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chang jiang chong dan shui ji qi hun he wen ti de chu bu tan tao
Pages: 183-206
Year: Issue:  3
Journal: Oceanologia et Limnologia Sinica

Keyword:  长江冲淡水均盐度合量平均气流射流近岸段月径流量桔果混合问题汉礼;
Abstract: 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.
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