[Antarctica] Southern Ocean [in 'State of the Climate in 2015']
The horizontal circulation of the Southern Ocean, which allows climate signals to propagate across the major ocean basins, is marked by eddies and the meandering fronts of the Antarctic Circumpolar Current (ACC). In 2015, large observed anomalies of sea surface height (SSH; Fig. 6.10a) contributed to variations in the horizontal ocean circulation. While many of these anomalies are typical of interannual variability, there were several regions where the 2015 anomaly was noteworthy due either to its extreme magnitude or its spatial coherence: north of the ACC in the Southwest Indian Ocean (~20°–90°E); in the entire South Pacific (~150°E–60°W), specifically the mid-Pacific basin around 120°W; and the anomalous negative SSH anomalies stretching around much of the Antarctic south of the ACC, especially over the Weddell Sea (0°–60°W). A large part of the 2015 SSH anomalies in the mid-Pacific, around Australia, and around South America was likely attributable to the strong El Nino event in 2015, though the low around Antarctica appears unrelated to ENSO variations (Sallee et al. 2008).