Spatial distribution of electron plasma oscillations in the Earth's foreshock at ISEE 3

Abstract

Electric field oscillations recorded by the 10–56 kHz channels of TRW's plasma wave detector during parts of two of the ISEE 3 circumterrestrial orbits in 1983 have been used to make the first mapping of Earth's electron plasma wave foreshock. By combining data from the two trajectory segments, each of which provided relatively meager spatial sampling outside the bow shock, but high variation of interplanetary magnetic field (IMF) direction, a first‐order pattern of occurrence of electron plasma waves, hence also backstreaming electrons, has been determined. We depict the pattern with an adaptation of the mapping program previously used for the Venus electron foreshock. As at Venus, plasma wave activity was concentrated most densely along the IMF line tangent to the bow shock where energized electrons stream against the solar wind from the quasi‐perpendicular part of the shock. The size of the Earth's electron plasma wave foreshock, however, is vastly greater than that of Venus, implying that a foreshock's dimension scales with the size of its diamagnetic obstacle and associated bow shock. Our mappings with three additional ISEE 3 channels surrounding the local electron plasma frequency indicate a richer distribution of waves in the foreshock than the single electron frequency channel of Pioneer Venus Orbiter could detect around Venus.