Vivien Parmentier

Abstract:

ABSTRACT We present results of 3D hydrodynamical simulations of HD209458b including a coupled, radiatively active cloud model (eddysed). We investigate the role of the mixing by replacing the default convective treatment used in previous works with a more physically relevant mixing treatment (Kzz) based on global circulation. We find that uncertainty in the efficiency of sedimentation through the sedimentation factor fsed plays a larger role in shaping cloud thickness and its radiative feedback on the local gas temperatures – e.g. hotspot shift and day-to-night side temperature gradient – than the switch in mixing treatment. We demonstrate using our new mixing treatments that simulations with cloud scales that are a fraction of the pressure scale height improve agreement with the observed transmission spectra, the emission spectra, and the Spitzer 4.5 µm phase curve, although our models are still unable to reproduce the optical and ultraviolet transmission spectra. We also find that the inclusion of cloud increases the transit asymmetry in the optical between the east and west limbs, although the difference remains small ($\lesssim 1{{\ \rm per\ cent}}$).

Abstract:

Radiative-transfer (RT) is a fundamental part of modelling exoplanet atmospheres with general circulation models (GCMs). An accurate RT scheme is required for estimates of the atmospheric energy transport and for gaining physical insight from model spectra. We implement three RT schemes for Exo-FMS: semigrey, non-grey ‘picket fence’, and real gas with correlated-k. We benchmark the Exo-FMS GCM, using these RT schemes to hot Jupiter simulation results from the literature. We perform a HD 209458b-like simulation with the three schemes and compare their results. These simulations are then post-processed to compare their observable differences. The semigrey scheme results show qualitative agreement with previous studies in line with variations seen between GCM models. The real gas model reproduces well the temperature and dynamical structures from other studies. After post-processing our non-grey picket fence scheme compares very favourably with the real gas model, producing similar transmission spectra, emission spectra, and phase curve behaviours. Exo-FMS is able to reliably reproduce the essential features of contemporary GCM models in the hot gas giant regime. Our results suggest the picket fence approach offers a simple way to improve upon RT realism beyond semigrey schemes.