  In a previous work, we reported on the discovery of supersonic magnetic
upflows on granular cells in data from the {\sc Sunrise}/IMaX instrument. In
the present work we investigate the physical origin of these events employing
data of the same instrument but with higher spectral sampling. By means of the
inversion of Stokes profiles we are able to recover the physical parameters
(temperature, magnetic field, line-of-sight velocity, etc) present in the solar
photosphere at the time of these events. The inversion is performed in a
Monte-Carlo-like fashion, that is, repeating it many times with different
initializations and retaining only the best result. We find that many of the
events are characterized by a reversal in the polarity of the magnetic field
along the vertical direction in the photosphere, accompanied by an enhancement
in the temperature and by supersonic line-of-sight velocities. In about half of
the studied events, large blue-shifted and red-shifted line-of-sight velocities
coexist above/below each other. These features can be explained in terms of
magnetic reconnection, where the energy stored in the magnetic field is
released in the form of kinetic and thermal energy when magnetic field lines of
opposite polarities coalesce. However, the agreement with magnetic reconnection
is not perfect and therefore, other possible physical mechanisms might also
play a role.
