Data-driven Magnetohydrodynamic Simulation of the Initiation of a Coronal Mass Ejection with Multiple Stages

Coronal mass ejections (CMEs) are the primary drivers of adverse space-weather events, yet their initiation and onset prediction remain insufficiently understood due to the complexity of the magnetic topology and physical processes in real solar source regions. Here, based on fully observational-data-driven magnetohydrodynamic simulation, we successfully reproduce the initiation of a CME originating from the super active region AR 13663, with only a one-minute time lag between the flare peak in observations and the velocity peak of the rising flux rope in the simulation. Moreover, the eruptive structure exhibits a multi-stage kinematic evolution: an initial slow acceleration, a plateau at a nearly stationary height, and a subsequent impulsive acceleration. These stages correspond to torus instability, the downward tension force exerted by the overlying toroidal field, and fast magnetic reconnection, respectively. Our results highlight the inherently multistage nature of CME initiation in real events. In configurations with strong overlying toroidal fields, the downward toroidal-field-induced tension force can suppress the rise of the flux rope and produce a plateau phase at a nearly stable height, even when torus instability occurs. In contrast, the subsequent fast magnetic reconnection beneath the flux rope can drive the impulsive eruption more effectively. The close agreement between the observed and simulated peak times over one minute demonstrates the strong potential of our data-driven model for predicting CME onset.

💡 Research Summary

This paper presents a fully observational data‑driven magnetohydrodynamic (MHD) simulation of the coronal mass ejection (CME) associated with the X1.3 flare on 2024 May 5 in NOAA active region (AR) 13663. The authors use vector magnetic field data from SDO/HMI, EUV images from SDO/AIA, and flare ribbon observations to initialise a three‑dimensional MHD model. Photospheric flows (shearing, converging, flux emergence) are imposed at the lower boundary in real time, allowing the magnetic configuration to evolve under realistic driving conditions.

The simulation reproduces the formation of a twisted flux rope around 04:46 UT, its slow rise, and the subsequent eruption. Three distinct kinematic phases are identified:

1. Initial slow acceleration (≈04:30–04:56 UT) – The first acceleration coincides with a confined C8.4 flare and is linked to reconnection within a fan–spine topology above sheared arcades. This early reconnection lifts the nascent flux rope and adds twist.

2. Plateau phase (≈05:04–05:36 UT) – After the flux rope reaches a height of ~30–35 Mm, its upward motion stalls despite the presence of torus instability (the poloidal‑field decay index nₚ reaches ~1.5). The authors demonstrate that a strong overlying toroidal magnetic field (Bₓ) produces a negative toroidal‑field decay index nₜ, generating a downward tension force that counteracts the torus‑driven lift. This explains the observed “flat” segment in the height‑time profile, a feature not seen in idealised bipolar simulations.

3. Impulsive acceleration (≈05:40–05:46 UT) – The final rapid acceleration is triggered by fast magnetic reconnection beneath the flux rope, evidenced by a sharp increase in the maximum current‑to‑magnetic‑field ratio (J/B) in the current sheet. The reconnection releases magnetic energy, propelling the flux rope to a peak speed that is about 3.5 times larger than the earlier peak.

Crucially, the simulated velocity peak occurs within one minute of the observed X‑ray flare peak, demonstrating that the data‑driven model can predict CME onset timing with unprecedented accuracy. The study highlights that CME initiation in realistic active regions is inherently multistage: torus instability may start the rise, but the overlying toroidal field can temporarily suppress eruption, and fast reconnection ultimately drives the impulsive phase.

The authors argue that the presence of a strong toroidal overlying field fundamentally alters the eruption pathway, implying that CME forecasting must consider not only the decay of the poloidal field (traditional torus‑instability criterion) but also the behavior of the toroidal component. Their findings reconcile observations of multi‑stage CME kinematics with theoretical models and suggest that data‑driven MHD simulations are a powerful tool for both scientific investigation and operational space‑weather prediction.