  Large-scale plasma flows in the Sun's convection zone likely play a major
role in solar dynamics on decadal timescales. In particular, quantifying
meridional motions is a critical ingredient for understanding the solar cycle
and the transport of magnetic flux. Because the signal of such features can be
quite small in deep solar layers and be buried in systematics or noise, the
true meridional velocity profile has remained elusive. We perform time-distance
helioseismology measurements on several years worth of GONG Doppler data. A
spherical harmonic decomposition technique is applied to a subset of acoustic
modes to measure travel-time differences to try to obtain signatures of
meridional flows throughout the solar convection zone. Center-to-limb
systematics are taken into account in an intuitive, yet ad hoc manner.
Travel-time differences near the surface that are consistent with a poleward
flow in each hemisphere and are similar to previous work are measured.
Additionally, measurements in deep layers near the base of the convection zone
suggest a possible equatorward flow, as well as partial evidence of a sign
change in the travel-time differences at mid-convection zone depths. This
analysis on an independent data set using different measurement techniques
strengthens recent conclusions that the convection zone may have multiple
"cells" of meridional flow. The results may challenge the common understanding
of one large conveyor belt operating in the solar convection zone. Further work
with helioseismic inversions and a careful study of systematic effects are
needed before firm conclusions of these large-scale flow structures can be
made.
