Cloud Microphysics of the Giant Planets

Abstract

The predominant cloud microphysical processes for the atmospheres of the giant planets are determined by a comparison of their characteristic time constants. These results are an extension of the earlier microphysical modeling by Rossow to other atmospheres and by a more thorough exploration of thermal structure and compositional effects. The NH3 clouds on Jupiter and Saturn are found to be weakly precipitating systems, similar to the thicker cirrus clouds on Earth, while the H2O clouds are much more massive than water clouds on Earth. The NH4SH clouds are very tenuous on Jupiter and Saturn but may produce precipitation on Uranus and Neptune. The CH4 and H2O clouds on Uranus and Neptune are completely unlike any cloud on Earth, being 10?100 times more massive than the densest water clouds on Earth. Horizontal contrasts in weakly precipitating systems, Such as the NH3 cloud on Jupiter may be muted and the vertical extent may be small in a weak dynamic regime or large in a multilayered haze complex, if stronger vertical motions exist. Denser precipitating cloud systems are expected to exhibit more horizontal structure with cumulus-style dynamics more likely due to larger latent heat effects. The massive CH4 and H2O clouds expected on Uranus and Neptune should dominate energy exchanges in the general circulation of these atmospheres.