  It is shown that the Truncated Euler Equations, i.e. a finite set of ordinary
differential equations for the amplitude of the large-scale modes, can
correctly describe the complex transitional dynamics that occur within the
turbulent regime of a confined 2D Navier-Stokes flow with bottom friction and a
spatially periodic forcing. In particular, the random reversals of the large
scale circulation on the turbulent background involve bifurcations of the
probability distribution function of the large-scale circulation velocity that
are described by the related microcanonical distribution which displays
transitions from gaussian to bimodal and broken ergodicity. A minimal 13-mode
model reproduces these results.
