Numerical Study On Several Hydrographic Phenomena In The Yellow Sea And The East China Sea

Several hydrographic phenomena in the Yellow Sea (YS) and the East China Sea(ECS) are studied using POM model as tool, with results as below:Observations show that in the ECS, the Kuroshio veers at about 129°E,30°N. In numerical simulations it is noticed that when the horizontal resolution is low, the simulated veering point of Kuroshio is often farther north than that observed, with the horizontal resolution increased, the veering point is shifted southward. In Chapter 2, this phenomenon is studied with POM model. The first run of numerical simulation shows that baroclinic effect has little effect on the veering position of the Kuroshio. The second run of numerical simulation shows the veering mechanism of the Kuroshio can be explained by the maximum velocity of Kuroshio. In the veering area, the Kuroshio flows in the formation of an arc, when the veering latitude is farther north, it can be considered that the veering radius is small, while it is large when the veering point is shifted southward. With different horizontal resolution, numerical models produce different velocities of the Kuroshio. If the horizontal resolution is low, the simulated Kuroshio often has lower velocity and corresponding smaller veering radius, if the horizontal resolution gets higher, the simulated velocity of Kuroshio will be intensified, the veering radius will get bigger, and the veering point will be shifted southward. The velocity of Kuroshio is the key factor in determining the veering latitude. In the real ocean, the Kuroshio also has seasonal migration on veering latitude, this can be explained by the same mechanism.In Chapter 3, the expansion mechanism of the Yangtze River Diluted Water (YRDW) during summer season, particularly in August is studied by numerical simulations based on POM model. The control experiment reproduces the main pattern of YRDW's expansion: After flowing eastward off the Yangtze River estuary, YRDW veers northeastward, it veers once again southeastward at reaching 123°E. This expansion pattern is mainly influenced by the combination of the thermal front and current. In the region southeast to the estuary, a band-shaped thermal front is uplifted from the bottom to the surface, prevents YRDW from expanding in this direction. In the region east to the estuary, the thermal front is uplifted to 5m below the surface, leaving this 5m-depth as the "passage" for YRDW. YRDW expands eastward through this "passage" to about 122.5°E, where happens to be the pathway of a northward Taiwan warm current. YRDW is carried by this current northeastward. Northeast to the estuary ,at about (122.5°E,34°N) there is another thermal front which is uplifted to the sea surface and acts as a barrier to the current, this current is forced to change its direction from northeastward to southeastward, then YRDW is carried southeastward.In Chapter 4, satellite remote sensing observations show that sea surface temperature (SST) presents the double warm tongue structure in the Yellow Sea Trough during winter: the western and the eastern warm tongues respectively. Numerical experiments based on POM are carried out to study the forming mechanism of this thermal structure and its relation to the Yellow Sea Warm Current (YSWC). The control experiment reproduces this phenomenon quite well, numerical experiments investigate the effects of wind and tide. It is found that the western warm tongue is mainly caused by YSWC, which can be strengthened by wintertime southward wind. The eastern warm tongue develops under the influence of an anti-clockwise circulation which is induced by the temperature front of the Yellow Sea Cold Water Mass (YSCWM) in summer and autumn. In the eastern portion of this circulation, the northward current carries warm water to north, forming the eastern warm tongue, which remains till winter.In Chapter 5, At about (124°E,32°N), in the northern East China Sea, the forming mechanism of a vertically well-mixed water column observed in August is studied. This column is surrounded by ambient stratified water. Numerical simulations based on POM model are carried out to investigate its forming mechanism. The results show that the wave-induced mixing from the surface is connected to the tide-induced mixing from the bottom at about 124°E,32°N. The combination of wave-induced mixing and tide-induced mixing makes the temperature of whole water column uniform. Both of them are indispensable for the yield of this water column.