Turbulent Exchange in Unsteady Air-Sea Interaction at Small and Submesoscales

An adequate description of the interaction between the atmosphere and ocean remains one of the most important problems of modern oceanology and climatology. The extremely wide variety of physical processes occurring in the coupled layers, large range of scales, and moving boundary all significantly complicate the creation of models that would allow calculating the physical characteristics in both media with the necessary accuracy. In this paper the temporal variability of dynamic parameters in the driving layer of the atmosphere and in the near-surface layer of the sea on small and submesoscales from one to several tens of hours is considered. The experimental data show a very high correlation between the friction wind velocity and turbulence intensity in the upper sea layer on all scales recorded. One important distinguishing feature of all measured physical quantities in both media is the presence of quasi-periodic oscillations with different periods. For a more accurate description of momentum and energy fluxes from the atmosphere, a nonstationary model of turbulent exchange in the near-surface layer of the sea is proposed. It takes into account quasi-periodicity in the intensity of dynamic interaction between the atmosphere and the sea at these scales. In the model we use the equations of momentum and turbulent energy balance, the system of equations is solved numerically, and the calculation results are compared with other models and with experimental data. It is shown that taking into account the nonstationarity of the wind strain improves the correspondence between the calculations and the experimental data. It is noted that, in the nonstationary case, the energy and momentum flux from the atmosphere and the turbulence intensity increases compared to the action of a constant average wind of the same duration. Therefore, the strong averaging often used in global models may markedly underestimate the intensity of the dynamic interaction between the atmosphere and ocean.