| 摘要: |
| 基于原正交ECOM(Estuarine Coastal and Ocean Model)模式, 把它改进为非正交曲线坐标系下模式, 以较好地拟合河口海岸岸线的变化, 有效提高局部空间分辨率, 提高计算速度和精度；应用预估修正法提高模式的稳定性；扣除局域平均密度层结提高σ坐标系下斜压压强梯度力的计算精度；采用Euler-Lagrange方法改进物质输运方程中的平流项计算方法。数值试验结果证明以上4种方法有效地提高了模式的计算精度。把改进的模式应用于长江河口、杭州湾及邻近海区，模拟结果与观测资料较为一致。改进后的模式可更好地应用于河口海岸的研究中。
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| 关键词: 模式改进,非正交曲线坐标,预估修正法,Euler-Lagrange方法,长江河口和杭州湾 |
| DOI：10.11693/hyhz200304003003 |
| 分类号: |
| 基金项目:国家重点基础研究发展规划项目(973),G1999043803号;高等学校优秀青年教师教育和科研奖励基金项目,2002;国家自然科学基金项目,49876002号 |
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| IMPROVEMENT OF THE ECOM WITH APPLICATION TO THE CHANGJIANG RIVER ESTUARY, HANGZHOU BAY AND ADJACENT WATERS |
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ZHU Jian-Rong, ZHU Shou-Xian
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State Key Lab of Estuarine and Coastal Research, East China Normal University
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| Abstract: |
| Grid lines of a model should fit coastlines in order to improve local spatial resolution, in estuarine and coastal research, but this cannot satisfy the condition of grid orthogonal. To solve this problem, a non-orthogonal curvilinear coordinate system was introduced to the original orthogonal ECOM (Estuarine Coastal and Ocean Model). The calculated Keweenaw current in the Lake Superior in July 1973 is much more consistent with the observation data at 3 buoys near the Eagle Harbor with the non-orthogonal ECOM than with the orthogonal ECOM. There exists weak numerical instability in the original ECOM for a small vertical eddy viscosity coefficient, especially when there is no tide and there exists stratification, because the basic pattern of numerical scheme in the original ECOM is the Eulerian scheme. The predict-correct scheme was adapted to improve the model stability and the comparison of the calculated wind-driven current in Lake Superior in summer time with predict-correct scheme and without predict-correct scheme verified it. The error of the baroclinic pressure gradient is large where the variation of bottom topography and the stratification is strong because the σ coordinate was adapted in vertical in the ECOM. The method of deducting the mean density stratification over the whole
calculation domain in the original ECOM was used to reduce this error, but the stratification between the local and whole
calculation domain is much more different in the estuary, shallow water and continental shelf area, so there is still larger error of baroclinic pressure gradient using this method. Thus, we introduce the local concept instead of the whole domain, and put forward the idea of deducting local mean density stratification, and the method of returning to Z coordinate system to calculate the baroclinic pressure gradient. The calculated results of the current in the Changjiang estuary show that this method improves the accuracy of the baroclinic pressure gradient. The difference scheme of the advection terms in the mass transport equations in the original ECOM is central difference scheme, with the pseudo-physical phenomenon taking the information from downstream to upstream. This scheme could produce larger error for strong tidal currents and varied current directions. Therefore, the Euler-Lagrange method was used to improve the calculation scheme of the advection terms in the mass transportation equations. First, the multi-step inverse trace method was used to determine the historical position of a water particle. Then, the Lagrange interpolation method was used to determine the concentration at this position. This new method was used to calculate the salinity variation in an idealized estuary and the results was much more reasonable compared with the central difference scheme of the advection terms. The improved model was used in the Changjiang Estuary, Hangzhou Bay and their adjacent waters; the simulated results are fairly consistent with observations. The errors of the calculated harmonic constants of amplitude and phase of the main 4 tidal constituents M2, S2, K1, O1 are less than 10% compared with the observation data from 27 gauging stations. The simulation of the current inthe Changjiang estuary in March 1996 shows that the current has asymmetry due to the runoff effect. The velocity of the ebb current is larger than the flood and the ebb tide duration is obviously longer than the flood in the South Branch due to the runoff effect. The ECOM was improved efficiently in the above 4 cases, and can be used more successfully in the estuarine and coastal areas.
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| Key words: Model Improvement, Non-orthogonal curvilinear, Coordinate System, Predict-Correct Scheme, Euler-Lagrange Method, Changjiang River estuary and Hangzhou bay |
