The Energy Balance in a Warm-Core Ring's Near-Inertial Critical Layer

The energy sink for near-inertial internal gravity waves encountering a vertical critical layer is examined with fine- and microstructure profiles collected in a warm-core ring. The hypothesis that the bulk of the trapped wave energy is lost to turbulence is tested by comparing the wave vertical energy-flux divergence ∂Cgz(KE + APE)/∂z with the turbulent dissipation rate ε. Assuming conservation of action flux, a balance is found to hold, implying negligible losses to untrapped waves and at most 7% losses to the background mean flow. This contrasts with the behavior at irrotational critical layers (where a substantial fraction of the wave energy can be absorbed into the mean) because of the relatively small Doppler shift encountered, k·ΔV/ωi.