abramenko

explanation blue bibcodes open ADS page with paths to full text

Author name code: abramenko
ADS astronomy entries on 2022-09-14
author:"Abramenko, Valentina I." OR author:"Abramenko, Valentyna I."

---------------------------------------------------------
Title: Synthetic solar cycle for active regions violating the Hale's
polarity law
Authors: Zhukova, A.; Khlystova, A.; Abramenko, V.; Sokoloff, D.
2022MNRAS.512.1365Z Altcode: 2022MNRAS.tmp..593Z; 2022arXiv220301274Z
Long observational series for bipolar active regions (ARs) provide
significant information about the mutual transformation of the poloidal
and toroidal components of the global solar magnetic field. The
direction of the toroidal field determines the polarity of leading
sunspots in ARs in accordance with the Hale's polarity law. The vast
majority of bipolar ARs obey this regularity, whereas a few per cent
of ARs have the opposite sense of polarity (anti-Hale ARs). However,
the study of these ARs is hampered by their poor statistics. The data
for five 11-yr cycles (16-18 and 23, 24) were combined here to compile
a synthetic cycle of unique time length and latitudinal width. The
synthetic cycle comprises data for 14838 ARs and 367 of them are the
anti-Hale ARs. A specific routine to compile the synthetic cycle
was demonstrated. We found that, in general, anti-Hale ARs follow
the solar cycle and are spread throughout the time-latitude diagram
evenly, which implies their fundamental connection with the global
dynamo mechanism and the toroidal flux system. The increase in their
number and percentage occurs in the second part of the cycle, which
is in favour of their contribution to the polar field reversal. The
excess in the anti-Hale ARs percentage at the edges of the butterfly
diagram and near an oncoming solar minimum (where the toroidal field
weakens) might be associated with the strengthening of the influence
of turbulent convection and magnetic field fluctuations on the arising
flux tubes. The evidence of the misalignment between the magnetic and
heliographic equators is also found.

---------------------------------------------------------
Title: Magnetic Field Re-configuration Associated With a Slow Rise
Eruptive X1.2 Flare in NOAA Active Region 11944
Authors: Yurchyshyn, Vasyl; Yang, Xu; Nita, Gelu; Fleishman, Gregory;
Abramenko, Valentina; Inoue, Satoshi; Lim, Eun-Kyung; Cao, Wenda
2022FrASS...916523Y Altcode:
Using multi-wavelength observations, we analysed magnetic field
variations associated with a gradual X1.2 flare that erupted on
January 7, 2014 in active region (AR) NOAA 11944 located near the disk
center. A fast coronal mass ejection (CME) was observed following the
flare, which was noticeably deflected in the south-west direction. A
chromospheric filament was observed at the eruption site prior to and
after the flare. We used SDO/HMI data to perform non-linear force-free
field extrapolation of coronal magnetic fields above the AR and to
study the evolution of AR magnetic fields prior to the eruption. The
extrapolated data allowed us to detect signatures of several magnetic
flux ropes present at the eruption site several hours before the
event. The eruption site was located under slanted sunspot fields
with a varying decay index of 1.0-1.5. That might have caused the
erupting fields to slide along this slanted magnetic boundary rather
than vertically erupt, thus explaining the slow rise of the flare
as well as the observed direction of the resulting CME. We employed
sign-singularity tools to quantify the evolutionary changes in the
model twist and observed current helicity data, and found rapid and
coordinated variations of current systems in both data sets prior to
the event as well as their rapid exhaustion after the event onset.

---------------------------------------------------------
Title: Probing the rotation rate of solar active regions: the
comparison of methods
Authors: Kutsenko, Alexander S.; Abramenko, Valentina I.
2022OAst...30..219K Altcode:
Sunspot groups are often used as tracers to probe the differential
rotation of the Sun. However, the results on the rotation rate variation
obtained by different authors are not always in agreement. The reason
for this might be a number of effects. In particular, faster decay of
the following part of a sunspot group results in a false apparent shift
of the area-weighted center of the group toward the leading part. In
this work we analyze how significantly this effect may contribute to
the derived rotation rate. For a set of 670 active regions, we compare
the rotation rate derived from continuum intensity images to that
derived from line-of-sight magnetograms. We found that the difference
between the calculated rotation rates is 0.45° day−1 on
average. This value is comparable to the difference between the rotation
rate of the solar surface near the equator and at 30° latitude. We
conclude that the accuracy of the rotation rate measurements using
white-light images is not satisfactory. Magnetograms should be used
in future research on the differential rotation of the Sun.

---------------------------------------------------------
Title: 11-year dynamics of coronal hole and sunspot areas
Authors: Andreeva, Olga; Abramenko, Valentina; Malashchuk, Valentina
2022OAst...31...22A Altcode:
The paper presents study the 11-year dynamics of solar activity on
the basis of new observational material on coronal holes (CHs) and
sunspots in the period from May 13, 2010 to May 13, 2021. We used
the Heliophysics Event Knowledgebase (HEK) to obtain information on
CHs areas. For 11 years of observations, we processed about 18000
CHs. Slightly more than 8000 are polar, the rest are nonpolar CHs. The
statistical volume of the presented material is quite extensive and
gives grounds for the study of the dynamics of different types of CHs
during the cycle. Our research has shown: in the 24th solar activity
cycle, the South led for polar CHs and the North led for nonpolar
ones. We established a relationship between the number and area of CHs
and the phase of the solar cycle. The number and daily total area of
polar CHs increases at the minima of solar activity and decreases at
the maximum of the cycle. This is consistent with the general concept
of polar CHs as the main source of the solar dipole magnetic field. An
asymmetry in both the number and areas of polar coronal holes in the
northern and southern hemispheres is observed. It is shown that the
areas of nonpolar CHs change quasi-synchronously with sunspot activity,
which suggests a physical connection between these two phenomena.

---------------------------------------------------------
Title: Coronal Holes of Cycle 24 in Observations at the Solar
Dynamics Observatory
Authors: Andreeva, O. A.; Abramenko, V. I.; Malashchuk, V. M.
2021Ge&Ae..61S...1A Altcode:
The dynamics of the areas of coronal holes and their localization
on the Sun in solar cycle 24 and the minimum of cycles 24-25 were
analyzed. The study is based on observational data obtained by the
Atmospheric Imaging Assembly instrument in the Fe XII 19.3 nm line
onboard the Solar Dynamics Observatory spacecraft in the period of May
13, 2010-December 31, 2020. The division of all coronal holes into polar
and nonpolar showed that the daily total area of polar coronal holes
increases during solar minima and decreases at the cycle maximum. This
is consistent with the general concept of polar coronal holes as the
main source of the solar dipole magnetic field. There is an asymmetry
in the areas of polar coronal holes in the northern and southern
hemispheres, which requires further explanation. It is shown that
the areas of nonpolar coronal holes vary quasi-synchronously with the
sunspot activity, which suggests the existence of a physical connection
between these two phenomena. Apparently, the nature of the magnetic
fields of polar and nonpolar coronal holes is different. The magnetic
field lines of nonpolar coronal holes are possibly very high loops that
close through the corona in other regions of the Sun, while the magnetic
field lines of polar coronal holes extend far into the heliosphere.

---------------------------------------------------------
Title: Parameters of Electric Currents in Active Regions
with Different Levels of Flare Productivity and Different
Magnetomorphological Types
Authors: Fursyak, Yu. A.; Abramenko, V. I.; Zhukova, A. V.
2021Ge&Ae..61.1197F Altcode:
In this paper, the magnetic-field and electric-current parameters are
calculated for a sample of 73 active regions (ARs) of solar activity
cycle 24 based on magnetographic data from the Helioseismic and Magnetic
Imager (HMI) instrument aboard the Solar Dynamics Observatory (SDO). The
calculated values are compared to the level of flare productivity and
features of the AR morphology. The following results are obtained. (1)
The imbalance of local vertical electric currents in the regions
of the studied sample does not exceed a few percent (the maximum
obtained value is 8.08%), in contrast to the magnetic-flux imbalance,
which can reach a few tens of percent (the maximum absolute value is
82.11%). (2) The highest correlation of the calculated parameters of
electric current with the level of AR flare productivity is observed
for the total unsigned vertical electric current $\overline {{{I}_{{z
{tot}}}}} $ (a Pearson correlation coefficient of k = 0.67) and the
average unsigned vertical electric current density $\left\langle
{\overline {\left| {{{j}z}} \right|} } \right\rangle $
(k = 0.66), which are averaged over the AR monitoring period. (3)
It is shown that the values of the electric-current parameters for
the Ars in which the basic empirical laws of the Babcock-Leighton
dynamo theory are violated are higher than the corresponding values of
the electric current parameters for the regular ARs. This result may
indicate that there is additional energy pumping by the local dynamo
mechanisms in the irregular regions.

---------------------------------------------------------
Title: Signature of the turbulent component of the solar dynamo on
active region scales and its association with flaring activity
Authors: Abramenko, Valentina I.
2021MNRAS.507.3698A Altcode: 2021arXiv211104425A
It is a challenging problem to obtain observational evidence of the
turbulent component of solar dynamo operating in the convective zone
because the dynamo action is hidden below the photosphere. Here we
present results of a statistical study of flaring active regions
(ARs) that produced strong solar flares of an X-ray class X1.0 and
higher during a time period that covered solar cycles 23 and 24. We
introduced a magneto-morphological classification of ARs, which allowed
us to estimate the possible contribution of the turbulent component
of the dynamo into the structure of an AR. We found that in 72 per
cent of cases, flaring ARs do not comply with the empirical laws of
the global dynamo (frequently they are not bipolar ARs or, if they
are, they violate the Hale polarity law, the Joy law, or the leading
sunspot prevalence rule). This can be attributed to the influence
of the turbulent dynamo action inside the convective zone on spatial
scales of typical ARs. Thus, it appears that the flaring is governed
by the turbulent component of the solar dynamo. The contribution into
the flaring from these AR 'violators' (irregular ARs) is enhanced
during the second maximum and the descending phase of a solar cycle,
when the toroidal field weakens and the influence of the turbulent
component becomes more pronounced. These observational findings are
in consensus with a concept of the essential role of non-linearities
and turbulent intermittence in the magnetic fields generation inside
the convective zone, which follows from dynamo simulations.

---------------------------------------------------------
Title: Magnetic Field Configuration Associated With A Slow Rise
Eruptive X1.2 Flare In Active Region 11944
Authors: Yang, X.; Yurchyshyn, V.; Nita, G.; Abramenko, V.; Lim, E.;
Cao, W.
2021AAS...23812707Y Altcode:
Using multi-wavelength observations, we studied a gradual X1.2 flare
that erupted on January 7, 2014, in active region (AR) NOAA 11944
located near the disk center. A fast coronal mass ejection (CME) was
observed following the flare; however, it was strongly deflected in the
south-west direction. We used SDO/HMI data to perform extrapolation of
coronal magnetic fields and to study the evolution of AR magnetic fields
before the eruption. Extrapolated data allowed us to detect a flux rope
(FR) present at the eruption site several hours before the event. That
was the only well-defined FR present in the AR. Although the strapping
and core fields in the model have significantly changed after the flare,
the model FR did not erupt. We note that a chromospheric filament
was observed at the eruption site prior to and after the flare. The
eruption site was located under sunspot canopy fields with a decay
index of about 0.5, which is not favorable for torus instability to
develop. That might have caused the erupting fields to slide along the
canopy rather than vertically erupt, thus explaining the slow rise of
the flare as well as the observed direction of the resulting CME. We
employed sign-singularity tools to quantify the evolutionary changes
in a model twist and observed current helicity data, and found rapid
enhancements in the current systems in both data sets prior to the
event as well as their rapid exhaustion after the event onset.

---------------------------------------------------------
Title: A statistical study of magnetic flux emergence in solar active
regions prior to strongest flares
Authors: Kutsenko, Alexander S.; Abramenko, Valentina I.; Plotnikov,
Andrei A.
2021arXiv210503886K Altcode:
Using the data on magnetic field maps and continuum intensity for
Solar Cycles 23 and 24, we explored 100 active regions (ARs) that
produced M5.0 or stronger flares. We focus on the presence/absence of
the emergence of magnetic flux in these ARs 2-3 days before the strong
flare onset. We found that 29 ARs in the sample emerged monotonously
amidst quiet-Sun area. A major emergence of a new magnetic flux within
pre-existing AR yielding the formation of a complex flare-productive
configuration was observed in another 24 cases. For 30 ARs, an
insignificant (in terms of the total magnetic flux of pre-existing
AR) emergence of a new magnetic flux within the pre-existing magnetic
configuration was observed; for some of them the emergence resulted
in a formation of a configuration with a small $\delta$-sunspot. 11
out of 100 ARs exhibited no signatures of magnetic flux emergence
during the entire interval of observation. In 6 cases the emergence
was in progress when the AR appeared on the Eastern limb, so that
the classification and timing of emergence were not possible. We
conclude that the recent flux emergence is not a necessary and/or
sufficient condition for strong flaring of an AR. The flux emergence
rate of analysed here flare-productive ARs was compared with that for
flare-quiet ARs analysed in our previous studies. We revealed that
the flare-productive ARs tend to display faster emergence than the
flare-quiet ones.

---------------------------------------------------------
Title: On the possibility of probing the flare productivity of an
active region in the early stage of emergence
Authors: Kutsenko, Alexander S.; Abramenko, Valentina I.; Kutsenko,
Olga K.
2021MNRAS.501.6076K Altcode: 2020arXiv201112062K
Prediction of the future flare productivity of an active region (AR)
when it is in the early-emergence stage is a longstanding problem. The
aim of this study is to probe two parameters of the photospheric
magnetic field, both derived during the emergence phase of an AR, and
to compare them with the flare productivity of a well developed AR. The
parameters are: (i) the index of the magnetic power spectrum (the slope
of the spectrum) at the stage of emergence, and (ii) the flux emergence
rate. Analysis of 243 emerging ARs showed that the magnetic power index
increases from values typical of quiet-Sun regions to those typical
of mature ARs within a day, while the emergence proceeds for several
days; frequently, after the increase, the value of the power index
oscillates around some mean value with the fluctuations being several
times smaller than the growth of the power index during the emergence
onset. For a subset of 34 flare-productive ARs we found no correlation
between the power spectrum index at the stage of emergence and the
flare index derived from the entire interval of the AR's presence on
the disc. At the same time, the flux emergence rate correlates well
with the flare index (Pearson's correlation coefficient is 0.74). We
conclude that a high flux emergence rate is a necessary condition for
an AR to produce strong flares in the future; thus the flux emergence
rate can be used to probe the future flare productivity of an AR.

---------------------------------------------------------
Title: Self-Organized Criticality of Solar Magnetism
Authors: Abramenko, V. I.
2020Ge&Ae..60..801A Altcode:
Self-organization is a property of any nonlinear, dynamic, dissipative
system that evolves under the influence of external forces and positive
feedback. Self-organization leads to the creation of order from chaos,
thus reducing the entropy of the system. As a result, numerous small
elements and/or short-lived elements form structures with large
spatiotemporal scales. One very important property of a nonlinear,
dissipative system is intermittency in space and time, which means that
the system is capable of spontaneous transition to a critical state,
the so-called state of self-organized criticality (SOC). In this state,
small fluctuations can become an impetus for an avalanche of any
scale. The object of our research, a constantly evolving convective
zone with a magnetic field and turbulent plasma flows, is an ideal
example of a nonlinear, dynamic, dissipative system. This review is
devoted to the systematization of recent studies on the identification
and study of self-organization in the processes of the generation,
evolution, and dissipation of magnetic fields on the Sun.

---------------------------------------------------------
Title: A Catalog of Bipolar Active Regions Violating the Hale Polarity
Law, 1989 - 2018
Authors: Zhukova, Anastasiya; Khlystova, Anna; Abramenko, Valentina;
Sokoloff, Dmitry
2020SoPh..295..165Z Altcode: 2020arXiv201014413Z
There is no list of bipolar active regions (ARs) with reverse polarity
(anti-Hale regions), although statistical investigations of such ARs
(bearing the imprint of deep subphotospheric processes) are important
for understanding solar-cycle mechanisms. We studied 8606 ARs from 1
January 1989 to 31 December 2018 to detect anti-Hale regions and to
compile a catalog. The Solar and Heliospheric Observatory (SOHO) and
the Solar Dynamics Observatory (SDO) data, as well as the Debrecen
Photoheliographic Data, the Mount Wilson Observatory catalog and
drawings, and the USAF/NOAA Solar Region Summary were used. Complex,
ambiguous cases related to anti-Hale region identification were
analyzed. Two basic and four additional criteria to identify an AR as
an anti-Hale region were formulated. The basic criteria assume that: i)
dominant features of an AR have to form a bipole of reverse polarity
with sunspots/pores of both polarities being present; ii) magnetic
connections between the opposite polarities have to be observed. A
catalog of anti-Hale regions (275 ARs) is compiled. The catalog
contains: NOAA number, date of the greatest total area of sunspots,
coordinates, and corrected sunspot area for this date. The tilt and the
most complex achieved Mount Wilson magnetic class are also provided. The
percentage of anti-Hale groups meeting the proposed criteria is
≈3.0 % from all studied ARs, which is close to early estimations by
authors who had examined each AR individually: ≈2.4 % by Hale and
Nicholson (Astrophys. J.62, 270, 1925) and ≈3.1 % by Richardson
(Astrophys. J.107, 78, 1948). The enhancement of the anti-Hale
percentage in later research might be related to: i) increasing
sensitivity of instruments (considering smaller and smaller bipoles);
ii) the ambiguities in the anti-Hale region identification. The catalog
is available as the Supplementary Information and at the CrAO website
(sun.crao.ru/databases/catalog-anti-hale/).

---------------------------------------------------------
Title: Sunspot magnetic fields: a comparison between the CrAO and
SDO/HMI data
Authors: Biktimirova, Regina; Abramenko, Valentina
2020AcAT....1b...1B Altcode:
We performed a digitization of maximum magnetic field measurements in
sunspots. The original data were acquired as drawings at the Crimean
Astrophysical Observatory of the Russian Academy of Sciences (CrAO
RAS). About 1000 sunspots observed in 2014 have been analyzed. The
data were compared to the corresponding measurements from the SDO/HMI
instrument (with both the line-of-sight magnetic field Bz(HMI) and the
modulus of the magnetic field vector B(HMI)). For the same sunspot, the
maximum modulus of the magnetic field derived at CrAO was compared to
the corresponding value from HMI. The Crimean data and the space-based
data (of both types) were found to be in direct proportion to each
other. A linear approximation over the entire range of measurements
(1-4) kilogauss (kG) shows a Pearson correlation coefficient of 0.71
(with the 95 % confidence boundaries of 0.68-0.74) and a slope of linear
regression of 0.65±0.02 for both types of the space-based data. A
linear approximation over the range of strong fields B(CrAO) &gt; 1.8 kG
gives a similar correlation, however the slope of linear regression is
far closer to unity and constitutes 0.90 for the relationship (Bz(HMI)
vs B(CrAO)) and 0.84 for the relationship (B(HMI) vs B(CrAO)). In
the range of weak fields B(CrAO) &lt; 1.8 kG, a non-linear deviation
(exceeding) of the space-based data is observed. Non-linearity can
be explained, in part, by a specific routine of the magnetic field
measurements at CrAO, however further investigations are needed to
explore sources of possible non-linearity in the HMI data. The Crimean
measurements of the maximum magnetic field in sunspots are concluded
to be in good agreement with the corresponding SDO/HMI measurements,
and therefore they can be used for scientific purposes.

---------------------------------------------------------
Title: Cyclic Variations, Magnetic Morphology, and Complexity of
Active Regions in Solar Cycles 23 and 24
Authors: Zhukova, A. V.; Sokoloff, D. D.; Abramenko, V. I.; Khlystova,
A. I.
2020Ge&Ae..60..673Z Altcode:
In this paper, 2046 active regions of solar cycle 23 and 1507
active regions of solar cycle 24 observed during the period from
May 1996 to December 2018 have been studied. The sunspot groups are
distributed according to the recently proposed magneto-morphological
classification. Regular active regions (obeing Hale's polarity law,
Joy's law, and having a leading sunspot that prevails over the main
tail sunspot), irregular sunspot groups, and unipolar spots have been
identified. It is shown that regular active regions make the major
contribution to the development of the cycle, which is consistent with
the magnetic cycle models. The contribution of irregular sunspot groups
is about two to five times smaller (at the cycle maxima) and comparable
with the contribution of regular active regions in the cycle minima,
which may indicate the joint action of the global mean field dynamo and
the fluctuation dynamo. The increase in the number of irregular active
regions in the southern hemisphere at the second maximum of each of
the studied cycles can be explained by weakening of the toroidal field
(produced by the global dynamo) and an increase in the contribution of
the fluctuation dynamo to their competitive interaction. Comparison of
the curves describing the time dependence of the sunspot group asymmetry
index of regular and irregular active regions showed that, when the
activity moves to the southern hemisphere, regular active regions are
ahead irregular active regions by ~1.5-2 years. The application of
the magneto-morphological classification made it possible to detect
the alternating activity of the northern and southern hemispheres
in both studied cycles; the order of a response of the hemispheres
changed from cycle to cycle; the opposite priority with respect to
each other was observed for regular and irregular active regions in
the given cycle. Comparison of our results with the results on the
cyclic variations of sunspot groups of simple and complex magnetic
configuration in different hemispheres obtained earlier by other authors
showed the following. An increase of the toroidal field produced by the
global dynamo makes it difficult to detect asymmetry manifestations
and to reveal the effect of the fluctuation dynamo on the magnetic
tubes of the active regions.

---------------------------------------------------------
Title: Analysis of quiet-sun turbulence on the basis of SDO/HMI and
goode solar telescope data
Authors: Abramenko, Valentina I.; Yurchyshyn, Vasyl B.
2020MNRAS.497.5405A Altcode: 2020arXiv200806264A; 2020MNRAS.tmp.2438A
We analysed line-of-sight magnetic fields and magnetic power
spectra of an undisturbed photosphere using magnetograms acquired
by the Helioseismic and Magnetic Imager (HMI) on-board the Solar
Dynamic Observatory and the Near InfraRed Imaging Spectrapolarimeter
(NIRIS) operating at the Goode Solar Telescope of the Big Bear Solar
Observatory. In the NIRIS data, we revealed thin flux tubes of 200-400
km in diameter and of 1000-2000 G field strength. The HMI power spectra
determined for a coronal hole, a quiet sun, and a plage areas exhibit
the same spectral index of -1 on a broad range of spatial scales from
10-20 Mm down to 2.4 Mm. This implies that the same mechanism(s)
of magnetic field generation operate everywhere in the undisturbed
photosphere. The most plausible one is the local turbulent dynamo. When
compared to the HMI spectra, the -1.2 slope of the NIRIS spectrum
appears to be more extended into the short spatial range until the
cut-off at 0.8-0.9 Mm, after which it continues with a steeper slope of
-2.2. Comparison of the observed and Kolmogorov-type spectra allowed
us to infer that the Kolmogorov turbulent cascade cannot account for
more than 35 per cent of the total magnetic energy observed in the
scale range of 3.5-0.3 Mm. The energy excess can be attributed to other
mechanisms of field generation such as the local turbulent dynamo and
magnetic superdiffusivity observed in an undisturbed photosphere that
can slow down the rate of the Kolmogorov cascade leading to a shallower
resulting spectrum.

---------------------------------------------------------
Title: Dynamics of Electric Current's Parameters in Active Regions
on the Sun and Their Relation to the Flare Index
Authors: Fursyak, Yu. A.; Abramenko, V. I.; Kutsenko, A. S.
2020Ap.....63..260F Altcode: 2020Ap....tmp...29F; 2020Ap....tmp...35F
Data from the Helioseismic and Magnetic Imager (HMI) on board the
Solar Dynamics Observatory (SDO) on the components of the magnetic
field vector in the photosphere for 39 active regions (AR) of the
24th solar activity cycle are used to calculate the parameters of
the electric current. The time variations in the electric current
parameters in the AR over the time the region is within ±35° of
the central meridian are studied. An attempt is made to relate the
parameters of the current in the photosphere and their dynamics to
the level of flare activity of the region. These studies have yielded
the following results: (1) The change in the total unsigned current
in an AR is synchronous or quasi-synchronous with changes in the
magnetic flux; (2) A relation between the total unsigned current and
the flare index (FI) exists, but is weak (correlation k = 0.48); (3)
The imbalance of the vertical electric currents for all 39 of the AR
studied here was low and did not exceed a few percent, which indicates
closure of the current structures on all scales within an AR; (4)
The highest correlation (k = 0.72) with the flare index is observed
for a time averaged absolute value of the density of the vertical
electric current; (5) Statistical studies yield a critical level
of &lt;|jz|&gt; equal to 2.7 mA/m2: when this
level is exceeded in an AR, flares with higher x-ray classes (M and X)
are observed and when the current density falls below the threshold
value, there is a reduction in the flare productivity of the region;
(6) For the example of two regions with an emerging magnetic flux it is
shown that pumping magnetic energy into the corona requires some time;
the time interval between the jump in &lt;|jz|&gt; and the
onset of the development of the first powerful flares in x-ray classes
M and X is at least 12-20 hours; (7) The character of the relation
between the time variations in the average value of the density of the
horizontal current &lt;|j⊥|&gt; and the imbalance in the
vertical current ρjz with the level of flare activity of
an AR is more complicated and requires separate, more detailed studies.

---------------------------------------------------------
Title: Spatial Distribution of the Origin of Umbral Waves in a
Sunspot Umbra
Authors: Yurchyshyn, Vasyl; Kilcik, Ali; Şahin, Seray; Abramenko,
Valentina; Lim, Eun-Kyung
2020ApJ...896..150Y Altcode: 2020arXiv200504202Y
Umbral flashes (UFs) are emissions in the core of chromospheric lines
caused by upward propagating waves steepening into shocks. UFs are
followed by an expanding blueshifted umbral wave and redshifted plasma
returning to the initial state. Here we use 5 s cadence images acquired
at ±0.04 nm off the H ${}_{\alpha }$ line center by the Visible Imaging
Spectrometer installed on the Goode Solar Telescope (GST) to detect
the origin of UFs and umbral waves (UWs) in a sunspot with a uniform
umbra free of light bridges and clusters of umbral dots. The data
showed that UFs do not randomly originate over the umbra. Instead, they
appear to be repeatedly triggered at locations with the lowest umbral
intensity and the most powerful oscillations of H ${}_{\alpha }$ -0.04
nm intensity. GST magnetic field measurements using the Near-Infrared
Imaging Spectropolarimeter also showed that the dominant location of
prevalent UF origin is cospatial associated with the strongest fields
in the umbra. Interface Region Imaging Spectrograph 149.0 nm images
showed that no bright UV loops were anchored in the umbra in general,
and near the UF patches in particular, suggesting that UFs and UWs
alone cannot be responsible for the origin of warm coronal loops. We
thus conclude that the existence of locations with prevalent origin of
UFs confirms the idea that they may be driven by a subsurface source
located near the axis of a flux rope, while the presence of several UFs
trigger centers may indicate the complex structure of a sunspot umbra.

---------------------------------------------------------
Title: Coronal Holes during the Period of Maximum Asymmetry in the
24th Solar Activity Cycle
Authors: Andreeva, O. A.; Abramenko, V. I.; Malaschuk, V. M.
2020Ap.....63..114A Altcode: 2020Ap....tmp...15A
The current 24th solar activity cycle differs substantially from
previous cycles in a number of parameters, especially in terms of a
large asymmetry in the number of sunspots (Sp) during the second peak
of its maximum. From March 2013 through December 2015. a significant
predominance was observed in the number of sunspots in the southern
hemisphere. The main purpose of this paper is to clarify the behavior
of coronal holes (CH) during this period. This study is based on an
analysis of data recorded by the 19.3 nm channel of the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO). Two
methods of detecting CH (simplified visual and the Spatial Possibilistic
Clustering Algorithm (SPoCA)) are used to obtain time series of daily
total CH areas for the Sun's northern and southern hemispheres. The
two methods agree on the estimated areas of the CH. A comparison of
the observed variations in the areas of the CH with the numbers and
areas of sunspots showed that in this period, activity predominates in
the S-hemisphere both in terms of sunspots and in terms of the total
CH area. Here a rise in the area of the CH follows a rise in sunspot
activity by roughly half a year. It is suggested that the CH and spots
are associated elements of the overall magnetic activity of the Sun,
in qualitative agreement with studies of activity complexes. A dipole
poloidal field in the form of open CH fields and a toroidal field in
the form of active regions are related on time scales substantially
shorter than the solar cycle.

---------------------------------------------------------
Title: Rapid Evolution of Type II Spicules Observed in Goode Solar
Telescope On-disk Hα Images
Authors: Yurchyshyn, Vasyl; Cao, Wenda; Abramenko, Valentina; Yang,
Xu; Cho, Kyung-Suk
2020ApJ...891L..21Y Altcode: 2020arXiv200504253Y
We analyze ground-based chromospheric data acquired at a high temporal
cadence of 2 s in wings of the Hα spectral line using the
Goode Solar Telescope operating at the Big Bear Solar Observatory. We
inspected a 30 minute long Hα-0.08 nm data set to find
that rapid blueshifted Hα excursions (RBEs), which are a
cool component of type II spicules, experience very rapid morphological
changes on timescales of the order of 1 s. Unlike typical reconnection
jets, RBEs very frequently appear in situ without any clear evidence
of Hα material being injected from below. Their evolution
includes inverted "Y," "V," "N," and parallel splitting (doubling)
patterns as well as sudden formation of a diffuse region followed
by branching. We also find that the same feature may undergo several
splitting episodes within about a 1 minute time interval.

---------------------------------------------------------
Title: Distributed Electric Currents in Solar Active Regions
Authors: Fursyak, Yuriy A.; Kutsenko, Alexander S.; Abramenko,
Valentina I.
2020SoPh..295...19F Altcode: 2019arXiv191207032F
Using magnetographic data provided by the Helioseismic and Magnetic
Imager on board the Solar Dynamics Observatory, we analyzed the
structure of magnetic fields and vertical electric currents in six
active regions (ARs) with different levels of flare activity. We found
that electric currents are well balanced over the entire AR; for all
of them the current imbalance is below 0.1%, which means that any
current system is closed within an AR. Decomposition of the transverse
magnetic field vector into two components allowed us to reveal the
existence of large-scale vortex structures of the azimuthal magnetic
field component around main sunspots of ARs. In each AR, we found a
large-scale electric current system occupying a vast area, which we
call distributed electric current. For ARs obeying the Hale polarity
law and the hemispheric helicity sign rule, the distributed current
is directed upward in the leading part of the AR and it appears to
be closing back to the photosphere in the following part through the
corona and chromosphere. Our analysis of the time variations of the
magnitude of the distributed electric currents showed that low-flaring
ARs exhibit small variations of the distributed currents in the range
of ±20 ×1012A, whereas the highly flaring ARs exhibited
significant slow variations of the distributed currents in the range
of 30 -95 ×1012A. Intervals of the enhanced flaring appear
to be co-temporal with smooth enhancements of the distributed electric
current.

---------------------------------------------------------
Title: Magnetic power spectrum in the undisturbed solar photosphere
Authors: Abramenko, Valentina; Kutsenko, Olga
2020AcAT....1a...1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic Power Spectra of Emerging Active Regions
Authors: Kutsenko, Olga K.; Kutsenko, Alexander S.; Abramenko,
Valentina I.
2019SoPh..294..102K Altcode: 2019arXiv190707952K
Magnetic field data provided by the Helioseismic and Magnetic Imager
on board the Solar Dynamics Observatory were utilized to explore the
changes in the magnetic energy of four active regions (ARs) during their
emergence. We found that at the very early stage of the magnetic flux
emergence, an abrupt steepening of the magnetic power spectrum takes
place leading to rapid increase of the absolute value of the negative
spectra power index α in E (k )∼kα. As the emergence
proceeds, the energy increases at all scales simultaneously implying
that elements of all sizes do appear in the photosphere. Meanwhile,
the energy gain at scales larger than ≈10 Mm prevails over that at
smaller scales. Both direct (i.e., fragmentation of large structures
into smaller ones) and inverse (i.e., merging of small magnetic
features into larger elements) cascades are readily observed during the
emergence. However, in the case of inverse cascade, the total energy
gained at large scales exceeds the energy loss at smaller scales
assuming simultaneous appearance of large-scale magnetic entities
from beneath the photosphere. We conclude that most of the time the
energy may grow at all scales. We also cannot support the point of view
regarding the dominant role of the inverse cascade in the formation of
an AR. Although coalescence of small magnetic elements into larger pores
and sunspots is observed, our analysis shows that the prevailed energy
contribution to an AR comes from emergence of large-scale structures.

---------------------------------------------------------
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: Preface
Authors: Abramenko, V. I.
2019A&AT...31..237A Altcode:
This issue of Astronomical and Astrophysical Transactions comprises
papers presented ares on the Sun and stars" whichivity cycles and fl
was held at the Crimean Astrophysical Observatory in Crimea, Russia
on June 3-7, 2018. Energy emitted by the Sun is the essential source
of energy for life on our planet.This is why our interest in the
physics of the Sun never ceases. The physical processes inside the
magnetized solar plasma are responsible for the solar activity and
its consequences in the near-Earth space. In addition, by exploring
the Sun we can learn about other stars, especially those which are
similar to the Sun. Many of the problems pertaining and related to
these topics were discussed during the conference ares on the Sun and
stars". In total, 81 scientists attended the conference, and three of
the scientists arrived from abroad (Israel and Kazakhstan). 75 oral
talks were delivered and 35 poster presentations were exhibited. The
wide range of scientific discussions and collaborations together with
acquaintance with beautiful Crimean landscapes were the highlights of
the successful conference.

---------------------------------------------------------
Title: Preface
Authors: Abramenko, V. I.
2019A&AT...31...61A Altcode:
This issue of Astronomical and Astrophysical Transactions comprises
papers presented at the conference "Magnetism activity cycles
and flares on the Sun and stars" which was held at the Crimean
Astrophysical Observatory in Crimea, Russia on June 3-7, 2018. Energy
emitted by the Sun is the essential source of energy for life on
our planet.This is why our interest in the physics of the Sun never
ceases. The physical processes inside the magnetized solar plasma
are responsible for the solar activity and its consequences in the
near-Earth space. In addition, by exploring the Sun we can learn about
other stars, especially those which are similar to the Sun. Many of the
problems pertaining and related to these topics were discussed during
the conference "Magnetism, activity cycles and flares on the Sun and
stars". In total, 81 scientists attended the conference, and three of
the scientists arrived from abroad (Israel and Kazakhstan). 75 oral
talks were delivered and 35 poster presentations were exhibited. The
wide range of scientific discussions and collaborations together with
acquaintance with beautiful Crimean landscapes were the highlights of
the successful conference.

