THE FORMATION OF OCEANIC EDDIES IN SYMMETRICAL AND ASYMMETRIC JETS .1. EARLY TIME EVOLUTION AND BULK EDDY TRANSPORTS

A numerical study of the life cycles of eddies formed in perturbed bar oclinic jets, emphasizing the influence of spanwise asymmetry in the i nitial structure of the jet on the downstream evolution of the now, is presented. In particular, attention is focused on the early time evol ution of two such currents that are fully determined by their lateral/ vertical cross sections of streamwise velocity and balanced temperatur e fields. The first jet profile is constructed so as to be representat ive of a typical observational cross section of the Gulf Stream off Ca pe Hatteras; it therefore has laterally asymmetric baroclinicity and b arotropy. The second cross section consists of a jet with laterally sy mmetric velocity shear. Primitive equation nonseparable linear stabili ty analyses of these two mean states are performed to determine the wa velengths, phase speeds, and growth rates of the fastest growing norma l modes of temporal instability. The life cycles of the eddies that de velop on these jets are investigated using a three-dimensional numeric al model that employs the nonhydrostatic Boussinesq equations of motio n in channel geometry with inflow/outflow streamwise boundary conditio ns. The wavelengths, phase speeds, and growth rates of the disturbance s that develop during the early stages of flow evolution are compared to those predicted by the temporal stability analysis presented herein , and also to previous temporal and spatial stability analyses. Bulk s panwise eddy transports of heat and momentum are examined to assess th e influence of asymmetry in the initial jet profile. The formation fre quency and strength of warm core and cold core rings in the two simula tions are compared and contrasted with observations of eddy formation in the Gulf Stream system. In a companion paper we explore the detaile d dynamical mechanisms through which individual coherent vortical stru ctures form and more fully analyze the associated horizontal and verti cal mixing of heat and potential vorticity.