A sinusoidal temperature perturbation is superimposed on the bottom plate of a cylindrical convection cell, and its decay is measured at the cell midheight. Rayleigh numbers up to $\mathrm{Ra}={10}^{13}$ and aspect ratios 1 and 4 are considered. The technique allows a dynamic measurement of the height of the layer interposed between the superconducting core and the boundary. This deduced height is in good agreement with results from recent numerical simulations.

• Received 30 November 2007

DOI:https://doi.org/10.1103/PhysRevLett.100.184502