CDS DISCOVERS SUPER-HOT, SUPER-FAST SOLAR TORNADOES
Surprises from SOHO include tornadoes on the Sun (click on image to view animation)
The Sun has tall gyrating storms far larger and faster than tornadoes on
the Earth. This unexpected finding is among the results from the
solar spacecraft SOHO, announced at a European Space Agency press
briefing on 28 April 1998. 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.
Surprises from SOHO include tornadoes on the Sun 
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