Abstract
Wave growth on the ocean surface is governed to the first order by momentum flux. A lack of quantitative measurement of wave growth and wind stress exists due to instrument limitations and harsh field conditions. Although empirical parameterizations used by numerical wave models are based on physical principles, the reliance on empirical parameters often constrains the accuracy of model forecasts, particularly under varying wind and wave conditions. To study the wave growth under wind forcing and improve the performance of numerical wave models, laboratory experiments were conducted for a wide range of wind forcing, from a mild sea breeze to Category-5 hurricane intensity, in the University of Miami's wind-wave facility SUSTAIN (SUrge-Structure-Atmosphere INteraction Facility). The wave-induced airside pressure, water surface displacement, and 3D wind speeds are directly measured at high sampling frequencies using both stationary and wave-following sampling techniques. We found that: 1. our wave growth rate agrees with the revisited empirical Miles’ Critical Layer Theory that incorporates air-side turbulence and slightly above the theoretical prediction of Non-Separated Sheltering, which accounts for 90% of the wave growth before airflow separates; 2. the empirical Jeffreys’ Sheltering hypothesis (JS) remains valid, although the JS depends on an empirical sheltering coefficient A that was conventionally treated as a constant. We found that A follows a “U” shape with wind forcing: the strongest aerodynamic sheltering, corresponding to the smallest A, was identified around the wind forcing of Category-1 hurricane intensity. 3. Our wind stress partition at the air-sea interface agrees with previous laboratory and model results: the sheltering-induced momentum transfer strengthens with wave steepness. Our findings stress the need to fine-tune some parameters in the existing parameterization of wave growth theories to improve the numerical wave models' forecast output.