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by Spektrum der Wissenschaft
Growth rings of a hailstone
30.4.2025
Translation: machine translated
Detailed insights into the ice layers of a hailstone show its changing path through the atmosphere. This is not just pretty to look at - the findings should also help to improve weather models.
Before a hailstone demolishes the bodywork of a car, it has travelled a long way up and down through the atmosphere. As the three-centimetre specimen pictured here, which fell in south-east China in March 2023, shows, the changeable journey leaves clear and cloudy layers inside. The ice deposits and the conditions under which they form have been studied in more detail by a team led by atmospheric researcher Qinghong Zhang from Peking University. The findings should help to improve weather models.
The 27 hailstones used in the study came from nine hailstorms that occurred between 2016 and 2023. They were collected as part of a citizen science project and sent to Zhang's laboratory. There, the research group analysed the trapped isotopes of oxygen and hydrogen. The proportion of these atomic variants depends on the temperature and altitude in the atmosphere.
The projectiles are formed as inconspicuous ice crystals when water droplets freeze on crystallisation nuclei. However, they do not immediately tumble to the ground; instead, updrafts whirl the hail embryos up into cold areas. More ice accumulates there and the grain sinks again. Upwinds pick it up again - until they can no longer carry the grain and it finally falls.
According to the study, however, only 8 of the 27 hailstones, including the one shown here, had undergone such a back and forth. 16 of them fell or rose monotonously, and 3 barely moved vertically; such grains were smaller on average. Zhang's team compared the findings with weather data. In this way, they hope to gain a better understanding of hailstorms, which sometimes cause billions in damage.
Spectrum of Science
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Originalartikel auf Spektrum.deHeader image: Xiangyu Lin, Peking University, Beijing
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