Effect of hot electrons on the polar wind

Abstract

A semikinetic model was used to study the effect that hot electron populations have on the polar wind. The model was used to describe the steady state plasma flow along diverging geomagnetic field lines in the collisionless regime at high altitudes. The plasma contained O+ and H+ ions and both hot and cold electron populations. Several hot electron populations were considered, including the polar rain, polar showers, and polar squall. Estimates of hot electron parameters based on characteristic energy and flux measurements indicate that the hot/cold electron temperature ratio varies from 10 to 104 and that the percentage of hot electrons varies from 0.1% to 10% at 4500 km. For ratios at the lower ends of these ranges the polar wind solutions with hot electrons are similar to those obtained previously for supersonic H+ outflow without hot electrons. For higher hot electron temperatures and a greater percentage of hot electrons, there is a discontinuity in the kinetic solution, which indicates the presence of a sharp transition. This transition corresponds to a contact surface between the hot and cold electrons. Along this surface, a double‐layer potential barrier exists which reflects the cold ionospheric electrons and prevents their escape. The presence of the hot electrons acts to increase the supersonic H+ outflow velocity and H+ energy but does not affect the already saturated H+ escape flux. The H+ energy gain may be as large as 1 to 2 keV. With regard to O+, the hot electrons act to reduce the potential barrier, thereby allowing more O+ ions to escape. A significant enhancement in the O+ escape flux can occur depending on the hot electron density and temperature.