of the Sun (SOLIS) is a suite of three instruments to study various aspects of solar activity. Vector Stokes Magnetograph (VSM) takes full disk longitudinal magnetograms in the photosphere (Fe I 6301 A-6302 A) and the chromosphere (Ca II 8542A), the photospheric vector magnetograms, and the full disk images of equivalent width for He I 10830A. The VSM data set goes back to August 2003. Integrated Sunlight Spectrometer (ISS) provides high-resolution spectra of sun-as-a-star for nine selected spectral bands (starting from December 2006). Full-Disk Patrol (FDP) observes full disk images of the Sun at high cadence in several selected wavelengths (starting from June 2011). In the last two years, the SOLIS instruments and data reduction went through a series of upgrades resulting in higher data quality. These upgrades include new CCD cameras, photo guider, and improved magbias calculations and data reduction of ISS line profiles. We will present the current status of SOLIS, and show the comparison between SOLIS observations with other instruments. Title: Nonlinear force-free field extrapolation in spherical geometry: improved boundary data treatment applied to a SOLIS/VSM vector magnetogram Authors: Tadesse, T.; Wiegelmann, T.; Inhester, B.; Pevtsov, A. Bibcode: 2011A&A...527A..30T Altcode: 2010arXiv1011.6285T Context. Understanding the 3D structure of coronal magnetic field is important to understanding: the onset of flares and coronal mass ejections, and the stability of active regions, and to monitoring the magnetic helicity and free magnetic energy and other phenomena in the solar atmosphere. Routine measurements of the solar magnetic field are mainly carried out in the photosphere. Therefore, one has to infer the field strength in the upper layers of the solar atmosphere from the measured photospheric field based on the assumption that the corona is force-free. Meanwhile, those measured data are inconsistent with the above force-free assumption. Therefore, one has to apply some transformations to these data before nonlinear force-free extrapolation codes can be applied.
Aims: Extrapolation codes in Cartesian geometry for modelling the magnetic field in the corona do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, e.g., a single active region. Here we apply a method for nonlinear force-free coronal magnetic field modelling and preprocessing of photospheric vector magnetograms in spherical geometry using the optimization procedure.
Methods: We solve the nonlinear force-free field equations by minimizing a functional in spherical coordinates over a restricted area of the Sun. We extend the functional by an additional term, which allows us to incorporate measurement errors and treat regions lacking observational data. We use vector magnetograph data from the Synoptic Optical Long-term Investigations of the Sun survey (SOLIS) to model the coronal magnetic field. We study two neighbouring magnetically connected active regions observed on May 15 2009.
Results: For vector magnetograms with variable measurement precision and randomly scattered data gaps (e.g., SOLIS/VSM), the new code yields field models that satisfy the solenoidal and force-free condition significantly better as it allows deviations between the extrapolated boundary field and observed boundary data within the measurement errors. Data gaps are assigned an infinite error. We extend this new scheme to spherical geometry and apply it for the first time to real data. Title: Temperature variability in X-ray bright points observed with Hinode/XRT Authors: Kariyappa, R.; Deluca, E. E.; Saar, S. H.; Golub, L.; Damé, L.; Pevtsov, A. A.; Varghese, B. A. Bibcode: 2011A&A...526A..78K Altcode:
Aims: We investigate the variability in temperature as a function of time among a sample of coronal X-ray bright points (XBPs).
Methods: We analysed a 7-h (17:00-24:00 UT) long time sequence of soft X-ray images observed almost simultaneously in two filters (Ti_poly and Al_mesh) on April 14, 2007 with X-ray telescope (XRT) onboard the Hinode mission. We identified and selected 14 XBPs for a detailed analysis. The light curves of XBPs were derived using the SolarSoft library in IDL. The temperature of XBPs was determined using the calibrated temperature response curves of the two filters by means of the intensity ratio method.
Results: We find that the XBPs show a high variability in their temperature and that the average temperature ranges from 1.1 MK to 3.4 MK. The variations in temperature are often correlated with changes in average X-ray emission. It is evident from the results of time series that the XBP heating rate can be highly variable on short timescales, suggesting that it has a reconnection origin. Title: Non-polar Coronal Holes and Solar Wind Authors: Karachik, N.; Pevtsov, A. A. Bibcode: 2010AGUFMSH11B1668K Altcode: We investigate properties of non-polar coronal holes (CHs) and their correlation with fast solar wind at 1 AU. Using EIT/SOHO observations taken from 1998-2008 in 195A and 284A wavelength bands, we identify boundaries of coronal holes, and compute their area, total brightness of corona integrated over the CH, as well as the area and total brightness of pixels inside the CH associated with coronal bright points (CBPs). We investigate the effect of each parameter on solar wind speed, the mutual dependency of the parameters, and their changes with the sunspot activity. Our findings suggest that the reconnection events associated with coronal bright points situated in CHs do not play a major role in acceleration of the fast solar wind. Title: Coronal Mass Ejections from Empty Filament Channels Authors: Pevtsov, A. A.; Panasenco, O. Bibcode: 2010AGUFMSH51A1659P Altcode: Well-developed filament channels may be present in solar atmosphere even when there is no trace of filament material inside it. When erupted, such “empty” filament channels could result in coronal mass ejections that might appear having no corresponding solar surface source region. We analyze the magnetic field configuration and eruption of a complete filament system, which includes magnetic neutral line, filament channel, and the coronal cavity, but without the filament material inside. We show that the presence of filament visible in H-alpha or He II 304 A is not necessary for the eruption of magnetic systems with "empty" filament channels. Title: Solar Dynamo: Comparing Models with Observations. (Invited) Authors: Pevtsov, A. A. Bibcode: 2010AGUFMSH42A..01P Altcode: Dynamo, an elusive process taking place in solar interior, is bedrock of solar activity. It converts thermal to magnetic energy and supplies magnetic fields to processes that ultimately define the solar upper atmosphere and the Sun’s short and long-term activity. The solar dynamo is twofold: strong magnetic fields are generated by a deep-seated dynamo, while surface fields are the results of a near-surface turbulent dynamo. Several theoretical and numerical models of these dynamo processes have been developed. Recent improvements in high resolution solar observations, helioseismology, and vector magnetography allow for in depth comparison with model predictions, and eventually, may serve as an ultimate test for or against a specific model. In this talk, I will review the existing dynamo models and contrast their predictions with the observations. Title: On the Origin of the Solar Moreton Wave of 2006 December 6 Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer, M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.; Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak, B.; White, S. M. Bibcode: 2010ApJ...723..587B Altcode: We analyzed ground- and space-based observations of the eruptive flare (3B/X6.5) and associated Moreton wave (~850 km s-1 ~270° azimuthal span) of 2006 December 6 to determine the wave driver—either flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic analysis favors a CME driver of the wave, despite key gaps in coronal data. The CME scenario has a less constrained/smoother velocity versus time profile than is the case for the flare hypothesis and requires an acceleration rate more in accord with observations. The CME picture is based, in part, on the assumption that a strong and impulsive magnetic field change observed by a GONG magnetograph during the rapid rise phase of the flare corresponds to the main acceleration phase of the CME. The Moreton wave evolution tracks the inferred eruption of an extended coronal arcade, overlying a region of weak magnetic field to the west of the principal flare in NOAA active region 10930. Observations of Hα foot point brightenings, disturbance contours in off-band Hα images, and He I 10830 Å flare ribbons trace the eruption from 18:42 to 18:44 UT as it progressed southwest along the arcade. Hinode EIS observations show strong blueshifts at foot points of this arcade during the post-eruption phase, indicating mass outflow. At 18:45 UT, the Moreton wave exhibited two separate arcs (one off each flank of the tip of the arcade) that merged and coalesced by 18:47 UT to form a single smooth wave front, having its maximum amplitude in the southwest direction. We suggest that the erupting arcade (i.e., CME) expanded laterally to drive a coronal shock responsible for the Moreton wave. We attribute a darkening in Hα from a region underlying the arcade to absorption by faint unresolved post-eruption loops. Title: Science Objectives for an X-Ray Microcalorimeter Observing the Sun Authors: Laming, J. Martin; Adams, J.; Alexander, D.; Aschwanden, M; Bailey, C.; Bandler, S.; Bookbinder, J.; Bradshaw, S.; Brickhouse, N.; Chervenak, J.; Christe, S.; Cirtain, J.; Cranmer, S.; Deiker, S.; DeLuca, E.; Del Zanna, G.; Dennis, B.; Doschek, G.; Eckart, M.; Fludra, A.; Finkbeiner, F.; Grigis, P.; Harrison, R.; Ji, L.; Kankelborg, C.; Kashyap, V.; Kelly, D.; Kelley, R.; Kilbourne, C.; Klimchuk, J.; Ko, Y. -K.; Landi, E.; Linton, M.; Longcope, D.; Lukin, V.; Mariska, J.; Martinez-Galarce, D.; Mason, H.; McKenzie, D.; Osten, R.; Peres, G.; Pevtsov, A.; Porter, K. Phillips F. S.; Rabin, D.; Rakowski, C.; Raymond, J.; Reale, F.; Reeves, K.; Sadleir, J.; Savin, D.; Schmelz, J.; Smith, R. K.; Smith, S.; Stern, R.; Sylwester, J.; Tripathi, D.; Ugarte-Urra, I.; Young, P.; Warren, H.; Wood, B. Bibcode: 2010arXiv1011.4052L Altcode: We present the science case for a broadband X-ray imager with high-resolution spectroscopy, including simulations of X-ray spectral diagnostics of both active regions and solar flares. This is part of a trilogy of white papers discussing science, instrument (Bandler et al. 2010), and missions (Bookbinder et al. 2010) to exploit major advances recently made in transition-edge sensor (TES) detector technology that enable resolution better than 2 eV in an array that can handle high count rates. Combined with a modest X-ray mirror, this instrument would combine arcsecondscale imaging with high-resolution spectra over a field of view sufficiently large for the study of active regions and flares, enabling a wide range of studies such as the detection of microheating in active regions, ion-resolved velocity flows, and the presence of non-thermal electrons in hot plasmas. It would also enable more direct comparisons between solar and stellar soft X-ray spectra, a waveband in which (unusually) we currently have much better stellar data than we do of the Sun. Title: Distribution of Magnetic Bipoles on the Sun over Three Solar Cycles Authors: Tlatov, Andrey G.; Vasil'eva, Valerya V.; Pevtsov, Alexei A. Bibcode: 2010ApJ...717..357T Altcode: We employ synoptic full disk longitudinal magnetograms to study latitudinal distribution and orientation (tilt) of magnetic bipoles in the course of sunspot activity during cycles 21, 22, and 23. The data set includes daily observations from the National Solar Observatory at Kitt Peak (1975-2002) and Michelson Doppler Imager on board the Solar and Heliospheric Observatory (MDI/SOHO, 1996-2009). Bipole pairs were selected on the basis of proximity and flux balance of two neighboring flux elements of opposite polarity. Using the area of the bipoles, we have separated them into small quiet-Sun bipoles (QSBs), ephemeral regions (ERs), and active regions (ARs). We find that in their orientation, ERs and ARs follow Hale-Nicholson polarity rule. As expected, AR tilts follow Joy's law. ERs, however, show significantly larger tilts of opposite sign for a given hemisphere. QSBs are randomly oriented. Unlike ARs, ERs also show a preference in their orientation depending on the polarity of the large-scale magnetic field. These orientation properties may indicate that some ERs may form at or near the photosphere via the random encounter of opposite polarity elements, while others may originate in the convection zone at about the same location as ARs. The combined latitudinal distribution of ERs and ARs exhibits a clear presence of Spörer's butterfly diagram (equatorward drift in the course of a solar cycle). ERs extend the ARs' "wing" of the butterfly diagram to higher latitudes. This high latitude extension of ERs suggests an extended solar cycle with the first magnetic elements of the next cycle developing shortly after the maximum of the previous cycle. The polarity orientation and tilt of ERs may suggest the presence of poloidal fields of two configurations (new cycle and old cycle) in the convection zone at the declining phase of the sunspot cycle. Title: Magnetic Fields and Hα Filament Formation during Solar Minimum Authors: Panasenco, O.; Pevtsov, A. Bibcode: 2010ASPC..428..123P Altcode: We use multi-instrument observations taken during April 2007, a period of extremely low sunspot activity, to investigate the properties of magnetic fields and their potential role in the formation of chromospheric filaments. For one studied case, we found that some of the necessary conditions for forming a filament are: (1) a well-developed filament channel exists, and (2) an overlying arcade is present, but apparently there is insufficient material in Hα in the chromosphere to form an enduring filament. Furthermore, when plasma observed in He II 304 Å is injected into the filament channel, we do see an Hα filament appearing for a short period of time. Therefore, we conclude that the main reason for the absence of filaments in Hα is that a mechanism supplying material for a filament into the filament channel does not work as efficiently as in other periods of the solar activity cycle. Title: Formation of Coronal Holes on the Ashes of Active Regions Authors: Karachik, Nina V.; Pevtsov, Alexei A.; Abramenko, Valentyna I. Bibcode: 2010ApJ...714.1672K Altcode: We investigate the formation of isolated non-polar coronal holes (CHs) on the remnants of decaying active regions (ARs) at the minimum/early ascending phase of sunspot activity. We follow the evolution of four bipolar ARs and measure several parameters of their magnetic fields including total flux, imbalance, and compactness. As regions decay, their leading and following polarities exhibit different dissipation rates: loose polarity tends to dissipate faster than compact polarity. As a consequence, we see a gradual increase in flux imbalance inside a dissipating bipolar region, and later a formation of a CH in place of more compact magnetic flux. Out of four cases studied in detail, two CHs had formed at the following polarity of the decaying bipolar AR, and two CHs had developed in place of the leading polarity field. All four CHs contain a significant fraction of magnetic field of their corresponding AR. Using potential field extrapolation, we show that the magnetic field lines of these CHs were closed on the polar CH at the North, which at the time of the events was in imbalance with the polar CH at the South. This topology suggests that the observed phenomenon may play an important role in transformation of toroidal magnetic field to poloidal field, which is a key step in transitioning from an old solar cycle to a new one. The timing of this observed transition may indicate the end of solar cycle 23 and the beginning of cycle 24. Title: Formation of Coronal Holes on the Ashes of Active Regions Authors: Karachik, Nina; Pevtsov, A.; Abramenko, V. Bibcode: 2010AAS...21640104K Altcode: 2010BAAS...41..857K We investigate the formation of isolated non-polar coronal holes (CHs) on the remnants of decaying active regions. We follow the evolution of four bipolar active regions, and measure their total magnetic flux, imbalance, and compactness. As regions decay, their leading and following polarities exhibit different dissipation rate. As a consequence, we see a gradual increase in flux imbalance inside dissipating bipolar magnetic field, and later, a formation of a coronal hole at the site of more compact magnetic flux. Out of four cases studied in detail, two CHs had formed at the following polarity of decaying active regions, and two coronal holes had developed at the leading polarity field. Using potential field extrapolation we show that the magnetic field lines of these coronal holes were closed on polar coronal hole at the North, which at the time of the events was in imbalance with the polar coronal hole at the South. This topology suggests that the observed phenomenon may play an important role in transformation of toroidal magnetic field to poloidal field, which is a key step in transitioning from the old solar cycle to a new cycle. Title: On Detection of Cosmic Ray Streaks in MDI Magnetograms Authors: Keys, Dustin M.; Pevtsov, A. Bibcode: 2010AAS...21641511K Altcode: Any attempt to automatically identify the small-scale features of magnetograms taken from space-borne instruments will be encumbered by the inevitable cosmic ray streak which can be comparable in size with physical features of interest. If the size of the data set is very large it becomes necessary for any method of removing cosmic ray streaks to be automated. In this work, we concentrate on geometric properties of cosmic ray streaks (long narrow linear features) as the main criteria for their identification.

Three automated methods were investigated as possible candidates. The first one is based on the linear fit of isolated contours. The standard deviation from the fit was used to identify linear features; however, this proved to be an insufficient filter since on such a small scale the contours of possible solar features may have a good linear fit and thus return false positives. The second method is an unsuccessful attempt to identify cosmic rays based on their values in the accumulator space of a Radon transformation of the image. After removing features in a binary scaled version of the image which were too large to be cosmic rays, the peaks in the accumulator space of that image were used to identify the rays. More sophisticated techniques for identifying the signature of the ray in accumulator space might have greater success. The final attempt uses morphological dilation and erosion operations of the binary scaled version of the image to bring out the shape of the cosmic ray by using linear structuring elements. The results of the last approach are the most promising and deserve further investigation. Title: Solar Cycle 23 in Coronal Bright Points Authors: Sattarov, Isroil; Pevtsov, Alexei A.; Karachik, Nina V.; Sherdanov, Chori T.; Tillaboev, A. M. Bibcode: 2010SoPh..262..321S Altcode: 2010SoPh..tmp...32S We describe an automatic routine to identify coronal bright points (CBPs) and apply this routine to SOHO/EIT observations taken in the 195 Å spectral range during solar cycle 23. We examine the total number of CBPs and its change in the course of this solar cycle. Unlike some other recent studies, we do find a modest ≈30% decrease in the number of CBPs associated with maximum of sunspot activity. Using the maximum brightness of CBPs as a criterion, we separate them on two categories: dim CBPs, associated with areas of a quiet Sun, and bright CBPs, associated with an active Sun. We find that the number of dim coronal bright points decreases at the maximum of sunspot cycle, while the number of bright CBPs increases. The latitudinal distributions suggest that dim CBPs are distributed uniformly over the solar disk. Active Sun CBPs exhibit a well-defined two-hump latitudinal profile suggestive of enhanced production of this type of CBPs in sunspot activity belts. Finally, we investigate the relative role of two mechanisms in cycle variations of CBP number, and conclude that a change in fraction of solar surface occupied by the quiet Sun's magnetic field is the primary cause, with the visibility effect playing a secondary role. Title: A new dynamo pattern revealed by solar helical magnetic fields Authors: Zhang, Hongqi; Sakurai, T.; Pevtsov, A.; Gao, Yu; Xu, Haiqing; Sokoloff, D. D.; Kuzanyan, K. Bibcode: 2010MNRAS.402L..30Z Altcode: 2009arXiv0911.5713Z; 2010MNRAS.tmpL...1Z A previously unobservable mirror asymmetry of the solar magnetic field - a key ingredient of the dynamo mechanism which is believed to drive the 11-year activity cycle - has recently been measured. This was achieved through systematic monitoring of solar active regions carried out for more than 20 years at observatories in Mees, Huairou and Mitaka. In this Letter we report on detailed analysis of vector magnetic field data, obtained at Huairou Solar Observing Station in China. Electric current helicity (the product of current and magnetic field components in the same direction) was estimated from the data and a latitude-time plot of solar helicity during the last two solar cycles has been produced. We find that like sunspots helicity patterns propagate equatorwards, but unlike sunspot polarity helicity in each solar hemisphere does not change sign from cycle to cycle, thus confirming the theory. There are, however, two significant time-latitudinal domains in each cycle when the sign briefly inverts. Our findings shed new light on stellar and planetary dynamos and are yet to be included in the theory. Title: Transport of open magnetic flux between solar polar regions Authors: Pevtsov, Alexei A.; Abramenko, Valentyna I. Bibcode: 2010IAUS..264..210P Altcode: We present the observations of coronal hole that has originated at the polar hole in one hemisphere, extended to equatorial region, got disconnected and transported across the equator to polar region of opposite hemisphere. Title: Groundbased synoptic observations of the Sun by SOLIS and their role in irradiance measurements. Authors: Pevtsov, Alexei Bibcode: 2010cosp...38.1688P Altcode: 2010cosp.meet.1688P Synoptic Optical Long-term Investigations of the Sun (SOLIS) is a synoptic facility for solar observations operated by the National Solar Observatory (NSO) at its Kitt Peak site. Current SOLIS data products include: daily full disk vector magnetograms in Fe I 630.2 nm, chromo-spheric line-of-sight magnetograms in Ca II 854.2 nm, full disk images in HeI 1083.0 nm and derived maps of coronal holes, as well as the spectral observations of the Sun as a star in the wavelength range of 350 nm -1100 nm. SOLIS magnetic and helium observations continue the historic synoptic data set from the NSO's Kitt Peak Vacuum Telescope facility from 1975-2002 to present, and can be used to construct proxies characterizing solar irradiance, and to bridge and calibrate the data sets taken with the space-borne instruments such as SOHO/MDI and SDO/HMI. In my talk, I review the current state of the SOLIS project, and discuss the irra-diance proxies based on the magnetic field and other traditional groundbased observations to better understand the origin of irradiance variations for climate studies. Title: The latitude of ephemeral regions as an indicator for solar-cycle strength . Authors: Tlatov, A. G.; Pevtsov, A. A. Bibcode: 2010MmSAI..81..814T Altcode: 2010arXiv1008.0185T Digitized images of full-disk Ca K spectroheliograms from two solar observatories were used to study the cycle variation of ephemeral regions (ERs) over the ten solar cycles 14-23. We calculate the monthly averaged unsigned latitude of ERs and compare it with the annual sunspot number. We find that the average latitude of ERs can be used as a predictor for the strength of a solar cycle. For a short-term prediction (dT ∼ 1-2 years), the maximum latitude of ERs (in the current cycle) defines the amplitude of that cycle (the higher the latitude of ERs, the larger the amplitudes of the sunspot cycle). For a long-term prediction (dT ∼ 1.5 solar cycles), the latitude of ERs during the declining phase of the nth cycle determines the amplitude of the (n+2)th cycle (the lower the latitude of ERs, the stronger is the sunspot cycle). Using this latter dependency, we forecast the amplitude of sunspot cycle 24 to be at W = 92 ± 13 (in units of annual sunspot number). Title: Formation of Coronal Holes on Ashes of Decaying Active Regions Authors: Karachik, N.; Pevtsov, A. A. Bibcode: 2010neme.confP..24K Altcode: No abstract at ADS Title: Vorticity of Granular Flows from NST Observations Authors: Pevtsov, A. A.; Abramenko, V.; Yurchyshyn, V.; Goode, P. R. Bibcode: 2009AGUFMSH53B..04P Altcode: We use observations taken with the New Solar Telescope (NST) at Big Bear Solar Observatory, the world largest solar optical telescope with diffraction limited spatial resolution of 0.06 arc seconds, to study vorticity of granular flows in quiet Sun areas. We employ sequence of images observed with TiO (705.7 nm) filter with time cadence of 30 seconds. The atmospheric seeing effects were removed using speckle-reconstruction technique. We compare vorticity of granular flows and intergranular vortices, and discuss our findings in the framework of surface (turbulent) dynamo. Title: Solar Magnetic Helicity Injected into the Heliosphere: Magnitude, Balance, and Periodicities Over Solar Cycle 23 Authors: Georgoulis, M. K.; Rust, D. M.; Pevtsov, A. A.; Bernasconi, P. N.; Kuzanyan, K. M. Bibcode: 2009ApJ...705L..48G Altcode: Relying purely on solar photospheric magnetic field measurements that cover most of solar cycle 23 (1996-2005), we calculate the total relative magnetic helicity injected into the solar atmosphere, and eventually shed into the heliosphere, over the latest cycle. Large active regions dominate the helicity injection process with ~5.7 × 1045 Mx2 of total injected helicity. The net helicity injected is lsim1% of the above output. Peculiar active-region plasma flows account for ~80% of this helicity; the remaining ~20% is due to solar differential rotation. The typical helicity per active-region CME ranges between (1.8-7) × 1042 Mx2 depending on the CME velocity. Accounting for various minor underestimation factors, we estimate a maximum helicity injection of ~6.6 × 1045 Mx2 for solar cycle 23. Although no significant net helicity exists over both solar hemispheres, we recover the well-known hemispheric helicity preference, which is significantly enhanced by the solar differential rotation. We also find that helicity injection in the solar atmosphere is an inherently disorganized, impulsive, and aperiodic process. Title: Just how much Helicity did the Sun Shed in Solar Cycle 23? Magnitude, Balance, Periodicities, and Further Implications Authors: Georgoulis, Manolis K.; Rust, D. M.; Pevtsov, A. A.; Bernasconi, P. N.; Kuzanyan, K. M. Bibcode: 2009SPD....40.0606G Altcode: Using solar magnetic field measurements, we calculate the total relative magnetic helicity injected in the solar atmosphere and eventually

