Chapter 5 Climate Research

WCRP Activities > World Ocean Circulation Experiment (WOCE)

The World Ocean Circulation Experiment (WOCE) was established as a decade-long study aimed at improving the understanding of the key elements of the global ocean circulation. The observational phase of WOCE ended in 1998 and the analysis and synthesis phase ended in 2002. A particular contribution of Australia to WOCE was a series of measurements and innovative scientific analyses in the Southern Ocean, research that is now being incorporated into the CLIVAR and CliC programs.

The final conference for WOCE was held in USA in November 2002, and Australian scientists, particularly from CSIRO Marine Research (CMR), played a significant role in the organisation of the conference. Australia was also well represented among the invited speakers and at the conference. Australians made several contributions to "Ocean Circulation and Climate", an account of WOCE science, including a key contribution as one of the three editors.

The third and final version of the WOCE Data DVD was produced in late 2002, and scientists from CMR and BMRC were involved in the generation of the data sets. The BMRC-CMR Joint Australian Facility for Ocean Observing Systems (JAFOOS) continues to provide scientific support for the national Ship of Opportunity Program (SOOP) involving the collection, quality control and analysis of expendable bathythermograph (XBT) data. There is also continuing collaboration on the deployment by Australia of Argo floats, with 22 floats deployed mainly in the region of the Indian Ocean Throughflow (Figure 5.6). The Australian FedSat satellite, developed by the CRC for Satellite Systems, was launched in December 2002, and the CRC is evaluating its capability to support data exchange for Argo floats.

Figure 5.6. Active float locations around Australia as of March 27. Closed circles indicate Argo floats from international sources and open circles show the location of the Australian floats.

The JAFOOS in collaboration with the Tasmanian Partnership for Advanced Computing (TPAC) has established a Distributed Ocean Data System (DODS) server, giving access to a range of ocean data products. In collaboration with USA, CMR is assembling a new archive of highquality XBT data for the Indian Ocean region which will be available for climate prediction, variability and change studies.

The international project office for the Global Ocean Data Assimilation Experiment (GODAE) continues to be located in BMRC. A significant milestone for GODAE was successful conclusion of the first GODAE Symposium, held in France in 2002. One GODAE project is aimed at improving our capability to monitor the detailed structure of sea-surface temperature. CSIRO and other institutes are involved in the validation of sea-surface temperatures estimated from the Advanced Along Track Scanning Radiometer (AATSR) satellite instrument.

CMR and the Antarctic CRC have con- ducted a number of oceanographic projects in the Southern Ocean. Analysis of a multiyear experiment in the Mertz Glacier polynya confirms that the region is a significant source of Antarctic Bottom Water. The section between Tasmania and Antarctica has been occupied for the seventh time since the start of WOCE, and the data are being used to quantify the rate of change of physical and chemical properties throughout the full depth of the ocean. In collaboration with the USA and Japan, an array of moorings has been deployed to monitor the transport and variability of the deep western boundary current on the flank of the Kerguelen Plateau. The transport of the Antarctic Circumpolar Current is being monitored through both in situ observations observations and satellite altimetry. Analysis of historical ocean data indicates that decadalscale changes in large-scale patterns of the ocean are consistent with coupled climate model simulations of the enhanced greenhouse effect.

Several modelling studies on the role of the Southern Ocean in climate have been carried out at the University of NSW (UNSW). A coupled model has been used to investigate the variability of Antarctic Intermediate Water, especially the sensitivity to surface flux variations. Controlling influences on the mean circulation of the Southern Ocean were also examined, including the influence of the large-scale variability of surface winds (Figure 5.7). In relation to climate change, there have been studies of the uptake of carbon dioxide in the Southern Ocean, and coupled model studies of past global climates to estimate the impact of changes in sea-floor topography in the Southern Ocean on geological time scales.

Figure 5.7. Fifty-year temperature change at 900 m depth. (a) Observed (between 1950 and 2000; after Gille 2002); and (b) modelled (between year 50 and 100) from Oke and England (2003). The model experiment involves a simple southward latitude shift in the location of the westerly wind belt over the Southern Ocean. The southward shift is only 5-degrees of latitude over 100 years. No other changes are imposed. The experiment suggests that part of the observed cooling at intermediate depths north of 40 S might be associated with a southward drift in the westerly wind belt over the past century.

Using historical observations of upperocean temperatures on the southwest Pacific archived at Macquarie University, there have been continuing studies of climate variability, including seasonal and inter-annual volume transports and the propagation of temperature anomalies across the region. This work is complemented by modelling studies of the propagation of Rossby waves across the Pacific Ocean. Researchers at Macquarie University have also used box models to examine water mass changes within the global thermohaline circulation under conditions of climate change.

The first Indian Ocean GOOS Conference was held in Mauritius in November 2002 with significant Australian contributions, and it demonstrated progress in the planning and implementation of the Sustained Observations of Climate in the Indian Ocean (SOCIO) initiative. It is expected that this process will promote the deployment of additional Argo floats in the Indian Ocean in future years.