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Hailstone Embryos

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  • 1 National Center for Atmospheric Research, Boulder, Colo
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Abstract

General properties of hailstone embryos, from hailstorms mostly in the western United States, are described and discussed in terms of the conditions of growth. Most embryos are composed of large crystals, indicating growth at environmental temperatures ≳−20C. Very wet or spongy growth gives spherical embryos, that presumably tumble because of this growth character. Dry growth leads to the more common, conical embryos. The almost universal presence of a distinct embryo stage in hailstone formation, coupled with certain systematic differences between embryo growth and hailstone growth, appears to be strong evidence that “trigger particles” (Weickmann) are usually necessary in hailstone formation.

Abstract

General properties of hailstone embryos, from hailstorms mostly in the western United States, are described and discussed in terms of the conditions of growth. Most embryos are composed of large crystals, indicating growth at environmental temperatures ≳−20C. Very wet or spongy growth gives spherical embryos, that presumably tumble because of this growth character. Dry growth leads to the more common, conical embryos. The almost universal presence of a distinct embryo stage in hailstone formation, coupled with certain systematic differences between embryo growth and hailstone growth, appears to be strong evidence that “trigger particles” (Weickmann) are usually necessary in hailstone formation.

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