Numerical Study of Shelf Water Motion Driven by the Kuroshio: Barotropic Model

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  • 1 Department of Applied science, Kochi Women's University, Kochi, Japan
  • | 2 Department of Geophysics, Faculty of Science, Kyoto University, Kyoto, Japan
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Abstract

The barotropic response of the shelf and coastal regions south of Japan to short-term variations in the Kuroshio was studied numerically with an inflow–outflow model. The onshore–offshore movements of the stream axis of the Kuroshio due to changes in the upstream volume transport have an important effect on shelf and coastal circulations off the coast of Japan. When the Kuroshio comes near the shelf south of Japan, topographic eddies of about 1.0 × 105 m diameter are produced on the shelf behind the capes by the separation of the Kuroshio from the subsurface tip of spurs at a depth of about 200 m projecting from the capes into the sea. On the other hand, when the Kuroshio moves away from the shelf, the eddies disappear. This implies that the periodic formation and disappearance of the eddies takes place on the shelf due to the combined effect of the short-term onshore–offshore movements of the Kuroshio axis and the irregular topography of the continental margin. Phenomena similar to the present experimental results are frequently detected in satellite imagery. This combined effect is one of the most important factors which control the shelf and coastal currents south of Japan. Tracking numerous labeled particles in the calculated velocity field by the Euler–Lagrangian method clearly showed that a large amount of the Kuroshio water is trapped in the eddy on the shelf. The net transport of the Kuroshio water to the shelf region over one event of the onshore–offshore movements was estimated to be 6 × 1012 m3 from the particle distributions. The net volume is as much as 20% of the water volume of the shelf and coastal region and shows that an effective water exchange takes place between the shelf and the Kuroshio. This is one of the major processes of water exchange between the shelf region south of Japan and the Kuroshio.

Abstract

The barotropic response of the shelf and coastal regions south of Japan to short-term variations in the Kuroshio was studied numerically with an inflow–outflow model. The onshore–offshore movements of the stream axis of the Kuroshio due to changes in the upstream volume transport have an important effect on shelf and coastal circulations off the coast of Japan. When the Kuroshio comes near the shelf south of Japan, topographic eddies of about 1.0 × 105 m diameter are produced on the shelf behind the capes by the separation of the Kuroshio from the subsurface tip of spurs at a depth of about 200 m projecting from the capes into the sea. On the other hand, when the Kuroshio moves away from the shelf, the eddies disappear. This implies that the periodic formation and disappearance of the eddies takes place on the shelf due to the combined effect of the short-term onshore–offshore movements of the Kuroshio axis and the irregular topography of the continental margin. Phenomena similar to the present experimental results are frequently detected in satellite imagery. This combined effect is one of the most important factors which control the shelf and coastal currents south of Japan. Tracking numerous labeled particles in the calculated velocity field by the Euler–Lagrangian method clearly showed that a large amount of the Kuroshio water is trapped in the eddy on the shelf. The net transport of the Kuroshio water to the shelf region over one event of the onshore–offshore movements was estimated to be 6 × 1012 m3 from the particle distributions. The net volume is as much as 20% of the water volume of the shelf and coastal region and shows that an effective water exchange takes place between the shelf and the Kuroshio. This is one of the major processes of water exchange between the shelf region south of Japan and the Kuroshio.

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