A troposphere–stratosphere–mesosphere general circulation model with parameterization of gravity waves: climatology and sensitivity studies

The climatology of the troposphere–stratosphere–mesosphere model of the Institute for Numerical Mathematics (INM) with the uppermost level at 0.003 hPa is presented. This model is vertically extended from the upper level of 10 hPa for the earlier version, and a drag parameterization due to internal gravity waves (GW) is included. The model describes the main features of the mesospheric circulation: decreasing and reversion of westerly and easterly winds, equator ward shift of the westerly wind maximum with height and reversal of the meridional temperature gradient in the upper mesosphere. The model underestimates to some extent the amplitude of wave number 1 for stationary waves in the winter hemisphere. The same holds for the internal low-frequency variability in the winter stratosphere. The sensitivity of the model climate is studied with respect to the inclusion of orographic gravity wave drag and the variation of the source height of internal gravity waves.