Three-dimensional simulations of the orientation and structure of reconnection X-lines

TL;DR

This study uses Hall MHD simulations to analyze the formation and evolution of three-dimensional reconnection X-lines in plasmas with varying magnetic field orientations and densities, revealing dominant orientations and challenging previous reconnection geometry assumptions.

Contribution

It demonstrates that in 3D Hall MHD simulations, reconnection X-lines tend to align with the direction maximizing outflow speed, contrary to earlier theories suggesting a normal-plane geometry.

Findings

Dominant X-line orientations align with maximum outflow speed direction

Reconnection occurs in a geometry different from previous normal-plane models

X-line growth stagnates, remaining shorter than the simulation domain

Abstract

This work employs Hall magnetohydrodynamic (MHD) simulations to study the X-lines formed during the reconnection of magnetic fields with differing strengths and orientations embedded in plasmas of differing densities. Although random initial perturbations trigger the growth of X-lines with many orientations, at late time a few robust X-lines sharing an orientation reasonably consistent with the direction that maximizes the outflow speed, as predicted by Swisdak and Drake [Geophys. Res. Lett., 34, L11106, (2007)], dominate the system. The existence of reconnection in the geometry examined here contradicts the suggestion of Sonnerup [J. Geophys. Res., 79, 1546 (1974)] that reconnection occurs in a plane normal to the equilibrium current. At late time the growth of the X-lines stagnates, leaving them shorter than the simulation domain.