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The Falling Behavior of Hailstones

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

A detailed examination and interpretation of hailstone structure and symmetry leads to the conclusion that the normal falling behavior of moderate-to-large hailstones is rapid, symmetrical tumbling. The tumbling behavior is evidently critically sensitive to one or more of the important parameters, such as surface roughness, density distribution, etc., because similar hailstones grow with different symmetries. The concept of aerodynamic molding is found to be inapplicable to the growth and shape of natural hailstones, with the possible exception of small stones and icicle lobe structures. If, as is the conclusion, hailstones tumble while falling, previous deductions of terminal velocities and heat transfer rates may be substantially incorrect.

Abstract

A detailed examination and interpretation of hailstone structure and symmetry leads to the conclusion that the normal falling behavior of moderate-to-large hailstones is rapid, symmetrical tumbling. The tumbling behavior is evidently critically sensitive to one or more of the important parameters, such as surface roughness, density distribution, etc., because similar hailstones grow with different symmetries. The concept of aerodynamic molding is found to be inapplicable to the growth and shape of natural hailstones, with the possible exception of small stones and icicle lobe structures. If, as is the conclusion, hailstones tumble while falling, previous deductions of terminal velocities and heat transfer rates may be substantially incorrect.

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