Eddy kinetic energy in the North Atlantic from surface drifters

Abstract

One hundred ten satellite‐tracked freely drifting buoys measured velocities and trajectories of the near‐surface currents in the North Atlantic. Mean velocity values and the velocity variance about the mean were calculated for different regions. A horizontal map of eddy kinetic energy was prepared on a 2°×2° grid between latitudes 20° and 55°N. Maximum eddy energy (∼3000 cm2 s−2) coincides with the high speed Gulf Stream jet where it begins large amplitude meanders near 37°N 67°W. A tongue of high eddy energy coincides with the Stream's path eastward and around the Grand Banks into the Newfoundland Basin where values of 1000 cm2 s−2 are found. A weaker tongue extends eastward across the mid‐Atlantic Ridge near 45°N. A second weak extension reaches southeastward from the Stream and crosses the mid‐Atlantic Ridge between 30° and 35°N. North and south of the Stream, eddy energy diminishes rapidly reaching an e folding at 300 km from the axis. Values of 200 cm2 s−2 were observed in the mid‐gyre region and 100 cm2 s−2 in the Eastern North Atlantic and North Equatorial Current. Although the gross distribution of eddy energy is similar to that determined from ship drift measurements, there are significant differences. Eddy energy from drifters amounts to about twice the value measured by ship drift in the Gulf Stream and one half the ship drift values in the mid‐gyre. It is suggested that these differences are due to the horizontal averaging of mesoscale motion and the errors in navigation, both of which are problems with the ship drift technique.