Coronal Mass Ejections Deflected by Newly Emerging Flux: A Combined Analytic and Numerical Study

TL;DR

This work addresses how newly emerging flux (NEF) near filaments influences both initiation and early propagation of solar eruptions. It combines an analytic catastrophe-theory model of a flux rope with a background field and a NEF dipole, with 2D resistive MHD simulations that use critical states as initial conditions. NEF reshapes coronal stability by creating or eliminating a higher equilibrium, enabling either failed eruptions or CMEs, and its asymmetry deflects eruptions away from radial directions, characterized by two predictor angles that are reproduced by the simulations. These findings advance understanding of NEF as a dual trigger and deflection agent, with implications for forecasting CME trajectories and onset timing in space weather. The study demonstrates a robust framework bridging quasi-static energy landscapes and dynamic eruption evolution in the low corona.

Abstract

Newly emerging flux (NEF) has been widely studied as a trigger of solar filament eruptions, but its influence on the subsequent dynamics remains poorly explored. Because NEF typically emerges adjacent to filaments, it imposes magnetic asymmetry that can drive non-radial eruptions and complicate space-weather forecasting. We bridge analytic catastrophe theory with 2D resistive MHD simulations: analytic solutions provide magnetic configurations containing a flux rope at the loss-of-equilibrium point, which are then used as initial conditions for simulations to examine the following dynamics. We find that NEF governs the kinematics of filament eruptions in two ways. First, by reshaping coronal stability, NEF can create or eliminate a higher equilibrium in corona, thereby producing failed eruptions or CMEs. In the transitional situation where a metastable equilibrium appears, the rising filament decelerates and stalls before re-accelerating into a CME, consistent with observed two-step eruptions. Second, by breaking symmetry, NEF deflects eruptions away from the radial direction: depending on its polarity, it acts as a repulsor or an attractor on eruptive filaments, and the deflection magnitude increases with the degree of asymmetry. Our theory yields two characteristic angles that predict the deflection directions of CMEs and failed eruptions, and simulations closely aligns with these predictors. These results highlight the NEF not only as a trigger but also as a key factor that governs both the acceleration and deflection of eruptions during their propagation in the low corona.

Figures (2)

• Figure 1: Schematic of the magnetic configuration produced by four components: the flux rope, the image of the flux rope, dipole 1 to generate the unchanged background field, and dipole 2 to model the NEF. The deflection angle $\theta$ is the angle between the CME direction and the solar radial direction. By convention, $-90^{\circ}<\theta<0$ when the CME deviates clockwise from the radial direction, and $0<\theta<90^{\circ}$ when it deviates counterclockwise. Since we only consider outward propagation ($v_y>0$), $\theta$ is restricted to $(-90^{\circ},\,90^{\circ})$, eliminating any $180^{\circ}$ ambiguity. This figure is reproduced from 2024ApJ...977L..26C
• Figure 2: Equilibrium evolution as the NEF strength $S$ increases quasi-statically given $y_d=2.5$ and $r_{00}=0.05$. From left to right, the columns show cases with the NEF fixed at $x_d=4$, $4.704$, and $7$. The top row plots the horizontal equilibrium position $x_h(S)$; the bottom row plots the height $y_h(S)$. Black curves are equilibrium branches. Dots denote the critical points where catastrophe occurs: purple for $S^*<0$ and orange for $S^*>0$. Orange stars mark a second equilibrium that may be reached after the loss of the original equilibrium at the same $S^*$; the orange dashed line indicates $S=S^*$. Insets in bottom panels illustrate the magnetic configuration at the corresponding critical states; border colors match that for critical points. These critical configurations are used as the initial conditions for following MHD simulations.