The Impact of Phase Equilibrium Cloud Models on GCM Simulations of GJ~1214b

TL;DR

This study uses a phase-equilibrium cloud model coupled with a GCM to analyze cloud effects on GJ 1214b, revealing high metallicity and extensive clouds are needed to match observations, affecting atmospheric dynamics and phase curves.

Contribution

First to couple the { extsc{EddySed}} cloud model with the { extsc{Unified Model}} GCM for GJ 1214b, exploring cloud impacts on atmospheric structure and observable properties.

Findings

High metallicity ($100\times$ solar) and low sedimentation factor ($f_{sed}=0.1$) best match observations.

Clouds reduce phase curve amplitude and phase offset, affecting observable atmospheric signatures.

Introduction of nightside shortwave heating alters jet speeds in the GCM.

Abstract

We investigate the impact of clouds on the atmosphere of GJ~1214b using the radiatively-coupled, phase-equilibrium cloud model {\sc EddySed} coupled to the {\sc Unified Model} general circulation model. We find that, consistent with previous investigations, high metallicity ($100\times$ solar) and clouds with large vertical extents (a sedimentation factor of $f_\mathrm{sed} = 0.1$) are required to best match the observations, although metallicities even higher than those investigated here may be required to improve agreement further. We additionally find that in our case which best matches the observations ($f_\mathrm{sed}=0.1$), the velocity structures change relative to the clear sky case with the formation of a superrotating jet being suppressed, although further investigation is required to understand the cause of the suppression. The increase in cloud extent with $f_\mathrm{sed}$ results in a cooler planet due to a higher albedo, causing the atmosphere to contract. This also results in a reduced day-night contrast seen in the phase curves, although the introduction of cloud still results in a reduction of the phase offset. We additionally investigate the impact the the {\sc Unified Model}'s pseudo-spherical irradiation scheme on the calculation of heating rates, finding that the introduction of nightside shortwave heating results in slower mid-latitude jets compared to the plane parallel irradiation scheme used in previous works. We also consider the impact of a gamma distribution, as opposed to a log-normal distribution, for the distribution of cloud particle radii and find the impact to be relatively minor.