Impact of mesoscale eddies on Kuroshio intrusion variability northeast of Taiwan

Abstract

Abundant 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.

Topographic Beta Spiral and Onshore Intrusion of the Kuroshio Current

“…Oey et al () concluded that winter cooling alone could cause a great northward intrusion of KBC onto the ECS shelf. It was reported that the Kuroshio intrusion can be partly attributed to vortex stretching of the intruded water column over topography (Yang et al, ) and to the westward impingement of eddies from the open ocean on the Kuroshio mainstream (Wu et al, ; Yin et al, ). The vertical structure of the Kuroshio intrusion was also inferred from the paths of major currents north of Taiwan (Yang et al, ); as shown in their Figure 14, the Kuroshio turns cyclonically from the surface to the bottom when it intrudes onto the ECS shelf (Yang et al, ).…”

Generation and Propagation of M2 Internal Tides Modulated by the Kuroshio Northeast of Taiwan

“…We established another numerical experiment, hereafter designated the M2K case, to investigate the M 2 internal tide variability modulated by the Kuroshio to the northeast of Taiwan. Generally, the Kuroshio intrusion in this area was thought to be a quasi‐steady process with dominant current and transport variability occurring at 100‐day timescales (Johns et al, ; Yin et al, ; Zhang et al, ), which is much longer than the timescale of internal tides. Therefore, the Kuroshio flows and the associated stratification structure could be regarded as a steady background field during the 10‐day period of the ideal tidal experiment (M2T case).…”

Impacts of pre‐existing ocean cyclonic circulation on sea surface chlorophyll‐a concentrations off northeastern Taiwan following episodic typhoon passages

“…Yin et al . [] showed a good agreement between the HYCOM reanalysis data and AVISO geostrophic currents, and drifter trajectories from Global Drifter Program northeastern of Taiwan (see their Figures and ). Both onshore (positive) and offshore (negative) transports are found.…”