The characteristics of solar cycles important for the development of dynamo theory can manifest themselves differently when different activity indices are used. To study the features of the north–south (N–S) asymmetry of solar activity, a comparison was made of the time profiles of active regions (ARs) of the 23rd and 24th cycles based on data on their number (the most accessible and frequently used) and magnetic flux (allowing a more complete assessment about the generative function of the dynamo process). We used data on 3047 ARs that appeared on the disk from June 1996 to December 2020 according to the MMC ARs CrAO (magneto-morphological classification of ARs of the Crimean Astrophysical Observatory) catalog ( http://sun.crao.ru/databases/catalog-mmc-ars ). The attribution of AR to the classes of the regular and irregular sunspot groups was taken into account in accordance with the MMC ARs CrAO. Analysis of the results showed the following. Variations of ARs of both MMC classes are associated with a cycle, which confirms their relationship with the action of the global dynamo. Due to the overlap of multipeak ARs profiles of different classes, a classic double-peak cycle structure is formed in the two hemispheres. Variations in the relative position of profiles for the number and magnetic flux of ARs (for groups of each class in each hemisphere) during the cycle can be associated with changes in the sizes of ARs. This makes it possible to suggest the multicomponent nature of the dynamo process, which consists in joint manifestation of global (responsible for the production of ARs) and turbulent (associated with the fragmentation of magnetic structures due to turbulence in the convection zone) components of the dynamo. The strongest magnetic fluxes observed for the irregular groups in the maximum of the cycle may also indicate action of the turbulent component of the dynamo distorting the regular flux tube. The pronounced N–S asymmetry of these fluxes agrees with the hypothesis on the possibility of weakening of the toroidal field in one of the hemispheres due to the interaction of the dipole and quadrupole components.

Vector-magnetograms acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) were utilized to explore the spatial correlation functions of the dissipative structures, such as the vertical magnetic field dissipation, Ediss, the squared density of the vertical electric current, J_z^2 , the current helicity density, Hc. Six mature active regions (ARs) were explored, three of them belong to the magneto-morphological class (MMC) A1—regular ARs that follow the empirical rules of the Babcock-Leighton dynamo theory, and the rest three ARs belong to the MMC B3 class, irregular multipolar ARs. We found that, on the contrary to the vertical magnetic field structures (see (Abramenko, Suleymanova 2024)), all considered here dissipative structures reveal a range of the power law in the correlation function. Parameters of the power law vary significantly for different types of the considered structures and for different ARs of different classes. The most pronounced difference in the power law parameters between the AR’s classes was found for both J_z^2 and Hc: the B3-class ARs demonstrate a capability for longer correlations and shallower power law slope than the A1-class ARs do. As soon as the power law correlation function is thought to indicate the self-organized criticality (SOC) state, we might conclude that in the photosphere, the SOC is rather observable in the magnetic dissipative structures, than in the magnetic field itself; a signature of SOC seems to be stronger manifested in the complex irregular B3-class ARs with high flaring activity. The proposed approach can facilitate to find a connection between the photosphere and upper layers in setting up the critical state, which is necessary for eruptions of all scales.

The solar dynamo generates a toroidal magnetic field that, forms active regions (ARs) on the surface of the Sun. The toroidal magnetic field lines rise through the turbulent convection zone, where distortions, deformation of already formed regular toroidal magnetic flux bundles and the formation of irregular, complex magnetic structures are possible. At the minimum of solar activity, the toroidal magnetic field of the old cycle disappears and the magnetic field of the new cycle is still very weak. During this period, it is possible to assess the role of the turbulence in the formation of an AR. In this paper, we analyzed ARs of two solar activity minima (between cycles 23–24 and between cycles 24–25). We analyzed ARs located within 60° from central meridian and exhibiting magnetic flux at the maximum development of at least 10 21 Mx. Bipolar and multipolar ARs were divided into regular ones (consistent with the mean-field dynamo theory) and irregular ones, the formation of which was influenced by the turbulence of the convection zone (unipolar spots were considered separately). It was found that regular ARs significantly predominate during solar minima, their magnetic flux is a half or more of the total magnetic flux (0.6 for the first period, 0.5 for the second period). Irregular ARs are fewer in number than regular ones, and in terms of magnetic flux they make up about one-third of the total magnetic flux (0.3 and 0.2 in the first and second periods, respectively). Irregular ARs are predominantly represented by bipolar structures of improper orientation, while very complex multipolar ARs are extremely rare. It is concluded that the generation of ARs with the magnetic flux exceeding 10 21 Mx occurs due to the global dynamo action, while the turbulence of the convection zone causes deformation of the magnetic flux bundles without significant magnetic flux generation.

