A Double-Index Method to Classify Kuroshio Intrusion Paths in the Luzon Strait

A double index （DI）, which is made up of two sub-indices, is proposed to describe the spatial patterns of the Kuroshio intrusion and mesoscale eddies west to the Luzon Strait, based on satellite altimeter data. The area-integrated negative and positive geostrophic vorticities are defined as the Kuroshio warm eddy index （KWI） and the Kuroshio cold eddy index （KCI）, respectively. Three typical spatial patterns are identified by the DI： the Kuroshio warm eddy path （KWEP）, the Kuroshio cold eddy path （KCEP）, and the leaking path. The primary features of the DI and three patterns are further investigated and compared with previous indices. The effects of the integrated area and the algorithm of the integration are investigated in detail. In general, the DI can overcome the problem of previously used indices in which the positive and negative geostrophic vorticities cancel each other out. Thus, the proportions of missing and misjudged events are greatly reduced using the DI. The DI, as compared with previously used indices, can better distinguish the paths of the Kuroshio intrusion and can be used for further research.

Influence of Island Chains on the Kuroshio Intrusion in the Luzon Strait

By applying a global high-resolution （0.1°） OGCM, the influence of the island chains in the Luzon Strait （LS） on the Kuroshio intrusion is studied systematically. The island chains in the LS are separated into three parts： the south island chain, the middle and north island chain, and Babuyan Island. One control and three sensitivity experiments are conducted by adding these three parts of the topography gradually. From comparisons of the circulation, temperature, and salinity structures, it is found that the south island chain decreases the westward bending of the main Kuroshio path, the middle and north island chain increases the westward bending, and Babuyan Island also increases the westward bending. These results are extremely clear in winter. Dynamic diagnoses suggest that the westward bending increases with an increase in the incidence angle of the Kuroshio and an increase in the Kuroshio east branch transport. Moreover, the middle and north island chain can split the Kuroshio into two parts, the Kuroshio west and east branches, which can be seen clearly in the satellite altimeter maps.