A Triply Nested Ocean Model for Simulating the Kuroshio—Roles of Horizontal Resolution on JEBAR

Abstract

A triply nested ocean general circulation model was used to examine how the model horizontal resolution influences the Kuroshio in the East China Sea (ECS) and the sea level variability. As the model resolution increases from 1/2° to 1/18° the path, current intensity, and vertical structure of the model Kuroshio and the variability of sea level become closer to observations. In general, the higher-resolution model improves the baroclinic as well as barotropic component of the Kuroshio and thus reproduces more realistic density and current fields. This improvement, in addition to better representation of topography, results in better reproduction of the interaction between baroclinicity and bottom topography, that is, JEBAR (joint effect of baroclinicity and bottom relief) in a high-resolution model. Modeling the Kuroshio in the ECS provides an ideal example of such improvement. In particular, the Kuroshio veering phenomenon at (30°N, 129°E) southwest of Kyushu is discussed, together with the seasonal meridional migration of the path. It is shown that JEBAR and advection of the geostrophic potential vorticity are two major contributions to the vorticity balance in this area. The summer intensification of JEBAR resulting from the intensified stratification yields a strong offshore volume transport across the shelf break, thereby leading to the southward shift of the veering latitude. In winter, the weakened JEBAR, combined with the increased wind stress curl, decreases the offshore volume transport in a considerable amount, explaining the northward shift of the veering latitude. The present reproduction of seasonal migration of the Kuroshio axis at 129°E is in good agreement with observation.