Energy redistribution through tidal and inertial wave interaction

Evidence for an interaction between inertial internal waves and semi-diurnal internal tides is described from oceanic velocity records. The resulting motions at the difference frequency between M2 and f, termed Internal Wave Induced Sub/Super-inertial Currents, or IWISC, are complicated structures whose existence suggests a new energy path from tidal and inertial internal waves directly to dissipative structures, independent of the assumed cascade of energy through the internal wave field from large to small scales.;We have observed an accumulation of energy in cyclonic rotary power spectral densities at the frequency of M2 - f (the IWISC frequency) over a broad range of depths and in numerous geographic locations throughout the worlds oceans. IWISC energy has been observed to vary considerably on quite small vertical scales, on the order of 30 meters. A hierarchy of vertical advection models has been created to establish if, when, and how vertical advection is a satisfactory explanation of IWISC. Displacement models including multiple semi-diurnal vertical modes and frequency constituents exhibit a temporal and spatial variability of IWISC and M 2 + f energies, consistent with observed variability. Bispectra and bicoherence analysis were tested on the complex displacement model velocities where they were unable to distinguish between reversible vertical advection and energy exchanging non-linearity.;An analysis of vertical profiles of horizontal currents from ADCP instruments deployed in the Hawaii Ocean Mixing Experiment revealed IWISC PSD peaks for both horizontal currents and their vertical shear. A Semi-Lagrange inversion revealed depth ranges where interaction peak energy (at IWISC and M2 + f) is diminished by the inversion and depth ranges where the energy peaks remained unaffected or were amplified. This leads to the conclusion that both periodic, reversible advection and other energy redistribution processes are present at this location. Bispectral and bicoherence analysis of the Semi-Lagrange inverted ADCP velocities suggests the presence of irreversible non-linear interaction at IWISC.