Antarctic Dipole: Its Index and Feedback to the Atmosphere

Antarctic Dipole (ADP) is a spatially coherent pattern with out of phase anomalies in sea ice/surface temperature fields in the South Pacific and South Atlantic. As early studies revealed, ADP is trigged by ENSO events and dominates the interannual variability in the Antarctic sea ice field. However, ADP does not disappear when ENSO forcing is diminished. It becomes more developed and persists in next 3-4 seasons after ENSO events mature in the tropics. This study focuses on ADP's high latitude characteristics and its feedback to the overlying atmospheric circulation at mid-high latitudes. The ADP index is defined by sea ice edge anomalies averaged in the ADP Atlantic center (50W-20W) minus the mean anomaly in the Pacific center (150W-120W). The index is dominated by interannual variability without a significant long-term trend. The index has a significant spectral peak at a 3-year period. Revealed by zero lag correlations, the ADP index co-varies with spatially consistent patterns in temperature, pressure and wind fields from sea level up to the tropopause. Spring ADP has significant correlations with summer Southern Annular Mode and Semi-Annual Oscillation indices. The correlations between the spring ADP index and summer atmospheric variables reveal different patterns from that of zero lag correlations, suggesting the sea ice's influence on the atmosphere.