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arXiv 2208.03387astro-ph.EP
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热木星大气中热阻不稳定性的变率

Variability from thermo-resistive instability in the atmospheres of hot jupiters

Raphaël Hardy, Andrew Cumming, Paul Charbonneau

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10 pages, 5 figures, submitted to ApJ
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摘要：

热木星的大气层可能会受到热阻不稳定性的影响，其中随着温度的增加，电导率会导致失控的欧姆加热。我们介绍了一个简化的模型，在赤道地区的热木星，包括对大气流动的反反应，增加电导率导致通量冻结，这反过来又淬火的流量，因此欧姆加热的本地动态。我们展示了一个新的时间依赖性的解决方案，出现了温度依赖性的电导率（而温度无关的电导率总是演变到一个稳态）。周期性循环由阿尔芬振荡的爆发组成，这些振荡被静止的间隔分开，磁雷诺数在小于和大于1的值之间交替，保持振荡。我们调查的区域的压力和温度的不稳定性工作。对于典型的赤道大气模型中看到的加速度，我们发现不稳定的压力$\sim 0.1$ -$1\ {\rm bar}$和温度$\approx 1300$ -$1800\ {\rm K}$磁场$\sim 10\ {\rm G}$。与以往基于恒定风速的研究不同，我们发现，较弱的磁场的不稳定性更强。我们的研究结果进一步支持了这样一种观点，即可变性应该是木星磁化热大气的一个特征，特别是在中等温度下。在热木星大气动力学的MHD模型中，电导率的温度依赖性是一个重要的组成部分。

英文摘要：

The atmosphere of a hot jupiter may be subject to a thermo-resistive instability, in which the increasing electrical conductivity with temperature leads to runaway Ohmic heating. We introduce a simplified model of the local dynamics in the equatorial region of a hot jupiter that incorporates the back reaction on the atmospheric flow as the increasing electrical conductivity leads to flux freezing, which in turn quenches the flow and therefore the Ohmic heating. We demonstrate a new time-dependent solution that emerges for a temperature-dependent electrical conductivity (whereas a temperature-independent conductivity always evolves to a steady-state). The periodic cycle consists of bursts of Alfven oscillations separated by quiescent intervals, with the magnetic Reynolds number alternating between values smaller than and larger than unity, maintaining the oscillation. We investigate the regions of pressure and temperature in which the instability operates. For the typical equatorial accelerations seen in atmospheric models, we find instability at pressures $\sim 0.1$--$1\ {\rm bar}$ and temperatures $\approx 1300$--$1800\ {\rm K}$ for magnetic fields $\sim 10\ {\rm G}$. Unlike previous studies based on a constant wind velocity, we find that the instability is stronger for weaker magnetic fields. Our results add support to the idea that variability should be a feature of magnetized hot jupiter atmospheres, particularly at intermediate temperatures. The temperature-dependence of the electrical conductivity is an important ingredient that should be included in MHD models of hot jupiter atmospheric dynamics.

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