Space & Science

Researchers Uncover Mysteries of Rare ‘Gigantic Reaction’ Lightning

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Ordinary lightning can be quite startling, but researchers are unlocking the secrets of a rarely observed kind of electric discharge called “gigantic jets”. They are extraordinary bursts of light from the top of the clouds that can reach the limits of space.

Only five sightings of these jets are made in an average year, usually by accident. Sometimes lucky photographers capture them in long exposure images, and every so often they are spotted by weather satellites.

A study published Wednesday in the journal Science Advances highlights on the structure and cause of gigantic jets. He analyzed a jet released in Oklahoma on May 14, 2018, which rose 50 miles above a thundercloud and delivered more charge than 100 traditional lightning bolts. It was the most powerful gigantic jet studied.

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

Elusive red sprites, like jellyfish glowing in the night sky, photographed in Oklahoma

The investigation was inspired when Levi Boggs, a researcher at the Georgia Tech Research Institute and one of the paper’s lead authors, discovered a photograph of the Oklahoma jet taken by a citizen scientist.

« Kevin Palivec [the photographer] has a low-light camera in central Texas that he sometimes uses randomly, and he had captured it a few years ago,” Boggs said. The photo “was sort of sitting. I was told about it and decided to investigate a bit.

It was then that Boggs assembled a team that looked at data from satellites, radar, and radio waves to piece together what had happened.

Researchers were able to develop a 3D model of the jet as it was seen by two satellite-based optical lightning instruments, including the Lightning Mapping Network on the GOES-15 weather satellite that overlooks the eastern United States .

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

Steve Cummer, a professor of electrical and computer engineering at Duke University, was able to extract high-frequency electromagnetic data from a series of nearby antennas in the storm’s vicinity. For the first time, he was able to confirm that the high-frequency signal emitted by lightning can in fact be attributed to small, tendril-like “streams” of electricity at the end of a lightning propagation channel.

Ground-based lightning detection networks also proved useful in investigating the jet, as they informed lightning rates in the storm before it hit.

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

Strangely, Boggs said, there were no conventional lightning strikes in the immediate area that produced the gigantic jet. He has a theory about it that ties into the most common location for jets: over the ocean rather than on land.

Thunderstorms usually present a tripolar electric field, meaning they consist of a positively charged area near the ground, a negatively charged area near the bottom of the cloud, and a positively charged area near the top of the cloud. The contrast between the negative charge at the bottom of the cloud and the positive charge near the ground triggers lightning.

“What’s happening is there’s a suppression of these cloud-to-ground discharges,” Boggs said.

This suppression of cloud-to-ground impacts occurs most often with ocean storms for reasons scientists still don’t understand, Boggs said.

The researchers found that in the absence of charge contrast between the cloud and the surface, a negative charge builds up in the clouds. Gigantic jets can then relieve this excess negative charge.

Some of the most prolific episodes of gigantic jets have been seen over tropical storms or hurricanes – which are notoriously devoid of ordinary lightning. On August 11-12, 2015, Hurricane Hilda produced a barrage of huge jets as it slid southeast of Hawaii.

There is still much that remains undiscovered and unknown in the realm of gigantic jets, which fall under the umbrella of TLEs, or transient light events – i.e. higher atmospheric flashes.

“We still don’t really know how often they happen,” Boggs said. “There are about five gigantic jet detections a year, but we’re hoping to get maybe tens of thousands.”

To do this, Boggs and his team are working on a machine-learning algorithm to embed into satellite geostationary lightning mapper data.

“We just haven’t seen them because sightings are so limited,” Boggs said. “It’s really difficult to coordinate with instruments in orbit, so we have a [National Science Foundation] grant coming soon. This will basically use [satellite data] to hunt these gigantic jets in huge quantities…hopefully we can detect these things across a hemisphere, hopefully 24 hours a day.

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