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 Resolution Radiometer) satellite data. This satellite derived cloud cover is used to evaluate the model generated cloud cover provided by two different cloud cover parameterization schemes established in a 3-D-chemical transport model. In the standard version of this model cloud cover depends on rain rate for raining clouds and on the relative humidity at cloud base for fair weather clouds. In the second cloud cover parameterization 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. Partial cloudiness is allowed to form when mesoscale relative humidity is less than 100%. The comparison of the model generated with the satellite derived cloud cover shows that the second cloud cover parameterization scheme substantially improves the determination of cloud cover by the model.