The "Canary Eddy Corridor"

Today, the announcement of an accepted paper by Sangrà et al. in Deep Sea Research I. They report, from remote sensing and in situ observations, a new type of permanent structure in the eastern subtropical Atlantic Ocean, that they call the "Canary Eddy Corridor". The phenomenon is a zonal long-lived (> 3 months) mesoscale eddy corridor, whose source is the flow perturbation of the Canary Current and the Trade Winds at the Canary Islands. The latitudinal range of the corridor spans 22ºN-29ºN, and extends from the Canaries to at least 32ºW, near the mid-Atlantic Ridge. This is the main region of longlived westward propagating eddies in the subtropical northeast Atlantic. Below is the information appeared in the Aviso web page. The first figure was elected as the image of the month!

Eddies are seemingly sowed more or less haphazardly in the ocean. 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.

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)



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)

Finally, a video of the relative vorticity from SSH. Observe the eddies (cyclonic and anticyclonic) shed by the Canary Islands and the drifting of those mesoscale structures (supplementary material of Deep Sea Research I).