Magnetic tornadoes as energy channels into the solar corona

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Abstract

Heating the outer layers of the magnetically quiet solar atmosphere to more than one million kelvin and accelerating the solar wind requires an energy flux of approximately 100 to 300 watts per square metre1,2,3,4,5,6, but how this energy is transferred and dissipated there is a puzzle and several alternative solutions have been proposed. Braiding and twisting of magnetic field structures, which is caused by the convective flows at the solar surface, was suggested as an efficient mechanism for atmospheric heating7. Convectively driven vortex flows that harbour magnetic fields are observed8,9,10 to be abundant in the photosphere (the visible surface of the Sun). Recently, corresponding swirling motions have been discovered11 in the chromosphere, the atmospheric layer sandwiched between the photosphere and the corona. Here we report the imprints of these chromospheric swirls in the transition region and low corona, and identify them as observational signatures of rapidly rotating magnetic structures. These ubiquitous structures, which resemble super-tornadoes under solar conditions, reach from the convection zone into the upper solar atmosphere and provide an alternative mechanism for channelling energy from the lower into the upper solar atmosphere.

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Figure 1: Observation of a swirl event and its coronal counterpart.
Figure 2: Detected swirl events in the solar observations on 8 May 2011.
Figure 3: Numerical model of a swirl event produced with CO 5 BOLD.

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Acknowledgements

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 including computing time through the Programme for Supercomputing (Notur). R.E. acknowledges M. Kéray 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 Astrofísica de Canarias. We thank the Computational Information Systems Laboratory at the National Center for Atmospheric Research for providing the VAPOR analysis tool.

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Authors

Contributions

S.W.-B. and E.S. produced and analysed the data with help from all authors. O.S., V.F. and R.E. gave advice on the data analysis, aspects of the physical interpretation and the applied numerical methods. J.d.l.C.R. and L.R.v.d.V. contributed to the collection and preparation of the observational data and its comparison with numerical data. All authors discussed the results and contributed to and commented on the manuscript.

Corresponding author

Correspondence to Sven Wedemeyer-Böhm.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Table 1, which outlines the properties of all 14 swirls; Supplementary Figures 1-3, which illustrate the expansion of the magnetic field in a tornado into the solar corona, the comparison of an observed and a simulated swirl, and the related transport of energy; and Supplementary Notes which describe the derivations of the average Poynting flux. (PDF 8301 kb)

41586_2012_BFnature11202_MOESM297_ESM.mov

This movie file shows a brief overview of the SST/CRISP (CRisp Imaging SpectroPolarimeter) data accumulated in this observational study of chromospheric swirls. The detection and properties (Doppler-shift structure and evolution to hotter channels as observed with the SDO) attributed to swirl #1 follows the overview. (MOV 4362 kb)

Supplementary Movie 1

This movie file shows a brief overview of the SST/CRISP (CRisp Imaging SpectroPolarimeter) data accumulated in this observational study of chromospheric swirls. The detection and properties (Doppler-shift structure and evolution to hotter channels as observed with the SDO) attributed to swirl #1 follows the overview. (MOV 4362 kb)

41586_2012_BFnature11202_MOESM298_ESM.mov

This movie file shows the temporal evolution of all of the 14 swirls detected. Each swirl was recorded during a 55 min observing run on 8th May 2011. (MOV 18241 kb)

Supplementary Movie 2

This movie file shows the temporal evolution of all of the 14 swirls detected. Each swirl was recorded during a 55 min observing run on 8th May 2011. (MOV 18241 kb)

41586_2012_BFnature11202_MOESM299_ESM.mov

This movie file outlines the results of a numerical simulation (CO5BOLD) of a solar magnetic tornado. The physical process describing the formation of the magnetic tornado is presented. The evolution of the flow field within the magnetic tornado through to the upper chromosphere is shown, thus, explaining its swirling nature. (MOV 21037 kb)

Supplementary Movie 3

This movie file outlines the results of a numerical simulation (CO5BOLD) of a solar magnetic tornado. The physical process describing the formation of the magnetic tornado is presented. The evolution of the flow field within the magnetic tornado through to the upper chromosphere is shown, thus, explaining its swirling nature. (MOV 21037 kb)

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Wedemeyer-Böhm, S., Scullion, E., Steiner, O. et al. Magnetic tornadoes as energy channels into the solar corona. Nature 486, 505–508 (2012). https://doi.org/10.1038/nature11202

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