Near-Surface Current and Temperature Variability Observed in the Equatorial Atlantic From Drifting Buoys

We examine data from 23 surface drifters which were deployed between June 1983 and July 1984 at 4°W, 1.5°–4°S. The drifters were equipped with a window shade drogue centered at 15-m depth and in most cases a 117-m-long thermistor chain. Drift data indicate a westward South Equatorial Current with typical speeds of about 20 cm s−1 south of the equator. Maximum westward flow of 30–40 cm s−1 occurred in June through September of 1983 and 1984, consistent with climatology. Near-zero westward flow, which was significantly weaker than was expected from climatology (by about 20 cm s−1), occurred from February to April, 1984. This probably represents real interannual variability and may be related to the fact that the equatorial Atlantic was warmer than usual in the spring and summer of 1984. Energetic variations on time scales of O(1 month) and less and space scales of O(100 km) and less are ubiquitous in the drift and temperature data. Kinetic energy levels associated with these variations south of the equator are typically 100 cm2 s−2, with slightly higher values in boreal summer. Energy levels north of the equator are about 500 cm2 s−2 on the basis of data available only during the boreal summer and fall. The sources of this energy include inertia-gravity waves, instabilities of the general circulation, and other phenomena for which there is no simple explanation.