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 (22.1oN - 29.1oN) as a zonal long-lived
mesoscale eddy corridor. In this work, we extend the study area and
redefine five zonal corridors that expand from 12oN to 40oN. 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.