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Show Meteorological Classification of Natural Snow Crystals 331 group. As'will be described later, snow crystals of plane type have spatial extensions parallel to the c- axis at the ends of their branches when they rapidly fall into a warmer cloud layer around - 10° C, therefore this spatial extension at the ends of branches are important meteorologically. Therefore snow crystals of this type were classified as another group, as seen in CP3 of Table 1. 3.8 Columnar crystals with extended side plane So called " powder snow particles" which are often found in cold temperatures lower than - 20° C, are composed from a combination of columns and side planes. The snow crystals of this type were classified into three groups, namely " side planes", " scalelike side planes" and a " combination of side planes, bullets and columns", as seen in SI, S2 and S3 of Table 1. After Weickmann's observation20*, it appears that the latter two groups are formed in temperature regions colder than the former one, namely between- 25 and - 35° C as described in Fig. 2. 3.9 Supplement of rimed snow crystal In Japan, most of snow crystals are more or less rimed. Therefore the grade of riming is very important. Nakaya classified this type into three groups, namely rimed crystals, graupellike snow, and graupel. The authors added an additional group between the rimed crystals and the graupellike snow, which will be called " densely rimed crystals". This group was named thick plates in Nakaya's classification. 3.10 Detailed classification of irregular snow crystals For the practical recording of the forms of natural snow crystals, the description of irregular crystals is very inconvenient, because Nakaya's classification was too rough in this irregular shape, while the percentage of occurrence of such irregular crystals is much higher than expected. The authors therefore added two groups, namely " rimed particles" and " broken pieces from a crystal" as described in 12 and 13 of Table 1. The broken pieces may be useful. as an indicator of the existence of a strong wind or strong turbulence in a layer below the snow cloud. 3.11 Supplement of the type of early stage Minute snow crystals in the early stage were frequently observed at the summit of Mt. Teine and were sampled by the snow crystal sondes designed by Magono and Tazawa18*. Because the sarnpling of such snow crystals in the early stage means that these crystals were formed just near |
