Magnetic reconnection during eruptive magnetic flux ropes^⋆

¹ Centre for mathematical Plasma Astrophysics, Department of Mathematics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
e-mail: meizhixing@ynao.ac.cn
² Yunnan Observatories, Chinese Academy of Sciences, Kunming, Yunnan, PR China
³ Division of Atmospheric and Geospace Sciences, National Science Foundation, Arlington, Virginia, USA
⁴ Center for Astronomical Mega-Science, Chinese Academy of Sciences, Chaoyang District, Beijing, PR China

Received: 10 May 2017
Accepted: 13 July 2017

Abstract

Aims. We perform a three-dimensional (3D) high resolution numerical simulation in isothermal magnetohydrodynamics to study the magnetic reconnection process in a current sheet (CS) formed during an eruption of a twisted magnetic flux rope (MFR). Because the twist distribution violates the Kruskal-Shafranov condition, the kink instability occurs, and the MFR is distorted. The centre part of the MFR loses its equilibrium and erupts upward, which leads to the formation of a 3D CS underneath it.

Methods. In order to study the magnetic reconnection inside the CS in detail, mesh refinement has been used to reduce the numerical diffusion and we estimate a Lundquist number S = 10⁴ in the vicinity of the CS.

Results. The refined mesh allows us to resolve fine structures inside the 3D CS: a bifurcating sheet structure signaling the 3D generalization of Petschek slow shocks, some distorted-cylindrical substructures due to the tearing mode instabilities, and two turbulence regions near the upper and the lower tips of the CS. The topological characteristics of the MFR depend sensitively on the observer’s viewing angle: it presents as a sigmoid structure, an outwardly expanding MFR with helical distortion, or a flare-CS-coronal mass ejection symbiosis as in 2D flux-rope models when observed from the top, the front, or the side.