Cumulus entrainment and cloud droplet spectra: a numerical model within a two-dimensional dynamical framework

Abstract

The cloud water mixing ratio at any grid location is equal to that predicted by a cloud model using bulk microphysics. Locally, only undiluted droplet concentrations are assumed to exist. Activation of cloud condensation nuclei is assumed to always produce the same initial spectrum of cloud droplets. Further condensational growth of this initial spectrum produces a set of base functions that are used to represent droplet spectral evolution. It is shown that, within the current framework, entrainment usually leads to fresh activation of cloud droplets and results in multimodal spectra in actively growing cells. Both broad and narrow cloud droplet spectra are predicted in old, highly diluted cells at cloud periphery. -from Authors