M_2分潮对夏季长江冲淡水扩展影响的数值研究

A NUMERICAL STUDY ON THE IMPACT OF M_2 TIDE ON THE EXPANSION OF THE CHANGJIANG RIVER DILUTED WATER IN SUMMER

利用σ坐标系下的斜压浅海环流模式，研究M2分潮对夏季长江冲淡水扩展的影响。在“准定常流”作用下，模拟出能反映夏季长江冲淡水扩展的盐度场，并模拟出与黄、东海实测资料相符的M2分潮。在此基础上，用两种方案讨论M2分潮对冲淡水的影响。第一种方案，仅考虑M2分潮，计算它对冲淡水扩展的影响。第二种方案，将M2分潮和“准定常流”耦合，计算冲淡水扩展的变化。结果表明，从分潮对冲淡水扩展有一定影响，其中包括潮混合和定向输运。

The objective of thes work was to study the M2 tide's impact on the exoansion of Changjiang River diluted water. The calculation was done with a baroclinic and shallow water model in coordinate system. The selected domain included the Bohai, Yellow, and East China Seas. The horizontal resoluhon is 7.5×7.5. The model had 11 layers. The quasi-steady crmnt was simulated first which was affected by the boundary forees, the summer wind and the baroclinic mecbosm. The expansion of the Changiiang hiver diluted water in summer can be described by the salinity field resultod from the quasi-steady currenL Then, the M2 tide in the Yellow Sea and the East Chna Sea was simulated. The results agreed with the observed clata. Based on these studies,tWo wnys were adopted to study the M hde's impact on the diluted water. The M2 hde was first considered individually tO calculate it8 impact on the expansion of the diluted water. When the calculated cimnt of M hde was steady, the salihity field indued by the quasi-steady current was taken as the initial field to be calculated with the M2 tide's current Then, couping M2 tide with quasi-steady current, the change of the diluted watees expansion was studied nurnerically. Taking the quasi-steady current as the inihal field, and keeping the wind and the baroclinic mechanism, the calculation of current was carried based on the water level on the open boundaries, which was the superposition of tha of the M2 tide and the quasi-steady current When the chane pattems of currents between two tidal periods were the same, the salinity was also calculated- The initial salinity field was induced by the qndi-steady cunent These calculations indicatod tha M2 tide had impact on the Changiiang River diluted waters expansion in summer, which involved tidal mixing and tidal transport.Mixing accelerated the diluted water's diffusing to the Yellow Sea and the East China Sea in all directions. Transport was northward near the Changiiang fover mouth, and southward far away from the mouth, but was northward again around Jizhou Island.