Giant solar tornadoes – formally called tornado prominences – are so called because of their striking shape and apparent resemblance to tornadoes on Earth, but that is where the comparison ends. A post written by Dr. Brigitte Schmieder, Dr. Nicolas Labrosse and Dr. Maciej Zapior, from (respectively) Observatoire de Paris (France), University of Glasgow (UK), and the Astronomical Institute of the Academy of Sciences of the Czech Republic.
Prominence observed with the IRIS satellite. The sequence of images show small dark fragments called “knots”, which are highlighted by coloured crosses and follow helical structures over the course of an hour. The reconstructed 3D knot trajectories appear in the last part of the movie with the same colours.
Solar tornadoes were first observed in the early 20th century, and the term was re-popularised a few years ago when scientists looked at movies obtained by the AIA instrument on the NASA Solar Dynamics Observatory (SDO). These show hot plasma in extreme ultraviolet light apparently rotating to form a giant structure taking the shape of a tornado (as we know them on Earth).
Giant solar tornadoes – formally called tornado prominences – are so called because of their striking shape and apparent resemblance to tornadoes on Earth, but that is where the comparison ends. Whereas terrestrial tornadoes are formed from intense winds and are very mobile, solar tornadoes are instead made of magnetized gas. They seem to be rooted somewhere further down the solar surface, and so stay fixed in place.
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 (2D) images.
Now, using the Doppler effect to add a third dimension to their data, 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. Despite how tornados appear in images, the magnetic field lines are not vertical but rather horizontal and the plasma flows along them. The tornado-like shapes on the 2D images are due to projection effects. The real nature of tornadoes and their origin could be determined by the 4-metre European Solar Telescope. The telescope will have multiple wavelength and polarimetric capabilities to infer the magnetic field and to provide new insights of this fascinating phenomenon.
For more information about this work, see Schmieder et al., 2017, A&A, 606, A30