Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, with Application to HD 209458b

Cooper, Curtis S.; Showman, Adam P.

doi:10.1086/506312

Cited by 236 publications

(367 citation statements)

References 83 publications

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“…Such approach is, however, a complicated task for numerical reasons. For the moment, insights into the influence of atmospheric dynamics on the chemistry must be addressed either coupling a three dimensional circulation model to a simple chemical kinetics scheme, as done by Cooper & Showman (2006), or by using a simplified dynamical model and a robust chemical network, as done in this study. We plan to overcome some of the limitations of our current modelling approach, which does not consider neither photochemistry nor the coupling between horizontal and vertical mixing, in a future study.…”

Section: Discussionmentioning

confidence: 99%

“…It is, however, difficult to disentangle from such complex circulation models whether is vertical or horizontal transport the dominant disequilibrium process. In their study, Cooper & Showman (2006) argue in terms of timescale estimates, and conclude that horizontal transport is not important compared to vertical mixing.…”

Section: Introductionmentioning

confidence: 94%

“…Focusing on horizontal advection (winds), three dimensional circulation models of hot Jupiters (e.g. Cooper & Showman 2005, 2006Showman et al 2008Showman et al , 2009Heng et al 2011) find that the atmospheric circulation is dominated by a fast eastward (superrotating) jet stream that develops at low latitudes and may reach wind speeds up to a few km s −1 . Equatorial superrotation dominates the dynamics of the atmosphere in the deep regions but as we move towards higher altitudes the circulation pattern changes.…”

Section: The Radiative Modelmentioning

confidence: 99%

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The impact of atmospheric circulation on the chemistry of the hot Jupiter HD 209458b

Agúndez

Venot

Iro

et al. 2012

A&A

142

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We investigate the effects of atmospheric circulation on the chemistry of the hot Jupiter HD 209458b. We use a simplified dynamical model and a robust chemical network, as opposed to previous studies which have used a three dimensional circulation model coupled to a simple chemical kinetics scheme. The temperature structure and distribution of the main atmospheric constituents are calculated in the limit of an atmosphere that rotates as a solid body with an equatorial rotation rate of 1 km s −1 . Such motion mimics a uniform zonal wind which resembles the equatorial superrotation structure found by three dimensional circulation models. The uneven heating of this tidally locked planet causes, even in the presence of such a strong zonal wind, large temperature contrasts between the dayside and nightside, of up to 800 K. This would result in important longitudinal variations of some molecular abundances if the atmosphere were at chemical equilibrium. The zonal wind, however, acts as a powerful disequilibrium process. We identify the existence of a pressure level of transition between two regimes, which may be located between 100 and 0.1 mbar depending on the molecule. Below this transition layer, chemical equilibrium holds, while above it, the zonal wind tends to homogenize the chemical composition of the atmosphere, bringing molecular abundances in the limb and nightside regions close to chemical equilibrium values characteristic of the dayside, i.e. producing an horizontal quenching effect in the abundances. Reasoning based on timescales arguments indicates that horizontal and vertical mixing are likely to compete in HD 209458b's atmosphere, producing a complex distribution where molecular abundances are quenched horizontally to dayside values and vertically to chemical equilibrium values characteristic of deep layers. Either assuming pure horizontal mixing or pure vertical mixing, we find substantial variations in the molecular abundances at the evening and morning limbs, up to one order of magnitude for CH 4 , which may have consequences for the interpretation of transmission spectra that sample the planet's terminator of hot Jupiters.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 94%

Section: The Radiative Modelmentioning

confidence: 99%

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The impact of atmospheric circulation on the chemistry of the hot Jupiter HD 209458b

Agúndez

Venot

Iro

et al. 2012

A&A

142

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“…Atmospheric dynamics should be properly represented, instead of being crudely approximated by eddy diffusion, which does not apply to situations where the length scale of atmospheric motion exceeds a pressure scale height. Initial investigations of the coupling of atmospheric dynamics with chemistry have been performed by Cooper & Showman (2006), Burrows et al (2010), and Agúndez et al (2012), albeit with (severe) approximations taken. Cooper & Showman (2006) used a single rate coefficient to describe the conversion between carbon monoxide and methane.…”

