Coupled 3D climate and cloud microphysics model for WASP-107 b

In the era of JWST and upcoming space- and ground-based observatories (PLATO, ARIEL, ELT, and TMT), we will see an unprecedented surge in data, including phase curves and morning–evening asymmetry measurements. To understand the physical processes that govern the 3D structure of the observed exoplanet atmosphere, a state-of-the-art 3D climate model and cloud microphysics are required. 

In this work, we couple ExoRad (a 3D climate model) with the DRIFT (cloud microphysics model), in which clouds (self-consistently generated) are used as a new non-grey opacity source in ExoRad, incorporating both heating and cooling effects. As cloud properties are intrinsically linked to the thermodynamic state and vice versa, we recalculate the cloud properties using the updated thermodynamic structure of the atmosphere and iterate between the DRIFT and the ExoRad, which quickly converges in a few iterations.

We apply this method to WASP-107b, an inflated warm gas giant with an equilibrium temperature of 770 K and an abnormally high interior temperature. WASP-107 b has been observed to host silicon clouds, morning–evening asymmetry, and disequilibrium chemical species (CH4 and SO2), linked to atmospheric dynamics. We run the model for several metallicity levels, ranging from solar to 40 times solar metallicity, based on the observed constraints.
We find that clouds have a significant impact on the overall thermal structure in all model runs. The presence of clouds makes the planet's atmosphere hotter in the infrared photosphere, producing a weak thermal inversion. The coupling among zonal wind jet, thermal structure and cloud microphysics processes is required to reproduce the observed 150–200 K temperature difference between the morning and evening terminators. We also observe the thermodynamic trends in the metallicity space, which includes the zonal wind jet, day-night and morning-evening temperature differences, and vertical wind structure.