[A-OS08] ECS-Kuroshio and Ryukyu Current System -Observation, modeling and theory-

[AOS08-07] Structure and variability of the Kuroshio current in the Tokara Strait

*Zhao-Jun Liu¹, Hirohiko Nakamura², Xiao-Hua Zhu¹, Ayako Nishina², Xinyu Guo³, Menghong Dong¹ (1.Second Institute of Oceanography, China, 2.Kagoshima University, Japan, 3.Ehime University, Japan)

Keywords:Tempo-spatial variations, Kuroshio, Tokara Strait

Transverse-vertical structure and temporal variability of the Kuroshio current across the Tokara Strait during 2003–2012 measured by ferryboat acoustic Doppler current profiler (ADCP) with a 2-km horizontal resolution and a 2-day interval are presented. The Kuroshio passing through the Tokara Strait exhibits a nearly permanent multicore velocity structure. The mean eastward Kuroshio transport is 25.84 Sv (1 Sv ≡ 10⁶ m³ s^-1) and the net baroclinic transport relative to 700 m is 19.57 Sv. The seasonal variation of the Kuroshio transport via the Tokara Strait is a “W”-shaped curve with a maximum in July and a second maximum in December–January. The baroclinic transport shows seasonal variation similar to that of the undecomposed transport, with a maximum in July. However, the barotropic transport displays a reversed seasonal variation—a “V”-shaped distribution—with a maximum in December. In the empirical orthogonal function (EOF) analyses of the cross-sectional velocity, with the exception of the well-known meander (EOF1: 41.1%) and transport (EOF2: 26.3%) modes, the third mode (EOF3: 19.2%) is first observed. The EOF3 mode exhibits a band-like structure, with a smaller horizontal scale than the first two EOF modes; such a band-like structure may be related to the wakes in the lee of the Tokara Islands. Additional analysis based on high-resolution JCOPE-T reanalysis data revealed that (1) many vortexes were generated around the Tokara Strait due to the strong flow-topography interaction; (2) the intensities of the island-induced wakes depend on the Kuroshio path position around the Tokara Strait.