Magnetic Properties of Solar Active Regions that Govern Large Solar Flares and Eruptions

TL;DR

This study analyzes magnetic properties of solar active regions to understand their role in large flares and eruptions, revealing key parameters that influence CME occurrence and potential for superflares.

Contribution

It systematically surveys flare events and identifies magnetic and structural parameters that govern flare and CME productivity, challenging previous assumptions about necessary conditions.

Findings

Ribbons' area normalized by sunspot area predicts CME eruption.

Even X-class flares can occur without delta-sunspots.

Largest ARs may produce superflares with energies around 10^34 erg.

Abstract

Solar flares and coronal mass ejections (CMEs), especially the larger ones, emanate from active regions (ARs). With the aim to understand the magnetic properties that govern such flares and eruptions, we systematically survey all flare events with GOES levels of >=M5.0 within 45 deg from disk center between May 2010 and April 2016. These criteria lead to a total of 51 flares from 29 ARs, for which we analyze the observational data obtained by the Solar Dynamics Observatory. More than 80% of the 29 ARs are found to exhibit delta-sunspots and at least three ARs violate Hale's polarity rule. The flare durations are approximately proportional to the distance between the two flare ribbons, to the total magnetic flux inside the ribbons, and to the ribbon area. From our study, one of the parameters that clearly determine whether a given flare event is CME-eruptive or not is the ribbon area normalized by the sunspot area, which may indicate that the structural relationship between the flaring region and the entire AR controls CME productivity. AR characterization show that even X-class events do not require delta-sunspots or strong-field, high-gradient polarity inversion lines. An investigation of historical observational data suggests the possibility that the largest solar ARs, with magnetic flux of 2x10^23 Mx, might be able to produce "superflares" with energies of order of 10^34 erg. The proportionality between the flare durations and magnetic energies is consistent with stellar flare observations, suggesting a common physical background for solar and stellar flares.