[论文解读] Patchy nightside clouds on ultra-hot Jupiters: General Circulation Model simulations with radiatively active cloud tracers

Thaddeus D. Komacek, Xianyu Tan+2 more|arXiv (Cornell University)|May 16, 2022

Stellar, planetary, and galactic studies参考文献 244被引用 54

一句话总结

本研究在一般环流模型（GCM）中使用具有辐射活性的云示踪物，模拟了超热木星的分块夜面云层，发现动力过程与辐射反馈导致部分云覆盖，从而加热低层大气并改变发射光谱。模拟结果表明，夜面云层因高层逆温层而被深藏于大气深处，对透射光谱影响甚微，但对相位依赖的发射光谱具有可探测的影响。

ABSTRACT

The atmospheres of ultra-hot Jupiters have been characterized in detail through recent phase curve and low- and high-resolution emission and transmission spectroscopic observations. Previous numerical studies have analyzed the effect of the localized recombination of hydrogen on the atmospheric dynamics and heat transport of ultra-hot Jupiters, finding that hydrogen dissociation and recombination lead to a reduction in the day-to-night contrasts of ultra-hot Jupiters relative to previous expectations. In this work, we add to previous efforts by also considering the localized condensation of clouds in the atmospheres of ultra-hot Jupiters, their resulting transport by the atmospheric circulation, and the radiative feedback of clouds on the atmospheric dynamics. To do so, we include radiatively active cloud tracers into the existing MITgcm framework for simulating the atmospheric dynamics of ultra-hot Jupiters. We take cloud condensate properties appropriate for the high-temperature condensate corundum from CARMA cloud microphysics models. We conduct a suite of GCM simulations with varying cloud microphysical and radiative properties, and we find that partial cloud coverage is a ubiquitous outcome of our simulations. This patchy cloud distribution is inherently set by atmospheric dynamics in addition to equilibrium cloud condensation, and causes a cloud greenhouse effect that warms the atmosphere below the cloud deck. Nightside clouds are further sequestered at depth due to a dynamically induced high-altitude thermal inversion. We post-process our GCMs with the Monte Carlo radiative transfer code gCMCRT and find that the patchy clouds on ultra-hot Jupiters do not significantly impact transmission spectra but can affect their phase-dependent emission spectra.

研究动机与目标

• 理解云凝结与辐射反馈在塑造超热木星大气动力学中的作用。
• 填补在极端温度系外行星大气中非均匀云覆盖及其辐射效应建模方面的空白。
• 研究云分布与辐射反馈如何影响大气环流与热力结构。
• 考察云特性对可观测发射光谱与透射光谱的影响。
• 评估超热木星气候中大气动力学、云微物理与辐射传输之间的耦合关系。

提出的方法

• 将具有辐射活性的云示踪物整合进MITgcm框架，以模拟超热木星的大气动力学。
• 采用来自CARMA模型的刚玉云微物理参数，以模拟与超热木星相关的高温凝结物。
• 开展一系列GCM模拟，涵盖不同的云微物理与辐射特性（如颗粒尺寸、消光截面）。
• 利用蒙特卡罗辐射传输代码gCMCRT对GCM输出进行后处理，生成合成光谱。
• 在强温度梯度与高恒星辐照条件下，模拟云的凝结与输送过程。
• 分析云辐射效应对大气温度结构与风场模式的反馈作用。

实验结果

研究问题

• RQ1 引入具有辐射活性的云示踪物如何影响超热木星模拟中的云分布与大气动力学？
• RQ2 大气动力学在形成分块而非均匀的夜面云覆盖中起到何种作用？
• RQ3 云辐射反馈如何影响大气热力结构与云的垂直分布？
• RQ4 分块云层对相位依赖的发射光谱与透射光谱分别产生何种影响？
• RQ5 高层逆温层的存在如何影响云的封存与云层深度？

主要发现

• 分块云覆盖是模拟的普遍结果，由大气动力学与平衡凝结驱动，而非均匀云层形成。
• 云层产生温室效应，使云层下方的大气变暖，尤其在部分云覆盖区域更为显著。
• 夜面云层因动力诱导的高层逆温层而被深藏于大气深处，限制了其垂直扩展。
• 相位依赖的发射光谱受分块云分布影响，而透射光谱则基本保持不变。
• 云颗粒尺寸减小与云消光截面增强会引发更强的辐射反馈，提高云质量混合比峰值，并改变垂直湍流混合效率。