Large-scale distribution of thermospheric vertical wind activity was studied using observations from the Wind and Temperature Spectrometer on the Dynamics Explorer-2 satellite. We calculated the vertical velocity standard deviation, &sgr;(Vz), within a sliding window of width 120 seconds, corresponding to an along-track distance of ~900 km. Maps of &sgr;(Vz) in local magnetic time and invariant latitude reveal a high-latitude region 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 nominal auroral oval latitude. We provisionally interpret our results as evidence of polar cap gravity waves with sources in or near the midnight-dawn auroral oval. Waves propagating poleward effectively fill the cap with vertical wind oscillations. Equatorward propagating waves move approximately parallel to the local thermospheric wind, resulting in the possibility of critical-layer dissipation. ¿ 2001 American Geophysical Union