Growth of snow crystals from frozen water droplets

Growth of frozen water droplets, falling freely in a supercooled cloud, was investigated by using a large cloud chamber 6.5 m in height. Water droplets containing silver iodide in suspension were dropped from the top of the chamber. The size of frozen water droplets was between 20 and 100 μm in diameter. They were nucleated at about − 5 °C in most cases and froze into single-crystalline particles. Frozen water droplets grew at temperatures between − 5 and − 33 °C. Two modes were confirmed at the initial growth stage. In one mode, twenty circular crystal faces appeared during the growth. They were 2 basal, 6 prism and 12 pyramidal faces. {1120} crystal faces, whose existence has been suggested by theory, were confirmed in this experiment. In the other mode, steps or irregular patterns appeared in place of circular pyramidal and prism faces. After further growth frozen water droplets grew to short column-like ice crystals in both modes, and finally grew to snow crystals with the crystal habit as shown by Nakaya's diagram.