Potential Vorticity and Vertical Velocity at the Iceland-Færœs Front

Abstract

Using data from high-resolution surveys of the Iceland- Fær?s Front, the authors have calculated synoptic maps of the geostrophic velocity, vorticity, and potential vorticity on isopycnal surfaces. The data have also been used to diagnose the vertical velocity field using the omega equation. These results are used to elucidate the dynamical processes occurring at the front. Across the front there was a large change in potential vorticity on the density surfaces σt = 27.4 ? 27.6. Instability generates meanders that propagate eastward along the front. A cyclonic vortex was observed to break off from a meander. Within the vortex the magnitude of the relative vorticity was large (?0.8 f), and the potential vorticity had high values similar to that of the water to the north of the front from which the vortex was derived. The eddy propagated northeastward relative to the underlying water resulting in large upward (downward) vertical velocities (of the order of 100 m d?1) ahead of (behind) the vortex.