  We report the discovery of isolated, small-scale emerging magnetic fields in
a plage region with the Solar Optical Telescope aboard Hinode.
Spectro-polarimetric observations were carried out with a cadence of 34 seconds
for the plage region located near disc center. The vector magnetic fields are
inferred by Milne-Eddington inversion. The observations reveal widespread
occurrence of transient, spatially isolated horizontal magnetic fields. The
lateral extent of the horizontal magnetic fields is comparable to the size of
photospheric granules. These horizontal magnetic fields seem to be tossed about
by upflows and downflows of the granular convection. We also report an event
that appears to be driven by the magnetic buoyancy instability. We refer to
buoyancy-driven emergence as type1 and convection-driven emergence as type2.
Although both events have magnetic field strengths of about 600 G, the filling
factor of type1 is a factor of two larger than that of type2. Our finding
suggests that the granular convection in the plage regions is characterized by
a high rate of occurrence of granular-sized transient horizontal fields.
