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

Abstract

Standard 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.

The wave-age dependent stress parameterization (WASP) for momentum and heat turbulent fluxes at sea in SURFEX v8.1

“…The parameterization presented here is meant to be used for atmospheric numerical modelling, either operationally with the models of Météo-France of for a large variety of case studies with Meso-NH, with typically the first level at 5 to 20 m above sea level (asl). Whereas it may be tempting to use much finer sampling close to the surface to better represent its influence on the surface-layer or boundary-layer processes, we believe that doing so within the MOST framework leads to inconsistency (see Pelletier et al, 2021, for a discussion).…”

Discrete analysis of Schwarz Waveform Relaxation for a simplified air-sea coupling problem with nonlinear transmission conditions

“…[4]). This approach, traditionally used to deal with solid walls, is also used in the ocean-atmosphere context, with additional complexity arising from the stratification effects [5]. In this context wall laws are referred to as surface layer parameterizations.…”

“…Finally, in Sec. 5, numerical experiments in the linear and nonlinear case are performed to illustrate the relevance of our analysis.…”