Mooring Observations of the current system southeast of Miyakojima Island

초록

The origin, structure, and variability of the Ryukyu Current (RC) has long been debated, mostly due tolimited observations. Using 2-year records from a mooring array southeast of Miyakojima Island, weillustrate the velocity structure and variability of the RC. Observations showed that the shorewardintensified currents flowed northeastward. The subsurface core of the RC was located near the 1000 misobath, with a maximum of 19.4 cm/s at 500 m. The observed velocity structure was reproduced wellby the HYCOM reanalysis, except that the observed current core was stronger and shallower. The meanestimated volume transport across the observation section was 9.0 Sv (1 Sv = 10^6 m^3/s) and a standarddeviation of 8.7 Sv, with near 100-day variability dominant in the upper layer but absent in the deeplayer. This study presents the existence of Ryukyu Current in its upstream region for the first time.