On the Stability of Oceanic Rings

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Abstract
Oceanic rings tend to have length scales larger than the deformation radius and also to he long-lived. This latter characteristic, in view of the former, is particularly curious as many quasigeostrophic and primitive equation simulations suggest such eddies are quite unstable. Large eddies eventually break into smaller deformation scale vortices, with the attendant production of considerable variability. Here it is argued that the stability characteristics of oceanic eddies and rings are sensitive to the presence of deep flows. In particular, eddies in which the deep flow is counter to the sense of the shallow flows are often more unstable than eddies with no deep flow, while eddies with circulations in the same sense as the shallow circulation can experience an enhanced stability. For a given vertical shear, oceanic eddy stability can vary dramatically. (This is in contrast to quasigeostrophic theory, where stability properties are largely determined by vertical shear.) The onset of these mechan... Abstract Oceanic rings tend to have length scales larger than the deformation radius and also to he long-lived. This latter characteristic, in view of the former, is particularly curious as many quasigeostrophic and primitive equation simulations suggest such eddies are quite unstable. Large eddies eventually break into smaller deformation scale vortices, with the attendant production of considerable variability. Here it is argued that the stability characteristics of oceanic eddies and rings are sensitive to the presence of deep flows. In particular, eddies in which the deep flow is counter to the sense of the shallow flows are often more unstable than eddies with no deep flow, while eddies with circulations in the same sense as the shallow circulation can experience an enhanced stability. For a given vertical shear, oceanic eddy stability can vary dramatically. (This is in contrast to quasigeostrophic theory, where stability properties are largely determined by vertical shear.) The onset of these mechan...

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