Experiments on convection in rotating hemispherical shells: Transition to a quasi‐periodic state

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Abstract
Convection driven by thermal buoyancy in the presence of the Coriolis force occurs in planetary atmospheres and interiors. In order to model convection subject to nearly spherically symmetric distributions of gravity and temperature, a hemisphere has been constructed which can be rotated about its axis of symmetry. The angular velocity is selected such that the paraboloidal surfaces of equal potential match closely surfaces of constant radius within the hemispherical fluid shell. While the baroclinicity of the fluid state is still noticeable, quantitative measurements can be obtained which can be compared with the theoretical calculations for the spherically symmetric case. The drift of the convection columns has been measured and a transition from the singly periodic state of convection to a modulated state has been visualized and determined quantitatively.