  The meridional circulation at high latitudes is crucial to the build-up and
reversal of the Sun's polar magnetic fields. Here we characterize the
axisymmetric flows by applying a magnetic feature cross-correlation procedure
to high resolution magnetograms obtained by the Helioseismic and Magnetic
Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We focus on
Carrington Rotations 2096-2107 (April 2010 to March 2011) - the overlap
interval between HMI and the Michelson Doppler Investigation (MDI). HMI
magnetograms averaged over 720 seconds are first mapped into heliographic
coordinates. Strips from these maps are then cross-correlated to determine the
distances in latitude and longitude that the magnetic element pattern has
moved, thus providing meridional flow and differential rotation velocities for
each rotation of the Sun. Flow velocities were averaged for the overlap
interval and compared to results obtained from MDI data. This comparison
indicates that these HMI images are rotated counter-clockwise by 0.075 degrees
with respect to the Sun's rotation axis. The profiles indicate that HMI data
can be used to reliably measure these axisymmetric flow velocities to at least
within 5 degrees of the poles. Unlike the noisier MDI measurements, no evidence
of a meridional flow counter-cell is seen in either hemisphere with the HMI
measurements: poleward flow continues all the way to the poles. Slight
North-South asymmetries are observed in the meridional flow. These asymmetries
should contribute to the observed asymmetries in the polar fields and the
timing of their reversals.
