| 摘要: |
| 以整个中国海为研究区域,把开边界取在TOPEX/POSEIDON(T/P)高度计资料数据点,利用趋近插值法将高度计资料同化到二维非线性潮汐数值模式中,反演了中国近海M2分潮的分布。计算结果与60个验潮站资料比较,符合良好振幅平均绝对偏差为6.7cm,相角偏差为5.5°,均方根偏差为12.6cm。根据计算结果给出东中国海和南海M2分潮的同潮图,与相关文献比较,符合良好。研究结果表明,以本方法利用T/P资料来反演中国海潮汐是可行的。 |
| 关键词: 高度计 开边界 M2分潮 同化 |
| DOI： |
| 分类号: |
| 基金项目:物理海洋教育部重点实验室开放课题基金资助项目,200307号;中国科学院海洋研究所领域前沿项目“卫星高度计在海洋动力过程中的应用研究”资助,KZCX2202号 |
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| ASSIMILATION OF THE M2 TIDES IN CHINA SEAS WITH TOPEX/POSEIDON DATA |
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QIU Zhong-Feng1,2, HE Yi-Jun1
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1.Institute of Oceanology, Chinese Academy of Sciences, Qingdao, 266071;2.Graduate School of the Chinese Academy of Sciences, Beijing, 100039
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| Abstract: |
| China seas include all the marine territories of China. In these regions, tides are the main contributors to ocean dynamics. Conditions such as complex coastlines and bathymetry, large dynamic difference, small tide spatial scale, and shallow water constituents, have driven many scientists to investigate tides. Great amounts of works have been done on tides in the seas, and significant progress has been made. However, previous investigations were mainly focus on some aspects instead of the whole area. In this paper, we treated the China seas as a whole on which the calculation was done.
Open boundary conditions are critical for local tidal modeling and usually acquired in two ways: near the open boundary (including in situ data and satellite data) and from global tidal model. In the simulations for the China seas tides, the first way was commonly used. However, for the locations with sparse observation, interpolation or other methods would be used to get tidal values in the open boundary points, and man-made bias that would bring about significant calculation error, is unavoidable. Therefore, we chose the track points of TOPEX/POSEIDON as the open boundary points, and set directly the M2 tidal values in the track points as the open boundary values, to eliminate the artificial errors.
Although the precision of investigating global tides with TOPEX/POSEIDON data is considerably high, it is still not good enough in near-shore, especially shallow water. To enhance the precision, various assimilation methods can be used. In our case, a method similar to nudging, was used.
In this paper, M2 tidal harmonic constants in the China seas were extracted from about 10-year TOPEX/POSEIDON altimetry data along the track points, and were assimilated into a two-dimension non-linear tidal model with the nudging method. The governing equations of the numerical model were the classic barotropic nonlinear shallow water ones. The TOPEX/POSEIDON data were put into the model with the factor β, the assimilation coefficient whose value is crucial to the results. β is related linearly to the constraint on the tendency of the observed. The calculation would overflow if β is too large. We found that β ranges between 0–1 through experiments. In overall, the deeper areas, the greater β values. Specifically, the value was set to 0 if the area shallower than 20m; 20–50m at 0.1; 50–100m at 0.12; 100–150m at 0.2; 150–200m at 0.3; 200–1000m at 0.3–0.7; 1000–1500m at 0.3–0.7; and >1500m, the value was set to 1.
The bias between calculations and observations for 60 gauge stations are as follow: the average absolute difference of amplitudes is 6.7cm; the average difference of phase-lags is 5.5°; and the RMS value is 12.6cm. To highlight the effects of the assimilation, we compared the results between assimilation and non-assimilation. The biases of non-assimilation are 12cm, 18.2° and 28.1cm respectively. The effects of assimilation were obvious. Then the M2 co-tidal charts were obtained according to the results. The results show that it is practicable to assimilate the M2 constituents in China seas with TOPEX/POSEIDON data. Furthermore, the precision would be probably improved upon the condition of optimizing the bottom friction coefficient simultaneously. |
| Key words: Altimetry, Open boundary condit ions, M2 constituent ,Assimilation |
