Investigating the impact of surface drag parameterization schemes on surface winds in WRF

Two surface drag parameterization schemes were made available in WRF recently (topo_wind options), each working in conjunction with the YSU planetary boundary layer scheme. The first (topo_wind=1) is a topographic correction for surface winds to represent extra drag from sub-grid topography and enhanced flow at hill tops (Jimenez and Dudhia 2011). The second (topo_wind=2) is a simpler terrain variance-related correction (Mass and Ovens 2012). Comprehensive tests of the two surface drag parameterization schemes and a baseline configuration (topo_wind=0 [off]) were conducted at the Developmental Testbed Center (DTC) using the Weather Research and Forecasting (WRF) Advanced Research WRF (ARW) physics suite employed in the High-Resolution Window (HIRESW) Forecast System at the National Centers for Environmental Prediction (NCEP). The test cases spanned a 12-month period from 1 July 2011 to 30 June 2012, with forecasts initialized every 36 hours and run out to 48 hours. This extensive testing period allows for an investigation into seasonal and regional forecast performance for each configuration. While standard meteorological variables were evaluated for each configuration, the impact of both topo_wind options on surface winds will be the focus of this talk.