The Formation of Oceanic Eddies in Symmetric and Asymmetric Jets. Part II: Late Time Evolution and Coherent Vortex Formation

Abstract

The dynamical processes involved in eddy genesis, evolution, and demise as revealed in a series of high-resolution numerical simulations of perturbed oceanic jets are investigated. Comparisons are provided between the simulated eddy life cycles and observations of Gulf Stream warm- and cold-core rings. The dynamics of the meandering process, in particular, are analyzed in terms of the quasigeostrophic (QG) geopotential tendency equation. The vertical motions that develop during eddy genesis are analyzed in terms of the contribution to the QG omega equation by the advection of temperature and differential vertical vorticity. An examination of the cross-stream flux of isentropic potential vorticity during warm core and cold core events emphasizes the role of the near-field circulations, associated with the baroclinic meanderings of the jet, in the detachment and evolution of the simulated eddies. Comments are offered concerning the total heat transport by a ring alone as opposed to that effected by the dipolar structure formed by the ring and its near-field circulation. The spinup of deep circulations by the eddies is also examined and a comparison provided between the flow structure that develops in the oceanic frontal zone during ring formation and the flow that obtains during an atmospheric tropopause fold event.