Correlative study of solar activity and cosmic ray intensity

Abstract

We perform a correlative study of solar activity (sunspot numbers) and cosmic ray intensity (neutron monitor count rates) for the last four solar cycles. Analysis of the running cross correlation between the two series shows that the behavior of cosmic ray modulation is similar, in general, for particles with different energy. However, a strong rigidity dependence as well as an unusual behavior of the cross correlation function is found for the descending phase of cycle 20. We study the evolution of cosmic ray and solar activity cycles in a three‐dimensional phase space by means of the delayed component method. While all solar activity cycles and most cosmic ray cycles are planar, cosmic ray cycle 20 is significantly three‐dimensional. A concept of the momentary phase of a cycle is introduced, and the phase evolution of cosmic ray and solar activity cycles is studied. We also discuss the heliospheric conditions responsible for the unusual behavior of cosmic ray modulation in the descending phase of cycle 20.