Forecast of solar wind parameters according to STOP magnetograph observations

Geomagnetism and Aeronomy - The paper discusses the results of the forecast of solar wind parameters at a distance of 1 AU made according to observations made by the STOP telescope magnetograph...     

LONG-TERM VARIATIONS OF THE TORSIONAL OSCILLATIONS OF THE SUN

We investigated long-term variations of the differential rotation of the solar large-scale magnetic field on 1024 H charts in the latitude zones from +45° to -45° in the period 1915–1990. We used the expansion in terms of Walsh functions. It turns out that the rotation of the Sun becomes more rigid than average during the cycle maximum and the rotation is more differential during minimum. From 1915 to 1990, 7 bands of faster- and 7 bands of slower-than-average rotation are revealed showing an 11-year period. These bands drift towards the equator: 45° in 2.5 to 8 years. The time span of the bands varies from 4 to 6.8 years and is in anti-phase with long-term solar activity. The latitude span of the bands of torsional oscillations varies from 0.5 R to 1.3 R and shows a long-term variation of about 55 years. The poloidal component of velocity, V varies from 2 ms ^-1 to 6 ms ^-1. The maximum rate of the equatorial drift occurs in the period between 1935 and 1955 and it develops prior to the highest maximum activity. At the modern epoch from 1965 to 1985, V does not exceed 3 ms ^-1, but now it has a tendency to increase. The bands of slower-than-average rotation correspond to the evolution of the magnetic activity towards the equator in the butterfly diagram.     

Bimodal Distribution of Magnetic Fields and Areas of Sunspots

We applied automatic identification of sunspot umbrae and penumbrae to daily observations from the Helioseismic Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to study their magnetic flux density (B) and area (A). The results confirm an already known logarithmic relationship between the area of sunspots and their maximum flux density. In addition, we find that the relation between average magnetic flux density ( $B_{\rm avg}$ ) and sunspot area shows a bimodal distribution: for small sunspots and pores (A≤20 millionth of solar hemisphere, MSH), $B_{\rm avg} \approx 800~\mbox{G}$ (gauss), and for large sunspots (A≥100 MSH), $B_{\rm avg}$ is about 600 G. For intermediate sunspots, average flux density linearly decreases from about 800 G to 600 G. A similar bimodal distribution was found in several other integral parameters of sunspots. We show that this bimodality can be related to different stages of sunspot penumbra formation and can be explained by the difference in average inclination of magnetic fields at the periphery of small and large sunspots.     

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.     

Reconstruction of sunspot characteristics for 1853–1879

The Carrington (1853?C1861) and Sp?rer (1861?C1879) catalogs of sunspot drawings have been digitized. In the Carrington catalog, 9831 sunspots and 4946 umbrages were detected on daily drawings and 3762 sunspots and 1730 umbrages on synoptic maps. This allowed us to reconstruct the characteristics of 3069 sunspot groups for the period from November 9, 1853, to April 1, 1861. In the Sp?rer catalogs, 12402 sun-spots and about 5000 umbrages were detected for 1861?C1879. Sunspots and umbrages were detected semiautomatically, a heliographic grid was plotted, and sunspot groups were formed when the images were processed. The digitized data made it possible to determine the coordinates, areas, relative position, and other geometric parameters of individual sunspots, umbrages, and sunspot groups. These data make it possible to study in detail the fine structure at the end of cycle 9 and in cycles 10 and 11. An electron database of the detected structures has been created.     

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.     

Asymmetry in the form of solar spots

We have analyzed the geometric characteristics of sunspots. The form of sunspots has been studied by sunspot image normalization to obtain the average profile of spots and the profile relative to the position of cores. The deviation of the sunspot form from the axisymmetric configuration has been studied. We have found that the spots of leading and trailing polarities have a drop shape. The cores of leading and trailing sunspots are shifted toward the western and eastern edges of the photosphere–penumbra boundary, respectively. The strength of the magnetic field of the cores of leading spots in the eastern hemisphere exceeds the field strength in the western hemisphere. We considered the tilt of the form of sunspots as a function of size. The form of spots of a large area (S > 1000 ppm of solar hemisphere) is elongated along the magnetic axis of the bipole of a group of sunspots.     

The Minimum Activity Epoch as a Precursor of the Solar Activity

This paper considers the indices characterizing the minimum activity epoch, according to the data of large-scale magnetic fields and polar activity. Such indices include: dipole–octopole index, area and average latitude of the field with dominant polarity in each hemisphere, polar activity seen in polar faculae and Ca?ii K line bright points, coronal emission line intensity (5303?Å) and others. We studied the correlation between these indices and the amplitude of the following sunspot cycle, and the relation between the duration of the cycle of large-scale magnetic fields and the duration of the sunspot cycle. The obtained relationships allow us to presume that the polar field is formed from the sources of both preceding and the current activity cycles during the decay phase and at the activity minimum. The balance in these sources would therefore determine the features of the following sunspot cycle. The prediction for the 24th activity cycle using these results leads to W=102±13.     

Rotation cycles of the sector structure of the solar magnetic field and its activity

We study the rotation of the sector structure of the solar magnetic field by using Stanford magnetographic observations from 1975 until 2000 and magnetic synoptic Hα-maps obtained from 1904 until 2000. The two independent series of observations yielded the same rotation periods of the two-sector (26.86 days) and four-sector (13.64 days) structures. We introduce a new index of the solar rotation, SSPM(t). The spectral power density of the sector structure of the magnetic field is shown to exhibit a 22-year cyclicity. The two-and four-sector structures of the magnetic field rotate faster at the maxima of even 11-year sunspot cycles. This phenomenon may be called the Gnevyshev-Ohl rule for the solar rotation. The 11-year sector-structure activity cycles are shown to lead the 11-year sunspot cycles (Wolf numbers) by 5.5 years. A 55-year component with the slowest rotation in the 18th cycle (1945–1955) was distinguished in the sector-structure rotation.     

Long-term variations in the rotation of the solar corona

The characteristic time scales for variations in the differential rotation of the solar corona are determined using measurements of the intensity of the FeXIV 5303 Å coronal line made from 1939–2004. Drift waves of the variations in the rotational speed with an 11-year periodicity can be distinguished. Moving averages with time intervals from two to five years are used to identify torsional waves. In addition, longer-period variations in the rotational speed can be distinguished when longer averaging intervals are used. When the interval used for the moving average is increased to 8–12 years, a quasi-22-year rotational period appears. The low-latitude corona rotates more slowly in odd cycles than in even cycles. Increasing the duration of the averaging interval further shows that rapid rotation at low latitudes was observed in 1940–1950 and 1990–2000, while slow rotation was observed in 1960–1980, possibly suggesting the presence of a 55-year period in the rotational variations. Long-term variations are found in the rotation of polar regions. The rotational variations for high-latitude corona are in antiphase with those for the low-latitude corona. The origins of zones of anomalous coronal rotation and their dynamics in the global activity cycle are discussed.