CORONAL CURRENTS, MAGNETIC-FIELDS, AND HEATING IN A SOLAR ACTIVE-REGION

We compare microwave images of a solar active region with state-of-the -art fully nonlinear force-free extrapolations of the photospheric fie lds in order to study the link between coronal currents and heating of the corona. This extrapolation fully takes into account the nonunifor m distribution of electric currents observed in the photosphere and it s role in the coronal magnetic structure. We carry out the comparison for AR 6615, a complex region observed with the VLA on 1991 May 7. Und er the assumption that the microwave emission is dominated by opticall y thick gyroresonance radiation, we may use the radio images to infer the temperature of the corona at different heights and locations. This is then compared with heating models based on the observed current di stribution. We are able to reproduce the radio images remarkably well with a model in which temperature is structured along magnetic field l ines, depends on the current on the field line, and increases with hei ght in a manner similar to that inferred from static heated loop model s. This result implies a direct link between electric currents and cor onal heating.