Mass sea level variation in the South China Sea from GRACE, altimetry and model and the connection with ENSO

Abstract

Mass sea level variation (SLV) in the South China Sea (SCS) is explored through three independent approaches. One is the mass change observed by the Gravity Recovery and Climate Experiment (GRACE) mission since 2002. The second approach is the steric-corrected altimetry. Mass SLV is calculated by subtracting steric SLV related to the seawater temperature and salinity from altimetry-based total SLV. This approach benefits from the accurate sea surface height observed by Topex/Poseidon since 1992 and its follow on missions. The third approach is based on ocean mass balance theory. Considering the SCS is a semi-closed basin, mass SLV is estimated by taking account of water balance among the precipitation (P), evaporation (E) and flux (F) of ocean currents, indicated as PEF (P-E-F) mass estimation. Consistent comparisons show that mass SLVs from Estimation of the Circulation and Climate of the Ocean (ECCO)-based and Ishii-based steric-corrected altimetry agree well with GRACE observations, whereas PEF (OFES, ocean general circulation model for the Earth Simulator) mass estimation is 86% larger than GRACE observations. On the annual scale, both ECCO-based and Ishii-based steric-corrected altimetry are similar with respect to GRACE, whereas PEF(OFES) mass estimation has significantly larger amplitudes and some outliers. On the interannual scale, ECCO-based steric-corrected altimetry has less ability to capture the interannual variation in the mass SLV. The mass SLVs from Ishii-based steric-corrected altimetry and PEF(OFES) are positively correlated with El Niño and Southern Oscillation (ENSO). The positive influence of ENSO on the mass SLV is mainly imposed by its effects on precipitation and flux of ocean currents in the SCS.