On the Isotopic Composition of Hailstones

I. H. Bailey Dept. of Physics, The University of Western Australia,Nedlands
Present affiliation: Dept. of Physics, The Western AustraliaInstitute of Technology, Bentley

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J. R. Hulston Institute of Nuclear Sciences, D.S.I.R., Lower Hutt, NewZealand

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J. R. Stewart Institute of Nuclear Sciences, D.S.I.R., Lower Hutt, NewZealand

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W. C. Macklin Dept. of Physics, The University of Western Australia,Nedlands
4 On leave at the Meteorological Office, Bracknell, Berkshire, England

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Abstract

Theoretical considerations show that isotopic fractionation can occur during the freezing of supercooled droplets accreted by a hailstone. This is due to evaporation from the liquid during the freezing process with consequent enrichment of the deuterium and O18 content of the accreted ice. The enrichment is greatest when the temperature of the hailstone is near OC. Calculations, based on the Rayleigh distillation formula and allowing for diffusivity effects, indicate that the maximum increase is about 6 for deuterium and1.5 for O18. Analyses of samples of accreted ice formed in an icing tunnel have confirmed these predictions.The effect is sufficiently large to affect the interpretation of isotopic analyses of hailstones.

Abstract

Theoretical considerations show that isotopic fractionation can occur during the freezing of supercooled droplets accreted by a hailstone. This is due to evaporation from the liquid during the freezing process with consequent enrichment of the deuterium and O18 content of the accreted ice. The enrichment is greatest when the temperature of the hailstone is near OC. Calculations, based on the Rayleigh distillation formula and allowing for diffusivity effects, indicate that the maximum increase is about 6 for deuterium and1.5 for O18. Analyses of samples of accreted ice formed in an icing tunnel have confirmed these predictions.The effect is sufficiently large to affect the interpretation of isotopic analyses of hailstones.

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