Assessment of the ocean circulation in the Azores region as predicted by a numerical model assimilating altimeter data from Topex/Poseidon and ERS-1 satellites

摘要

Two years of altimetric data from Topex/Poseidon(October 1992–September 1994) and ERS-1 (October 1992–December 1993) wereassimilated into a numerical model of the North Atlantic. The results of thesesimulations are analysed in the Azores region to assess the performance of ourmodel in this particular region. Maps of instantaneous dynamic topography andtransports show that the model performs well in reproducing the velocities andtransports of the Azores Front. Drifter data from the Semaphore experiment arealso used to study the correlation between the drifter velocities and thecorresponding model velocities. Some interesting oceanographic results are alsoobtained by examining the seasonal and interannual variability of thecirculation and the influence of bathymetry on the variability of the AzoresFront. Thus, on the basis of our two year experiment, it is possible to confirmthe circulation patterns proposed by previous studies regarding the seasonalvariations in the origin of the Azores Current. Moreover, it is shown that theAzores Current is quite narrow in the first year of assimilation (1992–1993),but becomes much wider in the second year (1993–1994). The role of thebathymetry appears important in this area since the mesoscale activity is shownto be strongly related to the presence of topographic slopes. Finally, spectralanalyses of sea-level changes over time and space are used to identify two typesof wave already noticed in other studies: a wave with (300 km)–1 wavenumber and (120 days)–1 frequency, which is characteristic ofmesoscale undulation, and a wave with (600 km)–1 wave number and (250days)–1 frequency which probably corresponds to a Rossby wavegenerated in the east of the basin.