716 / 2024-09-19 09:55:47

Influence of Boundary Layer Turbulence on Submesoscale Mixed Layer Eddy-Induced Restratification

Submesoscale,Turbulence,Vertical mixing,Restratification

Submesoscale mixed layer eddies have been recognized as an efficient mechanism for promoting potential energy extraction and restratification in ocean mixed layer. But the way these eddies interact with active boundary layer turbulence remains unclear. And to what extent these interactions can contribute to restratification is unknown. In this work, we aimed to investigate the existence of such interactions that can potentially impact the restratification of mixed layer. Since different parametrization schemes for boundary layer turbulence are distinct in describing vertical mixing behaviors, we carried out our analysis by testing the sensitivity of restratification rate to boundary layer turbulence parametrization schemes. MPAS-Ocean was used to simulate mixed layer eddies under various initial conditions, including a series of horizontal and vertical buoyancy gradients, initial mixed layer depth, front width as well as different wind and cooling forces. Two popular parametrization schemes for boundary layer turbulence, namely K profile parametrization and K-epsilon, were used to conduct comparative analysis. To eliminate the direct effects of boundary layer turbulence to restratification, vertical buoyancy flux described by parametrization schemes was subtracted from the total flux. According to our results, for the same initial conditions, two schemes exhibit similar vertical profile of overturning stream function, indicating nearly identical relative rates of restratification. However, stronger wind and cooling forces can result in larger discrepancy in the magnitude of the stream function. It means that under active boundary layer turbulence, the vertical mixing described by the two schemes imposes remarkably different influences on mixed layer eddy induced restratification. Furthermore, since the stream function was obtained by excluding direct effects of boundary layer turbulence, this also implies there are significant interactions between boundary layer turbulence and submesoscale mixed layer eddies, which may be non-negligible in future parametrization of mixed layer eddy induced restratification.