Acceleration of antiearthward electron fluxes in the auroral region

[ 1] This study presents a statistical analysis of antiearthward electron fluxes associated with the downward current region of the aurora based on 600 events from the FAST mission. A comparison between the observed particle energies and the electrostatic potentials inferred from the perpendicular electric field measurement suggests that the acceleration process can be separated into two types. One type fits a model with quasi-static parallel electric fields which can account roughly one half of the events. A second type consists of events in which the antiearthward electrons appear to be accelerated by a dynamic process such as Alfven waves or evolving parallel electric fields. We also point out that a nonaccelerated class of antiearthward electron fluxes produced by secondary electron production in the ionosphere also exists.