The Effect of Internal Gravity Waves on Cloud Evolution in Substellar Atmospheres

Substellar objects exhibit photometric variability which is believed to be caused by a number of processes such as magnetically-driven spots or inhomogeneous cloud coverage. Recent substellar models have shown that turbulent flows and waves, including internal gravity waves, may play an important role in dust cloud evolution. The aim of this paper is to investigate the effect of internal gravity waves on dust cloud nucleation and dust growth, and whether observations of the resulting cloud structures could be used to recover atmospheric density information. For a simplified atmosphere in two dimensions, we numerically solve the governing fluid equations to simulate the effect on dust nucleation and mantle growth as a result of the passage of an internal gravity wave. Furthermore, we derive an expression that relates the properties of the wave-induced cloud structures to observable parameters in order to deduce the atmosphere density. Numerical simulations show that the density, pressure and temperature variations caused by gravity waves lead to an up to 20-fold increase of the dust nucleation rate and an up to 80% increase of the dust growth rate in the linear regime. These variations lead to banded areas in which dust formation is much more pronounced. We show that internal gravity waves in substellar atmospheres lead to banded cloud structures similar to those observed on Earth. Using the proposed method, potential observations of banded clouds could be used to estimate the atmospheric density of substellar objects.