We use the CrAO catalog of the magneto-morphological classes (MMC) of active regions (ARs) to study the hemispheric distribution of the number and magnetic fluxes of ARs that appeared on the disk from May 1996 to December 2021. 3047 ARs were distributed between classes of the regular (bipolar groups that obey empiric rules for sunspots) and irregular (all the rest, except for unipolar sunspots) ARs. The analysis of the results showed that all the trends are more pronounced in the flux data. For the irregular ARs, the strongest peaks in time profiles are observed in the second maximum of the cycle in the S-hemisphere. ARs of both MMC types demonstrate noticeable N-S asymmetry. The most abrupt changes are shown by the irregular ARs fluxes. For the compiled quadrupolar-like component of the flux, the evidence of oscillations with a period of about 15 years is found for all studied ARs and for the irregular groups. For the regular ARs, cross-correlation of ARs fluxes in different hemispheres in adjacent cycles showed no features. For the irregular groups, a high correspondence in flux dynamics in the N-hemisphere of cycle 23 and in the S-hemisphere of cycle 24 is found.

The Spectro-Polarimeter (SP) is a new instrument installed at the upgraded Andrei B. Severny Solar Tower Telescope (STT) at the Crimean Astrophysical Observatory. The instrument is a traditional echelle slit dual-beam spectropolarimeter with temporal modulation of the polarization. STT-SP provides simultaneous spectropolarimetric observations of the Sun within three 15 Angstrom wide spectral ranges around photospheric Fe I 5250, Fe I 5324, and chromospheric Mg I b2 5172 spectral lines. The spectral resolution of the instrument reaches 70,000 with the seeing-constrained slit width of 1 arcsec. The field-of-view of STT-SP is 200 arcsec allowing one to map a moderate size active region within a single raster scan. The instrument will provide new opportunities in the analysis of magnetic fields and thermodynamics of the lower atmosphere of the Sun. In this paper we describe the optical design of STT-SP and present the preliminary results acquired during the commissioning of the instrument.

We used magnetograms acquired with the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to calculate and analyze spatial correlation functions and the multifractal spectra in solar active regions (ARs). The analysis was performed for two very different types of ARs: i) simple bipolar magnetic structures with regular orientation (the magnetomorphological class A1), and ii) very complex multipolar ARs (the magnetomorphological class B3). All ARs were explored at the developed phase during flareless periods. For correlation functions, the power-law and exponential approximations were calculated and compared. It was found that the exponential law holds for the correlation functions of both types of ARs within spatial scales of 1 – 36 Mm, while the power law failed to approximate the observed correlation functions. The property of multifractality was found in all ARs, being more pronounced for the complex B3-class ARs. Our results might imply that the photospheric magnetic field of an AR is a self-organized system, which, however, does not exhibit properties of self-organized criticality (SOC), and its fractal properties are an attribute of a broader (than SOC only) class of nonlinear systems.

We explore the properties and behavior of slow-decaying unipolar sunspot groups in the framework of the turbulent erosion model suggested by Petrovay and Moreno-Insertis (Astrophys. J. 485, 398, 1997). The basic concept of the model is the suppression of turbulent diffusivity inside a magnetic flux tube by strong magnetic fields. As a result, the outer turbulent plasma detaches magnetic features primarily from the external border of a magnetic flux tube. The radius of the tube exhibits inward progression at a constant rate. The model predicts older sunspots to decay slower, and it seems to be very promising to explain the slow decay of long-living unipolar sunspot groups. By analyzing the magnetic structure associated with a sunspot, we did reveal a gradual decrease in the magnetic structure radius at a constant rate, implying the validity of the model. However, in some cases, the derived velocity of the radius decrease was too low: our calculations provided implausibly high estimations for the lifetime and maximal area of such sunspots. We discuss possible additional mechanisms affecting the decay rate of such peculiar sunspots.

