  In rotating stars and planets, excitation of inertial waves in convective
envelopes provides an important channel for tidal dissipation, but the
dissipation rate due to inertial waves depends erratically on the tidal
frequency. Tidal dissipation is significantly enhanced at some frequencies,
suggesting possible resonances between the tidal forcing and some eigenmodes.
However, the nature of these resonances remains enigmatic owing to the
singularity of the eigenvalue problem of inertial waves, and the resonances are
often mistakenly attributed to wave attractors in the literature. In this
letter, we reveal that resonant tidal responses correspond to inertial modes
with large-scale flows hidden beneath localized wave beams. Strong couplings
between the tidal forcing and the hidden large-scale flows intensify the
localized wave beams emanating from the critical latitudes, leading to enhanced
tidal dissipation. This study resolves a long-standing puzzle regarding the
frequency-dependence of tidal dissipation due to inertial waves in convective
envelopes.
