The 12 November 2025 G4 geomagnetic storm—the third most intense of solar cycle 25—was triggered by a complex shock-ICME (interplanetary coronal mass ejection) structure as a result of three ICMEs and driven shocks that arrived on 11–12 November. The main enhancement in the interplanetary magnetic field occurred in the sheath region behind the shock driven by the second ICME. The Dst index reached −217 nT (the SYM-H index reached −254 nT) and the maximum Kp index was 9-. To comprehensively analyze the causes of the storm and its complex effects on near-Earth space, we used a multi-instrumental data set, involving data from satellite missions (ACE, SDO, PROBA2), GNSS networks, ionosondes, optical instruments, high-frequency radars (SuperDARN-like), and cosmic ray monitors. The auroral oval expanded equatorward (down to ~35° N in America). We recorded a super equatorial plasma bubble that almost reached the auroral oval boundary. The equatorial anomaly crests intensified, exceeding 175 TECU, and shifted poleward (8–10°). At mid-latitudes, the F2 layer critical frequency exhibited a strong negative disturbance (−50%) during the main phase, followed by an unusually prolonged and intense positive phase (+100%). GPS Precise Point Positioning errors increased to 2–3 m at high latitudes and in regions affected by the equatorial bubble. The event also featured a Forbush decrease and ground-level enhancement (GLE 77 according to the database hosted by the University of Oulu) associated with the X5.1 solar flare. The results underscore the complex chain of processes from solar storm to geomagnetic and ionospheric responses, highlighting the risks to satellite-based navigation and communication systems.

We investigated the conditions of the heliosphere, magnetosphere, and atmosphere from cosmic ray (CR) observations during the 2018 Aug 25-26 strong geomagnetic storm. The analysis involved the global survey (GS) and the spectrographic global survey (SGS) methods created and developed at the Yu.G. Shafer Institute of Cosmophysical Research and Aeronomy of the Siberian Branch of the Russian Academy of Sciences (ShICRA SB RAS) and at the Institute of Solar-Terrestrial Physics of the Siberian Branch of the Russian Academy of Sciences (ISTP SB RAS). Also, in our analysis, we used the data on direct measurements of the interplanetary medium parameters from the known OMNI database, CR measurements at the GOES geostationary satellites, from the global network of neutron monitors and muon detectors, from the Sayan spectrograph, and from the A.I. Kuzmin Yakutsk spectrograph of CR. When analyzing this event, the SGS enabled to obtain the data on the orientation of the mean interplanetary magnetic field, on the geomagnetic cutoff rigidity and its variations during the geomagnetic storm. Also, this method allowed us to estimate the bulk temperature over the point of recording CR, the ring current and the magnetopause current, as well as their contributions to the Dst-index, and also to establish differential rigidity spectra of CR at different stages of the magnetic storm evolution. Through the GS method, we determined the value and the directions for the first two spherical harmonics of CR distribution, and the direction to their anisotropy source. The results obtained through two different global survey methods are shown to be agree and mutually supplement each other. Using the Yakutsk spectrograph records enabled to determine the index for the power energy spectrum of variations in CR intensity during the investigated event. (c) 2024 COSPAR. Published by Elsevier B.V. All rights reserved.

Using a spectrographic global survey method, we carried out an analysis of two weak ground-level enhancements of cosmic rays: May 2 (GLE56) and August 24 (GLE58). We used data from the worldwide network of neutron monitors (time definition of 5 minutes) and data from GOES 9 and 10 spacecraft. Differential rigidity spectra of solar cosmic rays were obtained, and the maximum rigidities of particle acceleration in these events were determined. We confirmed that the maximum rigidity of accelerated particles for both GLEs is below ~2–3 GV. We also demonstrate spatial distributions of 2-GV primary particles. Bidirectional anisotropy has been found, which gives evidence of the Earth’s presence in a loop-like structure of the interplanetary magnetic field.

We present the results of near-Earth interplanetary space, magnetosphere, and atmosphere monitoring during large-scale solar wind disturbances at the end of August 2005. The monitoring was carried out using ground-level cosmic ray (CR) observations made at the worldwide network of neutron monitors as well as muon telescopes in Yakutsk and Novosibirsk. As a result of the analysis performed by different methods, we have obtained variation properties of CRs of different rigidities in Earth’s orbit, their pitch angle anisotropy, orientation and configuration of the interplanetary magnetic field, changes in the planetary system of geomagnetic cutoff rigidities during geomagnetic disturbances, as well as mass average air temperature over CR stations equipped with muon telescopes. For the periods of geomagnetic disturbances, we have determined parameters of magnetospheric ring current and magnetopause currents.

Ground-based observations of cosmic rays by the spectrographic global survey method were used to study the ground-level enhancement in cosmic ray intensity on August 24, 2002. Spectra of variations of primary cosmic rays and their anisotropy were obtained. Based on measurements from the GOES spacecraft and global network of cosmic ray stations, the differential rigidity spectra of accelerated particles in the vicinity of the Sun were calculated. The maximum rigidity to which solar particles were accelerated was estimated.

