Scientists Use Cold War-Era Spy Plane to Find Unexpected Gamma Rays in Thunderstorms

Two hundred and seventy-two years after that June afternoon when Benjamin Franklin flew his kite into a thunderstorm, scientists still aren’t completely sure how lightning forms.

“I think everyone assumes that we figured out lightning a long time ago,” Joseph Dwyer, a physicist at the University of New Hampshire, tells NASA’s James Riordon. “But it’s an overlooked area … we don’t understand what’s going on inside those clouds right over our heads.”

Part of the mystery comes from the fact that the electric fields seen in thunderclouds are far smaller than what’s required to start a spark, reports Newsweek’s Tom Howarth. Last year, researchers flew an upgraded version of Franklin’s kite—a retrofitted Cold War-era U-2 spy plane—into storms with hopes of finally getting to the bottom of lightning’s mystery. In a pair of studies published this week in the journal Nature, scientists describe new forms of energy that could help illuminate an answer.

Studying Thunderstorms with NASA's ER-2 Aircraft

Watch on

Sensitive instruments onboard the plane detected hundreds of events producing gamma rays in storms over the Caribbean and Central America. Gamma rays are a higher energy type of radiation than X-rays, and they form in extreme cosmic environments, such as around black holes.

Scientists had previously detected two types of gamma-ray emissions in thunderstorms. One type, called a gamma-ray glow, is a dim, long-lasting event that can roll on for multiple seconds or even minutes. Then there are terrestrial gamma-ray flashes, or TGF, which are bright enough to see from space and are very fleeting, lasting less than a millisecond.

Both kinds of events have only rarely been observed before, as Martino Marisaldi, a co-author of the new studies and high-energy atmospheric physicist at the University of Bergen in Norway, tells Nature News’ Elizabeth Gibney. But with their spy plane and specialized detectors, “we saw that, over these tropical storms, they are really very common,” he adds.

In fact, the researchers observed gamma-ray glows in nine of the plane’s ten flights and report that these phenomena lasted far longer than expected—over multiple hours—and covered thousands of square kilometers. The glows also brightened and dimmed as they spread across the sky, creating dynamic displays of radiation.

“Large storms are bubbling. It’s like a boiling pot,” Nikolai Østgaard, a physicist at the University of Bergen, says to Science News’ Emily Conover.

In a surprise twist, the team also detected a never-before-seen type of gamma radiation, which they called flickering gamma-ray flashes. These new events pulsed out of glows and lasted as long as 250 milliseconds. The flickering flashes could be a missing link between glows and TGFs, and they might prove to be important to the formation of lightning strikes.

Scientists think that gamma rays emerge in thunderstorms when electrons accelerate through strong electric fields in the clouds. The electrons collide with other particles and create more electrons in a cascading process. If the electrons from this cascade smack into an air molecule, it produces a gamma ray. But the researchers are still working out why different types of gamma-ray emissions form and how they’re related to each other, as well as how they connect to lightning.

The newly observed flickering gamma-ray flashes provide a clue. In addition to bridging the gap between short TGFs and long glows, flickering flashes tended to be closely followed by lightning.

The findings from these new studies will encourage other scientists to keep searching for answers inside big storm clouds, says Teruaki Enoto, an astrophysicist at the RIKEN Hakubi laboratory in Japan who was not involved in the work, to Nature News. “Kudos to the team,” he adds.

With more observations of these mysterious electrical and gamma-ray events, scientists hope to draw closer to understanding why lightning forms.

“There are 45 lightning strikes every second going on on the Earth, and at any given time there are more than 2,000 thunderstorms,” Marisaldi tells Newsweek. “I think it’s important to understand what is going on there and not just be passive receivers of this.”

Rudy Molinek | READ MORE

Rudy Molinek is Smithsonian magazine's 2024 AAAS Mass Media Fellow.