WHOI PO

Ocean waves profoundly contribute to the upper ocean turbulence and mixing. Most ocean waves are generated by the wind. However, a lack of quantitative measurement of wave growth under wind forcings exists due to instrument limitations. To thoroughly study the wave growth under wind forcing and improve numerical wave models, we conducted laboratory experiments for a wide range of wind forcing in the University of Miami's wind-wave facility SUSTAIN (SUrge STructural Air-sea INteraction Facility). Pure wind seas, irregular JONSWAP spectrum waves, and regular monochromatic waves at different frequencies were generated by the mechanical paddles for testing. We directly measured the static air pressure, wind speeds, and water surface displacement at sampling frequencies up to 1000 Hz. In addition, a wave follower was deployed to sample the static pressure behind the wave crest. Our wave growth rates agree with the revisited Miles' Theory that incorporates airside turbulence. The Jeffreys' Sheltering hypothesis remains valid, although it depends on an empirical constant: the sheltering coefficient A. We found that A follows a "U" shape with wind forcing: The strongest aerodynamic sheltering, corresponding to the smallest A, was identified at U10 around 33 m/s (Category-1 hurricane intensity). Our wind stress partition at the air-sea interface agrees with previous laboratory and model results. Our findings suggest that airflow separation plays a pivotal role in the wave growth and that some tuning of existing wave growth theories paves the way for a novel parameterization of wave growth and wind input in future wave models.