Anticyclonic Eddy Sheddings from Kuroshio Loop and the Accompanying Cyclonic Eddy in the Northeastern South China Sea

Sheddings of Kuroshio Loop Current (KLC) eddies in the northeastern South China Sea (SCS) are investigated using mooring arrays, multiple satellite data, and data-assimilative HYCOM products. Based on altimeter sea surface heights between 1992 and 2014, a total of 19 prominent KLC eddy shedding (KLCES) events were identified, among which four events were confirmed by the concurrent moored and satellite observations. Compared to the leaping behavior of Kuroshio, KLCES is a relatively short-duration phenomenon that primarily occurs in boreal autumn and winter. The KLC and its shedding anticyclonic eddy (AE) trap a large amount of Pacific water with high temperature–salinity and low chlorophyll concentration in the upper layer. The corresponding annual-mean transport caused by KLCES reaches 0.24–0.38 Sv (1 Sv ≡ 106 m3 s−1), accounting for 6.8%–10.8% of the upper-layer Luzon Strait transport. Altimeter-based statistics show that among ~90% of the historical KLCES events, a cyclonic eddy (CE) is immediately generated behind the AE southwest of Taiwan. Both energetics and stability analyses reveal that because of its large horizontal velocity shear southwest of Taiwan, the northern branch of KLC is strongly unstable and the barotropic instability of KLC constitutes the primary generation mechanism for the CE. After CE is generated, it quickly grows and gradually migrates southward, which in turn facilitates the detachment of AE from KLC. The intrinsic relationship between KLC and CE explains well why eddy pairs are commonly observed in the region southwest of Taiwan.