Post-frontal shower cells in the COSMO-DE model. A comparison with radar measurements

Abstract

The NWP model COSMO-DE is run operationally at the German Meteorological Service (Deutscher Wetterdienst, DWD) with a horizontal grid size of 2.8 km. Due to the high resolution the COSMO-DE model has no parameterization of the deep moist convection, so that the model must resolve the macrostructure of convective phenomena explicitly. This study analyses post-frontal rain areas of COSMO-DE model simulations with respect to their spatial and temporal structure. The same analysis is applied to the RZ product, a radar composite of the German Meteorological Service, for comparison. Ensemble properties like rain area size distribution and mean life cycle of shower cells have been analysed. The examined properties are based on different former investigations, that use radar measurements to characterize the structure of post-frontal rain areas. By comparing the statistical properties of rain cells as obtained from radar observations and model simulations one gets a first impression of model performance concerning precipitation forecast under convective situations. Basically the ensemble properties arising from the radar measurements also apply to the COSMO-DE simulations. Slight differences are related to the intensity of the rain areas or are connected to the different spatial resolution of the two datasets. Our analysis differs from usual model verifications, where ground based rain measurements are compared with precipitation forecasts over larger areas and time intervals.