Scientists have observed an intense burst of radiation with the collision of two lightning paths.
A study led by The University of Osaka observed the incident using a multi-sensor. Known as a terrestrial gamma-ray flash (TGF), the intense burst of radiation synchronized with a lightning discharge.
Researchers previously hypothesized that TGFs arise from lightning discharges as a result of the acceleration of electrons to very high speeds. However, the transient nature of this phenomenon, which lasts for only tens of microseconds, made it difficult to confirm this hypothesis, according to researchers.
The team set up a state-of-the-art multi-sensor setup to observe TGFs emerging from lightning storms in Kanazawa City, Ishikawa Prefecture, including optical, radio-frequency, and high-energy radiation.
Terrestrial gamma-ray flash (TGFs) originating in lightning
“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,” explained Yuuki Wada, lead author of the study.
Researchers observed two discharge paths, one descending from the thundercloud to the ground-based transmission tower and one ascending in the opposite direction. They found that a TGF occurred just before the two discharge paths met, creating a highly concentrated electric field that accelerated electrons in the air to near light speed.
The research team highlighted that the first TGF photon was observed 31 microseconds before the collision of the discharge paths, and the full burst lasted for 20 microseconds after they met to form the lightning strike. A discharge of −56 kA occurred as a result of the collision of lightning leaders.
Lightning discharges can produce transient gamma-ray emissions
Published in the journal Science Advances, the study reveals that lightning discharges can produce transient gamma-ray emissions called terrestrial gamma-ray flashes (TGFs), which originates from electrons accelerated to relativistic energies in strong electric fields.
The research reveals that how lightning produces an enormous number of relativistic electrons in dense atmospheres.
“We present that, thanks to a ground-based observation with optical, radio frequency and high-energy measurements focused on television transmission towers in Kanazawa, Japan, a TGF and a cloud-to-ground discharge of −56 kA occurred when a downward negative leader was colliding with an upward positive leader from the tower,” said researchers in the study.
Observation contributes critical data
This observation contributes critical data to the longstanding mystery of how lightning generates enough energy to produce gamma rays—phenomena typically associated with outer space events like supernovae or black hole jets.
The study also supports emerging theories about lightning leader dynamics and the potential role of thermal runaway or relativistic feedback in these extreme bursts, according to a press release.
Harufumi Tsuchiya, senior author, revealed that the multi-sensor observations performed here are world-first; although some mysteries remain, this technique has brought us closer to understanding the mechanism of these fascinating radiation bursts.
The study not only a rare glimpse into the inner workings of lightning, but also valuable data that could be used to improve the safety and resilience of structures vulnerable to high-energy atmospheric phenomena.