transported to the heliosphere in the course of the latest solar cycle. We report on (i) the magnitude of the heliospheric helicity over cycle 23, (ii) the net helicity and its significance, and (iii) the possible

periodicities of helicity injection in the solar atmosphere. Our simple calculations raise several questions regarding the fundamental nature of solar magnetism. The lack of significant net helicity may place the solar dynamo in the category of

astrophysical dynamos without a net helicity effect over an average time scale. The strong enhancement of the hemispheric helicity preference by solar differential rotation - although the latter has a much weaker effect than intrinsic active-region plasma flows - warrants further investigation. Finally, the absence of any credible periodicity of helicity injection, in spite of numerous reported periodicities in solar activity, perhaps prompts the re-evaluation of the notion that the Sun works through a sequence of internal cycles: active-region emergence and evolution appears as an inherently disorganized, aperiodic process. Title: The Solar Moreton Wave Of 6 December 2006: Evidence For A CME Driver Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Cliver, E. W.; Neidig, D. F.; Petrie, G. J. D. Bibcode: 2009SPD....40.3703P Altcode: We analyze ground- and space-based observations of the major eruptive flare and associated Moreton wave of 6 December 2006. The Moreton wave spanned 270° in azimuth and exhibited a variable speed time profile as it propagated away from the source region. The Hα wave traveled 1.2 Rsun from the S06E63 site of the eruption and white-light flare toward the southwest in 15 minutes where it disrupted a large quiescent filament. A preceding coronal wave was observed in a single He 10830 Å image. Potential field analysis of the active region magnetic fields and a comparison of ISOON images of the eruptive flare in line-center Hα with off-band images of the wave indicate that the Moreton wave was driven by a coronal mass ejection. Title: Erupting Chromospheric Filaments Authors: Balasubramaniam, K. S.; Cliver, E.; Pevtsov, A.; Martin, S.; Panasenco, O. Bibcode: 2009SPD....40.1010B Altcode: Erupting filaments are commonly associated with coronal mass ejections. They represent the chromospheric structures most closely tied to the underlying photospheric magnetic fields. We present an analysis of the eruption of an unusually large filament on the SE quadrant of the solar disc on 2003 June 11. The data are drawn from USAF/NSO Improved Solar Observing Optical Network, Solar and Heliospheric Observatory, and ground-based telescopes at NSO. The filament rises with an initial slow speed of 6-7 km/s over a period of 2 hours and later erupts by rapidly accelerating to 170 km/s second in the following 30 minutes. The filament eruption is accompanied by a flare in a neighboring active region. We trace morphological and topological changes in the filament and overlying arcade before and during its eruption, and interpret these changes in terms of physical structure of the filament and whole filament system. The destabilization of the filament and its overlying coronal arcade are related to interactions with a new emerging active region, and adjacent active region. Title: A Century of Solar Ca II Measurements and Their Implication for Solar UV Driving of Climate Authors: Foukal, Peter; Bertello, Luca; Livingston, William C.; Pevtsov, Alexei A.; Singh, Jagdev; Tlatov, Andrey G.; Ulrich, Roger K. Bibcode: 2009SoPh..255..229F Altcode: Spectroheliograms and disk-integrated flux monitoring in the strong resonance line of Ca II (K line) provide the longest record of chromospheric magnetic plages. We compare recent reductions of the Ca II K spectroheliograms obtained since 1907 at the Kodaikanal, Mt. Wilson, and US National Solar Observatories. Certain differences between the individual plage indices appear to be caused mainly by differences in the spectral passbands used. Our main finding is that the indices show remarkably consistent behavior on the multidecadal time scales of greatest interest to global warming studies. The reconstruction of solar ultraviolet flux variation from these indices differs significantly from the 20th-century global temperature record. This difference is consistent with other findings that, although solar UV irradiance variation may affect climate through influence on precipitation and storm tracks, its significance in global temperature remains elusive. Title: A New Method of Calibration of Photographic Plates from Three Historic Data Sets Authors: Tlatov, Andrey G.; Pevtsov, Alexei A.; Singh, Jagdev Bibcode: 2009SoPh..255..239T Altcode: We analyze the synoptic data taken in the Ca II K spectral line with spectroheliographs at Kodaikanal Observatory from 1907 to 1999, at Mount Wilson Observatory from 1915 to 1985, and at the National Solar Observatory at Sacramento Peak from 1963 to 2002. Photographic data were digitized and calibrated following the same set of procedures developed by the authors of this paper. Using calibrated data, we have outlined bright plages and have calculated a plage index defined as the fraction of solar hemisphere occupied by the chromospheric plages and enhanced network. We present a detailed description of our method and provide a brief comparison of Ca II K plage indices derived using data from these three historic data sets. Title: Causes of Solar Activity Authors: Giampapa, Mark S.; Gibson, Sarah; Harvey, J. W.; Hill, Frank; Norton, Aimee A.; Pevtsov, A. Bibcode: 2009astro2010S..92G Altcode: No abstract at ADS Title: Dynamos and magnetic fields of the Sun and other cool stars, and their role in the formation and evolution of stars and in the habitability of planets Authors: Schrijver, Karel; Carpenter, Ken; Karovska, Margarita; Ayres, Tom; Basri, Gibor; Brown, Benjamin; Christensen-Dalsgaard, Joergen; Dupree, Andrea; Guinan, Ed; Jardine, Moira; Miesch, Mark; Pevtsov, Alexei; Rempel, Matthias; Scherrer, Phil; Solanki, Sami; Strassmeier, Klaus; Walter, Fred Bibcode: 2009astro2010S.262S Altcode: No abstract at ADS Title: The Role of Heavy Ions as Coronal Diagnostics: Recent Results from Total Solar Eclipse Observations Authors: Habbal, S. R.; Daw, A. N.; Morgan, H.; Johnson, J.; Druckmuller, M.; Druckmullerova, H.; Scholl, I.; Arndt, M. B.; Pevtsov, A. Bibcode: 2008AGUFMSH11A..04H Altcode: Recent advancements in coronal imaging capabilities and image processing techniques, have led to new diagnostic capabilities for the exploration of the solar atmosphere during total solar eclipses. In particular, the suite of Fe spectral lines in the visible and near infrared, namely Fe XIV 5303, Fe X 6374 A, Fe XI 7892 A, and Fe XIII 10747 A, together with continuum white light emission, continue to unveil the intricate topology of the magnetic field, density structures and temperature distribution in the solar corona. These spectral lines are also yielding new insights into the role of heavy ions as diagnostics of the coronal plasma. This presentation will focus on the surprising results from the eclipse observations of 2006 and 2008. With observations in H alpha, neutral helium He I 5876 A and the Fe lines representing four different ionization states of iron, it is shown how the distribution of neutrals and heavy ions in select magnetic structures in the corona, provides new insights into the physics of the coronal plasma, with implications for models of coronal heating processes. These observations also shed light on the source regions and properties of neutrals and minor ions measured in interplanetary space. Title: Variations of solar activity over the last 100 years using observations in CaII-K spectral line. Authors: Tlatov, A.; Pevtsov, A. A.; Singh, J. Bibcode: 2008AGUSMSP53B..02T Altcode: We present analysis of synoptic full disk daily spectroheliograms taken in CaII-K spectral line at Kodaikanal Observatory (1907-1999), Mount Wilson Observatory (1915-1985), and the National Solar Observatory at Sacramento Peak (1963-2002). All Photographic images were digitized and reduced in a systematic way. The data reduction included circularization of solar disk images and correction for scattered light and response function of photographic film. Using localized intensity threshold, we identified three types of chromospheric features: plage, network element, and ephemeral bright point; and we study coordinates, total area, and irradiance of these features. In this talk, we discuss relationship between sunspot activity, total area of chromospheric plages and their irradiance over a period of several solar cycles. Title: On the Solar Cycle Variation of the Hemispheric Helicity Rule Authors: Pevtsov, A. A.; Canfield, Richard C.; Sakurai, T.; Hagino, M. Bibcode: 2008ApJ...677..719P Altcode: We study the statistical significance of observed temporal variations of the solar active-region hemispheric helicity rule, as measured by the latitudinal gradient of the best-fit linear force-free-field parameter, dα/dvarphi . Using data from four different vector magnetographs, we compute and compare average annual dα/dvarphi values for these instruments for 19 years from solar cycles 21, 22, and 23. We find that although every instrument shows the "wrong" sign for the hemispheric rule in some years, there is no agreement among the instruments on which years are abnormal. None of the four data sets shows annual values of dα/dvarphi departing from the hemispheric helicity rule by more than 3 σ. We conclude that because the hemispheric helicity rule is a weak tendency with significant scatter, an annual subset of active regions is likely to produce statistically unreliable results. Title: What helicity can tell us about solar magnetic fields Authors: Pevtsov, Alexei A. Bibcode: 2008JApA...29...49P Altcode: No abstract at ADS Title: Solar helicity as a constraint on the solar dynamo Authors: Pevtsov, Alexei Bibcode: 2008cosp...37.2424P Altcode: 2008cosp.meet.2424P Solar magnetic fields are the result of two types of dynamo. Strong magnetic fields of active regions are likely to be generated by helical dynamo operating at the base/low portion of the convective zone. Weak (intra-) network field is probably generated by a separate, non-helical dynamo. In this talk I will review the role of helicity in these two types of dynamo, and present observational tests allowing to characterize helical and non-helical dynamos by their helicity signature. Title: Evershed Flow, Oscillations, and Sunspot Structure Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Olmschenk, S. Bibcode: 2008ASPC..383..279B Altcode: Using high resolution spectroscopy at high cadence, we probe oscillatory properties of the Evershed effect flows. We employ Doppler measurements in several spectral lines to show that the Evershed flow is modulated at periods lasting a few tens of minutes, at the photosphere and chromosphere. The phase of this modulation is always outward propagating irrespective of whether the spectral line originates in the photosphere or chromosphere. From a power-spectrum analysis, we show that periods of peak power shift to longer periods as magnetic field strength increases (going from the umbra to the outer penumbra), at photospheric levels. At the chromosphere the periods shift to longer periods as the magnetic field shifts from stronger to weaker fields. An analysis of these phenomena and their influence on the sunspot structure will be presented. Title: Chromospheric observations of erupting filaments with the Optical Solar Patrol Network (OSPaN) telescope Authors: Cliver, Edward; Balasubramaniam, K. S.; Cliver, E. W.; Engvold, O.; Pevtsov, A.; Martin, S.; Panasenco, O. Bibcode: 2008cosp...37..562C Altcode: 2008cosp.meet..562C Using AFRL/NSO OSPaN telescope chromospheric images, we present movies and analyses of the eruption of a quiescent filament (11 June 2003) and an active region filament (13 May 2005). In both cases, widely separated regions of the solar surface were affected by the eruptions, either via the Moreton waves they generated (inferred from winking filaments) or through direct magnetic connection (manifested by sequential chromospheric brightenings). We investigate the topology of the magnetic fields in which these eruptions occur and use Doppler measurements to understand the dynamics of the eruptions. Title: Helicity as the Ultimate Test to the Surface Dynamo Problem Authors: Pevtsov, A. A.; Longcope, D. W. Bibcode: 2007ASPC..369...99P Altcode: It has become widely accepted that large-scale magnetic structures on the Sun, such as active regions, are the product of a dynamo of periodicity approximately 22 years situated at or near the base of the convection zone. There has been speculation that the intermixed, small-scale photospheric magnetic field is generated by a second dynamo operating at or near the solar surface. Numerical simulations have shown that such dynamo could work, although it would not be as effective in generating flux as the more conventional deep-seated dynamo. Since they are driven by flows of different sizes operating on different time scales, the magnetic fields generated by these two dynamos should be quantitatively different. In particular, there are well-studied helical trends in the large-scale magnetic which could be imprinted on them by the deep, slow flows of the dynamo which generates them; these helical trends would be absent from a field generated by a surface dynamo. We propose that observations of magnetic/current helicity at very small scales can be used to establish the role of the second, surface dynamo on the Sun. Title: Statistical Correlations between Parameters of Photospheric Magnetic Fields and Coronal Soft X-Ray Brightness Authors: Tan, Changyi; Jing, Ju; Abramenko, V. I.; Pevtsov, A. A.; Song, Hui; Park, Sung-Hong; Wang, Haimin Bibcode: 2007ApJ...665.1460T Altcode: Using observations of more than 160 active regions, we investigate the relationship between the coronal X-ray brightness, LB, and five parameters derived from the photospheric magnetic fields. The coronal X-ray brightness and the magnetic measures were obtained from co-aligned SFD composite images from the Yohkoh SXT and full-disk magnetograms from the SOHO MDI, respectively. The magnetic parameters are (1) the length of strong-gradient magnetic neutral lines, LGNL, (2) the magnetic energy dissipation, ɛ, (3) the unsigned line-of-sight magnetic flux, Φ, (4) the horizontal velocities, Vh, of random footpoint motions in the photosphere, and (5) a proxy for the Poynting flux, E=(1/4π)VhBz2, which characterizes the energy flux from the photosphere into the corona due to random footpoint motions. All measures except Vh were analyzed in both the extensive (total) and intensive (average over an area) forms. In addition, we used the area-averaged strong gradient (>50 G) of the magnetic field, ∇Bz, as an intensive form of LGNL. We found that the Pearson correlation coefficient between the total X-ray brightness and the total magnetic measures decreases as 0.97, 0.88, 0.86, and 0.47 for Φ, E, ɛ, and LGNL, respectively. The correlation coefficient between the averaged X-ray brightness and the averaged magnetic measures varied as 0.67, 0.71, 0.57, and 0.49 for <Φ>, , <ɛ>, and <∇Bz>, respectively. We also found that the velocities of the footpoint motions have no dependencies with Φ and LB. We concluded that the observed high correlation between LB and E is mainly due to the magnetic field. The energy of the Poynting flux is in the range 106.7-107.6 ergs cm-2 s-1 for the majority of active regions, which is sufficient to heat the corona due to footpoint random motions of magnetic flux tubes. Title: Magnetic Dissipation in the Photosphere and Heating of the Corona Authors: Abramenko, Valentyna; Pevtsov, A. Bibcode: 2007AAS...210.5301A Altcode: 2007BAAS...39..164A Spatio-temporal dynamics of magnetic flux tubes in the photosphere of the Sun is thought to be a driving mechanism for energy built-up and energy release phenomena in the solar atmosphere. Turbulent flows in the photosphere braid and intertwine magnetic flux tubes creating a complex topology of the magnetic field in the corona which might result in the coronal heating. Intensity of turbulent flows of the magnetic flux tubes in the photosphere can be quantified by the magnetic energy dissipation rate, which is proportional to the averaged transverse velocity increment of the magnetic flux tubes. We suggest to derive 2D magnetic energy dissipation structures from line-of-sight magnetograms of active regions and then calculate the dissipation rate. Our findings for 104 active regions showed that the magnetic dissipation rate is in a good agreement (with the correlation coefficient close to 0.7) with the temperature and the emission measure of the corona. Our results present strong observational support for those coronal heating models that rely on random footpoint motions as an energy source to heat the corona above active regions. Title: Online Catalog for Filament-Sigmoid Correlation Authors: Merriot, Ivy; Pevtsov, A.; Martens, P. Bibcode: 2007AAS...210.9504M Altcode: 2007BAAS...39..224M A new online catalog correlating H-alpha filaments with SXT sigmoids gives researchers, teachers and pre-college students the ability to access digital H-alpha images online that were previously available only at the physical location of the NSO at Sunspot, NM. This web-based catalog correlates SOHO's SXT sigmoids from 1993-1998 as described in a non-online catalog created by Zach Blehm under the direction of Richard Canfield, MSU-Bozeman, with H-alpha filament activity as described by Ivy Merriot under the direction of Alexei Pevtsov, NSO, and Petrus Martens, MSU-Bozeman. The H-alpha images were digitized from film archives of the Flare Patrol Telescope at Sunspot, NM. Use of the online catalog will be demonstrated at the poster site with critical comments encouraged. Title: Moreton Waves And Filament Eruptions Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F. Bibcode: 2007AAS...210.2504B Altcode: 2007BAAS...39..131B Moreton waves are traditionally associated with large flares, and may accompany filament and mass ejections. Using high-spectral resolution and high cadence full-disk chromospheric imaging measurements, we track two exceptional Moreton waves (2003 October 29 and 2006 December 6) to understand the nature of this phenomenon. We employ arguments drawn from spectroscopy, wave propagation and formation of prominences to affirm the location of Moreton waves to coronal heights. We present evidence that the Moreton wave sweeps filamentary material and thus became visible in chromospheric spectral line. We suggest a model to describe the associations between the flares, filament eruptions and coronal mass ejections. Title: Are Moreton Waves Coronal Phenomena? Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F. Bibcode: 2007ApJ...658.1372B Altcode: We report on permeability characteristics of the upper solar atmosphere due to the progression of a Moreton wave. An exceptional Moreton wave is tracked to cover most of the Sun, following an unusually large solar X-ray flare observed on 2003 October 29. Using Hα intensity and Doppler measurements, the Moreton wave is tracked for as long as 12 minutes. Moving outward, the wave circumnavigates strong-field active regions. The wave sweeps through solar magnetic neutral lines, disrupting material from filament and filament channels, thereby accentuating the visibility of the wave. We establish that the requirement for the visibility of a Moreton wave is the necessary presence of higher density material in the layers of the corona, besides reaffirming that Moreton waves are observed only when the speed of the disturbance exceeds Mach 2. We suggest that the cause can be a removal of significant amount of material from the solar upper atmosphere due to a coronal mass ejection. Title: On anticorrelation of number of coronal bright points with sunspot number during 1996 2006 Authors: Sattarov, Isroil; Pevtsov, Alexei A.; Karachik, Nina V.; Sherdanov, Chori T. Bibcode: 2007AdSpR..39.1777S Altcode: Using full disk SOHO/EIT data from 1996 to 2006, we study latitudinal distribution of coronal bright points over a period of one solar cycle. We confirm the presence of two distinct types of coronal bright points, and find that the number of "quiet corona" bright points in high latitudes anticorrelate with solar activity as defined by the sunspot numbers. Title: Helicity comparison among three magnetographs Authors: Xu, Haiqing; Gao, Yu; Zhang, Hongqi; Sakurai, T.; Pevtsov, A. A.; Sokoloff, D. Bibcode: 2007AdSpR..39.1715X Altcode: We compare vector magnetograms of 228 active regions observed by Solar Magnetic Field Telescope (SMFT) at Huairou (HR) Solar Observing Station and the Solar Flare Telescope (SFT) at Mitaka (MTK) of the National Astronomical Observatory of Japan from 1992 to 2005 and 55 active regions observed by SFT and Haleakala Stokes Polarimeter (HSP) at Mees Solar Observatory, University of Hawaii from 1997 to 2000. Two helicity parameters, current helicity density hc and αff coefficient of linear force free field are calculated. From this comparison we conclude: (1) the mean azimuthal angle differences of transverse fields between HR and MTK data are systematic smaller than that between MTK and Mees data; (2) there are 83.8% of hc and 78.1% of αff for 228 active regions observed at HR and MTK agree in sign, and the Pearson linear correlation coefficient between these two data sets is 0.72 for hc and 0.56 for αff. There are 61.8% of hc and 58.2% of αff for 55 active regions observed at MTK and Mees agree in sign, and the Pearson linear correlation coefficient between these two data sets is 0.34 for hc and 0.31 for αff; (3) there is a basic agreement on time variation of helicity parameters in active regions observed at HR, Mees, and MTK. Title: Sequential chromospheric brightenings: The case for chromospheric evaporation Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Hock, Rachel A. Bibcode: 2007AdSpR..39.1781P Altcode: Sequential chromospheric brightenings (SCBs [Balasubramaniam, K.S., Pevtsov, A.A., Neidig, D.F., Cliver, E.W., Thompson, B.J., Young, C.A., Martin, S.F., & Kiplinger, A., 630, 1160, 2005.]) are observed in conjunction with some strong solar flares, prominence eruptions, and coronal mass ejections (CMEs). SCBs are seen as wave-like trains of increased brightening of chromospheric network elements propagating away from the site of eruption (flare/CME). Although network magnetic field usually has mixed polarity, only areas of one (prevailing) polarity are seen as SCBs; there are no brightenings in neighboring network elements of opposite (minor) polarity. This polarity rule, relative timing of SCBs in respect to beginning of flare/CME, and their location in respect to overall topology of each event suggest that SCBs may be caused by high energy particles precipitating from the reconnection site at the tail of CME. In this work we use TRACE, SOHO/MDI, and H-alpha OSPAN data to demonstrate that indeed SCB locations exhibit several properties of chromospheric evaporation. Title: Multi-Line Spectro-Polarimetry of Filaments Authors: Balasubramaniam, K. S.; Sankarasubramanian, K.; Pevtsov, A. A. Bibcode: 2006ASPC..358...68B Altcode: We present a spectro-polarimetric study of magnetic structures supporting quiescent filaments, using the combined DLSP-Phase I and ASP observations. The observations were performed using the spectral lines Fe I 6301.5 Å and 6302.5 Å at the photospheric level, and Mg I 5172.7 Å and H I 6562.8 Å (Hα) at the chromospheric level. Using non-linear, force-free extrapolation models, we reconstruct the 3D magnetic loop-geometry and compare the viability of the magnetic filament dips as the true location of the filaments, as seen in Hα. Title: Plasma Flows in Emerging Sunspots in Pictures Authors: Pevtsov, A.; Lamb, J. B. Bibcode: 2006ASPC..354..249P Altcode: We present pictorial results of our study of plasma flows in fifteen emerging active regions using Dopplergrams, magnetograms, and white light observations from SOHO-MDI. The study focuses on: (1) asymmetric flows between two opposite polarities of the same active region, (2) search for systematic flows in area of active region development prior to flux emergence, and (3) timing between development of the Evershed flow and sunspot penumbra. Asymmetric flows are found in three active regions. In two regions, flows are directed from following to preceding polarity, and in one region material flows from the preceding to the following polarity. We observed no consistent plasma flows at the future location of an active region before its emergence. We describe one case when sunspot penumbra developed before establishing the Evershed flow. Title: An Overview of Existing Algorithms for Resolving the 180° Ambiguity in Vector Magnetic Fields: Quantitative Tests with Synthetic Data Authors: Metcalf, Thomas R.; Leka, K. D.; Barnes, Graham; Lites, Bruce W.; Georgoulis, Manolis K.; Pevtsov, A. A.; Balasubramaniam, K. S.; Gary, G. Allen; Jing, Ju; Li, Jing; Liu, Y.; Wang, H. N.; Abramenko, Valentyna; Yurchyshyn, Vasyl; Moon, Y. -J. Bibcode: 2006SoPh..237..267M Altcode: 2006SoPh..tmp...14M We report here on the present state-of-the-art in algorithms used for resolving the 180° ambiguity in solar vector magnetic field measurements. With present observations and techniques, some assumption must be made about the solar magnetic field in order to resolve this ambiguity. Our focus is the application of numerous existing algorithms to test data for which the correct answer is known. In this context, we compare the algorithms quantitatively and seek to understand where each succeeds, where it fails, and why. We have considered five basic approaches: comparing the observed field to a reference field or direction, minimizing the vertical gradient of the magnetic pressure, minimizing the vertical current density, minimizing some approximation to the total current density, and minimizing some approximation to the field's divergence. Of the automated methods requiring no human intervention, those which minimize the square of the vertical current density in conjunction with an approximation for the vanishing divergence of the magnetic field show the most promise. Title: Number of Bright Points at Low Temperature EIT Data over Entire Soho Mission Authors: Sattarov, I.; Pevtsov, A. A.; Karachik, N. V.; Sherdanov, C. T. Bibcode: 2006ESASP.617E.158S Altcode: 2006soho...17E.158S No abstract at ADS Title: Coronal Heating and Photospheric Turbulence Parameters: Observational Aspects Authors: Abramenko, V. I.; Pevtsov, A. A.; Romano, P. Bibcode: 2006ApJ...646L..81A Altcode: In this study, the soft X-ray luminosity of the solar corona, measured by the Yohkoh spacecraft for 104 well-developed and decaying active regions, is compared to the magnetic field parameters determined from SOHO MDI high-resolution magnetograms. We calculate and compare (1) two area-independent characteristics of the magnetic field: the index (α) of the magnetic power spectrum, E(k)~k-α, and the magnetic energy dissipation rate (ɛ¯/η), which is a proxy for the energy of random footpoint motions induced by turbulent convection in the photosphere and below; and (2) four area-independent parameters of the soft X-ray emission: the area-normalized flux in Yohkoh Al.1 and AlMgMn channels, and the emission measure and temperature of the coronal plasma. Here we report that the area-normalized soft X-ray flux correlates with both the power index α (Pearson correlation coefficient ρ=0.72/Al.1 and 0.73/AlMgMn) and the magnetic energy dissipation rate ɛ¯/η (ρ=0.68/Al.1 and 0.70/AlMgMn). Also, both magnetic parameters are well-correlated with the logarithm of the emission measure (ρ=0.72) and the logarithm of temperature [ρ=0.59/α and 0.63/(ɛ¯/η)]. Our results present strong observational support to those coronal heating models that rely on random footpoint motions as an energy source to heat the corona above active regions. Title: Does Visibility Effect Fully Explain Cycle Variations of Coronal Bright Points? Authors: Sattarov, I.; Pevtsov, A. A.; Karachik, N. V.; Sherdanov, C. T. Bibcode: 2006ESASP.617E...6S Altcode: 2006soho...17E...6S No abstract at ADS Title: Rotation of Solar Corona from Tracking of Coronal Bright Points Authors: Karachik, Nina; Pevtsov, Alexei A.; Sattarov, Isroil Bibcode: 2006ApJ...642..562K Altcode: An automated procedure for identification of coronal bright points is applied to selected EIT images observed at various phases of the solar cycle. The procedure finds about 400 bright points on a single EIT image observed at 195 Å. The positions of the bright points are tracked to study the profile of solar rotation in the solar corona. It is shown that the rotation of coronal bright points closely follows the latitudinal rotation profile of the underlying photospheric magnetic field. It is also demonstrated that coronal features situated at the same heliographic coordinates but different heights in the corona may exhibit different rotation rates. Title: Helicity Measurements from Two Magnetographs Authors: Pevtsov, A. A.; Dun, J. P.; Zhang, H. Bibcode: 2006SoPh..234..203P Altcode: We use 270 pairs of vector magnetograms observed by Haleakala Stokes Polarimeter (HSP) and Solar Magnetic Field Telescope (SMFT) of Huairou Solar Observing Station from 1997 to 2000 to compare current helicity derived by these two instruments. We apply the same approach to both data sets to resolve 180∘ azimuth ambiguity and compute α coefficient of linear force-free field. After careful consideration of various aspects of both data sets, we find that in ≈80% of cases SMFT and HSP data result in the same sign of α, and the Pearson linear correlation coefficient between two data sets is rp = 0.64. Title: On anticorrelation of number Coronal Bright Points with sunspot number during 1996-2005 Authors: Sattarov, I.; Pevtsov, A. A.; Karachik, N. V.; Sherdanov, Ch. T. Bibcode: 2006cosp...36..906S Altcode: 2006cosp.meet..906S X-ray Bright Points XBP were extensively studied using observations from various instruments Golub at all 1979 have found that number of XBP anticorralates with sunspot number and suggested that solar cycle may be characterized as an oscillator in wavenumber space This finding prompted Yoshmura 1983 to suggest the existence of a secondary cycle of magnetic activity running in opposite phase to the sunspot cycle Later however Nakakubo Hara 2000 concluded that the variation in number of XBPs might be visibility effect as the enhanced brightness of corona may hinder identification of dimmer XBPs Sattarov at al 2002 found that while the number of bright points exhibit cyclic variation the number of magnetic bipoles with a particular flux and separation does not change from solar minimum to the aximum Hence Sattarov et al 2002 concluded that cyclic variation in XBP number may be a visibility effect In this work we continue study the properties of coronal bright points CBPs features that include XBPs and bright points in other wavelengths using SOHO EIT 195A data from 1996-2005 We identify CBPs using automatic procedure developed by us Sattarov et al 2005 Karachik et al 2006 and calculate various parameters including heliographic position intensity area and background intensity around each CBP Analyzing this data we found that the latitude-cycle variations of CBPs cannot be completely explained by the visibility effect These irregularities suggest that in addition to the visibility effect the actual number of coronal bright points Title: Sequential Chromospheric Brightenings as Signature of Chromospheric Evaporation Authors: Pevtsov, A.; Balasubramaniam, K. Bibcode: 2006cosp...36.3671P Altcode: 2006cosp.meet.3671P Sequential Chromospheric Brightennings SCBs Balasubramaniam et al 2005 are observed in conjunction with some strong solar flares prominence eruptions and coronal mass ejections CMEs SCBs are seen as wave-like trains of increased brightenning of chromospheric network elements propagating away from the site of eruption flare CME Although network magnetic field usually has mixed polarity only areas of one polarity prevailing or unbalanced field are seen as SCBs there are no brightenings in neighboring network elements of opposite minor polarity This polarity rule relative timing of SCBs in respect to beginning of flare CME and their location in respect to overall topology of each event suggest that SCBs may be caused by high energy particles precipitating from the reconnection site at the tail of CME In this work we use TRACE SOHO MDI and H-alpha ISOON data to demonstrate that indeed SCB locations exhibit several properties of chromospheric evaporation Title: Large scale solar chromospheric eruptive activity - a signature of magnetic reconnection Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Hock, R. A. Bibcode: 2006ilws.conf...65B Altcode: A new class of large-scale solar chromospheric eruptive activity, sequential chromospheric brightenings (SCBs), has been reported by Balasubramaniam et al. (2005). SCBs are chromospheric network points (outside of active regions) that sequentially brighten over a narrow path of chromospheric network points. SCBs appear as single or multiple trains of brightenings, the underlying magnetic poles of each train having the same (negative or positive) polarity. SCBs may be associated with the following phenomena: solar flares, filament eruptions, CMEs, disappearing transequatorial loops, Moreton and EIT waves. We present an understanding of SCBs and their place in respect to these related eruptive phenomena. Title: On anticorrelation of number Coronal Bright Points with sunspot number during 1996-2005 Authors: Sattarov, I.; Pevtsov, A. A.; Karachik, N. V.; Sherdanov, Ch. T. Bibcode: 2006cosp...36..974S Altcode: 2006cosp.meet..974S X-ray Bright Points XBP were extensively studied using observations from various instruments Golub at all 1979 have found that number of XBP anticorralates with sunspot number and suggested that solar cycle may be characterized as an oscillator in wavenumber space This finding prompted Yoshmura 1983 to suggest the existence of a secondary cycle of magnetic activity running in opposite phase to the sunspot cycle Later however Nakakubo Hara 2000 concluded that the variation in number of XBPs might be visibility effect as the enhanced brightness of corona may hinder identification of dimmer XBPs Sattarov at al 2002 found that while the number of bright points exhibit cyclic variation the number of magnetic bipoles with a particular flux and separation does not change from solar minimum to the maximum Hence Sattarov et al 2002 concluded that cyclic variation in XBP number may be a visibility effect In this work we continue study the properties of coronal bright points CBPs features that include XBPs and bright points in other wavelengths using SOHO EIT 195A data from 1996-2005 We identify CBPs using automatic procedure developed by us Sattarov et al 2005 Karachik et al 2006 and calculate various parameters including heliographic position intensity area and background intensity around each CBP Analyzing this data we found that the latitude-cycle variations of CBPs cannot be completely explained by the visibility effect These irregularities suggest that in addition to the isibility effect the actual number of coronal bright points on Title: Case Study of A Sequential Chromospheric Brightening (SCB) Associated with May 6, 2005 event. Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Hock, R. A. Bibcode: 2005AGUFMSH13A0282B Altcode: A sequential chromospheric brightening on May 6, 2005 was accompanied by a long duration event, LDE (16:00 - 23:00 UT). Using data from ISOON/ H-alpha, TRACE (171 A), and SOHO/MDI (magnetograms) missions, we present a detailed sequential study of this event that includes large scale coronal disturbances(TRACE 171 A), ribbon-ed flares (ISOON & TRACE), large scale motion of magnetic fields (SOHO/MDI), filament eruptions (ISOON & TRACE), flares, and post-flare loops (TRACE). This event presents a good example in the continuity of events comprising an LDE. We present a model of the eruptive process of this LDE. Title: Large-scale Structures in Distribution of Coronal Bright Points Authors: Sattarov, I.; Pevtsov, A. A.; Karachik, N. V.; Sattarova, B. J. Bibcode: 2005ASPC..346..363S Altcode: We use an automatic procedure to find coronal bright points (BPs) in EIT 195 Å data observed in 1996 near deep minimum of solar activity. Identifying BPs as bright features with EUV flux above 80 DN/s and diameter about 2.6 -- 58 arcsec, we find about 463±22 BPs per solar disk. We also uncover small intensity fluctuations of diffuse corona surrounding the BPs. The intensity fluctuations correlate with BP brightness: increase in brightness of BPs causes increase in coronal intensity. Title: Large-scale Structures and their Role in Solar Activity Authors: Sankarasubramanian, K.; Penn, M.; Pevtsov, A. Bibcode: 2005ASPC..346.....S Altcode: No abstract at ADS Title: Accumulation of Filament Material at the Boundaries of Supergranular Cells Authors: Pevtsov, A. A.; Neidig, D. Bibcode: 2005ASPC..346..219P Altcode: We use ISOON full disk H-alpha images to study fragmented filaments whose main body consists of non-connected clumps of dark filament material. Fragmented filaments may represent the early evolution of filament development. We describe two filaments that began their formation with a few individual clumps, which later grew and interconnected to form a continuous body typical of a chromospheric filament. We show that there is a tendency for clumps to be situated over the boundaries of supergranular cells. We suggest that this preference in initial accumulation of material above areas of persistent downflows (boundary of supergranules) may be a key in understanding why the chromospheric filaments show a much stronger hemispheric helicity rule than other solar features (e.g. sunspots). Title: Active Longitudes in Distribution of EIT Bright Points Authors: Sattarov, I.; Pevtsov, A. A.; Karachik, N. V.; Sattarova, B. J. Bibcode: 2005ASPC..346..395S Altcode: Using a previously developed automatic procedure for identifying coronal bright points (BPs) in EIT/Fe XII 195 Å data, we study longitudinal and latitudinal distributions of EUV BPs on solar surface near the minimum of the solar activity cycle in 1996. Longitudinal distributions indicate the presence of active longitudes in coronal BPs. Latitudinal distributions are asymmetric relative to the equator and show secondary peaks associated with areas of emerging flux. We find this result as suggestive of two types of coronal BPs: quiet Sun and active Sun BPs. Title: ISOON H-alpha Survey of Sequential Chromospheric Brightenings Authors: Hock, R.; Balasubramaniam, K. S.; Pevtsov, A. A. Bibcode: 2005AGUFMSH13A0281H Altcode: Balasubramaniam et al. (2005, ApJ, 630, 1160) described a new phenomenon, sequential chromospheric brightenings (SCBs), associated with eruption of a transequatorial loop and a CME. We present a detailed survey of SCBs between December 2000 - May 2005. From this survey we have identified 17 SCBs observed during this period. We discuss the relationship between SCBs, and filament eruptions, coronal mass ejections (CME), and flares. The data were drawn from ISOON, SOHO/LASCO, and NOAA/GOES, and RHESSI missions. We find that: all SCBs are accompanied by filament eruption or disappearance; SCBs are more likely to be longer in duration than associated flares; and a large fraction of the SCBs (71%) are associated with CMEs. Title: Sequential Chromospheric Brightenings beneath a Transequatorial Halo Coronal Mass Ejection Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Cliver, E. W.; Thompson, B. J.; Young, C. A.; Martin, S. F.; Kiplinger, A. Bibcode: 2005ApJ...630.1160B Altcode: Analyses of multiwavelength data sets for a solar eruption at ~21:30 UT on 2002 December 19 show evidence for the disappearance of a large-scale, transequatorial coronal loop (TL). In addition, coronal manifestations of the eruption (based on SOHO EIT and LASCO images) include large-scale coronal dimming, flares in each associated active region in the northern and southern hemispheres, and a halo CME. We present detailed observations of the chromospheric aspects of this event based on Hα images obtained with the ISOON telescope. The ISOON images reveal distant flare precursor brightenings, sympathetic flares, and, of most interest herein, four nearly cospatial propagating chromospheric brightenings. The speeds of the propagating disturbances causing these brightenings are 600-800 km s-1. The inferred propagating disturbances have some of the characteristics of Hα and EIT flare waves (e.g., speed, apparent emanation from the flare site, subsequent filament activation). However, they differ from typical Hα chromospheric flare waves (also known as Moreton waves) because of their absence in off-band Hα images, small angular arc of propagation (<30°), and their multiplicity. Three of the four propagating disturbances consist of a series of sequential chromospheric brightenings of network points that suddenly brighten in the area beneath the TL that disappeared earlier. SOHO MDI magnetograms show that the successively brightened points that define the inferred propagating disturbances were exclusively of one polarity, corresponding to the dominant polarity of the affected region. We speculate that the sequential chromospheric brightenings represent footpoints of field lines that extend into the corona, where they are energized in sequence by magnetic reconnection as coronal fields tear away from the chromosphere during the eruption of the transequatorial CME. We report briefly on three other events with similar narrow propagating disturbances that were confined to a single hemisphere. Title: Coronal Bright Points at the Minimum of Sunspot Activity Authors: Pevtsov, A. A.; Sattarov, I.; Karachik, N. V.; Sattarova, B. J. Bibcode: 2005AGUSMSP22A..02P Altcode: We will present the results of our study of coronal bright points (XBPs) using SoHO/EIT data and an automatic identification procedure. The latitude-longitude distribution of XBPs obtained during the period of very low sunspot activity (March-April 1996) is not uniform; it exhibits structures reminiscent of active longitudes and large-scale circular patterns. We also find XBPs associated with emergence of ephemeral active regions. We interpret these results as a possible indication of two types of XBPs that are characteristic of quiet and active Sun. Title: First-Light Instrumentation for the Advanced Technology Solar Telescope Authors: Rimmele, T.; Balasubramaniam, K.; Berger, T.; Elmore, D.; Gary, A.; Keller, C.; Kuhn, J.; Lin, H.; Mickey, D.; Pevtsov, A.; Robinson, B.; Sigwarth, M.; Soccas-Navarro, H. Bibcode: 2005AGUSMSP34A..03R Altcode: The 4m Advanced Technology Solar Telescope (ATST) is the next generation ground based solar telescope. In this paper we provide an overview of the ATST post-focus instrumentation. The majority of ATST instrumentation is located in an instrument Coude lab facility, where a rotating platform provides image de-rotation. A high order adaptive optics system delivers a corrected beam to the Coude lab facility. Alternatively, instruments can be mounted at the Nasmyth focus. For example, instruments for observing the faint corona preferably will be mounted at Nasmyth where maximum throughput is achieved. In addition, the Nasmyth focus has minimum telescope polarization and minimum stray light. We give an overview of the initial set of first generation instruments: the Visible-Light Broadband Imager (VLBI), the Visible Spectro-Polarimeter (ViSP), the Near-IR Spectro-Polarimeter (NIRSP), which includes a coronal module, and the Visible Tunable Filter. We also discuss the unique and efficient approach to the ATST instrumentation, which builds on the use of common components such as detector systems, polarimetry packages and various opto-mechanical components. For example, the science requirement for polarimetric sensitivity (10-5 relative to intensity) and accuracy (5'10-4 relative to intensity) place strong constraints on the polarization analysis and calibration units. Consequently, these systems are provided at the facility level, rather than making it part of the requirement for each instrument. Title: Coronal Magnetography of Solar Active Region 8365 with the SSRT and NoRH Radio Heliographs Authors: Ryabov, B. I.; Maksimov, V. P.; Lesovoi, S. V.; Shibasaki, K.; Nindos, A.; Pevtsov, A. Bibcode: 2005SoPh..226..223R Altcode: Microwave maps of solar active region NOAA 8365 are used to derive the coronal magnetograms of this region. The technique is based on the fact that the circular polarization of a radio source is modified when microwaves pass through the coronal magnetic field transverse to the line of sight. The observations were taken with the Siberian Solar Radio Telescope (SSRT) on October 21 - 23 and with the Nobeyama Radio Heliograph (NoRH) on October 22 - 24, 1998. The known theory of wave mode coupling in quasi-transverse (QT) region is employed to evaluate the coronal magnetograms in the range of 10 - 30 G at the wavelength 5.2 cm and 50 - 110 G at 1.76 cm, taking the product of electron density and the scale of coronal field divergence to be constant of 1018 cm−2. The height of the QT-region is estimated from the force-free field extrapolations as 6.2 × 109 cm for the 20 G and 2.3 × 109 cm for 85 G levels. We find that on large spatial scale, the coronal magnetograms derived from the radio observations show similarity with the magnetic fields extrapolated from the photosphere. Title: On a Cyclic Variation of the Hemispheric Helicity Rule Authors: Pevtsov, A. A.; Hagyard, M. J.; Blehm, Z.; Smith, J. E.; Canfield, R. C.; Sakurai, T.; Hagino, M. Bibcode: 2005HiA....13..140P Altcode: We report the result of a study of magnetic helicity in solar active regions during 1980-2000 (cycles 21-23). Using the vector magnetograms from four different instruments (Haleakala Stokes Polarimeter Marshall Space Flight Center Mitaka Solar Flare Telescope and Okayama Observatory Solar Telescope) we calculated the force-free parameter alpha as in Pevtsov et al. (1995). We use alpha as the proxy for current helicity. For each instrument we computed a gradient dalpha/dL as the linear fit of alpha versus latitude L using annual subsets of data. The hemispheric helicity rule (negative/positive helicity in northern/southern hemisphere) can be expressed in terms of this gradient as dalpha/dL < 0. We find that each instrument exhibits change in sign of this gradient for some years which implies that the hemispheric helicity rule may not hold in some phases of a solar cycle (see Hagino and Sakurai 2002). However we do not see consistency between different instruments in regards to years disobeying the rule. The disagreement may be due to difference in observations and/or insufficient number of magnetograms in some years. We conclude that the present data sets do not allow to make statistically significant inference about possible cyclic variation of the hemispheric helicity rule. Title: Helicity of Magnetic Clouds and Their Associated Active Regions Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.; Lambkin, Keith; Lundberg, Brian J.; Pevtsov, Alexei A. Bibcode: 2005HiA....13..132L Altcode: Magnetic clouds are closely associated with Coronal Mass Ejections (CMEs). Most CMEs are associated with active regions. What is the relationship between the topology of these clouds and the associated active region? For our purposes magnetic clouds can be modeled adequately by a cylindrical force-free magnetic configuration (Lepping 1990). We have modeled the magnetic field topology of 14 magnetic clouds and their associated active regions to determine values of the force-free field parameter for both as well as total currents and fluxes. We find that the number of turns of the magnetic field in the full length of the cloud is typically an order of magnitude greater than the same quantity in the associated active region. This finding compels us to reject models of flux rope formation that do not invoke magnetic reconnection and helicity conservation. Title: Helicity Generation and Signature in Solar Atmosphere Authors: Pevtsov, A. A. Bibcode: 2005HiA....13...89P Altcode: To fully understand the origin evolution and topology of solar magnetic fields one should comprehend their magnetic helicity. Observationally non-zero helicity reveals itself in the patterns of electric currents inside active regions super-/penumbral sunspot whirls the shape of coronal loops and the fine structure of chromospheric filaments. The patterns of helicity are present on different spatial scales ranging from several arc seconds to a size of a solar hemisphere. Some patterns may bear information about deep subphotospheric processes (e.g. dynamo turbulent convection). Other may originate at or near the photosphere. In this talk we will review the observations of magnetic and current helicity on the Sun. We will also discuss the different mechanisms operating at or near the photosphere and we will compare them with the observations. Title: Of Tilt and Twist Authors: Holder, Zachary A.; Canfield, Richard C.; McMullen, Rebecca A.; Howard, Robert F.; Pevtsov, Alexei A. Bibcode: 2005HiA....13..135H Altcode: Using Haleakala Stokes Polarimeter active-region vector magnetograms and Mt. Wilson Observatory full-disk longitudinal magnetograms we measure both the overall twist (using the force-free-field parameter alpha) and tilt of 368 active regions. This dataset clearly shows two well-known phenomena Joy's law and the hemispheric helicity rule as well as a lesser-known twist-tilt relationship which is the point of this work. Those regions that closely follow Joy's law show no twist-tilt relationship as expected if the twist originates from convective buffeting of initially untwisted and unwrithed flux tubes within the convection zone through the Sigma effect. Those regions that strongly depart from Joy's law show significantly larger than average twist and a very strong twist-tilt relationship. These properties suggest that the twist-tilt relationship in these regions is due to kinking of flux tubes that are initially highly twisted but not strongly writhed perhaps as a result of dynamo action. Title: Plasma Flows in Emerging Sunspots Authors: Lamb, J. B.; Pevtsov, A. A. Bibcode: 2004AAS...205.1001L Altcode: 2004BAAS...36.1349L We study plasma flows in emerging active regions on the sun using data from the Michelson Doppler Imager (MDI) instrument on the SOHO satellite. Dopplergrams are compared with magnetograms and full continuum images in an effort to study the relationship between plasma flows and the magnetic and white light development of fifteen emerging active regions. This study focuses on the following flows in emerging active regions: (1) asymmetric flows from one polarity of the active region to the opposite polarity, (2) general trends of plasma flows before and immediately after emergence and (3) the emergence of Evershed flow with respect to penumbral development. The results of this study include (1) asymmetric flows found in three active regions. Two active regions exhibited flows from following to preceding polarity, confirming other observations of asymmetric flows. One active region exhibited a flow from the preceding to following polarity which has previously been theoretically predicted but until now has not been observed. (2) No consistent plasma flows were found before emergence. (3) After emergence, active regions exhibited overall downflows in the area around the region. (4) There also is some possible evidence for penumbra development before Evershed flow. This work was carried out through the National Solar Observatory Research Experiences for Undergraduates (REU) site program, which is co-funded by the Department of Defense in partnership with the National Science Foundation REU Program. Title: On the Role of the Large-Scale Magnetic Reconnection in the Coronal Heating Authors: Pevtsov, A. A.; Kazachenko, M. Bibcode: 2004ESASP.575..241P Altcode: 2004soho...15..241P No abstract at ADS Title: Temporal Variations in the Evershed Flow Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Olmschenk, S. Bibcode: 2004AGUFMSH13A1141B Altcode: We present results of an analysis of the temporal Doppler variations of the Evershed flow. Doppler shifts were calculated from a unique, high-resolution data set of 39 spectral lines, spanning the photosphere and chromosphere. Our results indicate a quasi-periodic structure of the Evershed flow with a typical period between 18-24 minutes in the photosphere and 12-18 minutes in the chromosphere. We discuss the implications of these results for both the siphon flow and the moving flux tube models. Title: On the Tilt and Twist of Solar Active Regions Authors: Holder, Zachary A.; Canfield, Richard C.; McMullen, Rebecca A.; Nandy, Dibyendu; Howard, Robert F.; Pevtsov, Alexei A. Bibcode: 2004ApJ...611.1149H Altcode: Tilt and twist are two measurable characteristics of solar active regions that can give us information about subsurface physical processes associated with the creation and subsequent evolution of magnetic flux tubes inside the Sun. Using Mees Solar Observatory active region vector magnetograms and Mount Wilson Observatory full-disk longitudinal magnetograms, we measure the magnetic twist and tilt angles of 368 bipolar active regions. In addition to two well-known phenomena, Joy's law and the hemispheric helicity rule, this data set also shows a lesser known twist-tilt relationship, which is the focus of this study. We find that those regions that closely follow Joy's law do not show any twist-tilt dependence. The dispersion in tilt angles and the dispersion in twist are also found to be uncorrelated with each other. Both of these results are predicted consequences of convective buffeting of initially untwisted and unwrithed flux tubes through the Σ-effect. However, we find that regions that strongly depart from Joy's law show significantly larger than average twist and very strong twist-tilt dependence-suggesting that the twist-tilt relationship in these regions is due to the kinking of flux tubes that are initially highly twisted, but not strongly writhed. This implies that some mechanism other than the Σ-effect (e.g., the solar dynamo itself or the process of buoyancy instability and flux tube formation) is responsible for imparting the initial twist (at the base of the solar convection zone) to the flux tubes that subsequently become kink-unstable. Title: Statistical Properties of Superpenumbral Whorls around Sunspots Authors: Balasubramaniam, K. S.; Pevtsov, Alexei; Rogers, Joey Bibcode: 2004ApJ...608.1148B Altcode: We study properties of 897 superpenumbral fibrils using Hα Big Bear Solar Observatory (BBSO) and photospheric magnetic field National Solar Observatory/Kitt Peak (NSO/KP) data of 139 sunspots between 2000 July and 2001 April. From this low-resolution data, we find that about one-third of all superpenumbral fibrils begin inside the penumbra. The typical length of fibrils is 2.7 times the sunspot white-light penumbral radius. A majority of the fibrils are curved, i.e., 67% of them exhibit bow-extent/footpoint separation greater than 0.1. Both clockwise and counterclockwise fibrils are typically present within the same superpenumbra. We show that the topology of fibrils is clearly affected by distribution of magnetic fields around the sunspot. Title: Photospheric and Coronal Currents in Solar Active Regions Authors: Burnette, Andrew B.; Canfield, Richard C.; Pevtsov, Alexei A. Bibcode: 2004ApJ...606..565B Altcode: Using photospheric line-of-sight magnetograms from the National Solar Observatory (NSO) Kitt Peak and coronal X-ray images from the Yohkoh Soft X-Ray Telescope (SXT), we have determined the value of the constant α of the linear force-free field model (∇XB=αB) that gives the best visual fit to the overall coronal X-ray structure (αc) of 34 flare-productive active regions of relatively simple bipolar morphology. Vector magnetograms for 24 of these active regions are available from the Haleakala Stokes Polarimeter at Mees Solar Observatory. For each of them, we determine the single best-fit value of α in the photosphere (αp) by three quite different methods and show that these methods give statistically consistent values. By combining this data set with that of the NSO and SXT, we are able to compare for the first time quantitatively and statistically the observed values of α in the photosphere and corona of these regions. We find that the distribution of αp and αc values is fully consistent with the hypothesis that the overall twist density of the magnetic fields of active regions, as measured by the linear force-free field parameter α, is the same in the photosphere and the corona. We therefore conclude that the electric currents that create the nonpotential structure of such solar coronal active regions are of subphotospheric origin and pass without significant modification through the photosphere. Title: Helicity of magnetic clouds and their associated active regions Authors: Leamon, Robert J.; Canfield, Richard C.; Jones, Sarah L.; Lambkin, Keith; Lundberg, Brian J.; Pevtsov, Alexei A. Bibcode: 2004JGRA..109.5106L Altcode: In this work we relate the magnetic and topological parameters of twelve interplanetary magnetic clouds to associated solar active regions. We use a cylindrically symmetric constant-α force-free model to derive field line twist, total current, and total magnetic flux from in situ observations of magnetic clouds. We compare these properties with those of the associated solar active regions, which we infer from solar vector magnetograms. Our comparison of fluxes and currents reveals: (1) the total flux ratios ΦMC/ΦAR tend to be of order unity, (2) the total current ratios IMC/IAR are orders of magnitude smaller, and (3) there is a statistically significant proportionality between them. Our key findings in comparing total twists αL are that (1) the values of (αL)MC are typically an order of magnitude greater than those of (αL)AR and (2) there is no statistically significant sign or amplitude relationship between them. These findings compel us to believe that magnetic clouds associated with active region eruptions are formed by magnetic reconnection between these regions and their larger-scale surroundings, rather than simple eruption of preexisting structures in the corona or chromosphere. Title: Observational Evidence of Magnetic Flux Submergence in Flux Cancellation Sites Authors: Chae, Jongchul; Moon, Yong-Jae; Pevtsov, Alexei A. Bibcode: 2004ApJ...602L..65C Altcode: Using high-resolution vector magnetograms of NOAA Active Region 10043, observed on 2002 July 26 with the Advanced Stokes Polarimeter and low-order adaptive optics system, we studied the magnetic field topology and line-of-sight velocities in two flux cancellation sites. We found that the magnetic field is near horizontal at the place where two opposite polarities cancel each other. In addition, we observed significant downflows of about 1 km s-1 near the polarity reversal line, where the field is horizontal. We interpret these observations as the direct evidence of the magnetic flux submergence of concave-down (Ω-shaped) magnetic loop at the flux cancellation sites. Title: Latitudinal Distribution of the Coronal Bright Points at Solar Minimum and the Rising Phase of Solar Activity Cycle 23 Authors: Sattarov, I.; Pevtsov, A. A.; Karachek, N. V.; Tillaboev, A. M. Bibcode: 2004IAUS..223..665S Altcode: 2005IAUS..223..665S We show that the latitudinal distribution of the coronal bright points (BPs) changes between the solar minimum and the rising phase of solar cycle 23. In 1996, the number of BPs peaks near the disk center. In 1998, the distribution shows bands of increased BPs' number at the ARs' latitudes. Title: Number of Coronal Bright Points in Different Phases of the Solar Activity Cycle Authors: Sattarov, I.; Pevtsov, A. A.; Karachek, N. V.; Sherdanov, Ch. T. Bibcode: 2004IAUS..223..667S Altcode: 2005IAUS..223..667S We present the preliminary results of study of the coronal bright points (BPs) using the SoHO/EIT data. We show that the number of BPs in quiet Sun areas does not vary between 1996 and 1997. In 1998 the BPs number (full disk) increases by about 20%. Title: Transequatorial Connections: Loops or Magnetic Separators? Authors: Pevtsov, Alexei A. Bibcode: 2004IAUS..223..521P Altcode: 2005IAUS..223..521P We provide a brief overview of properties of transequatorial loops (TLs) and show that some TLs fit the description of a loop, while others appear to be the magnetic separators. Title: The Relationship Between X-Ray Radiance and Magnetic Flux Authors: Pevtsov, Alexei A.; Fisher, George H.; Acton, Loren W.; Longcope, Dana W.; Johns-Krull, Christopher M.; Kankelborg, Charles C.; Metcalf, Thomas R. Bibcode: 2003ApJ...598.1387P Altcode: We use soft X-ray and magnetic field observations of the Sun (quiet Sun, X-ray bright points, active regions, and integrated solar disk) and active stars (dwarf and pre-main-sequence) to study the relationship between total unsigned magnetic flux, Φ, and X-ray spectral radiance, LX. We find that Φ and LX exhibit a very nearly linear relationship over 12 orders of magnitude, albeit with significant levels of scatter. This suggests a universal relationship between magnetic flux and the power dissipated through coronal heating. If the relationship can be assumed linear, it is consistent with an average volumetric heating rate Q~B/L, where B is the average field strength along a closed field line and L is its length between footpoints. The Φ-LX relationship also indicates that X-rays provide a useful proxy for the magnetic flux on stars when magnetic measurements are unavailable. Title: Coronal Radio Magnetography of Solar Active Region 8365 Authors: Ryabov, B. I.; Nindos, A.; Shibasaki, K.; Maksimov, V. P.; Lesovoi, S. V.; Pevtsov, A. A. Bibcode: 2003AGUFMSH42B0508R Altcode: Using the microwave radio observations with Siberian Solar Radio Telescope (SSRT) and Nobeyama Radio Heliograph (NoRH) we derived 2D coronal magnetograms of solar active region NOAA 8365. The circular polarization (CP) of radio source is modified, when the radiation passes through the overlying magnetic field transverse to the line-of-sight. This change in CP was used to study the properties of coronal fields. We employed the known theory of wave-mode coupling in quasi-transverse (QT) region to evaluate the distribution of the field strength at the level of transformation of 5.2 cm radiation (SSRT, field strength ∼ 10-30 G) and 1.76 cm (NoRH, ∼ 50-110 G). The magnetic field strength was derived under the assumption N~Lα = 1018 cm-2, where N is electron density and Lα is the scale of coronal field divergence along line-of-sight. The height of QT-region (HQTR) was estimated using force free field extrapolations, HQRT = 6.3 x 109 cm (2.3 x 109 cm) for 20 G (85 G). We then compared the coronal radio magnetograms and the force free field extrapolation of photospheric magnetic field, and we found close similarity between them on large spatial scale. Title: What Is the Role of the Kink Instability in Solar Coronal Eruptions? Authors: Leamon, Robert J.; Canfield, Richard C.; Blehm, Zachary; Pevtsov, Alexei A. Bibcode: 2003ApJ...596L.255L Altcode: We report the results of two simple studies that seek observational evidence that solar coronal loops are unstable to the MHD kink instability above a certain critical value of the total twist. First, we have used Yohkoh soft X-ray telescope image sequences to measure the shapes of 191 X-ray sigmoids and to determine the histories of eruption (evidenced by cusp and arcade signatures) of their associated active regions. We find that the distribution of sigmoid shapes is quite narrow and the frequency of eruption does not depend significantly on shape. Second, we have used Mees Solar Observatory vector magnetograms to estimate the large-scale total twist of active regions in which flare-related signatures of eruption are observed. We find no evidence of eruption for values of large-scale total twist remotely approaching the threshold for the kink instability. Title: Chirality of Chromospheric Filaments Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Rogers, Joey W. Bibcode: 2003ApJ...595..500P Altcode: We use the chromospheric full-disk Hα observations to study the chirality of 2310 filaments from 2000-2001. For each filament, we identify the spine and its barbs and determine the filament chirality as fraction of dextral/sinistral barbs of the total number of barbs. We find that 80.2% (558 out of 696) of quiescent filaments in the northern hemisphere are dextral and 85.5% (633 out of 740) of filaments in southern hemisphere are sinistral, in agreement with the well-known hemispheric helicity rule. Our data also show that the active-region filaments follow the same rule, though the hemispheric dependence is weaker: 74.9% (338 out of 451) of active-region filaments in the northern hemisphere are dextral, and 76.7% (297 out of 387) of filaments in the southern hemisphere are sinistral. We show that quiescent filaments formed on leading and returning arms of the same switchback exhibit the same chirality. We also investigate a possible change in the hemispheric rule with polarity reversal of the polar field, and we find no such change. Title: Helicity Evolution in Emerging Active Regions Authors: Pevtsov, Alexei A.; Maleev, Vasily M.; Longcope, Dana W. Bibcode: 2003ApJ...593.1217P Altcode: We study the evolution of twist and magnetic helicity in the coronal fields of active regions as they emerge. We use multiday sequences of Solar and Heliospheric Observatory Michelson Doppler Interferometer magnetograms to characterize the region's emergence. We quantify the overall twist in the coronal field, α, by matching a linear force-free field to bright coronal structures in EUV images. At the beginning of emergence, all regions studied have α~=0. As the active region grows, α increases and reaches a plateau within approximately 1 day of emergence. The inferred helicity transport rate is larger than differential rotation could produce. Following the 2000 work of Longcope & Welsch, we develop a model for the injection of helicity into the corona by the emergence of a twisted flux tube. This model predicts a ramp-up period of approximately 1 day. The observed time history α(t) is fitted by this model assuming reasonable values for the subphotospheric Alfvén speed. The implication is that helicity is carried by twisted flux tubes rising from the convection zone and transported across the photosphere by spinning of the poles driven by magnetic torque. Title: Chirality of Chromospheric Filaments Authors: Pevtsov, A. A.; Balasubramaniam, K. S.; Rogers, J. W. Bibcode: 2003SPD....34.0709P Altcode: 2003BAAS...35..821P We use the chromospheric full disk Hα observations to study chirality (sign of helicity) of 2310 filaments from 2000--2001. For each filament we identify the spine and its barbs and determine the filament chirality as fraction of dextral/sinistral barbs of total number of barbs. We find that 80.2% (558 out of 696) of quiescent filaments in northern hemisphere are dextral, and 85.5% (633 out of 740) of filaments in southern hemisphere are sinistral, in agreement with well known hemispheric helicity rule. Our data also show that the active region filaments follow the same rule, though the hemispheric dependence is weaker; 74.9% (338 out of 451) of active region filaments in northern hemisphere are dextral, and 76.7% (297 out of 387) of filaments in southern hemisphere are sinistral. We show that quiescent filaments formed on leading and returning arms of the same switch-back exhibit the same chirality. We also investigate a possible change in the hemispheric rule with polarity reversal of the polar field and we find no such change. Title: Transequatorial Loops: General Statistics Authors: Pevtsov, A. A. Bibcode: 2003SPD....34.1001P Altcode: 2003BAAS...35..825P Transequatorial loops (TLs), -- coronal structures connecting magnetic fields in opposite hemispheres -- were first found in Skylab data, and later studied in more detail using Yohkoh SXT images. TLs are most clearly found in a few MK data (including EIT284Å). They may connect quiet Sun and/or active region areas in opposite hemispheres. In some cases, TLs may develop shortly after emergence of active region magnetic field, but sometimes they may be present before the active region emerges. Helicity of connected areas appears to play more important role that the separation between the regions. In most cases interconnected regions have the same sign of helicity. Often, TLs may connect two regions of same helicity that are far apart (> 70o) and be absent between much closer regions (< 20o) whose helicity is opposite to each other. There is an indication that TLs may repeatedly appear at certain longitudes, similar to complexes of activity.

