Intra-seasonal variation of the Kuroshio southeast of Taiwan and its possible forcing mechanism

The intra-seasonal variation of the Kuroshio southeast of Taiwan has been studied using satellite data and a numerical model. Superimposed with the main stream of the Kuroshio, two intra-seasonal signals are revealed in the study region. The fluctuation with a period of 1-6 months results from offshore eddies. The westward propagating cyclonic eddies can reduce or reverse the northward flow east of the Kuroshio between 121 degrees and 123 degrees E, but only slightly touch the core velocity of the Kuroshio. The fluctuation with a period of 2-4 weeks is only significant between Taiwan and the Lan-Yu Island (the low-velocity region). Different mechanisms are responsible for the fluctuation in the low-velocity region in different seasons. In winter, the change of negative wind stress curl in the northeastern South China Sea modulates the circulation southeast of Taiwan, while the typhoon-induced intense wind is responsible for the current fluctuation in summer.