| R. I. Cullather and R. J. Harshvardhan Dept. of Earth and Atmospheric Sciences Purdue University, West Lafayette, IN 47907-1397 317-494-0693 |
K. A. Carnpana NOAA National Meteorological Center Washington, DC 20233 |
The simulated cloud cover, as viewed from space, generated by a T62 version of the operational weather forecast model at the National Meteorological Center (NMC), has been compared with corresponding fields cataloged by the International Satellite Cloud Climatology Project (ISCCP). The model was initialized with reanalyzed conditions for several days in July 1985. The monthly mean for an ensemble of runs as well as twelve-hour means for different forecasts were chosen for comparison with ISCCP data. Also, monthly mean outgoing longwave radiation (OLR) and corresponding cloud forcing was compared with Earth Radiation Budget Experiment (ERBE) data.
For the month of July 1985, the global mean OLR was found to exceed the ERBE value by 12 W m-2. This excess could be traced to the following:
(a) Convective anvils in the model have a maximum emittance of 0.6
(b) When supersaturation clouds and convective clouds occur simultaneously, the supersaturation cloud fraction is ignored.
(c) The relative humidity criterion for the generation of supersaturation clouds was tuned to give reasonable results in an early version of the European Center model and has not been re-adjusted at NMC.
Results will be presented for experiments in which the above mentioned
parameterizations have been altered to obtain cloudiness and OLR fields that
conform more closely to satellite data.