A Numerical Experiment on a New Current, the Ryukyu Current Extension, in the Shikoku Basin Part II Eddy Generating Model

摘要

This paper presents the results of a numerical experiment on a new current, the Ryukyu Current Extension, using the eddy generating model, following the Part 1 with the models of linear and weak nonlinear ranges. It is shown that four types of current patterns exist in the Shikoku Basin: the Super Nonlinear Pattern with a strong zonal How, the Nonlinear Pattern with the formation of an anticyclonic eddy, and the External and Internal Two Eddies Patterns with a spin-up and spin-down of the cyclonic eddy. In the External Two-Eddies Pattern, the cyclonic eddy is formed by the topographic effect of the Izu Ridge, but the cyclonic eddy is induced only by the anticyclonic eddy in the Shikoku Basin in the Internal Two Eddies Pattern. Selection of the current pattern depends on the Rossby number, which is controlled by the depth of the model ocean. However, since the Super Nonlinear Pattern with a significantly amplified meander with large volume transport is very different from the observed feature, the model parameter is not suitable for actual oceanic conditions. Results show that a chaotic change from the External Two-Eddies Pattern to the Nonlinear Pattern occurs and a multi-steady state is suggested among these flow patterns.