  Growing observations of brown dwarfs have provided evidence for strong
atmospheric circulation on these objects. Directly imaged planets share similar
observations, and can be viewed as low-gravity versions of brown dwarfs.
Vigorous condensate cycles of chemical species in their atmospheres are
inferred by observations and theoretical studies, and latent heating associated
with condensation is expected to be important in shaping atmospheric
circulation and influencing cloud patchiness. We present a qualitative
description of the mechanisms by which condensational latent heating influence
the circulation, and then illustrate them using an idealized general
circulation model that includes a condensation cycle of silicates with latent
heating and molecular weight effect due to rainout of condensate. Simulations
with conditions appropriate for typical T dwarfs exhibit the development of
localized storms and east-west jets. The storms are spatially inhomogeneous,
evolving on timescale of hours to days and extending vertically from the
condensation level to the tropopause. The fractional area of the brown dwarf
covered by active storms is small. Based on a simple analytic model, we
quantitatively explain the area fraction of moist plumes, and show its
dependence on radiative timescale and convective available potential energy. We
predict that, if latent heating dominates cloud formation processes, the
fractional coverage area by clouds decreases as the spectral type goes through
the L/T transition from high to lower effective temperature. This is a natural
consequence of the variation of radiative timescale and convective available
potential energy with spectral type.
