  Ring-diagram analysis of acoustic waves observed at the photosphere can
provide a relatively robust determination of the sub-surface flows at a
particular time under a particular region. The depth of penetration of the
waves is related to the size of the region, hence the depth extent of the
measured flows is inversely proportional to the spatial resolution. Most
ring-diagram analysis has focused on regions of extent ~15{\deg} (180 Mm) or
more in order to provide reasonable mode sets for inversions. HMI data analysis
also provides a set of ring fit parameters on a scale three times smaller.
These provide flow estimates for the outer 1% (7 Mm) of the Sun only, with very
limited depth resolution, but with spatial resolution adequate to map
structures potentially associated with the belts and regions of magnetic
activity. There are a number of systematic effects affecting the determination
of flows from local helioseismic analysis of regions over different parts of
the observable disk, not all well understood. In this study we characterize
those systematic effects with higher spatial resolution, so that they may more
effectively be accounted for in mapping temporal and spatial evolution of the
flows. Leaving open the question of the mean structure of the global meridional
circulation and the differential rotation, we describe the near-surface flow
anomalies in time and latitude corresponding to the torsional oscillation
pattern in differential rotation and analogous patterns in the meridional cell
structure as observed by SDO/HMI.
