scholarly journals Atmospheric circulation of brown dwarfs and directly imaged exoplanets driven by cloud radiative feedback: global and equatorial dynamics

2021 ◽  
Vol 502 (2) ◽  
pp. 2198-2219
Author(s):  
Xianyu Tan ◽  
Adam P Showman
Keyword(s):  
Time Evolution ◽  
Atmospheric Circulation ◽  
Rotation Period ◽  
Brown Dwarfs ◽  
Giant Planets ◽  
Time Variability ◽  
Equatorial Waves ◽  
Viewing Angle ◽  
Radiative Feedback ◽  
Cloud Radiative Feedback

ABSTRACT Brown dwarfs, planetary-mass objects and directly imaged giant planets exhibit significant observational evidence for active atmospheric circulation, raising critical questions about mechanisms driving the circulation, its fundamental nature and time variability. Our previous work has demonstrated the crucial role of cloud radiative feedback on driving a vigorous atmospheric circulation using local models that assume a Cartesian geometry and constant Coriolis parameters. In this study, we extend the models to a global geometry and explore properties of the global dynamics. We show that, under relatively strong dissipation in the bottom layers of the model, horizontally isotropic vortices are prevalent at mid-to-high latitudes while large-scale zonally propagating waves are dominant at low latitudes near the observable layers. The equatorial waves have both eastward and westward phase speeds, and the eastward components with typical velocities of a few hundred  m s−1 usually dominate the equatorial time variability. Lightcurves of the global simulations show variability with amplitudes from 0.5 per cent to a few percent depending on the rotation period and viewing angle. The time evolution of simulated lightcurves is critically affected by the equatorial waves, showing wave beating effects and differences in the lightcurve periodicity to the intrinsic rotation period. The vertical extent of clouds is the largest at the equator and decreases poleward due to the increasing influence of rotation with increasing latitude. Under weaker dissipation in the bottom layers, strong and broad zonal jets develop and modify wave propagation and lightcurve variability. Our modelling results help to qualitatively explain several features of observations of brown dwarfs and directly imaged giant planets, including puzzling time evolution of lightcurves, a slightly shorter period of variability in IR than in radio wavelengths, and the viewing angle dependence of variability amplitude and IR colors.

Multireanalysis Comparison of Variability in Column Water Vapor and Its Analysis Increment Associated with the Madden–Julian Oscillation

2015 ◽  
Vol 28 (2) ◽  
pp. 793-808 ◽  
Author(s):  
Satoru Yokoi
Keyword(s):  
Water Vapor ◽  
Forecast Model ◽  
Precipitation Anomaly ◽  
Boreal Winter ◽  
Madden Julian Oscillation ◽  
Radiative Feedback ◽  
Feedback Strength ◽  
Advection Term ◽  
Forecast Models ◽  
Cloud Radiative Feedback

Abstract This study conducts a multireanalysis comparison of variability in column water vapor (CWV) represented in three reanalysis products [Japanese 55-year Reanalysis Project (JRA-55), JRA-25, and ECMWF Interim Re-Analysis (ERA-Interim)] associated with the Madden–Julian oscillation (MJO) in boreal winter, with emphasis on CWV tendency simulated by forecast models and analysis increment calculated by data assimilation systems. Analyses of these variables show that, while the JRA-55 forecast model is able to simulate eastward propagation of the CWV anomaly, this model tends to weaken its amplitude. The multireanalysis comparison of the analysis increment further reveals that this weakening bias is related to excessively weak cloud radiative feedback represented by the model. This bias in the feedback strength makes anomalous moisture supply by the vertical advection term in the CWV budget equation too insensitive to precipitation anomaly, resulting in reduction of the amplitude of CWV anomaly. ERA-Interim has a nearly opposite feature: the forecast model represents excessively strong feedback. These results imply the necessity of accurate representation of the cloud radiative feedback strength for a short-term MJO forecast and may be evidence to support the argument that this feedback is essential for the existence of MJO. Furthermore, this study demonstrates that the multireanalysis comparison of the analysis increment will provide useful information for examining model biases and potentially for estimating parameters that are difficult to estimate from observational data, such as gross moist stability.

scholarly journals Properties which cannot be explained by Planetary Nebulae's progenitors

1997 ◽  
Vol 180 ◽  
pp. 367-367
Author(s):  
Noam Soker
Keyword(s):  
Main Sequence ◽  
Brown Dwarfs ◽  
Giant Planets ◽  
Main Sequence Stars ◽  
Substellar Objects ◽  
Earth Like Planets ◽  
Low Mass ◽  
Inner Region ◽  
Central Stars

Stellar binary companions account for bipolar PNe (∼ 11% of all PNe1), and some ellipticalls (22%2). The rest of axisymmetrical PNe (40% to 60% of all PNe) are due to substellar objects (planets and brown dwarfs)3. This classification of axi symmetrical PNe suggests that substellar objects are commonly present within several × AU around main sequence stars, and that several substellar objects must be present around most main sequence stars3. Some substellar and low mass stellar companions will enter the primary envelope only as the primary reaches the upper AGB. Thus, the early mass loss episode will be spherical, leading to the formation of a spherical halo around an elliptical inner region. Gas giant planets and brown dwarfs close to the primary, will not allow Earth-like planets to have stable orbits. Systems with no Jupiter-like planets will allow Earth-like planets to be present. These stars will form spherical PNe (10%-20% of all PNe, including spherically ejected PNe that have been deformed by the ISM through which they move4). Systems with substellar objects at large separation, as Jupiter in the solar system, will also allow Earth-like planets to be present. These systems will form PNe with spherical halo. Therefore, life may have been present in planets around the central stars of round PNe and elliptical PNe with round halos.

