Observing the large-scale variations of the ocean surface with Topex/Poseidon and a dynamical model: An application in the Gulf Stream region

First results with 16 months of Topex/Poseidon data are presented. The unprecedent accuracy (of the order of 5 cm including orbit) of this data set makes possible the study of large-scale signals. The global-averaged sea level exhibit seasonal and near-60-day signals at the sub-centimetric level, only partly explainable by errors or mismodelling of the altimeter corrections and which are strongly correlated with pressure fluctuations. The sea level variations outside the tropics are dominated by the steric height cycle of 5 to 8 cm amplitude. Variations of the major current positions may however be the causes for strong signals in the high eddy energy areas. The authors exhibit also interannual signals of that kind. A first assimilation experiment into a North Atlantic model is described. The dynamics of the Gulf Stream are well reproduced and this approach will help decorrelating the complexity of the ocean circulation in this region