physics – Eigenfrequency study in COMSOL

I am trying to model a photoacoustic resonator using COMSOL Multiphysics 6.0.

I am using the Thermoviscous-Acoustic, Frequency Domain(ta) physics interface with Eigenfrequency study.

While calculating the eigenfrequency of the resonator to compare the FEM value with an analytical solution for the resonance frequency, I not only get the correct resonant mode but other modes as well. I am unable to understand what is the significance of these modes and how to find whether these are longitudinal, azimuthal or radial modes?
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