NEAR-SURFACE MEAN CIRCULATION AND KINETIC-ENERGY IN THE CENTRAL NORTH-ATLANTIC FROM DRIFTER DATA

An analysis of a large drifting buoy data set is presented. The objective is to obtain a self-contained description of the properties of the near-surface circulation (drogue depth 100 m) in the central North Atlantic Ocean, independent of hydrographic data. A necessary preanalysis step was the removal of all data from undrogued buoys from the data set. The physical parameters of the circulation were deduced by averaging the remaining data in 2 degrees x 3 degrees boxes. The minimum amount of data which is necessary to get statistically stable results was determined by an empirical quality criterion. All important mean currents in the investigation area are reproduced by the near-surface mean velocity field. A separation of the mean velocity field into a nondivergent acid an irrational part shows that the flow field is almost nondivergent. The distribution of eddy kinetic energy is concentrated along the mean currents and provides the largest part of the total kinetic energy, but there are regional variations. Energy from inertial movements dominates the high-frequency part of the kinetic energy. Its distribution is very patchy. The analysis of the Reynolds stress terms shows an energy transfer from the eddy field to the mean circulation in the vicinity of the North Atlantic Current.