  The lowest-mass stars, brown dwarfs and extrasolar planets present challenges
and opportunities for understanding dynamics and cloud formation processes in
low-temperature atmospheres. For brown dwarfs, the formation, variation and
rapid depletion of photospheric clouds in L- and T-type dwarfs, and
spectroscopic evidence for non-equilibrium chemistry associated with vertical
mixing, all point to a fundamental role for dynamics in vertical abundance
distributions and cloud/grain formation cycles. For exoplanets, azimuthal heat
variations and the detection of stratospheric and exospheric layers indicate
multi-layered, asymmetric atmospheres that may also be time-variable
(particularly for systems with highly elliptical orbits). Dust and clouds may
also play an important role in the thermal energy balance of exoplanets through
albedo effects. For all of these cases, 3D atmosphere models are becoming an
increasingly essential tool for understanding spectral and temporal properties.
In this review, I summarize the observational evidence for clouds and dynamics
in cool dwarf and hot exoplanetary atmospheres, outstanding problems associated
with these processes, and areas where effective synergy can be achieved.
