Gyre Turbulence

Investigation of a two-dimensional model for large-scale oceanic gyres reveals the existence of an asymptotic turbulent regime in which the energy dissipation becomes independent of the fluid viscosity. The role of the no-slip boundary conditions is critical: the inverse cascading behaviour of two-dimensional turbulence described previously for free-slip conditions is halted by vortex fragmentation through collisions with lateral walls. This leads to a distribution of dissipation events resembling a lognormal function, but a departure from this lognormal pattern appears in the distribution's tail, corresponding to intense vortices that dominate the overall dissipation. While the instantaneous vorticity field is dominated by a vortex gas, the time-averaged flow remains close to an ocean gyre predicted by laminar theory. This regime shows an unexpected role of two-dimensional turbulence in the organisation of oceanic flow.