BACKGROUND

Introduction

The Agulhas Undercurrent was first observed as recently as March 1995, when measurements of full depth velocity were possible with LADCP (Beal and Bryden, 1997).

The first observations of the Undercurrent in March 1995 were made during the Agulhas Current Experiment (ACE), which included a large deployment of moorings to capture the variability of the Agulhas Current.

Although the mooring array was designed without knowledge of the Undercurrent, one time series did capture its northeastward flow.

Figure 1. Vertical section of LADCP velocities (cm/sec) across the Agulhas Current. Positive velocities flow to the southwest. Bathymetry is shaded black.
Two more sections of combined CTD/LADCP stations captured the Undercurrent during the WOCE Indian Ocean hydrographic program (Donohue et al., 2000). All three sections were repeats of a line first occupied in 1987, nominally at 32° S (Toole and Warren, 1993).

The second section (I7R) was occupied just two weeks later and only one profile of the Undercurrent was captured owing to coarse station spacing (Donohue et al., 2000)

The third section (I5W) was occupied in June and resolves the Undercurrent well.

These three available LADCP sections are consistent, suggesting that the Undercurrent is at least common, and probably permanent, at 32° S.

In the rest of this section we briefly describe the results of the analyses that have been carried out using the above-mentioned data, in order to provide an introduction to what is known of the structure and variability of the Agulhas Undercurrent (AUC).