A numerical study of Stokes drift and thermal effects on the oceanic mixed layer

This study explores the influence of Stokes drift and the thermal effects on the upper ocean bias which occurs in the summer with overestimated sea surface temperature(SST)and shallower mixed layer depth(MLD)using Mellor-Yamada turbulence closure scheme.The upper ocean thermal structures through Princeton ocean model are examined by experiments in the cases of idealized forcing and real observational situation.The results suggest that Stokes drift can generally enhance turbulence kinetic energy and deepen MLD either in summer or in winter.This effect will improve the simulation results in summer,but it will lead to much deeper MLD in winter compared to observational data.It is found that MLD can be correctly simulated by combining Stokes drift and the thermal effects of the cool skin layer and diurnal warm layer on the upper mixing layer.In the case of high shortwave radiation and weak wind speed,which usually occurs in summer,the heat absorbed from sun is blocked in the warm layer and prevented from being transferred downwards.As a result,the thermal effects in summer nearly has no influence on dynamic effect of Stokes drift that leads to deepening MLD.However,when the stratification is weak in winter,the thermal effects will counteract the dynamic effect of Stokes drift through enhancing the strength of stratification and suppress mixing impact.Therefore,the dynamic and thermal effects should be considered simultaneously in order to correctly simulate upper ocean thermal structures in both summer and winter.

Contributions of shortwave radiation to the formation of temperature inversions in the Bay of Bengal and eastern equatorial Indian Ocean:A modeling approach

Variations in incoming shortwave radiation influence the net surface heat flux,contributing to the formation of a temperature inversion.The effects of shortwave radiation on the temperature inversions in the Bay of Bengal and eastern equatorial Indian Ocean have never been investigated.Thus,a high-resolution(horizontal resolution of 0.07°×0.07° with 50 vertical layers) Regional Ocean Modeling System(ROMS) model is utilized to quantify the contributions of shortwave radiation to the temperature inversions in the study domain.Analyses of the mixed layer heat and salt budgets are performed,and different model simulations are compared.The model results suggest that a 30% change in shortwave radiation can change approximately 3% of the temperature inversion area in the Bay of Bengal.Low shortwave radiation reduces the net surface heat flux and cools the mixed layer substantially;it also reduces the evaporation rate,causing less evaporative water vapor losses from the ocean than the typical situation,and ultimately enhances haline stratification.Thus,the rudimentary outcome of this research is that a decrease in shortwave radiation produces more temperature inversion in the study region,which is primarily driven by the net surface cooling and supported by the intensive haline stratification.Moreover,low shortwave radiation eventually intensifies the temperature inversion layer by thickening the barrier layer.This study could be an important reference for predicting how the Indian Ocean climate will respond to future changes in shortwave radiation.