@misc{HellingKleinWoitkeetal.2003, author = {Helling, Christiane and Klein, Rupert and Woitke, Peter and Nowak, Ulrich and Sedlmayr, Erwin}, title = {Dust in Brown Dwarfs IV. Dust formation and driven turbulence on mesoscopic scales}, url = {http://nbn-resolving.de/urn:nbn:de:0297-zib-7555}, number = {03-33}, year = {2003}, abstract = {Dust formation {in brown dwarf atmospheres} is studied by utilizing a model for driven turbulence in the mesoscopic scale regime. We apply a pseudo-spectral method where waves are created and superimposed {within} a {limited} wavenumber interval. The turbulent kinetic energy distribution follows the Kolmogoroff spectrum which is assumed to be the most likely value. Such superimposed, stochastic waves may occur in a convectively active environment. They cause nucleation fronts and nucleation events and thereby initiate the dust formation process which { continues until} all condensible material is consumed. Small disturbances {are found to} have a large impact on the dust forming system. An initially dust-hostile region, which may originally be optically thin, becomes optically thick in a patchy way showing considerable variations in the dust properties during the formation process. The dust appears in lanes and curls as a result of the interaction with waves, i.e. turbulence, which form larger and larger structures with time. Aiming on a physical understanding of the variability of brown dwarfs, related to structure formation in substellar atmospheres, we work out first necessary criteria for small-scale closure models to be applied in macroscopic simulations of dust forming astrophysical systems.}, language = {en} }