Nonparametric Statistics on Magnetic Properties at the Footpoints of Erupting Magnetic Flux Ropes

TL;DR

This study applies nonparametric statistical tests to a larger sample of eruptive magnetic flux ropes to analyze their magnetic properties and current distributions, confirming some previous assumptions and highlighting the importance of current in eruption dynamics.

Contribution

It extends prior research by including additional events and rigorously tests magnetic properties, providing new statistical evidence on current neutrality and footpoint symmetry in eruptive MFRs.

Findings

No significant difference in magnetic properties between conjugated footpoints.

No significant difference between pre- and post-eruption dimming MFRs.

Medium association between net current and pre-eruption dimming.

Abstract

It is under debate whether the magnetic field in the solar atmosphere carries neutralized electric currents; particularly, whether a magnetic flux rope (MFR), which is considered the core structure of coronal mass ejections, carries neutralized electric currents. Recently Wang et al. (2023, ApJ, 943, 80) studied magnetic flux and electric current measured at the footpoints of 28 eruptive MFRs from 2010 to 2015. Because of the small sample size, no rigorous statistics has been done. Here, we include 9 more events from 2016 to 2023 and perform a series of nonparametric statistical tests at a significance level of 5\%. The tests confirm that there exist no significant differences in magnetic properties between conjugated footpoints of the same MFR, which justifies the method of identifying the MFR footpoints through coronal dimming. The tests demonstrate that there exist no significant differences between MFRs with pre-eruption dimming and those with only post-eruption dimming. However, there is a medium level of association between MFRs carrying substantial net current and those produce pre-eruption dimming, which can be understood by the Lorentz-self force of the current channel. The tests also suggest that in estimating the magnetic twist of MFRs, it is necessary to take into account the spatially inhomogeneous distribution of electric current density and magnetic field.