Assessment of Radiative Transfer in the Advanced Research WRF Weather Forecast Model

An evaluation of the radiation options in the Advanced Research WRF (Weather Research and Forecasting) model relative to surface and satellite observations will be presented. The broadband, correlated k-distribution model, RRTMG, developed at AER for the Atmospheric Radiation Measurement (ARM) program for application to climate and weather forecast models, was added as a radiative transfer option in WRF during 2009. RRTMG has been evaluated independently through comparison with measurements and higher resolution models, and it has been shown to retain a high level of accuracy for models of this type. An assessment of RRTMG and the other longwave and shortwave radiative transfer options in WRF will be presented for several 10-day forecast cases. Evaluation of the results and radiative closure are accomplished at the surface by comparison to measurements from the ARM Climate Modeling Best Estimate (CMBE) data set for the Southern Great Plains (SGP) and North Slope of Alaska (NSA) sites and at the top of the atmosphere by comparison to several satellite data sets. Since radiative transfer accuracy is highly dependent on the correct specification of the atmosphere and especially of clouds, the simulation of cloud amounts and cloud optical properties in WRF has also been examined. Finally, an assessment of the frequency of the radiative transfer calculation on the accuracy of the modeled radiative and dynamical fields will also be described.