Solar modulation of galactic cosmic rays

The modulation of galactic protons and He nuclei during the last solar cycle is analyzed according to Parker's theory. The mechanism of modulation remains essentially the same during several years of low solar activity (1961–1965). The modulation near solar maximum (1959) implies that the scale sizes of the magnetic inhomogeneities in the solar wind are reduced below the values at solar minimum. An adequate description at solar maximum would require further refinements of the theory. The proton-to-He-nucleus ratio outside the solar system is shown to be consistent with the value ≈6, in a kinetic-energy/nucleon representation, for the interval 100–1000 Mev/nucleon.