Mode-1 internal tides in the western North Atlantic Ocean

Mode-1 internal tides were observed the western North Atlantic using an ocean acoustic tomography array deployed in 1991-1992 centered on 25 degrees N, 66 degrees W. The pentagonal array, 700-km across, acted as an antenna for mode-1 internal-tides. Coherent internal-tide waves with O(1 m) displacements were observed traveling in several directions. Although the internal tides of the region were relatively quiescent, they were essentially phase locked over the 200-300 day data record lengths. Both semidiurnal and diurnal internal waves were detected, with wavenumbers consistent with those calculated from hydrographic data. The M-2 internal-tide energy flux was estimated to be about 70Wm(-1), suggesting that mode-1 waves radiate 0.2GW of energy, with large uncertainty, from the Caribbean island chain at this frequency. A global tidal model (TPXO 5) suggested that 1-2GW is lost from the M-2 barotropic tide over this region, but the precise value was uncertain because the complicated topography makes the calculation problematic. In any case, significant conversion of barotropic to baroclinic tidal energy does not occur in the western North Atlantic basin. It is apparent, however, that mode-1 internal tides have very weak decay and retain their coherence over great distances, so that ocean basins may be filled Lip with such waves. Observed diurnal arnplitUdes were an order of magnitude larger than expected. The amplitude and phase variations of the K-1 and O-1 constituents observed over the tomography array were consistent with the theoretical solutions for standing internal waves near their turning latitude. The energy densities of the resonant diurnal internal waves were roughly twice those of the barotropic tide at those frequencies. (c) 2006 Elsevier Ltd. All rights reserved.