Baroclinic and barotropic tidal amplitudes and phases are estimated from the survey and mooring observations in the upper 300 m of the 1800 m deep ocean by specifying their horizontal structures, as well as their vertical structures.
The barotropic tide is assumed to have zero horizontal wavenumber over the domain, while a component of the baroclinic tide that is phase-locked to the barotropic tide is determined by a searching method using plane wave fits to both the isopycnal and velocity data (Figure 2).
The estimated barotropic tidal current, which is most energetic in the zonal direction for both the M2 and S2 constituents, is in good agreement with tide models derived from TOPEX/POSEIDON observations (Figure 3). The plane wave analysis for the baroclinic tidal component shows horizontal and vertical structure consistent with a dominant mode one baroclinic wave propagating towards the northeast (Figure 4).
The second vertical mode can also be detected. Given the phase differences between the M2 and S2 constituents in the barotropic and baroclinic tides, the source of the baroclinic tide is determined to be about 320 km southwest of the observing region, at a series of islands and shallow ridges northeast of New Ireland (Figure 1).
The combined estimates of the barotropic and baroclinic tides typically account for only 40-60% of the observed semidiurnal band current variance in the mooring data (Figure 5), indicating the high degree of temporal and spatial variability of the baroclinic tide in this region (Figure 6). The results of this study suggest, however, that coherent barotropic and baroclinic tidal signals can be successfully distinguished in the deep ocean using shipboard survey data, even when the data are limited to the upper 300 m.
Last modified: October 27, 1997