pevtsov

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Author name code: pevtsov
ADS astronomy entries on 2022-09-14
author:"Pevtsov, A."

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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
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.

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

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Title: 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.
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 &gt; 55 G) and strong (B &gt; 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.

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Title: Long-Term Solar Variability and Solar Cycle Predictions:
Current State of Understanding
Authors: Nandi, Dibyendu; Usoskin, Ilya; Pevtsov, Alexei
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.

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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
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.

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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.
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.

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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.
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.

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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
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.

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Title: Measurements of the Multi-Height Solar Vector Magnetic Field
Authors: Bertello, L.; Pevtsov, A.; Pevtsov, A. A.
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.

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Title: Improving the Understanding of Subsurface Structure and
Dynamics of Solar Active Regions
Authors: Tripathy, S. C.; Jain, K.; Kholikov, S.; Pevtsov, A.
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.

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Title: Analysis of Solar Hemispheric Chromosphere Properties using
the Kodaikanal Observatory Ca-K Index
Authors: Chowdhury, Partha; Belur, Ravindra; Bertello, Luca; Pevtsov,
Alexei A.
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.

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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
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.

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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
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.

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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
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 &lt; 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.

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

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Title: The Next Generation GONG (ngGONG) Project: Ground-based
Synoptic Studies of the Sun
Authors: Pillet, Valentin; Gilbert, Holly; Pevtsov, Alexei; de Wijn,
Alfred
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.

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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.
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.

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Title: Continuous Solar Observations from the Ground-Assessing Duty
Cycle from GONG Observations
Authors: Jain, Kiran; Tripathy, Sushanta C.; Hill, Frank; Pevtsov,
Alexei A.
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.

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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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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, <A
href="https://www.iswat-cospar.org">https://www.iswat-cospar.org</A>,
@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.
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.
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.
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
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.
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 &amp; K λ3934 &amp; 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.
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 &amp; 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.
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.
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.
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
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.
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
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 <A
href="http://cdsarc.u-strasbg.fr/">http://cdsarc.u-strasbg.fr</A>
(ftp://130.79.128.5) or via <A
href="http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A103">http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A103</A>

---------------------------------------------------------
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.
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.
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.
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
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.
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
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.
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.
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.
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.
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 (&lt; B_tor^2 &gt;) and poloidal
(&lt; B_pol^2 &gt;) energies are related as &lt; B_tor^2 &gt; ∝
&lt; B_pol^2 &gt; ^{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
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.
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
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
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.
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
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 &gt;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.
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
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 &gt; 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
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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
2017ApJ...835...25E Altcode: 2016arXiv161104540E
The most commonly used index of stellar magnetic activity is the
instrumental flux scale of singly ionized calcium H &amp; 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
&lt; {S}23&gt; =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 &lt; {S}\min &gt;
=0.1621+/- 0.0008, &lt; {{Δ }}{S}{cyc}&gt; =0.0145+/-
0.0012, &lt; {S}{cyc}&gt; =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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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 &amp; K Activity
Authors: Egeland, Ricky; Soon, Willie; Baliunas, Sallie; Hall,
Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W.
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 &amp; K line cores, due to
non-thermal (i.e. magnetic) heating in the lower chromosphere. The large
variation in Ca II H &amp; 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
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.
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.
2016csss.confE..72E Altcode:
We present composite time series of Ca II H &amp; 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 &amp; 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.
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.
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
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.
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 &amp; K Activity
Authors: Egeland, Ricky; Soon, Willie H.; Baliunas, Sallie L.; Hall,
Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W.
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 &amp; K line cores, due to
non-thermal (i.e. magnetic) heating in the lower chromosphere. The large
variation in Ca II H &amp; 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
2016SPD....47.1002B Altcode:
Over the past year the Synoptic Optical Long-term Investigations of the
Sun (SOLIS) team has made significant improvements to the data products
provided to the solar and heliospheric community. In particular,
a considerable effort has been dedicated to reprocess the archive of
vector and longitudinal photospheric magnetograms, from 2003 to present,
using the latest production code. This endeavor is now near completion
and will assure that all derived magnetic products, such as synoptic
maps and flux time series, are consistently calibrated. In addition,
new products have been recently developed. For example, time series of
daily averages of the Sun's polar magnetic field derived from full-disk
photospheric FeI 630.15 nm longitudinal magnetograms are now available
from the SOLIS website at solis.nso.edu/0/vsm/vsm_plrfield.html.New
intensity calibration of high resolution Ca II K &amp; H spectra from
the Integrated Sunlight Spectrometer (ISS) led to significant reduction
in daily variations of parameters derived from these spectra. The
SOLIS team will soon also release Carrington synoptic maps for the
three components of the photospheric magnetic field derived from vector
measurements taken in the Fe I 630.15 nm spectral line. The addition,
in late 2015, of a new Ca II 854.2 nm full-Stokes polarimeter into
the SOLIS core program of magnetic observations will make available to
the community daily chromospheric measurements of the complete Stokes
polarization vector.We present here a summary of these improvements,
with particular emphasis on the new products that can be accessed
from the SOLIS data page at solis.nso.edu/0/solis_data.html. For
a description of the diagnostic capability of the new Ca II 854.2
nm spectro-polarimeter and preliminary results we refer to other
presentations by SOLIS team members at this meeting.This work utilizes
SOLIS data obtained by the NSO Integrated Synoptic Program (NISP),
managed by the National Solar Observatory, which is operated by
the Association of Universities for Research in Astronomy (AURA),
Inc. under a cooperative agreement with the National Science Foundation.

