8.3      WRF Diffusion in Complex Terrain

 

Mass, Cliff, and David Ovens, University of Washington

 

When the WRF model is run at high resolution in complex terrain, the model surfaces are substantially inclined, resulting in substantial vertical mixing when diffusion is computed on coordinate surfaces.   WRF offers a number of diffusion options, including second order diffusion on model or horizontal surfaces, and the ability to use 6th order diffusion on model surfaces.  This talk will describe the impacts of various diffusion options on a challenging situation;  gap flow inside and exiting the Columbia River Gorge of Oregon/Washington.  It is shown that the choice of diffusion option has a large impact of the fidelity of the gap flow and of precipitation type.  Further experiments were completed for other cases and for extended seasonal situation, and the results will be discussed in this talk.  The hope is that these results will help guide other users in making choosing diffusion options in the modeling system, particularly in areas in or near terrain.