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Flares and eruptions from solar active regions are associated withatmospheric electrical currents accompanying distortions of the coronal fieldaway from a lowest-energy potential state. In order to better understand theorigin of these currents and their role in M- and X-class flares, I review allactive-region observations made with SDO/HMI and SDO/AIA from 2010/05 through2014/10 within approximately 40 degrees from disk center. I select the roughly4% of all regions that display a distinctly nonpotential coronal configurationin loops with a length comparable to the scale of the active region, and allthat emit GOES X-class flares. The data for 41 regions confirm, with a singleexception, that strong-field, high-gradient polarity inversion lines (SHILs)created during emergence of magnetic flux into, and related displacementwithin, pre-existing active regions are associated with X-class flares. Obviousnonpotentiality in the active region-scale loops occurs in 6 of 10 selectedregions with X-class flares, all with relatively long SHILs along their primarypolarity inversion line, or with a long internal filament there.Nonpotentiality can exist in active regions well past the flux-emergence phase,often with reduced or absent flaring. I conclude that the dynamics of the fluxinvolved in the compact SHILs is of preeminent importance for the large-flarepotential of active regions within the next day, but that their associatedcurrents may not reveal themselves in active region-scale nonpotentiality. Incontrast, active region-scale nonpotentiality, which can persist for many days,may inform us about the eruption potential other than those from SHILs which isalmost never associated with X-class flaring.

The nonpotentiality of coronae of solar active regions, the dynamics of the surface magnetic field, and the potential for large flares