EVALUATION OF MODEL GENERATED CLOUD COVER BY MEANS OF SATELLITE DATA

An automated cloud retrieval algorithm has been developed and applied to determine cloud cover from NOAA9 AVHRR (Advanced Very High Resoluti on Radiometer) satellite data. This satellite derived cloud cover is u sed to evaluate the model generated cloud cover provided by two differ ent cloud cover parameterization schemes established in a 3-D-chemical transport model. In the standard version of this model cloud cover de pends on rain rate for raining clouds and on the relative humidity at cloud base for fair weather clouds. In the second cloud cover paramete rization scheme predictions of liquid water content and ice content in combination with values of water and ice content derived from several observations are used to generate the cloud cover by the model. Parti al cloudiness is allowed to form when mesoscale relative humidity is l ess than 100%. The comparison of the model generated with the satellit e derived cloud cover shows that the second cloud cover parameterizati on scheme substantially improves the determination of cloud cover by t he model.