Solar cycle modulation of galactic protons and electrons

Abstract

A solution of the time‐dependent, spherically symmetric cosmic ray transport equation, with a defensible diffusion coefficient and a natural model for an 11‐year cycle of diffusive scattering disturbances that originate on the sun and travel through interplanetary space, accounted simultaneously for the spectral changes of both galactic protons and electrons, for the time and phase lag of high‐ versus low‐energy protons, and for the integral radial gradients of protons > 100 MeV over most of the solar cycle and over large distances in the heliosphere. Each individual disturbance caused a sudden particle intensity decrease as it passed a point in space; recovery of intensity began immediately afterward. The characteristic recovery time at 1 AU was in the range found in neutron monitor and satellite data, except that the recovery time constant was rigidity‐dependent, contrary to these same data. Also, spectral changes over successive solar minima in 1965 and 1977, heretofore linked to drifts, can be explained as an adjunct to the hysteresis effect. Overall, the primary galactic cosmic ray flux over the 11‐year solar cycle is dominated in the ecliptic plane by turbulent scattering regions emitted by the sun and at best only secondarily affected by gradient and curvature drifts, effects which may be confined near 1 AU.