MONITORING OF THE GULF-STREAM PATH USING GEOSAT AND TOPEX POSEIDON ALTIMETRIC DATA ASSIMILATED INTO A MODEL OF OCEAN CIRCULATION/

Two years of altimetric data from the Geosat satellite and one year fr om Topex/Poseidon were assimilated into a numerical ocean circulation model of the North Atlantic. The results of these simulations were use d to compute statistics concerning the movements of the Gulf Stream fr om Cape Hatteras to 45 degrees W. This approach enabled us to obtain a lmost continuous spatio-temporal coverage of the phenomenon; it also a llowed observations of the vertical structure of the current to be mad e. The mean path of the Gulf Stream is described. This trajectory is a ffected 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 degrees W. Downstream from this chain, the Gulf Stream reaches its highest latitude, and favoured positions for m eanders were identified: two crests near 57 degrees W and 51 degrees W flanking a trough near 53 degrees W. In terms of the vertical structu re of the current, a southerly shift of the Gulf Stream path as a func tion of depth was clearly seen. The Gulf Stream has a marked seasonal cycle with northerly maxima in August-September and southerly maxima i n February-March. This cycle is not, however, in phase with that obser ved near to the North American continent. Secondary positional extrema , on the other hand, do not always occur at the same time of year. Spe ctra of the lateral displacements of the Gulf Stream are remarkably si milar at all points. The spectra considered are red spectra with slope s of almost -2, except to the east of the New England Seamount chain w here the slope falls off for periods of more than 50 days. The statist ics 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 curr ents.