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.