Lagrangian observations of surface flow patterns in the vicinity of Taiwan

Two satellite-tracked surface drifters were launched off the southwestern coast of Taiwan on October 7, 1997. Both traveled northward along the Taiwan Strait (TS) and into the seas north of Taiwan, lasting 20 and 53 days, respectively. From the drifter trajectories, their rotary spectra and satellite infrared imagery, several oceanic features have been detected and are discussed in this paper. Our results indicate that in the southern and central portions of the TS, the floats followed a northward flow with a mean speed of 30–50 cm/s. Upon reaching the northwestern Taiwan coast, the trajectories were strongly affected by the semidiurnal tides and interacted with the Kuroshio water in the southern East China Sea. The onset of the strong northeastern winter monsoon in early November decelerated the northward movement and eventually reversed the direction. This process was accompanied by wind-generated, near-inertial motion. One drifter was then captured by a counterclockwise circulation of a cold dome at the continental shelf break northeast of Taiwan. Finally the drifter was entrained by the mainstream of the Kuroshio and flowed towards the northeast.