Abstract
Turbulent motions in the thin ocean surface boundary layer control exchanges of momentum, heat and trace gases between the atmosphere and ocean. However, present parametric equations of turbulent motions that are applied to global climate models result in systematic or substantial errors in the ocean surface boundary layer. Significant mixing caused by surface wave processes is missed in most parametric equations. A Large Eddy Simulation model is applied to investigate the wave-induced mixed layer structure. In the wave-averaged equations, wave effects are calculated as Stokes forces and breaking waves. To examine the effects of wave parameters on mixing, a series of wave conditions with varying wavelengths and heights are used to drive the model, resulting in a variety of Langmuir turbulence and wave breaking outcomes. These experiments suggest that wave-induced mixing is more sensitive to wave heights than to the wavelength. A series of numerical experiments with different wind intensities-induced Stokes drifts are also conducted to investigate wave-induced mixing. As the wind speed increases, the influence depth of Langmuir circulation deepens. Additionally, it is observed that breaking waves could destroy Langmuir cells mainly at the sea surface, rather than at deeper layers.
Highlights
The ocean mixed layer is central to heat and momentum exchange processes between the upper ocean and the atmosphere
Deviating from past research which employs Equations (1) and (2), this study introduces the Stokes velocity Equation (5) proposed by McWilliams and Restrepo [52] and examines the response of the upper mixed layer to a variety of Langmuir circulation (LC) and breaking waves (BW) conditions under different wind speeds (Section 3.2)
In order to analyze the influence of BW and LC on the mixed layer, vertical velocity is examined in this subsection with four experiments being performed
Summary
The ocean mixed layer is central to heat and momentum exchange processes between the upper ocean and the atmosphere. Waves play an integral part as they modulate those exchanges across the air-sea interface and their influence on mixed layer dynamics and structure cannot be ignored [1]. As wind blows over the ocean surface, momentum is transported into the ocean, resulting in enhancement of both mixing and turbulent kinetic energy. Stokes drift plays a role in modulating upper-ocean turbulence through large-scale Coriolis-Stokes and small-scale. It is the interaction of Stokes drift with wind-driven surface shear flow that induces Langmuir circulation (LC) formation [2]. LC could enhance the vertical mixing and alter vertical profiles of temperature and velocity [6,7,8,9], making it crucial in upper ocean studies.
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