吕泗上升流观测和动力机制模拟分析

Observation and Modeling Analysis of Dynamic Mechanism of the Upwelling at Lusi

基于2000年8月长江口外现场观测的分析,首次发现在长江口外吕泗附近存在着上升流现象。该上升流将下层的冷水和营养盐带向上层,对海区的环境和生态具有重要的影响。为了解该上升流的动力机制,作者利用基于ECOM_si建立的一个水平球面坐标系的高分辨率湍流闭合的三维环流数值模式研究该上升流现象。该模式计算区域包括东海、黄海和渤海,考虑实际岸线和水深。在综合考虑风应力、开边界体积通量和密度梯度力的情况下,模拟结果再现了吕泗海区的上升流现象,与观测结果较为一致。数值试验结果表明,产生该处上升流的动力机制主要是盐淡水混合产生的斜压效应,风应力的作用较弱,边界水体积通量产生的正压效应不起作用。倾斜的底形与斜压效应、风应力的联合作用使吕泗海区的上升流更明显。

Based on the analysis of the observation we organized in August of 2000 off the Changjiag mouth,we found for the first time that there exists upwelling phenomenon at Lusi fish ground. The up-welling can bring the colder water and nutrient from the lower layer to the upper layer , and has an important effect on the environment and ecosystem. In order to understand the dynamic mechanism of the upwelling phenomenon,we used a three-dimension high resolution turbulent closure circulation model in spherical coordinates based on the modified ECOM_si model to study this upwelling. The calculated domain includes the East China Sea, Yellow Sea and Bohai Sea, and the real coastline and water depth were considered. In the case of considering all dynamic factors (water volume flux at the open boundaries, density gradient forcing and wind stress), the numerical model reconstructed successfully the upwelling phenomenon which is fairly consistent with the observations. The numerical experiments show that the dynamic mechanism of the up-welling is mainly produced by the baroclinic effect that is induced by the mixing between fresh water from the Changjiang River and the saline water. The wind stress has a little effect on it,and the water volume flux at open boundaries has no effect on it. The combination force of the slop of bottom with the baroclinic effect and wind stress makes the upwelling stronger.