Wave generation via oscillatory reconnection at a three-dimensional magnetic null point

This work conducts a three-dimensional (3D), nonlinear magnetohydrodynamic (MHD) simulation to investigate wave generating, time-dependent reconnection around a magnetic null point. A non-periodic perturbation (in the $xz$-plane) triggers oscillatory reconnection (OR) at the 3D null, resulting in a self-sustained oscillation with a constant period $P$. We investigate the response of the system using three distinct wave proxies (compressible parallel, compressible transverse and incompressible parallel) as well as Spectral Proper Orthogonal Decomposition for decoupling and analyzing the resultant MHD wave behavior. We find that OR generates a slow magnetoacoustic wave of period $P$ that propagates outwards in all directions along the spine and fan plane of the 3D null point. We also find the generation of a propagating Alfvén wave of period $P$, exclusively along the $y$-axis in the fan plane, i.e. in the direction perpendicular to the spine motion. These findings provide new insights into waves generated from a 3D null point and their implications for coronal seismology.

💡 Research Summary

This paper presents a comprehensive three‑dimensional (3D) magnetohydrodynamic (MHD) study of wave generation associated with oscillatory reconnection (OR) at a magnetic null point. Using the Lare3D code, the authors solve the full set of resistive MHD equations in a Cartesian domain that contains a single linear potential null (B = (x, y, −2z)). The fan surface lies in the z = 0 plane, while the spine aligns with the z‑axis. The plasma is initially uniform with density ρ = 1, pressure p ≈ 0.005 (β ≈ 0.01), and a constant resistivity η = 10⁻³.

A localized spherical magnetoacoustic pulse is introduced as a perturbation: the vector potential A′ = ψ exp