Vela 4 plasma observations near the Earth’s bow shock

Abstract

Concurrent measurements of electron and proton differential energy spectrums (each spectrum measurement requiring from 0.1 to 0.3 sec) have been obtained near the earth’s bow shock with the Vela 4B electrostatic analyzer. The following results have been derived from an analysis of 26 shock crossings during May and June 1967: (1) The jump in proton temperature is 2 to 4 times greater than the jump in electron temperature. (2) In the magnetosheath the proton temperature is nearly always greater than the electron temperature. (3) Te/Tp, upstream from the shock ranges between 0.6 and 4, and the shock remains well defined over this range. (4) Electron thermalization usually occurs in much less than 3 sec and has been observed to occur in ≈ 0.03 sec. (5) The magnetosheath electron velocity distribution is flat-topped or sometimes somewhat concave in shape within at least a few RE of the shock. (6) Evidence has been found that electrons are thermalized in a thin region upstream from the region in which most of the proton thermalization occurs. The observed increase in Te/Tp resulting from electron preheating may account for destabilization of electrostatic ion waves that may then produce strong ion heating by nonlinear Landau damping. Representative proton and electron velocity distributions from which the above results were derived are presented.