The wind in confined thermal convection

A large-scale circulation velocity, often called the 'wind', has been observed in turbulent convection in the Rayleigh-Benard 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 10(16). A possible physical explanation is attempted.