The role of ocean dynamics in determining the mean seasonal cycle of the South China Sea surface temperature

This study uses historical temperature data combined with climatological wind stress and surface heat flux to seek a better understanding of the role of ocean dynamics in determining the mean seasonal cycle of the South China Sea surface temperature. In most parts of the basin, we see a negative correlation between sea surface temperature (SST) and mixed layer depth (MLD). From late winter to early spring, when MLD shoals against the diminishing of the northeast monsoon, heat gained from the atmosphere is trapped in a shallower surface mixed layer and this eventually warms up the SST. The onset of the southwest monsoon marks the end of this heating process, and as a result SST drops during the rest of the year. Heat budget analysis further suggests that, although surface heat flux is fundamental to the seasonal excursion of SST, adding the contribution of ocean dynamics better closes the surface heat budget. Ekman advection forced by the northeast monsoon is the primary heating process in winter, but it becomes less important compared with other heat budget terms as horizontal temperature gradient decreases in the following seasons. Vertical entrainment is effective at cooling in summer, leading to a decrease of SST earlier by up to 5 months than surface heat flux starts to cool the ocean.