Abstract
The origin, structure, and variability of the Ryukyu Current (RC) have long been debated, mostly due to limited observations. A mooring array, deployed for two years southeast of Miyakojima in the southern portion of the Ryukyu Island chain, has provided, for the first time, data confirming the existence and revealing the characteristics of the RC in that upstream region, including its velocity structure and variability. The observations show a shoreward-intensified current flowing northeastward, with a subsurface core located near the 1,000 m isobath and having a record-long mean speed of up to 19.4 cm s−1 at 500 m depth. Estimated volume transport across the observation section had mean 9.0 Sv (1 Sv = 106 m3 s−1) and standard deviation 8.7 Sv. The RC shows significant barotropic character compared with other similar mid-latitude currents.
Highlights
The origin, structure, and variability of the Ryukyu Current (RC) have long been debated, mostly due to limited observations
We investigate the mean and time varying structure and volume transport (VT) of the RC in the southern Ryukyu region, as well as the influence of mesoscale eddies entering from the east, and we compare our results with model results from HYbrid Coordinate Ocean Model (HYCOM)
We first show the observations from all the current-measurement results (Figs. 2, 3)
Summary
The origin, structure, and variability of the Ryukyu Current (RC) have long been debated, mostly due to limited observations. The Kuroshio is the strongest western boundary current in the Pacific Ocean It has long been the focus of many scientific studies[1,2]. After it enters the East China Sea (ECS), the Kuroshio flows northeastward, west of the Ryukyu Island chain, until it reaches the region south of Kyushu, Japan and exits through the Tokara. Studies[3,4] have indicated the existence of another strong portion of the western boundary current, namely the Ryukyu Current (RC) flowing northeastward just east of the Ryukyu Island chain, accounting for the large difference in volume transport of the Kuroshio between the ECS The RC carries a large mass of water, heat, and nutrients poleward[21,22], greatly enhancing the Kuroshio when the two currents merge east of the Tokara Strait
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