Observations in the Canary Basin and the Azores frontal region using Geosat data

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Abstract
This paper discusses observations of the sea level in the Azores frontal region and the Canary Basin as seen by the Geosat altimeter frorn 5° to 45°W and 25° to 45°N. Two years of Geosat exact repeat data were processed by colocating the data on a 0.06° grid then removing the mean by the along track difference method and removing the orbit error by a crossover analysis technique. The data set was then interpolated by the successive correction method onto 15‐day, 0.5° maps to produce 47 residual height fields which were analyzed using complex empirical orthogonal functions (EOF) and spectral analysis. The results show that there is a region of high variability in the northwest corner reflecting the Gulf Stream extension and a region of medium variability at approximately 35°N reflecting the Azores Current. The variability changes only slightly throughout the year, with the winter season being the highest. The data set also shows first mode baroclinic Rossby waves between 30° and 35°N. There is evidence that these Rossby waves have different wavenumbers to the east and west of the Mid‐Atlantic Ridge. It is postulated that these waves have different generation mechanisms, the Mid‐Atlantic Ridge topography in the west and some other generation mechanism in the Canary Basin. Rossby waves are not apparent at 40°N.