Seasonal transport variations of the wind-driven ocean circulation in a two-layer planetary geostrophic model with a continental slope

Abstract

Using a simple two-layer planetary geostrophic model with a continental slope, the observed seasonal variation of the total transport of the Kuroshio is explained qualitatively for the first time in a quite concise way. During the period of weak winds in summer, the total transport is much larger than the nontopographic Sverdrup transport. This is because the joint effect of baroclinicity and bottom relief (so-called JEBAR) drives the barotropic flow with releasing the available potential energy accumulated in winter. In winter, on the other hand, the transport is much smaller than the nontopographic Sverdrup transport. This is mainly due to the topographic beta-effect. In addition to the available potential energy supplied directly by winds, the barotropic flow excited by the strong winds in winter impinges on the bottom slope to induce the baroclinic flow so that the wind-driven barotropic flow is converted into the available potential energy to be released in summer. Thus, the role of JEBAR is to make the total transport of the Kuroshio relatively insensitive to seasonal changes of winds as observed. This mechanism may be called JEBAR rectification for simplicity.