Formation mechanisms of multibranched snow crystals (twelve-, eighteen-, twenty-four-branched crystals)

Abstract

During the observations of low-temperature types of snow cyrstals which were carried out at Inuvik, Arctic Canada and Kautokeino, Northern Norway, a number of multibranched snow crystals, namely twelve-, eighteen-, and twenty-four-branched snow crystals were collected and microphotographed under relatively warm temperature conditions. The formation mechanisms of these crystals were discussed and compared with the rotation twinning theory introduced by [Kobayashi, T., Furukawa, Y., 1975. On twelve-branched snow crystals. J. Cryst. Growth 28, 21–28]. The three-dimensional structure of twelve-branched crystals, specifically, was analyzed with microphotographs taken from the direction perpendicular to the principal axis. Furthermore, for all multibranched snow crystals, the angles between the neighboring branches composed of each dendritic crystal were measured and examined. In these analyses, the ratio ( d) of the distance ( l) between the centers of each crystal and the maximum lengths ( L) of the crystals was discussed. From these analyses, it was concluded that the most probable formation mechanism of multibranched snow crystals is considered to be the snowflake theory, namely, aggregation theory based on the coalescence on a plane of normal sixfold symmetry dendrites, although a slight possibility existed of their formation by the rotation twinning theory (Kobayashi and Furukawa, 1975) and the frozen cloud droplet theory [Kikuchi, K., Uyeda, H., 1987. Formation mechanisms of eighteen-branched snow crystals. J. Fac. Sci., Hokkaido Univ., Ser. VII, 8, 109–119].