Humans are exposed to radiation in some form or fashion every day. But a new study demonstrates that radiation is coming from an unexpected source – thunderstorms.
The researchers have discovered that thunderstorms create radioactive particles in the atmosphere that are shot down to Earth as lightning strikes. They also found that gamma radiation is produced when lightning reacts with nitrogen in the atmosphere.
Dr. Teruaki Enoto, a scientist at Kyoto University, is the study’s lead author.
“We already knew that thunderclouds and lightning emit gamma rays, and hypothesized that they would react in some way with the nuclei of environmental elements in the atmosphere,” said Dr. Enoto.
The team focused their study on Japan’s western coast, which is ideal for viewing thunderstorms and lightning in the wintertime. In 2015, the experts started building small gamma-ray detectors and placed them in various locations along the coast.
During a storm in February, a gamma flash was recorded in Kashiwazaki city, Niigata. Immediately after lightning struck a few hundred feet away, detectors recorded the flash which had a duration of less than one millisecond.
“It was the moment we realized we’re seeing a new, hidden face of lightning,” said the study authors. “When we analyzed the data, we found three distinct gamma-ray bursts.”
The first spike was followed by a second gamma-ray afterglow that lasted dozens of milliseconds, while a third flash lasted over a minute.
“We could tell that the first burst was from the lightning strike. Through our analysis and calculations, we eventually determined the origins of the second and third emissions as well,” Dr. Enoto. “The second afterglow, for example, was caused by lightning reacting with nitrogen in the atmosphere.”
He continued, “The gamma rays emitted in lightning have enough energy to knock a neutron out of atmospheric nitrogen, and it was the reabsorption of this neutron by particles in the atmosphere that produced the gamma-ray afterglow.”
According to Dr. Enoto, the final emission was from the breakdown of the unstable nitrogen atoms. The neutron-deprived atoms released positrons, “which subsequently collided with electrons in annihilation events releasing gamma rays.”
While these radioactive particles have been detected for decades by various forms of observation such as aircrafts and satellites, it was unclear whether the nuclear reactions were caused by lightning.
The scientists say that the radiation is no more threatening to life on Earth than the radiation we are exposed to in everyday life.
The study is published in the journal Nature.