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The evolution of writhe in kink-unstable flux ropes and erupting filaments

  • The helical kink instability of a twisted magnetic flux tube has been suggested as a trigger mechanism for solar filament eruptions and coronal mass ejections (CMEs). In order to investigate if estimations of the pre-emptive twist can be obtained from observations of writhe in such events, we quantitatively analyze the conversion of twist into writhe in the course of the instability, using numerical simulations. We consider the line tied, cylindrically symmetric Gold-Hoyle flux rope model and measure the writhe using the formulae by Berger and Prior which express the quantity as a single integral in space. We find that the amount of twist converted into writhe does not simply scale with the initial flux rope twist, but depends mainly on the growth rates of the instability eigenmodes of higher longitudinal order than the basic mode. The saturation levels of the writhe, as well as the shapes of the kinked flux ropes, are very similar for considerable ranges of initial flux rope twists, which essentially precludes estimations ofThe helical kink instability of a twisted magnetic flux tube has been suggested as a trigger mechanism for solar filament eruptions and coronal mass ejections (CMEs). In order to investigate if estimations of the pre-emptive twist can be obtained from observations of writhe in such events, we quantitatively analyze the conversion of twist into writhe in the course of the instability, using numerical simulations. We consider the line tied, cylindrically symmetric Gold-Hoyle flux rope model and measure the writhe using the formulae by Berger and Prior which express the quantity as a single integral in space. We find that the amount of twist converted into writhe does not simply scale with the initial flux rope twist, but depends mainly on the growth rates of the instability eigenmodes of higher longitudinal order than the basic mode. The saturation levels of the writhe, as well as the shapes of the kinked flux ropes, are very similar for considerable ranges of initial flux rope twists, which essentially precludes estimations of pre-eruptive twist from measurements of writhe. However, our simulations suggest an upper twist limit of similar to 6 pi for the majority of filaments prior to their eruption.show moreshow less

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Author details:T. Toeroek, Bernhard KliemORCiDGND, M. A. Berger, M. G. Linton, P. Demoulin, L. van Driel-Gesztelyi
DOI:https://doi.org/10.1088/0741-3335/56/6/064012
ISSN:0741-3335
ISSN:1361-6587
Title of parent work (English):Plasma physics and controlled fusion
Publisher:IOP Publ. Ltd.
Place of publishing:Bristol
Publication type:Article
Language:English
Year of first publication:2014
Publication year:2014
Release date:2017/03/27
Tag:Sun: corona; Sun: filaments; magnetohydrodynamics (MHD)
Volume:56
Issue:6
Number of pages:7
Funding institution:NASA/LWS; ONR; DFG; European Commission [284461]; STFC Consolidated Grant [ST/H00260X/1]; Hungarian Research grant [OTKA K-081421]
Organizational units:Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie
Peer review:Referiert
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