A novel high resolution model without open boundary conditions applied to the China Seas: first investigation on tides
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A novel high resolution model without open boundary conditions applied to the China Seas: first investigation on tides YU Huaming1,2 , CHEN Xueen1∗ , BAO Xianwen1∗ , Thomas Pohlmann2 , WU Dexing1 1 2
Institute of Physical Oceanography, Ocean University of China, Qingdao 266100, China Institute of Oceanography, Centre for Marine and Climate Research, University of Hamburg, Hamburg 20146, Germany
Received 17 July 2009; accepted 5 January 2010 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2010
Abstract We developed a Global Ocean Circulation and Tide Model (GOCTM) with coarse grids in the open deep ocean degrading ‘smoothly’ into the highly resolved China Seas (CS) of refined grids to study the tides and circulation there. GOCTM is based on the framework of the Finite Volume approach for better mass conservation through improved transports across the discrete individual control volume. It also takes a full advantage of the geometric flexibility of unstructured mesh using a realistic global topography including the Arctic Ocean. The CS are given a special focus by refining the unstructured grids, but they are embedded into global domain naturally. Furthermore, GOCTM not only successfully avoids the treatment of the open boundaries, but also optimizes the trade-off between computational cost and model accuracy. Meanwhile, GOCTM is driven by the astronomical tide-generating potential and the secondary tide-generating potential directly, together with the wind stress and heat flux. GOCTM succeeds in reproducing the global eight principal tidal harmonic constants. Particularly, the simulated tidal results in the CS are improved compared to some other regional models with the discrepancy of 3.9 cm for M2 tide. This idea of GOCTM can also be referred for other regional ocean study. Key words: finite volume model, GOCTM, open boundary conditions, the China Seas
1 Introduction Circulation and tide in the CS, as two of the most important physical oceanography processes, have been studied using some regional tide models, circulation models and circulation-tide coupled numerical models before (Choi et al., 1984, 1985, 1989; Chen et al., 1995; Lefvre, 2000; Fang et al., 1999, 2004; Chen and Wu, 2006 and Xia et al., 2006; et al.). However, these studies show that two problems are associated with the hydrodynamic simulation in the CS. Firstly, the seas adjacent to China, including the East China Sea (ECS) and the South China Sea (SCS), are characterized by their complex geometry of the basin and topographies, numerous islands and narrow straits (see Fig.1), and thus it is necessary to set up fine grid models to resolve the hydrodynamics (Lefvre, 2000; Fang et al.,
2004; Greenberg, 2007). Secondly, it has long been recognized that the circulation and tide in the ECS, the SCS and the Japan/East Sea (JES) are closely related with those in the Pacific, especially with the Kuroshio Current (Hidaka, 1966; Nitani, 1972; Yang, 2007). Therefore, the input of precise open boundary conditions is another key point for
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