  Brown dwarfs of a variety of spectral types have been observed to be
photometrically variable. Previous studies have focused on objects at the L/T
transition, where the iron and silicate clouds in L dwarfs break up or
dissipate. However, objects outside of this transitional effective temperature
regime also exhibit variability. Here, we present models for mid-late T dwarfs
and Y dwarfs. We present models that include patchy salt and sulfide clouds as
well as water clouds for the Y dwarfs. We find that for objects over 375 K,
patchy cloud opacity would generate the largest amplitude variability within
near-infrared spectral windows. For objects under 375 K, water clouds also
become important and generate larger amplitude variability in the mid-infrared.
We also present models in which we perturb the temperature structure at
different pressure levels of the atmosphere to simulate hot spots. These models
show the most variability in the absorption features between spectral windows.
The variability is strongest at wavelengths that probe pressure levels at which
the heating is the strongest. The most illustrative types of observations for
understanding the physical processes underlying brown dwarf variability are
simultaneous, multi-wavelength observations that probe both inside and outside
of molecular absorption features.
