The paper is controversial since it is based on assumptions that require serious experimental con-firmation. An attempt has been made to relate an in-crease in the coronal mass ejection (CME) velocity at the initial stage of its motion with a decrease in the free magnetic energy Efree in the active region. In addition, we have examined how magnetic helicity Mh changes in the active region during the selected event. We have analyzed the motion of relatively energetic halo-type CME (the CME kinetic energy is 5.2•1031 erg) recorded on November 26, 2011 and linked to a C1.2 X-ray flare. It has been shown that when Efree increases with time and decreases with rising CME velocity the magnetic helicity varies in the same way: with increasing Efree, Mh intensifies and vice versa. For comparison, we show Efree and Mh variations during the event related to an X3.1 X-ray flare and unrelated to CME. It turned out that in this case Mh intensifies during the strongest decrease in Efree.

The paper examines the variation in the stratospheric polar vortex (SPV) area and the high-latitude stratosphere temperature from November to March for the winter periods 2022–2023 and 2023–2024 against the background of average long-term values of these parameters from 1979 to 2024. In 2022–2023, the SPV area significantly exceeded the climatic values in January and December, and a decrease in the SPV area occurred a month later than the climatic norm. This was accompanied by extremely low temperatures in the polar stratosphere in the first half of winter and a record-breaking “hot” sudden stratospheric warming (SSW) in the second half of winter. In the winter period 2023–2024, no extreme SPV and temperature values were observed, but four SSW episodes were recorded during the winter period, three of which were major. We analyze SPV areas, temperatures in the stratosphere, activity of planetary waves, and discuss the reasons for the differences between the two winter seasons in terms of wave activity.

We have analyzed electromagnetic ion-cyclotron oscillations of the Pc1 range (~1 Hz) recorded during the recovery phase of the March 25, 2023 magnetic storm at the network of ground stations in the Far East and at low-orbit SWARM satellites passing over the stations. The collected data made it possible to trace propagation of Pc1 waves through the ionosphere to Earth’s surface and along the ionosphere. While long-term (~1 hour) narrowband pulsations were observed at ground stations, satellites recorded only a short (~40 s) burst of transverse oscillations. Estimated coherence of signals between close SWARM-A and -C satellites, separated by ~1° longitude, gives a transverse scale of the wave packet in the ionosphere equal to ~90 km. The long duration of pulsations at ground stations is caused by waveguide propagation of signals along the ionosphere due to which the station “collects” signals from a large magnetospheric region. The presence of waveguide propagation is confirmed by the orientation of the polarization ellipse of ground-based Pc1 pulsations relative to the site of injection of waves into the ionosphere. It is hypothesized that ion-cyclotron instability develops in the form of localized and short-lived bursts, but the mechanism of such a regime remains unclear.

Due to the structural features of the geomagnetic field, Earth’s subpolar regions are the most affected by cosmic ray variations and other space weather phenomena. High grounds located in these regions are especially promising in terms of space weather research. Nowadays, there are only two high-altitude subpolar space weather observatories highly sensitive to solar activity, both located in Antarctica. In the Russian Arctic, we have several mountainous regions with geophysical conditions similar to that of the Antarctic ice sheet. In this paper, we calculate physical quantities that determine conditions for space weather observation in these regions and explore the expediency of building new scientific stations there. We show that establishment of the stations would enhance sensitivity of space weather observatory network and increase the number of detectable solar proton events.

The paper presents the results of the analysis of changes in Earth’s solar climate over the period from 1900 to 2100. It has been determined that the annual meridional gradient of irradiation intensity from 1900 to 2100 and latitudinal differences in the Earth irradiation intensity increase. A relative increase in winter irradiation intensity for the hemispheres is observed in the regions where extratropical cyclones develop, which may contribute to the activation of cyclonic processes in the atmosphere in the winter half-year. In the Northern Hemisphere, seasonal differences in the irradiation intensity increase during the period of interest, whereas in the Southern Hemisphere they smooth out. Meridional contrasts in irradiation in the summer half-year increase in the Southern and Northern hemispheres; in the winter half-year in the Northern Hemisphere, meridional contrasts in irradiation decrease; in the Southern Hemisphere, they increase. Insolation seasonality increases slightly in the Northern Hemisphere and increases in the Southern Hemisphere. The transfer of radiative heat from the summer Southern Hemisphere to the winter Northern Hemisphere prevails. There is, however, a tendency for it to decrease.

