In this paper, we calculate geomagnetic cutoff rigidities during the strong magnetic storm of March 23–24, 2023, using 1) the spectrographic global survey method based on observational data from cosmic ray recording by the global network of stations (Rsgs); 2) numerical trajectory calculations in a model magnetic field of the magnetosphere (Reff). The geomagnetic cutoff rigidity has been determined for nine cosmic ray stations at different latitudes. We calculated the correlations of the variations in the geomagnetic cutoff rigidity ΔRsgs and ΔReff with magnetic and dynamic solar wind parameters and the geomagnetic activity indices Dst and Kp. It has been found that the geomagnetic cutoff rigidity calculated by both methods correlate most strongly with Dst and the electromagnetic parameters of the solar wind. No significant correlation with the dynamic parameters was observed. The analysis has shown that the response of ΔRsgs to the controlling magnetic parameters and Dst changes with latitude of the observation station: the correlation reaches its highest values at midlatitudes and drops significantly toward the equator. The correlations of ΔReff calculated by the model do not reveal a latitudinal dependence.

We present an overview of the history, the main scientific results and prospects of the Chinese-Russian Joint Research Center on Space Weather. The Chinese-Russian Joint Research Center was established by the Institute of Solar-Terrestrial Physics SB RAS (ISTP SB RAS) and National Space Science Center CAS (NSSC CAS) in 2000. The center deals with fundamental issues in modern solar-terrestrial physics, such as quantitative description of the processes in complex interconnected system Sun — interplanetary medium — magnetosphere — ionosphere — atmosphere, assessment of capabilities of predicting interactions within this system, development of effective models for forecasting the state of the atmosphere and near-Earth space. Over the 24-year period, the Joint Research Center has united more than 10 scientific institutes in Russia and China; about 60 scientific projects have been implemented, and more than 400 joint scientific articles have been published. Joint efforts of Russian and Chinese researchers allowed obtaining important results in study of physical processes in near-Earth space. The Chinese-Russian Joint Research Center has proven its usefulness and continues studying the Sun, solar-terrestrial relations, and near-Earth space. The future work of the Joint Research Center will be closely linked to the implementation of major unique projects in China and Russia: the International Meridian Circle Program (IMCP) led by NSSC CAS, and the National Heliogeophysical Complex of the Russian Academy of Sciences (NHC RAS) led by ISTP SB RAS. We describe these projects in this paper

The paper presents the results of experiments on the impact of powerful high-frequency radio emission from the SURA mid-latitude heating facility (56.1° N, 46.1° E) on Earth's ionosphere. The disturbance in the ionosphere was created by a radio wave of extraordinary polarization under conditions when the ordinary component of the powerful wave was not reflected by the ionosphere. The sounding of the disturbed region was carried out with a probe radio wave of the same polarization at a frequency higher than the heating frequency by 228–400 kHz. During the impact on the ionosphere, a weak scattered signal with an amplitude 40–60 dB lower than the amplitude of the specular reflection signal from the F-region was received from the height of reflection of the powerful radio wave. This means that the artificial disturbance of the plasma density occurred in the region of reflection of the powerful radio wave of extraordinary polarization. Possible causes of the disturbance are discussed.

One of the very important international events in space science that has happened recently is the launch of the International Meridian Circle Program (IMCP). A key element of IMCP is a quite new instrument — the Solar Full-disk Multi-layer Magnetograph (SFMM) installed at Gan Yu Solar Station (GYSS) of the Purple Mountain Observatory (Jiangsu Province). The main objective of this telescope is to provide data on distribution of magnetic fields across the solar surface, which is necessary for prediction of some space weather (SW) parameters since this information is actually the low boundary condition for corresponding numerical simulations. There are plans to construct a network of such telescopes (similar to GONG or to ngGONG), so it is very important to test how reliable the measurements of weak large-scale magnetic fields (LSMF) are with these instruments. It is just LSMF, not strong magnetic fields in active regions (which are relatively easy to measure), that determines the structure of the heliosphere. To do this, using first observations with SFMM at GYSS, is the main purpose of this study. After a brief description of the instrument and some methodical issues, we present the results of comparison of SFMM observations with the Wilcox Solar Observatory (WSO) data. WSO measurements of LSMF are the most reliable in the world, and the results of such comparison are extremely important. We have found out that the correlation coefficient is high enough (≈0.70) if we consider the whole range of measured strengths, but it is lower (≈0.57) if the consideration is rerstricted only to relatively weak (|B|≤10.0 G) fields. Note that there is a significant difference between regression coefficients (R) for these two cases: R≈5.1 in first case and only R≈1.8 in the second one. The reason of this is still unclear and will be the subject of future investigations.

