Giant "Space Tornadoes" Spark Auroras on Earth

An aurora borealis (northern lights) rises above Alaska's Denali National Park in 2006. For an April 2009 study, THEMIS satellites (inset) helped reveal how fast-swirling, curving "space tornadoes" wider than Earth itself help "ignite" auroras.

Photograph by M. Scott Moon/AP; illustration courtesy A. Keiling et al/THEMIS/NASA


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.

"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.