Atmospheric Circulation of Hot Jupiters: Implications of Disequilibrium Chemistry and Photochemical Hazes

Abstract

Hot Jupiters are the only class of exoplanets for which detailed atmospheric characterization is possible with current instruments. Because of the strong horizontal temperature contrasts and the global-scale circulation expected on these planets, simulations with three-dimensional global circulation models (GCMs) are needed to place observations in context. Two effects that previously have been neglected in GCMs are transport-induced disequilibrium chemistry and photochemical hazes. Both have the potential to substantially change temperature structure, atmospheric circulation and predicted spectra. In the first part of this dissertation, I simulated the effects of disequilibrium abundances of methane, carbon monoxide and water on radiative transfer, temperature structure and phase curves in a GCM of hot Jupiter HD 189733b. The temperature changes by 50 to 100 K for the range of methane abundances expected from chemical kinetics calculations, with the dayside cooling and the nightside warming. I found little effect on the model-predicted 4.5 µm phase curve but large changes to the 3.6µm phase curve. This disproves a previous hypothesis that disequilibrium chemistry could explain the low nightside fluxes observed in the 4.5 µm band. In the second part, I developed a model simulating hazes as passive tracers in a GCM to study the 3D distribution of photochemical hazes in the atmospheres of hot Jupiters. The results show that the haze mass mixing ratio varies horizontally by over an order of magnitude. Contrary to previous predictions, hazes with small particle sizes (<30 nm) are more abundant at the nightside and morning terminator than at the dayside and evening terminator. Finally, I included haze radiative feedback in the GCM to investigate how heating and cooling by photochemical hazes change temperature structure and atmospheric circulation. The dayside heats up by hundreds of Kelvin at low pressures. The response of the atmospheric circulation to the haze radiative feedback strongly depends on the assumed haze optical properties. For soot-like hazes, the jet strength somewhat decreases, and the haze distribution remains qualitatively similar to simulations without haze radiative feedback. For refractive indices resembling Titan-type hazes, the jet strength increases dramatically, leading to much higher haze abundances near the evening terminator.