The timelapse and photograph of the lightning being recorded live on the camera. A Penn State-led research team has uncovered the long-stan...
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| The timelapse and photograph of the lightning being recorded live on the camera. |
The findings, published in the Journal of Geophysical Research: Atmospheres, reveal how strong electric fields in thunderclouds accelerate electrons to near-relativistic speeds. These high-energy electrons collide with nitrogen and oxygen molecules, releasing bursts of X-rays and producing a cascade of additional electrons and photons—a runaway chain reaction that sets lightning into motion.
“Our findings provide the first precise, quantitative explanation for how lightning initiates in nature. It connects the dots between X-rays, electric fields and the physics of electron avalanches.” —Victor Pasko.
The research team confirmed their explanation using mathematical modeling of terrestrial gamma-ray flashes (TGFs), brief bursts of X-rays and gamma rays produced in thunderstorms. TGFs had long been observed by satellites and high-altitude aircraft, but their relationship to lightning initiation had not been fully understood—until now.
Doctoral student Zaid Pervez matched the team’s model to real-world data collected by satellites, ground-based sensors and NASA’s specialized spy planes. By replicating the extreme conditions inside simulated thunderclouds, the model provided a comprehensive explanation for the observed photoelectric phenomena, radio emissions and invisible flashes that precede a lightning strike.
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| How lightining occurs in physics. |
The breakthrough builds on the Photoelectric Feedback Discharge model, originally published by Pasko and collaborators in 2023. This model explains how cosmic rays from outer space seed initial high-energy electrons in the atmosphere, which are then accelerated by thunderstorm electric fields to produce powerful X-ray bursts. These cascades of electrons and photons create the conditions for a lightning bolt to ignite.
Gamma-Ray Flashes
Interestingly, the researchers also explained why gamma-ray flashes are sometimes observed without visible lightning or thunder. According to their model, the high-energy avalanches that create TGFs can occur in very compact regions of a thundercloud and sometimes with minimal optical or radio emissions. This means lightning-related processes may unfold invisibly, detectable only through sensitive satellite instruments.
“In our modeling, the high-energy X-rays produced by relativistic electron avalanches generate new seed electrons driven by the photoelectric effect in air, rapidly amplifying these avalanches,” Pasko explained. “This explains why gamma-ray flashes can emerge from regions that appear optically dim and radio silent.”
The study was a global collaboration, with contributions from scientists at the University of Orléans in France, École Polytechnique in France, NASA Goddard Space Flight Center, Brno University of Technology in the Czech Republic, and the Technical University of Denmark. The research was supported by the U.S. National Science Foundation, the French Space Agency (CNES), the Institut Universitaire de France, and the Czech Ministry of Defense.
By resolving the question of how lightning begins, the research opens the door to better forecasting of extreme weather and improved protection of infrastructure, such as power grids, aircraft and spacecraft. Understanding lightning initiation at a fundamental level could also help scientists assess the role of thunderstorms in global atmospheric chemistry, particularly in generating nitrogen oxides that influence climate and air quality.
Ultimately, this work provides a physics-based foundation for one of nature’s most spectacular and dangerous phenomena—helping humans better prepare for and understand the storms that electrify our skies.
