On the Isotopic Composition 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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