In this talk, I will review the observational properties of transequatorial loops and the corresponding magnetic fields. Title: Building an On-line Catalog of Correlated Solar Prominence and Sigmoid Images Authors: Merriot, I. V.; Pevtsov, A.; Martens, P. Bibcode: 2003SPD....34.0310M Altcode: 2003BAAS...35R.809M Predicting solar weather is a complex endeavor. The correlation between X-ray sigmoids and coronal mass ejections (CMEs) has been established but the role of the prominence in association with the sigmoid and CME is not yet clear. This study catalogs the correlation between prominence behavior and sigmoids --before and after-- a CME takes place.

CME, sigmoid and filament occurrences were correlated using the Yashiro online catalog (SOHO), the SXT sigmoid catalog (Yohkoh) and archived H-alpha film from the flare patrol telscope (NSO/SP). When correlations were found, the H-alpha full disk images were digitized to embrace time periods of 2-3 hours before and after the CME event where changes in filament were notable. The culmination of this study will be a web-based catalog of data in text and images showing filament dynamics when sigmoids leading to CMEs are present.

This study is funded, in part, by the Murdoch Foundation. Title: Signatures of Large Scale Coronal Eruptive Activity, Associated Flares, and Propagating Chromospheric Disturbances Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Cliver, E. W.; Young, C. A.; Martin, S. F.; Kiplinger, A. L. Bibcode: 2003SPD....34.0505B Altcode: 2003BAAS...35..814B Analyses of multi-wavelength data sets on 2002 December 19 at approximately 2150 UT show evidence of a large-scale, transequatorial coronal eruption associated with simultaneous flares in active regions in both hemispheres. The coronal manifestations (based on EIT, LASCO, and TRACE images) include a large coronal dimming, an opening/restructuring of magnetic fields, the formation of a transient coronal hole, and a halo CME. In the chromosphere, ISOON H-alpha images show distant flare precursor brightenings and several sympathetic flares. Originating near the main flare is a rapidly propagating (800 km/s), narrowly channeled disturbance detectable as a sequential brightening of numerous pre-existing points in the H-alpha chromospheric network. This disturbance is not a chromospheric Moreton wave, but it does produce a temporary activation of a transequatorial filament. This filament does not erupt nor do any other filaments in the vicinity. MDI magnetograms show that the brightened network points are all of the same polarity (the dominant polarity among the points in the disturbance's path), suggesting that the affected field lines extend into the corona where they are energized in sequence as the eruption tears away.

