SPATIAL-DISTRIBUTION OF ELECTRON-PLASMA OSCILLATIONS IN THE EARTHS FORESHOCK AT ISEE-3

Electric field oscillations recorded by the 10-56 kHz channels of TRW' s plasma wave detector during parts of two of the ISEE 3 circumterrest rial orbits in 1983 have been used to make the first mapping of Earth' s electron plasma wave foreshock. By combining data from the two traje ctory segments, each of which provided relatively meager spatial sampl ing outside the bow shock, but high variation of interplanetary magnet ic field (IMF) direction, a first-order pattern of occurrence of elect ron plasma waves, hence also backstreaming electrons, has been determi ned, We depict the pattern with an adaptation of the mapping program p reviously used for the Venus electron foreshock. As at Venus,. plasma wave activity was concentrated mast densely along the IMF line tangent to the bow shock where energized electrons stream against the solar w ind from the quasi-perpendicular part of the shock. The size of the Ea rth's electron plasma wave foreshock, however, is vastly greater than that of Venus, implying that a foreshock's dimension scales with the s ize 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 foresh ock than the single electron frequency channel pf Pioneer Venus Orbite r could detect around Venus.