Vol 57, No 6 (2019)

During a solar flare, the magnetic energy of ~10³² erg is released in a few dozens of minutes. The invariability of the magnetic field on the solar surface during flares proves the appearance of a flare in the corona. An analysis of the dynamics of the electron temperature of the solar atmosphere provides independent evidence of the coronal origin of the flare. The appearance of the flare in the corona is explained by the release of the energy accumulated in the magnetic field of the current sheet. To study the flare situation, numerical MHD simulation was performed for a real active region. The simulation results showed the appearance of a current sheet, which position coincides with the position of the observed source of thermal X-ray emission. A methodology for calculations in real time scale has been developed. Based on the mechanism of energy release in the current sheet, an electrodynamic model of a solar flare is proposed, which explains its main observed manifestations. Sources of hard X-ray emission appear due to deceleration in the lower dense layers of the solar atmosphere of electron beams accelerated in field-aligned currents. The acceleration of solar cosmic rays occurs in the current sheet by the electric field E = –V × B/c, and not in shock waves.

This study is aimed at finding an answer to the following question: are there any fundamental differences in the generation of coronal mass ejections (CMEs) with different speeds, especially low and high speeds, detected in the field of view of LASCO coronagraphs? Fast CMEs are conventionally understood as mass ejections with a linear projection velocity in LASCO field of view \({{V}_{{LIN}}}\) > 1500 km/s; slow CMEs are those with \({{V}_{{LIN}}}\) ≤ 600 km/s. CMEs with \({{V}_{{LIN}}}\) between 600 and 1500 km/s are referred to as mass ejections with intermediate speed. The results of the analysis are presented by the example of three halo-type CME events (fast, slow, and intermediate) with sources in the sunspot groups removed from the center of the solar disk by no more than 45°. For analysis, we used data from SDO/AIA telescopes and the SDO/HMI instrument, as well as the LASCO C2 and C3 coronagraphs. The properties of active regions in which CMEs with different speeds have occurred are compared. The morphological features of the formation of the selected mass ejections based on the observations in the extreme ultraviolet lines are compared with features of their kinematics. Using the data of vector measurements of the photospheric magnetic field with the SDO/HMI instrument over the regions of CME formation, the altitude distributions of the magnetic field are calculated in the nonlinear force-free approximation. The analysis of these distributions showed that before the onset of a CME-related flare, the rate of altitude variation in the magnetic field above the CME generation site is noticeably different for all selected events.

This study gives a comparison of characteristics of small-scale ion flux fluctuations based on measurements of the SPEKTR-R spacecraft in slow and fast solar wind streams. Fast quasi-stationary streams and fast disturbed streams, associated with transient phenomena in the solar corona, are considered separately. The use of high-time-resolution data from the Bright Monitor of Solar Wind (BMSW) instrument makes it possible to analyze plasma fluctuations in a wide range of scales, including small scales, where kinetic effects can make a significant contribution. It is shown in the study that the nature of small-scale fluctuations can significantly differ in fast streams with the same mean solar wind velocity but having a different nature.

Based on an analysis of the F2-layer critical frequency (foF2) at Irkutsk station during the extreme storm of March 13–15, 1989, it is found that geomagnetic activity index aa is a more adequate indicator than ap for foF2 during the maximum of an extreme storm. This is related to the existence of the upper limit of changes in ap (ap = 400) and this fact imposes some limitations on using the ap index for extreme events. In the initial period of the recovery phase of the considered storm, a rapid decrease of geomagnetic activity occurred. A strong deviation of the experimental values of foF2 from the values calculated by the semi-empirical model, which considers the dependences of the thermospheric temperature and composition on geomagnetic activity by the NRLMSISE-00 atmospheric model, was observed during that period. It is assumed that this could be related to the effect of disturbance of thermospheric wind velocity due to the rapid decrease of geomagnetic activity. This assumption is rather qualitative and requires a special study.

In a recent paper [1], based on the data from the OMNI solar wind measurement database and our catalog of large-scale solar wind phenomena (ftp://ftp.iki.rssi.ru/pub/omni/ [2]), it was shown that magnetic clouds contain an electric current with an elevated content of helium ions in the center of the event interval, while in Ejecta such structures are not observed. From simple geometric considerations, an upper estimate is obtained for the size of the cross section of the electric current, which is equal to ~10% of the linear size of the cross section of the magnetic cloud.