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<\/div>A destructive 2022 storm in Spain produced large hailstones up to 12 centimetres in diameter<\/p>\n
Tomeu Rigo Ribas<\/p>\n<\/div>\n<\/figcaption><\/figure>\n<\/p>\n
A scanner at a dentist\u2019s office has produced the first high-resolution 3D images of the internal structure of large hailstones. Such detailed views could help researchers better forecast which storms will generate these destructive pieces of ice.<\/p>\n
\u201cThe first result was impressive,\u201d says Carme Farnell Barqu\u00e9<\/a> at the Meteorological Service of Catalonia in Spain. \u201cWow! We can see the interior of the stone without breaking it. We could see different layers, with different densities.\u201d<\/p>\n The hailstones fell during an intense storm that struck the northeast of Spain in 2022, killing one child, injuring dozens of people and causing millions of dollars\u2019 worth of damage. The largest hailstones that fell had diameters of 12 centimetres, about twice the size of a tennis ball.<\/p>\n A few days after the storm, Farnell Barqu\u00e9 and her colleagues asked around to see if anyone had kept any of the hail. They collected 14 hailstones, up to 8.5 centimetres in diameter, that people had stored in plastic bags in their freezers.<\/p>\n <\/p>\n Hailstones form when layers of supercooled water accumulate on an initial embryonic ice particle in a storm. The shape and density of these layers of ice within hailstones can reveal details about the growth process. But normally, researchers can only study a few cross-sections of a single hailstone by slicing open the ice with a hot knife.<\/p>\n In this case, an orthodontist friend of Farnell Barqu\u00e9 suggested the researchers instead use a CT scanner to reveal the hailstones\u2019 complete internal structure. And a scanner was available in a dentist\u2019s office.<\/p>\n The team scanned three of the hailstones, generating hundreds of cross-sections showing variations in density within each piece of ice. Some of the details were surprising: for instance, although the hailstones were spherical, their nuclei were located far off centre. Farnell Barqu\u00e9 says this suggests the thickest part of the stone formed as it was falling, rather than when it was cycling between different altitudes on updrafts within the storm.<\/p>\n Julian Brimelow<\/a> at the Northern Hail Project in Canada says a few other small hailstones<\/a>\u00a0have been scanned this way, but the stones from Spain are much larger. \u201cThis is important, because we are still not certain how and where in a thunderstorm hail grows to achieve such impressive sizes,\u201d he says.<\/p>\n This better understanding could improve forecasts of hail size in future storms. \u201cWe can associate each layer of the growing part with the radar data on the evolution of the thunderstorm,\u201d says Tomeu Rigo<\/a> at the Meteorological Service of Catalonia. \u201cThen it\u2019s possible to relate this with new thunderstorms and project our results to the future.\u201d<\/p>\n \u201cWe probably do need to look at this for more hailstones,\u201d says John Allen<\/a> at Central Michigan University, who is planning a large hailstone-collecting survey in the US Great Plains in 2025. \u201cThe question is: how viable is this method for large numbers of stones?\u201d<\/p>\n Topics:<\/p>\n<\/section><\/div>\n