Wednesday, January 7, 2015

Gamma-ray Flashes & Storms

Thunderstorms create about a 1000 quick bursts of gamma rays (i.e., high energy light on Earth). Recent data from NASA's Fermi Gamma-ray Space Telescope compared to ground-based radar and lightning detectors, gave scientists detailed information on the different types of thunderstorms and their produced energy.

Terrestrial gamma-ray flashes (TGFs), were discovered in the 1990s by NASA's Compton Gamma-Ray Observatory. TGFs, lasting less than a thousandth of a second, are poorly understood.

"Remarkably, we have found that any thunderstorm can produce gamma rays, even those that appear to be so weak a meteorologist wouldn't look twice at them," said Themis Chronis, who led the research at the University of Alabama in Huntsville (UAH).

The Fermi data, combined with info from ground-based radar and lightning, shows that terrestrial gamma-ray flashes come from a diversity of storms and may be more common than earlier expectations. In fact, the upper part of an intracloud lightning bolt disrupts the storm's electric field creating an avalanche of electrons that surge upward at high speed. These fast-moving electrons are deflected by air molecules and emit gamma rays, creating a TGF.  

The new study confirms previous findings that TGFs tend to occur near the highest parts of a thunderstorm, between about 7 and 9 miles (11 to 14 kilometers) high.

As climate change unfolds, it will be interesting to see if TGFs increase or decrease with storms. I'm sure the Fermi folks will keep an eye to the skies. Go science!

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