Abstract
Evolution of nonpotential structures in a complex, flare-productive active region NOAA AR 6555 has been studied during the period March 23–26, 1991, using a quantitative description of the degree of magnetic shear at both local and regional scales. Distinct shear evolution in four subareas of AR 6555 is inferred from daily variation of their shear indices. Subareas which showed significant evolution in their overall magnetic structure are found to be most active. Hα flare ribbons mostly formed bordering, andnot within, areas of large shear and expanded over areas of lower shear.
Magnetic shear changes are also detected during several flares, including a major X4.7/4B flare. Out of the 14 events for which temporally contiguous magnetograms were available, a decrease, or dip, in area-averaged shear index around flare onset time followed by an increase was observed in eight cases. There were two events with increase, three events with continuous decrease, and one event with no change in the shear index during the flare.
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Ambastha, A., Hagyard, M. J., Kalman, B., and Csepura, Gy.: 1993, in preparation.
Birn, J., Goldstein, H., and Schindler, K.: 1978,Solar Phys. 57, 81.
Canfield, R. C., de La Beaujardiere, J., and Leka, K. D.: 1991, in Culhane and Jordan (eds.),The Physics of Solar Flares, The Royal Society, London.
Canfield, R. C., Priest, E. R., and Rust, D. M.: 1974, in D. M. Rust and Y. Nakagawa (eds.),Flare Related Magnetic Field Dynamics, National Center for Atmospheric Research, Boulder, Colorado, p. 361.
De Jager, C.: 1986,Adv; Space Res. 6(6), 353.
Gary, G. A. and Hagyard, M. J.: 1990,Solar Phys. 126, 21.
Gary, G. A., Moore, R. L., Hagyard, M. J., and Haisch, B. M.: 1987,Astrophys. J. 314, 786.
Gaizauskas, V.: 1986,Solar Phys. 105, 67.
Hagyard, M. J.: 1970,NASA TM X-64541.
Hagyard, M. J.: 1990,Mem. Soc. Astron. Ital. 61(2), 337.
Hagyard, M. J. and Rabin, D. M.: 1986,Adv. Space Res. 6(6), 7.
Hagyard, M. J., Gary, G. A., and West, E. A.: 1988,NASA TM-4048, p. 26.
Hagyard, M. J., Low, B. C., and Tandberg-Hanssen, E.: 1981,Solar Phys. 73, 257.
Hagyard, M. J., Venkatakrishnan, P., and Smith, J. B., Jr.: 1990,Astrophys. J. Suppl. Series 73, 159.
Hagyard, M. J., Smith, J. B., Jr., Teuber, D., and West, E. A.: 1984,Solar Phys. 91, 115.
Machado, M. E. and Moore, R. L.: 1986,Adv. Space Res. 6(6), 217.
Martin, S. F., Livi, S. H. B., and Wang, J.: 1985,Australian J. Phys. 38, 929.
Metcalf, T. R., Sakao, T., Acton, L. W., Canfield, R. C., Hudson, H. S., Inda, M., Kosugi, T., and Wulser, J. P.: 1992,Bull. Am. Astron. Soc. 24, 776.
Moore, R. L., Hagyard, M. J., and Davis, J. M.: 1987,Solar Phys. 113, 347.
Rabin, D. M., Moore, R. L., and Hagyard, M. J.: 1984,Astrophys. J. 287, 404.
Stenflo, J. O.: 1985, in M. J. Hagyard (ed.),Measurement of Solar Vector Magnetic Fields, NASA CP-2374, p. 263.
Teuber, D., Tandberg-Hanssen, E., and Hagyard, M. J.: 1977,Solar Phys. 53, 97.
Venkatakrishnan, P. and Gary, G. A.: 1989,Solar Phys. 120, 235.
Venkatakrishnan, P., Hagyard, M. J., and Hathaway, D. H.: 1988,Solar Phys. 115, 125.
Wang, H.: 1992,Solar Phys. 140, 85.
West, E. A. and Balasubramaniam, K. S.: 1992, ‘Cross-Talk in Solar Polarization Measurements’, inPolarization Analysis and Measurement, SPIE Proceedings, Vol. 1746, p. 281.
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NRC Resident Research Associate.
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Ambastha, A., Hagyard, M.J. & West, E.A. Evolutionary and flare-associated magnetic shear variations observed in a complex, flare-productive active region. Sol Phys 148, 277–299 (1993). https://doi.org/10.1007/BF00645091
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DOI: https://doi.org/10.1007/BF00645091