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The Wang–Shelley–Arge (WSA) solar wind (SW) model is based on the idea that weakly expanding coronal magnetic field tubes are associated with fast SW sources and vice versa. The Flux-Tube Expansion factor (FTE) is used to determine the degree of expansion of magnetic tubes. The FTE is calculated based on a model of the coronal magnetic field, usually in the potential approximation. The second input parameter of the WSA model is the distance from the base of the magnetic tube on the photosphere to the boundary of the corresponding coronal hole (Distance to the Coronal Hole Boundary, DCHB). These two parameters of the coronal magnetic field are related empirically to the speed of the solar wind near the Sun. The WSA model has shortcomings and does not fully explain the mechanisms of SW formation. This paper presents an analysis of the degree of correlation of various parameters of the magnetic field (length of field lines, latitude of the base of field lines, etc.) with the observed velocity SW. The parameters are calculated in potential (PFSS) and nonpotential approximations based on three synoptic series of magnetographic observations: the Kislovodsk Solar Telescope for Operative Predictions (STOP), SDO/HMI, and WSO. We found that the FTE correlates relatively weakly with solar wind speed, in contrast to field line lengths and DCHB. We propose an alternative relation to the WSA model that relates the length of field lines, the DCHB, and the amplitude of the magnetic field at the source surface with the velocity SW. The presented relationship is not based on the FTE and shows a better correlation with observations compared to the WSA model. We also optimized the formula in the WSA model for the STOP magnetograph. [ABSTRACT FROM AUTHOR]

This paper presents a procedure for reconstructing the longitudinal magnetic field from observational data of the complete profile of spectral magnetic lines. The method is based on a fast search algorithm for curve fitting for complete profiles of magnetically sensitive lines 6301.5 Å and 6302.5 Å. The magnetic field is calculated as the distance between the centers of the I-profiles of different polarization components. The centers are defined as the midpoints of the Gaussians approximating the I + V, I – V profiles. This approach makes it possible to carry out calculations rather quickly. The presented method makes it possible to reduce the noise in maps of a large-scale magnetic field and improve the accuracy of measurements, primarily of weak fields. The method has been tested to reconstruct the large-scale magnetic field from observations with the STOP full-disk magnetograph telescope (Kislovodsk) in 2014–2022. [ABSTRACT FROM AUTHOR]

The lifetime of individual solar pores and sunspots is analyzed according to the data of the HMI/SDO space observatory observations in the 24th and 25th activity cycles. It is found that the lifetime of individual sunspots and pores T differs from the Gnevyshev–Waldmeier rule formulated for groups of sunspots. For regular sunspots, that is, spots with nuclei, there is a linear dependence on the maximum area Smx: Tsp = –0.019(±0.2) + 0.027(±0.002)Smx. For solar pores, the dependence of the lifetime on the area has a logarithmic form Tpor = –0.24(±0.1) + 0.055(±0.014) log(Smx). Possible mechanisms of disintegration of spots and pores are studied. The lifetime for regular spots is probably related to convective currents. It has been established that the average velocity of the matter flow, determined from observations of Doppler velocities, increases with a decrease in the area of sunspots. This can accelerate the decay rate of sunspots with a decrease in the area of sunspots. For solar pores, the lifetime can be determined by the heating mechanism. [ABSTRACT FROM AUTHOR]

Based on the method of averaging the shape of sunspots identified in the HMI/SDO images in the 2010–2022 period, an analysis was made of the relative position of sunspot nuclei during their passage across the solar disk. To do this, in different ranges of sunspot areas, we constructed averaged boundaries of the photosphere-penumbra and the core-penumbra. We then tracked changes in sunspot shape at various distances from the center of the disk in the eastern and western hemispheres. A shift of the boundary of sunspot nuclei to the western edge of the sunspot has been observed. The relative value of the shift increases with the area of sunspots. We estimated the value of the Wilson depression for sunspots of various sizes. The magnitude of the depression varies from 100 km for small sunspots to 1000 km for large sunspots. There is some imbalance of the Wilson depression near the eastern and western boundaries of the core-penumbra, depending on the area of the sunspots and their latitude. [ABSTRACT FROM AUTHOR]

