24th Pacific Science Congress (PSC-24)

The Southern Annular Mode (SAM) is the predominant mode of climate variability across the Southern Hemisphere (SH) extratropical region. During the late 20^th century, the SAM has undergone a remarkable positive trend, particularly pronounced in austral summer (December-January-February, DJF), which is mainly attributed to the ozone depletion in Antarctic stratosphere. However, 42 state-of-the-art models archived in CMIP6 exhibit noteworthy inter-model spread of the simulated long-term trend of the DJF SAM, with an inter-model standard deviation of 0.19 (per decade) both in AMIP and historical experiments. This study aims to explore the potential sources of model uncertainty in simulating the DJF SAM trend. Corresponding results from AMIP experiments indicate that the dominant mode of SH extratropical sea surface temperature (SST), namely the Southern Ocean Dipole (SOD), plays an important role in model performance in reproducing the SAM variability. Models with stronger linkage between the SOD and the SAM tend to simulate a more positive trend as well as a more realistic inter-annual variability of the DJF SAM, the averaged explained variance is over 30% in AMIP experiment.
 

Southern Annular Mode (SAM) · Southern Ocean Dipole (SOD) · Temporal variability · Inter-model diversity