Spatial-Temporal Variations and Mechanisms of the Upper Ocean Heat Content in the South China Sea

摘要

The variability of the upper ocean heat content (OHC) of the South China Sea (SCS) has a significant regional climate impact on the surrounding East and Southeast Asian countries. In this paper, the spatial-temporal variations of the upper OHC in the SCS and their relations to El Nino-Southern Oscillation (ENSO) are analyzed using empirical orthogonal functions and correlation analysis. The mechanisms for the interannual OHC variability associated with ENSO and regime shift in 1998 are further examined using composite and correlation analysis methods. The results show that the OHC anomaly field is mainly composed of two leading modes, i.e., an in-phase oscillation mode and a zonal anti-phase oscillation mode. The in-phase oscillation mode exhibits strong interannual variability with periods of 2-5years, which is well related to ENSO at a lead of 6months, and experienced a regime shift in 1998. The anti-phase oscillation mode shows only a strong interannual variability with periods of 2-4years well related to ENSO at a lag of 4months. The composite analysis reveals that horizontal thermal advection mainly controlled by wind forcing plays a primary role in modulating the interannual OHC variability associated with ENSO, while net surface heat flux is the secondary source. And the OHC regime shift in 1998 primarily results from both the strong cold advection during the extremely strong El Nino in 1997 and the subsequent warm advection during the strong La Nina in 1998.