The possibilities for organizing a solar activity observation service for space weather forecasting are considered. At this stage, the most promising approach is the establishment of a ground-based observation network. This network should include solar magnetographs for observing large-scale magnetic fields of the Sun and patrol optical telescopes for detecting coronal mass ejections and solar flares. Magnetographic observations provide data for assessing recurrent solar wind streams. Patrol telescopes operating in continuous mode make it possible to detect eruptive moments and determine parameters of coronal mass ejections at the initial stage. The network can be complemented by other types of observations in radio and optical bands. The article discusses the composition of observation tools as well as methods and models of forecasting. [ABSTRACT FROM AUTHOR]

This paper analyzes the observations of an original spectroheliograph telescope installed at the Kislovodsk Mountain Astronomical Station of the GAO RAS. The telescope is intended for continuous observation of the activity of the solar chromosphere. The tool makes it possible to register the full profile of the H-alpha spectral line in each pixel of the solar disk with a frequency of approximately 1 minute. We analyzed observational data from September 2015 to July 2020 and found downdrafts with average velocities Vav is approximately 0.5 km/s. The flows are directed predominantly downwards with a small horizontal component. The properties of the streams do not significantly depend on the phase of the solar cycle, the area, or the relative brightness of active regions. We assume that these streams can influence the speed of the solar wind over active regions. [ABSTRACT FROM AUTHOR]

In this paper, we performed an analysis of the areas of sunspot groups of various classes according to the Zurich group classification. To do this, observations of sunspots at the Locarno Observatory (Locarno, Switzerland) for 21–24 activity cycles were digitized. In the Zurich classification of sunspot groups, there are classes from A to J. The classes correspond to the process of development and decay of sunspot groups. We combined the Locarno data with the measurements of the areas of sunspot groups performed at the Kislovodsk mountain astronomical station of the GAO RAS. Average areas were obtained for groups of different classes. In counting the number of sunspot groups, the contribution of groups of classes A and B, consisting of pores, is 34% and only 5.1% in the total area. It is shown that groups of classes A + B form a separate distribution of areas from groups of other classes. The areas separately of class A and class B, in turn, are also divided into two independent distributions. This indicates different physical mechanisms for the formation of pores and regular spots. The H + J unipolar sunspots make up ~19% of the total sunspot area, and the H and J classes can be described by a single distribution. [ABSTRACT FROM AUTHOR]

The paper presents an analysis of a series of observations of the full H-alpha line profile in the solar chromosphere. The analysis is based on data from the spectroheliograph patrol telescope developed at the Kislovodsk Mountain Astronomical Station, which has been in operation since 2015. The telescope conducts continuous observations with a scanning time of the entire solar disk of about 1 min. The problem of measurement of the parameters of the H-alpha line with various methods of profile approximation is considered. The possibility of determining the Doppler shift in the H-alpha line with the use of a convolutional, artificial neural network has been studied. Also considered are the characteristic forms of the H-alpha profile in active regions of the Sun and the evolution of the line profile and Doppler velocities during the formation of a solar flare on the example of an X-class flare. [ABSTRACT FROM AUTHOR]

In this paper we studied long-term variations in the areas of coronal holes (CHs) reconstructed on the basis of synoptic Hα charts for the period 1887–2016 and occurrences of magnetic storms with gradual commencements. It was found that the temporal variations in mean yearly values of the CH areas in the northern and southern hemispheres are characterized by a pronounced ∼11-year periodicity, but they differ markedly on a multidecadal time scale. The wavelet spectra of the CH areas in the southern hemisphere, unlike those of the northern one, demonstrate persistent periodicities of ∼30–35 years, which are also observed in geomagnetic activity and climatic characteristics. The results of cross-wavelet analysis revealed a link between annual occurrences of magnetic storms with gradual commencements and variations in CH areas in both hemispheres. The obtained results allow us to conclude that the evolution of solar coronal holes may be considered as a possible factor of the formation of multidecadal cycles in geomagnetic activity, as well as climatic cycles. [ABSTRACT FROM AUTHOR]

The results of long-term mesoscale observations in the microwave range are reviewed. The rationale for the resumption of observations at the Havana Radio Astronomy Station is justified. Domestic observations at a wavelength of λ5 cm have a long observation interval and can effectively complement the global series of observations. A comparative analysis of the results of solar observation in the radio range and satellite observations in the UV and X-ray range is performed. The value of continuous observations for the assessment of space weather factors is shown. [ABSTRACT FROM AUTHOR]

