Radar forward operator for data assimilation and model verification for the COSMO-model

A new radar forward operator for simulating terrestrial weather radar measurements from NWP model output is currently developed. It is suitable for a broad range of applications like, e.g., radar data assimilation in the framework of Ensemble Kalman Filter Systems, or verification of cloud microphysical parameterizations. This operator calculates the radar observables reflectivity and radial wind (later also polarisation parameters) from the prognostic model output. The rationale is to have a comprehensive radar simulator, which comprises all relevant physical aspects of radar cloud measurements in a quite accurate way, but at the same time to provide the possibility for simplifications in a modular fashion. This enables the user to configure and tailor the operator for special applications, that is, to find the ”best” balance between physical accuracy and computational effort. This operator is currently implemented as a module in the non-hydrostatic fully compressible state-ofthe-art NWP model of the Consortium for Small Scale Modeling (COSMO), called ”COSMO-model” (formerly ”Lokal Modell” LM; Doms and Schättler, 2002; Baldauf et al., 2011). COSMO is a cooperation of 7 European National Meteorological Services, and Germany is one of the partners. More information can be found online at http://www.cosmo-model.org. The new weather radar network of the DWD comprises 17 C-Band dual polarisation Doppler radar systems evenly distributed throughout Germany for complete coverage. They provide unique information about cloud structure and precipitation in three dimensions and high spatial and temporal resolution. Up to now these data are not used in the operational COSMOmodel of DWD, except within the framework of the latent heat nudging and for a simple nudging method of the radial wind. Future applications are however planned to make better use of radar data within an upcoming new LETKF data assimilation system (Hunt et al., 2007), which will be based on a convection-allowing high resoluton ensemble forecasting system (grid spacing 2.8 km over Central Europe, 40 members, 8 runs a day out to +21 h). Here, the use of weather radar data is a promis-