Nature of the heating mechanism for the diffuse solar corona


The temperature of the Sun's outer atmosphere (the corona) exceeds that of the solar surface by about two orders of magnitude, but the nature of the coronal heating mechanisms has long been a mystery1. The corona is a magnetically dominated environment, consisting of a variety of plasma structures including X-ray bright points, coronal holes and coronal loops. The latter are closed magnetic structures that occur over a range of scales and are anchored at each end in the solar surface. Large-scale regions of diffuse emission are made up of many long coronal loops2. Here we present X-ray observations of the diffuse corona from which we deduce its likely heating mechanism. We find that the observed variation in temperature along a loop is highly sensitive to the spatial distribution of the heating. From a comparison of the observations and models we conclude that uniform heating gives the best fit to the loop temperature distribution, enabling us to eliminate previously suggested mechanisms of low-lying heating near the footpoints of a loop. Our findings favour turbulent breaking and reconnection of magnetic field lines as the heating mechanism of the diffuse solar corona.

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Figure 1: Soft X-ray image of the Sun from the Yohkoh Soft X-ray Telescope on 3October 1992.
Figure 2: Observed temperature (in MK = 106K) as a function of distance (in Mm = 1,000 km) along the length of the loop from one coronal footpoint to the other with the error as shown.
Figure 3: Observed temperature as a function of height at the summits of the loops that comprise the arcade whose outermost loop is shown in Fig. 1.


  1. 1

    Ulmschneider, P., Priest, E. R. & Rosner, R. Mechanisms of Chromospheric and Coronal Heating (Springer, Berlin, (1991).

    Google Scholar 

  2. 2

    Culhane, J. L. Yohkoh observations of the solar corona. Adv. Space Res. 19, 1839–1848 (1997).

    ADS  Article  Google Scholar 

  3. 3

    Priest, E. R., Parnell, C. E. & Martin, S. F. Aconverging flux model of an x-ray bright point and an associated cancelling magnetic feature. Astrophys. J. 427, 459–474 (1994).

    ADS  Article  Google Scholar 

  4. 4

    Parnell, C. E., Golub, L. & Priest, E. R. The 3D structure of x-ray bright points. Solar Phys. 151, 57–74 (1994).

    ADS  Article  Google Scholar 

  5. 5

    Jordan, C. Modelling of solar coronal loops. Mem. Soc. Astron. Ital. 63, 605–620 (1992).

    ADS  Google Scholar 

  6. 6

    Acton, L. W. Comparison of Yohkoh x-ray and other solar activity parameters for November 1991 to November 1995. Astron. Soc. Pacific. Conf. Ser. 109, 45–54 (1996).

    ADS  CAS  Google Scholar 

  7. 7

    Shimizu, T., Tsuneta, S., Acton, L. W., Lemen, J. R. & Uchida, Y. Transient brightenings in active regions observed by the Yohkoh soft X-ray telescope. Publ. Astron. Soc. Japan 44, L147–L153 (1992).

    ADS  Google Scholar 

  8. 8

    Yoshida, T. & Tsuneta, S. Temperature structure of solar active regions. Astrophys. J. 459, 342–346 (1996).

    ADS  Article  Google Scholar 

  9. 9

    Tsuneta, S. & Lemen, J. R. in Physics of Solar and Stellar Coronae 113–130 (eds Linsky, J. & Serio, S.) (Kluwer, Dordrecht, (1993).

    Google Scholar 

  10. 10

    Kano, R. & Tsuneta, S. Temperature distributions and energy scaling law of solar coronal loops obtained with Yohkoh. Publ. Astron. Soc. Japan 48, 535–543 (1996).

    ADS  Article  Google Scholar 

  11. 11

    Sturrock, P. A., Wheatland, M. S. & Acton, L. W. Yohkoh soft x-ray telescope images of the diffuse solar corona. Astrophys. J. 461, L115–L117 (1996).

    ADS  Article  Google Scholar 

  12. 12

    Foley, C. A., Culhane, J. L., Weston, D., Acton, L. W. & Hara, H. Solar Phys. (submitted).

