Global Ocean Tide Assimilation Modeling And The Study Of The Role Of Tidal Current On The Ocean Circulation In The East China Seas

In order to further improve our global ocean tide prediction accuracy and develop high-resolution global ocean circulation and tide numerical model, the Global Ocean Circulation and Tide Model based on Unstructured Mesh (GOCTM-UM) is configured and established, based on Finite Volume Coastal Ocean Model (FVCOM), in this dissertation. This model takes advantage of the unstructured triangular grids, which have the different spatial resolutions in the different regions, to design the global ocean mesh according to the different scales of the circulation and tides in different regions. Thus, the model avoides introducting the open boundary conditions cleverly, and balances the contradiction between the high resolution requirement and the large computation. Furthermore, the model uses the general layers in the vertical coordinate, which can improve the vertical resolution of mixing layers effectively in both the sea surface and the sea bottom.Considering the Effects of the Sea Water Self-Attraction and Earth-Loading (SAL), GOCTM-UM assimilates the tidal elevation data of TOPEX/POSEIDON satellite altimeter model using the optimal interpolation. That improves the accuracy of our global ocean tide numerical simulation in some aspects so that it has some broad application prospects. By comparing the numerical simulation results with the data of tide gauges in the pelagic ocean, the data of coastal tidal gauges and the satellite altimeter data, as well as with other tidal models and the results of general circulation models, the credibility of the GOCTM-UM's results is verified, and the solution of the numerical simulation is feasible.By utilizing the GOCTM-UM model with fine unstructured triangular grids in the Bohai Sea, the Yellow Sea, the East China Sea and the South China Sea, a variety of numerical simulation experiments have been conducted to analyse the energy structure of ocean circulation and tidal current, and discuss the mechanism of the tidal current effects on the ocean circulation in the East China Sea and its adjacent waters. The results show that:(1) The roles of ocean tidal current on the ocean circulation include the tidal residual current, the non-linear advection interaction and the turbulent mixing dissipation. Overall, the non-linear advection and the turbulent mixing nonlinear interaction play important roles on the ocean circulation of the East China Shelf Seas. Compared to the winter circulation in the East China Seas, the tidal residual current is relatively weak, only in some straits and the coastal sea area of shallow water, the tidal residual current has more important influence.(2) The change of the kinetic energy takes 9.8% of the kinetic energy of the ocean circulation, of which about 6.3% at the surface and about 15.7% at the bottom, when the tidal current is added into the ocean circulation model in the East China Seas in winter. By the theoretical analyses and the numerical analyses, the ocean interaction of nonlinear advection and the interaction of the mixing dissipation between the ocean tidal current and the ocean circulation take important roles in the ocean dynamic numerical simulation. If ignoring the nonlinear interaction between the ocean tidal current and the ocean circulation, it will produce more than 10% errors of these two items. And the results of the theoretical analyses are consistent with the results of the numerical analyses.(3) Tide has great effects on the ocean bottom turbulent mixing in the East China Seas, and the effects at the bottom are much stronger than that at the sea surface. Paticularly, in the areas of large topographic gradient and in the shallow water areas, the turbulent mixing is stronger at the bottom layer. The turbulent edd viscosity can be changed significantly at the scale about 10-3 m2/s when the ocean tidal current is added into the ocean circulation model. The sum of turbulent eddy viscosity obtained from barotropic tide model and that obtained from the ocean circulation model is different from that obtained from the circulation and tide coupling model, especially, at the bottom. This is what should be considered when improving the turbulent closure scheme of the ocean circulation model.