Thermo-compositional Diabatic Convection in the Atmospheres of Brown Dwarfs and in Earth’s Atmosphere and Oceans

Tremblin, Pascal; Padioleau, Thomas; Phillips, Mark; Chabrier, G.; Baraffe, I.; Fromang, Sébastien; Audit, E.; Bloch, Hélène; Burgasser, Adam J.; Drummond, Benjamin; González, M.; Kestener, Pierre; Kokh, Samuel; Lagage, Pierre-Olivier; Stauffert, Maxime

doi:10.3847/1538-4357/ab05db

Cited by 56 publications

(75 citation statements)

References 34 publications

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“…To investigate the potential mechanism at play reducing the temperature gradient in brown dwarf atmospheres, Tremblin et al (2019) generalised convection and mixing length theory to include diabatic processes through thermal and compositional source terms, demonstrating that a number of convective systems in the Earth's atmosphere and oceans derive from the same instability criterion. In brown dwarf atmospheres, the thermal and compositional source terms are represented by radiative transfer and CO → CH 4 or N 2 → NH 3 chemistry, respectively, with the convective instability driven by opacity and/or mean molecular weight differences in the different chemical states.…”

Section: Future Workmentioning

confidence: 99%

“…A reduction in the atmospheric temperature gradient has also been explored in 1D models to provide an alternative explanation to the cloudy scenario for this reddening observed along the cooling sequence (Tremblin et al 2015;Tremblin et al 2016;Tremblin et al 2017a). This reduction in the temperature gradient has been linked to diabatic convection triggered by the CO/CH 4 transition in brown dwarf atmospheres (Tremblin et al 2019).…”

Section: Introductionmentioning

confidence: 99%

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A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

Phillips

Tremblin

Baraffe

et al. 2020

A&A

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We present a new set of solar metallicity atmosphere and evolutionary models for very cool brown dwarfs and self-luminous giant exoplanets, which we term ATMO 2020. Atmosphere models are generated with our state-of-the-art 1D radiative-convective equilibrium code ATMO, and are used as surface boundary conditions to calculate the interior structure and evolution of 0.001 − 0.075 M objects. Our models include several key improvements to the input physics used in previous models available in the literature. Most notably, the use of a new H-He equation of state including ab initio quantum molecular dynamics calculations has raised the mass by ∼ 1 − 2% at the stellar-substellar boundary and has altered the cooling tracks around the hydrogen and deuterium burning minimum masses. A second key improvement concerns updated molecular opacities in our atmosphere model ATMO, which now contains significantly more line transitions required to accurately capture the opacity in these hot atmospheres. This leads to warmer atmospheric temperature structures, further changing the cooling curves and predicted emission spectra of substellar objects. We present significant improvement for the treatment of the collisionally broadened potassium resonance doublet, and highlight the importance of these lines in shaping the red-optical and near-infrared spectrum of brown dwarfs. We generate three different grids of model simulations, one using equilibrium chemistry and two using non-equilibrium chemistry due to vertical mixing, all three computed self-consistently with the pressure-temperature structure of the atmosphere. We show the impact of vertical mixing on emission spectra and in colourmagnitude diagrams, highlighting how the 3.5 − 5.5 µm flux window can be used to calibrate vertical mixing in cool T-Y spectral type objects.

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Section: Future Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

Phillips

Tremblin

Baraffe

et al. 2020

A&A

Self Cite

220

262

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“…N = 0), the potential temperature is constant with atmospheric height and internal gravity waves cannot propagate (Sutherland 2010). This scenario is expected deeper in the atmosphere at higher gas pressures (for example, see Tremblin et al 2015Tremblin et al , 2019.…”

Section: Resultsmentioning

confidence: 95%

“…frequency of the wave is set by the frequency of the source for frequencies below the buoyancy frequency. In sub-stellar atmospheres the length scale of convective motions deep in the atmosphere is related to the atmospheric pressure scale height by a factor between 1 and 10 2 (Marley & Robinson 2015;Tremblin et al 2019) -for example, l conv ≈ 10 3 km in Freytag et al (2010) -varying with timescales of the order of 10 3 s (Tremblin et al 2019). 10 11 10 9 10 7 10 5 10 3 10 1 10 1 p/bar Fig.…”

Section: Resultsmentioning

confidence: 99%

The effect of internal gravity waves on cloud evolution in sub-stellar atmospheres

