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The velocity and temperature distributions are measured for natural convection in a hor izontal concentric annulus at high Rayleigh numbers with using a hot-wire anemometer and a thermocouple. Dealing with these data statistically, the average velocity and temperature profiles as well as their turbulence quantities are obtained. By carrying out the spectrum analysis of these velocity fluctuations, a transition from the laminar natural convection to the turbulent one is clarified. With increasing Rayleigh number, the stable flow pattern becomes unstable to a periodic one. The periodicity diminishes when the Rayleigh number is further increased. A comparison of these experimental data with the time-dependent three-dimensional numerical results, which were reported in our previous paper, shows a good agreement.

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