---------------------------------------------------------
Title: Turbulent and fractal nature of solar and stellar magnetism
Authors: Abramenko, V. I.
2019A&AT...31...63A Altcode:
Since the Babcock-Leighton phenomenological solar dynamo concept,
a variety of solar dynamo models (in particular, mean-field dynamo
models) were proposed to explain the 11-year cyclicity of solar
magnetic activity. Similar magnetic cycles are observed on stars of
the solar type. As the observational and computational facilities
improved, ubiquitous irregularities in a broad range of scales
appeared implying that the mean- field dynamo alone is not enough to
explain the observed picture. A concept of small- field dynamo alone
is not enough to explain the observed picture. A concept of small-
scale near-surface dynamo was suggested to explain a magnetic carpet -
population of mixed-polarity small magnetic elements in an undisturbed
photosphere. Besides, an origin of irregularities on larger scales
(scales of active regions, ARs) is still an open question. A question
appears: is it necessary to introduce two independent mech- anisms to
explain the magnetism on the Sun and stars? Using the magneto-graphic
observations of the Sun, we have shown that solar magnetic field
possesses properties of multifractality, its near-surface plasma
evolves in a state of developed turbulence, the flux dispersion occurs
in a regime of anomalous diffusion (super-diffusivity). Therefore, the
process of magnetic field generation can be explained by unique dynamo
mechanism operating as a non-linear dynamical dissipative system in
a broad range of scales: from a typical AR size down to the size of
smallest observable magnetic features. Pragmatic consequences can be
as follows: i) strong fluctuations (e.g., flares) are unpredictable
and not rare; ii) transport processes occur on a percolation cluster,
which differs significantly from transport in continuous medium; iii)
Gaussian statistics and central limit theorem are not applicable,
individual probability density functions should be utilized for
statistical estimates.

---------------------------------------------------------
Title: Time variations of the total unsigned magnetic flux of active
regions during the solar cycle 24
Authors: Zhukova, A. V.; Abramenko, V. I.; Kutsenko, A. S.
2019A&AT...31...75Z Altcode:
Ingredients of the total unsigned flux from all active regions (ARs)
on the solar disc during cycle 24 (July 2010 to December 2017)
were explored using line-of-sight magne- tograms acquired by the
Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We classified ARs into three categories: A-type,
regular bipolar ARs (attributed to global mean field dynamo); U-type,
unipolar spots; B-type, irregular ARs, violating either Hale polarity
law or Joy's law or having the leading spot less than the main
following spot. A special subset of anti-Hale ARs (the most plausible
result of small-scale turbulent dynamo) was formed by combining the
subsets of anti-Hale ARs from both B and U categories. Total unsigned
magnetic flux was calculated for each AR. In total, 1567 ARs with
flux above 1020 Mx were detected. Our inferences are:
i) One-rotation-averaged flux data show high cycle dependence for
the A-type ARs (correlation coefficient r = 0.84) and very low cycle
dependence for the anti-Hale ARs (r = 0.36). ii) Depending on the cycle
phase, 45-70% of the total flux comes from regular A-type ARs, 20-45%
from irregular B-type ARs, 10-25% from unipolar spots. Anti-Hale ARs
contribute up to 10% on occasional times during the maximum and their
very low contribution grows from 3 to 6% as the minimum proceeds. Thus,
during the maximum, the cycle-dependent fluctuations b of the mean
field B contributes noticeably to the anti-Hale ARs production, along
with the cycle-independent fluctuations h associated with small-scale
dynamo. iii) The amount of anti-Hale flux observed on an instant
full-disc magnetogram in 2016-2017 (near minimum) is nearly constant
on the level about 1021¹ Mx, which can be considered as
the lower boundary of the small-scale dynamo productivity on spatial
scales of ARs. We can conclude that small-scale turbulent dynamo
on scales of typical ARs displays a very weak productivity, which is
approximately 2 orders of magnitude lower than disc-integrated unsigned
flux from quiet-sun. However, the more important inference is that
the small-scale turbulent dynamo is present deep in the solar interior
(where ARs are rooted) and is not restricted by the near-surface layer
of the convective zone.

---------------------------------------------------------
Title: Contributions from Different-Type Active Regions Into the
Total Solar Unsigned Magnetic Flux
Authors: Abramenko, V. I.; Zhukova, A. V.; Kutsenko, A. S.
2018Ge&Ae..58.1159A Altcode:
Data set acquired by the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO) during 2010-2017 allowed
us to classify active regions (ARs) into three categories: A-type—
regular bipolar ARs; U-type—unipolar spots; B-type—irregular ARs,
violating either Hale polarity law or Joy's law or having the leading
spot less than the main following spot. A separate subset of anti-Hale
ARs was formed. We selected 1494 ARs in total and found the following:
(i) Pearson correlation coefficient r between the total unsigned flux
for a given category and the International Sunspot Number smoothly
decreases with transition from A-type ( r = 0.57) to B-type ( r =
0.53) to anti-Hale ARs ( r = 0.31) to U-type ( r = 0.18); (ii) yearly
contributions into the total flux from categories also gradually
decreases: from 50-70% from A-type ARs to 20-40% from B-type ARs
to 10-20% from U-type ARs to 5-11% from anti-Hale ARs. (iii) At the
beginning of the solar minimum, the fraction of flux from anti-Hale
groups increased from 5 to 9% and amount of flux per magnetogram was
constant at about 1021 Mx level. The data are compatible with
a concept that generation of the magnetic field on the Sun occurs as
a united process in a non-linear dynamical dissipative system, i.e.,
global and local (fluctuation) dynamos are inseparable and operate
together. The observed enhancement of the anti-Hale flux during the
solar maximum can be due to the combined mechanisms of global mean-field
and local fluctuation dynamos.

---------------------------------------------------------
Title: Intermittency spectra of current helicity in solar active
regions
Authors: Kutsenko, A. S.; Abramenko, V. I.; Kuzanyan, K. M.; Xu,
Haiqing; Zhang, Hongqi
2018MNRAS.480.3780K Altcode: 2018MNRAS.tmp.2012K; 2018arXiv180202323K
We analyse the spatial distribution of current helicity in solar
active regions. A comparison of current helicity maps derived from
three different instruments (Helioseismic and Magnetic Imager on board
the Solar Dynamics Observatory, SDO/HMI, Spectro-Polarimeter on board
the Hinode, and Solar Magnetic Field Telescope at the Huairou Solar
Observing Station, China, HSOS/SMFT) is carried out. The comparison
showed an excellent correlation between the maps derived from the
space-borne instruments and moderate correlation between the maps
derived from SDO/HMI and HSOS/SMFT vector magnetograms. The results
suggest that the obtained maps characterize real spatial distribution
of current helicity over an active region. To analyse intermittency
of current helicity, we traditionally use the high-order structure
functions and flatness function approach. The slope of a flatness
function within some range of scales - the flatness exponent - is a
measure of the degree of intermittency. SDO/HMI vector magnetograms
for three active regions (NOAA 11158, 12494, and 12673) were
used to calculate the flatness exponent time variations. All three
active regions exhibited emergence of a new magnetic flux during the
observational interval. The flatness exponent indicated the increase
of intermittency 12-20 hours before the emergence of a new flux. We
suppose that this behaviour can indicate subphotospheric fragmentation
or distortion of the pre-existed electric current system by emerging
magnetic flux.

---------------------------------------------------------
Title: Dispersion of small magnetic elements inside active regions
on the Sun
Authors: Abramenko, Valentina I.
2018MNRAS.480.1607A Altcode: 2018MNRAS.tmp.1871A; 2018arXiv181205469A
A process of diffusion of small-scale magnetic elements inside
four active regions (ARs) was analysed. Line-of-sight magnetograms
acquired by the Helioseismic and Magnetic Imager (HMI) onboard the
Solar Dynamic Observatory during a two-day time interval around the
AR culmination time were utilized. Small magnetic elements of size
3-100 squared HMI pixels with the field strength above the detection
threshold of 30 Mx sm-2 were detected and tracked. The
turbulent diffusion coefficient was retrieved using the pair-separation
technique. Comparison with the previously reported quiet-sun diffusivity
was performed. It was found that: (i) dispersion of small-scale magnetic
elements inside the AR area occurs in the regime close to normal
diffusion, whereas well-pronounced superdiffusion is observed in QS;
(ii) the diffusivity regime operating in an AR (the magnitude of the
spectral index and the range of the diffusion coefficient) does not
seem to depend on the individual properties of an AR, such as total
unsigned magnetic flux, state of evolution, and flaring activity. We
conclude that small-scale magnetic elements inside an AR do not
represent an undisturbed photosphere, but they rather are intrinsic
part of the whole coherent magnetic structure forming an AR. Moreover,
turbulence of small-scale elements in an AR is not closely related to
processes above the photosphere, but it rather carries the footprint
of the sub-photospheric dynamics.

---------------------------------------------------------
Title: High-resolution Observations of a White-light Flare with
Goode Solar Telescope
Authors: Yurchyshyn, Vasyl; Kumar, Pankaj; Abramenko, Valentyna; Xu,
Yan; Goode, Philip R.; Cho, Kyung-Suk F.
2018tess.conf21702Y Altcode:
Using high resolution data from the Goode Solar Telescope (GST)
we studied the fine spatial and temporal structure of an M1.3 white
light (WL) flare, which was one of the three homologous solar flares
(C6.8, M1.3, and M2.3) observed in a close proximity to the west solar
limb. The RHESSI photon spectra for the M1.3 flare showed strongly
accelerated electrons with energies above 100 keV. Comparison of
HXR photon spectra for the three flares suggests that either thermal
energy of order of 1030 ergs and/or high energy electrons
(&gt;50 keV) are necessary to produce a WL flare. The strong and
compact WL cores were ≈0.15 Mm across with an area of about
1014 cm2 . The observed TiO enhancements are
not normally distributed and are structured by the magnetic field of
the penumbra. Several of the TiO cores were not co-spatial with the Hα
emission, which suggests that the TiO and chromospheric emission did not
originate in the same chromospheric volume as some models suggest. We
thus conclude that fine temporal and spatial structure of the WL flare
was largely defined by the associated magnetic fields, which favors
the direct heating models, where the flare energy is directly deposited
in the temperature minimum region by the accelerated electrons.

---------------------------------------------------------
Title: Order out of Randomness: Self-Organization Processes in
Astrophysics
Authors: Aschwanden, Markus J.; Scholkmann, Felix; Béthune, William;
Schmutz, Werner; Abramenko, Valentina; Cheung, Mark C. M.; Müller,
Daniel; Benz, Arnold; Chernov, Guennadi; Kritsuk, Alexei G.; Scargle,
Jeffrey D.; Melatos, Andrew; Wagoner, Robert V.; Trimble, Virginia;
Green, William H.
2018SSRv..214...55A Altcode: 2017arXiv170803394A
Self-organization is a property of dissipative nonlinear processes
that are governed by a global driving force and a local positive
feedback mechanism, which creates regular geometric and/or
temporal patterns, and decreases the entropy locally, in contrast
to random processes. Here we investigate for the first time a
comprehensive number of (17) self-organization processes that
operate in planetary physics, solar physics, stellar physics,
galactic physics, and cosmology. Self-organizing systems create
spontaneous " order out of randomness", during the evolution from an
initially disordered system to an ordered quasi-stationary system,
mostly by quasi-periodic limit-cycle dynamics, but also by harmonic
(mechanical or gyromagnetic) resonances. The global driving force
can be due to gravity, electromagnetic forces, mechanical forces
(e.g., rotation or differential rotation), thermal pressure, or
acceleration of nonthermal particles, while the positive feedback
mechanism is often an instability, such as the magneto-rotational
(Balbus-Hawley) instability, the convective (Rayleigh-Bénard)
instability, turbulence, vortex attraction, magnetic reconnection,
plasma condensation, or a loss-cone instability. Physical models
of astrophysical self-organization processes require hydrodynamic,
magneto-hydrodynamic (MHD), plasma, or N-body simulations. Analytical
formulations of self-organizing systems generally involve coupled
differential equations with limit-cycle solutions of the Lotka-Volterra
or Hopf-bifurcation type.

---------------------------------------------------------
Title: Flux emergence rate of active regions as a probe for turbulent
dynamo action
Authors: Kutsenko, Aleksandr S.; Abramenko, Valentina I.
2018IAUS..340..299K Altcode:
We analyze the flux emergence rate of solar active regions
(ARs). Numerical simulations by other authors suggest that the flux
emergence rate depends on the AR's twist. To prove this statement
observationally, we make a comparison of the flux emergence rate and
twist of 215 emerging ARs. Our results confirm that the correlation
exists: the higher the twist the higher the flux emergence rate of
an AR. We suppose that the difference in the twist can be caused by
chaotic influence of the convective plasma motions on the lifting
magnetic flux tube.

---------------------------------------------------------
Title: Turbulent diffusion in the photosphere as observational
constraint on dynamo theories
Authors: Abramenko, Valentina I.
2018IAUS..340..281A Altcode:
We utilized line-of-sight magnetograms acquired by HMI/SDO to
derive the value of turbulent magnetic diffusivity in undisturbed
photosphere. Two areas, a coronal hole area (CH) and an area a
super-granulation pattern, SG, were analyzed. The behavior of the
turbulent diffusion coefficient on time scales of 1000-40000 s and
spatial scales of 500-6000 km was explored. Small magnetic elements
in both CH and SG areas disperse in the same way and they are more
mobile than the large elements. The regime of super-diffusivity
is found for small elements (the turbulent diffusion coefficient K
growths from 100 to 300 km2 s-1). Large magnetic
elements disperse differently in the CH and SG areas. Comparison of
these results with the previously published shows that there is a
tendency of saturation of the diffusion coefficient on large scales,
i.e., the turbulent regime of super-diffusivity gradually ceases so
that normal diffusion with a constant value of K ~ 500 km2
s-1 might be observed on time scales longer than a day. The
results show that the turbulent diffusivity should not be considered
in modeling as a scalar, the flux- and scale-dependence is obvious.

---------------------------------------------------------
Title: Diagnostics of Turbulent Dynamo from the Flux Emergence Rate
in Solar Active Regions
Authors: Abramenko, V. I.; Tikhonova, O. I.; Kutsenko, A. S.
2017Ge&Ae..57..792A Altcode:
Line-of-sight magnetograms acquired by the Helioseismic and Magnetic
Imager (HMI) onboard the Solar Dynamic Observatory (SDO) and by the
Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric
Observatory (SOHO) for 14 emerging ARs were used to study the derivative
of the total unsigned flux-the flux emergence rate, R( t). We found
that the emergence regime is not universal: each AR displays a unique
emergence process. Nevertheless, two types of the emergence process can
be identified. First type is a "regular" emergence with quasi-constant
behavior of R( t) during a 1-3 day emergence interval with a rather
low magnitude of the flux derivative, R max = (0.57 ±
0.22) × 1022 Mx day-1. The second type can be
described as "accelerated" emergence with a long interval (&gt;1 day)
of the rapidly increasing flux derivative R( t) that result in a rather
high magnitude of R max= (0.92 ± 0.29) × 1022
Mx day-1, which later changes to a very short (about a
one third of day) interval of R( t) = const followed by a monotonous
decrease of R( t). The first type events might be associated with
emergence of a flux tube with a constant amount of flux that rises
through the photosphere with a quasi-constant speed. Such events can
be explained by the traditional largescale solar dynamo generating the
toroidal flux deep in the convective zone. The second-type events can
be interpreted as a signature of sub-surface turbulent dynamo action
that generates additional magnetic flux (via turbulent motions) as
the magnetic structure makes its way up to the solar surface.

---------------------------------------------------------
Title: Possibilities for Estimating Horizontal Electrical Currents
in Active Regions on the Sun
Authors: Fursyak, Yu. A.; Abramenko, V. I.
2017Ap.....60..544F Altcode: 2017Ap....tmp...51F
Part of the "free" magnetic energy associated with electrical current
systems in the active region (AR) is released during solar flares. This
proposition is widely accepted and it has stimulated interest in
detecting electrical currents in active regions. The vertical component
of an electric current in the photosphere can be found by observing the
transverse magnetic field. At present, however, there are no direct
methods for calculating transverse electric currents based on these
observations. These calculations require information on the field
vector measured simultaneously at several levels in the photosphere,
which has not yet been done with solar instrumentation. In this paper we
examine an approach to calculating the structure of the square of the
density of a transverse electrical current based on a magnetogram of
the vertical component of the magnetic field in the AR. Data obtained
with the Helioseismic and Magnetic Imager (HMI) on board the Solar
Dynamic Observatory (SDO) for the AR of NOAA AR 11283 are used. It
is shown that (1) the observed variations in the magnetic field of
a sunspot and the proposed estimate of the density of an annular
horizontal current around the spot are consistent with Faraday's law
and (2) the resulting estimates of the magnitude of the square of
the density of the horizontal current {j}_{\perp}^2 = (0.002- 0.004)
A2/m4 are consistent with previously obtained
values of the density of a vertical current in the photosphere. Thus,
the proposed estimate is physically significant and this method can
be used to estimate the density and structure of transverse electrical
currents in the photosphere.

---------------------------------------------------------
Title: Dispersion of the solar magnetic flux in the undisturbed
photosphere as derived from SDO/HMI data
Authors: Abramenko, Valentina I.
2017MNRAS.471.3871A Altcode: 2017arXiv170901724A
To explore the magnetic flux dispersion in the undisturbed solar
photosphere, magnetograms acquired by Helioseismic and Magnetic Imager
(HMI) onboard the Solar Dynamic Observatory (SDO) were utilized. Two
areas, a coronal hole (CH) area and an area of super-granulation (SG)
pattern, were analysed. We explored the displacement and separation
spectra and the behaviour of the turbulent diffusion coefficient,
K. The displacement and separation spectra are very similar to each
other. Small magnetic elements (of size 3-100 squared pixels and
the detection threshold of 20 Mx sm-2) in both CH and SG
areas disperse in the same way and they are more mobile than the large
elements (of size 20-400 squared pixels and the detection threshold
of 130 Mx sm-2). The regime of super-diffusivity is found
for small elements (γ ≈ 1.3 and K growing from ∼100 to ∼ 300
km2 s-1). Large elements in the CH area are scanty
and show super-diffusion with γ ≈ 1.2 and K = (62-96) km2
s-1 on a rather narrow range of 500-2200 km. Large elements
in the SG area demonstrate two ranges of linearity and two diffusivity
regimes: sub-diffusivity on scales 900-2500 km with γ = 0.88 and K
decreasing from ∼130 to ∼100 km2 s-1, and
super-diffusivity on scales 2500-4800 km with γ ≈ 1.3 and K growing
from ∼140 to ∼200 km2 s-1. A comparison
of our results with the previously published shows that there is a
tendency of saturation of the diffusion coefficient on large scales,
I.e. the turbulent regime of super-diffusivity is gradually replaced
by normal diffusion.

---------------------------------------------------------
Title: Contribution to the Solar Mean Magnetic Field from Different
Solar Regions
Authors: Kutsenko, A. S.; Abramenko, V. I.; Yurchyshyn, V. B.
2017SoPh..292..121K Altcode: 2017arXiv170705971K
Seven-year-long seeing-free observations of solar magnetic fields
with the Helioseismic and Magnetic Imager (HMI) on board the Solar
Dynamics Observatory (SDO) were used to study the sources of the solar
mean magnetic field, SMMF, defined as the net line-of-sight magnetic
flux divided over the solar disk area. To evaluate the contribution
of different regions to the SMMF, we separated all the pixels of
each SDO/HMI magnetogram into three subsets: weak (BW),
intermediate (BI), and strong (BS) fields. The
BW component represents areas with magnetic flux densities
below the chosen threshold; the BI component is mainly
represented by network fields, remains of decayed active regions (ARs),
and ephemeral regions. The BS component consists of magnetic
elements in ARs. To derive the contribution of a subset to the total
SMMF, the linear regression coefficients between the corresponding
component and the SMMF were calculated. We found that i) when the
threshold level of 30 Mx cm−2 is applied, the BI
and BS components together contribute from 65% to 95% of the
SMMF, while the fraction of the occupied area varies in a range of 2 -
6% of the disk area; ii) as the threshold magnitude is lowered to 6 Mx
cm−2, the contribution from BI+BS
grows to 98%, and the fraction of the occupied area reaches a value
of about 40% of the solar disk. In summary, we found that regardless
of the threshold level, only a small part of the solar disk area
contributes to the SMMF. This means that the photospheric magnetic
structure is an intermittent inherently porous medium, resembling a
percolation cluster. These findings suggest that the long-standing
concept that continuous vast unipolar areas on the solar surface are
the source of the SMMF may need to be reconsidered.

---------------------------------------------------------
Title: Analysis of the Flux Growth Rate in Emerging Active Regions
on the Sun
Authors: Abramenko, V. I.; Kutsenko, A. S.; Tikhonova, O. I.;
Yurchyshyn, V. B.
2017SoPh..292...48A Altcode: 2017arXiv170300739A
We studied the emergence process of 42 active regions (ARs) by analyzing
the time derivative, R (t ), of the total unsigned flux. Line-of-sight
magnetograms acquired by the Helioseismic and Magnetic Imager (HMI)
onboard the Solar Dynamics Observatory (SDO) were used. A continuous
piecewise linear fitting to the R (t )-profile was applied to detect
an interval, Δ t2, of nearly constant R (t ) covering
one or several local maxima. The magnitude of R (t ) averaged over Δ
t2 was accepted as an estimate of the maximum value of the
flux growth rate, RMAX, which varies in a range of (0.5 -5
)×1020Mxhour−1 for ARs with a maximum total
unsigned flux of (0.5 -3 )×1022Mx. The normalized flux
growth rate, RN, was defined under the assumption that the
saturated total unsigned flux, FMAX, equals unity. Out of 42
ARs in our initial list, 36 events were successfully fitted, and they
form two subsets (with a small overlap of eight events): the ARs with
a short (&lt;13 hours) interval Δ t2 and a high (&gt;0.024
hour−1) normalized flux emergence rate, RN,
form the "rapid" emergence event subset. The second subset consists of
"gradual" emergence events, and it is characterized by a long (&gt;13
hours) interval Δ t2 and a low RN (&lt;0.024
hour−1). In diagrams of RMAX plotted versus
FMAX, the events from different subsets do not overlap,
and each subset displays an individual power law. The power-law index
derived from the entire ensemble of 36 events is 0.69 ±0.10 . The
rapid emergence is consistent with a two-step emergence process of a
single twisted flux tube. The gradual emergence is possibly related
to a consecutive rising of several flux tubes emerging at nearly the
same location in the photosphere.

---------------------------------------------------------
Title: High-resolution Observations of a White-light Flare with NST
Authors: Yurchyshyn, V.; Kumar, P.; Abramenko, V.; Xu, Y.; Goode,
P. R.; Cho, K. -S.; Lim, E. -K.
2017ApJ...838...32Y Altcode:
Using high-resolution data from the New Solar Telescope, we studied
fine spatial and temporal details of an M1.3 white-light (WL) flare,
which was one of three homologous solar flares (C6.8, M1.3, and M2.3)
observed in close proximity to the west solar limb on 2014 October 29
in NOAA active region 12192. We report that the TiO WL flare consists of
compact and intense cores surrounded by less intense spatial halos. The
strong and compact WL cores were measured to be ≈ 0.2 Mm across,
with an area of about 1014 cm2. Several TiO
features were not cospatial with Hα flare ribbons and were displaced
toward the disk center by about 500 km, which suggests that the TiO
and Hα radiation probably did not originate in the same chromospheric
volume. The observed TiO intensity enhancements are not normally
distributed and are structured by the magnetic field of the penumbra.

---------------------------------------------------------
Title: Diagnostics of turbulent and fractal properties of photospheric
plasma outside active regions of the Sun
Authors: Abramenko, V. I.
2016Ge&Ae..56..842A Altcode:
Results of analysis of multi-scale and turbulent properties of
observed photospheric granulation patterns in undisturbed solar
photosphere are presented. Data were obtained with the New Solar
Telescope at Big Bear Solar observatory. Different types of magnetic
environment were explored: a coronal hole (CH) area, a quiet sun (QS)
intranetwork area, a QS/network area, and an area with small pores. The
property of multifractality was revealed for granulation patterns in all
environments on scales below 600 km. The degree of multifractality tends
to be stronger as the magnetic environment becomes weaker. Analysis
of turbulent diffusion on scales less than 1000-2000 km revealed
the regime of super-diffusivity for all data sets. Super-diffusion
becomes stronger from the QS/network to the QS/intranetwork to the
CH. Both multifractality and super-diffusivity on very small scales
are associated with the fast turbulent dynamo action. The results show
that the most favorable conditions for the fast turbulent dynamo are
met outside the network, inside vast areas of weakest magnetic fields,
which supports the idea of nonlocal, deep turbulent dynamo.

---------------------------------------------------------
Title: Using SDO/HMI Magnetograms as a Source of the Solar Mean
Magnetic Field Data
Authors: Kutsenko, A. S.; Abramenko, V. I.
2016SoPh..291.1613K Altcode: 2016arXiv160603710K; 2016SoPh..tmp..104K
The solar mean magnetic field (SMMF) provided by the Wilcox
Solar Observatory (WSO) is compared with the SMMF acquired by the
Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We found that despite the different spectral lines
and measurement techniques used in both instruments, the Pearson
correlation coefficient between these two datasets equals 0.86, while
the conversion factor is very close to unity: BHMI=0.99 (2
)BWSO. We also discuss artifacts of the SDO/HMI magnetic
field measurements, namely the 12- and 24-hour oscillations in the
SMMF and in sunspot magnetic fields that are thought to be caused by
orbital motions of the spacecraft. The artificial harmonics of the
SMMF reveal significant changes in amplitude and the nearly stable
phase. The connection between the 24-hour harmonic amplitude of the
SMMF and the presence of sunspots is examined. We also found that
opposite-phase artificial 12- and/or 24-hour oscillations exist in
magnetic field strength of sunspots of opposite polarities.

---------------------------------------------------------
Title: 25 Years of Self-organized Criticality: Numerical Detection
Methods
Authors: McAteer, R. T. James; Aschwanden, Markus J.; Dimitropoulou,
Michaila; Georgoulis, Manolis K.; Pruessner, Gunnar; Morales, Laura;
Ireland, Jack; Abramenko, Valentyna
2016SSRv..198..217M Altcode: 2015SSRv..tmp...31M; 2015arXiv150608142M
The detection and characterization of self-organized criticality
(SOC), in both real and simulated data, has undergone many
significant revisions over the past 25 years. The explosive
advances in the many numerical methods available for detecting,
discriminating, and ultimately testing, SOC have played a critical
role in developing our understanding of how systems experience and
exhibit SOC. In this article, methods of detecting SOC are reviewed;
from correlations to complexity to critical quantities. A description
of the basic autocorrelation method leads into a detailed analysis
of application-oriented methods developed in the last 25 years. In
the second half of this manuscript space-based, time-based and
spatial-temporal methods are reviewed and the prevalence of power
laws in nature is described, with an emphasis on event detection and
characterization. The search for numerical methods to clearly and
unambiguously detect SOC in data often leads us outside the comfort
zone of our own disciplines—the answers to these questions are often
obtained by studying the advances made in other fields of study. In
addition, numerical detection methods often provide the optimum link
between simulations and experiments in scientific research. We seek
to explore this boundary where the rubber meets the road, to review
this expanding field of research of numerical detection of SOC systems
over the past 25 years, and to iterate forwards so as to provide some
foresight and guidance into developing breakthroughs in this subject
over the next quarter of a century.

---------------------------------------------------------
Title: Possibilities of predicting flare productivity based on
magnetic field power spectra in active regions
Authors: Abramenko, V. I.
2015Ge&Ae..55..860A Altcode:
Photospheric plasma is in a state of developed turbulence. Chaotic
motions in the photosphere and below are among the main sources of
eruptive processes in the solar atmosphere. The magnetic field power
spectra, as measured in the active region (AR) photosphere, were used
as a source of information on the photospheric plasma turbulent state
and as a tool for predicting AR flare productivity. It was shown that,
first, ARs with the Kolmogorov power spectrum evolve mainly without
catastrophes—strong flares—and have rather regular and simple
magnetic configurations. At the same time, ARs with a spectrum steeper
than the Kolmogorov have increased flare productivity and complex
magnetic configurations. Second, a steep non-Kolmogorov spectrum in the
early stage of AR development indicates that the AR flare productivity
is high over the followingdays. Third, the time fluctuations in the
spectral index in flare-active regions reach 30% and are much higher
than the fluctuations in low-flaring ARs. Periods with an increased
absolute value of the spectral index, i.e., periods with a steeper
spectrum, are observed approximately 1-2 days before a powerful
flare. The data make it possible to assume that an energy relationship
exists between the photosphere and the overlying atmosphere and to use
the magnetic power spectrum as a tool for predicting AR flare activity.

---------------------------------------------------------
Title: Multiwavelength Observations of a Slow-rise, Multistep X1.6
Flare and the Associated Eruption
Authors: Yurchyshyn, V.; Kumar, P.; Cho, K. -S.; Lim, E. -K.;
Abramenko, V. I.
2015ApJ...812..172Y Altcode:
Using multiwavelength observations, we studied a slow-rise, multistep
X1.6 flare that began on 2014 November 7 as a localized eruption of core
fields inside a δ-sunspot and later engulfed the entire active region
(AR). This flare event was associated with formation of two systems
of post-eruption arcades (PEAs) and several J-shaped flare ribbons
showing extremely fine details, irreversible changes in the photospheric
magnetic fields, and it was accompanied by a fast and wide coronal mass
ejection. Data from the Solar Dynamics Observatory and IRIS spacecraft,
along with the ground-based data from the New Solar Telescope, present
evidence that (i) the flare and the eruption were directly triggered
by a flux emergence that occurred inside a δ-sunspot at the boundary
between two umbrae; (ii) this event represented an example of the
formation of an unstable flux rope observed only in hot AIA channels
(131 and 94 Å) and LASCO C2 coronagraph images; (iii) the global
PEA spanned the entire AR and was due to global-scale reconnection
occurring at heights of about one solar radius, indicating the global
spatial and temporal scale of the eruption.

---------------------------------------------------------
Title: Solar small-scale dynamo and polarity of sunspot groups
Authors: Sokoloff, D.; Khlystova, A.; Abramenko, V.
2015MNRAS.451.1522S Altcode: 2015arXiv150501557S
In order to clarify a possible role of small-scale dynamo in
formation of solar magnetic field, we suggest an observational test
for small-scale dynamo action based on statistics of anti-Hale sunspot
groups. As we have shown, according to theoretical expectations the
small-scale dynamo action has to provide a population of sunspot
groups which do not follow the Hale polarity law, and the density of
such groups on the time-latitude diagram is expected to be independent
on the phase of the solar cycle. Correspondingly, a percentage of the
anti-Hale groups is expected to reach its maximum values during solar
minima. For several solar cycles, we considered statistics of anti-Hale
groups obtained by several scientific teams, including ours, to find
that the percentage of anti-Hale groups becomes indeed maximal during
a solar minimum. Our interpretation is that this fact may be explained
by the small-scale dynamo action inside the solar convective zone.

---------------------------------------------------------
Title: The Chromosphere above the sunspot umbra as seen in the New
Solar Telescope and Interface Region Imaging Spectrograph
Authors: Yurchyshyn, Vasyl; Goode, Phil; Abramenko, Valentyna;
Kilcik, Ali
2015TESS....131202Y Altcode:
Recent observations of sunspot's umbra suggested that it may be finely
structured at a sub-arcsecond scale representing a mix of hot and cool
plasma elements. In this study we report observations from the New Solar
Telescope (NST) of the umbral spikes, which are cool jet-like structures
seen in the chromosphere of an umbra. Our analysis indicates that
the spikes are not associated with photospheric umbral dots and they
tend to occur above darkest parts of the umbra, where magnetic fields
are strongest. The spikes exhibit up and down oscillatory motions and
their spectral evolution suggests that they might be driven by upward
propagating shocks generated by photospheric oscillations.We analyze
sunspot oscillations using Interface Region Imaging Spectrograph
(IRIS) data and narrow-band NST images and found long term variations
in the intensity of chromospheric shocks. Also, sunspot umbral flashes
(UFs) appear as narrow bright lanes running along the light bridges
(LBs) and clusters of umbral dots (UDs). Time series suggested that
UFs preferred to appear on the sunspot-center side of LBs, which may
indicate the existence of a compact sub-photospheric driver of sunspot
oscillations. We find that the sunspot's umbra appears bright in IRIS
images above LBs and UDs. Co-spatial and co-temporal SDO/AIA data showed
that these locations were associated with bright footpoints of umbral
loops suggesting that LBs may play an important role in heating these
loops. The power spectra analysis showed that the intensity of umbral
oscillations significantly varies across the umbra and with height,
suggesting that umbral non-uniformities and the structure of sunspot
magnetic fields may play a role in wave propagation and heating of
umbral loops.

