Survey of Magnetic Field Parameters Associated With Large Solar Flares (2402.18890v1)

Abstract: Until now, how the magnetic fields in M/X-class flaring active regions (ARs) differ from C-class flaring ARs remains unclear. Here, we calculate the key magnetic field parameters within the area of high photospheric free energy density (HED region) for 323 ARs (217 C- and 106 M$/$X-flaring ARs), including total photospheric free magnetic energy density E${free}$, total unsigned magnetic flux $\Phi$${HED}$, mean unsigned current helicity h${c}$, length of the polarity inversion lines $L$${PIL}$ with a steep horizontal magnetic gradient, etc., and compare these with flare/coronal mass ejection (CME) properties. We first show the quantitative relations among the flare intensity, the eruptive character and $\Phi$${HED}$. We reveal that $\Phi$${HED}$ is a measure for the GOES flux upper limit of the flares in a given region. For a given $\Phi$${HED}$, there exists the lower limit of F$\mathrm{SXR}$ for eruptive flares. This means that only the relatively strong flares with the large fraction of energy release compared to the total free energy are likely to generate a CME. We also find that the combinations of E${free}$-$L$${PIL}$ and E${free}$-h${c}$ present a good ability to distinguish between C-class and M$/$X-class flaring ARs. Using determined critical values of E${free}$ and $L$${PIL}$, one predicts correctly 93 out of 106 M/X-class flaring ARs and 159/217 C-class flaring ARs. The large $L$${PIL}$ or h${c}$ for M$/$X-class flaring ARs probably implies the presence of a compact current with twisted magnetic fields winding about it.