Explicit simulation of mesospheric gravity-wave drag in an idealized GCM with high vertical resolution

We estimate the effects of inertia-gravity waves on the general circulation of the upper mesosphere using a mechanistic GCM with moderate horizontal resolution (T85) and high vertical resolution from the boundary layer to the lower thermosphere (L190). Horizontal and vertical diffusion are based on nonlinear mixing-length parameterizations. Wave reflection at the model top is controlled by gradually increasing the mixing lengths above 80 km. Under these conditions, the resolved inertia-gravity waves dissolve around the mesopause and generate considerable wave drag and frictional heating, amounting to about two thirds of previous estimates derived from gravity-wave parameterizations. In addition, synoptic waves develop in the baroclinic zone of the upper summer mesosphere and partly offset the resolved gravity-wave drag. The total wave drag in the upper summer mesosphere leads to a clear reversal of the mean zonal wind and to temperatures being far below the assumed radiatively determined state.