A large-scale circulation velocity, often called the ‘wind’, has been observed in
turbulent convection in the Rayleigh–Bénard apparatus, which is a closed box with a
heated bottom wall. The wind survives even when the dynamical parameter, namely
the Rayleigh number, is very large. Over a wide range of time scales greater than
its characteristic turnover time, the wind velocity exhibits occasional and irregular
reversals without a change in magnitude. We study this feature experimentally in an
apparatus of aspect ratio unity, in which the highest attainable Rayleigh number is
about 1016. A possible physical explanation is attempted.