On field line slippage rates in the solar corona

TL;DR

This paper introduces a local approach to studying magnetic reconnection in the solar corona, linking field line slippage rates to local magnetic field geometry and non-ideal effects, providing a new perspective beyond traditional non-local methods.

Contribution

It presents a novel local description of magnetic reconnection that depends only on local quantities, connecting field line slippage to the magnetic field's local geometry and non-ideal effects.

Findings

The local description relates slippage rates to local magnetic field geometry.

The approach is mathematically equivalent to anomalous resistivity in MHD simulations.

Illustrated with models of flux ropes, showing practical application.

Abstract

Magnetic reconnection is one of the fundamental dynamical processes in the solar corona. The method of studying reconnection in active region-scale magnetic fields generally depends on non-local methods (i.e. requiring information across the magnetic field under study) of magnetic topology, such as separatrix skeletons and quasi-separatrix layers. The theory of General Magnetic Reconnection is also non-local, in that its measure of the reconnection rate depends on determining the maxima of integrals along field lines. In this work, we complement the above approaches by introducing a local description of magnetic reconnection, that is one in which information about reconnection at a particular location depends only on quantities at that location. This description connects the concept of the field line slippage rate, relative to ideal motion, to the underlying local geometry of the magnetic field characterized in terms of the Lorentz force and field-aligned current density. It is argued that the dominant non-ideal term for the solar corona, discussed in relation to this new description, is mathematically equivalent to the anomalous resistivity employed by many magnetohrdrodynamic simulations. However, the general application of this new approach is adaptable to the inclusion of other non-ideal terms, which may arise from turbulence modelling or the inclusion of a generalized Ohm's law. The approach is illustrated with two examples of coronal magnetic fields related to flux ropes: an analytical model and a nonlinear force-free extrapolation. In terms of the latter, the slippage rate corresponds to the reconnection which would happen if the given (static) force-free equilibrium were the instantaneous form of the magnetic field governed by an Ohm's law with non-ideal terms.