High energy cosmic ray intensity variations associated with the unusual Forbush decrease of August 1972

Abstract

Spectacular temporal cosmic-ray variations at relativistic energies were recorded by all ground-based cosmic ray monitors during August 1972 when Forbush decreases (FD) and other associated intensity changes occurred. These included at least two major relativistic solar particle enhancements and three FD events, one of which was the largest observed to date. Large anisotropies in the intensities were also indicated throughout the entire period during these events. From a comparison with the interplanetary plasma and field parameters observed by various spacecraft during this period, a comprehensive model is developed for the FD in terms of a shock front, containing tangled magnetic fields with large-scale tangential discontinuities, sweeping past the earth.