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Energy release in the solar corona from spatially resolved magnetic braids


It is now apparent that there are at least two heating mechanisms in the Sun’s outer atmosphere, or corona1,2,3,4,5. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000 K (refs 1, 2, 3). The active corona needs additional heating to reach 2,000,000–4,000,000 K; this heat has been theoretically proposed6,7,8,9,10,11,12 to come from the reconnection and unravelling of magnetic ‘braids’. Evidence favouring that process has been inferred13,14, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought1,2,3,15,16,17 to have an angular width of about 0.2 arc seconds have not been resolved10,18,19,20. Fine-scale braiding has been seen21,22 in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2 arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000 K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.

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Figure 1: The 1.5-MK sun.
Figure 2: A coronal loop seen at several different coronal temperatures by AIA and Hi-C.
Figure 3: A time series from Hi-C data.
Figure 4: The light curves for example two.


  1. 1

    Wedemeyer-Böhm, S. et al. Magnetic tornadoes as energy channels into the solar corona. Nature 486, 505–508 (2012)

    ADS  Article  Google Scholar 

  2. 2

    McIntosh, S. et al. Alfvenic waves with sufficient energy to power the quiet solar corona and fast solar wind. Nature 475, 477–480 (2011)

    ADS  CAS  Article  Google Scholar 

  3. 3

    De Pontieu, B. et al. Chromospheric Alfevic waves strong enough to power the solar wind. Science 318, 1574–1577 (2007)

    ADS  CAS  Article  Google Scholar 

  4. 4

    Cirtain, J. et al. Evidence for Alfven waves in solar X-ray jets. Science 318, 1580–1582 (2007)

    ADS  CAS  Article  Google Scholar 

  5. 5

    Priest, E. et al. Nature of the heating mechanism for the diffuse solar corona. Nature 393, 545–547 (1998)

    ADS  CAS  Article  Google Scholar 

  6. 6

    Parker, E. Magnetic neutral sheets in evolving fields. I. General Theory. Astrophys. J. 264, 635–641 (1983)

    ADS  Article  Google Scholar 

  7. 7

    Parker, E. Magnetic neutral sheets in evolving fields. II. Formation of the solar corona. Astrophys. J. 264, 642–647 (1983)

    ADS  Article  Google Scholar 

  8. 8

    Schrijver, K. Braiding-induced interchange reconnection of the magnetic field and the width of solar coronal loops. Astrophys. J. 662, L119–L122 (2007)

    ADS  Article  Google Scholar 

  9. 9

    Gudiksen, B. V. & Nordlund, Å. An ab initio approach to the solar coronal heating problem. Astrophys. J. 618, 1020–1030 (2005)

    ADS  CAS  Article  Google Scholar 

  10. 10

    Klimchuk, J. On solving the coronal heating problem. Sol. Phys. 234, 41–77 (2006)

    ADS  Article  Google Scholar 

  11. 11

    Gold, T. in Stellar and Solar Magnetic Fields (ed. Lüst, R. ) 390–398 (Proc. IAU Symp. 22, International Astronomical Union, 1965)

    Google Scholar 

  12. 12

    Warren, H. P., Winebarger, A. R. & Hamilton, P. S. Hydrodynamic modeling of active region loops. Astrophys. J. 579, L41–L44 (2002)

    ADS  Article  Google Scholar 

  13. 13

    Schrijver, K. et al. Large-scale coronal heating by the small-scale magnetic field of the Sun. Nature 394, 152–154 (1998)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Lee, J. et al. Coronal currents, magnetic fields, and heating in a solar active region. Astrophys. J. 501, 853–865 (1998)

    ADS  Article  Google Scholar 

  15. 15

    De Pontieu, B. et al. Observing solar coronal heating-in the chromosphere. Astrophys. J. 701, L1–L6 (2009)

    ADS  CAS  Article  Google Scholar 

  16. 16

    De Pontieu, B. et al. The origins of hot plasma in the solar corona. Science 331, 55–58 (2011)

