Weather scientists have used 3D scans to delve deep into the inner anatomy of hailstones, providing them with information that could help mitigate future hailstone damage.

In a study published in Frontiers in Environmental Science, researchers in Catalonia have used computed tomography (CT) scans to investigate the cores of hailstones.

“It is the first time that we have a direct observation of the entire internal structure of hailstones, which can provide clues to improve hail formation forecasting,” says lead author of the study Carme Farnell Barqué, a researcher at the Meteorological Service of Catalonia.

While scientists have been studying hailstone anatomy and growth since the 1960s, it has often involved breaking the stones in the process.

“We show that the CT scanning technique enables the observation of the internal structure of the hailstones without breaking the samples,” Farnell Barqué says.

The researchers examined hailstones up to 12 cm in diameter. They were collected from a particularly strong thunderstorm from bad weather which hit southwest Europe along the Iberian Peninsula on 30 August 2022.

They used equipment, similar to those used in a dental clinic, to scan some of the stones.

“We didn’t expect to obtain as clear imagery as we got,” says senior author Professor Xavier Úbeda, a researcher at the University of Barcelona.

“We wanted to use a technique that would provide more information regarding the internal layers of the hailstones, but without breaking the samples.”

After analysing the scans, the researchers observed that the shape of the internal hailstone layers differed from its external shape, something that previous researchers had assumed was not possible.

“In one case, we have demonstrated that the sample exhibited heterogeneous growth but had a regular external shape. Conversely, stones with irregular external shapes showed homogeneous growth,” says Farnell Barqué.

“Until now, it was believed that very large hailstones could only have irregular shapes.”

The size of a hailstone depends on how much moisture there is in the air, with more moisture leading to larger hailstones.

As climate change heats up the Earth’s atmosphere, this also increases the amount of moisture in the air. Depending on how much we decrease greenhouse gas emissions, a recent study from Northern Illinois University has projected that the frequency of large hailstones could increase by 75%.

The researchers also found that the core of the stones was not always located in the centre, as they had expected.

“This fact implies that the stones can grow heterogeneously in three directions,” says co-author Dr Tomeu Rigo Ribas.

Although the CT scans might be expensive, the team believe their work into understanding how hailstones grow will help to model and predict future hailstone patterns and better prepare society to mitigate the risk of hailstone damage in wild weather.

Hail damage can cause destruction to cars, buildings and agriculture which can have considerable impacts on the economy.

“CT scans provide information related to the density, which allows us to identify the different stones’ layers associated with the growth stages of the hailstorm,” says Professor Javier Martin-Vide, a co-author of the study.

“They also help us understand the processes that contributed to its formation.”

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