Spontaneous inertia-gravity-wave generation by surface-intensified turbulence
Spontaneous inertia-gravity-wave generation by surface-intensified turbulence
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DOI：
10.1017/jfm.2012.90
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发表时间：
2012-04
影响因子：
3.7
通讯作者：
Eric Danioux;J. Vanneste;P. Klein;H. Sasaki
中科院分区：
文献类型：
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作者：
Eric Danioux;J. Vanneste;P. Klein;H. Sasaki
摘要：通过对理想化海洋结构中的原始方程进行高分辨率模拟，研究了表面强化、近平衡运动自发产生的惯性重力波（IGW）。在大尺度和中尺度上，由地表附近的斜压不稳定性驱动的动力学是平衡的，并且可以通过地表准地转模型得到很好的定性描述。然而，这预示着罗斯贝数随着空间尺度的减小而增加，因此，小尺度上的平衡会被破坏； IGW 的产生是这种崩溃的结果。波场在远离表面的深度进行分析，其中相关的垂直速度与与平衡运动相关的垂直速度具有相同的数量级。准地转关系，特别是欧米茄方程，证明足以将地转引力波与运动的平衡贡献分开。频谱分析表明，波能集中在自由IGW 的色散关系附近，并且随着频率和水平波数的增加而缓慢衰减。 IGW的产生在时间和空间上具有高度间歇性：当表面密度中的细丝因应变而形成时，会发射局域波包，从而导致大的垂直涡度和相应的大罗斯贝数。深入来说，IGW 场是一系列生成事件的结果；远离产生地点，它采取相对均匀、明显随机的波场的形式。据估计，自发产生的 IGW 场的能量比海洋中典型的 IGW 能量小几个数量级。
Abstract The spontaneous generation of inertia-gravity waves (IGWs) by surface-intensified, nearly balanced motion is examined using a high-resolution simulation of the primitive equations in an idealized oceanic configuration. At large scale and mesoscale, the dynamics, which is driven by baroclinic instability near the surface, is balanced and qualitatively well described by the surface quasi-geostrophic model. This however predicts an increase of the Rossby number with decreasing spatial scales and, hence, a breakdown of balance at small scale; the generation of IGWs is a consequence of this breakdown. The wave field is analysed away from the surface, at depths where the associated vertical velocities are of the same order as those associated with the balanced motion. Quasi-geostrophic relations, the omega equation in particular, prove sufficient to separate the IGWs from the balanced contribution to the motion. A spectral analysis indicates that the wave energy is localized around dispersion relation for free IGWs, and decays only slowly as the frequency and horizontal wavenumber increase. The IGW generation is highly intermittent in time and space: localized wavepackets are emitted when thin filaments in the surface density are formed by straining, leading to large vertical vorticity and correspondingly large Rossby numbers. At depth, the IGW field is the result of a number of generation events; away from the generation sites it takes the form of a relatively homogeneous, apparently random wave field. The energy of the IGW field generated spontaneously is estimated and found to be several orders of magnitude smaller than the typical IGW energy in the ocean.