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arXiv 1401.7571astro-ph.EPphysics.ao-phphysics.flu-dyn
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系外行星大气的分析模型。I.通过浅水系统的大气动力学

Analytical Models of Exoplanetary Atmospheres. I. Atmospheric Dynamics via the Shallow Water System

Kevin Heng, Jared Workman

摘要:

在系外行星大气的背景下,我们提出了一个全面的线性分析强迫,阻尼,磁化浅水系统,探索维度,几何形状(笛卡尔,伪球形和球形),旋转,磁张力和流体动力学和磁摩擦源的影响。在广泛的条件下,我们发现,大气和量子谐振子的关键控制方程是相同的,即使当强迫(恒星辐射),摩擦源(分子粘度,瑞利阻力和磁阻力)和磁张力。全球大气结构在很大程度上由一个单一的关键参数控制,该参数涉及Rossby和Prandtl数。当分子粘性或磁阻力在整个纬度上不均匀地起作用时,或者存在极向磁场时,这种近乎普遍性的现象就消失了,这表明这些效应将给大气环流模拟中所见的熟悉的人字形特征带来质的变化。我们还发现,流体动力学和磁摩擦源有不同的相位签名,并从根本上不同的方式影响流,这意味着使用瑞利阻力来模仿磁阻力是不准确的。我们详尽地奠定了理论形式主义(色散关系,控制方程和时间依赖波的解决方案)的一个广泛的模型套件。在所有情况下,我们得出的大气,这是相关的解释红外相位和日食地图的系外行星大气的稳态。我们阐明了箍缩效应,限制了大气结构的赤道附近。我们的分析模型套件可用于决定性地发展物理直觉,并作为大气环流的三维磁流体动力学(MHD)模拟的参考点。

英文摘要:

Within the context of exoplanetary atmospheres, we present a comprehensive linear analysis of forced, damped, magnetized shallow water systems, exploring the effects of dimensionality, geometry (Cartesian, pseudo-spherical and spherical), rotation, magnetic tension and hydrodynamic and magnetic sources of friction. Across a broad range of conditions, we find that the key governing equation for atmospheres and quantum harmonic oscillators are identical, even when forcing (stellar irradiation), sources of friction (molecular viscosity, Rayleigh drag and magnetic drag) and magnetic tension are included. The global atmospheric structure is largely controlled by a single, key parameter that involves the Rossby and Prandtl numbers. This near-universality breaks down when either molecular viscosity or magnetic drag acts non-uniformly across latitude or a poloidal magnetic field is present, suggesting that these effects will introduce qualitative changes to the familiar chevron-shaped feature witnessed in simulations of atmospheric circulation. We also find that hydrodynamic and magnetic sources of friction have dissimilar phase signatures and affect the flow in fundamentally different ways, implying that using Rayleigh drag to mimic magnetic drag is inaccurate. We exhaustively lay down the theoretical formalism (dispersion relations, governing equations and time-dependent wave solutions) for a broad suite of models. In all situations, we derive the steady state of an atmosphere, which is relevant to interpreting infrared phase and eclipse maps of exoplanetary atmospheres. We elucidate a pinching effect that confines the atmospheric structure to be near the equator. Our suite of analytical models may be used to decisively develop physical intuition and as a reference point for three-dimensional, magnetohydrodynamic (MHD) simulations of atmospheric circulation.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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