We study the spatiotemporal variations of ionospheric parameters over the regions of Eurasia by analyzing data from chains of high- and mid-latitude ionosondes during the extreme magnetic storm in May 2024. The analysis of ionospheric parameters allowed us to note strong latitudinal and longitudinal differences in variations of the analyzed parameters under quiet conditions before the onset of the magnetic storm and during its development. Almost immediately after the onset of the storm at 17:00 UT on May 10, 2024, according to data from all ionosondes, a sharp drop in the electron density at the height of the F2-layer maximum was recorded, regardless of the local time at the measurement point. Ionosondes of the high-latitude chain showed a complete absence of data (radio signal blackout) during the main and early recovery phases of the storm until the evening of May 12, 2024, i.e. more than one and a half days. Additional bursts of geomagnetic activity during the recovery phase of the storm were also accompanied by significant and prolonged decreases in the electron density according to ionosonde measurements at all longitudes of Eurasia. The recovery of ionospheric ionization began on May 14–15 at all longitudes of the mid- and high-latitude regions of Eurasia. A long-term negative disturbance of electron density covering a huge territory of mid-latitude Eurasia was caused by an extraordinary, catastrophic drop in the [O]/[N2] ratio according to satellite measurements of GUVI TIMED during the superstorm for almost three days. The response of the thermospheric composition of neutral gas to the processes developing at high latitudes of the Northern Hemisphere on May 10–15, 2024 was global, with penetration of the thermospheric disturbance at almost all longitudes up to the equatorial latitudes (~10° N) and with very low values of the [O]/[N2] ratio ~0.1÷0.4. Significant differences in the spatiotemporal variations of the thermospheric composition of neutral gas were revealed during the most extreme geomagnetic storms of the current 21st century — in May 2024 and October–November 2003 (Halloween storms). The magnetic superstorm in May 2024 was much more geoeffective than the superstorms in October–November 2003, and caused a significantly different ionospheric response at different longitudes and latitudes of the Northern Hemisphere.

During the North Pole–41 expedition, three components of the VLF electromagnetic field were simultaneously measured on a drifting ice-resistant platform and at the Lovozero and Barentsburg observatories. We consider three VLF events that occurred in magnetically quiet time. During two of them (the events on January 24, 2023 and March 12, 2024), auroral hiss bursts were recorded at three stations located in the auroral and circumpolar regions and spaced up to 2.600 km apart. The spectral and temporal characteristics of the bursts at all the stations were almost the same. The fact that hiss was recorded with the same properties at such large distances can be explained under the assumption of a homogeneous flow of auroral electrons with energies from 0.1 to 10 keV throughout the precipitation area, which generate quasi-electrostatic waves at altitudes 10–20 thousand km, along with the simultaneous presence of small-scale ionospheric irregularities in the vicinity of all three stations, where these waves are scattered into the propagation cone to the Earth surface. We examine the case of hiss recording (the January 25, 2023 event) demonstrating the locality of the hiss recording area during one day — a hiss burst is first observed at one station, then at another. This is probably due to the appearance/disappearance of local areas of small-scale irregularities, where quasi-electrostatic waves are scattered providing propagation to the Earth surface.

The growing amount of space debris (SD) in near-Earth space already poses a threat to space activities, interferes with astronomical observations, and may lead to negative environmental consequences on Earth in the future. This paper estimates the current attenuation of solar radiation in the wavelength range from vacuum ultraviolet to infrared. We determine the rate of exponential increase in SD mass. Estimates of the future SD mass are also obtained at which the logarithm of solar radiation attenuation will increase to 10⁻⁶–10⁻³. We find the time required for the logarithm of solar radiation attenuation to increase to 10⁻⁶.

Using the previously proposed semi-empirical method (Kozlov et al., 2022; Kozlov, Nikolaishvili, 2024), which is a fairly simple mathematical model (a system of five algebraic equations for calculating the concentrations of primary and cluster positive ions, primary and complex negative ions, as well as the electron density), we have calculated the ionospheric parameters that determine the behavior of the D-region under conditions of increased ionization (Solar Proton Events (SPE) on November 2–5, 1969, and the High-altitude Nuclear Explosion (HNE) conducted in 1962). Detailed analysis of the obtained parameter values has shown that the calculation results do not contradict the generally accepted photochemical mechanisms occurring under the SPE and HNE conditions considered. We identified the main trends in the changes of these parameters. A conclusion is made about the possibility of using the semi-empirical method in various heliogeophysical conditions and the need to develop a model for the transitional time of day (morning and evening twilight), and some possible directions for further research are outlined.

