Statistical Characteristics of Radar Echoes of Precipitating Snow Clouds over the Ishikari Bay, Hokkaido, Japan ( Radar Echo Climatology; Part 1)

摘要

The characteristics of radar echoes of the precipitating snow clouds over the Ishikari Bay, Hokkaido, Japan were investigated statistically during four months, February and March of 1983 and 1984. In this analysis, the precipitating snow clouds were divided into three types: typical monsoon, final period of monsoon type and low pressure type based on the daily weather maps. Examined elements in this analysis were as follows; Size distributions of radar echo population, percentage occupied by the strong echo areas as against total precipitating echo areas, time changes of echo areas, locations of the center of individual large echo areas, life time of the echoes, and so on. Highly interesting characteristics were obtained; the log-normal distribution was obtained for the size ranges of radar echoes of all snowfall types; the percentage occupied by the echoes stronger than level 2 accounted for less than 40% of all echo areas; the total echo area showed sharp fluctuations; the locations at which the radar echo areas when the snow clouds invading the plain reached their maximal sizes were along the coast line; the average echo area having a life time of 1 hour was approximately 25km2 etc.