A Study On The Impact Of Mesoscale Eddies On Kuroshio Intrusion Variations Northeast Of Taiwan And Its Underlying Mechanism

As an important mechanism of both water mass and energy exchanges betweenthe East China Sea continental shelf and the Kuroshio, the Kuroshio intrusionnortheast of Taiwan has been drawn extensive attention by oceanographic community.Mesoscale eddies in the Northwestern Subtropical Pacific carry the information fromthe open ocean and propagate to the east of Taiwan, which not only has an impact onthe Kuroshio itself but also modulates its intrusion northeast of Taiwan. In this study,the characteristics of the Kuroshio intrusion variation and its mechanism are studiedvia the analysis of extensive in situ observations,20-year satellite sea level anomalyand9-year data assimilative HYCOM Analysis data. The conclusions are summarizedas below.Using the Self Organizing Map analysis, the seasonal and intra-seasonalcirculation anomaly patterns of the Kuroshio intrusion northeast of Taiwan areextracted. The results confirm previous evidence on the impact of mesoscale eddy onthe Kuroshio intrusion, and show the circulation anomaly pattern induced by themesoscale eddies, for the first time. The cyclonic (anticyclonic) eddy east of Taiwanwill lead to an anticyclonic (cyclonic) circulation anomaly pattern northeast of Taiwan,the westward (eastward) migration of the intrusion position and the inshore intrusionincreasing (decreasing) along200-m isobath.For the first time, the Kuroshio intrusion induced by a cyclonic eddy is shown byin situ ADCP velocity. The eddy induced Kuroshio intrusion is proven to be a veryeffective cross-shelf water exchange process by comparing the volume transportduring and after the eddy impact periods. Combing9-year data assimilative HYCOMsolution, the mechanism of the Kuroshio intrusion induced by mesoscale eddies is raised, for the first time, as follows. The impact of the cyclonic (anticyclonic) eddyadjusts the vertical stratification around the shelf break. In the upper layer, thechanging of the stratification tends to decrease (increase) the cross-shelf potentialvorticity gradient, which could weaken (strengthen) the cross-shelf potential vorticitybarrier and enhance (weaken) the Kuroshio intrusion. In the lower layer, the impact ofthe cyclonic (anticyclonic) eddy can decrease (increase) the Kuroshio volumetransport and strengthen (weaken) the lower layer stratification, thus decreases(increases) the lower layer velocity significantly. At this time, the upper layer is less(more) sensitive to the bottom topography, which could (less likely) intrude on to theshelf easily.The seasonal variation of mesoscale eddy number east of Taiwan contributes tothe seasonal variations of the Kuroshio intrusion northeast of Taiwan. In summer, thenumber of anticyclonic eddies is larger than the number of cyclonic eddies. It leads tothe increase in frequency of occurrence of the cyclonic circulation anomaly patternnortheast of Taiwan. In contrast, in winter, the number of cyclonic eddies is largerthan anticyclonic eddies, which leads to the increase of frequency of occurrence of theanticyclonic circulation anomaly pattern northeast of Taiwan.