---------------------------------------------------------
Title: Dynamics in Sunspot Umbra as Seen in New Solar Telescope and
Interface Region Imaging Spectrograph Data
Authors: Yurchyshyn, V.; Abramenko, V.; Kilcik, A.
2015ApJ...798..136Y Altcode: 2014arXiv1411.0192Y
We analyze sunspot oscillations using Interface Region Imaging
Spectrograph (IRIS) slit-jaw and spectral data and narrow-band
chromospheric images from the New Solar Telescope (NST) for the main
sunspot in NOAA AR 11836. We report that the difference between the
shock arrival times as measured by the Mg II k 2796.35 Å and Si IV
1393.76 Å line formation levels changes during the observed period,
and peak-to-peak delays may range from 40 s to zero. The intensity
of chromospheric shocks also displays long-term (about 20 min)
variations. NST's high spatial resolution Hα data allowed us to
conclude that, in this sunspot, umbral flashes (UFs) appeared in the
form of narrow bright lanes stretched along the light bridges and around
clusters of umbral bright points. The time series also suggested that
UFs preferred to appear on the sunspot-center side of light bridges,
which may indicate the existence of a compact sub-photospheric
driver of sunspot oscillations. The sunspot's umbra as seen in the
IRIS chromospheric and transition region data appears bright above
the locations of light bridges and the areas where the dark umbra
is dotted with clusters of umbral dots. Co-spatial and co-temporal
data from the Atmospheric Imaging Assembly on board the Solar Dynamics
Observatory showed that the same locations were associated with bright
footpoints of coronal loops suggesting that the light bridges may play
an important role in heating the coronal sunspot loops. Finally, the
power spectra analysis showed that the intensity of chromospheric and
transition region oscillations significantly vary across the umbra and
with height, suggesting that umbral non-uniformities and the structure
of sunspot magnetic fields may play a role in wave propagation and
heating of umbral loops.

---------------------------------------------------------
Title: The multifractal nature of solar magnetism and the solar
dynamo problem
Authors: Abramenko, V. I.
2014Ge&Ae..54..892A Altcode:
Based on observation data with a high spatial resolution, the
multifractal properties of turbulent magnetized plasma in a nonperturbed
solar atmosphere are revealed. It is shown that magnetic fluxes in
elements of the magnetic field, as well as the size of elements, are
distributed lognormally, which is indicative of multifractality. In
coronal holes (CHs), the multifractality of magnetic fields is observed
on scales of 10000-400 km; at the same time, it is observed on smaller
scales as the resolution improves, and its degree increases. It is
shown that two subsets of granules exist: the usual granules, with a
characteristic size of 1000-1300 km and Gaussian size distribution,
and mini-granules, which do not have a well-pronounced characteristic
size and are mostly less than 600 km in diameter. The size distribution
function of the mini-granules obeys lognormal law and their multifractal
character is seen on small scales down to 50 km, which allows one to
make a conclusion about the presence of multifractality of photospheric
plasma flows in CHs and in a nonperturbed photosphere. A conclusion
is made that multifractality takes place for small-scale magnetic
fields of quiet regions, as well as for large-scale fields of active
regions. This makes it possible to suppose that solar magnetic fields
are generated by a common nonlinear dynamical process.

---------------------------------------------------------
Title: High Resolution Observations of Chromospheric Jets in
Sunspot Umbra
Authors: Yurchyshyn, Vasyl B.; Abramenko, Valentyna; Kosovichev,
Alexander G.; Goode, Philip R.
2014AAS...22432301Y Altcode:
Recent observations of sunspot's umbra suggested that it may be finely
structured at a sub-arcsecond scale representing a mix of hot and cool
plasma elements. In this study we report the first detailed observations
of the umbral spikes, which are cool jet-like structures seen in the
chromosphere of an umbra. The spikes are cone-shaped features with
a typical height of 0.5-1. Mm and a width of about 0. Mm. Their life
time ranges from 2 to 3 ~min and they tend to re-appear at the same
location. The preliminary analysis indicates that the spikes are not
associated with photospheric umbral dots and they rather tend to
occur above darkest parts of the umbra, where magnetic fields are
strongest. The spikes exhibit up and down oscillatory motions and
their spectral evolution suggests that they might be driven by upward
propagating shocks generated by photospheric oscillations. It is worth
noting that triggering of the running penumbral waves seems to occur
during the interval when the spikes reach their maximum height.

---------------------------------------------------------
Title: High Resolution Observations of Chromospheric Jets in
Sunspot Umbra
Authors: Yurchyshyn, V.; Abramenko, V.; Kosovichev, A.; Goode, P.
2014ApJ...787...58Y Altcode: 2014arXiv1404.7444Y
Recent observations of a sunspot's umbra have suggested that it may
be finely structured on a subarcsecond scale representing a mix of hot
and cool plasma elements. In this study, we report the first detailed
observations of umbral spikes, which are cool jet-like structures seen
in the chromosphere of an umbra. The spikes are cone-shaped features
with a typical height of 0.5-1.0 Mm and a width of about 0.1 Mm. Their
lifetime ranges from 2 to 3 minutes and they tend to re-appear at
the same location. The spikes are not associated with photospheric
umbral dots and they instead tend to occur above the darkest parts of
the umbra where magnetic fields are strongest. The spikes exhibit up
and down oscillatory motions and their spectral evolution suggests
that they might be driven by upward propagating shocks generated by
photospheric oscillations. It is worth noting that triggering of the
running penumbral waves seems to occur during the interval when the
spikes reach their maximum height.

---------------------------------------------------------
Title: Solar dynamo, meridional circulations, emergence and expansion
of magnetic fields
Authors: Abramenko, Valentyna
2014cosp...40E..20A Altcode:
The magnetic field is a key agent of the solar activity. Processes of
generation, emergence, dispersal over the solar surface and expansion
to the corona determine solar activity on all scales: from the solar
cycle to nano-flares. The past peculiar solar minimum allowed us to
further explore meridional flows, magnetic field evolution in quiet
sun, and expansion of the flux into the corona. Our understanding of
the dynamo process made a new circle along the dialectic spiral: from
the classical Babcock-Leighton model that explains the global dynamo
and solar cycle, to the acceptance of the small-scale local turbulent
dynamo, which might operate inside the near-surface layer and to be
responsible for generation of small-scale magnetic fields forming the
magnetic carpet. And yet, this scenario of simultaneous action of two
dynamos seems to be oversimplified. Finally, closing the circle, we
suggest that the solar dynamo is both chaotic and cyclic and performs
as a nonlinear dynamical system. An enormous progress, achieved during
the last decade in modeling and observations of the magnetic field
generation, emergence and dispersion will be the focus of this talk.

---------------------------------------------------------
Title: Diagnostics of multi-fractality of magnetized plasma inside
coronal holes and quiet sun areas
Authors: Abramenko, Valentyna
2014cosp...40E..21A Altcode:
Turbulent and multi-fractal properties of magnetized plasma in solar
Coronal Holes (CHs) and Quiet Sun (QS) photosphere were explored using
high-resolution magnetograms measured with the New Solar Telescope
(NST) at the Big Bear Solar Observatory (BBSO, USA), Hinode/SOT and
SDO/HMI instruments. Distribution functions of size and magnetic flux
measured for small-scale magnetic elements follow the log-normal law,
which implies multi-fractal organization of the magnetic field and the
absence of a unique power law for all scales. The magnetograms show
multi-fractality in CHs on scales 400 - 10000 km, which becomes better
pronounced as the spatial resolution of data improves. Photospheric
granulation measured with NST exhibits multi-fractal properties on
very small scales of 50 - 600 km. While multi-fractal nature of solar
active regions is well known, newly established multi-fractality of
weakest magnetic fields on the solar surface, i.e., in CHs and QS,
leads us to a conclusion that the entire variety of solar magnetic
fields is generated by a unique nonlinear dynamical process.

---------------------------------------------------------
Title: Characteristic Length of Energy-containing Structures at the
Base of a Coronal Hole
Authors: Abramenko, V. I.; Zank, G. P.; Dosch, A.; Yurchyshyn, V. B.;
Goode, P. R.; Ahn, K.; Cao, W.
2013ApJ...773..167A Altcode: 2013arXiv1307.4421A
An essential parameter for models of coronal heating and fast solar
wind acceleration that rely on the dissipation of MHD turbulence is
the characteristic energy-containing length λ of the
squared velocity and magnetic field fluctuations (u 2
and b 2) transverse to the mean magnetic field inside a
coronal hole (CH) at the base of the corona. The characteristic length
scale directly defines the heating rate. We use a time series analysis
of solar granulation and magnetic field measurements inside two CHs
obtained with the New Solar Telescope at Big Bear Solar Observatory. A
data set for transverse magnetic fields obtained with the Solar Optical
Telescope/Spectro-Polarimeter on board the Hinode spacecraft was
utilized to analyze the squared transverse magnetic field fluctuations
b_t^2. Local correlation tracking was applied to derive the squared
transverse velocity fluctuations u 2. We find that for u
2 structures, the Batchelor integral scale λ varies in
a range of 1800-2100 km, whereas the correlation length sigmav and
the e-folding length L vary between 660 and 1460 km. Structures for
b_t^2 yield λ ≈ 1600 km, sigmav ≈ 640 km, and L ≈ 620 km. An
averaged (over λ, sigmav, and L) value of the characteristic length
of u 2 fluctuations is 1260 ± 500 km, and that of b_t^2
is 950 ± 560 km. The characteristic length scale in the photosphere
is approximately 1.5-50 times smaller than that adopted in previous
models (3-30 × 103 km). Our results provide a critical
input parameter for current models of coronal heating and should yield
an improved understanding of fast solar wind acceleration.

---------------------------------------------------------
Title: Fractal multi-scale nature of solar/stellar magnetic fields
Authors: Abramenko, Valentina I.
2013IAUS..294..289A Altcode: 2013arXiv1305.5282A
An abstract mathematical concept of fractal organization of certain
complex objects received significant attention in astrophysics
during last decades. The concept evolved into a broad field including
multi-fractality and intermittency, percolation theory, self-organized
criticality, theory of catastrophes, etc. Such a strong mathematical
and physical approach provide new possibilities for exploring various
aspects of astrophysics. In particular, in the solar and stellar
magnetism, multi-fractal properties of magnetized plasma turned to be
useful for understanding burst-like dynamics of energy release events,
conditions for turbulent dynamo action, nature of turbulent magnetic
diffusivity, and even the dual nature of solar dynamo. In this talk,
I will briefly outline how the ideas of multi-fractality are used to
explore the above mentioned aspects of solar magnetism.

---------------------------------------------------------
Title: Dynamics of Chromospheric Upflows and Underlying Magnetic
Fields
Authors: Yurchyshyn, V.; Abramenko, V.; Goode, P.
2013ApJ...767...17Y Altcode: 2013arXiv1303.4766Y
We used Hα-0.1 nm and magnetic field (at 1.56μ) data obtained with
the New Solar Telescope to study the origin of the disk counterparts to
type II spicules, so-called rapid blueshifted excursions (RBEs). The
high time cadence of our chromospheric (10 s) and magnetic field
(45 s) data allowed us to generate x-t plots using slits parallel
to the spines of the RBEs. These plots, along with potential field
extrapolation, led us to suggest that the occurrence of RBEs is
generally correlated with the appearance of new, mixed, or unipolar
fields in close proximity to network fields. RBEs show a tendency
to occur at the interface between large-scale fields and small-scale
dynamic magnetic loops and thus are likely to be associated with the
existence of a magnetic canopy. Detection of kinked and/or inverse
"Y"-shaped RBEs further confirm this conclusion.

---------------------------------------------------------
Title: Granules in the Quiet and Magnetic Sun
Authors: Stein, Robert; Abramenko, Valentyna; Nordlund, Aake
2013enss.confE..17S Altcode:
High resolution magneto-convection simulations reveal that there are
significant differences in granulation in quiet and magnetic regions
of the Sun. In non-magnetic regions the granules have scalloped edges
(not smooth intergranualr lanes) in the emergent continuum radiation
and the vertical velocity at the edges of the intergranular lanes form
a branching tree structure extending into the granules. In magnetic
regions the intergranular lanes are smooth in both intensity and
vertical velocity but with swirls (vortices) in both. These differences
are borderline visible in data from the Big Bear NST.

---------------------------------------------------------
Title: Investigation of Small-Scale Turbulent MHD Phenomena Using
Numerical Simulations and NST Observations
Authors: Kitiashvili, I.; Abramenko, V.; Goode, P. R.; Kosovichev,
A.; Mansour, N.; Wray, A.; Yurchyshyn, V.
2012IAUSS...6E.104K Altcode:
Recent progress in observational capabilities and numerical modeling
have provided unique high-resolution information demonstrating
complicated dynamics and structures of turbulent flows and magnetic
field on the Sun. The realistic approach to numerical simulations is
based on physical first principles and takes into account compressible
fluid flow in a highly stratified magnetized medium, 3D multi-bin
radiative energy transfer between fluid elements, a real-gas equation
of state, ionization, and excitation of all abundant species, magnetic
effects and sub-grid turbulence. We present new results of 3D radiative
MHD simulations of the upper solar convection zone and chromosphere
that reveal a fundamental role of small-scale vortex dynamics, and
compare the numerical results and predictions with observational
results from the 1.6 m clear aperture New Solar Telescope (NST) at
Big Bear Observatory. In particular, we investigate formation and
dynamics of ubiquitous small-scale vortex tubes mostly concentrated
in the intergranular lanes and their role in magnetic structuring
and acoustic emission of the Sun. These whirlpool-like flows are
characterized by very strong horizontal shear velocities (7 - 11 km/s)
and downflows (~7 km/s), and are accompanied by sharp decreases in
temperature, density and pressure at the surface. High-speed whirlpool
flows can attract and capture other vortices, penetrate into the low
chromosphere, and form stable magnetic flux tubes. The simulations also
reveal a strong connection between acoustic wave excitation events and
the dynamics of vortex tubes. In this talk, we will discuss different
aspects of small-scale turbulent dynamics of the low atmosphere from the
high-resolution simulations in comparison with recent NST observations,
and the strategy for future synergies of numerical simulations and
observations with large aperture solar telescopes.

---------------------------------------------------------
Title: Energy-Containing Length Scale at the Base of a Coronal Hole:
New Observational Findings
Authors: Abramenko, V.; Dosch, A.; Zank, G. P.; Yurchyshyn, V.; Goode,
P. R.
2012AGUFMSH33D2253A Altcode:
Dynamics of the photospheric flux tubes is thought to be a key
factor for generation and propagation of MHD waves and magnetic
stress into the corona. Recently, New Solar Telescope (NST, Big
Bear Solar Observatory) imaging observations in helium I 10830 Å
revealed ultrafine, hot magnetic loops reaching from the photosphere
to the corona and originating from intense, compact magnetic field
elements. One of the essential input parameters to run the models of
the fast solar wind is a characteristic energy-containing length scale,
lambda, of the dynamical structures transverse to the mean magnetic
field in a coronal hole (CH) in the base of the corona. We used NST
time series of solar granulation motions to estimate the velocity
fluctuations, as well as NST near-infrared magnetograms to derive
the magnetic field fluctuations. The NST adaptive optics corrected
speckle-reconstructed images of 10 seconds cadence were an input for the
local correlation tracking (LCT) code to derive the squared transverse
velocity patterns. We found that the characteristic length scale for
the energy-carrying structures in the photosphere is about 300 km,
which is two orders of magnitude lower than it was adopted in previous
models. The influence of the result on the coronal heating and fast
solar wind modeling will be discussed.; Correlation functions calculated
from the squared velocities for the three data sets: a coronal hole,
quiet sun and active region plage area.

---------------------------------------------------------
Title: The relationship between the occurrence of type II spicules
and the dynamics of underlying magnetic fields
Authors: Yurchyshyn, V.; Abramenko, V.; Goode, P. R.
2012AGUFMSH32A..05Y Altcode:
Type II spicules are thought to be small-scale chromospheric
up-flows. When observed against the solar disk they can be identified
as rapid blue shifted events (or excursions, RBE, Rouppe van der
Voort et al.). While their nature is being questioned and their
associated driving mechanism remains elusive, these up-flows may be
instrumental in the processes of coronal heating and solar wind. We use
high resolution photospheric, chromospheric and magnetic field data
from the New Solar Telescope operating at Big Bear Solar Observatory
to further determine the properties of these events and refine the
role that they may play. We find that the majority of RBEs, occurring
around network clusters of bright points, can be linked to episodes
of small flux emergence, in particular appearance of opposite polarity
fields. Case studies further indicate that some of the RBEs appear to
have kink and inverted "Y" shaped roots. The data thus suggest that
magnetic reconnection may be responsible for at least some fraction
of observed RBEs. We will present these observations in details and
discuss possible implications.Sequence of H-alpha-0.075nm images
spanning 7 min showing evolution of RBE activity near a cluster
of network fields. The two yellow circles enclose the area where
multipolar fields rapidly appeared. Comparing panels 19:05:11 UT and
19:05:55 UT one may notice that a new magnetic dipole and a dark jet
appeared in the encircled area. The same is true about the encircled
area in 19:07:26UT panel. The RBE activity ceased as soon as the the
field of view was cleared from small-scale magnetic elements.

---------------------------------------------------------
Title: Turbulent Pair Dispersion of Photospheric Bright Points
Authors: Lepreti, F.; Carbone, V.; Abramenko, V. I.; Yurchyshyn, V.;
Goode, P. R.; Capparelli, V.; Vecchio, A.
2012ApJ...759L..17L Altcode:
Observations of solar granulation obtained with the New Solar Telescope
of Big Bear Solar Observatory are used to study the turbulent pair
dispersion of photospheric bright points in a quiet-Sun area, a
coronal hole, and an active region plage. In all the three magnetic
environments, it is found that the pair mean-squared separation
Δ2(t) follows a power-law timescaling Δ2(t) ~ t
η in the range 10 s &lt;~ t &lt;~ 400 s. The power-law index
is found to be η ~= 1.5 for all the three investigated regions. It
is shown that these results can be explained in the same framework as
the classical Batchelor theory, under the hypothesis that the observed
range of timescales corresponds to a non-asymptotic regime in which the
photospheric bright points keep the memory of their initial separations.

---------------------------------------------------------
Title: Non-thermal Response of the Corona to the Magnetic Flux
Dispersal in the Photosphere of a Decaying Active Region
Authors: Harra, L. K.; Abramenko, V. I.
2012ApJ...759..104H Altcode:
We analyzed Solar Dynamics Observatory line-of-sight magnetograms
for a decaying NOAA active region (AR) 11451 along with co-temporal
Extreme-Ultraviolet Imaging Spectrometer (EIS) data from the Hinode
spacecraft. The photosphere was studied via time variations of the
turbulent magnetic diffusivity coefficient, η(t), and the magnetic
power spectrum index, α, through analysis of magnetogram data from the
Helioseismic and Magnetic Imager (HMI). These measure the intensity of
the random motions of magnetic elements and the state of turbulence of
the magnetic field, respectively. The time changes of the non-thermal
energy release in the corona was explored via histogram analysis of
the non-thermal velocity, v nt, in order to highlight the
largest values at each time, which may indicate an increase in energy
release in the corona. We used the 10% upper range of the histogram
of v nt (which we called V upp nt)
of the coronal spectral line of Fe XII 195 Å. A 2 day time interval
was analyzed from HMI data, along with the EIS data for the same
field of view. Our main findings are the following. (1) The magnetic
turbulent diffusion coefficient, η(t), precedes the upper range of
the v nt with the time lag of approximately 2 hr and the
cross-correlation coefficient of 0.76. (2) The power-law index, α, of
the magnetic power spectrum precedes V upp nt
with a time lag of approximately 3 hr and the cross-correlation
coefficient of 0.5. The data show that the magnetic flux dispersal in
the photosphere is relevant to non-thermal energy release dynamics
in the above corona. The results are consistent with the nanoflare
mechanism of the coronal heating, due to the time lags being consistent
with the process of heating and cooling the loops heated by nanoflares.

---------------------------------------------------------
Title: Detection of Small-scale Granular Structures in the Quiet
Sun with the New Solar Telescope
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Goode, P. R.;
Kitiashvili, I. N.; Kosovichev, A. G.
2012ApJ...756L..27A Altcode: 2012arXiv1208.4337A
Results of a statistical analysis of solar granulation are presented. A
data set of 36 images of a quiet-Sun area on the solar disk center was
used. The data were obtained with the 1.6 m clear aperture New Solar
Telescope at Big Bear Solar Observatory and with a broadband filter
centered at the TiO (705.7 nm) spectral line. The very high spatial
resolution of the data (diffraction limit of 77 km and pixel scale of
0farcs0375) augmented by the very high image contrast (15.5% ± 0.6%)
allowed us to detect for the first time a distinct subpopulation of
mini-granular structures. These structures are dominant on spatial
scales below 600 km. Their size is distributed as a power law with an
index of -1.8 (which is close to the Kolmogorov's -5/3 law) and no
predominant scale. The regular granules display a Gaussian (normal)
size distribution with a mean diameter of 1050 km. Mini-granular
structures contribute significantly to the total granular area. They are
predominantly confined to the wide dark lanes between regular granules
and often form chains and clusters, but different from magnetic bright
points. A multi-fractality test reveals that the structures smaller
than 600 km represent a multi-fractal, whereas on larger scales the
granulation pattern shows no multi-fractality and can be considered
as a Gaussian random field. The origin, properties, and role of the
population of mini-granular structures in the solar magnetoconvection
are yet to be explored.

---------------------------------------------------------
Title: Variations of Current Helicity in Active Region 10930 as
Inferred from Hinode Spectropolarimeter Data and Cancellation Exponent
Authors: Yurchyshyn, V.; Abramenko, V.; Watanabe, H.
2012ASPC..454..311Y Altcode:
Current helicity derived from vector magnetograms possesses a
well-pronounced scaling behavior, which can be studied by introducing
a signed measure and calculating the power-law exponent (cancellation
exponent). The time variations of this exponent seem to be related
to flare activity of an active region. Here we focus on changes
of current helicity in active region NOAA 10930 as derived from
a set of Hinode spectropolarimeter data. Our findings are that the
cancellation exponent first strongly increased on Dec 11 then rapidly
decreased after a small sunspot-satellite developed. Afterward, the
cancellation exponent began its gradual increase without significant
new magnetic flux emergence. These two different modes of behavior
may indicate different processes that ultimately led to an eruption:
the first process is rapid injection of current helicity, while the
second process is gradual redistribution of injected helicity over
all spatial scales in the active region.

---------------------------------------------------------
Title: Transverse Motions of Chromospheric Type II Spicules Observed
by the New Solar Telescope
Authors: Yurchyshyn, V.; Kilcik, A.; Abramenko, V.
2012arXiv1207.6417Y Altcode:
Using high resolution off-band \ha\ data from the New Solar Telescope
and Morlet wavelet analysis technique, we analyzed transverse motions
of type II spicules observed near the North Pole of the Sun. Our new
findings are that i) some of the observed type II spicules display
kink or an inverse "Y" features, suggesting that their origin may be
due to magnetic reconnection, and ii) type II spicules tend to display
coherent transverse motions/oscillations. Also, the wavelet analysis
detected significant presence of high frequency oscillations in type
II spicules, ranging from 30 to 180 s with the the average period of 90
s. We conclude that at least some of type II spicules and their coherent
transverse motions may be caused by reconnection between large scale
fields rooted in the intergranular lanes and and small-scale emerging
dipoles, a process that is know to generate high frequency kink mode
MHD waves propagating along the magnetic field lines.

---------------------------------------------------------
Title: Small Scale Field Emergence and Its Impact on Photospheric
Granulation
Authors: Yurchyshyn, V.; Ahn, K.; Abramenko, V.; Goode, P.; Cao, W.
2012arXiv1207.6418Y Altcode:
We used photospheric intensity images and magnetic field measurements
from the New Solar Telescope in Big Bear and Helioseismic Magnetic
Imager on board Solar Dynamics Observatory (SDO) to study the the effect
that the new small-scale emerging flux induces on solar granulation. We
report that emerging flux appears to leave different types of footprint
on solar granulation: i) diffuse irregular patches of increased
brightness, ii) well defined filament-like structures and accompanied
bright points, and iii) bright point-like features that appear inside
granules. We suggest that the type of the footprint depends on the
intensity of emerging fields. Stronger fields, emerging as a part of
large magnetic structure, create on the solar surface a well defined
filamentary pattern with bright points at the ends of the filaments,
while weak turbulent fields are associated with bright patches inside
the host granule.

---------------------------------------------------------
Title: New solar telescope in Big Bear: evidence for super-diffusivity
and small-scale solar dynamos?
Authors: Goode, Philip R.; Abramenko, Valentyna; Yurchyshyn, Vasyl
2012PhyS...86a8402G Altcode:
The 1.6 m clear aperture New Solar Telescope (NST) in Big Bear Solar
Observatory (BBSO) is now providing the highest resolution solar data
ever. These data have revealed surprises about the Sun on small-scales
including the observation that bright points (BPs), which can be
used as proxies for the intense, compact magnetic elements that are
apparent in photospheric intergranular lanes. The BPs are ever more
numerous on ever smaller spatial scales as though there were no limit
to how small the BPs can be. Here we discuss high resolution NST data
on BPs that provide support for the ideas that a turbulent regime
of super-diffusivity dominates in the quiet Sun, and there are local
dynamos operating near the solar surface.

---------------------------------------------------------
Title: Turbulent Kinetic Energy Spectra of Solar Convection from
NST Observations and Realistic MHD Simulations
Authors: Kitiashvili, I. N.; Abramenko, V. I.; Goode, P. R.;
Kosovichev, A. G.; Lele, S. K.; Mansour, N. N.; Wray, A. A.;
Yurchyshyn, V. B.
2012arXiv1206.5300K Altcode:
Turbulent properties of the quiet Sun represent the basic state of
surface conditions, and a background for various processes of solar
activity. Therefore understanding of properties and dynamics of this
`basic' state is important for investigation of more complex phenomena,
formation and development of observed phenomena in the photosphere and
atmosphere. For characterization of the turbulent properties we compare
kinetic energy spectra on granular and sub-granular scales obtained
from infrared TiO observations with the New Solar Telescope (Big Bear
Solar Observatory) and from 3D radiative MHD numerical simulations
('SolarBox' code). We find that the numerical simulations require a high
spatial resolution with 10 - 25 km grid-step in order to reproduce the
inertial (Kolmogorov) turbulence range. The observational data require
an averaging procedure to remove noise and potential instrumental
artifacts. The resulting kinetic energy spectra show a good agreement
between the simulations and observations, opening new perspectives for
detailed joint analysis of more complex turbulent phenomena on the Sun,
and possibly on other stars. In addition, using the simulations and
observations we investigate effects of background magnetic field,
which is concentrated in self-organized complicated structures in
intergranular lanes, and find an increase of the small-scale turbulence
energy and its decrease at larger scales due to magnetic field effects.

---------------------------------------------------------
Title: Observational Signatures of the Small-Scale Dynamo in the
Quiet Sun
Authors: Abramenko, V.; Yurchyshyn, V.; Goode, P. R.
2012ASPC..455...17A Altcode:
The generation and diffusion of the magnetic field on the Sun is a key
mechanism responsible for solar activity on all spatial and temporal
scales—from the solar cycle down to the evolution of small-scale
magnetic elements in the quiet Sun. The solar dynamo operates as
a non-linear dynamical process and is thought to be manifest in two
types: as a global dynamo responsible for the solar cycle periodicity,
and as a small-scale turbulent dynamo responsible for the formation
of the magnetic carpet in the quiet Sun. Numerous MHD simulations of
solar turbulence did not yet reach a consensus as to the existence
of a turbulent dynamo on the Sun. At the same time, high-resolution
observations of the quiet Sun from Hinode instruments suggest
possibilities for the turbulent dynamo. Analysis of characteristics of
turbulence derived from observations would be beneficial in tackling
the problem. We analyze magnetic and velocity energy spectra as derived
from Hinode/SOT, SOHO/MDI, SDO/HMI and the New Solar Telescope (NST)
of Big Bear Solar Observatory (BBSO) to explore the possibilities for
the small-scale turbulent dynamo in the quiet Sun.

---------------------------------------------------------
Title: Flare-associated Energy Exchange Between the Photosphere
and Corona
Authors: Abramenko, Valentyna; Harra, L.
2012AAS...22020414A Altcode:
In recent decades, it has been clearly demonstrated that strong
flares in ARs (referred before as chromospheric flares) are not
restricted to some closed volume in the chromosphere but rather
involve a huge volume from deep sub-photospheric layers to the
outer heliosphere. Undoubtedly, there exists interaction and energy
exchange between different parts of the volume occupied by a flare,
e.g., reconnection between up-welling loops and the pre-existing flux,
waves and shocks, seismic response to a flare, momentum distribution and
Lorentz Force acting, accelerated particle, heat, X-ray propagation,
Poynting flux transport, etc. However, mechanisms of the processes,
as well as their relationship with the flare itself (is a phenomenon
a prelude to the flare, its consequence or non of such) is not well
understood yet. We explore new metrics of the photospheric magnetic
field: we monitor the magnetic energy dissipation rate. For three
strong flares, we found that the magnetic energy dissipation rate sets
to a monotonous ceasing several hours before the flare onset. Assuming
nearly gradual energy input, the reduction of the energy dissipation
rate implies that somewhere in the active region, the energy is being
accumulated. The non-dissipated and accumulated energy amounts to (3 -
10) x 1032 ergs. We presume that at least part of the energy
accumulated immediately before the flare is transferred into the corona
and further drives the corona to a trigger point when flare occurs.

---------------------------------------------------------
Title: Oscillations of Rapid Blueshifted Events as Derived from
NST Data
Authors: Yurchyshyn, Vasyl B.; Kilcik, A.; Abramenko, V.
2012AAS...22020304Y Altcode:
We studied oscillations of type II spicules observed near the north
pole of the sun. The study is based on high-resolution data recorded by
the New Solar Telescope at the Big Bear Solar Observatory. The spicule
oscillations were probed by applying the global wavelet method to a 34
min continuous time series of off-band Halpha images. The main findings
are: i) Type II spicules are oscillating with about 1 min period,
while the outside quiet regions show dominance of 3 min periods. ii)
Spicules belonging to a cluster, tend to oscillate as a group. We will
present details of these findings and discuss possible implications.

---------------------------------------------------------
Title: Origin of Rapid Blueshifted Events in Coronal Holes
Authors: Yurchyshyn, Vasyl B.; Ahn, K.; Abramenko, V.; Goode, P.;
Cao, W.
2012AAS...22042304Y Altcode:
Clusters of photospheric bright points are surrounded by chromospheric
rosette-like structures. These rosettes, when observed in the far
off-band (-0.1nm) Halpha images often appear to consist of short living,
narrow rapid blueshifted events (RBEs). RBEs, in turn, are thought to
be disk counterparts of type II spicules (spicules II), detected in
Hinode data, which may be playing play an important role in coronal
heating since they are thought to supply mass to the solar corona. The
search for the origin of type II spicules was one of the main focus of
solar physics research in the recent years. Here we present our
findings on the possible driving mechanism of spicules II, which are
based on high resolution photospheric, chromospheric and magnetic field
data from the New Solar Telescope (NST) collected in a coronal hole. We
report that the majority of RBEs, occurring around a network cluster,
are associated with appearance of opposite polarity features within
the unipolar cluster fields, suggesting that magnetic reconnection
may be the driving mechanism. We will present these observations in
details and discuss possible implications.

---------------------------------------------------------
Title: Observational Criteria For Small-scale Turbulent Dynamo In
The Solar Photosphere
Authors: Abramenko, Valentyna; Goode, P.; Yurchyshyn, V.
2012AAS...22011002A Altcode:
Generation and dispersal of the magnetic field on the Sun is a key
mechanism responsible for solar activity on all spatial and temporal
scales - from the solar cycle down to the evolution of small-scale
magnetic elements in the quiet Sun. The solar dynamo operates as
a non-linear dynamical process and is thought to be manifested
in two types: as a global dynamo responsible for the solar cycle
periodicity, and as a small-scale turbulent dynamo (SSTD) responsible
for the formation of magnetic carpet in the quiet Sun. Numerous MHD
simulations of the solar turbulence did not yet reach a consensus
as to the existence and role of SSTD on the Sun. At the same time,
high-resolution observations of the quiet Sun are capable to provide
certain criteria to prove or rule out SSTD. We suggest to probe four
possible criteria: i) mutual behaviour of the kinetic and magnetic power
spectra; ii) intermittency/multifractality of the magnetic field; iii)
smallest observed scale of magnetic flux tubes; iv) regime of magnetic
diffusivity on smallest observable scales. We analyse magnetic, velocity
and solar granulation data as derived from Hinode/SOT, SOHO/MDI, SDO/HMI
and the New Solar Telescope (NST) of Big Bear Solar Observatory (BBSO)
to explore the possibilities for SSTD in the quiet Sun.

---------------------------------------------------------
Title: Properties of Umbral Dots as Measured from the New Solar
Telescope Data and MHD Simulations
Authors: Kilcik, A.; Yurchyshyn, V. B.; Rempel, M.; Abramenko, V.;
Kitai, R.; Goode, P. R.; Cao, W.; Watanabe, H.
2012ApJ...745..163K Altcode: 2011arXiv1111.3997K
We studied bright umbral dots (UDs) detected in a moderate size sunspot
and compared their statistical properties to recent MHD models. The
study is based on high-resolution data recorded by the New Solar
Telescope at the Big Bear Solar Observatory and three-dimensional (3D)
MHD simulations of sunspots. Observed UDs, living longer than 150 s,
were detected and tracked in a 46 minute long data set, using an
automatic detection code. A total of 1553 (620) UDs were detected
in the photospheric (low chromospheric) data. Our main findings
are (1) none of the analyzed UDs is precisely circular, (2) the
diameter-intensity relationship only holds in bright umbral areas, and
(3) UD velocities are inversely related to their lifetime. While nearly
all photospheric UDs can be identified in the low chromospheric images,
some small closely spaced UDs appear in the low chromosphere as a single
cluster. Slow-moving and long-living UDs seem to exist in both the low
chromosphere and photosphere, while fast-moving and short-living UDs
are mainly detected in the photospheric images. Comparison to the 3D
MHD simulations showed that both types of UDs display, on average, very
similar statistical characteristics. However, (1) the average number
of observed UDs per unit area is smaller than that of the model UDs,
and (2) on average, the diameter of model UDs is slightly larger than
that of observed ones.

---------------------------------------------------------
Title: Magnetic and Kinetic Power Spectra as a Tool to Probe the
Turbulent Dynamo
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Goode, P. R.
2011arXiv1112.2750A Altcode:
Generation and diffusion of the magnetic field on the Sun is a key
mechanism responsible for solar activity on all spatial and temporal
scales - from the solar cycle down to the evolution of small-scale
magnetic elements in the quiet Sun. The solar dynamo operates as
a non-linear dynamical process and is thought to be manifest in two
types: as a global dynamo responsible for the solar cycle periodicity,
and as a small-scale turbulent dynamo responsible for the formation
of magnetic carpet in the quiet Sun. Numerous MHD simulations of the
solar turbulence did not yet reach a consensus as to the existence
of a turbulent dynamo on the Sun. At the same time, high-resolution
observations of the quiet Sun from Hinode instruments suggest
possibilities for the turbulent dynamo. Analysis of characteristics of
turbulence derived from observations would be beneficial in tackling
the problem. We analyse magnetic and velocity energy spectra as derived
from Hinode/SOT, SOHO/MDI, SDO/HMI and the New Solar Telescope (NST)
of Big Bear Solar Observatory (BBSO) to explore the possibilities for
the small-scale turbulent dynamo in the quiet Sun.

