Cross correlation and time-lag between cosmic ray intensity and solar activity during solar cycles 21, 22 and 23

Abstract

In the present paper a systematic study is carried out to validate the similarity or co-variability between daily terrestrial cosmic-ray intensity and three parameters of the solar corona evolution, i.e., the number of sunspots and flare index observed in the solar corona and the Ap index for regular magnetic field variations caused by regular solar radiation changes. The study is made for a period including three solar cycles starting with cycle 21 (year 1976) and ending on cycle 23 (year 2008). A cross-correlation analysis was used to establish patterns and dependence of the variables. This study focused on the time lag calculation for these variables and found a maximum of negative correlation over $CC_{1}\approx 0.85$, $CC_{2}\approx 0.75$ and $CC_{3}\approx 0.63$ with an estimation of 181, 156 and 2 days of deviation between maximum/minimum of peaks for the intensity of cosmic rays related with sunspot number, flare index and Ap index regression, respectively.