The main results of a randomized hail suppression experiment, Grossversuch IV, are presented in this paper. Grossversuch IV tested the “Soviet” hail prevention method during five years (1977–81). The field experiment took place in central Switzerland with the participation of research groups from France, Italy and Switzerland.
A very dense hailpad network (330 hailpads over 1300 km2) and a carefully calibrated 10-cm radar were used to measure in two independent ways the hail kinetic energy of seeded and unseeded hail cells. The total sample included 216 cells. The main result of the confirmatory as well as most of the exploratory analyses is that there is no statistically significant difference between seeded and unseeded hail cells. A detailed discussion of the reliability of the measurements, tests and methods is given together with a discussion about possibilities of future evaluations of the Grossversuch IV data and other cloud seeding experiments.