A regional study on the Eddy Kinetic Energy transfers of the Meso and Submesoscale reservoirs in the Ocean

This is the PhD presentation, carried out in the Laboratory for Ocean Physics and Satellite remote sensing (Brest, France), under the supervision of Pierrick Penven, Jonathan Gula and Claire Ménesguen, on the subject of : " A regional study on the Eddy Kinetic Energy transfers of the Meso and Submesoscale reservoirs in the Ocean ".

Abstract :

This PhD is based on regional numerical simulations and addresses, from an energetic perspective, the Meso (O(10-100)km) and Submesoscale (O(0.1- 10)km) variability of the Agulhas Current.

(i) Submesoscale variability at the transition between the two Agulhas Current branches (28° E-26°E) is dominated, in the absence of mesoscale meanders, by cyclonic frontal eddies forming a ’vortex street’. The frontogenetic background strain intensifies the frontal shear, which then triggers the barotropic instability leading to submesoscale eddies generation.

(ii) A modal Eddy Kinetic Energy budget characterizes the energy transfers between the different vertical structures. The Agulhas Current is a generation region for mesoscale eddies. Interactions forced by stratification-topography gradients (3 contributions) globally result in a larger energy loss than dissipation processes (bottom friction and wind) for mesoscale eddies. The offshore areas are characterized by an inverse vertical cascade (triadic interactions).

(iii) The ageostrophic and nonlinear dynamics of the barotropic and the 1st baroclinic modes dominate the mesoscale eddy dynamics in the Agulhas Current region. The eddy energy budget diagnostic from altimetry data alone therefore does not allow to assess the net eddy-energy sources and sinks.