Mechanism of Ice Crystal Growth Habit and Shape Instability Development Below Water Saturation.

Ice phase process in supercooled clouds play dominant roles in development of updrafts and downdrafts as well as various forms of precipitation. In a supercooled cloud, an ice phase process begins normally with vapor diffusional growth of ice crystals. Consequently, the vapor diffusional growth of ice crystals is of importance in cloud physics. Starting from the concept of the wedge-shaped ice thermal diffusion chamber of Schaller and Fukuta, where ice crystals can be grown under a range of ice supersaturations at a constant temperature in quiescent, temperature-stratified air, and by considering design and operational limitations, a new wedge-shaped ice thermal diffusion chamber was designed and constructed for this study of ice crystal growth habit and shape instability. This chamber and supporting apparatus define an experimental system capable of adequately controlling the temperature and supersaturation fields around the growing crystal. In addition to the wedge-shaped chamber, apparatus defining this experimental system are the pre-chamber, ice crystal slide mechanism, lateral microscope slide mechanism, sample transfer device, and outer environmental chamber.