Acoustic imaging and time-distance analysis of TON

We review the development of acoustic imaging, including the recent results on the inversion of phase-travel-time perturbation to obtain the three-dimensional distribution of wave-speed perturbation. We discuss the solar-cycle variations of meridional flows measured with time-distance analysis, which relates to the active latitudes. We present the result from a recent study using solar-cycle variations of p-mode travel time of different wave packets to probe magnetic fields at the base of convection zone. The result shows the evidence of the magnetic fields at the base of the convection zone.