P94  Compatibility of High Resolution Terrain with High Resolution Model Grid

William Y.Y. Cheng and Yubao Liu, National Center for Atmospheric Research/RAL

As computing power increases, mesoscale models are being run at a higher and higher resolution. Naturally, the user wants to represent the underlying terrain in the mesoscale model as realistically as possible by matching the terrain resolution to that of the model. However, from a theoretical standpoint, this may not be the best option. For example, it has been shown by Skamarock (2004) that the effective resolution of ARW WRF is 7 Dx. Terrain features of 7 Dx or smaller may impose forcings on the WRF model that are unphysical, generating noise or instability. One way to alleviate this problem is to apply smoothing to the terrain. However, there is a drawback in this procedure. Smoothing decreases the realism of the terrain and defeats the purpose of running a high resolution model. In this paper, the flow over complex terrain in the Korean Peninsula will be examined using WRF-RTFDDA with a nested grid down to 900-m. Sensitivity experiments will be run with the underlying terrain of the 900-m grid smoothed using wavelets by removing the 2 Dx, 4 Dx, and 8 Dx features. These sensitivity experiments will be compared with the experiment with the unsmoothed terrain to show how the smoothing will affect phenomena such as sea/land breeze and flow around/over mountains. The ultimate goal of this study is find a balance between smoothing the underlying terrain while maintaining realism of flow over complex terrain.