Polar and low-latitude faculae were identified in daily images based on white-light observations from the MDI (1996–2011) and SOHO (2010–2019) space observatories. The boundaries of the faculae were combined with magnetic field observations at the closest possible instant of observation. The time and latitude distributions, as well as other properties of polar and low-latitude faculae, were analyzed. The resulting data on polar faculae were supplemented with observational data from Mitaka Observatory (Japan) for the period of 1951–1999. Thus, we compiled a summary series of polar activity for the period of 1951–2019. The distributions of polar faculae by area and magnetic field intensity are considered. The maximum distribution of the facula area at latitudes above θ > 55° occurs at values of approximately 6–10 mhs. The magnetic field of polar faculae has a maximum of B ~ 70–100 G. The amplitude of polar activity at the minimum in the 25th cycle approximately matches the amplitude in the 24th cycle. It can be expected that the amplitude of the sunspot activity cycle will be close to that of cycle 24. [ABSTRACT FROM AUTHOR]

Data from observations of the photospheric magnetic field at a number of ground stations (STOP, WSO, GONG) and by the SDO/HMI satellite for 2014–2019 are examined in terms of the accuracy of the model calculations of the speed of calm solar wind and the areas of coronal holes obtained on their basis. A high positive correlation was found (R > 0.5) between the simulation results and satellite observations (ACE, SDO/AIA193) for separate time periods. The best results in the modeling of the speed of the calm solar wind are given by the data from the ground stations WSO and STOP (Kislovodsk Mountain Astronomical Station, 2014). The temporal variability of the empirical coefficients of the model used in the forecasts was determined. [ABSTRACT FROM AUTHOR]

The solar activity at different latitudes is analyzed based on daily observations at Kodaikanal, Mount Wilson, Sacramento Peak, and Meudon observatories in the CaIIK line. Activity elements of various sizes, from the elements of the chromospheric network to the flocculi, are identified. A joint database of observation results that provides information on solar activity for 1905–2018 is created. Bright elements at middle and high latitudes are distinguished in the CaIIK line in daily images, in addition to the low-latitude activity that accompanies the appearance of sunspots. The activity can be represented as a single process that begins at high latitudes during the decline phase of the previous solar cycle and continues at low latitudes as sunspot activity. The activity-drift pattern is studied for Cycles 14–24. It is more consistent with the hypothesis of an extended solar cycle than the concept of two activity waves from the midlatitudes to poles and equator obtained from the processing of faculae in white light. [ABSTRACT FROM AUTHOR]

A comparative analysis of the drift velocity of high-latitude prominences to the poles in solar cycles 13–24 is carried out. Data on the positions of prominences on weather maps from Wolfer (1887–1899) and (1904–1915) are used for the analysis. The data from digitized photographic plates with solar prominences obtained in the CaIIK line of the Kodaikanal Solar Observatory (India) for 1907–1956 are also used. These data are supplemented with daily observations of the prominences at Kislovodsk Mountain Astronomical Station (1957–2018). The dependence of the drift velocity of polar-crown prominences on the solar cycle strength is different for the northern and southern hemispheres. The drift velocity tends to decrease with increasing solar activity. This may be due to the fact that a strong large-scale magnetic field is observed at high latitudes before strong solar cycles. Its displacement rate, which is traced by the drift of polar prominences, then slows with the development of a cycle with an increasing polar field. [ABSTRACT FROM AUTHOR]

A comparative analysis of sunspot sizes in sunspot groups was performed. For this analysis, we used the database of characteristics of individual sunspots and pores according to observations at the Kislovodsk Mountain Astronomical Station (KMAS) and the photoheliographic data from the Debrecen Heliographical Observatory, Hungary (DPD). We found agreement in the full area index for sunspot groups. However, in the DPD data for 1974–2018, the number of groups is ~50% higher than that for the KMAS data. The difference is that there are a large number of groups in the DPD data with an area of 1 mdp or less. We also found a significant difference in the properties of spots and pores of different types within the group. A significant difference in the distribution pattern of the sunspot area, which is the largest in the group Smax and other spots Snomax, was detected. There are two local maxima, ~ 8–10 mdp and ~ 130–180 mdp, in the area distribution of the largest sunspot Smax in the group. The first maximum is associated with the existence of pores and transition spots in which the penumbra is at the formation stage. The second maximum Smax in the distribution is associated with the existence of regular spots. For the remaining spots Snomax in the group, the area distribution function monotonically decreases with increasing area. [ABSTRACT FROM AUTHOR]

