Wind-generated Rossby waves dynamics and effects on low-frequency Sea Surface Height variability in the South Pacific Ocean

We investigate in this work the dynamics of wind-generated Rossby waves and their effects on low-frequency altimetry signals in the South Pacific Ocean in order to provide a better understanding of the Qiu's model and shed light into the origin of this model empirical term. We assess the contribution of barotropic and baroclinic processes and study the effects of the seafloor non-uniformity on the low-frequency SSH signals variability induced by Rossby waves, by the means of specific theoretical analyses and numerical experiments. Low-frequency SSHa signals from AVISO data over the period from 1995 through 2019 exhibit a slow westward propagation behavior connected with baroclinic Rossby Waves. In addition to the Qiu's model with an appropriate empirical damping rate, these signals are properly reproduced by the one-and-a-half-layer MICOM model with a Qiu-like damping rate. Theoretical analyses reveal that for wind stress forcings with specific scales and for moderate seabed slope, the wind energy is mostly transferred to the barotropic mode. Then, simulations with the two-layer MICOM model show that the barotropic mode energy is dissipated/scattered due to the non-uniformity of the seafloor. Barotropic processes are the most affected by topography, and have no signature on the low-frequency evolution of the SSH. The successful empirical damping term introduced by Qiu accounts for the splitting of the wind energy among baroclinic and barotropic modes, and the dissipation of the barotropic mode energy by seafloor variations.