| A study of the internal wave field generated by the tide around the Hawaiian Ridge is presented. To examine the processes controlling the generation, the evolution, and ultimately the dissipation of the internal tide, a new data set consisting of high-resolution density and velocity measurements recorded from the Research Platform FLIP is analyzed. As part of the Hawaiian Ocean Mixing Experiment, FLIP was moored for 2 six-weeks deployments: 450 km southwest of Oahu in 2001 (Farfield Program), and in the Kauai Channel in 2002 (Nearfield Program).; The variability of internal wave field as function of time, depth, and temporal frequency is described. The semidiurnal internal tide is found to be surprisingly variable in space as well as in time. Several internal wave beams at the dominant tidal frequencies are resolved in the Nearfield. In the Farfield, the internal tide is almost exclusively mode 1.; Cross-spectral techniques are used to compute the energy flux directly from the observations, both in terms of temporal frequencies and vertical wavenumbers (or modes). The M2 internal tide energy flux dominates the spectrum by an order of magnitude in both sites. Higher harmonics, virtually absent in the Nearfield, carry significant energy away from the Ridge in the Farfield. In both cases, there are also large fluxes associated with higher mode waves at frequency M2/2, indicating that nonlinear interactions rapidly transfer energy across the spectrum.; The mechanisms affecting the propagation of the low-mode internal tide in the ocean are discussed using a ray model. In addition to latitude, stratification, and depth, the mesoscale currents (derived from satellite altimetry) are shown to be a dominant factor affecting the paths, travel speeds, and the phases of all modes. The mesoscale field makes modes 3 and higher completely incoherent within a few tens of km from their source. Altimetric measurements of the sea-surface manifestation of the internal tide are interpreted. The M2 internal tide does not seem to lose much energy as it propagates southward, but its phase rapidly becomes random. The northward propagating internal tide should remain phase-locked but appears to rapidly lose energy. |
