Parameterization and influence of the orographic gravity-wave drag in the LMD-GCM

The fields of atmospheric modelling and numerical weather prediction are ever changing and evolving. Theoretical and observational studies confirm that orographically — forced gravity waves lead to a significant drag in the troposphere rather than the stratosphere. The present study describes the parameterization of orographic gravity-wave drag as used in LMD-GCM. The complete wave-breakdown is assumed to occur in the model layer, where the convective instability condition is first satisfied. The beneficial impact of the parameterization of gravity wave drag helps in removing the excess of westerlies in the northern hemisphere. There is very little impact on southern hemispheric circulation.