The Southern Ocean is the expanse of ocean encircling the Antarctic continent. Often it is defined as all ocean areas south of 35°S (e.g., Chelton et al. 1990) or 40°S (e.g., Mestas-Nuñez et al. 1992). Because of its vast size, encompassing nearly 30% of the global ocean, because of its notoriously strong wind and wave conditions, and because it is nearly unbroken by land, the Southern Ocean is difficult to monitor from ships. Sea surface height (SSH) measurements from satellite altimetry have proved crucial in characterizing both the time-mean features and the variability of the region.