  Supergranules are convection cells seen at the Sun's surface as a space
filling pattern of horizontal flows. While typical supergranules have diameters
of about 35 Mm, they exhibit a broad spectrum of sizes from ~10 Mm to ~100 Mm.
Here we show that supergranules of different sizes can be used to probe the
rotation rate in the Sun's outer convection zone. We find that the equatorial
rotation rate as a function of depth as measured by global helioseismology
matches the equatorial rotation as a function of wavelength for the
supergranules. This suggests that supergranules are advected by flows at depths
equal to their wavelengths and thus can be used to probe flows at those depths.
The supergranule rotation profiles show that the surface shear layer, through
which the rotation rate increases inward, extends to depths of ~50 Mm and to
latitudes of at least 70 degrees. Typical supergranules are well observed at
high latitudes and have a range of sizes that extend to greater depths than
those typically available for measuring subsurface flows with local
helioseismology. These characteristics indicate that probing the solar
convection zone dynamics with supergranules can complement the results of
helioseismology.
