Lightning creates radiation-safe zone.

A relatively safe region inside the treacherous seas of radiation that surround our planet owes its existence to lightning storms on Earth, scientists have determined.

Previous research suggested that radio waves clear out a zone within the region of radiation called the Van Allen belts. The waves knock charged particles, a form of radiation that would otherwise be trapped in the belts, into the atmosphere. That leaves a charge-depleted zone within the radiation belt, a venue just right for placing sensitive satellites. But scientists weren't sure where the radio waves were coming from.

That's where James L. Green of the NASA Goddard Space Center in Greenbelt, Md., and his coworkers come in. Green's team found that the intensity of the radio waves sweeping through the safe zone tended to match the amount of lightning activity on Earth. They compared variations in the radio waves measured by the IMAGE and Dynamics Explorer satellites with trends in lightning activity captured by the Micro Lab 1 satellite.

Lightning flashes generate bursts of radio waves that leak out into space and sweep the belts, Green's group concludes in the March Journal of Geophysical Research (Space Physics).

"If we didn't have lightning, we wouldn't have this ... safe zone," says Green, adding that it might even be possible to make the safe zone larger by using transmitters to broadcast radio waves of the right frequency.--D.S.