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 correlated with bathymetry, and dominated by a complex tidal pattern. M2, N2 and O1 altimetric cotidal maps are constructed. Their amplitudes decrease strongly off the river mouth, probably by dissipation in the estuary. Strong maxima are found on both sides of the river. In particular, a M2 amplitude of 2.9 m is found near 2°N–50°W, just north of Cape Norde. These results are in very good agreement with in situ tide gage data as well as with a preliminary analysis of Topex-Poseidon altimeter data. The models of Schwiderski (1980, Review of Geophysics and Space Physics, 18, 243–268) and Cartwright et al. (1991, NASA Technical memorandum, No. 104544) are out of phase with these observations, probably because of their low resolution. The M2 phase signal is rather well reproduced by the high resolution finite element tidal model of the north Atlantic Ocean, developed for the correction of Topex-Poseidon data. However, in this model, amplitude is too low off the river mouth, and the maximum north of Cape Norde is absent. This is probably due to inaccurate bathymetry in the model.