Investigating the wind–wave interaction on mean wind and turbulence structure using COAWST with WRF-LES during a storm event

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 simulation (LES) domains within the Weather Research and Forecasting model have been coupled with the Simulating WAves Nearshore (SWAN) model through the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) system. The simulation consists of six nested domains, three outer mesoscale domains with horizontal grid spacings of 9.9, 3.3, and 1.1 km and three inner large-eddy simulation domains with coarse (100 m) 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, which is however associated with excessive simulated vertical wind shear. Above this height, the mesoscale and LES winds become much closer, both overestimating the measured winds. The measured wind direction is well captured across all 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 shown in the vertical profiles of velocity variances and covariances. Although it is a case study, these findings demonstrate the impact of high-resolution coupled modeling for capturing offshore boundary layer dynamics and on wind and wave predictions under severe weather conditions.