Giant "Space Tornadoes" Spark Auroras on Earth

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Giant "Space Tornadoes" Spark Auroras on Earth


April 24, 2009
Even Dorothy would struggle to survive a "space tornado."
Whirling at more than a million miles per hour, these invisible, funnel-shaped solar windstorms carry electrical currents of more than a hundred thousand amps—roughly ten times that of an average lightning strike—scientists announced Thursday.
And they're huge: up to 44,000 miles (70,000 kilometers) long and wide enough to envelop Earth.

Led by the University of California astrophysicist Andreas Keiling, scientists have made the most detailed measurements yet of the space tornadoes, also known as substorm current wedges.

Their results shed light on how space tornadoes help spark auroras, also known as the southern or northern lights—the glowing colors that light up the night in polar regions.

(Related: "Aurora 'Power Surges' Triggered by Magnetic Explosions.")

The findings were made as part of the NASA's THEMIS (Time History of Events and Macroscale Interactions during Substorms) mission. THEMIS links 5 spacecraft and 20 ground observatories to measure how solar winds (charged particles from the sun) interact with Earth's magnetic field.

(Related: "Earth Atmosphere 'Breathes,' Thanks to Solar Winds").

"It is the first time that measurements from ground-based instruments and spacecraft have been combined in this way, and it gives us the most detailed picture yet" about the way our magnetic field responds to solar wind, said Timothy Horbury, a space physicist at Imperial College London, who wasn't involved in the study.
Spinning Up Auroras

As well as revealing the vast size and speed of these rotating plasmas of ionized gas, the team has pinpointed how space tornadoes kick-start the auroras we see on Earth.

"The tornado appears to ignite the aurora," said study leader Keiling, who presented the findings at a European Geosciences Union meeting in Vienna, Austria.
Barrages of the wind's charged particles hit the dayside of Earth, then flow around the planet, stretching our magnetic field into a tail—or magnetotail—extending away from the sun.

A magnetotail is "like a rubber band being stretched and snapped back again. This creates lots of turbulence and forms the tornado," Keiling said.
Stanley Cowley, a solar and planetary physicist at the University of Leicester, U.K., noted that "the connection between aurora and these storms has been known about for 40 years."

What's new, added Cowley, who was not involved in the new study, are the team's detailed figures on the sizes, shapes, speeds, amperage, and frequency of the space tornadoes.

Space Tornadoes: Fast, Furious—And Frequent

The new measurements show that a space tornado forms roughly every three hours and takes just one minute to reach Earth's ionosphere—our outermost atmospheric layer, between 62 and 250 miles (100 and 400 kilometers) above the ground.

Auroras are created when the electrons inside the tornadoes collide with particles in the ionosphere, releasing energy and making the molecules glow.

Unlike their counterparts on Earth, space tornadoes are not directly dangerous to humans.

But "sometimes [space tornadoes] generate large currents in conducting structures"—such as power transformers—"on the ground," Keiling said. And in near space, the storms can disrupt satellite communications, including GPS.


Giant "Tornadoes" Seen Erupting From the Sun
The sun produces giant tornado-like jets that stretch thousands of miles into space, new satellite data shows.
see video-> http://news.nationalgeographic.com/news/2008/06/080603-solar-tornadoes.html

The solar tornadoes typically last about ten minutes and occur near the sun's poles.

"These solar tornadoes are almost a thousand times faster than a terrestrial tornado and are very big," said Spiros Patsourakos, a researcher at George Mason University.

Scientists have known since the 1990s that jets of gas wider than North America were erupting from the sun's poles, but it is only now that they discovered these jets are rotating.

That's because a new pair of NASA satellites called STEREO allowed the features to be observed from two directions at once, revealing their three-dimensional structures.

"The main element [of the new observations] is that the erupting structures possess twist," said Patsourakos, who described his findings last week at an American Geophysical Union meeting in Florida.

(See striking images of the sun.)

Magnetic Field

That twist comes from the sun's magnetic field, said Etienne Pariat, also of George Mason University.
"The magnetic field lines act like a spring, which expands and jumps outward," said Pariat, who has used computer simulations to model the forces producing the jets.
The forces originate in the solar interior, he added, where the sun's rotation twists the magnetic field.
"But the twist cannot be stored, so it must be ejected."

Understanding these forces is important, Patsourakos added, because other solar phenomena can affect our lives here on Earth.
The jets may be a "Rosetta stone for understanding all kinds of ejections from the sun," he said.

Space Weather

The biggest and most dangerous of these events are massive solar storms called coronal mass ejections, which affect "space weather" by producing radiation that can extend all the way to Earth.

Their impacts range from vivid auroras to electromagnetic storms that can damage satellites. The radiation can also put astronauts at risk.
In another presentation at the Fort Lauderdale meeting, another team of scientists said they had found similar twisting in a recent coronal mass ejection.

Although such ejections are well studied, the twisting hadn't been seen before, partly because superbright solar flares make it difficult for satellite instruments to see their details.
But on April 9, 2008, the flare was out of sight, just around the edge of the sun.

This allowed the scientists' instruments to take detailed images of the ejection without being blinded by the flare itself. (Read about how satellites are probing secrets of the Sun.)
The new pictures provided "a beautiful view of the process," said Ed DeLuca, an astronomer at the Harvard-Smithsonian Center for Astrophysics.
This advantageous angle allowed instruments from the Japanese spacecraft Hinode to spot the twist.
Unlike the polar jets in which the twist appeared quite simple, the ejection twist proved to be much more complex, DeLuca said. Parts of it were rotating clockwise, while others were rotating counter-clockwise.

Similar Twisting

Nevertheless, DeLuca believes the twisting is due to similar mechanisms to those which cause the tornadoes to rotate.
The difference, he said, is that mass ejections are much larger with much more complex magnetic fields at their bases.
Also, the jets occur near the poles, where the background magnetic field is directed primarily up and down.

The mass ejections also occur closer to the sun's equator, where the background magnetic field is almost horizontal, producing much more complicated interactions.
DeLuca hopes that by comparing observations from multiple instruments, scientists will be able to determine the magnetic conditions at the sun's surface at the time of the ejection.
This would allow computer modelers such as Pariat to know what parameters to use for their simulations.