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[Thunder]

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[Thunder]

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[Thunder] [Music]

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Deep within their roiling clouds, thunderstorms hold an elusive

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surprise. Under just the right conditions, they produce some of the highest

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energy radiation naturally found on Earth: terrestrial gamma-ray

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or TGFs for short.

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Studies by NASA's Fermi Gamma-ray Space Telescope

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have shown that TGFs fire up about 1,100 times a day.

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Now, new research combines Fermi detections

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with ground-based radar and lightning location data.

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These studies show that TGFs come from more diverse types of storms than previously thought

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In a thunderstorm, collisions among rain and snow cause different

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parts of the clouds to develop positive and negative electrical charges.

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When the strength of the electric field overcomes the insulating properties in 

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the thundercloud, a lighting flash occurs.

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Most lightning occurs entirely within the cloud and is called an intracloud flash.

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All lightning produces a strong and sudden change in the storm's electric field,

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but the upward portion of an intracloud flash sometimes sends a surge

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of electrons rushing toward the upper part of the storm. Reaching

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speeds nearly as fast as light, these accelerated electrongs give off

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gamma rays when their paths are deflected by air molecules. Using

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global lightning location networks, scientists can determine a TGF

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position more accurately than with Fermi data alone. Two dozen

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localized TGFs occurred within areas covered by next-generation weather

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radar systems. This gives scientists the opportunity to begin studying

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the kinds of storms that produce TGFs. These slices of

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radar data capture different types of storms encompassing a wide range of

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updraft strengths. Even the weakest of them produced a TGF.

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Another finding: TGFs seem to occur

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in the same altitude range, between 7 and 9 miles high.

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Lightning can form at much lower altitudes, so there's every reason

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to think TGFs can too, but gamma-rays from TGFs occuring

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deeper in the atmosphere are greatly weekend, they're too dim for Fermi to detect,

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which probably means the satellite is undercounting them. 

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TGFs may be far more common than we think. With this

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knowledge, scientists can design experiments to track storms and

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study how TGFs relate to their strength and evolution. This will give us

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an even better understanding of planet Earth's most powerful natural particle

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accelerator. [Beeping]

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[Beeping and thunder]

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[Thunder]