Rotating turbulent convection at high Rayleigh and Taylor numbers

We report heat transport measurements in a cylindrical convection apparatus rotating about the vertical axis. The aspect ratio was 1/2. The working fluid was cryogenic helium gas and the following parameter ranges applied: The Rayleigh number, $Ra$, varied in the range $10^{11} < Ra < 4.3 \times 10^ {15}$, the Taylor number, $Ta$, in the range $10^{11} < Ta < 3 \times 10^{15}$, the convective Rossby number, $Ro$, in the range $0.4 < Ro < 1.6$, and the Prandtl number, $Pr$, in the range $0.7 < Pr < 5.9$. Boussinesq conditions applied quite closely. The heat transport for steady rotation, under all conditions of the present experiments, was smaller than that for the non-rotating case. When the rotation rate varied periodically in time a sharp transition to a state of significantly enhanced heat transport was observed for modulation Taylor numbers $Ta^* \ga 10^{14}$, where $Ta^*$ is based on the maximum of the modulation angular velocity.