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arXiv 2108.13795astro-ph.EPphysics.flu-dynphysics.geo-ph
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类行星旋转椭球中的声学和惯性模式

Acoustic and inertial modes in planetary-like rotating ellipsoids

Jérémie Vidal, David Cébron

摘要:

旋转的充满流体的椭球体的有界振荡可以提供物理洞察变形行星内部的流动动力学。由科里奥利力维持的惯性模式在快速旋转的流体中普遍存在,并且Vantieghem(2014,Proc. R. Soc. A,470,20140093,doi:10.1098/rspa.2014.0093)开创了一种在不可压缩流体椭圆体中计算它们的方法。然而,考虑到密度(和压力)的变化是需要精确的行星应用,这在很大程度上被忽略了椭球模型。为了超越不可压缩的理论,我们提出了一个在刚性无芯椭球的Galerkin方法,基于一个整体的多项式描述。我们应用该方法来研究完全可压缩,旋转和无扩散流体的正常模式。我们考虑一个理想化的模型,它公平地再现了地球的液体核心和类星体的气体行星的密度变化。我们成功地对标准的有限元计算结果进行基准测试。值得注意的是,我们发现,准地转惯性模式可以显着修改的压缩性,即使在中等可压缩的内部。最后,我们讨论了使用正常模式建立简化的动力学模型的行星流。

英文摘要:

The bounded oscillations of rotating fluid-filled ellipsoids can provide physical insight into the flow dynamics of deformed planetary interiors. The inertial modes, sustained by the Coriolis force, are ubiquitous in rapidly rotating fluids and Vantieghem (2014, Proc. R. Soc. A, 470, 20140093, doi:10.1098/rspa.2014.0093) pioneered a method to compute them n incompressible fluid ellipsoids. Yet, taking density (and pressure) variations into account is required for accurate planetary applications, which has hitherto been largely overlooked in ellipsoidal models. To go beyond the incompressible theory, we present a Galerkin method in rigid coreless ellipsoids, based on a global polynomial description. We apply the method to investigate the normal modes of fully compressible, rotating and diffusionless fluids. We consider an idealized model, which fairly reproduces the density variations in the Earth's liquid core and Jupiter-like gaseous planets. We successfully benchmark the results against standard finite-element computations. Notably, we find that the quasi-geostrophic inertial modes can be significantly modified by compressibility, even in moderately compressible interiors. Finally, we discuss the use of the normal modes to build reduced dynamical models of planetary flows.

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