THERMALLY-INDUCED FLUCTUATIONS BELOW THE ONSET OF RAYLEIGH-BENARD CONVECTION

We report quantitative experimental results for the intensity of noise -induced fluctuations below the critical temperature difference Delta T-c for Rayleigh-Benard convection. The structure factor of the fluctu ating convection rolls is consistent with the expected rotational inva riance of the system. In agreement with predictions based on stochasti c hydrodynamic equations, the fluctuation intensity is found to be pro portional to 1/root-epsilon, where epsilon Delta T/Delta T-c - 1. The noise power necessary to explain the measurements agrees with the pred iction for thermal noise.