On the Correlation of Cosmic-Ray Intensity with Solar Activity and Interplanetary Parameters

Abstract

We investigated correlations between cosmic-ray intensity and 14 solar and interplanetary parameters, which were classified into four cases. We used the modulation of cosmic-ray intensity observed at six distinct stations with different latitudes and cut-off rigidities. We used the partial least-squares (PLS) method to rank the parameters. In the first case, we employed 11 parameters without considering halo-type coronal mass ejections (CMEs) and solar proton events (SPEs). In addition, we considered energetic phenomena associated with halo CMEs for the second case and SPEs in the third case. In the fourth case, we combined all of the parameters. The results based on the magnitude of the first principal component show that the sunspot number (SN), interplanetary magnetic field (IMF), heliospheric current sheet (HCS), and plasma velocity are the parameters with the strongest influence on the modulation of the cosmic-ray intensity at all six stations and in the first case we considered. For a halo-type CME (second case), SN, IMF, HCS, CME speed, and proton density were identified as the most significant parameters, which is identical to the results obtained in the fourth case. During an SPE (third case), the most significant parameters were SN, IMF, HCS, SPEs, and plasma velocity. The INVK and OULU stations, with nearly the same latitude and altitude, exhibit similar results. Our analysis of the results from the low-latitude stations (PSNM and TSMB) yielded different results from the other three stations at higher latitude. For the PSNM and TSMB stations, \(B_{y}\), \(B_{x}\), and the cone angle are the parameters that most strongly influence the modulation of the cosmic-ray intensity. This occurs because the influence of these parameters on cosmic-ray modulation depends on the latitude.