Eddies Impact on the Kuroshio in the East of Taiwan Observed by HF Radars

Six SeaSonde long-ranger HF radars along the east coast of Taiwan to map the surface Kuroshio east of Taiwan in 2013. Each of the SeaSonde radar systems is a practical spatial observation radius up to 220 km with horizontal resolution around 8 km in the radial direction and 2° in azimuth. The raw radar signals included the natural (e.g., ionosphere effect) and manmade (e.g., reflected signal from artificial structure) ambient noise. After subtracting the noise, we combined the radial velocities from the six radar sites to obtain the sea surface currents east of Taiwan. These results were compared with the shipboard acoustic Doppler current profiler (ADCP) and SVP drifter observations and the averaged coefficient of determination (r²) was 0.74. These data show the large variability of the Kuroshio in the east of Taiwan, including its velocity, main stream position, and flow structure. The one of the effects of the Kuroshio variation is relate to eddy influence. Two cyclonic eddies that impinged on the Kuroshio caused cyclonically-moving surface currents observed by HF radars in the May and November, 2013, respectively. The associated flow pattern was a large cyclonic Kuroshio meander east of Taiwan. A corresponding SVP drifter trajectory crossed the Kuroshio main stream with the cyclonic currents of second eddy, passing from the offshore side of the Kuroshio to the east coast of Taiwan. The influences of two cyclonic eddies have also been recorded by the moored ADCP and pressure-sensor equipped inverted echo sounder (PIES) observations. The acoustic travel time anomalies by the PIESs increased due to eddy-induced isopycnal uplift in the upper water column, whereas the volume transport decreased through ADCP moorings in the Kuroshio region.