Spectrographic Global Survey Research Articles

Ground level enhancements of cosmic rays in solar cycle 24

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.

Analyzing the June 2015 Forbush effect by the spectrographic global survey

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.

Analysis of ground level enhancement on January 6, 2014

Variations in the rigidity spectrum and anisotropy of cosmic rays during ground level enhancement (GLE) on January 6, 2014, is investigated using ground-based observations of cosmic rays (CRs) from the worldwide network of stations and spacecraft measurements obtained via a spectrographic global survey. The CR rigidity spectrum and relative variations in the intensity of CRs with rigidity of 4 GV are presented in the solar–ecliptic geocentric coordinate system in certain periods of the investigated event. It is shown that protons were accelerated during this GLE up to a particle rigidity of R ~ 2.4 GV. In the ~0.3 to ~2.4 GV range of rigidity, the CR differential rigidity spectra during the considered event were described by neither a power function nor an exponential function of particle rigidity. At the time of GLE, the Earth was in a loop-like IMF structure.

Ground level enhancement of cosmic rays on November 6, 1997: Spectra and anisotropy

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.

Вариации жесткостей обрезания космических лучей во время сильной геомагнитной бури в ноябре 2004 г.

Very strong interplanetary and magnetospheric disturbance observed on 7–13 November 2004 can be regarded as one of the strongest events during the entire period of space observations. In this paper, we report on the studies of cosmic ray cutoff rigidity variations during 7–13 November 2004 showing how storm conditions can affect the direct cosmic ray access to the inner magnetosphere. Effective cutoff rigidities have been calculated for selected points on the ground by tracing trajectories of cosmic ray particles through the magnetospheric magnetic field of the “storm-oriented” Tsyganenko 2003 model [Tsyganenko, 2002a, b; Tsyganenko et al., 2003]. Cutoff rigidity variations have also been determined by the spectrographic global survey method on the basis of experimental data of the neutron monitor network. Correlations between the calculated and experimental cutoff rigidities, as well as between geomagnetic Dst index and interplanetary parameters have been investigated. Correlation coefficients between the cutoff rigidities obtained by the trajectory tracing method and the spectrographic global survey method have been found to be in the limits of 0.76–0.89 for all stations except the low-latitude station Tokyo (0.35). The most pronounced correlation has been revealed between the cutoff rigidities that exhibited a very large variation of 1–1.5 GV during the magnetic storm, and the Dst index.

Features of cosmic ray modulation in October and November 2003

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.

Спектры вариаций и анизотропия космических лучей в период GLE 11 июня 1991 г.

We have studied variation spectra and cosmic-ray (CR) anisotropy, using the ground-based and satellite observations of the CR intensity on the worldwide network of stations during the ground level enhancement (GLE) of June 11, 1991. The spectro-graphic global survey has been used. Variation spectra of primary CRs at different moments of the event are presented. Note that the CR variation spectra during this period are not described by a power or an exponential function of particle rigidity. The maximum rigidity, up to which the protons were accelerated on June 11, 1991, was ~2.8 GV (06:00 UT; i.e., two hours after GLE started). We show relative variations in the CR intensity in the geocentric solar ecliptic coordinate system during certain periods of the event under study. On June 11, 1991, the bidirectional anisotropy dominated in the distribution of particles with rigidity of 4 GV and 10 GV, which implies that the Earth passed the loop-like IMF structure.

Rigidity spectrum and cosmic ray anisotropy during sporadic events in July 2000

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.

Comparing the geomagnetic thresholds of cosmic rays for two empirical models of the magnetosphere during the period of an extreme geomagnetic storm in November 2003

The accuracy of determining the geomagnetic cutoff rigidity (the geomagnetic threshold) is closely related to that of describing the magnetic field of the magnetosphere with the model used for calculations. Geomagnetic thresholds are calculated for two empirical models of the magnetosphere, Ts0l and Ts04, constructed on the basis of the same initial experimental data. The Ts01 model describes the average magnetosphere for certain conditions in the solar wind and interplanetary field. The Ts01 model focuses on describing the large-scale evolution of magnetospheric currents during a storm. A comparison of the geomagnetic thresholds for Ts0l and Ts04 with experimental thresholds calculated by the Spectrographic Global Survey from data of the CR global network stations shows that the Ts01 model describes the magnetic field of the magnetosphere more realistically. Our study was conducted for the period of a strong geomagnetic storm in November 2003.

July 2000 Forbush-effect from world network of cosmic rays stations

We studied variations in the galactic cosmic ray (CR) rigidity spectrum and anisotropy during the July 2000 strong magnetic storm from the ground-based observations of cosmic rays within the world network of neutron monitor stations through spectrographic global survey. We show the time history for amplitude variations in the rigidity spectrum of cosmic rays, their anisotropy and planetary system of the geomagnetic cutoff rigidity during the Forbush-effect evolution over that period.

Comparison of cosmic ray cutoff rigidities as calculated with two empirical magnetospheric models for the extreme event of November 2003

Cosmic ray cutoff rigidities control the access of CR particles to any location in the magnetosphere, and, hence, they are an important factor of space weather. The accuracy of determining geomagnetic cutoff rigidities is closely connected with the magnetospheric model used for the calculations. Using the trajectory tracing method and the Tsyganenko magnetospheric Ts01 and Ts04 models, we estimated changes in the effective vertical cutoff rigidities for a highly stormy period of November, 2003. The Ts01 and Ts04 models were developed on the basis of the same experimental data. The results of our calculations are compared with the geomagnetic cutoff rigidities obtained by the spectrographic global survey method using the neutron monitor world-wide network data. Our calculations were performed for several stations with quiet cutoff rigidities covering the major part of the cutoffs influenced by the geomagnetic field. Comparison shows that the cutoff rigidities calculated by using the Ts01 and Ts04 models differ by 0.8-0.9 GV during the main phase of the storm.

