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arXiv 1803.01736physics.flu-dyn
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两层旋转浅水波方程中的快、慢共振波

Fast and slow resonant triads in the two layer rotating shallow water equations

Alex Owen, Roger Grimshaw, Beth Wingate

摘要:

在本文中,我们研究三重共振旋转浅水系统时,有两个自由界面。这允许在一个相对简单的模式,斜压和正压动力学之间的相互作用的上下文中,也有一个地转模式的检查。与人们研究较多的单层旋转浅水系统相比,我们发现,除了通常的慢地转模态外,现在还有两种快波,一种是正压模态,一种是斜压模态。这一特征允许三重共振发生在三个快波之间,正压和斜压模式的混合,这方面不能发生在一层系统。现在也有两个分支的慢地转模与重复分支的色散关系。的后果进行了探讨,在一个完整的三元组相互作用方程的推导,使用多尺度渐近展开的基础上的一个小振幅参数。推导出的非线性相互作用系数确认使用能量和涡度拟能守恒。这些三元组相互作用方程进行了探讨,重点是小Rossby和弗劳德数的参数制度。

英文摘要:

In this paper we examine triad resonances in a rotating shallow water system when there are two free interfaces. This allows for an examination in a relatively simple model of the interplay between baroclinic and barotropic dynamics in a context where there is also a geostrophic mode. In contrast to the much-studied one-layer rotating shallow water system, we find that as well as the usual slow geostrophic mode, there are now two fast waves, a barotropic mode and a baroclinic mode. This feature permits triad resonances to occur between three fast waves, with a mixture of barotropic and baroclinic modes, an aspect which cannot occur in the one-layer system. There are now also two branches of the slow geostrophic mode with a repeated branch of the dispersion relation. The consequences are explored in a derivation of the full set of triad interaction equations, using a multi-scale asymptotic expansion based on a small amplitude parameter. The derived nonlinear interaction coefficients are confirmed using energy and enstrophy conservation. These triad interaction equations are explored with an emphasis on the parameter regime with small Rossby and Froude numbers.

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