On the turbulence and wave-induced stresses imposed by the airflow above surface waves

When wind blows over waves, the wave's windward side shelters the leeward side, inducing a windward high pressure and a leeward low pressure. Buckley & Veron (2019) reported wave's phase-locked turbulent kinetic energy and intermittent flow separation in the air from Particle Image Velocimetry results. They suggested the waves' amplitude, frequency and wind speed affect the structure of the airflow and wind stress above the wave, which in turn fuel the wave growth. However, systematic research on the airflow structure above waves with different amplitudes and frequency has been scarce. Therefore, we tested a wide range of wind-wave conditions in the wave tank facility at the University of Miami accompanied by vertical profilings of air pressure with Elliot probes and wind speed with hotfilm anemometer above the waves with high acquisition frequency. We report different wave growth mechanisms: under low & moderate wind forcing, the waves grow from a pressure work "suction" effect on the crests due to the combination of pressure and airflow. Under strong wind forcing, however, a high form stress caused by pressure dipoles at waves' windward / leeward dominates the wave growth. This is accompanied by airflow separation and vortices on the leeward side. Eventually, this study will provide insights on future wave models' wind input parameterizations.