Enhanced vertical inhomogeneity in turbulent rotating convection

In this Letter we report experimental evidence that rotation enhances vertical inhomogeneity in turbulent convection, in spite of the increased columnar flow ordering under rotation. Measurements using stereoscopic particle image velocimetry (SPIV) have been carried out on turbulent rotating convection in water. At constant Rayleigh number Ra=1.11x10^9 several rotation rates have been used, so that the Rossby number takes values from Ro=\infty (no rotation) to 0.09 (strong rotation). The three-component velocity data, obtained at two vertical positions, are used to investigate the anisotropy of the flow through the invariants of the Reynolds-stress anisotropy tensor and the Lumley triangle, as well as to correlate the vertical velocity and vorticity. In the center plane rotation causes the turbulence to be `rod-like,' while closer to the top plate a trend toward isotropy is observed.