Annual variation of sea surface height, dynamic topography and circulation in the South China Sea —— A TOPEX/Poseidon satellite altimetry study

The South China Sea (SCS) is a semi-enclosed deep basin with complex topography includ-ing broad continental shelves, steep slopes, and a large deep basin. It is dominated by prevailing southwest monsoon in summer and by much stronger northeast monsoon in…

Annual variation of sea surface height, dynamic topography and circulation in the South China Sea--A TOPEX/Poseidon satellite altimetry study

TOPEX/Poseidon satellite altimetry data from 1993 to 1999 were used to study mean annual variation of sea surface height anomaly (SSHA) in the South China Sea (SCS) and to re-produce its climatological monthly surface dynamic topography in conjunction with historical hy-drographic data. The characters and rules of seasonal evolution of the SCS dynamic topography and its upper circulation were then discussed. Analyses indicate that annual variation of the SCS large-scale circulation could be divided into four major phases. In winter (from November to Feb-ruary), the SCS circulation is mainly controlled by double cyclonic gyres with domination of the northern gyre. Other corresponding features include the Kuroshio intrusion from the Luzon Strait and the northeastward off-shelf current in the area northwest off Kalimantan Island. The double gyre structure disassembled in spring (from March to April) when the northern gyre remains cyc-lonic, the southern gyre becomes anticyclonic, and the general circulation pattern shows a dipole. There is no obvious large-scale closed gyre inside the SCS basin in both summer (from May to July) and autumn (from August to October) when the SCS Monsoon Jet dominates the circulation, which flows northeastward across the SCS. Even so, circulation patterns of these two phases di-verse significantly. From May to July, the SCS monsoon jet flows northward near the Vietnam coast and bends eastward along the topography southeast off Hainan Island at about 18N form-ing an anticyclonic turn. It then turns northeastward after crossing the SCS. From August to Octo-ber, however, the monsoon Jet leaves the coast of Vietnam and enters interior of the basin at about 13N, and the general circulation pattern becomes cyclonic. The Kuroshio intrusion was not obvious in spring, summer and autumn. It is suggested from these observations that dynamic ad-justment of the SCS circulation starts right after the peak period of the prevailing monsoon.