Effects of Radiative Transfer on Helioseismic Signatures in Active Regions

Models of active regions based on helioseismology have been heavily based on acoustics in which compression is assumed to be adiabatic. Acoustics in the outer atmospheres of the quiet Sun and active regions are thought to depart strongly from adiabatic compression, due to radiative-transfer effects. If these departures were similar in active regions and the quiet Sun, they could plausibly be ignored. However, this is unlikely, because the radiative environments in active regions are different from those in the quiet Sun. We discuss efforts to simulate acoustics in photospheric/chromospheric media with an account of radiative-transfer effects in both the quiet Sun and active regions.