Currents in the Taiwan Strait as observed by surface drifters

The trajectories of 110 satellite-tracked surface drifters from 1989 to 2007 were analyzed to elucidate near-surface circulation in the Taiwan Strait. Although the summer circulation observed generally agrees with previous studies, several aspects of the winter circulation were revealed by the analyses. Unlike many earlier studies, which have suggested that a northward (southward) current prevails in the eastern (western) part of the Taiwan Strait during the northeast monsoon season, this study shows that almost all winter drifters that entered the Taiwan Strait eventually moved southward. Inside the Taiwan Strait, northward moving tracks can only be found in the Penghu Channel. After passing the Penghu Channel, the drifters were blocked by the northeast monsoon wind and the Yun-Chang Rise, and turned southward. None of the drifters flowed persistently northward through the Taiwan Strait in winter. In the southern Taiwan Strait, three typical patterns of circulation were observed for the winter trajectories—the “throughflow” pattern that enters the South China Sea flowing westward along the slope; the loop current pattern that circulates anticyclonically and returns to the Kuroshio; and the blocked intrusion pattern that penetrates into the Taiwan Strait through the Penghu Channel.