The source of magnetic storms in space that intensify the northern lights and disrupt satellites and power grids has been identified by scientists.

The aurora borealis or northern lights are a spectacular visual phenomenon seen in the skies close to the pole. They are caused by interactions between the Earth's magnetic field and the solar wind of charged particles that flows from the Sun.

This sometimes peaks into flurries of brighter activity after magnetic disturbances known as “substorms”, for which competing explanations have been advanced.

Research using the Nasa Themis observatory has now shown that they occur when two magnetic field lines join together, releasing energy and heat. The result of these “magnetic reconnections” is to accelerate plasma from the Sun towards Earth, causing a more intense aurora.

“We discovered what sparks the magnificent light show of the aurora,” said Vassilis Angelopoulos, of the University of California Los Angeles, who led the study.

The discovery is significant because magnetic substorms can affect the Earth's electrical systems.

These peaks of magnetic activity can knock out or disable satellites and even disrupt electricity generation and transmission systems.

Full-scale magnetic storms, caused by sudden emissions of charged plasma from the Sun, can have the same effect. Substorms also pose a potential danger to any astronauts who are in space at the time, a likely challenge for proposed missions to the Moon and to Mars.

The findings, which are published in the journal Science, should help scientists to predict substorms more accurately.

“We need to understand this environment and eventually be able to predict when these large energy releases will happen, so astronauts

can go inside their spacecraft and we can turn off critical systems on satellites so they will not be damaged,” Dr Angelopoulos said.

“This has been exceedingly difficult in the past because previous missions, which measured the plasma at one location, were unable to determine the origin of the large space storms.

“To resolve this question properly requires correlations and signal timing at multiple locations. This is precisely what was missing until now.

“Armed with this knowledge, we are not only putting to rest age-old questions about the origin of the spectacular auroral eruptions but will also be able to provide statistics on substorm evolution and model its effects on space weather.”

The Themis observatory, which identified the origin of substorms, consists of five satellites launched in February last year and an array of 20 ground-based observatories in the northern US and Canada. Together, they take images of substorms and aurorae as they happen.

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