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