Aging of Accreted Ice

Abstract

The effect of annealing in accreted ice has been investigated for artificially grown ice deposits after ?100 days of storage in a deep freeze unit. Cross sections of the cylindrical deposits have been cut and replicated soon after growth and after annealing to determine the average cross section σ?, the maximum length li, the maximum width wi, and the orientation of the c axis of the crystal grains. Significant grain growth has been observed even at the relatively low temperature of ?19°C. The average grain cross section increased for nearly all the deposits, and a decrease of the grain elongation was observed while the crystals tended to assume compact final shapes. The statistical distributions of the orientations of crystal grains was not modified substantially by annealing, thus indicating that information on hailstone growth may be contained more firmly in the orientation of crystals rather than in their size. The change of the crystal dimensions is interpreted in terms of a polycrystalline grain growth process. The consequences of annealing on the crystal size analysis in hailstones are examined.