Structure and Transport of the Agulhas Current and

Authors: Harry L Bryden Lisa M Beal Louise M Duncan

Publish Date: 2005/06/01

Volume: 61, Issue: 3, Pages: 479-492

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Abstract

Using a yearlong moored array of current meters and wellsampled synoptic sections we define the variability and mean structure and transport of the Agulhas current Nineteen current meter records indicate that time scales for the temporal variability in the alongshore and offshore velocities are 102 and 54 days respectively Good vertical correlation exists between the alongshore or onshore velocity fluctuations excluding the Agulhas Undercurrent The lateral scale for the thermocline Agulhas current is about 60 km and the onshore velocity correlations are positive throughout the Agulhas Current system Mean velocities from the array determine that the offshore edge of the Agulhas Current lies at 203 km and the penetration depth is 2200 m offshore of the Undercurrent Hence daily averaged velocity sections determined by interpolation and extrapolation of current meter locations for a 267day period from the surface to 2400 m depth and from the coast out to 203 km offshore encompass the main features of the Agulhas Current system The Agulhas current is generally found close to the continental slope within 31 km of the coast for 211 of 267 days There are only five days when the core of the current is found offshore at 150 km Total transport is always poleward varying from −121 to −9 Sv with maximum transport occurring when the core is 62 km from the coast Average total transport for the 267 day period is −697 Sv the standard deviation in daily transport values is 215 Sv and the mean transport has an estimated standard error of 43 Sv The Agulhas Undercurrent which hugs the continental slope below the zero velocity isotach has an average equatorward transport of 42 Sv standard deviation of 29 Sv and an estimated standard error of 04 Sv Transports from the moored array are in reasonable agreement with transport results from synoptic sections Based on time series measurements at about 30° latitude in each ocean basin the Agulhas Current is the largest western boundary current in the world ocean

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