  We study the plasma flows in the solar photosphere during the emergence of
two small active regions, NOAA 9021 and 10768. Using SOHO/MDI data, we find
that the strong plasma upflows appear at the initial stage of active region
formation, with maximum upflow velocities of -1650 and -1320 m/s. The
structures with enhanced upflows have size about 8 Mm in diameter, and they
exist for 1-2 hr. The parameters of the enhanced upflows are consistent with
those of the large active region NOAA 10488, which may suggest the possibility
that the elementary emerging magnetic loops that appear at the earliest phase
of active region formation have similar properties, irrespective of scales of
active regions. Comparison between the observations and a numerical simulation
of magnetic flux emergence shows a striking consistency. We find that the
driving force of the plasma upflow is at first the gas pressure gradient and
later the magnetic pressure gradient.
