Instabilities of Finite‐Amplitude Internal Wave Beams
Instabilities of Finite‐Amplitude Internal Wave Beams
复制标题
有限振幅内波梁的不稳定性
DOI：
10.1029/2019gl082570
复制
发表时间：
2019
影响因子：
5.2
通讯作者：
Tanaka Y.
中科院分区：
文献类型：
--
作者：
Onuki Y.;Tanaka Y.
梁状内波通常由海洋中的潮汐产生，但对引起垂直混合的耗散过程仍然知之甚少。先前的研究检查了小振幅梁，发现参数亚谐不稳定性（PSI）引起与纬度相关的波耗散。使用基于Floquet理论的新方法，本研究分析了有限振幅梁在宽参数范围内的稳定性。当光束振幅较小时，当f/σ≤ 0.5（其中f为Coriolis参数，σ为光束频率）时，PSI确实是主模，并且当等式成立时，增长率最大。然而，随着波束振幅的增加，即使f/σ>0.5，不稳定性也会出现，但最大不稳定性的位置向较低的f/σ移动，因此，不稳定性的纬向依赖性显著改变。此外，所得到的能量谱被强烈地多普勒频移到更高的频率，这因此将这种配置与PSI的常见情况区分开。
Beam‐like internal waves are commonly generated by tides in the ocean, but their dissipation processes that cause vertical mixing remain poorly understood. Previous studies examined small‐amplitude beams to find that parametric subharmonic instability (PSI) induces latitude‐dependent wave dissipation. Using a novel approach based on Floquet theory, this study analyzes the stability of finite‐amplitude beams over a wide range of parameters. If beam amplitude is small, PSI is indeed the principal mode under the conditionf/σ≤ 0.5, wherefis the Coriolis parameter andσis the beam frequency, and the growth rate is maximum when equality holds. However, as beam amplitude is increased, instability arises even whenf/σ>0.5, but the location of maximum instability shifts toward lowerf/σ; thus, the latitudinal dependence of instability is significantly altered. Furthermore, the resulting energy spectrum is strongly Doppler shifted to higher frequencies, which therefore distinguishes this configuration from the common cases of PSI.