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  • [Thunder]

  • [Thunder]

  • [Thunder] [Music]

  • Deep within their roiling clouds, thunderstorms hold an elusive

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

  • energy radiation naturally found on Earth: terrestrial gamma-ray

  • or TGFs for short.

  • Studies by NASA's Fermi Gamma-ray Space Telescope

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

  • Now, new research combines Fermi detections

  • with ground-based radar and lightning location data.

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

  • In a thunderstorm, collisions among rain and snow cause different

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

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

  • the thundercloud, a lighting flash occurs.

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

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

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

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

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

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

  • global lightning location networks, scientists can determine a TGF

  • position more accurately than with Fermi data alone. Two dozen

  • localized TGFs occurred within areas covered by next-generation weather

  • radar systems. This gives scientists the opportunity to begin studying

  • the kinds of storms that produce TGFs. These slices of

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

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

  • Another finding: TGFs seem to occur

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

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

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

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

  • which probably means the satellite is undercounting them.

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

  • knowledge, scientists can design experiments to track storms and

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

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

  • accelerator. [Beeping]

  • [Beeping and thunder]

  • [Thunder]

[Thunder]

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