Development of One-Way Coupling Between MIKE 3 Wave FM Model and WRF-LES for the Evaluation of a Storm Simulation

Abstract We develop a coupling system between the Weather Research and Forecasting model in a large eddy simulation (WRF-LES) configuration and the MIKE 3 Wave Flexible Mesh (M3W FM) model. So far, the coupling system is one-way and offline. We investigate coupled model performance for the simulation of the atmospheric flow within the marine atmosphere over an irregular long-crested wavy surface generated by the M3W FM model. The M3W FM model generates irregular sea surface elevations for given wave spectrum parameters, including significant wave height and peak wave period. This wavy surface elevation realization is then used as a static lower boundary condition in the WRF-LES simulations. For validation, we simulate an event with the largest observed significant wave height from a two-month measurement campaign (equal to a one-year return period storm) in a location in the North Sea near Denmark. To explore the impact of using the wavy surface on the marine atmosphere, a non-coupled WRF-LES simulation over a flat surface is conducted for comparison. Three types of wind and potential temperature profiles were used to initialize the atmosphere in WRF-LES: the first uses constant velocity profiles, the second ERA5 data, and the third mesoscale WRF model output. There is a very good agreement between the sea state measurements and the output of M3W FM model. Vertical profiles of mean wind speed and direction from both coupled and non-coupled simulations also show good agreement with measurements from a buoy lidar. When compared with results from the non-coupled simulations, the coupled model reveals a much higher impact of waves on the turbulence characteristics, which include enhanced velocity covariances and spectra throughout the atmosphere.