Near-zonal wavefronts and related features of equatorial dynamics derived from satellite altimeter data

A new statistical approach to analyzing large-scale oceanic motions characterized by strong statistical inhomogeneity in the meridional direction is developed and applied to a 9-year series of satellite altimeter observations in the Tropical Pacific between 20°° S and 20°°N. A special treatment of meridional variations permits quantitative characterization of latitudinally alternating, zonally elongated features of the sea surface height field. Their frequency and length scales demonstrate that these features pertain to baroclinic large-scale wave motions, such as highly irregular Rossby waves. Since the sea surface height field at each latitude is generally found to be dominated by a few strong spectral peaks (semi-annual, annual, near-tetra-annual) for both westward and eastward propagating motions, a dominant wavevector may be associated with each such selected range of temporal and zonal scales. The meridional component of the wavevector is derived from the phase shift of the cross-spectrum between two neighboring latitudes 1°1°apart. The latitude dependence of these wavevectors may be instructively represented as a set of wavefronts that provide a global picture of the dominant flows.