Cyclonic ring spin-down in the North Atlantic

Abstract

A study of the spin-down mechanism of the North Atlantic cyclonic rings is undertaken. Both data analysis and numerical modelling are employed to describe the decay process. The numerical studies consider a stationary, axially symmetric ring in an ocean at rest. A similarity hypothesis is applied to the equations of motion to obtain a parametric representation of the depth dependence of the density and velocity structure. The dependent variables after this transformation are the thermocline depth, the surface density variation and the surface tangential and radial velocities. The model is developed to obtain the first three variables by prognostic relations and the radial velocity by a diagnostic relation. A simple diffusion model is also considered to ascertain the effect of the radial velocity. The data analysis and the numerical model suggest the cause of the observed decay process to be mixing along constant isopycnal surfaces initiated by inward directed radial velocities.