MHD Modeling for Formation Process of Coronal Mass Ejections: Interaction between Ejecting Flux Rope and Ambient Field

TL;DR

This study uses MHD simulations to explore how the interaction between an ejecting flux rope and ambient magnetic fields influences the formation, orientation, and rotation of coronal mass ejections, highlighting the importance of magnetic reconnection.

Contribution

It introduces a detailed simulation analysis of CME formation considering different ambient magnetic field configurations and identifies key parameters affecting CME evolution.

Findings

Flux rope disappears in anti-parallel ambient field case.

Flux ropes evolve into CMEs with varying rotation in other cases.

Magnetic flux and reconnection are crucial for CME formation and orientation.

Abstract

We performed magnetohydrodynamic simulation of a formation process of coronal mass ejections (CMEs), focusing on interaction (reconnection) between an ejecting flux rope and its ambient field. We examined three cases with different ambient fields: no ambient field, and cases with dipole field of two opposite directions which are parallel and anti-parallel to that of the flux rope surface. As a result, while the flux rope disappears in the anti-parallel case, in other cases the flux ropes can evolve to CMEs and show different amounts of rotation of the flux rope. The results imply that the interaction between an ejecting flux rope and its ambient field is an important process for determining CME formation and CME orientation, and also show that the amount and direction of magnetic flux within the flux rope and the ambient field are key parameters for CME formation. Especially, the interaction (reconnection) plays a significant role to the rotation of the flux rope, with a process similar to "tilting instability" in a spheromak-type experiment of laboratory plasma.