EDDY KINETIC-ENERGY OF THE NORTH-ATLANTIC SUBPOLAR GYRE FROM SATELLITE ALTIMETRY

The surface eddy kinetic energy field of the North Atlantic subpolar gyre (40-65 degrees N, 5-60 degrees W) is studied using the altimetric satellites Geosat (1987-1988) and ERS-1 (1992-1993). This is; on the whole, an area of low eddy activity; previous studies of the North Atlantic have usually concentrated on the highly variable Gulf Stream system. We review what is known of the surface circulation of the region. We confirm that there is a close relationship between the eddy kinetic energy and the mean currents and that it is strongly constrained by the topography; the eddy field occurs in deep water and follows the contours, particularly around the Flemish Cap. High eddy kinetic energy is seen on the flanks of topography and is higher where the slope is steeper. This is particularly clear on both east and west flanks of the Rockall Plateau. Interannual changes in the currents are revealed by the differences between the Geosat and ERS-1 eddy kinetic energy maps. In some years (1988 and 1992-1993) the northern core of the North Atlantic Current (NAC), usually assumed to be tied to the Charlie Gibbs Fracture Zone (52 degrees N), is considerably weaker and may not exist at all, while in 1987 there is a distinct core here. In 1988 and 1992-1993 the main eddy region shifts farther to the south, to about 49 degrees N in 1988 and 50 degrees N in 1992-1993. In 1987 there is also a current core; even farther south, centered at about 47 degrees N, implying that in that year the NAC is arranged into two distinct branches.