Monitoring of the Gulf Stream path using Geosat and Topex/Poseidon altimetric data assimilated into a model of ocean circulation

Abstract

Abstract Two years of altimetric data from the Geosat satellite and one year from Topex/Poseidon were assimilated into a numerical ocean circulation model of the North Atlantic. The results of these simulations were used to compute statistics concerning the movements of the Gulf Stream from Cape Hatteras to 45 °W. This approach enabled us to obtain almost continuous spatio-temporal coverage of the phenomenon; it also allowed observations of the vertical structure of the current to be made. The mean path of the Gulf Stream is described. This trajectory is affected by the New England Seamount chain which gives rise to a south-easterly deflection and to an increase in positional variability which reaches a maximum near 61 °W. Downstream from this chain, the Gulf Stream reaches its highest latitude, and favoured positions for meanders were identified: two crests near 57 °W and 51 °W flanking a trough near 53 °W. In terms of the vertical structure of the current, a southerly shift of the Gulf Stream path as a function of depth was clearly seen. The Gulf Stream has a marked seasonal cycle with northerly maxima in August–September and southerly maxima in February–March. This cycle is not, however, in phase with that observed near to the North American continent. Secondary positional extrema, on the other hand, do not always occur at the same time of year. Spectra of the lateral displacements of the Gulf Stream are remarkably similar at all points. The spectra considered are red spectra with slopes of almost — 2, except to the east of the New England Seamount chain where the slope falls off for periods of more than 50 days. The statistics presented in this article are very much in agreement with earlier work on the subject and thus show the feasibility and value of such a joint model/data assimilation approach for monitoring major ocean currents.