Geometry-Forced Coherent Structures as a Model of the Kuroshio Large Meander

Toshio Yamagata Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan

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Shin-Ichiro Umatani Research Institute for Applied Mechanics, Kyushu University, Kasuga, Japan

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Abstract

The bimodality of the Kuroshio path south of Japan is presented from a new viewpoint of direct interaction of current with local coastal geometry. By solving the barotropic quasi-geostrophic equation in a channel with steplike coastal geometry, we demonstrate that the model Kuroshio can actually show the localized, bimodal behavior for a reasonable range of inlet current speed. The amplitude of the large meander is approximately given by 2Umax/β. In contrast to all “nonlocal” model results, our local coherent structures have nothing to do with the basin-size geometry such as Kyushu and the Izu-Ogasawara Ridge. In general, the present study suggests that even a small feature of coastline geometry may trigger a big change in a nearshore current.

Abstract

The bimodality of the Kuroshio path south of Japan is presented from a new viewpoint of direct interaction of current with local coastal geometry. By solving the barotropic quasi-geostrophic equation in a channel with steplike coastal geometry, we demonstrate that the model Kuroshio can actually show the localized, bimodal behavior for a reasonable range of inlet current speed. The amplitude of the large meander is approximately given by 2Umax/β. In contrast to all “nonlocal” model results, our local coherent structures have nothing to do with the basin-size geometry such as Kyushu and the Izu-Ogasawara Ridge. In general, the present study suggests that even a small feature of coastline geometry may trigger a big change in a nearshore current.

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