A Synoptic Map of Isopycnic Potential Vorticity in the Seasonal Thermocline

Abstract

The distribution of isopycnic potential vorticity (IPV) has been mappedin the seasonal thermocline from a single ship using relative velocitymeasurements plus absolute ship motion, and density profiles froma CTD mounted on an undulating towed vehicle. The advantage of thistechnique is that the measurements are quasi-synoptic and no geostrophicassumptions have to be made since the current measurements are independentof the hydrographic data. The data were collected during an 11-daysurvey at the North Atlantic Polar Front near the Charlie Gibbs FractureZone (50 ^{\circ} -52 ^{\circ} N, 33 ^{\circ} -37 ^{\circ}W) in summer 1981.The synoptic-scale IPV was calculated from thedensity field first with planetary vorticity alone and then withabsolute vorticity. Both versions show a meander structure with awavelength of about 200 km and 100 km amplitude