  The L/T transition is an important evolutionary phase in brown dwarf
atmospheres, providing us with a unique opportunity to explore the effects of
clouds, convection, winds, gravity and metallicity across a very narrow
temperature range. Understanding these physical processes is critical for
understanding ultracool atmospheres. In the next decade, we will answer three
key questions regarding L/T transition atmospheres: 1. What is the physical
mechanism behind the L/T transition? 2. What is the spatial extent of
atmospheric structures at the L/T transition? 3. How do gravity and metallicity
affect the L/T transition? The theory and methods developed for brown dwarfs
will be used in the 2030s and beyond for solar-system age giant exoplanets and
eventually habitable zone earth analogues. Developing these techniques now are
crucial.
