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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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) > 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) < 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 <|jz|> 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 <|jz|> 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 <|j|> 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 2019MNRAS.484.4393K Altcode: 2019MNRAS.tmp..310K; 2018arXiv181112089K We use observations of line-of-sight magnetograms from Helioseismic and Magnetic Imager onboard of Solar Dynamics Observatory to investigate polarity separation, magnetic flux, flux emergence rate, twist and tilt of solar emerging active regions. Functional dependence of polarity separation and maximum magnetic flux of an active region is in agreement with a simple model of flux emergence as the result of buoyancy forces. Our investigation did not reveal any strong dependence of emergence rate on twist properties of active regions. Title: Preface Authors: Abramenko, V. I. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 (>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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (>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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 (<13 hours) interval Δ t2 and a high (>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 (>13 hours) interval Δ t2 and a low RN (<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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 <~ t <~ 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 (>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. Bibcode: 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. Bibcode: 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 (<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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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 Bibcode: 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 Bibcode: 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 , 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. Bibcode: 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 Bibcode: 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. Bibcode: 2010ApJ...714.1672K Altcode: We investigate the formation of isolated non-polar coronal holes (CHs) on the remnants of decaying active regions (ARs) at the minimum/early ascending phase of sunspot activity. We follow the evolution of four bipolar ARs and measure several parameters of their magnetic fields including total flux, imbalance, and compactness. As regions decay, their leading and following polarities exhibit different dissipation rates: loose polarity tends to dissipate faster than compact polarity. As a consequence, we see a gradual increase in flux imbalance inside a dissipating bipolar region, and later a formation of a CH in place of more compact magnetic flux. Out of four cases studied in detail, two CHs had formed at the following polarity of the decaying bipolar AR, and two CHs had developed in place of the leading polarity field. All four CHs contain a significant fraction of magnetic field of their corresponding AR. Using potential field extrapolation, we show that the magnetic field lines of these CHs were closed on the polar CH at the North, which at the time of the events was in imbalance with the polar CH at the South. This topology suggests that the observed phenomenon may play an important role in transformation of toroidal magnetic field to poloidal field, which is a key step in transitioning from an old solar cycle to a new one. The timing of this observed transition may indicate the end of solar cycle 23 and the beginning of cycle 24. Title: Formation of Coronal Holes on the Ashes of Active Regions Authors: Karachik, Nina; Pevtsov, A.; Abramenko, V. Bibcode: 2010AAS...21640104K Altcode: 2010BAAS...41..857K We investigate the formation of isolated non-polar coronal holes (CHs) on the remnants of decaying active regions. We follow the evolution of four bipolar active regions, and measure their total magnetic flux, imbalance, and compactness. As regions decay, their leading and following polarities exhibit different dissipation rate. As a consequence, we see a gradual increase in flux imbalance inside dissipating bipolar magnetic field, and later, a formation of a coronal hole at the site of more compact magnetic flux. Out of four cases studied in detail, two CHs had formed at the following polarity of decaying active regions, and two coronal holes had developed at the leading polarity field. Using potential field extrapolation we show that the magnetic field lines of these coronal holes were closed on polar coronal hole at the North, which at the time of the events was in imbalance with the polar coronal hole at the South. This topology suggests that the observed phenomenon may play an important role in transformation of toroidal magnetic field to poloidal field, which is a key step in transitioning from the old solar cycle to a new cycle. Title: Magnetic Energy Spectrum and Intermittency in Solar Active Regions of Different Flare Productivity Authors: Abramenko, Valentyna Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2010IAUS..264..210P Altcode: We present the observations of coronal hole that has originated at the polar hole in one hemisphere, extended to equatorial region, got disconnected and transported across the equator to polar region of opposite hemisphere. Title: Vorticity of Granular Flows from NST Observations Authors: Pevtsov, A. A.; Abramenko, V.; Yurchyshyn, V.; Goode, P. R. Bibcode: 2009AGUFMSH53B..04P Altcode: We use observations taken with the New Solar Telescope (NST) at Big Bear Solar Observatory, the world largest solar optical telescope with diffraction limited spatial resolution of 0.06 arc seconds, to study vorticity of granular flows in quiet Sun areas. We employ sequence of images observed with TiO (705.7 nm) filter with time cadence of 30 seconds. The atmospheric seeing effects were removed using speckle-reconstruction technique. We compare vorticity of granular flows and intergranular vortices, and discuss our findings in the framework of surface (turbulent) dynamo. Title: Turbulence in the solar photosphere as derived from NST observations of the granulation Authors: Abramenko, V. Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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 Bibcode: 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. Bibcode: 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 < jh > ~ (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 < 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 Bibcode: 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 Bibcode: 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 $<j_h > \sim (0.008 - 0.028)$ 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. Bibcode: 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. Bibcode: 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. Bibcode: 2008sprt.book...95A Altcode: No abstract at ADS Title: Do active regions emerge in a similar regime? Authors: Abramenko, Valentyna Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 2007ApJ...665.1460T Altcode: Using observations of more than 160 active regions, we investigate the relationship between the coronal X-ray brightness, LB, and five parameters derived from the photospheric magnetic fields. The coronal X-ray brightness and the magnetic measures were obtained from co-aligned SFD composite images from the Yohkoh SXT and full-disk magnetograms from the SOHO MDI, respectively. The magnetic parameters are (1) the length of strong-gradient magnetic neutral lines, LGNL, (2) the magnetic energy dissipation, ɛ, (3) the unsigned line-of-sight magnetic flux, Φ, (4) the horizontal velocities, Vh, of random footpoint motions in the photosphere, and (5) a proxy for the Poynting flux, E=(1/4π)VhBz2, which characterizes the energy flux from the photosphere into the corona due to random footpoint motions. All measures except Vh were analyzed in both the extensive (total) and intensive (average over an area) forms. In addition, we used the area-averaged strong gradient (>50 G) of the magnetic field, ∇Bz, as an intensive form of LGNL. We found that the Pearson correlation coefficient between the total X-ray brightness and the total magnetic measures decreases as 0.97, 0.88, 0.86, and 0.47 for Φ, E, ɛ, and LGNL, respectively. The correlation coefficient between the averaged X-ray brightness and the averaged magnetic measures varied as 0.67, 0.71, 0.57, and 0.49 for <Φ>, , <ɛ>, and <∇Bz>, respectively. We also found that the velocities of the footpoint motions have no dependencies with Φ and LB. We concluded that the observed high correlation between LB and E is mainly due to the magnetic field. The energy of the Poynting flux is in the range 106.7-107.6 ergs cm-2 s-1 for the majority of active regions, which is sufficient to heat the corona due to footpoint random motions of magnetic flux tubes. Title: Magnetic Dissipation in the Photosphere and Heating of the Corona Authors: Abramenko, Valentyna; Pevtsov, A. Bibcode: 2007AAS...210.5301A Altcode: 2007BAAS...39..164A Spatio-temporal dynamics of magnetic flux tubes in the photosphere of the Sun is thought to be a driving mechanism for energy built-up and energy release phenomena in the solar atmosphere. Turbulent flows in the photosphere braid and intertwine magnetic flux tubes creating a complex topology of the magnetic field in the corona which might result in the coronal heating. Intensity of turbulent flows of the magnetic flux tubes in the photosphere can be quantified by the magnetic energy dissipation rate, which is proportional to the averaged transverse velocity increment of the magnetic flux tubes. We suggest to derive 2D magnetic energy dissipation structures from line-of-sight magnetograms of active regions and then calculate the dissipation rate. Our findings for 104 active regions showed that the magnetic dissipation rate is in a good agreement (with the correlation coefficient close to 0.7) with the temperature and the emission measure of the corona. Our results present strong observational support for those coronal heating models that rely on random footpoint motions as an energy source to heat the corona above active regions. Title: 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. Bibcode: 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. Bibcode: 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 > 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'' (ApJ, 644, 1273 [2006]) Authors: Jing, Ju; Song, Hui; Abramenko, Valentyna; Tan, Changyi; Wang, Haimin Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 2006SoPh..237..267M Altcode: 2006SoPh..tmp...14M We report here on the present state-of-the-art in algorithms used for resolving the 180° ambiguity in solar vector magnetic field measurements. With present observations and techniques, some assumption must be made about the solar magnetic field in order to resolve this ambiguity. Our focus is the application of numerous existing algorithms to test data for which the correct answer is known. In this context, we compare the algorithms quantitatively and seek to understand where each succeeds, where it fails, and why. We have considered five basic approaches: comparing the observed field to a reference field or direction, minimizing the vertical gradient of the magnetic pressure, minimizing the vertical current density, minimizing some approximation to the total current density, and minimizing some approximation to the field's divergence. Of the automated methods requiring no human intervention, those which minimize the square of the vertical current density in conjunction with an approximation for the vanishing divergence of the magnetic field show the most promise. Title: Coronal Heating and Photospheric Turbulence Parameters: Observational Aspects Authors: Abramenko, V. I.; Pevtsov, A. A.; Romano, P. Bibcode: 2006ApJ...646L..81A Altcode: In this study, the soft X-ray luminosity of the solar corona, measured by the Yohkoh spacecraft for 104 well-developed and decaying active regions, is compared to the magnetic field parameters determined from SOHO MDI high-resolution magnetograms. We calculate and compare (1) two area-independent characteristics of the magnetic field: the index (α) of the magnetic power spectrum, E(k)~k, 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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, 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>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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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>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. Bibcode: 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 Bibcode: 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. Bibcode: 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 < F < 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 > 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 Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 > 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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 < 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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<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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 >= 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Topology in November 5, 1998 Two-Ribbon Flare as Inferred from Ground-Based Observations and Linear Force-Free Field Modeling Authors: Yurchyshyn, V.; Wang, H.; Qiu, J.; Goode, P. R.; Abramenko, V. I. Bibcode: 2000ESASP.463..463Y Altcode: 2000sctc.proc..463Y No abstract at ADS Title: Magnetic Power Spectra in the Solar Photosphere derived from Ground and Space based Observations Authors: Abramenko, V.; Yurchyshyn, V. B. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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&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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 < 0) in the northern hemisphere and positive (ρh > 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1986psf..conf...32A Altcode: No abstract at ADS Title: The accuracy of potential field restoration using the Neumann problem. Authors: Abramenko, V. I. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1974SoSAO..12...43A Altcode: No abstract at ADS