What is the role of the kink instability in eruption of X-ray sigmoids?

Details What is the role of the kink instability in eruption of X-ray sigmoids? What is the role of the kink instability in eruption of X-ray sigmoids?

May 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aas...200.2001c&link_type=abstract

American Astronomical Society, 200th AAS Meeting, #20.01; Bulletin of the American Astronomical Society, Vol. 34, p.672

Astronomy and Astrophysics

Astronomy

Scientific paper

Observers see ample evidence of helical structures in erupting solar filaments, X-ray sigmoids and CMEs. It has been argued that the total amount of twist in a given loop is a factor in its MHD stability [Priest, 1984]. A simple model illustrates this point. Consider a cylindrical force-free magnetic field with constant α = T /L, where L is the length of the tube and T is the total twist contained within it. The tube is stable to the MHD kink instability for total twist below a critical value Tc ~ 2 π . Rust and Kumar [1996] compared the shape of 49 transient, bright sigmoid structures to the signature of a helically kinked flux rope. From a study of the aspect ratios of these transient sigmoid brightenings, they inferred that the cause of CMEs is the eruption of an unstable, kinked magnetic field. We have analyzed 191 X-ray sigmoids in the the Yohkoh SXT data, measuring the angle γ at which the sigmoid crosses its central axis and the length of the sigmoid along that axis (which is not identical to L, but is closely related to it). In a simple 2D force-free analysis, Pevtsov et al. [1997] showed that α = ( π / L ) sin γ , implying that sin γ is a measure of the total twist T. By simple visual inspection of the Yohkoh SXT movies, we have identified well-known signatures of eruption, i.e., X-ray cusps and arcades. We find no relationship between the frequency of occurrence of such signatures of eruption and sin γ .

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