Eddies in the northeastern North Atlantic: Statistics from observations from a moving ship

Abstract

Statistics of currents and hydrographic data collected from a moving ship in the northeastern North Atlantic have been used to investigate the role of eddies in the circulation of the ocean. The mean currents show, besides a North Atlantic Current of about 12 cm s−1, a significant westward flow, perhaps 4 cm s−1 just north of the Azores. Eddy kinetic energies in the Western Basin reach about 1000 cm2 s−2, while there is indication of a weak secondary maximum of about 300 cm2 s−2 in the Eastern Basin. Both the eddy kinetic energy and the thermohaline variability show a strong asymmetry with greater variability on the south side of the main branch of the North Atlantic Current at about 51°N. The momentum budget of the North Atlantic current shows a dominant geostrophic balance with terms of order 10 cm s−1. The gradients of the Reynolds stresses contribute about 0.1 cm s−1 and the nonlinear terms less than 0.01 cm s−1. The residual meridional velocity implied by the meridional heat transport is of order 3 cm s−1. The eddy scale was estimated by means of the average zero‐crossing length scale of the transverse velocity correlation function to be 46 km. There is significant interannual variability of both mean conditions and mesoscale variability in the region of the North Atlantic Current. The northward eddy heat transport appears to be zero in the mixed layer but may be a significant proportion of the total oceanic heat transport at the intergyre boundary in the thermocline. Estimates of the magnitudes of eddy diffusivities for both momentum and heat give values of about 104 m2 s−1.