  Meridional flow in the solar interior plays an important role in
redistributing angular momentum and transporting magnetic flux inside the Sun.
Although it has long been recognized that the meridional flow is predominantly
poleward at the Sun's surface and in its shallow interior, the location of the
equatorward return flow and the meridional flow profile in the deeper interior
remain unclear. Using the first two years of continuous helioseismology
observations from the Solar Dynamics Observatory / Helioseismic Magnetic
Imager, we analyze travel times of acoustic waves that propagate through
different depths of the solar interior carrying information about the solar
interior dynamics. After removing a systematic center-to-limb effect in the
helioseismic measurements and performing inversions for flow speed, we find
that the poleward meridional flow of a speed of 15 m/s extends in depth from
the photosphere to about 0.91 R_sun. An equatorward flow of a speed of 10 m/s
is found between 0.82 to 0.91 R_sun in the middle of the convection zone. Our
analysis also shows evidence of that the meridional flow turns poleward again
below 0.82 R_sun, indicating an existence of a second meridional circulation
cell below the shallower one. This double-cell meridional circulation profile
with an equatorward flow shallower than previously thought suggests a
rethinking of how magnetic field is generated and redistributed inside the Sun.
