Most lightning travels between clouds and the ground, or within and between clouds. But a curious phenomenon known as “gigantic jets” fires powerful bursts of electrical charge – as much as 10 times larger than ordinary lightning – out the tops of clouds and into the lower portion of the ionosphere where the Earth’s atmosphere transitions into space.

The massive transfer of energy from the Earth’s atmosphere to space could affect satellites in low earth orbit, communications that bounce off the ionosphere, and radars that look over the horizon. A new three-year study funded by the National Science Foundation will attempt to understand how gigantic jets affect the ionosphere and what that could mean for these critical technologies.

Using a systematic data analysis approach, machine learning techniques, and correlation with other observations, a research team headed by the Georgia Tech Research Institute (GTRI) hopes to boost into the thousands the number of gigantic jets studied each year, going well beyond the handful of observations now reported annually.

“We’re hoping to get thousands of detections per year or more, and then we’ll correlate those detections with ground-based sensing instruments that remotely sense the ionosphere,” said Levi Boggs, a GTRI research scientist and the project’s principal investigator. “We’ll compare those detections with the ionospheric measurements to try to understand how these gigantic jets perturb and affect the ionosphere.”

Gigantic Jets have mostly been observed by happenstance, such as when airline passengers spot them or ground-based cameras looking for something else catch the colorful bursts of light above cloud tops. Boggs and collaborators recently reported a detailed 3D study of a massive gigantic jet that rose 50 miles into space above an Oklahoma thunderstorm. The discharge, reported Aug. 3 in the journal Science Advances, was the most powerful gigantic jet studied so far, carrying 10 times as much electrical charge as a typical thunderstorm lightning bolt.

Boggs and the NSF-funded team will start by analyzing optical satellite data recorded since 2018 by geostationary lightning mapping satellites. They will use machine learning techniques to separate data on gigantic jets – which have a unique signature – from that of other lightning emissions, and will correlate those observations with information from very low frequency (VLF) radio networks that remotely sense what is happening in the ionosphere 80 to 100 kilometers above the Earth. The research will create a database containing thousands of gigantic jet observations to which data on new observations will be added as they become available.

Beyond the Georgia Tech researchers, the ream will include scientists from the Universities Space Research Association (USRA), Duke University, Texas Tech University, Los Alamos National Laboratory, and the Search for Extraterrestrial Intelligence (SETI). In addition to the VLF data, the project will use information from the Atmospheric Space Interactions Monitor (ASIM) and the Duke ELF Network.

Bombarded by radiation from the sun, the lower part of the ionosphere is difficult to observe by either high-altitude balloons or satellites. Morris Cohen, an associate professor in Georgia Tech’s School of Electrical and Computer Engineering, studies this highly-ionized region using very low frequency (VLF) radio waves produced by lightning.

“We can use VLF sort of like a radar,” he said. “VLF is extremely difficult to generate, but luckily lightning gives us a little pulse of VLF called a sferic that we can pick up from many thousands of miles away. Sferics are difficult signals to deal with, but we’ve recently pushed the envelope on the information we can extract from the ionosphere by detecting these signals.”

Signals from sferics are detected by a network of VLF receivers across North America. “Since lightning happens millions of times per day, we have a lot of opportunities to diagnose the ionosphere between where the lightning was and where the receiver was,” added Cohen, who is the co-principal investigator for the project. “With a network of VLF receivers, we can use tomographic techniques to reconstruct a ‘map’ of what the lower ionosphere is doing at a given moment over a decently-sized region.”

But there is a catch. The researchers will only be able to use VLF to observe the effects of gigantic jets that occur along a path between lightning and one of the receivers. Until the data is analyzed and correlated, researchers won’t know how often that will provide useful information.

Better understanding gigantic jets will be useful for fundamental physics, understanding space weather, and assessing the potential impact of the charge transfer on technology that transmits data through the ionosphere or uses it as a giant reflector from which to bounce signals.

From a fundamental physics perspective, researchers want to know how gigantic jets propagate 50 miles into space from the tops of storms. They’d like to know whether these bursts of energy produce high-energy photon emissions such as gamma rays. There are also questions about how the emissions affect the global atmospheric electrical circuit, and whether the incidence of gigantic jets might be correlated to hurricane intensity.

The researchers also want to understand whether the current flowing into space might damage satellites in low earth orbit or affect their ability to send and receive data. This issue could be become more critical as CubeSats and other small satellites play an increasingly important role in space-based operations.

“The lower ionosphere is very important for different types of communications that depend upon the Earth-ionosphere waveguide effect, which can bend certain frequencies of radio waves back toward the Earth’s surface,” Boggs said. “To accurately communicate that way requires understanding the height and the electron density of the ionosphere. Because gigantic jets inject electric charge into that region, they more than likely affect the ionosphere.”

Writer: John Toon
GTRI Communications
Georgia Tech Research Institute
Atlanta, Georgia USA

_{About GTRI: The Georgia Tech Research Institute (GTRI) is the nonprofit, applied research division of the Georgia Institute of Technology (Georgia Tech). Founded in 1934 as the Engineering Experiment Station, GTRI has grown to more than 2,800 employees, supporting eight laboratories in over 20 locations around the country and performing more than $700 million of problem-solving research annually for government and industry. GTRI's renowned researchers combine science, engineering, economics, policy, and technical expertise to solve complex problems for the U.S. federal government, the state, and industry. For more information, please visit www.gtri.gatech.edu.}

_{About USRA: Founded in 1969, under the auspices of the National Academy of Sciences at the request of the U.S. government, the Universities Space Research Association (USRA) is a nonprofit corporation chartered to advance space-related science, technology, and engineering. USRA operates scientific institutes and facilities, and conducts other major research and educational programs. USRA engages the university community and employs in-house scientific leadership, innovative research and development, and project management expertise. More information about USRA is available at www.usra.edu.}