We analyze the effect of changes in the cosmic radio noise absorption in the lower ionosphere on propagation of the auroral hiss to the ground, using observational data from the Lovozero and Tumanny observatories. Three bursts of auroral hiss have been examined whose termination is accompanied by an increase in riometric absorption up to 0.6–2.2 dB. Modeling their propagation from the magnetosphere to the ground under conditions of a perturbed electron density profile, caused by precipitation of energetic electrons, shows that even a small absorption of 0.6 dB in the ionosphere causes the auroral hiss to weaken by 45–50 dB relative to its power at an altitude of 800 km. Calculations show that with such absorption the auroral hiss power near the ground is comparable to the level of natural noise of the Earth — ionosphere waveguide, and with riometric absorption of 2.2 dB a complete termination of the auroral hiss on the ground can be expected.

We have analyzed spatial and temporal variations in ionospheric parameters over high and middle latitudes of Eurasia, using data from chains of high- and mid-latitude ionosondes during a severe magnetic storm in March 2015. To analyze the ionospheric response to the severe geomagnetic disturbance of solar cycle 24, we have employed ionosonde data on hourly average values of the critical frequency foF2 of the ionospheric F2 layer, the critical frequency of the sporadic layer foEs, and the minimum reflection frequency fmin. There are strong latitudinal and longitudinal differences between the features of temporal variations in the analyzed ionospheric parameters both under quiet conditions before the magnetic storm onset and during the storm. We discuss possible causes of the observed spatial variations in ionospheric parameters. The source of spatio-temporal variations in ionospheric ionization parameters may be inhomogeneities generated in the high-latitude ionosphere under conditions of increased helio-geomagnetic activity. During the magnetic storm main and recovery phases, periods of blackouts of radio signals from ionosondes were observed at both high and middle latitudes. During these periods, there was a significant increase in the absorption of radio waves used in ionosonde sounding, as well as in the frequency of occurrence of screening sporadic Es layers. The long-term effect of the negative ionospheric storm over high and middle latitudes of Europe is explained by the movement of the vast region of the reduced density ratio [O]/[N2] at thermosphere heights from the Far East and Siberia westward to Europe during the late recovery phase of the magnetic storm. Increased ionization of the ionospheric F2 layer with foF2 exceeding the level for quiet days before the onset of the magnetic disturbance over the vast region of Eastern, Western Siberia and Eastern Europe after the end of the magnetic storm in March 2015 is a manifestation of the aftereffect of magnetic storms. The increase in ionization was especially pronounced, as measured by the chain of mid-latitude ionosondes.

The Geminid meteor shower has been studied using data obtained by the method of baseline video observations during the period from December 01, 2021 to December 17, 2021. The meteors were examined in the brightness range from –3m to 2m and with an angular track length of at least 2°; the sample size was 327 events. The behavior of the shower is considered in terms of the interacting DRG (December ρ-Geminids) and GEM (Geminids) branches, which are closely related to each other and share a common origin. The shower activity was ZHR=127, Flux=19 at the general maximum of DRG+GEM (λsol~261.8°) and ZHR=32, Flux=4 at the putative local maximum of DRG (λsol~258.8°). Daily drift values were obtained for GEM (Δα=0.84°, Δδ=–0.27°, Δλec=0.75°, Δβ=–1.17°) and DRG (Δα=1.29°, Δδ=0.09°, Δλec=1.09°, Δβ=0.23°) in the equatorial and ecliptic coordinate systems; the intrinsic drift in the λec–λsol system was 0.09° and –0.26° for the DRG and GEM components respectively. We have found the opposite nature of the drift of both branches with a tendency for them to intersect at the point α=112.1°, δ=32.5°, λsol=259.8°. We have determined the kinematic and orbital parameters of meteoroids and have identified differences between the most probable geocentric velocities for the DRG (vg=35 km/s) and GEM (vg=34 km/s) branches. The morphology of the distribution of orbits within the plume has been studied. We give recommendations for reliably determining whether the meteors belong to one or another branch.

We present the results of numerical simulations of normal modes of the mean flow due to the superposition of cyclonic and anticyclonic vortices at high latitudes. Such a flow structure is often observed in the upper troposphere — the lower stratosphere in winter. Our aim is to identify normal modes in the oscillation spectrum that resemble torsional oscillations. We solve the problem numerically, using a barotropic quasi-geostrophic model. Additionally, we estimate the dependence of the normal modes on experimental parameters (the number of spherical harmonics in the stream function field expansion, the parameterization of viscosity and hyperviscosity). The simulation results show that flow instability almost always increases with increasing amplitude of the anticyclonic vortex to varying degrees at different viscosities and different numbers of harmonics in the field expansion. The spatial structure of the most unstable normal modes changes most chaotically when the experiment parameters and the mean flow change. This significantly complicates the interpretation of real oscillations in terms of normal modes, including the interpretation of torsional oscillations. Axisymmetric normal modes are often present in the spectrum, but they do not have all the properties of torsional oscillations and do not dominate the spectrum.

