Cosmic-ray intensity related to solar and terrestrial activity indices in solar cycle no. 20

The 11-year modulation of cosmic-ray intensity is studied using the data from nine world-wide neutron monitoring stations over the period 1965-1975. From this analysis the following relation among the modulated cosmic-ray intensity I, the relative sunspot number R, the number of proton events Nsub(p) and the geomagnetic index Asub(p) has been derived which describes the long-term modulation of cosmic rays I = C - 10-3(KR + 4Nsub(p) + 12Asub(p)), where C is constant which depends on the rigidity of each station, and K is a coefficient related to the diffusion coefficient of cosmic rays and its transition in space. The standard deviation between the observed and calculated values of cosmic-ray intensity is about 5-9%. This relation has been explained by a generalization of the Simpson solar wind model which has been proved by the spherically symmetric diffusion-convection theory. (orig.)