Parent

Falconer

Lee

et al. 2020

A&A

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Context. Sub-stellar objects exhibit photometric variability, which is believed to be caused by a number of processes, such as magnetically-driven spots or inhomogeneous cloud coverage. Recent sub-stellar models have shown that turbulent flows and waves, including internal gravity waves, may play an important role in cloud evolution. Aims. The aim of this paper is to investigate the effect of internal gravity waves on dust nucleation and dust growth, and whether observations of the resulting cloud structures could be used to recover atmospheric density information. Methods. For a simplified atmosphere in two dimensions, we numerically solved the governing fluid equations to simulate the effect on dust nucleation and mantle growth as a result of the passage of an internal gravity wave. Furthermore, we derived an expression that relates the properties of the wave-induced cloud structures to observable parameters in order to deduce the atmospheric density.Results. Numerical simulations show that the density, pressure, and temperature variations caused by gravity waves lead to an increase of the dust nucleation rate by up to a factor 20, and an increase of the dust mantle growth rate by up to a factor 1.6, compared to their equilibrium values. Through an exploration of the wider sub-stellar parameter space, we show that in absolute terms, the increase in dust nucleation due to internal gravity waves is stronger in cooler (T dwarfs) and TiO 2 -rich sub-stellar atmospheres. The relative increase, however, is greater in warm (L dwarf) and TiO 2 -poor atmospheres due to conditions that are less suited for efficient nucleation at equilibrium. These variations lead to banded areas in which dust formation is much more pronounced, similar to the cloud structures observed on Earth.Conclusions. We show that internal gravity waves propagating in the atmosphere of sub-stellar objects can produce banded clouds structures similar to that observed on Earth. We propose a method with which potential observations of banded clouds could be used to estimate the atmospheric density of sub-stellar objects.

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“…This assessment confirms our conclusion that the upward transport of condensable elements through the atmosphere by mixing is indeed the key to understand cloud formation. However, challenges arise from the choice of the inner boundary condition (Carone et al 2019), chemical gradients (Tremblin et al 2019), and the need to include cloud particle feedback in order to test mixing parameterisations. A particular interesting case will be the ultra-hot Jupiters where day and night-sides can be expected to have very distinct (vertical) mixing patterns and scales.…”

Section: Introductionmentioning

confidence: 99%

Dust in brown dwarfs and extra-solar planets

Woitke

Helling

Gunn

2020

A&A

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The precipitation of cloud particles in brown dwarf and exoplanet atmospheres establishes an ongoing downward flux of condensable elements. To understand the efficiency of cloud formation, it is therefore crucial to identify and quantify the replenishment mechanism that is able to compensate for these local losses of condensable elements in the upper atmosphere, and to keep the extrasolar weather cycle running. In this paper, we introduce a new cloud formation model by combining the cloud particle moment method we described previously with a diffusive mixing approach, taking into account turbulent mixing and gas-kinetic diffusion for both gas and cloud particles. The equations are of diffusion-reaction type and are solved time-dependently for a prescribed 1D atmospheric structure, until the model has relaxed toward a time-independent solution. In comparison to our previous models, the new hot-Jupiter model results (Teff ≈ 2000 K, log g = 3) show fewer but larger cloud particles that are more concentrated towards the cloud base. The abundances of condensable elements in the gas phase are featured by a steep decline above the cloud base, followed by a shallower, monotonous decrease towards a plateau, the level of which depends on temperature. The chemical composition of the cloud particles also differs significantly from our previous models. Through the condensation of specific condensates such as Mg2SiO4[s] in deeper layers, certain elements, such as Mg, are almost entirely removed early from the gas phase. This leads to unusual (and non-solar) element ratios in higher atmospheric layers, which then favours the formation of SiO[s] and SiO2[s], for example, rather than MgSiO3[s]. These condensates are not expected in phase-equilibrium models that start from solar abundances. Above the main silicate cloud layer, which is enriched with iron and metal oxides, we find a second cloud layer made of Na2S[s] particles in cooler models (Teff ⪅ 1400 K).

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Thermo-compositional Diabatic Convection in the Atmospheres of Brown Dwarfs and in Earth’s Atmosphere and Oceans

Cited by 56 publications

References 34 publications

A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

A new set of atmosphere and evolution models for cool T–Y brown dwarfs and giant exoplanets

The effect of internal gravity waves on cloud evolution in sub-stellar atmospheres

Dust in brown dwarfs and extra-solar planets

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