Potential for Snow Augmentation in Cold Orographic Clouds

Abstract

A simple numerical model is formulated for a mixed-phase cold cloud which simulates the interaction among the updraft, crystal growth, droplet growth or evaporation, and ice crystal concentration. The model accounts for temperature and pressure changes due to vertical displacements, and crystal concentrations are specified as a function of cloud-top temperature. Cloud temperature and updraft speed were varied in the model and equations integrated for a time period of up to 1 hr. Results indicate that a cloud-top temperature of about ?25C will demarcate cold orographic cloud systems with respect to a potential for snowfall augmentation. There is also a suggestion that the concentrations of artificial ice nuclei, one would add to maximize snowfall, probably need not be considered single-valued. Rather, it appears that crystal concentrations may exceed a critical concentration by an order of magnitude without noticeable adverse effects on precipitation efficiency, even in the absence of agglomeration mechanisms.