Internal hydraulic jumps and overturning generated by tidal flow over a tall steep ridge
Internal hydraulic jumps and overturning generated by tidal flow over a tall steep ridge
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DOI：
10.1175/2008jpo3777.1
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发表时间：
2008-09-01
影响因子：
3.5
通讯作者：
Klymak, Jody
中科院分区：
文献类型：
--
作者：
Legg, Sonya;Klymak, Jody
夏威夷海脊最近的观测表明，在海脊顶部附近发生了倾覆和强烈的消散以及潮汐周期。具有真实地形和分层的模拟表明，这种倾覆起源于在最大落潮时发生在陆架断裂下方的瞬时内部水力跳跃，然后在水流逆转时作为内部钻孔沿斜坡向上传播。一系列数值模拟探索了地形坡度、正压速度、层结和强迫频率的参数空间，以确定这些内部跳跃可能发生的参数区域。理论分析预测，当垂直潮汐漂移较大时，可能会发生潮汐驱动跳跃，这意味着地形坡度较陡，使得dh/dxN/omega>；1.预测跳跃的垂直长度尺度取决于水流速度，从而使跳跃弗劳德数具有量级单位。数值计算结果与理论预测一致，在陡坡强离坡潮流作用下，发生了有限幅度的内部水跃和倾覆。这些结果表明，在高陡峭的地形上，内部水跃可能是局部潮汐混合的重要机制。
Recent observations from the Hawaiian Ridge indicate episodes of overturning and strong dissipation coupled with the tidal cycle near the top of the ridge. Simulations with realistic topography and stratification suggest that this overturning has its origins in transient internal hydraulic jumps that occur below the shelf break at maximum ebb tide, and then propagate up the slope as internal bores when the flow reverses. A series of numerical simulations explores the parameter space of topographic slope, barotropic velocity, stratification, and forcing frequency to identify the parameter regime in which these internal jumps are possible. Theoretical analysis predicts that the tidally driven jumps may occur when the vertical tidal excursion is large, which is shown to imply steep topographic slopes, such that dh/dxN/omega > 1. The vertical length scale of the jumps is predicted to depend on the flow speed such that the jump Froude number is of order unity. The numerical results agree with the theoretical predictions, with finite-amplitude internal hydraulic jumps and overturning forming during strong offslope tidal flow over steep slopes. These results suggest that internal hydraulic jumps may be an important mechanism for local tidally generated mixing at tall steep topography.