Kislovodsk Mountain Astronomical Station Research Articles

Coronal Field Geometry and Solar Wind Speed

The Wang–Sheeley–Arge (WSA) solar wind (SW) model is based on the idea that weakly expanding coronal magnetic field tubes are associated with sources of fast SWs and vice versa. A parameter called the “flux tube expansion” (FTE) is used to determine the degree of expansion of magnetic tubes. The FTE is calculated based on the coronal magnetic field model, usually in the potential approximation. The second input parameter for the WSA model is the great circle distance from the base of the open magnetic field line in the photosphere to the boundary of the corresponding coronal hole (DCHB). These two coronal magnetic field parameters are related by an empirical relationship with the solar wind velocity near the Sun. The WSA model has shortcomings and does not fully explain the solar wind formation mechanisms. In the present work, we model various coronal magnetic field parameters in the potential-field source-surface (PFSS) approximation from a long series of magnetographic observations: the Solar Telescope-magnetograph for Operative Prognoses (STOP) (Kislovodsk Mountain Astronomical Station), the Helioseismic and magnetic imager (SDO/HMI), and data from the Wilcox Solar Observatory (WSO). Our main goal is to identify correlations between the coronal magnetic field parameters and the observed SW velocity in order to use them for modeling SW. We found that the SW velocity correlates relatively well with some geometric properties of the magnetic tubes, including the force line length, the latitude of the force line footpoints, and the DCHB. We propose a formula for calculating the SW velocity based on these parameters. The presented relationship does not use FTE and showed a better correlation with observations compared to the WSA model.

Average annual total sunspot area in the last 410 yr: the most probable values and limits of their uncertainties

ABSTRACT The aim of this work is to create a long (410-yr) series of average annual total sunspot areas AR – a physically based index of sunspot activity. We use telescopic observations of the AR index in 1832–1868 and 1875–2020, as well as the relationship between AR and long series of sunspot indices SN (international sunspot numbers, version 2.0) and sunspot groups GN (Svalgaard and Schatten’s version of group sunspot numbers). The Royal Greenwich Observatory series after 1976 is extended by the Kislovodsk Mountain Astronomical Station data. When reconstructing AR from SN, it is taken into account that the function AR = f(SN) has a non-linear systematic character and uncertainty associated with the heterogeneity of these indices. Therefore, in addition to modelling the most probable AR values, predictive limits of reconstruction uncertainty are determined. In the interval 1610–1699 we carried out the reconstruction on the basis of the GN series using the previously proposed decomposition in pseudo-phase space (DPS) method. The resulting series NO21y is freely available online. We show that for this series the empirical Gnevyshev–Ohl rule and Waldmeier effect are fulfilled. Wavelet analysis reveals periodicities of 8.4–13.8 yr for the main cycle (with a sharp decrease of the period before the global Maunder and Dalton minima) and a two-component Gleissberg cycle with typical periods of 50–60 and 90–110 yr.

“Generative” Indices of Sunspot Solar Activity: 145-Year Composite Series

Traditional indices, which we call apparent indices, describe the current state of solar activity and are very important for understanding the influence of the Sun on Earth. To study the productivity of the solar dynamo, however, we need a different index that would describe each magnetic region once – at the moment of its maximum area. We refer to such indices as generative ones. The aim of this work is to produce such a generative series improving the procedure by Nagovitsyn et al. (Geomagn. Aeron. 58, 1170, 2018). We use sunspot group data from two archives – Royal Greenwich Observatory (1875 – 1976) and Kislovodsk Mountain Astronomical Station (1955 – 2019). We produce generative indices with annual values of sunspot group areas $A$ , and counts of sunspot groups $C$ . Unified 145-year series of these indices were compiled. We study the characteristics of the indices $A$ and $C$ , and indices derived from them for two sunspot group populations – large long-living groups and small short-living groups according to Nagovitsyn and Pevtsov (Astrophys. J. 833, 94, 2016) – for the northern and southern hemispheres separately. We find a 50-year variation in several indices on the 145-year interval, and detect a similar phase variation in the north-south asymmetry taken with the opposite sign. Perhaps this indicates the existence of another secular cycle along with the Gleissberg cycle on the Sun. The obtained series of indices $A$ and $C$ can be useful for studying the long-term properties of the solar dynamo.

