SEASONAL-VARIATIONS IN EQUATORIAL ATLANTIC-OCEAN ZONAL VOLUME TRANSPORT AT 28-DEGREES-W

Zonal volume transport is examined over the upper 150 m of the water c olumn at 28-degrees-W, using the Seasonal Response of the Equatorial A tlantic experiment moored current meter data at 0.75-degrees-S, 0.0-de grees, and 0.75-degrees-N and a time domain empirical orthogonal funct ion (EOF) analysis to improve spatial and temporal resolution. Gaussia n distributions are fit to the mean volume transports per unit width a nd the fluctuations about these means that are found to be represented by a single EOF mode. The mean volume transport is distributed symmet rically both about the equator and about 75 m depth, with a meridional scale width of 101 km and a magnitude of 20.3 Sv. The standard deviat ion for the fluctuations is 4.7 Sv, and in contrast to the mean the fl uctuations are confined to above 100 m depth, with a larger meridional scale width. The scale width for the mean is consistent with an inert ial scale associated with conservation of potential vorticity, while t he scale width for the fluctuations is consistent with an equatorial R ossby radius of deformation associated with equatorially trapped waves . These findings support a hypothesis that different physical processe s are controlling the volume transport, as integrated from the surface across the Equatorial Undercurrent, over different time scales. On th e time scale of the record length average, inertial dynamics appear to be controlling, while on the time scales of the seasonal fluctuations , linear equatorial long-wave dynamics appear to be controlling. Howev er, given the limited record length, there are insufficient degrees of freedom to test this hypothesis statistically.