Anticyclonic rings from the Kuroshio in the South China Sea

The Kuroshio is the western boundary current of the North Pacific Ocean. It flows north-ward east of Luzon and Taiwan islands. It is free to interact with the South China Sea through the Luzon Strait between these islands; intrusions of the Kuroshio as a loop into the northeastern South China Sea have been observed. However, no observed shedding of eddies from the Kuroshio into the South China Sea have previously been reported. In September 1994, a closed current ring of probable Kuroshio origin was observed in the northeastern South China Sea near the slope of the Chinese continent. The ring was a warm-core, anticyclone centered at about 21°N, 117.5°E just off the continental slope with a scale of ∼150 km and a vertical expression as deep as 1000 m. Near surface current speeds of about 1 m s -1 were estimated from ADCP measurements and from geostrophic calculations. T– S diagrams show water characteristics inside the ring different from those of the South China Sea and suggest an origin from the Kuroshio. At the time of observation, another anticyclone may have been in the process of detaching from the Kuroshio within the Luzon Strait.