Normalised velocity power spectra near the surface (left panel), middle (middle), and base (right) of the CZ from runs in Set A with Co varying between 0 and 16.5. The inset in the left panel shows the mean scale and wavenumber where E(k) has its maximum () as functions of Co for z/d = 0.85. The error bars indicate the standard deviation. The grey dashed line shows a power law proportional to Co^1/2.