included into model atmosphere codes that iteratively search for self-consistent atmospheric structures. No such ideal model yet exists.

We aim to fill this void by presenting a simple model describing precipitating clouds in substellar atmospheres. We limit our treatment to condensation clouds, and hence do not consider photochemically driven hazes likely to appear in illuminated stratospheres. We depart from previous work by explicitly treating the downward transport of raindrops with sizes greater than that predicted from the convective velocity scale. Including rainfall produces clouds of thinner vertical extent, which can better reproduce observations of Jupiter’s ammonia cloud. The resulting model is general enough to be applied to iron and silicate clouds appearing in brown dwarf atmospheres (e.g., objects with effective temperatures, $T_{\rm eff} \sim 1500\ \rm K$) as well as the atmospheres of cool extrasolar giant planets ($T_{\rm eff} \sim 400\,\rm K$) in which water clouds dominate the atmosphere. The few free parameters in the model can produce clouds with dramatically different characteristics; ultimately observations will constrain these parameters and hopefully provide information on the underlying atmospheric dynamics and cloud physics.

In this paper we first summarize previous cloud modeling efforts, then describe the new model. We use the ammonia 