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An exact threshold for separator bifurcation

Prior, C. and Wyper, P. F. (2022) 'An exact threshold for separator bifurcation.', Geophysical & Astrophysical Fluid Dynamics .


Reconnection involving magnetic separators is known to lead to the spontaneous generation of new separator pairs. In this work, we explore the bifurcation process for a system composed of a pair of null points with a joining separator. We begin with a simplified analytical model to derive the basic principles of bifurcation in this system and then consider models with more general separator curve geometry and generic localised null structure. We demonstrate that the maximum pairwise linking (net-winding) of the separator and the local fan plane always approaches a multiple of 0.25 just before bifurcation. Additionally, we show the integrated twisting along the separator (the field strength normalised parallel current) can be used to determine when this limit will definitely lead to bifurcation. We present step-by-step algorithms to assess how close such systems are to bifurcation.

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Available under License - Creative Commons Attribution Non-commercial No Derivatives 4.0.
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Publisher statement:© 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License (, which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited, and is not altered, transformed, or built upon in any way.
Date accepted:31 May 2022
Date deposited:22 June 2022
Date of first online publication:21 June 2022
Date first made open access:22 June 2022

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