Magnetic tornadoes as energy channels into the solar corona

This page contains further information and material for the article "Magnetic tornadoes as energy channels into the solar corona", which appeared in the prestigous journal Nature on June 28th, 2012. Summary Frequently asked questions and quotes Research team Pictures and animations Links Acknowledgments Press information Contact information Our results have been reported in the media world-wide. Click here for an overview with about 80 links to news articles, youtube videos, podcasts etc.. The page also includes a list of common misconceptions.

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SUMMARY

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We report the discovery of abundant 'magnetic tornadoes' above the surface of the Sun. Magnetic tornadoes resemble tornadoes on the Earth but have a magnetic skeleton and are hundreds to thousands times larger in diameter. One such observed tornado occupies the area equivalent of Europe or the USA.
We find that magnetic tornadoes have swirling speeds of many 10,000 km/hour. Magnetic tornadoes transport energy from the Sun's surface into its uppermost layer, the corona, where they contribute to the heating of the Sun's outer atmosphere. Consequently, magnetic tornadoes may well be the crucial missing piece of a long-standing puzzle in astrophysics: the heating of the outer solar and stellar atmospheres.

We estimate that there are as many as 11,000 of these swirling events above the Sun's surface at all times. The discovery has been made possible through state-of-the-art technology, namely the combination of extremely high resolution observations from the Swedish 1-m Solar Telescope located at La Palma [Canary Isl.] with data from the NASA's space-borne Solar Dynamics Observatory. With the help of state-of-the-art 3-D numerical simulations of the solar atmosphere, we unraveled the fascinating physics of this new and important phenomena.

This discovery has been published in the journal Nature on June 28th, 2012, and was featured on the cover page.

Importance of magnetic tornadoes: One would expect that the atmosphere of the Sun should become cooler with increasing distance from its surface. Remarkably, the opposite occurs and the temperature rises to over a million degrees. How the atmosphere is heated to these temperatures is a fundamental question of modern astrophysics, also referred to as coronal heating problem. Solving the heating problem is crucial for understanding our Sun, including the generation of the solar `wind' and its impact on the Earth's atmosphere (e.g. solar storms, Northern lights) and spacecraft in Earth's Orbit (e.g. satellite communication disruption). It is generally believed that large magnetic arcades that exist in the Sun's outer regions, which are anchored to the bubbling Sun surface, can transport outwards the energy required for heating. We have discovered an alternative but widespread way of transporting enough energy for atmospheric heating due to relentless twisting of the magnetic arcades at their footpoints. A manifestation of this twisting appears close to the Sun surface, which we observe in incredible detail (see Fig. 1), and describe as a `solar magnetic tornado'.

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FREQUENTLY ASKED QUESTIONS AND QUOTES

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• Are these tornadoes on the Sun the same as on Earth?
  S. Wedemeyer-Böhm: "In both cases, particles are forced into spirals. The resulting funnel is narrow at the bottom and widens with height in the atmosphere. On the other hand, the physical processes behind the formation of the tornadoes are very different. Tornadoes on the Earth occur in connection with rotating thunderstorms (or supercells) as a result of temperature and gas pressure differences and strong shear winds. The solar tornadoes are generated by rotating magnetic field structures, which force the plasma, i.e. the ionized gas, to move in spirals."
  


• Are these solar tornadoes threatening our Earth?
  S. Wedemeyer-Böhm: "No. You may think of these magnetic tornadoes as a local 'weather' phenomenon on the Sun far away. While they may play an important role for heating the outer layers of the Sun, magnetic tornadoes do not seem to have a direct influence on our Earth. A similar effect in large-scale solar tornadoes (as observed with SDO) may contribute to triggering solar storms but this hypothesis has yet to be investigated."
  


• Are the magnetic tornadoes the same as the solar tornadoes that were in the news earlier this year?
  S. Wedemeyer-Böhm: "The solar tornadoes that have been in the news earlier this year are much larger than those reported here. The large tornadoes extend over 100,000 km and more while the magnetic tornadoes reported here have dimensions of a few 1,000 km. The large tornadoes are (most likely) caused by rotating solar prominences and may occur in connection with coronal mass ejections. While they are rather extreme, the smaller magnetic tornadoes are by far more abundant, which results in a more basal contribution to the energy balance of our Sun. Both types of tornado have been observed with SDO."
  


