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Image of the month
2009
Jun. 2009: A corridor of eddies

A corridor of eddies

Image of the Month - June 2009

Paths of (at least) 6 month-old eddies in the North-East Atlantic. In red, anticyclonic eddies, in blue cyclonic ones, over the October 1992 - September 2006 period. A group of anticyclonic eddies can be seen moving from the South of the Canary islands westward to the mid-Atlantic. (Credits Universidad de Las Palmas de Gran Canaria/IMEDEA)

Eddies are seemingly sowed more or less haphazardly in the ocean (Image of the Month, September 2007). However, regular features exist, especially when there are dominant winds and/or currents, and islands or other topographic features. The "Canary Eddy Corridor" is a recurrent feature that can be detected in the more than 16 years of merged altimeter data. The phenomenon is an East-West corridor of eddies, born of the perturbation of the Canary Current flow and of the Trade Winds at Canary Islands. It extends from the Canaries to at least 32°W, close to the Mid Atlantic Central Ridge. Anticyclonic long-lived eddies (a few years life span) have been observed as far west as 50°W, well beyond this Ridge.

Altimeter observations and drifter trajectories indicate that the eddies in this corridor first propagate South (following the Canary Current flow); then, at about (18°W, 25°N), they move westward (with a slight southward direction for anticyclonic eddies), on average at about one degree per month.

The availability of a long series of altimetry measurements enable to detect and visualise permanent features of the ocean dynamics.

Geostrophic velocities computed from altimetry in September (left) and December 1998 (right), tracking the centre of an intense anticyclonic eddy South of Gran Canaria. The blue line corresponds to a drifter trajectory three days before and after the altimetry map. The buoy trajectory clearly matches the altimeter observations of this eddy. (Credits Universidad de Las Palmas de Gran Canaria/IMEDEA)

Left, depth-averaged (0 to 100 m) velocities as obtained from ADCP data (black arrows), superposed onto sea surface height as derived from merged altimeter data on September 2002. Both data sources show an intense anticyclonic eddy south of El Hierro island (South-Westernmost Canary island). Right, geostrophic velocities superposed onto a drifter trajectory (blue line). The trajectory corresponds to 15 days before and after the corresponding image, tracking the periphery of the same anticyclonic eddy observed left, one month later. The shape and eddy intensity from both data sources coincide well, with a size close to 100 km. (Credits Universidad de Las Palmas de Gran Canaria/IMEDEA)

References

Sangrà, P., A. Pascual, Á. Rodríguez-Santana, F. Machín, E. Mason, J.C. McWilliams, J.L. Pelegrí, C. Dong, A. Rubio, J. Arístegui, Á. Marrero-Díaz, A. Hernández-Guerra, A. Martínez-Marrero, M. Auladell, The Canary Eddy Corridor: a major pathway for long-lived eddies in the subtropical North Atlantic, submitted to Deep Sea Research

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