MICROPHYSICAL PROCESSES AND DYNAMICS OF A JOVIAN THUNDERCLOUD

An axisymmetric time-dependent cloud model with dynamics and detailed microphysics of Jupiter's water cumulus clouds is presented. The micro physical processes operating in these clouds are analyzed and compared to those of terrestrial clouds. Diffusional growth and coagulation of water drops and ice crystals were found to be faster and more efficie nt in Jupiter. Large particles were formed on short time scales and ke pt suspended by the strong updraft in the core of the developing cloud , which allowed them to grow by coalescence as they ascended to the up per regions of the cloud. Thus, clouds retained high values of mass mi xing ratio (10 g kg(-1)) and high concentrations of large particles (D > 100 mu m). An evaluation of the minimum cloud condensation nuclei ( CCN) and ice nuclei (IN) concentrations in Jupiter's troposphere showe d that for convective clouds to develop a vertical dimension of 45-50 km, CCN concentrations should be of the order of 100 cm(-3); much lowe r concentrations resulted in relatively shallow clouds (10 km) and low er mass contents. The formation of ice by freezing or nucleation was f ound to contribute significantly to cloud development, due to the rele ase of latent heat which counteracted the negative buoyancy created by the condensed mass. The required IN concentration was of the order of 0.1 cm(-3). (C) 1995 Academic Press, Inc.