Effects of vertical resolution on a parameterization of convective gravity waves

We investigate effects of vertical resolution on a parameterization of convective gravity waves (SGWDC) developed in Song and Chun (2005) through offline and online tests of the SGWDC parameterization. For offline tests, numerical simulations of the SGWDC parameterization with different number of vertical levels (L66, L117, L168, L219 and L270) from the surface to 120 km are performed for two different saturation methods. It is found that the wave momentum forcing is overestimated or underestimated in the SGWDC parameterization with different vertical resolutions, depending on the saturation methods. The increase of the vertical resolution modifies the magnitude and distribution of the wave momentum forcing in the parameterization, and this is mainly due to modification of wave saturation levels in the wave saturation processes. However the wave momentum forcing converges in the parameterizations with vertical resolutions higher than L168. For online test, the SGWDC parameterizations with vertical resolutions of L66 and L164 are implemented into a climate model with vertical resolution of L66, separately. In the L164 experiment, the wave momentum forcing decreases in the mid-latitude winter mesosphere in July and zonal mean flows are more realistically reproduced in the tropical regions compared with those in the L66 experiment. These results demonstrate that the wave momentum forcing calculated in the parameterization is sensitive to the vertical resolution, and the implementation of the SGWDC parameterization into high resolution models is required for realistic representation of the gravity wave momentum forcing in large-scale numerical models.