The solar radial gradient of galactic cosmic rays

Abstract

The radial gradient of cosmic rays in the interplanetary region has been investigated taking into account convection, diffusion, energy losses, and differential streaming S. At high energies the analysis given here shows that S can be neglected and the radial gradient written C(r, T)Gs(r, T), where Gs(r, T) is the gradient given by the convection–diffusion theory and C(r, T) is an energy-dependent correction factor which can be computed from the observed differential intensity spectrum. During 1964–65 this result can probably be used for protons and helium nuclei down to a few hundred MeV/nucleon, with, at that time, [Formula: see text]. At lower energies Gs will be quite inaccurate as an estimate of the radial gradient unless changes in C are offset by streaming. Combining observations with this analysis it is shown that the radial anisotropy of protons (ξ) is: (i) positive but small (< 0.02%) at kinetic energies [Formula: see text]; (ii) negative in the range 40–600 MeV with ξmax = −0.75% (which should be observable); (iii) positive for energies less than about 40 MeV.