Wednesday, 5 June 2002
Evaluating the newly implemented NCEP cloud/radiative parameterizations with CERES
The recent release of CERES data provides a timely opportunity for validating the newly implemented cloud/radiation physics in the NCEP operational global forecast system. NCEP replaced the original diagnostic cloud parameterization with a prognostic cloud condensate formulation in the May 2001. Radiative transfer calculations now incorporate optical thickness from the predicted cloud condensate path. Cloud properties, such as ice/liquid water path, and radiative fluxes from CERES are now can be utilized for comparison with model outputs. Estimated surface fluxes from CERES observations are also relevant for evaluating NCEP Regional Reanalysis.
A first comparison of operational GDAS OLR with CERES ERBE-Like fluxes shows substantial improvement from the new model. The global mean bias was reduced from 3..4 W/M^2 to 2.1 W/M^2, a reduction of ~ 40%, and erroneous regional stratification in the mid-high latitudes are virtually eliminated. Further details regarding validation of NCEP cloud property and ra diative flux forecasts, as well as model formulation specifics, will be presented.