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7/25/2008
03:43 PM
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NASA Unravels Mysteries Of Northern Lights

Researchers believe stressed magnetic field lines suddenly snap to a new shape, like a rubber band that's been stretched too far, during a process called magnetic reconnection.


Northern Lights Over Alaska

Northern Lights over Alaska. Credit: NASA
(click for larger image)

Researchers have discovered that explosions of magnetic energy a third of the way to the moon power substorms that create the Northern Lights.

Five NASA satellites helped researchers pinpoint how sudden brightening and rapid movements of the aurora borealis take place. NASA said this week that researchers believe stressed magnetic field lines suddenly snap to a new shape, like a rubber band that's been stretched too far, during a process called magnetic reconnection.

"We discovered what makes the Northern Lights dance," Vassilis Angelopoulos, a principal investigator for the Time History of Events and Macroscale Interactions during Substorms mission (Themis) at the University of California, Los Angeles, said.

Substorms change the auroral displays at the North and South poles, causing the lights to flicker. The substorms also frequently occur with space storms that disrupt radio communications and GPS signals and cause power outages, NASA said. Scientists hope the new information helps them improve substorm models and forecasts.

"As they capture and store energy from the solar wind, the Earth's magnetic field lines stretch far out into space," said David Sibeck, Themis project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Magnetic reconnection releases the energy stored within these stretched magnetic field lines, flinging charged particles back toward the Earth's atmosphere. They create halos of shimmering aurora circling the northern and southern poles."

The satellites, launched in February 2007, and a network of 20 ground observatories in Canada and Alaska allow scientists to observe the beginning of substorms. Every four days, the satellites line up with the Earth's equator to gather and record data showing where, when, and how substorms develop.

Synchronized ground stations also point a magnetometer and camera skyward to determine where and when an auroral substorm will begin. NASA explained that research instruments measure auroral light through particles that flow along Earth's magnetic field and the electrical currents they generate.

Recently, the satellites observed an isolated substorm beginning in space, as the observatories recorded the lights and currents over North America. That lent support to the theory that magnetic reconnection causes substorms, NASA said. The theory is that when a substorm begins, it follows a pattern that includes reconnection, rapid auroral brightening, and rapid expansion toward the Earth's poles. That, in turn, redistributes electrical currents flowing in space and around the Earth.

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