Tropical background and wave spectra: contribution of wave-wave interactions in a moderately nonlinear turbulent flow
Tropical background and wave spectra: contribution of wave-wave interactions in a moderately nonlinear turbulent flow
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热带背景和波浪谱：中等非线性湍流中波与波相互作用的贡献
DOI：
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发表时间：
2021
影响因子：
3.1
通讯作者：
N. Paldor
中科院分区：
文献类型：
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作者：
C. Garfinkel;O. Shamir;I. Fouxon;N. Paldor
热带大气的可变性集中在波数-频率组合上，线性理论表明波模可以自由传播，但在两者之间有相当大的能量。这项研究表明，在中等湍流流体中，这种功率谱可以由小尺度对流通过波-波相互作用引发大尺度波而产生。用一个非线性旋转浅水模式对热带动力学的这种解释提供了两个关键证据：一个是参数扫描实验，其中外部强迫的幅度逐渐增大，另一个是外部强迫，其中只有对称或反对称模强迫。这些实验不支持一种普遍接受的机制，即强迫直接投射到具有强烈响应的波模上，但仍模拟出与观察到的功率谱相似的功率谱，尽管线性投影机制仍然可以补充这里在观测中提出的机制。用湍流解释观测到的热带功率谱提供了一个简单的解释，解释了为什么能量应该集中在理论波模上，也为常见的背景谱是红色的假设提供了坚实的基础，即使它澄清了为什么不会出现具有特定的理论推导斜率的湍流级联，例如-5/3。然而，它确实解释了为什么级联应该朝向更低的波数，这是一个逆能量级联，类似于中纬度，尽管可压缩波模对热带动力学很重要。
Variability in the tropical atmosphere is concentrated at wavenumber-frequency combinations where linear theory indicates wave-modes can freely propagate, but with substantial power in between. This study demonstrates that such a power spectrum can arise from small scale convection triggering large scale waves via wave-wave interactions in a moderately turbulent fluid. Two key pieces of evidence are provided for this interpretation of tropical dynamics using a nonlinear rotating shallow water model: a parameter sweep experiment in which the amplitude of an external forcing is gradually ramped up, and also an external forcing in which only symmetric or only anti-symmetric modes are forced. These experiments do not support a commonly accepted mechanism involving the forcing projecting directly onto the wave-modes with a strong response, yet still simulate a power spectrum resembling that observed, though the linear projection mechanism could still complement the mechanism proposed here in observations. Interpreting the observed tropical power spectrum using turbulence offers a simple explanation as to why power should be concentrated at the theoretical wave-modes, and also provides a solid footing for the common assumption that the back-ground spectrum is red, even as it clarifies why there is no expectation for a turbulent cascade with a specific, theoretically derived slope such as -5/3. However it does explain why the cascade should be towards lower wavenumbers, that is an inverse energy cascade, similar to the midlatitudes even as compressible wave-modes are important for tropical dynamics.
影响因子：
8.9
作者：
P. Roundy
通讯作者：
P. Roundy