SOLAR TORNADOES


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, and now updated information on follow-up work and current research.
As a result, the Research Council of Norway is funding the continued research on solar tornadoes until 2017: Project home page at the Institute of Theoretical Astrophysics, University of Oslo.

Our Nature article has received world-wide media attention.
Click here for an overview with some 80 links to news articles, youtube videos, podcasts etc..


SUMMARY OF THE NATURE ARTICLE



Magnetic tornadoes as energy channels into the solar corona

S. Wedemeyer-Böhm, E. Scullion, O. Steiner, L. Rouppe van der Voort, J. de la Cruz Rodriguez, V. Fedun, R. Erdélyi
Nature, 486, 505 - 508, June 28th, 2012

In our 2012 Nature article, 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'.

Please note: The magnetic tornadoes found so far are smaller than the large-scale tornadoes observed with SDO earlier in 2012. We refer to the latter as giant tornadoes to distinguish between them and the (small-scale) magnetic tornadoes. Giant tornadoes seem to be connected to solar prominences while such a connection has not been made for magnetic tornadoes. Both phenomena are currently further investigated.


FURTHER PUBLICATIONS THAT APPEARED SINCE THEN

Are Giant Tornadoes the Legs of Solar Prominences?
Wedemeyer, Sven; Scullion, Eamon; Rouppe van der Voort, Luc; Bosnjak, Antonija; Antolin, Patrick
The Astrophysical Journal, Volume 774, Issue 2, article id. 123, 15 pp. (2013)
(Entry in SAO/NASA Astrophysics Data System)
Abstract: "Observations in the 171 A channel of the Atmospheric Imaging Assembly of the space-borne Solar Dynamics Observatory show tornado-like features in the atmosphere of the Sun. These giant tornadoes appear as dark, elongated, and apparently rotating structures in front of a brighter background. This phenomenon is thought to be produced by rotating magnetic field structures that extend throughout the atmosphere. We characterize giant tornadoes through a statistical analysis of properties such as spatial distribution, lifetimes, and sizes. A total number of 201 giant tornadoes are detected in a period of 25 days, suggesting that, on average, about 30 events are present across the whole Sun at a time close to solar maximum. Most tornadoes appear in groups and seem to form the legs of prominences, thus serving as plasma sources/sinks. Additional Halpha observations with the Swedish 1 m Solar Telescope imply that giant tornadoes rotate as a structure, although they clearly exhibit a thread-like structure. We observe tornado groups that grow prior to the eruption of the connected prominence. The rotation of the tornadoes may progressively twist the magnetic structure of the prominence until it becomes unstable and erupts. Finally, we investigate the potential relation of giant tornadoes to other phenomena, which may also be produced by rotating magnetic field structures. A comparison to cyclones, magnetic tornadoes, and spicules implies that such events are more abundant and short-lived the smaller they are. This comparison might help to construct a power law for the effective atmospheric heating contribution as a function of spatial scale."

Magnetic tornadoes and chromospheric swirls - Definition and classification
Wedemeyer, Sven; Scullion, Eamon; Steiner, Oskar; de la Cruz Rodriguez, Jaime; Rouppe van der Voort, L. H. M.
Journal of Physics: Conference Series, Volume 440, Issue 1, article id. 012005 (2013)
Abstract: "Chromospheric swirls are the observational signatures of rotating magnetic field structures in the solar atmosphere, also known as magnetic tornadoes. Swirls appear as dark rotating features in the core of the spectral line of singly ionized calcium at a wavelength of 854.2 nm. This signature can be very subtle and difficult to detect given the dynamic changes in the solar chromosphere. Important steps towards a systematic and objective detection method are the compilation and characterization of a statistically significant sample of observed and simulated chromospheric swirls. Here, we provide a more exact definition of the chromospheric swirl phenomenon and also present a first morphological classification of swirls with three types: (I) Ring, (II) Split, (III) Spiral. We also discuss the nature of the magnetic field structures connected to tornadoes and the influence of limited spatial resolution on the appearance of their photospheric footpoints."
(Entry in SAO/NASA Astrophysics Data System)

Three-dimensional magnetohydrodynamic simulations of M-dwarf chromospheres
Wedemeyer, S.; Ludwig, H.-G.; Steiner, O.
Astronomische Nachrichten, Vol.334, Issue 1-2, p.137-140 (2013)
(Entry in SAO/NASA Astrophysics Data System)
Abstract: "We present first results from three-dimensional radiation magnetohydrodynamic simulations of M-type dwarf stars with CO5BOLD. The local models include the top of the convection zone, the photosphere, and the chromosphere. The results are illustrated for models with an effective temperature of 3240 K and a gravitational acceleration of log g = 4.5, which represent analogues of AD Leo. The models have different initial magnetic field strengths and field topologies. This first generation of models demonstrates that the atmospheres of M dwarfs are highly dynamic and intermittent. Magnetic fields and propagating shock waves produce a complicated fine-structure, which is clearly visible in synthetic intensity maps in the core of the Ca II K spectral line and also at millimeter wavelengths. The dynamic small-scale pattern cannot be described by means of one-dimensional models, which has important implications for the construction of semi-empirical model atmospheres and thus for the interpretation of observations in general. Detailed three-dimensional numerical simulations are valuable in this respect. Furthermore, such models facilitate the analysis of small-scale processes, which cannot be observed on stars but nevertheless might be essential for understanding M-dwarf atmospheres and their activity. An example are so-called ``magnetic tornadoes'', which have recently been found on the Sun and are presented here in M-dwarf models for the first time."


FREQUENTLY ASKED QUESTIONS AND QUOTES

  • 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 in 2012 are much larger than those reported in our Nature article. 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 (small-scale) 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.]
    [Giant solar tornadoes (mostly the legs of prominences) have been observed already since the 1990s with other instruments like TRACE and SOHO, while the term "tornado" has been used already since the 1930s for a particular type of prominences.]


  • 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)


THE RESEARCH TEAM

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-Böhm1University of Oslo, NorwayGerman sven.wedemeyer@astro.uio.no
Eamon Scullion1University of Oslo, NorwayIrish e.m.scullion@astro.uio.no
Oskar Steiner3Kiepenheuer Institute for Solar Physics, GermanySwiss steiner@kis.uni-freiburg.de
Luc Rouppe van der Voort1University of Oslo, NorwayDutch v.d.v.l.rouppe@astro.uio.no
Jaime de la Cruz Rodriguez4Uppsala University, SwedenSpanish jaime.cruz@physics.uu.se
Viktor Fedun5University of Sheffield, U.K.British / Ukrainian v.fedun@sheffield.ac.uk
Robert Erdélyi5University of Sheffield, U.K.Hungarian robertus@sheffield.ac.uk


PICTURES AND ANIMATIONS



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:


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.

LINKS



ACKNOWLEDGMENTS

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. 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.


PRESS INFORMATION

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

CONTACT

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 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

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


S. Wedemeyer. Last modified: Mon Oct 3 11:12:23 CEST 2016