Through an overlooked mechanism, the energy from lightning reaches the highest layers of the atmosphere, where it could endanger the safety of satellites and astronauts.

When lightning strikes, the energy it carries sometimes creates special electromagnetic waves called whistlers, so called because they can be converted into sound signals. For decades, researchers thought that whistlers caused by lightning would remain trapped relatively close to the Earth’s surface, at a distance of less than 1,000 kilometers.

Now Vikas Sonwalkar and Amani Reddy of the University of Alaska Fairbanks have discovered that some whistlers can bounce off a layer of the atmosphere called the ionosphere, which is filled with charged particles. This allows the waves and the energy they carry to reach distances of up to 20,000 kilometers above the Earth’s surface. This means they can penetrate deep into the magnetosphere, the region of space dominated by the Earth’s magnetic field.

The researchers found evidence of these reflected whistlers in data from the Van Allen probes, two robotic space probes that surveyed the magnetosphere between 2012 and 2019. They also discovered signs of this phenomenon in studies published as early as the 1960s. Old and new data all suggest that it is very common and happens all the time, says Reddy.

In fact, the lightning could generate twice as much energy in that area of ​​space as previous estimates suggested, the team says. And that energy charges and accelerates nearby particles, creating electromagnetic radiation that can damage satellites and endanger the health of astronauts.

“Lightning has always been considered a somewhat smaller phenomenon. We only had this data a decade ago and we certainly haven’t studied it in this much detail,” says Jacob Bortnik of the University of California in Los Angeles. The new work is an invitation to other researchers to develop a more accurate picture of the magnetosphere, he says.

Establishing the connection between lightning and the magnetosphere is also important because changes in the Earth’s climate could cause thunderstorms with violent lightning to occur more frequently, says Sonwalkar.

The team now plans to analyze data from more satellites. They hope to learn more about how lightning-based whistlers populate the magnetosphere and how they may be affected by space weather.