A LABORATORY STUDY OF BAROCLINIC WAVES AND TURBULENCE IN AN INTERNALLY HEATED ROTATING FLUID ANNULUS WITH SLOPING ENDWALLS

New laboratory experiments have been performed in a rotating fluid ann ulus, subject to internal heating and sidewall cooling, in which a rad ial depth gradient has been created by the inclusion of oppositely slo ping boundaries. Endwall configurations that cause the fluid depth (D) to increase with radius (partial derivative D/partial derivative r > 0) and to decrease with radius (partial derivative D/partial derivativ e r < 0) have been studied, as the former is applicable to the terrest rial atmosphere and oceans, while the latter may be relevant to deep a tmospheres such as those of the giant planets. Even with the steepest boundary slopes, isolated or periodic chains of stable coherent eddies are observed with both endwall configurations, and these regular eddy modes are seen to drift relative to the walls of the convection chamb er concordant with simple Rossby wave ideas. When the boundary slope ( delta) is small, no difference is observed in the range of azimuthal w avenumbers seen in the regular wave regimes of the two endwall configu rations. At larger values of delta, however, this symmetry is lost, si nce regular modes m = 2 to 8 are observed with partial derivative D/pa rtial derivative r > 0 endwalls, while only a large vertically trapped anticyclonic gyre is seen with partial derivative D/partial derivativ e r < 0 endwalls. The other effects of the radial depth gradient are t he observed reduction in both the lateral and vertical scale of the ed dy features, and the formation of two independent trains of eddies wit hin the gap width at sufficiently high rotation rates in the partial d erivative D/partial derivative r > 0 endwall experiments. The zonal me an flow is also found to develop a significant barotropic component, s uperimposed on the vertically and horizontally sheared zonal jets gene rated by the non-monotonic thermal gradient of the experiment. This ba rotropic component is predominantly prograde (retrograde) in the parti al derivative D/partial derivative r > 0 (partial derivative D/partial derivative r < 0) endwall experiments, and confined close to the oute r (inner) wall where the fluid depth is greatest. There is evidence of the formation of increased numbers of zonal jets in the partial deriv ative D/partial derivative r > 0 endwall experiments above that expect ed from the form of the thermal forcing. These multiple zonal jets are highly localized in the vertical, and are trapped close to the top bo undary. Their radial scale is, nevertheless, close to that given by th e Rhines argument. No comparable increase in the radial wavenumber of the mean flow is observed in the partial derivative D/partial derivati ve r < 0 endwall experiments in the present system.