Buoyancy period T_N = 2π∕N for the DRIFT-PHOENIX brown dwarf (logg = 5.0, T_eff = 1500 K) atmosphere model used in numerical simulations, as well as typical and low-gravity L and T dwarfs (see Fig. 1, Table 2). The range of periods for higher surface gravity levels (10¹ –10²s) is consistent with the atmospheric models and simulation results published by Freytag et al. (2010). In lower-density brown dwarfs, the buoyancy period rises to the order of 10³ s.