Image: Chorus Waves
A schematic diagram showing aurora over North America and a spacecraft in space (magenta) embedded in the energetic plasma source (blue cloud). These two regions are connected by the Earth's magnetic field line. Energetic plasma interacts with waves (red) and precipitates into the upper atmosphere (blue arrows) and generate aurora. The geometry of the plasma cloud determines the aurora shape.
updated 9/30/2010 3:34:59 PM ET 2010-09-30T19:34:59

Scientists have long known the colorful northern lights that amaze skywatchers are more than just pretty light shows in the sky. But until now, the engine behind their diversity has been a mystery.

A new study has found a connection between pulsating aurora displays around Earth's North Pole and the intensity of so-called chorus waves, which are electromagnetic fluctuations that occur in space within our planet's magnetosphere. The findings could help paint a clearer view of the drivers behind different kinds of aurora.

"Our study determined that the specific process occurring in space is responsible for some types of northern lights," Yukitoshi Nishimura, lead author of the study and a visiting scholar in the Department of Atmospheric and Oceanic Sciences at UCLA, told "While scientists have only had a rough idea about what is happening in space when northern lights occur, we realized through this study what specific features in space we should focus on for further studies of the cool night sky show."

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The pulsing northern lights
Pulsating auroras typically occur in the night sky around the Earth's polar regions and are characterized as a group of luminous patches that blink on and off with recurrence periods of roughly 5 to 40 seconds, Nishimura explained.

"This is different from typical aurora, which does not show such regular pulsation," Nishimura said.

Compared with typical aurora, the pulsating variety is often more difficult to see, because it is much weaker, said Richard Thorne, a professor at UCLA and one of the study's co-authors.

The team of researchers made their discovery by combining satellite and ground-based observations from NASA's THEMIS mission, which includes five space probes that sift through Earth's magnetic field, searching for the stormy beginnings of our planet's most dynamic auroras.

Electromagnetic chorus
Nishimura and his colleagues used one of the THEMIS mission's ground-based All-Sky Imagers to monitor the sky on Feb. 15, 2009. They found that chorus waves in Earth's magnetosphere, which were simultaneously detected by one of the THEMIS satellites, were directly related to changes observed in the pulsating aurora.

"We found that when the intensity of chorus waves increases, the luminosity of the aurora also correspondingly increases," Nishimura said. "The timing of these modulations matched almost perfectly."

Likewise, when the intensity of the chorus waves decreased, the luminosity of the pulsating aurora also decreased.

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"It sounds like birds chirping when the signal is played through a speaker that's why it is called 'chorus,'" Nishimura said. "Chorus has two frequency bands. The lower frequency band interacts with energetic electrons that have appropriate energies to cause aurora when precipitating toward the upper atmosphere."

In other words, pulsating auroras are caused by particles from solar wind that strike the Earth's magnetic field and travel through the planet's magnetic field lines. When these electrons reach the upper atmosphere, they are sometimes expressed in bursts of chorus waves.

"This points to the fact that the waves in space are an important part of the magnetospheric environment," Thorne told "It has been speculated for years that it could be important, but this is the first piece of information that quantifies that relationship in detail."

The results of the study will be published in the Oct. 1 issue of the journal Science. The findings could help other scientists create more accurate models of Earth's magnetic field something that has been problematic, because it changes drastically with fluctuations in solar activity, Nishimura said.

The study will also contribute to future studies of atmospheric dynamics and chemistry, and closer examinations of other types of northern lights.

"There are many kinds of aurora, and our study solved the problem for part of them," Nishimura said. "We should keep the ongoing research in the community active. Someday, we will be able to say not only "beautiful" but to describe what is going on in space by just looking at the sky."

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Photos: Auroral lights

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  1. St. Patrick's Day green

    The aurora borealis, or northern lights, fill the early morning sky on March 17, 2013, above the Holy Assumption of the Virgin Mary, a Russian Orthodox Church in Kenai, Alaska. (M. Scott Moon / AP) Back to slideshow navigation
  2. Snowy landscape

    The northern lights glow over a snowy Finnish landscape in a photo taken on the night of Jan. 16-17, 2013, by Thomas Kast.

