A numerical experiment on the path dynamics of the Kuroshio with reference to the formation of the large meander path south of Japan

Abstract

Path dynamics of the Kuroshio south of Japan are investigated with reference to the formation of the large meander of the Kuroshio south of Japan. The observed formation process is a composite of two subprocesses: generation of a small meander off eastern Kyushu (process I) and implification of the small meander south of central Japan (process II). Particularly, we have focused upon the observed evidence that the amplification of the small meander (process I) has a tendency to occur in a flat part of the Shikoku Basin, while a small meander staying on the continental slope decays in a short time without process II. On the basis of this evidence, a numerical experiment on the formation process of the large meander of the Kuroshio is carried out. topography south of Japan is modeled. In the numerical experiments, 10 runswith different in- and outflow transport, initial current path and/or bottom topography are performed. It is shown that if the inflow volume transport is less than 60 Sv, the current path is forced to flow along the coastal boundary due to the topography of the continental slope and the planetary β effect. Even if a small meander is given in the initial current path with inflow of 30 Sv, the small meander decays in a short time and the current path resumes a no-meander path. However, in the model with inflow greater than 60 Sv, the large meander path is formed. If a small meander path is given initially in the same model, a larger meander and a cyclonic eddy are formed with spin-up and spin-down processes; the results agree with the observational features of the cyclonic cold water mass south of Japan. The amplification of the large meander is carried out in a flat region. The spin-up of the large meander path and cold water mass is mainly due to the stretching of the water column when the meander shifts westward from the shallower west side slope of the Izu Ridge to the deeper region in the Shikoku Basin. If the topography of the Izu Ridge is excluded in the numerical model, the large meander is not formed. The bimodal path characteristics of the Kuroshio are discussed on the basis of the numerical results.