The Seasonal Variation Of Sea Surface Height In The South China Sea: Characteristics And Its Mechanism

POP model is used to simulate the seasonal variation of Sea Surface Height (SSH) in the South China Sea (SCS). In combination with TOPEX/Poseidon (T/P) altimeter data and Ishii temperature/salinity data, simulation results were used to analyze the characteristics and mechanism of seasonal variations of SSH .Dynamic Sea Level (DSL) is controlled by the structure of the circulation. For the purpose of better simulating the circulation of SCS, the North Pacific was chosen as the simulation area to include/involve the impacts of the Kuroshio. The horizontal distributions of simulated North Pacific surface circulation, South Equatorial Current and Equatorial Countercurrent coincide with the observation results. The seasonal variations of the SCS circulation were also reasonably simulated. In winter, the cyclonic circulation is exhibited, and the Kuroshio intrusion current is stronger than other seasons. The centre of Luzon Cold Eddy is at (18oN,117oE). The long-shore current along Vietnam coast is strongly southward. In summer, the circulation is mainly clockwise. The northward long-shore current is observed along Vietnam coast, while the current along Guangdong Province is northeastward. In spring and autumn, the circulations are relatively weaker due to reversal of the SCS monsoon.The vertical distributions of simulated temperature and salinity, which determine the calculating accuracy of Steric Sea Level (SSL), were compared with Levitus (2005) data on 18.75°N and 118.25°E sections. The agreement between them indicates that the three-dimensional temperature and salinity fields were well simulated.The simulated SSH is similar with T/P height, while the simulated SSL also coincides with the SSL computed from Ishii(2005) very well. The sea surface height anomaly and steric sea level anomaly fields are completely opposite between winter and summer, as well as between spring and autumn.In winter, the SSH in deep basin reach lowest value around the year. There are two negative SSHA centers around 18oN,119oE and 10oN,112oE. The simulated lowest extremes are -14cm and -4cm respectively. The west, south and northwest parts of the SCS are basically dominated by positive anomalies, and the anomaly value reaches 22cm in the Thailand Bay. In summer, the SSH in deep basin reach highest value. Corresponding to the negative centers in winter, there are two positive centers in summer. The simulated extreme values are 12cm and 6 cm respectively. The SSH along Vietnam coast is lowest in summer.The distribution of DSL and current field correspond with each other exactly. In winter, the Luzon cold eddy and the cyclonic circulation on the southeast of the Vietnam coast is corresponded with two negative anomaly centre, and the DSL in the west coast of SCS reaches its highest value of a year because of Ekman Transport; In summer, the anticyclonic circulation on the southeast of the Vietnam coast is correspond with a positive anomaly centre, the DSL in the east coast is relatively large while the DSL in the west coast falls to its lowest value of a year.In the margin of the SCS, the DSL plays a critical role in the seasonal variation of the total SSH. In the most part of deep basin, the contribution of DSL to the SSH is about 50-60%, while SSL takes up about 40-50% of the SSH.