We have studied the relationship between the Dst index and heliospheric parameters during 933 isolated geomagnetic storms observed over the period from 1964 to 2010. The storms were classified by their onset type (sudden or gradual) and intensity (weak, moderate, and strong). We have analyzed the Dst index, solar wind, and interplanetary magnetic field (IMF) data accumulated using the epoch superposition method. It is shown that over the time interval of development of varying intensity storms with sudden and gradual onset the trajectory of Dst change depending on heliospheric parameters during the main phase of the storms does not coincide with its trajectory during the recovery phase, which is typical of the hysteresis phenomenon. During the storms, Dst forms hysteresis cycles with all analyzed solar wind and IMF parameters. The obtained dependences Dst(B), Dst(Bz), Dst(Ey), Dst(V), Dst(Pdyn), and Dst() have the shape of a hysteresis loop during the excitation of weak, moderate, and strong storms. The shape and area of hysteresis loops was found to change depending on heliospheric parameters and storm intensity. It is shown that the shape of the average Dst dynamics during the storms does not depend on their intensity, i.e. it is invariant. Invariant behavior is also characteristic of the shape of the average dynamics of heliospheric parameters during the magnetic storms of different intensities. Based on the nonlinear relationship of the Dst index with interplanetary parameters and the invariance of the shape of its dynamics, an integral equation of the Volterra type is proposed to describe the Dst dependence on solar wind and IMF parameters. The proposed model is suitable for interpreting the results obtained from the experimental study of hysteresis effects associated with phase shifts between changes in Dst and heliospheric parameters.

Using numerical calculations with a model of the high-latitude ionosphere in Eulerian variables, we study the influence of magnetospheric convection on the large-scale structure of the ionosphere during a moderate geomagnetic storm for winter solstice conditions. The disturbed electric field of convection is shown to cause changes in the shapes and sizes of the main structural formations of the ionosphere. We have found out that the effect of a geomagnetic storm depends on the time of the beginning of the disturbance due to the mismatch between the geographic and geomagnetic poles (UT control). The effect is most pronounced in the case of a storm that begins at 16 UT, when the disturbed electric field of magnetospheric convection transfers plasma of the daytime ionosphere to the nightside. It is shown that during periods of disturbances along with the horizontal component of the electromagnetic drift its vertical component, which causes an increase in the height of the F2-layer maximum on the dayside and its decrease on the nightside, also has a significant effect.

Neutron monitors (NMs), located at different points on the planet, allow us to study the time, energy, and angular characteristics of galactic and solar particle fluxes. Since NMs are located inside Earth's magnetosphere, their response depends on their location on the planet's surface, which can be characterized by the geomagnetic cutoff rigidity. Its calculation depends on the magnetic field model, the date, and even on numerical methods. The paper presents calculated geomagnetic cutoff rigidities at the locations of some neutron monitors and compares the cutoff values with the calculation results obtained by other authors, including a comparison of the time dynamics over the past decade. We show that the geomagnetic cutoff rigidities obtained for 2020 by the IGRF-14 model differ from those derived by IGRF-13; however, for 2015 the difference between the models is negligible. We demonstrate a tendency for the geomagnetic cutoff rigidity to decrease over time, especially at midlatitudes. Comparison of the obtained geomagnetic cutoff rigidities with those obtained by other authors has shown that in most cases the difference does not exceed 0.2 GV. Such discrepancies are significant only in the circumpolar region, where particles are mostly shielded by Earth’s atmosphere rather than by the geomagnetic field. We show that the accuracy of the algorithm in use is comparable to that of other existing instruments and is sufficient for calculating neutron monitor responses.

In the paper, we examine the spatial structure of eigenharmonics of the poloidal Alfvén resonator recorded by the RBSP-B satellite on 23 October 2012 at 19:12–20:24 UT. We employ the method of phase portraits, which is a set of plots of magnetic/electric field components of oscillations as well as the phase shift between transverse components, to interpret the data. Based on the theoretical description of magnetospheric MHD waves, an analytical solution for eigenharmonics of the poloidal Alfvén resonator is framed. The phase shift of individual harmonics of the observed oscillations is shown to have a quasi-periodic structure, which allows us to confirm that they have resonator modes, and the magnetic field components analytically calculated along the satellite trajectory qualitatively coincide with the satellite data. From comparison of theoretical calculations of the structure of transverse magnetic field components with observational data, we put forward an assumption that the second and fourth harmonics of the poloidal resonator make the main contribution to the observed oscillations.

In July–August 2024 on the Kola Peninsula, the FENICS-2024 experiment was conducted to generate artificial electromagnetic signals at night, using two power transmission lines as a horizontal radiating antenna. The generator frequency varied discretely from session to session from 1 to 194 Hz with current amplitude from ~150 A at low frequencies to ~40 A at high frequencies. The paper presents the results of the first stage of the experiment when the power transmission line Vykhodnoy—Olenegorsk with a distance between earth electrodes of substances L=84 km was utilized as a radiating antenna. Magnetic stations, located from ~1200 to ~2100 km from the nodal substation, recorded signals with frequencies from 1 to 9 Hz with ~0.3–~6.0 fT/A amplitudes normalized to the emitter current. The observations have shown the promise of the new type of active experiments on creating a probing signal for magnetotelluric sounding over a large area. The observation results will be compared with theoretical models in the subsequent work.