scholarly journals Atmospheric dynamics on tidally locked Earth-like planets in the habitable zone of an M dwarf star

2013 ◽  
Vol 8 (S299) ◽  
pp. 376-377 ◽  
Author(s):  
Ludmila Carone ◽  
Rony Keppens ◽  
Leen Decin
Keyword(s):  
Atmospheric Circulation ◽  
Large Scale ◽  
Rotation Period ◽  
Circulation Model ◽  
Return Flow ◽  
Parameter Study ◽  
Global Circulation Model ◽  
Dwarf Star ◽  
Global Circulation ◽  
M Dwarf

AbstractWe investigated the large scale atmospheric circulation of Gl581g, a potentially habitable planet around an M dwarf star, using an idealized dry global circulation model (GCM) with simplified thermal forcing as a first step towards a systematic extended parameter study. The results are compared with the work of Joshi et al. (1997) who investigated a tidally-locked habitable Earth analogue with less than half the rotation period of Gl581g. The extent, form and strength of the atmospheric circulation in each model generally agree with each other, even though the models differ in key parameters such as planetary radius, surface gravity, forcing scheme and rotation period. The substellar point is associated with an uprising direct circulation-branch of a Hadley-like cell with return flow over the poles. It is compelling to assume that the substellar point of a tidally locked terrestrial exoplanet behaves dynamically like the Earth's tropic associated with clouds and precipitation, making it an ideal target for habitability.

scholarly journals AKARI near-infrared spectroscopy of brown dwarfs

2009 ◽  
Vol 5 (H15) ◽  
pp. 545-545
Author(s):  
Issei Yamamura ◽  
Takashi Tsuji ◽  
Toshihiko Tanabé ◽  
Tadashi Nakajima
Keyword(s):  
Infrared Spectroscopy ◽  
Low Temperature ◽  
Near Infrared Spectroscopy ◽  
Near Infrared ◽  
Infrared Camera ◽  
Brown Dwarfs ◽  
Giant Planets ◽  
Dust Clouds ◽  
Molecular Abundances ◽  
Observation Programme

Brown dwarfs (hereafter BDs) are of particular interest because of their extremely low-temperature atmospheres for comparison with atmospheres of giant planets. Aiming to obtain clues to understand the formation and disappearance of dust clouds and molecular abundances in BD photospheres, we conducted an observation programme of space-borne near-infrared spectroscopy of bright BDs with the Infrared Camera (IRC) on-board AKARI.

Clouds in brown dwarfs and giant planets

2013 ◽  
Vol 334 (1-2) ◽  
pp. 40-43 ◽  
Author(s):  
S. Metchev ◽  
D. Apai ◽  
J. Radigan ◽  
É. Artigau ◽  
A. Heinze ◽  
...  
Keyword(s):  
Brown Dwarfs ◽  
Giant Planets

scholarly journals The Sonora Substellar Atmosphere Models. II. Cholla: A Grid of Cloud-free, Solar Metallicity Models in Chemical Disequilibrium for the JWST Era

2021 ◽  
Vol 923 (2) ◽  
pp. 269
Author(s):  
Theodora Karalidi ◽  
Mark Marley ◽  
Jonathan J. Fortney ◽  
Caroline Morley ◽  
Didier Saumon ◽  
...  
Keyword(s):  
Near Infrared ◽  
Chemical Species ◽  
Brown Dwarfs ◽  
Eddy Diffusion ◽  
Giant Planets ◽  
James Webb Space Telescope ◽  
Solar Metallicity ◽  
Composition Profiles ◽  
Thermochemical Equilibrium

Abstract Exoplanet and brown dwarf atmospheres commonly show signs of disequilibrium chemistry. In the James Webb Space Telescope (JWST) era, high-resolution spectra of directly imaged exoplanets will allow the characterization of their atmospheres in more detail, and allow systematic tests for the presence of chemical species that deviate from thermochemical equilibrium in these atmospheres. Constraining the presence of disequilibrium chemistry in these atmospheres as a function of parameters such as their effective temperature and surface gravity will allow us to place better constraints on the physics governing these atmospheres. This paper is part of a series of works presenting the Sonora grid of atmosphere models. In this paper, we present a grid of cloud-free, solar metallicity atmospheres for brown dwarfs and wide-separation giant planets with key molecular species such as CH4, H2O, CO, and NH3 in disequilibrium. Our grid covers atmospheres with T eff ∈ [500 K, 1300 K], log g ∈ [3.0, 5.5] (cgs) and an eddy diffusion parameter of log K zz = 2 , 4 and 7 (cgs). We study the effect of different parameters within the grid on the temperature and composition profiles of our atmospheres. We discuss their effect on the near-infrared colors of our model atmospheres and the detectability of CH4, H2O, CO, and NH3 using the JWST. We compare our models against existing MKO and Spitzer observations of brown dwarfs and verify the importance of disequilibrium chemistry for T dwarf atmospheres. Finally, we discuss how our models can help constrain the vertical structure and chemical composition of these atmospheres.

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