Despite their appearance solar tornadoes are not rotating after all, according to a European team of scientists.
A new analysis of these gigantic structures, each one several times the size of the Earth, indicates that they may have been misnamed because scientists have so far only been able to observe them using 2-dimensional images. Dr Nicolas Labrosse will present the work, carried out by researchers at the University of Glasgow, Paris Observatory, University of Toulouse, and Czech Academy of Sciences, at the European Week of Astronomy and Space Science (EWASS) in Liverpool on Friday 6 April.
A solar tornado observed by the NASA satellite SDO between April 23-29, 2015. The tornado prominence erupted on 28 April. An image of the Earth is superimposed for scale.
Credit: SDO data courtesy of NASA. Movie created using the ESA and NASA funded Helioviewer Project.
Composite image of an erupting solar prominence observed by SDO on 31 August 2012.
Now, using the Doppler effect to add a third dimension to their data, the scientists have been able to measure the speed of the moving plasma, as well as its direction, temperature and density. Using several years' worth of observations, they were able to build up a more complete picture of the magnetic field structure that supports the plasma, in structures known as prominences.
Giant solar tornadoes – formally called tornado prominences – have been observed on the Sun for around a hundred years. They are so called because of their striking shape and apparent resemblance to tornadoes on Earth, but that is where the comparison ends.
Composite image of the prominence observed on 15 July 2014 showing, after co-alignment: the EIS raster in green, the IRIS slit-jaw image in red, and an SOT image in blue. The white contours show the THEMIS D3 intensity image and indicate where the tornadoes are observed in extreme ultraviolet. The background image is an AIA 304 angstrom image (greyscale).
Whereas terrestrial tornadoes are formed from intense winds and are very mobile, solar tornadoes are instead magnetized gas. They seem to be rooted somewhere further down the solar surface, and so stay fixed in place.
"They are associated with the legs of solar prominences – these are beautiful concentrations of cool plasma in the very hot solar corona that can easily be seen as pink structures during total solar eclipses," adds Labrosse.
"Perhaps for once the reality is less complicated than what we see!" comments Dr Brigitte Schmieder, another scientist involved in the work.
A solar tornado observed by the NASA satellite SDO between 23 April and 29 April 2015. The tornado prominence erupted on 28 April. An image of the Earth is superimposed for scale. Credit: SDO data courtesy of NASA. Movie created using the ESA and NASA funded Helioviewer Project.