Long-lived Mesoscale Eddies in the Northeastern Atlantic Ocean: Demography, Geometric Properties and Transport

Abstract:

In the northeastern Atlantic Ocean, the eastward-flowing Azores Current converges towards the southwestward-flowing Canary Current, following the African coastline and leading the Eastern Boundary Current System of the North Atlantic Subtropical Gyre. Based on satellite altimetry measurements (1992-2006) and in situ observations (1998, 2002), Sangrà et al. (2009) described for the first time the Canary Eddy Corridor in the northeastern Atlantic Ocean (22.1^oN - 29.1^oN) as a zonal long-lived mesoscale eddy corridor.

In this work, we extend the study area and redefine five zonal corridors that expand from 12^oN to 40^oN. The aim is to assess the potential role of these eddy corridors as zonal conveyors of mass and ocean properties. To ease its identification, we name these corridors following their generation sites: Cape Verde, Cape Blanc, Canary Islands, Madeira, and the Azores Front. We do this using an altimeter-based dataset of global mesoscale ocean eddies (1992-2018). The analyses are performed in terms of the eddy demography and eddy geometric properties.

Generally, we find that cyclonic eddies (CEs) are the most frequent type of long-lived eddies (> 6 months) everywhere but in the Cape Verde Corridor and the Azores Front Corridor, where anticyclonic eddies (AEs) and CEs are of similar number. On average, CEs propagate the farthest away due to the combination of longer lifetimes and higher track stabilities, although AEs also reach on occasions as far as 1000 km away from their generation site.

Zonally, results agree well with theory and show recurrent patterns about their geometric eddy properties, where both anticyclonic (AEs) and cyclonic (CEs) eddies display significant differences. Both eddy types increase (decrease) its radius and decrease (increase) its amplitude and rotational speeds when their corridor locates at lower (higher) latitudes. Also, observed eddies propagate west at approximately the phase speed of nondispersive baroclinic Rossby waves, according to their latitude.

These results highlight the implications of the geographical location (latitude) of the eddy corridors, suggesting that low latitude eddy corridors may generate the best candidates to convey ocean properties to remote places while these candidates are significantly less frequent than eddies of higher latitude corridors.