Despite their appearance, sun tornadoes are not tornadoes at all. This is the conclusion of the work conducted by a team of European researchers and reported on Friday, April 6, 2018 at the European Week of Astronomy and Space Science Conference (EWASS) in Liverpool.
A recent analysis of “sun tornadoes”, i.e. the structures observed on the surface of the Sun, gigantic in size that can reach several times that of the Earth, shows that this phenomenon has been poorly described since it has been observed only in two-dimensional images.
The phenomenon was observed for the first time in the early twentieth century on the surface of the Sun. More recently, it has been closely observed using instruments such as AIA fitted to NASA’s Solar Dynamics Observatory (SDO) probe, but was still being called a “tornado” by scientists, wrongly.
To gain a more detailed understanding of this phenomenon, the scientists then sought to obtain a third dimension, by combining observational data collected over several years on different types of ground-based instruments. By determining the Doppler effect, they were able to calculate the plasma velocity (40 kilometers per second) as well as the direction of its movement, temperature and density. They have thus managed to “reconstruct” the complete magnetic structure that supports these giant masses. They deduced that they were structures well known elsewhere and studied under the name of “protuberances”.
Solar giant tornadoes, now renamed “tornado protuberances”, were first observed on the Sun about a century ago. They had thus been named because of their apparent movement of rotation, similar to that of the terrestrial tornadoes, but this perception was erroneous. In fact, the comparison with terrestrial tornadoes proves to be abusive. While these are caused by intense winds, the solar protuberances are formed from magnetized gases rooted under the surface of the Sun without displacement.
“For once, the reality is much simpler than what we thought”, comments Brigitte Schmieder, astronomer of the Observatory of Paris.
“We see that despite the vertical appearance of tornadoes and protuberances at the edge of the Sun, the magnetic field that supports them is not vertical, as it seemed, but horizontal, parallel to the edge of the Sun. Their apparent verticality is an effect due to the projection of all the structures on the plane of the sky,” explains Nicolas Labrosse, researcher at the University of Glasgow (School of Physics and Astronomy).
“This effect is similar to the trajectories of an airplane left in the sky. If the plane still flies at the same altitude, its trail seems to stop on the horizon. That does not mean that the plane crashed on the ground,” says Arturo López Ariste, a CNRS researcher at the Institute for Research in Astrophysics and Planetology.
“These protuberances-tornadoes can be stable for several days and months, before exploding and causing coronal mass ejections whose consequences in the terrestrial environment are known as space weather,” said Brigitte Schmieder. “They can cause disruption in power plants, satellites and communications networks on Earth.”