By simulating a heavy rainfall case, we investigated the sensitivity of the MM5 to the different horizontal resolutions of the terrain data. The complex mountainous terrain could lift air parcels and might enhance precipitation. The Jiri mountain area has a complex terrain shape and frequently experiences heavy rainfalls. A heavy rainfall occurred on 31 July 1998 had favorable synoptic conditions, which are adequate to examine the terrain effects on the precipitation of the mountainous region.

We used the horizontal resolutions of 5 minutes and 3 seconds terrain data for the lower boundary conditions. The 3 seconds ultra-high resolution data was used for realistic terrain features. And we simulated the heavy rainfall case with varying the two different terrain data. The processed topographic elevation and shape by the MM5 TERRAIN were more realistic in the fine terrain experiment than in the coarse one.

The maximum amount of the 12 hour accumulated rainfall was almost two times larger in the fine terrain than in the coarse terrain. The horizontal pattern of the fine minus the coarse terrain elevation was similar to the horizontal distribution of the corresponding precipitation difference. The condensation heating matched very well with cloud mixing ratios near the surface in the vertical section crossing the heavy rainfall area. Our simulation showed more rainfall amount in the fine terrain due to the enhanced lifting by the realistic terrain. The rugged terrain seemed to play a crucial role in the development and the distribution of the precipitation on the mountainous region.