This paper presents the results of a study on the behavior of parameters of the ionospheric F2 layer, such as the critical frequency (f₀F2) and the peak height of the layer (hₘF2), under geomagnetic storms of varying intensities. The study is based on vertical sounding measurements from the DIDBase database and the Dst index calculated by the World Data Center for Geomagnetism. We examine a methodology for identifying the presence of a geomagnetic storm using Dst-index time series. The main patterns of f₀F2 and hₘF2 variations for different geographic latitudes, seasons, and storm intensities are identified and analyzed. The obtained results can be useful for forecasting and modeling ionospheric conditions, which is of great importance for various applications, including satellite communications, global positioning systems, and shortwave radio communications.

The paper presents the results of MHD modeling of corotating interaction regions (CIRs) at distances of 0.1 AU from the Sun (inner boundary) to much larger distances (20–30 AU) in two variants in which the magnetic field on the photosphere (1) is determined from a detailed synoptic map and (2) is represented only by the dipole component. The calculations are made for Carrington rotation 2066 (January–February 2008), using two independent software packages of Russian and Chinese groups. The time period under study is characterized by the presence of long-lived coronal holes on the Sun and a stable recurrent variation in heliosphere characteristics, as well as in the intensity of galactic cosmic rays. We discuss the advantages and disadvantages of modeling CIRs by detailed and dipole models of the photospheric magnetic field, as well as with the two mentioned software packages. The mechanisms of formation and evolution of CIRs with distance in the two models are compared and correlated to the conclusions of our previous works.

Since 2013, continuous monitoring of spatial-angular distribution of CRs for each hour of measurements has been carried out at SHICRA SB RAS, using data from the international neutron monitor database NMDB and the method of real-time global survey. For this purpose, nine parameters of the CR distribution are automatically calculated which result from the first two angular moments of the spatial distribution function of particles in interplanetary space. Our earlier studies have shown that before the onset of most geomagnetic storms with the amplitude of the geomagnetic activity Dst index lower than –50 nT there is a sharp increase in amplitudes of north-south components of CR distribution. This can serve as a predictor of the onset of geomagnetic disturbances with a lead time from several hours to 1–2 days. This paper presents the results of forecasting of geomagnetic storms with a Dst amplitude <–50 nT, observed in April–November 2024. It is also shown that the appearance of false predictors is associated with Earth’s entry into large-scale SW disturbances without geomagnetic effects.

We examine magnetic field variations within the frequency range of several millihertz (Pc5-6/Pi3 geomagnetic pulsations) in the near-Earth magnetotail and adjacent flank magnetosheath regions, using data from Cluster satellites for 2016. Dependence of spectral coherence on interval length is analyzed for a satellite pair Cluster-1 and Cluster-4 at different satellite positions relative to the magnetopause. It is shown that absolute coherence and the rate of its decline with increasing time interval length differ for the longitudinal and transverse magnetic field components, as well as for different satellite positions. We also present a case study of a coherent pulsation recorded in the magnetosheath at low solar wind velocity and weak fluctuations in front of the bow shock.

The dynamics of the parameters of ionized and neutral components of Earth’s upper atmosphere at midlatitudes near the equinox was studied for several days under quiet geomagnetic conditions. The ionospheric parameters were obtained by an incoherent scatter radar; the parameters of the neutral atmosphere at ionospheric altitudes, from characteristics of the atomic oxygen glow at a wavelength of 630 nm with a Fabry—Perot interferometer. Synchronous variations similar in relative amplitudes were detected in the glow intensity and plasma concentration, the nature of which was explained using numerical modeling, as well as a combination of model and empirical data. It is shown that the vertical wind effect is of decisive importance for the vertical transport of plasma and the enhancement of the atomic oxygen glow in the period of time considered. The phenomenon under study was associated with the midnight temperature maximum, which was first observed at 52° N. A method for calibrating optical measurements using radiophysical data is presented in the approximation of the dominant role of plasma parameter variations over neutral atmosphere parameter variations.