Electron Heating in Quasi-Perpendicular Shocks

TL;DR

This study analyzes electron heating mechanisms in Earth's quasi-perpendicular bow shocks using THEMIS satellite data, revealing that electric field fluctuations cause electron demagnetization and isotropic heating, challenging traditional wave or adiabatic explanations.

Contribution

It provides new insights into electron heating processes, highlighting the role of large amplitude electric field fluctuations in demagnetizing electrons and causing isotropic heating in collisionless shocks.

Findings

Electron temperature increases differ from magnetic field increases by up to a factor of three.

Parallel electron temperature increase is not caused by parallel electric fields.

Electric field fluctuations are of finite amplitude and induce chaotic electron trajectories.

Abstract

Seventy crossings of the Earths bow shock by the THEMIS satellites have been used to study thermal electron heating in collisionless, quasi-perpendicular shocks. It was found that the temperature increase of thermal electrons differed from the magnetic field increase by factors as great as three, that the parallel electron temperature increase was not produced by parallel electric fields, and that the parallel and perpendicular electron temperature increases were the same on the average. It was also found that the perpendicular and parallel electron heating occurred simultaneously so that the isotropization time is the same as the heating time. These results cannot be explained by energy transfer from waves to electrons or by the motion of magnetized electrons through the shock. Electric field fluctuations on the scale of the electron gyro-diameter were found to be of finite amplitude in the shock ramp, which requires that the electron trajectories be more random and chaotic than orderly and adiabatic. The data may be explained by the large amplitude electric field fluctuations that demagnetize electrons as they move through the cross-shock electric field