Abstract
The temporal and spatial variations of EUV emission from a small growing active region were investigated. Frequent localized short term (∼ few minutes) fluctuations in EUV emission were observed throughout the 7.2 hr interval when the most continuous observations were acquired. Approximately 20% of the 5 ″ x 5 ″ pixels had intensity variations exceeding a factor of 1.3 for the chromospheric Lα line, a factor of 1.5 for lines formed in the chromospheric-coronal transition region and a factor of 1.4 for the coronal Mg x line. A subflare in the region produced the largest intensity enhancements, ranging from a factor of ∼ 2.3 for the chromospheric Lα line to ∼ 8 for the transition region and coronal lines. The EUV fluctuations in this small active region are similar to those observed in coronal bright points, suggesting that impulsive heating is an important, perhaps dominant form of heating the upper chromospheric and lower coronal plasmas in small magnetic bipolar regions. The responsible mechanism most likely involves the rapid release of magnetic energy, possibly associated with the emergence of magnetic flux from lower levels into the chromosphere and corona.
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References
Athay, R. G.: 1984, Solar Phys. 93, 123.
Athay, R. G. and White, O. R.: 1978a, Astrophys. J. Suppl. 39, 333.
Athay, R. G. and White, O. R.: 1978b, Astrophys. J. 226, 1135.
Athay, R. G. White, O. R., Lites, B. W., and Bruner, E. C: 1980, Solar Phys. 66, 357.
Bruner, E. C., Jr and Lites, B. W.: 1979, Astrophys. J. 228, 322.
Dere, K. P., Bartoe, J. D. F., Brueckner, G. E., Dykton, M. D., and van Hoosier, M. E.: 1981, Astrophys. J. 249, 333.
Habbal, S. R. and Withbroe, G. L.: 1981, Solar Phys. 69, 177.
Lites, B. W. and Hansen, E. R.: 1978, Solar Phys. 55, 347.
Parker, E. N.: 1981a, Astrophys. J. 244, 631.
Parker, E. N.: 1981b, Astrophys. J. 244 644.
Parker, E. N.: 1983a, Astrophys. J. 264, 635.
Parker, E. N.: 1983b, Astrophys. J. 264, 642.
Porter, J. G., Toomre, J., and Gebbie, K. B.: 1984, Astrophys. J. 283, 879.
Reeves, E. M., Huber, M. C. E., and Timothy, J. G.: 1977a, Appl. Opt. 16, 837.
Reeves, E. M., Huber, M. C. E., Timothy, J. G., and Withbroe, G. L.: 1977b, Appl. Opt. 16, 849.
Rosner, R., Golub, L., Coppi, B., and Vaiana, G. S.: 1978a, Astrophys. J. 222, 317.
Rosner, R., Tucker, W. H., and Vaiana, G. S.: 1978b, Astrophys. J. 220, 643.
Sturrock, P. A. (ed.): 1980, Solar Flares, Colo. Assoc. Univ. Press, Boulder.
Tucker, W. H.: 1973, Astrophys. J. 186, 285.
Vaiana, G. and Rosner, R.: 1978, Ann. Rev. Astron. Astrophys. 16, 393.
Wentzel, D.: 1981, in S. Jordan (ed.) The Sun as a Star, NASA SP-450, p. 331.
Withbroe, G. L.: 1977, in Proceedings of OSO-8 Workshop, Univ. of Colorado, Boulder.
Withbroe, G. L. and Habbal, S. R.: 1983, Rapid Magnetic Energy Release, its Possible Role in Coronal Heating and Solar Wind Acceleration, AFGL-TR-83–0086, Air Force Geophys. Lab., Hanscom AFB, MA.
Withbroe, G. L. and Noyes, R. W.: 1977, Ann. Rev. Astron. Astrophys. 15, 363.
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Withbroe, G.L., Habbal, S.R. & Ronan, R. Impulsive phenomena in a small active region. Sol Phys 95, 297–310 (1985). https://doi.org/10.1007/BF00152407
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DOI: https://doi.org/10.1007/BF00152407