The Effects Of The Kuroshio On The Main Current Systems In The East China Sea

Based on the existence of pressure gradient between the southern and northern ends of the Kuroshio associated areas, especially the possible existence of interaction constraints between the Kuroshio and the Taiwan Island or Japanese Islands, this paper proposes a hypothesis that, the pressure gradient in the area is the dominant forcing, and the Island Integral Constraint, Mass Conservation Constraint and the mass sink effect of the Japan/East Sea (JES) are the essential dynamics that govern the formation and maintenance of the main warm current systems. And several numerical sensitive experiments are conduct to validate the above dynamics hypothesis. This paper also preliminarily investigates the mechanism of energy propagation in the East China Sea (ECS) and adjacent regions.The results of sensitive experiments show that, the Taiwan Strait Current is forced primarily by the oceanic circulation in the open-ocean basin through the KC, the western boundary current of the subtropical gyre in the North Pacific Ocean. The local wind-stress forcing plays an important but secondary role. The KC will set a pressure gradient from the southern to the northern tip of the Taiwan Island. The reverse friction associated with the Kuroshio, will get balance on the annual mean basis. Because of the connectivity of the ocean, at the other side of the island, the balance should be satisfied, and then there should be a flow in the Taiwan Strait with the same direction as the KC, which is the mechanism for the formation of the northward Taiwan Strait Current. These results also can be explained by the Island Rule derived by Pedlosky et al. Supposed a homogeneous ocean, the integration along a closure curve such as an island of the momentum equation results in a simple form of balance that the integration of friction along the island should be zero, when ignored the inertial term and wind stress. To balance the clockwise drag caused by the KC and the topography at the east of the Taiwan Island, there must be an anti-clockwise drag at the west of the TI, which caused the current flows northward in the Taiwan Strait.The dominant mechanism for the formation of the Tsushima Warm Current is due to the source-sink driven mechanism that formed by Island Integral Constraint between the Kuroshio and Japanese Islands, Mass Conservation Constraint that supply in the JES, and the east and west boundary currents in the JES that arise from Potential Vorticity Integral Constraint. The local wind-stress forcing plays only a secondary role. Both local and remote forcings play important roles in the seasonal variation. The local forcing is by the wind stress affecting the pressure difference across the Tsushima Strait, and the remote forcing is by the Kuroshio Current induced Kelvin waves propagating to the strait. The two forcings are roughly in phase, hereinto, the remote forcing is dominant, the local forcing is important but secondary, and the ratio of the former to the latter is about 2 to 1.There is an obvious seasonal variation for the Yellow Sea Warm Current (YSWC): in winter, the YSWC penetrates northward along the Yellow Sea Trough towards the Bohai Sea; in summer, the YSWC becomes much less intrusive and is limited mostly in the southern trough, contrasting with a deep winter penetration well into the trough. In the annual mean the YSWC is a compensating current for the Korea Coastal Current (KCC) and China Coastal Current (CCC). Driven by the KC, the southward KCC is induced by the TSWC as a source- and sink-driven flow along bathymetry. Under the monsoonal forcing, the northerly wind in winter causes the southward CCC, and promotes the southward KCC; the southerly wind in summer restrains the CCC, and weakens the KCC. As a result, the deep northwestward intrusion of the YSWC in winter is mainly due to a robustly developed CCC and KCC, which draws water along the Yellow Sea trough to feed the two southward flows. In summer, the YSWC almost vanish due to the only effect of the KCC. As a result, the Kuroshio will induce the YSWC through the Tsushima Strait, and the Mass Conservation play a leading role in the seasonal variation, so the monsoonal wind will dominant the strength variation of the YSWC.The energy in the ECS can propagate upstream from the lower reaches of the KC as a form of continental shelf waves, and then affect the circulation on the way. The Tsushima Strait plays an important role in the energy propagation, and acts as a junction of the Kuroshio effects on the East Asian Marginal Sea. The sea level variability along the east coast of Japan can propagate clockwise through the Tsushima Strait into the JES and then northward along the west coast. The sea level variability along the west coast of Japan is remotely forced by the Kuroshio Extension off the east coast. Boundary Kelvin waves facilitate the connection. The open-ocean forcing, through the Kuroshio Extension variability, is the leading forcing mechanism for sea level change along the west coast of Japan. The variation of the Tsushima Strait itself, can propagate to the Taiwan Strait anti-clockwise along the coastline of ECS, as a form of topographic Rossby waves, and affect the KCC and Taiwan Strait Current, etc on the way.The scientific significances of this study are: construct the theory frame of the formation and maintenance of circulations in the ECS under the basic dynamics; reveal the dominant role of the KC; investigate the modulating role of the local wind stress; introduce the mechanism of energy propagation in the continental shelf sea. The above results will play a promoting effect in the study of global climate changes, especially how to affect the physical environment of the ECS through the variation of general circulation in the North Pacific Ocean, and lay a good foundation for the construction and perfection of the continental shelf physical environmental evolution theory system.