  Recent observations of the super-Earth GJ 1214b show that it has a relatively
featureless transmission spectrum. One suggestion is that these observations
indicate that the planet's atmosphere is vertically compact, perhaps due to a
water-rich composition that yields a large mean molecular weight. Another
suggestion is that the atmosphere is hydrogen/helium-rich with clouds that
obscure predicted absorption features. Previous models that incorporate clouds
have included their effect without a strong physical motivation for their
existence. Here, we present model atmospheres of GJ 1214b that include
physically-motivated clouds of two types. We model the clouds that form as a
result of condensation in chemical equilibrium, as they likely do on brown
dwarfs, which include KCl and ZnS for this planet. We also include clouds that
form as a result of photochemistry, forming a hydrocarbon haze layer. We use a
photochemical kinetics model to understand the vertical distribution and
available mass of haze-forming molecules. We model both solar and
enhanced-metallicity cloudy models and determine the cloud properties necessary
to match observations. In enhanced-metallicity atmospheres, we find that the
equilibrium clouds can match the observations of GJ 1214b if they are lofted
high into the atmosphere and have a low sedimentation efficiency (fsed=0.1). We
find that models with a variety of hydrocarbon haze properties can match the
observations. Particle sizes from 0.01 to 0.25 micron can match the
transmission spectrum with haze-forming efficiencies as low as 1-5%.
