Rare solar flare caused radiation in Earth's atmosphere to spike to highest levels in nearly 20 years, researchers say
Rare Solar Flare Causes Radiation Spike in Earth's Atmosphere
A powerful solar flare erupted from the sun on November 11, unleashing a stream of super-charged protons that increased radiation levels around Earth to a bi-decadal high. The solar flare, an extremely bright flash of light, erupted from the AR4274 sunspot and was classified as a powerful X5.1. This flare followed a series of milder flares and coronal mass ejections (CMEs) that treated skywatchers to mesmerizing aurora displays as far south as Florida.
Understanding the Physics Behind the Event
The X-class flare also unleashed a stream of high-speed protons and other energetic particles toward our planet, something very few solar flares do. This year, about 20 X-flares hit Earth, but only the one from November 11 was accompanied by the high-speed proton stream. The researchers released several stratospheric balloons with sensors to see how radiation levels evolved throughout the atmosphere. They found that at altitudes where most commercial aircraft travel, around 40,000 feet (12 kilometers), radiation briefly rose to levels ten times higher than the normal cosmic-ray-related background.
The Risk to Human Health
If a pregnant woman were to be exposed to such radiation levels for more than 12 hours, she would have exceeded a limit officially considered as safe for a fetus. Fortunately, in this case, the worst was over in about two hours, according to Benjamin Clewer, a space weather researcher at the University of Surrey in the U.K. "Typically, these events peak right at the beginning and that might only last about half an hour," Clewer told Space.com. "In this case, the event officially finished in 15 hours, but only the first two hours were significant."
The Phenomenon of Ground Level Events
CMEs also expel clouds of energetic particles into interplanetary space. Those particles, contained in clouds of magnetized plasma, take days to reach the planet. The protons unleashed by a solar flare, however, travel at nearly the speed of light and arrive within minutes, Clewer said. When those energetic protons hit the top of Earth's atmosphere, they interact with molecules of air, triggering showers of secondary, less energetic particles including neutrons, muons, and electrons. Such particles constantly trickle down onto Earth's surface as a result of the battering our planet experiences due to cosmic rays that arrive from the most distant parts of the galaxy.
The Rarity of Ground Level Events
The phenomenon is called a Ground Level Event (GLE) and is rather rare. In fact, since measurements began in the 1940s, only 77 such GLEs have been registered, according to Clewer. Scientists don't understand why some solar flares cause GLEs and some do not and therefore cannot predict when a spike in radiation occurs. "We don't understand the physics of it that well as to why some solar flares eject these really high-speed particles and other ones don't," said Clewer, whose team made measurements of the event that revealed its intensity.
The Potential for Disruption to Aircraft Electronics
The GLE on November 11, however, was only a mild example of what the sun is capable of. The most intense GLE ever detected happened in 1956 and was sixty times more intense. Even stronger ones, over a thousand times as intense as the November 11 GLE, are possible, as evidenced by radioisotope studies in tree rings. The GLEs are not only potentially dangerous for human health but can also wreak havoc with aircraft electronics. An animation of an X5.1-class solar flare on November 11, 2025, shows the potential for disruption to aircraft electronics.
The Need for Radiation Monitors on Aircraft
Researchers are campaigning for all aircraft to be equipped with radiation monitors to help pilots understand what's going on. During severe radiation events, radio links that allow communication with ground control are likely to be disrupted too, preventing the pilots from learning about the cause of the problems. Because GLEs come suddenly and can't be predicted, many aircraft will be caught in those events mid-air. "If you're in the air and still can communicate with air traffic, you could descend to a lower altitude or change your latitude," Clewer said. "But there is a likelihood that the pilots won't be able to talk on the radio and have to do all the other mitigations on top of that."
Conclusion
The recent solar flare and the resulting Ground Level Event serve as a reminder of the potential risks and disruptions that can occur when the sun unleashes its energy towards our planet. While the event was not as intense as some of the more extreme GLEs that have occurred in the past, it highlights the need for continued research and monitoring of solar activity. By understanding the physics behind these events and developing strategies to mitigate their effects, we can better prepare for and respond to these events, ensuring the safety of both people and aircraft.
