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arXiv · 1603.09098

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

E. K. H. Lee·I. Dobbs-Dixon·Ch. Helling·K. Bognar·P. Woitke
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Abstract

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. We investigate the thermo-hydrodynamic properties of cloud formation processes in the atmospheres of hot Jupiter exoplanets. 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 \textit{effective medium theory} and Mie theory is applied to calculate the wavelength dependent opacity of the cloud component. 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 $\mu$m) at pressures less than 1 bar with hotter equatorial regions containing the smallest grains. Denser cloud structures occur near terminator regions and deeper ($\sim$ 1 bar) atmospheric layers. Silicate materials such as MgSiO$_{3}$[s] are found to be abundant at mid-high latitudes, while TiO$_{2}$[s] and SiO$_{2}$[s] dominate the equatorial regions.

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E. K. H. Lee, I. Dobbs-Dixon, Ch. Helling, K. Bognar, P. Woitke. 2016-03-30. Dynamic mineral clouds on HD 189733b I. 3D RHD with kinetic, non-equilibrium cloud formation. https://doi.org/10.1051/0004-6361/201628606

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