Performance of various radiation parameterizations in the climate version of the Eta regional model driven by reanalysis and HadAM3P

The climate version (Eta CCS) of the NCEP Eta model was run over South America (SA) for the period from 1979 to 1985. Two sets of boundary conditions were used, derived from reanalysis and from output of the HadAM3P atmospheric global model. The two convection schemes, three shortwave radiation schemes, and two longwave radiation schemes are currently included in the model as options. The model runs were made with each optional radiation scheme. The model Output fields are compared with the observational data of the CRU and GPCP projects. In this study, the impact of change in shortwave radiation parameterizations on the precipitation rate is analyzed. The difference in precipitation rate associated with the change in shortwave radiation scheme is particularly noticeable over the regions of the South American continent with strong convective activity during austral summer. The magnitude of this difference is comparable with that related to the change in boundary conditions. During the winter months, the modeled precipitation rate is affected more by the change in boundary conditions than by the change in shortwave radiation scheme. The study demonstrates that implementing more sophisticated radiation schemes in a model does not always improve model performance. Improvement can be achieved by adjusting other physical parameterizations in the model in conjunction with its radiation scheme.