Three other similar eruptive events (non-transequatorial) that we studied, while they are less impressive, show most of the same phenomena including distant sympathetic flares and a propagating disturbance showing close adherence to the monopolarity rule. Two of these events do include filament eruptions near the main flare. We conclude that the observations of these four events are consistent with large scale coronal eruptive activity that triggers nearly simultaneous surface activity of various forms separated by distances on the same scale as the coronal structures themselves. A filament eruption at the main flare site appears not to be a necessity in this type of eruptive activity. Title: On a Cyclic Variation of the Hemispheric Helicity Rule. Authors: Pevtsov, Alexei A.; Hagyard, Mona J.; Blehm, Zachary; Smith, James E.; Canfield, Richard C.; Sakurai, Takashi; Hagino, Masaoki Bibcode: 2003IAUJD...3E..35P Altcode: We report the result of a study of magnetic helicity in solar active regions during 1980-2000 (cycles 21-23). Using the vector magnetograms from four different instruments (Haleakala Stokes Polarimeter Marshall Space Flight Center Mitaka Solar Flare Telescope and Okayama Observatory Solar Telescope) we calculated the force-free parameter alpha as in Pevtsov et al. (1995). We use alpha as the proxy for current helicity. For each instrument we computed a gradient dalpha/dL as the linear fit of alpha versus latitude L using annual subsets of data. The hemispheric helicity rule (negative/positive helicity in northern/southern hemisphere) can be expressed in terms of this gradient as dalpha/dL < 0. We find that each instrument exhibits change in sign of this gradient for some years which implies that the hemispheric helicity rule may not hold in some phases of a solar cycle (see Hagino and Sakurai 2002). However we do not see consistency between different instruments in regards to years disobeying the rule. The disagreement may be due to difference in observations and/or insufficient number of magnetograms in some years. We conclude that the present data sets do not allow to make statistically significant inference about possible cyclic variation of the hemispheric helicity rule. Title: Vorticity patterns of sunspot H α whirls Authors: Pevtsov, A. A.; Balasubramaniam, K. S.; Rogers, W. J. Bibcode: 2003AdSpR..32.1905P Altcode: We study vorticity patterns of 897 superpenumbral filaments (in 142 sunspots) using Hα (BBSO) observations from July 2000 - April 2001. A majority (69%) of filaments show noticeable curvature in clockwise (CW) or counter-clockwise (CCW) sense. 73% of all sunspots contain both CW and CCW filaments in their superpenumbrae. Only 27% of sunspots have all their superpenumbral filaments twisted in the same direction. The average sunspot vorticity exhibits well-known hemispheric preference, but the dependence is weaker than in the previous studies: 34 (54%) out of 63 sunspots in the northern hemisphere exhibit CCW pattern of superpenumbral whirls, and 45 (69%) of 65 sunspots in the southern hemisphere show CW pattern. We suggest that the local distribution of magnetic fields around sunspots may affect the curvature of superpenumbral filaments and, hence, weaken the hemispheric helicity rule. Title: Statistical Study of X-ray and EUV Bright Points Authors: Sattarov, I.; Pevtsov, A. A.; Begimqulov, U.; Sherdonov, C.; Saidalieva, M. Bibcode: 2003ASPC..286..393S Altcode: 2003ctmf.conf..393S No abstract at ADS Title: Preface Authors: Buechner, Joerg; Pevtsov, Alexei A. Bibcode: 2003AdSpR..32.1817B Altcode: No abstract at ADS Title: Helicity transport and generation in the solar convection zone Authors: Longcope, D. W.; Pevtsov, A. A. Bibcode: 2003AdSpR..32.1845L Altcode: Magnetic helicity provides a theoretical tool for characterizing the solar dynamo and the evolution of the coronal field. The magnetic helicity may be inferred from several types of observation including vector magnetograms of the photospheric magnetic fields. The helicity of an active region reflects, to some degree, the twist in the magnetic field below it. Photospheric observations reveal a tendency for left-handed chirality in the Northern hemisphere, although one-quarter to one-third of the active regions twist in the opposite sense. This means that coronal magnetic field has negative helicity in the North. Sub-photospheric fields will have left-handed twist in the North, although the net helicity also depends on the writhe of the flux tube axes. We show that buffeting by turbulence; the so-called Σ-effect, can explain the handedness and level of intrinsic variation of observed twist. This mechanism does not generate helicity, rather it produces twist and writhe of opposite signs. In this scenario, helicity of one sign propagates into the corona, while opposing helicity propagates downward in the form of torsional Alfvén waves. Title: Magnetic twist and writhe of active regions. On the origin of deformed flux tubes Authors: López Fuentes, M. C.; Démoulin, P.; Mandrini, C. H.; Pevtsov, A. A.; van Driel-Gesztelyi, L. Bibcode: 2003A&A...397..305L Altcode: 2014arXiv1411.5626L We study the long term evolution of a set of 22 bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. We first show that differential rotation is not at the origin of this large change in the tilt angle. A possible origin of this distortion is the nonlinear development of a kink-instability at the base of the convective zone; this would imply the formation of a non-planar flux tube which, while emerging across the photosphere, would show a rotation of its photospheric polarities as observed. A characteristic of the flux tubes deformed by this mechanism is that their magnetic twist and writhe should have the same sign. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the flux tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 35% of the 20 cases for which the sign of the twist can be unambiguously determined. Since at most only a fraction of the tilt evolution can be explained by this process, we discuss the role that other mechanisms may play in the inferred deformation. We find that 36% of the 22 cases may result from the action of the Coriolis force as the flux tube travels through the convection zone. Furthermore, because several bipoles overpass in their rotation the mean toroidal (East-West) direction or rotate away from it, we propose that a possible explanation for the deformation of all these flux tubes may lie in the interaction with large-scale vortical motions of the plasma in the convection zone, including also photospheric or shallow sub-photospheric large scale flows. Title: Current Theoretical Models and Future High Resolution Solar Observations: Preparing for ATST Authors: Pevtsov, Alexei A.; Uitenbroek, Han Bibcode: 2003ASPC..286.....P Altcode: 2003ctmf.conf.....P No abstract at ADS Title: Helicity Generation and Signature in the Solar Atmosphere Authors: Pevtsov, Alexei A. Bibcode: 2003IAUJD...3E..21P Altcode: To fully understand the origin evolution and topology of solar magnetic fields one should comprehend their magnetic helicity. Observationally non-zero helicity reveals itself in the patterns of electric currents inside active regions super-/penumbral sunspot whirls the shape of coronal loops and the fine structure of chromospheric filaments. The patterns of helicity are present on different spatial scales ranging from several arc seconds to a size of a solar hemisphere. Some patterns may bear information about deep subphotospheric processes (e.g. dynamo turbulent convection). Other may originate at or near the photosphere. In this talk we will review the observations of magnetic and current helicity on the Sun. We will also discuss the different mechanisms operating at or near the photosphere and we will compare them with the observations. Title: Of Twist and Tilt Authors: Holder, Zachary A.; Canfield, Richard C.; McMullen, Rebecca A.; Howard, Robert F.; Pevtsov, Alexei A. Bibcode: 2003IAUJD...3E..27H Altcode: Using Haleakala Stokes Polarimeter active-region vector magnetograms and Mt. Wilson Observatory full-disk longitudinal magnetograms we measure both the overall twist (using the force-free-field parameter alpha) and tilt of 368 active regions. This dataset clearly shows two well-known phenomena Joy's law and the hemispheric helicity rule as well as a lesser-known twist-tilt relationship which is the point of this work. Those regions that closely follow Joy's law show no twist-tilt relationship as expected if the twist originates from convective buffeting of initially untwisted and unwrithed flux tubes within the convection zone through the Sigma effect. Those regions that strongly depart from Joy's law show significantly larger than average twist and a very strong twist-tilt relationship. These properties suggest that the twist-tilt relationship in these regions is due to kinking of flux tubes that are initially highly twisted but not strongly writhed perhaps as a result of dynamo action Title: Helicity patterns on the sun Authors: Pevtsov, A. A.; Balasubramaniam, K. S. Bibcode: 2003AdSpR..32.1867P Altcode: Solar magnetic fields exhibit hemispheric preference for negative (positive) helicity in northern (southern) hemisphere. The hemispheric helicity rule, however, is not very strong, — the patterns of mixed helicity were observed at different spatial scales in each hemisphere. Helicity patterns on scales larger than the size of typical active region were observed in distribution of active regions with abnormal (for a give hemisphere) helicity, in large-scale photospheric magnetic fields and coronal flux systems. We review the observations of large-scale patterns of helicity in solar atmosphere and their possible relationship with (sub-)photospheric processes. Title: Calculation of Magnetic Helicity in a Force-Free Field Authors: Updike, A. C.; Pevtsov, A. Bibcode: 2002AAS...201.8306U Altcode: 2002BAAS...34.1242U One of the goals of solar physics is to understand the solar dynamo. By studying the nature of magnetic helicity, we are studying the solar magnetic field driven by the dynamo. We used chromospheric magnetographs in the Ca II line (8543 Å) and EIT images in the Fe XII line (195 Å) to determine the degree of twist in the magnetic field. Using this degree of twist and the known magnetic energy for a given active region, we were able to measure the magnetic helicity in this force-free region. Over a period of three years (August 1996 to November 1998), we studied 37 active regions. We found a 73% hemispheric preference in the sign of the helicity - in the northern hemisphere, 70% of the active regions exhibited negative helicity; in the southern hemisphere, 76.5% of the active regions exhibited positive helicity. Our observations agree with earlier studies of the sign of helicity, which used vector magnetograms and studies of quiescent filiments. Title: Current Helicity of Emerging Active Regions Authors: Pevtsov, A. Bibcode: 2002AGUFMSH52A0466P Altcode: We employ the SOHO MDI magnetograms and EIT images to study evolution of current helicity of solar active regions during early stages of their emergence. Using longitudinal magnetograms we compute linear force-free fields ∇ x B = α B and compare extrapolated field lines with bright coronal structures to constrain the value of α. At the beginning of emergence all studied regions have small α ~eq 0. As active region grows, α gradually increases and reaches a "plateau" within approximately one day of emergence. Using change in separation between negative and positive fluxes, we divide regions on "slow" and "rapid" emergence. Three regions show "slow" (> 1 day) emergence. For these regions α increases faster than the separation. In two "rapid" (< 1 day) emerging regions α grows slower that the separation. This observed evolution of current helicity is in agreement with Longcope and Welsch (2000) model of emergence of subphotospheric twisted flux rope into the corona. škip 0.5 truecm V. Maleev is NSO 2002 Summer Research Assistant from St. Petersburg State University, Russia Title: On the origin of peculiar active regions Authors: Mandrini, C. H.; López Fuentes, M. C.; Démoulin, P.; van Driel-Gesztelyi, L.; Pevtsov, A. A. Bibcode: 2002ESASP.505..121M Altcode: 2002solm.conf..121M; 2002IAUCo.188..121M We study the long term evolution of a set of bipolar active regions (ARs) in which the main photospheric polarities are seen to rotate one around the other during several solar rotations. After showing that differential rotation cannot produce this large change in the tilt angle, we interpret this peculiar evolution as being the result of the emergence of magnetic flux tubes that are distorted with respect to the classical Ω-loop shape. A possible origin of this distortion is the nonlinear development of a kink-instability. Flux tubes deformed by this mechanism must have the same sign of twist and writhe. From the observed evolution of the tilt of the bipoles, we derive the sign of the writhe of the tube forming each AR; while we compute the sign of the twist from transverse field measurements. Comparing the handedness of the magnetic twist and writhe, we find that the presence of kink-unstable flux tubes is coherent with no more than 32% of the studied cases; so, a small fraction of these peculiar ARs can be explained by this process. Then we discuss the role that other mechanisms may play inducing the inferred deformation, such as the Coriolis force or external rotational motions of the plasma as the tube ascends in the convection zone. Title: Properties of magnetic clouds and geomagnetic storms associated with eruption of coronal sigmoids Authors: Leamon, Robert J.; Canfield, Richard C.; Pevtsov, Alexei A. Bibcode: 2002JGRA..107.1234L Altcode: We study 46 solar coronal eruptions associated with sigmoids seen in images from the Yohkoh Soft X-ray Telescope (SXT). We relate the properties of the sigmoids to in situ measurements at 1 AU and geomagnetic storms. Our primary result is that erupting sigmoids tend to produce geoeffective magnetic clouds (MCs): 85% of the erupting sigmoidal structures studied spawned at least a "moderate" (|Dst| ≥ 50 nT) geomagnetic storm. A collateral result is that MCs associated with sigmoids do not show the same solar-terrestrial correlations as those associated with filaments and, as such, form a distinct class of events. First, rather than reversing with the global solar dipole (at solar maximum), the leading field in MCs weakly (2:1) shows a solar cycle (Hale polarity) based correlation (reversing at solar minimum). Second, whereas the handedness of MCs associated with filament eruptions is strongly (95%) related to their launch hemisphere, that of MCs associated with sigmoid eruptions is only weakly (∼70%) so related. Finally, we are unaware of any model of the magnetic fields of sigmoids and their eruption that gives a useful prediction of the leading field orientation of their associated MC. Title: The Twist and Tilt of Active Region Magnetic Fields Authors: Holder, Z. A.; McMullen, R. A.; Canfield, R. C.; Howard, R. F.; Pevtsov, A. A. Bibcode: 2002AAS...200.0305H Altcode: 2002BAAS...34..642H We combine two large datasets to study the formation of the overall twist that is present in solar active-region magnetic fields. For purposes of discussion, we adopt a simplified model in which the magnetic flux bundles that form active regions start as axisymmetric toroids, without intrinsic twist, and rise in Ω -shaped loops through the convection zone, acquiring writhe through the effect of the Coriolis force on the large-scale flows within them, as well as buffeting by turbulent convection. The tilt of active regions with respect to the equator is an observable manifestation of such writhe, at photospheric levels. Owing to magnetic helicity conservation, we expect this tilt to be related to twist of the fields of these same regions. Using Mees Solar Observatory active-region vector magnetograms and Mount Wilson Observatory full-disk longitudinal magnetograms, we have measured both the tilt (Mount Wilson) and twist (Mees) of their magnetic fields, on active-region scales. This dataset clearly shows two well-known phenomena, Joy's law and the hemispheric handedness rule. In this paper we present the relationship between twist and tilt and estimate the extent to which that relationship is due to a mutual dependence of tilt and twist on latitude. We then compare our observational results to the simplified model. Title: Comparison of Helicity Proxies Observed by Haleakala Stokes Polarimeter and Huairou Solar Observing Station Vector Magnetograph Authors: Pevtsov, A. A.; Dun, J. P.; Zhang, H. Bibcode: 2002AAS...200.0304P Altcode: 2002BAAS...34..642P We conduct detailed comparison of the current helicity measurements derived using observations from two vector magnetographs - Haleakala Stokes Polarimeter (HSP) at Mees Solar Observatory, and Solar Magnetic Fields Telescope (SMFT) at Huairou Solar Observing Station. The data, -- 269 pairs of vector magnetograms -- are observed in 1997-2000. We apply the same procedure to both data sets to resolve 180\arcdeg\ azimuth ambiguity and compute the linear force free field coefficient α . We find that in 205 (76%) of 269 cases the SMFT and HSP data show the same sign of α . Remaining 64 (24%) magnetograms that exhibit opposite sign of helicity in two instruments can be explained by several reasons including incorrect heliographic coordinates of active regions, lack of persistence in polarimetric measurements, spatial misalignment between Stokes I, Q, U and V maps, difference in noise level and active regions evolution. Title: Active-Region Filaments and X-ray Sigmoids Authors: Pevtsov, Alexei A. Bibcode: 2002SoPh..207..111P Altcode: We use Yohkoh soft X-ray telescope data and Hα full-disk observations to study the evolution of chromospheric filaments and coronal sigmoids in 6 active regions in association with coronal mass ejections (CMEs). In two cases, CMEs are directly observed by the SOHO/LASCO C2 coronagraph. In four cases, other observations (magnetic clouds, geomagnetic storms, sigmoid-arcade evolution) are used as CME indicators. Prior to eruption, each active region shows a bright coronal sigmoidal loop and underlying Hα filament. The sigmoid activates, erupts and gets replaced by a cusp, or an arcade. In contrast, the Hα filament shows no significant changes in association with sigmoid eruption and CME. We explain these observations in a framework of the classical two-ribbon flare model. Title: What is the role of the kink instability in eruption of X-ray sigmoids? Authors: Leamon, R.; Canfield, R.; Blehm, Z.; Pevtsov, A. Bibcode: 2002AGUSMSH32D..03L Altcode: Observers see ample evidence of helical structures in erupting solar filaments, X-ray sigmoids and CMEs. It has been argued that the total amount of twist in a given loop is a factor in its MHD stability [Priest, 1984]. A simple model illustrates this point. Consider a cylindrical force-free magnetic field with constant α = T /L, where L is the length of the tube and T is the total twist contained within it. The tube is stable to the MHD kink instability for total twist below a critical value Tc ~ 2 π . Rust and Kumar [1996] compared the shape of 49 transient, bright sigmoid structures to the signature of a helically kinked flux rope. From a study of the aspect ratios of these transient sigmoid brightenings, they inferred that the cause of CMEs is the eruption of an unstable, kinked magnetic field. We have analyzed 155 X-ray sigmoids in the the Yohkoh SXT data, measuring the angle γ at which the sigmoid crosses its central axis and the length of the sigmoid along that axis (which is not identical to L, but is closely related to it). In a simple 2D force-free analysis, Pevtsov et al. [1997] showed that α = ( π / L ) sin γ , implying that sin γ is a measure of the total twist T. By simple visual inspection of the Yohkoh SXT movies, we have identified well-known signatures of eruption, i.e., X-ray cusps and arcades. We find no relationship between the frequency of occurrence of such signatures of eruption and sin γ . {Pevtsov, A. A.}, {Canfield, R. C.}, and {McClymont, A. N.}, Astrophys J., 481, 973, 1997. {Priest, E. R.}, {Solar Magneto-Hydrodynamics}, {Reidel: Dordrecht}, {1984}. {Rust, D. M.}, and {Kumar, A.}, Astrophys J., 464, L199, 1996. Title: What is the role of the kink instability in eruption of X-ray sigmoids? Authors: Canfield, R. C.; Leamon, R. J.; Blehm, Z.; Pevtsov, A. A. Bibcode: 2002AAS...200.2001C Altcode: 2002BAAS...34..672C Observers see ample evidence of helical structures in erupting solar filaments, X-ray sigmoids and CMEs. It has been argued that the total amount of twist in a given loop is a factor in its MHD stability [Priest, 1984]. A simple model illustrates this point. Consider a cylindrical force-free magnetic field with constant α = T /L, where L is the length of the tube and T is the total twist contained within it. The tube is stable to the MHD kink instability for total twist below a critical value Tc ~ 2 π . Rust and Kumar [1996] compared the shape of 49 transient, bright sigmoid structures to the signature of a helically kinked flux rope. From a study of the aspect ratios of these transient sigmoid brightenings, they inferred that the cause of CMEs is the eruption of an unstable, kinked magnetic field. We have analyzed 191 X-ray sigmoids in the the Yohkoh SXT data, measuring the angle γ at which the sigmoid crosses its central axis and the length of the sigmoid along that axis (which is not identical to L, but is closely related to it). In a simple 2D force-free analysis, Pevtsov et al. [1997] showed that α = ( π / L ) sin γ , implying that sin γ is a measure of the total twist T. By simple visual inspection of the Yohkoh SXT movies, we have identified well-known signatures of eruption, i.e., X-ray cusps and arcades. We find no relationship between the frequency of occurrence of such signatures of eruption and sin γ . Title: X-Ray Bright Points and Photospheric Bipoles during Cycles 22 and 23 Authors: Sattarov, Isroil; Pevtsov, Alexei A.; Hojaev, Alisher S.; Sherdonov, C. T. Bibcode: 2002ApJ...564.1042S Altcode: We use the Yohkoh soft X-ray telescope (SXT) full-disk images made from 1993 to 2000 to manually identify X-ray bright points (XBPs). We also employ the National Solar Observatory (Kitt Peak) full-disk longitudinal magnetograms made between 1992 April and 2001 April and an automatic procedure to identify photospheric bipoles whose magnetic field strength is above 20 G, with a pole size (cross-section) between 5" and 55.2", and with pole separation between 5.5" and 48.3". We use these data to study statistical properties of XBPs and photospheric bipoles during the declining phase of solar cycle 22 and the rising phase of cycle 23. The XBP number follows well-known anti-cycle variation. The average number of XBPs (~10 per disk image) remained approximately the same from 1993 to 1994. Beginning in 1995 it grew, reached a maximum around 1996 December (~50 XBPs per image), and then dropped back to pre-1995 levels in 1998. By contrast, the average number of photospheric bipoles remained approximately the same (~250 per disk image) between 1992 and 2001, despite sunspot activity changes from high (1992, cycle 22) to low (1996, solar minimum) and a return to high activity again in 2000 (solar maximum, cycle 23). Since we expect that a fraction of photospheric bipoles associated with X-ray bright points is independent of solar activity, we see this as a clear indication that the anti-cycle variation of XBP numbers is not real. Most likely, the variation in XBP numbers is the result of a change in the background brightness of the quiet-Sun corona, which is affected by the presence of active regions. On the other hand, annual latitudinal histograms of XBPs show an excess of coronal bright points at active region latitudes, contrary to the effect of changing background brightness. Photospheric bipoles show no enhancement of their distribution at active latitudes. We consider two alternative explanations for this inconsistency. Title: Solar Cycle Dependency of X-Ray Bright Points and Photospheric Bipoles Authors: Sattarov, I.; Pevtsov, A. A.; Hojaev, A. S.; Sherdonov, C. T. Bibcode: 2002mwoc.conf...97S Altcode: Using daily Yohkoh SXT full disk images from 1991-2000 we manually identify X-ray bright points (XBPs). We also employ the NSO/KP full disk magnetograms from April 1992-June 2000 to identify the photospheric bipoles with particular magnetic flux and poles separation. We use these data to study statistical properties of XBPs and photospheric bipoles during declining phase of cycle 22 and rising phase of cycle 23. The number of X-ray bright points follows well-known anti-cycle variation, reaching a maximum in 1996 (sunspot minimum). By contrast, the averaged number of photospheric bipoles remains approximately the same during 1992-2000. We see this inconsistency between X-ray and magnetic data as clear indication that anti-cycle variation of XBP number is apparent, not real effect. Title: Inferring the Writhe of Emerging Flux Tubes from the Evolution of the Orientation of Bipole Axes Authors: López Fuentes, M. C.; Mandrini, C. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Pevtsov, A. Bibcode: 2002RMxAC..14..108L Altcode: No abstract at ADS Title: Property and evolution of EUV and X-ray bright points in coronal holes Authors: Sattarov, I.; Pevtsov, A.; Hojaev, A.; Begimqulov, U.; Saydalieva, M.; Sherdonov, C. Bibcode: 2002cosp...34E1156S Altcode: 2002cosp.meetE1156S It has been shown (e.g, Sattarov et al. 2002, ApJ, 564, 1042) that solar cycle variation of number of X-ray bright points (XBPs) can be caused by the visibility effect, i.e., the increased background due to scattering from bright active regions alters identification of XBPs. In contrast, the number of photospheric bipoles - the magnetic counterparts of bright points - is independent of solar cycle. On the other hand, several previous studies reported enhanced density of XBPs in coronal holes. It has also been shown that there is positive correlation between XBP number in coronal holes and solar wind density. We study magnetic and thermal properties, location and motions of EUV and X-ray bright points in coronal holes using observations from SOHO EIT (171, 195 and 304 A) and Yohkoh SXT. Title: Helicity patterns on the Sun Authors: Pevtsov, A. Bibcode: 2002cosp...34E3178P Altcode: 2002cosp.meetE3178P Solar magnetic fields exhibit hemispheric preference for negative (pos- itive) helicity in northern (southern) hemisphere. The hemispheric he- licity rule, however, is not very strong, - the patterns of opposite sign helicity were observed on different spatial scales in each hemisphere. For instance, many individual sunspots exhibit patches of opposite he- licity inside the single polarity field. There are also helicity patterns on scales larger than the size of typical active region. Such patterns were observed in distribution of active regions with abnormal (for a give hemisphere) helicity, in large-scale photospheric magnetic fields and coronal flux systems. We will review the observations of large-scale pat- terns of helicity in solar atmosphere and their possible relationship with (sub-)photospheric processes. The emphasis will be on large-scale pho- tospheric magnetic field and solar corona. Title: Property and evolution of EUV and X-ray bright points in coronal holes Authors: Sattarov, I.; Pevtsov, A.; Hojaev, A.; Begimqulov, U.; Saydalieva, M.; Sherdonov, C. Bibcode: 2002cosp...34E1152S Altcode: 2002cosp.meetE1152S It has been shown (e.g, Sattarov et al. 2002, ApJ, 564, 1042) that solar cycle variation of number of X-ray bright points (XBPs) can be caused by the visibility effect, i.e., the increased background due to scattering from bright active regions alters identification of XBPs. In contrast, the number of photospheric bipoles - the magnetic counterparts of bright points - is independent of solar cycle. On the other hand, several previous studies reported enhanced density of XBPs in coronal holes. It has also been shown that there is positive correlation between XBP number in coronal holes and solar wind density. We study magnetic and thermal properties, location and motions of EUV and X-ray bright points in coronal holes using observations from SOHO EIT (171, 195 and 304 A) and Yohkoh SXT. Title: Vorticity patterns of sunspot H-alpha whirls Authors: Pevtsov, A.; Balasubramaniam, K.; Rogers, J. Bibcode: 2002cosp...34E1105P Altcode: 2002cosp.meetE1105P We study vorticity patterns of 1003 superpenumbral filaments using H (BBSO) data of 145 sunspots observed from July 2000 - April 2001. A majority (67%) of filaments show noticeable curvature in clockwise (CW) or counter-clockwise (CCW) sense. The 75% of all sunspots contain both CW and CCW filaments in their superpenumbrae. Only 25% of sunspots have all their superpenumbral filaments twisted in the same direction. The average sunspot vorticity exhibits well known hemispheric preference, but the dependence is weaker than in previous studies. The 42 (58%) out of 73 sunspots in the northern hemisphere exhibit CCW pattern of superpenumbral whirls. The 43 (61%) of 70 sunspots in the southern hemisphere show CW pattern. The weak hemispheric asymmetry suggests that the mechanisms with strong hemispheric dependency (e.g., Coriolis force, solar differential rotation) may not play a dominant role in the hemispheric chirality (helicity) rule. Mr. J. Rogers was supported by the 2001 NSF/RET Program at NSO/SP. Title: Property and evolution of EUV and X-ray bright points in coronal holes Authors: Sattarov, I.; Pevtsov, A.; Hojaev, A.; Begimqulov, U.; Saydalieva, M.; Sherdonov, C. Bibcode: 2002cosp...34E1155S Altcode: 2002cosp.meetE1155S It has been shown (e.g, Sattarov et al. 2002, ApJ, 564, 1042) that solar cycle variation of number of X-ray bright points (XBPs) can be caused by the visibility effect, i.e., the increased background due to scattering from bright active regions alters identification of XBPs. In contrast, the number of photospheric bipoles - the magnetic counterparts of bright points - is independent of solar cycle. On the other hand, several previous studies reported enhanced density of XBPs in coronal holes. It has also been shown that there is positive correlation between XBP number in coronal holes and solar wind density. We study magnetic and thermal properties, location and motions of EUV and X-ray bright points in coronal holes using observations from SOHO EIT (171, 195 and 304 A) and Yohkoh SXT. Title: Property and evolution of EUV and X-ray bright points in coronal holes Authors: Sattarov, I.; Pevtsov, A.; Hojaev, A.; Begimqulov, U.; Saydalieva, M.; Sherdonov, C. Bibcode: 2002cosp...34E1154S Altcode: 2002cosp.meetE1154S It has been shown (e.g, Sattarov et al. 2002, ApJ, 564, 1042) that solar cycle variation of number of X-ray bright points (XBPs) can be caused by the visibility effect, i.e., the increased background due to scattering from bright active regions alters identification of XBPs. In contrast, the number of photospheric bipoles - the magnetic counterparts of bright points - is independent of solar cycle. On the other hand, several previous studies reported enhanced density of XBPs in coronal holes. It has also been shown that there is positive correlation between XBP number in coronal holes and solar wind density. We study magnetic and thermal properties, location and motions of EUV and X-ray bright points in coronal holes using observations from SOHO EIT (171, 195 and 304 A) and Yohkoh SXT. Title: Sinuous Coronal Loops at the Sun [Invited] Authors: Pevtsov, A. A. Bibcode: 2002mwoc.conf..125P Altcode: The sinuous coronal loops - sigmoids, first noted in the Skylab X-ray