A self-consistent, data-driven approach to classifying data obtained at the ISTP SB RAS mid-latitude coherent scatter radars has been developed. Based on 2021 data, a solution of the problem of automatic data classification is presented without their labeling by an expert and without postulating the number of classes. The algorithm automatically labels the data, determines the optimal number of signal classes observed by the radars, and trains a two-layer classifying neural network of an extremely simple structure. The trajectory calculations use the wave optics method and international reference models of the ionosphere and the geomagnetic field. The model is trained on signals coming from the main lobe of the antenna pattern. During training, to adapt part of the data obtained with improved spectral resolution, it is artificially coarsened to the standard resolution. Each signal class determined by the neural network is interpreted from a physical point of view, using statistical characteristics of the signals belonging to it. The number of classes in the data is demonstrated to range from 23 to 35. The significance of various parameters of the input data is assessed. It is shown that the most important parameters for the classification are the calculated scattering height and the elevation of the trajectory at the scattering point, and the least important are the spectral width of the received signal and the calculated number of reflections from the underlying surface.

The paper describes the current state of the lightning location network deployed in the Irkutsk Region and the Republic of Buryatia, which includes four stations. It is based on the results obtained during several stages of the project “Fundamental principles, methods, and technologies for digital monitoring and forecasting of environmental situation of the Baikal Natural Territory”. We present a diagram of the VLF receiver in use. Data processing, features of some algorithms, and the rationale for their choice are described in detail. Developing processing algorithms and further upgrading them have provided lightning discharge maps with a period of several minutes. We present intermediate results of the network operation, a lightning discharge distribution map and give recommendations for further developing and upgrading the lightning location network.

The paper studies statistical patterns of regional electron content responses to geomagnetic events at high, middle, and equatorial latitudes. The regional electron content is the total electron content averaged over all longitudes in a given latitudinal zone. The statistical analysis includes the following: 1) identification of geomagnetic events based on the AE index and calculation of “reference” geomagnetic storms; 2) calculation of the regional electron content (REC) for five latitudinal zones (equatorial zone, mid-latitude zones of the Northern and Southern hemispheres, and high-latitude zones of the Northern and Southern hemispheres); 3) calculation of REC disturbances (ΔREC), which are relative (percentage) deviations of the observed values, from the 27-day running mean of REC and 4) obtaining the “reference” ionospheric response in the form of the dynamics of average ΔREC, obtained by the superposed epoch method. The superposed epoch method is implemented with the hourly resolution and key moments corresponding to the AE index maximum. Compared with our previous statistical analysis, implemented with daily resolution based on geomagnetic storm identification by the Dst index, the new method leads to a significant increase in the amplitude and the time-focusing of the response. The seasonal behavior of ionospheric responses was analyzed for correspondence to the thermospheric storm concept. The responses of the equatorial and mid-latitude zones of the Southern Hemisphere fit the thermospheric storm concept. In the mid-latitude zone of the Northern Hemisphere, there are a number of exceptions. The responses of the high-latitude zone show the need to take into account the mechanisms behind the formation of positive disturbances, which are absent in the thermospheric storm concept

The work analyzes dependences of eddy diffusion coefficients in the X, Y, and Z directions of the GSM coordinate system on the plasma parameter β, taking into account the distance from Earth, the direction of the interplanetary magnetic field, and conditions of geomagnetic activity in the magnetotail according to MMS mission data. These parameters are determined by root-mean-square velocities of ions and their autocorrelation time. Eddy diffusion coefficients characterize the magnitude of turbulent transport in the magnetotail and are the parameters of the model of turbulent plasma sheet. We have analyzed more than 20000 12-min intervals during which the MMS satellites were located within a region with plasma density more than 0.1 cm–3 and average ion energy more than 0.5 keV. It is shown that as the plasma parameter increases, the eddy diffusion coefficients increase as well. This increase stops at β~1. Analysis of the relative contribution of changes in root-mean-square velocity and autocorrelation time to the eddy diffusion coefficient has revealed that there is no significant dependence on autocorrelation time.