Kelvin-Helmholtz instability and collapse of a twisted magnetic nullpoint with anisotropic viscosity

Quinn, J. , MacTaggart, D. and Simitev, R. D. (2021) Kelvin-Helmholtz instability and collapse of a twisted magnetic nullpoint with anisotropic viscosity. Astronomy and Astrophysics, 650(3), A143. (doi: 10.1051/0004-6361/202140460)

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Abstract

Context. Magnetic null points are associated with high-energy coronal phenomena such as solar flares and are often sites of reconnection and particle acceleration. Dynamic twisting of a magnetic null point can generate a Kelvin-Helmholtz instability (KHI) within its fan plane and can instigate spine-fan reconnection and an associated collapse of the null point under continued twisting. Aims. This article aims to compare the effects of isotropic and anisotropic viscosity in simulations of the KHI and collapse in a dynamically twisted magnetic null point. Methods. We performed simulations using the 3D magnetohydrodynamics code Lare3d with a custom anisotropic viscosity module. A pair of high-resolution simulations were performed, one using isotropic viscosity and another using anisotropic viscosity, keeping all other factors identical. We analysed the results in detail. A further parameter study was performed over a range of values for viscosity and resistivity. Results. Both viscosity models permit the growth of the KHI and the eventual collapse of the null point. Over all studied parameters, anisotropic viscosity allows a faster growing instability, while isotropic viscosity damps the instability to the extent of stabilisation in some cases. Although the viscous heating associated with anisotropic viscosity is generally smaller, the ohmic heating dominates and is enhanced by the current sheets generated by the instability. This leads to a greater overall heating rate when using anisotropic viscosity. The collapse of the null point occurs significantly sooner when anisotropic viscosity is employed.

Item Type:Articles
Additional Information:JQ was funded via an EPSRC studentship: EPSRC DTG EP/N509668/1.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Simitev, Professor Radostin and Quinn, Jamie and Mactaggart, Dr David
Authors: Quinn, J., MacTaggart, D., and Simitev, R. D.
College/School:College of Science and Engineering > School of Mathematics and Statistics > Mathematics
Journal Name:Astronomy and Astrophysics
Publisher:EDP Sciences
ISSN:0004-6361
ISSN (Online):1432-0746
Published Online:19 April 2021
Copyright Holders:Copyright © J. Quinn et al. 2021
First Published:First published in Astronomy and Astrophysics 2021
Publisher Policy:Reproduced under a Creative Commons Licence
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
172865EPSRC DTP 16/17 and 17/18Tania GalabovaEngineering and Physical Sciences Research Council (EPSRC)EP/N509668/1Research and Innovation Services