European Week of Astronomy and Space Science press release
RAS PR 18/20 (EWASS 16)
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.
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).
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.
Dr Nicolas Labrosse, lead scientist in the study, explains: “We found that despite how prominences and tornadoes appear in images, the magnetic field is not vertical, and the plasma mostly moves horizontally along magnetic field lines. However we see tornado-like shapes in the images because of projection effects, where the line of sight information is compressed onto the plane of the sky.”
Dr Arturo López Ariste, another member of the team, adds: “The overall effect is similar to the trail of an aeroplane in our skies: the aeroplane travels horizontally at a fixed height, but we see that the trail starts above our heads and ends up on the horizon. This doesn’t mean that it has crashed!”
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.
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.
She continues: “Solar tornadoes sound scary but in fact they normally have no noticeable consequences for us. However, when a tornado prominence erupts, it can cause what’s known as space weather, potentially damaging power, satellite and communication networks on Earth.”
Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699
Ms Anita Heward
Royal Astronomical Society
Mob: +44 (0)7756 034 243
Dr Morgan Hollis
Royal Astronomical Society
Mob: +44 (0)7802 877 700
Dr Helen Klus
Royal Astronomical Society
Ms Marieke Baan
European Astronomical Society
Dr Nicolas Labrosse
School of Physics and Astronomy
University of Glasgow
Mob: +44 (0)7983 380 380
Dr Brigitte Schmieder
Observatoire de Paris
Tel : +33 (0)1 4507 7817
Dr Arturo López Ariste
Institut de Recherche en Astrophysique et Planétologie
Université de Toulouse
Tel : +33 (0)5 6133 4716
Animation and caption
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.
Images and captions
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).
Credit: P. Levens
Composite image of an erupting solar prominence observed by SDO on 31 August 2012.
Credit: NASA / SDO / GSFC
The presentation slides are available here.
Dr Nicolas Labrosse will be giving an outreach talk on this topic at the Merseyside Astronomy Day (MAD) on Saturday 7 April. Full details can be found at: http://www.astro.ljmu.ac.uk/mad/labrosse.html
The full team consists of:
Dr Nicolas Labrosse, SUPA, School of Physics and Astronomy, University of Glasgow, UK
Dr Peter Levens, SUPA, School of Physics and Astronomy, University of Glasgow, UK
Dr Arturo López Ariste, Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS, CNES, France
Dr Brigitte Schmieder, LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris-Diderot, Sorbonne Paris Cité, Meudon, France
Dr Maciej Zapiór, Astronomical Institute, Academy of Sciences of the Czech Republic, Ondřejov, Czech Republic
Details of the techniques used to obtain these results can be found in the following publications:
B. Schmieder, M. Zapior, A. Lopez Ariste, P. Levens, N. Labrosse, R. Gravet, “Reconstruction of a helical prominence in 3D from IRIS spectra and images”; A&A, 606, A30 (2017)
B. Schmieder, P. Mein, N. Mein, P. Levens, A. Lopez Ariste, N. Labrosse, L. Ofman, “H alpha Doppler shifts in a tornado in the solar corona”; A&A, 597, 109 (2017)
P. Levens, B. Schmieder, N. Labrosse, A. Lopez Ariste, “Structure of prominence legs: plasma and magnetic fields”; ApJ, 818, 31 (2016)
P. Levens, B. Schmieder, A. Lopez Ariste, N. Labrosse, K. Dalmasse, B. Gelly, “Magnetic field in atypical prominences: Bubble, tornado and eruption”; ApJ, 826, 164 (2016)
P. Levens, N. Labrosse, B. Schmieder, A. Lopez Ariste, L. Fletcher, “Comparison between UV/EUV line parameters and magnetic field parameters in a quiescent prominence with tornadoes”; A&A, 607, A16 (2017)
Notes for editors
The European Week of Astronomy and Space Science (EWASS 2018) will take place at the Arena and Conference Centre (ACC) in Liverpool from 3 – 6 April 2018. Bringing together around 1500 astronomers and space scientists, the conference is the largest professional astronomy and space science event in the UK for a decade and will see leading researchers from around the world presenting their latest work.
EWASS 2018 is a joint meeting of the European Astronomical Society and the Royal Astronomical Society. It incorporates the RAS National Astronomy Meeting (NAM), and includes the annual meeting of the UK Solar Physics (UKSP) group. The conference is principally sponsored by the Royal Astronomical Society (RAS), the Science and Technology Facilities Council (STFC) and Liverpool John Moores University (LJMU).
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