Captured from a distance of 350 km, a gigantic jet of lightning travels 65 km from the top of a thunderstorm to the edge of space.
Credit: Duke University
SYDNEY: U.S. scientists have photographed what may be the biggest and brightest gigantic lightning jet ever recorded, as it travelled some 65 km from the top of thunderclouds to the edge of space.
As detailed in the journal Nature Geoscience, the images of this rare and highly charged meteorological event were captured during Tropical Storm Cristobal as it passed nearby Duke University in Durham, North Carolina, in July 2008.
"[Gigantic jets] are essentially upward lightning from thunderclouds that deliver charge just like conventional cloud-to-ground lightning. What struck us was the size of this event," said study co-author Steven Cummer, an electrical engineer at the university.
Radio signatures
"We were close enough to also record, for the first time, clear radio signatures," he added. "[These] show that these jets are in fact very powerful lightning that goes from thunderclouds all the way to the edge of space."
Gigantic jets were discovered in 2001, but only five have been recorded since and experts still know relatively little about them. What they do know shows that they result from the direct electrical coupling between thunderstorms in the lower (troposphere) and upper (ionosphere) layers of the atmosphere.
A jet begins as a thin channel that rises out of a cloud, moving negative charge upwards, said Cummer. After taking a few seconds for the channel to reach high altitudes, it makes a strong electrical connection to the upper atmosphere, brightens, and moves charge from the thunderstorm to the lower edge of space. The jet remains bright for a fraction of a second before fading away, he said.
Low light photography
While the jets do not occur every time there is conventional lightning, the amount of electricity discharged by each is comparable.
The two forms of lightning differ in that upward travelling jets can travel farther and faster than their cloud-to-ground cousins, because thinner air between the clouds and the ionosphere provides less resistance. A conventional flash of lightning travels no more than 7.5 km.
In order to take images and video, the team used equipment intended to capture another weather phenomenon called 'sprites', which are red- or blue-coloured electrical discharge that occurs above thunderstorms. The equipment includes a low-light video camera trained on the sky and controlled remotely.
