WRF Simulations to Investigate Processes Across Scales (WRFSCALE)

Several scientific aspects ranging from boundary layer research and land modification experiments to data assimilation applications were addressed with the Weather Research and Forecasting (WRF) model from the km-scale down to the turbulence-permitting scale. Case study simulations in as different regions as the central United States, the United Arab Emirates and southwestern Germany were performed to investigate the evolution of the convective boundary layer. The multi-nested WRF setup, driven by the operational analysis of the European Centre for Medium-range Weather Forecasts (ECMWF), high-resolution terrain, and land cover data sets simulated a realistic evolution of the internal turbulent structure of the boundary layer including the transitions between daytime and nighttime conditions. Land modification simulations in the United Arab Emirates demonstrated that plantations as small as 10\(\,\times \,\)10 km\(^2\) could modify the weather pattern in this area in a way that more precipitation reaches the desert. Data assimilation experiments demonstrated the beneficial influence of state-of-the-art lidar measurements on the forecast performance of WRF. A further improvement was found when the more sophisticated hybrid 3DVAR-ETKF method was applied, since this method includes a flow-dependent model error contribution and thus more realistically spreading the information of the observations.