Aerodynamical Effects in Snow Crystal Growth

We review several aspects of aerodynamics that affect the growth, morphology, and symmetry of snow crystals. We derive quantitative estimates for aerodynamical forces that orient falling snow crystals, estimate how air flow around snow crystals affects their growth rates (the ventilation effect), and examine how the combination of orientation and growth modification can stabilize or destabilize different growth behaviors. Special attention is given to the formation of triangular snow crystals, since it appears that aerodynamical effects are responsible for producing this unusual morphology, both in nature and in the laboratory.