COSMIC RAY VARIATIONS in November, 2012

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.

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.

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.

Solar, geomagnetic and cosmic ray intensity changes, preceding the cyclone appearances around Mexico

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.

Investigation on contribution of neutron monitor data to estimation of aviation doses

The pressure corrected hourly data from the global network of cosmic ray detectors, measurements of the interplanetary magnetic field (IMF) intensity (B) at Earth’s orbit and its components B x , B y , B z (in the geocentric solar ecliptic coordinates) are used to conduct a comprehensive study of the galactic cosmic ray (GCR) intensity fluctuations caused by the halo coronal mass ejection of 13 May 2005. Distinct differences exist in GCR timelines recorded by neutron monitors (NMs) and multidirectional muon telescopes (MTs), the latter respond to the high rigidity portion of the GCR differential rigidity spectrum. The Forbush decrease (FD) onset in MTs is delayed (∼5 h) with respect to the onset of a geomagnetic storm sudden commencement (SSC) and a large pre-increase is present in MT data before, during, and after the SSC onset, of unknown origin. The rigidity spectrum, for a range of GCR rigidities (≤200 GV), is a power law in rigidity (R) with a negative exponent (γ=−1.05) at GCR minimum intensity, leading us to infer that the quasi-linear theory of modulation is inconsistent with observations at high rigidities (>1 GV); the results support the force field theory of modulation. At present, we do not have a comprehensive model for the FD explaining quantitatively all the observational features but we present a preliminary model listing physical processes that may contribute to a FD timeline. We explored the connections between different phases of the FD and the power spectra of IMF components but did not find a sustained relationship.

The correlation between the variations of geomagnetic cutoff rigidity ΔR and interplanetary parameters and the Dst index of geomagnetic activity during one moderate and six strong storms of solar cycles 23 and 24 has been calculated. The ΔR values have been obtained with two methods: (1) the spectrographic global survey method (SGS), in which the determination of the cutoff rigidity RSGS is based on observational data from the neutron monitor network, and (2) a method in which the particle trajectories are calculated numerically in a model magnetic field of the magnetosphere to determine the cutoff rigidity Reff. In general, the results obtained by the two methods are in close agreement. The Dst index of geomagnetic activity has the greatest effect on ΔR, and the correlation increases with storm intensity. The sensitivity of ΔR to interplanetary parameters vary greatly for different storms. The most geoeffective interplanetary parameter is the solar-wind speed V. A significant anticorrelation of ΔR and V can be traced for almost all storms. The correlation of ΔRSGS with the Bz component of the interplanetary magnetic field is observed only for two storms, on November 7–14, 2003, and November 7–8, 2004, for which the absolute Bz value was very high (≈−50 nT). At the same time, there is a rather high correlation of ΔReff with Bz for most storms. The azimuthal component of the interplanetary field By and the solar-wind dynamic pressure P show almost no connection with ΔR.

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 the results of an investigation of the relation between space-weather parameters and cosmic ray (CR) intensity modulation using algorithm-selected Forbush decreases (FDs) from Moscow (MOSC) and Apatity (APTY) neutron monitor (NM) stations during solar cycle 23. Our FD location program detected 408 and 383 FDs from MOSC and APTY NM stations respectively. A coincident computer code employed in this work detected 229 FDs that were observed at the same Universal Time (UT) at the two stations. Out of the 229 simultaneous FDs, we formed a subset of 139 large FDs(%) ≤ − 4 at the MOSC station. We performed a two-dimensional regression analysis between the FD magnitudes and the space-weather data on the two samples. We find that there were significant space-weather disturbances at the time of the CR flux depressions. The correlation between the space-weather parameters and decreases in galactic cosmic ray (GCR) intensity at the two NM stations is statistically significant. The implications of the present space-weather data on CR intensity depressions are highlighted.

The Earth’s atmosphere is incessantly bombarded by energetic charged particles called cosmic rays (CR) which are having either solar or non-solar origin. Analysis based on information theoretic estimators can be effectively employed as a potential technique to analyze the dynamical changes in cosmic ray intensity during different solar cycles. In the present study, dynamical complexity based analysis using Jensen-Shannon divergence (JSD) has been employed which reveals the existence of some peculiar fluctuation properties in CRI flux at Jung neutron monitor station. JSD based dynamical complexity analyses confirm the existence of difference in dynamical properties of CR flux during solar cycles 20-21 and 22-23.

We have studied the latitude behavior of cosmic ray cutoff rigidity and their sensitivity to Bz and By components of the interplanetary magnetic field and geomagnetic activity indices Dst and Kp for different phases of the November 7–8, 2004 strong magnetic storm. Cutoff rigidities have been calculated using two methods: the spectrographic global survey method in which the cutoff rigidity is determined from observational data, acquired by the neutron monitor network, and the method in which particle trajectories are calculated numerically in a model magnetic field of the magnetosphere. We have found that the sensitivity of observed cutoff rigidities to Dst changes with latitude (threshold rigidity of stations) is in antiphase with changes in the sensitivity to By. During the recovery phase of the storm, the Dst correlation with By is significantly greater than that with Bz, and the Kp correlation with Bz is greater than that with By. The By component is shown to be a predominant driver of the current systems that determine the Dst evolution during the recovery phase.

The space weather impacts propagation of galactic cosmic rays (CRs) in the heliosphere as explained by the diffusion-convection mechanism which predicts that the variation in CR intensity should be anticorrelated with changes in solar wind velocity (${\mathrm{V}}_{\mathrm{SW}}$). Several unrelated solar phenomena, including periodic ones such as 27 d solar rotation, annual, 11 yr solar activity, 22 yr solar magnetic cycle etc., and transient ones, for example, Forbush decreases (FDs), and ground level enhancements generally caused by solar flares or coronal mass ejections also affect CR intensity on Earth. These solar phenomena make a quantitative study of dependence of CR intensity on ${\mathrm{V}}_{\mathrm{SW}}$ rather difficult. Here, the high statistics muon data of six years (2000--2005) from the large GRAPES-3 muon telescope have been used to study the correlation between ${\mathrm{V}}_{\mathrm{SW}}$ and CR intensity. Data gathered during these six years were used after minimizing the contribution of various unrelated solar phenomena outlined above. We observed a strong anticorrelation between the variations in ${\mathrm{V}}_{\mathrm{SW}}$ and CR intensity at a significance of $19\ensuremath{\sigma}$.

Some workers have claimed that the observed temporal correlations of (low level) terrestrial cloud cover with the cosmic ray intensity changes, due to solar modulation, are causal. The possibility arises, therefore, of a connection between cosmic rays and Global Warming. If true, the implications would be very great. We have examined this claim in some detail. So far, we have not found any evidence in support and so our conclusions are to doubt it. From the absence of corroborative evidence we estimate that less than 15% at the 95% confidence level, of the 11‐year cycle warming variations are due to cosmic rays and less than 2% of the warming over the last 43 years is due to this cause. The origin of the correlation itself is probably the cycle of solar irradiance although there is, as yet, no certainty.

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.