Paper: astro-ph/0506204
Date: Thu, 9 Jun 2005 13:54:28 GMT (472kb)

Title: The need for small-scale turbulence in atmospheres of substellar objects

Authors: Christiane Helling
Comments: 7 pages, 2 figues, contribution to the Workshop on Interdisciplinary
Aspects of Turbulence, April 18 - 22, 2005, Castle Ringberg, Germany
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Brown dwarfs and giant gas planets are substellar objects whose spectral
appearance is determined by the chemical composition of the gas and the
solids/liquids in the atmosphere. Atmospheres of substellar objects possess two
major scale regimes: large-scale convective motions + gravitational settling
and small-scale turbulence + dust formation. Turbulence initiates dust
formation spot-like on small scale, while the dust feeds back into the
turbulent fluid field by its strong radiative cooling. Small, imploding dust
containing areas result which eventually become isothermal. Multi-dimensional
simulations show that these small-scale dust structures gather into large-scale
structures, suggesting the formation of clouds made of dirty dust grains. The
chemical composition of the grains, and thereby the chemical evolution of the
gas phase, is a function of temperature and depends on the grain's history.

\\ ( http://arXiv.org/abs/astro-ph/0506204 , 472kb)