A two-layers model for the summer circulation of the East China Sea

A two-layers numerical model is developed to study the dynamical structures and the formation mechanisms of the summer shelf circulation and the Kuroshio system in the East China Sea(ECS).On the whole,the main features of this region are highly correlated and dynamically stable.The Kuroshio northeast of Taiwan Island always intrudes into the shelf,and manifests itself chiefly in the lower layer.The horizontal advection and bottom friction are the triggering mechanisms for this ageostrophic intrusion current,while the topographic beta-effect make it intensified towards the northern edge of Taiwan Island.After intruding into the shelf,most of the lowerlayer Kuroshio water turns anticyclonically,forming the outer branch of the lower-layer Taiwan Warm Current(TWC).Whether its inner partner can form depends upon the ratio of the upper-to the lower-layer speeds of the Kuroshio inflow,and the northward extending of the upper-layer strait warm water.The upper-layer TWC results from the Taiwan Strait inflow,and a part of it branches out in the open sea off Wenzhou.In this paper,we also point out that the cold-core water mass northeast of Taiwan Island is,in fact,the manifestation of the lower-layer intrusive loop,and the interaction between it and the upper-layer TWC leads to the formation of the well-known warm-core gyre.Besides,a preliminary study is also made on the frontal eddy north of Diaoyu Island.