Abstract

We study geostrophic turbulence in the limit of very high bottom friction, for a two-layer model forced by a baroclinically unstable mean flow. Remarkably, the flow spontaneously self-organizes into regions of homogenized potential vorticity separated by strong, surface intensified and meandering jets (the ribbons). We interpret the emergence of these ribbons as a tendency to reach an equilibrium state of the 1-1/2 quasi-geostrophic model. The statistical mechanics theory predicts that the interface separating the regions of homogenized potential vorticity should be minimal, just like bubbles in usual thermodynamics. We argue that the ribbon dynamics result from a competition between this effect, and baroclinic instability of the jets that tends to destabilize the interface between regions of homogenized potential vorticity.