Modeling and Verification of the Subsurface Current Core of the Ryukyu Current

Abstract

In recent years, several observations based on direct current measurements and model simulations have been successful in detecting a northeastward undercurrent, "the Ryukyu Current", along the Pacific side of the Ryukyu Islands with a unique "subsurface northeastward current core" structure. The volume transport (20-25 Sv) of the Ryukyu current completes the volume transport budget (45-50 Sv) of the Kuroshio system. A Pacific Ocean circulation model based on the RIAM Ocean Model (RIAMOM) with 1/12 degrees horizontal resolution successfully reproduced the observed structures of the northeastward Ryukyu Current with a subsurface core at 500-600 m. A three-layer model simulation shows the existence of the Ryukyu Current and explains the mechanism of subsurface current maximum through blocking effect of bottom topography around the Ryukyu Islands.