Assessing influence of tidal wetting and drying on near-coast wind field and wind power production via mesoscale simulations

As the grid spacing of numerical weather prediction models decreases below the scale of several kilometers, modelling previously neglected spatial details and associated processes becomes more relevant. One such process is the wetting and drying of the large tidal flats which result in semi-diurnal modification of surface temperature, moisture and roughness length over the area whose width, in the specific case of the Wadden Sea tidal flat at the northwest German coast, varies from 3 to 20 km. 

To explore the potential effects that including this process has on the near-coast wind field and wind power generation, we use a customized version of the Weather Research and Forecasting (WRF) model (WRF-TIDE). The modification itself was originally developed by a research team from the Kyungpook University of Daegu (South Korea), and was subsequently adapted at ForWind for the area of the German Bight. Research questions we are interested in include the tidal impacts on the long-term and large-scale patterns – such as the coastal wind speed gradients under various stability regimes – as well as transient events like the low-level jets which modify the power generation on the scale of several hours. Therefore, a representative year was simulated using both the default WRF and the modified WRF-TIDE model configuration. We analyze both the mean atmospheric fields and the specific intervals with large differences between the two WRF configurations. 

While a comprehensive comparison of the wind field produced by the WRF-TIDE model against fixed LIDAR and mast-based measurements is not the focus of this contribution (although this is a major part of the future work), comparison with aircraft-based measurements show that the surface temperature variation between the periods of flood and ebb are treated in a more realistic manner, as opposed to the fixed-coastline treatment in the default WRF configuration.