observations in association with a CME, - are commonly observed in Yohkoh soft X-ray telescope (SXT) data. The S-shape of these loops is a manifestation of the helical structure of the coronal magnetic fields and, hence, follows the hemispheric helicity (chirality) rule established for quiescent filaments and photospheric magnetic fields. The forward-S (inverse-S) sigmoids prevail in southern (northern) hemisphere, independent of the solar cycle. Sigmoids are often associated with the CMEs; they exist prior to eruption and disappear after. In addition, active regions that exhibit sinuous loops are more likely to be eruptive than non-sigmoidal regions. Once erupted, sigmoids tend to produce stronger geomagnetic storms, and often the orientation of magnetic field in interplanetary disturbance can be directly linked to the coronal field of a sigmoid. In this talk we review the observational properties of sigmoids, current theoretical models and application of sinuous loops to space weather forecasting. Title: Helicity transport and creation in the solar convection zone Authors: Longcope, D.; Pevtsov, A. Bibcode: 2002cosp...34E3177L Altcode: 2002cosp.meetE3177L Magnetic helicity provides a theoretical tool for characterizing the solar dynamo and the evolution of the coronal field. The magnetic helicity may be inferred from several types of observation including vector magnetograms of the photospehric magnetic fields. The helicty of an active region reflects, to some degree, that produced by the solar cycle dyanmo which is believed to be operating at the base of the convection zone, where the Rossby number is small. The helicty of the active region is affected by the turbulence through which it rises, and this process must be taken into account when interpreting helicity observations. The subsequent dispersal of the active region magnetic field will further affect the observed helicty of the photospheric field. This transport process suggests an observational method of identifying, through helicty measurements, the source of quiet Sun field from either a surface (non-helical) dynamo or the fragmentation of helical active region fields. Title: Solar magnetic fields and geomagnetic events Authors: Pevtsov, Alexei A.; Canfield, Richard C. Bibcode: 2001JGR...10625191P Altcode: Some interplanetary studies lead one to expect that the toroidal fields of individual active regions are directly related to their heliospheric structure. Other studies conclude that the large-scale solar dipolar field is more important. We have carried out two studies that bear on these apparently conflicting views. We first studied geomagnetic events temporally associated with the eruption of 18 individual coronal X-ray sigmoids, which occurred while the large-scale solar dipolar magnetic field pointed southward. We found that if a coronal flux rope model is used to interpret magnetic structure, eruptions with a southward leading magnetic field are associated with stronger geomagnetic storms, but those with a northward leading field are associated with more storms. We next studied three full magnetic cycles, solar cycles 17-22. We examined the temporal variation of the ratio of the geomagnetic Ap index to the sunspot number. We found no statistically compelling fluctuations of this quantity on solar cycle time scales that are in phase with the reversal of active region polarities. On the other hand, we found a weak tendency for fluctuations that are in phase with the reversal of the large-scale solar dipole field. From these two studies we infer that the magnetic structure of individual active regions plays a role in geomagnetic events, but their geoeffectiveness is complicated by asymmetries in the leading and following magnetic field and density. We conclude that simple cycle-dependent generalizations have only statistical significance, and cannot dependably be used to predict the geomagnetic effects of a given solar eruption. Title: Soft X-Ray Luminosity and Photospheric Magnetic Field in Quiet Sun Authors: Pevtsov, Alexei A.; Acton, Loren W. Bibcode: 2001ApJ...554..416P Altcode: We use full-disk soft X-ray data from Yohkoh and Kitt Peak daily magnetograms to study the coronal irradiance and photospheric magnetic field remote from active regions between 1991 November and 1998 December. For every image of our data set we extract three areas 4°×4° in size centered at N00° W00°, N50° W00°, and S50° W00° and compute X-ray irradiance and unsigned magnetic flux for each of these areas. Between 1991 (active Sun) and 1996 (quiet Sun) the X-ray irradiance at the heliographic center decreased by more than a factor of 7, while the magnetic flux decreased by only a factor of 2. A similar tendency is observed for our high-latitude samples. Apart from the cycle-related variations, all three areas of quiet Sun exhibit significant nonperiodic changes in X-ray irradiance. These variations occur on 9-12 month intervals and clearly correlate with changes in sunspot activity. Similar variations are present in the total X-ray irradiance averaged over the solar disk. By contrast, the magnetic fluxes from the photosphere beneath these same areas show no corresponding variations on this time scale. In our opinion, coronal heating models based on the reconnection of quiet-Sun magnetic elements (variously called chromospheric network, ``magnetic carpet,'' or ``salt and pepper'' field) can at best account for a minimal contribution to heating the million-degree corona observed by the Yohkoh soft X-ray telescope. We conclude that the X-ray irradiance in the quiet Sun (at least in the Yohkoh temperature range, >2 MK) is primarily associated with the strong magnetic fields of active regions, not with weak photospheric fields. The association, however, is not direct. We interpret the enhanced X-ray irradiance above the quiet Sun not as a result of the coronal ``canopy'' formed by the active-region magnetic field above the quiet-Sun areas, but as the large-scale relaxation process in the corona triggered by the evolution of active regions. To further support this conclusion, we show examples of active and quiet hemispheres in 1996 with similar weak-field properties but greatly different global X-ray emission and a pronounced change in X-ray irradiance over the entire visible hemisphere that was associated with the emergence of a single small active region. Title: Where the Quiet Sun Magnetic Field Comes From? Authors: Pevtsov, A. A.; Longcope, D. W. Bibcode: 2001AGUSM..SP41C06P Altcode: It has been recently suggested that there is two separate dynamo operating on the Sun. A subphotospheric (e.g. overshoot region) dynamo is responsible for strong magnetic fields of active regions, while the quiet Sun field is generated by the local (surface) dynamo driven by granular flows (Cattaneo 1999). Compelling observational evidence in support of the surface dynamo is still lacking. Because of the small characteristic size and lifetime of granular flows, the Coriolis force has no significant effect on them. Consequently the kinetic helicity of granules will not depend of hemisphere or vary with latitude; it will almost certainly average to zero. Magnetic field generated by such a (non-helical) dynamo should exhibit no hemispheric helicity rule either. In contrast, the sub-photospheric dynamo flows have non-zero kinetic helicity that changes sign across the solar equator. This dynamo will introduce hemispheric asymmetry in magnetic field's twist: positive helicity in southern hemisphere and negative in northern hemisphere. An observed hemispheric helicity rule for active region magnetic fields is well documented (e.g. Pevtsov et al 1995). Thus, the helicity approach can be used to distinguish between sub-photospheric (helical) and surface (non-helical) solar dynamos. Using vector magnetograms from the Advanced Stokes Polarimeter we measure current helicity density α z = Jz / Bz of photospheric field in the quiet Sun at few fixed latitudes. Our results indicate a weak hemispheric asymmetry in distribution of α z with a tendency for averaged helicity to be negative in the northern hemisphere and positive in the southern hemisphere. We interpret this asymmetry in a framework of the sub-photospheric origin of the photospheric field in the quiet Sun. Title: Evidence of Separator Reconnection in a Survey of X-Ray Bright Points Authors: Longcope, D. W.; Kankelborg, C. C.; Nelson, J. L.; Pevtsov, A. A. Bibcode: 2001ApJ...553..429L Altcode: X-ray bright points are among the simplest coronal structures hypothesized to be powered by magnetic reconnection. Their magnetic field appears to consist of a simple loop of field lines connecting positive to negative photospheric sources. Quantitative three-dimensional models of reconnection in this geometry are therefore expected to apply directly to X-ray bright points. We assemble a survey from archival Solar and Heliospheric Observatory data of 764 X-ray bright points (EUV Imaging Telescope) along with their associated photospheric magnetic fields (Solar Oscillation Imager/Michelson Doppler Imager). Measurements are made of each quantity relevant to the simple three-dimensional reconnection model. These data support several predictions of a magnetic reconnection model providing further evidence in favor of the hypothesis that magnetic reconnection supplies heating power to the quiet solar corona. Title: Properties of Magnetic Clouds Resulting from Eruption of Coronal Sigmoids Authors: Leamon, R. J.; Canfield, R. C.; Pevtsov, A. A. Bibcode: 2001AGUSM..SH31C08L Altcode: We study over 40 eruptions which originated with coronal sigmoids seen in Yohkoh SXT images, with subsequently observed in situ magnetic clouds (MCs) and geomagnetic storms at 1~AU. We correlate solar and interplanetary features so as to infer terrestrial event properties from their solar sources. A collateral result from studying this database is that CMEs and MCs resulting from erupting sigmoids seem not to adhere to rules such as leading Bz versus solar dipole orientation and, as such, form a distinct class of events. % Instead of a large-scale dipole rule, we find there is a weak (3:2) solar cycle (Hale polarity)-based rule for leading interplanetary field in MCs. We find that the helicity of magnetic clouds is much more strongly correlated (>90%) with launch hemisphere than the 60--70%\ rule of photospheric active region helicity. This rule appears to hold for all CMEs, taking the 28 years of events of Bothmer &\ Rust [``Coronal Mass Ejections,'' AGU Monograph Series 99, 139, 1997]. % At least half of Bothmer &\ Rust's events are associated with disparitions brusques, outside active regions. We therefore suggest that active region sigmoids and disappearing filaments are the origins of two different classes of CMEs. Title: Hemispheric Helicity Trend for Solar Cycle 23 Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Latushko, Sergei M. Bibcode: 2001ApJ...549L.261P Altcode: Applying the same methods we used in solar cycle 22, we study active region vector magnetograms, full-disk X-ray images, and full-disk line-of-sight magnetograms to derive the helicity of solar magnetic fields in the first 4 years of solar cycle 23. We find that these three data sets all exhibit the same two key tendencies-significant scatter and weak hemispheric asymmetry-as were observed in solar cycle 22. This supports the interpretation of these tendencies as signatures of the writhing of magnetic flux by turbulence in the convection zone. Title: Origin of Helicity in the Quiet Sun Authors: Pevtsov, A. A.; Longcope, D. W. Bibcode: 2001ASPC..236..423P Altcode: 2001aspt.conf..423P No abstract at ADS Title: Using X-ray Bright Points to Infer the Large-Scale Magnetic Field of the Quiet Sun Authors: Nelson, J. L.; Longcope, D. W.; Pevtsov, A. A. Bibcode: 2000SPD....31.0143N Altcode: 2000BAAS...32.1289N X-ray bright points (XBPs) form above magnetic bipoles in the quiet Sun, often at the site of convergence. According to models, the power radiated by the XBP is supplied by magnetic reconnection as flux is transfered from some overlying field into the bipole itself. It follows that the morphology of an XBP depends on both the bipole and on the large-scale overlying field. We demonstrate a novel technique which exploits this fact to map the horizontal component of the Sun's large-scale field using the morphology of observed XBPs. We test this technique using data from SOHO's Michaelson Doppler Interferometer (MDI) and EUV Imaging Telescope (EIT). The resulting measurements are compared to masurements made using standard polarimetric methods, and to models of the Sun's diffuse field. This material is based upon work supported by the National Science Foundation under Grant No. ATM-9733424. Title: Helicity Computation Using Observations From two Different Polarimetric Instruments Authors: Bao, S. D.; Pevtsov, A. A.; Wang, T. J.; Zhang, H. Q. Bibcode: 2000SoPh..195...75B Altcode: We compare vector magnetograms of active region NOAA 5747 observed by two very different polarimetric instruments: the imaging vector magnetograph of Huairou Solar Observing Station (HSOS) and the Haleakala Stokes Polarimeter of Mees Solar Observatory (MSO). Unlike previous comparative studies, we concentrate our attention on differences in observations and data reduction techniques that can affect the helicity computation. Overall, we find a qualitative agreement between the HSOS and MSO vector magnetograms. The HSOS data show slightly higher field strength, but the distribution of inclination angles is similar in measurements from the two instruments. There is a systematic difference (up to ∼20°) in the azimuths of transverse fields, which is roughly proportional to the longitudinal field strength. We estimate that Faraday rotation in the HSOS magnetograms contributes ∼12° in the azimuth difference if possible sources of error are taken into account. Next, we apply two independent methods to both data sets to resolve 180° azimuth ambiguity and to compute two helicity measures - the force-free field parameter αbest and the current helicity fractional imbalance ρh. The methods agree reasonably well in sign and value of the helicity measures, but the HSOS magnetograms show systematically smaller values of ρh and αbest in agreement with an expected contribution of Faraday rotation. Finally, we discuss the role of Faraday rotation in computation of αbest and ρh and conclude that it does not affect the strength of the hemispheric helicity rule. The strength of the rule appears to be related to a helicity parameter: αbest shows weaker hemispheric asymmetry than ρh. Title: Vector Magnetic Fields, Sub-surface Stresses and Evolution of Magnetic Helicity Authors: Canfield, R. C.; Pevtsov, A. A. Bibcode: 2000JApA...21..213C Altcode: No abstract at ADS Title: Coronal Structures as Tracers of Sub-surface Processes Authors: Pevtsov, A. A.; Canfield, R. C. Bibcode: 2000JApA...21..185P Altcode: No abstract at ADS Title: Soft X-ray Luminosity and Photospheric Magnetic Field in Quiet Sun. Authors: Pevtsov, A. A.; Acton, L. W. Bibcode: 2000SPD....31.1306P Altcode: 2000BAAS...32..845P We are using full disk soft X-ray data from Yohkoh and Kitt Peak daily magnetograms to study the coronal luminosity and photospheric magnetic field in the quiet Sun between 1991 November and 1998 December. For every image of our data set we extract three areas 4 by 4 solar degrees in size centered at 00N00W, 50N00W and 50S00W and compute X-ray luminosity and unsigned magnetic flux for each of these areas. Between 1991 (active Sun) and 1996 (quiet Sun) the X-ray luminosity at the heliographic center decreases by more than a factor of 7...while the magnetic flux decreases by only a factor of 2. A similar tendency is observed for our high latitude samples. Apart from the cycle-related variations, all three areas of quiet Sun exhibit significant non-periodic changes in X-ray luminosity. These variations occur on 9-12 month intervals and clearly correlate with increase/decrease in sunspot activity. Similar variations are present in the total X-ray irradiance averaged over the solar disk. On the contrary, the magnetic fluxes from the same areas of quiet Sun show no corresponding variations on this time scale. In our opinion, coronal heating models based on the reconnection of quiet sun magnetic elements (variously called chromospheric network, "magnetic carpet" or "salt and pepper" field) can not explain the million degree corona observed by the Yohkoh soft X-ray telescope. We conclude that the X-ray luminosity in the quiet Sun (at least in the Yohkoh temperature range, >2 MK) is primarily associated with the strong magnetic fields of active regions, not with weak photospheric fields. To further support this conclusion, we show one example of a dramatic change in X-ray luminosity over the entire visible corona that was associated with the emergence of a single small active region. Title: Transequatorial Loops in the Solar Corona Authors: Pevtsov, Alexei A. Bibcode: 2000ApJ...531..553P Altcode: Using X-ray coronal images, full-disk longitudinal magnetograms, and vector magnetograms of active regions, we study active regions connected across the solar equator. We survey the Yohkoh data set between 1991 October and 1998 December and find 87 transequatorial loop systems (TLSs). We classify these loops in four different categories and study a separation between regions, their rotation rates, and the sign of the current helicity (chirality) of the magnetic fields. We find that approximately one-third of all active regions on the Sun exhibit transequatorial loops. The fraction of TLSs is solar-cycle independent. Transequatorial loops may develop between existing active regions or between mature regions and new magnetic flux shortly after flux emergence. Observations suggest, however, that formation of TLSs is not a random process-a connection between two areas may exist well before the reconnection takes place. We find that the reconnected regions have approximately the same rotation rate and tend to appear on certain longitudes, similar to the complexes of activity. In most cases transequatorial interconnected regions have the same handedness of their magnetic field. Title: The Solar Dynamo and Emerging Flux - (Invited Review) Authors: Fisher, G. H.; Fan, Y.; Longcope, D. W.; Linton, M. G.; Pevtsov, A. A. Bibcode: 2000SoPh..192..119F Altcode: The largest concentrations of magnetic flux on the Sun occur in active regions. In this paper, the properties of active regions are investigated in terms of the dynamics of magnetic flux tubes which emerge from the base of the solar convection zone, where the solar cycle dynamo is believed to operate, to the photosphere. Flux tube dynamics are computed using the `thin flux tube' approximation, and by using MHD simulation. Simulations of active region emergence and evolution, when compared with the known observed properties of active regions, have yielded the following results: (1) The magnetic field at the base of the convection zone is confined to an approximately toroidal geometry with a field strength in the range (3-10)×104 G. The latitude distribution of the toroidal field at the base of the convection zone is more or less mirrored by the observed active latitudes; there is not a large poleward drift of active regions as they emerge. The time scale for emergence of an active region from the base of the convection zone to the surface is typically 2-4 months. The equatorial gap in the distribution of active regions has two possible origins; if the toroidal field strength is close to 105 G, it is due to the lack of equilibrium solutions at low latitude; if it is closer to 3×104 G, it may be due to modest poleward drift during emergence. (2) The tilt of active regions is due primarily to the Coriolis force acting to twist the diverging flows of the rising flux loops. The dispersion in tilts is caused primarily by the buffeting of flux tubes by convective motions as they rise through the interior. (3) The Coriolis force also bends the active region flux tube shape toward the following (i.e., anti-rotational) direction, resulting in a steeper leg on the following side as compared to the leading side of an active region. When the active region emerges through the photosphere, this results in a more rapid separation of the leading spots away from the magnetic neutral line as compared to the following spots. This bending motion also results in the neutral line being closer to the following magnetic polarity. (4) Active regions behave kinematically after they emerge because of `dynamic disconnection', which occurs because of the lack of a solution to the hydrostatic equilibrium equation once the flux loop has emerged. This could explain why active regions decay once they have emerged, and why the advection-diffusion description of active regions works well after emergence. Smaller flux tubes may undergo `flux tube explosion', a similar process, and provide a source for the constant emergence of small-scale magnetic fields. (5) The slight trend of most active regions to have a negative magnetic twist in the northern hemisphere and positive twist in the south can be accounted for by the action of Coriolis forces on convective eddies, which ultimately writhes active region flux tubes to produce a magnetic twist of the correct sign and amplitude to explain the observations. (6) The properties of the strongly sheared, flare productive δ-spot active regions can be accounted for by the dynamics of highly twisted Ω loops that succumb to the helical kink instability as they emerge through the solar interior. Title: Current Helicity of the Large-Scale Photospheric Magnetic Field Authors: Pevtsov, Alexei A.; Latushko, Sergei M. Bibcode: 2000ApJ...528..999P Altcode: This paper presents the first results of a study of current helicity of the large-scale magnetic field (LSMF) using full-disk longitudinal Blong magnetograms from the Michelson Doppler Imager on board the SOHO spacecraft. We employ a known technique to reconstruct the vector magnetic field under the assumption of relatively slow evolution of the LSMF and treat the variations of Blong, occurring during a defined period of time as the result of the changing projection angle only. We compute the synoptic maps of radial (Br) and toroidal (Bλ) magnetic fields and the latitudinal profile of current helicity density hc=Br(\b.nabla XB)r. For eight solar rotations (1910-1917) that have been analyzed, hc shows significant variations within +/-40° of solar latitude with no strong hemispheric sign asymmetry. Asymmetry is present, however, in high latitudes, where hc is negative/positive in the northern/southern hemisphere. Title: Studies of Solar Helicity Using Vector Magnetograms Authors: Hagyard, M. J.; Pevtsov, A. A. Bibcode: 1999SoPh..189...25H Altcode: Observations of photospheric magnetic fields made with vector magnetographs have been used recently to study helicity on the Sun. In this paper we indicate what can and cannot be derived from vector magnetograms, and point out some potential problems in these data that could affect the calculations of `helicity'. Among these problems are magnetic saturation, Faraday rotation, low spectral resolution, and the method of resolving the ambiguity in the azimuth. Title: Interconnecting Active Regions - Where, When, Why? Authors: Pevtsov, A. Bibcode: 1999AAS...194.5504P Altcode: 1999BAAS...31..910P It has been shown albeit in a limited dataset that the transequatorial loops are observed preferentially between active regions of same chirality. One can argue that such selectivity is a natural result of the reconnection, which simply "averages" helicities of involved regions and redistribute new chirality over the system. According to this scenario, the reconnected regions may have either same or opposite chirality before the reconnection. On the other hand, the reconnection rate depends on the magnetic helicity of involved fields. In presence of electric currents, the magnetic fields of same chirality are more likely to reconnect (electric currents closure argument), and hence the magnetic field should have same chirality before the reconnection. Which of these scenarios takes place on the Sun? We are using Yohkoh soft X-ray observations and HSP vector magnetograms to study a history of few selected areas on the Sun, where the transequatorial interconnecting regions were observed. In several cases, we find a clear indication of pre-existing connection between the areas before the active regions were formed. The distribution of the magnetic field implies a close relation between the interconnecting regions and complexes of activity. We speculate that the fact that the magnetic field has the same chirality within a complex of activity implies a long-term organization of the dynamo flows in the convection zone. Title: A Survey of X-ray Bright Points: Implications for a Reconnection Model Authors: Kankelborg, C. C.; Nelson, J.; Longcope, D. W.; Pevtsov, A. A. Bibcode: 1999AAS...194.1601K Altcode: 1999BAAS...31..849K We present a survey of over 350 bright points from archival SOHO data. Extreme ultraviolet images were measured to determine orientation, length, and brightness in the EIT 171 angstrom (Fe X, 1 MK) and 195 angstrom (Fe XII, 1.5 MK) passbands. MDI data were analyzed to obtain the size, orientation, and magnetic flux of the corresponding magnetic bipoles. The three-dimensional reconnection theory of Longcope (1998) makes several predictions that may be tested with these data. For this, the first phase of the study, we concentrate on the scaling of EUV brightness with magnetic flux and the distribution of displacement angles between EUV bright points and their magnetic counterparts. We also verify the assumption of Longcope & Kankelborg (1999) that the distribution of magnetic orientations is random and independent of latitude. Title: The Origin and Role of Twist in Active Regions Authors: Fisher, G. H.; Longcope, D. W.; Linton, M. G.; Fan, Y.; Pevtsov, A. A. Bibcode: 1999soho....9E..56F Altcode: The implications of twist in active region magnetic fields is considered in this paper. The latitudinal distribution of twist that has been derived from recent vector magnetogram observations may be explained by the effects of convective turbulence with a non-zero kinetic helicity acting on active region scale magnetic flux tubes as they rise through the convection zone. Highly twisted, kink unstable flux tubes are then discussed as a possible explanation for many of the observed properties of flare productive, "d-spot'' active regions. Title: Magnetic helicity attracts interdisciplinary participation at chapman conference Authors: Canfield, R. C.; Pevtsov, A. A. Bibcode: 1999EOSTr..80...13C Altcode: During the last 5 years interest in magnetic helicity has grown dramatically in solar physics as a result of improved capabilities to measure and image magnetic fields. Magnetic helicity was introduced by K. Moffatt in the late 1950s as a topological invariant that describes the complexity of a magnetic field. The topological aspect of helicity is readily visualized in a Moebius strip, in which the system of interest is closed and helicity takes two forms, the writhing of the central axis of the strip and the twisting of the edges of the strip about that axis.In many plasmas (but not in atmospheres like that of Earth, for example), helicity is conserved, just as the sum of twist and writhe is conserved in a Moebius strip. Mathematically, it is related to linking integrals, which K. F. Gauss employed to study asteroid paths on the sky. In the late 1970s the concept of magnetic helicity was introduced in laboratory plasma physics, turbulence theory, space physics, and statistical theory. Title: Twisted Flux Tubes and How They Get That Way Authors: Longcope, Dana; Linton, Mark; Pevtsov, Alexei; Fisher, George; Klapper, Isaac Bibcode: 1999GMS...111...93L Altcode: According to present theories, the Sun's magnetic field rises through the convection zone in the form of slender strands known as flux tubes, traditionally studied using "thin flux tube" models. While these models have been remarkably successful they have only recently begun to account for tubes with twisted magnetic flux, in spite of observational evidence for such twist. In this work we review the recent developments pertaining to twisted magnetic flux tubes and compare quantitative predictions to observations. Hydrodynamic theory predicts a role for twist in preventing fragmentation. Excessive twist can also lead to magnetohydrodynamic instability affecting the dynamics of the tube's axis. A thin tube model for a twisted tube suggests several possibilities for the origin of twist. The most successful of these is the Sigma-effect whereby twist arises from deformation of the tube's axis by turbulence. Simulations show that the Sigma-effect agrees with observations in magnitude as well as latitudinal dependence. Title: The Origin and Role of Twist in Active Regions Authors: Fisher, G. H.; Longcope, D. W.; Linton, M. G.; Fan, Y.; Pevtsov, A. A. Bibcode: 1999ASPC..178...35F Altcode: 1999sdnc.conf...35F No abstract at ADS Title: The Solar Dynamo and Emerging Flux Authors: Fisher, G. H.; Fan, Y.; Longcope, D. W.; Linton, M. G.; Pevtsov, A. A. Bibcode: 1999soho....9E..18F Altcode: Much has been learned about the dynamics of magnetic flux tubes in the solar interior over the past decade. By using theoretical models for the dynamics of active region flux ropes, it is possible to estimate observable properties of active regions, such as their orientation, position on the disk, and morphology, and then compare these properties with active region observations. By varying conditions of the magnetic flux ropes as the base of the convection zone until observed properties are matched, one can deduce properties of the magnetic field in the dynamo layer, such as the magnetic field strength. Observed properties such as the active region tilt angle, the dispersion of the tilt angle, and magnetic helicity in active regions will be discussed in terms of the dynamics of flux tubes rising through the convection zone and their interaction with convective motions. Properties of Delta spot active regions will be discussed in terms of the kink instability of magnetic flux ropes. Title: Magnetic Helicity in Space and Laboratory Plasmas Authors: Brown, Michael R.; Canfield, Richard C.; Pevtsov, Alexei A. Bibcode: 1999GMS...111.....B Altcode: 1999mhsl.conf.....B Using the concept of magnetic helicity, physicists and mathematicians describe the topology of magnetic fields: twisting, writhing, and linkage. Mathematically, helicity is related to linking integrals, which Gauss introduced in the 19th century to describe the paths of asteroids in the sky. In the late 1970s the concept proved to be critical to understand laboratory plasma experiments on magnetic reconnection, dynamos, and magnetic field relaxation. In the late 1980s it proved equally important in understanding turbulence in the solar wind and the interplanetary magnetic field. During the last five years interest in magnetic helicity has grown dramatically in solar physics, and it will continue to grow as observations of vector magnetic fields become increasingly sophisticated. Title: Coronal Heating in Active Regions as a Function of Global Magnetic Variables Authors: Fisher, George H.; Longcope, Dana W.; Metcalf, Thomas R.; Pevtsov, Alexei A. Bibcode: 1998ApJ...508..885F Altcode: A comparison of X-ray images of the Sun and full disk magnetograms shows a correlation between the locations of the brightest X-ray emission and the locations of bipolar magnetic active regions. This correspondence has led to the generally accepted idea that magnetic fields play an essential role in heating the solar corona.

