  We investigate numerically the statistical properties of the large scale flow
in Rayleigh--B\'enard convection. By using an external random perturbation on
the temperature field, we were able to decrease the effective Prandtl number of
the flow while keeping the Rayleigh number relatively small; this increases the
Reynolds number thus making possible the numerical investigation of the
long--term flow statistics. We also propose a simple and quantitative
explanation for the experimental findings on the statistical distribution of
flow reversals and reorientations.
