for National Geographic News
The formation of gamma rays—the most energetic form of light—in thunderclouds may be linked to lightning production, a new study shows.
Gamma rays are typically produced by cosmic cataclysms like supernovae, but terrestrial thunderstorms can also energize particles enough to create the powerful rays.
Scientists first spotted gamma rays in thunderstorms in the early 1990s. The Compton Gamma Ray Observatory unexpectedly detected radiation originating from the ground while peering at distant supernovae.
"The fact that they are [even] created in something as garden variety as thunderstorms is a surprise," said Steven Cummer, an electrical engineer and lightning researcher at Duke University in Durham, North Carolina.
How thunderclouds produce the rays has not been explained. Neither has the nature of their apparent link to lightning formation, about which many long-standing mysteries remain.
But a new study led by Teruaki Enoto of the University of Tokyo and Harufumi Tsuchiya of RIKEN, Japan's Institute of Physical and Chemical Research, has provided the best look yet at the phenomena.
The team trained an array of gamma ray detectors on two powerful low-pressure air masses that collided over the Sea of Japan on January 6, 2007.
The researchers found that gamma rays were produced some 70 seconds before a lightning strike. They also determined that gamma bursts, which had been previously measured to last less than a second, could occur for almost a minute.
The findings suggest that whatever triggers gamma rays might also be involved in creating lighting—and that their origin might be tied to powerful particles known as cosmic rays that continually rain down from space.
(Related: "Massive Cosmic Explosion Has Astronomers Stumped" [December 20, 2006].)
The work will appear in an upcoming issue of the journal Physical Review Letters.
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