Kuroshio Water Intrusion into the South China Sea Inferred from the Lagrangian Coherent Structure

Kuroshio Intrusion into the South China Sea (SCS) via the Luzon Strait show significant transient features and are usually categorized into several different types in previous studies. Here we show a Lagrangian view of upper water exchanges across the Luzon Strait based on the finite time Lyapunov exponents (FTLE) fields computed from altimetric geostrophic current. The Lagrangian coherent structures (LCSs) extracted from FTLE fields well identify the typical flow patterns and eddy activities related to the Kuroshio intrusion. In addition, these LCSs also reveal the intricate transport trajectories and fluid domains around the Luzon Strait, which are validated by the tracks of satellite-tracked surface drifters and cannot be visually inspected in the velocity maps. The Kuroshio’s eddy shedding events during 2000-2018 are further analyzed and the importance of considering LCSs in estimating transport by eddies is highlighted. The anticyclonic eddies (ACEs) mainly originate from the looping paths of Kuroshio and thus could effectively trap the Kuroshio water before eddy detachment. LCSs provide useful information to predict the positions of the upstream waters which finally enter the ACEs. By contrast, during the formations of CEs, the LCS snapshots indicate that most of CEs are not connected with the trajectories of Kuroshio water. So they have little contribution to the water exchanges from the Pacific into the SCS.