Relationship of first two harmonics of cosmic ray daily variation with solar activity

Abstract

Systematic correlative studies have been performed since long to establish the relationship of cosmic ray anisotropy with solar activity parameters, and the studies are extended for the recent periods. In this analysis, yearly averages of sunspot numbers <i>R</i>_z have been used to correlate with the yearly average amplitudes and phases of the first two harmonics of the daily variation of cosmic rays derived from the data of stations Kiel and Tokyo, representative of low and high cut-off rigidity, respectively. Significant positive correlations, both for the diurnal amplitude and phase, have been observed. Similarly, positive correlations with sunspot numbers are also noticed in case of semi-diurnal phase for both the stations. However, the semi-diurnal amplitudes of the daily variation of cosmic rays show small negative correlation with <i>R</i>_z.