A light scattering experiment of turbulent convection in water is carried out in a convection cell with rough upper and lower surfaces. The vertical heat flux is found to be increased by $\sim 20\%$ when the Rayleigh number becomes larger than a transition value. The experiment reveals that the main effect of the surface roughness is to increase the emission of large thermal plumes, which travel vertically through the central region. These extra thermal plumes enhance the heat transport, and they are also responsible for the anisotropic behavior of velocity fluctuations at the cell center.

• Received 21 September 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.908