Radio transmitters on Earth cause charged particles to leak out of the inner Van Allen radiation belt in space, new observations confirm.
Future satellite transmitters may take advantage of the effect, which had been predicted theoretically, to help clear the belt of charged particles from intense solar outbursts or nuclear explosions in space that could threaten satellites.
The Earth’s geomagnetic field traps charged particles in two concentric belts that gird the planet. Particles can escape the outer belt in about a week, but the inner belt can hold onto particles for about a year.
That could potentially lead to a dangerous buildup of particles after solar storms or a nuclear blast in space. High levels of charged particles could damage global positioning and other types of satellites that orbit in the Van Allen zone.
Previous observations had suggested that very-low-frequency (VLF) radio waves (from 5 to 25 kilohertz) transmitted on Earth were helping to clear particles from the inner belt. “But it was very hard to nail down,” says Craig Rodger of the University of Otago in New Zealand.
Now, he and colleagues have compared simultaneous observations taken on the ground and in space to confirm the effect.
At night, when more VLF signals can pass through the Earth’s atmosphere, a French satellite called DEMETER measured more electrons near the inner belt when a powerful transmitter in Australia was turned on than when it was off.
“It seems convincing to me that the . . . transmitter is helping to scatter electrons,” says Jay Albert of the US Air Force Research Laboratory. But he says the strength of the effect remains to be determined, noting that the radiation belts did not change noticeably during several months in 2004 when the transmitter was shut down.
The Air Force plans tests with a satellite-based VLF transmitter at about the time of the next solar maximum, expected around 2011.
Interestingly, the new work suggests researchers have never observed the Van Allen belts as they are “naturally”. That’s because VLF radio transmitters have been used since at least the 1920s to send telegraph messages and communicate with submarines, and the belts’ existence was only confirmed in 1958.
“Electron lifetime [in the belts] now must be different than it was before the transmitters were built, but we don’t know how different,” Rodger told New Scientist.
Journal reference: Geophysical Research Letters (doi:10.1029/2008GL033194)