Cloud-convection feedback in brown dwarfs atmosphere

Abstract

Numerous observational evidence has suggested the presence of active meteorology in the atmospheres of brown dwarfs. A near-infrared brightness variability has been observed. Clouds have a major role in shaping the thermal structure and spectral properties of these atmospheres. The mechanism of such variability is still unclear and both 1D and global circulation model cannot fully study this topics due to resolution. In this study, a convective resolving model is coupled to grey-band radiative transfer in order to study the coupling between the convective atmosphere and the variability of clouds over a large temperature range with a domain of several hundreds of kilometers. Six types of clouds are considered, with microphysics including settling. The clouds are radiatively active using Rosseland mean coefficient. Radiative cloud feedback can drive spontaneous atmospheric variability in both temperature and cloud structure, as modeled for the first time in three dimensions. Silicate clouds have the most effect of the thermal structure with the generation of a secondary convective layer in some cases, depending on the assumed particle size. Iron and Aluminum clouds also have a substantial impact on the atmosphere. Thermal spectra were computed, and we find the strongest effect of clouds is the smoothing of spectral features at optical wavelengths. Compared to observed L and T dwarfs on color-magnitude diagram, the simulated atmospheres are redder for most of the cases. The simulations with the presence of cloud holes are closer to the observations.