Based on ground-based observations of cosmic rays (CRs) on the global network of neutron monitors, the Yakutsk complex of muon telescopes, and the URAGAN muon hodoscope (Moscow), the spectra of CR variations and anisotropy during the Forbush effects of March 15 and 23, 2023 were calculated using the spectrographic global survey method. It is shown that the spectrum of CR variations during these periods is not described by a power function in a wide range of rigidities. It was found that the Earth was in a loop-shaped structure of the interplanetary magnetic field on March 15 and that it entered a magnetic cloud with closed field lines on March 23.

From the data (uncorrected for temperature effect) of the global network of neutron monitors (GNNM), along with the data of the Yakutsk muon telescope suite and the URAGAN muon hodoscope (Moscow), we applied a modified spectrographic global survey (SGS) for the 2018 Aug event to split cosmic ray variations into components of primary, magnetospheric, and atmospheric origin. Obtained were the time evolutions for the different-rigidity primary particle isotropic flux, pitch-angle anisotropy of cosmic rays (CRs), and interplanetary magnetic field (IMF) orientation. We provide variations in the rigidity of the geomagnetic cutoff (RGC) in Irkutsk and in the average bulk temperature at the points that observe charged components.

We address variations in the rigidity spectrum and anisotropy of cosmic rays (CRs) during the 1998 Aug 24 Ground Level Enhancements (GLEs) from the satellite (GOES-10) and ground-based observations at the global network of neutron monitors by using the Spectrographic Global Survey techniques. We also determined CR differential rigidity spectra for different hours of the investigated event. The accelerated proton maximal rigidity in the GLE was shown to be 2.5 GV.

From ground-based observations of cosmic rays (CR) at the global network of neutron monitors, Yakutsk suite of muon telescopes, and the URAGAN muon hodoscope (Moscow), through the modified method of the spectrographic global survey we investigated variations in CR of magnetospheric and atmospheric origin for September, 2017. We demonstrated the possibility to use the data on the unstable charged component of secondary CRs for the study of CR variations without the need to introduce corrections for temperature effect. Obtained were temporal variations in the planetary system of the CR rigidities of geomagnetic cutoff (RGC) and in the mass average air temperature at the points of observation of the charged components. Based on the data on the RGC planetary system variations within the axisymmetric model for the Earth bounded magnetosphere, we calculated the parameters for some magnetospheric current systems during the 2017 September geomagnetic disturbances.

For the 2017 Sep 6–9 geomagnetic disturbance, we calculated (within the Tsyganenko magnetospheric magnetic field model Ts01) the cosmic ray (CR) geomagnetic cutoff threshold rigidities. We also compared those values with the calculation results obtained from ground-based observations at the global network of neutron monitors (GNNM) through the spectrographic global survey (SGS). Shown is a satisfactory correlation between the geomagnetic cutoff threshold rigidity variations obtained based on the Ts01 model and those obtained from the GNNM ground-based observations. An intercorrelation of the CR geomagnetic threshold variations with the parameters for geomagnetic activity, for solar wind, and for the interplanetary magnetic field (IMF) was established to be different at different stages of the magnetospheric-geomagnetic disturbance. This is because such an intercorrelation is caused by the dynamics of current systems, whose intensifying and damping occur differently over different time intervals. During the storm main phase, the geomagnetic cutoff rigidity threshold variation is shown to be governed, mainly, by the Dst and by the solar wind velocity, as well as by the IMF southern component and by the electric field azimuth component.

The geomagnetic cutoff rigidity of cosmic rays (CRs) is the main factor regulating the arrival of CR particles at a given point on Earth's surface or inside the magnetosphere. To study the relationship between cutoffs and near-Earth space parameters, we have selected the strongest magnetic storm that occurred on March 8–11, 2012 during the CAWSES-II interval, recommended by SCOSTEP for detailed studies of solar-terrestrial relations. We have found the geomagnetic cutoffs by two methods: 1) by trajectory calculations in the magnetic field of the perturbed magnetosphere according to the Ts01 model and 2) by the spectrographic global survey method according to the data from the world network of neutron monitors. The largest drop in the cutoffs (−1.1 GV) obtained by the latter method was observed during the recovery phase of the storm. Apparently, this is due to the influence of the supersubstorms that occurred at that time. The analysis has shown that the closest connection of variations in the cutoffs can be traced with the geomagnetic activity index Dst, which indicates the determining contribution of the ring current to the transport of CRs. In addition, we have found a significant connection with the electromagnetic field parameters (with the Bz component of the interplanetary magnetic field and the azimuthal component of the electric field Ey). The dynamic solar wind parameters practically do not control variations in CR geomagnetic cutoff rigidities.

Parameters of the systems of magnetospheric currents in events of May, 1998, are obtained using data from the spectrographic global survey by the global network of neutron monitors. Systems of currents in the magnetopause and the ring current of the inner magnetosphere are determined using an axisymmetric model of the Earth’s limited magnetosphere, along with their contribution to the Dst index and variations in the rigidity of the geomagnetic cutoff over the considered period.

