Dipole rings and vortex interactions of the Brazil Current

A reexamination of satellite-derived sea surface temperature imagery reveals many examples of Brazil Current rings, both warm and cold, in dipole configurations. The dynamical significance of the dipole model is established by considering the interaction of a cold (cyclonic) eddy with a warm (anticyclonic) ring. The ring is shown to exist as a dipole for about 60 days, or two rotation periods based on its original rotation rate of approximately 12' per day. The observed interaction of the dipole ring with a solitary (or monopole) cold eddy is complicated, but results in the two vortices coalescing. The latter point is particularly important, since coalescence between two eddies with opposing vorticities cannot occur if they are both monopoles-one of them has to be a dipole. After coalescence, the rotation of the dipole ring temporarily reverses due to the addition of cyclonic vorticity, but the original rotation of the dipole is reestablished after an adjustment phase.