Concentrations of Ice Crystals in Clouds

Abstract Some cumulus clouds appear to be capable of producing ice crystals in concentrations of 10–100l−1 at temperatures approaching −5C. This has serious implications for cloud seeding with ice nuclei. We discuss various possible mechanisms by which these unexpectedly high concentrations may originate. Circumstantial evidence from field work points to their production in the riming process, but laboratory confirmation is lacking.