Primary Cosmic-Ray Intensity near Solar Maximum

Abstract

Measurements of the primary cosmic-ray proton and alpha-particle fluxes and energy spectra have been extended to the recent period of solar maximum. While the rigidity dependence of both components changed greatly during the solar cycle, it is observed that alpha particles and protons maintain the same relative rigidity spectra during the solar cycle. Measured geomagnetic cutoff values are in agreement with those obtained at solar minimum. An electric field model gives excellent agreement for the general form of the longterm change. However, at low rigidities this model predicts a splitting of the proton and alpha-particle differential rigidity spectra which is not observed.