A PRELIMINARY STUDY OF THE YANGTZE DILUTED WATER AND ITS MIXING PROCESSES
A PRELIMINARY STUDY OF THE YANGTZE DILUTED WATER AND ITS MIXING PROCESSES
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发表时间：
1963
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通讯作者：
H. Mao
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作者：
H. Mao
本文根据长江口附近地区的水文资料，研究了长江冲淡水的分布、变化及其混合过程。本研究分为三个部分，第一部分研究了长江冲淡水的分布和变化与长江月流量、月气流等的关系，已经进行了统计学研究。相关性分析结果表明：（1）以S = 32 ‰的等值线作为长江冲淡水区的边界是合理的S = 26 ‰的等值线可作为长江冲淤区核心带的边界。（2）长江月流量的变化是影响该核心区大小变化及其运动方向的主要因素，本文第二部分较详细地研究了1959年4~9月长江冲淡水的运动方向，并对1959年4~9月长江冲淡水的运动方向作了初步的分析。研究了该稀释水与邻近水团的混合过程。分析结果表明，长江冲淡水可分为近岸段和近海段。后段冲淡水向东或东北方向迁移，表层盐度分布较有规律。对该地区σ i剖面的定性分析表明，如果假定速度场与质量场完全一致，则该冲淡水近岸段的性质与分层介质中的射流性质十分相似。因此，可以初步得出结论，横向混合过程必须是重要的。长江冲淡水近岸段的水文情势相当复杂。然而，值得注意的是，这里长江冲淡水突然从东南向东或东北方向改变了方向;这意味着，在这个冲淡水运动的流线上，这里出现了一个明显的气旋弯曲。对涡度方程项的定性分析表明，除反气旋风应力外，其它因素都有利于这种气旋性曲率的存在。本文第三部分详细分析了1959年7月长江冲淡水近岸断面的淡水浓度分布。结果表明，该海域淡水浓度的横向分布与正态分布非常相似。因此，它表明，如果作出某些相当一般的假设，那么，通过显示稳定状态下的涡流扩散的简化方程，可以容易地获得支配这种分布的规律。计算结果表明，近岸段的横向涡动扩散系数为4-5 × 106cgs单位。这一结果与本研究所的其他研究人员最近用完全不同的方法所得到的结果相一致，但令人满意。最后，本文还粗略估计了同一地区垂直速度和垂直涡动扩散系数的数量级。
In this paper, the distributions and variations of the Yangtze Diluted Water and its mixing processes have been studied on the basis of the hydrographic data of the area off the mouth of the Yangtze river. The study is divided into three parts.In the first section, relationships between the distribution and variation of the Yangtze Diluted Water and the monthly flow of the Yangtze, the monthly air current, etc., have been studied statistically. Results of correlation analysis show: (1) that the isoline of S=32‰ may be reasonably taken as the boundary of the area of the Yangtze Diluted Water (i.e. the Yangtze Diluted Area) and that the isoline of S=26‰ may be rightly considered as the boundary of the core zone of the Yangtze Diluted Area, (2) that the variation of the monthly flow of the Yangtze is undoubtly the predominant factor which influences the changes of the size of this core zone and also the direction of its movement, the effect of the mean air current (or wind) which was presumably considered as the most essential factor, is actually less important.In the second part of this article, the directions of movement of the Yangtze Diluted Water during the months from April to September, 1959 have been studied in a rather detailed manner, and the mixing processes of this Diluted Water with its neighboring water masses have been investigated. Results of the analysis show that the Yangtze Diluted Water may be subdivided into two parts, i.e. the near-shore section and the offshore section. In the latter section, the Diluted Water moves to the east or to the northeast, the distribution of surface salinity is in a quite regular manner. Results of qualitative analysis of σi-sections of this area show that the nature of off-shore section of this Diluted Water is quite analogous to that of the jet flow in a stratified medium, if we assume that the velocity field is in complete adjustment with the mass field. It may, therefore, be tentatively concluded that lateral mixing process must be important here. The hydrographic regime of the near-shore section of the Yangtze Diluted Water is rather complex. It is, however, important to note that here the Yangtze Diluted Water suddenly changes its direction from southeast to the east or to the northeast; that means, on the streamline of the movement of this Diluted Water, a pronounced cyclonic curvature appears here. Qualitative analysis of the terms of vorticity equation show that all factors, probably with the only exception of the anticylonic wind stress, favor the existence of such a cyclonic curvature.In the third part of this article, the distribution of the fresh water concentration of the off-shore section of the Yangtze Diluted Water of July, 1959, have been analyzed in detail. Results show that the transverse distribution of the fresh water concentration in this area is very similar to the normal distribution. Therefore, it suggests -that the law which governs such a distribution may be easily obtained by showing the simplified equation of eddy diffusion in a steady state, if a certain quite general assumptions are made. Calculations show that the lateral coefficient of eddy diffusion is 4-5×106 cgs unit in the off-shore section. This result agrees satisfactorily with those obtained very recently by other investigators of this institute, using entirely different methods, however.At the end of this article, the order of magnitude of the vertical velocity and the vertical coefficient of eddy diffusion of the same area have been roughly estimated.