Investigation on the Predictive Potentiality of Photospheric Magnetic Parameters for Distinguishing Confined from Eruptive Solar Flares

TL;DR

The paper addresses predicting whether a solar flare will be eruptive or confined using pre-flare photospheric magnetic properties. It analyzes 277 flares (GOES M1.0+, 2010–2023) within $45^\circ$ of disk center, using SHARP vector magnetograms to compute AR-wide and PIL-focused parameters, including the total unsigned flux $Φ$, AR-wide free energy $E_f$, centroid distance $d$, and PIL shear $Θ$, among HiFER-related metrics. Nonparametric statistics show that $Φ$, $E_f$, $d$, and $Θ$ have medium discriminative power between eruptive and confined events, with $Φ$ showing the strongest association and a strong $Φ$–$E_f$ coupling ($r_s ≈ 0.87$). In a subset of 77 events with high-gradient PILs, the area of HiFERs $A_{Hi}$ emerges as the most effective predictor, indicating confinement when HiFERs cover larger areas. The results support a core–cage framework where overlying confinement (reflected in $Φ$, $E_f$, and $d$) and core non-potentiality ($Θ$) regulate eruptive potential, with practical implications for CME forecasting from pre-flare AR properties.

Abstract

A question often arises as to why some solar flares are confined in the lower corona while others, termed eruptive flares, are associated with coronal mass ejections (CMEs). Here we intend to rank the importance of pre-flare magnetic parameters of active regions in their potentiality to predict whether an imminent flare will be eruptive or confined. We compiled a dataset comprising 277 solar flares of GOES-class M1.0 and above, taking place within 45 deg from the disk center between 2010 and 2023, involving 94 active regions. Among the 277 flares, 135 are confined and 142 are eruptive. Our statistical analysis reveals that the magnetic parameters that are most relevant to the flare category are: total unsigned magnetic flux $Φ$, mean magnetic shear angle $Θ$ along the polarity inversion line (PIL), photospheric free magnetic energy $E_f$, and centroid distance $d$ between opposite polarities. These four parameters are not independent of each other, but in combination, might be promising in distinguishing confined from eruptive flares. For a subset of 77 flares with high-gradient PILs, the area of high free energy regions ($A_{\mathrm{Hi}}$) becomes the most effective parameter related to the flare type, with confined flares possessing larger $A_{\mathrm{Hi}}$ than eruptive ones. Our results corroborate the general concept that the eruptive behavior of solar flares is regulated by an interplay between the constraining overlying flux, which is often dominant in both $Φ$ and $E_f$ and related to $d$, and the current-carrying core flux, which is related to $Θ$.

Figures (5)

• Figure 1: Overview of the solar flare events. Red (blue) dots mark the eruptive (confined) events, which are bracketed by the $45^\circ$ range from the central meridian. A list of the events and corresponding magnetic parameters is available online.
• Figure 2: Example of the calculation results of all the parameters in AR 12192 (first column) and AR 12673 (second column). The top row shows the magnetograms of ARs. Red dots and dashed lines indicate the flux weighted centers and centroid distance. Orange color indicates the PIL regions and blue color outlines the HiFERs. The middle row shows the maps of $J_Z$. Magenta color indicates the negative $J_z$ while green color represents positive $J_z$. The last row shows the maps of the magnetic shear. The regions where the absolute value of magnetic field weaker than 150 $\mathrm{G}$ are shown in white.
• Figure 3: Distribution of the physical parameters for all the events. The red bars represent eruptive flares and the blue bars represent the confined flares. The overlapping portion is shown in deep brownish red. The dotted lines indicate the mean values of the parameters for eruptive flares (red) and confined flares (blue).
• Figure 4: Correlation matrix showing Spearman correlation coefficient between different physical parameters for all the flares investigated. The correlation coefficients between $\Phi$, $E_\mathrm{f}$, $d$, and $\Theta$ are highlighted by red bounding boxes.
• Figure 5: Distribution of the physical parameters for a subset of flares with high-gradient PILs. The red bars represent eruptive flares and the blue bars the confined flares. The overlapping portion is shown in deep brownish red. The dotted lines indicate the medians of the parameters for eruptive flares (red) and confined flares (blue).