  13. 13

    Neupert, W., Nakagawa, Y. & Rust, D. M. Energy balance in a magnetically confined coronal structure observed by OSO-7. Solar Phys. 43, 359–376 (1975).

    ADS  Article  Google Scholar 

  14. 14

    Landini, M. & Monsignori-Fossi, B. C. Aloop model of active coronal regions. Astron. Astrophys. 42, 213–220 (1975).

    ADS  Google Scholar 

  15. 15

    Hollweg, J. V. in Solar Wind 5 (NASA CP 2280) 5–21 (NASA, Washington DC, (1983).

    Google Scholar 

  16. 16

    Roberts, B. in Hydromagnetics of Sun (ESA SP-220) 137–145 (ESA, Noordwijk, (1984).

    Google Scholar 

  17. 17

    Heyvaerts, J. & Priest, E. R. Coronal heating by phase-mixed shear Alfven waves. Astron. Astrophys. 117, 220–234 (1983).

    ADS  MATH  Google Scholar 

  18. 18

    Hood, A. W., Ireland, J. & Priest, E. R. Heating of coronal holes by phase mixing. Astron. Astrophys. 318, 957–961 (1997).

    ADS  Google Scholar 

  19. 19

    Goedbloed, J. P. Lecture Notes on Ideal MHD (Rijnhuizen Report) 83–145 (1983).

    Google Scholar 

  20. 20

    Goossens, M. in Advances in Solar System MHD (eds Priest, E. R., Hood, A. W.) 137–172 (Cambridge Univ. Press, (1991).

    Google Scholar 

  21. 21

    Davila, J. M. Heating of the solar corona by resonant absorption of Alfvèn waves. Astrophys. J. 317, 514–521 (1987).

    ADS  Article  Google Scholar 

  22. 22

    Tucker, W. H. Heating of solar active regions by magnetic energy dissipation: the steady state case. Astrophys. J. 186, 285–289 (1975).

    ADS  Article  Google Scholar 

  23. 23

    Levine, R. Evidence for opposed currents in active-region loops. Solar Phys. 46, 159–170 (1976).

    ADS  CAS  Article  Google Scholar 

  24. 24

    Galeev, A. A., Rosner, R., Serio, S. & Vaiana, G. S. Dynamics of coronal structures: magnetic field related heating and loop energy balance. Astrophys. J. 243, 301–308 (1981).

    ADS  Article  Google Scholar 

  25. 25

    Parker, E. N. Spontaneous Current Sheets in Magnetic Fields (Oxford Univ. Press, (1994).

    Google Scholar 

  26. 26

    Berger, M. A. in Advances in Solar System MHD (eds Priest, E. R. & Hood, A. W.) 241–256 (Cambridge Univ. Press, (1991).

    Google Scholar 

  27. 27

    Heyvaerts, J. & Priest, E. R. Aself-consistent turbulent model for coronal heating. Astrophys. J. 390, 297–308 (1993).

    ADS  Article  Google Scholar 

  28. 28

    Einaudi, G., Velli, M., Politano, H. & Pouquet, A. Energy release in a turbulent corona. Astrophys. J. 457, L113–L116 (1996).

    ADS  Article  Google Scholar 

  29. 29

    Hendrix, D. L., Van Hoven, G., Mikic, Z. & Schnack, D. D. The viability of Ohmic dissipation as a coronal heating source. Astrophys. J. 470, 1192–1197 (1996).

    ADS  Article  Google Scholar 

  30. 30

    Galsgaard, K. & Nordlund, A. Heating and activity of the solar corona 1. Boundary shearing of an initially homogeneous magnetic field. J. Geophys. Res. 101, 13445–13460 (1996).

    ADS  Article  Google Scholar 

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We are most grateful for financial support from the UK Particle Physics and Astronomy Research Council and to S. T. Buckland for helpful suggestions. Part of the work was carried out while one of us (J.L.C.) was a visiting professor at the Institute for Space and Astronautical Science (ISAS) of Japan. C.R.F. was supported by a Research Studentship from PPARC. NASA supported the work of L.W.A. The Yohkoh mission and its continued operation are projects of ISAS in Japan.

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

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