In other words, thanks to VLF, we now have anthropogenic (or human-made) space weather.
“A number of experiments and observations have figured out that, under the right conditions, radio communications signals in the VLF frequency range can in fact affect the properties of the high-energy radiation environment around the Earth,” says one of the team, Phil Erickson from the MIT Haystack Observatory in Massachusetts.
Most of us won’t have much to do with VLF signals in our everyday life, but they’re a mainstay in many engineering, scientific, and military operations.
With frequencies between 3 and 30 kilohertz, they’re far too weak to carry audio transmissions, but they’re perfect for broadcasting coded messages across long-distances or deep underwater.
One of the most common uses of VLF signals is to communicate with deep-sea submarines, but because their large wavelengths can diffract around large obstacles such as mountain ranges, they’re also used to achieve transmissions across tricky terrain.
It was never the intention for VLF signals to go anywhere other than on Earth, but it turns out they’ve been leaking into the space surrounding our planet, and have lingered long enough to form a giant protective bubble.
When the Van Allen Probes compared the location of the VLF bubble to the bounds of Earth’s radiation belts, they found what initially looked like an interesting coincidence – “The outward extent of the VLF bubble corresponds almost exactly to the inner edge of the Van Allen radiation belts,” says NASA.