A Numerical Experiment on a New Current, the Ryukyu Current Extension, in the Shikoku Basin Part I Linear and Weak Nonlinear Model

摘要

The existence of two western boundary currents along the eastern continental slopes off the Nansei Islands (Ryukyu Current) and the Izu Ridge in the subtropical circulation in the North Pacific has been pointed out to occur from late winter to spring due to the barotropic ocean response being dominant for seasonal variations in wind stress. As a results, a new connecting new current from the Ryukyu Current to the western boundary current east of the Izu Ridge is predicted, which is referred to as the Ryukyu Current Extension. In order to see the flow characteristics of the Ryukyu Current Extension, some numerical experiments are carried out with a barotropic flat bottom model driven by Sverdrup in-and outflow in winter and in spring. The results of the numerical experiment with a linear and weak nonlinear parameters are presented in the present paper. It is shown that there exist four types of the current patterns in the Shikoku Basin: the Munk Pattern, the Moore Pattern, the Nonlinear Pattern and the Super Nonlinear Pattern. In case with the larger eddy viscosity, only the Munk Pattern is formed. If the eddy viscosity is decreased, the Moore Pattern is formed in the small in- and outflow models (deep models), while the Nonlinear Pattern appears in large in- and outflow models (shallow models) and the Super Nonliar Pattern in the largest in- and outflow model (shallowest model). It is also shown that the formation of the Ryukyu Current Extension is clear in cases of the Moore and Munk Patterns, but unclear in cases of the Nonlinear and Super Nonlinear Patterns.