Tomographic imaging of the sun's interior

A new method is presented of determining the three-dimensional sound-speed structure and flow velocities in the solar convection zone by inversion of the acoustic travel-time data recently obtained by Duvall and coworkers. The initial inversion results reveal large-scale subsurface structures and flows related to the active regions, and are important for understanding the physics of solar activity and large-scale convection. The results provide evidence of a zonal structure below the surface in the low-latitude area of the magnetic activity. Strong converging downflows, up to 1.2 km s^-1, and a substantial excess of the sound speed are found beneath growing active regions. In a decaying active region, there is evidence for the lower than average sound speed and for upwelling of plasma.