Acceleration of Auroral Particles by Electric Double Layers

Abstract

Recent observations of precipitating particles and motions of auroral forms indicate that auroral particles are accelerated by electric fields directed along the magnetic field. Such electric fields have also been observed. It is argued that large field aligned potential drops should sometimes be concentrated in thin double layers (sheaths). Properties and consequences of such sheaths are reviewed and compared with evidence from several rocket and satellite observations.

It is pointed out that parallel electric fields due to anomalous resistivity may not produce secondary energy distribution peaks, nearly monoenergetic precipitation, and anisotropics since anomalous resistivity is due to scattering processes that should wipe out such peaks. It seems more likely that the acceleration occurs in sheaths, and the velocity distributions may then be partly smoothed out by instabilities.