A Comparison of Simulated Clouds to ISCCP Data

Abstract

An evaluation of the cloud parameterization scheme in the High-Resolution Regional Model (HRM) of the Deutscher Wetterdienst was conducted using data from the International Satellite Cloud Climatology Project (ISCCP). Uncertainties in the model and in the measurements were first quantified. Then, criteria for comparisons of simulated and measured data were chosen in order to identify model deficiencies. The simulated clouds were subsequently classified by their parameterization so model deficiencies could be easily attributed to a certain parameterization scheme. Following this evaluation, an overestimation of simulated mean cloud amount was identified as a deficiency of the HRM. The overestimation occurred mainly during the night and was due to an overprediction of subscale clouds at low-level emissivity heights. At medium-level emissivity heights during the day, the cloud amount is underpredicted. This leads to an underestimation of the diurnal cycle. These deficiencies were connected with the relative humidity parameterization used to characterize subscale cloudiness.