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Cosmic Rays May Reveal Why Lightning Strikes

Irene Klotz, Discovery News

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What's the Spark? | Discovery News Video

June 9, 2009 -- A team of Florida researchers is testing a novel idea that radio waves dancing in particles created by cosmic rays can solve a long-standing mystery about what sparks lightning.

"How does lightning get started? How does it move around? All the basic questions have not been answered," said Joseph Dwyer, a professor of physics and space sciences at the Florida Institute of Technology in Melbourne, Fla.

Rather than trying to measure electric fields within storms directly, the scientists are looking to measure how storms' electric fields alter cosmic ray particles that rain down from space and then pass through Earth's atmosphere.

Measurements of the electric fields inside clouds are difficult to make, though scientists have been trying for decades to fly instrumented aircraft and balloons into storms without much success.

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What information has been collected suggests that the electric fields aren't big enough to spark lightning, though it obviously occurs.

"It takes something like 30,000 volts per centimeter (of static electricity) to get a spark off your finger to a doorknob. That type of spark doesn't exist in thunderstorm electric fields, or we haven't been measuring in the right place," Martin Uman, director of University of Florida's Lighting Research Laboratory, told Discovery News.

The new technique, described in a recent paper in the Journal of Geophysical Research, bypasses the need to send sensors into stormy skies. Instead, Dwyer and colleagues use the naturally-occurring fallout from cosmic ray impacts on the atmosphere to remotely probe storms' electric fields.

This summer, instruments at the International Center for Lightning Research and Testing at Camp Blanding, Fla., include a particle detector and electric field antenna to study radio frequencies generated by cosmic rays passing through storms.

Cosmic rays, which are believed to spawned by distant supernova explosions, regularly , triggering cascades of high-energy particles and showers of secondary particles, including electrons, positrons and muons.

"By the time you get to the ground most of the particles that are left are muons," Dwyer said in an interview.