A Study of a Compound Solar Eruption with Two Consecutive Erupting Magnetic Structures

TL;DR

This paper investigates a complex solar eruption involving two magnetic structures in a double-decker configuration, revealing how their successive destabilization leads to a compound eruption and a merged coronal mass ejection.

Contribution

It presents the first detailed analysis of a double-decker magnetic structure eruption, linking magnetic configuration and eruption dynamics in a solar active region.

Findings

High-lying magnetic structure erupted first as a hot channel.

Low-lying structure erupted 12 minutes later at higher speed.

The two structures interacted and merged into a single CME.

Abstract

We report a study of a compound solar eruption that was associated with two consecutively erupting magnetic structures and correspondingly two distinct peaks, during impulsive phase, of an M-class flare (M8.5). Simultaneous multi-viewpoint observations from $\textit{SDO}$, $\textit{GOES}$ and $\textit{STEREO-A}$ show that this compound eruption originated from two pre-existing sigmoidal magnetic structures lying along the same polarity inversion line. Observations of the associated pre-existing filaments further show that these magnetic structures are lying one on top of the other, separated by 12 Mm in height, in a so-called "double-decker" configuration. The high-lying magnetic structure became unstable and erupted first, appearing as an expanding hot channel seen at extreme ultraviolet wavelengths. About 12 minutes later, the low-lying structure also started to erupt and moved at an even faster speed compared to the high-lying one. As a result, the two erupting structures interacted and merged with each other, appearing as a single coronal mass ejection in the outer corona. We find that the double-decker configuration is likely caused by the persistent shearing motion and flux cancellation along the source active region's strong-gradient polarity inversion line. The successive destabilization of these two separate but closely spaced magnetic structures, possibly in the form of magnetic flux ropes, led to a compound solar eruption. The study of the compound eruption provides a unique opportunity to reveal the formation process, initiation, and evolution of complex eruptive structures in solar active regions.