Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model

Cataria Quam Cyrille Akuetevi (1, 2, 3) , Achim Wirth (3)

1 LGGE - Laboratoire de glaciologie et géophysique de l'environnement
2 UGA [2016-2019] - Université Grenoble Alpes [2016-2019]
3 LEGI - Laboratoire des Écoulements Géophysiques et Industriels [Grenoble]

The dynamics of low latitude turbulent western-boundary currents (WBCs) crossing the Equator are considered using numerical results from integrations of a reduced-gravity shallow-water model. For viscosity values of 1000 m 2 s −1 and greater, the boundary layer dynamics compares well to the analytical Munk-layer solution. When the viscosity is reduced, the boundary layer becomes turbulent and coherent structures in the form of anticyclonic eddies, bursts (violent detachments of the viscous sub-layer, VSL) and dipoles appear. Three distinct boundary layers emerge, the VSL, the advective boundary layer and the extended boundary layer. The first is characterized by a dominant vor-ticity balance between the viscous transport and the advec-tive transport of vorticity; the second by a balance between the advection of planetary vorticity and the advective transport of relative vorticity. The extended boundary layer is the area to which turbulent motion from the boundary extends. The scaling of the three boundary layer thicknesses with viscosity is evaluated. Characteristic scales of the dynamics and dissipation are determined. A pragmatic approach to determine the eddy viscosity diagnostically for coarse-resolution numerical models is proposed .

Domaines: Sciences de l'environnement

Cataria Quam Cyrille Akuetevi, Achim Wirth. Dynamics of turbulent western-boundary currents at low latitude in a shallow-water model. Ocean Science, 2015, 11, pp.471-481. ⟨10.5194/os-11-471-2015⟩. ⟨insu-01275263⟩