Two‐sided turbulent surface‐layer parameterizations for computing air–sea fluxes

Abstract

AbstractStandard methods for determining air–sea fluxes typically rely on bulk algorithms set in the frame of Monin–Obukhov similarity theory (MOST), using ocean surface fields and atmosphere near‐surface fields. In the context of coupled ocean–atmosphere simulations, the shallowest ocean vertical level is usually used as bulk input and, by default, the turbulent closure is one‐sided: it extrapolates atmosphere near‐surface solution profiles (for wind speed, temperature, and humidity) to the prescribed ocean surface values. Using near‐surface ocean fields as surface ones is equivalent to considering that, in the ocean surface layer, solution profiles are constant instead of also being determined by turbulent closure. Here we introduce a method for extending existing turbulent parameterizations to a two‐sided framework by explicitly including the ocean surface layer within the aforementioned parameterizations. The formalism we use for this method is derived from that of classical turbulent closures, so that our novelties can easily be implemented within existing formulations. Special care is taken to ensure the smoothness of the resulting solution profiles. Other physical phenomena, such as the penetration of radiative fluxes in the ocean and the formation of waves, are then included within our formalism, and their effects are assessed. We also investigate the impact of such two‐sided bulk formulations on air–sea fluxes evaluated from a setting similar to those of coupled ocean–atmosphere simulations.