Apr. 30, 1998 The Sun has tall gyrating storms far larger and faster than tornadoes on the Earth. This unexpected finding is among the latest results from the solar spacecraft SOHO, announced at a European Space Agency press briefing on 28 April. British scientists discovered the solar tornadoes in images and data from SOHO's scanning spectrometer CDS. So far they have detected a dozen such events. They occur most frequently near the north and south poles of the Sun and are almost as wide as the Earth.
Steady windspeeds of 15 kilometres per second and gusts ten times faster (which means 500,000 kilometres per hour) occur in the solar tornadoes. For comparison, tornadoes on the Earth blow at 400-500 kilometres per hour. The solar measurements are made by the Doppler effect -- the same principle as that used by police radars to detect speeding motorists. The observed wavelength of emission from hot oxygen atoms changes according to whether the gas is moving towards the detector or away from it, and the CDS instrument is very sensitive to these variations.
One of SOHO's main tasks is to trace the sources of the wind from the Sun that pervades the Solar System. Gusts and shocks in the solar wind buffet the Earth's environment, causing auroras and magnetic storms and endangering satellites and power supplies. The newly discovered tornadoes may contribute to the solar wind, especially to a fast windstream that emanates from relatively cool parts of the solar atmosphere called coronal holes.
"We see the hot gas in the tornadoes spiralling away from the Sun and gathering speed," says David Pike of the Rutherford Appleton Laboratory, UK, who is co-discoverer of the solar tornadoes with Helen Mason of Cambridge University. "These spectacular events in the Sun's atmosphere must have widespread effects. Our next step will be to try to relate the solar tornadoes to observations of the fast solar wind farther out in space, as seen by other instruments in SOHO."
Built in Europe for the European Space Agency, SOHO carries twelve sets of instruments provided by European and American investigators, and it was dispatched into space on 2 December 1995 by a NASA launcher. SOHO is a project of international cooperation between ESA and NASA.
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