| 摘要: |
| 基于ADCP走航观测得到长江河口北槽弯道附近3个横向断面（AD3、AD5和AD6）的流速资料，采用涡度方法，本文计算、分析了弯道环流与混合在垂直横向上的时空分布、影响因素及其重要性。3个横向断面上均存在由不规则界面分开的二层结构的横向环流。半拉格朗日余流的计算结果显示：（1）小潮期间，AD3、AD5和AD6断面呈现表层向海、底层向陆的纵向环状半拉格朗日余流；大潮期间，呈现表、底层均向海的纵向半拉格朗日余流；（2）小潮期间，AD3断面呈现表层向北导堤、底层向南导堤的横向环状半拉格朗日余流；大潮期间，AD3断面中间区域呈现表层向北导堤、底层向南导堤的、而断面两端区域则呈现表层向南导堤、底层向北导堤的横向环状半拉格朗日余流；（3）小、大潮期间，横向断面AD5和AD6均呈现表层向北导堤、底层向南导堤的横向环状半拉格朗日余流；（4）“纵向半拉格朗日余流”在-0.2-0.7m/s；横向半拉格朗日余流”在-0.15-0.2m/s；（5）纵向半拉格朗日余流在横向上有明显变化。对弯道环流的进一步分析表明：（1）斜压梯度、内部摩擦致混合和底部摩擦致混合这三项各自的纵向分量是驱动纵向环流形成的主要因素，“纵向动量的横向重新分布项”次之，离心力和地转的影响可忽略；（2）横向斜压梯度和内部摩擦致混合项是驱动横向环流形成的主要因素，离心力、地转和底部摩擦致混合次之；（3）横向环流可能通过“纵向动量的横向重新分布项”减弱纵向动量，从而可能减弱纵向环流。 |
| 关键词: 长江河口 北槽弯道 横向环流 纵向环流 涡度方法 半拉格朗日余流 |
| DOI：10.11693/hyhz20161000217 |
| 分类号:P731 |
| 基金项目:海洋工程国家重点实验室自主研究项目，GKZD010068号，GKZD010071号。 |
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| CIRCULATION WITHIN CURVED CHANNEL OF THE NORTH PASSAGE IN THE CHANGJIANG RIVER ESTUARY:A VORTICITY APPROACH |
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LI Wei1, John Z. SHI1, PU Xiang1, HU Guo-Dong2
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1.State Key Laboratory of Ocean Engineering and Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai 200030, China;2.Survey Bureau of Hydrology and Water Resources of the Changjiang River Estuary, Changjiang Water Resources Commission, Shanghai 200136, China
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| Abstract: |
| Vessel mounted ADCP measurements were made of tidal currents along the cross-channel sections AD3, AD5, and AD6 within the Curved Channel of the North Passage in the Changjiang (Yangtze) River estuary on Feb. 23-24, 2014 (dry season, neap tide) and Feb. 28 to Mar. 1, 2014 (dry season, spring tide). These data were analyzed by using a vorticity approach to examine the temporal and spatial variability of circulation and mixing in the vertical-lateral plane, their physical mechanisms, as well as the relative importance of each mechanism. Lateral secondary flows, which have "two-layered" structure separated by irregular interfaces, are present along the three sections. Calculated semi-Lagrangian residual flows show that:(1) along the three sections during neap tide, longitudinal circulating semi-Lagrangian residual flows at the surface are seaward, and landward at the bottom; during spring tide, longitudinal semi-Lagrangian residual flows at both the surface and bottom are seaward. (2) Along the section AD3 during neap tide, lateral circulating semi-Lagrangian residual flows at the surface are towards the Northern Dikes and at the bottom towards the Southern Dikes, while in the middle part of the section AD3 towards the Northern Dikes at the surface and towards the Southern Dikes at the bottom; at the two ends of the section AD3 during spring tide, towards the Southern Dikes at the surface and towards the Northern Dikes at the bottom. (3) Along sections AD5 and AD6, lateral circulating semi-Lagrangian residual flows are towards the Northern Dikes at the surface layer and towards the Southern Dikes at the bottom during both neap and spring tides. (4) The magnitudes of longitudinal semi-Lagrangian residual flows range from -0.2 to 0.7m/s and those of lateral semi-Lagrangian residual flows from -0.15 to 0.2m/s. (5) Apparent lateral variability of longitudinal semi-Lagrangian residual flow is present. Further analyses of circulations within the Curved Channel show that:(1) Longitudinal baroclinic pressure gradient, longitudinal internal friction induced mixing, and longitudinal bottom friction induced mixing seem to be the primary physical mechanisms driving longitudinal circulation, while the lateral redistribution of along-channel momentum the secondary one, and the centrifugal force and the Coriolis force can be neglected. (2) Lateral baroclinic pressure gradient and the internal friction induced mixing are the primary physical mechanisms driving lateral secondary flows, while the centrifugal force, the Coriolis force, and the bottom friction induced mixing the secondary ones. (3) The lateral circulation may weaken longitudinal momentum and then circulation via lateral redistribution of along-channel momentum. |
| Key words: Changjiang River estuary the Curved Channel of the North Passage lateral circulation longitudinal circulation vorticity approach semi-Lagrangian residual flow |
