Determining whether the squashing factor, Q, would be a good indicator of reconnection in a resistive MHD experiment devoid of null points

¹ School of Mathematics and Statistics, University of St Andrews, St Andrews, Fife KY16 9SS, UK
e-mail: jr93@st-andrews.ac.uk, cep@st-andrews.ac.uk
² Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK

Received: 2 October 2019
Accepted: 21 November 2019

Abstract

The squashing factor of a magnetic field, Q, is commonly used as an indicator of magnetic reconnection, but few studies seek to evaluate how reliable it is in comparison with other possible reconnection indicators. By using a full, self-consistent, three-dimensional, resistive magnetohydrodynamic experiment of interacting magnetic strands constituting a coronal loop, Q and several different quantities are determined. Each is then compared with the necessary and sufficient condition for reconnection, namely the integral along a field line of the component of the electric field parallel to the magnetic field. Among the reconnection indicators explored, we find the squashing factor less successful when compared with alternatives, such as Ohmic heating. In a reconnecting magnetic field devoid of null points, our work suggests that Q, being a geometric measure of the magnetic field, is not a reliable indicator of the onset or a diagnostic of the location of magnetic reconnection in some configurations.