The dynamical coupling of wind-waves and atmospheric turbulence: a review of theoretical and phenomenological models

Abstract

When wind blows over the ocean, short wind-waves (of wavelength smaller than 10 meters) are generated, rapidly reaching an equilibrium with the overlying turbulence (at heights lower than 10 meters). Understanding this equilibrium is key to many applications since it determines (i) air-sea fluxes of heat, momentum and gas, essential for numerical models, (ii) energy loss from wind to waves, which regulates how swell is generated and how energy is transferred to the ocean mixed layer and (iii) the ocean surface roughness, visible from remote sensing measurements. Here we review phenomenological models describing this equilibrium: those couple a TKE and wave action budget through several wave-growth processes, including airflow separation events induced by breaking waves. Even though those models aim at reproducing measurements of air-sea fluxes and wave growth, some of the observed variability is still unexplained. Hence, after reviewing several state-of-the-art phe-nomenological models, we discuss recent numerical experiments to give hints about future improvements. We suggest three main directions, which should be addressed both through dedicated experiments and theory: (i) a better quantification of the variability of wind-wave growth and of the role played by the modulation of short and breaking wind-waves by long wind-waves, (ii) an improved understanding of the imprint of wind-waves on turbulent coherent structures and (iii) a quantification of the interscale interactions for a realistic wind-waves sea, where several wind-and-waves coupling processes coexist at multiple time and space scales.