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 28.8°–30.5°N 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.

Surface velocity time series derived from satellite altimetry data in a section across the Kuroshio southwest of Kyushu

“…As for shorter periods, the energy of the major-axis component at ACCM2 is particularly large in broad periods of 13-30 days, and that at ACCM3 is concentrated in periods near 13 days and 30-40 days. Energetic meanders in these spectral peaks correspond to those known previously as high-frequency (periods of about 8-16 days), intermediatefrequency (periods of about 16-24 days), and low-frequency (periods longer than about 32 days) meanders in the northern Okinawa Trough (e.g., Nakamura et al 2003).…”

“…The spatial resolution of this time series is about 6 km along the track, allowing it to represent the cross-current structure of the Kuroshio. Because its temporal resolution is 10 days, it is not sufficient to represent temporal evolution of the Kuroshio front meanders with typical periods of 10-20 days (e.g., Nakamura et al 2003). The aliasing problem is therefore considered to be serious for time-series data analyses of this dataset.…”

“…Between the continental slope and Tokara Strait, the Kuroshio's path exhibits meanders, with the largest displacements in the Okinawa Trough. This is because a cyclonic eddy, which develops from frontal meanders propagating downstream along the continental slope, grows spatially in this area (Nakamura et al 2003). It is known that such Kuroshio path variations, which are characterized by dominant periods of 30-90 days, tend to occur with larger amplitudes in the winter-spring period, while they diminish in the summer-autumn period (Nakamura et al 2006).…”

“…This is because the latter's variations are submesoscale phenomena, such as Kuroshio front meanders and associated cyclonic eddy's evolutions, whose typical horizontal scales are several tens of kilometers (e.g., see figs. 7 and 8 in Nakamura et al 2003). In order to capture these submesoscale phenomena, the present study uses the along-track SLA data because its spatial resolution is about 6 km along the track.…”

Characteristics of Thermal Finestructure in the Southern Yellow Sea and the East China Sea from Airborne Expendable Bathythermograph Measurements

“…In the warm seasons the Tsushima Warm Current connects to the southern tongue of the CYF and is contributed by the Taiwan Warm Current (Isobe, 1999;Ichikawa and Beardsley, 2002;Furey and Bower, 2005;Park and Chu, 2007b). Meanders and eddies often occur in just a short distance from the branching location, where the bottom relief is complex (Lie et al, 1998;Nakamura et al, 2003) (Fig. 16).…”