The Collection and Analysis of Freshly Fallen Hailstones

K. A. Browning National Severe Storms Laboratory, Norman, Okla.

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J. Hallett National Severe Storms Laboratory, Norman, Okla.

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T. W. Harrold National Severe Storms Laboratory, Norman, Okla.

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D. Johnson National Severe Storms Laboratory, Norman, Okla.

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Abstract

Attempts have been made to obtain samples of freshly fallen hailstones from severe storms in Oklahoma with the purpose of studying the nature and extent of spongy ice within natural hail. Interception by automobile of radar echoes with Ze > 105 mm6 m−3 has been found to provide a workable technique for collecting large hailstones as they fall to the ground. Observations suggest that the regions of highest reflectivity were associated more closely with the falls of large hail than with the accompanying heavy rain.

Immediate sectioning of the freshly fallen hailstones revealed the presence of thin shells of spongy ice in many of the larger stones. Calorimetric analyses gave liquid water contents of up to 12 ± 4% of the mass of the stones. Some of the hailstones were aspherical owing to preferential melting of the regions of spongy ice during fall. In the case of hailstones that were stored at sub-freezing temperatures, spongy ice shells could often still be identified from the presence of millimeter size cavities embedded within ice composed of large crystals.

Abstract

Attempts have been made to obtain samples of freshly fallen hailstones from severe storms in Oklahoma with the purpose of studying the nature and extent of spongy ice within natural hail. Interception by automobile of radar echoes with Ze > 105 mm6 m−3 has been found to provide a workable technique for collecting large hailstones as they fall to the ground. Observations suggest that the regions of highest reflectivity were associated more closely with the falls of large hail than with the accompanying heavy rain.

Immediate sectioning of the freshly fallen hailstones revealed the presence of thin shells of spongy ice in many of the larger stones. Calorimetric analyses gave liquid water contents of up to 12 ± 4% of the mass of the stones. Some of the hailstones were aspherical owing to preferential melting of the regions of spongy ice during fall. In the case of hailstones that were stored at sub-freezing temperatures, spongy ice shells could often still be identified from the presence of millimeter size cavities embedded within ice composed of large crystals.

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