  We report the experimental study of the bifurcations of a large-scale
circulation that is formed over a turbulent flow generated by a spatially
periodic forcing. After shortly describing how the flow becomes turbulent
through a sequence of symmetry breaking bifurcations, we focus our study on the
transitions that occur within the turbulent regime. They are related to changes
in the shape of the probability density function (PDF) of the amplitude of the
large scale flow. We discuss the nature of these bifurcations and how to model
the shape of the PDF.