Cosmic ray rigidity spectrum and anisotropy during GLE on 14 July 2000

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.

Cosmic ray geomagnetic cutoff rigidities in the magnetic field of two empirical models during a strong disturbance in November 2003: A comparison of models

Cosmic ray (CR) fluxes, which penetrate into the Earth’s magnetosphere and atmosphere from the interplanetary space, are an important factor of space weather. The geomagnetic field allows or forbids CR particles to enter into a given point in the magnetosphere depending on their energy. The geomagnetic cutoff rigidity regulates the distribution of CR fluxes in the magnetosphere. The geomagnetic cutoff rigidity (geomagnetic threshold) determination accuracy is closely related to the accuracy of the magnetospheric model used in calculations. Using a method for tracing of charged CR particle trajectories in the magnetic field of a model magnetosphere, we obtained geomagnetic thresholds for two magnetosphere empirical models (Ts01 and Ts04), constructed based on the same initial database. The Ts01 model describes the middle magnetosphere for certain conditions in the solar wind and interplanetary field. The Ts04 model pays the main attention to describing the large-scale evolution of magnetospheric currents during a storm. The theoretically obtained geomagnetic thresholds have been compared with experimental thresholds, calculated using the spectrographic global survey method based on data from the global network of CR stations. The study has been performed for the period of a strong geomagnetic storm that occurred in November 2003.

Variations in cosmic ray cutoff rigidities during the great geomagnetic storm of November 2004

A very strong interplanetary and magnetospheric disturbance observed on 7–13 November 2004 can be regarded as one of the strongest events during the entire period of space observations. In this paper we report on the studies of cosmic ray cutoff rigidity variations during 7–13 November 2004 showing how storm conditions can affect the direct cosmic ray access to the inner magnetosphere. Effective cutoff rigidities have been calculated for selected points on the ground by tracing trajectories of cosmic ray particles through the magnetospheric magnetic field of the “storm-oriented” Tsyganenko 2003 model. Cutoff rigidity variations have also been determined by the spectrographic global survey method on the basis of experimental data of the neutron monitor network. Relations between the calculated and experimental cutoff rigidities and the geomagnetic Dst-index and interplanetary parameters have been investigated. Correlation coefficients between the cutoff rigidities obtained by the trajectory tracing method and the spectrographic global survey method have been found to be in the limits 0.76–0.89 for all stations except the low-latitude station Tokyo (0.35). The most pronounced correlation has been revealed between the cutoff rigidities that exhibited a very large variation of ∼1–1.5GV during the magnetic storm and the Dst index.

Effects in cosmic rays in March 1991

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.

Analysis of the Forbush effect in May 2005 using the spectrographic global survey method

Based on the data from ground observations of cosmic rays (CRs) obtained by the spectrographic global survey method on the worldwide network of stations, the variations in the rigidity spectrum and anisotropy of galactic cosmic rays were investigated, along with changes in the geomagnetic cutoff rigidity in May 2005. A high degree of anisotropy (∼40–60% for the first spherical harmonics and ∼5–6% for the second spherical harmonics) was observed for particles with a rigidity of 4 GV at the moments of the maximum modulation of cosmic rays.

Multichannel complex for cosmic ray observation as an element of the global station network

Observational data obtained with the multichannel complex for cosmic ray observation in Novosibirsk and the global network of neutron monitors are analyzed using the spectrographic global survey method. In comparing the results, we demonstrate the possibilities for effectively using the data obtained with the complex and the data from the global station network, which substantially expand the database of ground-based observations of cosmic rays.

Strong cosmic ray cutoff rigidity decreases during great magnetospheric disturbances

The theoretical and experimental cosmic ray cutoff rigidities during great magnetospheric disturbances in November 2004 and May 2005 have been determined. The theoretical geomagnetic cutoffs were calculated by the trajectory tracing method in the magnetic field of Tsyganenko’s magnetospheric model T03, which describes great magnetospheric disturbances (at Dst < 65 nT). The experimental geomagnetic cutoffs were determined by the spectrographic global survey method on the basis of the world network data. The cutoff rigidity decreases at Dst minima can reach 70–80% for theoretical cutoffs and ∼40% for experimental cutoffs at mid latitudes.

Correction of data from the neutron monitor worldwide network

The method for correcting data from individual neutron monitors at the worldwide network of cosmic ray stations, characterized by the instrument drift and sporadic variations, has been proposed. The correction is performed using the method of spectrographic global survey. The proposed method makes it possible to correct data from the global network of stations immediately during processing and can be used in studies of cosmic-ray intensity long-term variations and in the real-time operation mode.

On the possibility to check the magnetosphere’s model by CR: The strong geomagnetic storm in November 2003

We report on a study of cosmic ray cutoff rigidity variations during the strong geomagnetic storm of 18–24 November 2003. We employed the most recent Tsyganenko magnetospheric model to represent the very strong disturbed Magnetosphere. We used this magnetic field for the cosmic ray trajectory calculations to determine the geomagnetic cutoff rigidity throughout this period of severe geomagnetic disturbance. We determine the cutoff rigidity changes during this period by two methods, by trajectory calculations and by the spectrographic global survey method. The values of the change of cutoff rigidities obtained by two different methods are correlated with the D st and interplanetary magnetic field and plasma parameters and result in correlation coefficients in the range 0.63–0.84 for the various cosmic ray stations. The result of this study indicates that the most significant contributions to the cutoff rigidity changes are due to D st variation although the influence of solar wind density and B z and B y components of IMF variations is significant.