Model Study of Flow Conditions Causing the Large Meander of the Kuroshio South of Japan

Abstract

The upstream conditions for large-meander (LM) and non-large-meander (NLM) paths of the Kuroshio south of Japan were examined by calculating the current axis with a steady model imposed upstream flow conditions at the origin put in the Tokara Strait south of Kyushu. The calculation in each case, defined by velocity at the origin U0 and volume transport of the Kuroshio, was made with respect to the conditions at the origin, that is, a curvature of current axis ?0, a spatial change of current depth ?H, and a direction of the current axis. The depth change ?H accompanies the spatial changes of current velocity and width. The ?0 and ?H are greatly effective to the downstream path. Nearly realistic ?0 is necessary for producing a realistic path. The spatial changes at the origin, a decrease of velocity and increases of current width and depth (?H > 0), are necessary for producing LM paths for realistic ?0 in case of medium and large U0. The LM paths are caused by smaller ?0 than the NLM paths. This is firmly concluded by considering realistic ranges of current width and a realistic relation between ?0 and ?H. The LM path, therefore, is caused by Small ?0 in a realistic range and a decrease of velocity at the origin. These conditions for the LM path are not thought to be realized in the case of small transport and velocity in which an LM path has never been observed. These conclusions well explain the observation facts and show that the path of the Kuroshio, LM or NLM, is almost determined by the flow conditions in the Tokara Strait south of Kyushu.