Why scientists scanned giant hailstones in a dentist’s office

A dentist’s scanner has produced the first high-resolution 3D images of the internal structure of large hailstones. Such detailed insights can help researchers better predict which storms will produce these destructive chunks of ice.

“The first result was impressive,” he says Carme Farnell Barque In Spain at the Meteorological Service of Catalonia. “Wow! We can see the inside of the stone without breaking it. We could see different layers, with different densities.”

In 2022, hail fell during a severe storm that hit northeastern Spain, killing a child, injuring dozens of people and causing millions of dollars in damage. The largest hailstones that fell were 12 centimeters in diameter, twice the size of a tennis ball.

A few days after the storm, Farnell Barqué and his colleagues asked if anyone had saved the hail. They collected 14 hailstones, up to 8.5 centimeters in diameter, that people kept in plastic bags in the freezer.

Hail forms when layers of supercooled water accumulate on an early embryonic ice particle in a storm. The shape and density of these ice layers can reveal details about the growth process within the hail. But typically, researchers can only study a few cross-sections of a single hailstone by cutting open the ice with a hot knife.

In this case, an orthodontist friend of Farnell Barqué suggested the researchers use a CT scanner to show the entire internal structure of the hail. And there was a scanner in the dentist’s office.

The team scanned three of the hailstones, creating hundreds of slices that show density variations within each piece of ice. Some of the details were surprising: for example, although the hailstones were spherical, their nuclei were far from the center. Farnell Barqué says this suggests the thickest part of the rock formed during the fall, rather than cycling between different altitudes in updrafts within the storm.

Julian Brimelow Canada’s Northern Hail Project says a other small hailstones they have been scanned like this, but the stones from Spain are much larger. “This is important because we still don’t know for sure how and where hailstones grow to such impressive sizes,” he says.

This better understanding could improve forecasts of hail size in future storms. “We can match each layer of the growing part with radar data about the evolution of the thunderstorm,” he says. Take Rigo Meteorological Service of Catalonia. “It is then possible to relate this to new storms and project our results into the future.”

“We’ll probably have to look into this for more hail,” he says John Allen at Central Michigan University, which is planning a major survey of hail collection in the US Great Plains in 2025. “The question is: how feasible is this method for large numbers of stones?”