Two processes by which short-period fluctuations in the meander of the Kuroshio affect its countercurrent

Direct current velocity measurements in the countercurrent of the Kuroshio, south of Japan, were carried out to investigate the influence of short-period fluctuations in the small-scale meander of the Kuroshio on its countercurrent. When the Kuroshio took a path having a meander west of the Izu Ridge and approaching the Izu Peninsula, the countercurrent freely intruded into coastal seas with a period of 17 d and a phase velocity almost equal to that of the Kuroshio itself. However, when the Kuroshio did not significantly bend and deflect off the Izu Peninsula, even when taking the same path, the velocity of the countercurrent was considerably reduced and the periodic fluctuations propagated into the coastal seas as a continental shelf wave. The results indicate that a small change in the Kuroshioʹs path can cause a different process of propagation of the small-scale meandering; this difference probably explains why there are two kinds of phase velocity in coastal temperature fluctuations.