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Title:
Nonlinear fast magnetoacoustic wave propagation in the neighbourhood of a 2D magnetic X-point: oscillatory reconnection
Authors:
McLaughlin, J. A.; De Moortel, I.; Hood, A. W.; Brady, C. S.
Affiliation:
AA(School of Mathematics and Statistics, University of St Andrews, KY16 9SS, UK ), AB(School of Mathematics and Statistics, University of St Andrews, KY16 9SS, UK), AC(School of Mathematics and Statistics, University of St Andrews, KY16 9SS, UK), AD(Physics Department, University of Warwick, CV4 7AL, Coventry, UK)
Publication:
Astronomy and Astrophysics, Volume 493, Issue 1, 2009, pp.227-240 (A&A Homepage)
Publication Date:
01/2009
Origin:
EDP Sciences
Keywords:
magnetohydrodynamics (MHD), waves, shock waves, Sun: corona, Sun: magnetic fields, Sun: oscillations
DOI:
10.1051/0004-6361:200810465
Bibliographic Code:
2009A&A...493..227M

Abstract

Context: This paper extends the models of Craig & McClymont (1991, ApJ, 371, L41) and McLaughlin & Hood (2004, A&A, 420, 1129) to include finite β and nonlinear effects.
Aims: We investigate the nature of nonlinear fast magnetoacoustic waves about a 2D magnetic X-point.
Methods: We solve the compressible and resistive MHD equations using a Lagrangian remap, shock capturing code (Arber et al. 2001, J. Comp. Phys., 171, 151) and consider an initial condition in {v}×{B} \cdot {hat{z}} (a natural variable of the system).
Results: We observe the formation of both fast and slow oblique magnetic shocks. The nonlinear wave deforms the X-point into a “cusp-like” point which in turn collapses to a current sheet. The system then evolves through a series of horizontal and vertical current sheets, with associated changes in connectivity, i.e. the system exhibits oscillatory reconnection. Our final state is non-potential (but in force balance) due to asymmetric heating from the shocks. Larger amplitudes in our initial condition correspond to larger values of the final current density left in the system.
Conclusions: The inclusion of nonlinear terms introduces several new features to the system that were absent from the linear regime.

A movie is available in electronic form at http://www.aanda.org

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