To quantify the relationship between magnetic fields and coronal heating, the X-ray luminosity of many different active regions is compared with several global (integrated over entire active region) magnetic quantities. The X-ray measurements were made with the SXT Telescope on the Yohkoh spacecraft; magnetic measurements were made with the Haleakala Stokes Polarimeter at the University of Hawaii's Mees Solar Observatory.

The combined data set consists of 333 vector magnetograms of active regions taken between 1991 and 1995; X-ray luminosities are derived from time averages of SXT full-frame desaturated (SFD) images of the given active region taken within +/-4 hours of each magnetogram. Global magnetic quantities include the total unsigned magnetic flux Φtot ≡ \smallint dA|Bz|, B2z,tot≡ dAB2z, Jtot ≡ \smallint dA|Jz|, and B2⊥,tot≡ dAB2⊥, where Jz is the vertical current density and Bz and B⊥ are the vertical and horizontal magnetic field amplitudes, respectively.

The X-ray luminosity LX is highly correlated with all of the global magnetic variables, but it is best correlated with the total unsigned magnetic flux Φtot. The correlation observed between LX and the other global magnetic variables can be explained entirely by the observed relationship between those variables and Φtot. In particular, no evidence is found that coronal heating is affected by the current variable Jtot once the observed relationship between LX and Φtot is accounted for. A fit between LX and Φtot yields the relationship LX ~= 1.2 × 1026 ergs s-1(Φtot/1022 Mx)1.19.

The observed X-ray luminosities are compared with the behavior predicted by several different coronal heating theories. The Alfvén wave heating model predicts a best relationship between LX and Φtot, similar to what is found, but the observed relationship implies a heating rate greater than the model can accommodate. The ``Nanoflare Model'' of Parker predicts a best relationship between LX and B2z,tot rather than Φtot, but the level of heating predicted by the model can still be compared to the observed data. The result is that for a widely used choice of the model parameters, the nanoflare model predicts 1.5 orders of magnitude more heating than is observed. The ``Minimum Current Corona'' model of Longcope predicts a qualitative variation of LX with Φtot that agrees with what is observed, but the model makes no quantitative prediction that can be tested with the data. A comparison between LX and the magnetic energy Emag in each active region leads to a timescale that is typically 1 month, or about the lifetime of an active region, placing an important observational constraint on coronal heating models.

Comparing the behavior of solar active regions with nearby active stars suggests that the relationship observed between LX and Φtot may be a fundamental one that applies over a much wider range of conditions than is seen on the Sun. Title: NOAA 7926: A Kinked Ω-Loop? Authors: Pevtsov, Alexei A.; Longcope, Dana W. Bibcode: 1998ApJ...508..908P Altcode: Using vector magnetograms and X-ray images, we study the evolution of the decaying active region NOAA AR 7926. The active region had bipolar structure with a leading sunspot of positive (northern [N]) polarity--non-Hale polarity of cycle 22. Observations suggest that the following (southern [S]) polarity of this active region was in fact the leading (S) polarity of Active Region 7918 (AR 7918) of the previous solar rotation. Analyzing the rotation rate of both active regions and their magnetic field topology, we conclude that they form a single magnetic system resembling a kinked Ω-loop. During the first rotation, the upper part of the loop was exposed, forming a bipolar active region of normal (Hale) polarity. The rest of the Ω-loop had emerged by the time of the second rotation, giving the appearance of non-Hale polarity. Title: Flux-Tube Twist Resulting from Helical Turbulence: The Σ-Effect Authors: Longcope, D. W.; Fisher, G. H.; Pevtsov, A. A. Bibcode: 1998ApJ...507..417L Altcode: Recent observational studies suggest that active region magnetic flux emerges in a twisted state and that the sense of twist depends weakly on solar hemisphere. We propose that this twist is imparted to the flux through its interaction with turbulent velocities in the convection zone. This process, designated the Σ-effect, operates on isolated magnetic flux tubes subjected to buffeting by turbulence with a nonvanishing kinetic helicity <u \b.dot \b.nabla × u>. The Σ-effect leads to twist of the same sense inferred from observation and opposite to that predicted by the α-effect. A series of numerical calculations are performed to estimate the magnitude of the Σ-effect in the solar convective zone. The results compare favorably with observations in both mean value and statistical dispersion. We find a further relationship with total magnetic flux that can be tested in future observations. The model also predicts that twist is uncorrelated with the tilt angle of the active region. Title: Helicity of Solar Active-Region Magnetic Fields Authors: Canfield, Richard C.; Pevtsov, Alexei A. Bibcode: 1998ASPC..140..131C Altcode: 1998ssp..conf..131C No abstract at ADS Title: On the Origin of Helicity in Active Region Magnetic Fields Authors: Pevtsov, A. A.; Canfield, R. C. Bibcode: 1998ASSL..229...85P Altcode: 1998opaf.conf...85P No abstract at ADS Title: On the Origin of Helicity in Active Region Magnetic Fields Authors: Canfield, Richard C.; Pevtsov, Alexei A. Bibcode: 1997SPD....28.1705C Altcode: 1997BAAS...29..921C The magnetic helicity of flux tubes consists of twist and writhe. If flux bundles at the base of the convection zone are simple axisymmetric toroids, and rise in omega-shaped loops through the convection zone, they acquire writhe through the effect of the Coriolis force on flows within them. The tilt of active regions with respect to the equator is an observable manifestation of this writhe, at photospheric levels. As a consequence of helicity conservation, we expect active regions to acquire twist to compensate for this writhe. The non-zero curl of the large-scale magnetic fields in active-region vector magnetograms is the observable manifestation of twist. Recent observations have revealed many interesting properties of the helicity of solar magnetic fields. Hemispheric preferences exist: active region fields predominantly have left-handed topology in the Northern hemisphere. Prominence structures also predominantly have left-handed writhe in the Northern hemisphere. Large-scale structures have been observed to exist in the distribution of both twist and writhe with longitude and latitude, and to persist for many solar rotations. To study the physical origin of these properties, we have used a dataset of about 100 active regions for which vector magnetograms were obtained at Mees Solar Observatory. We have measured both the overall tilt and the overall twist of these active regions. The dataset clearly shows Joy's law, the well-known dependence of tilt on latitude, as well as the hemispheric dependence of twist. However, our analysis shows that twist and tilt are not related as they should be if both twist and tilt are a consequence of the Coriolis force. Hence, we conclude that the twist seen in active regions is the consequence of a deep-seated phenomenon, presumably that of the solar dynamo itself. Title: NOAA 7926: A Kinked, Submerging Omega -loop ? Authors: Pevtsov, Alexei A.; Canfield, Richard C. Bibcode: 1997SPD....28.0238P Altcode: 1997BAAS...29..900P Using vector magnetograms and X-ray images, we study the evolution of decaying active region NOAA AR 7926. This active region had bipolar structure with non-Hale polarity. Observations suggest that the following polarity of this active region was in fact the leading polarity of active region NOAA AR 7918 on the previous solar rotation. Analyzing the rotation rate of both active regions and the topology of their magnetic field, we conclude that they belong to a single magnetic system resembling a kinked Omega loop. During the first rotation the upper part of the loop was exposed, forming the bipolar active region of normal (Hale) polarity. The rest of the Omega loop had emerged on the time by the second rotation, giving the appearance of non-Hale polarity. The major soft X-ray coronal loops of NOAA AR 7926 closely relate to the weak magnetic field in the middle part of the region. In that area, the photospheric field stayed concave-down in the course of dissipation of the active region, and the coronal loops decreased their length. We also find that coronal loops decrease their height derived using E and W limb observations of the two active regions NOAA AR 7926 and NOAA AR 7918. Hence, we concluded that the magnetic field of the active region submerged under the photosphere. Title: On the Subphotospheric Origin of Coronal Electric Currents Authors: Pevtsov, Alexei A.; Canfield, Richard C.; McClymont, Alexander N. Bibcode: 1997ApJ...481..973P Altcode: Using photospheric vector magnetograms from the Haleakala Stokes Polarimeter and coronal X-ray images from the Yohkoh Soft X-Ray Telescope (SXT), we infer values of the force-free field parameter α at both photospheric and coronal levels within 140 active regions. We determine the value of α for a linear force-free field that best fits each magnetogram in a least-squares sense. We average values from all available magnetograms to obtain a single mean photospheric α-value <αp> for each active region. From the SXT images we estimate α in the corona by determining (π/L) sin γ for individual loops, where γ is the observed shear angle of X-ray loops of length L. We then average these values of α to obtain a single coronal α value, <αc>, for each active region.

