Linear and nonlinear MHD mode coupling of the fast magnetoacoustic wave about a 3D magnetic null point

Abstract

Context: Coronal magnetic null points have been implicated as possible locations for localised heating events in 2D models. We investigate this possibility about fully 3D null points. Aims: We investigate the nature of the fast magnetoacoustic wave about a fully 3D magnetic null point, with a specific interest in its propagation, and we look for evidence of MHD mode coupling and/or conversion to the Alfvén mode. Methods: A special fieldline and flux-based coordinate system was constructed to permit the introduction of a pure fast magnetoacoustic wave in the vicinity of proper and improper 3D null points. We considered the ideal, β = 0, MHD equations, which are solved using the LARE3D numerical code. The constituent modes of the resulting wave were isolated and identified using the special coordinate system. Numerical results were supported by analytical work derived from perturbation theory and a linear implementation of the WKB method. Results: An initially pure fast wave is found to be permanently decoupled from the Alfvén mode both linearly and nonlinearly for both proper and improper 3D null points. The pure fast mode also generates and sustains a nonlinear disturbance aligned along the equilibrium magnetic field. The resulting pure fast magnetoacoustic pulse has transient behaviour, which is found to be governed by the (equilibrium) Alfvén-speed profile, and a refraction effect focuses all the wave energy towards the null point. Conclusions: Thus, the main results from previous 2D work do indeed carry over to the fully 3D magnetic null points and

11 pages, 6 figures

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Cited by in corpus (10)

• Three-dimensional oscillatory magnetic reconnection
• On the Periodicity of Oscillatory Reconnection
• Magnetoacoustic Waves in a Stratified Atmosphere with a Magnetic Null Point
• Oscillatory Reconnection of a 2D X-point in a hot coronal plasma
• Three-dimensional MHD wave propagation near a coronal null point: a new wave mode decomposition approach
• White-light QFP Wave Train and the Associated Failed Breakout Eruption
• Is Magnetic Topology Important for Heating the Solar Atmosphere?
• Phase Mixing of Alfvén Waves Near a 2D Magnetic Null Point
• The behaviour of magnetoacoustic waves in the neighbourhood of a two-dimensional null point: initially cylindrically-symmetric perturbations
• The independence of oscillatory reconnection periodicity from the initial pulse