An evaluation of the classical and extended Rossby wave theories in explaining spectral estimates of the first few baroclinic modes in the South Pacific Ocean

Angela M. Maharaj1, Paolo Cipollini2, Neil J. Holbrook1, Peter D. Killworth2and Jeffrey R. Blundell2

1Department of Physical Geography, Macquarie University, Sydney, 21 09, Australia

2National Oceanography Centre, Southampton, European Way, Southampton, SO14 3ZH, UK.

Abstract

Previous literature has suggested that multiple peaks in sea level anomalies (SLA) detected by two-dimensional Fourier transform (2D-FT) analysis are spectral components of multiple propagating signals which may correspond to different baroclinic Rossby wave modes. We test this hypothesis in the South Pacific Ocean by applying a 2D-FT analysis to the long Rossby wave signal determined from filtered TOPEX/Poseidon and ERS-1 /2 satellite altimeter derived SLA. The first four baroclinic mode dispersion curves for the classical linear wave theory and the Killworth and Blundell extended theory are used to determine the spectral signature and energy contributions of each mode. South of 17°S, the first two extended theory modes explain more of the observed power spectral energy than their classical linear theory counterparts. We find that Rossby wave modes 2-3 are indeed present in the Rossby wave energy in the SLA data. The second mode contributes significantly over most of the basin. The third modes is also evident in some localised regions of the South Pacific but may be ignored at the large scale. Examination of a selection of case study sites suggest that the effects of bathymetry may dominate at longer wavelengths or permit higher order mode solutions but, typically, mean flow is the more influential factor in the extended theory. Furthermore, we find regional variability in the frequency and wavenumber characteristics of the extended theory modes across the South Pacific basin.