The turbulent equilibration of baroclinic jets: asymmetric jets and barotropic governor

A two-layer, quasi-geostrophic numerical model is used to investigate the lifecycles of unstable baroclinic jets. The waves grow and subsequently break, resulting in turbulence in both layers and finally the equilibration of the flow to a quasi-steady state. In previous work a theory was introduced to predict this equilibrated flow from the initial parameters. The idea is that potential energy is minimized subject to the dynamical constraints of energy and momentum conservation and a kinematic constraint that potential vorticity (PV) is completely homogenized within well-delineated 'mixing' regions in each layer. It was shown that this theory accurately predicts the final flow structures and characteristics of a range of symmetric jets.

The investigation is extended to jets in the presence of linear barotropic shear, the `barotropic governor', and to those with latitudinally asymmetric structures. The minimization principle itself is also extended to investigate other possible governing principles. Comparison of theoretical predictions and numerical results reveals that an alternative formulation of the theory, in which the area of the mixing zones over both layers is maximized, result in equally good agreement for symmetric jets. For asymmetric jets, the new theory is shown to result in significantly better predictions than minimization of potential energy.