Nucleation characteristics of polycrystalline ice crystals

Polycrystalline ice crystals which were microphotographed by the authors in the Arctic and Antarctic regions were classified into twelve types. Almost all of them were crossed plates type and their production rate was approximately less than 5% of usual ice crystals. To investigate the shapes of these ice crystals and their production rate, laboratory experiments using a cloud chamber were carried out under temperature conditions between -18 and -42 degrees C. As a result, almost all shapes that were observed in the polar regions occurred in the chamber and their rate was less than 5%. This value was similar to that of an observational result.