Understanding how magnetic properties of solar active regions influence coronal mass ejection (CME) dynamics is essential for constraining eruption models and improving space-weather prediction. In this work, we investigate the relationship between magnetic field diagnostics derived from potential-field extrapolations and the 3D speeds of CMEs.
We focus on physically motivated parameters associated with eruption onset, including the critical height of torus instability (hcrit), the strength of the overlying magnetic field strength (Bt), and the flare ribbon flux (Rf). While hcrit and Bt are traditionally evaluated directly above polarity inversion lines (PILs), ; however, identifying PILs can involve threshold-dependent and partially manual selection procedures. To reduce this dependency, we test whether these diagnostics retain predictive power when computed over broader regions of interest (ROIs) within the active region, without relying on explicit PIL selection.
Using decay index profiles derived from photospheric magnetograms, we find a strong correlation between hcrit and CME speed (r ≈ 0.71). When evaluated over progressively larger ROIs centered on the PIL, weighted hcrit from the largest region considered provides the strongest correlation (r ≈ 0.73), indicating that the broader active-region field structure is as informative as measurements strictly above the PIL. In contrast, Bt shows weaker (r = 0.33) predictive capability, and combining it with hcrit offers only marginal improvement. Ribbon flux exhibits moderate correlation (r = 0.44) with CME speed, but the highest predictive power is consistently obtained when hcrit is included.
These results suggest that, within potential-field models, the critical height of torus instability is the dominant magnetic diagnostic of CME speed, and that the large-scale magnetic environment of active regions plays a key role in regulating eruption dynamics.
