Vol 65, No 6 (2025)

Ultraviolet radiation fluxes in the MgII 280 nm and Lyman-alpha 121.6 nm lines, as well as the relative number of sunspots and the F10.7 radio emission flux were studied. It was found that the relative difference in the amplitudes of these activity indices changed significantly from solar minimum to maximum during the transition from the activity cycles 22 and 23 to cycle 24. In cycle 24, we examined the solar extreme ultraviolet radiation (EUV). Using the SDO/EVE archive of daily observations for 2010-2018, we created a time series of daily EUV radiation fluxes outside of flares. We also analyzed fluxes in the neutral helium lines (He I 58.4 nm and 53.7 nm) and ionized helium lines (He II 30.4 nm and 25.6 nm) during the activity cycle 24. Finally, we estimated how the intensity of these lines was changing with solar activity from the minimum to the maximum of the activity cycle 24. The study of double peaks at the maximum of solar activity, started by M.N.Gnevyshev [Gnevyshev, 1967], was continued. Double peaks were observed in all layers of the solar atmosphere (photosphere, chromosphere and corona).

The article presents the results of studying the dynamics of relativistic electron fluxes of the Earth’s outer radiation belt during a long period of low geomagnetic activity on January 07–24, 2018. The arrival of high-speed solar wind streams that caused minor geomagnetic disturbances with an amplitude of about 20 nT was observed during three successive intervals on January 07–13, 14–18, and 19–24. A comparative analysis was carried out to study variations in the parameters of the solar wind and interplanetary magnetic field and the response of the magnetosphere to external influences. The work is based on experimental data on relativistic electron fluxes obtained from the GOES-15 geostationary satellite and the Van Allen Probes A spacecraft, whose orbit passed through the core of the outer radiation belt near the equatorial plane. It is shown that the magnetic field variations associated with external influences on the magnetosphere (pressure pulses) and with the proper dynamics of the latter (substorm activity) control the dynamics of electron fluxes in the outer radiation belt.

A sudden increase in the flux of quasi-trapped energetic electrons in the forbidden zone is known as the phenomenon of forbidden energetic electrons. The Energies characteristic of the enhanced electron fluxes are tens and hundreds of keV. The flux in the forbidden zone exceeds the background values of ~10³ (cm² s sr)^–1 by several orders of magnitude and can reach 10⁷ (sm² s sr)^–1 during powerful storms. The mechanism of increases in quasi-trapped electron fluxes is still not entirely clear. The probability of flux enhancements displays an ambiguous dependence on the level of geomagnetic activity. However, during extremely powerful magnetic storms with |Dst| ≥ 400 nT, this phenomenon is always observed. In this paper, we check the hypothesis of earthward fast transport of particles associated with the electrical drift. The flux enhancements during five superstorms in the period from 2000 to 2025 (March 31, 2001; October 29–31, 2003; November 20, 2003; November 7–10, 2004; and May 10–13, 2024) were selected for the analysis. The solar wind and interplanetary magnetic field parameters during superstorms were analyzed to determine the most probable external drivers of the ejection of electrons with energies of 30–300 keV. Strong increases of electron flux can be caused by sudden jumps (positive and/or negative) in the total plasma pressure, as well as by inhomogeneous magnetic structures with sharp boundaries (bends or rotations of the magnetic field vector, MHD discontinuities). The intervals of near-radial field can also be considered as suitable conditions for the flux enhancement events. The time of the electric drift and the electric field intensity required for a rapid particle transport into the quasi-trapped zone are estimated.

The influence of wind in the ionosphere on the characteristics of internal gravity waves is considered. It is shown that the ionospheric wind interacts with the geomagnetic field leading to the appearance of the Ampere force, the vertical gradient of which modifies the properties of the waves. Equations of internal gravity waves in a moving ionosphere are derived and their dispersion characteristics are analyzed. Generation of waves by linear and point sources and their propagation in the moving ionosphere are considered. The transformation coefficients of atmospheric internal gravity waves and their reflection from the boundary of the moving ionosphere are found. It is shown that the ionospheric wind leads to an exponential increase in the wave amplitudes in the direction predominantly normal to the wind direction. The characteristics of internal gravity waves are analyzed depending on the ionosphere and wind parameters. The results of the theoretical study are applied to interpret the observed properties of medium-scale moving ionospheric disturbances.

The impact of large atmospheric vortices on the stratosphere, upper atmosphere, and ionosphere is considered using tropical cyclones as an example. At stratospheric heights in the ozone layer, the influence manifests itself as variations in the ozone concentration and total content, while in the upper atmosphere and ionosphere, it is manifested as disturbances of the electron concentration. To analyze such disturbances in the upper atmosphere, we used data from a regional network of VLF radio occultation stations. The ionosphere was studied using the Swarm satellite observations. Experimental data suggest that disturbances can be transmitted in the atmosphere by a wave mechanism. Theoretical estimates based on meteorological data were carried out to determine the frequencies of waves generated by cyclones. The internal gravity waves generated by the cyclone partly reach the stratosphere and ionosphere and can cause variations not only in the total Ozone content in the stratosphere, but also in the phase and amplitude of the VLF signal in the lower ionosphere and directly in the plasma density in the upper ionosphere. The structure of the selected responses shows the possibility of interaction of internal waves from different sources.

Complete information on the space-time variability of the Earth’s magnetic field is especially important in the vicinity of geomagnetic observatories. The distribution of sources of anomalies in the Earth’s crust associated with rocks and other geological structures allows a better understanding of the origin of the area and the spatial and temporal peculiarities of the Earth’s magnetic field. The magnetic properties of the geological section are also important for assessing the contribution of geomagnetically induced currents during strong geomagnetic disturbances. Temporal changes in the total values of components of the magnetic induction vector T are recorded by the observatory itself. The next question that arises is what part of the magnetic induction vector T is determined by the normal Earth’s magnetic field T₀ and what part is determined by its anomalous component T_a. To select the optimal approach to calculating the components of the anomalous magnetic field, we considered the methods for restoring its spatial structure used in the exploration magnetometry. It should be noted that the solution of the problem is based on the algorithms for modelling the equivalent distribution of magnetic sources of an anomalous field. The use of multilevel magnetic surveys allows us to obtain a more correct model of the magnetic field than that based on single-level ground or aeromagnetic survey data.

Based on an expanded network of world magnetic observatory data, a comprehensive analysis of secular geomagnetic variations observed over a 100-year period has been carried out to determine the role of jerks in the formation of secular variations belonging to the high-frequency range of the spectrum of variations of the Earth's main magnetic field. Jerks – sharp changes in the direction of the linear trend characteristic of time series of values of secular variations of the magnetic field generated in the Earth's liquid core over decades – have been identified. Epochs of global jerks, manifesting on the scale of the entire Earth's surface with an interval of about ten years, have been identified and their spherical harmonic models have been constructed. Analysis of the morphology of the global jerk fields confirmed the idea that their source are processes occurring in the Earth's liquid core. Spectral analysis of series of secular variations, performed by the Fourier series decomposition method, made it possible to identify the main periods constituting the spectrum of secular variations with T < 10² years. Taking into account the jerk phenomena showed that all identified periods of secular variations can be interpreted within the framework of the concept of geomagnetic jerks, stochastic in the variability of manifestation both in regional and temporal aspects. Based on the analysis of the results of the conducted comprehensive research, a hypothesis is put forward that the dynamics of the Earth's main magnetic field, within centennial intervals, is formed due to the spatio-temporal superposition of global jerks caused by a sharp restructuring of the flow system on the surface of the Earth's liquid core.