Thunderstorms are far more radioactive than previously thought, routinely producing gamma rays—the highest-energy form of electromagnetic radiation typically associated with supernovas and other cosmic events.
This phenomenon is not just common but nearly universal in large tropical thunderstorms, challenging our understanding of these powerful weather events, according to two new studies published in the scientific journal Nature.
Using a retrofitted U2 spy plane owned by NASA, scientists were able to fly directly over active thunderstorms at an altitude of 12.4 miles—more than twice as high as a commercial aircraft flies. This unique vantage point allowed them to make unprecedented observations of gamma radiation emanating from the storms below.
"We can really have this process that you can test experimentally only in accelerators, actually," Martino Marisaldi, a professor at the University of Bergen in Norway and lead author of one of the studies, told Newsweek. "We can think of thunderclouds as the most energetic natural particle accelerators on Earth."
The research team discovered two significant phenomena.
First, they found that long-lasting gamma ray emissions are intrinsic to thunderstorms, occurring frequently and on large spatial and temporal scales. Second, they identified a completely new phenomenon dubbed "flickering gamma ray flashes"—pulses of gamma rays occurring over hundreds of milliseconds.
The mechanism behind these gamma rays involves electrons being accelerated to relativistic speeds—close to the speed of light—by the enormous electric fields—as strong as 100 million AA batteries stacked end-to-end—within thunderclouds.
When these high-energy electrons collide with air molecules, they can trigger a cascade effect, producing gamma rays, other forms of radiation and antimatter.
The energy that is obtained can be up to 10-20 times greater than that found in the natural radioactive background, Marisaldi noted.
The findings have significant implications for our understanding of thunderstorms and lightning. One of the "big mysteries of atmospheric electricity," according to Marisaldi, is why lightning starts at all.
The electric fields measured in thunderclouds are typically "a factor of 10 lower than what is needed to start a spark."
The team believes their discoveries about electron acceleration and gamma ray production could provide some insights.
While the new studies don't solve the whole puzzle, they're an important step toward understanding one of the most powerful and ubiquitous forces of nature.
"There are 45 lightning strikes every second going on on the Earth, and at any given time there are more than 2000 thunderstorms," Marisaldi pointed out. "I think it's important to understand what is going on there and not just be passive receivers of this."
The journey to these discoveries took time. Marisaldi described it as "a long collaboration that started more than 10 years ago." The team conducted an initial flight campaign in 2017, but it wasn't until 2023 that they were able to fly with their full suite of instruments in the exact conditions they needed.
Looking ahead, the researchers are eager to continue their investigations.
"We have some ideas on how to test this further, so we would really be happy to go on and plan for another flight campaign," Marisaldi said.
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References
Marisaldi, M., Østgaard, N., Mezentsev, A., Lang, T., Grove, J. E., Shy, D., Heymsfield, G. M., Krehbiel, P., Thomas, R. J., Stanley, M., Sarria, D., Schultz, C., Blakeslee, R., Quick, M. G., Christian, H., Adams, I., Kroodsma, R., Lehtinen, N., Ullaland, K., Yang, S., Hasan Qureshi, B., Søndergaard, J., Husa, B., Walker, D., Bateman, M., Mach, D., Cummer, S., Pazos, M., Pu, Y., Bitzer, P., Fullekrug, M., Cohen, M., Montanya, J., Younes, C., van der Velde, O., Roncancio, J. A., Lopez, J. A., Urbani, M., & Santos, A. (2024). Highly dynamic gamma-ray emissions are common in tropical thunderclouds. Nature. https://doi.org/10.1038/s41586-024-07936-6
Østgaard, N., Mezentsev, A., Marisaldi, M., Grove, J. E., Quick, M., Christian, H., Cummer, S., Pazos, M., Pu, Y., Stanley, M., Sarria, D., Lang, T., Schultz, C., Blakeslee. R., Adams, I., Kroodsma, R., Heymsfield, G., Lehtinen, N., Ullaland, K., Yang, S., Hasan Qureshi, B., Søndergaard, J., Husa, B., Walker, D., Shy, D., Bateman, M., Bitzer, P., Fullekrug, M., Cohen, M., Montanya, J., Younes, C., van der Velde, O., Krehbiel, P., Roncancio, J. A., Lopez, J. A., Urbani, M., Santos A., & Mach D. (2024). Flickering gamma-ray flashes, the missing link between gamma glows and TGFs. Nature. https://doi.org/10.1038/s41586-024-07893-0
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