Numerous observations show that the rotation rates of active regions (ARs) across the solar disk are higher than those of the local plasma at the surface. This discrepancy is often interpreted as the presence of some “magnetic roots” that are located in faster‑rotating layers of the convection zone and which determine the rotation rate of ARs. This hypothesis may indicate the depth of the generation of a magnetic bundle forming an AR. In the present paper, we analyzed the rotation of anti‑Hale ARs across the solar disk. For the analysis, we used full‑disk line‑of‑sight magnetograms acquired by SDO/HMI. The Crimean catalog of bipolar ARs violating the Hale polarity law for 1989–2018 was used as a list of bipolar reversed polarity groups. In total, the rotation rates of 44 active regions observed between 2010 and 2018 were measured. In order to compare the obtained rotation rates of anti‑Hale ARs with those of the rest ARs, we performed a statistical test χ 2 of both distributions. The test showed these distributions to be statistically indistinguishable. These results suggest that, if the rooting hypothesis is correct, anti-Hale ARs and other ARs are formed within the same depths in the convection zone and there is no reason to suggest a separate mechanism for the formation of anti-Hale ARs.

Polar coronal holes are large-scale configurations with open magnetic fields on the surface of the Sun. They are most active during the period of minimum solar activity and almost disappear during the period of maximum solar activity. We present the evolution of two coronal holes that were observed during the polarity reversal of cycle 23. Data were taken from SOHO/MDI/fd and SOHO/EIT/284 Å. These coronal holes had the polarity of the next, 24th, cycle. Instead of localization at the pole, in both cases, the propagation of coronal holes to the opposite hemisphere was observed. Thus, the open magnetic fields actively interacted with the toroidal magnetic field of the active regions during the polarity reversal period.

Systematic studies of the rotation rate of sunspot groups using white-light images yield controversial results on the variations of the rotation rate: sunspot groups were found to either accelerate or decelerate systematically. This disagreement might be related to shortcomings of the method used to probe the rotation rate of sunspot groups. In contrast to previous works, in this study we use magnetic field maps to analyse the variations of the rotation rate of active regions. We found that an active region may exhibit either acceleration or deceleration during the emergence while the rotation rate remains almost unchanged during decay. Hence, we suppose that there is no systematic geometrical inclination to the radial direction of the apex of the subsurface magnetic flux loop forming an active region. A thorough comparison of the rotation rate of unipolar and bi/multipolar active regions revealed no significant changes in the rotation rate of decaying active regions. In contrast to previous works, we presume the rotation rate to keep constant (within the expected uncertainties) during the evolution of an active region after emergence.

ABSTRACT We used line-of-sight magnetograms acquired by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory to derive the decay rate of total unsigned magnetic flux for 910 ephemeral and active regions (ARs) observed between 2010 and 2017. We found that (i) most of the ARs obey the power law dependence between the peak magnetic flux and the magnetic flux decay rate, DR, so that DR ∼ Φ0.70; (ii) larger ARs lose smaller fraction of their magnetic flux per unit of time than the smaller ARs; (iii) there exists a cluster of ARs exhibiting significantly lower decay rate than it would follow from the power law and all of them are unipolar sunspots with total fluxes in the narrow range of (2–8) × 1021 Mx; and (iv) a comparison with our previous results shows that the emergence rate is always higher than the decay rate. The emergence rate follows a power law with a shallower slope than the slope of the decay-rate power law. The results allowed us to suggest that not only the maximum total magnetic flux determines the character of the decaying regime of the AR, some of the ARs end up as a slowly decaying unipolar sunspot; there should be certain physical mechanisms to stabilize such a sunspot.

We used the elaborated earlier catalog of the magneto-morphological classes (MMC) of active regions (ARs) to study 2046 ARs of the solar cycle (SC) 23 and 1507 ARs of the SC24. According to empiric rules for sunspot groups (Hale's polarity law, Joy's law, etc.) and MMC, all ARs (except for unipolar spots) were sorted out between two categories: A-type - regular bipolar ARs; B-type - all the rest irregular ARs. We found that the number of both regular and irregular ARs follows the cycle with the Pearson's correlation coefficient of 0.92 and 0.78, respectively. The regular ARs are distributed evenly between the two maxima of each cycle. The irregular ARs are also distributed evenly between the two maxima in the SC 23, however their number is enhanced in the second maximum of the SC 24. Both regular and irregular ARs exhibit strong north-south (N-S) asymmetry. The significance of asymmetry is confirmed using the Pearson's v-square test and one more test based on the normal approximation to a binomial distribution. During the two maxima of a cycle, the peaks in two hemispheres for both regular and irregular ARs number do not vary synchronously. This can be explained by the fluctu-ations in Babcock-Leighton mechanism. In general, there are more irregular ARs in the S-hemisphere in both cycles, which might be the result of an additional weakening of the toroidal field due to interplay between the dipole and quadrupole components of the global magnetic field. (c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.

