Interplanetary and solar electrons of energy 3–12 MeV

Abstract

This paper reviews two topics related to the low-energy relativistic electrons detected in interplanetary space with the satellites IMP-I, IMP-II, and IMP-III:1. The first observations of 3–12-MeV solar-flare electrons in interplanetary space are presented. The solar electrons detected have kinetic energies nearly two orders of magnitude higher than any previously studied; thus, although flare events with a detectable flux of such particles occur relatively rarely, their study provides a new parameter in solar physics. The 7 July and 14 September 1966 events are outlined in detail, having the greatest relativistic electron to medium-energy proton ratios of the events detected before 1967. These events contrast with the 28 August 1966 event, which was intense in nucleons but contained no detectable component of relativistic electrons. The electron time histories are shown to have delayed onsets, and to be similar in form to those of high-energy protons, and the energy spectra and other features are described.2. Progress in the study of the solar modulation of interplanetary 3–12-MeV electrons is reviewed. Characteristics of the electron-intensity time variations during parts of 1963–67 are outlined; they are shown to be consistent with the hypothesis of the primary cosmic-ray nature of these particles and with a strong dependence on the local field conditions.