Initiation of ice: comparison of numerical model results with observations of ice development in a cumulus cloud

The results from a recently revised microphysical model are compared with airborne measurements and observations of a small cumulus. The model used was a parcel model with explicit microphysics. A gaseous tracer, sulfur hexafluoride, was used to tag a region of the cloud to help observe the behavior of one region of the cloud. The model reproduced several features of the observed cloud microphysics, including the peak size of the observed droplet spectra and the development of large precipitation particles through riming. The major nucleation mechanisms were predicted to be deposition and condensation freezing. The effects of precipitation falling into the observed cloud region and mixing between adjacent parcels (processes that are not simulated in the model) were the likely cause of the discrepancy between the observed size spectra and those simulated by the model.