Impact of Langmuir Turbulence on the Ocean Upper Mixed Layer in a 3D Coupled Regional Model of the South China Sea

Langmuir turbulence (LT) can have a significant impact on the ocean mixing in the ocean surface boundary layer. In this study, using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COWAST) modeling system, a 3D wave-current coupled regional model of the South China Sea (SCS) was developed. And the second-moment closure model developed recently by Harcourt, which includes the effects of LT, was introduced into the circulation model to investigate its influence on the coupled models’ performance. Comparisons between the model results with and without LT effects and between the model results and the observations are analyzed. Overall, with the LT effects, the simulated results are more consistent with the observations. When the LT effects are not considered, the mean annual deviation between the model simulated sea surface temperature (SST) and the observed data in the SCS is 1.09℃, as the LT effects introduced, the mean annual SST deviation decrease to -0.06℃ and the deviation almost disappear. Compared with the huge improvement in SST simulation, the introduction of LT has less influence on the simulation of the upper mixing layer depth (MLD). Nevertheless, the model results have also been improved to some extent, with the model performance is improved by 12.7%. Moreover, the eastern and southern parts of the SCS show a more pronounced amelioration than other regions. From the intercomparisons among the experiments, it is also found that the LT exerts more significant impacts on both SST and MLD during spring and summer.