Thunderstorms are typically recognized for their fierce winds, heavy rain, and dazzling lightning, but another intriguing phenomenon often accompanies them: gamma radiation. However, thanks to an innovative upgrade to an old U-2 spy plane by NASA, researchers can now directly study these brief bursts of radioactive energy that occur worldwide every day. The latest discoveries have been shared in two recent studies published on October 3 in the journal Nature—and they reveal that radioactive storms are far more common than previously thought.
The first detection of gamma rays in thunderstorms was serendipitous; in the 1990s, NASA satellites initially intended for observing supernovas recorded unexpected signals from below as they monitored high-energy cosmic events. Since that moment, scientists have had to utilize these satellites and other non-specialized equipment to maximize their research efforts regarding lightning phenomena.
Despite the preliminary understanding of gamma radiation generation, the processes involved have become clearer over time. As thunderstorms form, winds lift droplets, ice, and hail into turbulent drafts, generating electric charges like static electricity. This process causes positive ions to rise while negative ions descend, cultivating an electric field comparable to the power of 100 million AA batteries. Within this electric field, energized particles, including electrons, speed up and can knock off additional electrons from air molecules, creating a chain reaction that ultimately generates millisecond bursts of gamma rays, antimatter, and other forms of radiation.
Gamma radiation is so common that pilots have reported witnessing faint glows within storm clouds. However, certain unknown factors seem to impede these reactions from becoming explosive.
“Several aircraft campaigns have attempted to determine the frequency of these phenomena, but results were mixed. Multiple campaigns over the United States failed to detect any gamma radiation at all,” commented Steve Cummer, a Distinguished Professor of Engineering at Duke University and co-author of the studies, on Wednesday.
Finally, after many years of indirect observations, NASA provided Cummer and his team access to an upgraded version of the U-2, known as the ER-2 High-Altitude Airborne Science Aircraft. This aircraft can fly as high as 72,000 feet and travel at speeds of 475 mph, making it ideal for surveying extensive areas for gamma radiation during thunderstorms. With the right equipment installed, experts hoped that this variant could definitively answer lingering questions.
The outcomes astonished even Cummer and his co-researchers.
“There’s much more happening in thunderstorms than we ever anticipated,” Cummer stated. “It turns out nearly all significant thunderstorms produce gamma rays continuously throughout the day in various forms.”
During the research period, 10 flights were conducted over storms in tropical southern Florida, with 9 of the flights revealing the presence of gamma radiation more dynamic than initially expected.
“It resembles a huge gamma-emitting boiling pot, both in its pattern and behavior,” remarked Martino Marisaldi, a physics professor at the University of Bergen and co-author of the study.
Numerous confirmed gamma radiation sightings correlated with those observed by NASA satellites over three decades ago, nearly always observed alongside active lightning. This suggests that lightning may play a pivotal role in gamma ray production by energizing high-energy electrons in the electric field. However, the study also identified entirely new findings.
The research team noted that at least two additional types of brief gamma bursts can emerge in thunderstorms—one lasting less than a thousandth of a second and another forming as about 10 sequential bursts within roughly a tenth of a second. Cummer highlighted these discoveries as particularly fascinating.
“These bursts don’t appear to be linked to any developing lightning flashes. They seem to occur spontaneously,” he explained, adding that some data suggests these gamma bursts might connect to specific thunderstorm mechanisms related to the initiation of lightning. However, the specifics of these processes remain elusive and a puzzle for scientists.
Future ER-2 flights high above gamma-rich storms may eventually provide answers to these mysteries and others related to storm phenomena. Until then, Cummer emphasizes that there’s no need for concern about the presence of high-altitude gamma radiation “boiling pots” during thunderstorms.
“If you ever find yourself in a thunderstorm, the radiation will likely be the least of your worries,” he remarked.
