Effects of entrainment and droplet sedimentation on the microphysical structure of status and stratocumulus clouds

A new cloud model has been developed based upon a reconsideration of cloud‐top entrainment mechanisms. A finite‐thickness entrainment layer at cloud top allows the cloudy air to lose liquid water to dry entrained air by sedimentation. The model use a steady‐state ensemble of one‐dimensional updraughts and downdraughts, combined with a simplified traetment of droplet sedimentation, autoconversion, and collection of cloud drops by drizzle, to examine vertical profiles of cloud liquid‐water content and droplet concentration. The model is demonstrated both for idealized cases and in comparison with a nocturnal stratocumulus case from the ASTEX. The sedimentation flux divergence in the entrainment layer at cloud top is shown to have a large impact on the cloud microphysics.