---------------------------------------------------------
Title: The solar dynamo process as a non-linear dynamical system
Authors: Abramenko, V.
2011AGUFMSH51C2023A Altcode:
The solar activity cycle is one of the most astonishing and widely
known examples of the self-organized generation of the magnetic
field. Persistency and regularity of the solar periodicity through
thousands of years remains impressive. A drastically different picture
arises when one takes a closer look at the photosphere: chaos of
continuously renewing mixed-polarity magnetic elements is revealed on
all scales, until the resolution limits of modern instruments. One
promising approach to explain the dualism is to consider the solar
dynamo process as a non-linear dynamical system (NDS). Like any NDS,
the solar dynamo is capable of self-organization on large scales and
displays chaotic nature on small scales. In this case, the dynamo is
intrinsically a multi-scale process, when the inter-scale exchange
is at work and parameters of the system are scale-dependent. This
paradigm offers new approaches to understand the solar dynamo. One
of the conditions for the dynamo to operate on diminishing scales
is the diminishing with scale turbulent magnetic diffusivity - the
super-diffusion regime. Moreover, this regime implies multifractality
and intermittency of the photospheric magnetized plasma. We present
our resent results on super-diffusivity and multifractality detected
in the quiet sun photosphere on scales below 1 Mm and shorter than 10
minutes from observations with the New Solar Telescope (NST) of Big Bear
Solar observatory. Consequences of the varying with scales diffusivity
on supergranular scales for mean-field dynamo models are also discussed.

---------------------------------------------------------
Title: Turbulent Diffusion in the Photosphere as Derived from
Photospheric Bright Point Motion
Authors: Abramenko, V. I.; Carbone, V.; Yurchyshyn, V.; Goode, P. R.;
Stein, R. F.; Lepreti, F.; Capparelli, V.; Vecchio, A.
2011ApJ...743..133A Altcode: 2011arXiv1111.4456A
On the basis of observations of solar granulation obtained with the
New Solar Telescope of Big Bear Solar Observatory, we explored proper
motion of bright points (BPs) in a quiet-sun area, a coronal hole, and
an active region plage. We automatically detected and traced BPs and
derived their mean-squared displacements as a function of time (starting
from the appearance of each BP) for all available time intervals. In all
three magnetic environments, we found the presence of a super-diffusion
regime, which is the most pronounced inside the time interval of 10-300
s. Super-diffusion, measured via the spectral index, γ, which is the
slope of the mean-squared displacement spectrum, increases from the
plage area (γ = 1.48) to the quiet-sun area (γ = 1.53) to the coronal
hole (γ = 1.67). We also found that the coefficient of turbulent
diffusion changes in direct proportion to both temporal and spatial
scales. For the minimum spatial scale (22 km) and minimum time scale
(10 s), it is 22 and 19 km2 s-1 for the coronal
hole and the quiet-sun area, respectively, whereas for the plage area
it is about 12 km2 s-1 for the minimum time
scale of 15 s. We applied our BP tracking code to three-dimensional
MHD model data of solar convection and found the super-diffusion with
γ = 1.45. An expression for the turbulent diffusion coefficient as
a function of scales and γ is obtained.

---------------------------------------------------------
Title: Properties of Umbral Dots as Measured from the New Solar
Telescope Data and MHD Simulations
Authors: Yurchyshyn, V.; Kilcik, A.; Rempel, M.; Abramenko, V.; Kitai,
R.; Goode, P. R.; Cao, W.; Watanabe, H.
2011sdmi.confE..86Y Altcode:
We studied bright umbral dots (UDs) detected in the main sunspot
of AR NOAA 11108 and compare their statistical properties to a
state-of-the-art MHD model of a sunspot. The study is based on
high resolution data recorded on September 20, 2010 by the New Solar
Telescope (NST) at Big Bear Solar Observatory and 3D MHD simulations of
sunspots. The 46 min data set included photospheric (0.3nm TiO filter
centered at 705.7 nm) and chromospheric (0.025nm Hα Lyot filter)
adaptive optics corrected and speckle reconstructed images. Bright
UDs, living longer than 150 s, were detected and tracked using an
automatic UD detection code. Total 1553 (620) UDs were detected
in the photospheric (chromospheric) data. Our main findings are:
i) none of the analyzed UDs is of an exact circular shape, ii) the
diameter-intensity relationship only works for bright umbral areas, and
iii) UD velocities inversely related to their life time. Comparison of
photospheric and chromospheric data showed that nearly all photospheric
UDs can be identified in the chromospheric images. However, it appears
that some small closely spaced UDs appear in the chromospheric images
as a single cluster, which may lead to the underestimation of the total
number of detected chromospheric UDs. Also, while slow moving and long
living UDs seem to exist in both chromosphere and photosphere, fast
moving and short living ones are detected mainly in the photospheric
images. Comparison of model and observed data shows that both types
of UDs display very similar statistical characteristics. The main
difference between parameters of model and observed UDs is that i)
the average number of observed UDs per unit area is smaller than that
of the model UDs, and ii) on average, the diameter of model UDs is
slightly larger than that of observed ones.

---------------------------------------------------------
Title: Turbulent Diffusion on Very Small Scales in the Quiet
Photosphere
Authors: Abramenko, Valentyna
2011sdmi.confE..83A Altcode:
Turbulent diffusion is the key mechanism that dominates the magnetic
flux dispersal over the solar surface on small spatial and time
scales. To explore the nature of the turbulent diffusion (normal or
anomalous diffusivity), data of high spatial and time resolution are
needed. Modern data from SDO/HMI and from New Solar Telescope (NST)
of Big Bear Solar Observatory allow to study diffusivity on scales
down to 140 s/1000 km and 10 s/77 km, respectively. We find the regime
of anomalous super-diffusivity on all available scales from both data
sets. Interestingly, super-diffusivity regime is different for different
magnetic environments on the Sun. Thus, super-diffusion, measured
via the spectral index, gamma, which is the slope of the mean-squared
displacement spectrum, increases from the plage area (gamma=1.48) to
the quiet sun area (gamma=1.53) to the coronal hole (gamma=1.67). The
result is discussed in the framework of the small-scale turbulent
dynamo action in various magnetic environments on the solar surface.

---------------------------------------------------------
Title: Photospheric Signatures of Granular-scale Flux Emergence and
Cancellation at the Penumbral Boundary
Authors: Lim, Eun-Kyung; Yurchyshyn, Vasyl; Abramenko, Valentyna;
Ahn, Kwangsu; Cao, Wenda; Goode, Philip
2011ApJ...740...82L Altcode: 2011arXiv1107.5254L
We studied flux emergence events of sub-granular scale in a solar
active region. The New Solar Telescope (NST) of the Big Bear Solar
Observatory made it possible to clearly observe the photospheric
signature of flux emergence with very high spatial (0farcs11 at 7057
Å) and temporal (15 s) resolution. From TiO observations with the
pixel scale of 0farcs0375, we found several elongated granule-like
features (GLFs) stretching from the penumbral filaments of a sunspot
at a relatively high speed of over 4 km s-1. After a
slender arched darkening appeared at the tip of a penumbral filament,
a bright point (BP) developed and quickly moved away from the filament,
forming and stretching a GLF. The size of a GLF was approximately
0farcs5 wide and 3” long. The moving BP encountered nearby structures
after several minutes of stretching, and the well-defined elongated
shape of the GLF faded away. Magnetograms from the Solar Dynamics
Observatory/Helioseismic and Magnetic Imager and NST/InfraRed Imaging
Magnetograph revealed that those GLFs are photospheric indicators of
small-scale flux emergence, and their disappearance is related to
magnetic cancellation. From two well-observed events, we describe
detailed development of the sub-structures of GLFs and different
cancellation processes that each of the two GLFs underwent.

---------------------------------------------------------
Title: On the Origin of Intergranular Jets
Authors: Yurchyshyn, V. B.; Goode, P. R.; Abramenko, V. I.; Steiner, O.
2011ApJ...736L..35Y Altcode: 2011arXiv1106.5535Y
We observe that intergranular jets, originating in the intergranular
space surrounding individual granules, tend to be associated with
granular fragmentation, in particular, with the formation and evolution
of a bright granular lane (BGL) within individual granules. The BGLs
have recently been identified as vortex tubes by Steiner et al. We
further discover the development of a well-defined bright grain
located between the BGL and the dark intergranular lane to which it
is connected. Signatures of a BGL may reach the lower chromosphere
and can be detected in off-band Hα images. Simulations also indicate
that vortex tubes are frequently associated with small-scale magnetic
fields. We speculate that the intergranular jets detected in the New
Solar Telescope (NST) data may result from the interaction between
the turbulent small-scale fields associated with the vortex tube
and the larger-scale fields existing in the intergranular lanes. The
intergranular jets are much smaller and weaker than all previously known
jet-like events. At the same time, they appear much more numerous than
the larger events, leading us to the speculation that the total energy
release and mass transport by these tiny events may not be negligible in
the energy and mass-flux balance near the temperature minimum atop the
photosphere. The study is based on the photospheric TiO broadband (1.0
nm) filter data acquired with the 1.6 m NST operating at the Big Bear
Solar Observatory. The data set also includes NST off-band Hα images
collected through a Zeiss Lyot filter with a passband of 0.025 nm.

---------------------------------------------------------
Title: Sunspot Umbral Dots Detected with the New Solar Telescope
Authors: Kilcik, Ali; Yurchyshyn, V.; Abramenko, V.; Goode, P.; Cao, W.
2011SPD....42.1901K Altcode: 2011BAAS..43S.1901K
We present a study of bright umbral dots detected inside a large sunspot
of NOAA AR 11108. This study is based on high resolution data recorded
on September 20, 2010 with the New Solar Telescope (NST) at Big Bear
Solar Observatory. The data set, spanning 46 min, consists of a total
of 184 adaptive optics corrected and speckle reconstructed images
obtained with a 0.3 nm passband TiO filter centered on the 705.7 nm
spectral line. The image cadence is 15 s and the pixel size of 0.0375
arcsec. Bright umbral dots (UDs) were detected and tracked using
an automatic routine. Here we only focus on long living UDs (&gt;150
s in life time) and a total of 513 such features were detected during
the observed period. We found that the average lifetime of a UD is 7.4
min and an average size is 0.34 arcsec. There is a tendency for larger
UDs to be brighter (and more circular). Many UDs are not of circular
shape. We will also present probability distribution of various physical
parameters and compare the results to similar earlier studies.

---------------------------------------------------------
Title: NST and Photospheric Fine -scale Structures Indicating the
Small Scale Flux Emergence in an Active Region
Authors: Lim, Eunkyung; Yurchyshyn, V.; Abramenko, V.; Goode, P.;
Ahn, K.
2011SPD....42.0604L Altcode: 2011BAAS..43S.0604L
We have studied very small-scale flux emergence events on granular
scales in a solar active region. The New Solar Telescope of Big Bear
Solar Observatory made it possible to clearly observe the photospheric
signature of flux emergence with a very high spatial (0".034/pixel) and
temporal (15s) resolution. From the TiO observations, we found several
elongated thread-like granules protruding from the penumbral filaments
of a sunspot at a relatively high speed of over 4km s-1. A slender
arched darkening protrudes from the tip of the penumbral filament, then
quickly stretches its length along the intergranular lane with a slight
bright point developing at the previously shaded leading edge. The size
of such granules is approximately 0".5 wide and 3” long, and their
stretching lasts for several minutes before contacting other magnetic
structures nearby. Magnetograms from HMI/SDO and IRIM/BBSO show that
such elongated granules are photospheric indicators of small-scale
flux emergence. The cancellation process is also described in detail
for two events that show different chromospheric signatures, such
as brightenings and jets during the cancellation. We speculate that
subsurface connectivity and the depth of the roots of magnetic field
are the main keys to determining different cancellation phenomena.

---------------------------------------------------------
Title: New View on Quiet-Sun Photospheric Dynamics Offered by NST Data
Authors: Abramenko, Valentyna; Yurchyshyn, V.; Goode, P. R.
2011SPD....42.0603A Altcode: 2011BAAS..43S.0603A
Recent observations of the quiet sun photosphere obtained with the
1.6 meter New Solar telescope (NST) of Big Bear Solar observatory
(BBSO) delivered new information about photospheric fine structures
and their dynamics, as well as posing new questions. The 2-hour
uninterrupted data set of solar granulation obtained under excellent
seeing conditions on August 3, 2010 (with cadence of 10 sec) was the
basis for the study. Statistical analysis of automatically detected and
tracked magnetic bright points (MBPs) showed that the MBPs population
monotonically increases as their size decreases, down to 60-70 km. Our
analysis shows that if the smallest magnetic flux tubes exist, their
size is still smaller that 60-70 km, which impose strong restrictions on
the modeling of these structures. We also found that the distributions
of the MBP's size and lifetime do not follow a traditional Gaussian
distribution, typical for random processes. Instead, it follows a
log-normal distribution, typical for avalanches, catastrophes, stock
market data, etc. Our data set also demonstrated that a majority (98.6
%) of MBPs are short live (&lt;2 min). This remarkable fact was not
obvious from previous studies because an extremely high time cadence
was required. The fact indicates that the majority of MBPs appear for a
very short time (tens of seconds), similar to other transient features,
for example, chromospheric jets. The most important point here is that
these small and short living MBPs significantly increase dynamics
(flux emergence, collapse into MBPs, and magnetic flux recycling)
of the solar surface magnetic fields.

---------------------------------------------------------
Title: Response of Granulation to Small-scale Bright Features in
the Quiet Sun
Authors: Anđić, A.; Chae, J.; Goode, P. R.; Cao, W.; Ahn, K.;
Yurchyshyn, V.; Abramenko, V.
2011ApJ...731...29A Altcode: 2011arXiv1102.3404A
We detected 2.8 bright points (BPs) per Mm2 in the quiet
Sun with the New Solar Telescope at Big Bear Solar Observatory, using
the TiO 705.68 nm spectral line at an angular resolution ~0farcs1 to
obtain a 30 minute data sequence. Some BPs formed knots that were
stable in time and influenced the properties of the granulation
pattern around them. The observed granulation pattern within ~3”
of knots presents smaller granules than those observed in a normal
granulation pattern, i.e., around the knots a suppressed convection
is detected. Observed BPs covered ~5% of the solar surface and were
not homogeneously distributed. BPs had an average size of 0farcs22,
they were detectable for 4.28 minutes on average, and had an averaged
contrast of 0.1% in the deep red TiO spectral line.

---------------------------------------------------------
Title: Time Distributions of Large and Small Sunspot Groups Over
Four Solar Cycles
Authors: Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.;
Ozguc, A.; Rozelot, J. P.; Cao, W.
2011ApJ...731...30K Altcode: 2011arXiv1111.3999K
Here we analyze solar activity by focusing on time variations of
the number of sunspot groups (SGs) as a function of their modified
Zurich class. We analyzed data for solar cycles 20-23 by using Rome
(cycles 20 and 21) and Learmonth Solar Observatory (cycles 22 and 23)
SG numbers. All SGs recorded during these time intervals were separated
into two groups. The first group includes small SGs (A, B, C, H, and
J classes by Zurich classification), and the second group consists
of large SGs (D, E, F, and G classes). We then calculated small and
large SG numbers from their daily mean numbers as observed on the
solar disk during a given month. We report that the time variations
of small and large SG numbers are asymmetric except for solar cycle
22. In general, large SG numbers appear to reach their maximum in the
middle of the solar cycle (phases 0.45-0.5), while the international
sunspot numbers and the small SG numbers generally peak much earlier
(solar cycle phases 0.29-0.35). Moreover, the 10.7 cm solar radio
flux, the facular area, and the maximum coronal mass ejection speed
show better agreement with the large SG numbers than they do with
the small SG numbers. Our results suggest that the large SG numbers
are more likely to shed light on solar activity and its geophysical
implications. Our findings may also influence our understanding of
long-term variations of the total solar irradiance, which is thought
to be an important factor in the Sun-Earth climate relationship.

---------------------------------------------------------
Title: Maximum Coronal Mass Ejection Speed as an Indicator of Solar
and Geomagnetic Activities
Authors: Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.;
Gopalswamy, N.; Ozguc, A.; Rozelot, J. P.
2011ApJ...727...44K Altcode: 2011arXiv1111.4000K
We investigate the relationship between the monthly averaged maximal
speeds of coronal mass ejections (CMEs), international sunspot number
(ISSN), and the geomagnetic Dst and Ap indices covering the 1996-2008
time interval (solar cycle 23). Our new findings are as follows. (1)
There is a noteworthy relationship between monthly averaged maximum CME
speeds and sunspot numbers, Ap and Dst indices. Various peculiarities
in the monthly Dst index are correlated better with the fine structures
in the CME speed profile than that in the ISSN data. (2) Unlike the
sunspot numbers, the CME speed index does not exhibit a double peak
maximum. Instead, the CME speed profile peaks during the declining
phase of solar cycle 23. Similar to the Ap index, both CME speed and
the Dst indices lag behind the sunspot numbers by several months. (3)
The CME number shows a double peak similar to that seen in the sunspot
numbers. The CME occurrence rate remained very high even near the
minimum of the solar cycle 23, when both the sunspot number and the
CME average maximum speed were reaching their minimum values. (4) A
well-defined peak of the Ap index between 2002 May and 2004 August was
co-temporal with the excess of the mid-latitude coronal holes during
solar cycle 23. The above findings suggest that the CME speed index may
be a useful indicator of both solar and geomagnetic activities. It may
have advantages over the sunspot numbers, because it better reflects
the intensity of Earth-directed solar eruptions.

---------------------------------------------------------
Title: Photosphere-Chromosphere Connection as Derived from Nst
Observations
Authors: Yurchyshyn, V.; Abramenko, V.; Goode, P. R.
2010AGUFMSH31C1807Y Altcode:
Largest ground-based new solar telescope (NST) of Big Bear Solar
Observatory allows us to simultaneously observe photospheric
granulation with luxurious filigree of bright points (BPs) and
low/middle chromosphere in H- alpha spectral line. Excellent climate
conditions of Big Bear Valley, augmented with an adaptive optics system
and speckle-reconstruction applications produce diffraction limited
images. Recent observations (July- August 2010) showed that BPs visible
in the photosphere with the TiO filter (centered at a wavelength of
705.7 nm) are co-spatial with the BPs visible in the blue wind of
H-alpha line. As evidenced from these data, the H-alpha BPs, in turn,
are frequently at origin of small-scale chromospheric jets. These jets
are visible at all scales down to the smallest resolved features. As
long as photospheric BPs are co-spatial with the magnetic elements,
one might conclude that photospheric magnetic fields are relevant
to the chromospheric jet formation. NST Ha-0.13nm image acquired on
June 28, 2010. The dark features are upward directed flows that have
velocities up to 60km/sec seen against the background of photospheric
granulation with inclusions of BPs. The corresponding movie shows
reveals significant dynamics associated with these rosette like
structures stemming from clusters of BPs.

---------------------------------------------------------
Title: Relationship between orientations of halo CMEs and the
underlying filament / active regions
Authors: Kilcik, A.; Yurchyshyn, V.; Abramenko, V.; Goode, P. R.
2010AGUFMSH51C1684K Altcode:
Coronal mass ejections (CMEs) are the most important objects of space
weather studies. Although they have been at focus of many studies for
a long time now, there are still many unanswered questions. Here we
focus on the possible relationship between the direction of CME rotation
and the prevailing magnetic twist of the CME's source region. We could
determine the predominant helicity for 45 filaments and active regions
that appeared on both hemispheres of the Sun. We thus further confirm
that 76% of all source regions in the southern hemisphere were “S”
shaped, while 79% of northern hemisphere events were reverse “S”
(“Z”) shaped. These ratios agree with the well known hemispheric
segregation rule. According to theoretical considerations, (Green,
et al. 2007; Lynch, et al. 2009) CMEs, associated with eruption of
“S” (“Z') shaped structures are expected to rotate clockwise
(counterclockwise). Here we report that 67% of all source regions in
the southern hemisphere showed a predominant twist that agreed with
the direction of rotation of the corresponding CMEs. In the northern
hemisphere this ration was 63%. These findings may significantly
improve our understanding of CME evolution and their connection to
magnetic clouds. They may are affect our ability to predict severity
of geomagnetic storms.

---------------------------------------------------------
Title: Size and Life Time Distributions of Bright Points in the
Quiet Sun Photosphere
Authors: Abramenko, V.; Yurchyshyn, V.; Goode, P. R.
2010AGUFMSH31C1806A Altcode:
We present results of two-hour uninterrupted observations of solar
granulation obtained at excellent seeing conditions on August 3, 2010
with the largest ground-based new solar telescope (NST) operating
at Big Bear Solar observatory. Adaptive optics corrected data were
acquired with a broad-band TiO filter (centered at a wavelength of
705.7 nm). The time cadence was 10s and the pixel size was 0.0375
arcsec. Photospheric bright points (BPs) were automatically detected
and traced. We find that NST TiO BPs are co-spatial with those visible
in Hinode/SOT G-band images. In cases where Hinode/SOT detects one
large BP, NST shows several fully resolved BPs. Extended filigree
features running along intergranular lanes appear in NST images clearly
fragmented into separate BPs. The distribution function of the NST
BPs size is exponential and extends to the diffraction limit of NST
(77 km) without any saturation. The life time distribution function
follows a power law with an index of -1.9. About 98.6% of all detected
BPs live shorter than 120 s, and the most persistent BP lasted for
44 minutes. The size and the maximum intensity of BPs were found to
be proportional to the life time. Results are discussed in framework
of coronal heating and turbulent dynamo. Left - Hinode G-band image
obtained on 2010 August 3 at 12:22:11 UT (pixel size 0.109"). Right -
NST TiO image obtained on 2010 August 3 at 12:22:10 UT. Both images
cover the same area of 18.8" x 18.8" on the Sun. PDFs of the BPs
diameter calculated from NST TiO images (black) and from Hinode/SOT
G-band images (by Utz et al. 2009, blue).

---------------------------------------------------------
Title: Statistical Distribution of Size and Lifetime of Bright Points
Observed with the New Solar Telescope
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Goode, Philip;
Kilcik, Ali
2010ApJ...725L.101A Altcode: 2010arXiv1012.1584A
We present results of 2 hr non-interrupted observations of solar
granulation obtained under excellent seeing conditions with the largest
aperture ground-based solar telescope—the New Solar Telescope
(NST)—of Big Bear Solar Observatory. Observations were performed
with adaptive optics correction using a broadband TiO filter in the
705.7 nm spectral line with a time cadence of 10 s and a pixel size
of 0farcs0375. Photospheric bright points (BPs) were detected and
tracked. We find that the BPs detected in NST images are cospatial with
those visible in Hinode/SOT G-band images. In cases where Hinode/SOT
detects one large BP, NST detects several separated BPs. Extended
filigree features are clearly fragmented into separate BPs in NST
images. The distribution function of BP sizes extends to the diffraction
limit of NST (77 km) without saturation and corresponds to a log-normal
distribution. The lifetime distribution function follows a log-normal
approximation for all BPs with lifetime exceeding 100 s. A majority
of BPs are transient events reflecting the strong dynamics of the
quiet Sun: 98.6% of BPs live less than 120 s. The longest registered
lifetime was 44 minutes. The size and maximum intensity of BPs were
found to be proportional to their lifetimes.

---------------------------------------------------------
Title: Chromospheric Signatures of Small-scale Flux Emergence as
Observed with New Solar Telescope and Hinode Instruments
Authors: Yurchyshyn, V. B.; Goode, P. R.; Abramenko, V. I.; Chae,
J.; Cao, W.; Andic, A.; Ahn, K.
2010ApJ...722.1970Y Altcode: 2011arXiv1102.1034Y
With the ever-increasing influx of high-resolution images of the solar
surface obtained at a multitude of wavelengths, various processes
occurring at small spatial scales have become a greater focus of our
attention. Complex small-scale magnetic fields have been reported that
appear to have enough stored energy to heat the chromosphere. While
significant progress has been made in understanding small-scale
phenomena, many specifics remain elusive. We present here a detailed
study of a single event of disappearance of a magnetic dipole and
associated chromospheric activity. Based on New Solar Telescope Hα
data and Hinode photospheric line-of-sight magnetograms and Ca II
H images, we report the following. (1) Our analysis indicates that
even very small dipoles (elements separated by about 0farcs5 or less)
may reach the chromosphere and trigger non-negligible chromospheric
activity. (2) Careful consideration of the magnetic environment where
the new flux is deposited may shed light on the details of magnetic
flux removal from the solar surface. We argue that the apparent
collision and disappearance of two opposite polarity elements may
not necessarily indicate their cancellation (i.e., reconnection,
emergence of a "U" tube, or submergence of Ω loops). In our case, the
magnetic dipole disappeared by reconnecting with overlying large-scale
inclined plage fields. (3) Bright points (BPs) seen in off-band Hα
images are very well correlated with the Ca II H BPs, which in turn
are cospatial with G-band BPs. We further speculate that, in general,
Hα BPs are expected to be cospatial with photospheric BPs; however,
a direct comparison is needed to refine their relationship.

---------------------------------------------------------
Title: Intermittency and Multifractality Spectra of the Magnetic
Field in Solar Active Regions
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl
2010ApJ...722..122A Altcode: 2010arXiv1012.1586A
We present the results of a study of intermittency and multifractality
of magnetic structures in solar active regions (ARs). Line-of-sight
magnetograms for 214 ARs of different flare productivity observed at
the center of the solar disk from 1997 January until 2006 December
are utilized. Data from the Michelson Doppler Imager (MDI) instrument
on board the Solar and Heliospheric Observatory operating in the high
resolution mode, the Big Bear Solar Observatory digital magnetograph,
and the Hinode SOT/SP instrument were used. Intermittency spectra
were derived from high-order structure functions and flatness
functions. The flatness function exponent is a measure of the degree
of intermittency. We found that the flatness function exponent at
scales below approximately 10 Mm is correlated with flare productivity
(the correlation coefficient is -0.63). The Hinode data show that the
intermittency regime is extended toward small scales (below 2 Mm) as
compared to the MDI data. The spectra of multifractality, derived from
the structure functions and flatness functions, are found to be broader
for ARs of higher flare productivity as compared to those of low flare
productivity. The magnetic structure of high-flaring ARs consists of
a voluminous set of monofractals, and this set is much richer than
that for low-flaring ARs. The results indicate the relevance of the
multifractal organization of the photospheric magnetic fields to the
flaring activity. The strong intermittency observed in complex and
high-flaring ARs is a hint that we observe a photospheric imprint of
enhanced sub-photospheric dynamics.

---------------------------------------------------------
Title: Magnetic Energy Spectra in Solar Active Regions
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl
2010ApJ...720..717A Altcode: 2010arXiv1007.3702A
Line-of-sight magnetograms for 217 active regions (ARs) with different
flare rates observed at the solar disk center from 1997 January until
2006 December are utilized to study the turbulence regime and its
relationship to flare productivity. Data from the SOHO/MDI instrument
recorded in the high-resolution mode and data from the BBSO magnetograph
were used. The turbulence regime was probed via magnetic energy spectra
and magnetic dissipation spectra. We found steeper energy spectra for
ARs with higher flare productivity. We also report that both the power
index, α, of the energy spectrum, E(k) ~ k -α, and the
total spectral energy, W = ∫E(k)dk, are comparably correlated with the
flare index, A, of an AR. The correlations are found to be stronger than
those found between the flare index and the total unsigned flux. The
flare index for an AR can be estimated based on measurements of α and
W as A = 10 b (αW) c , with b = -7.92 ± 0.58
and c = 1.85 ± 0.13. We found that the regime of the fully developed
turbulence occurs in decaying ARs and in emerging ARs (at the very
early stage of emergence). Well-developed ARs display underdeveloped
turbulence with strong magnetic dissipation at all scales.

---------------------------------------------------------
Title: Oscillatory Behavior in the Quiet Sun Observed with the New
Solar Telescope
Authors: Anđić, A.; Goode, P. R.; Chae, J.; Cao, W.; Ahn, K.;
Yurchyshyn, V.; Abramenko, V.
2010ApJ...717L..79A Altcode: 2010arXiv1007.0272A
Surface photometry of the quiet Sun has achieved an angular resolution
of 0farcs1 with the New Solar Telescope at Big Bear Solar Observatory,
revealing that a disproportionate fraction of the oscillatory events
appear above observed bright point-like structures. During the tracking
of these structures, we noted that the more powerful oscillatory events
are cospatial with them, indicating that observed flux tubes may be
the source of many observed oscillatory events.

---------------------------------------------------------
Title: Flare Productivity Forecast Based on the Magnetic Energy
Spectrum of Active Regions
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl
2010shin.confE.104A Altcode:
Line-of-sight magnetograms for 217 active regions (ARs) of different
flare rate observed at the solar disk center from January 1997 until
December 2006 are utilized to study the turbulence regime and its
relationship to the flare productivity. Data from SOHO/MDI instrument
recorded in the high resolution mode were used. The turbulence regime
was probed via magnetic energy spectra and magnetic dissipation
spectra. We found steeper energy spectra for ARs of higher flare
productivity. We also report that both the power index, α, of the
energy spectrum, E(k)= const k^{-α}, and the total spectral energy,
W=\int E(k)dk, are comparably correlated with the flare index, A,
of an active region. The flare index for an AR can be forecasted
based on measurements of α and W as A=10^b (α W)^c, with b=-7.92
± 0.58 and c=1.85 ± 0.13. We find that regime of the classical
fully-developed turbulence occurs in decaying ARs and in emerging
ARs only at the very early stage of emergence. Well-developed ARs
display under-developed turbulence with strong magnetic dissipation
at all scales. The signature of under-developed turbulence indicates
that free cascading of energy from large to small scales is no longer
possible in mature active regions, and active region can no longer
evolve through series of quasi-stable states. Fraction of energy now
dissipates "along the way" via burst like energy release, a process
know as flaring in an active region.

---------------------------------------------------------
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: Magnetic Energy Spectrum and Intermittency in Solar Active
Regions of Different Flare Productivity
Authors: Abramenko, Valentyna
2010AAS...21632103A Altcode: 2010BAAS...41..912A
Solar photosphere is in a state of highly developed turbulence
owing to the sub-photospheric convection. The strength and growth
of turbulence determines eventually the degree of complexity of
the magnetic field. Complexity is thought to be responsible for the
flaring productivity of an active region (AR). Due to the inherently
non-linear nature of turbulence, complexity hardly can be adequately
presented by a single scalar parameter. Rather a spectrum of values
representing the behavior of the field at different scales should be
analyzed. Here the results of analysis of the magnetic energy spectra
and intermittency spectra for 186 ARs observed during 2000-2006 with
SOHO/MDI in the high-resolution mode are presented. We thus found that
steeper energy spectra are related to higher flaring productivity
(the correlation coefficient CC=0.69). The intermittency spectrum
was determined via a hyper flatness function (ratio of the 6th-order
structure function to the squared 3rd-order structure function)
for a set of spatial scales. It was found that the range of scales
where the hyper-flatness decreases (a signature of intermittency and
multifractality) can vary for different ARs, however, there is a strong
tendency for ARs with higher flare productivity to posses steeper and
broader intermittency spectrum at small scales (below 10-20 Mm). Very
steep and broad intermittency spectra found for several ARs showing
extremely high flaring activity seem to be related to shredded magnetic
fields along the neutral line of a delta-structure. Our results indicate
that the capability of an active region to produce solar flares is
directly related to the development of intermittent structures in an
active region magnetic field. Prospects of applying this approach to
new high resolution data from Hinode, SDO and NST acquired during the
oncoming solar maximum will be also discussed.

---------------------------------------------------------
Title: Highest Resolution Observations of the Quietest Sun
Authors: Goode, Philip R.; Yurchyshyn, Vasyl; Cao, Wenda; Abramenko,
Valentyna; Andic, Aleksandra; Ahn, Kwangsu; Chae, Jongchul
2010ApJ...714L..31G Altcode:
Highest resolution observations made with the new 1.6 m aperture solar
telescope in Big Bear Solar Observatory during this time of historic
inactivity on the Sun reveal new insights into the small-scale dynamics
of the Sun's photosphere. The telescope's unprecedented resolution
enabled us to observe that the smallest scale photospheric magnetic
field seems to come in isolated points in the dark intergranular lanes,
rather than the predicted continuous sheets confined to the lanes, and
the unexpected longevity of the bright points implies a deeper anchoring
than predicted. Further, we demonstrated for the first time that the
photospheric plasma motion and magnetic fields are in equipartition
over a wide dynamic range, and both cascade energy to ever-smaller
scales according to classical Kolmogorov turbulence theory. Finally,
we discovered tiny jet-like features originating in the dark lanes that
surround the ubiquitous granules that characterize the solar surface.

---------------------------------------------------------
Title: Low-Latitude Coronal Holes at the Minimum of the 23rd Solar
Cycle
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Linker, Jon; Mikić,
Zoran; Luhmann, Janet; Lee, Christina O.
2010ApJ...712..813A Altcode: 2010arXiv1002.1685A
Low- and mid-latitude coronal holes (CHs) observed on the Sun during
the current solar activity minimum (from 2006 September 21, Carrington
rotation (CR) 2048, to 2009 June 26, CR 2084) were analyzed using Solar
and Heliospheric Observatory/Extreme ultraviolet Imaging Telescope and
STEREO-A SECCHI EUVI data. From both the observations and Potential
Field Source Surface modeling, we find that the area occupied by
CHs inside a belt of ±40° around the solar equator is larger in
the current 2007 solar minimum relative to the similar phase of the
previous 1996 solar minimum. The enhanced CH area is related to a
recurrent appearance of five persistent CHs, which survived during 7-27
solar rotations. Three of the CHs are of positive magnetic polarity
and two are negative. The most long-lived CH was being formed during
2 days and existed for 27 rotations. This CH was associated with fast
solar wind at 1 AU of approximately 620 ± 40 km s-1. The
three-dimensional magnetohydrodynamic modeling for this time period
shows an open field structure above this CH. We conclude that the global
magnetic field of the Sun possessed a multi-pole structure during
this time period. Calculation of the harmonic power spectrum of the
solar magnetic field demonstrates a greater prevalence of multi-pole
components over the dipole component in the 2007 solar minimum compared
to the 1996 solar minimum. The unusual large separation between the
dipole and multi-pole components is due to the very low magnitude
of the dipole component, which is three times lower than that in the
previous 1996 solar minimum.

