Influence of mountain gravity waves upon the large scale flow in the presence of critical levels.

The effect of mountain gravity waves breaking at critical levels, upon the large scale flow, is studied as a production of potential vorticity in the framework of the Eady model. Concerning the synoptic scales, we use a linearized semi-geostrophic model forced by a parameterized force. We show notably that the effect is cyclolytic for a cold front, and cyclogenetic for a warm front. Then the complete nonlinear 2D dynamics is computed with anelastic primitive equations. The subsynoptic scale response to the mountain forcing (parameterized or direct) contains notably nongeostrophic Eady modes, coupling a surface Eady wave with an inertia-gravity wave of the same scale, and inertia-gravity wave trains generated spontanously by the balanced flow associated to the dipole of potential vorticity. The study of the nonlinear saturation of these responses yields amplitudes rather weak but significant.