Neutral wind vortices in the high-latitude thermosphere.

Abstract

An investigation into the neutral dynamics of the high-latitude thermosphere has been carried out using measurements obtained from the Dynamics Explorer-2 spacecraft and ground-based Fabry-Perot interferometers located in Greenland, and numerical simulations from the National Center for Atmospheric Research - Thermosphere/Ionosphere General Circulation Model (NCAR-TIGCM). In this thesis, large-scale mean neutral wind patterns under various geophysical conditions have been determined through extensive analysis of the neutral wind observations made by the DE-2 spacecraft. The mean neutral wind observations demonstrate the existence of coherent, large-scale neutral wind vortices in the high-latitude thermosphere and show that these vortices are persistent features in the mean neutral wind circulation. The mean neutral wind vortices in the high-latitude thermosphere are shown to vary spatially depending on the orientation of the interplanetary magnetic field (IMF) and the level of geomagnetic activity. In this work, the NCAR-TIGCM has been used to provide numerical simulations of the high-latitude neutral circulation corresponding to the geophysical conditions under which the averaged neutral wind patterns from DE-2 observations were organized. The high-latitude neutral wind vortices determined from the DE-2 observations and simulated by the NCAR-TIGCM have been analyzed in detail in this thesis by determining the kinematic properties of the wind fields. This analysis has shown that the dynamics of the high-latitude neutral thermosphere is dominated by rotational motion, imparted primarily through the ion-drag force, rather than by divergent motion, imparted primarily through the pressure gradient force set up by Joule and solar heating. The numerical simulations of the NCAR-TIGCM provide information on the forces which generate the neutral wind forces in the high-latitude thermosphere. The force analysis illustrates that the ion-drag force contributes significantly to the local time rate of change of the non-divergent component of the neutral wind, while the pressure gradient, Coriolis, and momentum advection forces, as well as the ion-drag force contribute to the local time rate of change of the irrotational component of the neutral wind. (Abstract shortened with permission of author.)