Evaluation of the performance of a new prognostic cloud/radiation package in NCEP's Global Forecast System (GFS)

Y.-T. Hou, S. Moorthi, K.A. Campana, S.-K. Yang, H.-L. Pan, P. Caplan, G. White, and S. Saha


A prognostic cloud condensate scheme along with an improved simplified Arakawa-Shubert (SAS) convection scheme were implemented in the NCEP's Global Forcast System (GFS) in May, 2001. Cloud condensate is represented as a prognostic model variable. Cloud cover fraction is obtained diagnostically from the predicted cloud condensate. Cloud-radiative properties were parameterized from cloud condensate (liquid/ice) path. Model clouds, radiation fluxes and other fields are evaluated against observations such as the R-T Nephanalysis and CERES surface fluxes. Comparing to the previous version of the model, the new physics package has produced improvement in model radiative fluxes, and in circulation patterns in both the extratropics and the tropics. A preliminary comparison of GDAS OLR with CERES flux shows substantial improvement from the new package. The new model performed very well in the tropical storm track prediction for the year 2001. However, it also changed the model temperature from warm bias to cold bias. Results from these evaluations will be presented at the workshop.