    ADS  CAS  Article  Google Scholar 

  17. 17

    DeForest, C. E. On the size of structures in the corona. Astrophys. J. 661, 532–542 (2007)

    ADS  Article  Google Scholar 

  18. 18

    Berger, M. &. Asgari-Targhi, M. Self-organized braiding and the structure of coronal loops. Astrophys. J. 705, 347–355 (2009)

    ADS  Article  Google Scholar 

  19. 19

    van Ballegooijen, A. Heating of the solar chromosphere and corona by Alfven wave turbulence. Astrophys. J. 736, 3–9 (2011)

    ADS  Article  Google Scholar 

  20. 20

    Malanushenko, A., Yusuf, M. H. & Longcope, D. Direct measurements of magnetic twist in the solar corona. Astrophys. J. 736, 97–109 (2011)

    ADS  Article  Google Scholar 

  21. 21

    Rutten, R. Hα as chromospheric diagnostic. ASP Conf. Ser. 397, 54–58 (2008)

    ADS  CAS  Google Scholar 

  22. 22

    Martin, S. Conditions for the formation and maintenance of filaments. Sol. Phys. 182, 107–137 (1998)

    ADS  Article  Google Scholar 

  23. 23

    Lemen, J. R. et al. The Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Sol. Phys. 275, 17–40 (2012)

    ADS  Article  Google Scholar 

  24. 24

    Culhane, L. et al. The EUV imaging spectrometer for Hinode. Sol. Phys. 243, 19–61 (2007)

    ADS  Article  Google Scholar 

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We thank the NASA Low-Cost Access to Space programme for supporting the development of the Hi-C instrument, the NASA Sounding Rocket Office for the launch of the instrument and the NASA Marshall Space Flight Center for instrument development support. This LPI work was supported in part by the Russian Foundation for Basic Research (project 11–02–01079-a), Program No. 22 of the Presidium of the Russian Academy of Sciences.

Author information




J.W.C., A.R.W., B.D.P., P.M. and C.E.D. performed image processing and analysis of observations. M.W., K.K., B.D.P., C.E.D. and A.R.W. all contributed to the calibration and alignment of the instrument and science data. J.W.C., L.G., K.K. and K.E.K. managed the design, construction and testing of the experiment. J.W.C. and A.R.W. determined velocities and J.W.C and R.L.M. calculated the stored energy. A.T., R.W.W. and S.K. contributed to the instrumentation.

Corresponding author

Correspondence to J. W. Cirtain.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Info


Experiment regions of interest

This video shows the full sun AIA images taken during the Hi-C flight. It zooms into the Hi-C field of full field of view and extracts the two examples from the paper, and shows comparison movies for AIA and Hi-C. The first comparison is for example 1 shown in Fig 2 and Supplementary Fig. 2 and Supplementary Video 2. The second comparison is for example 2 and goes with Fig. 3 and Supplementary Videos 3 & 4. (MOV 4672 kb)

Evolution of loops during component reconnection

This video presents the evolution of a set of loops that are interacting and wrapped together. As the structures evolve, reconnection allows the loops to relax into a less curved and thus more potential geometry. (MOV 4160 kb)

Evolution in a Braided Loop Ensemble

This braided loop has several loops near the 'base' that appear to be unwinding with significant apparent outflow. This is evidence of untwisting, and the braided structure also seeming to unwind with time. (MOV 5888 kb)

The Temperature history of the Braided Structure

Within the braided bundle, several episodic intensity increases are observed in many of the AIA passbands. This is direct evidence of impulsive energy release likely the result of reconnection. The process is observed many times in the AIA data over a long period of observations leading to the conclusion that the region is constantly being sheared, thus storing energy, and frequently releases some of this energy in these localized heating events. (MOV 1664 kb)

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Cirtain, J., Golub, L., Winebarger, A. et al. Energy release in the solar corona from spatially resolved magnetic braids. Nature 493, 501–503 (2013).

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