Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

A Re-Evaluation of the Swiss Hail Suppression Experiment using Permutation Techniques shows Enhancement of Hail Energies when Seeding

Version 1 : Received: 28 July 2021 / Approved: 29 July 2021 / Online: 29 July 2021 (14:21:23 CEST)

How to cite: Auf der Maur, A.; Germann, U. A Re-Evaluation of the Swiss Hail Suppression Experiment using Permutation Techniques shows Enhancement of Hail Energies when Seeding. Preprints 2021, 2021070666 (doi: 10.20944/preprints202107.0666.v1). Auf der Maur, A.; Germann, U. A Re-Evaluation of the Swiss Hail Suppression Experiment using Permutation Techniques shows Enhancement of Hail Energies when Seeding. Preprints 2021, 2021070666 (doi: 10.20944/preprints202107.0666.v1).

Abstract

Grossversuch IV is a large and well documented experiment on hail suppression by silver iodide seeding. The original 1986 evaluation remained vague, although indicating a tendency to increase hail when seeding. The strategy to deal with distributions of hail energy far from normal was not optimal. The present re-evaluation sticks to the question asked and avoids both misleading transformations and unsatisfactory meteorological predictors. The raw data show an increase by about a factor of 3 for the hail energy when seeding. This is the opposite of what seeding is supposed to do. The probability to obtain such a result by chance is below 1%, calculated by permutation and bootstrap techniques applied on the raw data. Confidence intervals were approximated by bootstrapping as well as by a new method called "correlation imposed permutation" (CIP).

Keywords

hail prevention; non-normal distributions; permutation; bootstrap; confidence intervals

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