The Wave-induced Mixing In The Ocean Surface Boundary Layer And Its Parameterization

The upper-ocean boundary layer is an intermediate layer connecting the bottom boundary layer of the atmosphere and the upper ocean.It plays an important role in the exchange of water vapor,heat and momentum between the atmosphere and ocean.Due to model resolution,sub-mesoscale processes need to be parameterized in oceanic or atmospheric models.Many parameterization schemes have been developed,but the role of wave-induced mixing is not considered in the commonly applied parameterization schemes.Based on previous research,this thesis focuses on adding the influence of waves to existing parametric schemes.In this study,the large eddy simulation(LES)method was used to study the wave-induced Langmuir circulation through experiments.The results confirmed that the appearance of Stokes drift leads to the generation of Langmuir circulation.By comparing the output from the experiments,it was found that wave breaking generates small-scale turbulence and enhances the surface velocity field strength.In the presence of Langmuir circulation,the vertical downwelling speed is greater than the upwelling speed,but the influence depth is limited,and the eddy viscosity is increased.Small-scale turbulence caused by wave breaking destroys the surface Langmuir circulation.However,the effect of Langmuir circulation is still felt below the near-surface layer.In this case,the impact depth of Langmuir circulation is greater than that of wave breaking.In the wavelength and wave height test experiments,it was found that the influence of Langmuir circulation is more sensitive to the change of wave height than to the change of wavelength.Sensitivity tests are carried out on wind speed.The eddy viscosity of the panchromatic spectrum becomes greater than that of a monochromatic wave.As wind speed increases,the influence depth increases.Through the analysis of LES data,a parameterized equation relating the surface average Langmuir turbulence number,surface friction velocity,boundary layer depth and seawater depth is finally obtained.This equation is substituted into the parameterization equation,so that the wave-induced mixing effects are added to the turbulent closure model.By substituting the new parameterized equation into the one-dimensional turbulence model for verification.By comparing the results with the Papa Ocean Observatory data,it is found that the development trend of the temperature curve simulated by the one-dimensional turbulence model is consistent with observation.Also,the overestimationof simulated water temperature is reduced in summer.The mixing layer is deeper than that without wave effects in winter.By using statistical methods,the parameterization scheme with wave effect can improve both the water temperature and mixing layer simulation.By applying the parametric equation to climate models,and comparing with the results without the influence of wave parameterization,the deviation primarily exists in the monsoon regions.The intensity changes with the seasons.In the equatorial regions the difference is faint,and the absolute value of the mixing layer deviation has a higher correlation with the wind stress.Compared with observation,the parameterized experimental simulation of the mixing layer in the Southern Ocean region considering the influence of waves is closer to the measured value,displaying a large improvement of the mixing layer.Regional comparison with temperature data shows that there is an improvement in the sea surface temperature simulation.The eddy diffusivity with wave effects is larger than that without wave effects,the parameterization scheme considering the influence of waves can improve the eddy diffusivity.Wave-induced mixing can improve the water temperature and mixing layer simulation.