Evolution of reconnection flux during eruption of magnetic flux ropes

TL;DR

This work addresses how reconnection flux evolves during the early evolution of magnetic flux ropes and its influence on CME speeds. It combines a fully compressible 3D MHD simulation, driven by quasi-static emergence of a twisted torus into a pre-existing coronal arcade, with observational validation from SDO/HMI/AIA and STEREO-A data, using the reconnection flux $\phi_{RC}=\int B_n\,dS=\int B_r\,dA$ as a key diagnostic. The study finds two homologous eruptions linked to recurrent current-sheet formation beneath the rising MFR, with reconnection flux rate correlating with CME acceleration both in simulation ($r$-values up to $0.81$) and in observation ($r$ up to $0.98$ after eruption). These results support a reconnection-driven picture of CME initiation and progression and highlight the predictive potential of reconnection flux dynamics for eruption speeds. The work advances solar eruption modeling by bridging 3D MHD simulations with multi-perspective observations, offering insights for space weather forecasting and CME physics.

Abstract

Coronal mass ejections (CMEs) are powerful drivers of space weather, with magnetic flux ropes (MFRs) widely regarded as their primary precursors. However, the variation in reconnection flux during the evolution of MFR during CME eruptions remains poorly understood. In this paper, we develop a realistic 3D magneto-hydrodynamic model using which we explore the temporal evolution of reconnection flux during the MFR evolution using both numerical simulations and observational data. Our initial coronal configuration features an isothermal atmosphere and a potential arcade magnetic field beneath which an MFR emerges at the lower boundary. As the MFR rises, we observe significant stretching and compression of the overlying magnetic field beneath it. Magnetic reconnection begins with the gradual formation of a current sheet, eventually culminating with the impulsive expulsion of the flux rope. We analyze the temporal evolution of reconnection fluxes during two successive MFR eruptions while continuously emerging the twisted flux rope through the lower boundary. We also conduct a similar analysis using observational data from the Helioseismic and Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) for an eruptive event. Comparing our MHD simulation with observational data, we find that reconnection flux play a crucial role in determination of CME speeds. From the onset to the eruption, the reconnection flux shows a strong linear correlation with the velocity. This nearly realistic simulation of a solar eruption provides important insights into the complex dynamics of CME initiation and progression.

Figures (10)

• Figure 1: The radiative cooling function in used in this work is a modified version of Cook1989
• Figure 2: The twisted torus before emerging through the bottom boundary. The major ($r$) and minor ($a$) radius of the torus is $0.25R_{\odot}$ and $0.042R_{\odot}$. The number of turns of one of the field lines is shown in black.
• Figure 3: The 3D evolution of the magnetic field of the twisted flux rope emerging into the corona at the specified times (in hours). Red field lines have footpoints in the ambient arcade, while blue (core), green (middle), and cyan (periphery) field lines originate from the emerging flux region at different distances from the flux rope axis. An animation of this evolution is available in the online article with a running time of 36 s. The period covered by the animation (in solar hours) spans from $t=19.65$ hrs to $t=40.25$ hrs from the start of the simulation. The flux rope starts emerging into the corona at $t=20.3$ hrs.
• Figure 4: Total kinetic energy $E_{kin}$ (red) and total magnetic energy $E_{mag}$ (blue) as a function of time. The dashed vertical line represents the time when the flux emergence stops.
• Figure 5: Identification of current sheet and field lines of the flux rope from different viewing angles. The current sheet (in white) traced from the temperature isosurface with a value $\log_{10} T = 6.6$ shown in panel (a). The height of the current sheet iso-surface (white) from lower boundary is about $1.4R_\odot$. The field lines passing through such sheets gives the reconnection flux. The sigmoid fieldlines are shown in panels (b) and (c). The time in all these panels are taken at $t=27.32$ hours.