The Numerical Simulation Study Of The River Plumes In The East Asian Seas

Based on the ECOM-si 3-D numerical model, we set up a 3-D plume model including BoHai Sea, Yellow Sea, East China Sea and South China Sea, thus simulating the transportation and diffusion of the river plumes in the seas of East Asia. And we took a full consideration of a series factor which could influence the extension of the river plumes, like tide, shelf current, monsoon and air-sea heat fluxes. As the model was fully validated, we used the passive tracer to identify the plumes from different rivers. According the simulation results, we discussed the issues of river plumes from the extension and distribution, the vertical variation, the finally flow direction et al, and got a series of authentic conclusions:1. Except for the Mekong river plume, the river plumes are all interacting with each other, forming an obvious plume belt along the Chinese coast. It is a common phenomenon that more than one type of river plumes exist in the BoHai Sea, Yellow Sea, East China Sea and South China Sea.2. By the effect of the monsoon and shelf current, it is similar for the patterns of the river plumes’ extension. In summer, most part of the river plume exist in surface, showing the feature of the surface-advected plume. For the river plume whose estuary is in the East China Sea or South China Sea, the plume’s extension direction is northeastward. In winter, the difference of the plumes from surface to bottom is small, the plumes show the feature of the bottom-advected plume. For the river plume whose estuary is in the East China Sea or South China Sea, the plume’s extension direction is southwestward.3. There are obvious regional differences for the extension of the different river plumes. In the BoHai Sea and the North Yellow Sea, the import of the freshwater is small, but the influence area of the plume, the mount and the thickness of the fresh water is big. The influence area of the plume, the mount and the thickness of the fresh water in East China Sea and South Yellow Sea depend largely on the extension of Changjiang River plume. In South China Sea, the extension of Pearl River plume’s main body is restricted in 50m isobath. The accumulation of the Red River plume in the Beibu Gulf increase the influence area and the concentration of the plume. The shelf current around the Mekong River Estuary much stronger, so the effect of the dispersion by the shelf current is more intensive.4. We gave the south boundary for the extension of the Changjiang plume and the Pearl River plume. In winter, the Changjiang River plume moves southward along the coast by the monsoon and the shelf current. Through the freshwater mount in the Taiwan Strait and the South China Sea, and the distribution of the freshwater thickness, we can tell that the south boundary is the interface between Taiwan Strait and the South China Sea. And the plume arrived in the Taiwan Strait in winter will return to the East China Sea in spring time. The Pearl River Plume can’t cross the Qiongzhou Strait in winter by the block of the Hainan Island and the Leizhou Peninsula, which is showed by the distribution of the Pearl River freshwater thickness.5. We also discuss the finally flow directions of the river plumes. For the river plume whose estuary is in the Bohai Sea or North Yellow Sea, a large part of the river plumes run into the T/K Strait by the transportation of the Tsushima current. About 70% of the Changjiang River plume flows into Japanese Sea through the T/K Strait, about 20% of the Changjiang River plume flows into the Pacific Ocean through the Tokara Strait, and the other river plumes flows into the Yellow Sea by the effect of tide and shelf current. For the other river plume whose estuary is in the East China Sea, as the estuary location moves southward, the ratio of the plume running into the Tokara is increased, and the ratio of the plume running into the T/K Strait is decreased. By the transportation of the Taiwan Warm Current, most of the Pearl River plume and Hanjiang(china) plume flow into the East China Sea, and the Tokara Strait is the main channel for these plume to get through. As the sea area exists the coherent hydrodynamic, there are also 1/2 of the Red River plume and a little Mekong River plume flow into the East China Sea.