Tracing magnetic separators and their dependence on IMF clock angle in global magnetospheric simulations

TL;DR

This paper introduces a new, precise method for tracing magnetic separators in global magnetospheric simulations, demonstrating its accuracy across various IMF clock angles and comparing results with analytic models.

Contribution

The paper presents a novel, efficient technique for accurately tracing magnetic separators in complex simulations with arbitrary IMF orientations.

Findings

Separator tracing is accurate for all IMF clock angles.

Qualitative similarities and quantitative differences between models are identified.

Dependence of separators on solar wind density is briefly analyzed.

Abstract

A new, efficient, and highly accurate method for tracing magnetic separators in global magnetospheric simulations with arbitrary clock angle is presented. The technique is to begin at a magnetic null and iteratively march along the separator by finding where four magnetic topologies meet on a spherical surface. The technique is verified using exact solutions for separators resulting from an analytic magnetic field model that superposes dipolar and uniform magnetic fields. Global resistive magnetohydrodynamic simulations are performed using the three-dimensional BATS-R-US code with a uniform resistivity, in eight distinct simulations with interplanetary magnetic field (IMF) clock angles ranging from 0 (parallel) to 180 degrees (anti-parallel). Magnetic nulls and separators are found in the simulations, and it is shown that separators traced here are accurate for any clock angle, unlike the last closed field line on the Sun-Earth line that fails for southward IMF. Trends in magnetic null locations and the structure of magnetic separators as a function of clock angle are presented and compared with those from the analytic field model. There are many qualitative similarities between the two models, but quantitative differences are also noted. Dependence on solar wind density is briefly investigated.