• What makes magnetic tornadoes so interesting?
  S. Wedemeyer-Böhm: "We demonstrated that magnetic tornadoes channel energy upwards from the surface of the Sun into its corona. Magnetic tornadoes constitute thus an important step towards solving the long-standing coronal heating problem. It is also intriguing that only two ingredients are needed to generate this phenomenon: 1) magnetic fields and 2) vortex flows that occur in the downdrafts close to the solar surface as a consequence of the 'bathtub effect'. Both are ubiquitous on the surface of our Sun, which explains the vast abundance of at least 11,000 magnetic tornadoes at all times. Their large abundance is a very important finding, because ubiquity is a necessary condition for a viable mechanism of coronal heating."
  


• Why have solar magnetic tornadoes not been found before?
  S. Wedemeyer-Böhm: "These events are rather small details of the Sun. They are most visible as rotating structures in the chromosphere, the atmospheric layer between the photosphere (i.e., the "surface") and the corona above. The chromosphere is very difficult to observe. The discovery was made possible only now by combining a state-of-the-art ground-based solar telescope (Swedish 1-m Solar Telescope) with a new solar space telescope (NASA's Solar Dynamics Observatory), which allow us to see even small details on our Sun."
  [Chromospheric swirls have first been discovered by Wedemeyer-Böhm & Rouppe van der Voort in 2008; published in Astronomy & Astrophysics, 507, L9 - L12.]"
  


• These tornadoes are so far away. How is it possible to observe them?
  S. Wedemeyer-Böhm: "We used telescopes that can show us small details of the Sun in high resolution. NASA's space telescope SDO was important for spotting the imprint of the tornadoes in the corona. The true clue to the study, however, is the Swedish 1-m Solar Telescop. The high quality images, which it delivered, made it possible to find the tornadoes in the solar chromosphere."
  


• Are the magnetic tornadoes unique for the Sun? Or could exist on other stars, too?
  S. Wedemeyer-Böhm: "It is indeed very likely that magnetic tornadoes also exist on other stars. The basic ingredients, magnetic fields and vortex flows at the surface, are probably abundantly present for most stars (as long as they show convection at the surface). I presented first numerical simulations of magnetic tornadoes in cool stars at the 17th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun on June 28th, 2012, in Barcelona, Spain. "
  (see Figure 11)

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THE RESEARCH TEAM

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The international research team consists of seven scientists, led by Dr. Sven Wedemeyer-Böhm from the University of Oslo, Norway. The collaboration involved institutes from Norway, Germany, Sweden and U.K.

Name	Institute	Nationality	E-Mail
Sven Wedemeyer-Böhm1	University of Oslo, Norway	German	sven.wedemeyer@astro.uio.no
Eamon Scullion1	University of Oslo, Norway	Irish	e.m.scullion@astro.uio.no
Oskar Steiner3	Kiepenheuer Institute for Solar Physics, Germany	Swiss	steiner@kis.uni-freiburg.de
Luc Rouppe van der Voort1	University of Oslo, Norway	Dutch	v.d.v.l.rouppe@astro.uio.no
Jaime de la Cruz Rodriguez4	Uppsala University, Sweden	Spanish	jaime.cruz@physics.uu.se
Viktor Fedun5	University of Sheffield, U.K.	British / Ukrainian	v.fedun@sheffield.ac.uk
Robert Erdélyi5	University of Sheffield, U.K.	Hungarian	robertus@sheffield.ac.uk

