The Arctic and Antarctic oscillations in the IPCC AR4 coupled models.

This study evaluates the fidelity of Arctic and Antarctic Oscillation (AO and AAO for short, respectively) in the coupled general circulation models participating in the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR4). The AO and AAO during 1970-1999 in twenty four models were analyzed and compared with those in the ERA-40 and NCEP/NCAR reanalysis data1. Models' performance is seasonally dependent, with the best reproducibility of both spatial structures and trends in winter. In most models, the spatial pattern and temporal trend of AAO during this period were simulated better than those of AO. After picking out models with better performance according to Taylor diagram, we found that their ensemble mean obviously improved models' reproducibility. The AO and AAO under the Special Report on Emission Scenarios (SRES) A1B Scenario during the 21st century were also briefly analyzed. The results during the period 1970-2099 reveal that both the AO and AAO indices keep increasing during the whole period, with a relatively steadier pace in the AO. The spatial difference in sea level pressure between 2060-2089 and 1970-1999 also shows decreased values in the two polar regions, and increased values in the mid-latitudes. Results also manifest that the ozone recovery in the mid -21st century may not weaken such a trend.