Features of Gravity Wave Drag

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    Introduction of Gravity Wave Drag Parameterization 

 Gravity waves can be excited when stably stratified air flows over irregular terrain. Such waves may propagate feely to considerable altitudes before being significantly dissipated or absorbed. While orographic excitation is one of the more common sources of vertically propagating gravity waves they may also occur in association with a number of other processes such as the onset of shear instabilities and the rapid development of convective complexes and squall lines.

 Vertically propagating gravity waves can play a role what transfer momentum from source to sink. Gravity wave drag process is important to simulate upper atmospheric momentum well, but the resolution of current GCMs is too sparse to simulate gravity wave by mountains. So parameterization of wave characteristics in large scale flow is needed. The parameterization of gravity wave is based on simple linear theory of single retarded wave having momentum flux divergence by wave breaking. Absorbing waves break out at a critical altitude where gradient Richardson number is much greater than 0.25.