About a thousand times a day, thunderstorms fire off fleeting bursts of some of the highest-energy light naturally found on Earth. These events, called terrestrial gamma-ray flashes (TGFs), last less than a millisecond and produce gamma rays with tens of millions of times the energy of visible light. Since its launch in 2008, NASA's Fermi Gamma-ray Space Telescope has recorded more than 4,000 TGFs, which scientists are studying to better understand how the phenomenon relates to lightning activity, storm strength and the life cycle of storms.
About a thousand times a day, thunderstorms fire off fleeting bursts of some of the highest-energy light naturally found on Earth. These events, called terrestrial gamma-ray flashes (TGFs), last less than a millisecond and produce gamma rays with tens of millions of times the energy of visible light. Since its launch in 2008, NASA's Fermi Gamma-ray Space Telescope has recorded more than 4,000 TGFs, which scientists are studying to better understand how the phenomenon relates to lightning activity, storm strength and the life cycle of storms.
Now, for the first time, a team of NASA scientists has analyzed dozens of TGFs launched by the largest and strongest weather systems on the planet: tropical storms, hurricanes and typhoons. A paper describing the research was published March 16 in the Journal of Geophysical Research: Atmospheres.
"One result is a confirmation that storm intensity alone is not the key factor for producing TGFs," said Oliver Roberts, who led the study at the University College Dublin, Ireland, and is now at NASA's Marshall Space Flight Center in Huntsville, Alabama. "We found a few TGFs were made in the outer rain bands of major storms, hundreds of kilometers from the powerful eye walls at their centers, and one weak system that fired off several TGFs in a day."
Scientists suspect TGFs arise from the strong electric fields near the tops of thunderstorms. Under certain conditions, these fields become strong enough to drive an "avalanche" of electrons upward at nearly the speed of light. When these accelerated electrons race past air molecules, their paths become deflected slightly. This change causes the electrons to emit gamma rays.
Continue reading at NASA / Goddard Space Flight Center
Photo: This photograph, taken in May 2008 as the Fermi Gamma-ray Space Telescope was being readied for launch, highlights the detectors of the spacecraft's Gamma-ray Burst Monitor (GBM). An identical set of detectors is mounted on the opposite side of the spacecraft. The GBM is an array of 14 crystal detectors designed for transient lower-energy gamma-ray outbursts, such as TGFs.
Credits: NASA / Jim Grossmann
