A MODELING STUDY OF THE COUPLED IONOSPHERIC AND THERMOSPHERIC RESPONSE TO AN ENHANCED HIGH-LATITUDE ELECTRIC-FIELD EVENT

A modelling study of the effect of a short-lived, localized enhancement in the high-latitude dawn-side convection electric field has been made using the Sheffield/UCL/SEL (Boulder) coupled ionosphere/thermosphere model. The conditions imposed on the model are intended to represent a single fluctuation of the type often observed in this region and thought to be responsible for a number of dynamic effects in both the ionosphere and thermosphere. Results from the simulation show frictional heating of both ions and neutrals producing an expansion of the atmosphere. The ionospheric expansion, when combined with greatly enhanced chemical reaction rates, leads quickly to the establishment of an ionospheric trough accompanied by significant increases in the proportions of the molecular ions NO+ and O2+. The initial expansion of the atmosphere is followed by a subsequent relaxation, leading to the formation of a large-scale gravity wave which propagates equatorwards and polewards from the event region. The dynamics of the complete coupled system during the event are studied, with particular attention to coupling and feedback processes.