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

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.

Impact of Correction Target Selection on Long-Term Spectral Nudging in Luzon Strait and Its Adjacent Regions

“…As a large strait along the western boundary of the Pacific Ocean, the Luzon Strait is also the main channel connecting the Northwest Pacific Ocean and the South China Sea [27,28]. When the Kuroshio passes through this area, the westward invasion branch contributes to the heat, salinity, circulation, eddy activity, and even energy budget of the South China Sea [29][30][31][32][33][34].…”

Submesoscale Vertical Heat Transport at the Kuroshio Extension: Characteristics and Mechanisms

“…The advantage of this method is that it can provide both direction and magnitude of the causal relationships between variables (Liang, 2014, 2015, 2021b). Therefore, it has been widely used in the field of physical oceanography, such as El Niño, sea surface chlorophyll‐a concentration, ocean heat content, Arctic surface temperature, Arctic sea ice, and the intrusion of Kuroshio (Docquier et al., 2022; Liang, 2014; Liang et al., 2021; G. Wang et al., 2020; Xiao et al., 2020; Y. Yang et al., 2023; Y. Zhang & Liang, 2022; H. Zhang et al., 2017; Zhao et al., 2023).…”