The Shape and Riming Properties of Ice Crystals in Natural Clouds

Individual ice crystals have been collected and replicated. The effect of the falling motion is found to enhance the growth along the “c” axis of columns and the dendritic growth of plane ice crystals. It is found that the onset of riming of ice crystals is controlled by crystal size; for columnar crystals the most sensitive parameter is the length along the “a” axis, while for plane crystals it is the diameter. Freely-falling ice crystals are oriented so as to present the maximum resistance to motion. Some consideration is also given to the collection efficiency of columnar ice crystals for cloud droplets.