Statistical Characteristics of Graupel Precipitation over the Japan Islands

The occurrence and amount of graupel precipitation over the Japan Islands are studied using routine surface observation data at 150 stations. The results of statistical analysis of the annual and monthly number of days with graupel for 1971-1986 in the geographical map and in annual cycles show that graupel fall is predominant in winter over the Japan Sea coastal area in Tohoku and Hokuriku District. Furthermore, monthly precipitation amount of graupel in January for 1982-1986 at five stations in the coastal area are statistically estimated to be at least one-fourth to one-third of the monthly precipitation amount. Based on the statistical results of graupel precipitation, weather modification potential by cloud seeding is discussed.