— This study is devoted to the interplay between the global dynamo and small-scale dynamo and their mutual manifestations in the solar cycle. The cyclic variations of active regions violating the Hale’s Polarity Law (anti-Hale ARs) from 1989 to 2020 are investigated. Synthetic cycle data (14 838 sunspot groups from solar cycles 16–18, 23, and 24, including 367 anti-Hale ARs) are also used to improve the statistics. The temporal variations in the number and area of the anti-Hale groups are found to be synchronous with the cycle, which indicates their intrinsic connection to the global dynamo. During the second maximum of the cycle, the number of anti-Hale ARs is greater than during the first maximum. This can be due to the loss of regularity of the toroidal field and the possible interference of the small-scale dynamo. In the ascending phase and during the cycle maximum (when the toroidal field is strong), the relative number of anti-Hale groups is almost constant. During spatiotemporal intervals of the weakened toroidal field on the butterfly diagram, the global dynamo action is less pronounced and the role of the small-scale dynamo in their interplay is more significant. The weak tendency for the fraction of anti-Hale ARs to increase as the cycle progresses and activity is approaching the equator can indicate the presence of obstacles to dynamo-wave propagation and be related to the α-quenching known from mean-field dynamo theory.

In the present work, we compared the areas of anti-Hale active regions (ARs) with the areas of rest ARs.For this analysis, we used monthly averages USAF/NOAA data of the sunspot areas in units of millionths of a hemisphere as well as a catalog of bipolar active regions violating the Hale polarity law for 1989-2018.In all, 143 anti-Hale ARs observed between February 1996 and August 2018 (Solar Cycles 23 and 24) were selected.The comparison showed that the areas of anti-Hale and other ARs change synchronously with strong positive correlation.This fact allows us to presume the anti-Hale and rest ARs to be generated as a result of a unified dynamo process with an 11-year cyclicity.

В работе описываются результаты наблюдений Солнца с высоким временным и пространственным разрешением на Башенном солнечном телескопе им. А.Б. Северного КрАО РАН (БСТ-1), которые проводились в октябре и ноябре 2021 г. При наблюдениях с Земли пространственное разрешение оптических телескопов ограничено атмосферой, которое можно увеличить путем математической обработки сотен изображений объекта, сделанных с короткой экспозицией. Для получения данных оптическая схема БСТ-1 была дополнена камерой и быстрым детектором, позволяющим получать десятки изображений поверхности Солнца в секунду, а также воспользоваться программными пакетами для спекл-реконструкции астрономических наблюдений. Детальное визуальное изучение полученных изображений и их сравнение с данными космической обсерватории SDO/HMI показали обнадеживающие результаты. На восстановленных кадрах надежно разрешаются гранулы и видна тонкая структура солнечных пятен. Наблюдения с высоким пространственным разрешением на БСТ-1 открывают новые возможности для исследования Солнца.

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.

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.

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 percent 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-year 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 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.

Data for 3046 solar active regions (ARs) observed since 1996 May 12 to 2021 December 27 were utilized to explore how the magnetic fluxes from ARs of different complexity follow the solar cycle. Magnetograms from the Michelson Doppler Imager instrument on the Solar and Heliospheric Observatory and from the Helioseismic and Magnetic Imager instrument on the Solar Dynamics Observatory were utilized. Each AR was classified as a regular bipolar AR (classes A1 or A2), or as an irregular bipolar AR (class B1), or as a multipolar AR (classes B2 or B3). Unipolar ARs were segregated into a specific class U. We found the following results. Unsigned magnetic fluxes from ARs of different classes evolve synchronously following the cycle, the correlation coefficient between the flux curves varies in a range of 0.70-0.99. The deepest solar minimum is observed simultaneously for all classes. Only the most simple ARs were observed during a deepest minimum: A1- and B1-class ARs. The overall shape of a cycle is governed by the regular ARs, whereas the fine structure of a solar maximum is determined by the most complex irregular ARs. Approximately equal amount of flux (45-50 percent of the total flux) is contributed by the A-class and B-class ARs during a solar maximum. Thus, observations allow us to conclude that the appearance of ARs with the magnetic flux above 10(21) Mx is caused by the solar dynamo that operates as a unique process displaying the properties of a non-linear dynamical dissipative system with a cyclic behaviour and unavoidable fluctuations.

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.