Internal tides observed at 2°S-156°E by in situ and TOPEX/POSEIDON data during the coupled Ocean-Atmosphere Response Experiment (COARE)

During the enhanced monitoring phase of the Coupled Ocean-Atmosphere Experiment (COARE), semidiurnal baroclinic tides were observed. At 2 degrees S-156 degrees E (1739 m depth)the Tropical Atmosphere-Ocean (TAO) mooring outfitted with additional sensors from surface to bottom provides an interesting tool for describing the internal tides. M2, S2, and N2 baroclinic components were detected, explaining 59% of the semidiurnal variance on surface dynamic height. At the semidiurnal frequency, vertical displacements of isopycnals, highly variable in time, can reach 30 m and are mostly a combination of the M2, S2, and N2 internal waves. The two first baroclinic modes explain 70% of the variance in vertical displacement. M2 and S2 internal waves have different vertical structure: M2 resembles the first baroclinic mode and S2 resembles the second baroclinic mode. The M2 and S2 internal waves projected on their respective baroclinic mode are highly related to the modeled barotropic tide. Two TOPEX/POSEIDON tracks cross over the mooring every 10 days, and the internal wave signature can be expected in sea level along the tracks despite the weakness of the signal. Sea level spectra along both ascending and descending tracks show the existence of energy around the 250 km and the 120 km wavelength, respectively, which is in accordance with a first baroclinic wave propagating northeastward, as suggested in previous studies. From wavelet transform, the baroclinic tide signatures on the ascending (descending) track are centered around 2.5 degrees S (3.5 degrees S) with a 1 degrees (2 degrees) latitudinal extension, respectively, limited to the Ontong Java Plateau. We confirm the northeastward propagation of the baroclinic tides, and their source could be a series of islands parallel to the Kilinailau Trench or the large sloping topography between the Kilinailau Trench and the Ontong Java Plateau.