定常切变流中反向传播核重力波的不稳定性
The instability of counter-propagating kernel gravity waves in a constant shear flow
摘要：
对最近发展起来的核重力波概念的机制进行了回顾，并利用这种结构解释了一个分层平面平行切变流的不稳定动力学。这种流动具有恒定的垂直切变，在垂直范围内是无限的，其特征是两个密度跳跃的大小相等，每个连续减少的高度，其中跳跃位于对称远离系统的中平面。我们发现，对于一个适当定义的体理查森数存在一个带的水平波数，表现出正常模式的不稳定性。不稳定性机制与反向传播的罗斯贝波问题中的不稳定性机制密切相关。在这个问题中，不稳定性产生于反向传播的重力波的相互作用。我们认为，不稳定性满足Hayashi-Young波动不稳定性准则。我们还认为，不稳定性是最简单的一个，可以出现在一个分层的大气与恒定的切变流。这里详细描述的反向传播重力波机制解释了为什么分层情况下不需要满足非分层情况下切变流不稳定性的瑞利准则。这说明了迈尔斯-霍华德定理如何通过分层来支持不稳定。一个正交模分析的泡沫层组成的两个密度不等的幅度跳跃进行了分析。结果被认为是在观测的海飓风接口。
英文摘要：
The mechanism describing the recently developed notion of kernel gravity waves (KGWs) is reviewed and such structures are employed to interpret the unstable dynamics of an example stratified plane parallel shear flow. This flow has constant vertical shear, is infinite in the vertical extent, and characterized by two density jumps of equal magnitude each decreasing successively with height, in which the jumps are located symmetrically away from the midplane of the system. We find that for a suitably defined bulk-Richardson number there exists a band of horizontal wavenumbers which exhibits normal-mode instability. The instability mechanism closely parallels the mechanism responsible for the instability seen in the problem of counter-propagating Rossby waves. In this problem the instability arises out of the interaction of counter-propagating gravity waves. We argue that the instability meets the Hayashi-Young criterion for wave instability. We also argue that the instability is the simplest one that can arise in a stratified atmosphere with constant shear flow. The counter propagating gravity waves mechanism detailed here explains why the Rayleigh criteria for shear flow instability in the unstratified case does not need to be satisfied in the stratified case. This illustrates how the Miles-Howard theorem may support destabilization through stratification. A normal mode analysis of a foamy layer consisting of two density jumps of unequal magnitude is also analyzed. The results are considered in terms of observations made of sea-hurricane interfaces.
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