24 April 2009

Space tornadoes drive Earthly auroras

Cosmos Online
A cluster of NASA probes have revealed the existence of vast "space tornadoes" which are big enough to envelop the Earth, and produce electrical currents exceeding 100,000 amps.
Space tornadoes

Whipping up a storm: Diagram illustrating how the vortices form on the dark side of the Earth. Credit: Andreas Keiling, THEMIS/NASA

SYDNEY: A cluster of NASA probes have revealed the existence of vast “space tornadoes” which – at 70,000 km in length – are big enough to envelop the Earth, and produce electrical currents exceeding 100,000 amps.

The five THEMIS (Time History of Events and Macroscale Interactions during Substorms) probes recorded the extent and power of these electrical funnels as they passed through them.

Ground measurements further showed that the tornadoes channel electrical current into Earth’s ionosphere to create bright and colourful auroras.

Intense currents

Originating in the solar wind, the space tornadoes are rotating plasmas of hot, ionized gas flowing at speeds of more than one million km/h – far faster than the 300 km/h winds of terrestrial tornadoes, said Andreas Keiling, an astrophysicist at the University of California, Berkeley.

The tornadoes are actually vortices created by the release of energy on the dark side of the Earth in the trailing ‘magnetotail’ region of the planet’s magnetic field.

“What we observed we can call a space tornado – it looks very much like a tornado,” said Keiling. He presented the discovery on Thursday at the European Geosciences Union meeting in Vienna, Austria.

Both terrestrial and space tornadoes consist of funnel-shaped structures. Space tornadoes, however, generate huge amounts of electrical currents inside the funnel.

These currents flow along twisted magnetic field lines from space into the ionosphere where they power several processes, most notably bright auroras such as the Northern and Southern Lights, Keiling said.

Electrical connection

While these intense currents do not cause any direct harm to humans, on the ground they can damage man-made structures, such as power transformers.

NASA launched the THEMIS probes in February 2007 to solve a decades-long mystery about the origin of magnetic storms that power the Northern and Southern Lights.

The spacecraft observed these tornadoes, or “flow vortices,” at a distance of about 40,000 miles from Earth. Simultaneous measurements by THEMIS ground observatories confirmed the tornadoes’ connection to the ionosphere.

With the European Geosciences Union and the University of California, Berkeley.
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