Modelling of time-dependention outflows at high geomagnetic latitudes

Abstract

In a recent paper, Gombosi and Killeen (1987) applied a highly parameterized thermospheric Joule heat source as a boundary condition in the time-dependent, ion outflow model of Gombosi et al. (1985) to show that episodic ion outflows at high geomagnetic latitudes could result from low altitude ion frictional heating. To delineate more realistically the time-dependent thermosphere/ionosphere environment, we extend this previous study by using output from the Thermospheric General Circulation Model (TGCM) of the National Center for Atmospheric Research (NCAR) as input to the same hydrodynamic polar wind code for a set of case studies which follow the thermal forcing history of individual, ionospheric, convecting flux tubes. Using derived, time-varying frictional heating rates such as those experienced by these flux tubes, we show that transverse ion heating below 500 km can provide sufficient energy to perturb the velocity distribution of the major ion species. The time-dependent flux tube heating results in localized regions of field-aligned O + upflows. These results demonstrate that localized heating, generated from thermosphere/ionosphere interactions, may initiate heavy ion upwellings which, through further energization at higher altitudes, could evolve into the transient ion outflows as seen by the Dynamics Explorer 1 satellite.