Solar Tornadoes

Vast tornadoes ravage the sun at speeds up to 200,000 kilometers per hour, astronomers reported today at a meeting at Rutherford Appleton Laboratory (RAL) near Oxford, U.K., celebrating the extension of the Solar and Heliospheric Observatory (SOHO) satellite for a further 5 years. These solar tornadoes--blisteringly hot and about a thousand times larger than their earthly counterparts--may be funneling heat into the sun's atmosphere and whipping up the solar wind.

The sun's atmosphere is a turbulent gas of charged particles, hundreds of times hotter than the sun's surface. At the poles, the particles stream away to become the solar wind, which bathes the whole solar system and can wreak havoc on satellites and power grids on Earth. The question of what drives the solar wind led David Pike of RAL and collaborator Helen Mason, from the University of Cambridge, U.K., to search for clues in ultraviolet light from the sun's surface, detected with SOHO.

The duo witnessed spurts of material rising from the sun's poles into the ultrahot corona, its outer atmosphere. These so-called microspicules have been seen before, but by measuring the Doppler shift--the train-whistle effect that shifts the wavelength of light from a moving source--the team discovered that the material appears to be rotating. "The most immediate and easiest interpretation is [that] it is swirling around much like a tornado," says Pike.

The tornadoes occur at the poles, where lines of magnetic force point out into space. As the magnetic fields in the lower atmosphere channel the charged gas, the churning of the gas in turn distorts the field lines. The magnetic 'pipelines' may crack and spew their contents in a spinning torrent, suggests Pike. Usually, this material is contained by the sun's magnetic field, but in the polar regions the open magnetic field lines railroad it away from the sun.

"It's really quite a discovery", says Eric Priest, from the University of St. Andrews, U.K. One surprise is the high temperature of the material in the tornadoes, around 250,000 degrees Celsius--well in excess of the 6000 degrees Celsius of the sun's surface. With the outer regions of the sun's atmosphere reaching millions of degrees, tornadoes might offer "an important clue" to the heating mechanism, says Priest. What's more, he says, tornadoes "may be blowing the material out at very high speeds from the surface of the sun."

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