On the state of a solar active region before flares and CMEs

Several attempts have been made to find reliable diagnostic tools to determine the state prior to flares and related coronal mass ejections (CMEs) in solar active regions (ARs). Characterization of the level of mixed states is carried out using the Debrecen sunspot Data for 116 flaring ARs. Conditional flare probabilities (CFPs) are calculated for different flaring classes. The association with slow/fast CMEs is examined. Two precursor parameters are introduced: (i) the sum of the (daily averaged) horizontal magnetic gradient G _S (G _DS) and (ii) the separation parameter $S_{l-f}$. We found that if $S_{l-f}⩽1$ for a flaring AR then the CFP of the expected highest-intensity flare being X-class is more than 70%. If $1⩽S_{l-f}⩽3$ the CFP is more than 45% for the highest-intensity flare(s) to be M-class, and if $3⩽S_{l-f}⩽13$ there is larger than 60% CFP that C-class flare(s) may have the strongest intensity within 48 hr. Next, from analyzing G _S for determining CFP we found: if $5.5⩽log\left(G_S\right)⩽$6.5, then it is very likely that C-class flare(s) may be the most intense; if $6.5⩽log\left(G_S\right)⩽7.5$ then there is ∼45% CFP that M-class could have the highest intensity; finally, if $7.5⩽log\left(G_S\right)$ then there is at least 70% chance that the strongest energy release will be X-class in the next 48 hr. ARs are unlikely to produce X-class flare(s) if $13⩽S_{l-f}$ and log(G _S) $⩽$ 5.5. Finally, in terms of providing an estimate of an associated slow/fast CME, we found that, if $log\left(S_{l-f}\right)⩾$ 0.4 or $log\left(G_{DS}\right)⩽$ 6.5, there is no accompanying fast CME in the following 24 hr.