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PICTURES AND ANIMATIONS

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Figure 1: Cover page of the edition of Nature, which will be published on June 28th, 2012. Credits: Nature Publishing Group. Click here for an image with better resolution (4.8 MB).		Figure 2: Intensity image recorded with the Swedish 1-m Solar Telescope in the line core of the spectral line of singly ionised calcium (infrared triplet, wavelength 854.2 nm). The detected chromospheric swirl (dark ring) is the observational signature of a magnetic tornado. Credits: Scullion, Wedemeyer-Böhm et al.. Click here for an image with better resolution (1.9 MB).
Figure 3: Illustration of an observed magnetic tornado vortex in the solar atmosphere. The background image was recorded with NASA's Solar Dynamics Observatory, while the stacked images were obtained with the Swedish 1-m Solar Telescope (Canary Isl.). The bluish images reveal the swirl signature of a magnetic tornado. We include a map of Europe to scale. Credits: Scullion & Wedemeyer-Böhm (2012); NASA Click here for an image with better resolution (4.6 MB).		Figure 4: Visualisation of a close-up region in our advanced 3D numerical simulations of a magnetic tornado in the solar atmosphere. The spiral lines represent the velocity field in the tornado vortex. The images contain the observed swirl signature (top, bluish) and the Sun's surface (bottom, reddish). Credits: Wedemeyer-Böhm et al. (2012). Image produced with VAPOR. Click here for an image with better resolution (17.4 MB).
Figure 5: Visualisation of a close-up region in our advanced 3D numerical simulations of a magnetic tornado in the solar atmosphere. The green lines represent the velocity field in the tornado vortex, the red lines represent the magnetic field. The simulated Sun surface is in grey-scale. Credits: Wedemeyer-Böhm (2012). Image produced with VAPOR. Click here for an image with better resolution (7.4 MB).		Figure 6: Schematic view of the atmospheric layers of the Sun, the extent of simulated magnetic tornado, and the resulting net energy transport. Credits: Wedemeyer-Böhm (2012). Parts of the image produced with VAPOR. Click here for an image with better resolution (209 kB).
Figure 7: Visualisation of a close-up region in our advanced 3D numerical simulations. The red mostly vertical lines represent the magnetic field, whereas the spiral lines represent the streamlines of the ionized gas in the magnetic tornado. The lower plane shows the granulation pattern of the solar surface and the magnetic footpoints (red), whereas the swirl signature (pink ring) can be seen on the top. Credits: Wedemeyer-Böhm (2012). Image produced with VAPOR. Click here for an image with better resolution (1.0 MB).		Figure 8: Visualisation of a close-up region in our advanced 3D numerical simulations. The red mostly vertical lines represent the magnetic field, whereas the spiral lines represent the streamlines of the ionized gas in the magnetic tornado. The lower plane shows the granulation pattern of the solar surface and the magnetic footpoints (red), whereas the swirl signature (pink ring) can be seen on the top. Credits: Wedemeyer-Böhm (2012). Image produced with VAPOR. Click here for an image with better resolution (0.8 MB).
Figure 9: Group photo (montage) with all members of the international research collaboration who made the discovery. From left to right: Dr. J. de la Cruz Rodriguez, Dr. L. Rouppe van der Voort, Dr. O. Steiner, Dr. S. Wedemeyer-Böhm, Dr. E. Scullion, Prof. Dr. R. Erdélyi, Dr. V. Fedun. (Credits for background image: SDO, NASA) Click here for an image with better resolution (10 MB).		Figure 10: The first four authors in front of the Institute of Theoretical Astrophysics, University of Oslo, Norway. From left to right: Dr. Oskar Steiner, Dr. Luc Rouppe van der Voort, Dr. Sven Wedemeyer-Böhm and Dr. Eamon Scullion. Click here for an image with better resolution (6.7 MB).
Figure 11: First example of a tornado in a numerical simulation of a cool star with a surface temperature of 3200 K (compared to the Sun with 5780 K). This unpublished result will be presented for the first time at the 17th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun on June 28th, 2012, in Barcelona, Spain. Credits: Wedemeyer-Böhm (2012). Image produced with VAPOR. Click here for an image with better resolution (1.7 MB).
Movie 1: Animation of a computer simulation of a magnetic tornado in the solar atmosphere. Temporal evolution and different perspectives of the magnetic field and the streamlines of the ionised gas. Credits: Wedemeyer-Böhm et al. (2012) The animation can be downloaded in the following sizes: 1200 x 885 pixel (256MB) 800 x 590 pixel (127MB) 600 x 442 pixel (76 MB)		Movie 2: First observation of a chromospheric swirl (i.e. a tornado signature) in 2008. The image sequence was recorded with the CRISP instrument at the Swedish 1-m Solar Telescope in a magnetically quiet region of the Sun (in the core of a spectral line of singly ionized calcium at a wavelength of 854.2 nm). Credit: This result has been published in 2009: Wedemeyer-Böhm & Luc Rouppe van der Voort, Astronomy and Astrophysics, Volume 507, Issue 1, 2009, pp.L9-L12. Click here to download the movie in full size (18 MB).