Abstract: The paper presents a study of the evolution of the photospheric magnetic field of active regions (ARs) of the Sun in which flares (larger than the M9 class in the Geostationary Operational Environmental Satellite (GOES) X-ray classification) occurred in 2010-2017. The purpose of this paper is to detect the precursors of flares. Thirteen ARs at a distance of not more than 45 degrees from the central meridian are selected for analysis out of 31 ARs in which flares larger than M9.0 were detected in the specified period. The magnetographic characteristics of the selected ARs are studied based on the Solar Dynamics Observatory (SDO) data. A flare index is proposed. It is calculated from the data of the Helioseismic and Magnetic Imager of SDO (SDO/HMI) and reflects the distance between regions of opposite magnetic polarity computed between the field boundaries by the threshold value. The analysis showed that a sharp increase in the flare index is detected in all the studied ARs 2-3 days before large flares. Flares larger than the M9.0 class occurred 5-20 h after the global or local maximum of the flare index. It is shown using the example of individual events that regions of the opposite polarity first converged and then relatively quickly separated from each other before large flares. The revealed features of evolution of ARs before large flares can be used to develop methods for predicting them. [ABSTRACT FROM AUTHOR]

Abstract: The properties of solar bipoles based on data from magnetic field observations at Mount Wilson Observatory during the period of 1917-2016 are considered. Special attention is given to variations in the size of the bipole magnetic axis during the solar cycle. It is shown that the distribution of the length of the bipole magnetic axis is close to lognormal with the exception of secondary local peaks. Secondary peaks are also present in the distribution of the tilt angles of bipoles at different latitudes. The influence of matter flows in supergranules on the length of the magnetic axis and the tilt angles of sunspot bipoles is discussed. [ABSTRACT FROM AUTHOR]

Abstract: The results of the digitalization of the centennial series of solar activity are considered. The data contain information on sunspots since 1918, sunspot umbra since 1917, plages since 1907, and spectral corona since 1939. In particular the digitalization of prominences from the observations in the Ca II K line in 1910-1954 and solar filaments from the observations in the H-alpha line in 1912-2002 acquired at the Kodaikanal Observatory are described. The methods of constructing composite maps of solar activity and presenting the resulting data series on the Internet are described. The long-term variations in solar activity are analyzed. [ABSTRACT FROM AUTHOR]

We present a model for the propagation of coronal mass ejections (CMEs) based on the interaction of CMEs with the solar wind through aerodynamic drag. The parameters of the solar wind are calculated based on observational data of the STOP magnetograph. The CME parameters, namely, the velocity vector and the estimated density at the initial stage of propagation, can be determined from the data of patrol telescopes. In the model, we consider a CME in the form of a cloud, represented by a set of points, and we track the trajectory of the motion of each point in the heliosphere. The simulation data can be used to estimate the geoefficiency of coronal mass ejections. [ABSTRACT FROM AUTHOR]

This paper continues the cycle of authors’ works on the detection of precursors of large flares (M5 and higher classes) in active regions (ARs) of the Sun by their microwave radiation and magnetographic characteristics. Generalization of the detected precursors of strong flares can be used to develop methods for their prediction. This paper presents an analysis of the development of NOAA AR 12242, in which an X1.8 flare occurred on December 20, 2014. The analysis is based on regular multiazimuth and multiwavelength observations with the RATAN-600 radio telescope in the range 1.65-10 cm with intensity and circular polarization analysis and data from the Solar Dynamics Observatory (SDO). It was found that a new component appeared in the AR microwave radiation two days before the X-flare. It became dominant in the AR the day before the flare and significantly decreased after the flare. The use of multiazimuth observations from RATAN-600 and observations at 1.76 cm from the Nobeyama Radioheliograph made it possible to identify the radio source that appeared before the X-flare with the site of the closest convergence of opposite polarity fields near the neutral line in the AR. It was established that the X-flare occurred 20 h after the total gradient of the magnetic field of the entire region calculated from SDO/HMI data reached its maximum value. Analysis of the evolution of the microwave source that appeared before the X-flare in AR 12242 and comparison of its parameters with the parameters of other components of the AR microwave radiation showed that the new source can be classified as neutral line associated sources (NLSs), which were repeatedly detected by the RATAN-600 and other radio telescopes 1-3 days before the large flares. [ABSTRACT FROM AUTHOR]

