THE MAINTENANCE OF THE LAST GREAT ICE SHEETS - A UGAMP GCM STUDY

A 5-yr simulation of the last glacial maximum using the UGAMP GCM is p resented. It has a full seasonal cycle, T42 resolution, and interactiv e land surface and sea ice. Boundary conditions of SST, sea ice extent , and land ice elevation are taken from the CLIMAP dataset, and orbita l parameters and carbon dioxide concentration are adjusted. It is comp ared with a 10-yr simulation of present-day climate using the same mod el. The results are analyzed in terms of processes leading to the main tenance of the atmospheric circulation and temperature structure, midl atitude transient behavior, precipitation, and eventually accumulation of ice over the glaciers. The model responds in a similar manner to p revious studies in global mean statistics but differs in its treatment of regional climates. Changes in sea ice and orography are equally im portant in determining the positions of the upper-level jets. The Atla ntic jet and storm track in particular are much stronger than in the p resent-day simulation, and the associated distribution of precipitatio n and snowfall changes accordingly. Both major ice sheets are maintain ed by snowfall at the center and ablation at the edges at a reasonable rate through the annual cycle. The results with a full seasonal cycle are compared to perpetual integrations by the authors and found to be very similar in most measures.