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An investigation is performed of variations in anisotropy and the rigidity spectrum during ground-level enhancement of the intensity of cosmic rays on September 10, 2017. It is shown that protons were accelerated to rigidities of 5–7 GV during this event.

According to the data of ground-based measurements of cosmic rays (CRs) from the world network of stations, the behavior of CR intensity during the geomagnetic disturbance in January 2015 has been studied using the spectrographic global survey method. The spectra of CR variations and spectrum indexes of these variations are presented, when approximating the spectrum by the power function of the particle rigidity in the rigidity range from 10 to 50 GV, as well as pitch-angular anisotropy of CRs. It is shown that the spectrum indexes of CR variations at its approximation by the power function of the particle rigidity in the phase of maximum modulation are greater than in the phases of decay and recovery of CR intensity.

By employing the method of spectrographic global survey, the spectra of protons and anisotropy of cosmic rays during the firstGround-Level Enhancement (GLE) of the intensity of cosmic rays in the solar cycle 24 onMay 17, 2012, a GLE71 event, are studied on the basis of data from ground-based observations of cosmic rays by means of the worldwide network of stations and data from spacecrafts. The rigidity spectra of cosmic rays and relative variations in the intensity of cosmic rays with rigidity 2 GV in the solarecliptic geocentric coordinate system are presented within individual periods of the event under study. It is shown that, in GLE71 periods, protons were accelerated to rigidities in the range of R ~ 2.3−2.5 GV and that the respective differential rigidity spectra of solar cosmic rays are not described by a power-law or an exponential function of the particle rigidity. During the event being considered, the Earth was in the loop-shaped structure of the interplanetary magnetic field.

The data from terrestrial observations of cosmic rays at the global network of stations by the method of spectrographic global survey were used to analyze two Forbush decreases during the geomagnetic storms in March and June 2015. The spectra of cosmic ray variations, pitch angle anisotropy of cosmic rays at different phases of Forbush decrease development, and the changes in the planetary system of geomagnetic cutoff rigidities are presented. It is shown that, during the approximation of the spectra of variations by the power function of particle rigidity in the interval of 10–50 GV, the spectrum index is softer at the maximum modulation phase than during the phases of cosmic ray intensity decline and recovery. In the axisymmetric model of the bounded magnetosphere of the Earth, which takes into account the currents at the magnetopause and the ring current, the distance to the subsolar point and the radius of the ring current, as well as the contribution of the ring current to the changes in geomagnetic cutoff rigidity and to the Dst index during the studied events, are determined.

Using data from ground-based observations of cosmic rays (CRs) on the worldwide network of stations and spacecraft, we have investigated the proton spectra and the CR anisotropy during the ground level enhancements of CRs on May 17, 2012 (GLE71) and January 6, 2014 (GLE72) occurred in solar cycle 24 by the spectrographic global survey method. We provide the CR rigidity spectra and the relative changes in the intensity of CRs with a rigidity of 2 GV in the solar–ecliptic geocentric coordinate system in specific periods of these events. We show that the proton acceleration during GLE71 and GLE72 occurred up to rigidities R ~ 2.3−2.5 GV, while the differential rigidity spectra of solar CRs are described neither by a power nor by an exponential function of particle rigidity. At the times of the events considered the Earth was in a loop-like structure of the interplanetary magnetic field.

We propose a mechanism for proton propagation from the Sun to Earth orbit in the electromagnetic field presented, in the simplest case, through the Parker model. Within this model, proton ingress on the Earth is shown possible in the case when the Earth is in the surroundings of the heliospheric current sheet neutral line (HCSNL), at the distance from the latter that is smaller than the Larmor radius of the protons drifting along the HCSNL. Based on that model, we analyzed the paths of the protons with energies characteristic of solar proton events. As a result of such an analysis, solar proton events on the Earth appear to be observed only in the case when energetic protons eject from an active region (AR) located in the northern (southern) hemisphere of the Sun, at the positive (negative) polarity of the solar global magnetic field in that AR. There is a minimal value for the proton energy below which solar proton events on the Earth are not observed. This energy value is proportional to the value for the angle of the latitude at which the flare AR is located.

