Intra-seasonal variation in the velocity field of the northeastern South China Sea

Two subsurface Acoustic Doppler Current Profilers (ADCP) were deployed in the northeastern South China Sea to study the circulation structure in the area as well as the path and process of the Kuroshio intrusion. The 48 h low-pass filtered data, for the first time, reveal significant intra-seasonal variations in the velocity field. Flow is alternately cyclonic or anticyclonic even within a single month. Local wind forcing dominated by monsoon winds fails to address the phenomena. The present study suggests that intruding current patterns are likely triggered by the strong wind stress curls. Strong negative wind stress curls off the southern tip of Taiwan introduce negative vorticity to form anticyclonic circulation in the intruding current. With diminishing wind stress curls, the intruding current weakens, forming a cyclonic circulation pattern.