Numerical Investigations of Thermospheric/Ionospheric Coupling in the Polar Regions

Abstract

The dynamics of the high-latitude thermosphere is strongly forced by magnetospheric plasma convection at all altitudes from 100 km up to the exobase. Momentum is imparted to the neutral gas from convecting ions via ion-neutral collisions. Joule heating, which also results from this interaction, modifies the thermospheric temperature structure both locally and globally. In turn, this feeds back into the thermospheric dynamics. The dynamics and temperature structure subsequently modifies the neutral composition distribution in a number of ways. At high altitude the plasma convection velocity is virtually unchanged by the relatively infrequent collisions with the neutral atmosphere, whereas below 150 km the ion drift vectors rotate and decrease in magnitude as the result of collisional interactions with the neutral gas. Similarly, ionospheric plasma densities are modified by the neutral thermosphere composition and wind velocity. Some of these interactions between the thermosphere and ionosphere are illustrated in the context of a range of numerical simulations.