Kuroshio path meander between the continental slope and the Tokara Strait in the East China Sea

Abstract

Horizontal patterns and meander motions of the Kuroshio paths in the northern Okinawa Trough between the continental slope and the Tokara Strait are investigated using surface drifter buoy trajectory data, NOAA sea surface temperature (SST) measurements, and shipboard acoustic Doppler current profiler ( ADCP) current observations. Temporal variations are also examined by spectral analyses of 1-year moored velocity/temperature records along the continental slope near 28.8degrees - 30.5 degreesN and of the Kuroshio position time series in the Tokara Strait. Drifter buoy trajectories show that the Kuroshio paths in the northern Okinawa Trough are quasibimodal in character consisting of the northern paths and southern ones, which are associated with anticyclonic and cyclonic Kuroshio circulations, respectively. The Kuroshio position time series show that the northern paths tend to be persistent and intermittently undergo transition to southern paths at periods of 1 - 3 months. Moored current variations in the slope area and the Kuroshio path variations in the Tokara Strait are highly coherent near a period of 34 days due to the meander motions resulting from the transitions between the northern and southern paths. Successive NOAA SST images and shipboard ADCP current fields show that the transition from the northern path to the southern one is associated with a spatially growing cyclonic eddy, which is initially generated from a downstream-propagating frontal meander with wavelength of about 200 km. When the cyclonic eddy grows into the scale of the northern Okinawa Trough ( about 200-km E - W, 250-km N-S), the Kuroshio path changes from the northern path to the southern one.