The Maintenance of the Last Great Ice Sheets: A UGAMP GCM Study

Abstract

A 5-yr simulation of the last glacial maximum using the UGAMP GCM is presented. It has a full seasonal cycle, T42 resolution, and interactive land surface and sea ice. Boundary conditions of SST, sea ice extent and land ice elevation are taken from the CLIMAP dataset and orbital parameters and carbon dioxide concentration are adjusted. It is compared with a 10-yr simulation of present-day climate using the same model. The results are analyzed in terms of processes leading to the maintenance of the atmospheric circulation and temperature structure, midlatitude transient behavior, precipitation, and eventually accumulation of ice over the glaciers. The model responds in a similar manner to previous studies in global mean statistics but differs in its treatment of regional climates. Changes in sea ice and orography are equally important in determining the positions of the upper-level jets. The Atlantic jet and storm track in particular are much stronger than in the present-day simulation, and the associated distribution of precipitation and snowfall changes accordingly. Both major ice sheets are maintained 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.