Evidence for nonlinear interaction between internal waves of inertial and semidiurnal frequency

Observational evidence is presented for pervasive nonlinear interaction between inertial and M 2 frequency oscillations in the northeast Pacific. Enhanced currents at the sum frequency (termed the “ f M 2 frequency”) have the rotary spectral properties of freely propagating waves suggesting permanent energy exchange from the inertial and semidiurnal bands to the f M 2 band. The interaction may be responsible for the greater than predicted decay of inertial energy observed in the ocean and may contribute significantly to oceanic mixing.