Researchers uncover secrets of rare ‘giant jet’ lightning


A simple lightning bolt can be shocking enough, but researchers are uncovering the secrets behind a rare species of electrical discharge called “giant jets.” These are extraordinary bursts of light from above clouds that can brush up to the edge of space.

Only five observations of these jets are made in an average year, usually by accident. Sometimes lucky photographers capture them in long-exposure images, and sometimes they are seen by weather satellites.

A study published on Wednesday Journal Science Advances sheds light On the structure and cause of giant jets. It analyzed a jet that left Oklahoma on May 14, 2018, shot 50 miles above a storm cloud and delivered more charge than 100 conventional lightning bolts. It was the most powerful giant jet studied.

Researchers mapped the jet in 3D and identified structural features in greater detail than ever before.

The elusive red sprite, like a glowing jellyfish in the night sky, photographed in Oklahoma

The investigation was prompted when Levi Boggs, a research scientist at the Georgia Tech Research Institute and one of the paper’s lead authors, learned of a photograph of an Oklahoma jet by a citizen scientist.

“Kevin Palivesi [the photographer] There’s an l0w-light camera in central Texas that he operates sometimes randomly, and he captured it a few years ago,” Boggs said. The picture was “sitting around. I was told about it and decided to do a little research.”

That’s when Boggs assembled a team that reviewed satellite, radar and radio-wave data to reconstruct what had happened.

The researchers were able to develop a model of the jet in 3D as it was observed by two satellite-based optical Lightning instruments, including the lightning mapping array on the GOES-15 weather satellite that hovers over the eastern United States.

“I think it left an area of ​​about 50 kilometers by 50 kilometers within the cloud,” Boggs said. “It transferred that charge into the ionosphere,” the atmospheric layer about 50 to 400 miles above Earth’s surface.

Steve Kummer, a professor of electrical and computer engineering at Duke University, was able to extract high-frequency electromagnetic data from a series of antennas surrounding the storm. For the first time, he was able to confirm that the high-frequency signal emitted by lightning can in fact be detected at the tip of a power channel propagating small tendril-like “streamers”.

Ground-based lightning-detection networks also came in handy in Jet’s investigation, as they reported lightning rates in storms before unheard of.

“We were able to determine the type of peak currents and discharge for the original storm,” Boggs said.

Oddly, Boggs said, there was no conventional lightning strike in the immediate area that produced the giant jet. He has a theory about it tied to the jet’s most common location: over the ocean rather than over land.

thunderstorms generally display a tri-polar electric field, which means they consist of a positively charged region near the ground, a negatively charged region near the bottom of the cloud, and a positively charged region near the top of the cloud. The difference between the negative charge at the bottom of the cloud and the positive charge near the ground triggers lightning.

“What happens is the suppression of these cloud-to-ground discharges,” Boggs said.

Boggs said this suppression of cloud-to-ground attacks occurs most often with ocean storms, as scientists still don’t understand.

The researchers found that, in the absence of a charge contrast between the cloud and the surface, negative charge builds up in the clouds. The giant jets can then take away that extra negative charge.

Some of the most prolific episodes of giant jets have been noted over tropical storms or hurricanes—the ones notoriously short of simple lightning. On August 11 and 12, 2015, Hurricane Hilda created a barrage of giant jets as it slid southeast of Hawaii.

Much still remains undiscovered and unknown in the field of giant jets, which fall under the umbrella of TLEs, or transient luminous phenomena – that is, upper atmospheric lightning.

“We still don’t really know how often they happen,” Boggs said. “About five of the giant jets are detected per year, but we’re probably expecting to get tens of thousands.”

To do this, Boggs and his team are working on machine learning algorithms to integrate into satellite-based Geostationary Lightning Mapper data.

“We just haven’t seen them because the observations are so limited,” Boggs said. “It’s really hard to coordinate with the equipment in the classroom, so we have a [National Science Foundation] Grant coming soon. he will basically use [satellite data] To hunt for these huge jets in large quantities … hopefully we’ll be able to detect these things 24 hours a day in a hemisphere.”

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