  Spatial distributions of the dominant oscillation frequency obtained for four
sunspots show a feature shared by all the analysed levels of the solar
atmosphere in these sunspots. This feature located in the inner penumbrae
indicates that this region has favourable conditions for 2.5-4 mHz oscillation
propagation. This agrees with the fact that the spectral composition of the
oscillations at three atmospheric heights (FeI 6173{\AA}, 1700{\AA}, and He II
304{\AA}) in this region are similar. There have been previous evidence of
particular similarities along height of photospheric magnetic field strength,
line-of-sight velocity, and temperature profile in the inner penumbra, where
the internal boundary of the Evershed flow is located. The finding of the same
dominant oscillation frequency at a range of altitudes from the chromosphere up
to the transition region extends the height range, suggesting similarities in
physical conditions.
