The Arctic and Antarctic Oscillations in the IPCC AR4 Coupled Models

This study evaluates the fidelity of Arctic and Antarctic oscillations (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 24 models are analyzed and compared with that in ERA-40 and NCEP-1. Models' performance is seasonally dependent, with best reproducibility of both spatial structure and trend in winter. In most models, the spatial pattern and temporal trend of AAO during this period are more delicately simulated than AO. After picking out models with better performance according to the Taylor diagram, we find that their ensemble mean can obviously improve models' reproducibility. The AO and AAO in the Special Report on Emission Scenarios (SRES)A1B Projection during the 21st century are also briefiy analyzed. The results reveal that both the AO and AAO indices keep increasing during 1970-2099, with a steadier pace of AO than AAO. The spatial difference of sea level pressure between 2060-2089 and 1970-1999 shows decreased values in polar regions,and increased values in midlatitudes. The results manifest that the ozone recovery during the mid 21st century may not weaken such a trend.