High-frequency internal waves in Lake Geneva
High-frequency internal waves in Lake Geneva
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日内瓦湖的高频内波
DOI：
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发表时间：
1996
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：
S. Thorpe;J. Keen;R. Jiang;U. Lemmin
在引起温跃层深度迅速增加或“跳跃”的扰动通过后的几个小时内，在日内瓦湖的温跃层中观察到了高频内波序列。本文提出了内波产生的三种可能机制，并与已有的资料作了比较：（1）内波是跳跃后的孤立子包，（2）内波是跳跃经过局部粗糙地形时产生的，以及（iii）跳跃在海岸线附近产生一个运动扰动，内波在它后面形成一个尾流。对最后一种可能性的研究涉及到解在平均流存在的情况下，内波尾流的形式问题，平均流的深度在其强度和方向上都不同。本文描述了实测的流场分布和层结中的尾流波型，并与无切变时的尾流波型进行了比较。本文还导出了在剪切流中传播的内波能量的表达式，发现从跳跃到波的能量损失率很小。平均切变波和内波共存所产生的最小Richardson数略大于1/4，表明切变流不稳定性可能限制了内波。然而，没有一种产生和传播机制与现有数据完全兼容。
Trains of high-frequency internal waves have been observed in the thermocline of Lake Geneva within a few hours after the passing of disturbances which cause a rapid increase or ‘jump’ in the depth of the thermocline. Three possible mechanisms for the source of the internal waves are proposed and compared with available data, (i) that the waves are a soliton packet following the jump, (ii) that the waves are generated as the jump passes over or around a local region of rough topography, and (iii) that the jump produces a moving disturbance near the shoreline with internal waves forming a wake behind it. The investigation of the last possibility involves the solution of the problem of the form of an internal wave wake in the presence of mean currents which vary in depth both in their strength and direction. The wave pattern of the wake in the observed current distribution and stratification of the lake is described and compared with that in the absence of shear. An expression for the energy of internal waves propagating in a shear flow is also derived, and it is found that the rate of energy loss from the jump to the waves is small. The minimum Richardson number resulting from the co-existence of the mean shear and the internal waves is marginally greater than 1/4, suggesting that the waves may be limited by shear-flow instability. However, none of the mechanisms for their generation and propagation is fully compatible with the available data.