Variations in the cosmic ray intensity (specifically, Forbush effects) and in the geomagnetic cutoff rigidity planetary system during powerful geomagnetic disturbances in cycle 23 were studied based on worldwide station network data by the global spectrographic survey method. The cosmic ray variation spectra during these periods and the spectral indices of these variations when the spectrum was approximated by the power function of the particle rigidity varying from 10 to 50 GV during different Forbush effect development phases are presented. It was indicated that the spectral indices of cosmic ray variations during spectrum approximation by the power function of the particle rigidity are larger during the maximal modulation phase than during the cosmic ray intensity decline and recovery phases. The fact that the amplitude of the second harmonic of the cosmic ray pitch angle anisotropy did not increase on November 20, 2003, confirms that the Earth fell into a Sun-independent spheromark magnetic cloud. The increased amplitudes of the second harmonic of the cosmic ray pitch angle anisotropy during other Forbush effects in July 2000, March–April 2001, October 2003, and November 2004 indicate that the Earth was in the coronal mass ejection region, in which the interplanetary magnetic field structure was loop-like during these periods.

Variations of the rigidity spectrum and anisotropy of cosmic rays in the period of the ground-level enhancement (GLE) of cosmic rays on November 6, 1997, according to the data from the worldwide network of ground-based stations and satellites have been studied by the unique spectrographic global survey method developed at the Institute of Solar–Terrestrial Physics, Siberian Branch, Russian Academy of Sciences. Rigidity spectra of cosmic rays in various periods of the event under study have been determined. It has been shown that the acceleration of protons in the period of this GLE event was observed to a rigidity of ~10–12 GV, and neither a power-law nor an exponential function of the rigidity of particles describes the differential rigidity spectra of cosmic rays in the event under consideration. The analysis has indicated that the Earth at the time of the GLE event was in a looplike structure of the interplanetary magnetic field.

Using data from a worldwide network of neutron monitors, we have investigated the cosmicray (CR) energy spectra and anisotropy during the CR increases attributable to the solar events of June 11 and 15, 1991, by the spectrographic global survey method. By jointly analyzing ground-based and satellite measurements, we have determined the parameters of the CR rigidity spectrum reflecting the electromagnetic characteristics of the heliospheric fields in each hour of observations within the framework of the model of CR modulation by regular heliospheric electromagnetic fields. The CR spectra and relative CR intensity variations in the solar—ecliptic geocentric coordinate system are presented at specific times of these events.

Using data from the worldwide network of cosmic ray stations, Forbush decreases on October 29–31 and November 20–21, 2003 were studied using method of spectrographic global survey. The indices of the variation spectrum for the power representation of the particle magnetic rigidity over the range of 10–50 GV are given for different stages of the development of Forbush decreases, which proved to be greater for the event on November 20–21 than for the one on October 29–31, 2003. A high degree of anisotropy in the angular distribution of cosmic rays in the Forbush decrease periods and its phase variability indicate the dispersal of magnetic clouds and the high degree of regularity of the interplanetary magnetic field (IMF) in these structures; the presence of bidirectional anisotropy suggests a loop structure of the IMF during the events of October 29, 2003.

The June 2015 Forbush effect is studied using ground-based measurement data on cosmic rays (CRs), obtained from the worldwide network of stations by the spectrographic global survey. When approximating the variation spectra via the exponential function of particle rigidity in the 10–50 GV range, the spectrum index is higher at the phase of maximum modulation than at those of the drop in CR intensity and its recovery.

