Meridional-Flow Measurements from Global Oscillation Network Group Data

We present measurements of the solar meridional flow using time-distance analysis based on Global Oscillation Network Group (GONG) data. In an attempt to detect the deep equatorward flow, which is believed to be a very small amplitude motion, we averaged time-difference measurements over a 15-year period and utilized both phase-velocity and high-m filtering techniques. These method seem to be capable of extending the meridional-flow measurements to the deep layers of the convection zone, down to 0.7?R _⊙. Typical uncertainties for most depths within ±?35^° latitude are less than 0.03 s. At higher latitudes, the uncertainties are about 0.06 s. There is a significant abrupt decrease in the nature of the travel-time differences for measurements that probe the bottom of the convection zone.