Abstract

Water clouds are expected to form on Y dwarfs and giant planets with equilibrium temperatures near or below that of Earth, drastically altering their atmospheric compositions and their albedos and thermal emission spectra. In this talk I will discuss how we used the 1D Community Aerosol and Radiation Model for Atmospheres (CARMA) to investigate the microphysics of water clouds on cool substellar worlds to constrain their typical particle sizes and vertical extent, taking into consideration nucleation and condensation, which have not been considered in detail for water clouds in H/He atmospheres. I will present comparisons with the Ackerman & Marley parameterization of cloud physics to extract the optimal sedimentation efficiency parameter (f_sed) using Virga. We find that no Virga model replicates the CARMA water clouds exactly and that a transition in f_sed occurs from the base of the cloud to the cloud top.  In the simulated thermal emission and geometric albedo spectra, we find large, wavelength-dependent differences between the CARMA and Virga models, especially in the M band where we expect Y dwarfs to be the brightest when observed by JWST.