Large-scale eddy motion in the western Atlantic

Analysis of the current data gathered near Bermuda during the period 1959–1960, shows, in terms of a two-layer model, that 78% of the kinetic energy is in the barotropic mode. The theoretical linear response function for the meridional velocity in a barotropic ocean subject to a time-dependent zonal wind stress and bottom friction has a broad-band structure at moderately low frequencies and moderately small distances from the western coast. The frequencies and wavelengths of this band fit the Bermuda observations, but the theory underestimates the amplitudes. Introduction of baroclinicity in the form of a two-layer linear model produces little change in response at periods shorter than that of the fastest baroclinic free mode (250 days), and it therefore fails to explain the large amplitudes. It is suggested that nonlinear interactions in the Gulf Stream are important and that these forced transients form part of the dissipation mechanism of the Gulf Stream.