Loop Current West of the Luzon Strait Triggered by Kuroshio Cut-Off Events East of Taiwan Island

Abstract

This study aimed to examine the variations in vorticity in the northern South China Sea (NSCS) resulting from the cut-off of the Kuroshio main path east of Taiwan Island. Absolute dynamic topography and satellite altimeter eddy tracking data from 1993 to 2021 were employed to analyze the momentum ratio of the Kuroshio and mesoscale eddies concerning Kuroshio cut-off events through their interaction. The results revealed 12 events where mesoscale cyclonic eddies east of Taiwan Island cut off the Kuroshio main path, resulting in intensified loop currents in the Luzon Strait and increased negative vorticity in the NSCS. Six of these events occurred between 1998 and 2013, coinciding with the negative Pacific Decadal Oscillation (PDO) regime. During this period, negative vorticity triggered by Kuroshio cut-off events rose by 79% in the NSCS, compared to 34% during the positive PDO regime. The Kuroshio interacted with mesoscale cyclonic eddies east of Taiwan for 28 days during the negative PDO regime and 41 days during the positive PDO regime. The Kuroshio velocity strengthened east of Luzon Island but weakened east of Taiwan Island during the negative PDO regime, elucidating the observed disparity. The average duration between the occurrence of mesoscale cyclonic eddy impinging on the Kuroshio east of Taiwan Island and the peak negative vorticity observed in the NSCS was approximately 28 days. This was comparable to data obtained using field measurements.