E-mail: bolton@hess.geology.yale.edu

Experimental Rotating-Annulus Convection

Convection driven by centrifugal buoyancy in a rotating annulus with sloping end boundaries creates drifting thermal-Rossby waves. The convection columns align with the rotational axis. This flow regime is dynamically similar to convection in the Earth's liquid core and in the deep atmospheres of the major planets. In an experimental study [Azouni, Bolton, and Busse 1986], we were the first to collect time series and convective amplitudes of the traveling waves induced by sloping end boundaries (such waves had been previously measured in wide gap annulus experiments with non-sloping end boundaries by White and Koschmieder, 1981; Koschmieder and White, 1981). The convective amplitudes were found to reach a maximum and then decay as the Rayleigh number was increased.

I have constructed a rotating annulus convection experiment with periodic heating wires in one of the cylindrical cell walls [Bolton and Sayler, 1990, abst.]. The heating wires are parallel to the rotational axis and are spaced at the wavelength expected for the onset of convection. In addition to the periodic heating, the cell walls are adjacent to uniform warm temperatures on the outside, and cooling is provided on the cell interior. Sloping end boundaries force thermal Rossby waves, which drift in the prograde sense. By increasing the ratio of inhomogeneous to homogeneous heating, I expect to observe the locking phenomena. Up to now, the results with the heating wires turned on have not been conclusive, due to excessive noise. I am redesigning the means to supply power to the heating wires. I set up a data acquisition system using National Instrument hardware and software in a Macintosh IIx computer. With only homogeneous heating, the results are of much better quality than Azouni, Bolton, and Busse [1986].

Azouni, M.A., E.W. Bolton and F.H. Busse, Convection driven by centrifugal buoyancy in a rotating annulus, Geophys. Astroph. Fluid Dyn., 34, 301-317, 1986.

I.A. Quintanar, E.W. Bolton, F.H. Busse and M.A. Azouni, Experimental measurements of drifting convection columns in a rotating annulus, paper presented on 6 Dec. 85 at the Fall Meeting of the Am. Geoph. Union, San Francisco, CA, EOS, Trans. Am. Geoph. Union, 65, No. 45, p. 871, 1984.

E.W. Bolton and B. Sayler, The influence of lateral variations of thermal boundary conditions on core convection: Numerical and laboratory experiments, presented at Santa Fe, Studies of the Earth's Deep Interior (SEDI) symposium, August, 1990.