Steven A. Cummer et al., Nature Geoscience, 2009, Quantification of the troposphere-to-ionosphere charge transfer in a gigantic jet

Nature Geoscience, published online 23 August 2009; doi: 10.1038/ngeo607

Quantification of the troposphere-to-ionosphere charge transfer in a gigantic jet

Steven A. Cummer¹, Jingbo Li¹, Feng Han¹, Gaopeng Lu¹, Nicolas Jaugey¹, Walter A. Lyons² and Thomas E. Nelson²

Abstract

Gigantic jets are the clearest manifestation of direct electrical coupling between tropospheric thunderstorms and the ionosphere. They are leaders^{1, 2, 3} that emerge from electrical breakdown near the top of thunderstorms⁴ and extend all the way to the lower edge of the ionosphere near 90-km altitude⁵. By contrast, blue jets⁶ and other related events^{7, 8} terminate at much lower altitudes. Gigantic jets have been observed from the ground^{5, 9, 10} and from orbit¹¹. Some seem to be consistent with an upward-propagating negative discharge of 1,000-2,000 C km total charge moment change ⁹, but others have not been connected to distinguishable electromagnetic signatures¹⁰. Here we report simultaneous low-light video images and low-frequency magnetic field measurements of a gigantic jet that demonstrate the presence and dynamics of a substantial electric charge transfer between the troposphere and the ionosphere. The signatures presented here confirm the negative polarity of gigantic jets⁴ and constrain the lightning processes associated with them. The observed total charge transfer from the thunderstorm to the ionosphere is 144 C for the assumed channel length of 75 km, which is comparable to the charge transfer in strong cloud-to-ground lightning strokes.

¹Electrical and Computer Engineering Department, Duke University, Durham, NC 27708, U.S.A.

²FMA Research, Inc., Yucca Ridge Field Station, Fort Collins, CO 80524, U.S.A.

*Correspondence: Steven A. Cummer¹ e-mail: cummer@ee.duke.edu

Link to abstract: http://www.nature.com/ngeo/journal/vaop/ncurrent/abs/ngeo607.html

Steven Cummer et al.: Gigantic jets blast electricity into upper atmosphere

Gigantic jets blast electricity into upper atmosphere

The gigantic jet observed by Steven Cummer and his team. The thunderstorm that produced this jet was over 300 kilometres away, below the visible horizon (Image: Steven Cummer)

See YouTube video: Gigantic jets

by Michael Marshall, New Scientist, August 23, 2009

The ancient Greeks might have thought Zeus was furious with heaven itself. The power of lightning strikes that shoot upwards from storm clouds has been measured for the first time – and they turn out to be every bit as powerful as normal lightning.

First caught on camera in 2003, "gigantic jets" shoot upwards from thunderclouds and can reach altitudes above 80 kilometres. But it wasn't until 21 July last year that Steven Cummer at Duke University in Durham, North Carolina, and his colleagues managed to measure the electrical discharge from a single gigantic jet, released from tropical storm Cristobal.

"No one had been very close to one with the right radio instrumentation before," Cummer says. "So we didn't know whether they just petered out without doing anything much, or whether they actually took some charge and dumped it somewhere."

Electric jet

The jet came out of a high storm cloud, beginning at an altitude of about 14 kilometres, and shot upwards for a further 75 kilometres.

At those heights, the atmosphere is a much better electrical conductor than at ground level because of ionising radiation from space. As a result, the jet was able to discharge 144 coulombs of charge into the upper atmosphere in about 1 second.

This is comparable to the charge transferred by a large cloud-to-ground lightning strike.

"It's fantastic that they see such a high charge transfer between the thundercloud and the ionosphere," says Victor Pasko of Pennsylvania State University in University Park.

Changing weather

Gigantic jets could be important for our ability to predict lightning strikes.

"There is this newly identified path for discharging the thunderstorm, and a lot of charge can be moved," says Cummer. "In storms that can produce gigantic jets, it might influence what other lightning is happening in the storm."

This time, however, the team found no difference in the rate of ordinary lightning strikes around the time of the gigantic jet. "I'm surprised they saw no drop in lightning rates before or after the jet – but that might be because of the sheer size of the storm," says Pasko.

Gigantic jets are one of a host of new atmospheric phenomena discovered in recent years. Other examples are sprites and blue jets.

Journal reference: Nature Geoscience, DOI: 10.1038/ngeo607 (in press)

Link: http://www.newscientist.com/article/dn17664-gigantic-jets-blast-electricity-into-upper-atmosphere.html