International Support for the SA Agulhas's mission in Antarctica

Jan 12, 2006
Author: Ian Hunter, Principal Researcher, SA Weather Services

The 'SA Agulhas' left Penguin Bukta (*) on Sunday 8 January to deploy nine drifting weather buoys, plus one automatic weather station (AWS) on South Thule Island.
South Thule is the southernmost island in the chain that makes up the South Sandwich group.

Following the departure from Cape Town on 1 December, various global weather and wave prediction models were used by SA Weather Service's (SAWS) National Forecast Centre (NFC) to provide the ship with marine forecasts through the 40's and 50's. At around 60S, however, sea ice became the most important consideration for navigation. The University of Bremen makes available daily the microwave imagery from the Aqua satellite's AMSR-E sensor (National Space Agencies of the US and Japan).

Figure 1 shows the pack ice imagery on 9 January 2005. This time last year the situation was very different with a broad wedge of pack ice still in place between the Bukta and South Thule.

The National Snow and Ice Data Center (NSIDC) in Colorado uses another sensor onboard NASA's Aqua satellite - the Moderate Resolution Imaging Spectroradiometer (MODIS) - to produce detailed imagery of the Fimbul Ice Shelf. They processed additional imagery especially for SAWS in order to help the 'Agulhas' navigate through the last section of pack ice. The most recent MODIS image is shown in figure 2 - there was still a lot of fast ice attached to the coast between Penguin Bukta and Atka Bay (where the German base Neumeyer, is situated)

Now back at sea with most of the pack ice melted, the 'Agulhas' once again faces the weather and the waves (the latter are largely absorbed by the pack ice when a vessel is to the south of the ice). The Antarctic Mesoscale Model Prediction System (AMPS) group in Boulder has created several new products to help SAWS in its support for the ship. These include 5-day meteograms for South Thule and Bouvet islands (the 'Agulhas' will be visiting the latter on the return voyage to replace the AWS for Norway). There are also meteograms (surface and upper air time series predictions of pressure, wind, humidity and temperature) - for the vicinity of the Bukta and one for Vesleskarvet (the site of SANAE IV). The group have developed two new model domains : Queen Maud (20 km resolution) - and a 15 km domain concentrated on the expected track of the ship.

As in the past, the team replacing the AWS on South Thule will be going ashore by boat. Sea state predictions will thus be important. Model guidance is available to NFC from both the UK Met. Office and NOAA's Wavewatch III model.

Sub-sea seismic activity

A fairly recent development which was of some concern for safe navigation around the South Sandwich Islands was some severe sub-sea seismic activity. Undersea earthquakes can result in significant changes to the bathymetry. The Geological Survey Department in the United States posts detailed information on all recent earthquake events on the Internet. Two have been recorded to the east of the islands this year. The first, on 2 January was of magnitude 7.3, fortunately with a deep epicentre (46km).

More spectacular was the volcanic activity on Montagu Island. See figure 3 - this image was captured by the ASTER sensor, flying on NASA's Terra satellite on 23 September 2005. It was provided by the Thermal Alert Team based at the University of Hawaii, who also sent SAWS information on other volcanic activity in the island chain. The Global Volcanism Program (Smithsonian Institution, Washington) also provided very useful information and imagery on the current volcanic activity on Montagu Island.

Mt Belinda started erupting in 2001 and lava flows reaching the north coast have resulted in the island being extended by about 500m.

(*) a bay/ indentation in the coastal ice shelf - usually surrounded by high cliffs



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