Particle trapping and acceleration during the August 1972 event

Abstract

Several features of the August 1972 events are studied using neutron monitor data together with solar wind streamlines calculated on the basis of an approximate kinematic approach. Examination of the evolution of these streamlines shows that the streamline which passes from the Earth undergoes dramatic changes during the main phase of these events. In a few hours this streamline, which was estimated with HEOS-2 solar wind velocity data, was decreased (i.e., compressed) to a total radial extend of 0.2 AU (at the beginning of 5 August), although its initial length was 1 AU. An exact MHD time-dependent solution by Dryer et al. (1978a) gives similar results.The relative cosmic ray increase (3-7 UT, 5 August), immediately after the deep F.d., is attributed to trapping and acceleration of particles between two shock waves. Similar acceleration was found by Pomerantz and Duggal (1974) and Levy et al. (1976) for another cosmic ray increase during this event.The extremely large solar wind velocities during the main phase of the event are not only due to the large energy of the flare but also to the fact that the ambient solar wind was already almost empty because of the sweeping action of previous shock waves.