  Clouds in the atmospheres of exoplanets confound characterization efforts by
reducing, eliminating, and distorting spectral signatures of molecular
abundances. As such, interpretations of exoplanet spectra strongly depend on
the choice of cloud model, many of which are highly simplified and lack
predictive power. In this work, we use a cloud model that treat microphysical
processes to simulate potassium chloride (KCl) and zinc sulfide (ZnS) clouds in
the atmosphere of the super Earth GJ 1214b and how they vary as a function of
the strength of vertical mixing and the atmospheric metallicity. Microphysical
processes control the size and spatial distribution of cloud particles,
allowing for the computation of more physical cloud distributions than simpler
models. We find that the mass and opacity of KCl clouds increase with mixing
strength and metallicity, with the particle size and spatial distribution
defined by nucleation, condensation, evaporation, and transport timescales. ZnS
clouds cannot form without the presence of condensation nuclei, while
heterogeneous nucleation of ZnS on KCl reduces particle sizes compared to pure
KCl cases. In order to explain the flat transmission spectrum of GJ 1214b with
homogeneously nucleated KCl clouds, the atmospheric metallicity must be at
least 1000 $\times$ solar, and the eddy diffusivity must be at least 10$^{10}$
cm$^2$ s$^{-1}$. We predict that JWST observations of GJ 1214b may reveal the
presence of methane, carbon monoxide, and water, allowing for constraints to be
placed on atmospheric metallicity and C/O ratio.

Earth and Planetary Astrophysics