Estimates of the first to third baroclinic Rossby wave mode variability in the South Pacific Ocean from the TOPEX/Poseidon and ERS1/2 altimeter observed sea level anomalies

Long wavelength baroclinic oceanic planetary (Rossby) waves play a significant role in ocean dynamics and are clearly visible in sea level anomalies (SLA) observed with satellite altimeters. Multiple westward propagating signals are often detected in these SLA and are suggestive of a surface manifestation of higher order baroclinic Rossby wave modes. We test this hypothesis in the South Pacific Ocean by applying a two-dimensional Fourier transform analysis to the long Rossby wave signal determined from filtered TOPEX/Poseidon and ERS1/2 satellite altimeter data. Dispersion relations for the first three baroclinic modes from the classic linear wave theory and the Killworth and Blundell extended theory are used to determine the spectral signature and energy contributions of each mode. Results show that the presence of higher order modes is largely confined to the Tropics (equatorwards of 20°S) and the southwest Pacific Ocean around New Zealand. We then test whether multiple peaks as detected in a Radon Transform analysis (a method that is often used to objectively estimate the phase speed of Rossby waves from altimeter data) correspond to these observed higher order modes with a view to determining the first to third baroclinic Rossby wave phase speeds in the South Pacific Ocean.