Influence of the Southern Ocean Dipole on the inter-model diversity of temporal trend of the austral summer Southern Annular Mode in CMIP6 models

The Southern Annular Mode (SAM) is the predominant mode of climate variability across the Southern Hemisphere (SH) extratropical region. During the late 20th 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. The possible reason for the inter-model uncertainty in depicting the responses of the SAM to the SOD in DJF could be explained by the different sensitivities of atmospheric baroclinicity in middle and high latitudes to the underlying SST anomalies in each model, which may be associated with the internal processes of the climate system.