Impacts of the mid-latitude westerlies anomaly on the decadal sea level variability east of China

Abstract

The present analysis has revealed that both the altimetry and tide gauge records show a prominent sea level rise from 1993 to 2016 in the coastal seas east of China, including Bohai, Yellow Sea, and East China Sea (BYECS). The regional mean sea level rise rate for the BYECS continental shelf area is ~ 3.2 mm/year, which is close to the global mean (2.9 mm/year). Besides the rising trend, the BYECS sea level anomaly (SLA) also shows obvious interannual and decadal oscillation. It is found that the mid-latitude westerlies, rather than the steric height variability, are responsible for these oscillations. By analyzing the 67-year (1950–2016) hindcast outputs from an eddy-resolving ocean general circulation model, a 14.2 years decadal period is found to dominate the BYECS SLA variability, and the decadal oscillation is positively correlated with the North Pacific Gyre Oscillation (NPGO). The composite analysis and causality analysis demonstrate that during the positive phase of the NPGO, the mid-latitude westerlies decrease and a positive wind stress curl anomaly at the same latitude of the East China Sea’s Kuroshio occurs to the south of the westerlies. Consequently, the Kuroshio Current volume transport and sea surface height difference between the two sides of the Kuroshio decrease, that is, the sea level in the BYECS rises.