Section: New Results

Contribution and influence of coherent mesoscale eddies off the North-West African upwelling on the open ocean

Participants : A. El Aouni , K. Daoudi , H. Yahia , K. Minaoui .

Eastern Boundary Upwelling zones include some of the most productive ecosystems in the world, particularly the NorthWest (NW) African upwelling which presents one of the world's major upwelling regions. This latter is forced by the equator-ward trade winds which are known to exhibit mesoscale instabilities; thus, in addition to upwelled cold and nutrient-rich deep waters, significant energy is transferred into mesoscale fronts and eddies in the upper ocean. Oceanic structures of type eddies are well know to stir and mix surrounding water masses. However, they can also carry and transport organic matter and marine in a coherent manner. Here, we are interested in those that remain coherent. The Aim of this work, is to understand the impact and the contribution of the mesoscale eddies off the NW African margin on the open ocean. Our approach to analyze such coherent eddies is based upon the use of our recently developed technique from nonlinear dynamics theory, which is capable of identifying coherent vortices and their centers in an automatic manner. The role of these mesoscale eddies is investigated based on a statistical study of eddies properties off NW African margin (cyclone/anticyclone, their lifetimes, traveled distance, translational speeds, quantity of water masses transported to the open ocean...). This statistical study is carried out over a sets of 24 years (spans from January 1993 to December 2016) of sea surface velocity field derived from satellite surface altimetry under the geostrophic approximation.

Publication: SIAM Conference on Mathematics of Planet Earth, (MPE18) HAL