"Upside Down" Lightning as Strong as Earth-bound Bolts
for National Geographic News
|August 23, 2009|
Lightning that shoots upward from clouds can be as powerful as the strongest bolts that strike the ground, according to researchers who caught the strange phenomenon on film. (Watch the video, slowed down to show how the lightning bolt moves.)
Known as gigantic jets, these rare "upside down" bolts had previously been seen reaching into the uppermost layers of the atmosphere, up to 56 miles (90 kilometers) above the storm itself.
But researchers had witnessed gigantic jets just a handful of times, leaving much unknown about the strength and electrical activity of the unusual lightning strikes.
Stroke of Luck
On July 21, 2008, a team led by Steven Cummer at Duke University in North Carolina had a stroke of luck.
The scientists had set up an automated video system equipped to study magnetic activity from thunderstorms moving through the area around the university.
"My research group had actually been interested in studying sprites, a different lightning phenomenon in the upper atmosphere," Cummer said.
(Related: "Mysterious 'Sprites' Light Shows Captured on Film.")
Six months into the project, tropical storm Cristobal moved over the region, and the video system captured a gigantic jet rising from the tempest.
"Essentially nothing was known about the electrical nature of gigantic jets, [so] we immediately started analyzing our data to understand what was going on," Cummer said.
The researchers found that the upward lightning carried 144 Coulombs of electrical charge.
"This gigantic jet carried as much charge to the upper atmosphere as the very biggest cloud-to-ground lightning strokes about a hundred to a thousand times bigger than a typical lightning stroke," Cummer said.
The finding totally shocked the research team, since it's the first clear proof that an electric charge can move directly from the troposphere into the ionosphere, two layers of Earth's atmosphere.
Until now "we didn't know whether gigantic jets actually made electrical contact with the upper atmosphere to discharge the thunderstorm," Cummer said.
"That thunderstorms can be electrically connected to the upper atmosphere and push quite a bit of electric charge up there is a surprise."
Findings appear in the August 23 issue of the journal Nature Geoscience.
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