GCM SIMULATIONS OF ATMOSPHERIC TRACERS IN THE POLAR LATITUDES - SOUTH-POLE (ANTARCTICA) AND SUMMIT (GREENLAND) CASES

Simulation results from two global atmospheric tracer/climate models in the interior of the two major ice sheets at high northern and southern latitudes are presented and discussed. The models are based on two existing general circulation models (GCMs) of the atmosphere, complemented with tracer formulations (sources, transport, mixing, deposition, etc.). The seasonal and shorter term variability of desert dust, sea salt, Rn-222, Pb-210, and Be-7 has been studied at the South Pole in Antarctica and at Summit in Greenland. This choice of tracers and test regions serves to focus on the interactions between atmospheric parameters (e.g. the strong and durable surface inversions characteristic of the ice sheets) and tracers, and to limit other influences such as source variability and chemistry. Comparison with available observations is not consistently favorable. Short-term variability in the atmosphere (Rn-222 and Pb-210) appears qualitatively reasonable. Seasonal cycles are in some instances opposite to those observed, and mean deposition is clearly too high. The coarseness of model resolution at the high latitudes and the difficulty of setting up efficient formulations for microphysical tracer processes (e.g. dry and wet deposition) are major sources of problems. If these obstacles are overcome, the combined tracer/climate modelling approach can offer quantitative interpretation of the observed features of atmospheric contaminants, or sensitive tests of GCM simulated atmospheric circulation.