Observations of a Cold-Core Gulf Stream Ring with an “Explosive” Elliptical Instability

A large cold-core Gulf Stream ring rapidly elongated approximately three weeks after its formation. Over a four-day period the aspect ratio of the cold core of the ring increased from about 2.8 to 6.4 as it took the form of a slender ellipse. During the next week further elongation occurred; a dipolar structure possibly formed. While the elongation and breakup of the ring may have been influenced by the proximity of the Gulf Stream, the observations support the predictions that isolated, large-enough vortices have an elliptical mode baroclinic instability.