Bi-lognormal Distribution of Sunspot Group Areas

Abstract We use daily observations from the Royal Greenwich Observatory and Kislovodsk Mountain Astronomical Station of Pulkovo Observatory to study the distribution properties of sunspot areas. To mitigate the poor statistics in the distribution of small areas, we introduce a “precision randomization” approach based on the assumption that all measured areas have a random component within the measurement uncertainty of 1 millionth of the solar hemisphere (M.S.H.). We confirm the presence of two distinct components in the distribution of sunspots previously reported by several authors, and show that the area distribution is described by the sum of two lognormal distributions responsible for small and large groups (sunspots), respectively. We also demonstrate that the area of the main spots in the groups correlates well with the total area of the group, and, thus, the findings derived for the total group areas are equally applicable to the main spots of groups.

Comparative Analysis of Terrestrial and Satellite Observations of Photospheric Magnetic Field in an Appendix to Simulation of Parameters of Coronal Holes and Solar Wind

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.

Comparative Analysis of the Catalog of Individual Sunspots Based on Data from Kislovodsk Mountain Astronomical Station

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, $${\text{S}}_{{{\text{spt}}}}^{1}$$ ~ 8–10 mdp and $${\text{S}}_{{{\text{spt}}}}^{2}$$ ~ 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.

Drift of Polar Prominences in Solar Cycles 13–24

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.

The Characteristic Sizes of the Sunspots and Pores in Solar Cycle 24

We present a comparative analysis of the size of spots in sunspot groups. For the analysis, we have used the characteristics of individual sunspots and pores according to the daily synoptic observations of the Kislovodsk Mountain astronomical station in Solar Cycle 24. We have constructed the distribution of area for the different types of the spots: pores, transitional sunspots, regular sunspots, and sunspots umbrae. We have found that the properties of the sunspots with largest area $[S_{ \mathrm{max}}]$ differ from the other spots $[S_{\mathrm{nomax}}]$ in sunspot groups. In the distribution of area for $S_{ \mathrm{max}}$ there are two local maxima $S^{\mathrm{mx}}_{ 1}\approx 10~\mbox{msh}$ and $S^{\mathrm{mx}}_{\mathrm{2}}\approx130\,\mbox{--}\,180~\mbox{msh}$ . The $S^{\mathrm{mx}}_{1}$ is connected with the transitional spots where the penumbra is not fully developed. For sunspots with $S_{\mathrm{max}}$ where a penumbra is formed or the ratio $S_{\mathrm{sp}}/S_{\mathrm{um}}> 3.5$ , the maximum $S^{\mathrm{mx}} _{2}$ corresponds to the diameter of a round spot with $d \approx25~\mbox{Mm}$ . This size is close to the size of the supergranules. In the distribution of area, the two-vertex character is absent for sunspots in the groups with the exception of the spot having the largest area. For developed sunspots with $S_{\mathrm{max}}$ , in the distribution of area of the sunspot’s umbra we have a maximum $S^{\mathrm{mx}}_{\mathrm{um}} \approx25~\mbox{msh}$ . Thus, the two-vertex nature of the distribution of area is a consequence of the existence of pores and sunspots with developing penumbra.

Stable Sunspot Area Level of Debrecen Photoheliographic Data and Multivariate Correction Factor of SOON Data

