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The Association of Flares to Cancelling Magnetic Features on the Sun

Published online by Cambridge University Press:  12 April 2016

Silvia H. B. Livi
Affiliation:
Universidade Federal do Rio Grande do Sul, 90 049 Porto Alegre RS, Brazil
Sara Martin
Affiliation:
Big Bear Solar Observatory, California Institute of Technology, Pasadena, CA 91125, U.S.A.
Haimin Wang
Affiliation:
Big Bear Solar Observatory, California Institute of Technology, Pasadena, CA 91125, U.S.A.
Guoxiang Ai
Affiliation:
Beijing Astronomical Observatory, Beijing, China

Abstract

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Previous work relating flares to evolutionary changes of photospheric solar magnetic fields are reviewed and reinterpreted in the light of recent observations of cancelling magnetic fields. In line-of-sight magnetograms and H-alpha filtergrams from Big Bear Solar Observatory, we confirm the following 3 associations: (a) the occurrence of many flares in the vicinity of emerging magnetic flux regions (Rust, 1974), but only at locations where cancellation has been observed or inferred; (b) the occurrence of flares at sites where the magnetic flux is increasing on one side of a polarity inversion line and concurrently decreasing on the other (Martres et al, 1968; Ribes, 1969); and (c) the occurrence of flares at sites where cancellation is the only observed change in the magnetograms for at least several hours before a flare (Martin, Livi, and Wang, 1985). Because cancellation (or the localized decrease in the line-of-sight component of magnetic flux) is the only common factor in all of these circumstances, suggest that cancellation is the more general association that includes the other associations as special cases. We propose the hypothesis that cancellation is a necessary, evolutionary precondition for flares. We also confirm the observation of Martin, Livi, and Wang (1985) that the initial parts of flares occur in close proximity to cancellation sites but that during later phases, the flare emission can spread to other parts of the magnetic field that are weak, strong, or not cancelling.

Type
Research Article
Copyright
Copyright © Kluwer 1989

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