  Flares and eruptions from solar active regions are associated with
atmospheric electrical currents accompanying distortions of the coronal field
away from a lowest-energy potential state. In order to better understand the
origin of these currents and their role in M- and X-class flares, I review all
active-region observations made with SDO/HMI and SDO/AIA from 2010/05 through
2014/10 within approximately 40 degrees from disk center. I select the roughly
4% of all regions that display a distinctly nonpotential coronal configuration
in loops with a length comparable to the scale of the active region, and all
that emit GOES X-class flares. The data for 41 regions confirm, with a single
exception, that strong-field, high-gradient polarity inversion lines (SHILs)
created during emergence of magnetic flux into, and related displacement
within, pre-existing active regions are associated with X-class flares. Obvious
nonpotentiality in the active region-scale loops occurs in 6 of 10 selected
regions with X-class flares, all with relatively long SHILs along their primary
polarity 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 flux
involved in the compact SHILs is of preeminent importance for the large-flare
potential of active regions within the next day, but that their associated
currents may not reveal themselves in active region-scale nonpotentiality. In
contrast, active region-scale nonpotentiality, which can persist for many days,
may inform us about the eruption potential other than those from SHILs which is
almost never associated with X-class flaring.
