Magnetic helicity and energy of emerging solar active regions and their erruptivity

TL;DR

This study analyzes how the accumulation of magnetic helicity and energy in emerging solar active regions influences their likelihood to produce coronal mass ejections, identifying thresholds that predict eruptions.

Contribution

It introduces a combined analysis of magnetic helicity and energy budgets to predict CME eruptions in emerging active regions, highlighting their joint importance.

Findings

Eruptive ARs accumulate larger magnetic helicity and energy than noneruptive ones.

Thresholds of $9 imes 10^{41}$ Mx$^2$ for helicity and $2 imes 10^{32}$ erg for energy predict eruptions.

Decay index analysis suggests overlying magnetic fields can suppress eruptions despite high helicity and energy.

Abstract

Aims. We investigate the role of the accumulation of both magnetic helicity and magnetic energy in the generation of coronal mass ejections (CMEs) from emerging solar active regions (ARs). Methods. Using vector magnetic field data obtained by the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we calculate the magnetic helicity and magnetic energy injection rates as well as the resulting accumulated budgets in 52 emerging ARs from the start time of magnetic flux emergence until they reach heliographic longitude of 45$^{\circ}$ West (W45). Results. Seven of the ARs produced CMEs while 45 did not. In a statistical sense, the eruptive ARs accumulate larger budgets of both magnetic helicity and energy than the noneruptive ones over intervals that start from flux emergence start time and end (i) at the end of flux emergence phase, and (ii) when the AR produces its first CME or crosses W45, whichever happens first. We found magnetic helicity and energy thresholds of $9 \times 10^{41}$ Mx$^2$ and $2 \times 10^{32}$ erg, respectively, which, if crossed, ARs are likely to erupt. The segregation, in terms of accumulated magnetic helicity and energy budgets, of the eruptive ARs from the noneruptive ones is violated in one case when an AR erupts early in its emergence phase and in six cases with noneruptive ARs exhibiting large magnetic helicity and energy budgets. Decay index calculations may indicate that these ARs did not erupt because the overlying magnetic field provided stronger or more extended confinement than in eruptive ARs. Conclusions. Our results indicate that emerging ARs tend to produce CMEs when they accumulate significant budgets of both magnetic helicity and energy. Any study of their eruptive potential should place magnetic helicity on equal footing with magnetic energy.