The Effect of Disequilibrium Carbon Chemistry on the Atmospheric Circulation and Phase Curves of Hot Jupiter HD 189733b
The Effect of Disequilibrium Carbon Chemistry on the Atmospheric Circulation and Phase Curves of Hot Jupiter HD 189733b
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不平衡碳化学对热木星 HD 189733b 大气环流和相位曲线的影响
DOI：
10.3847/1538-4357/ab2598
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
R. Lupu
中科院分区：
文献类型：
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作者：
M. Steinrueck;V. Parmentier;A. Showman;J. Lothringer;R. Lupu
在炎热的木星系外行星上，强烈的水平风和垂直风应该比化学反应恢复化学平衡的速度快得多，使重要的吸收物质CH$4和CO的丰度均匀。这种通常被大气环流模式(GCMS)忽略的影响被认为是观测到的红外光曲线与GCMS预测的不一致的原因：在几个热木星的夜面上，GCMS预测出太大的流出通量，特别是在斯皮策4.5美元/亩/米波段。我们对SPARC/MITgcm进行了修正，使之包含了CH$4$、CO和H$2$O的不平衡丰度，假定CH$4$/CO比值在整个模拟区域内是恒定的。我们对热木星HD 189733b进行了8个CH_4$/CO比的模拟。在更可能的CO主导区，我们发现与平衡化学情况相比，大区域的温度变化约为50K。这种影响大到足以影响预测的发射光谱，因此应该包括在平衡温度低于1300K的热木星的GCM中。我们发现，在甲烷吸收较强的区域，包括斯皮策3.6和8美元/百万带，光谱受到不平衡丰度的强烈影响。我们预计化学猝灭将在3.6美元/亩波段产生更大的夜间通量，这与观测结果形成了鲜明的对比。同时，我们发现，由于CO和H$2$O的不透明度变化相互抵消，对4.5×10-6波段的预报观测值几乎没有影响。因此，我们得出结论，不平衡的碳化学不能解释4.5美元/亩波段观测到的低夜间通量。
On hot Jupiter exoplanets, strong horizontal and vertical winds should homogenize the abundances of the important absorbers CH$_4$ and CO much faster than chemical reactions restore chemical equilibrium. This effect, typically neglected in general circulation models (GCMs), has been suggested as explanation for discrepancies between observed infrared lightcurves and those predicted by GCMs: On the nightsides of several hot Jupiters, GCMs predict outgoing fluxes that are too large, especially in the Spitzer 4.5 $\mu$m band. We modified the SPARC/MITgcm to include disequilibrium abundances of CH$_4$, CO and H$_2$O by assuming that the CH$_4$/CO ratio is constant throughout the simulation domain. We ran simulations of hot Jupiter HD 189733b with 8 CH$_4$/CO ratios. In the more likely CO-dominated regime, we find temperature changes of $\sim$50 K compared to the equilibrium chemistry case across large regions. This effect is large enough to affect predicted emission spectra and should thus be included in GCMs of hot Jupiters with equilibrium temperatures below 1300 K. We find that spectra in regions with strong methane absorption, including the Spitzer 3.6 and 8 $\mu$m bands, are strongly impacted by disequilibrium abundances. We expect chemical quenching to result in much larger nightside fluxes in the 3.6 $\mu$m band, in stark contrast to observations. Meanwhile, we find almost no effect on predicted observations in the 4.5 $\mu$m band, as the opacity changes due to CO and H$_2$O offset each other. We thus conclude that disequilibrium carbon chemistry cannot explain the observed low nightside fluxes in the 4.5 $\mu$m band.