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The ubiquity of clouds in the atmospheres of exoplanets, especially ofsuper-Earths, is one of the outstanding issues for transmission spectra survey.The understanding about the formation process of clouds in super-Earths isnecessary to interpret the observed spectra correctly. In this study, weinvestigate the vertical distributions of particle size and mass density ofmineral clouds in super-Earths using a microphysical model that takes intoaccount the vertical transport and growth of cloud particles in aself-consistent manner. We demonstrate that the vertical profiles of mineralclouds significantly vary with the concentration of cloud condensation nucleiand atmospheric metallicity. We find that the height of the cloud top increaseswith increasing metallicity as long as the metallicity is lower than athreshold. If the metallicity is larger than the threshold, the cloud-topheight no longer increases appreciably with metallicity because coalescenceyields larger particles of higher settling velocities. We apply our cloud modelto GJ1214 b and GJ436 b for which recent transmission observations suggest thepresence of high-altitude opaque clouds. For GJ436 b, we show that KClparticles can ascend high enough to explain the observation. For GJ1214 b, bycontrast, the height of KCl clouds predicted from our model is too low toexplain its flat transmission spectrum. Clouds made of highly porous KClparticles could explain the observations if the atmosphere is highlymetal-rich, and hence the particle microstructure might be a key to interpretthe flat spectrum of GJ1214 b.

Microphysical Modeling of Mineral Clouds in GJ1214 b and GJ436 b: Predicting Upper Limits on the Cloud-Top Height