Climate variability in the Southern Hemisphere (SH) extratropical regions is dominated by the SH annular mode (SAM). Future changes in the SAM could have a large influence on the climate over broad regions. In this paper, the authors utilized model simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5) to examine projected future changes in the SAM during the austral summer [December-February (DJF)]. To start off, first, the ability of the models in reproducing the recently observed spatial and temporal variability was assessed. The 12 CMIP5 models examined were found to reproduce the SAM's spatial pattern reasonably well in terms of both the symmetrical and the asymmetric component. The CMIP5 models show an improvement over phase 3 of CMIP (CMIP3) in simulating the seesaw structure of the SAM and also give improvements in the recently observed positive SAM trend. However, only half the models appeared to be able to capture two major recent decadal SAM phases. Then, the future SAM trends and its sensitivity to greenhouse gas (GHG) concentrations using simulations based on the representative concentration pathways 4.5 (RCP4.5) and 8.5 (RCP8.5) were explored. With RCP4.5, a very weak negative trend for this century is found. Conversely, with RCP8.5, a significant positive trend was projected, with a magnitude similar to the recently observed trend. Finally, model uncertainty in the future SAM projections was quantified by comparing projections from the individual CMIP5 models. The results imply the response of SH polar region stratospheric temperature to GHGs could be a significant controlling factor on the future evolution of the SAM.

The tropical Atlantic is home to multiple coupled climate variations covering a wide range of timescales and impacting societally relevant phenomena such as continental rainfall, Atlantic hurricane activity, oceanic biological productivity, and atmospheric circulation in the equatorial Pacific. The tropical Atlantic also connects the southern

[1] This study investigates the existence of a dipole mode in the sea surface temperatures (SST) over the South Atlantic Ocean (SAO), using observational and reanalysis data sets from 1950 to 2008. Our results demonstrate that an opposite SST mode, the SAO dipole (SAOD) occurs in the SAO as the anomalous surface waters in the northeastern part; that is, the Atlantic Niño sector and the southwestern part off the Argentina-UruguayBrazil coast are consistently anticorrelated in all months. A typical SAOD episode has a life cycle of about eight months, although the peak intensity in which the SST anomalies are evidently coupled to atmospheric circulation and precipitation anomaly fields lasts for four months during the austral winter (May-August). This coupled atmosphere-ocean interaction mechanism appears to be unique, distinct from the classical Atlantic Niño and independent of the direct influence of the Pacific Ocean-based El Niño or global SST variability. The SAOD may provide a useful framework for investigating climate variability and for improved predictions especially over parts of Africa and the Americas, and some preliminary results are already indicated, e.g., the SAOD is widely related to precipitation anomalies in these regions particularly during the austral winter.