Multiple westward propagating signals in South Pacific sea level anomalies

Abstract

The characteristics of multiple westward propagating signals in the satellite observed South Pacific sea level anomalies (SLA) between 10°S and 50°S are analyzed using the two‐dimensional Radon transform (2D‐RT). We test the hypothesis that these signals are most likely to be the signature of the first few baroclinic Rossby wave modes. This involves a comparison of the estimated phase speeds of the 2D‐RT peaks against the first four baroclinic mode Rossby wave speeds predicted from the extended theory. The 2D‐RT analysis typically identified up to three propagating signals in the SLA and very occasionally, a fourth. The first Radon transform (RT) peak phase speeds corresponded very well with first baroclinic mode Rossby wave phase speed estimates from linear theory between 15°S and 25°S and the extended theory phase speed estimates poleward of 25°S. RT peak 2 speeds were less coherent but fell within the range of extended theory estimates of the first four baroclinic Rossby wave modes, consistent with large‐scale Rossby wave dynamics. The relationship between peaks 3 and 4 and the extended theory higher‐order baroclinic mode speed estimates varied markedly across the basin. Regional variability in the spectral characteristics of the peaks suggests that different dynamical regimes dominate north and south of 30°S in the South Pacific basin. The presence of secondary peaks in the middle to high latitudes suggests that higher‐order modes may play a role in these regions.