Intra-Seasonal Variation in the Velocity Field of the Northeastern South China Sea

Abstract

Two subsurface Acoustic Doppler Current Profilers (ADCP) were deployed at the northeastern South China Sea to study circulation structure in the area as well as the path and process of Kuroshio intrusion. The 48-hour low-pass filtered data reveal significant intra-seasonal variations in the velocity field. The current pattern alternates between clockwise and counterclockwise even within a single month. Local wind forcing dominated by monsoon winds fails to address the phenomena and variations. The present study suggests that wind stress curl forcing is the dominant process controlling the circulation picture in the area. While a stronger wind stress curl appeared and developed off southern tip of Taiwan, it will provide negative vorticity to the intruded current and form an anticyclonic eddy. The stronger current is always going along with the stronger wind stress curl. On the other hand, while the curl in the area looses or decays, the intruded current becomes weakened and forms a cyclonic eddy. The agreement between wind stress curl and the velocity field suggests that changes in the wind stress curl contribute to the intra-seasonal variations in the northeastern South China Sea.