The paper overviews the main results of the study of long-term variations in characteristics of the upper neutral atmosphere and ionosphere, obtained during the implementation of Russian Science Foundation Project No. 22-17-00146 “Experimental and theoretical study of the coupling neutral and ionized components of Earth’s atmosphere”. We study and compare long-term variations in the peak electron density and temperature of the mesopause region. Their dependences on solar, geomagnetic, and atmospheric activity, as well as long-term trends, are analyzed. The analysis is based on data from long-term measurements with the ISTP SB RAS complex of instruments. The peak electron density (NmF2) data was acquired with the Irkutsk analog automatic ionospheric station for 1955–1996 and the Irkutsk digital ionosonde DPS-4 for 2003–2021. The atmospheric temperatures at mesopause altitudes (Tm) were obtained from spectrometric observations of the hydroxyl molecule emission (OH (6-2) band, 834.0 nm, emission maximum height ~87 km) for 2008–2020. The analysis uses solar (F10.7) and geomagnetic (Ap) activity indices, as well as data on variations in the Southern Oscillation Index (SOI). The study employs simple and multiple linear regression methods. Annual average NmF2 values are found to be predominantly controlled by changes in solar flux. Analysis of regression residuals shows that the largest deviations from regression (for both simple and multiple regression) are observed in years near the maxima of solar cycles 19 (1956–1959) and 22 (1989–1991). Annual average temperature variability in the mesopause region correlates with changes in the SOI index: day-to-day variability exhibits a positive correlation with SOI; and intra-diurnal variability, a negative correlation with SOI. No significant relationship was found between year-to-year variations in the NmF2 and Tm variability.

The article presents the results of long-term observations of cosmic ray variations and changes in atmospheric parameters at midlatitudes in the Novosibirsk Region. The atmospheric response to Forbush decreases in galactic cosmic rays (CR) and solar proton events is analyzed. The analysis involves 181 Forbush decreases and 18 GLEs (Ground Level Enhancement) for the period 1967–2019. This makes it possible to examine the effect depending on season. The effect of increasing pressure during the Forbush decrease in cosmic rays is more pronounced in the autumn-winter period. Nonetheless, it also occurs in the warm season. For midlatitudes, there is also a tendency for pressure to increase after GLE. At the Forbush decrease front, with a decrease in CR intensity and an increase in atmospheric pressure, an increase in the average mass and surface temperature is observed. In the intensity recovery phase after the Forbush decrease, a decrease in the average mass and surface temperature occurs. The observed variations in atmospheric parameters are assumed to be due to changes in the ionization rate under the influence of cosmic rays in variations in atmospheric transparency and cloudiness.

Precision neutron monitors providing continuous monitoring with a statistical accuracy of ~0.15 %/hr are effective for studying cosmic ray variations; therefore, contributions from other error sources should not exceed the contribution of this statistical error. Such possible sources primarily include changes in atmospheric pressure and humidity. The aim of the work is to estimate the barometric effect of the neutron component of cosmic rays for the low-latitude stations Tashkent and Alma-Ata (mountain), including periods of maximum solar activity. The technique developed on the basis of multifactor correlation analysis is applicable to processing data from any detectors of the worldwide network of neutron monitors. As a result, we have obtained annual average barometric coefficients of the neutron component at the stations Tashkent and Alma-Ata. The humidity effect was also estimated for the mid-latitude station Moscow. The study draws the conclusion that the approach considered can effectively solve the problem.

This paper presents the results of analysis of oblique ionospheric sounding data obtained with continuous chirp signal on the subauroral paths Magadan—Irkutsk and Norilsk—Irkutsk. It specifies the interplanetary sources of magnetic storms in November–December 2023. It was established that signals propagating outside the great-circle arc and additional diffuse reflections can be found in oblique sounding ionograms in intense magnetospheric convection field. Their appearance can be related to refraction of radio waves on the polar wall of the main ionospheric trough and scattering by small-scale inhomogeneities. Connection has been revealed between variations in the maximum observed frequencies of HF radio wave propagation modes with the spatial position of the main ionospheric trough and the equatorial boundary of diffuse electron precipitation zone.

We study the relationship between space weather disturbances and spatial distribution of failures in railway automatics at segments of Northern and October railways in 2001–2006. During the most intensive magnetic storms that caused numerous failures, latitude distribution of auroral electron precipitation and local geomagnetic disturbance, determined as mean absolute value of time derivative of the geomagnetic field horizontal component |dBH/dt|, are examined. We show that in magnetic storm main and recovery phases the segments, where the failures were recorded, correspond to the region of intense auroral precipitation and |dBH/dt| exceeded 5 nT/s. The relationship between position of auroral oval equatorial boundary and spatial distribution of failures is analyzed for individual magnetic storms and statistically for five years of observations. Both individual cases and statistic tests show that southward displacement of the auroral oval equatorial boundary correlates with increase in the proportion of failures at lower latitude railway segments.