Abstract
Sensitive observations of the quiet Sun observed by EIT on the SOHO satellite in high-temperature iron-line emission originating in the corona are presented. The thermal radiation of the quiet corona is found to fluctutate significantly, even on the shortest time scale of 2 min and in the faintest pixels. The power spectrum of the emission measure time variations is approximately a power law with an exponent of 1.79±0.08 for the brightest pixels and 1.69±0.08 for the average and the faintest pixels. The more prominent enhancements are identified with previously reported X-ray network flares (Krucker et al., 1997) above the magnetic network of the quiet chromosphere. In coronal EUV iron lines they are amenable to detailed analysis suggesting that the brightenings are caused by additional plasma injected from below and heated to slightly higher temperature than the preexisting corona. Statistical investigations are consistent with the hypothesis that the weaker emission measure enhancements originate from the same parent population. The power input derived from the impulsive brightenings is linearly proportional to the radiative loss in the observed part of the corona. The absolute amount of impulsive input is model-dependent. It cannot be excluded that it can satisfy the total requirement for heating. These observations give strong evidence that a significant fraction of the heating in quiet coronal regions is impulsive.
Similar content being viewed by others
References
Benz, A. O. and Güdel, M.: 1994, Astron. Astrophys. 285, 621.
Benz, A. O., Krucker, S., Acton, L. W., and Bastian, T. S.: 1997, Astron. Astrophys. 320, 993.
Brueckner, G. E. and Bartoe, J.-D.F.: 1983, Astrophys. J. 272, 329.
Clette, F. and Berghmans, D.: 1997, The Corona and Solar Wind Near Minimum Activity, ESA SP-404, p. 283.
Delaboudinière, J.-P. et al.: 1995 Solar Phys. 162, 291.
Dowdy, J. F., Moore, R. L., and Emslie, G. A.: 1987 Solar Phys. 112, 255.
Gold T.: 1964, in W. N. Hess (ed.), AAS-NASA Symp. in the Phys. of Solar Flares, NASA-SP 50, Washington DC, p. 389.
Habbal, S. R., Ronan, R. S., Withbroe, G. L., Shevgaonkar, R. K., and Kundu, M. R.: 1986, Astrophys. J. 306, 740.
Harrison, R. A.: 1997, The Corona and Solar Wind Near Minimum Activity, ESA SP-404, p. 7.
Kaastra, J. S., Mewe, R., and Nieuwenhuijzen, H.: 1996, in K. Yamashita and T. Wanatabe (eds.), UV and X-ray Spectroscopy of Astrophysical and Laboratory Plasmas, Universal Academy Press, Inc., Tokyo, p. 411.
Koutchmy, S., Hara, H., Suematsu, Y., and Reardon, K.: 1997, Astron. Astrophys. 320, L33.
Krucker, S., Benz, A. O., and Delaboudinière, J.-P.: 1997, The Corona and Solar Wind Near Minimum Activity, ESA SP-404, p. 465.
Krucker, S., Benz, A. O., Acton, L. W., and Bastian, T. S.: 1997, Astrophys. J. 488, 499.
Kundu, M. R., Raulin, J. P., Pick, M., and Strong, K. T.: 1995, Astrophys. J. 444, 922.
Moses, D. et al.: 1994, Astrophys. J. 430, 913.
Parker, E. N.: 1983, Astrophys. J. 264, 635.
Porter, J. G. et al.: 1987, Astrophys. J. 323, 380.
Priest, E. R.: 1981, Solar Flare Magnetodynamics, Gordon and Breach, London.
Shimizu, T., Tsuneta, A., Acton, L. W., Lemen, J. R., Ogawara, Y., and Uchida, Y.: 1994, Astrophys. J. 422, 906.
Ulmschneider; P., Rosner, R., and Priest, E. R. (eds.): 1991, Mechanisms of Chromospheric and Coronal Heating, Springer-Verlag, Berlin.
Withbroe, G. L. and Noyes, R. W.: 1977, Ann. Rev. Astron. Astrophys. 15, 363.
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Benz, A.O., Krucker, S. Heating Events in the Quiet Solar Corona. Solar Physics 182, 349–363 (1998). https://doi.org/10.1023/A:1005046620684
Issue Date:
DOI: https://doi.org/10.1023/A:1005046620684