Investigating the wind-wave interaction on mean wind and turbulence structure using COAWST with WRF-LES

Abstract. We investigate wind-wave interactions within the marine atmospheric boundary layer during a storm event over the North Sea, using a multiscale coupled modeling framework. Large eddy simulations run within the Weather Research and Forecasting model have been coupled with the Simulating WAves Nearshore model through the Coupled Ocean-Atmosphere-Wave–Sediment Transport system. The simulation consists of six nested domains, three outer mesoscale domains with horizontal grid spacings (9.9, 3.3, and 1.1 km), and three innermost large eddy simulation domains with coarse and fine horizontal grid spacings. Wind and wave outputs from both the finest mesoscale domain and the coarsest LES domain are evaluated against metocean and lidar measurements collected during the storm. The results show that the coarsest LES domain represents wind speeds up to 150 m height more accurately than the mesoscale output but due to excessive simulated vertical wind shear. Above this height, the mesoscale and LES outputs become much closer, and both tend to overestimate the wind speed. The wind direction is well captured across both domains. The significant wave height, peak wave period, and mean wave direction simulated by SWAN show better agreement with observations when forced by the LES output than the mesoscale output. Additionally, the coupled simulations exhibit stronger turbulence fluxes than the uncoupled simulations, which is clearly observed in the vertical profiles of velocity variances and covariances. These findings demonstrate the benefits of high-resolution coupled modeling for capturing offshore boundary layer dynamics and improving wind and wave predictions under severe weather conditions.