Apparent Persistence Effects in the Nelspruit Area from Silver Iodide Seeding for Hail Suppression

Graeme K. Mather CloudQuest, Nelspruit South Africa

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E. K. Bigg Castle Hill, Australia

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Susan Renton Ipswich, Australia

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Abstract

Daily precipitation records during the period of the hail suppression seeding program in the Eastern Transvaal around Nelspruit, South Africa are examined for evidence of persistence effects from silver iodide iodine similar to those reported by Bigg and Turton in Australia. Using their method of analysis, a positive anomaly is found in the comparison of target-to-control rainfall commencing 11 to 12 days after a seed day and lasting 10 to 11 days. The Australian anomaly commences 9 to 10 days after a day and lasts about 9 days. Otherwise, the “peristence signatures” in the two areas are very similar. This repetition of apparent persistence effects in another area on a different continent raises serious doubts about conventional statistical assessments of the success of randomized seeding experiments when silver iodide is used.

Abstract

Daily precipitation records during the period of the hail suppression seeding program in the Eastern Transvaal around Nelspruit, South Africa are examined for evidence of persistence effects from silver iodide iodine similar to those reported by Bigg and Turton in Australia. Using their method of analysis, a positive anomaly is found in the comparison of target-to-control rainfall commencing 11 to 12 days after a seed day and lasting 10 to 11 days. The Australian anomaly commences 9 to 10 days after a day and lasts about 9 days. Otherwise, the “peristence signatures” in the two areas are very similar. This repetition of apparent persistence effects in another area on a different continent raises serious doubts about conventional statistical assessments of the success of randomized seeding experiments when silver iodide is used.

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