Effects of stratification on the stable paths of the Kuroshio and on their variation

To investigate the effects of stratification on the stable paths of the Kuroshio, we have executed numerical experiments with a two-layer, wind-driven ocean model changing the upper layer thickness h1h1 and the density difference ΔρΔρ between the two layers. The maximum wind stress amplitude for a multiple equilibrium regime is determined by that for meandering paths, τ0max, and greatly depends on these parameters. The “wavelength” of the large meander is found to be given by 2πU/(β+β*) including the topographic beta β*β* due to change of the interfacial depth (UU is the Kuroshio velocity, ββ the planetary beta), and the meandering paths exist until this “wavelength” exceeds a certain value (the zonal length of the southern coast of Japan). Therefore, the upper limit of UU, or τ0max, for the meandering path changes with β*β*. This is a great contrast to the previous scenario based on the wavelength of 2πU/β. β*β* has the same sign as ββ. Its magnitude depends on both h1h1 and ΔρΔρ. Especially, the dependence on ΔρΔρ is very significant, and β*β* becomes comparable to ββ in cases with smaller ΔρΔρ while it is only fractional in cases with large ΔρΔρ. Thus the upper limit of UU, or τ0max, becomes larger in the former case than in the latter. The generation mechanism of β*β* and applicability of the present results are also examined.