Brief description of ICM1

As a UK contribution to the international Indian Ocean survey carried out during 1995-96, an array of 6 moorings with 26 current meters was deployed across the Agulhas Current curing a two-week cruise aboard RRS DISCOVERY, 26 February to 9 March 1995, Durban to Capetown.

The Agulhas Current is the thermocline western boundary current for the South Indian Ocean and it has long been considered to be the strongest of the Southern Hemisphere western boundary currents. Direct measurements of its size and temporal variablility, however, had never been made; and arguments over the appropriate choice of reference level for geostrpohic transport estimates from hydrographic sections have led to a range of transport values from 35 to 95 Sv for the region where it closely follows the African continental slope. An accurate estimate of the transport of the Agulhas Current is a key to defining the large-scale circulation of the Indian Ocean. Thus, the primary objective for DISCOVERY Cruise 214 was to deploy this array of moored current meters, labelled ICM1 in international WOCE plans, to measure the transport and variability of the Agulhas Current over a year-long period.

The current meter array was recovered on cruises aboard R/V ALGOA in April-May 1996. The four offshore moorings (C, D, E, F) were recovered intact. The innermost mooring (A) had been dragged by a fishing trawler in mid deployment and as a result had lost its buoyancy. Dragging operations for mooring A were unsuccessful. Mooring B also was not recovered during the initial cruise despite dragging operations. Just after returning to the UK, the mooring team was recalled to South Africa to rejoin ALGOA and recover the drifing top of Mooring B located by ARGOS transmissions. Only the uppermost ACDP and FSI current meter were recovered from Mooring B. Thus, of the 26 current meters deployed in the Agulhas Current, 19 were recovered: 15 Aanderaa, 2 FSI and 2 ADCP instruments.

Related publications

Bryden, H. L., et al (1995): RRS Discovery Cruise 214, 26 Feb to 09 Mar 1995, Agulhas Current Experiment. Institute of Oceanographic Sciences Cruise Report No. 249, 85p.

Bryden, H.L. (1995): Agulhas Current Experiment (ACE). Sigma, the UK WOCE Newsletter, 16, 6-7.

Beal, L. M., and H. L. Bryden (1997): Observations of an Agulhas Undercurrent. Deep-Sea Research I, 44(9/10), 1715-1724.

Beal, L. M. (1997): Observations of the Velocity Structure of the Agulhas Current. PhD thesis, Department of Oceanography, University of Southampton, 158p.

Beal, L. and H. Bryden (1999): The velocity and vorticity structure of the Agulhas Current at 32S. J. Geophys. Res., 104(C3), 5151-5176.

Format of the current records

These files have been compressed with the ZIP compression utility. After downloading them, you will need to expand them. On a PC, WinZip or Pkunzip will do the job. Other utilities are available for the Unix and Macintosh environments. After expansion, you will have ascii files in OSU's stranger format.

The stranger format begins with several lines of header information that are meant to be machine-readable. They contain a Fortran format specification that will be useful in reading the file, a pointer to the first line of data, and a description of the data. Each line of the current record itself contains the time of the sample, the values recorded, and a line count.

Please be aware that end-of-line in these files is a carriage-return plus line-feed (the PC convention). This means that in a Unix environment (where a single line-feed serves as end-of-line) you may want to remove the carriage-returns.