Two surface drag parameterization schemes are now available in WRF (topo_wind), each working in conjunction with the YSU planetary boundary layer scheme. The first is a topographic correction for surface winds to represent extra drag from sub-grid topography and enhanced flow at hill tops (Jimenez and Dudhia). The second is a simpler terrain variance-related correction (Mass). Using a physics suite that is currently being run in the High-Resolution Window (HIRESW) Forecast System at the National Centers for Environmental Prediction (NCEP), the Developmental Testbed Center (DTC) extensively tested three configurations; the only difference in the configurations was the topo_wind namelist option. The baseline configuration set topo_wind = 0, the second set topo_wind = 1, and the third set topo_wind = 2. The test cases span a 12-month period from 1 July 2011 to 30 June 2012, with forecasts being initialized every 36 hours and run out to 48 hours. This extensive testing period allows for robust results to be discussed with an assessment of statistical and practical significance and also allows for an investigation into seasonal and regional performance of each configuration. The impact of both topo_wind options on surface winds will be the focus of this talk, while surface temperature and other variables, will be discussed in a companion presentation
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