Using ground-based cosmic-ray (CR) observations on the worldwide network of neutron monitors, we have studied the variations in CR rigidity spectrum, anisotropy, and planetary system of geomagnetic cutoff rigidities during Forbush decreases in March-April 2001 by the global spectrographic method. By jointly analyzing ground-based and satellite measurements, we have determined the parameters of the CR rigidity spectrum that reflect the electromagnetic characteristics of the heliospheric fields in each hour of observations within the framework of the model of CR modulation by the heliosphere’s regular electromagnetic fields. The rigidity spectra of the variations and the relative changes in the intensity of CRs with rigidities of 4 and 10 GV in the solar-ecliptic geocentric coordinate system are presented in specific periods of the investigated events.

We propose a model for the modulation of cosmic rays (CRs) based on changes in the CR energy in different regular electromagnetic fields of the interplanetary medium. Within the framework of the elaborated concept, an analytical expression for the CR rigidity spectrum has been obtained. It allows us to describe variations in proton intensity observed in the energy range from several MeV to several tens of GeV per hour of observation. We give a description of a method for determining parameters of the model spectrum that reflect the electromagnetic characteristics of the interplanetary medium with a different nature. Using ground-based and satellite measurements of the CR intensity, we have examined variations in the CR rigidity spectrum and anisotropy and variations in the planetary system of geomagnetic cutoff rigidities during different manifestations of solar activity. A whole set of phenomena under observation has been interpreted.

A spectrographic global survey is performed to study the rigidity spectrum and anisotropy of galactic cosmic rays using spacecraft data and data obtained via ground-based observations of cosmic rays (CRs) by a worldwide network of stations during the GLE of July 14, 2000, and the strong magnetic storm related to the coronal mass ejection (CME) accompanying the solar flare. The CR rigidity spectrum observed over the range of 1 to ∼20 GV during this period is shown to be described not only by the power function of particle rigidity; the distribution of CRs in the earthward direction varies over time and depends on their energy.

This work presents our findings on the rigidity spectrum of cosmic ray (CR) variations during certain Forbush decreases recorded by the global neutron monitor network in 1991–2005. In most of the events we consider, the rigidity spectrum of primary CR variations is not described by a power function of rigidity in the energy range at which the neutron monitors are most sensitive.

Using the spectrographic global survey method, variations in the rigidity spectrum and anisotropy of galactic cosmic rays (March 1991) have been studied using data from ground-based observations of cosmic rays (CR) at the worldwide network of stations. Variations in geomagnetic cutoff rigidity (GCR) have been calculated. The paper also presents latitudinal GCR variations at certain moments of the considered period for different geomagnetic field disturbance levels. Calculation results of GCR variations have been compared with those of effect of the westward current flowing with a strength proportional to the latitude cosine along parallels on the sphere, for different radii of the current ring in the dipole field.

According to the ground-based measurements of cosmic ray intensity on the worldwide network of stations and GOES spacecrafts, variations in cut-off rigidity in Irkutsk for the period 2004–2005 have been calculated. The calculated variations in cut-off rigidity are presented along with the Dst variations of the geomagnetic field.

We study 27-day variations of the galactic cosmic ray (GCR) intensity for 2005- 2008 period of the solar cycle #23. We use neutron monitors (NMs) data corrected and uncorrected for geomagnetic disturbances. Besides the limited time intervals when the 27-day variations are clearly established, always exist some feeble 27-day variations in the GCR 5 intensity related to the constantly present weak heliolongitudinal asymmetry in the heliosphere. We calculate the amplitudes of the 27-day variation of the GCR intensity based on the NMs data corrected and uncorrected for geomagnetic disturbances. We show that these amplitudes do not differ for NMs with cut-off rigidities smaller than 4-5 GV comparing with NMs of higher cut-off rigidities. Rigidity spectrum of the 27-day variation of the GCR intensity found in the uncorrected data is soft while it is hard in the case of the corrected data. For both cases exists definite tendency of softening the temporal changes of the 27-day variation's rigidity spectrum in period of 2005 to 2008 approaching the minimum of solar activity. We believe that a study of the 27-day variation of the GCR intensity based on the data uncorrected for geomagnetic disturbances should be carried out by NMs with cut-off rigidities smaller than 4-5 GV., Comment: 8 pages, 6 figures, presented on 24th European Cosmic Ray Symposium 2014

The variations of the cosmic-ray rigidity spectrum in the energy range from 0.8 MeV to several dozen GeV at solar proton events in January 2005 and December 2006 have been analyzed. A comparison of the observed and model spectra revealed the power range of direct detection of solar cosmic rays and moments of their observations.

