The Magnetic Environment of a Stealth Coronal Mass Ejection

TL;DR

This study investigates the magnetic environment of a stealth CME, revealing that magnetic reconnection at a null point facilitates its eruption despite weak observational signatures.

Contribution

The paper provides the first detailed magnetic field analysis of a stealth CME, demonstrating the role of a coronal null point in its eruption mechanism.

Findings

Evidence of a coronal null point connecting the source region to other active regions.

Magnetic reconnection at the null point aids the CME eruption.

Stealth CMEs share similar eruption mechanisms with typical CMEs.

Abstract

Interest in stealth coronal mass ejections (CMEs) is increasing due to their relatively high occurrence rate and space weather impact. However, typical CME signatures such as extreme-ultraviolet dimmings and post-eruptive arcades are hard to identify and require extensive image processing techniques. These weak observational signatures mean that little is currently understood about the physics of these events. We present an extensive study of the magnetic field configuration in which the stealth CME of 3 March 2011 occurred. Three distinct episodes of flare ribbon formation are observed in the stealth CME source active region (AR). Two occurred prior to the eruption and suggest the occurrence of magnetic reconnection that builds the structure which will become eruptive. The third occurs in a time close to the eruption of a cavity that is observed in STEREO-B 171A data; this subsequently becomes part of the propagating CME observed in coronagraph data. We use both local (Cartesian) and global (spherical) models of the coronal magnetic field, which are complemented and verified by the observational analysis. We find evidence of a coronal null point, with field lines computed from its neighbourhood connecting the stealth CME source region to two ARs in the northern hemisphere. We conclude that reconnection at the null point aids the eruption of the stealth CME by removing field that acted to stabilise the pre-eruptive structure. This stealth CME, despite its weak signatures, has the main characteristics of other CMEs, and its eruption is driven by similar mechanisms.