Seasonal SAM Zonal Asymmetries and their Connection to Antarctic Temperature Variability

The Southern Hemisphere Annular Mode (SAM) is the dominant mode of climate variability in the extra-tropical Southern Hemisphere. Representing variations in pressure and the corresponding changes to the circumpolar zonal flow, it is typically thought of as an ';annular' or ring-like structure. However, on seasonal timescales the zonal symmetry observed in the SAM in monthly or annual mean data is much less marked. This presentation will examine the seasonal changes in the SAM structure, and explores temperature signals across West Antarctica and the Antarctic Peninsula that are strongly tied to the asymmetric SAM structure. The SAM asymmetries are most marked in the Pacific sector and in austral winter and spring, related to changes in the jet entrance and exit regions poleward of 30S. Depending on the season, the asymmetric SAM structure explains over 25% of the variance in the overall SAM structure and has strong connections with ENSO or zonal wave number 3. Across the Pacific sector, including the Antarctic Peninsula, temperature variations are strongly tied to the asymmetric SAM structure, while temperatures across East Antarctica are more strongly tied to the zonally symmetric SAM structure. This suggests that temperature changes in these regions are more strongly modulated by the asymmetric, meridional circulations rather than changes in the zonal mean flow, in agreement with recent research.