VARIATIONS OF THE SEA-LEVEL IN THE AMAZON ESTUARY

We analyze the Geosat altimeter data off the mouth of the Amazon river . Variations of the sea level of up to 6 m are observed, which are cor related with bathymetry, and dominated by a complex tidal pattern. M(2 ), N-2 and O-1 altimetric cotidal maps are constructed. Their amplitud es decrease strongly off the river mouth, probably by dissipation in t he estuary. Strong maxima are found on both sides of the river. In par ticular, a M(2) amplitude of 2.9 m is found near 2 degrees N-50 degree s W, just north of Cape Norde. These results are in very good agreemen t with in situ tide gage data as well as with a preliminary analysis o f Topex-Poseidon altimeter data. The models of Schwiderski (1980, Revi ew of Geophysics and Space Physics, 18, 243-268) and Cartwright ei al. (1991, NASA Technical memorandum, No. 104544) are out of phase with t hese observations, probably because of their low resolution. The M(2) phase signal is rather well reproduced by the high resolution finite e lement tidal model of the north Atlantic Ocean, developed for the corr ection of Topex-Poseidon data. However, in this model, amplitude is to o low off the river mouth, and the maximum north of Cape Norde is abse nt. This is probably due to inaccurate bathymetry in the model.