We consider the prospects for developing a forecast system for space weather (SPW) parameters with the use of home facilities for groundbased observations of solar activity. The space weather forecast can be conventionally divided into three components: (i) the prediction of recurrent, slowly changing events connected with the topology of the large-scale magnetic field, (ii) the estimation of fluxes of UV and high-energy radiation, and (iii) the observation of high-speed phenomena, such as solar flares and eruption processes, and the prediction of their consequences at the the Earth's orbit. At present, to predict recurrent events, data from regular observations of the large-scale field of the Sun by the solar telescope-magnetographs for operative (realtime) prediction (STOP) are effectively used. To estimate high-energy fluxes, to register eruption events, and to estimate their geoefficiency, data from the patrol optical telescope-spectrographs may be used. Patrol telescopes operate in automatic mode and register the processes with an interval of approximately one minute. To detect eruption processes, we propose a method based on the difference between the intensity values in the wings of chromospheric spectral lines. The results of the use of the observational complex of the Kislovodsk Mountain Astronomical Station for the SW forecast are considered in the paper. [ABSTRACT FROM AUTHOR]

The preliminary results of solar filaments distinguished in daily H-alpha observations at Kodaikanal (1912-2002) are presented. To mark the boundaries of solar filaments, methods based on automated procedures of marking low-contrast objects on the solar disk, as well as editing of the marked boundaries in a semiautomated manner, were developed. The characteristics of solar filaments were analyzed. Latitudinal diagrams of filaments number in 15-23 activity cycles were constructed. As is shown, one maximum in the filament latitudinal distribution may be clearly distinguished during activity cycles in both hemispheres. This maximum is located slightly higher (θ ~ 25°-30°) than the sunspot distribution maximum (θ ~ 14°-17°). However, there are no other local maxima related to the zonal structure of the large-scale magnetic field (Makarov and Sivaraman, 1989). [ABSTRACT FROM AUTHOR]

The results of the work of the global observation network are considered, and a comparative analysis of the data of various coronal observatories is performed. The coronal activity index has been reconstructed for the period 1939-2016 based on the data of various observatories in Kislovodsk system. For this purpose, the corona daily intensity maps from the Sacramento Peak and Lomnický Štít observatories according to the Solar-Geophysical Data journal have been digitized; they supplement the data of other observatories. The homogeneity and continuity of the corona observations at the Kislovodsk station, including activity cycle 24, is confirmed. Unfortunately, the only observatory at present that continues observation of the spectral corona in Fe XIV 5303 Å and Fe XIV 6374 Å lines is the Kislovodsk astronomical station Mountain Astronomical Station (MAS) of the Central Astronomical Observatory, Russian Academy of Sciences (Pulkovo). The data on the combined corona in 5303 Å line are analyzed. It is shown that there is a high correlation of the intensity index of green corona with solar radiation measurements in the vacuum UV region. Data on the beginning of the new 25th activity cycle in the corona at high latitudes are presented. [ABSTRACT FROM AUTHOR]

Relative variations in the number of sunspots and sunspot groups in activity cycles have been analyzed based on data from the Kislovodsk Mountain Astronomical Station and international indices. The following regularities have been established: (1) The relative fraction of small sunspots decreases linearly and that of large sunspots increase with increasing activity cycle amplitude. (2) The variation in the average number of sunspots in one group has a trend, and this number decreased from ∼12 in cycle 19 to ∼7.5 in cycle 24. (3) The ratio of the sunspot index (Ri) to the sunspot group number index ( Ggr) varies with a period of about 100 years. (4) An analysis of the sunspot group number index ( Ggr) from 1610 indicates that the Gnevyshev-Ohl rule reverses at the minimums of secular activity cycles. (5) Ratio of the total area to area of Ssp/Sum nuclei has long-term variation with a period approximately 8 cycles. Minimum ratio falls on 16–17 cycles of activity. (6) It has been indicated that the magnetic field intensity and sunspot area in the current cycle are related to the amplitude of the next activity cycle. [ABSTRACT FROM AUTHOR]