Impact of mesoscale eddies on Kuroshio intrusion variability northeast of Taiwan

Abstract

AbstractAbundant mesoscale eddies propagate to the east of Taiwan and affect the Kuroshio Current and its onshore intrusion northeast of Taiwan. But the dynamical process of how eddy activities modulate the Kuroshio intrusion is still unclear. In this study, in situ ocean velocity observations, drifter trajectories, tide gauge measurements, satellite sea surface height data, and assimilative Hybrid Coordinate Ocean Model (HYCOM) reanalysis outputs were used to analyze a cyclonic eddy‐induced large Kuroshio onshore intrusion during late autumn 2008. Along with nine anticyclonic eddy events and seven cyclonic eddy events extracted from long‐term HYCOM reanalysis outputs, the variability of the eddy‐induced intrusion was quantified. The impacts of the cyclonic eddy and the anticyclonic eddy were opposite. Under the impact of cyclonic (anticyclonic) eddy, the total onshore intrusion between 122°E and 124°E across the 200 m isobaths was decreased (increased) by 15.7% (7.3%), while the onshore intrusion west of 122.6°E and the northeastward current on the outer shelf were increased (decreased) by 30.6% (4.7%) and 31% (10.1%), respectively. The arrival of cyclonic (anticyclonic) eddy brought positive (negative) potential vorticity (PV) flux and modulated the local ocean vertical stratification, which weakened (enhanced) the cross‐slope PV gradient and the shelf slope constraint on the upper layer current and, therefore, favored (inhibited) the Kuroshio onshore intrusion.