The Kuroshio Intrusion Into the South China Sea at Luzon Strait Can Be Remotely Influenced by the Downstream Intrusion Into the East China Sea

Abstract

Abstract The intrusion of Kuroshio into the South China Sea through Luzon Strait has been of enormous interest in western boundary current studies. Here we show that this intrusion can be remotely influenced by the downstream intrusion of the Kuroshio northeast of Taiwan into the East China Sea, at a lead time of about 220 days. This remarkable finding is first revealed by a quantitative causality analysis which is rigorously established from first principles in physics; it is originally motivated by the observation of a wake southeast of Taiwan, whose influence on the loop current, also revealed by causality analysis, is traced downstream to the Kuroshio intrusion into the East China Sea. Further analysis suggests that the two important Kuroshio intrusions are connected via a coastal trapped wave mode with a period of 1.5 years propagating southward along the eastern Taiwan coast, as supported by both theoretical and numerical models. Upon approaching the Luzon Strait, its negative (positive) phase functions to intensify (reduce) the loop current. At a speed of 1.37 km day −1 , the mode takes about 220 days for the disturbances northeast of Taiwan to travel along the coast to Luzon Strait, leading to the same time delay for the downstream‐upstream causal relation.

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