Evaluation of Polar WRF forecasts of the atmospheric hydrologic cycle over the ASR domain

Polar version 3.1.1 of the Weather Research and Forecasting model (WRF) is used to simulate conditions for December 2006 – November 2007. The domain mirrors that of the Arctic System Reanalysis (ASR), an assimilation of model fields with Arctic observations being conducted partly by the Byrd Polar Research Center at The Ohio State University. Seasonal progression of sea ice albedo previously developed for limited area simulations of Polar WRF is extended to the entire Arctic Ocean. Boundary conditions are specified by the NCEP Final global gridded analysis archive (FNL), a 1° x 1° global grid updated every 6 hours. Simulations are performed in 48 hour increments initialized daily at 0000 UTC, with the first 24 hours discarded for model spin-up of the hydrologic cycle and boundary layer processes. Analysis has been conducted on the surface, upper air, and hydrologic cycle with results of precipitation, clouds, incident shortwave, and downwelling longwave radiation presented here. Annual and monthly precipitation analysis reveals a general overprediction of precipitation in the mid-latitudes, especially during spring and summer when convection is high. Precipitation in the polar region is underpredicted in all seasons except spring. Additional analysis on river basins important for Arctic climate shows a positive bias in precipitation of up to 28% of the annual total. Comparisons of surface radiation at selected sites show that both longwave and shortwave are well captured in the mid-latitudes. However, too much shortwave and too little longwave radiation at polar stations during July suggests a misrepresentation of clouds over Arctic land. Grid nudging of moisture in the planetary boundary layer decreases convection and the positive bias of precipitation in the mid-latitudes, with little effect on radiation biases in the polar region. Combined with the surface and upper level evaluation, this examination provides guidance for further development of Polar WRF as ASR's primary model.