---------------------------------------------------------
Title: New Solar Telescope Observations of Magnetic Reconnection
Occurring in the Chromosphere of the Quiet Sun
Authors: Chae, Jongchul; Goode, P. R.; Ahn, K.; Yurchysyn, V.;
Abramenko, V.; Andic, A.; Cao, W.; Park, Y. D.
2010ApJ...713L...6C Altcode:
Magnetic reconnection is a process in which field-line connectivity
changes in a magnetized plasma. On the solar surface, it often
occurs with the cancellation of two magnetic fragments of opposite
polarity. Using the 1.6 m New Solar Telescope, we observed the
morphology and dynamics of plasma visible in the Hα line, which is
associated with a canceling magnetic feature (CMF) in the quiet Sun. The
region can be divided into four magnetic domains: two pre-reconnection
and two post-reconnection. In one post-reconnection domain, a small
cloud erupted, with a plane-of-sky speed of 10 km s-1,
while in the other one, brightening began at points and then tiny
bright loops appeared and subsequently shrank. These features support
the notion that magnetic reconnection taking place in the chromosphere
is responsible for CMFs.

---------------------------------------------------------
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: 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: Turbulence in the solar photosphere as derived from NST
observations of the granulation
Authors: Abramenko, V.
2009AGUFMSH51A1256A Altcode:
We present results of analysis of images of solar granulation obtained
with BBSO’s 1.6 m clear aperture New Solar Telescope (NST) at
BBSO. Observations were carried out on 2009 July 21 near the central
meridian of the solar disk in the TiO (705 nm) spectral line. Eleven
consecutive 30s bursts were speckle reconstructed to derive the
transverse velocity map, as well as the power spectra of the velocity
and temperature fluctuations. The FOV was about 60x60 arcsec. We
found that the transverse velocity spectrum displays the classical
Kolmogorov-type turbulent exponent, -5/3 over spatial scales of 1-8
Mm, while below 1 Mm we observe a dissipative spectrum characterized
by an exponent of -7/2. The observed dissipation regime is much more
moderate than the -17/3 regime, which is typical for the classical
turbulence and was reported earlier for the Doppler velocities in the
photosphere of the quiet sun. One might conclude that on scales below
1 Mm the turbulence is being suppressed by the presence of the magnetic
field. The temperature spectrum displays a very narrow Kolmogorov-type
spatial range of 0.9 - 0.5 Mm, which is followed at smaller scales by
the -3.5 range. Again, the dissipation of the temperature fluctuations
does not follow the classical dissipation regime. Joint consideration
of the velocity and temperature spectra shows that there seems to be
no reasonable possibility to interpret them in framework of the highly
developed isotropic turbulence of a fluid flow. We shall discuss the
implications of these results, as well as more recent results.

---------------------------------------------------------
Title: Parameters of the Magnetic Flux inside Coronal Holes
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Watanabe, Hiroko
2009SoPh..260...43A Altcode: 2009arXiv0908.2460A
The parameters of the magnetic flux distribution inside low-latitude
coronal holes (CHs) were analyzed. A statistical study of 44 CHs
based on Solar and Heliospheric Observatory (SOHO)/MDI full disk
magnetograms and SOHO/EIT 284 Å images showed that the density of
the net magnetic flux, Bnet, does not correlate with the
associated solar wind speeds, Vx. Both the area and net flux
of CHs correlate with the solar wind speed and the corresponding spatial
Pearson correlation coefficients are 0.75 and 0.71, respectively. A
possible explanation for the low correlation between Bnet
and Vx is proposed. The observed non-correlation might
be rooted in the structural complexity of the magnetic field. As a
measure of the complexity of the magnetic field, the filling factor,
f(r), was calculated as a function of spatial scales. In CHs, f(r)
was found to be nearly constant at scales above 2 Mm, which indicates a
monofractal structural organization and smooth temporal evolution. The
magnitude of the filling factor is 0.04 from the Hinode SOT/SP data
and 0.07 from the MDI/HR data. The Hinode data show that at scales
smaller than 2 Mm, the filling factor decreases rapidly, which means
a multifractal structure and highly intermittent, burst-like energy
release regime. The absence of the necessary complexity in CH magnetic
fields at scales above 2 Mm seems to be the most plausible reason
why the net magnetic flux density does not seem to be related to the
solar wind speed: the energy release dynamics, needed for solar wind
acceleration, appears to occur at small scales below 1 Mm.

---------------------------------------------------------
Title: Rotation of White-light Coronal Mass Ejection Structures as
Inferred from LASCO Coronagraph
Authors: Yurchyshyn, Vasyl; Abramenko, Valentyna; Tripathi, Durgesh
2009ApJ...705..426Y Altcode:
Understanding the connection between the magnetic configurations of a
coronal mass ejection (CME) and their counterpart in the interplanetary
medium is very important in terms of space weather predictions. Our
previous findings indicate that the orientation of a halo CME elongation
may correspond to the orientation of the underlying flux rope. Here
we further explore these preliminary results by comparing orientation
angles of elongated LASCO CMEs, both full and partial halos, to the
EUV Imaging Telescope post-eruption arcades (PEAs). By analyzing a
sample of 100 events, we found that the overwhelming majority of CMEs
are elongated in the direction of the axial field of PEAs. During their
evolution, CMEs appear to rotate by about 10° for most of the events
(70%) with about 30°-50° for some events, and the corresponding time
profiles display regular and gradual changes. It seems that there is
a slight preference for the CMEs to rotate toward the solar equator
and heliospheric current sheet (59% of the cases). We suggest that the
rotation of the ejecta may be due to the presence of a heliospheric
magnetic field, and it could shed light on the problems related to
connecting solar surface phenomena to their interplanetary counterparts.

---------------------------------------------------------
Title: How the Magnetic Flux Inside Coronal Holes is Distributed:
New Insight from Hinode Data
Authors: Abramenko, Valentyna
2009SPD....40.0601A Altcode:
Distribution of the magnetic flux inside low-latitude coronal holes
(CHs) was analyzed. A statistical study based on SOHO/MDI full
disk magnetograms showed that the density of the net magnetic flux
does not correlate with the associated solar wind speeds. A possible
interpretation is that the density of the magnetic flux derived from the
4 arcsec resolution data is not a suitable parameter to probe energetics
in CHs. A reason might be rooted in the structural organization of the
magnetic flux, in its fractal nature. As a measure of multifractality
of the magnetic field, the filling factor was calculated as a function
of spatial scales. The filling factor is independent from scale for
a monofractal structure, and it varies with scale for a multifractal
structure of burst-like energy release dynamics. Magnetic field filling
factor in CHs was found to be nearly constant at scales above 2 Mm,
which indicates a monofractal structural organization and smooth
temporal evolution. The magnitude of the filling factor is 0.04 from
the Hinode SOT/SP data and 0.07 from the MDI/HR data. The Hinode data
shows that at scales smaller than 2 Mm, the filling factor decreases
rapidly, which means a mutlifractal structure and highly intermittent,
burst-like energy release regime. The observed monofractality of the
coronal hole magnetic field at scales above 2 Mm seems to be a most
plausible reason why the net magnetic flux density does not correlates
with the solar wind speed. The bulk of energy release needed for
the solar wind acceleration occurs at smaller scales, the scales of
multifractality regime, below 1 Mm.

---------------------------------------------------------
Title: Statistical Assessment of Photospheric Magnetic Features in
Imminent Solar Flare Predictions
Authors: Song, Hui; Tan, Changyi; Jing, Ju; Wang, Haimin; Yurchyshyn,
Vasyl; Abramenko, Valentyna
2009SoPh..254..101S Altcode:
In this study we use the ordinal logistic regression method to establish
a prediction model, which estimates the probability for each solar
active region to produce X-, M-, or C-class flares during the next
1-day time period. The three predictive parameters are (1) the total
unsigned magnetic flux Tflux, which is a measure of an
active region's size, (2) the length of the strong-gradient neutral
line Lgnl, which describes the global nonpotentiality of an
active region, and (3) the total magnetic dissipation Ediss,
which is another proxy of an active region's nonpotentiality. These
parameters are all derived from SOHO MDI magnetograms. The ordinal
response variable is the different level of solar flare magnitude. By
analyzing 174 active regions, Lgnl is proven to be the
most powerful predictor, if only one predictor is chosen. Compared
with the current prediction methods used by the Solar Monitor at the
Solar Data Analysis Center (SDAC) and NOAA's Space Weather Prediction
Center (SWPC), the ordinal logistic model using Lgnl,
Tflux, and Ediss as predictors demonstrated
its automatic functionality, simplicity, and fairly high prediction
accuracy. To our knowledge, this is the first time the ordinal logistic
regression model has been used in solar physics to predict solar flares.

---------------------------------------------------------
Title: Evolution of Optical Penumbral and Shear Flows Associated
with the X3.4 Flare of 2006 December 13
Authors: Tan, Changyi; Chen, P. F.; Abramenko, Valentyna; Wang, Haimin
2009ApJ...690.1820T Altcode:
The rapid and irreversible decay of penumbrae related to X-class flares
has been found in a number of studies. Since the optical penumbral
flows are closely associated with the morphology of sunspot penumbra,
we use state-of-the-art Hinode data to track penumbral flows in flaring
active regions as well as shear flows close to the flaring neutral
line. This paper concentrates on AR 10930 around the time of an X3.4
flare on 2006 December 13. We utilize the seeing-free solar optical
telescope G-band data as a tracer to obtain the horizontal component
of the penumbral and shear flows by local correlation tracking, and
Stokes-V data to register positive and negative magnetic elements along
the magnetic neutral line. We find that: (1) an obvious penumbral decay
appears in this active region intimately associated with the X3.4 flare;
(2) the mean magnitude of the horizontal speeds of the penumbral flows
within the penumbral decay areas temporally and spatially varies from
0.6 to 1.1 km s-1 (3) the penumbral flow decreases before
the flare eruption in two of the four penumbral decay areas; (4) the
mean shear flows along the magnetic neutral line of this δ-sunspot
started to decrease before the flare and continue to decrease for
another hour after the flare. The magnitude of this flow apparently
dropped from 0.6 to 0.3 km s-1. We propose that the decays
of the penumbra and the penumbral flow are related to the magnetic
rearrangement involved in the coronal mass ejection/flare events.

---------------------------------------------------------
Title: Horizontal Electric Currents in the Photosphere
Authors: Abramenko, V.
2008AGUFMSH41A1600A Altcode:
We propose a proxy for horizontal electric currents in the solar
photosphere based on spectral and spatial distributions of magnetic
energy dissipation. For a set of evolving active regions (ARs)
observed with SOHO/MDI in the high resolution mode, the dissipation
spectrum, k2E(k), and the spatial structure of dissipation, i.e.,
the Stokes dissipation function ɛ(x,y), were calculated from the
observed line-of-sight component of the magnetic field. These functions
allowed us to calculate (a part of) the horizontal electric current
density in the photosphere. We found that as an active region emerges,
large-scale horizontal electric currents are gradually generated and
they determine the bulk of dissipation. When an active region decays,
the large-scale horizontal currents decay faster than the small-scale
currents. The density of transverse currents in active regions is in
the range of &lt; jh &gt; ~ (0.008 - 0.028) A/m2, that is comparable
with the density of vertical currents in active regions. We estimated
the upper boundary of the plasma conductivity to be σ &lt; 5× 10-8
s/m2, which is four orders of magnitude lower than the classical ohmic
conductivity for the photosphere. We suggest two possible mechanisms
for generation of these horizontal currents in the photosphere. One
of them is the horizontal drift of charged particles in the medium of
varying plasma pressure gradient at the periphery of a sunspot. Such
drift can produce quasi-circular closed horizontal currents around
sunspots. Another possibility could be the existence of horizontal axial
current within a highly twisted horizontal magnetic structure laying in
the photosphere along the magnetic neutral line. The horizontal currents
may contribute significantly to the dynamics of the photosphere/corona
coupling, as well as the estimation of non-potentiality of ARs.

---------------------------------------------------------
Title: Intermittency in the Photosphere and Corona above an Active
Region
Authors: Abramenko, Valentyna; Yurchyshyn, Vasyl; Wang, Haimin
2008ApJ...681.1669A Altcode: 2009arXiv0903.2882A
Recent studies have demonstrated without doubt that the magnetic field
in the photosphere and corona is an intermittent structure, opening
new views of the underlying physics. In particular, such problems
as the existence in the corona of localized areas with extremely
strong resistivity (required to explain magnetic reconnection at all
scales) and the interchange between small and large scales (required
in the study of photospheric-coronal coupling), to name a few, can be
easily captured by the concept of intermittency. This study focuses
on simultaneous time variations of intermittency properties derived
in the photosphere, chromosphere, and corona. We analyze data for
NOAA Active Region 10930 acquired between 2006 December 8, 12:00 UT,
and December 13, 18:45 UT. Photospheric intermittency is inferred
from Hinode magnetic field measurements, while intermittency in the
transition region and corona is derived from Nobeyama 9 GHz radio
polarization measurements and high-cadence Hinode XRT (thin-Be) data,
as well as GOES 1-8 Å flux. The photospheric dynamics and its possible
relationship with the intermittency variations are also analyzed
by calculating the kinetic vorticity. In this case study, we find
the following chain of events: The intermittency of the photospheric
magnetic field peaked after the specific kinetic vorticity of plasma
flows in the active region reached its maximum (4 hr time delay). In
turn, a gradual increase of coronal intermittency occurred after the
peak of the photospheric intermittency. The time delay between the peak
of photospheric intermittency and the occurrence of the first strong
(X3.4) flare was approximately 1.3 days. Our analysis seems to suggest
that the enhancement of intermittency/complexity first occurs in the
photosphere and is later transported toward the corona.

---------------------------------------------------------
Title: Spectrum of Magnetic Dissipation and Horizontal Electric
Currents in the Solar Photosphere
Authors: Abramenko, Valentyna
2008arXiv0806.1547A Altcode:
A proxy for horizontal electric currents in the solar photosphere was
suggested. For a set of evolving active regions (ARs) observed with
{\it Solar and Heliospheric Observatory (SOHO)} Michelson Doppler
Imager (MDI) in the high resolution mode, the dissipation spectrum,
$k^2E(k)$, and the spatial structure of dissipation, i.e., the Stokes
dissipation function $\epsilon(x,y)$, were calculated from the observed
$B_z$ component of the magnetic field. These functions allowed us
to calculate (a part of) the horizontal electric current density
in the photosphere. It was shown that as an active region emerges,
large-scale horizontal electric currents are gradually generated
and determine a bulk of dissipation. When an active region decays,
the large-scale horizontal currents decay faster than the small-scale
ones. The density of horizontal currents in active regions is in the
range of $&lt;j_h &gt; \sim (0.008 - 0.028)$ A/m$^2$, that is compatible
with the density of vertical currents in active regions. We suggest two
possible mechanisms for generation of such horizontal currents in the
photosphere. One of them is the drift motions of charged particles in
the medium of varying plasma pressure gradient in a horizontal plane at
the periphery of a sunspot. Such a drift can produce quasi-circular
closed horizontal currents around sunspots. Another possibility
could be an existence of horizontal axial current inside a highly
twisted horizontal magnetic structure laying in the photosphere along
the magnetic neutral line. The horizontal currents may contribute
significantly to the dynamics of the photosphere/corona coupling,
as well as the estimation of non-potentiality of ARs.

---------------------------------------------------------
Title: Evolution of Evershed and Shear Flows Associated With the
X3.4 Flare of December 13, 2006
Authors: Tan, C.; Shine, R. A.; Abramenko, V. I.; Wang, H.
2008AGUSMSP51C..03T Altcode:
Liu et al. (2006) presented the observation of rapid penumbra decay
associated with a number of X-class flares. As the Evershed flows
are closely associated with morphology of sunspot penumbra, in this
work, we use the state-of-art Hinode data to track Evershed flow in
flaring active regions as well as shear flows close to the flaring
neutral line. This paper concentrates on the study of AR10930 around
the time of the X3.4 flare time on December 13, 2006. We utilize the
seeing-free data from Hinode SOT G-band data as the tracer to obtain
the horizontal component of the Evershed flows by local correlation
tracking. We find that: (1) The penumbra decay appears obviously in
this active region associated with the X3.4 flare. (2) The Evershed
flow decreases slightly immediately following the flare, indicating
that magnetic fields become more vertical associated with the flare. In
addition, we will discuss the evolution of shear flows near the neutral
line of this delta spot leading to and following the flare.

---------------------------------------------------------
Title: Intermittency in the photosphere and corona as derived from
the Hinode data
Authors: Abramenko, V.; Yurchyshyn, V.; Wang, H.
2008AGUSMSP21B..01A Altcode:
Recent studies undoubtedly demonstrate that the magnetic fields in the
photosphere and corona are strongly non-Gaussian and can be represented
as intermittent structures, which offers new views on the underlying
physics. In particular, such problems as the existence in the corona of
localized areas with extremely strong resistivity (required to explain
magnetic reconnection of all scales) and the interchange between
small and large scales (required in study of the photosphere/corona
coupling), to name a few, can be easily captured by the concept of
intermittency. This study is focused on simultaneous time variations
of intermittency properties derived in the photosphere, chromosphere
and corona. We analyzed data for NOAA AR 10930 acquired between Dec 08,
2006 12:00 UT and Dec 13, 2006 18:45 UT. Photospheric intermittency was
inferred from Hinode magnetic field measurements, while intermittency
in the transition region and corona was derived from Nobeyama 9 GHz
radio polarization measurements, high cadence Hinode/XRT/Be-thin data
as well as GOES 1-8Å~ flux. Photospheric dynamics and its possible
relationship with the intermittency variations were also analyzed by
calculating the kinetic vorticity. For this case study we found the
following chain of events. Intermittency of the photospheric magnetic
field peaked after the specific kinetic vorticity of plasma flows
in the AR reached its maximum level (4 hour time delay). In turn,
gradual increase of coronal intermittency occurred after the peak
of the photospheric intermittency. The time delay between the peak
of photospheric intermittency and the occurrence of the first strong
(X3.4) flare was approximately 1.3 days. Our analysis seems to suggest
that the enhancement of intermittency/complexity first occurs in the
photosphere and is later transported toward the corona.

---------------------------------------------------------
Title: Multifractal Nature of Solar Phenomena
Authors: Abramenko, Valentyna I.
2008sprt.book...95A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Do active regions emerge in a similar regime?
Authors: Abramenko, Valentyna
2008cosp...37...15A Altcode: 2008cosp.meet...15A
New magnetic flux emerges on the solar surface in response to the
subsurface dynamo and plasma convection motions. Observations of the
dynamics of active regions emergence might be promising to shead light
on the subsurface dynamics. Whether the emergence regime is essentially
the same for active regions (of the same flux content at the same
time scales), or it can substantially differ from one active region
to another? How information on the emergence rates can be utilized
to diagnose the subsurface stage of emergence and subsequent coronal
response? We attempt to tackle these questions by examining the flux
emergence rates, energy injection rates and energy dissipation rates
for several active regions observed by SOHO/MDI instrument in the high
resolution mode.

---------------------------------------------------------
Title: Calculation of Intermittency in the Photosphere and Corona
From Hinode Data
Authors: Abramenko, V.; Yurchyshyn, V.
2007AGUFMSH34A..05A Altcode:
High spatial and temporal resolution observations of the photospheric
magnetic field and solar corona, offered recently by Hinode instrument,
provide us a unique opportunity to simultaneously estimate degree of
intermittency in the photosphere and the corona and to track their
variations in time. To do this, we adopted a flatness-function
technique, where the slope of the function defines degree of
intermittency. The function itself is calculated as the ratio of
the sixth-order structure function to the cube of the second-order
structure function. Three independent data sets, that were utilized
to calculate the intermittency in the corona (XRT/Hinode, GOES, and
Nobeyama 9.4 Hz polarization flux), showed a synchronous increase of
intermittency during a 5-day time interval that ends with the occurrence
of the X3.4 flare in the NOAA 10930. Photospheric intermittency,
calculated from SOT-FG/Hinode magnetograms, peaked approximately 1.5
days before the flare onset. The result allows to suggest a preceding
gain of intermittency in the photosphere with a following transport
of intermittency into the corona.

---------------------------------------------------------
Title: Role and Nature of Intermittency and Self-Organized Criticality
in Solar Phenomena
Authors: Abramenko, V.
2007AGUFMNG34A..01A Altcode:
In Solar Physics, last decades demonstrated a considerable progress in
understanding of both macro-scale processes (e.g., magneto-hydro-dynamic
modeling of the heliosphere, magnetic field modeling in coronal
structures, etc.), on the one hand, and micro-scale phenomena (e.g.,
turbulence of the solar plasma), on the other hand. Further progress
seems to be associated with our realization of how various micro-scale
processes are involved and manifested in the macro-scale behavior of the
entire Sun. A similar problem unavoidably arises in studies of any other
non-linear dynamical dissipative system in Nature. Such systems that can
be placed in between a chaos and a completely determined structure. The
goal of this talk is to show how the conceptions of intermittency,
multifractality, percolation, and self-organized criticality are closely
intertwined, and how they are currently elaborated in Solar Physics
and help in understanding of unpredictable behavior of our closest star.

---------------------------------------------------------
Title: Solar-Wind Discontinuities and the Potential Role of Alfvénic
Turbulence
Authors: Vasquez, B. J.; Abramenko, V. I.; Haggerty, D. K.; Smith,
C. W.
2007AGUFMSH23A1154V Altcode:
Magnetohydrodynamic (MHD) simulations of Alfvénic turbulence show
that a cross-field cascade predominates and generates small scale
current sheets across the magnetic field. In these current sheets
turbulent energy significantly dissipates. In collisionless plasmas,
the width of these sheets should approach the proton inertial length or
proton gyroradius and dissipation within the sheets may also occur in
association with wave-particle interactions. The nearly collisionless
solar wind has long been known to contain discontinuities of these
widths, but the identity of these discontinuities and the originating
source became unclear after Cluster spacecraft measurements established
that discontinuity normals were nearly perpendicular to the background
magnetic field. In addition to static tangential discontinuities,
the possibility that the discontinuities arise in association with
turbulence needs to be considered. We have identified over 6000
discontinuities from a 27-day period using magnetic field data at
1/3 per second resolution with the ACE spacecraft. We conclude that
turbulence can account for the origin of the discontinuities, their
small or zero normal field components, their small intensity change,
and their correlated velocity and magnetic field fluctuations. Using
cross-product normals and plasma data, we have found that discontinuity
width averages about 4 proton inertial lengths at small proton
β(= ratio of gas to magnetic pressure) and 4 proton gyroradii at
large proton β. The distribution of separations between successive
discontinuities is lognormal which can arise in association with a
multiplicative random cascade. In contrast, synthetic phase-random
magnetic fields are found to contain less coherent discontinuities
confined mostly to small field rotations and a Poisson distribution
of successive separations. Solar-wind discontinuities are then
substantially coherent which is consistent with sheets generated by
turbulence. This work is performed in association with the Living With
A Star focus team on Heliospheric Magnetic Fields.

---------------------------------------------------------
Title: Numerous small magnetic field discontinuities of Bartels
rotation 2286 and the potential role of Alfvénic turbulence
Authors: Vasquez, Bernard J.; Abramenko, Valentyna I.; Haggerty,
Dennis K.; Smith, Charles W.
2007JGRA..11211102V Altcode:
Magnetic field data at 1/3 s resolution are used from the ACE spacecraft
for days 7 to 33 in 2001 (Bartels rotation 2286) to characterize
the statistical properties of discontinuities during this period. A
method is developed for finding discontinuities independent of spread
angle between magnetic fields across the discontinuity. This was
viewed as necessary since larger spread angle discontinuities can
occur in close proximity with smaller ones, and the smaller ones
are numerous. Discontinuities are found to occur in groupings, and
the separation between successive discontinuities has a distribution
which is lognormal. With the expectation that most discontinuities have
normals across or nearly across the magnetic field, the cross-product
method is used to find the normal. Combining normal direction and plasma
data from the ACE spacecraft, we find that the most probable width for
discontinuities is 4 to 8 proton inertial lengths or gyroradii. For
small β(≡ratio of proton gas and magnetic pressure), the widths
scale better with proton inertial length while for large β with
proton gyroradius. Most discontinuities have small changes in the
total magnetic intensity and are ramp-like. The statistical properties
of the discontinuities appear to come from a single population. To
identify this population, rotational and tangential discontinuities
and also discontinuities associated with Alfvénic turbulence are
considered. The population is most consistent with turbulence.

---------------------------------------------------------
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: The Evolution of Photospheric Magnetic Fields Inside and
Around the Coronal Holes
Authors: Tan, Changyi; Fu, G.; Abramenko, V. I.; Jing, J.; Song, H.;
Wang, H.
2007AAS...210.9126T Altcode: 2007BAAS...39..208T
We investigated the evolution of photospheric magnetic fields around
the boundaries of 22 coronal holes with a variety of sizes and
complexities from August 21 2003 to December 30 2006. The boundary
of each coronal hole was defined from the 195Å. images obtained by
SOHO Extreme ultraviolet Imaging Telescope (EIT). The SOHO Michelson
Doppler Imager (MDI) full disk data were employed to study the magnetic
element evolution. The coronal hole area was divided into three parts
(inside, outside and the boundary of the coronal hole), via image
process techniques. The movies of each part of the 22 coronal holes
were made. The positive and negative magnetic elements were calculated
in each of the three parts respectively. We present the results on
the rates of flux emergence cancellations and flow patterns in these
3 parts.

---------------------------------------------------------
Title: Emerging Active Regions: Turbulence in the Photosphere versus
Flaring in the Corona
Authors: Abramenko, V. I.
2006ASPC..354..195A Altcode:
In this study, turbulence of the magnetic field in the photosphere
is explored by means of power spectra of line-of-sight photospheric
magnetograms obtained for 16 active regions of different flare
activity. Magnetic field measurements were made in the high resolution
mode with the Michelson Doppler Imager instrument, onboard the Solar
and Heliospheric Observatory. For each active region, we determined
the daily soft X-ray flare index, A, which characterizes the flare
productivity of an active region, being equal to one when the specific
flare productivity is one C1.0 flare per day. The power index, α,
of the magnetic power spectrum, E(k) ∼ k^{-α}, averaged over all
analyzed magnetograms for a given active region, was then compared with
the flare index. Here we report that those active regions which produced
X-class flares possessed a steep power spectrum with α &gt; 2.0, while
the flare-quiet active regions with small A displayed a Kolmogorov-type
spectrum of α ≈ 5/3. The data suggest that the flare index A may be
determined from the power index α via the following equation: A(α)=
409.5 (α-5/3)^{2.49}. We also found that the magnitude of the power
index at the stage of emergence of an active region is not related to
the current flaring level of this active region but instead reflects
its future flare productivity, when the magnetic configuration becomes
well-evolved. This finding enables us to distinguish, at a very early
stage, those solar active regions that are “born bad” and have a
potential to produce powerful solar flares and significant disturbances
in the Earth's magnetosphere.

---------------------------------------------------------
Title: Erratum: “The Statistical Relationship between the
Photospheric Magnetic Parameters and the Flare Productivity of
Active Regions” (<A href="/abs/2006ApJ...644.1273J">ApJ, 644, 1273
[2006]</A>)
Authors: Jing, Ju; Song, Hui; Abramenko, Valentyna; Tan, Changyi;
Wang, Haimin
2006ApJ...652.1796J Altcode:
Because of an error in generating math images, variables
for the derivative terms are missing from the published
versions of equations (1) and (2). The correct forms of these equations
are:∇Bz=[((dBz)/dx)2+((dBz)/dy)21/2
(1)ɛ(Bz)=4[((dBz)/dx)2+((dBz)/dy)2+2((dBz)/dx+(dBz)/dy)2.
(2)The Press sincerely regrets this error.

---------------------------------------------------------
Title: The May 13, 2005 Eruption: Observations, Data Analysis and
Interpretation
Authors: Yurchyshyn, V.; Liu, C.; Abramenko, V.; Krall, J.
2006SoPh..239..317Y Altcode: 2006SoPh..tmp...72Y
In this study, we present detailed description and analysis of the May
13, 2005 eruption, the corresponding coronal mass ejection (CME) and
intense geomagnetic storm observed near the Earth on May 15, 2005. This
isolated two-ribbon M8.0 flare and the very fast CME occurred in a
relatively simple magnetic configuration during a quiet period of solar
activity, which enabled us to reliably associate the solar surface event
with its counterpart observed in the Earth magnetosphere. In our study,
we utilized (i) various tools to analyze a multi-wavelength data set
that includes ground (BBSO vector magnetograms, Hα) and space (SOHO,
TRACE, RHESSI and ACE) based data; (ii) linear force-free modeling
to reconstruct the coronal field above the active region and (iii)
erupting flux rope (EFR) model to simulate a near-Sun halo CME and
a near-Earth interplanetary CME (ICME). Our findings indicate that
persisting converging and shearing motions near the main neutral line
could lead to the formation of twisted core fields and eventually
their eruption via reconnection. In the discussed scenario, the in
situ formed erupting loop can be observed as a magnetic cloud (MC)
when it reaches the Earth. The EFR model was able to produce both a
model halo CME and ICME providing a good global match to the overall
timing and components of the magnetic field in the observed MC. The
orientation of the model ICME and the sense of the twist, inferred
from the EFR model, agree well with the orientation and the magnetic
helicity found in the source active region.

---------------------------------------------------------
Title: Directional Discontinuities Found During Bartels Rotation 2286
Authors: Vasquez, B. J.; Abramenko, V. I.; Haggerty, D. K.; Smith,
C. W.
2006AGUFMSH53A1473V Altcode:
Cluster spacecraft triangulation measurements demonstrate that most,
if not, all directional discontinuities (DDs) have small normal
magnetic field components, consistent with tangential discontinuities
(TDs). However, many of these have small total magnetic intensity
jumps which render them unclassifiable by conventional two-parameters
methods. In general, these DDs can occur in association with Alfvénic
fluctuations. As a result, classification is not unique and it could
also be that some share of the DDs belong to persistent, nondissipative
rotational discontinuities (RDs) or to transient, dissipative turbulent
current sheets. To move beyond individual classification, we adopt a
statistical approach. With 1/3 per second magnetic field data from
the ACE spacecraft from days 7 to 33 in 2001, we use an automated
technique to find discontinuities individually in each of the RTN
field components and then overlap them. This technique is independent
of spread angle. We have found that the distance separating neighboring
DDs forms a log-normal distribution. The tendency for DDs to cluster in
close vicinity to each other is inconsistent with an in situ population
of RDs generated by wave steepening. Widths are determined by the
cross-product method and peak at 4 proton inertial lengths for DDs
with spread angles exceeding 3°. The magnetic intensity jumps are
mostly small and layers behave as smooth ramps. Little indication is
seen of a transient character. The statistical properties appear to
come from a single population which is most likely TDs. This work is
performed in association with the Living With A Star focus team on
Heliospheric Magnetic Fields.

---------------------------------------------------------
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: 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: The Statistical Relationship between the Photospheric Magnetic
Parameters and the Flare Productivity of Active Regions
Authors: Jing, Ju; Song, Hui; Abramenko, Valentyna; Tan, Changyi;
Wang, Haimin
2006ApJ...644.1273J Altcode:
Using line-of-sight Michelson Doppler Imager (MDI) magnetograms of
89 active regions and Solar Geophysical Data (SGD) flare reports,
we explored, for the first time, the magnitude scaling correlations
between three parameters of magnetic fields and the flare productivity
of solar active regions. These parameters are (1) the mean value of
spatial magnetic gradients at strong-gradient magnetic neutral lines,
(∇Bz)NL (2) the length of strong-gradient
magnetic neutral lines, LGNL; and (3) the total magnetic
energy, ɛ(Bz)dA, dissipated in a layer of 1 m during 1 s
over the active region's area. The MDI magnetograms of active regions
used for our analysis are close to the solar central meridian (within
+/-10°). The flare productivity of active regions was quantified
by the soft X-ray flare index for different time windows from the
time interval of the entire disk passage down to +1 day from the
time of the analyzed magnetogram. Our results explicitly indicate
positive correlations between the parameters and the overall flare
productivity of active regions, and imminent flare production as
well. The correlations confirm the dependence of flare productivity
on the degree of nonpotentiality of active regions.

---------------------------------------------------------
Title: Progress on the 1.6-meter New Solar Telescope at Big Bear
Solar Observatory
Authors: Denker, C.; Goode, P. R.; Ren, D.; Saadeghvaziri, M. A.;
Verdoni, A. P.; Wang, H.; Yang, G.; Abramenko, V.; Cao, W.; Coulter,
R.; Fear, R.; Nenow, J.; Shoumko, S.; Spirock, T. J.; Varsik, J. R.;
Chae, J.; Kuhn, J. R.; Moon, Y.; Park, Y. D.; Tritschler, A.
2006SPIE.6267E..0AD Altcode: 2006SPIE.6267E..10D
The New Solar Telescope (NST) project at Big Bear Solar Observatory
(BBSO) now has all major contracts for design and fabrication in place
and construction of components is well underway. NST is a collaboration
between BBSO, the Korean Astronomical Observatory (KAO) and Institute
for Astronomy (IfA) at the University of Hawaii. The project will
install a 1.6-meter, off-axis telescope at BBSO, replacing a number
of older solar telescopes. The NST will be located in a recently
refurbished dome on the BBSO causeway, which projects 300 meters into
the Big Bear Lake. Recent site surveys have confirmed that BBSO is
one of the premier solar observing sites in the world. NST will be
uniquely equipped to take advantage of the long periods of excellent
seeing common at the lake site. An up-to-date progress report will
be presented including an overview of the project and details on the
current state of the design. The report provides a detailed description
of the optical design, the thermal control of the new dome, the optical
support structure, the telescope control systems, active and adaptive
optics systems, and the post-focus instrumentation for high-resolution
spectro-polarimetry.

