THREE-DIMENSIONAL STRUCTURE OF A SOLAR ACTIVE REGION FROM SPATIALLY AND SPECTRALLY RESOLVED MICROWAVE OBSERVATIONS

We report on the structure of the solar atmosphere above active region (AR) 10923, observed on 2006 November 10, as deduced from multi-wavelength studies including combined microwave observations from the Very Large Array (VLA) and the Owens Valley Solar Array (OVSA). The VLA observations provide excellent image quality at a few widely spaced frequencies, while the OVSA data provide information at many intermediate frequencies to fill in the spectral coverage. Images at 25 distinct frequencies are used to provide spatially resolved spectra along many lines of sight in the AR, from which microwave spectral diagnostics are obtained for deducing maps of temperature, magnetic field, and column density. The derived quantities are compared with multiwavelength observations from the Solar and Heliospheric Observatory and Hinode spacecraft, and with a current-free magnetic field extrapolation. We find that a two-component temperature model is required to fit the data, in which a hot (>2MK) lower corona above the strong-field plage and sunspot regions (emitting via the gyroresonance process) is overlaid with somewhat cooler (similar to 1MK) coronal loops that partially absorb the gyroresonance emission through the free-free (Bremsstrahlung) process. We also find that the extrapolated potential magnetic fields can quantitatively account for the observed gyroresonance emission over most of the AR, but in a few areas a higher field strength is required. The results are used to explore the coronal configuration needed to explain the observations. These results show that the bulk of free-free emission in both radio and X-rays emanates from two loop systems, distinguished by the location of their loop footpoints. We discuss the implications of such comparisons for studies of AR structure when better microwave spectral imaging becomes available in the future.