A Model for Flux Rope Formation and Disconnection in Pseudostreamer Coronal Mass Ejections

TL;DR

This paper presents a magnetohydrodynamic simulation of pseudostreamer CMEs, revealing their formation, disconnection, and morphological evolution, and highlighting their similarities and differences with coronal jets and helmet-streamer CMEs.

Contribution

It introduces a detailed simulation model for pseudostreamer CMEs, showing their magnetic evolution and disconnection process, distinct from helmet-streamer CMEs.

Findings

Pseudostreamer CMEs involve breakout reconnection and flux rope instability.

Disconnection occurs via interchange reconnection, causing flux rope rotation.

Pseudostreamer CMEs share magnetic evolution features with coronal jets.

Abstract

Coronal mass ejections (CMEs) from pseudostreamers represent a significant fraction of large-scale eruptions from the Sun. In some cases, these CMEs take a narrow jet-like form reminiscent of coronal jets; in others, they have a much broader fan-shaped morphology like CMEs from helmet streamers. We present results from a magnetohydrodynamic simulation of a broad pseudostreamer CME. The early evolution of the eruption is initiated through a combination of breakout interchange reconnection at the overlying null point and ideal instability of the flux rope that forms within the pseudostreamer. This stage is characterised by a rolling motion and deflection of the flux rope toward the breakout current layer. The stretching out of the strapping field forms a flare current sheet below the flux rope; reconnection onset there forms low-lying flare arcade loops and the two-ribbon flare footprint. Once the CME flux rope breaches the rising breakout current layer, interchange reconnection with the external open field disconnects one leg from the Sun. This induces a whip-like rotation of the flux rope, generating the unstructured fan shape characteristic of pseudostreamer CMEs. Interchange reconnection behind the CME releases torsional Alfv\'en waves and bursty dense outflows into the solar wind. Our results demonstrate that pseudostreamer CMEs follow the same overall magnetic evolution as coronal jets, although they present different morphologies of their ejecta. We conclude that pseudostreamer CMEs should be considered a class of eruptions that are distinct from helmet-streamer CMEs, in agreement with previous observational studies.