Summary
This letter explores the hypothesis that gravity wave drag may account for the observed deceleration of the thermospheric anti-sunward wind near the nightside auroral oval, which at times has been seen to reduce to near zero in a horizontal distance of a few hundred kilometres. Other high-latitude observations have revealed thermospheric gravity waves that appear to propagate across the polar cap from the nightside to the dayside, and hence are moving counter to the wind near magnetic midnight. Approximate constancy with altitude of the vertical velocity amplitudes of these waves suggests a moderate level of energy dissipation is present. Calculations indicate a wave-mean flow interaction could lead to a deceleration of the wind of magnitude comparable to that observed.