This series of images, taken from a video, shows the formation of a gigantic jet over Oklahoma in May 2018. Credit: Chris Holmes
A detailed 3D study of a massive electrical discharge that rose 80 km into space above a thunderstorm in Oklahoma has provided new insights into an elusive atmospheric phenomenon known as jumbo jets. The Oklahoma Landfill was the most powerful gigantic jet studied to date, carrying 100 times more electrical charge than a typical thunderstorm.
The gigantic jet is estimated to have moved 300 coulombs of electrical charge into the ionosphere (the lower edge of space) from the storm. Typical lightning carries less than five coulombs between cloud and ground or within clouds. The upward discharge included relatively cold plasma currents (about 205°C), as well as very hot structures called leaders (more than 4500°C).
“We were able to map this gigantic jet in three dimensions with very high quality data,” said Levi Boggs, researcher at Georgia Tech Research Institute (GTRI) and corresponding author of the paper. “We were able to see very high frequency (VHF) sources above the cloud tops, which had never been seen before in this level of detail. Thanks to satellite and radar data, we were able to learn where the very hot leading part of the discharge was located above the cloud. »
Boggs worked with a multi-organization research team, including the University Space Research Association (USRA), Texas Tech University, University of New Hampshire, Politecnica de Catalunya, Duke University, University of ‘Oklahoma, NOAA’s National Severe Storms Laboratory and Los Alamos National Laboratory. This research is published August 3 in Science Advances.
Steve Cummer, professor of electrical and computer engineering at Duke, uses electromagnetic waves emitted by lightning to study this powerful phenomenon. He runs a research site where sensors resembling conventional antennae sit in an empty field, waiting to pick up signals from local thunderstorms.
“The VHF and optical signals have definitively confirmed what researchers suspected but had not yet proven: VHF radio from lightning is emitted from small structures called streamers that sit at the tip of developing lightning, while that the strongest electrical current flows considerably behind this end in an electrically conductive channel called the leader,” Cummer said.
Doug Mach, co-author of the paper at the Universities Space Research Association (USRA), said the study was unique in that it determined that the 3D locations of optical lightning emissions were high above the cloud tops.
Sources of radio-mapping extending upward from the convective structure of the storm. The gray plane represents the top of the storm. Credit: Science Advances (2022). DOI: 10.1126/sciadv.abl8731
“The fact that the gigantic jet was detected by multiple systems, including the Lightning Mapping Array and two geostationary optical lightning instruments, is a unique event and gives us much more information about the gigantic jets,” Mach said. “More importantly, this is probably the first time that a gigantic jet has been mapped in three dimensions above the clouds with the Geostationary Lightning Mapper (GLM) instrument set. »
The gigantic jets have been observed and studied for the past two decades, but because there is no specific observing system to look for them, detections have been rare. Boggs learned of the Oklahoma event from a colleague, who told him about a gigantic jet that had been photographed by a citizen-scientist who had a working low-light camera on May 14, 2018.
Coincidentally, the event occurred at a location with a nearby VHF lightning mapping system, within range of two Next Generation Weather Radar (NEXRAD) locations and accessible to satellite network instruments. Geostationary Operational Environmental (GOES) from NOAA. Boggs determined that data from these systems was available and worked with his colleagues to bring it together for analysis.
“The detailed data showed that these cold currents are starting to spread just above the cloud tops,” Boggs said. “They propagate down to the lower ionosphere at an altitude of 80-100 km, establishing a direct electrical connection between the cloud top and the lower ionosphere, which is the lower boundary of space. »
This connection transfers thousands of amperes of current in about one second. The upward discharge transferred a negative charge from the cloud to the ionosphere, which is typical of gigantic jets.
The data showed that as the discharge rose from the cloud top, VHF radio sources were detected at altitudes of 22 to 45 kilometers), while optical emissions from the flashes remained near the top of the cloud. top of the cloud at an altitude of 15 to 20 kilometers. Simultaneous 3D radio and optical data indicate that VHF lightning arrays detect emissions from the streamer corona rather than the leader channel, which has broad implications for lightning physics beyond that of gigantic jets.
Why do gigantic jets launch charges into space? The researchers speculate that something may be blocking the flow of charge down, or to other clouds. Records of the Oklahoma event show the storm had little lightning activity before launching the massive record-breaking jet.
“For some reason, there’s usually a suppression of cloud-to-ground discharges,” Boggs said. “There’s a buildup of negative charges, and then we think the conditions at the top of the storm are weakening the top charge layer, which is usually positive. In the absence of the lightning discharges we normally see, the gigantic jet can relieve the buildup of excessive negative charge in the cloud. »
For now, many questions remain unanswered regarding the gigantic jets, which are part of a category of mysterious transient light events. Indeed, the sightings are rare and are the result of chance, whether they are pilots or passengers of planes who see them by chance or observers on the ground who use cameras at night.
Estimates of the frequency of giant jets range from 1,000 to 50,000 per year. They have been reported more often in tropical regions of the globe. However, Oklahoma’s gigantic jet – which was twice as powerful as the next one – was not part of a tropical storm system.
Beyond their novelty, the gigantic jets could impact the operation of satellites in low Earth orbit, Boggs said. As these space vehicles are launched, signal degradation and performance issues may become more prominent. The gigantic jets could also impact technologies such as “over the horizon” radars that bounce radio waves off the ionosphere.
Mr. Boggs is affiliated with the Severe Storms Research Center, which was established at GTRI to develop better warning technologies for severe storms, such as tornadoes, which are common in Georgia. Work on gigantic jets and other atmospheric phenomena is part of this effort.