THEMIS Mission’s Three Discoveries On Earth’s Light Display

A fleet of NASA spacecraft, launched less than eight months ago, has made three important discoveries about spectacular eruptions of Northern Lights called "substorms" and the source of their power. Caption for photo as follows - The Aurora Borealis, or Northern Lights, shines above Bear Lake, Eielson Air Force Base, Alaska. Image Credit: Wikipedia - Picture of the Year 2006

THEMIS Mission’s Three Discoveries On Earth’s Light Display

NASA's Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission is the official name given our government’s effort to better understand space weather around our Oblate Spheroid.

Aurora Borealis, named after the Roman goddess of the dawn, Aurora, and the Greek name for north wind, Boreas, have long been the curiosity of people who have witnessed the magnificent sky light display either from the ground or pressed against the glass of an airline window as they fly over the (northern) polar route on their way to Europe.

On Tuesday, at the annual meeting of the American Geophysical Union held in San Francisco, THEMIS reported on their observations of the more bizarre and fascinating visual phenomenon known as the Northern Lights.

This visualization shows the 20 THEMIS ground station locations. These ground stations will assist the THEMIS satellite constellation in measuring the Aurora Borealis over North America. Each ground station has an all-sky imaging white-light auroral camera and a magnetometer. The ground stations' radial coverage (blue circles) is rendered at 540km (335 miles). An artist's conception of an aurora is added to the visualization for context (red and green stripes). Image Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

A fleet of NASA spacecraft, launched less than eight months ago, has made three important discoveries about spectacular eruptions of Northern Lights called "substorms" and the source of their power.

Image Credit: NASA Themis Mission

This excerpted from CNN -

Northern Lights energy source discovered
By CNN.com via Associated Press - updated 10:22 a.m. EST, Thu December 13, 2007

Scientists think they have discovered the energy source of auroras borealis, the spectacular color displays seen in the upper latitudes of the Northern Hemisphere.

New data from NASA's Themis mission, a quintet of satellites launched this winter, found the energy comes from a stream of charged particles from the sun flowing like a current through twisted bundles of magnetic fields connecting Earth's upper atmosphere to the sun.

The energy is then abruptly released in the form of a shimmering display of lights, said principal investigator Vassilis Angelopoulos of the University of California at Los Angeles.
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To scientists' surprise, the geomagnetic storm powering the auroras raced 400 miles in a minute across the sky. Angelopoulos estimated the storm's power was equal to the energy released by a magnitude 5.5 earthquake.

"Nature was very kind to us," Angelopoulos said.

Although researchers have suspected the existence of wound-up bundles of magnetic fields that provide energy for the auroras, the phenomenon was not confirmed until May, when the satellites became the first to map their structure some 40,000 miles above the Earth's surface.

Scientists hope the satellites will record a geomagnetic storm next year and end the debate about when the storms are triggered.
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Northern Lights as seen in Finland. The Finnish name for the lights (revontulet) comes from a Sami, or Lapp, legend whereby the tail of a fox running along snow-covered fells strikes the snow drifts, sending a trail of sparks into the sky. Revontulet literally means "foxfire". Image Credit: Emagine UK Ltd

This excerpted from the THEMIS Mission website –

The discoveries began on March 23, when a substorm erupted over Alaska and Canada, producing vivid auroras for more than two hours. A network of ground cameras organized to support THEMIS photographed the display from below while the satellites measured particles and fields from above.

“The substorm behaved quite unexpectedly," says Vassilis Angelopoulos, the mission's principal investigator at the University of California, Los Angeles. "The auroras surged westward twice as fast as anyone thought possible, crossing 15 degrees of longitude in less than one minute. The storm traversed an entire polar time zone, or 400 miles, in 60 seconds flat.”

Photographs taken by ground cameras and NASA's Polar satellite (also supporting the THEMIS mission) revealed a series of staccato outbursts each lasting about 10 minutes. Angelopoulos said that some of the bursts died out while others reinforced each other and went on to become major onsets.
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Where does all that energy come from? THEMIS may have found the answer.

"The satellites have found evidence of magnetic ropes connecting Earth's upper atmosphere directly to the sun," said David Sibeck, project scientist for the mission at NASA's Goddard Space Flight Center, Greenbelt, Md. "We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras."

A magnetic rope is a twisted bundle of magnetic fields organized much like the twisted hemp of a mariner's rope. Spacecraft have detected hints of these ropes before, but a single spacecraft was insufficient to map their 3D structure. THEMIS' five identical micro-satellites were able to perform the feat.

"THEMIS encountered its first magnetic rope on May 20," said Sibeck. "It was very large, about as wide as Earth, and located approximately 40,000 miles (70,000 km) above Earth's surface in a region called the magnetopause." The magnetopause is where the solar wind and Earth's magnetic field meet and push against one another like sumo wrestlers locked in combat. There, the rope formed and unraveled in just a few minutes, providing a brief but significant conduit for solar wind energy.

THEMIS also has observed a number of small explosions in Earth's magnetic bow shock. "The bow shock is like the bow wave in front of a boat," explained Sibeck. "It is where the solar wind first feels the effects of Earth's magnetic field. Sometimes a burst of electrical current within the solar wind will hit the bow shock and—Bang! We get an explosion."

The THEMIS satellites are equipped with instruments that measure ions, electrons and electromagnetic radiation in space. The satellites will line up along the sun-Earth line next February to perform their key measurements.

Researchers expect to observe, for the first time, the origin of substorm onsets in space and learn more about their evolution. Scientists from the US, Canada, Western Europe, Russia and Japan are contributing to the scientific investigation over the next two years.
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