Estimating the rate of field line braiding in the solar corona by photospheric flows

TL;DR

This study investigates how photospheric motions braid coronal magnetic field lines, using simulations and observations, to understand the timescale of magnetic complexity development relevant to coronal heating.

Contribution

It compares topological complexity induced by magneto-convection simulations and observed photospheric flows, providing insights into the braiding timescale in the solar corona.

Findings

Simulations show high field line winding and entropy, indicating rapid braiding.

Observed flows produce significantly less topological complexity.

Photospheric motions can induce complex tangling within hours.

Abstract

In this paper we seek to understand the timescale on which the photospheric motions on the Sun braid coronal magnetic field lines. This is a crucial ingredient for determining the viability of the braiding mechanism for explaining the high temperatures observed in the corona. We study the topological complexity induced in the coronal magnetic field, primarily using plasma motions extracted from magneto-convection simulations. This topological complexity is quantified using the field line winding, finite time topological entropy and passive scalar mixing. With these measures we contrast mixing efficiencies of the magneto-convection simulation, a benchmark flow known as a ``blinking vortex', and finally photospheric flows inferred from sequences of observed magnetograms using local correlation tracking. While the highly resolved magneto-convection simulations induce a strong degree of field line winding and finite time topological entropy, the values obtained from the observations from the plage region are around an order of magnitude smaller. This behavior is carried over to the finite time topological entropy. Nevertheless, the results suggest that the photospheric motions induce complex tangling of the coronal field on a timescale of hours.