Characteristics and mechanisms of sea surface height in the South China Sea

Fifty years (1960–2009) sea surface height (SSH) data derived from ECMWF ORA-S3 are analyzed in the South China Sea (SCS). Using stochastic dynamic analytic method to investigate characteristics of SSH on different timescales, it could be found that SSH in the SCS displays distinct seasonal (including annual and semiannaul) and interannual variations. The annual signal has minimum value in February and maximum value in August, and its amplitude is 1.81 cm. The interannual SSH variability in the SCS is coherent with the ENSO/PDO/NPGO based on the lead-lag relationship. The seasonal SSH variations are induced by buoyancy fluxes and local wind stress. The local wind stress contribution to seasonal SSH in the east SCS is dominant (explain 20–65%), and buoyancy fluxes contribution is secondary (explain 30–40%). Buoyancy fluxes are determined by net heat fluxes in the upper ocean. Effect of freshwater fluxes can be neglected. Interannual variations are closely related to the subsurface water (depth about 100–300 m). ENSO/PDO/NPGO signals affect the temperature and salinity changes of the subsurface water and further lead to interannual variations of SSH.