Quantifying Gyrotropy in Magnetic Reconnection

TL;DR

This paper introduces a new scalar measure of gyrotropy in magnetic reconnection, demonstrating its effectiveness over previous measures through simulations and providing a method for its calculation from spacecraft data.

Contribution

A novel scalar gyrotropy measure is proposed, shown to be more complete and physically consistent than existing measures, with applications to spacecraft data analysis.

Findings

The new measure peaks at separatrices and X-points in simulations.

Previous measures can give unphysical results in some cases.

The method for calculating the measure from arbitrary coordinate systems is derived.

Abstract

A new scalar measure of the gyrotropy of a pressure tensor is defined. Previously suggested measures are shown to be incomplete by means of examples for which they give unphysical results. To demonstrate its usefulness as an indicator of magnetic topology, the new measure is calculated for electron data taken from numerical simulations of magnetic reconnection, shown to peak at separatrices and X-points, and compared to the other measures. The new diagnostic has potential uses in analyzing spacecraft observations and so a method for calculating it from measurements performed in an arbitrary coordinate system is derived.