Variability in horizontal current velocities in the central and eastern equatorial Atlantic in 2002

Near-surface current velocity data from the Pilot Research Moored Array in the Tropical Atlantic at 23 degrees W in the year 2002 were re-examined and compared to simultaneous unpublished velocity data at 10 degrees W, near the surface. Strong 7-day-period fluctuations were observed in the zonal velocity component and in temperature records at 23 degrees W. The large temperature fluctuations near the thermocline depth suggest a vertical velocity component at the same 7-day period. The 7-day-period signals occurred in June/July simultaneously with the seasonal upwelling. The meridional velocity component presented similar spectral contents at 23 degrees W and at 10 degrees W. Two distinguishable quasiperiodic signals were observed in the meridional component at both locations: The first signal occurred in the spring, had a periodicity of about 14 days, was subsurface intensified, and had the characteristics of a mixed Rossby-gravity wave. The second signal occurred three times in the year ( once in winter 2001-2002, another in summer, and another during fall 2002), had a periodicity of about 20 days, was strongest close to the surface, and was the result of the passage of tropical instability waves (TIWs). Satellite sea surface temperature (SST) data show the same periodicities as the meridional velocity records, and present a spatial structure in accordance with the TIW-SST signature. The summer of 2002 showed different TIW-SST patterns depending upon location, suggesting the existence of different types of TIWs. Overall, variability in the current meter data for the year 2002 was mainly due to current instabilities, except around boreal spring, where intraseasonal variability in surface winds was strongest.