3D structure, mesoscale interactions and potential vorticity conservation in a swoddy in the Bay of Biscay

From an intensive oceanographic survey carried out in the Bay of Biscay (Northern Iberian Peninsula) in August 1998, an anticyclonic Slope Water Oceanic eDDY (swoddy) was identified and studied. Satellite data showed a central anticyclonic structure to which two smaller scale cyclones were attached. Its hydrographic parameters showed a central homogeneous core warmer and saltier than the surroundings situated between 80 and 200 dbar with typical near-constant salinity (35.70) and a weak potential temperature gradient from 12.75 to 12.55 °C. The dynamic front between the swoddy and its surroundings appeared intensified and deflected as a response to the interference of the swoddy with the pair of cyclones to the north and south. This interaction gave rise to E–W asymmetry. Baroclinicity associated with the cyclones caused the most intense advections of relative geostrophic vorticity and subsequent departures of the isopycnic potential vorticity from the Sverdrupian potential vorticity. Associated with these anomalies, vertical movements were inferred along the swoddy periphery.