Signatures of Coronal Currents in Microwave Images

Microwave emission from solar active regions at frequencies above 4 GHz is dominated by gyroresonance opacity in strong coronal magnetic elds, which allows us to use radio observations to measure coronal magnetic eld strengths. In this paper we demonstrate one powerful consequence of this fact: the ability to identify coronal currents from their signatures in microwave images. Speciically, we compare potential-eld (i.e., current{free) extrapolations of photospheric magnetic elds with microwave images and are able to identify regions where the potential extrapolation fails to predict the magnetic eld strength required to explain the microwave images. Comparison with photospheric vector magnetic eld observations indicates that the location inferred for coronal currents agrees with that implied by the presence of vertical currents in the photosphere. The location, over a neutral line exhibiting strong shear, is also apparently associated with strong heating.