For decades, scientists have puzzled over the anatomy of hailstones. How do these icy missiles grow to such colossal sizes? Can understanding their formation help us predict the next destructive storm? Recent research from Catalonia sheds new light on these questions, offering surprising insights into the structure and development of giant hailstones using an unconventional tool—CT scans.
Hailstones form during thunderstorms when raindrops are thrust into the freezing layers of clouds, turning them into ice. As they fall, these icy particles grow by collecting more moisture and refreezing, eventually becoming heavy enough for gravity to pull them to the ground. While their descent marks the end of their journey, their development remains a subject of intense scientific inquiry.
Scanning the Storm’s Legacy
The summer of 2022 brought an extraordinary storm to Catalonia, Spain and unleashed hailstones up to 12 cm in diameter. To unravel the mystery of their formation, researchers at the Meteorological Service of Catalonia and the University of Barcelona turned to computed tomography (CT) scans. Unlike traditional methods that break hailstones to study them, CT scans allowed scientists to analyze the internal structure without destroying the samples.
“This technique enables direct observation of the entire internal structure, which can provide clues to improve hail formation forecasting,” explained Carme Farnell Barqué, lead author of the study published in Frontiers in Environmental Science. With the help of storm witnesses and frozen hailstone samples, the researchers tracked the storm’s path and transported their specimens to a dental clinic for scanning.
Unveiling the Anatomy of Hailstones
The CT scans produced 3D images by compiling 512 cross-sectional slices of each hailstone. This detailed imaging revealed unexpected intricacies. For example, the cores of hailstones were often off-center, even in spherical stones, suggesting that growth occurs unevenly in three dimensions. Researchers also found variations in density across different layers of the hailstones, hinting at the turbulent journey through the storm clouds.
“We observed that the stones grow heterogeneously, and their external shapes don’t always reflect their internal complexity,” noted Dr. Tomeu Rigo Ribas. Surprisingly, hailstones with irregular outer shapes exhibited uniform internal growth, while spherical ones displayed diverse internal structures.
A New Perspective on Hail Formation
These findings overturn long-held assumptions about hailstone development. Previously, it was thought that only irregularly shaped hailstones could grow to massive sizes. However, this study demonstrates that external and internal structures can differ significantly. Some hailstones even showed thicker layers on one side, likely the side facing downward as they fell.
“CT scans provide not only structural details but also density information, helping us identify different growth stages and understand the processes behind hail formation,” added Prof. Javier Martin-Vide.
By studying these complex internal patterns, scientists can connect the structure of hailstones to the environmental conditions in which they formed. This includes understanding the wind speeds, temperatures, and humidity levels within the storm that contributed to their growth. Such detailed knowledge is vital for advancing weather prediction models and potentially reducing the risks associated with severe hailstorms.
Challenges and Future Implications
While CT scanning offers unparalleled insights, the technique is costly, and some anomalies in the images remain unexplained. Despite these challenges, the research team is optimistic about the future applications of their findings. As climate change increases the likelihood of extreme hail events, understanding how these ice giants form could help mitigate their societal and economic impacts.
“This work provides new information that could refine hail formation forecasting, ultimately aiding in damage prevention,” emphasized Prof. Xavier Úbeda.
Additionally, the study highlights the importance of interdisciplinary collaboration. By utilizing equipment typically found in dental clinics, the researchers demonstrated that innovative approaches can yield groundbreaking results in unexpected ways.
Looking Ahead
By peering inside these icy enigmas, scientists are not only uncovering the mysteries of hailstones but also paving the way for better storm predictions. Their work serves as a reminder that even the most destructive natural phenomena can be better understood through persistence and creativity. As extreme weather events continue to challenge communities worldwide, studies like these offer a glimmer of hope—and a valuable lesson in the importance of looking deeper.
