Large structures and temporal change in the Azores Front during the SEMAPHORE experiment

Type Article
Date 1998-10
Language English
Author(s) Tychensky Aude, Le Traon Pierre-Yves, Hernandez Fabrice, Jourdan D
Affiliation(s) Ctr Mil Oceanog, Serv Hydrog & Oceanog Marine, F-31401 Toulouse 4, France.
Collecte Localisat Satellites, F-31526 Ramonville St Agne, France.
Source Journal Of Geophysical Research-oceans (Amer Geophysical Union), 1998-10 , Vol. 103 , N. C11 , P. 25009-25027
DOI 10.1029/98JC00782
WOS© Times Cited 22
Abstract The Structure des Echanges Mer-Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) mesoscale experiment took place from July to November 1993 in the northern Canary Basin, where the circulation is dominated by the eastward flowing Azores Current (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 new 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 intensified (velocities reaching 40-50 cm s(-1)). Whereas at the beginning of the experiment (phase 1) the AC was mainly zonal with weak oscillations, large meridional meanders were observed from phase 2 until the end of the experiment. They seem to be related to the arrival of two Mediterranean eddies (Meddies), which interacted with the AC [Kase and Zenk, 1996; Tychensky and Carton, this issue]. The front had a deep dynamical signature (down to 2000 m), with a 16-18 sverdrup (Sv) volume transport (0-2000 m depth integrated). The southward recirculation branch 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). Some interesting new oceanographic results were obtained by examining the RAFOS float trajectories over the abyssal plain. The circulation is similar 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 barotropic component in the Azores-Madeira flow field of roughly 3-3.5 cm s(-1).
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