  While the velocity fluctuations of supergranulation dominate the spectrum of
solar convection at the solar surface, very little is known about the
fluctuations in other physical quantities like temperature or density at
supergranulation scale. Using SDO/HMI observations, we characterize the
intensity contrast of solar supergranulation at the solar surface. We identify
the positions of ${\sim}10^4$ outflow and inflow regions at supergranulation
scales, from which we construct average flow maps and co-aligned intensity and
magnetic field maps. In the average outflow center, the maximum intensity
contrast is $(7.8\pm0.6)\times10^{-4}$ (there is no corresponding feature in
the line-of-sight magnetic field). This corresponds to a temperature
perturbation of about $1.1\pm0.1$ K, in agreement with previous studies. We
discover an east-west anisotropy, with a slightly deeper intensity minimum east
of the outflow center. The evolution is asymmetric in time: the intensity
excess is larger 8 hours before the reference time (the time of maximum
outflow), while it has almost disappeared 8 hours after the reference time. In
the average inflow region, the intensity contrast mostly follows the magnetic
field distribution, except for an east-west anisotropic component that
dominates 8 hours before the reference time. We suggest that the east-west
anisotropy in the intensity is related to the wave-like properties of
supergranulation.
