The Oklahoma gigantic jet. Image: Chris Holmes
Lightning strikes can be an exhilarating and terrifying sight to behold from the ground, but what’s wilder is that these intense bolts of plasma sometimes powerfully erupt in the opposite direction, zigzagging up into space in dazzling displays known as gigantic jets. Now, scientists led by Levi Boggs, a research scientist at the Georgia Tech Research Institute, have described the strongest gigantic jet ever seen, which sprang up from cloudtop in Oklahoma and darted 50 miles above Earth’s surface, where it delivered the largest charge transfer to space on record.
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Whereas most lightning bolts carry fewer than five coulombs (a measurement of charge), this jet transferred a gobsmacking 300 coulombs to the ionosphere, the low end of space, when it struck on May 14, 2018. That is nearly double the previous largest charge by a gigantic jet and is on par with the largest ever recorded for cloud-to-ground strokes.The jet was captured on film by a nearby citizen scientist with a low-light camera, along with other instruments on the ground and in space, revealing never-before-seen details about these mysterious upward strikes that have “broad implications to lightning physics beyond that of gigantic jets,” according to a study published last week in Science Advances. “I was really intrigued because observations of gigantic jets are really rare—only a few per year if that,” Boggs said in an email. “So I seize any chance to study them, because trying to capture them with dedicated field campaigns is very difficult. This was a random chance that I was told about this video, and luckily the event in the video was also observed by a ground-based radio mapping network and optical instruments in geostationary orbit.”In addition to its immense charge, the jet has puzzled scientists like Boggs because it emerged from “unusual circumstances” in a “unique thundercloud,” according to the study. Most gigantic jets occur in tropical environments and are located near parts of a storm that are strongly convective, but this one occurred in an area of weak convection.
“Usually gigantic jets occur from tropical storms near the equator that have really tall cloud tops (18 km) that penetrate into the stratosphere and associated cloud top turbulence, but this event occurred in the middle of the continental U.S. and had relatively low cloud tops (14 km) with little cloud top turbulence,” Boggs said. “There was no lightning activity before the gigantic jet in the parent storm cell, which has never been the case from past observations,” he continued. “This allowed the parent storm to accumulate a significant amount of electric charge, which enabled the gigantic jet to transfer the largest amount of charge on record to the ionosphere (300 coulombs).”The citizen scientist footage was shot from the ground in Hawley, Texas, just across the state border, but the jet was also detected by a sophisticated mapping system for very high frequency (VHF) radio signals sparked by lightning bolts, two Next Generation Weather Radar (NEXRAD) stations, and NOAA's Geostationary Operational Environmental Satellite (GOES) network.Boggs and his colleagues scoured through this fortuitous glut of data looking for clues about the origin and dynamics of the Oklahoma jet. The results confirmed theories about the behavior of key plasma components of lightning bolts, called streamers and leaders, which are about 400 degrees Fahrenheit and a whopping 8,000 degrees Fahrenheit, respectively.
“The combined 3D radio and optical data provide key insight into the plasma nature of gigantic jets,” the team said. “In addition, the radio and optical data show the first clear evidence that the VHF observed by lightning networks is produced by streamers ahead of the leader.”Though the Oklahoma jet provided this amazing glimpse into an unrivaled jet, many questions about these elusive events remain. Solving these mysteries is an intriguing scientific endeavor on its own merits, but it also has practical consequences because gigantic jets may scramble spacecraft operations.“Since these events connect with the lower edge of space, and transfer charge to that region, they could potentially have effects on space weather which could affect communications and electromagnetic signals between ground and satellites in orbit,” Boggs said. He also noted that while it's possible that the jets could strike an aircraft, it is very unlikely because pilots avoid flying over thunderclouds.Nobody is even sure how many of these jets strike space each year, with estimates ranging from 1,000 to 50,000, leaving plenty of room for future discoveries. To that end, Boggs and his colleagues are hoping to observe more of these brilliant events, which might potentially illuminate the skies with gamma rays, the most energetic form of light. “Our results suggest that as the discharge escapes the cloud, the electric field at the tip should be extremely large, potentially large enough to produce gamma rays,” Boggs concluded. “Terrestrial gamma ray flashes (TGFs) have been observed for several years now from lightning, but never from a gigantic jet. Our results indicate that gigantic jets may also produce TGFs.”