We investigate the spatial and temporal variation of sunspot group areas reported by the Greenwich Photoheliographic Results (GPR), the Solar Optical Observing Network (SOON), the Kislovodsk Mountain Astronomical Station (KMAS), and the Debrecen Photoheliographic Data (DPD) databases. We identify improved correction factors for reconciling these individual records to a common scale. Our results show that the DPD sunspot group areas are stable over the studied interval (1974 – 2014). We find an improved fit between GPR and DPD sunspot group areas when using a correction factor such that $\mathrm{GPR} = 0.975(\pm 0.006) \times \mathrm{DPD}$ , independent of the position of the sunspot group on the solar disk. We also find that the scale of KMAS sunspot group areas fits that of DPD well, but has a small position-dependent trend near the limb. However, in order to set SOON sunspot group area records onto the scale of DPD, we find that there is a need for a multivariate correction factor. This multivariate correction factor has a value ranging between 1.1 and 1.9 and is dependent upon the time of the SOON observation, the distance of the group from disk center, and the observatory within the SOON network. Finally, we provide further context to the systematic bias in SOON sunspot group area observations toward lower values relative to those recorded in the GPR and DPD databases that has previously been reported in the literature. We have identified the two main contributors to the SOON area deficit; some penumbral parts are unobserved, and the spot areas are underestimated. Our analysis is vital for studies that require stable, long-term solar activity records such as solar irradiance models that estimate irradiance reduction from records of sunspot group numbers, areas, and locations.

Chromospheric and Coronal Radio Sources from Observations of the Partial Solar Eclipse of March 20, 2015, at the Mountain Astronomical Station of the Central Astronomical Observatory

This paper presents the results of processing the data on the partial solar eclipse that occurred on March 20, 2015, and was observed with the RT-3 (λ = 4.9 cm) and RT-2 (λ = 3.2 cm) radio telescopes of the Kislovodsk Mountain Astronomical Station, Central Astronomical Observatory, Russian Academy of Sciences (MAS CAO RAS). They were compared with observations in the optical and X-ray ranges. The local radio sources at the limb and on the disc of the Sun were identified: an eruptive and a quiet prominence; filaments; a coronal hole; facular plages; and a sunspot group. The curves of the center-to-limb variations in the radio brightness of the undisturbed regions of the Sun were plotted for λ = 4.9 and λ = 3.2 cm. The solar radio maps were presented. The altitude of the radiating layer in the chromosphere above the sunspot and the facular sources for λ = 4.9 cm λ = 3.2 cm was compared.

The Waldmeier Effect for Two Sunspot Populations

This paper continues our studies in which we showed that sunspot groups form two populations differing by physical properties—populations of small and large groups. The known Waldmeier effect has been individually considered for these populations. Two formulations of this effect were verified: the classical one, which connects the solar activity index at the maximum of the 11-year cycle with the length of the ascending phase of a cycle, and the modified one, connecting the index value at the cycle maximum with the highest rate of the index change along the ascending branch. We used the data from the Greenwich Observatory and the Kislovodsk Mountain Astronomical Station for the solar activity cycles from 12 to 24 to construct the series of indices for the areas and the numbers of sunspot groups. It has been shown that the Waldmeier effect works more strictly for the population of large sunspot groups than for that of small groups. The results of this analysis may find an application in the dynamo theory.

Prominence Characteristics in 16th Activity Cycle

Digitization of the daily prominence sketches based on data from the global observational network of visual solar spectroscopes was performed for 1922–1934. More than 55000 prominences were distinguished. The results of analysis of distributions by area, height, and prominence location are presented. In addition, the prominence characteristics were compared to those obtained from more recent observations at the Kislovodsk Mountain Astronomical Station of Pulkovo Observatory. The distributions of prominence areas and heights are close to lognormal. The maximal height distribution corresponds to ~25–40 arcsecs. A second maximum also exists for prominence heights of ~70–90 arcsecs.

Space Weather Parameters: Modeling and Prediction from the Data of Groundbased Observations of Solar Activity

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.

The Forecast of Space Weather According to Ground-Based Observatories

AbstractThe space weather forecast can be conditionally divided into three components: 1) The forecast of recurrent slowly varying events which are associated with the topology of a large-scale magnetic field; 2) Evaluation of fluxes of ultraviolet and extreme radiation; 3) Detecting and determining the parameters of eruptions and CME. All three components can be observed and evaluated by ground-based telescopes. In this article we describe the telescopes of the space weather service in Kislovodsk Mountain Astronomical Station. Telescope-magnetograph STOP for the forecast of recurrent events and patrol telescopes-spectrographs for detecting CME and estimating hard radiation fluxes.

