A Numerical Study Of Cross-front Water Exchange

In this thesis, the cross-front water exchange is studied by numerical simulation. The simulation includes two areas: shelf front in the Northern South China Sea (NSCS) and tidal front in the Yellow Sea (YS). The results show the cross-front circulation and the dominant mechanisms of cross-front water exchange.It is the first time to use 3D numerical model to study shelf front in NSCS, and it is the first time to calculate the cross-front water exchange, too. In NSCS, we have in situ observations, high resolution CTD, ADCP data, satellite pictures and CODAR data. These data are used to validate the results of the model.After the validation the good agreement between simulated results and observed ones, the characteristics of the shelf front in NSCS are studied. Some sensitive experiments are done to study the dominant mechanism of cross-front water exchange. We draw a series of meaningful conclusions as follows, the main of these are:1) The front is along isobath the 30-40m, and the gradient of the front is l℃/n m. The cross-front circulation is double cells. The two important currents are Guangdong Coastal Current and South China Sea Warm Current. The position and the gradient of the front is controlled by these two currents.2) The calculated water exchange with the observation is 1.5 Sv onshore, and which in the simulation is 1.89 Sv. In the observation, the up-layer is about 25-30m onshore and the bottom layer is 5-10m offshore.3) There are two component in the cross-front water exchange, one is non-front mechanism which is wind force in this study, the other is front mechanism which is baroclinic instability.In thesis, we also use a numerical model (HAMSOM) to study the tidal front in the Yellow Sea. It is the first time to do some comparison of two different fronts. Themain conclusions we draw are:1) The tidal front in YS is in strong tidal area, and the shelf front in NSCS is in weak tidal area. The dominant mechanism of cross-front water exchange in NSCS is wind and baroclinic instability, and the one in YS is tidal mixing.2) The jet along the tidal front is very clear in YS, while the velocity shear in NSCS can not be seen. The vertical circulation of tidal front is multi-cell, and which of the shelf front is double cells.3) The cross-front water exchanges in both fronts are in the upper layer. The water exchange in both fronts can not be neglected for its importance in sendiment transportation.