Nonlinear energy transfer within the oceanic internal wave spectrum at mid and high latitudes
Nonlinear energy transfer within the oceanic internal wave spectrum at mid and high latitudes
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DOI：
10.1029/2001jc001210
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发表时间：
2002-11
影响因子：
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通讯作者：
T. Hibiya;M. Nagasawa;Y. Niwa
中科院分区：
文献类型：
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作者：
T. Hibiya;M. Nagasawa;Y. Niwa
[1]为了研究M2内潮提供的能量如何通过局部内波谱级联到耗散尺度，进行了两组数值试验，其中49°N处的Garrett-Munk准定常内波谱（实验I）和28°N（实验II），分别，首先再现，然后在最低垂直波数和M2潮汐频率下以能量尖峰的形式瞬时扰动。这些实验试图分别模拟阿留申海岭和夏威夷海岭附近准定常内波场的非线性能量传递，这两个海岭都是大振幅M2内潮的生成区域。在实验I中，能量尖峰停留在最低波数处，在那里它被嵌入，并且在能量尖峰被注入之后频谱保持准平稳。在实验II中，相反，在高水平和垂直波数的能量水平迅速增加后，注入的能量尖峰，表现出很强的相关性与高垂直波数的增强，近惯性电流剪切。这意味着，随着高垂直波数，近惯性流切变被加强，高水平波数的内波有效地多普勒频移，使垂直波数迅速增加，并加强湍流耗散发生。在高垂直波数，近惯性频带，这起着关键作用的级联能量耗散尺度的谱密度升高，被认为是由参数次谐波不稳定性。与此相反，在实验Ⅰ中，M2潮汐频率是49°N处惯性频率的1.2倍，因此M2内潮没有参数亚谐不稳定性。因此，即使可能产生大量的M2内部潮汐能，也无法支持局部深水混合。
[1] In order to examine how the energy supplied by M2 internal tides cascades through the local internal wave spectrum down to dissipation scales, two sets of numerical experiments are carried out where the Garrett-Munk-like quasi-stationary internal wave spectra at 49°N (experiment I) and 28°N (experiment II), respectively, are first reproduced and then perturbed instantaneously in the form of an energy spike at the lowest vertical wave number and M2 tidal frequency. These experiments attempt to simulate the nonlinear energy transfer within the quasi-stationary internal wave fields near the Aleutian Ridge and the Hawaiian Ridge, respectively, both of which are generation regions of large-amplitude M2 internal tides. In experiment I, the energy spike stays at the lowest wave number, where it is embedded and the spectrum remains quasi-stationary after the energy spike is injected. In experiment II, in contrast, the energy level at high horizontal and vertical wave numbers rapidly increases after the injection of the energy spike, exhibiting strong correlation with the enhancement of high vertical wave number, near-inertial current shear. This implies that as the high vertical wave number, near-inertial current shear is intensified, high horizontal wave number internal waves are efficiently Doppler shifted so that the vertical wave number rapidly increases and enhanced turbulent dissipation takes place. The elevated spectral density in the high vertical wave number, near-inertial frequency band, which plays the key role in cascading energy to dissipation scales, is thought to be caused by parametric subharmonic instability. In experiment I, in contrast, the M2 tidal frequency is 1.2 times the inertial frequency at 49°N so that M2 internal tide is free from parametric subharmonic instability. Accordingly, even though significant M2 internal tidal energy may be generated, it is not available to support local deep water mixing.