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Sunspots host a large variety of oscillatory phenomena, whose propertiesdepend on the nature of the wave modes and the magnetic and thermodynamicstructure of the spot. Umbral chromospheric oscillations exhibit significantdifferences compared to their photospheric counterparts. They show an enhancedpower and a shorter dominant period, from waves with an amplitude of a fewhundred meters per second in the five-minute band at the photosphere, toamplitudes of several kilometers per second in the three-minute band at thechromosphere. Various models have been proposed to explain this behaviour,including the presence of a chromospheric resonance cavity between thephotosphere 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 numericalsimulations. Here, it is shown that the observational insight reported by Jesset al. is not a common property of sunspots. More importantly, numericalmodelling also shows that it is not an unequivocal signature of an acousticresonator.

Signatures of sunspot oscillations and the case for chromospheric resonances