Scientists reveal that hail forms differently than commonly believed

Research shows hailstones form simpler, revising previous beliefs.

: New research by an international team challenges the traditional understanding of hail formation. Analyzing the chemical signatures within hailstones, they found most hailstones form via simpler, direct paths rather than repeated cycling through storm clouds. Out of 27 samples, only one showed signs of consistent cycling in clouds. This study, involving researchers like Qinghong Zhang, offers new insights for improving severe weather forecasts.

Recently, a groundbreaking study has revised our understanding of how hailstones form. Previously, it was believed that hailstones cycled through storm clouds, gaining layers by moving up and down until they were too heavy to be supported by updrafts. This assumption has been overturned by new research, as presented in a publication in the journal Advances in Atmospheric Sciences, led by Qinghong Zhang from Peking University. The team, including researchers from China and the U.S., analyzed the chemical signatures within the ice of 27 Chinese hailstones.

The method used involved examining stable isotopes, non-radioactive atom forms, to trace the formation conditions of the hailstones at differing altitudes and temperatures. Results showed that only one hailstone indicated multiple cycles through the storm clouds, challenging long-held beliefs. Most of the hailstones formed through simpler, more direct paths, some only making a single upward journey or growing during descent. This direct formation process has significant implications for improving severe weather predictions.

In particular, the study found that hailstones larger than 25 mm typically experienced at least one period of upward movement due to strong updrafts. Hailstone growth generally occurs at altitudes where the temperature is between -10 and -30 degrees Celsius, but the research discovered that hail 'embryos' could develop in a broader thermal range, from -8.7 to -33.4 degrees Celsius. These climate conditions were identified through trajectory analysis of the collected samples.

Citizen scientists in China collected these hailstones as part of a project organized by the World Meteorological Organization. Moving forward, the research team expressed intentions to extend their analysis to include particulate matter found in hailstones for further studies. This continued research could not only provide deeper insights into the processes behind hail formation but also guide better forecasting techniques.

Understanding hail formation more accurately is increasingly important as global warming contributes to the frequency and intensity of severe weather events. Scientists warn that warming could lead to the development of even larger hailstones, underscoring the importance of continued investigation in this area.

Sources: Peking University, Advances in Atmospheric Sciences, World Meteorological Organization

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