Statistics of Brazil current rings observed from AVHRR: 1993 to 1998

Abstract

A 6-year time series of sea surface temperature fields derived from NOAA polar-orbiter AVHRR 5-day composites is used to estimate the lifetime, size, and trajectory of 43 warm-core rings shed by the Brazil Current at the Southwestern Atlantic region in a consistent fashion for the first time. Ring lifetimes range from 11 to 95 days, and are not bi-modal as is the case for the Gulf Stream anticyclones. Translational speeds range from 4.2 to 27.2 km/day with a mean value of 13.1 km/day. After formation, rings are mostly elliptical with a mean major radius of 126 ± 50 km and a minor radius of 65 ± 22 km. None of the rings seem to last more than four months in the region. An attempt to explore possible connections between ring shedding variability and the Antarctic Dipole is also addressed.