Summer in the U.S. brings big thunderstorms. Towering thunderhead clouds fill the skies and energy permeates the air as positive and negative electrical charges build up between the earth and the atmosphere. Lightning bolts reset the tension with a tremendous jolt of energy.
Now researchers discover glows of gamma rays – high-energy electromagnetic radiation – appear just before lightning strikes. The discovery may help scientists predict when and where lightning will strike next, researchers report Tuesday in the journal Communications Physics.
“Forever, people have seen lightning and heard thunder. These were the ways we could experience this power of nature,” University of Tokyo physicist Yuuki Wada, who led the new research, said in a press release.
“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.”
Rays and Bolts
Wada and colleagues developed portable radiation detectors and set them up around the city of Kanazawa in central Japan. During a thunderstorm last January, two detectors recorded gamma ray glows — radiation from thunderclouds that can last from a few seconds to several minutes. When lightning struck, the gamma-ray glows vanished.
As the lightning struck, the detectors registered a different radiation burst known as a terrestrial gamma ray flash (TGF) that only lasts a fraction of a second. Although TGFs are known to coincide with lightning strikes, scientists have only seen gamma ray glows and TGFs at the same time once before.
Scientists suspect TGFs form near the top of thunderstorms where strong electric fields produce an avalanche of electrons. As the electrons jostle against air molecules the slight deflection, and change in momentum it brings, causes the electrons to emit gamma rays. How exactly TGF’S and lightning strikes are related is still unknown. But gamma rays seem to be present before lightning strikes as well.
“Our monitors detected a simultaneous TGF and lightning strike. This is fairly common, but interestingly we also saw a gamma-ray glow in the same area at the same time,” Wada said. “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.”
Lightning Forecast
The researchers are unsure how the minutes-long gamma ray glow and the instantaneous TGF events are related. The findings suggest the gamma-ray glow may have helped spark the TGF. The team plans to deploy more radiation sensors to get a better idea of how the two high-energy events might interact. Paired with the discovery that gamma ray glows precede strikes, the additional gamma-ray sensors will also help forecast where lightning will strike,
“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. With more sensors, we could greatly improve predictive models,” Wada said. “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.”
