Abstract

Using multiple dataset, including remotely sensed SST, rainfall, surface winds, sea level anomaly and assimilated temperature product, seasonal changes of the upper mixed layer hydrodynamic features are investigated in the Sulawesi Sea. Our results reveal that the Sulawesi Sea maintains a high SST exceeding 28.5°C all-year round and specifically, a cold tongue-like SST pattern emanating from eastern gap between Philippines and Sangihe Islands can be detected in wet season. Further study shows that it is assumed to be a branch of the ITF intrusion under favorable northeast monsoon forcing.
By employing a thermal equilibrium equation, contributions from Surface heat forcing, Ekman advection, Geostrophic advection and Vertical entrainment to the mixed layer temperature tendency are diagnosed quantitatively. It presents that upper mixed layer temperature has drastic seasonality in Sulawesi Sea. As regard to the wet season, Surface heat forcing, Ekman advection and Geostrophic advection all tends to warm the mixed layer during the cooling period (October-January), except the Vertical entrainment, which acts to cool the mixed layer with -0.14°C/monthcooling rate. Comparatively, Surface heat forcing contributes over 79% to the mixed layer warming in the warming phase from February to April. As for the dry season, Ekman advection and Vertical entrainment contributes -0.23°C/ monthand -0.25°C/month, respectively, to the mixed layer cooling and largely offsets warming effect induced by Surface heat forcing in the cooling phase of the mixed layer. And for the warming period, again, Surface heat forcing is testified to be a dominant contributor, with 0.27°C/monthwarming effect. Further exploration suggests that impacts from Geostrophic advection on the mixed layer temperature exists throughout the whole calender year, but with relatively subtle contribution.

Keywords:Mixed layer; Surface heat forcing; Ekman advection; Geostrophic advection; Vertical entrainment