Comparison of Solar Subsurface Flows Assessed by Ring and Time-Distance Analyses

The solar near-surface shear layer exhibits a rich medley of flows that are now being measured by a variety of local helioseismic techniques. We present comparisons of the horizontal flows obtained with two of these techniques, ring and time-distance analyses, applied to Michelson Doppler Imager (MDI) Dynamics Program data from the years 1998 and 1999. The ring analyses use the frequencies of both f and p modes in inversions to obtain flows within the near-surface shear layer as a function of depth. The f-mode time-distance analyses make velocity inferences just beneath the photosphere. After degrading the spatial resolution of the time-distance analyses to match the coarser resolution of the ring analyses, we find that the flows deduced with the two methods are remarkably similar, with common inflow and outflow sites as well as agreement in flow direction. The flows from ring and time-distance analyses are highly correlated with each other (correlation coefficients ~0.8); direct correspondence of features in the flows is largely realized in both the quiet-Sun and magnetic active regions.