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

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

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

---------------------------------------------------------
Title: The Solar Dynamo Zoo
Authors: Egeland, Ricky; Soon, Willie H.; Baliunas, Sallie L.; Hall,
Jeffrey C.; Pevtsov, Alexei A.; Henry, Gregory W.
2016SPD....47.1103E Altcode:
We present composite time series of Ca II H &amp; 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 &amp; 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.
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.
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
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
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.
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
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.
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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: Quantifying Photospheric Processes Using a New Pixel Dynamics
Model
Authors: Rasca, A.; Chen, J.; Pevtsov, A. A.
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.
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
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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
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.
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.
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&lt; |Br| &lt;500 G)and strong (|Br| &gt;1000 G) radial
magnetic fields. We find that while the current helicity of strong
fields follows the well-known hemispheric rule (i.e., θ.Hc &lt; 0),
Hc of weak fields exhibits an inverse hemispheric behavior (i.e., θ.Hc
&gt; 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&lt; |Br| &lt;500 G)and strong (|Br| &gt;1000 G) radial
magnetic fields. We find that while the current helicity of strong
fields follows the well-known hemispheric rule (i.e., θ.Hc &lt; 0),
Hc of weak fields exhibits an inverse hemispheric behavior (i.e.,
θ.Hc &gt; 0) albeit with large statistical scatter.

---------------------------------------------------------
Title: New Synoptic Measurements of Umbral Magnetic Fields
Authors: Harvey, J. W.; Hughes, A.; Marble, A.; Livingston, W. C.;
Pevtsov, A.; SOLIS Team
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.
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.
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&lt; |Br| &lt;500 G)and strong (|Br| &gt;1000 G) radial magnetic
fields. We find that while the current helicity of strong fields
follows the well-known hemispheric rule (i.e., ? &lt; 0), Hc of weak
fields exhibits an inverse hemispheric behavior (i.e., ? &gt; 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
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.
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.
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.
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.
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.
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.
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.
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 &amp; 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 &amp; Livingston.

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

---------------------------------------------------------
Title: 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.
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.
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.
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.
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.
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
(&lt;1000 G), while the fraction of sunspots with strongest field
strengths (&gt;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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 &amp; 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.
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.
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.
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.
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
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
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
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
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.
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.
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.
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.
2008JApA...29...49P Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Solar helicity as a constraint on the solar dynamo
Authors: Pevtsov, Alexei
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.
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.
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.
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
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
(&gt;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 &lt;Φ&gt;, , &lt;ɛ&gt;,
and &lt;∇Bz&gt;, 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.
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.
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.
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.
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.
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.
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.
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., &amp; 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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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 &amp; TRACE),
large scale motion of magnetic fields (SOHO/MDI), filament eruptions
(ISOON &amp; 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.
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.
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.
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.
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.
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.
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 (&lt;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.
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.
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.
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.
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 &lt; 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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 &amp; 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.
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.
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 (&gt; 70o)
and be absent between much closer regions (&lt; 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.
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.
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
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 &lt; 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.
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.
2003ASPC..286..393S Altcode: 2003ctmf.conf..393S
No abstract at ADS

