This study presents a Lagrangian view of upper water exchanges across the Luzon Strait based on the finite-time Lyapunov exponents (FTLE) fields computed from the surface geostrophic current. The Lagrangian coherent structures (LCSs) extracted from the FTLE fields well identify the typical flow patterns and eddy activities around the Luzon Strait. In addition, they reveal the intricate transport paths and fluid domains, which are validated by the tracks of satellite-tracked surface drifters and cannot be visually recognized in the velocity maps. The FTLE fields indicate that there are mainly four types of transport patterns near the Luzon Strait; among them, the Kuroshio northward-flowing “leaping” pattern and the clockwise rotating “looping” pattern occur more frequently than the “leaking” pattern of the direct Kuroshio branch into the SCS and the “outflowing” pattern from the SCS to the Pacific. The eddy shedding events of the Kuroshio at the Luzon Strait are further analyzed, and the importance of considering LCSs in estimating transport by eddies is highlighted. The anticyclonic eddy (ACE) shedding cases reveal that ACEs mainly originate from the looping paths of Kuroshio and thus could effectively trap the Kuroshio water before eddy detachments. LCSs provide useful information to predict the positions of the upstream waters that finally enter the ACEs. In contrast, LCS snapshots indicate that during the formation of cyclonic eddies (CEs), most CEs are not connected with the pathways of Kuroshio water. Hence, the contribution of CEs to the surface water exchanges from the Pacific into the SCS is tiny.

这项研究基于根据地表地转流计算的有限时间Lyapunov指数（FTLE）场，给出了吕宋海峡上层水交换的拉格朗日视图。从FTLE场提取的拉格朗日相干结构（LCS）很好地识别了吕宋海峡周围的典型流型和涡流活动。此外，它们还揭示了复杂的传输路径和流体域，这些已通过卫星跟踪的表面漂移器的轨道进行了验证，并且无法在速度图中直观识别。FTLE字段表明，吕宋海峡附近主要有四种类型的运输方式。其中，黑潮向北流动的“泄漏”模式和顺时针旋转的“循环”模式比直接黑潮分支进入南海的“泄漏”模式和从南海到太平洋的“流出”模式更为频繁。进一步分析了吕宋海峡黑潮的涡流事件，并着重指出了在考虑涡流估计运输中考虑LCS的重要性。反气旋涡流（ACE）脱落案例表明，ACEs主要来自黑潮的环流路径，因此可以有效地在涡旋脱离之前捕获黑潮水。LCS提供有用的信息以预测最终进入ACE的上游水域的位置。相比之下，LCS快照表明在旋风涡流（CE）形成期间，大多数CE与黑潮的水路无关。因此，CEs对从太平洋到SCS的地表水交换的贡献很小。