Variability in the South Pacific Deep Western Boundary Current from current meter observations and a high‐resolution global model

Abstract

Observations of the South Pacific Deep Western Boundary Current from the World Ocean Circulation Experiment Pacific current meter array 9 (WOCE PCM‐9) current meter array are compared with the Los Alamos National Laboratory high‐resolution global ocean model. A simple integration of PCM‐9 velocity yields a mean northward transport of water deeper than 3000 m that is some 5 times greater than the model mean transport of 3.35 × 106 m3 s−1. The low modeled abyssal transport suggests a poor simulation of the mean thermohaline circulation. However, model and observed transport variability correlate significantly. Space‐time spectral analysis shows planetary waves are responsible for most of the variability and are resolved well in the model. The details of interaction of the long waves at the western boundary are different in model and data. The model reflects these waves predominantly as planetary short waves, which decay over the region 600–800 km east of the Kermadec Ridge. PCM‐9 has a higher proportion of energy as topographic waves along the Kermadec Ridge. These two classes of waves are associated with the two observed zonal scales in the boundary current. The model results can be separated into vertical modes. Baroclinic energy is found at all timescales, including those too short for free baroclinic waves. The baroclinic flow correlates with the barotropic so as to enhance surface, and reduce abyssal, kinetic energy. This is the signature of planetary wave scattering at the submerged western boundary ridge, and results in enhanced baroclinic wave energy in the Tasman Sea.