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Dynamic mineral clouds on HD 189733b : I. 3D RHD with kinetic, non-equilibrium cloud formation

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Date
10/10/2016
Author
Lee, G.
Dobbs-Dixon, I.
Helling, Ch.
Bognar, K.
Woitke, P.
Funder
European Research Council
Grant ID
257431 257431
Keywords
Planets and satellites: atmospheres
Planets and satellites: individual: HD 189733b
Hydrodynamics
Radiative transfer
Methods: numerical
QB Astronomy
QC Physics
NDAS
BDC
R2C
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Abstract
Context. Observations of exoplanet atmospheres have revealed the presence of cloud particles in their atmospheres. 3D modelling of cloud formation in atmospheres of extrasolar planets coupled to the atmospheric dynamics has long been a challenge. Aims. We investigate the thermo-hydrodynamic properties of cloud formation processes in the atmospheres of hot Jupiter exoplanets. Methods. We simulate the dynamic atmosphere of HD 189733b with a 3D model that couples 3D radiative-hydrodynamics with a kinetic, microphysical mineral cloud formation module designed for RHD/GCM exoplanet atmosphere simulations. Our simulation includes the feedback effects of cloud advection and settling, gas phase element advection and depletion/replenishment and the radiative effects of cloud opacity. We model the cloud particles as a mix of mineral materials which change in size and composition as they travel through atmospheric thermo-chemical environments. All local cloud properties such as number density, grain size and material composition are time-dependently calculated. Gas phase element depletion as a result of cloud formation is included in the model. In situ effective medium theory and Mie theory is applied to calculate the wavelength dependent opacity of the cloud component. Results. We present a 3D cloud structure of a chemically complex, gaseous atmosphere of the hot Jupiter HD 189733b. Mean cloud particle sizes are typically sub-micron (0.01−0.5 μm) at pressures less than 1 bar with hotter equatorial regions containing the smallest grains. Denser cloud structures occur near terminator regions and deeper (~1 bar) atmospheric layers. Silicate materials such as MgSiO3[s] are found to be abundant at mid-high latitudes, while TiO2[s] and SiO2[s] dominate the equatorial regions. Elements involved in the cloud formation can be depleted by several orders of magnitude. Conclusions. The interplay between radiative-hydrodynamics and cloud kinetics leads to an inhomogeneous, wavelength dependent opacity cloud structure with properties differing in longitude, latitude and depth. This suggests that transit spectroscopy would sample a variety of cloud particles properties (sizes, composition, densities).
Citation
Lee , G , Dobbs-Dixon , I , Helling , C , Bognar , K & Woitke , P 2016 , ' Dynamic mineral clouds on HD 189733b : I. 3D RHD with kinetic, non-equilibrium cloud formation ' , Astronomy & Astrophysics , vol. 594 , A48 . https://doi.org/10.1051/0004-6361/201628606
Publication
Astronomy & Astrophysics
Status
Peer reviewed
DOI
https://doi.org/10.1051/0004-6361/201628606
ISSN
0004-6361
Type
Journal article
Rights
Copyright © ESO 2016. This work is made available online in accordance with the publisher’s policies. This is the final published version of the work, which was originally published at: https://dx.doi.org/10.1051/0004-6361/201628606
Description
Funding: European community under the FP7 ERC starting grant 257431 (G.L., Ch. H.).
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  • University of St Andrews Research
URL
https://arxiv.org/abs/1603.09098
URI
http://hdl.handle.net/10023/9698

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