Impact of Orographic Anisotropy For All Flow Directions On The East Asian Rainfall In A General Circulation Model

Current generation of climate models often have significant wet biases in mountainous region where the gradient of elevation is extremely steep and the terrain is complex. Among these are the renowned mountain regions of the Himalayas. One reason is the unreasonable representation of orographic anisotropy in general circulation model (GCM). In this study, a new orographic drag scheme that includes 3-D orographic anisotropy (3D-AFD), is implemented into a GCM to examine the impact of this effect on East Asian orographic rainfall. It was shown that the new scheme improved the model simulation rainfall in both summer and winter in the mountainous region of Himalayas and Nanling Mountain. This is mostly due to the enhanced drag and representation of orographic anisotropy in the region.