Structure and transport of the Agulhas current and its temporal variability

Harry L. Bryden, Lisa Beal, Louise M. Duncan

Research output: Contribution to journalArticle

114 Citations (Scopus)

Abstract

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.

Original languageEnglish (US)
Pages (from-to)479-492
Number of pages14
JournalJournal of Oceanography
Volume61
Issue number3
DOIs
StatePublished - Jun 2005

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undercurrent
continental slope
coast
western boundary current
ocean basin
thermocline
interpolation
penetration
time series
timescale
ocean

Keywords

  • Agulhas current
  • Agulhas undercurrent
  • Boundary current variability
  • Circulation
  • Sverdrup transport
  • Western boundary currents

ASJC Scopus subject areas

  • Oceanography

Cite this

Structure and transport of the Agulhas current and its temporal variability. / Bryden, Harry L.; Beal, Lisa; Duncan, Louise M.

In: Journal of Oceanography, Vol. 61, No. 3, 06.2005, p. 479-492.

Research output: Contribution to journalArticle

Bryden, Harry L. ; Beal, Lisa ; Duncan, Louise M. / Structure and transport of the Agulhas current and its temporal variability. In: Journal of Oceanography. 2005 ; Vol. 61, No. 3. pp. 479-492.
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