Oceanic rings and jets as statistical equilibrium states

Antoine Venaille (1) , Freddy Bouchet (2)

1 GFDL - NOAA Geophysical Fluid Dynamics Laboratory
2 Phys-ENS - Laboratoire de Physique de l'ENS Lyon

Equilibrium statistical mechanics of two-dimensional flows provides an explanation and a prediction for the self-organization of large scale coherent structures. This theory is applied in this paper to the description of oceanic rings and jets, in the framework of a $1.5$ layer quasi-geostrophic model. The theory predicts the spontaneous formation of regions where the potential vorticity is homogenized, with strong and localized jets at their interface. Mesoscale rings are shown to be close to a statistical equilibrium: the theory accounts for their shape, their drift, and their ubiquity in the ocean, independently of the underlying generation mechanism. At basin scale, inertial states presenting mid basin eastward jets (and then different from the classical Fofonoff solution) are described as marginally unstable states. These states are shown to be marginally unstable for the equilibrium statistical theory. In that case, considering a purely inertial limit is a first step toward more comprehensive out of equilibrium studies that would take into account other essential aspects, such as wind forcing.

Mots clés: potential vorticity homogenization; Two-dimensional turbulence; self-organization; coherent structures; statistical mechanics; Van der Waals-Cahn-Hilliard model for phase transitions; oceanic rings; oceanic jets; westward drift; potential vorticity homogenization.

Domaines: Physique Atmosphérique et Océanique [physics.ao-ph]; Dynamique des Fluides [physics.flu-dyn]

Antoine Venaille, Freddy Bouchet. Oceanic rings and jets as statistical equilibrium states. Journal of Physical Oceanography, 2011, 41 (10), pp.1860-1873. ⟨hal-00534406v2⟩