---------------------------------------------------------
Title: Flux Emergence Rate In Coronal Holes And In Adjacent Quiet-sun
Regions
Authors: Abramenko, Valentyna; Fisk, L.; Yurchyshyn, V.
2006SPD....37.1403A Altcode: 2006BAAS...38..243A
The rate of emergence of new magnetic flux in coronal holes, and in
surroundingregions on the quiet Sun was analyzed from observations
from the MichelsonDoppler Imager and the EUV Imager Telescope on the
Solar and HeliosphericObservatory (SOHO). Coronal holes are regions
where the open magnetic flux ofthe Sun, the component that forms the
heliospheric magnetic field, isconcentrated. It is determined that
the rate of emergence of new magnetic fluxis systematically lower,
by a factor of 2, in coronal holes relative to thesurrounding quiet
Sun. This result is consistent with a prediction in a recentmodel for
the transport of open magnetic flux on the Sun, which demonstratedthat
open flux tends to accumulate and concentrate in regions where the
rate ofemergence of new magnetic flux is a local minimum.

---------------------------------------------------------
Title: The Statistical Relationship between the Photospheric Magnetic
Parameters and the Flare Productivity of Active Regions
Authors: Jing, Ju; Song, H.; Abramenko, V.; Tan, C.; Wang, H.
2006SPD....37.3403J Altcode: 2006BAAS...38..259J
Using line-of-sight Michelson Doppler Imager (MDI) magnetograms of
89 active regions and Solar Geophysical Data (SGD) flare reports,
we explored the magnitude scaling correlations between two parameters
of photospheric magnetic fields and the flare productivity of solar
active regions. These parameters are: (1) the length of strong-gradient
magnetic neutral lines, and (2) the total magnetic energy dissipated in
a layer of 1m during 1 second over the active region's area. The MDI
magnetograms of active regions used for our analysis are close to the
solar central meridian. The flare productivity of active regions was
quantified by the soft X-ray flare index for different time windows:
from the time interval of the entire disk passage down to +1 day from
the time of analyzed magnetogram. Our results explicitly indicate
positive correlations between the parameters and the overall flare
productivity of active regions, and imminent flare production as
well. The correlations confirm the dependence of flare productivity
on the degree of nonpotentiality of active regions, as well as
proving the good potential of photospheric magnetic parameters in
flare forecasting.JJ, HS, CT and HW are supported by NSF under grant
ATM-0313591, ATM-0342560, ATM-0536921, ATM-0548952 and NASA under
grant NAG5-13661. VA is supported by NASA under grant NNG0-5GN34G.

---------------------------------------------------------
Title: The Rate of Emergence of Magnetic Dipoles in Coronal Holes
and Adjacent Quiet-Sun Regions
Authors: Abramenko, V. I.; Fisk, L. A.; Yurchyshyn, V. B.
2006ApJ...641L..65A Altcode:
Observations from the Michelson Doppler Imager and the EUV Imaging
Telescope on the Solar and Heliospheric Observatory are analyzed to
determine the rate of emergence of new magnetic flux in coronal holes
and in surrounding regions on the quiet Sun. Coronal holes are regions
where the open magnetic flux of the Sun, the component that forms the
heliospheric magnetic field, is concentrated. It is determined that
the rate of emergence of new magnetic flux is systematically lower,
by a factor of ~2, in coronal holes relative to the surrounding quiet
Sun. This result is consistent with a prediction in a recent model for
the transport of open magnetic flux on the Sun, which demonstrated
that open flux tends to accumulate and concentrate in regions where
the rate of emergence of new magnetic flux is a local minimum.

---------------------------------------------------------
Title: The statistical relationship between the photospheric magnetic
parameters and the flare productivity of active regions
Authors: Jing, J.; Song, H.; Abramenko, V.; Tan, C.; Wang, H.
2006cosp...36..107J Altcode: 2006cosp.meet..107J
Using line-of-sight Michelson Doppler Imager MDI magnetograms of
89 active regions and Solar Geophysical Data SGD flare reports we
explored for the first time the magnitude scaling correlation between
three magnetic parameters and the flare productivity of solar active
regions These parameters are 1 the average value of spatial gradients
of the magnetic field on the magnetic neutral line overline nabla B z
NL 2 the length of magnetic neutral line with strong magnetic gradient
L GNL and 3 total magnetic energy int epsilon B z dA dissipated in
a layer of 1m during 1 second over the active region s area The MDI
magnetograms of active regions used for our analysis are close to the
solar central meridian within pm 10° The flare productivity of active
regions was quantified by the soft X-ray flare index for different
time windows from the time interval of the disk passage down to 1
day from the magnetogram recording Our results explicitly indicate
a positive correlation between the parameters and the overall flare
productivity of active regions and imminent flare production as well
The correlations of three parameters with flare productivity confirm
respectively the dependence of flare productivity on 1 complexity of
magnetic field 2 the degree of nonpotentiality of active regions and 3
intensity of turbulent motions of magnetic flux tubes in the photosphere
The parameters might usefully complement each other in flare forecasting

---------------------------------------------------------
Title: The Visible--Light Magnetograph at the Big Bear Solar
Observatory: Hardware and Software
Authors: Shumko, S.; Abramenko, V.; Denker, C.; Goode, P.; Tritschler,
A.; Varsik, J.
2005ASPC..347..509S Altcode: 2005adass..14..509S
In this paper we report about the current status of the control and
acquisition software package developed to control the visible-light
imaging magnetograph (VIM) system at the Big Bear Solar Observatory
(BBSO). The instrument is designed to perform high-spatial and
high-temporal observations of the solar photosphere and chromosphere
utilizing the remodeled Coudé-feed of the 65 cm vacuum telescope.

---------------------------------------------------------
Title: Flaring capability of solar active regions versus their
magnetic power spectra: observational aspects
Authors: Abramenko, V.
2005AGUFMSH11C..01A Altcode:
Spatio-temporal dynamics of magnetic flux tubes in the photosphere
and beneath is thought to be a driving mechanism for energy built-up
and energy release phenomena in the solar atmosphere. We calculated
magnetic power spectra from high-resolution SoHO/MDI magnetograms
for 16 active regions and revealed that non-flaring active regions
possess Kolmogorov-type spectra, whereas active regions that launched
X-class flares display much steeper, non-Kolmogorov spectra. Moreover,
the non-Kolmogorov spectrum was observed since the very beginning of
the emergence of flaring active regions. The Kolmogorov-type spectra
that was found in non-flaring active regions might suggest a nearly
stationary turbulent regime when the dynamical equilibrium between
the energy input at large scales and energy output at small scales
provides premises for a smooth evolution without catastrophes. On the
other hand, the non-Kolmogorov spectra of flaring active regions imply
the inhomogeneous non-stationary turbulence regime when the dissipation
of energy might occur in a catastrophe-like manner (flares). We will
also discuss an implication of our findings to the problem of the
energy build-up in solar eruptions.

---------------------------------------------------------
Title: Evolution of the Magnetic Energy Budget in AR 10486 from
Potential and Nonlinear Force-Free Models
Authors: Régnier, S.; Fleck, B.; Abramenko, V.; Zhang, H. -Q.
2005ESASP.596E..61R Altcode: 2005ccmf.confE..61R
No abstract at ADS

---------------------------------------------------------
Title: Structure of magnetic fields in NOAA active regions 0486 and
0501 and in the associated interplanetary ejecta
Authors: Yurchyshyn, Vasyl; Hu, Qiang; Abramenko, Valentyna
2005SpWea...3.8C02Y Altcode:
Spectacular burst of solar activity in October-November 2003, when large
solar spots and intense solar flares dominated the solar surface for
many consecutive days, caused intense geomagnetic storms. In this paper
we analyze solar and interplanetary magnetic fields associated with the
storms in October-November 2003. We used space- and ground-based data in
order to compare the orientations of the magnetic fields on the solar
surface and at 1 AU as well as to estimate parameters of geomagnetic
storms during this violent period of geomagnetic activity. Our study
further supports earlier reports on the correlation between the
coronal mass ejection speed and the strength of the magnetic field in
an interplanetary ejecta. A good correspondence was also found between
directions of the helical magnetic fields in interplanetary ejecta and
in the source active regions. These findings are quite significant in
terms of their potential to predict the severity of geomagnetic activity
1-2 days in advance, immediately after an Earth directed solar eruption.

---------------------------------------------------------
Title: Relationship between Magnetic Power Spectrum and Flare
Productivity in Solar Active Regions
Authors: Abramenko, V. I.
2005ApJ...629.1141A Altcode:
Power spectra of the line-of-sight magnetograms were calculated
for 16 active regions of different flare activity. Data obtained
by the Michelson Doppler Imager instrument on board the Solar and
Heliospheric Observatory in high-resolution mode were used in this
study. For each active region, the daily soft X-ray flare index, A,
was calculated. This index characterizes the flare productivity of
an active region per day, being equal to 1 when the specific flare
productivity is one C1.0 flare per day. The power index, α, of the
magnetic power spectrum, E(k)~k-α, averaged over all
analyzed magnetograms for a given active region, was compared with
the flare index. It was found that active regions, which produced
X-class flares, possessed a steep power spectrum with α&gt;2.0,
while flare-quiet active regions with low magnitude of A displayed
a Kolmogorov-type spectrum of α~5/3. Observational data suggest
that the flare index A may be determined from the power index α
by A(α)=409.5(α-5/3)2.49. The magnitude of the power
index at the stage of emergence of an active region seems not to be
related to the current flaring level of this active region, but rather
reflects its future flare productivity, when the magnetic configuration
becomes well evolved. This finding shows the way to distinguish at
the very early stage those solar active regions that are “born bad”
and have a potential to produce significant disturbances in the Earth
magnetosphere.

---------------------------------------------------------
Title: Multi-scale analysis of solar structures: flatness functions
of magnetograms
Authors: Abramenko, V.; Romano, P.
2005AGUSMSP41B..04A Altcode:
The fine small-scale structure of the solar surface becomes more
pronounced as the observational techniques improve. Complex filigree
structures of solar granulation, sunspots, photospheric magnetic and
velocity fields can not be described adequately by a single parameter
(e.g., filling factor, fractal dimension, or power law index,
etc.). Methods which incorporate parameters that are a function of
scale (multi-scale methods) to describe the complexity of a field
under study should be involved. The multifractal approach offers
such a possibility. Multifractality can manifest itself through the
shape of a flatness function defined as a ratio of the sixth structure
function to the cube of the second structure function (Frisch 1995). For
monofractal structures, the flatness is constant with a scale, whereas
for multifractal structures the flatness grows as a power-law when the
scale decreases. Calculating the flatness functions for SOHO/ MDI high
resolution magnetograms of active regions from the catalog available
at http://www.bbso.njit.edu/~avi/MDI_catalog.htm we found that the
flatness function is unique for each active region. The power-law index,
as well as the range of the flatness growth (the scale interval of
multifractality), vary for different active regions that indicates the
difference in mutlifractality. We found that flare-quiet active regions
tend to possess lower degree of multifractality than flaring active
regions do. The increase in multifractality is a signal that a magnetic
structure is driven to a critical state, thus gaining tangential
discontinuities of various length scales. The above suggestion about
the relation between the degree of multifractality and level of flare
productivity seems to be reasonable and deserves further investigations.

---------------------------------------------------------
Title: Multifractal Analysis Of Solar Magnetograms
Authors: Abramenko, Valentyna I.
2005SoPh..228...29A Altcode:
As solar observational techniques improve, fine small-scale structures
observed on the solar surface become more pronounced. Complex filigree
structures of solar granulation, sunspots, photospheric magnetic and
velocity fields cannot be described adequately by a single parameter
(e.g., filling factor, fractal dimension, or power-law index). Methods
which incorporate parameters that are a function of scale (multiscale
methods) to describe the complexity of a field under study, should
be involved. The multifractal approach offers such a possibility. In
this paper the scaling of structure functions is proposed in order
to analyze multifractality. Application of the approach to SOHO/MDI
high-resolution magnetograms of active regions show that the structure
functions differ for all active regions studied. For a given active
region, the functions may maintain their shape during several hours;
however, they can significantly change during a day. Flare-quiet
active regions tend to possess a lower degree of multifractality than
flaring active regions do. The increase in multifractality is a signal
that a magnetic structure is driven to a critical state, thus gaining
tangential discontinuities of various length scales.

---------------------------------------------------------
Title: Spatio-temporal dynamics of magnetic fields in the photosphere
and flaring productivity of active regions
Authors: Abramenko, V.
2005AGUSMSH53B..04A Altcode:
The role of spatio-temporal dynamics of the photospheric magnetic flux
tubes in processes of energy built-up and energy release seems to be a
subject of much controversy. To provide an insight into the problem,
we propose to study the turbulence state, the multifractality and
the fragmentation process in the photospheric magnetic structures and
examine their relationship with the flare activity of different active
regions (ARs). By calculating magnetic power spectra and structure
functions of the line-of-sight magnetograms, as well as distribution
functions of the the magnetic flux in magnetic elements, we found that
parameters of these functions correlate with the flare productivity
of an AR. Namely, flare-productive ARs display non-stationary
non-homogeneous turbulent regime, high degree of multifractality and
very intensive fragmentation of magnetic elements. On the contrary,
for flare-quiet ARs we found a Kolmogorov-type homogeneous stationary
turbulent regime, nearly monofractal structure of the field and
low fragmentation rate. This study demonstrates that structural and
dynamical characteristics of the magnetic field as measured in the
photosphere are relevant to the intensity of non-stationary processes
in the entire magnetic configuration.

---------------------------------------------------------
Title: Distribution of the Magnetic Flux in Elements of the Magnetic
Field in Active Regions
Authors: Abramenko, V. I.; Longcope, D. W.
2005ApJ...619.1160A Altcode:
The unsigned magnetic flux content in the flux concentrations of two
active regions is calculated by using a set of 248 high-resolution Solar
and Heliospheric Observatory Michelson Doppler Imager magnetograms
for each active region. Data for flaring active region NOAA 9077
(2000 July 14) and nonflaring active region NOAA 0061 (2002 August 9)
were analyzed. We present an algorithm to automatically select and
quantify magnetic flux concentrations above a threshold p. Each
active region is analyzed using four different values of the
threshold p (p=25, 50, 75, and 100 G). Probability distribution
functions and cumulative distribution functions of the magnetic
flux were calculated and approximated by the lognormal, exponential,
and power-law functions in the range of flux Φ&gt;1019
Mx. The Kolmogorov-Smirnov test, applied to each of the approximations,
showed that the observed distributions are consistent with the lognormal
approximation only. Neither exponential nor power-law functions can
satisfactorily approximate the observed distributions. The parameters
of the lognormal distribution do not depend on the threshold value;
however, they are different for the two active regions. For flaring
active region 9077, the expectation value of the magnetic flux content
is μ=28.1×1018 Mx, and the standard deviation of the
lognormal distribution is σ=79.0×1018 Mx. For nonflaring
active region NOAA 0061, these values are μ=23.8×1018 and
σ=29.6×1018 Mx. The lognormal character of the observed
distribution functions suggests that the process of fragmentation
dominates over the process of concentration in the formation of the
magnetic structure in an active region.

---------------------------------------------------------
Title: Statistical Distributions of Speeds of Coronal Mass Ejections
Authors: Yurchyshyn, V.; Yashiro, S.; Abramenko, V.; Wang, H.;
Gopalswamy, N.
2005ApJ...619..599Y Altcode:
We studied the distribution of plane-of-sky speeds determined for
4315 coronal mass ejections (CMEs) detected by the Large Angle and
Spectrometric Coronagraph Experiment on board the Solar and Heliospheric
Observatory (SOHO LASCO). We found that the speed distributions
for accelerating and decelerating events are nearly identical and
to a good approximation they can be fitted with a single lognormal
distribution. This finding implies that, statistically, there is no
physical distinction between the accelerating and the decelerating
events. The lognormal distribution of the CME speeds suggests that
the same driving mechanism of a nonlinear nature is acting in both
slow and fast dynamical types of CMEs.

---------------------------------------------------------
Title: Topological changes of the photospheric magnetic field inside
active regions: A prelude to flares?
Authors: Sorriso-Valvo, Luca; Carbone, Vincenzo; Veltri, Pierluigi;
Abramenko, Valentina I.; Noullez, Alain; Politano, Hélène; Pouquet,
Annick; Yurchyshyn, Vasyl
2004P&SS...52..937S Altcode:
The detection of magnetic field variations as a signature of flaring
activity is one of the main goals in solar physics. Past efforts gave
apparently no unambiguous observations of systematic changes. In the
present study, we discuss recent results from observations that scaling
laws of turbulent current helicity inside a given flaring active region
change in response to large flares in that active region. Such changes
can be related to the evolution of current structures by a simple
geometrical argument, which has been tested using high Reynolds number
direct numerical simulations of the MHD equations. Interpretation
of the observed data within this picture indicates that the change
in scaling behavior of the current helicity seems to be associated
with a topological reorganization of the footpoint of the magnetic
field loops, namely with the dissipation of small scales structures
in turbulent media.

---------------------------------------------------------
Title: Statistical Distribution of Magnetic Flux Concentrations in
an Active Region
Authors: Abramenko, V. I.
2004AAS...204.2004A Altcode: 2004BAAS...36..686A
Probability distribution functions (PDFs) of the unsigned magnetic
flux content in flux concentrations in a mature active region NOAA
9077 were calculated by using a set of 248 high resolution SOHO/MDI
magnetograms. Two independent routines to outline magnetic flux
concentrations were elaborated. The analysis was performed with 4
different values of the threshold, p, of the magnetic flux density
(p=25, 50, 75, 100 G). We have found that: i) the best analytical
approximation of the observed PDFs in the range of low flux (1
x 1018 Mx &lt; F &lt; 150 x 1018 Mx ) is a
lognormal distribution, LN(m ,s2), with the expected value
m=(0.7-5) x 1018 Mx and the standard deviation s = (10-45)
x 1018 Mx. The peak of the lognormal distribution tends to
shift toward the lower flux as the threshold p decreases. This tendency
suggests that the real expected value may be even smaller than 0.7
x 1018 Mx; ii) for the flux F &gt; 150 x 1018
Mx the observed PDFs fall off slower than the lognormal approximation
predicts. In this flux range, the power law is found to be the best
analytical approximation with the power law index approximately equal
to 2. The transition region between the lognormality and the power law
shifts toward the lower flux as the threshold p is lowered. This implies
that the functional form of the distribution changes continuously with
the scale. The above findings are consistent with the concept of highly
intermittent (or multifractal) nature of photospheric magnetic fields
and offer a new tool to study their multifractality. SOHO is a
project of international cooperation between ESA and NASA. This work
was supported by NSF-ATM 0076602, 9903515 and NASA NAG5-12782 grants.

---------------------------------------------------------
Title: Magnetic Field, Hα, and RHESSI Observations of the 2002 July
23 Gamma-Ray Flare
Authors: Yurchyshyn, Vasyl; Wang, Haimin; Abramenko, Valentyna;
Spirock, Thomas J.; Krucker, Säm
2004ApJ...605..546Y Altcode:
In this paper we examine two aspects of the 2002 July 23 gamma-ray flare
by using multiwavelength observations. First, the data suggest that the
interaction of the erupted field with an overlying large-scale coronal
field can explain the offset between the gamma-ray and the hard X-ray
sources observed in this event. Second, we pay attention to rapid and
permanent changes in the photospheric magnetic field associated with
the flare. MDI and BBSO magnetograms show that the following magnetic
flux had rapidly decreased by 1×1020 Mx immediately after
the flare, while the leading polarity was gradually increasing for
several hours after the flare. Our study also suggests that the changes
were most probably associated with the emergence of new flux and the
reorientation of the magnetic field lines. We interpret the magnetograph
and spectral data for this event in terms of the tether-cutting model.

---------------------------------------------------------
Title: Evidence of Rapid Flux Emergence Associated with the M8.7
Flare on 2002 July 26
Authors: Wang, Haimin; Qiu, Jiong; Jing, Ju; Spirock, Thomas J.;
Yurchyshyn, Vasyl; Abramenko, Valentina; Ji, Haisheng; Goode,
Phillip R.
2004ApJ...605..931W Altcode:
In this paper, we present a detailed study of the M8.7 flare
that occurred on 2002 July 26 using data from the Big Bear Solar
Observatory (BBSO), Ramaty High Energy Solar Spectroscopic Imager
(RHESSI), the Transition Region and Coronal Explorer (TRACE), and the
Solar and Heliospheric Observatory (SOHO). This flare has interesting
properties similar to a number of flares that we studied previously,
such as a rapid increase of magnetic flux in one polarity and an
increase in transverse fields and magnetic shear associated with the
flare. However, this event had the most comprehensive observations; in
particular, the high-resolution high-cadence BBSO vector magnetograph
observations. At the time of the flare, across the flare neutral
line, there was a sudden emergence of magnetic flux at the rate
of 1020 Mx hr-1 in both the longitudinal and
transverse components. The emerging flux mostly occurred at the sites
of the flare. It was very inclined and led to impulsively enhanced
shear in the magnetic fields. We discuss these observations in the
context of magnetic reconnection triggered by rapid flux emergence. It
is also possible that the new flux signifies flare-related change in
the field line inclination.

---------------------------------------------------------
Title: Flare-related changes in the profiles of six photospheric
spectral lines
Authors: Abramenko, Valentina I.; Baranovsky, Edward A.
2004SoPh..220...81A Altcode:
The profiles of six photospheric absorption spectral lines (Fe i
5250 Å, Fe i 5324 Å, Fe i 5576 Å, Ca i 5590 Å, Ca i 6103 Å and
Fe i 6165 Å), measured in the kernel of a 2N solar flare and in a
quiet-Sun area, were compared. The observations were carried out with
an echelle spectrograph of the Crimean Astrophysical Observatory. It
was shown that, compared to the quiet-Sun profiles, the flare
profiles are shallower in the line core and are less steep in the
wings. Therefore, measurements of the longitudinal magnetic field made
with a magnetograph system which uses the Ca i 6103 Å spectral line,
can be underestimated by 18-25% in areas of bright Hα ribbons of a
moderate solar flare. Modeling of the solar photosphere performed by
using a synthesis method showed that, in a solar flare, the enhanced
core emission seems to be related to heating of the photosphere by the
flare, whereas the decrease of the slope of the wings was presumably
caused by the inhomogeneity of the photospheric magnetic field.

---------------------------------------------------------
Title: Correlation between speeds of coronal mass ejections and the
intensity of geomagnetic storms
Authors: Yurchyshyn, Vasyl; Wang, Haimin; Abramenko, Valentyna
2004SpWea...2.2001Y Altcode:
We studied the relationship between the projected speed of coronal
mass ejections (CMEs), determined from a sequence of Solar and
Heliospheric Observatory/Large Angle and Spectrometric Coronagraph
Experiment (SOHO/LASCO) images, and the hourly averaged magnitude of
the Bz component of the magnetic field in an interplanetary
ejecta, as measured by the Advanced Composition Explorer (ACE)
magnetometer in the Geocentric Solar Magnetospheric Coordinate System
(GSM). For CMEs that originate at the central part of the solar
disk we found that the intensity of Bz is correlated with
the projected speed of the CME, Vp. The relationship is
more pronounced for very fast ejecta (Vp &gt; 1200 km/s),
while slower events display larger scatter. We also present data which
support earlier conclusions about the correlation of Bz
and the Dst index of geomagnetic activity. A possible application of
the results to space weather forecasting is discussed.

---------------------------------------------------------
Title: Multifractality of Solar Magnetic Fields
Authors: Abramenko, V.
2003AGUFMSH22A0173A Altcode:
Eruptive phenomena in the solar atmosphere are thought to be caused
by reconnection processes in complex magnetic structures. Therefore,
the complexity of the magnetic field is closely related to the eruption
activity. We propose to determine the measure of the magnetic complexity
in terms of multifractality (intermittency) of a given magnetic
structure. Our choice of a mathematical approach was stimulated by
the fact that a multifractal, in time and in space domains, structure
displays a burst-like (catastrophic) behavior which is consistent
with catastrophe-like eruptions in the solar atmosphere. We propose
a new multifractal method for quantitative estimation of the degree
of complexity of solar magnetic fields. We discuss results of the
application of the method to SOHO/MDI and ground-based measurements
of solar magnetic fields.

---------------------------------------------------------
Title: Signature of an Avalanche in Solar Flares as Measured by
Photospheric Magnetic Fields
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
2003ApJ...597.1135A Altcode:
We analyzed time variations of turbulent parameters of the photospheric
magnetic field of four active regions obtained during the course of
major solar flares using longitudinal magnetograms from the Big Bear
Solar Observatory and from SOHO/MDI full-disk measurements. Analysis of
the data indicated that, before each flare, the degree of intermittency
of the magnetic field had been increasing for 6-33 minutes and reached
a maximum value approximately 3-14 minutes before the peak of the
hard X-ray emission for each event. This result seems to suggest the
existence in an active region of a turbulent phase prior to a solar
flare. We also found that the maximum of the correlation length of
the magnetic energy dissipation field tends to follow (or to occur
nearly simultaneously) with the peak of the hard X-ray emission. The
data suggest that the peak in the correlation length might be a trace
of an avalanche of coronal reconnection events. We discuss the results
in the framework of the concept of self-organized criticality.

---------------------------------------------------------
Title: Cancellations and structures in the solar photosphere:
signature of flares
Authors: Sorriso-Valvo, L.; Abramenko, V.; Carbone, V.; Noullez, A.;
Politano, H.; Pouquet, A.; Veltri, P.; Yurchyshyn, V.
2003AIPC..679..695S Altcode:
The topological properties of the typical current structures in
a turbulent magnetohydrodynamic flow can be measured using the
cancellations analysis. In two-dimensional numerical simulations, this
reveals current filaments being the most typical current structures. The
observations of the topology of photospheric current structures within
active regions shows that modifications occur correspondingly with
strong flares.

---------------------------------------------------------
Title: Signature of Avalanche in Solar Flares as Measured by
Photospheric Magnetic Fields
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
2003SPD....34.1507A Altcode: 2003BAAS...35..831A
Turbulent/fractal parameters of the longitudinal magnetic field,
Bz, for four powerful solar flares were analyzed utilizing
the correlation length, l, of the magnetic energy dissipation
field and the scaling exponent, b, which characterizes the measure
of intermittency of the Bz structure. We select a set of
four two-ribbon flares, which were followed by coronal mass ejections,
for the study of magnetic structure. During the course of each flare,
we found a peak in b which was followed by a peak in l in all of the
cases studied in this paper. These two peaks were separated by the time
interval tl during which a rapid growth of the soft X-ray
and Hα flux occurred. The peak in b was preceded by a time period
tb during which b increased gradually. For all of the flares
tb was longer than the time interval tl. The
maximum of l occurred nearly simultaneously, within an accuracy of
about 2-5 minutes, with the maximum of the hard X-ray emission. For
the four flares considered in this paper, we concluded that the more
impulsive and/or more powerful a flare is, the shorter the b growth
time, tb, and the l growth time, tl, are. In
the framework of the theory of non-linear dissipative processes,
these results may be interpreted as follows. Before a solar flare
occurs there is a significant increase in the number of magnetic field
discontinuities (b increasing), which is followed by an avalanche
(increase of the correlation length) of magnetic energy dissipation
events. The avalanche event occupies the entire active region from the
corona to the photosphere. Our study indicates that the more abrupt
is the avalanche, the stronger and/or more impulsive a flare is. The
time profiles of an avalanche is either Gaussian, which satisfies
the logistic avalanche model, or exponential with an abrupt drop,
which satisfies the exponential avalanche model. The driving time,
tb, was longer than the avalanching time, tl,
for all of the events. This qualitatively agrees with the requirements
of the self-organized criticality theory. This work was supported
by NSF-ATM 0076602, 0205157, 9903515 and NASA NAG5-12782 grants.

---------------------------------------------------------
Title: Rapid Changes in the Longitudinal Magnetic Field Associated
with the July 23, 2002 γ -ray Flare
Authors: Yurchyshyn, V. B.; Wang, H.; Abramenko, V. I.; Spirock,
T. J.; Krucker, S.
2003SPD....34.1508Y Altcode: 2003BAAS...35Q.832Y
In this paper we analyze and discuss rapid changes of the magnetic field
associated with the July 23, 2002 γ -ray flare. MDI magnetic flux
profiles and BBSO vector magnetograms showed that immediately after
the flare the leading polarity had increased by 2*E20Mx,
while the following polarity decreased only by 1*E20Mx. The
observed changes were permanent and not caused by variations in seeing
or changes in the line profile, which we used to measure the magnetic
field. In this active region we distinguish two separate locations,
which show the most dramatic changes in the magnetic field. The
first location showed an increase in the magnetic field strength
and a new penumbra area and it was associated with emergence of new
magnetic flux. At the second location the position of the neutral
line had changed and it coincided with the footpoints of a rapidly
growing post-flare loop system. Linear force-free field simulations
showed that the re-orientation of the magnetic field during the flare
was capable of producing the observed changes in the total magnetic
flux. We also discuss a possible magnetic configuration responsible
for the flare. This work was supported in part by NSF ATM-0086999 and
ATM-0205157 and under NASA NAG5-10910 NAG5-12782 grants.

---------------------------------------------------------
Title: Pre-Flare Changes in the Turbulence Regime for the Photospheric
Magnetic Field in a Solar Active Region
Authors: Abramenko, V. I.
2003ARep...47..151A Altcode:
Observations of the total magnetic field in the active region NOAA
6757 have been used to study the turbulence regime from 2.5 h before
the onset of a 2B/X1.5 flare until two minutes after its maximum. The
curvature of the exponent ζ(q) for the structure functions of the B z
field increases monotonically before the flare (i.e., the multifractal
character of the B z field becomes more complex) but straightens at
the flare maximum and coincides with a linear Kolmogorov dependence
(implying a monofractal structure for the B z field). The observed
deviations of ζ(q) from a Kolmogorov line can be used for short-term
forecasting of strong flares. Analysis of the power spectra of the
B z field and the dissipation of magnetic-energy fluctuations shows
that the beginning of the flare is associated with the onset of a
new turbulence regime, which is closer to a classical Kolmogorov
regime. The scaling parameter (cancellation index) of the current
helicity of the magnetic field, k h , remains at a high level right
up until the last recording of the field just before the flare but
decreases considerably at the flare maximum. The variations detected in
the statistical characteristics of the turbulence can be explained by
the formation and amplification of small-scale flux tubes with strong
fields before the flare. The dissipation of magnetic energy before the
flare is primarily due to reconnection at tangential discontinuities
of the field, while the dissipation after the flare maximum is due
to the anomalous plasma resistance. Thus, the flare represents an
avalanche dissipation of tangential discontinuities.

---------------------------------------------------------
Title: How directions and helicity of erupted solar magnetic fields
define geoeffectiveness of coronal mass ejections
Authors: Yurchyshyn, Vasyl; Wang, Haimin; Abramenko, Valentyna
2003AdSpR..32.1965Y Altcode:
In this study we report on the relationship between the projected speed
of CMEs, measured at 20R from SOHO/LASCO images, and the hourly averaged
magnitude of the southwardly directed magnetic field, B z,
at the leading edge of interplanetary ejecta, as measured by the ACE
magnetometer. We found that those CMEs that originate at the central
part of the solar disk ( r &lt; 0.6 R⊙) are the most
geoeffective and the intensity of B z is an exponential
function of the CME's speeds. We propose an approach to estimate the
strength of the southward IMF at least one day in advance, immediately
after a CME started. The predicted value of the B z
component can be then used to estimate the intensity of a geomagnetic
storm caused by the eruption. The prediction method is based on the
correlation between the speeds of CMEs and magnitudes of the southward
IMF as well as the fact that the orientation and chirality of the
erupted solar filaments correspond to the orientation and chirality
of interplanetary ejecta.

---------------------------------------------------------
Title: Cancellations analysis of photospheric magnetic structures
and flares
Authors: Sorriso-Valvo, L.; Abramenko, V.; Carbone, V.; Noullez, A.;
Politano, H.; Pouquet, A.; Veltri, P.; Yurchyshyn, V.
2003MmSAI..74..631S Altcode:
The topological properties of the typical current structures in
a turbulent magnetohydrodynamic flow can be measured using the
cancellations analysis. In two-dimensional numerical simulations, this
reveals current filaments being the most typical current structures. The
observations of the topology of photospheric current structures within
active regions shows that modifications occur correspondingly with
strong flares.

---------------------------------------------------------
Title: Pre-flare changes in current helicity and turbulent regime
of the photospheric magnetic field
Authors: Abramenko, V.
2003AdSpR..32.1937A Altcode:
Measurements of the vector magnetic field in an active region NOAA
6757 were used to compare current helicity and turbulent regime of
the magnetic field 2.5 - 0.5 hours prior and 2 minutes after the
maximum of a strong 2B/X1.5 solar flare. First, we calculated the
imbalance, ϱh, of current helicity over the area of
the flare. During a forty minute time interval, which includes the
impulsive phase of the flare, total positive (negative) helicity
decreased by 20% (27%), while the imbalance ϱh changed
from -5% to +1%. This implies that before the flare the necessary
conditions for the α-effect in the solar photosphere were fulfilled,
whereas after the flare maximum the generation of the electromotive
force due to small-scale fluctuations of the magnetic field seems to be
exhausted. Second, we calculated a cancellation exponent, kh,
of current helicity and an exponent, Σ(q), of structure functions
of the longitudinal magnetic field. The curvature of Σ(q) indicates
multifractality (intermittent turbulence) of the magnetic field,
while kh describes the intensity of oscillations of the
sign of current helicity and, therefore, the strength of tangential
discontinuities in the magnetic field. We found that the value of
kh was large until the last field measurement before the
flare. After the flare maximum, the cancellation exponent was found
to be significantly smaller. Meanwhile, observed behavior of Σ(q)
implies that multifractality of the Bz component became
more complicated before the flare, whereas, immediately after the
flare maximum monofractality (non-intermittent turbulence) of the
Bz component was set. Such changes in both kh and
Σ(q) complement each other as evidence that a flare can be treated as
an avalanche of small-scale reconnections at tangential discontinuities
of the magnetic field.

