Study of the Cosmic-Ray Modulation During the Passage of ICMEs and CIRs

Abstract

We compare the cosmic-ray response to interplanetary coronal mass ejections (ICMEs) and corotating interaction regions (CIRs) during their passage in near-Earth space. We study the relative importance of various structures/features identified during the passage of the ICMEs and CIRs observed during Cycle 23 (1995 – 2009). The identified ICME structures are the shock front, the sheath, and the CME ejecta. We isolate the shock arrival time, the passage of the sheath region, the arrival of ejecta, and the end time of their passage. Similarly, we isolate the CIR arrival, the associated forward shock, the stream interface, and the reverse shock during the passage of a CIR. For the cosmic-ray intensity, we utilize the data from high counting rate neutron monitors. In addition to neutron monitor data, we utilize near-simultaneous and same time-resolution data of interplanetary plasma and field, namely the solar-wind velocity, the interplanetary magnetic field (IMF) vector, and its variance. Further, we also utilize some derived interplanetary parameters. We apply the method of the superposed-epoch analysis. As the plasma and field properties are different during the passage of different structures, both in ICMEs and CIRs, we systematically vary the epoch time in our superposed-epoch analysis one by one. In this way, we study the role and effects of each of the identified individual structures/features during the passage of the ICMEs and CIRs. Relating the properties of various structures and the corresponding variations in plasma and field parameters with changes of the cosmic-ray intensity, we identify the relative importance of the plasma/field parameters in influencing the amplitude and time profiles of the cosmic-ray intensity variations during the passage of the ICMEs and CIRs.

Appendices

Appendix A

Table 3 The calculated mean, standard deviation (SD) for each distribution, and t-values and p-values for each pair of distribution (ICMEs associated with/without shock) using statistical t-test of two independent samples at significance level 0.01 with the help of Gaussian-fitted parameters for plasma and magnetic field parameters [$V_{\max}$, $F_{\max}$, $(\mathit{FV})_{\max}$, $(\sigma_{F})_{\max}$, $(\mathit{FV}^{2})_{\max}$].

Table 4 The calculated mean, standard deviation (SD) for each distribution, t-values and p-values for each pair of distribution (ICMEs associated with/without shock) using statistical tests (two sample t-test using raw data of $V_{\max}$, $F_{\max}$, $(\mathit{FV})_{\max}$, $(\sigma_{F})_{\max}$, $(\mathit{FV}^{2})_{\max}$; non-parametric (Mann Whitney) test of two independent samples using raw data of GCR-intensity decrease) at significance level 0.01 with the help of an SPSS statistics software package.

Appendix B

Table 5 The calculated mean, standard deviation (SD) for each distribution, and t-values, p-values for each pair of distribution (CIRs associated with/without shock) using the statistical t-test of two independent samples at significance level 0.01 with the help of Gaussian-fitted parameters for plasma and magnetic field parameters [$V_{\max}$, $F_{\max}$, $(\mathit{FV})_{\max}$, $(\sigma_{F})_{\max}$, $(\mathit{FV}^{2})_{\max}$].

Table 6 The calculated mean, standard deviation (SD) for each distribution, t-values and p-values for each pair of distribution (CIRs associated with/without shock) using statistical tests (two sample t-test using raw data of $V_{\max}$, $F_{\max}$, $(\mathit{FV})_{\max}$, $(\sigma_{F})_{\max}$, $(\mathit{FV}^{2})_{\max}$; non-parametric (Mann Whitney) test of two independent samples for raw data of GCR-intensity decrease) at significance level 0.01 with the help of an SPSS statistics software package. The p-values are given up to the third decimal place only.