Lateral Confinement and the Remarkably Self-similar Nature of Coronal Pseudostreamer Mass Ejections

Abstract

Coronal mass ejections (CMEs) that originate from pseudostreamers, which separate coronal holes of the same magnetic polarity, are characterized by a narrow (∼5°–30°), fan-shaped appearance in white-light coronagraph images. Despite this striking morphological similarity, a wide variety of underlying eruptions are observed, including not only coronal jets, but also larger-scale filament eruptions, footpoint flares, and even extreme-ultraviolet (EUV) waves that reflect off the coronal hole boundaries. Using EUV images recorded by the Solar Dynamics Observatory during the early rising phase of cycle 25 (2020–2022), we describe examples of the different kinds of underlying eruptions and identify the corresponding fan-like ejections in Large Angle and Spectrometric Coronagraph images. We attribute the narrowness of the white-light CMEs to lateral confinement by the like-polarity open flux surrounding the pseudostreamer and point out that, although the multipolar topology facilitates the “breakout” of material through the cusp region, it also tends to inhibit the eruption of the pseudostreamer as a whole. We also note that the self-similar “continuum” formed by the pseudostreamer mass ejections does not include the larger, more space-weather-effective CMEs associated with helmet streamers, which are surrounded by open flux of opposite polarity and undergo much greater lateral expansion.