The objectives of this research are three-fold: (1) an experimental investigation of "cirrus" crystal growth during free-fall in an evacuated chamber; the growth of natural crystals by both diffusion of vapor and riming, particularly the transition from the former to the latter as the temperature is decreased; (2) an experimental investigation, using a thermal diffusion chamber of natural ice nuclei, especially their capacity to nucleate ice as a function of supersaturation; (3) the development of a theory to explain ice crystal growth, including habitat (i.e. crystal shape).
