Abstract
Hydrographic data and a specially designed expendable bathythermograph survey are used to study the dynamics of a Gulf Stream cyclonic ring over a period of four months. The analysis includes an examination of the ring vorticity balance under the gradient current approximation (geostrophy with centripedtal correction), ring energetics, and the three-dimensional structure of perturbations to a symmetric ring. The ring is shown to have a frontal layer comparable to strong mid-tropospheric fronts in the atmosphere that persists over the entire four-month period. Consideration of potential vorticity conservation indicates that the frontal layer with its potential vorticity maxima can be of major importance to the longevity of t-S anomalies in the ring core. Energy calculations lead to the conclusion that a flux of available potential energy occurs across the frontal layer and that this flux of energy can be accounted for in terms of the presence of waves superimposed on the ring. These waves are primarily at azimuthal modes n = 1 and 2 (one and two waves around the ring) with the n = 1 wave aligned with respect to the far field potential vorticity gradient and n = 2 aligned such that the major axis is normal to the direction of ring translation. A consistent appearance of higher amplitude disturbances to ring shape in the lee of the ring relative to translation which could be attributed to internal ring dispersion tis noted. An evaluation of the three-dimensional thermal structure around the ring suggests a transfer from the mean ring potential energy to the perturbations via baroclinic instability although the evidence is not conclusive. There are also indications that the flow in the neighborhood of the ring front involves baroclinic modes greater than one in the vertical. The observational results are compared with several ring models.
Olson, Donald Bruce (1979). Frontal dynamics of a gulf stream ring. Doctoral dissertation, Texas A&M University. Texas A&M University. Libraries. Available electronically from
https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -151741.