Kelvin waves activity in the eastern tropical Atlantic
Alban Lazar(1) , Irene POLO(2) , Gildas MAINSANT(1) , and Sabine ARNAULT(1)
Univ. Paris VI,
75252 paris cedex 05,
(2) Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, 28040, Madrid, Spain
Ocean Kelvin waves have long been considered as processes able to communicate subsurface stratification perturbations from the equator to higher latitude coastal regions. In the Atlantic, it has been argued that they could this way remotely control upwelling activity and SST variability, in particular in the Gulf of Guinea and the Benguela upwelling systems. Few studies though have been able to provide evidences of this happening in nature, maybe due to the weakness of Tropical Atlantic sea level anomalies relative to measurement errors. Continuous lessening of this error encouraged us to address this question using the Aviso Ssalto/Duacs SLA gridded data set in parallel with the output of an Ocean GCM and SSM/I SSTs over the period 1993-2003.
Both SLA datasets show uninterrupted and clear equatorial propagations at intra-seasonal scale along the equator as well as along some parts of the coasts, when appropriately filtered. The speeds are consistent with those of first mode Kelvin waves. We evidence interannual stronger signals which appear capable of propagating from the equator to the coast towards north and south. The study of the coastal signals reveal large changes in the speeds at certain fixed key points possibly due to stratification changes. We finally present quantitative analyses of other ocean and atmosphere variables like wind, SST and subsurface stratification in order to better assess the physics and the impact of these signals.