Shear Photospheric Forcing and the Origin of Turbulence in Coronal Loops

TL;DR

This paper uses numerical simulations to explore how shear photospheric forcing leads to turbulence in coronal loops, revealing that turbulence arises from nonlinear dynamics rather than footpoint motion complexity.

Contribution

It demonstrates that turbulence in coronal loops originates from inherent nonlinear processes, not the complexity of footpoint velocity patterns, through MHD simulations of the Parker model.

Findings

Tearing instability leads to magnetic islands and turbulence.

Energy spectra follow a power law indicating developed turbulence.

Magnetic field remains complex and does not revert to initial state.

Abstract

We present a series of numerical simulations aimed at understanding the nature and origin of turbulence in coronal loops in the framework of the Parker model for coronal heating. A coronal loop is studied via reduced magnetohydrodynamics simulations in Cartesian geometry. A uniform and strong magnetic field threads the volume between the two photospheric planes, where a velocity field in the form of a 1D shear flow pattern is present. Initially the magnetic field which developes in the coronal loop is a simple map of the photospheric velocity field. This initial configuration is unstable to a multiple tearing instability which develops islands with X and O points in the plane orthogonal to the axial field. Once the nonlinear stage sets in the system evolution is characterized by a regime of MHD turbulence dominated by magnetic energy. A well developed power law in energy spectra is observed and the magnetic field never returns to the simple initial state mapping the photospheric flow. The formation of X and O points in the planes orthogonal to the axial field allows the continued and repeated formation and dissipation of small scale current sheets where the plasma is heated. We conclude that the observed turbulent dynamics are not induced by the complexity of the pattern that the magnetic field-lines footpoints follow but they rather stem from the inherent nonlinear nature of the system.