Colliding auroras produce an explosion of light

Dec 17, 2009
This is a locations and field of view map of the twenty all-sky imagers used in support of the THEMIS mission. Twenty all-sky imagers (ASIs) were deployed by researchers from the University of California Berkeley, the University of Calgary, and the University of Alaska in support of the THEMIS mission. Credit: THEMIS/UC Berkeley

(PhysOrg.com) -- A network of cameras deployed around the Arctic in support of NASA's THEMIS mission has made a startling discovery about the Northern Lights. Sometimes, vast curtains of aurora borealis collide, producing spectacular outbursts of light. Movies of the phenomenon were unveiled at the Fall Meeting of the American Geophysical Union today in San Francisco.

"Our jaws dropped when we saw the movies for the first time," said space scientist Larry Lyons of the University of California-Los Angeles (UCLA), a member of the team that made the discovery. "These outbursts are telling us something very fundamental about the nature of auroras."

The collisions occur on such a vast scale that isolated observers on Earth -- with limited fields of view -- had never noticed them before. It took a network of sensitive cameras spread across thousands of miles to get the big picture.

Colliding auroras photographed by THEMIS all-sky imagers (ASIs) on Feb. 29, 2008. Click 'Enlarge' for Animation. Credit: Toshi Nishimura/UCLA

and the Canadian Space Agency created such a network for THEMIS, short for "Time History of Events and Macroscale Interactions during Substorms." THEMIS consists of five identical probes launched in 2006 to solve a long-standing mystery: Why do auroras occasionally erupt in an explosion of light called a substorm?

Twenty all-sky imagers (ASIs) were deployed across the Alaskan and Canadian to photograph auroras from below while the spacecraft sampled charged particles and electromagnetic fields from above. Together, the on-ground cameras and spacecraft would see the action from both sides and be able to piece together cause and effect—or so researchers hoped. It seems to have worked.

The breakthrough came earlier this year when UCLA researcher Toshi Nishimura assembled continent-wide movies from the individual ASI cameras. "It can be a little tricky," Nishimura said. "Each camera has its own local weather and lighting conditions, and the auroras are different distances from each camera. I've got to account for these factors for six or more cameras simultaneously to make a coherent, large-scale movie."

The first movie he showed Lyons was a pair of auroras crashing together in Dec. 2007. "It was like nothing I had seen before," Lyons recalled. "Over the next several days, we surveyed more events. Our excitement mounted as we became convinced that the collisions were happening over and over."

The explosions of light, they believe, are a sign of something dramatic happening in the space around Earth—specifically, in Earth's "plasma tail." Millions of kilometers long and pointed away from the sun, the plasma tail is made of charged particles captured mainly from the solar wind. Sometimes called the "plasma sheet," the tail is held together by Earth's magnetic field.

This three frame animation of THEMIS/ASI images shows auroras colliding on Feb. 29, 2008. Credit: Toshi Nishimura/UCLA

The same magnetic field that holds the tail together also connects it to Earth's polar regions. Because of this connection, watching the dance of Northern Lights can reveal much about what's happening in the plasma tail.

THEMIS project scientist Dave Sibeck of NASA's Goddard Space Flight Center, Greenbelt, Md. said, "By putting together data from ground-based cameras, ground-based radar, and the THEMIS spacecraft, we now have a nearly complete picture of what causes explosive auroral substorms,"

Lyons and Nishimura have identified a common sequence of events. It begins with a broad curtain of slow-moving auroras and a smaller knot of fast-moving auroras, initially far apart. The slow curtain quietly hangs in place, almost immobile, when the speedy knot rushes in from the north. The auroras collide and an eruption of light ensues.

A schematic diagram of Earth's magnetosphere. Earth is the circle near the middle and the plasma tail is denoted in yellow. Credit: Larry Lyons/UCLA

How does this sequence connect to events in the plasma tail? Lyons believes the fast-moving knot is associated with a stream of relatively lightweight plasma jetting through the tail. The stream gets started in the outer regions of the plasma tail and moves rapidly inward toward Earth. The fast knot of auroras moves in synch with this stream.

Meanwhile, the broad curtain of auroras is connected to the stationary inner boundary of the plasma tail and fueled by plasma instabilities there. When the lightweight stream reaches the inner boundary of the plasma tail, there is an eruption of plasma waves and instabilities. This collision of plasma is mirrored by a collision of auroras over the poles.

National Science Foundation-funded radars located in Poker Flat, Alaska, and Sondrestrom, Greenland, confirm this basic picture. They have detected echoes material rushing through Earth's upper atmosphere just before the auroras collide and erupt. The five THEMIS spacecraft also agree. They have been able to fly through the plasma tail and confirm the existence of lightweight flows rushing toward Earth.

Explore further: Space sex geckos at risk as Russia loses control of satellite

add to favorites email to friend print save as pdf

Related Stories

Northern lights research enters final frontier

Jan 12, 2007

An international team of scientists -- including physicists from the University of Calgary -- will begin gathering the most detailed information yet about the ever-changing northern lights, as a multi-year research project ...

Spring is Aurora Season

Mar 04, 2008

What are the signs of spring? They are as familiar as a blooming daffodil, a songbird at dawn, a surprising shaft of warmth from the afternoon sun. And, oh yes, don’t forget the aurora borealis. Spring is ...

THEMIS probes view auroral substorms, bowshock explosions

Dec 11, 2007

Five satellites launched last February to probe magnetic storms around the Earth will move into prime observing position next month, but they already have produced important new information on the interactions ...

University of Alberta space research to solve aurora mystery

Jan 10, 2007

On February 15, NASA will launch the largest number of scientific satellites ever sent into orbit aboard a single rocket. A handful of Alberta scientists will be at Kennedy Space Center watching and waiting. For Dr. Ian Mann ...

Study finds Earth's auroras are not mirror images

Apr 06, 2005

Thanks to observations from the ground and satellites in space, scientists know that the North and South Poles light up at night with Auroras because a "solar wind" of electrified gas continually flows outward ...

Scientists solve 30-year-old aurora borealis mystery

Jul 24, 2008

UCLA space scientists and colleagues have identified the mechanism that triggers substorms in space; wreaks havoc on satellites, power grids and communications systems; and leads to the explosive release of ...

Recommended for you

Video: A dizzying view of the Earth from space

15 hours ago

We've got vertigo watching this video, but in a good way! This is a sped-up view of Earth from the International Space Station from the Cupola, a wraparound window that is usually used for cargo ship berthings ...

NEOWISE spots a comet that looked like an asteroid

15 hours ago

Comet C/2013 UQ4 (Catalina) has been observed by NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) spacecraft just one day after passing through its closest approach to the sun. The comet ...

What the UK Space Agency can teach Australia

16 hours ago

Australia has had an active civil space program since 1947 but has much to learn if it is to capture a bigger share of growing billion dollar global space industry. ...

Discover the "X-factor" of NASA's Webb telescope

16 hours ago

NASA's James Webb Space Telescope and Chandra X-ray observatory have something in common: a huge test chamber used to simulate the hazards of space and the distant glow of starlight. Viewers can learn about ...

User comments : 0