Emergence of intense jets and Jupiter's Great Red Spot as maximum-entropy structures

Abstract

We explain the emergence and robustness of intense jets in highly turbulent planetary atmospheres, like that on Jupiter, by a general statistical mechanics approach to potential vorticity patches. The idea is that potential vorticity mixing leads to the formation of a steady organized coarse-grained flow, corresponding to the statistical equilibrium state. Our starting point is the quasi-geostrophic 1-1/2 layer model, and we consider the relevant limit of a small Rossby radius of deformation. Then narrow jets are obtained, in the sense that they scale like the radius of deformation. These jets can be either zonal, or closed into a ring bounding a vortex. Taking into account the beta-effect and a sublayer deep shear flow, we predict organization of the turbulent atmospheric layer into an oval-shaped vortex within a background shear. Such an isolated vortex is centred over an extremum of the equivalent topography, combining the interfacial geostrophic tilt due to the deep shear flow and the planetary beta-effect (the resulting effective beta-effect is locally quadratic). This prediction is in agreement with an analysis of wind data in major Jovian vortices (Great Red Spot and Oval BC).