The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

It was found that a strong downwelling accompanied with a positive (anti-clockwise) vorticity on its downstream side often occurred near the Cape Shiono-misaki after the formation of the Kuroshio large meander (LM). This downwelling was caused by a strong horizontal convergence between the strong southwestward coastal current and the southeastward Kuroshio main stream near the Cape Shiono-misaki. The strong southwestward coastal current, which was regulated by the Kii Peninsular, was a part of the cyclonic (anti-clockwise) recirculation gyre formed within the Kuroshio LM. The southwestward coastal current impinged almost perpendicularly on the Kuroshio current. This explains why the downwelling near the Cape Shiono-misaki only occurred during the LM period. The strong horizontal convergence was generated in the upper layer, where the downward velocity increased with

depth, thereby causing a stretching of the water column to generate the positive vorticity in the upper layer.

After occurring near the Cape Shiono-misaki, the downwelling area and the accompanied positive vorticity area propagated eastward on the Kuroshio axis one after another with a time scale of dozens of days. During this process, the accompanied positive vorticity developed the trough (anti-clockwise circulation) of the Kuroshio meander, and it sometimes induced the offshore detachment of a small eddy from the Kuroshio current. Therefore, it was concluded that the downwelling and the accompanied positive vorticity occurring near the Cape Shiono-misaki contribute to the maintenance and/or the development of the Kuroshio LM.