Section: Comparison To Previous Work and Opportunities For Future Workmentioning

confidence: 99%

VULCAN: An Open-source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres

Tsai

Lyons

Grosheintz

et al. 2017

ApJS

177

238

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We present an open-source and validated chemical kinetics code for studying hot exoplanetary atmospheres, which we name VULCAN. It is constructed for gaseous chemistry from 500 to 2500 K, using a reduced C-H-O chemical network with about 300 reactions. It uses eddy diffusion to mimic atmospheric dynamics and excludes photochemistry. We have provided a full description of the rate coefficients and thermodynamic data used. We validate VULCAN by reproducing chemical equilibrium and by comparing its output versus the disequilibriumchemistry calculations of Moses et al. and Rimmer & Helling. It reproduces the models of HD 189733b and HD 209458b by Moses et al., which employ a network with nearly 1600 reactions. We also use VULCAN to examine the theoretical trends produced when the temperature-pressure profile and carbon-to-oxygen ratio are varied. Assisted by a sensitivity test designed to identify the key reactions responsible for producing a specific molecule, we revisit the quenching approximation and find that it is accurate for methane but breaks down for acetylene, because the disequilibrium abundance of acetylene is not directly determined by transport-induced quenching, but is rather indirectly controlled by the disequilibrium abundance of methane. Therefore we suggest that the quenching approximation should be used with caution and must always be checked against a chemical kinetics calculation. A one-dimensional model atmosphere with 100 layers, computed using VULCAN, typically takes several minutes to complete. VULCAN is part of the Exoclimes Simulation Platform (ESP; exoclime.net) and publicly available at https://github.com/exoclime/VULCAN.

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“…TiO and VO will therefore have a negligible effect on the availability of oxygen in the atmosphere. We use T crit = 1500 K, P crit = 10 7 Pa. Non-equilibrium chemistry, due to photochemical or mixing processes, might be important in hot Jupiter atmospheres (Cooper & Showman 2006). We are currently developing a nonequilibrium chemistry scheme, but for the sake of present tests we limit our analysis to equilibrium chemistry.…”

Section: Molecular Abundancesmentioning

confidence: 99%

Accuracy tests of radiation schemes used in hot Jupiter global circulation models

Amundsen

Baraffe

Tremblin

et al. 2014

A&A

166

229

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The treatment of radiation transport in global circulation models (GCMs) is crucial for correctly describing Earth and exoplanet atmospheric dynamics processes. The two-stream approximation and correlated-k method are currently state-of-the-art approximations applied in both Earth and hot Jupiter GCM radiation schemes to facilitate the rapid calculation of fluxes and heating rates. Their accuracy have been tested extensively for Earth-like conditions, but verification of the methods' applicability to hot Jupiter-like conditions is lacking in the literature. We are adapting the UK Met Office GCM, the Unified Model (UM), for the study of hot Jupiters, and present in this work the adaptation of the Edwards-Slingo radiation scheme based on the two-stream approximation and the correlated-k method. We discuss the calculation of absorption coefficients from high-temperature line lists and highlight the large uncertainty in the pressure-broadened line widths. We compare fluxes and heating rates obtained with our adapted scheme to more accurate discrete ordinate (DO) line-by-line (LbL) calculations ignoring scattering effects. We find that, in most cases, errors stay below 10% for both heating rates and fluxes using ∼10 k-coefficients in each band and a diffusivity factor D = 1.66. The two-stream approximation and the correlated-k method both contribute non-negligibly to the total error. We also find that using band-averaged absorption coefficients, which have previously been used in radiative-hydrodynamical simulations of a hot Jupiter, may yield errors of ∼100%, and should thus be used with caution.

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Dynamics and Disequilibrium Carbon Chemistry in Hot Jupiter Atmospheres, with Application to HD 209458b

Cited by 236 publications

References 83 publications

The impact of atmospheric circulation on the chemistry of the hot Jupiter HD 209458b

The impact of atmospheric circulation on the chemistry of the hot Jupiter HD 209458b

VULCAN: An Open-source, Validated Chemical Kinetics Python Code for Exoplanetary Atmospheres

Accuracy tests of radiation schemes used in hot Jupiter global circulation models

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