The Magnetic Mechanism for Hotspot Reversals in Hot Jupiter Atmospheres
The Magnetic Mechanism for Hotspot Reversals in Hot Jupiter Atmospheres
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DOI：
10.3847/1538-4357/ac0e2e
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发表时间：
2021-07
期刊：
影响因子：
--
通讯作者：
A. Hindle;P. Bushby;T. Rogers
中科院分区：
文献类型：
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作者：
A. Hindle;P. Bushby;T. Rogers
利用浅水磁流体系统的非线性数值模拟和赤道SWMHD波的线性分析，研究了热木星中磁力驱动的热点变化(与大气风变化有关)。在流体动力学模式中，中高纬度地转环流引起赤道热能从西向东的净转移，从而驱动热点向东偏移。我们发现，较强的环向磁场会阻碍这些能量传输循环。这导致风与磁场一致，并在热点区域产生向西的洛伦兹力加速，最终导致向西的热点偏移。在随后的线性分析中，我们发现这种反转机制与行星尺度的赤道磁Rossby波具有类似的赤道波。我们将我们的发现与三维MHD模拟进行了定量和定性的比较，确定了磁驱动热点和风反转之间的机制之间的联系。我们使用发展的理论来确定物理驱动的反转准则，该准则可以用来限制具有观测到的西移热点的超热木星的磁场。
Magnetically driven hotspot variations (which are tied to atmospheric wind variations) in hot Jupiters are studied using nonlinear numerical simulations of a shallow-water magnetohydrodynamic (SWMHD) system and a linear analysis of equatorial SWMHD waves. In hydrodynamic models, mid-to-high-latitude geostrophic circulations are known to cause a net west-to-east equatorial thermal energy transfer, which drives hotspot offsets eastward. We find that a strong toroidal magnetic field can obstruct these energy transporting circulations. This results in winds aligning with the magnetic field and generates westward Lorentz force accelerations in hotspot regions, ultimately causing westward hotspot offsets. In the subsequent linear analysis we find that this reversal mechanism has an equatorial wave analogy in terms of the planetary-scale equatorial magneto-Rossby waves. We compare our findings to three-dimensional MHD simulations, both quantitatively and qualitatively, identifying the link between the mechanics of magnetically driven hotspot and wind reversals. We use the developed theory to identify physically motivated reversal criteria, which can be used to place constraints on the magnetic fields of ultra-hot Jupiters with observed westward hotspots.