    Watch the time-lapse video on Vimeo. (Thomas Kast) Back to slideshow navigation
  3. Starry night

    Swirls of green and red appear in an aurora over Whitehorse in Canada's Yukon Territory on the night of Sept. 3, 2012. The northern lights were sparked by a storm of electrically charged particles that was thrown off by the sun on Aug. 31. (David Cartier, Sr. / NASA via Reuters) Back to slideshow navigation
  4. View from above

    NASA astronaut Joe Acaba, flight engineer of the Expedition 32 crew onboard the International Space Station, recorded this image of Aurora Australis, also known as the Southern Lights, on July 15, 2012, from an altitude of approximately 240 miles.The Canadarm2 robot arm is in the foreground. (Joe Acaba / NASA via AP) Back to slideshow navigation
  5. Summer delight

    Robert Snache, a photographer living in the Rama First Nation in Ontario, captured this view of the northern lights on the night of July 8-9, 2012. For more about Snache and his work, check out Spirithands Photography on Facebook. (Robert Snache / Spirithands Photography) Back to slideshow navigation
  6. Norwegian lights

    Thorbjørn Haagensen took this picture of the northern lights on April 3, 2012, from Hillesøy, close to Tromsø in northern Norway. The winter season is prime time for auroral displays, but with the onset of spring, the northern lights begin to pale up north. "Beginning in the middle of May, the midnight sun brings sunshine all night long," Haagensen said. (Thorbjørn Haagensen) Back to slideshow navigation
  7. Heavenly glow

    Jonina Oskarsdottir captured this picture of the northern lights on March 8, 2012, over Faskrudsfjordur, Iceland. "No words can describe the experience of the northern lights tonight," Oskarsdottir told She used a Canon EOS 5D Mark II camera to take the shot, with a Canon 14mm f/2.8L USM II lens set for ISO 1600 ... and a 1-second exposure. (Jonina Oskarsdottir / via AP) Back to slideshow navigation
  8. Alaskan green

    The skies over the frozen Susitna River near Talkeetna, Alaska, are lit up by a display of the northern lights on Jan. 23, 2012. The aurora was enhanced by solar flares in the days preceding the event. (Michael Dinneen / AP) Back to slideshow navigation
  9. Spectral scene

    It's almost as if these two separate events of nature were fuming at each other. The northern lights are seen above the ash plume of Iceland's Eyjafjallajokull volcano on the evening of April 22, 2010. (Lucas Jackson / Reuters) Back to slideshow navigation
  10. Halloween treat

    A geomagnetic storm produced a colorful show of aurora borealis in the skies over Hyvinka in southern Finland on the morning of Oct. 31, 2003. (Pekka Sakki / AFP - Getty Images) Back to slideshow navigation
  11. Majestic mountains and sky

    The colors of sunrise and the northern lights add to this view of a Perseid meteor streak on Aug. 12, 2000, as seen from the Colorado Rockies. (Jimmy Westlake / Colorado Mountain College) Back to slideshow navigation
  12. Graceful ballet of light

    The northern lights dance over the Knik River near Palmer, Alaska, on Nov. 29, 2006. (Bob Martinson / AP) Back to slideshow navigation
  13. Otherworldly feel

    John Carlson of Lutsen, Minn., said he was "surprised by the intense activity of the aurora" on Aug. 29, 2008. He took this beautiful but eerie photograph. (John Carlson / John and Sallie Carlson) Back to slideshow navigation
  14. Midwestern dazzle

    Northern lights are shown above a covered bridge at Wilkinson Pioneer Park in Rock Falls, Iowa, on Nov. 7, 2004. (Arian Schuessler / Mason City Globe Gazette via AP) Back to slideshow navigation
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