A computer-based measurement system for characteristics of snowfall is described. To measure the size and velocity of falling snowflakes quantitatively, images of snowflakes were input to an image processor and the primary data were analyzed in real time. In this process, maximum diameter in a horizontal plane and falling velocity were recorded in previously set intervals, then stored on a disk. Since a lot of data were obtained during a full winter season, data had to be processed to make up a database after an experiment. Using this database, the data of the distribution of size and velocity of snowflakes can be retrieved at anytime.
We observed snowflakes during winter months of 1986-92 in Sapporo and Toyama, which are located near the north east and middle of the Japan Sea coast respectively. The data indicate that the average size of snowflakes in Toyama was larger than that in Sapporo, while the number concentration of snowflakes in Sapporo was rather higher. The fall velocity tends to increase with increasing size of snowflakes, as observed in both areas.