South China Sea Surface Elevation Variability Determined From TOPEX / POSEIDON Data

1. Introduction The South China Sea (SCS) is a semi-enclosed tropical and subtropical sea located between the Asian land mass (including Taiwan) to the west and north, the Phillipine Islands to the east and Malaysia and Borneo to the south (Figure 1), a total of 3.5×10 6 km 2 surface area. It includes the shallow Gulf of Thailand and connections to the East China Sea (through the Taiwan Strait), the Pacific Ocean (through the Luzon Strait), the Sulu Sea (through the Balabac Strait), the Java Sea (through the Gasper and Karimata Straits) and to the Indian Ocean (through the Strait of Malacca). All of these straits are shallow except the Luzon Strait whose maximum depth is 1800 m. Consequently the SCS is considered a semi-enclosed water body. The complex topography includes the broad shallows of the Sunda Shelf in the south and southwest; the continental shelf of the Asian landmass in the west and north, extending from the Gulf of Tonkin to the Taiwan Strait; a deep, elliptical shaped basin in the center, and numerous reef islands and underwater plateaus scattered throughout. The shelf that extends from the Gulf of Tonkin to the Taiwan Strait is consistently about 70 m deep, and averages 150 km in width from the shoreline; the central deep basin is 1900 km along its major axis (northeast-southwest) and approximately 1100 km along its minor axis, and extends to over 4000 m deep. The Sunda Shelf is the submerged connection between southeast Asia, Malaysia, Sumatra, Java and Borneo and is 100 m deep in the middle; the Gulf of Thailand is about 70 m deep in its central part. The observed circulation patterns of the intermediate to upper layers of the SCS are also primarily forced by the local monsoon systems. Based on limited data, Wyrtki (1961) constructed the surface circulation pattern. From April to August, the weaker southwesterly summer monsoon winds result in a wind stress of over 0.1 N/m 2 (Figure 2a) which drives a northward