  Supergranules are believed to be an evidence for large-scale subsurface
convection. The vertical component of the supergranular flow field is very hard
to measure, but it is considered only a few m/s in and below the photosphere.
Here I present the results of the analysis using three-dimensional inversion
for time-distance helioseismology that indicate existence of the
large-magnitude vertical upflow in the near sub-surface layers. Possible issues
and consequences of this inference are also discussed.
