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.

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.

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.

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.

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.

In the paper, we examine the atmospheric part of the global electric circuit. When studying large-scale currents in the atmosphere flowing from the ionosphere to the ground, the ionosphere and Earth’s surface can be considered as ideal conductors with high accuracy. These currents are determined by the ground-ionosphere voltage and the spatial distribution of conductivity in the atmosphere. We employ a one-dimensional model of atmospheric electric fields and currents in which currents are assumed to be nearly vertical. Then it is possible to reduce the spatial distribution of conductivity to longitude and latitude distribution of conductivity of atmospheric columns. By integrating the conductivity over the entire Earth surface, we obtain the total conductivity of the atmosphere. Inside clouds, air conductivity decreases due to the ion attachment to water drops. Using available data on decrease in local conductivity within individual clouds, we analyze the effect of cloud density in latitude, longitude, and height on geographical distribution of conductivity and total conductivity of the atmosphere. By the example of 2009, it is shown that cloudiness reduces the total conductivity of the atmosphere by 20 %. Its variations during the day and year are so small that the model fair-weather electric field varies only by 2 % due to cloudiness. Judging by the results obtained, the influence of clouds on atmospheric conductivity does not explain the diurnal and seasonal cycles of the fair-weather electric field strength (Carnegie diagram).

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 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.

Effects of the May 10–13, 2024 extreme magnetic storm in the Asian region of Russia have been studied using experimental data from vertical and oblique sounding of the ionosphere with a continuous chirp signal. Features of ionospheric disturbances induced by the magnetic storm have been revealed: the long-lasting negative ionospheric disturbance that was manifested as a significant decrease in F2-layer critical frequencies and maximum observed frequencies of radio paths; the absence of HF signal reflections from F-region due to sporadic Es layer and increased absorption of HF signals; recording of auroral and oblique Es layers; the long-lasting G-effect during local daytime during which the F1-layer critical frequency exceeded the F2-layer critical frequency; the dusk enhancement of electron density and F2-layer peak height. We have found a correlation of variations in ionospheric parameters and the maximum observed frequencies of HF radio wave propagation modes with spatial location of the main ionospheric trough and the equatorial boundary of the diffuse electron precipitation zone.