  Clouds of metal-bearing condensates play a critical role in shaping the
emergent spectral energy distributions of the coolest classes of low-mass stars
and brown dwarfs, L and T dwarfs. Because condensate clouds in planetary
atmospheres show distinct horizontal structure, we have explored a model for
partly cloudy atmospheres in brown dwarfs. Our model successfully reproduces
the colors and magnitudes of both L and T dwarfs for the first time, including
the unexpected brightning of the early- and mid-type T dwarfs at J-band,
provided that clouds are rapidly removed from the photosphere at T_eff ~ 1200
K. The clearing of cloud layers also explains the surprising persistence and
strengthening of gaseous FeH bands in early- and mid-type T dwarfs. The breakup
of cloud layers is likely driven by convection in the troposphere, analogous to
phenomena observed on Jupiter. Our results demonstrate that planetary-like
atmospheric dynamics must be considered when examining the evolution of
free-floating brown dwarfs.
