Equatorial current measurements, Pt. 1, Moored observations

The low-frequency fluctuations in the western Indian Ocean are dominated by energetic variability with relatively small horizontal and vertical scales. The time series of horizontal current and temperature exhibit a number of energetic events which, for the most part, are not sufficiently resolved to assign a spatial scale to the underlying process. An exception to this is the 200-m equatorial jet that persists over the first two months of the record. It is shown that there is a westward intensification of the eddy field toward the east African coast and that, in the energetic region, the eddy kinetic energy is proportional to the local buoyancy frequency. At periods of the order of 50 days and longer, the current variability is principally zonal, although there is a marked dominance of meridional fluctuations at intermediate frequencies. At periods of 50 days and longer, which might be associated with equatorial planetary waves, corroborative evidence is found for such a wave field in the correlations between orthogonal velocity components away from the Equator. The general lack of coherence between instruments separated spatially is consistent with the small-scale variability observed in the velocity profiles. The mean flow in the upper layers appears to be toward the west, whereas at depth, there is evidence for a weak northward flow into the Somali Basin.