Eddy energy in the oceans

Observations of surface drift currents made by merchant ships are used to calculate the kinetic energy of the mean flow as well as the kinetic energy of the fluctuations, which is interpreted as eddy kinetic energy. The distribution of these properties is charted for the North Atlantic Ocean based on 1° squares and for the world oceans based on 5° squares. Both distributions show essentially the same features, namely, high values in the western boundary currents and in the equatorial current system and low values in the subtropical gyres. The ratio between mean energy and eddy energy is high (about 1 to 2) in the strong currents and low (about 1/20 to 1/40) in the central and eastern portions of the gyres. Comparing mean and eddy energies in ocean and atmosphere, it becomes apparent that eddy energies in the two systems are uncorrelated. The results are consistent with the idea that eddy motion in the ocean is generated in areas of strong mean shear flow and is subsequently distributed over the whole ocean.