Tracer Transport Model

An important tool for improving our understanding of the biogeochemical cycles of atmospheric trace gases that cause climate change and for studying the release of radioactive gases at the regional scale is a high resolution three-dimensional global atmospheric circulation model which can be used to investigate the sources, removal processes and atmospheric chemistry of these trace gases. In the past, even low resolution three-dimensional models have placed enormous computational demands on supercomputers.

This continuing project has involved the development of a computationally efficient high-resolution simulation model for atmospheric transport and chemistry, the Australian National University Chemical Transport Model (ANU-CTM) (Taylor, 1989, 1991; Taylor et al., 1991) with parameterised interactions between the oceans and the biosphere. Models of the sources and sinks of the trace gases CFC-11, CFC-12 (Taylor, 1991), methyl chloroform (Taylor et al., 1991), methane (Taylor et al, 1991), CO2 (Taylor, 1989, 1993, 1995; Taylor and Lloyd,1992), radon (Taylor, 1991), CO (Erickson and Taylor,1992; Taylor et al 1995), N2O (Taylor, 1992; Bouwman and Taylor, 1996) have been developed and incorporated into the transport model.

Key Physical Processes represented in the model include

The basic approach of the stochastic Lagrangian model is to divide the troposphere into air parcels of equal mass. Trajectories for these air parcels are calculated using observed wind field data obtained from the European Centre for Medium Range Weather Forecasting. While the simulated air parcels are being transported around the globe, they can exchange chemical compounds with the oceans, the biosphere and one another and take up industrial emissions of trace gases. The model runs on the Silicon Graphics Power Challenge and VP2200 supercomputers at the Australian National University Supercomputing Facility. Model runs with up to 1 000 000 air parcels, giving an effective model resolution below 1 x 1 degree, have easily been achieved. Model runs at higher resolution are possible and will be required in the future to answer questions about sources and sinks of greenhouse gases at a regional scale and to investigate the release of radioactive tracers at the regional scale.

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