For the first time, scientists have captured a terrestrial gamma-ray flash (TGF) triggered by lightning using ground-based instruments. The observation marks a major milestone in understanding how thunderstorms can emit radiation levels typically associated with the universe’s most extreme phenomena.
The discovery was made by researchers from the University of Osaka, who documented the split-second event with a sophisticated multi-sensor system in Kanazawa City, Japan.
Twin Lightning Paths Led to the Gamma Event
The recorded event showed lightning splitting into two discharges: one moving downward from a thundercloud and the other shooting upward from a transmission tower on the ground. A flash of gamma rays erupted just 31 microseconds before the discharges connected.
“Most TGFs have been detected by satellites, but spaceborne observations can provide limited information,” said Yuuki Wada, lead author and researcher at the University of Osaka, in an email to Gizmodo. “In this research, we performed a ground-based observation to see TGFs in detail.”
Terrestrial Gamma-Ray Flashes: Still Not Fully Understood
TGFs have intrigued scientists since the 1990s, when they were first discovered via satellite. Despite years of research, the mechanisms behind them remain only partly understood. In 2023, two studies in Nature shed light on radiation “glows” and intermittent gamma flashes during tropical storms. Those airborne investigations used retrofitted spy planes to fly into storm systems, revealing a wide range of storm-related radiation activity.
What sets the Osaka study apart is its precision. Rather than providing a broad view of radiation levels across a storm, the Japanese team’s system was able to isolate a single event in real time, pinpointing the exact moment gamma radiation was released.
A Step Closer to Solving Lightning’s Mysteries
The team believes the gamma flash occurred when a highly charged electric field accelerated electrons to near light speed, releasing a TGF as the discharges converged. The link between the gamma-ray burst and the lightning’s final strike supports longstanding theories about how such extreme bursts are produced.
“The recent Nature papers are based on airborne observations,” Wada added. “They are also very interesting, but ground-based observations can be achieved much less expensively.”
Harufumi Tsuchiya, co-author and researcher at the Japan Atomic Energy Agency, said in a University of Osaka press release: “The multi-sensor observations performed here are a world-first; although some mysteries remain, this technique has brought us closer to understanding the mechanism of these fascinating radiation bursts.”
Understanding TGFs could unlock deeper knowledge about the physics of lightning and the behaviour of electric fields during storms. These high-energy events, once attributed to mythology, are now revealing their secrets. The new study suggests they are even more powerful and complex than previously imagined.
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