Using a recently developed spectral nonlinear gravity wave (GW) parameterization implemented into a 3-D coupled general circulation model, the effects of a broad spectrum of small-scale internal GWs of lower atmospheric origin on the equinoctial thermosphere are studied for the first time. GWs propagate to F region altitudes in both hemispheres, producing appreciable drag on the mean zonal wind. Some modifications of the two-cell equinoctial mean circulation by GWs are simulated, too. The mean zonal GW drag is comparable to the ion drag up to $ 260 km in the middle-and high-latitudes. While the mean dynamical effect of GWs is the deceleration of the mean flow, the instantaneous GW body force can have both signs. In the Southern Hemisphere high-latitude, GWs are found to produce large torque of more than 1000 m s À 1 day À 1 the mechanism of which is investigated in detail. GW anisotropy plays a crucial role in offsetting and modulating wave filtering, introducing increased favourable conditions for westerly harmonics in the high-latitudes. This leads to a very large localized eastward GW drag reaching a maximum in the upper thermosphere as a consequence of enhanced molecular viscosity, thermal conduction, and ion drag. Finally, the high-latitude distribution of the GW body force is presented in the upper thermosphere along with the comparison with ion drag. It demons-trates significant interhemispheric differences and large longitudinal variations in GW momentum deposition.