The Impact of Mixing Treatments on Cloud Modelling in 3D Simulations of Hot Jupiters

TL;DR

This study uses 3D hydrodynamical simulations with a coupled cloud model to explore how different mixing treatments affect cloud properties and observable spectra of Hot Jupiters, highlighting sedimentation's dominant role.

Contribution

It introduces a physically motivated mixing treatment based on global circulation and demonstrates its impact on cloud modeling and spectral predictions for Hot Jupiters.

Findings

Sedimentation efficiency significantly influences cloud thickness and radiative feedback.

Cloud scale height improvements align models better with observed spectra.

Cloud inclusion slightly increases transit asymmetry between planetary limbs.

Abstract

We present results of 3D hydrodynamical simulations of HD209458b including a coupled, radiatively-active cloud model ({\sc 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 ($K_{zz}$) based on global circulation. We find that uncertainty in the efficiency of sedimentation through the sedimentation factor $f_\mathrm{sed}$ plays a larger role in shaping cloud thickness and its radiative feedback on the local gas temperatures -- e.g. hot spot 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 which are a fraction of the pressure scale height improve agreement with the observed transmission spectra, the emission spectra, and the Spitzer 4.5 $\mathrm{\mu m}$ phase curve, although our models are still unable to reproduce the optical and UV 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 ($\lesssim 1\%$).