Pure Inertial Waves Radiating From Low-Frequency Flows Over Large-Scale Topography

Mooring data collected at a flat-topped seamount suggest the generation of pure inertial waves (PIWs; waves with a dominant frequency equal to the local inertial frequency f) by low-frequency flows over large-scale topography. Energetic PIWs were observed within a narrow depth range (similar to 100 m) near the seafloor at the edge of the summit. These waves could be associated with low-frequency flows. A two-dimensional nonhydrostatic model was used to show that the observed PIWs are most likely internal wave beams generated by low-frequency flows over the seamount. Two types of PIWs were identified via observation and model. The first is a PIW that can only travel horizontally. The other propagates upward, with super-inertial intrinsic frequency that is Doppler-shifted by the flows to f. Nonlinear triadic interactions among waves with the frequencies [0, f, f] may transfer energy from mean flows to PIWs, promoting energy decay of geostrophic flows over large-scale topography.