How does ice crystals form in the clouds?
Rosinski gives evidence from filter measurements that evaporated droplets occasionally left aerosol particle residues that acted as sorption ice nuclei at temperatures as high as -5C and water vapor saturation over ice of 0.2%. Since cloud droplet concentrations are typically 10-100 cm, high concentrations of ice nuclei could potentially be produced by such a mechanism. Beard [1992] for instance, suggests that only the residue of 1 in 200 evaporated cloud droplets would need to serve as ice nuclei in order to explain the rapid ice production observed near the tops of maritime cumulus clouds by Hobbs and Rangno, and Rangno and Hobbs. Rosinski [1991] also suggested a positive feedback mechanism for the production of “evaporation ice nuclei.” As ice crystals start to form on newly produced evaporation ice nuclei, cloud droplets close to the growing ice crystal will evaporate, leading to the production of more evaporation ice nuclei. Calculations are needed to determine the time scale of
