Do field‐aligned auroral particle distributions imply acceleration by quasi‐static parallel electric fields?

Abstract

Charged particle observations from several high‐altitude sounding rocket flights launched from Churchill Research Range into auroral events when magnetic‐field‐aligned electron precipitation was observed are presented. Large field‐aligned enhancements were observed near the edges of regions of intense electron precipitation (auroral arcs), while only small or no enhancements were observed inside these regions. Field alignment was spread over a large energy range, at times from 0.5 to 60 keV, and showed no enhancement near the characteristic peak in the energy spectrum. These and other observations are compared with predictions of models involving acceleration by quasi‐static parallel electric fields, including the possibility of beam‐plasma instability effects, and are shown to be inconsistent. Acceleration by broadband electrostatic waves is suggested as a possible energization mechanism for field‐aligned particles.