Characteristics of snowflake size distributions connected with the difference of formation mechanism

Observation of snowflake size distribution was carried out on the ground in order to reconsider the past observational results obtained from only a small amount of data. Based on the large quantity of data obtained in our studies, the characteristics of snowflake size distributions and their formation mechanisms are discussed. It was found that averaged size distributions of snowflakes moved parallel to a higher number concentration, maintaining their exponential distributions with increase in snowfall intensity. These characteristics differ from those of Gunn and Marshall (1958), who reported that size distributions became broader with increase in snowfall intensity. A small variation superposed on the averaged size distribution, and changed its slope even under the condition of equal snowfall intensity. The density and riming proportion of snowflakes are shown to be the factor that determines the slope. In other words, the slope of the size distribution becomes more gentle when snowflakes have low density and are not composed of rimed snow crystals.