What Determines the Intensity of Solar Flare/CME Events?

Abstract

We present a comprehensive statistical study addressing the question of what determines the intensity of a solar flare and associated coronal mass ejection (CME). For a sample of 18 two-ribbon flares associated with CMEs, we have examined the correlations between the GOES soft X-ray peak flare flux (PFF), the CME speed (V_CME) obtained from SOHO LASCO observations, and six magnetic parameters of the flaring active region. These six parameters measured from both TRACE and SOHO MDI observations are: the average background magnetic field strength (B), the area of the region where B is counted (S), the magnetic flux of this region (Φ), the initial shear angle (θ₁, measured at the flare onset), the final shear angle (θ₂, measured at the time when the shear change stops), and the change of shear angle (θ₁₂=θ₁-θ₂) of the footpoints. We have found no correlation between θ₁ and the intensity of flare/CME events, while the other five parameters are either positively or negatively correlated with both log10(PFF) and V_CME. Among these five parameters, Φ and θ₁₂ show the most significant correlations with log10(PFF) and V_CME. The fact that both log10(PFF) and V_CME are highly correlated with θ₁₂ rather than with θ₁ indicates that the intensity of flare/CME events may depend on the released magnetic free energy rather than the total free energy stored prior to the flare. We have also found that a linear combination of a subset of these six parameters shows a much better correlation with the intensity of flare/CME events than each parameter itself, and the combination of log10Φ, θ₁, and θ₁₂ is the top-ranked combination.