When lightning leaders collide gamma rays burst from Earth's atmosphere

TGFs are extremely brief but intense bursts of gamma rays, lasting mere microseconds, and are generally difficult to detect. The study, soon to appear in Science Advances, presents a landmark finding by using a cutting-edge multi-sensor system that tracked optical signals, radio waves, and high-energy radiation during a storm over Kanazawa City in Ishikawa Prefecture.

Two lightning leaders-one descending from a thundercloud and another ascending from a transmission tower-were observed approaching each other. A powerful TGF was emitted 31 microseconds before the lightning paths collided, and radiation continued for 20 microseconds after the contact, which produced a -56 kA discharge.

"The ability to study extreme processes such as TGFs originating in lightning allows us to better understand the high-energy processes occurring in Earth's atmosphere," said lead author Yuuki Wada.

This observation confirms theories that TGFs are caused by electrons accelerated to relativistic speeds in strong electric fields formed during lightning events. It also aligns with models involving thermal runaway and relativistic feedback mechanisms.

Senior author Harufumi Tsuchiya emphasized the novelty of the method, stating, "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."

Beyond scientific curiosity, the findings hold practical implications for enhancing the protection of infrastructure against the energetic effects of lightning.

Research Report:Downward Terrestrial Gamma-ray Flash Associated with Collision of Lightning Leaders