Institute of Computational Mathematics and Mathematical Geophysics

Abstracts

Mathematical modeling of processes in atmosphere and hydrosphere

A three-dimensional primitive equation, free-surface, eta-coordinate coastal ocean circulation model was developed. Having free surface and adopting eta-coordinate are two apparently features of this model. Having free surface can ensure the right transformation between kinetic energy and available potential energy with the consideration of available surface energy. The eta-coordinate can well-represent the steep bottom topography and avoids the problem of the pressure force error inherent to the terrain-following coordinate, i.e. sigma-coordinate. The model is applied to two regions in order to study the circulation in the China Sea. One is the Pacific Ocean, which covers from 99^o E to 289^o E and 62^o S to 62^o N, the horizontal resolution is 1^o x 1^o. The other is the China Sea, extending from 99^o E to 143^o E and 0^o N to 51^o N with the horizontal resolution 0.5^o x 0.5^o. These two domains are nested together. The model for Pacific Ocean is run with close boundary, its results provide the initial boundary and lateral boundary to the model for the China Sea. The main current system, such as the Kuroshio, Mindanao Current, South China Sea Warm Current (SCSWC), Taiwan Warm Current (TWC), Yellow Sea Warm Current (YSWC), Tsushima Warm Current (TsWC) have been well reproduced. Some of the baroclinic structure and characteristic are also discussed.

Ocean temperature variational data assimilation is used to modify the variables in the integration process of the model. We use Optimal Interpolation (OI) to make spatial objective analysis, but the cost function is computed based on variational data assimilation method. The World Ocean Database 1998 is adopt as the observation temperature which has plenty of observation stations in the China Sea, especially in the region of Kuroshio. As a preliminary test, 8 years (from Nov. 1981 to Dec. 1989) data assimilation have been made. The preliminary results is encouraging. Compared with the simulating results without data assimilation, The Kuroshio flowing axis become more narrow and the current is enhanced which is more close to the observation evidences. The Subtropical Countercurrent (STCC) is also revealed clearly in the assimilation product which is close to the one that computed by using P-vector method and high resolution climatological temperature and salinity dataset. Further works will be carried out in order to the deeply understanding and tentatively prediction of the circulation in the China sea.

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