The Tidal Effects on the Upper Sea Temperature Cooling Northeast off the Hainan Island

Using a 3-D, high-resolution ocean model, this paper aims to explore the mechanism that causes the upper sea cooling centers northeast off the Hainan Island in summer, which can be detected by satellite-observed sea surface temperature. Results from the sensitivity experiments show that two cooler water centers, one east off the Wenchang City and another east off the Qiongzhou Strait, occur when tides are included in the model, mainly due to the inhomogenous tidal mixing between the coastal region and open ocean that changes the pressure gradient and thus the circulations in the northwestern SCS. Further heat transport analysis suggests that the mechanisms associated with the two cooler water centers are different: the former is mainly caused by the upwelling induced by tides, while the latter is caused by compensation of cooler water from the surrounding regions due to the tide-induced westward current anomalies in the Qiongzhou Strait which suppresses the eastward warmer water transport from the Qiongzhou Strait. On the inter-annual scale, the tidal effects on the sea temperature vary with anomalous large-scale surface forcings; while weaken during La Niña years, they enhance during El Niño years.