---------------------------------------------------------
Title: Preface
Authors: Buechner, Joerg; Pevtsov, Alexei A.
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.
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.
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
2003ASPC..286.....P Altcode: 2003ctmf.conf.....P
No abstract at ADS

---------------------------------------------------------
Title: Helicity Generation and Signature in the Solar Atmosphere
Authors: Pevtsov, Alexei A.
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.
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.
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.
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.
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" (&gt; 1 day) emergence. For
these regions α increases faster than the separation. In two "rapid"
(&lt; 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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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, &gt;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.
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.
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.
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 (&gt;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 &amp;\ Rust
[“Coronal Mass Ejections,” AGU Monograph Series 99, 139, 1997]. %
At least half of Bothmer &amp;\ 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.
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.
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.
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.
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.
2000JApA...21..213C Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Coronal Structures as Tracers of Sub-surface Processes
Authors: Pevtsov, A. A.; Canfield, R. C.
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.
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,
&gt;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.
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.
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.
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.
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.
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.
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 &amp; 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.
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.
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
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 Solar Dynamo and Emerging Flux
Authors: Fisher, G. H.; Fan, Y.; Longcope, D. W.; Linton, M. G.;
Pevtsov, A. A.
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.
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.
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.
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.
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 &lt;u \b.dot \b.nabla × u&gt;. 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.
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.
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.
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.
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.
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 &lt;αp&gt; 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, &lt;αc&gt;, for each active region. In active regions for which the photospheric α-map is predominantly
of one sign, we find that the values of &lt;αp&gt; and
&lt;αc&gt; 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 &lt;αp&gt;
and &lt;αc&gt; 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.
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
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.
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.
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.
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.
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.
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.
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.
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.

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Title: Line-of-sight velocity measurements using a
dissector-tube. 1. an instrument description
Authors: Druzhinin, S. A.; Pevtsov, A. A.
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.

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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.
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.

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Title: Relation Between the Longitudinal Field and Radial Velocity
in Sunspots
Authors: Pevtsov, A. A.
1993ASPC...46...78P Altcode: 1993IAUCo.141...78P; 1993mvfs.conf...78P
No abstract at ADS

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Title: The relationship between the longitudinal magnetic field and
the line-of-sight velocity at different angular positions of sunspots
Authors: Pevtsov, A. A.
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.

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Title: Spatial distribution of line-of-sight velocities in a quiescent
prominence.
Authors: Druzhinin, S. A.; Pevtsov, A. A.; Mashnich, G. P.
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″.

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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.
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.

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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.
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.

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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.
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.

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Title: Electric currents in a unipolar sunspot
Authors: Pevtsov, A. A.; Peregud, N. L.
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.

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Title: The system of electric currents of a unipolar sunspot.
Authors: Pevtsov, A. A.; Peregud, N. L.
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.

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Title: Ring Structures of the Transverse Magnetic Field in the
Solar Photosphere
Authors: Pevtsov, A. A.
1989ATsir1535...21P Altcode:
No abstract at ADS

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Title: A two-component model of the magnetic field and velocity
field in a sunspot
Authors: Pevtsov, A. A.
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).

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Title: A photoelectric guide for sunspot images
Authors: Druzhinin, S. A.; Maslov, I. L.; Pevtsov, A. A.
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.

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Title: An evaluation of the stray light influence upon line-of sight
velocity measurements in sunspots.
Authors: Pevtsov, A. A.
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.

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Title: Unusual Behavior of Averaged K CAII Line Profile in Solar
Disk Center
Authors: Druzhinin, S. A.; Pevtsov, A. A.; Teplitskaja, R. B.
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.

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Title: On the relationship between magnetic field and velocity field
in a sunspot.
Authors: Grigor'ev, V. M.; Pevtsov, A. A.
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.

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Title: A Study of Helical Oscillations in Sunspots
Authors: Pevtsov, A. A.; Sattarov, I. S.
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.

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Title: A study of helical oscillations in sunspots.
Authors: Pevtsov, A. A.; Sattarov, I. S.
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.