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

Abstract

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 Alfv\'en 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.