Further Exploratory Evaluations of Grossversuch IV Using Hailpad Data: Analysis of Hail Patterns and Stratification by Storm Type for Seeding Effect

Abstract

Further exploratory evaluations of the Grossversuch IV randomized hail suppression experiment using hailpad data are presented. These deal with the spatial distribution of the ground-measured variables within hail patterns. The possibility of a seeding effect limited to a part of a hailfall or to various objectively stratified types of precipitation cells is investigated. The results show an increase in the ratio of the hailed areas with maximum hailstone diameters greater than 10 mm versus the total hailed area (P value = 0.008) and an increase in Dmax, the maximum hailstone diameter, for type II repetitive evolution cells (P value = 0.04). Differences observed for the main test variables in relation to the various cell types are shown to largely exceed those that could stem from a possible seeding effect. A satisfactory physical interpretation of the differential tendency related to the storm type is impossible, however, due to the simple storm model on which the Grossversuch IV experiment is based on the lack of 3D storm measurements. Future test experiments should be based on several test variables characteristic of the overall hailfall phenomenon and especially of the area factor. In addition, storms should be physically stratified in an objective manner.