Impact of Mesoscale Eddies on the Southwestward Countercurrent Northeast of Taiwan Revealed by ADCP Mooring Observations

Abstract ADCP mooring observations were collected for one year and used to study the vertical structure and variability in the southwestward countercurrent in the slope region northeast of Taiwan. The reversion of the mean along-shelf velocity from northeastward to southwestward occurred at a depth of 125 m, and the depth-averaged southwestward velocity from 125 m to 478 m was −0.14 m s−1. The southwestward countercurrent was enhanced by a stronger, more offshore Kuroshio Current, while the current direction had a weaker anti-clockwise rotation with depth. The intraseasonal variability of the countercurrent was attributed to mesoscale eddies east of Taiwan: the arrival of anticyclonic eddies east of Taiwan favoured a stronger countercurrent northeast of Taiwan and a weaker current rotation with depth, while the arrival of cyclonic eddies inhibited the countercurrent and enhanced the current rotation with depth.