EFFECTS OF A PARALLEL ELECTRIC-FIELD AND THE GEOMAGNETIC-FIELD IN THETOPSIDE IONOSPHERE ON AURORAL AND PHOTOELECTRON ENERGY-DISTRIBUTIONS

The consequences of electric field acceleration and an inhomogeneous m agnetic field on auroral electron energy distributions in the topside ionosphere are investigated. The one-dimensional, steady state electro n transport equation includes elastic and inelastic collisions, an inh omogeneous magnetic field, and a field-aligned electric field. The cas e of a self-consistent polarization electric field is considered first . The self-consistent field is derived by solving the continuity equat ion for all ions of importance, including diffusion of O+ and H+, and the electron and ion energy equations to derive the electron and ion t emperatures. The system of coupled electron transport, continuity, and energy equations in solved numerically. Recognizing observations of p arallel electric fields of larger magnitude than the baseline case of the polarization field, the effect of two model fields on the electron distribution function is investigated. In one case the field is incre ased from the polarization field magnitude at 300 km to a maximum at t he upper boundary of 800 km, and in another case a uniform field is ad ded to the polarization field. Substantial perturbations of the low en ergy portion of the electron flux are produced: an upward directed ele ctric field accelerates the downward directed flux of low-energy secon dary electrons and decelerates the upward directed component. Above ab out 400 km the inhomogeneous magnetic field produces anisotropies in t he angular distribution of the electron flux. The effects of the pertu rbed energy distributions on auroral spectral emission features are no ted.