Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: effects of rotation
Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: effects of rotation
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由云辐射反馈驱动的褐矮星和直接成像的系外行星的大气环流：旋转的影响
DOI：
10.1093/mnras/stab060
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发表时间：
2020
影响因子：
4.8
通讯作者：
A. Showman
中科院分区：
文献类型：
--
作者：
Xianyu Tan;A. Showman
对褐矮星（BD）、自由漂浮的行星质量物体和直接成像的太阳系外巨行星（EGP）的观测展示了大规模天气的丰富证据。云辐射反馈已被认为是驱动BD和直接成像EGP上剧烈大气环流的潜在机制，但尚未在相关条件下的三维动力学模型中得到证实。在这里，我们提出了一系列大气环流模型，这些模型将动力学与理想化云的形成及其辐射效应自洽地耦合起来。我们证明，云辐射反馈可以触发和自我维持剧烈的大气环流。典型的等压温度变化可达 100 K 以上，水平平均风速可达数百 $\, {\rm m\, s^{-1}}$。环流以云形成和晴空涡旋为主，其演变时间从几个小时到几十小时不等。主涡的典型水平长度尺度接近罗斯贝变形半径，显示出与旋转速率倒数的线性相关性。更强的旋转往往会削弱蒸汽和云的垂直传输，导致云整体变薄。由于风暴的统计演化，域平均出射辐射通量在数十小时的时间尺度上表现出变化。模型中不同的底部边界条件可能导致可观测层附近的环流质量不同。由云辐射反馈驱动的环流代表了一种强大的机制，产生显着的表面不均匀性以及不规则的通量时间变化。我们的结果对尘土飞扬的 BD 和 EGP 的近红外 (IR) 颜色具有重要意义，包括近红外颜色幅度图中的散射和依赖于观察几何形状的近红外颜色。
Observations of brown dwarfs (BDs), free-floating planetary-mass objects, and directly imaged extrasolar giant planets (EGPs) exhibit rich evidence of large-scale weather. Cloud radiative feedback has been proposed as a potential mechanism driving the vigorous atmospheric circulation on BDs and directly imaged EGPs, and yet it has not been demonstrated in three-dimensional dynamical models at relevant conditions. Here, we present a series of atmospheric circulation models that self-consistently couple dynamics with idealized cloud formation and its radiative effects. We demonstrate that vigorous atmospheric circulation can be triggered and self-maintained by cloud radiative feedback. Typical isobaric temperature variation could reach over 100 K and horizontally averaged wind speed could be several hundreds of $\, {\rm m\, s^{-1}}$. The circulation is dominated by cloud-forming and clear-sky vortices that evolve over time-scales from several to tens of hours. The typical horizontal length-scale of dominant vortices is closed to the Rossby deformation radius, showing a linear dependence on the inverse of rotation rate. Stronger rotation tends to weaken vertical transport of vapour and clouds, leading to overall thinner clouds. Domain-mean outgoing radiative flux exhibits variability over time-scales of tens of hours due to the statistical evolution of storms. Different bottom boundary conditions in the models could lead to qualitatively different circulation near the observable layer. The circulation driven by cloud radiative feedback represents a robust mechanism generating significant surface inhomogeneity as well as irregular flux time variability. Our results have important implications for near-infrared (IR) colours of dusty BDs and EGPs, including the scatter in the near-IR colour–magnitude diagram and the viewing-geometry-dependent near-IR colours.
DOI：
10.3847/1538-3881/ab9114
发表时间：
2020
期刊：
The Astronomical Journal
影响因子：
--
作者：
Miles, Brittany E.;Skemer, Andrew J.;Morley, Caroline V.;Marley, Mark S.;Fortney, Jonathan J.;Allers, Katelyn N.;Faherty, Jacqueline K.;Geballe, Thomas R.;Visscher, Channon;Schneider, Adam C.
通讯作者：
Schneider, Adam C.
DOI：
10.3847/1538-4357/ab6ef2
发表时间：
2020-05
期刊：
The Astrophysical Journal
影响因子：
--
作者：
M. Millar-Blanchaer;J. Girard;T. Karalidi;M. Marley;R. G. van Holstein;S. Sengupta;D. Mawet;T. Kataria;F. Snik;J. D. Boer;R. Jensen-Clem;A. Vigan;S. Hinkley
通讯作者：
M. Millar-Blanchaer;J. Girard;T. Karalidi;M. Marley;R. G. van Holstein;S. Sengupta;D. Mawet;T. Kataria;F. Snik;J. D. Boer;R. Jensen-Clem;A. Vigan;S. Hinkley
年轻的多云 L 矮星伴星 VHS J1256–1257 b 的强烈近红外光谱变化
DOI：
10.3847/2041-8213/ab8197
发表时间：
2020
期刊：
The Astrophysical Journal
影响因子：
--
作者：
Bowler, Brendan P.;Zhou, Yifan;Morley, Caroline V.;Kataria, Tiffany;Bryan, Marta L.;Benneke, Björn;Batygin, Konstantin
通讯作者：
Batygin, Konstantin