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Hailstones causes billions in damage in the U.S. alone, but meteorologists know little about how they form.
A new study using isotope analysis successfully recreated the “history” of 27 hailstones as they formed in nine separate storms across China.
This data shows that hailstones primarily form by descending steadily or pushing upward in an updraft only once, which is in contrast to the traditional idea that hailstones form in a recycling process inside a storm cloud.
Every year, hailstorms cause billions in damage to homes, businesses, and crops, yet how these ice balls of destruction form in the upper troposphere has remained somewhat of a mystery. The predominant theory was that hailstones went through a recycling motion, which explained why they often contained varying layers of a clear and opaque ice.
Now, a new study from the Chinese Academy of Sciences suggests that this recycling motion is only a small part of the story. In the study, Peking University’s Qinghong Zhang, lead author of the study published in the journal Advances in Atmospheric Sciences, used stable isotope analysis to effectively recreate the “history” of 27 hailstone specimens produced by nine separate storms in China by analyzing the ‘fingerprints’ left in each stone by unique layers of the atmosphere. Using this precise method, Zhang and her colleagues could pinpoint at what level in the atmosphere certain layers of the hailstones formed, creating a vertical map of the ice chunk’s journey toward the earth.
“This work fundamentally changes how we understand hail formation,” Zhang said in a press statement. “By moving beyond assumptions to actual chemical evidence, we’re building a more accurate picture of these destructive weather phenomena.”
Of the 27 hailstones studied, only one of them displayed tell-tale signs of the hypothesized recycling method, in which hail travels up and down within a storm cloud. Some 10 stones showed that they formed while steadily descending toward the atmosphere, and another 13 displayed evidence of only one single upward push. Surprisingly, three even showed signs of nearly horizontal movement.
According to the researchers, hail typically forms in a temperature “sweet spot” of between roughly -30 and -10 degrees Celsius. However, Zhang’s data showed that embryos of hailstones can actually form outside that gradient, between about -33.4 and -8.7 degrees Celsius. Although this largely refutes the previous theory behind hailstone formation, larger hailstones do require extended time (at least one upward growth) in this zone for supercooled water to form more layers. This explains why stronger storms—with more powerful updrafts—often produce larger hailstones.
Zhang hopes that understanding the inner workings of hailstorm formation will help improve weather forecasting and our ability to estimate the potential dangers of a passing hailstorm (this research is in collaboration with the U.S. National Center for Atmospheric Research). However, improving forecasting capabilities in the U.S. may prove difficult under the Trump Administration, as it steadily levies cuts on the National Oceanic and Atmospheric Administration (NOAA), which oversees the National Weather Service. Meteorologists at NWS have already reported degraded forecasting services due to curtailed weather balloon launches used to help gather data for accurate storm prediction.
Although unlocking the secret of hailstone formation could help protect people in the path of dangerous storms, it helps to be able to identify that a storm is coming in the first place.
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