Using data (uncorrected for the temperature effect) from the global network of neutron monitors (GNNM), along with data from the Yakutsk muon telescope complex and the muon hodoscope URAGAN (Moscow), we have applied a modified spectrographic global survey (SGS) method to the 2018 August event in order to split cosmic ray variations into components of primary, magnetospheric, and atmospheric origin. We obtained time variations in the 4 GV-rigidity primary particle isotropic flux and pitch-angle anisotropy, as well as in the interplanetary magnetic field (IMF) orientation. We also showed variations in the geomagnetic cutoff rigidity (GCR) in Irkutsk. Using the obtained data on the changes in the planetary system of GCR within a simple model of a bounded magnetosphere, we have calculated some parameters of magnetospheric current systems, namely, the ring current radius, the magnetopause current radius, and the Dst index.

We have studied the features of the latitudinal behavior of geomagnetic thresholds of cosmic rays R , as well as their sensitivity to the interplanetary medium and magnetospheric parameters during three phases of the magnetic storm on September 7–8, 2017, in the initial, main, and recovery phases. For this purpose, values of R were calculated in two different ways—by the method of spectrographic global survey ( R sgs ) and by the method of tracing the trajectories of cosmic-ray (CR) particles in the model magnetic field ( R ef ). The maximum lowering of thresholds is observed at the storm maximum ( Dst = –142 nT), reaching the values of Δ R sgs = –0.52 GV and Δ R ef = –0.66 GV. The curve of Δ R sgs variations, depending on the observation station (latitude) cutoff rigidity, assumes a classical form with a maximum dropping the thresholds at midlatitudinal stations. Δ R correlates most strongly with the Dst index, which indicates that the ring current plays a main part in the dependence of variations of CR cutoff rigidities. The significant influence of solar-wind velocity V and interplanetary magnetic field (IMF) parameters on Δ R sgs and Δ R ef is also seen. In the main phase, Δ R ef depends on B and Bz of the IMF, and Δ R sgs depends on B and By . For Δ R sgs , the correlation with electromagnetic parameters varies, depending on the observation station, in a regular manner. There is no such tendency for Δ R ef .

Using data from the worldwide network of neutron monitors (39 stations) and the method of global spectrographic survey, we have studied pitch-angle anisotropy and differential rigidity spectra of cosmic rays during the ground level enhancements on May 2 and 6, 1998. We obtained differential rigidity spectra of solar cosmic rays in these events and determined the maximum rigidities to which protons accelerated. The maximum rigidities of accelerated protons during the ground level enhancements on May 2 was ~2.4; on May 6, ~1.8 GV. The revealed bidirectional pitch-angle anisotropy indicates that Earth was in the IMF loop structure during these events.

We analyze the Sun-to-Earth transport of energetic protons accelerated in solar flares. We use a model which assumes that protons move earthward in the Parker electromagnetic field. In this model, protons are shown to be recorded on Earth when they, moving away from the solar flare region, reach the vicinity of the heliospheric current sheet, while Earth is at a distance smaller than the proton Larmor radius from the current sheet neutral line. We present the analysis of experimental data on solar flares in August–September 2011. This analysis shows that the absence of energetic protons recording in the vicinity of Earth for some major solar flares can be explained by the proposed model.

We present a modified spectrographic global survey method to split the cosmic ray variations into components of the interplanetary, geomagnetospheric, and atmospheric origin from ground-based observations of the cosmic ray intensity. We show a possibility to use all the available suite of ground-based instrumentation recording cosmic rays (global network of the neutron monitors located at different locations and altitudes, ground-and underground-based muon telescopes, etc.) for such studies without involving the data from aerologic atmospheric sounding. As a demonstration of the method functionality, we provide the calculation results for the variations in the isotropic flux, pitch angle anisotropy of primary cosmic rays in the interplanetary space, changes in the planetary system of geomagnetic cutoff rigidities for every observational hour, as well as the atmosphere temperature above the point of observation of cosmic ray charged components for selected time intervals.

The correlations between variations in the geomagnetic cutoff rigidity of cosmic rays and the Dst and Kp geomagnetic indices and solar-wind and IMF parameters are calculated for the three phases of the magnetic storm of November 20–21, 2003: before the storm and during its main and recovery phases. The correlations are the strongest between variations in the cutoff rigidity and the Dst index during all stages. A significant correlation was recorded with the By component of IMF and the field magnitude B; the correlation with By dominated during the main phase, and the correlation with B was dominant during the recovery phase. There is also a high correlation with the dynamic parameters of solar activity during the main phase, especially with the solar-wind speed. As far as we know, hysteresis phenomena have been discovered for the first time in the relationship between the cosmic-ray cutoff rigidities and the parameters of the helio- and magnetosphere on the scale of the magnetic storm (with Moscow station as an example). Loop-like patterns formed, because the trajectories of variations in the cutoff rigidities versus the studied parameters during storm intensification (development of current systems) did not coincide with the trajectories during the recovery phase (decay of current systems). The correlations of the cutoff rigidities with Dst and Kp indices were characterized by a narrow hysteresis loop, and their correlations with the IMF parameters were characterized by a wide hysteresis loop. The hysteresis loops for the relationship between the cutoff rigidities and solar-wind density and pressure were disordered.