Interbasin exchange and mixing in the hypolimnion of a large lake: The role of long internal waves
Interbasin exchange and mixing in the hypolimnion of a large lake: The role of long internal waves
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大湖底层的跨流域交换和混合：长内波的作用
DOI：
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
U. Lemmin
中科院分区：
文献类型：
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作者：
L. Umlauf;U. Lemmin
我们用场和数值相结合的方法研究了幕式内开尔文波对底边界湍流的影响以及一个大湖(日内瓦湖)的主盆地和边盆地之间的被动示踪剂的交换。对25公里长、70m深的侧盆地入口处附近垂直流结构的高分辨率测量表明，次极磁流速度经常超过0.2m S™1，导致数米厚的对数流剖面的湍流底部边界层，并在温跃层上形成强切变区。通过一个湖泊的三维数值模型再现了水流的时间序列和垂直结构。结果表明，在经历了几次来自东北和西南方向的大风后，开尔文内部波的交换流动能够暂时使侧盆地的低磁体积增加一半或两倍，导致日内瓦湖侧盆地中高达40%的低磁水在几个波周期内不可逆地交换。数值模拟结果表明，交换的主要机制是尺度水平扩散和底部边界层小范围的剪切扩散。结果表明，底边界层湍流和盆间交换可以分别解释侧盆和主盆氧气剖面的结构差异。
We conducted a combined field and numerical study of the effects of episodic internal Kelvin‐type waves on bottom boundary turbulence and the exchange of a passive tracer between the main basin and the side basin of a large lake (Lake Geneva). High‐resolution measurements of the vertical current structure near the entrance of the 25‐km‐long and 70‐m‐deep side basin revealed that hypolimnetic current speeds frequently exceed 0.2 m s™1, leading to a turbulent bottom boundary layer several meters thick with logarithmic current profiles and to a region of strong shear across the thermocline. The time series and vertical structure of the currents were reproduced by a threedimensional numerical model of the lake. It was demonstrated that, after episodes of strong winds from the northeast and southwest, exchange flows due to internal Kelvin waves were able to temporarily half or double the hypolimnetic volume of the side basin, leading to an irreversible exchange of up to 40% of the hypolimnetic water in the side basin of Lake Geneva within only a few wave cycles. With the help of the numerical model, it was shown that the key mechanisms of exchange are horizontal dispersion by resolved scales and, to a small extent, shear dispersion in the bottom boundary layer. It is suggested that bottom boundary‐layer turbulence and the interbasin exchange can explain the structural differences in the oxygen profiles observed in the side basin and the main basin, respectively.