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J. Bader, W. A. Stahel, and W. Schmid


The data obtained in Grossversuch IV about hail prevention triggered the hypothesis that only the first rocket launched into a potential hail cell decreases hail kinetic energy in an effect-time interval around 10 min after launching time. Several variations of a randomization test were applied to substantiate this hypothesis. All showed a tendency to confirm the hypothesis, the most significant result being a p value of 0.2%. However, since the test was applied to the data that had been explored to generate the hypothesis, the significant result should be interpreted as a strong hint rather than as a statistical proof.

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B. Federer, A. Waldvogel, W. Schmid, H. H. Schiesser, F. Hampel, Marianne Schweingruber, W. Stahel, J. Bader, J. F. Mezeix, Nadie Doras, G. D'Aubigny, G. DerMegreditchian, and D. Vento


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.

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