VOA标准英语2008年-Scientists Solve Mystery of Brilliant Northern,（在线收听）

Scientists have solved the mystery behind the brilliant northern and southern light show known as Aurora Borealis. The phenomenon is caused by electromagnetic energy from the sun, which experts say also wreaks havoc on ground-based power grids and satellites. VOA's Jessica Berman reports.

Just like atmospheric conditions can affect weather on the ground, experts say the sun is responsible for weather in outer space.

They say the Sun's atmosphere emits high energy solar winds that bathe the Earth continuously with electromagnetic energy.

Nicola Fox is with the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

"You could really think of it as us living in the atmosphere of the Sun," Fox explained. "So, if the Sun changes, the Earth will feel its effects. So, if the Sun sneezes, the Earth will catch a cold."

But until now, space scientists have been unable to pinpoint the source of energy releases in the earth's atmosphere that are responsible for the spectacular light show, aurora borealis, in the extreme northern and southern latitudes.

The same energy releases are responsible for dangerous sub-storms that disrupt ground-based power grids and communications systems.

Scientists at the University of California at Los Angeles discovered the source of the space blasts using five satellites of the U.S. space agency's THEMIS program.

The researchers explain that the Sun's and Earth's electromagnetic fields normally glide past one another in many different directions.

But when enough energy builds between the two fields, they snap and right themselves in a process scientists call reconnection.

David Sibek is THEMIS project scientist with the U.S. space agency NASA.

He says reconnection releases a huge amount of electrical current into the magnetosphere that surrounds the planet.

"When reconnection occurs, that current is broken and it flows down to the Earth so you have like a short-circuit out in the Earth's magnetic field," explained Sibek. "And it's that current that's going to power the aurora and dump into the Earth's ionosphere and cause power line disruption in Canada for example by blowing out transformers."

Scientists say it is important to know about sub-storms in order to take measures to protect valuable technical equipment, and possibly the lives of spacewalking astronauts.

The discovery of the mechanism behind sub-storms is reported in the journal Science.