Horizontal Structure of the Upper Ocean Velocity and Density Fields in the Western Equatorial Pacific Warm Pool: Depth Range from 20 to 250 m

Abstract

Wavenumber spectra of velocity and density fields in the western equatorial Pacific warm pool on scales 6?120 km are estimated using the shipboard survey data collected during the TOGA Coupled Ocean?Atmosphere Response Experiment (COARE). The spectra are averaged over three depth intervals: 20?60, 60?110, and 110?250 m (corresponding to the Yoshida jet, the South Equatorial Current, and the southern edge of Equatorial Undercurrent). The velocity spectra are corrected for the mean flow shear advection, which is important under conditions of low gradient Richardson number (Ri). After that, both velocity and density spectra are consistent with an internal wave spectral model including a random component (equatorial version of the Garrett and Munk spectrum) and a tidal component (the Feng et al. tidal model). Tidal peaks, previously found by other COARE investigators as being prominent on the ?moored? spectra (i.e., on the spectra derived from mooring data), appear to be much less significant on the ?towed? spectra (i.e., on the spectra derived from shipboard surveys). The model and observations reveal some directional anisotropy of the towed velocity spectra depending on Ri.