Fig 1: The model geometry near the coast of Japan. Readers refer to Mitsudera et al (1997) for the geometry of the entire domain. The three typical paths by Kawabe (1985) are also indicated.
These works use simple reduced gravity or quasi-geostrophic models, with inflow-outflow boundary conditions for Kuroshio. Simple models are useful to identify the important physical processes. However, these are in turn so simple that direct comparison with observations was difficult.
Here we will describe results from a high-resolution regional model with realistic topography, coastal line, and stratification. The Kuroshio flow is forced by inflow/outflow boundary conditions, so that we can discuss the sensitivity of the Kuroshio path to various infow conditions. The modeled Kuroshio flow field is found to be remarkably similar to that of observation as shown later. This makes us examine the Kuroshio path problem in a realistic framework, and in fact, we have obtained transition of the paths in realistic range in transport.
In this paper, the role of the anti-cyclonic recirculation gyre off Shikoku in the Kuroshio path dynamics is to be highlighted. For a modeled meandering path, the potential vorticity is homogenized in the recirculation gyre, leading to further enhancement of the meander of the Kuroshio. The recirculation gyre accompanies 50-100 days variations, which is particularly pronounced when the path takes the large meander. These suggest the eddy Sverdrup balance of recirculation gyres discussed by Jayne et al (1997). It is worth pointing out that sea-level observation by TOPEX/POSEIDON (e.g. Imawaki et al, 1997) also shows such strong 50-100 days variations in the recirculation gyre off Shikoku.
