Heat Transport in the Geostrophic Regime of Rotating Rayleigh-Benard Convection

We report experimental measurements of heat transport in rotating Rayleigh-Benard convection in a cylindrical convection cell with an aspect ratio of Gamma = 1-2. The fluid is helium gas with a Prandtl number Pr = 0.7. The range of control parameters for Rayleigh numbers 4 x 10(9) < Ra < 4 x 10(11) and for Ekman numbers 2 x 10(-7) < Ek < 3 x 10(-5) (corresponding to Taylor numbers 4 x 10(9) < Ta < 1 x 10(14) and convective Rossby numbers 0.07 < Ro < 5). We determine the transition from weakly rotating turbulent convection to rotation dominated geostrophic convection through experimental measurements of the heat transport Nu. The heat transport, best collapsed using a parameter RaEk(beta) with 1.65 < beta < 1.8, defines two boundaries in the phase diagram of Ra/Ra-c versus Ek and elucidates properties of the geostrophic turbulence regime of rotating thermal convection. We find Nu similar to (Ra/Ra-c)(gamma) with gamma approximate to 1 from direct measurement and 1.2 < gamma < 1.6 inferred from scaling arguments.