Behind the Power and Beauty of Northern Lights

by Nancy Atkinson on July 28, 2008

Northern Lights.  Credit:  NASA

Northern Lights. Credit: NASA

The Aurora Borealis or Northern Lights are stunningly beautiful. But they can also disrupt radio communications and GPS signals, and even cause power outages. What’s behind the ethereal Northern Lights that causes them to shimmer and dance with colorful lights while sometimes wreaking havoc with electrical systems here on Earth? Using a fleet of five satellites, NASA researchers have discovered that explosions of magnetic energy a third of the way to the moon power substorms that cause sudden brightenings and rapid movements of the aurora borealis, called the Northern Lights. “We discovered what makes the Northern Lights dance,” said Dr. Vassilis Angelopoulos of the University of California, Los Angeles. Angelopoulos is the principal investigator for the Time History of Events and Macroscale Interactions during Substorms mission, or THEMIS.

The cause of the shimmering in Northern Lights is magnetic reconnection, a common process that occurs throughout the universe when stressed magnetic field lines suddenly snap to a new shape, like a rubber band that’s been stretched too far.

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

An explosion of energy increases in the brightness and movement of Northern Lights. Credit: NASA/Goddard Space Flight Center

An explosion of energy increases in the brightness and movement of Northern Lights. Credit: NASA/Goddard Space Flight Center

The data was gathered by five strategically positioned Themis satellites, combined with information from 20 ground-based observatories located throughout Canada and Alaska. Launched in February 2007, the five identical satellites line up once every four days along the equator and take observations synchronized with the ground observatories. Each ground station uses a magnetometer and a camera pointed upward to determine where and when an auroral substorm will begin. Instruments measure the auroral light from particles flowing along Earth’s magnetic field and the electrical currents these particles generate.

See animation of magnetic reconnection.

During each alignment, the satellites capture data that allow scientists to precisely pinpoint where, when, and how substorms measured on the ground develop in space. On Feb. 26, 2008, during one such THEMIS lineup, the satellites observed an isolated substorm begin in space, while the ground-based observatories recorded the intense auroral brightening and space currents over North America.

These observations confirm for the first time that magnetic reconnection triggers the onset of substorms. The discovery supports the reconnection model of substorms, which asserts a substorm starting to occur follows a particular pattern. This pattern consists of a period of reconnection, followed by rapid auroral brightening and rapid expansion of the aurora toward the poles. This culminates in a redistribution of the electrical currents flowing in space around Earth.

Solving the mystery of where, when, and how substorms occur will allow scientists to construct more realistic substorm models and better predict a magnetic storm’s intensity and effects.

More about Themis.

Original News Source: NASA press release


Nancy Atkinson is Universe Today's Senior Editor. She also works with Astronomy Cast, and is a NASA/JPL Solar System Ambassador.

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