Electron heating and the potential jump across fast mode shocks

Abstract

The electron heating and the electrostatic potential jump across collisionless shocks play an important, if not dominant, role in the electron momentum balance. We present here a survey of these two quantities over a large sample of fast mode collisionless shocks. Results for estimates of the electrostatic potential (as measured in the de Hoffmann‐Teller reference frame) based on an estimate of the jump in electron enthalpy and on Liouville's theorem correlate well with each other, although the latter are consistently higher, perhaps due to irreversible processes affecting the shock electron dynamics. The size of the potential does not appear to be strongly controlled by any of the various upstream parameters (shock geometry, Mach number, etc.) and represents approximately 12% of the incident ion ram kinetic energy, this figure showing some tendency to decrease with increasing Mach number. The electron contribution to the total (ion plus electron) heating across the shock varies systematically from 50% or more at subcritical Mach numbers to less than 10% at the highest Mach number shocks in the sample. The electron heating shows only modest, but systematic, departure from that which would result by preserving the ratio of the perpendicular temperature to the magnetic field strength.