Critical and near-critical reflections of near-inertial waves off the sea surface at ocean fronts
Critical and near-critical reflections of near-inertial waves off the sea surface at ocean fronts
复制标题
近惯性波在海洋前沿海面的临界和近临界反射
DOI：
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发表时间：
2015
影响因子：
3.7
通讯作者：
L. Thomas
中科院分区：
文献类型：
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作者：
N. Grisouard;L. Thomas
在平衡的海洋锋中，由于倾斜的等斜线和相关的热风切变，内波群速度矢量的可能方向偏离了经典的圣安德鲁十字。然而，对于以科里奥利频率f振荡的波，其中一个方向保持水平，而另一个方向允许能量垂直传播。这意味着海洋表面存在临界反射，在此之后，波浪能量从下面传播，不能向下传播。这类似于内部波的反射，从与群速度矢量平行的底部在静止介质中传播。我们首先通过对不同频率${itomega}$的波进行一系列线性Boussinesq数值实验来说明这一现象，探索临界（${itomega}=f$）、正向（${itomega}>f$）和反向（${itomega}<f$）反射。然后我们进行这些模拟的非线性等效。与经典情况一致，反向反射抑制三元共振，不表现出明显的非线性效应，而正向反射则产生强烈的谐波，从表面向外辐射能量。但令人惊讶的是，临界反射与从地表向下延伸的振荡运动有关。这些运动不是自由传播的波，而是采取一组非共振三和弦的形式，通过摩擦随深度衰减。
Abstract In a balanced oceanic front, the possible directions of the group velocity vector for internal waves depart from the classic Saint Andrew’s cross as a consequence of sloping isopycnals and the associated thermal wind shear. However, for waves oscillating at the Coriolis frequency $f$ , one of these directions remains horizontal, while the other direction allows for vertical propagation of energy. This implies the existence of critical reflections from the ocean surface, after which wave energy, having propagated from below, cannot propagate back down. This is similar to the reflection of internal waves, propagating in a quiescent medium, from a bottom that runs parallel to the group velocity vector. We first illustrate this phenomenon with a series of linear Boussinesq numerical experiments on waves with various frequencies, ${itomega}$ , exploring critical ( ${itomega}=f$ ), forward ( ${itomega}>f$ ), and backward ( ${itomega}<f$ ) reflections. We then conduct the nonlinear equivalents of these simulations. In agreement with the classical case, backward reflection inhibits triadic resonances and does not exhibit prominent nonlinear effects, while forward reflection shows strong generation of harmonics that radiate energy away from the surface. Surprisingly though, critical reflections are associated with oscillatory motions that extend down from the surface. These motions are not freely propagating waves but instead take the form of a cluster of non-resonant triads which decays with depth through friction.
影响因子：
3.5
作者：
S. Waterman;K. Polzin;A. N. Garabato;K. Sheen;A. Forryan
通讯作者：
S. Waterman;K. Polzin;A. N. Garabato;K. Sheen;A. Forryan