Variations in the cosmic-ray (CR) rigidity spectrum during events of January 2005 have been investigated on the basis of the ground-based observations of the CR intensity performed at the world network of stations using spectrographic global survey. The parameters of the CR rigidity spectrum reflecting the electromagnetic characteristics of heliospheric fields during the events under study have been determined in the combined analysis of ground-based and satellite measurements of protons with energies from several megaelectronvolts to several tens of gigoelectronvolts. The CR variations in a wide energy range are explained on the basis of the analysis performed.

The paper presents findings of rigidity spectrum of cosmic ray (CR) variations during certain Forbush decreases recorded at the worldwide network of neutron monitors over the period 1991-2005. In the majority of events under consideration, rigidity spectrum of primary CR variations is not described by the power function of rigidity over the energy range to which neutron monitors are most sensitive.

Forbush decreases (Fd) of the galactic cosmic ray (GCR) intensity and geomagnetic storms are observed almost at the same time. Geomagnetic storm is a reason of significant disturbances of the magnetic cut off rigidity causing the distortion of the time profile of the Fd of the GCR intensity. We show some differences in the temporal changes of the rigidity spectra of Fd calculated by neutron monitors experimental data corrected and uncorrected for the changes of the geomagnetic cut off rigidity. Nevertheless, the general features of the temporal changes of the rigidity spectrum of Fd maintain as it was found in our previous investigations. Namely, at the beginning phase of Fd rigidity spectrum is relatively soft and gradually becomes hard up to reaching the minimum level of the GCR intensity; then the rigidity spectrum gradually becomes soft during the recovery phase of Fd. We also confirm that for the established temporal profiles of the rigidity spectrum of Fd a structural changes of the interplanetary magnetic field turbulence in the range of frequencies, 10 -6 10 -5 Hz are responsible.

Using the method of spectrographic global survey, rigidity spectrum and anisotropy of galactic cosmic rays during GLE on 14 July 2000 have been studied with the data from ground-based observations of cosmic rays (CR) at the world-wide network of stations. The CR rigidity spectrum observed during this period over the range 1 to ~ 20 GV is shown to be described not only by power function of particle rigidity: distribution of CRs in the earthward direction varies with time and depends on their energy.

The Forbush decrease (Fd) of the Galactic cosmic ray (GCR) intensity and disturbances in the Earth’s magnetic field generally take place simultaneously and are caused by the same phenomenon, namely a coronal mass ejection (CME) or a shock wave created after violent processes in the solar atmosphere. The magnetic cut-off rigidity of the Earth’s magnetic field changes because of the disturbances, leading to additional changes in the GCR intensity observed by neutron monitors and muon telescopes. Therefore, one may expect distortion in the temporal changes in the power-law exponent of the rigidity spectrum calculated from neutron monitor data without correcting for the changes in the cut-off rigidity of the Earth’s magnetic field. We compare temporal changes in the rigidity spectrum of Fds calculated from neutron monitor data corrected and uncorrected for the geomagnetic disturbances. We show some differences in the power-law exponent of the rigidity spectrum of Fds, particularly during large disturbances of the cut-off rigidity of the Earth’s magnetic field. However, the general features of the temporal changes in the rigidity spectrum of Fds remain valid as they were found in our previous study. Namely, at the initial phase of the Fd, the rigidity spectrum is relatively soft and it gradually becomes hard up to the time of the minimum level of the GCR intensity. Then during the recovery phase of the Fd, the rigidity spectrum gradually becomes soft. This confirms that the structural changes of the interplanetary magnetic field turbulence in the range of frequencies of 10−6 – 10−5 Hz are generally responsible for the time variations in the rigidity spectrum we found during the Fds.