A Binned Approach to Cloud-Droplet Riming Implemented in a Bulk Microphysics Model

Abstract

This paper presents the development and application of a binned approach to cloud-droplet riming within a bulk microphysics model. This approach provides a more realistic representation of collision?coalescence that occurs between ice and cloud particles of various sizes. The binned approach allows the application of specific collection efficiencies, within the stochastic collection equation, for individual size bins of droplets and ice particles; this is in sharp contrast to the bulk approach that uses a single collection efficiency to describe the growth of a distribution of an ice species by collecting cloud droplets. Simulations of a winter orographic cloud event reveal a reduction in riming when using the binned riming approach and, subsequently, larger amounts of supercooled liquid water within the orographic cloud.