HYDROLOGICAL AND DYNAMICAL CHARACTERIZATION OF MEDDIES IN THE AZORES REGION - A PARADIGM FOR BAROCLINIC VORTEX DYNAMICS

The Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneit es Oceaniques: Recherche Experimentale (SEMAPHORE) oceanographic exper iment surveyed a 500 x 500 km(2) domain south of the Azores from June to November 1993 and collected hydrological data, float trajectories, and current meter recordings. This data exhibited three intrathermocli ne eddies of Mediterranean water (Meddies), mio of them being repeated ly sampled. Their hydrological and dynamical properties are quantified here by an isopycnic analysis. For the three Meddles, intense tempera ture and salinity anomalies (up to 4 degrees C and 1.1 practical salin ity units (psu)) are observed extending vertically over up to 1000 m a nd centered around 1000 m. Horizontally, these anomalies spread out to radii of 50-60 km, while the maximum azimuthal velocities (30 cm s(-1 ), as computed by geostrophy) lie only at 35-40 km from the central ax is. These Meddles followed curved trajectories, with drift velocities up to 7.5 cm s(-1), under the influence of the neighboring mesoscale f eatures (cyclonic vortices or Azores Current meanders). The three-dime nsional structure of potential vorticity in and around these features evidences their complex interactions. Northwest of the domain, a Meddy was coupled to a subsurface anticyclone, forming an ''aligned'' vorte x. It later interacted with the Azores Current, creating a large-ampli tude northward meander by vertical alignment of vorticity. In the sout heastern part of the domain, another Meddy was vertically aligned with an anticyclonic meander of the Azores Current and horizontally couple d with a cyclone of large vertical extent. These two features, as well as a small warm and salty fragment in their vicinity, seem to result from the southward crossing of the Meddy under the Azores Current. The se observations illustrate previous theoretical studies of baroclinic vortex dynamics.