Multiple Transitions in Rotating Turbulent Rayleigh-Benard Convection

Sometimes it is thought that sharp transitions between potentially different turbulent states should be washed out by the prevailing intense fluctuations and short coherence lengths and times. Contrary to this expectation, we found a sequence of such transitions in turbulent rotating Rayleigh-Benard convection as the rotation rate was increased. This phenomenon was observed in cylindrical samples with aspect ratios (diameter/height) Gamma = 1.00 and 0.50. It became most prominent at very large Rayleigh numbers up to 2 x 10(12), where the fluctuations are extremely vigorous, and was manifested most clearly for Gamma = 1.00. It was found in the heat transport as well as in the temperature gradient near the sample center. We conjecture that the transitions are between different large-scale structures which involve changes of symmetry and thus cannot be gradual [L. Landau, Zh. Eksp. Teor. Fiz. 7, 19 (1937); L. D. Landau, Phys. Z. Sowjetunion 11, 26 (1937); L. D. Landau, in Collected Papers of L. D. Landau, (Oxford University Press, Oxford, 1965), pp. 193-216].