The Signature of Flare Activity in Multifractal Measurements of Active Regions Observed by SDO/HMI

Recent studies indicate that measurements of fractal and multifractal parameters of active regions (ARs) are inefficient tools for distinguishing ARs on the basis of the flare activity or to predict flare events. In an attempt to validate this result on a large observation data set of higher spatial and temporal resolution and higher flux sensitivity than employed in previous studies, we analyzed high-cadence time series of line-of-sight magnetograms of 43 ARs characterized by different flare activity, which were observed with SDO/HMI from May 2010 to December 2013. On these data, we estimated four parameters, the generalized fractal dimensions D (0) and D (8), and the multifractal parameters C (div) and D (div). We found distinct average values of the parameters measured on ARs that have hosted flares of different class. However, the dispersion of values measured on ARs that have produced the same class of events is such that the parameters deduced from distinct classes of flaring regions can also largely overlap. Based on the results of our measurements, C- and M-class flaring ARs are practically indistinguishable, and the same is true for M- and X-class flaring ARs. We only found consistent changes on the time series of the measured parameters on a parts per thousand aEuro parts per thousand 50 % of the ARs and a parts per thousand aEuro parts per thousand 50 % of the M- and X-class events. We show that these results hold for fractal and multifractal parameter estimates based on total unsigned and signed flux data of the ARs. OI Stangalini, Marco/0000-0002-5365-7546; Romano, Paolo/0000-0001-7066-6674; giorgi, fabrizio/0000-0002-0974-2401; ermolli, ilaria/0000-0003-2596-9523