Titre de la thèse : Oceanic mesoscale eddies dissipation
Encadrants : Pierrick Penven, Jonathan Gula et Claire Ménesguen
Financements : demi bourses IFREMER et région Bretagne
Date de début : 01/10/2018
Résumé : Most of the ocean kinetic energy is contained in the vigorous geostrophic eddy field, at horizontal scales of order 100 km. To achieve equilibrium the geostrophic currents must redistribute or viscously dissipate their kinetic energy at much smaller scale. However, geostrophic turbulence is characterized by an inverse cascade of energy towards larger scale, and the pathways of energy toward smaller scales or directly to dissipation are still in question. The aim of this project is to understand which mechanisms contribute to the direct energy cascade. We focus on the Agulhas Current and a comparison with the Gulf Stream could be done. These two western boundary currents are highly energetic regions. Their variability in the submesoscale range has recently been highlighted (Krug et al. 2017 and Gula et al. 2015) and they are also known to act as sinks for eddy energy (Zhai et al. 2010). We study both processes : the destabilization of these currents in the submesoscale range and the dissipation of, remotely formed, mesoscale eddy when they reach the gyre western boundary. Our studies are based on high-resolution simulations, using a nesting procedure, with the CROCO (Coastal and Regional Ocean COmmunity) model. Our work addresses the concepts of kinetic energy and vorticity budgets, energy transfers, current-topography interactions, front intensification and instability triggering.