Please note: The publication is accompanied with online material, which can be found on the journal home page at http://www.nature.com.
It also includes additional animations.
Some of the animations have been used for movies that are available on youtube. Click here for an overview and links.

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LINKS

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• Nature - international weekly journal of science: http://www.nature.com
  
• University of Oslo, Norway: http://www.uio.no
  
• Institute of Theoretical Astrophysics at the University of Oslo, Norway: http://www.mn.uio.no/astro
  
• NASA's Solar Dynamics Observatory: http://sdo.gsfc.nasa.gov/
  
• The Swedish 1-m Solar Telescope: http://www.solarphysics.kva.se/NatureNov2002/telescope_eng.html
  
• Large solar tornadoes observed with SDO, reported in National Geographic (March 2012): http://news.nationalgeographic.com/news/2012/03/120329-sun-solar-tornadoes-biggest-nasa-sdo-space-science/
  

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ACKNOWLEDGMENTS

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We acknowledge discussions with R. Hammer, M. Carlsson, V. Hansteen and S. McIntosh. M. Carlsson and B. Gudiksen are thanked for providing BIFROST simulation data and input on its analysis. This work was supported by the Research Council of Norway through the project 'Solar Atmospheric Modelling' and through grants of computing time from the Programme for Supercomputing. S.W.B thanks I. Vesleoygard for kind support. R.E. acknowledges M. Keray for encouragement and is also grateful to the NSF, Hungary. R.E. and V.F. also acknowledge the support received from the Science and Technology Facilities, UK. The Swedish 1-m Solar Telescope is operated on the island of La Palma by the Institute for Solar Physics of the Royal Swedish Academy of Sciences in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias. We gratefully acknowledge usage of NASA's Solar Dynamics Observatory. We thank the Computational Information Systems Laboratory at the National Center for Atmospheric Research, USA, for providing the VAPOR analysis tool.

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PRESS INFORMATION

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The discovery outlined was published as a letter in the prestigious journal Nature. Competition for publication in this journal is intense as it covers a broad range of sciences, hence, only break-through results are generally considered. Movies of the observed and simulated tornadoes are provided below and also as online material on the webpages of Nature.

Press releases had been prepared in the following languages:

• English
• Norwegian
• German
• Spanish
• Swedish

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CONTACT

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For further information you may contact the corresponding author Dr. Sven Wedemeyer-Böhm or our public outreach official Dr. Anna Kathinka Dalland Evans.

Name:	Dr. Sven Wedemeyer-Böhm	Dr. Anna Kathinka Dalland Evans
Mail address:	Institute of Theoretical Astrophysics University of Oslo Postboks 1029 Blindern N-0315 Oslo Norway	Institute of Theoretical Astrophysics University of Oslo Postboks 1029 Blindern N-0315 Oslo Norway
Phone:	+47-22 85 65 20 (office; travelling until July 2nd)	+47-22 84 55 77
Fax:	+47-22 85 65 05	+47-22 85 65 05
E-mail:	svenwe@astro.uio.no	a.k.d.evans@astro.uio.no
www:	http://folk.uio.no/svenwe http://www.mn.uio.no/astro/personer/vit/svenwe About Sven Wedemeyer-Böhm	http://www.mn.uio.no/astro/personer/adm/aevans/

Mail addresses of all involved research institutions:

• 1: Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, N-0315 Oslo, Norway
  
  
• 2: Center of Mathematics for Applications, University of Oslo, PO Box 1053 Blindern, N-0316 Oslo, Norway
  
  
• 3: Kiepenheuer Institute for Solar Physics, Schöneckstrasse 6-7, D-79104 Freiburg, Germany
  
  
• 4: Department of Physics and Astronomy, Uppsala University, Box 516, SE-75120 Uppsala, Sweden
  
  
• 5: Solar Physics & Space Plasma Research Centre, School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK
  
  

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S. Wedemeyer (2012)