Patterns in spherical Rayleigh-Bénard convection: a giant spiral roll and its dislocations.

Thermal convection in a moderately thin spherical fluid layer in the presence of spherically symmetric gravity, spherical Rayleigh-Bénard convection, is investigated through fully three-dimensional numerical simulations. A steady spherical pattern in the form of a single giant spiral roll covering the whole spherical surface without defects is discovered near the onset of convection. Successive dislocations of the giant spiral roll are also found at larger Rayleigh numbers.