Thermospheric vertical wind activity maps derived from Dynamics Explorer-2WATS observations

Large-scale distribution of thermospheric. vertical wind activity was studi ed using observations from the Wind and Temperature Spectrometer on the Dyn am- ics Explorer-2 satellite. We calculated the vertical velocity standard deviation, sigma (V-z), within a sliding window of width 120 seconds, corre sponding to an along-track distance of similar to 900 km. Maps of sigma (V- z) in local magnetic time and invariant latitude reveal a high-latitude reg ion of enhanced activity that largely fills the polar cap. Activity appears to be a maximum in the midnight-dawn sector of the cap, possibly at the no minal auroral oval latitude. We provisionally interpret our results as evid ence of polar cap gravity waves with sources in or near the midnight-dawn a uroral oval. Waves propagating poleward effectively fill the cap with verti cal wind oscillations. Equatorward propagating waves move approximately par allel to the local thermospheric wind, resulting in the possibility of crit ical-layer dissipation.