Additive self-helicity as a Kink mode threshold

AMS Citation:
Malanushenko, A., D. W. Longcope, Y. Fan, and S. E. Gibson, 2009: Additive self-helicity as a Kink mode threshold. The Astrophysical Journal, 702, 580-592, doi:10.1088/0004-637X/702/1/580.
Resource Type:article
Title:Additive self-helicity as a Kink mode threshold
Abstract: In this paper, we propose that additive self-helicity, introduced by Longcope and Malanushenko, plays a role in the kink instability for complex equilibria, similar to twist helicity for thin flux tubes. We support this hypothesis by a calculation of additive self-helicity of a twisted flux tube from the simulation of Fan and Gibson. As more twist gets introduced, the additive self-helicity increases, and the kink instability of the tube coincides with the drop of additive self-helicity, after the latter reaches the value of HA /Φ2 ≈ 1.5 (where Φ is the flux of the tube and HA is the additive self-helicity). We compare the additive self-helicity to twist for a thin subportion of the tube to illustrate that HA /Φ2 is equal to the twist number, studied by Berger and Field, when the thin flux tube approximation is applicable. We suggest that the quantity HA /Φ2 could be treated as a generalization of a twist number, when the thin flux tube approximation is not applicable. A threshold on a generalized twist number might prove extremely useful studying complex equilibria, just as the twist number itself has proven useful studying idealized thin flux tubes. We explicitly describe a numerical method for calculating additive self-helicity, which includes an algorithm for identifying a domain occupied by a flux bundle and a method of calculating potential magnetic field confined to this domain. We also describe a numerical method to calculate twist of a thin flux tube, using a frame parallelly transported along the axis of the tube.
Subject(s):instabilities, magnetic fields, Sun: corona, Sun: coronal mass ejections (CMEs), Sun: flares, Sun: magnetic fields
Peer Review:Refereed
Copyright Information:An edited version of this article was published by IOP Publishing Ltd on behalf of the American Astronomical Society. Copyright 2009 the American Astronomical Society.
OpenSky citable URL: ark:/85065/d7pg1srx
Publisher's Version: 10.1088/0004-637X/702/1/580
  • A. Malanushenko
  • D. Longcope
  • Yuhong Fan - NCAR/UCAR
  • Sarah Gibson - NCAR/UCAR
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