Long‐term variations in sunspot magnetic field–area relation

BackgroundSeveral recent studies indicated possible long‐term variations of physical properties of sunspots.Materials and MethodsUsing observations of sunspot magnetic field strengths (H) from the Crimean Astrophysical Observatory and area (S) of sunspots from the Kislovodsk Mountain Astronomical Station of Pulkovo Observatory, we investigate the changes in the relation between H and S over the period of about two solar cycles (1994– 2013). The data were fitted by H = A + B log S, where A = (778 ± 46) and B = (778 ± 25).ResultsWe show that the correlation between H and S varies with the phase of solar cycle, and A coefficient decreases significantly after year 2001, while B coefficient does not change significantly. Furthermore, our data confirm the presence of two distinct populations in the distribution of sunspots (small sunspots with weaker field strength and large sunspots with stronger field). We show that the relative contribution of each component to the distribution of sunspots by their area changes with the phase of solar cycle and on longer‐than‐cycle periods.ConclusionWe interpret these changes as a signature of a long‐term (centennial) variations in the properties of sunspots.

Observations of long-period oscillations of the solar active regions in the visible and UV spectral intervals

The variation of intensity in spectral line wings, which was obtained from observations of the patrol telescope at the Kislovodsk Mountain Astronomical Station of the Pulkovo Observatory, Russian Academy of Science (KMAS) and the Interface Region Imaging Spectrograph (IRIS) space observatory, are considered. A series of observations lasting a few hours near the solar active regions, in which both short- and longperiod oscillations were observed simultaneously during 2014–2015, are analyzed. It is found out that oscillations with a period of 3–5 min can exist at one time and in one place with oscillations with a period of about 100 min. The amplitude of long-period oscillations can be comparable with that for short-period oscillations. The conditions for excitation of the wave processes are considered. Oscillations with a period of 100 min have a weak dependence on the area of the active region.

Tilt Angles of Solar Filaments over the Period of 1919 – 2014

The spatial and temporal distributions of solar filaments were analyzed using data from the Meudon Observatory for the period 1919-2003 and the Kislovodsk Mountain Astronomical Station for the period 1979-2014. We scanned $H_\alpha$ solar synoptic charts on which the filaments were isolated and digitized. The data on each filament comprise its location, length, area, and other geometrical characteristics. The temporal distributions of the number and total length of the filaments have been obtained. We also found latitudinal migration of filament locations with the solar cycle, and analyzed the longitudinal distribution and asymmetry of filaments in the northern and southern hemispheres, and other properties of their distribution. The tilt angles of filaments with respect the solar equator ($\tau$) were analyzed. On average, the eastern tips of filaments are closer to the poles than the western ones ($\tau \sim 10^\circ$). On the other hand, the filaments in the polar regions ($\theta>50^\circ$, where $\theta$ is the latitude) usually have negative tilts ($\tau <0^\circ$). The tilt angles vary with the phases of the 11 year sunspot cycle and are at their highest values in the epoch of the activity maximum. In the century-long modulation of the solar activity (Gleissberg cycle), the mean tilt angles of filaments in the mid-latitude zone ($\theta \sim \pm 40^\circ$) were maximum in the middle of the 20th century in solar sunspot cycles 18-19. We hereby propose using the statistical properties of solar filaments as an additional coherent measure of manifestation of the solar cycle which covers all latitudes and for which almost a century long systematically calibrated data series is available.

The properties of solar cycle 24 and their connection with common relationships of cycles 19–23

A set of properties of solar activity cycle 24 is considered on the base of the data of Kislovodsk Mountain Astronomical Station. Some of those properties are in connection with common relationships of previous cycles.

Long-term variations in sunspot characteristics

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 (G gr) varies with a period of about 100 years. (4) An analysis of the sunspot group number index (G gr) 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.

The Peculiarities Of The Initial Phase Of The 24-th Solar Activity Cycle

A set of peculiarities of the 24-th solar activity cycle is considered on the base of the data of Kislovodsk Mountain Astronomical Station (www.solarstation.ru) as well as NASA/Marshall data. The peculiarities of the 24-th cycle are: the asymmetry between sunspot areas of northern and southern solar hemispheres; the difference between sunspot latitudes in northern and southern solar hemispheres; low activity of the first years of the cycle; large relative amount of single sunspots.