A huge lightning bolt which rose 50 miles into space above a thunderstorm has offered new insights into mysterious ‘gigantic jets’, which carry huge amounts of electrical charge.
Scientists believe up to 50,000 ‘gigantic jets’ may occur every year - and the new research may help to explain why they shoot up into space rather than down towards the ground.
The gigantic jet rose out of a thunderstorm in Oklahoma and is the most powerful ever studied.
Normal lightning bolts carry less than five coulombs of electrical charge: the gigantic jet moved an estimated 300 coulombs of electrical charge into the ionosphere, the lower edge of space.
The upward discharge included structures known as ‘leaders’ which were 4,400C, as well as streamers of cooler plasma.
Corresponding author Levi Boggs, a research scientist at the Georgia Tech Research Institute (GTRI) said, "We were able to map this gigantic jet in three dimensions with really high-quality data.
“We were able to see very high frequency (VHF) sources above the cloud top, which had not been seen before with this level of detail.
“Using satellite and radar data, we were able to learn where the very hot leader portion of the discharge was located above the cloud."
Steve Cummer, professor of electrical and computer engineering at Duke, uses the electromagnetic waves that lightning emits to study the powerful phenomenon.
He operates a research site where sensors resembling conventional antennas are arrayed in an otherwise empty field, waiting to pick up signals from locally occurring storms.
Cummer said, "The VHF and optical signals definitively confirmed what researchers had suspected but not yet proven: that the VHF radio from lightning is emitted by small structures called streamers that are at the very tip of the developing lightning, while the strongest electric current flows significantly behind this tip in an electrically conducting channel called a leader,".
Gigantic jets have been observed and studied over the past two decades, but because there's no specific observing system to look for them, detections have been rare.
Boggs learned about the Oklahoma event from a colleague, who told him about a gigantic jet that had been photographed by a citizen-scientist who had a low-light camera in operation on May 14, 2018.
Fortuitously, the event took place in a location with a nearby VHF lightning mapping system, within range of two Next Generation Weather Radar (NEXRAD) locations and accessible to instruments on satellites from NOAA's Geostationary Operational Environmental Satellite (GOES) network.
Boggs determined that the data from those systems were available and worked with colleagues to bring it together for analysis.
Boggs explained, "The detailed data showed that those cold streamers start their propagation right above the cloud top.
“They propagate all the way to the lower ionosphere to an altitude of 50–60 miles, making a direct electrical connection between the cloud top and the lower ionosphere, which is the lower edge of space."
Why do the gigantic jets shoot charge into space? Researchers speculate that something may be blocking the flow of charge downward—or toward other clouds.
Records of the Oklahoma event show little lightning activity from the storm before it fired the record gigantic jet.
Boggs said, "For whatever reason, there is usually a suppression of cloud-to-ground discharges.
“There is a buildup of negative charge, and then we think that the conditions in the storm top weaken the uppermost charge layer, which is usually positive. In the absence of the lightning discharges we normally see, the gigantic jet may relieve the buildup of excess negative charge in the cloud."
Estimates for the frequency of gigantic jets range from 1,000 per year up to 50,000 per year.
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