An Investigation of Ice Production Mechanisms in Small Cumuliform Clouds Using a 3D Model with Explicit Microphysics. Part I: Model Description

Abstract

A new cloud model that combines a three-dimensional nonhydrostatic dynamical framework with explicit liquid- and ice-phase microphysics and a detailed treatment of ice nucleation and multiplication processes is presented. The use of 28 size bins to describe each cloud drop and ice particle spectra allows the authors to account for all major microphysical processes. A detailed scavenging model has been implemented to calculate the collection rate of contact ice nuclei by cloud drops. In addition to contact nucleation, the model accounts for deposition, condensation-freezing, and immersion ice nucleation mechanisms, as well as for secondary ice production via rime splintering. The model performance is illustrated by a simulation of a New Mexican cumulus cloud. Combination of high 100-m spatial resolution with a new initialization procedure that promotes development of small eddies results in a cloud with a more realistic distribution of liquid water content compared to simulations initialized by the standard ?bubble? approach.