  Potentially habitable exoplanets are targets of great interest for the James
Webb Space Telescope and upcoming mission concepts such as the Habitable Worlds
Observatory. Clouds strongly affect climate and habitability, but predicting
their properties is difficult. In Global Climate Models (GCMs), especially
those aiming at simulating Earth, cloud microphysics is often crudely
approximated by assuming that all cloud particles have a single, constant size
or a prescribed size distribution and that all clouds in a grid cell are
identical. For exoplanets that range over a large phase space of planetary
properties, this method could result in large errors. In this work, our goal is
to determine how cloud microphysics on terrestrial exoplanets, whose
condensable is mainly water vapor, depend on aerosol properties and planetary
parameters such as surface pressure, surface gravity, and incident stellar
radiation. We use the Community Aerosol and Radiation Model for Atmospheres as
a 1D microphysical model to simulate the formation and evolution of clouds
including the processes of nucleation, condensation, evaporation, coagulation,
and vertical transfer. In these 1D idealized experiments, we find that the
parameters that determine the macrophysical thermal structure of the
atmospheres, including surface pressure and stellar flux, impact cloud
radiative effect (CRE) most significantly. Parameters such as gravity and
number density of aerosols working as cloud condensation nuclei affect the
microphysical processes of cloud formation, including activation and vertical
transfer. They also have a significant, though weaker effect on CRE. This work
motivates the development of more accurate GCM cloud schemes and should aid in
the interpretation of future observations.
