  A two-layer quasi-geostrophic flow is quite insulated from the surrounding
fluid, while the layers interact each other by means of the modulation of the
interface between them and of the turbulence affecting the layers in the
proximity of the interface. In this framework, the time evolution of the
circulation of the flow along the lateral boundaries (upper and lower) is
investigated under the assumption of arbitrary initial conditions. The analytic
solution shows the glue-like behaviour of turbulence, which is parameterized in
the standard way (Pedosky, 1996): initially the glue is wet and each layer
evolves almost independently of the other while, for times far enough from that
initial, the glue hardens and the system converges to a singlelayer one.
Indeed, the circulation of the thinner layer tends to adjust itself in a
parallel way with respect to the thicker layer and the final circulation of the
consequent single-layer system is given by the average of the initial
circulations, each being weighted by the thickness of the related layer.
