Convection at finite Rayleigh numbers in large-aspect-ratio containers

The phase diffusion and mean drift equations which describe the behavior of a convection pattern are derived, a step which is essential for obtaining quantitative comparisons between theory and experiment. The theory recovers the boundaries of the Busse Balloon, agrees closely with the dominant wave numbers observed by Heutmaker and Gollub [Phys. Rev. A 35, 242 (1987)] and Steinberg, Ahlers, and Cannell [Phys. Sci. 30, 534 (1985)] in natural and target patterns, predicts a new instability which is important in facilitating wave-number adjustment in circular target patterns and in initiating time dependence, and predicts the Rayleigh numbers at which loss of spatial correlation due to global defect nucleation will occur.