Regime Shift of the Sea Level Trend in the South China Sea Modulated by the Tropical Pacific Decadal Variability

During the altimeter era, the sea level in the South China Sea (SCS) and western tropical Pacific (WTP) experienced significant decadal variability. The sea level rose during 1993–2009 and fell during 2010–2019. The decadal variability of Walker Circulation associated with the Pacific Decadal Oscillation can explain the sea level variability in the WTP to a great extent. The wind forced westward propagating Rossby waves increased (decreased) the sea level in the WTP during 1993–2009 (2010–2019). However, the interior wind forcing has a negligible contribution to the decadal variability of the sea level in the SCS. The remote forcing from WTP through the oceanic bridge was supposed to play a dominant role. The sensitive experiments of a 1½‐layer model and Regional Oceanic Modeling System suggested that the sea level signals via the Sibutu Passage and Mindoro Strait accounted for the decadal variability of sea level in the central basin of SCS. Plain Language Summary During the altimeter era, the global mean sea level rose continuously, while the regional sea level trends are not uniform. The atmospheric and oceanic processes associated with climate modes played an important role. The Walker Circulation anomalies, connected closely with the “atmospheric bridge” of the Pacific Decadal Oscillation (PDO), forced a reverse sea level trend in the western and eastern tropical Pacific via propagations of Kelvin/Rossby waves. The sea level signals propagated into the South China Sea (SCS) via the Sibutu Passage and Mindoro Strait, which dominated the sea level variations in the central SCS. Unlike in the tropical Pacific, the decadal variability of sea level in the SCS was associated with PDO through “oceanic bridge.” The results in this study shed light on our understanding on the dynamics of sea level and upper‐layer circulation changes in the SCS and adjacent regions. Key Points Sea level trends in the South China Sea (SCS) and western tropical Pacific experienced regime shift during the altimeter era Remote forcing originated from tropical Pacific dominated the decadal variability of sea level in the SCS Tropical Pacific conveys its impact on the sea level in the central SCS mainly via the Sibutu Passage and Mindoro Strait