---------------------------------------------------------
Title: Scaling Behavior of Structure Functions of the Longitudinal
Magnetic Field in Active Regions on the Sun
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
2002ApJ...577..487A Altcode:
In the framework of a refined Kolmogorov hypothesis, the scaling
behavior of the Bz-component of the photospheric
magnetic field is analyzed and compared with flaring activity in
solar active regions. We use Solar and Heliospheric Observatory
Michelson Doppler Imager, Huairou (China), and Big Bear measurements
of the Bz-component in the photosphere for nine active
regions. We show that there is no universal behavior in the scaling
of the Bz-structure functions for different active
regions. Our previous study has shown that scaling for a given active
region is caused by intermittency in the field, ɛ(B)(x),
describing the magnetic energy dissipation. When intermittency is
weak, the Bz field behaves as a passive scalar in the
turbulent flow, and the energy dissipation is largely determined by
the dissipation of kinetic energy in the active regions with low flare
productivity. However, when the field ɛ(B)(x) is highly
intermittent, the structure functions behave as transverse structure
functions of a fully developed turbulent vector field, and the scaling
of the energy dissipation is mostly determined by the dissipation of the
magnetic energy (active regions with strong flaring productivity). Based
on this recent result, we find that the dissipation spectrum of the
Bz-component is strongly related to the level of flare
productivity in a solar active region. When the flare productivity is
high, the corresponding spectrum is less steep. We also find that during
the evolution of NOAA Active Region 9393, the Bz dissipation
spectrum becomes less steep as the active region's flare activity
increases. Our results suggest that the reorganization of the magnetic
field at small scales is also relevant to flaring: the relative fraction
of small-scale fluctuations of magnetic energy dissipation increases
as an active region becomes prone to producing strong flares. Since
these small-scale changes seem to begin long before the start of a
solar flare, we suggest that the relation between scaling exponents,
calculated by using only measurements of the Bz-component,
and flare productivity of an active region can be used to monitor and
forecast flare activity.

---------------------------------------------------------
Title: Topological changes of the photospheric magnetic field inside
active regions: a prelude to flares
Authors: Sorriso-Valvo, L.; Carbone, V.; Abramenko, V.; Yurchyshyn,
V.; Noullez, A.; Politano, H.; Pouquet, A.; Veltri, P.
2002astro.ph..7244S Altcode:
The observations of magnetic field variations as a signature of flaring
activity is one of the main goal in solar physics. Some efforts in
the past give apparently no unambiguous observations of changes. We
observed that the scaling laws of the current helicity inside a given
flaring active region change clearly and abruptly in correspondence with
the eruption of big flares at the top of that active region. Comparison
with numerical simulations of MHD equations, indicates that the change
of scaling behavior in the current helicity, seems to be associated to a
topological reorganization of the footpoint of the magnetic field loop,
namely to dissipation of small scales structures in turbulence. It is
evident that the possibility of forecasting in real time high energy
flares, even if partially, has a wide practical interest to prevent
the effects of big flares on Earth and its environment.

---------------------------------------------------------
Title: Limb Prominence Eruption on 11 August 2000 as Seen From Ground-
and Space-Based Observations
Authors: Shakhovskaya, A. N.; Abramenko, V. I.; Yurchyshyn, V. B.
2002SoPh..207..369S Altcode:
We report on a prominence eruption as seen in Hα with the Crimean
Lyot coronagraph, the global Hα network, and coronal images from
the LASCO C2 instrument on board SOHO. We observed an Hα eruption
at the northwest solar limb between 07:38:50 UT and 07:58:29 UT on
11 August 2000. The eruption originated in a quiet-Sun region and
was not associated with an Hα filament. No flare was associated with
the eruption, which may indicate that, in this case, a flux rope was
formed prior to the eruption of the magnetic field. The Hα images
and an Hα Dopplergram show a helical structure present in the erupted
magnetic field. We suggest that the driving mechanism of the eruption
may be magnetic flux emergence or magnetic flux injection. The limb
Hα observations provide missing data on CME speed and acceleration
in the lower corona. Our data show that the prominence accelerated
impulsively at 5.5 km s−2 and reached a speed slightly
greater than 800 km s−1 in a narrow region (h&lt;0.14
R⊙) above the solar surface. The observations presented
here also imply that, based only on a CME's speed and acceleration,
it cannot be determined whether a CME is the result of a flare or an
eruptive prominence.

---------------------------------------------------------
Title: Scaling Behavior of Structure Functions of the Longitudinal
Magnetic Field in Active Regions on the Sun
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Spirock,
T. J.; Goode, P. R.
2002AAS...200.0309A Altcode: 2002BAAS...34..643A
In the framework of a refined Kolmogorov's hypotheses, the scaling
behavior of the BZ--component of the photospheric magnetic
field is analyzed and compared with flaring activity in solar active
regions. We used SOHO/MDI, Huairou (China) and Big Bear measurements
of the Bz-component in the photosphere for nine active
regions. We show that there is no universal behavior in the scaling
of the Bz-structure functions for different active
regions. Scaling for a given active region is caused by intermittency
in the field, ǎrepsilon(B)(ěc x), of magnetic energy
dissipation. When intermittency is weak, the Bz-field
behaves as a passive scalar in the turbulent flow and the energy
dissipation is largely determined by the dissipation of kinetic energy
in active regions with low flare productivity. However, when the field
ǎrepsilon(B)(ěc x) is highly intermittent, the structure
functions behave as transverse structure functions of a fully developed
turbulent vector field and the scaling of the energy dissipation is
mostly determined by the dissipation of the magnetic energy (active
regions with strong flaring productivity). We found that the spectrum
of dissipation of the Bz component is strongly related
to the level of flare productivity of a solar active region. When
the flare productivity is high, the corresponding spectrum is less
steep. We also found that during the evolution of an NOAA AR 9393 the
Bz dissipation spectrum becomes less steep as the active
region's flare activity increases. We suggest that the relation between
scaling exponents and flare productivity of an active region enables
us to monitor and forecast flare activity using only measurements of
the Bz component of the photospheric magnetic field. This
work was supported in part by the Ukrainian Ministry of Science and
Education, NSF-ATM (0076602 and 0086999) and NASA (9682 and 9738)
grants. SOHO is a project of international cooperation between ESA
and NASA.

---------------------------------------------------------
Title: Solar MHD Turbulence in Regions with Various Levels of Flare
Activity
Authors: Abramenko, V. I.
2002ARep...46..161A Altcode:
The paper continues investigations of MHD turbulence in active solar
regions. The statistical distributions of the increments (structure
functions) of the turbulent field are studied analytically in the
context of a refined Kolmogorov theory of turbulence. Since photospheric
transport of the B z component of the magnetic field is quite similar
to that of a scalar field in a turbulent flow, the theory of transport
of a passive scalar can be applied. This approach enables us to show
that the structure functions are determined by the competition between
the dissipation of the magnetic and kinetic energies and to obtain
a number of relations between the structure-function parameters and
energy characteristics of the MHD turbulence. Taking into account
general conclusions that can be drawn on the basis of the refined
Kolmogorov turbulence theory, the structure functions of the B z field
are calculated for eight active regions (from measurements of SOHO/MDI
and the Huairou Solar Observing Station, China). These calculations
show that the behavior of the structure functions is different for the
B z field of each active region. The energy-dissipation index of the
fluctuation spectrum (which is uniquely determined by the structure
functions) is closely related to the level of flare activity: the more
activity, the less steep the dissipation spectrum for a given active
region. This provides a means to test and, consequently, forecast the
flare activity of active regions.

---------------------------------------------------------
Title: Cancellation Analysis and Structures: A Prelude To Flares
Authors: Sorriso-Valvo, L.; Abramenko, V.; Yurcyshyn, V.; Carbone,
V.; Noullez, A.; Politano, H.; Pouquet, A.; Veltri, P.
2002EGSGA..27..600S Altcode:
The observations of magnetic field variations as a signature of flaring
activity is one of the main goal in solar physics. Some efforts in
the past give apparently no unambigu- ous observations of changes. We
observed that the scaling laws of the current helicity inside a given
flaring active region change clearly and abruptly before the eruption
of big flares at the top of that active region. Comparison with
numerical simulations of MHD equations, indicates that the change of
scaling behavior in the current helicity, seems to be associated to a
topological reorganization of the footpoint of the magnetic field loop,
namely to dissipation of small scales structures in turbulence. It is
evident that the possibility of forecasting in real time high energy
flares, even if partially, has a wide practical interest to prevent
the effects of big flares on Earth and its environment.

---------------------------------------------------------
Title: JOSO national report 2000-2001 - Ukraine
Authors: Abramenko, V. I.
2002joso.book..122A Altcode:
The launching of the international space station CORONAS-F took place
in 2001 and the first observational data from CORONAS-F began coming.

---------------------------------------------------------
Title: Pre-flare changes in current helicity and turbulent regime
ofthe photospheric magnetic field
Authors: Abramenko, V.
2002cosp...34E1514A Altcode: 2002cosp.meetE1514A
Measurements of the vector magnetic field in an active region NOAA 6757
were used here to study changes in current helicity and turbulent state
of the magnetic field prior to a strong 2B/X1.5 solar flare. The time
interval considered here begins 2 hours before the flare onset and
ends 2 minutes after the flare maximum. First, using vector magnetic
field data we calculated cancellation exponent kh , which describes
intermittency in current helicity of the magnetic field. We found that
the value of the kh was high and almost constant until the last field
measurements just before the flare. After the flare maximum, the kh
was found to be significantly reduced. According to Parker's concept,
an avalanche of nanoflares could reduce the strength of tangential
discontinuities in the magnetic field. As a result, current helicity
became less intermittent and, therefore, the calcellation exponent
kh had decreased. Second, we calculated a structure function of the
Bz component and ploted its exponent(q ). We found that the(q ) is
a concave outward function, whose curvature gradually increases as
the active region evolves toward the flare. Such behaviour of the(q )
implies that the multifractality of the Bz component of the magnetic
field becomes more complicated. Just after the flare maximum the plot
of the(q ) nearly coincides with the classical Kolmogorov's straight
line that seems to be a manifestation of monofractality of the Bz
-component. Power spectra, calculated for both the Bz measurements and
magnetic energy dissipation fields, have shown that at the begining
of the flare the turbulent state in the magnetic field changes and it
becomes very close to the classical Kolmogorov's turbulence. Finally,
we would like to note that the preflare variations of the kh and
of the curvature of the(q ) can be used for the short-time flare
forecast. However, more studies are needed to establish a reliable
forecasting procedure.

---------------------------------------------------------
Title: Analysis of Cancellations of Photospheric Current Helicity
and Flares Forecasting
Authors: Sorriso-Valvo, L.; Abramenko, V.; Carbone, V.; Noullez, A.;
Politano, H.; Pouquet, A.; Veltri, P.; Yurchyshyn, V.
2002EGSGA..27.3215S Altcode:
The observations of magnetic field variations as a signature of flaring
activity is one of the main goal in solar physics. Some efforts in
the past give apparently no unambigu- ous observations of changes. We
observed that the scaling laws of the current helicity inside a given
flaring active region change clearly and abruptly before the eruption
of big flares at the top of that active region. Comparison with
numerical simulations of MHD equations, indicates that the change of
scaling behavior in the current helicity, seems to be associated to a
topological reorganization of the footpoint of the magnetic field loop,
namely to dissipation of small scales structures in turbulence. It is
evident that the possibility of forecasting in real time high energy
flares, even if partially, has a wide practical interest to prevent
the effects of big flares on Earth and its environment.

---------------------------------------------------------
Title: Parameters of the Turbulent Magnetic Field in the Solar
Photosphere: Power Spectrum of the Line-of-Sight Field
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Wang, H.; Goode, P. R.
2001ARep...45..824A Altcode:
Ground-based (Big Bear Solar Observatory) and extra-atmospheric
(SOHO/MDI) measurements of the photospheric line-of-sight magnetic field
of one active and two quiet regions are used to calculate power spectra
of the field, taking into account the characteristic function for the
diffraction limit of the telescope resolution. At high frequencies, the
physically meaningful linear interval in the spectrum extends to a wave
number of k=4.6 Mm-1 (spatial scale l=1.4 Mm) for the quiet regions and
k=3.35 Mm-1 (l=1.9 Mm) for the active region. A high-frequency spectral
break at k≥3 Mm-1 is associated with the characteristic telescope
function; the position of the break and the spectral slope beyond the
break do not reflect the turbulent state of the field. As the field
recording improves, the break shifts toward higher frequencies. The
spectral indices in the physically meaningful linear interval are
substantially different for the active and quiet regions: in the active
region (NOAA 8375), the spectrum behaves as E(k)≈k -1.7 (very close
to the Kolmogorov index, -5/3) in the interval 0.78≤k≤3.35 Mm-1,
while in the quiet regions E(k)≈k -1.3 for 0.77≤k≤4.57 Mm-1. This
difference can be explained by the additional effect of a small-scale
turbulent dynamo in the unperturbed photosphere. In this case, this
mechanism can generate at least 6% of the magnetic energy of the
photospheric line-of-sight field in quiet regions.

---------------------------------------------------------
Title: Magnetic Power Spectra Derived from Ground and Space
Measurements of the Solar Magnetic Fields
Authors: Abramenko, V.; Yurchyshyn, V.; Wang, H.; Goode, P. R.
2001SoPh..201..225A Altcode:
We study magnetic power spectra of active and quiet regions by using
Big Bear Solar Observatory and SOHO/MDI measurements of longitudinal
magnetic fields. The MDI power spectra were corrected with Gaussian
Modulation Transfer Function. We obtained reliable magnetic power
spectra in the high wave numbers range, up to k=4.6 Mm−1,
which corresponds to a spatial scale l=1.4 Mm. We find that the
occurrence of the spectral discontinuity at high wave numbers,
k≥3 Mm−1, largely depends on the spatial resolution
of the data and it appears at progressively higher wave numbers as
the resolution of the data improves. The spectral discontinuity in
the raw spectra is located at wave numbers about 3 times smaller
than wave numbers, corresponding to the resolution of the data, and
about 1.5-2.0 times smaller in the case of the noise- and-resolution
corrected spectra. The magnetic power spectra for active and quiet
regions are different: active-region power spectra are described as
∼k−1.7, while in a quiet region the spectrum behaves
as ∼k−1.3. We suggest that the difference can be
due to small-scale dynamo action in the quiet-Sun photosphere. Our
estimations show that the dynamo can generate more than 6% of the
observed magnetic power.

---------------------------------------------------------
Title: Magnetic Power Spectra Derived From Photospheric Magnetic
Fields
Authors: Abramenko, V. I.; Yurchyshyn, V.; Wang, H.; Goode, P. R.
2001AGUSM..SP41C04A Altcode:
We study magnetic power spectra of active and quiet regions by using
Big Bear Solar Observatory and SOHO/MDI measurements of longitudinal
magnetic fields. The MDI power spectra were corrected with Gaussian
Modulation Transfer Function. We obtained reliable magnetic power
spectra in the high wave numbers range, up to k=4.6 Mm-1,
which corresponds to a spatial scale l=1.4 Mm. We find that the
occurrence of the spectral discontinuity at high wavenumbers, k &gt;=
3 Mm-1, largely depends on the spatial resolution of the data
and it appears at progressively higher wave numbers as the resolution
of the data improves. The spectral discontinuity in the raw spectra
is located at wave numbers about 3 times smaller than wavenumbers,
corresponding to the resolution of the data, and about 1.5 -- 2.0 times
smaller in the case of the noise-and-resolution corrected spectra. The
magnetic power spectra for active and quiet regions are different:
active region power spectra are described as ~ k-1.7,
while in a quiet region the spectrum behaves as ~ k-1.3. We
suggest, that the difference can be due to small-scale dynamo action
in the quiet sun photosphere. Our estimations show that the dynamo
can generate more than 6% of the observed magnetic power.

---------------------------------------------------------
Title: Magnetic Topology in 1998 November 5 Two-Ribbon Flare as
Inferred from Ground-based Observations and Linear Force-free Field
Modeling
Authors: Yurchyshyn, V. B.; Wang, H.; Qiu, J.; Goode, P. R.; Abramenko,
V. I.
2000ApJ...540.1143Y Altcode:
We analyzed the three-dimensional structure of the linear force-free
magnetic field. A longitudinal magnetogram of Active Region NOAA
8375 has been used as the photospheric boundary condition. The 1998
November 5 2B/M8.4 two-ribbon flare can be explained in the framework
of quadrupolar reconnection theory: the interaction of two closed
magnetic loops that have a small spatial angle. The energy derived from
soft X-ray telescope (SXT)/Yohkoh data (3-6×1030 ergs)
is 1 order of magnitude higher than the lower limit of flare energy
predicted by Melrose's model. The latter estimation was made using
the linear force-free extrapolation. It was suggested that, taking
into account the nonlinear character of the observed magnetic field,
we can increase the lower limit of the magnetic energy stored in the
studied magnetic configuration. The revealed magnetic configuration
allows us to understand the observed location and evolution of the flare
ribbons and the additional energy released during the gradual phase
of the flare, as well. Besides, reconnection of closed magnetic loops
can logically explain the connection between a two-ribbon flare and a
giant X-ray postflare arch, which usually is observed after the flare
onset. We emphasize that unlike the Kopp and Pneuman configuration,
the model discussed here does not necessarily require destabilization
and opening of the magnetic field.

---------------------------------------------------------
Title: Flare-Related Changes of an Active Region Magnetic Field
Authors: Yurchyshyn, V. B.; Abramenko, V. I.; Carbone, V.
2000ApJ...538..968Y Altcode:
It was shown recently that current helicity, calculated
using the photospheric magnetic field vector measurements,
possesses a well-pronounced scaling behavior. The sign
singularity of two-dimensional structures of current helicity,
hc=Bz˙(∇XB)z, can be studied by
introducing a signed measure and by calculating the power-law exponent,
the cancellation exponent κ. The time variations of the cancellation
exponent seem to be related to flare activity of an active region
(AR). Periods of enhanced flaring are accompanied by a drop and
subsequent rise of the cancellation exponent. Here we focus on the
changes in the vortex structure of the photospheric magnetic field
during the transition of an active region from low flaring to enhanced
flaring state. We analyzed variations of the cancellation exponent,
helicity imbalance, and total electric current in four flaring active
regions and one quiet one. We show that the transition of an active
region from a low flaring state to an enhanced one is always accompanied
(in this study, the corresponding time interval is less than 2 hr)
by the 30%-45% decrease of the cancellation exponent. In two active
regions, a reliable 13%-22% decrease of the total electric current took
place, and in three active regions the helicity imbalance changed. This,
possibly, implies a reinforcement of the anticoriolis twist of the whole
magnetic configuration. For comparison, the decrease of κ in the quiet
active region does not exceed 10%. This can be interpreted as a real
preflare reorganization of the vortex structure of the photospheric
magnetic field: a combination of the exhausting of small-scale eddies
along with the reinforcement of the total anticoriolis twist of the
magnetic structure.

---------------------------------------------------------
Title: Evolution of magnetic field twist in an emerging flux region
Authors: Wang, Tongjiang; Abramenko, V. I.
2000A&A...357.1056W Altcode:
The observations of vector magnetic field for the emerging active region
NOAA 7321 are analyzed. The measurements were performed with SMFT of
Huairou Solar Observing Station. The aim is to study the variations
of the total flux, total electric current and alpha parameter (as a
measure of the field twist) throughout the flux emergence. We show that:
(1) the total positive (negative) electric current grew simultaneously
and linearly with the increase of the total positive (negative) flux;
(2) the linear extrapolation to the zero flux gives non-vanishing
total current which can be regarded as an indirect support for the
idea of pre-existing twist of the emerging flux tube; (3) the change
in alpha parameter during three days of the observation was rather
small. This fact suggests that alpha remains the same throughout the
flux emergence, and may further explain the good agreement between
Longcope et al.'s (\cite{Longcope1998}) simulation of deep thin flux
tubes and observations.

---------------------------------------------------------
Title: Magnetic Topology in November 5, 1998 Two-Ribbon Flare as
Inferred from Ground-Based Observations and Linear Force-Free Field
Modeling
Authors: Yurchyshyn, V. B.; Wang, H.; Qiu, J.; Goode, P. R.; Abramenko,
V. I.
2000SPD....31.0153Y Altcode: 2000BAAS...32..810Y
We analyzed the 3D structure of the linear force-free magnetic field in
an active region. A longitudinal magnetogram of AR NOAA 8375 has been
used as the photospheric boundary condition. The Nov 5, 1998 2B/M8.4
two-ribbon flare can be explained in the framework of quadrupolar
reconnection theory: the interaction of two closed magnetic loops which
have a small spatial angle. The energy derived from SXT/YOHKOH data (3
- 6 x 1030 ergs) is one order of magnitude higher than the
lower limit of flare energy predicted by Melrose's model. The latter
estimation was made using the linear force-free extrapolation. It is
suggested that by taking into account the non-linear character of the
observed magnetic field we can increase the lower limit of the magnetic
energy stored in the studied magnetic configuration. The revealed
magnetic configuration allows us to understand the observed location
and evolution of the flare ribbons and the additional energy released
during the gradual phase of the flare, as well. Also, the reconnection
of closed magnetic loops can logically explain the connection between
a two-ribbon flare and the giant X-ray post-flare arch which usually
is observed after flare onset. We emphasize that unlike the Kopp and
Pneuman configuration, the model discussed here doesn't necessarily
need destabilization and opening of the magnetic field. This work was
supported in part by NSF-ATM (97-14796) and NASA (NAG5-4919) grants.

---------------------------------------------------------
Title: Magnetic Power Spectra in the Solar Photosphere derived from
Ground and Space based Observations
Authors: Abramenko, V.; Yurchyshyn, V. B.
2000ESASP.463..273A Altcode: 2000sctc.proc..273A
No abstract at ADS

---------------------------------------------------------
Title: Evolution of Twist in An Emerging Flux Region NOAA 7321
Authors: Wang, T. J.; Abramenko, V. I.
1999ESASP.448..671W Altcode: 1999ESPM....9..671W; 1999mfsp.conf..671W
No abstract at ADS

---------------------------------------------------------
Title: Flare Associated Changes in the Helicity of the Solar
Magnetic Field
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Carbone, V.
1999ESASP.448..679A Altcode: 1999mfsp.conf..679A; 1999ESPM....9..679A
No abstract at ADS

---------------------------------------------------------
Title: Fractal analysis of the vortical structure of magnetic fields
on the Sun
Authors: Abramenko, V. I.
1999ARep...43..622A Altcode:
We have detected scale invariance of the current helicity H_c =
B_z . (nabla x B)_z of the photospheric magnetic field in 20 solar
active regions. This indicates that the vortical field structure has
a fractal nature. The scal- ing exponents of the signed measure of
the current helicity are different in the leading and following parts
of large bipolar active regions. The helicity is scale invariant from
about 15 000 km to the resolution limit of about 1000 km, suggesting
that scale-to-scale energy transport can take place, at least within
this range. Two to three hours prior to a strong flare, the scaling
exponent k_h begins to decrease, a property that can be used to predict
strong flares.

---------------------------------------------------------
Title: The Changes of the Current Helicity Scaling Prior to a Strong
Solar Flare
Authors: Yurchyshyn, V. B.; Abramenko, V. I.; Carbone, V.
1999AAS...194.5404Y Altcode: 1999BAAS...31..909Y
Recently it has been shown (Abramenko et al., Sol. Phys. 178) the
current helicity calculated by the photospheric magnetic field vector
possesses a well pronounced scaling behavior. The sign-singularity of
the 2D structures of current helicity can be studied by introducing the
signed measure and by calculating some power-law exponent: cancellation
exponent kappa . The time variations of the cancellation exponent
seem to be related to flare activity of an active region: the periods
of enhanced flaring are accompanied by a drop and subsequent rise of
the cancellation exponent (Abramenko et al., A&amp;A. 334). Here we
continue to study the flare-related changes of cancellation exponent
paying special attention to the preflare situation. We have found
that the significant decrease of kappa begins 1-3 hours prior to
a strong flare. The reduce of the kappa means the changes in the
transverse magnetic field structure. The preflare energy release
produced by small-scale currents dissipation seems to supply observed
preflare energetic phenomena such as preflare flocculi brightening and
enhanced X-ray and microwave emission. So we are able to conclude that
small-scale energy release in the transverse photospheric magnetic
field take place prior to a strong flare. As soon as the evaluation
of kappa needs only the calibrated vector magnetogram and some minutes
for calculations the preflare drop of the cancellation exponent could
be used for the short-time prediction of strong flares.

---------------------------------------------------------
Title: Evidence of preflare small-scale energy release on the basis
of the magnetic field fractal analysis.
Authors: Abramenko, V. I.; Yurchyshyn, V. B.; Carbone, V.
1999joso.proc..188A Altcode:
The preflare changes in the complexity of the photospheric magnetic
fields were studied. The two-dimensional structures of the current
helicity of magnetic field were analyzed using the method of fractal
analysis. It was shown that several hours prior to a strong flare the
decreasing of the cancellation exponent of current helicity begins. This
result assumes the preflare dissipation of small-scale photospheric
electric currents and should be used for the short-time prediction of
strong flares.

---------------------------------------------------------
Title: Does the photospheric current take part in the flaring process?
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998A&A...334L..57A Altcode:
On the basis of vector magnetograms of two flaring active regions
(ARs) we analyze the scaling behavior of the current helicity H_c
in the photosphere. The signed measure so obtained possesses a well
pronounced sign-singularity in the range of scales from more than 10(4)
Km down to the resolution limit of observations. We found that during
the flaring process there is a signature both of a reorganization
of the current helicity in the photosphere and of a strong magnetic
energy dissipation of the photospheric magnetic field.

---------------------------------------------------------
Title: The photospheric magnetic field response to a solar flare.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998KFNT...14..210A Altcode: 1998KNFT...14..210A
Using the vector magnetic field measurements the authors have studied
the scaling of photospheric magnetic field and current helicity
Bz·(∇×B)z during the periods of high flare
activity in two active regions. The results allow to assume that
from the very onset of a flare the transverse photospheric magnetic
field undergoes significant changes, namely, the fluctuations energy
is reduced as well as the spatial structure gets more simple: the
transverse field becomes more smooth what seems to be explained by
the dissipation of the pre-existing internal tangential discontinuities.

---------------------------------------------------------
Title: Sign-singular behaviour of current helicity of the magnetic
field of active regions on the Sun.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998KFNT...14...99A Altcode: 1998KNFT...14...99A
Using the measurements of a magnetic field vector in the photosphere
of active regions (ARs), the authors have shown that well-pronounced
scaling laws take place for 2D structures hc of current
helicity in ARs, indicating that the signed measure obtained with
hc is sign-singular, say the cancellations follow a
nontrivial anomalous scaling. The cancellation exponent kh =
0.3 - 0.7 obtained is significantly larger than that for the vertical
magnetic field. The linear region on the measure is well-pronounced
and can be determined reliably. Sign-singularity of the signed measure
obtained with hc means that at any scale (at least within
the linear region of the spectrum) the dominance of current helicity
of some sign takes place. This is the necessary condition for the
transformation of the energy of small-scale fluctuations of the magnetic
field and velocity into the energy of large-scale mean field, say the
energy of large-scale DC currents in the corona.

---------------------------------------------------------
Title: Sign-Singularity of the Current Helicity in Solar Active
Regions
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998SoPh..178...35A Altcode: 1998SoPh..178..473A
On the basis of vector magnetograms of 20 active regions we analyzed
the scaling behavior of the current helicity Hc in the
photosphere. We show that Hc possesses well pronounced
sign-singularity in the range of scales from more than 104
km up to the resolution limit of observations.

---------------------------------------------------------
Title: Linear Force-free Magnetic Field over an Active Region with
Due Regard to Coronal Magnetic Field
Authors: Abramenko, V. I.; Yurchishin, V. B.
1998ASPC..155...85A Altcode: 1998sasp.conf...85A
No abstract at ADS

---------------------------------------------------------
Title: Response of the photospheric magnetic field to a solar flare.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998KPCB...14..162A Altcode:
Based on magnetic field vector measurements, the authors studied the
scaling of the photospheric magnetic field and the current helicity
Bz·(∇×B)z at high flare activity periods
in two active regions NOAA 7315 and NOAA 7585. The current helicity
cancellation exponent kh is found to diminish drastically
(from 0.5 to 0.3 on average) with the beginning of the Hα flare (within
1 - 2 min); at the same time the Holder exponent of the transverse
magnetic field vector, grows from 0.5 to 0.7 and the energy spectrum
exponent of transverse field fluctuations grows from 2.0 to 2.4. The
cancellation exponent retains its lower value for at least several hours
but regains its preflare value when the flare activity declines. The
total current helicity is also observed to decrease (by about 36
percent) with the flare beginning, synchronously with kh,
while the total magnetic flux Bz diminishes insignificantly
(by about 6%). These results suggest that the photospheric transverse
magnetic field experiences significant changes from the very onset of
a flare-its fluctuation energy decreases and its spatial structure
gets simpler: the field is smoother, which may be associated with a
drop in the number and intensity of tangential discontinuities. The
results, which are based on observations, support Parker's view that
"a flare is a consequence of many very small reconnection events",
they are also in accord with the SOC flare model.

---------------------------------------------------------
Title: Scaling behaviour of the current helicity in active regions.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998joso.proc...83A Altcode:
Using the measurements of magnetic field vector in the photosphere
of 20 active regions (ARs) it is shown that well pronounced scaling
laws take place for 2D structures of current helicity hc
in ARs, indicating that the signed measure obtained with hc
is sign-singular, say the cancellations follow a nontrivial anomalous
scaling. Sign-singularity of the signed measure obtained with
hc means that at every scale (at least within the linear
region of the spectrum) the dominance of current helicity of some sign
takes place.

---------------------------------------------------------
Title: Electric currents and Hα emission in the active regions on
the Sun (abstract)
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1998PAICz..88...30A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Scaling laws of the current helicity in active
regions. II. Flaring related variations.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998IBUAA..12...27A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Scaling laws of the current helicity in active regions:
I. Statistical study.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998IBUAA..12...26A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Scaling laws of current helicity in flaring regions.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998joso.proc...85A Altcode:
On the basis of vector magnetograms of flaring active regions (ARs)
the authors analyze the scaling behavior of the current helicity in
the photosphere. The signed measure so obtained possesses as well
pronounced sign-singularity in the range of scales from more than
104km up to the resolution limit of observations. It is
found that during the flaring process there is a signature both of
a reorganization of the current helicity in the photosphere and of a
strong magnetic energy dissipation of the photospheric magnetic field.

---------------------------------------------------------
Title: On the Relation Between the Photospheric Current and the
Flaring Process
Authors: Carbone, V.; Consolini, G.; Abramenko, V. I.; Yurchishin,
V. B.
1998ESASP.417..209C Altcode: 1998cesh.conf..209C
No abstract at ADS

---------------------------------------------------------
Title: Sign-singular behavior of current helicity of magnetic fields
in active regions on the Sun.
Authors: Abramenko, V. I.; Yurchishin, V. B.; Carbone, V.
1998KPCB...14...75A Altcode:
Based on the measurements of magnetic field vector in active
regions, the authors show that well-pronounced scaling laws hold for
two-dimensional structures of current helicity, hs, in
active regions. The hc scaling was studied by calculating
the spectrum of sign-singular measure and finding a linear section
in it. The scaling for the current helicity is more pronounced
than for the vertical magnetic field: the cancellation exponent
kh is by an order of magnitude larger than the cancellation
exponent kb for the vertical field component. The shape of
sign-singular measure spectra suggests that the same scaling is retained
below the limit of the authors' resolution. The sign-singular measures
obtained for hc point to the fact that current helicity of
some sign dominates on any scale (at least within the linear region
of the spectrum). This is a necessary condition for the transformation
of the energy of small-scale field and velocity fluctuations into the
energy of large-scale electric currents in the corona.

---------------------------------------------------------
Title: Electric Current Helicity in 40 Active Regions in the Maximum
of Solar Cycle 22
Authors: Abramenko, V. I.; Wang, Tongjiang; Yurchishin, V. B.
1997SoPh..174..291A Altcode:
Using vector magnetograms of 40 active regions (ARs) of the maximum
of solar cycle 22, we calculated the imbalance ρh (over
the AR area) of the current helicity hc ≡ Bz
(∇ × B)z in the photosphere. In 82.5% of the cases the
predominant current helicity was negative (ρh &lt; 0)
in the northern hemisphere and positive (ρh &gt; 0) in
the southern hemisphere. Thus, the predominance of counter-clockwise
(clockwise) vortices in the northern (southern) hemisphere seems to be
valid not only for unipolar spots with obvious vortex structure (Hale,
1927; Richardson, 1941; McIntosh, 1979; Ding, Hong, and Wang, 1987)
but also for ARs of different types. The forces of rotation of the Sun
(Coriolis force and/or differential rotation) seem to take effect in
the twisting of various magnetic structures.

---------------------------------------------------------
Title: Calculation of the linear force-free magnetic field above a
solar active region
Authors: Abramenko, V. I.
1997AZh....74..625A Altcode:
Modeling the linear force-free fields above solar active regions
involves the use of either Fourier transforms or Green functions. The
modeling results depend on the a priori conditions specified for
the edges of the volume studied. However, none of the methods that
have been developed allow direct specification of the values for the
field at the nonphotospheric boundaries of the volume. A method that
allows this would make it possible to study the influence of lateral
boundary conditions on the solution inside the volume of interest and
to use a priori information about the field in the corona. Here, an
algorithm is presented for calculation of the linear force-free field
in a limited volume (in the shape of a parallelepiped, Omega) using
the distribution of the Bz component of the field at all boundaries
of Omega and the distribution of Bx and Bv in a frame made up by the
intersection of a lateral surface of Omega and a single arbitrarily
chosen plane z = const. The algorithm is verified using a numerical
model, permitting calculation of the linear force-free field of a
dipole in a half-space using exact formulas. The rms deviation of the
calculated and analytical solutions at each layer along the z axis does
not exceed 1 percent. Substituting potential boundary conditions for
force-free conditions at the nonphotospheric border of the Omega volume
leads to a substantial change in the resulting magnetic configuration.

