Warm outbreaks of the Gulf Stream into the Sargasso Sea


  • Peter Cornillon,

  • David Evans,

  • William Large


A warm outbreak is a large body of Gulf Stream water with apparent anticyclonic circulation that detaches from the Gulf Stream and exists as a well-defined entity in the Sargasso Sea. Because warm outbreaks are warmer at the surface than Sargasso Sea water, they are often clearly visible in satellite thermal infrared imagery. From a survey of over 750 satellite images covering the Sargasso Sea immediately to the south of the Gulf Stream between 64° and 74°W and spanning a 5-year period, 18 possible outbreaks have been observed. All formed west of 65°W, with the majority forming between 67° and 72°W. Five of the 18 were observed to detach completely from the Gulf Stream and have the following properties in common: (1) they all formed in several days at or near the point of maximum cyclonic curvature of a large Gulf Stream meander, (2) the surface expression was relatively short-lived, of the order of 10 to 20 days, and (3) their dimensions (and those of the other 13) were of the order of 100 by 200 km. Given the similarity between the characteristics of warm outbreaks and those of “opposite vortices” predicted by Ikeda and Apel (1981) from a two-layer, quasi-geostrophic model of an eastward flowing jet, it is suggested that the two phenomena are related. Further support of this hypothesis is the fact that the rate of formation of warm outbreaks, between two and six per year, is similar to that of anticyclonic eddies observed in expendable bathythermograph surveys of this area.