In search of emerging magnetic flux underneath the solar surface with acoustic imaging

With the method of acoustic imaging in helioseismology, we study an emerging flux region, NOAA 7978, using data taken with instruments of the Taiwan Oscillation Network (TON) and the Michelson Doppler Imager (MDI). Phase-shift maps of NOAA 7978 focusing at different depths are constructed, which show the evolution of emerging magnetic flux. Although the emerging flux below the solar surface is not easy to be directly recognized in the phase-shift maps, average phase shifts over the active region reveal the signature of upward-moving magnetic flux in the solar interior. The average phase shifts in the interior normalized to their surface values are larger at earlier times in both the TON and the MDI data. This suggests that the flux below the surface is moving upward during the development of the active region.