COMPARISON OF STRATOCUMULUS CLOUD MODELING WITH SATELLITE-OBSERVATIONS AND IN-SITU MEASUREMENTS

As part of the European Cloud and Radiation Experiment campaign, we co nducted studies with the regional atmospheric modeling system in order to simulate stratocumulus clouds observed on April 18, 1994, over Bri ttany (France). This three-dimensional model was used in its non hydro static mode, with bulk microphysical and radiative transfer parameteri zations. The first initialization employed data provided by the Europe an Center for Medium-range Weather Forecasts (ECMWF) and radiosounding s obtained at the Guipavas ground station. The model outputs were then compared with the corresponding NOAA-AVHRR (advanced very high resolu tion radiometer) satellite image and aircraft data collected in situ d uring the experiment. The relative differences between modeled and act ual microphysical quantities (i.e., mixing ratio of water vapor, liqui d water content, or liquid water path) were found to be less than 25% along the airplane trajectory; this disagreement was as large as 200% elsewhere in the experimental domain, principally because cloud cover was underestimated. The development of a simple time-to-space analysis made it possible to force the mesoscale model with satellite images c ombined with vertical profiles and tridimensional data of the ECMWF, l eading to a more accurate spatial distribution of clouds over a large domain and diminishing these errors to 10%.