  High-resolution imaging observations from the Hinode spacecraft in the CaII H
line are employed to study the dynamics of the chromosphere above a sunspot. We
find that umbral flashes and other brightenings produced by the oscillation are
extremely rich in fine structure, even beyond the resolving limit of our
observations (0.22"). The umbra is tremendously dynamic, to the point that our
time cadence of 20 s does not suffice to resolve the fast lateral (probably
apparent) motion of the emission source. Some bright elements in our dataset
move with horizontal propagation speeds of 30 km/s. We have detected
filamentary structures inside the umbra (some of which have a horizontal
extension of ~1500 km) which, to our best knowledge, had not been reported
before. The power spectra of the intensity fluctuations reveals a few distinct
areas with different properties within the umbra that seem to correspond with
the umbral cores that form it. Inside each one of these areas the dominant
frequencies of the oscillation are coherent, but they vary considerably from
one core to another.
