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Convective storms hold an extraordinary 

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surprise. Under just the right conditions, 

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they fire off some of the highest-energy light naturally found on Earth--

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terrestrial gamma-ray flashes, or TGFs.

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Rising and falling snow and ice particles

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repeatedly collide, filling the cloud with electrical charge. Once the

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electric field is strong enough, a current flows and a lightning flash

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occurs. The flash produces an abrupt reconfiguration of 

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the electric field. In some cases, a surge of electrons

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rushes toward the upper part of the storm at speeds nearly as

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fast as light. When deflected by air molecules, these

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accelerated electrons give off gamma rays, producing a TGF.

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Data from NASA's Fermi Gamma-ray Space Telescope

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suggest more than a thousand TGFs occur each day all over the globe.

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For the first time, improved data link dozens of

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TGFs to specific tropical weather systems.

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Tropical storms far from land tend to generate less frequent lightning.

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Nevertheless, observations show they are surprisingly prolific producers

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of TGFs. Tropical Storm Manuel

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made landfall just shy of hurricane strength. As it rapidly

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weakened, it produced two TGFs within 24 hours.

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More typically, TGFs are associated with the strengthening

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phase of a storm. As Typhoon Bolaven rapidly

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developed in 2012, thunderstorms nearly 500 miles from 

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its center launched a TGF with four distinct pulses.

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So far, the record-holder for TGFs

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is the rapidly strengthening tropical wave that later gave birth

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to Hurricane Julio. It produced four TGFs within

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100 minutes. A fifth followed the next day, with nothing further.

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What scientists learned so far

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is that weather tropical storms are capable of producing more TGFs,

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and those events can arise anywhere in the storm.

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For stronger storms, like hurricanes and typhoons, TGFs are more common

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in the outer rain bands, which host the highest lightning flash rates

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in these storms. The findings provide new insights

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into the relationship between storm intensity, lightning frequency, 

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and TGFs. This adds another important piece to the puzzle

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of our understanding of TGFs and how they are created in thunderstorms--

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the most powerful natural particle accelerators on planet Earth.

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On-screen text: NASA astrophysics

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