Abstract
Evidence is presented that small regular ice crystals found in maritime cumulus clouds with summit temperature warmer than -10C were formed in clouds near the sampling level. Their concentrations were far larger than those usually observed for natural ice nuclei, so that it is supposed that they were the secondary products and the primary ice crystals growing on natural ice nuclei could be multiplied many times in the course of the formation of small regular ice crystals. Their sizes, concentrations and microphysical conditions of occurrence support the hypothesis that they were formed when ice fragments were thrown off from water drops freezing after accreting on ice crystals.
