A discussion on ocean currents and their dynamics - Current measurements in the western Atlantic

Abstract

About 350 instrumented moorings have been set during the past decade to develop and exploit a technique of ocean-current measurement. Nearly all the records are characterized by intermittent oscillatory motions with random changes of amplitude and phase near the local inertial frequency and at the semidiurnal tidal frequency. Local generation of inertial currents by winds has been observed in the surface mixed layer. Above tidal frequencies the motion is irregular and nearly isotropic horizontally. The kinetic energy density decreases with frequency and depth, with considerable day-to-day fluctuations. At a given depth, the kinetic energy is remarkably constant when averaged over a month or longer, and varies only within a narrow range over a large extent of the Atlantic Ocean. Below inertial frequencies, the kinetic energy density increases with decreasing frequency. The motions have stronger vertical coherence and larger horizontal scale. Deep currents are dominated by the meandering of the Gulf Stream. Speeds up to one knot (0.5ms-1) are found near the bottom under the Stream. North of the Gulf Stream, a 3-year average from intermittent records indicates a westward flow, approximately parallel to the continental shelf and bottom topography.