NASA’s Fermi Telescope Captures Extreme Burst Of Gamma Rays From Tropical Storms

Posted: Apr 29 2017, 3:48pm CDT | by , Updated: Apr 29 2017, 3:50pm CDT, in News | Latest Science News

 
NASA’s Fermi Telescope Captures Extreme Burst of Gamma Rays from Tropical Storms
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For the first time, researchers analyse flashes of some of the highest-energy light found on Earth

Gamma rays are the most energetic form of light in the universe. In outer space, these powerful explosions are caused by dying stars or feeding black holes. On Earth, the bursts often occur in thunderstorms and the gamma rays found in Earth’s atmosphere are known as terrestrial gamma-ray flashes.

The terrestrial gamma-ray flashes or TGFs last less than a millisecond and produce gamma rays at a very short wavelength of less than one tenth of a nanometer.

NASA’s Fermi Gamma-ray Space Telescope has been studying gamma radiation since 2008 and has recorded more than 4,000 terrestrial gamma-ray flashes throughout that period. But the instrument had never captured gamma rays produced by tropical storms, hurricanes or typhoons before.

Initially, Fermi’s Gamma-ray Burst Monitor (GBM) instrument could detect TGFs within about 500 miles of the spacecraft, which is not too impressive in terms of understanding specific storms. In 2012, however, Fermi scientists upgraded the instrument which increased its sensitivity and allowed it to pinpoint the flashes with much greater precision.

Researchers believe that terrestrial gamma rays arise from the strong electric fields in the upper regions of thunderstorms. Under certain conditions, these electric fields become strong enough to trigger a cascade of electrons upward at nearly the speed of light. When these electrons pump into air molecules, their paths change slightly and this change causes the electrons to emit gamma rays. But new observations suggest that TFGs are not solely dependent on storm intensity. In fact, weaker storms are capable of producing more numbers of TGFs, which may arise anywhere in the storm. In hurricanes and typhoons, TGFs are more common in the outermost rain bands. These areas also have the highest lightning rates during storms.

Generally, most of the tropical storm TGFs occurs as the systems intensifies. The intensity drives clouds higher into the atmosphere where they can generate powerful electric fields and set the stage for intense lightning and TGFs.

The upgraded GBM version also showed that most TGFs generate a strong pulse of very low frequency radio waves as well. These signals previously attributed only to lightning.

“Combining TGF data from GBM with precise positions from these lightning detection networks has opened up our ability to connect the outbursts to individual storms and their components.” Co-author Michael Briggs from Center for Space Plasma and Aeronomic Research at University of Huntsville said.

The new findings helped researchers better understand how terrestrial gamma rays relate to lightning activity, the strength of storm and the regions where they can occur most.

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