When lightning strikes on Earth, it can cause high-energy electrons to be released from the planet’s inner radiation belt, according to a recent study. This phenomenon, referred to as an electron ‘rain,’ poses potential risks to satellites and even humans in orbit.
When lightning strikes, electrons come streaming down.
Researchers from the University of Colorado Boulder, led by an undergraduate student, have identified a new connection between terrestrial weather and space weather. By analyzing satellite data, the team revealed that lightning storms can dislodge particularly high-energy electrons, called “extra-hot” electrons, from the inner radiation belt—a region in space filled with charged particles surrounding Earth like an inner tube.
Their findings could assist in protecting satellites and astronauts from harmful radiation in space. “This is a type of downpour you really want to avoid,” remarked lead author and undergraduate Max Feinland.
“These particles are dangerous—some people might refer to them as ‘killer electrons,'” said Feinland, who graduated with a degree in aerospace engineering sciences from CU Boulder in spring 2024. “They can penetrate satellite metal, damage circuit boards, and pose a cancer risk to individuals in space.”
This study was published on October 8 in the journal Nature Communications.
The results indicate that the radiation belts, shaped by Earth’s magnetic field, are more interconnected with atmospheric phenomena. Co-author Lauren Blum, an assistant professor in the Laboratory for Atmospheric and Space Physics (LASP) at CU Boulder, explained that two radiation belt regions orbit our planet. The inner belt, fluctuating over time, generally starts more than 600 miles above the surface, while the outer belt begins around 12,000 miles away. These encircling belts trap charged particles streaming towards Earth from the sun, acting as a protective barrier between our atmosphere and the solar system.
However, they’re not completely sealed. Scientists have long understood that high-energy electrons can fall toward Earth from the outer belt, but Blum and her colleagues are the first to observe a similar phenomenon from the inner belt.
In essence, Earth and space may not be as distinct as they appear.
“Space weather is influenced by events from both above and below,” Blum stated.
A Lightning Strike’s Impact
This highlights the might of lightning.
When a lightning bolt flashes overhead on Earth, it emits radio waves that may reach deep into space. If these waves collide with electrons in the radiation belts, they can dislodge them—similar to shaking raindrops off an umbrella. In certain instances, this “lightning-induced electron precipitation” can even alter the chemistry of Earth’s atmosphere.
Up to now, direct measurements had only been taken of lower energy, or “colder,” electrons falling from the inner radiation belt.
“The inner belt is usually seen as kind of uneventful,” said Blum. “It’s considered stable and persistent.”
The team’s groundbreaking discovery occurred almost serendipitously. Feinland was reviewing data from NASA’s now-retired Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite when he noticed something unusual: clusters of high-energy electrons moving through the inner belt.
“I showed Lauren some of my findings, and she remarked, ‘These aren’t supposed to be here,'” Feinland explained. “Some studies suggest that high-energy electrons don’t exist in the inner belt at all.”
Motivated by curiosity, the team decided to investigate further.
In total, Feinland identified 45 incidents of high-energy electrons in the inner belt from 1996 to 2006. He compared these occurrences with records of lightning strikes across North America. It turned out that some spikes in electron activity occurred mere seconds after lightning lit up the ground.
The Electron Bouncing Game
This is the team’s proposed explanation: After a lightning strike, Earth’s radio waves initiate a chaotic pinball-like action in space. They knock into electrons in the inner belt, sending them ricocheting between Earth’s northern and southern hemispheres at remarkable speed—just 0.2 seconds for each back and forth.
With each bounce, some of these electrons drop out of the belt and into our atmosphere.
“You have a large concentration of electrons bouncing around, and with each return, they hit again,” Blum described. “Initially, there’s a strong signal that fades away.”
Blum is uncertain how frequently such events happen; they may mostly arise during periods of intense solar activity when high-energy electrons are abundant in the inner belt.
The researchers aspire to better understand these occurrences so they can predict them, potentially enhancing safety for people and electronics in orbit.
For Feinland, the experience of studying these awe-inspiring storms has been invaluable.
“I didn’t realize how much I enjoyed research until I worked on this project,” he reflected.
