Evidence for magnetic disconnection of mass ejections in the corona

Abstract

Coronal mass ejections (CMEs) involve the expulsion of significant amounts of mass and magnetic flux into the heliosphere, a process which implies an unobserved continuous buildup of the net interplanetary magnetic flux. Some form of disconnection of the flux near the Sun, either directly associated with the CME or occurring elsewhere in the corona, appears to be required to prevent this buildup. Field line reconnection in the wake of CMEs is also a fundamental aspect of some types of magnetically driven eruptive flare/CME models. However, to date there have been very few reports of CMEs which exhibited evidence for disconnection, despite the detection of several thousand CMEs over nearly 2 decades of observations. We report on the results of a systematic search for candidate magnetic disconnection features, defined as transient large‐scale, concave‐outward bright regions usually following the CME leading edge, using both ground‐based solar eclipse and spaceborne coronagraph data. We conclude that ≥ 10% of all CMEs observed in the corona have possible disconnection structures. We propose a simple classification scheme for these features based on their morphology. The most common type of candidate disconnection feature (65% of all the features) had a circular or ovoid shape; 35% of the features consisted of concave‐outward partial arcs. The average leading edge speed and latitudinal span of these CMEs were slightly less than those of typical CMEs. The results are discussed in the context of recent studies of magnetic disconnection and reconnection in the corona.