Ensemble-based regional reanalysis system for Central Europe: Observation data converter, setup, test results and outlook

The development of regional reanalyses aims at the provision of high-resolution data sets that are suitable for climate applications and climate services. As the desired high-resolution information can barely be provided by either synoptic or remote sensing observation data, a growing interest in high-quality regional reanalyses is recognisable. Particular demand arises from the renewable energy sector. Further quality gains are expected by using an ensemble approach, e.g. by making available the desired uncertainty information when moving towards higher resolution. Within the framework of the Innovation Programme for applied Researches and Developments (IAFE) at Germany's national meteorological service (DWD) our project aims to develop and evaluate an operational ensemble-based regional reanalysis system incorporating the current NWP model of DWD (ICON). One final goal of the project is to provide a basic framework for user-oriented verification.  

For our new reanalysis system we plan to use observation data sets or subsets of the ECMWF ERA5 reanalysis. Thus, a converter has been developed providing the ERA5 observation data (odb files) to the operational DWD data assimilation scheme. Numerous test experiments have been performed to 1) assess the specifications for our future reanalysis system and 2) evaluate the performance of the observation data assimilation. For testing we use the Basic Cycling Environment (BACY) being characterized by its modularity, robustness, user-friendlyness and high complexity. Here we present the resulting set of "frozen" BACY specifications such as model resolution, number of ensemble members, domain size, choice of output variables as well as results of the assimilation experiments.