6.4      Evaluating simulated microphysics using GPM satellite observations in the Pacific Northwest.

Conrick, Robert, and Clifford F. Mass, University of Washington

This study evaluates moist physics in the Weather Research and Forecasting (WRF) model using observations collected during the Olympic Mountains Experiment (OLYMPEX) field campaign by the Global Precipitation Measurement satellite (GPM). Even though WRF using Thompson et al. (2008) microphysics was able to realistically simulate water vapor concentrations approaching the barrier, there was underprediction of cloud water content and rain rates offshore and over western slopes of terrain.  We show that underprediction of rain rate occurred when cloud water was underpredicted, establishing a connection between cloud water and rain rate deficits. Evaluations of vertical hydrometeor mixing ratio profiles indicated that WRF produced too little cloud and rain water content, particularly below 2.5 km, with excessive snow above this altitude. Simulated mixing ratio profiles were less influenced by coastal proximity or midlatitude storm sector than were GMI profiles. Evaluations of different synoptic storm sectors suggested that postfrontal storm sectors were simulated most realistically, while warm sectors had the largest errors in cloud and rain water contents. Finally, WRF underpredicted radar reflectivity below 2 km and overpredicted above 2 km, consistent with GMI vertical mixing ratio profiles.