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

With the method of acoustic imaging in helioseismology, we study an emergin g flux region, NOAA 7978, using data taken with instruments of the Taiwan O scillation Network (TON) and the Michelson Doppler Imager (MDI). Phase-shif t maps of NOAA 7978 focusing at different depths are constructed, which sho w 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 t imes in both the TON and the MDI data. This suggests that the flux below th e surface is moving upward during the development of the active region.