Spiral defect chaos in Rayleigh-Be´nard convection: defect population statistics

We report a number of observations regarding the populations of defects in the spiral-defect-chaos state of Rayleigh-Be´nard convection. The experiments were carried out using CO2 at 32 bar with a Prandtl number σ = 0.98 in a cylindrical convection cell with radius-to-height ratio Γ = 52. The populations of spirals, targets, and sidewall foci were measured as functions of ≡ΔT/ΔTc−1 and were used to describe the transition to spiral-defect chaos. The probability distributions of the number and size of defects were determined and compared to Poisson and Gaussian distributions. The populations of spirals were further characterized by size and sense of winding (clockwise or counterclockwise) and the normalized difference is presented as a function of .