The evolution of writhe in kink-unstable flux ropes and erupting filaments
van Driel-Gesztelyi, L.
Plasma Physics and Controlled Fusion
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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 of pre-eruptive twist from measurements of writhe. However, our simulations suggest an upper twist limit of ~6π for the majority of filaments prior to their eruption.
European Commission’s Seventh Framework Programme
Science & Technology Facilities Council (STFC)
Copyright © 2014 IOP Publishing Ltd. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence (http://creativecommons.org/licenses/by/3.0/). Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Vol. 56 (6), article 064012
Grant agreement No 284461 (eHEROES project)
Consolidated Grant ST/H00260X/1
Grant OTKA K-081421