Ring-diagram analysis of the structure of solar active regions

We measure differences in structure between active and quiet regions of the Sun using the frequencies of high-degree modes determined from ring-diagram analyses. We find that both the speed of sound and the adiabatic index Gamma(1) differ in active regions as compared with quiet regions. In the immediate subsurface layers, the sound speed is lower in active regions, but below a depth of about 7 Mm the opposite is true. A comparison of sound-speed inversion results with those for Gamma(1) indicates that at least a part of the differences between active and quiet regions is likely to be due to the structural and thermal perturbations caused by magnetic fields in the active region.