Dynamic Topology and Flux Rope Evolution During Non-linear Tearing of 3D Null Point Current Sheets

TL;DR

This paper investigates the complex evolution of magnetic null points and flux ropes in a 3D current sheet during tearing instability, revealing new null bifurcation processes and flux rope dynamics relevant to heliophysics.

Contribution

It provides a detailed analysis of null point creation, annihilation, and flux rope evolution during 3D tearing, highlighting novel bifurcation mechanisms and their effects on magnetic field dynamics.

Findings

Null bifurcation leads to flux rope pair formation

Nulls form within flux ropes during reconnection

Flux ropes generate torsional MHD waves and magnetic braiding

Abstract

In this work the dynamic magnetic field within a tearing-unstable three-dimensional (3D) current sheet about a magnetic null point is described in detail. We focus on the evolution of the magnetic null points and flux ropes that are formed during the tearing process. Generally, we find that both magnetic structures are created prolifically within the layer and are non-trivially related. We examine how nulls are created and annihilated during bifurcation processes, and describe how they evolve within the current layer. The type of null bifurcation first observed is associated with the formation of pairs of flux ropes within the current layer. We also find that new nulls form within these flux ropes, both following internal reconnection and as adjacent flux ropes interact. The flux ropes exhibit a complex evolution, driven by a combination of ideal kinking and their interaction with the outflow jets from the main layer. The finite size of the unstable layer also allows us to consider the wider effects of flux rope generation. We find that the unstable current layer acts as a source of torsional MHD waves and dynamic braiding of magnetic fields. The implications of these results to several areas of heliophysics are discussed.