Ensemble-based regional reanalysis system for Central Europe: Assimilation experiments with ERA5 observations, data conversion, 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 only observation data of the ECMWF ERA5 reanalysis will be used. To provide these data to the operational DWD assimilation scheme a converter has been developed. Test experiments have been performed to evaluate whether the current system performance can be improved by using ERA5 observation datasets instead of the operationally used observations from DWDs data base. For testing we use the Basic Cycling Environment (BACY) of DWD being characterized by different modules for each cycling step (e.g boundary data, ICON run, assimilation scheme). BACY enables users to perform cycling over multiple time steps (automatization) as well as repeated tests of a single module for debugging or binary checks. Here we present the BACY specifications chosen for the reanalysis production as well as results of the assimilation experiments.