风应力和科氏力对长江河口没冒沙淡水带的影响

Impact of wind stress and Coriolis Force on the freshwater zone near Meimaosha in the Changjiang Estuary

应用改进的三维数值模式ECOM,考虑径流、潮汐潮流、地形、混合和口外陆架环流等多种动力因子,研究风应力和科氏力对枯季长江河口南槽没冒沙淡水带形成的影响.枯季没冒沙区域存在着淡水带,其形成的动力机制主要是长江径流和振荡的潮流.本文的数值计算结果表明,在分叉的长江河口,枯季北风产生向岸的埃克曼输运,导致北港流进南港和南槽流出的水平风生环流,阻挡了南槽外海盐水的入侵,有利于没冒沙水域淡水带的形成.在北半球科氏力使水流运动向右偏转,上游径流带来的淡水沿南汇边滩下泄,有利于没冒沙水域沿岸淡水带的形成.

Considering multiple dynamic factors of the river discharge, tide and tidal current, topography, mixing and continental shelf current, a modified 3-D numerical ECOM model was used to study the impact of wind stress and Coriolis Force on the formation of a freshwater zone in the Meimaosha area in the South Passage of the Changjiang Estuary. There existed freshwater zone in Meimaosha area during dry season, and its formation dynamic mechanism is mainly the Changjiang runoff and tidal current oscillation. The numerical calculation results in this paper indicate that onshore Ekman transport induced by the north wind during dry season result in a wind-driven circulation, which flows toward land in the North Channel and flows toward sea in the South Channel in the bifurcation estuary. This wind-driven current prevents the saltwater intrusion from the out sea, and consequently, facilitates the formation of the freshwater zone in the South Passage. The Coriolis Force turns the water flow to the right in the northern hemisphere, and drives the upstream freshwater move downstream along the Nanhui tidal flat, which facilitates the formation of the freshwater zone in the Meimaosha area.