Seasonal-interannual-decadal variations of sea level in the South China Sea and connections with the tropical-subtropical Pacific

Different timescale contributions to the sea-level variation in the South China Sea (SCS) are evaluated in this paper. On seasonal timescale, the large variance of the sea-level anomaly (SLA) could account for more than 70% of the monthly sea-level variation in the western shallow continental shelf and the area of Luzon cold eddy. Besides, the seasonal explained variance percentage (skill) has 2 weak centres (50%-70%) off eastern Vietnam, which is related to the summertime eddy pair in the SCS. On interannual-to-decadal (low-frequency) timescale, the skill has two large-value regions (Zone A and Zone B). Zone A is characterized by double centres off eastern Vietnam, but the meridional position of the double centres is farther north than that of the eddy pair. The skill in Zone A is in the range of 35%-55%, and about 50%-70% of the low-frequency variation comes from the steric effect. Zone B is off the west coast of the Philippines. The skill in Zone B increases southward, and it is dominated by the wind-induced dynamic process which is attributed to the remote Rossby wave from the tropical Pacific. Based on the S-EOF analysis, the SEOF-1 mode mainly portrays the decadal variation of the SLA, while the SEOF-2 mode reflects the interannual variation of the SLA. In Zone B, almost all of the low-frequency variation could be attributed to ENSO and PDO, especially to PDO which has a larger contribution. However, the double centres in Zone A are governed by the SCS summer monsoon, instead of ENSO and PDO.