Annual westward propagating anomalies near 26°N and eddy generation south of the Canary Islands: remote sensing (altimeter/SeaWiFS) and in situ measurement

Abstract

Seasonal changes in altimeter data are derived for the North Atlantic Ocean. Altimeter data are then used to examine annually propagating structure along 26°N. By averaging the altimeter data into monthly values or by Fourier analysis, a positive anomaly can be followed from 17°W to ∼50°W along ∼26°N. The methods give a westward travel speed of 1° of longitude a month and a half-life of one year for the average decaying structure. At ∼50°W 26°N, the average structure is about 2·8 years old with an elevation signal of ∼1 cm, having travelled ∼3300 km westward. The mean positive anomaly results from the formation of anticyclonic eddies which are generally formed annually south of the Canary Islands by late summer and which then travel westward near 26°N. Individual eddy structure along 26°N is examined and related to in situ measurements and anomalies in the annual seasonal concentration cycle of SeaWiFS chlorophyll-a.