By Ron Cowen
Each time the sun hurls a planet-size cloud of charged particles toward Earth, there’s a potential for power outages and satellite damage. But it’s when the magnetic field carried by these billion-ton clouds points opposite to Earth’s magnetic field that geomagnetic storms are most severe. In that configuration, our planet’s field, which usually shields Earth from the sun’s outbursts, connects directly to the field accompanying the cloud. That magnetic handshake opens up a hole in Earth’s shield, permitting energetic ions and electrons from the sun to gush through and induce large electrical currents in and around the planet.
A report in the Dec. 4 Nature reveals that once such breaches are created, they can persist for hours, rather than closing up soon after they’ve formed. The finding ends a 2-decades-long debate about the duration of holes in Earth’s magnetic shield, says Ron Zwickl of the National Oceanic and Atmospheric Administration’s Space Environment Center in Boulder, Colo. The results, he adds, should be incorporated into models of geomagnetic storms and could be crucial for placing regional hot spots–places where solar ions most easily punch through–on global space-weather maps.