The discovery could help protect vulnerable satellites, communications networks and power grids which are all affected by solar storms.
Scientists have known for years that the auroras are caused by the interplay of charged particles from the Sun in the Earth's magnetic field, but have only recently witnessed the trigger event that precedes the aurora displays.
Lines of the Earth's magnetic field far out into space snap into a different shape during solar 'sub-storms', showering the Earth with charged particles.
Scientists may now be able to set up an early warning system for operators of vulnerable equipment. Solar storms can knock out satellites and disrupt Earth-bound communications and power networks.
The discovery was made from data gathered by the Time, History of Events and Macroscale Interactions during Substorms (Themis) mission.
Themis uses five weather satellites which can photograph the entire surface of the Earth every four days, and a powerful network of supercomputers based in Alaska and Canada to analyse the data.
Nasa has set up a real-time feed from the satellites.
Nasa boffins reveal aurora trigger
By Staff Writers on Jul 30, 2008 8:14AM