---------------------------------------------------------
Title: Calculation of the linear force-free magnetic field above a
solar active region
Authors: Abramenko, V. I.
1997ARep...41..552A Altcode:
Modeling of the linear force-free fields above solar active regions
is based on application of either Fourier transforms or Green
functions. The modeling results depend significantly on the a priori
conditions specified for the edges of the volume studied. However,
none of the methods that have been developed allow direct specification
of the values for the field at the nonphotospheric boundaries of the
volume. A method that allowed for this would make it possible to study
the influence of lateral boundary conditions on the solution inside
the volume of interest, and to use a priori information about the
field in the corona. Here, an algorithm is presented for calculation
of the linear force-free field in a limited volume (in the shape of a
parallelepiped, Omega) using the distribution of the B_z component of
the field at all boundaries of Omega and the distribution of B_x and
B_y in the frame made up by the intersection of a lateral surface of
Omega and a single arbitrarily chosen plane z = const. The algorithm is
verified using a numerical model, permitting calculation of the linear
force-free field of a dipole in a half-space using exact formulas. The
rms deviation of the calculated and analytical solutions at each
layer along the z axis does not exceed 1%. Exchanging the force-free
boundary conditions with the potential boundary conditions at the
nonphotospheric border of the volume Omega leads to a substantial
change in the resulting magnetic configuration.

---------------------------------------------------------
Title: Modeling of the force-free magnetic field in the active region
NOAA 7216 taking information on the coronal fields into account
Authors: Abramenko, V. I.; Yurchishin, V. B.
1997KFNT...13c..49A Altcode:
The method of calculating the linear force-free magnetic field in
a bounded domain proposed by us earlier is applied here to AR NOAA
7216. The B(z) component of the photospheric field was used, with
the available information on coronal magnetic fields employed as
complementary data. It is shown that the coronal magnetic field of
AR 7216 (4 July 1992, 00h30 TM UT, NI2, El7) was nonlinear force-free
with positive alpha. The electric current density in the coronal loops
decreases with height. The twisting of the coronal field (clockwise) is
atypical for active regions in the northern hemisphere. The large-scale
electric current system connecting the leader with the tail spots was
very weak. Two necessary conditions for the growth of its energy were
not fulfilled: the dominance (over the AR area) of the current helicity
was virtually absent, and large-scale vortical motions around the main
spots were not found. As a result, the increase of free magnetic energy
in the corona appeared to be retarded. This can explain the low flare
activity of this large active region.

---------------------------------------------------------
Title: Sign-Singularity of the Current Helicity in Solar Active
Regions
Authors: Abramenko, V. I.; Carbone, V.; Yurchishin, V. B.
1997IAUJD..19E..10A Altcode:
Signed measures of stochastic fields show a sign-singular behavior
related to extreme and violent oscillations in sign. On the basis of
vector magnetic field measurements in active regions, we calculate the
current helicity in the photosphere and we show that, for all 22 active
regions we examined, the signed measure is sign-singular. Our results
allow us to address the problem of (dc) magnetic field energy build up
in the solar atmosphere. In fact, it has been shown that the necessary
condition for the alpha-effect is the presence of a predominant sign
of current helicity over a given volume. Sign-singularity represents a
signature of a scaling phenomenon underlying the dominance of a sign of
the current helicity at a certain scale, thus experimentally confirming
the presence of necessary condition for alpha-effect. With our method,
we are able to address also the scaling laws of turbulence in the
transverse magnetic field of the photosphere. Our method represents
a new way of investigating vector magnetograms in the photosphere by
looking at new statistical concepts. In this sense it can be applied
to active regions where the determination of quantities through the
visual inspection of H alpha patterns is not reliable.

---------------------------------------------------------
Title: On the Possibility of alpha-effect in the Solar Atmosphere:
Observational Aspects
Authors: Yurchishin, V. B.; Abramenko, V. I.; Wang, T. -J.
1997IAUJD..19E..61Y Altcode:
The way the DC magnetic energy build-up in the atmosphere of an active
region (AR) is not yet completely clear. Along with a prominent concept
for the energy build-up due to shearing motions at the photosphere
recently another possibility was proposed. Under the assumption that
magnetic field of an AR evolves through the sequence of force-free
states Seehafer shown that the energy of fluctuations of magnetic field
and velocity may be transferred into the energy of large-scale current
system (the alpha-effect). The necessary condition for the alpha-effect
is the presence of predominant sign of current helicity H_c = {B}cdot
(nabla times {B}) in the volume of study. The main our purpose is to
clear up how frequently this condition occurs in various ARs. On the
basis of vector magnetic field measurements for 40 ARs of 22 solar cycle
maximum we calculated the current helicity in the photosphere. For 36
ARs a significant (5-75%) imbalance of current helicity took place,
for 33 of them the excess of current helicity was positive in the
southern hemisphere and negative in the northern hemisphere. Thus,
very frequently in ARs the necessary condition for the magnetic energy
transport from fluctuations to large-scale current systems take place.

---------------------------------------------------------
Title: Modeling a force-free field in the active region NOAA 7216
with information on coronal fields taken into account.
Authors: Abramenko, V. I.; Yurchishin, V. B.
1997KPCB...13c..37A Altcode: 1997KPCB...13...37A
The method proposed earlier by the authors for calculating a linear
force-free field in a bounded region is applied to the active region
NOAA 7216. The calculations are based on the Bz component
of the photospheric field with the available information on coronal
fields taken as ancillary data. The coronal field in AR 7216 was found
to be nonlinear and force-free with positive α, the current density
in loops diminishing with height. The general clockwise curling of
the coronal field is not typical for active regions in the northern
hemisphere. The observed photospheric field was not force-free,
its energy in a unit layer was by a factor of 1.4 higher than in a
force-free field. The large-scale current system linking the leading
and the trailing spots was rather weak at the time of the observations,
and there were no conditions necessary for the system energy growth:
neither a sign-dominant current helicity of the photospheric field nor
large-scale vortical motions in the photosphere and chromosphere were
observed. As a result, the free magnetic energy in the corona had no
way of growing, and this may account for a low flaring activity in
this strong active region.

---------------------------------------------------------
Title: Statistical analysis of the spiral structure of sunspots on
the basis of vectormagnetograms.
Authors: Abramenko, V.; Yurchishin, V.
1997joso.proc...47A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Accumulation of magnetic field energy in an active region
due to the alpha-effect
Authors: Abramenko, V. I.; Yurchishin, V. B.; Wang, T. J.
1996R&QE...39..930A Altcode:
The problem of accumulation of magnetic field energy in an active
region (AR) as the energy of electric currents in the AR atmosphere
is not yet completely clear. Along with the commonly accepted concept
of generation of electric current systems in an AR due to large- scale
shearing motions at the photospheric level [1,2], another possibility
of magnetic field energy accumulation has recently been proposed
theoretically [3]. Assuming that the AR magnetic field evolves via a
sequence of force- free configurations, Seehafer shows that the energy
of small- scale field and velocity fluctuations can be transformed
into that of large-scale current systems of an AR (alpha-effect). The
necessary condition for the alpha-effect to exist is the presence of
the sign- dominant current helicity H c = B · (∇×B) in
the volume is considered. The purpose of this paper is to clarify the
fulfillment of this condition in various ARs. Based on the measurements
of magnetic field vector in 40 active regions of the maximum of the 22nd
cycle we calculated the current helicity of the field Bz ·
(∇×B) z in the photosphere and obtained the following
results. In 36 ARs we found a significant imbalance of the current
helicity of the field (5 to 75%) such that in 33 ARs the excess of the
current helicity was positive in the southern hemisphere and negative
in the northern hemisphere. Therefore, in ARs the necessary condition
for transfer of the energy of small-scale fluctuations of the field
and velocity into the energy of large- scale electric currents in ARs
is fulfilled rather frequently.

---------------------------------------------------------
Title: Analysis of Electric Current Helicity in Active Regions on
the Basis of Vector Magnetograms
Authors: Abramenko, V. I.; Wang, Tongjiang; Yurchishin, V. B.
1996SoPh..168...75A Altcode:
The problem of (dc) magnetic field energy build up in the solar
atmosphere is addressed. Although large-scale current generation may
be due to large-scale shearing motions in the photosphere, recently a
new approach was proposed: under the assumption that the magnetic field
evolves through a sequence of force-free states, Seehafer (1994) found
that the energy of small-scale fluctuations may be transferred into
energy of large-scale currents in an AR (the α-effect). The necessary
condition for the α-effect is revealed by the presence of a predominant
sign of current helicity over the volume under consideration. We
studied how frequently such a condition may occur in ARs.

---------------------------------------------------------
Title: Modeling of a Linear Force-Free Magnetic Field in a Bounded
Domain
Authors: Abramenko, V. I.; Yurchishin, V. B.
1996SoPh..168...47A Altcode:
A method for the reconstruction of the linear force-free magnetic field
in a bounded domain (as a rectangular box, Ω) is presented here. The
Dirichlet boundary-value problem for the Helmholtz equation is solved
for the Bzcomponent specified at the Ω boundary. Chebyshev's
iteration method with the optimal rearrangement of the iteration
parameters sequence was used. The solution is obtained as for the
positive-definite, and for the non-sign-definite difference analogue of
the differential operator ▽2u + α2u. Specifying
two scalar functions, Bxand Byon the intersection
of the lateral part of the Ω boundary with one selected plane z
= constant, and using Bzinside the Ω, we have found
Bxand Bythroughout Ω.

---------------------------------------------------------
Title: Solving the equations of the linear force-free field in a
limited region of space by Chebyshev's iteration method.
Authors: Abramenko, V. I.
1996KPCB...12a...1A Altcode: 1996KPCB...12Q...1A
A stable, highly accurate algorithm is presented for calculating
the linear force-free field in a limited region of space, Ω, which
has the shape of a parallelepiped. The Dirichlet boundary-value
problem for the Helmholtz equation is solved separately for every
Bx, By, Bz component given at the
Ω boundary. The problem is solved with Chebyshev's iteration method
with the optimum rearrangement of iteration parameter sequence. The
solution is obtained for the difference analog of the differential
operator ∇2u+α2u when the analog is of
both the positive and unfixed sign. The method was tested with a
numerical simulation which produced the exact solution B of the
linear force-free field equations for a dipole in a half-space. The
root-mean-square deviation of the exact analytic solution B from the
calculated solution B' is no more than 1.5%. The method was used to
calculate the field B″ which was linear and force-free in a limited
region of space (the field satisfied the Helmholtz equation inside
the region Ω only and was zero at its sides and upper bound). The
author shows that the strength, the general energy, and the shape of
lines of force in the field B″in Ω differ essentially from the same
parameters of the field B', which is linear and force-free in a half
space and is calculated in Ω with the same boundary conditions at the
bottom of Ω. The energy of B″inside Ω exceeds the energy of B'
by about a factor of 1.5. The method allows any boundary conditions
at the sides and an upper bound of Ω, and thus the simulation of a
magnetic field which is force-free in a limited region of space above
an active region in the solar photosphere is made possible by the use
of a preliminary information on the coronal magnetic field.

---------------------------------------------------------
Title: Comparison of a longitudinal field observed in Hβ
with the potential field in active regions on the Sun
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Yurchishin, V. B.
1995BCrAO..89....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Comparison of the longitudinal magnetic field observed in
Hβ with the potential field in an active region on the Sun.
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Yurchishin, V. B.
1995IzKry..89....3A Altcode:
The study of the magnetic field structure in an active region on the
basis of simultaneous observations in Fe I 5253 Å and Hβ lines is
being continued. Investigations are carried out through a comparison
of the observed field with the potential field, computed on the basis
of the observed photospheric field. Such a method allowed to derive
the most probable difference between line-formation levels (about
1300 km for the investigated region). It has been established that
the strength of the field observed in Hβ is smaller practically over
the whole AR than the strength of the potential longitudinal field,
calculated on the level of Hβ formation. Such a difference is being
interpreted by the presence of transverse circular electric currents in
the chromosphere. Their magnetic field should be antiparallel with the
potential field. The current value can reach 3×1011A. The
following possibilities for such currents generation are suggested:
drift currents due to pressure gradient forces and/or due to
gravitational forces. The total energy store in the magnetic field of
such current system is not lower than 1029-1030erg
(over the whole active region). The difference between plasma pressure
inside and outside the hills of magnetic field is evaluated.

---------------------------------------------------------
Title: Possibility of electric field determination in flare loops
based on X-ray observations
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1993BCrAO..87....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: A study of the magnetic field and electric currents in the
active region based on observations of the longitudinal field at
two levels and Hα-structure
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.; Yurchishin,
V. B.
1993BCrAO..88...63A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Two-level longitudinal magnetic field observations as a
perspective for transverse electric current investigation in active
regions on the Sun.
Authors: Abramenko, V. I.; Gopasiuk, S. I.; Ogir', M. B.; Iurchishin,
V. B.
1992KFNT....8...50A Altcode: 1992KNFT....8...50A
Possibilities of studying the magnetic field structure and transverse
electric currents in an active region on the basis of a longitudinal
magnetic field observed at two levels are demonstrated. On the
average, the longitudinal potential field exceeds the one at the
level of Hβ formation by 5 mT and, in some places of the
active region, by 20 mT and more. The calculations of the potential
field are made by the observed photospheric longitudinal field. This
difference is ascribed to circular transverse electric currents in
the chromosphere. Their magnetic field must be antiparallel to the
potential field. The intensity of these currents may be as high as
3·1011A.

---------------------------------------------------------
Title: Prospects for studying transverse electric currents in active
regions on the Sun from two-level observations of the longitudinal
magnetic field.
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir', M. B.; Yurchishin,
V. B.
1992KPCB....8e..43A Altcode: 1992KPCB....8...43A
The scope is demonstrated for studying the magnetic field structure and
transverse electric currents in an active region from the longitudinal
field component observed at two levels. The potential field calculated
from the photosperic field observations at the Hβ formation
level is stronger by 5 mT on the average than the field observed in this
line; in some areas in the active region the difference may be 20 mT
and more. It is due to the transverse circular electric currents in the
chromosphere. Their magnetic field must be antiparallel to the potential
field, and their intensity may be as high as 3·1011A.

---------------------------------------------------------
Title: Electric currents and magnetic-field loops in solar active
regions.
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir', M. B.
1992BCrAO..82...99A Altcode:
Observations have been used on the magnetic-field vector from the
5250 Å Fe I line with Hα pictures for two active regions
to examine the magnetic-field loop structures and the relationships
between the electric currents and the fields. Much of the photospheric
transverse field in an active region is due to currents flowing in
the photosphere. Most of the filamentary structures in Hα
do not coincide with projections of the field lines calculated in the
potential approximation from the vertical component H2. Those
few that do coincide with line projections form three systems of loop
structures differing in height. The numbers of these filaments are
dependent on the active-region evolution. Currents flow in the upper
chromosphere and adjacent corona. The self-induction coefficient for
unit length of a current loop is 0.1 - 0.4, and it is larger where the
transverse field is stronger. The energy stored in the local-current
field is exceptionally high and is sufficient to provide the energy
input to the most powerful flares.

---------------------------------------------------------
Title: Electric currents in quiet and active regions on the Sun and
their comparison
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1992BCrAO..86..116A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electric currents in an undisturbed region on the Sun
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1992BCrAO..84..117A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electric Currents and Hα Emission in Two Active Regions on
the Sun
Authors: Abramenko, V. I.; Gopasiuk, S. I.; Ogir', M. B.
1991SoPh..134..287A Altcode:
We investigated the structure of magnetic field and vertical electric
currents in two active regions through a comparison of the observed
transverse field with the potential field, which was computed according
to Neumann boundary-value problem for the Laplace equation using the
observed Hz-value. Electric currents were calculated from
the observations of the transverse magnetic field.

---------------------------------------------------------
Title: Magnetic loops with current in the neighborhood of
Hα flares
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1991BCrAO..83....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Magnetic loops with current in the vicinity of H-alpha flares
Authors: Abramenko, V. I.; Gopasiuk, S. I.; Ogir', M. B.
1991IzKry..83....3A Altcode:
The relationship of flare and flocculus knots with H-alpha fibrils,
electric currents, and magnetic fields is investigated on the basis of
observations of the total vector of the magnetic field and vertical
currents computed from them, as well as H-alpha films of two active
regions (ARs). It is found that knots of flares are either connected
with each other or with the flocculus knot by the magnetic loops bearing
the currents. The shortest loops connect the brightest knots. The places
where magnetic loops converge with current (from both close and very
remote areas in the AR) are characterized by the most powerful flare
activity. It is concluded that the total energy store of the AR is the
source of flare energy. A dynamical model of a flare based on current
redistribution in the system of ascending loops and a concentration
of current in a loop with minimum ascent velocity is proposed.

---------------------------------------------------------
Title: Electric Currents in the Atmosphere of the Sun
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1990IAUS..138..267A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Plasma motions and electric currents in an active region
Authors: Abramenko, V. I.; Gopasiuk, S. I.; Ogir', M. B.
1990IzKry..81....3A Altcode:
The connection between the proper motions of sunspots and the vortical
structure of the transverse field vector and the electric currents
of two active regions is investigated. Plasma motions directed at an
angle to the magnetic field are found to dominate the entire area of
the active region; plasma motions directed along the magnetic field
lines occur more rarely. The existence of two global plasma vortices is
discovered. One of them is twisted clockwise and covers the entire part
of the active region; the other is twisted in the opposite direction
and occupies the tail part of the active region.

---------------------------------------------------------
Title: Plasma motion and electric currents in an active region
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1990BCrAO..81....1A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electric currents and magnetic-field loops in solar active
regions
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1990BCrAO..82...99A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Electric currents and magnetic field loop structures of active
regions on the Sun.
Authors: Abramenko, V. I.; Gopasiuk, S. I.; Ogir', M. B.
1990IzKry..82..108A Altcode:
Both, magnetic field loop structures and connection between
electric currents and magnetic fields were studied on the basis
of observational data for the magnetic field vector in λ5250 Å Fe
I-line and Hα-pictures of two active regions. It is established that a
considerable part of the photospheric transverse magnetic field depends
on photospheric electric currents. In most cases the Hα-structure
orientation do not coincide with projections of magnetic field lines
calculated in the potential field approximation. Those few filaments
that coincide with line projections, form three loop structure systems
differing in height. The number of such filaments varies in the course
of the active region evolution. It is concluded that the electric
currents flow in the upper chromosphere and corona. The magnetic energy
stored in local currents is extremely high and sufficient to produce
most powerful flares.

---------------------------------------------------------
Title: The variety of solar flares revealed on the basis of the
electric currents investigation.
Authors: Abramenko, V. I.; Gopasiuk, S. I.; Ogir', M. B.
1990IzKry..81....8A Altcode: 1990IzKry..81....9A
The influence of various processes of the magnetic field changes,
leading to the appearance of the electric currents in the Hα emission
in an active region, is studied. Two types of flares are discovered:
the first one is the most numerous, comprising the flares located
in stable Hα plages. Here the electric current is determined
by the turnoff of the potential transverse magnetic field vector
H0⊥ and plasma motion is directed at some
angle to its lines. These are extended flares with gradual development
occurring generally in places of upward electric currents. The second
type comprises rare flares occurring beyond Hα plages. The electric
current here is determined by the change of H0⊥
vector length and plasma is moving along the transverse field force
lines. As a rule, these flares are compact and impulsive, their radio
emission spectrum being more shortwave.

---------------------------------------------------------
Title: Refining flare types from current patterns
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1990BCrAO..81....6A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Variations of the orientation and intensity of the magnetic
field and their role in the formation of current structures
Authors: Abramenko, V. I.; Gopasyuk, S. I.
1988BCrAO..80...85A Altcode: 1990BCrAO..80...85A
A concept of the vertical component of the solar electric current in
the form of components is validated. The first component, which is
governed by the rotation of the potential transverse field vector,
determines the structure of the true current better than the others
(correlation coefficient 0.5 - 0.7). However, the current determined
by this component may be high by a factor of approximately 2. The
difference decreases with increasing structural importance of the
second-component current, which is due to variation of the length of
the transverse magnetic field vector. Representing the current in the
form of components makes it possible to obtain information on which
processes dominate and when they dominate. This opens new opportunities
for study of dynamic processes on the Sun that cause rotation of the
transverse magnetic field vector and variation of its length.

---------------------------------------------------------
Title: Determination of electric currents from vertical component
of magnetic field and Hα fibrils
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1988BCrAO..80...93A Altcode: 1990BCrAO..80...93A
Representing the vertical electric current in the form of components
related to the rotation of the potential-field vector and variation of
its length has made it possible to obtain information on the structure
and magnitude of the current on the basis of relatively accessible data:
the vertical magnetic-field component Hz and photographs
of Hα fibrils. Very satisfactory agreement was obtained
between the current structures calculated by this procedure and those
from observations of the transverse field in the photosphere. The
assumption that the twist of the magnetic field with height is constant
(or that the orientation of the field is constant) made it possible
to compute the currents at heights all the way up to 50,000 km. The
electric currents in an active region decrease more rapidly with
height than the potential-field magnetic flux. It is concluded that
a system of current loops at various heights exists in the active
region. The field structure of a magnetic loop becomes more similar
to the potential structure as its height increases.

---------------------------------------------------------
Title: Evolution of the active region, its current systems and
flare activity
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1988BCrAO..78..163A Altcode: 1989BCrAO..78..163A
The structure of the vertical electric currents and Hα
flares was studied in two active regions. The electric currents were
calculated on the basis of the transverse component of the observed
photospheric magnetic fields. It is shown that weak magnetic fields
have higher current densities referred to unit transverse-field
intensity (higher relative current densities). Current density is
highly sensitive to changes in the sunspot group. As the active region
disintegrates, the currents decay more rapidly in the weaker fields,
and on the whole the field tends to potential. Hα flares
appear preferentially at points where the electric currents are directed
upward. It is concluded that the Hα emission of the flares
is goverend by both electrons and protons that have been accelerated
at the tops of magnetic loops.

---------------------------------------------------------
Title: Hα plages and electric currents in active regions
of the Sun
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir, M. B.
1988BCrAO..79...21A Altcode: 1990BCrAO..79...21A
The radiation of Hα plages versus the structure of the
vertical component of electric currents was studied. The electric
currents were calculated using the observations of the magnetic field
carried out in Fe I λ5250.2 Å line at the vector-magnetograph of the
Crimean observatory. It is shown that the plage area in places with
high current density increases with the growth of plage brightness. It
means that the electric currents play an important role for plage
heating. It is also established that the brighter the plages, the
more often they occur in the places of upward currents. The authors
conclude that, besides Joule losses, high-energy particles, which are
probably constantly accelerated in the corona, are also important for
plage heating. Similar asymmetry with respect to the current sign is
observed in Hα flares location. The homogeneity of flare
and plage phenomena is manifested by their heating by anisotropical
beams of high-energy charged particles. They differ only in the power
of the process.

---------------------------------------------------------
Title: Evolution of the active region, its current systems and
flare activity.
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir', M. B.
1988IzKry..78..151A Altcode:
The structure of vertical electric currents and Hα flares
of two active regions were studied. Electric currents are calculated
on the basis of transversal component of the observed photospheric
magnetic field. It is shown that weak magnetic fields have more current
density with respect to the unit of transversal magnetic field strength
(the higher degree of current). As the active region destructs the
currents in weaker magnetic fields decay faster and the field as a
whole tends to potential. Hα flares occur mainly in places
of upward direction of local electric currents. It is concluded that
Hα flare radiation is caused by both electrons and protons
accelerated on top of magnetic loops.

---------------------------------------------------------
Title: Hα plages and electric currents in the active
regions of the Sun.
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir', M. B.
1988IzKry..79...23A Altcode:
The radiation of Hα plages versus the structure of vertical
component of the electric currents was studied. The electric currents
were calculated using the observations of the magnetic field carried
out in Fe I λ5250.2 Å line at the vector-magnetograph of the Crimean
Observatory. It is shown that the plage area in places with high
current density increases with the growth of plage brightness. It
means that the electric currents play an important role for plage
heating. It is also established, that the brighter the plages, more
often they occur in the places of upward currents. The authors conclude,
that besides Joule losses high energy particles which are probably
constantly accelerated in the corona, are also important for plage
heating. Similar asymmetry with respect to the current sign is observed
in Hα flares' location. The homogeneity of flare and plage
phenomena is manifested by their heating by anisotropical beams of high
energy charged particles. They differ only by the power of the process.

---------------------------------------------------------
Title: The determination of the electric currents regarding the
vertical component of the magnetic field and Hα fibrils.
Authors: Abramenko, V. I.; Gopasyuk, S. I.; Ogir', M. B.
1988IzKry..80...97A Altcode:
The vertical component of the electric currents, being displayed as
a sum of items, connected with the turnoff of the potential field
vector and the change of its length permitted to obtain information
about the structure and the value of the current on the basis of the
available observational data: the vertical component Hz
of the magnetic field and Hα pictures. A satisfactory agreement of
the current structures, computed by the suggested method and by the
observational data of the transverse magnetic field in the photosphere
is attained. The assumption, that the twist of the field with height
(or its stable orientation) is constant, allowed to compute the
currents at the altitudes up to 50000 km. The electric currents in the
active regions decrease with height faster, than the magnetic flux
of the potential field. It is concluded, that in the active region
there exists a system of current loops of different height. With the
increase of the magnetic loop height, its structure tends to potential.

---------------------------------------------------------
Title: Changes of the magnetic field orientation and its value;
their role in the formation of current structures.
Authors: Abramenko, V. I.; Gopasyuk, S. I.
1988IzKry..80...89A Altcode:
It has been substantiated, that the vertical component of the electric
current of the Sun might be displayed as a pattern of items. The first
one, determined by a turnoff of the potential transverse field vector
fits the structure of a real current (the correlation coefficient is
0.5 - 0.7). But the value of the current being determined by this item,
might be overestimated by a factor of 2. The difference decreases with
the increase of the role of the second item, which is determined by
the changes of the length of the transverse field vector. The current
being displayed as a pattern of items permits to obtain information
about particular processes dominating in the formation of current
structures and gives the possibility to investigate the dynamical
processes on the Sun, leading to the turnoff of the transverse magnetic
field vector and the changes of its length.

---------------------------------------------------------
Title: A system of electric currents and magnetic field structure
in the active region
Authors: Abramenko, V. I.; Gopasyuk, S. I.
1987BCrAO..76..163A Altcode: 1989BCrAO..76..163A
No abstract at ADS

---------------------------------------------------------
Title: The system of electric currents and magnetic field structure
in active regions.
Authors: Abramenko, V. I.; Gopasiuk, S. I.
1987IzKry..76..147A Altcode:
The magnetic field structure of two solar active regions was
investigated by comparing the observed magnetic field vector with the
computed one in the framework of a potential model. Results indicate
the existence of a global electric current distribution over the entire
area of the active region. The observed magnetic field exceeds the
potential field in strength only in the central part of the transverse
magnetic field humps with a maximum field strength exceeding 200
G. This feature of the observed magnetic field is connected with the
presence of local currents. The energy of the magnetic field of the
global current amounts to 10 to the 32nd erg, which corresponds to
the energy of the most intense flares.

---------------------------------------------------------
Title: Structure of the magnetic field and electric streams in an
active region.
Authors: Abramenko, V. I.; Gopasyuk, S. I.
1986psf..conf...32A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: The accuracy of potential field restoration using the Neumann
problem.
Authors: Abramenko, V. I.
1986BSolD1986...83A Altcode:
The accuracy of potential field restoration using the boundary Neumann
problem for the Laplace equation has been studied. The restored field
coincides well with the true one provided there are no sources of
perturbation around the area of calculation in the distance of the
order of the area itself. The disbalance of the magnetic fluxes is
negligible. The true potential field significantly differs from the
restored one if there exist some misaccounted sources of the field
in the vicinity of the area. The error of the field restoration
depends upon the distance between the opposite charges in the group
of perturbation, on the distance between the group and the boundary
of the area and on the value of the changes.

---------------------------------------------------------
Title: The Accuracy of Potential Field Restoration Using Neuman
Problem
Authors: Abramenko, V. I.
1986BSolD...8...83A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: On quasi-periodicity of the flare activity of the sun.
Authors: Abramenko, V. I.; Ogir, M. B.
1985IzKry..70....8A Altcode:
On the basis of flare activity observations all over the solar disk
carried out in summer of 1980 and 1981 the time distribution of flare
appearances on the surface and their energies were investigated by the
Fourier-analysis method. The following groups of authentic quasi-periods
surpassing the 3σ level were discovered: 109 - 166m,
68 - 78m, 25 - 46m. The quasi-periods 68 -
78m and 25 - 46m characterize the repetition of
flare groupings, and quasi-periods 109 - 166m are manifested
as modulations of the flare energy of the groupings.

---------------------------------------------------------
Title: Three-minute oscillations in the polarized radio emission
from local radio sources on the Sun. Part 1.
Authors: Abramenko, V. I.; Tsvetkov, L. I.
1985BCrAO..73...49A Altcode: 1985BuCri..73...49A; 1987BCrAO..73...49A
No abstract at ADS

---------------------------------------------------------
Title: Quasiperiodicity of the flare activity of the Sun
Authors: Abramenko, V. I.; Ogir, M. B.
1985BCrAO..70....6A Altcode: 1985BuCri..70....6A; 1987BCrAO..70....6A
No abstract at ADS

---------------------------------------------------------
Title: 3-minute oscillations of the polarized radio emission of
local sources on the sun.
Authors: Abramenko, V. I.; Tsvetkov, L. I.
1985IzKry..73...53A Altcode:
Consideration is given to the 3-min oscillations of circularly polarized
radio-emission of the local source associated with sunspot group SD
No. 401. Observations were carried out on the RT-22 radiotelescope
at the Crimean Astrophysical Observatory during August 15-21, 1980
at a wavelength of 2.25 cm. The modulation depth of the polarized
radio-emission flux density varies from zero to several percent with
a period greater than 20 min. These oscillations are less distinct in
the total intensity. The flux densities, the degree of polarization,
and the angular dimensions of the source are determined. The dynamics
of the power spectra of the local source oscillations is studied
during the passage of the sunspot group over the solar disk. It is
shown that the oscillatory processes in both the total intensity and
in the source's polarized radio-emission develop and fade during a
time span of 0.5-1.0 days. The appearance of a second modulation of
2-min to 6-min oscillations is explained by MHD-wave passage across
the coronal condensation.

---------------------------------------------------------
Title: Fluctuations in the degree of circular polarization of the
radioemission of an active region on the Sun
Authors: Abramenko, V. I.; Tsvetkov, L. I.
1984BCrAO..69..116A Altcode: 1986BCrAO..69..116A
No abstract at ADS

---------------------------------------------------------
Title: Fluctuations of the degree of circular polarization of radio
emission from a proton region on the sun
Authors: Abramenko, V. I.; Tsvetkov, L. I.
1984IzKry..69..123A Altcode:
Fluctuations of the degree of circulation polarization from a local
radio source associated with the spot group of McMath Region 13043
were studied with the RT-22 telescope of the Crimean Observatory at
wavelengths of 3.5, 2.5, and 1.9 cm. The fluctuations were analyzed
by Fourier analysis and the maximum entropy method. Reliable periods
in the variations were observed: 351-345 m, 330-220 m, and 160-60
m. Possible magnetic-field variations in the lower corona above an
active region were investigated on the assumption of a gyroradiation
mechanism of radio emission.

---------------------------------------------------------
Title: An analogy between superposed-epoch and Fourier-transform
methods - The effect of a trend on the reduction of data nonuniformly
distributed in time
Authors: Abramenko, V. I.; Rachkovskii, D. N.
1983IzKry..66...71A Altcode:
The use of the stepped-curves approximation of the harmonic function has
shown that the Fourier transform of a digital data set is equivalent to
superposed epoch analysis. The presence of trends in data is studied on
the basis of numerical models. The authors show that the 160.01 min line
(or period) in the power spectrum of the solar global oscillations
cannot be explained in terms of signal trends and low-frequency
filtering of data by the use of 2nd order polynomials.

---------------------------------------------------------
Title: Analogy between the method of superimposed epochs and the
Fourier transform. Effect of signal trend on highly-sampled data
processing
Authors: Abramenko, V. I.; Rachkovskii, D. N.
1983BCrAO..66...62A Altcode: 1985BCrAO..66...62A
No abstract at ADS

---------------------------------------------------------
Title: Quasi-periodic radioemission pulsations of the proton region
of the sun in July 1974 at wavelengths of 3.5, 2.5, and 1.9 CM
Authors: Abramenko, V. I.; Eriushev, N. N.; Tsvetkov, L. I.
1982IzKry..65...87A Altcode:
Observational data obtained at the Crimean Astrophysical Observatory
using the 22-m radiotelescope with the three-channel polarimeter are
analysed. These data are typical for preburst conditions in the local
sources during days with different levels of activity. A comparison
is made between calculated power spectra and spectral characteristics
of a rectangular impulse packet.

---------------------------------------------------------
Title: Quasi-periodic pulsations of the radio emission of a proton
region on the sun in July 1974 at 3.5, 2.5, and 1.9 cm
Authors: Abramenko, V. I.; Eryushev, N. N.; Tsvetkov, L. I.
1982BCrAO..65...80A Altcode: 1984BCrAO..65...80A; 1982BuCri..65...80A
No abstract at ADS

---------------------------------------------------------
Title: Computation of polarization parameters of systems by the
symbolic method
Authors: Rachkovskii, D. N.; Abramenko, V. I.; Tsvetkov, L. I.
1981BCrAO..63..205R Altcode: 1981BuCri..63..205R
No abstract at ADS

---------------------------------------------------------
Title: Computation of polarized characteristics of systems by the
symbolic method.
Authors: Rachkovskij, D. N.; Abramenko, V. I.; Tsvetkov, L. I.
1981IzKry..63..189R Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Quasi-periodic pulsations of radio emission of a proton region
on the sun in July 1974 at 3.5, 2.5 and 1.9 cm.
Authors: Abramenko, V. I.; Eryushev, N. N.; Tsvetkov, L. I.
1981riss.conf...28A Altcode:
No abstract at ADS

---------------------------------------------------------
Title: Radio emission from the central region of the Galaxy
(lII = 351-8 ) at 7700 MHz.
Authors: Abramenko, V. I.; Ipatov, A. V.; Lipovka, N. M.; Obolenskij,
A. K.
1974SoSAO..12...43A Altcode:
No abstract at ADS