SOHO reveals tornadoes on the Sun
Copyright: SOHO/CDS (ESA & NASA)
A gyrating high-speed storm wider than Africa projects like a chimney from the south pole of the Sun, in the lower picture. It is one of a dozen such tornadoes found by the SOHO solar spacecraft of ESA and NASA.
The scanning spectrometer CDS, built and operated by a British-led team, made the discovery. It has imaged this previously unknown type of feature of the Sun's weather in gas at 250 000 °C. Measurements reveal flows of around 150 kilometres per second, or 500 000 kilometres per hour. For comparison, tornadoes on the Earth blow at 400-500 kilometres per hour.
The colouring of the image shows, not the intensity of the emission, but the speed of the gas in the tornado. In the lighter right-hand side, the gas is moving towards SOHO, and away from SOHO in the darker left-hand side. The speed measurements come from shifts in the apparent wavelength of an emission from charged oxygen atoms (Doppler effect).
The upper picture, used to show the position of the tornado, was obtained on a different date by EIT, which is SOHO's extreme ultraviolet imaging telescope. EIT keeps a daily watch on the Sun's weather at four different ultraviolet wavelengths.
