A numerical study on the formation of the Kuroshio Counter Current and the Kuroshio Branch Current in the East China Sea

Abstract

The Kuroshio Counter Current (KCC) and the Kuroshio Branch Current (KBC) are two unique features of the Kuroshio in the East China Sea. The mechanisms that generate the KCC and the KBC are studied using a barotropic inflow-outflow model with a simplified basin configuration of the East China Sea. The present study shows that the KCC can only exist on a β-plane frame of reference and its flow pattern is independent of the offshore Ryukyu Islands. In the East China Sea, the continental slope plays the role of a western boundary for the Kuroshio. Whether the Kuroshio protrudes onto the slope region, however, is found to have little influence on the KCC. Concerning the formation of the KBC, we found that the planetary β-effect and the existence of Taiwan Island are two indispensible conditions: the planetary β-effect drives part of the Kuroshio inflow to branch southwestward and Taiwan Island blocks this branched current causing it to protrude onto the continental shelf. Based on the numerical calculation, we further found that the branch current is reinforced by topographic Rossby waves induced by the repeated crossing of the Kuroshio over the continental slope.