Structure and Transport of the Agulhas Current and Its Temporal Variability
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Using a year-long moored array of current meters and well-sampled 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 10.2 and 5.4 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 267-day 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 −69.7 Sv; the standard deviation in daily transport values is 21.5 Sv; and the mean transport has an estimated standard error of 4.3 Sv. The Agulhas Undercurrent, which hugs the continental slope below the zero velocity isotach, has an average equatorward transport of 4.2 Sv, standard deviation of 2.9 Sv and an estimated standard error of 0.4 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.
KeywordsAgulhas Current Agulhas Undercurrent western boundary currents Sverdrup transport circulation boundary current variability
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- Beal, L. M. (1997): Observations of the velocity structure of the Agulhas Current. Ph.D. Thesis, Department of Ocea-nography, University of Southampton, 158 pp.Google Scholar
- Bryden, H. L. (1976): Horizontal advection of temperature for low-frequency motions. Deep-Sea Res., 23, 1165–1174.Google Scholar
- Bryden, H. L. et al. (1995): RRS Discovery cruise 214, 26 Feb–09 Mar 1995: Agulhas Current Experiment. Cruise Report 249, Institute of Oceanographic Sciences, Wormley, 85 pp.Google Scholar
- Grindlingh, M. L. (1979): Observation of a large meander in the Agulhas Current. J. Geophys. Res., 84, 3776–3778.Google Scholar
- Grindlingh, M. L. (1983): On the course of the Agulhas Current. South African Geographical Journal, 65, 49–57.Google Scholar
- Imawaki, S., H. Uchida, H. Ichikawa, M. Fukasawa, S. Umatani and the ASUKA Group (2001): Satellite altimeter monitoring the Kuroshio transport south of Japan. Geophys. Res. Lett., 28, 17–20.Google Scholar
- Johns, W. E., T. N. Lee, D. Zhang and R. Zantopp (2001): The Kuroshio east of Taiwan: Moored transport observations from the WOCE PCM-1 Array. J. Phys. Oceanogr., 31, 1031–1053.Google Scholar
- Josey, S. A., E. C. Kent and P. K. Taylor (2002): Wind stress forcing of the ocean in the SOC climatology: Comparisons with the NCEP/NCAR. ECMWF, UWM/COADS and Hellerman and Rosenstein datasets. J. Phys. Oceanogr., 32, 1993–2019.Google Scholar
- Schouten, M. W., W. P. M. de Ruijter and P. J. van Leeuwen (2002): Upstream control of Agulhas Ring shedding. J. Geophys. Res., 107(C8), 10,1029/2001JC000804.Google Scholar
- van Leeuwen, P. J., W. P. M. de Ruijter and J. R. E. Lutjeharms (2000): Natal pulses and the formation of Agulhas rings. J. Geophys. Res., 105, 6425–6436.Google Scholar