LARGE STRUCTURES AND TEMPORAL CHANGE IN THE AZORES FRONT DURING THE SEMAPHORE EXPERIMENT

The Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneit es Oceaniques: Recherche Experimentale (SEMAPHORE) mesoscale experimen t took place from July to November 1993 in the northern Canary Basin, where the circulation is dominated by the eastward flowing Azores Curr ent (AC). A large data set was acquired from three hydrographic arrays (phases 1, 2, 3), current meter moorings, surface drifters drogued at 150 m, and 2000 m deep RAFOS floats. The analysis confirmed the large -scale observations previously made in this region but also provided n ew insights into fine-scale dynamics of the AC. The front was observed over the 6-month period. It was narrow (100 km) and mostly surface in tensified (velocities reaching 40-50 cm s(-1)). Whereas at the beginni ng of the experiment (phase 1) the AC was mainly zonal with weak oscil lations, large meridional meanders were observed from phase 2 until th e end of the experiment. They seem to be related to the arrival of two Mediterranean eddies (Meddies), which interacted with the AC [Kase an d Zenk, 1996; Tychensky and Carton, this issue]. The front had a deep dynamical signature (down to 2000 m), with a 16-18 sverdrup (Sv) volum e transport (0-2000 m depth integrated). The southward recirculation b ranch of the AC near 22 degrees-23 degrees W [Klein and Siedler, 1989] corresponds to meridional transport of 5-6 Sv. Then, 4.5 Sv of these waters are recirculating westward (along 31 degrees-32 degrees N). Som e interesting new oceanographic results were obtained by examining the RAFOS float trajectories over the abyssal plain. The circulation is s imilar to that observed at the surface, with mean velocities of about 1-3 cm s(-1) and eddy kinetic energy <4 cm(2) s(-2). In agreement with the analysis of current meter data this reveals a significant barotro pic component in the Azores-Madeira flow field of roughly 3-3.5 cm s(- 1).