On the Characteristics of Hail Size Distribution Related to Crop Damage

Abstract

The total kinetic energy of a hailfall derived from hailpad is known to be closely related to the degree of crop damage. The hail size distribution (space concentration distribution) is also considered as one of the factors related to crop damage. Hailpad data, however, contain no information on the time of hail. Therefore, the hail size distribution can not be calculated directly from hailpad. In this paper an attempt was made to estimate hailfall duration from hailpad data in the damaged area of approximately 4km width and 8km length suffered by the northern Kanto hailstorm on 9 June 1975. The degree of crop damage had been classified into 5 groups. The hailpad data were classified according to the degrees of crop damage and averaged over each class. The number frequency distribution obtained from hailpad was converted to hail size distribution with the estimated hailfall duration. The characteristics seen in the size distributions were described in relation to crop damage. Furthermore, the size distributions were fitted by the equations of Marshall and Palmer (1948) and Shiotsuki (1975). From the relations of the parameters in these equations to crop damage, it was found that the mean diameter was closely related to crop damage. Thus, as the mean diameter can be derived directly from hailpad, the hailpad observation system is suggested to be useful for the objective assessment of crop-hail damage.