Parameterization of the Cool Skin of the Ocean and of the Air-Ocean Gas Transfer on the Basis of Modeling Surface Renewal

Heat and gas transport in molecular sublayers at the air-sea interface is governed by similar laws. A model of renewal type based on the physics of molecular sublayers allows the derivation of a parameterization of the temperature difference across the cool skin of the ocean and of the coefficient of the direct air-sea gas transfer. The surface Richardson number controls the transition from convective instability to wind-induced instability (“rollers” on breaking wavelets) and the Keulegan number controls the transition from the regime of rollers to long-wave breaking. A critical value of the surface Richardson number and of a nondimensional constant can be evaluated by comparing the parameterizations of the cool skin with field data. The critical value of the Keulegan number is determined from the wind speed at which long-wave breaking appears. The parameterizations have been compared with cool skin data obtained from campaigns in the tropical and subtropical Atlantic Ocean, while the gas transfer data are compiled from several experiments in the global ocean. The cool skin data have been used for an adjustment of the parameterization of the direct gas transfer. The parameterization does not include effects of bubble and droplet production in whitecaps, which can be important at high wind speed conditions.