In active regions for which the photospheric α-map is predominantly of one sign, we find that the values of <αp> and <αc> are well correlated. Only for active regions in which both signs of α are well represented, and in which our method of analysis therefore breaks down, are the values of <αp> and <αc> poorly correlated. The former correlation implies that coronal electric currents typically extend down to at least the photosphere. However, other studies imply subphotospheric origin of the currents, and even current systems, that are observed in the photosphere. We therefore conclude that the currents responsible for sinuous coronal structures are of subphotospheric origin. Title: Coronal Structure as a Diagnostic of the Solar Dynamo Authors: Sandborgh, S.; Canfield, R. C.; Pevtsov, A. A. Bibcode: 1997SPD....28.0151S Altcode: 1997BAAS...29..888S This paper is motivated by the discovery of large-scale structures in the distribution of twist of magnetic fields with solar longitude and latitude. These structures are observed to persist for many solar rotations (Pevtsov and Latushko, BAAS 27, 978, 1995; Pevtsov, Canfield, and Metcalf, 4th SOHO Workshop: Helioseismology, Asilomar, 2-6 April 1995; Pevstov, Canfield, and Glatzmaier, Geophysical and Astrophysical Convection, NCAR, 10-13 October 1995). The large scale of these patterns, in space and time, implies that they are a deep-seated phenomenon, presumably that of the solar dynamo itself. Recent observations of twist and tilt of active regions (Pevstov and Canfield, Yohkoh Fifth Anniversary Symposium, Yoyogi, 6-8 November 1996, and Canfield and Pevtsov, this meeting) and the relationship between photospheric and coronal manifestations of twist (Pevstov, Canfield, and McClymont, ApJ 481, in press) confirm this conclusion. The Yohkoh Soft X-Ray Telescope images from the first five years of operations often clearly show the presence of topologically distinct regions. We have developed and used IDL software that allows us to identify and transfer to Carrington coordinates the boundaries of these systems, which we identify with magnetic flux systems. In this paper we present the results of our studies of these systems over many solar rotations, and relate them to the previously discovered persistent large-scale structures in the distribution of twist of active region magnetic fields with longitude and latitude. Title: Reconnection and Helicity in a Solar Flare Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Zirin, Harold Bibcode: 1996ApJ...473..533P Altcode: Using X-ray images, Hα images, and vector magnetograms, we have studied the evolution of the coronal structure and magnetic field of NOAA Active Region 7154 during 1992 May 5-12. A two-ribbon 4B/M7.4 flare associated with an Hα filament eruption was observed on May 8, 15:13-19:16 UT. An interesting feature of the region was a long, twisted X-ray structure, which formed shortly before the flare and disappeared after it, being replaced by a system of unsheared postflare loops. Neither the X-ray nor Hα morphology nor the photo spheric magnetic field shows any indication of gradual buildup of nonpotential energy prior to the flare. Rather, the long structure appears to result from the reconnection of two shorter ones just tens of minutes before the filament eruption and flare.

Using vector magnetograms and X-ray morphology, we determine the helicity density of the magnetic field using the force-free field parameter α. The observations show that the long structure retained the same helicity density as the two shorter structures, but its greater length implies a higher coronal twist. The measured length and α value combine to imply a twist that exceeds the threshold for the MHD kink instability in a force-free cylindrical flux tube. We conclude that theoretical studies of such simple models, which have found that the MHD kink instability does not lead to global dissipation, do not adequately address the physical processes that govern coronal magnetic fields. Title: Coronal Heating in Active Regions as a Function of Global Magnetic Variables Authors: Fisher, G. H.; Longcope, D. W.; Metcalf, T. R.; Pevtsov, A. A. Bibcode: 1996AAS...188.3304F Altcode: 1996BAAS...28..868F A comparison of X-ray images of the Sun and full disk magnetograms shows a correlation between the locations of the brightest X-ray emission and the locations of bipolar magnetic regions. This correspondence has led to the generally accepted idea that magnetic fields play an essential role in heating the Solar corona. To quantify the relationship between magnetic fields and coronal heating, we have compared the X-ray luminosity of many different Active Regions with several global (integrated over entire active region) magnetic quantities. The X-ray measurements were made with the SXT Telescope on the Yohkoh spacecraft; magnetic measurements were made with the Haleakala Stokes Polarimeter at the University of Hawaii's Mees Solar Observatory. Our combined dataset consists of 333 vector magnetograms of active regions taken between 1991 and 1995; SXT luminosities consist of time averages of SFD images of the given active region taken within +/- 4 hours of each magnetogram. Global magnetic quantities include the total unsigned magnetic flux, area integrals of B(2) , J_z(2) (J_z is the vertical component of the electric current density), and the best-fit alpha of the linear force-free field for the entire active region (nabla x B = alphaB ). Our results show clear and unmistakable relationships between the X-ray luminosity and most of these magnetic variables. The relationship between total unsigned magnetic flux and X-ray luminosity is especially compelling, holding over 2 orders magnitude in both quantities. These measurements provide important contraints on coronal heating mechanisms. This work was supported in part by NASA grant NAGW-3429, NSF grant AST-9218085, and Cal Space grant CS-17-95. Title: Magnetic Chirality and Coronal Reconnection Authors: Pevtsov, A. A.; Canfield, R. C.; McClymont, A. N. Bibcode: 1996AAS...188.3503P Altcode: 1996BAAS...28..871P We have used Mees Solar observatory vector magnetograms and Yohkoh Soft X-Ray Telescope images to study the role of magnetic chirality (handedness) in the trans-equatorial reconnection of active regions. Transequatorial reconnections are identified using SXT images. The chirality of the active regions is inferred from vector magnetograms and SXT images. Our results indicate that active regions reconnect preferentially with others of the same chirality. We have identified the 9 closest pairs of active regions separated by up to +/- 20° in latitude and longitude. All six pairs of active regions having the same sign of chirality showed transequatorial connection. All three pairs of active regions of opposite chirality indicated no inter-connection. Less close pairs of active regions, with separation up to +/- 40° in latitude and +/- 20° in longitude, showed the same tendency: 15 of 17 regions with the same chirality were inter-connected in the corona, and 8 of 10 regions having the opposite chirality did not show inter-connection. We explain this result with a simple model of current-system closure. Title: Magnetic Chirality and Coronal Reconnection Authors: Canfield, Richard C.; Pevtsov, Alexei A.; McClymont, Alexander N. Bibcode: 1996ASPC..111..341C Altcode: 1997ASPC..111..341C The authors have used Mees Solar Observatory vector magnetograms and Yohkoh Soft X-ray Telescope images to study the role of magnetic chirality in the trans-equatorial reconnection of active regions. They conclude that active regions reconnect preferentially with others of the same chirality. They explain this result with a simple model of the closure of their current systems. Title: Helicity of Large Scale Photospheric Magnetic Fields Authors: Pevtsov, A. A.; Latushko, S. M. Bibcode: 1995SPD....26.1008P Altcode: 1995BAAS...27..978P No abstract at ADS Title: Latitudinal Variation of Helicity of Photospheric Magnetic Fields Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Metcalf, Thomas R. Bibcode: 1995ApJ...440L.109P Altcode: Using a 1988-1994 data set of original photospheric vector magnetograms as well as published data, we have studied the average magnetic helicity of 69 diverse active regions, adopting the linear force-free field parameter alpha as a measure. This average value was determined by minimizing the differences between the computed constant-alpha force-free and observed horizontal magnetic fields. The average magnetic helicity shows a sign difference at the 2 sigma level in opposite hemispheres. In our data set, 76% of the active regions in the northern hemisphere have negative helicity, and 69% in the southern hemisphere, positive. Although the data show considerable variation from one active region to the next, the data set as a whole suggest that the magnitude of the average helicity increases with solar latitude, starting at zero near the equator, reaches a maximum near 15 deg - 25 deg in both hemispheres, and drops back toward smaller values avove 35 deg - 40 deg. Qualitative comparison with published models shows that such latitudinal variation of the average magnetic helicity may result from either turbulent convective motions or differential rotation, although our studies of rotating sunspots lead us to favor the former. Title: Patterns of Helicity in Solar Active Regions Authors: Pevtsov, Alexei A.; Canfield, Richard C.; Metcalf, Thomas R. Bibcode: 1994ApJ...425L.117P Altcode: Using 46 vector magnetograms from the Stokes Polarimeter of Mees Solar Observatory (MSO), we studied patterns of local helicity in three diverse solar active regions. From these magnetograms we computed maps of the local helicity parameter alpha = Jz/Bz. Although such maps are noisy, we found patterns at the level approximately 2 to 3 sigmaJ(sub z), which repeat in successive magnetograms for up to several days. Typically, the alpha maps of any given active region contain identifiable patches with both positive and negative values of alpha. Even within a single sunspot complex, several such alpha patches can often be seen. We followed 68 alpha patches that could be identified on at least two successive alpha maps. We found that the persistence fraction of such patches decrease exponentially, with a characteristic time approximately 27 hr. Title: Line-of-sight velocity measurements using a dissector-tube. II. Time variations of the tangential velocity component in the Evershed effect Authors: Druzhinin, S. A.; Pevtsov, A. A.; Levkovsky, V. L.; Nikonova, M. V. Bibcode: 1993A&A...277..242D Altcode: We present the results of measurements of sunspot torsional oscillations. For six sunspots, a study was made of the spectral composition of Doppler velocity signals from two areas of penumbra, symmetric about the sunspot umbra located near the limb. The spectrograph slit was directed parallel to the nearest solar limb. The observations were made in the lines Fe i 543.45 nm and Hβ 486.13 nm using a dissector tube. Its electronic scanning was controlled in such a way that two channels measure spectral line shifts in two different parts of the photo-cathode. Attention mainly was paid to periods from 1 min to several hours. The results of the work indicate that the sunspot penumbra exhibits several kinds of oscillations: quasi-five-min vertical oscillations of small areas of penumbra (4 arcsec), vertical oscillations of large areas of penumbra (periods from 20 min to 1 h), and the sunspot torsional oscillations. Periodic variations in sunspot position are observed to have an amplitude of about 1 arcsec and periods close to those of the sunspot torsional oscillations. Title: Line-of-sight velocity measurements using a dissector-tube. 1. an instrument description Authors: Druzhinin, S. A.; Pevtsov, A. A. Bibcode: 1993A&A...272..378D Altcode: A description of an electronic device for solar Doppler velocity measurements based on a TV dissector- tube is given. As to the principle of measurements, this instrument is the electronic analog of the magnetograph Doppler compensator. The advantages of this device over existing Doppler compensators using a tilting glass plate are the absence of moving parts, the flexibility of the scan parameters, and the high speed. The instrument provides quasi-simultaneous measurements of (a) the shifts of two neighbouring spectral lines, (b) the shifts in a single spectral line at two intensity levels (nearer to the core and the wings), and (c) the spectral line shifts at two points spaced along spectrum height.

The non-uniformity of the photocathode sensitivity must be regarded as the disadvantage of the device. The functional principles of this instrument are described, and some specific errors of measurements are considered. We discuss the influence of: (a) the non-uniformity of photocathode sensitivity, (b) spectral-line inclination in the spectrum, (c) the illumination non-uniformity of the spectrograph entrance slit, and (d) interference and stray light. Title: Line-of-sight velocity measurements using a dissector-tube. III - Prominence oscillations Authors: Mashnich, G. P.; Druzhinin, S. A.; Pevtsov, A. A.; Levkovskij, V. I. Bibcode: 1993A&A...269..503M Altcode: We discuss the results of line-of-sight velocity observations in an active prominence and in three quiescent prominences. The observations were made by using a TV dissector-tube. At 2 x 3 arcsec spatial resolution the prominences showed oscillations in a wide range, from short-period (2-10 min) to long-period ones, covering a time span of 40-200 min. Short-period oscillations seem to refer to small-scale ones and are in their character close to oscillations occurring with the same periods in the chromosphere. Some interesting features of the line-of-sight velocity oscillations in the active prominence have been revealed. At the time of activation the amplitude of the short-period oscillations increases to exceed the level of quasi-hour oscillations. The range 2-20 min exhibits a transformation of the oscillation spectrum with height, from short to longer periods. Title: Relation Between the Longitudinal Field and Radial Velocity in Sunspots Authors: Pevtsov, A. A. Bibcode: 1993ASPC...46...78P Altcode: 1993IAUCo.141...78P; 1993mvfs.conf...78P No abstract at ADS Title: The relationship between the longitudinal magnetic field and the line-of-sight velocity at different angular positions of sunspots Authors: Pevtsov, A. A. Bibcode: 1992SoPh..141...65P Altcode: Using observational data on 14 sunspots from the Sayan Observatory vector magnetograph, a study was made of the relationship between the sunspot magnetic field and the Evershed motions. It is shown that the central area of the solar disk is dominated by an anti-correlation of the longitudinal magnetic field B∥ and the line-of-sight velocity V∥ when a maximum of V∥ corresponds to the neutral line of the longitudinal field. Near the limb there usually is a coincidence of the field and velocity neutral lines. There is evidence for the possible asymmetric character of the effect with respect to the central meridian. Title: Spatial distribution of line-of-sight velocities in a quiescent prominence. Authors: Druzhinin, S. A.; Pevtsov, A. A.; Mashnich, G. P. Bibcode: 1992ESASP.344..161D Altcode: 1992spai.rept..161D In 26 - 29 June 1990 Doppler velocity observations in a quiescent prominence were carried out. Using a device based on a image dissector, the Doppler velocity profile in prominence height were measured quasi-simultaneously at two intensity levels in the line Hβ. It was found that through the entire height of the prominence, there are 3 - 4 elements with quasi-hourly oscillations. Relative to each other, the oscillations in these elements show a random phase. The distance between such elements is about 20″ Quasi-five-minute oscillations have a train-like character and a random phase at neighbouring points of the prominence (separation ≍4″. Title: Time variations of the tangential component of velocity in the Evershed effect. Authors: Druzhinin, S. A.; Pevtsov, A. A.; Levkovskii, V. I.; Nikonova, M. V. Bibcode: 1991KFNT....7...51D Altcode: 1991KNFT....7...51D Results of observations of the tangential component of velocity in the Evershed effect (torsional oscillations of sunspots) are presented. For six sunspots, the spectral composition of line-of-sight velocity signals from two areas of the penumbra located symmetrically relative to the sunspot umbra has been studied. The areas chosen are located perpendicular to the direction toward the solar image centre, i.e., gas rotation velocities in a sunspot were measured. The observations were made in lines of Fe I λ543.45 nm and Hβ λ486.13 nm using a dissector-tube, whose electronic scanning control permits measuring (quasi-simultaneously in two channels) spectral line shifts on two sections of its photocathode. The results obtained confirm the presence of torsional oscillations of sunspots at the photospheric level with a period of about one hour. For the first time such oscillations have been measured at the chromospheric level (with a period of about 30 minutes). Based on observations of two sunspots during 3 and 4 days, respectively, it is concluded that these sunspots involve torsional oscillations with a period of several days. Title: Time variations of the tangential velocity component in the Evershed effect. Authors: Druzhinin, S. A.; Pevtsov, A. A.; Levkovskij, V. I.; Nikonova, M. V. Bibcode: 1991KPCB....7e..46D Altcode: 1991KPCB....7...46D Observations of the tangential velocity component in the Evershed effect (torsional oscillations of sunspots) are reported. The spectral composition of the radial-velocity signals from two penumbral areas at positions symmetric about the umbra was investigated for six sunspots. The selected fields were on a line perpendicular to the direction to the center of the Sun's image, i.e., the rotational velocities of the gas in the sunspot were measured. The observations were made in the lines Fe I λ543.45 nm and Hβ 486.13 nm. The results of the study confirm the existence of torsional oscillations of sunspots at photosphere level with a period of about an hour. These oscillations were measured for the first time at chromosphere level (period about 30 min). It is concluded from observations of two sunspots over three and four days that torsional oscillations with a period of several days occurred in these sunspots. Title: Direct measurements of short-period torsional oscillations of sunspots. I. First results. Authors: Druzhinin, S. A.; Pevtsov, A. A.; Levkovskii, V. I.; Nikonova, M. V. Bibcode: 1990KFNT....6...29D Altcode: 1990KNFT....6...29D The first results of direct measurements of one of varieties of proper motions of sunspots, i. e., their torsional oscillations are presented. For three sunspots a study has been made of the spectral composition of line-of-sight velocity signals from two penumbra areas symmetric relative to the sunspot umbra near the limb. The penumbra areas chosen were located on a line perpendicular to the direction of the solar image. Main attention is paid to periods from one minute to several hours. The results reported here do not give convincing evidence for the presence of torsional oscillations of sunspots with a period of about an hour as detected by Gopasyuk, 1985 and Berton and Rayrode, 1985. Finally the authors discuss some typical features of quasi-five-minute oscillations in the sunspot penumbra and of non-periodic single velocity fluctuations in different penumbra areas. Title: Electric currents in a unipolar sunspot Authors: Pevtsov, A. A.; Peregud, N. L. Bibcode: 1990GMS....58..161P Altcode: A study is made of longitudinal electric currents of a unipolar sunspot (NOAA No. 4744). The pattern of longitudinal currents in the sunspot umbra indicates the presence of a common current system with predominance of the tangential component. The direction of this component, together with the sunspot's polarity, suggests the conclusion that currents flowing in the umbra sustain, at least, the sunspot magnetic field. The Lorentz force that is calculated in cylindrical symmetry is directed largely in radius out of the sunspot and exceeds considerably the horizontal gas pressure gradient. The nature of electric currents is discussed. Title: The system of electric currents of a unipolar sunspot. Authors: Pevtsov, A. A.; Peregud, N. L. Bibcode: 1989KFNT....5...12P Altcode: 1989KNFT....5...12P The structure of longitudinal electric currents of a unipolar sunspot (group SD 42/86) is studied. The pattern of longitudinal currents in the sunspot umbra shows evidence for the presence of a common system of currents with the tangential component predominance. The direction of this component and the sunspot polarity suggest that currents flowing in the umbra, at least, sustain the sunspot magnetic field. Under the assumption of cylindrical symmetry three components of the electric current density vector are calculated. Title: Ring Structures of the Transverse Magnetic Field in the Solar Photosphere Authors: Pevtsov, A. A. Bibcode: 1989ATsir1535...21P Altcode: No abstract at ADS Title: A two-component model of the magnetic field and velocity field in a sunspot Authors: Pevtsov, A. A. Bibcode: 1988IGAFS..83...85P Altcode: It is suggested that a sunspot penumbra consists of two types of elements: (1) a dark component with a nearly horizontal magnetic field of greater strength and (2) a light component with a nonhorizontal field of lesser strength. In the dark component material flows out of the spot (at a maximum velocity of 4 km/s), whereas in the light component material falls into the spot (at a velocity of 1 km/s). Title: A photoelectric guide for sunspot images Authors: Druzhinin, S. A.; Maslov, I. L.; Pevtsov, A. A. Bibcode: 1988IGAFS..83..149D Altcode: A photoelectric guide designed to directly handle sunspot images is described. A quadrant photodiode (serving as the photodetector) is placed in the beam reflected from the Dove prism face. The actuators are two plane-parallel plates attached to low-inertia electromagnetic drives, ensuring a high frequency (up to 3 Hz) of control action in response to image motion. The guide is placed in front of the spectrograph entrance slit and can be used with any standard AZU-5 telescope. Title: An evaluation of the stray light influence upon line-of sight velocity measurements in sunspots. Authors: Pevtsov, A. A. Bibcode: 1988BSolD1987...89P Altcode: Using Fe I 525.022 nm line profiles as inferred by J. Staude, the relative errors of line-of-sight velocity measurements were estimated for different areas of a sunspot and various fractions of stray light. The presence of 10% stray light reduces penumbral velocities by 20 to 30% and umbral velocities by 50%. A correction was made for the stray light of a sunspot velocity field map obtained with the Sayan Observatory vector magnetograph on 25 August 1986. Title: Unusual Behavior of Averaged K CAII Line Profile in Solar Disk Center Authors: Druzhinin, S. A.; Pevtsov, A. A.; Teplitskaja, R. B. Bibcode: 1987ATsir1512....5D Altcode: Averaged profiles of the solar Ca II K line were observed at the Solar Telescope on the Sayansk Observatory on July 6 and 9, 1986. At the limb the profile has the usual structure with the K3 minimum and two K2 emission peaks. In the centre of the disc, the profile has an unusual asymmetry with the red emission peak K2R completely lacking. The disappearance of the K2R peak was earlier observed in some fine-structure features on the Sun but it was never seen in averaged profiles. This effect seems to be not instrumental but of solar origin. Title: On the relationship between magnetic field and velocity field in a sunspot. Authors: Grigor'ev, V. M.; Pevtsov, A. A. Bibcode: 1987KFNT....3Q...3G Altcode: 1987KNFT....3Q...3G The paper deals with studying the relationship between magnetic fields and velocity fields in sunspots at the early stage of their development using observations with the vector magnetograph of the Sayan Observatory. It is pointed out that when the maps of the magnetic field's longitudinal component and the radial velocity are superimposed, the maximum velocity in the sunspot region corresponds mainly to the magnetic field zero line. A dependence of the radial velocity on the slope of the magnetic field vector to the line of sight is investigated. The approximation of cylindrical symmetry is used to reconstruct the velocity and magnetic field vectors for the leading sunspot of the group SD 135/1984. The results obtained testify the existence of two systems of motions. The matter within the sunspot is moving mainly across the magnetic field lines, but the sunspot umbra involves the region in which the directions of the magnetic field and of mass motion are the same. Title: A Study of Helical Oscillations in Sunspots Authors: Pevtsov, A. A.; Sattarov, I. S. Bibcode: 1985BSolD...3...65P Altcode: On the basis of observations and published data of 17 sunspots helical oscillations of different type have been detected: close to harmonic, and increasing and decreasing with time (Figure 1a). The mean period of oscillations is T=7.1 ± 3.0 days, mean amplitude A=40+/- 23 degrees, mean rotation rate C=17+/- 15 degrees per day. The depth of the penetration of the sunspot under the photosphere has been evaluated as 7500 km and the mass of oscillating portion of sunspot as M=2 x 1023 g using a simple mathematics model. The kinetic energy of rotation of sunspot is 1x1031 erg. Title: A study of helical oscillations in sunspots. Authors: Pevtsov, A. A.; Sattarov, I. S. Bibcode: 1985BSolD1985...65P Altcode: On the basis of observations and published data on 17 sunspots helical oscillations of different types have been detected: close to harmonic, and increasing and decreasing with time.