Crystalline, microscopic particle, either of ice or some other substance, which can induce the growth of ice crystals upon it from saturated air in cloud at temperatures of about -25 °C or below. Deposition of water in this way—directly from vapour to form ice, without forming liquid in between—is called ‘sublimation’. During growth, splintering of the crystals (e.g. as a result of updrafts) causes large numbers of new nuclei to be formed. Compare freezing nuclei.
Subjects: Ecology and Conservation — Earth Sciences and Geography.