Internal Tides near the Kermadec Ridge

Abstract

Current meter data from the WOCE PCM-9 array, extending 1000 km eastward from the Kermadec Ridge northeast of New Zealand, are used to investigate the internal tide. A high degree of spatial and temporal variability in the semidiurnal tide, but not in the diurnal tide, suggests that there is a conversion from barotropic to baroclinic tidal energy at the semidiurnal periods. Comparison between observed tidal constituents and those predicted by the TPXO.3 model indicates that the model may be used as an estimate of the barotropic tide. Once the barotropic tide has been removed, the remaining semidiurnal energy propagates predominantly at the first vertical mode phase speed of 3.5 m s−1, consistent with linear theory. A frequency-domain empirical orthogonal function analysis is used to extract signals that have phase propagation consistent with a coherent internal tide. These modes represent a phase-locked semidiurnal internal tide having about 0.65 of the baroclinic energy. Tidal energies at the M2 period associated with the phase-locked tide are about 155 J m−2 over the Kermadec Ridge and 98 J m−2 over the abyssal plain east of the ridge. Total tidal power radiation along the ridge is estimated to be about 0.8 GW.