Generation and Evolution of a Cyclonic Ring at Drake Passage in Early 1979

Abstract

An equatorward meander in the Antarctic Polar Front at Drake Passage was observed to amplify and pinch off during January and early February 1979, forming a cold-core. cyclonic current fins with a radius of ?50 km. This ring appeared to move directly across the Passage parallel to a submarine ridge before turning northeastward upon reaching a gap between the ridge and the South American continental rise. Its net motion was across the Polar Frontal Zone and the ring was last observed to be pushing through the Subantarctic Front. Geostrophic surface speeds of up to 90 cm s?1 relative to 3500 m wore observed where the northern sector of the ring and the Subantarctic Front were In proximity. A stability analysis of the banded flow regime across Drake Passage suggests that necessary conditions for baroclinic instability exist everywhere within the zonal current and those for barotropic instability exist adjacent to the fronts. The beat and salt anomalies of this ring relative to the Polar Frontal Zone are estimated as ?8 ? 1018 J and ?2 ? 1011 kg, respectively, and relative to the Subantarctic Zone as ?3 ? 1019 J and ?8 ? 1011 kg, respectively. The process of ring migration across these fronts is potentially important to the heat and salt budgets of the Southern Ocean.