  Sunspots host a large variety of oscillatory phenomena, whose properties
depend on the nature of the wave modes and the magnetic and thermodynamic
structure of the spot. Umbral chromospheric oscillations exhibit significant
differences compared to their photospheric counterparts. They show an enhanced
power and a shorter dominant period, from waves with an amplitude of a few
hundred meters per second in the five-minute band at the photosphere, to
amplitudes of several kilometers per second in the three-minute band at the
chromosphere. Various models have been proposed to explain this behaviour,
including the presence of a chromospheric resonance cavity between the
photosphere and the transition region. Jess et al. (2020, Nature Astronomy, 4,
220) claimed the detection of observational evidence supporting this model,
obtained from the comparison of spectropolarimetric observations and numerical
simulations. Here, it is shown that the observational insight reported by Jess
et al. is not a common property of sunspots. More importantly, numerical
modelling also shows that it is not an unequivocal signature of an acoustic
resonator.
