A comparison of methods for finding magnetic nulls in simulations and in situ observations of space plasmas

TL;DR

This paper systematically compares methods for detecting magnetic nulls in space plasma data, evaluating their accuracy and reliability in simulations and in situ observations, and provides a benchmark configuration for testing null-finding algorithms.

Contribution

It introduces a benchmark magnetic field with known nulls and compares the effectiveness of Poincare index, FOTE, and trilinear methods across different data discretizations.

Findings

FOTE and trilinear are most reliable for spacecraft and grid data, respectively.

Poincare index works well on tetrahedral and hexahedral meshes.

The benchmark aids in evaluating and improving null detection techniques.

Abstract

Magnetic nulls are ubiquitous in space plasmas, and are of interest as sites of localized energy dissipation or magnetic reconnection. As such, a number of methods have been proposed for detecting nulls in both simulation data and in situ spacecraft data from Earth's magnetosphere. The same methods can be applied to detect stagnation points in flow fields. In this paper we describe a systematic comparison of different methods for finding magnetic nulls. The Poincare index method, the first-order Taylor expansion (FOTE) method, and the trilinear method are considered. We define a magnetic field containing fourteen magnetic nulls whose positions and types are known to arbitrary precision. Furthermore, we applied the selected techniques in order to find and classify those nulls. Two situations are considered: one in which the magnetic field is discretized on a rectangular grid, and the second in which the magnetic field is discretized along synthetic `spacecraft trajectories' within the domain. At present, FOTE and trilinear are the most reliable methods for finding nulls in the spacecraft data and in numerical simulations on Cartesian grids, respectively. The Poincare index method is suitable for simulations on both tetrahedral and hexahedral meshes. The proposed magnetic field configuration can be used for grading and benchmarking the new and existing tools for finding magnetic nulls and flow stagnation points.