Flux rope formation through flux cancellation of sheared coronal arcades in a 3D convectively driven MHD simulation

¹ Rosseland Centre for Solar Physics, University of Oslo PO Box 1029 Blindern 0315 Oslo, Norway
² Institute of Theoretical Astrophysics, University of Oslo PO Box 1029 Blindern 0315 Oslo, Norway
³ Sorbonne Université, Observatoire de Paris-PSL, École Polytechnique, IP Paris, CNRS, Laboratoire de Physique des Plasmas Paris, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 24 February 2025
Accepted: 19 December 2025

Abstract

Context. Space weather and its potential negative consequences for life on Earth have received increasing scientific attention in recent decades. In particular, predicting the onset of coronal mass ejections (CMEs) has become important from a security perspective. To predict CMEs, one must first understand the dynamics leading to preeruptive magnetic field configurations, which in many theories include a flux rope.

Aims. In this study, we investigate the realistic formation of coronal flux ropes above the solar photosphere. The aim is to find out if and how flux ropes can form there, and how the formation is related to flux cancellation at the photosphere. Previously, such formation has been shown in smooth boundary-driven line-tied simulations and in idealized non-convective and symmetric flux-emergence simulations.

Methods. We ran a convective nonsymmetric 3D radiative magnetohydrodynamic (MHD) simulation with the code Bifrost. Within the simulation box of 24 Mm × 24 Mm horizontal extent, a linear force-free field with sheared coronal arcades was slowly inserted. Following the insertion, the self-consistent stochastic plasma flows of the convection zone drove several small-scale flux cancellations and magnetic reconnection, without external influence. Lagrangian markers called corks were used to track the dynamic evolution of the magnetic field.

Results. Over a period of 2.5 h, a flux rope was generated with photospheric footpoints separated by up to 12 Mm. The flux rope was gradually formed through several individual events, such as slipping reconnection, U-loop emergence, and thick-photosphere tether-cutting reconnection.

Conclusions. Flux ropes, which can lead to CMEs, can be formed in the solar atmosphere solely driven by convection and flux cancellations at the photosphere. However, not all flux cancellations contribute to the buildup of the flux rope, and some coronal reconnection events that do are not clearly related to flux cancellation. The formation process of flux ropes from coronal sheared arcades driven by convection is therefore more complex than in the original smooth flux cancellation model. However, the end result is qualitatively the same. Flux cancellation works. A flux rope is formed.