Decadal Linkage of Sea Level Anomalies Between the South China Sea and Western Tropical Pacific

Abstract

The decadal variability of sea level anomalies (SLA) in the South China Sea (SCS) is coherent with those in the Western Tropical Pacific (WTP), and both correlate with the Pacific Decadal Oscillation (PDO) with changing correlation across different decades, characterized by an enhanced relationship after 1993. This study analyzed the underlying factors in the relationship between SLA in the SCS and PDO based on observations and simple ocean model experiments. The results reveal that the key factor is the anomalous atmospheric anticyclonic circulation over the tropical western North Pacific (WNPAAC), which can induce positive decadal SLA responses. The WNPAAC index, defined as the regional mean Wind Stress Curl in the Tropical Western North Pacific (TWNP, 3°–18°N, 130°E–160°W), exhibits a negative correlation (r = −0.68 for 1940–2022, exceeding the 95% confidence level) with the decadal steric sea level first mode principal component of empirical orthogonal function. The index can thus characterize the decadal SLA variations in the SCS and the WTP well. Sensitivity experiments using a 1.5-layer nonlinear Reduced-Gravity Ocean model demonstrate that the TWNP wind field accounts for most of the decadal SLA variations in the SCS, with an explained variance percentage (skill) of 60.95%. This study suggests that the TWNP wind field, influenced by tropical central Pacific sea surface temperature anomalies through the Matsuno-Gill response after 1965, dominates decadal SLA variability in the SCS. This wind field functions as a subsystem within the PDO dynamics, showing relative independence from the PDO.