The compatibility of various interplanetary field models with cosmic ray modulation data

Abstract

Convective diffusion models for the motion of cosmic rays in the interplanetary, electromagnetic field are presented for both isotropic and anisotropic diffusion situations. Measurements of the long-term modulation, including recent high-altitude data obtained in 1965, fit the following simple model. Spherical symmetry is assumed for the solar cavity with the boundary at 50 a.u. In the solar equatorial plane, the magnetic field follows the archimedian spiral predicted by Parker with superimposed scattering centres. The particle mean free path, λ. is proportional to r2 where r is the distance from the Sun. Between particle rigidity limits 1 GV < P < 15 GV, λ ∝ P throughout the solar cycle whereas below 1 GV, observations close to solar minimum at least show that λ is independent of rigidity. A modulation theory based on energy loss alone in a scalar electric potential field, even when the path traversed is rigidity dependent, does not explain the experimental observations.