Scientists Uncover Mysterious High-Radiation Phenomenon in Thunderclouds While Lightning Is Forming

Scientists have uncovered a mysterious phenomenon which casts new light on our understanding of lightning and could potentially reveal a new mechanism behind what causes these electrical discharges.

The consensus is that lightning bursts occur when differences in charge build-up within thunderstorm clouds—or between these clouds and the ground—generating high energy sparks. But some aspects of the processes taking place within these thunderclouds during a storm are not so well understood.

Around 30 years ago, researchers began detecting gamma-rays—the highest-energy form of electromagnetic radiation—inside storms. These gamma rays come in two forms: relatively weak emissions lasting about a minute which are described as "glows" and much more intense bursts lasting for only fractions of a second called TGFs (terrestrial gamma ray flashes) that have been detected in the emissions given off by lightning bolts.

While scientists know that these strange gamma-ray emissions are associated with lightning, there is a significant lack of knowledge about the nature of the relationship between the two phenomena.

Now, a team of researchers led by Yuuki Wada from the University of Tokyo, Japan, has discovered a previously unknown connection between the gamma-ray emissions and lightning.

"Forever, people have seen lightning and heard thunder," Wada said. "These were the ways we could experience this power of nature. With the discovery of electromagnetism, scientists learned to see lightning with radio receivers. But now we can observe lightning in gamma rays—ionizing radiation. It's like having four eyes to study the phenomena."

For a study published in the journal Communications Physics, Wada and colleagues set up radiation monitors on buildings in the central Japanese city of Kanazawa.

They chose this area because the region in which the city lies experiences unique meteorological conditions. Importantly for the scientists, winter thunderclouds in Kanzawa appear very close to the ground—unlike many places around the world—making them easier to observe with affordable radiation monitoring equipment.

The results of this experiment indicated that gamma ray glows occur just before lightning discharges—and associated TGFs—and are likely connected in some way.

"During a winter thunderstorm in Kanazawa, our monitors detected a simultaneous TGF and lightning strike," Wada said. "This is fairly common, but interestingly we also saw a gamma-ray glow in the same area at the same time. Furthermore, the glow abruptly disappeared when the lightning struck. We can say conclusively the events are intimately connected and this is the first time this connection has been observed."

According to the researchers, the findings suggest that the glows may actually have a role to play in causing the lightning discharges to occur in the first place, although they stress that this idea needs to be investigated further before any firm conclusions can be drawn.

"Our finding marks a milestone in lightning research and we will soon double our number of radiation sensors from 23 to about 40 or 50," Wada said. "With more sensors, we could greatly improve predictive models. It's hard to say right now, but with sufficient sensor data, we may be able to predict lightning strikes within about 10 minutes of them happening and within around 2 kilometers of where they happen. I'm excited to be part of this ongoing research."

A bolt of lightning emanating from a thundercloud. Yuuki Wada