Cyclonic Ring Research Articles

Cyclonic ring formation at the polar front in the Drake Passage

THE first summary of geographical locations of the antarctic convergence (polar front) by Mackintosh1 showed that >50% of the instantaneous locations of the front differed from the mean location by as much as ±50 km. Early hydrographic section work could not resolve the temporal or spatial fluctuations in the horizontal structure of the front. During FDRAKE 75 Gordon2 observed comparable fluctuations in the frontal position in the Scotia Sea but again the spacing between sections was too wide. During FDRAKE 76 (refs 3, 4 and T. M. Joyce et al., unpublished) the small scale structure of the polar front was studied in the Drake Passage. Two ships, the RV Thompson (University of Washington) and the Chilean naval vessel AGS Yelcho, combined efforts in the program which took place during the onset of the austral autumn. We describe here the evolution of the polar front between February 29 and April 5, 1976, a time span of ∼5 weeks.

On Entrainment and Diffusion in a Gulf of Mexico Anticyclonic Ring

Abstract The parametric model used by Schmitz and Vastano (1975) to investigate a Gulf Stream cyclonic ring has been applied to successive observations of a Gulf of Mexico anticyclonic ring. Coefficients for a polynomial representation of the transverse streamfunction ψ(r,z) were determined for pairs of eddy diffusivity coefficients. Using the minimum least-squares error residual as a criterion, the best flow pattern for the ring occurred for (Kh,Kz)=(106,0) cm2 s−1. The total transverse transport through the ring was found to be an order of magnitude larger than that found in the Gulf Stream cyclonic ring.

Entrainment and Diffusion in a Gulf Stream Cyclonic Ring

The mixing and entrainment processes present in a cyclonic ring are investigated by means of a parametric model which is fitted to serial temperature data for a North Atlantic ring. The physical model assumes an axially symmetric ring in which the temperature is presumed to be governed bywhere KA and KZ are the horizontal and vertical eddy diffusivity coefficients and J(ψT) is the (r,z) Jacobian of the transverse streamfunction ψ and the temperature T. Data from two cruises during the 1967 observation of a ring by the Woods Hole Oceanographic Institution provided estimates of the derivatives of the temperature. Regression analysis was used to determine the coefficients for polynomial representations of ψ(r,z) for selected combinations of Kh and Kz. The study indicates upper bounds on the order of magnitude for the diffusivities (Kh,Kz)=(105,10) cm2 s−1 based upon near-minimum least-squares error estimates from the regression analysis. An important result is that little differentiation exists between a purely advective entrainment regime and those regimes including both entrainment and diffusion; i.e., the entrainment circulation appears to be the dominant mechanism in the temporal changes of the ring for a time scale of at least two months. The results provide streamline patterns for the transverse flow from the surface to 1000 m depth consistent with isotherm movement and changes in the ring water masses.

On the Acoustic Characteristics of a Gulf Stream Cyclonic Ring

Abstract The acoustic properties of a cyclonic Gulf Stream ring have been studied with field data and ray computations. Cyclonic rings represent relatively low sound velocity regions with large horizontal gradients of sound velocity embedded in the Sargasso Sea. Ray computations have shown the development of deep sound-channel-axis propagation from a near-surface source within a cyclonic ring.