  This work aims to provide a more complete understanding of the resonance
mechanisms that occur in turbulent jets at high subsonic Mach number, as shown
by Towne et al. (2017). Resonance was suggested by that study to exist between
upstream- and downstream-travelling guided waves. Five possible resonance
mechanisms were postulated, each involving different families of guided waves
that reflect in the nozzle exit plane and a number of downstream turning
points. But the study did not show which of these mechanisms are active in the
flow. In this work, the waves underpinning resonance are identified via a
biorthogonal projection of the Large Eddy Simulation data on eigenbases
provided by locally parallel linear stability analysis. Two of the scenarios
postulated by Towne et al. (2017) are thus confirmed to exist in the turbulent
jet data. The reflection-coefficients in the nozzle exit and turning-point
planes are, furthermore, identified.
