  Flare productivity varies among solar active regions (ARs). This study
analyzed 20 ARs of contrasting sunspot areas and flare productivities to
understand the super flare productivity of certain ARs. We used the flare index
(FI) as an indicator of flare activity. We examined the pattern of
morphological evolution of magnetic features. Further, we derived a set of
magnetic feature parameters to quantitatively characterize ARs. Our study found
that the correlation coefficient is the highest (r = 0.78) between FI and the
length of the strong gradient polarity inversion line (SgPIL), while the
coefficient is the lowest (r = 0.14) between FI and the total unsigned magnetic
flux. For the selected ARs, this study also found that the super flare
productive ARs have SgPILs (R value) longer (greater) than 50 Mm (4.5). These
results suggest that flare productivity is mainly controlled by the size of the
subregion that comprises close interaction of opposite magnetic polarities and
is weakly correlated with the size of the whole ARs. Further, even though
magnetic flux emergence is important, this study shows that it alone is
insufficient to increase flare productivity. New emergence can drive either the
interaction of like or opposite magnetic polarities of nonconjugate pairs
(i.e., polarities not from the same bipole). In the former case, the magnetic
configuration remains simple, and flare productivity would be low. In the
latter case, the convergence of opposite magnetic fluxes of nonconjugate pairs
results in a magnetic configuration with long SgPIL and an increase in flare
productivity.
