Topographic control of non-axisymmetric stratified spin-up

An experimental study was conducted to elucidate the influence of a sloping bottom boundary on global stratified spin-up. The system consisted of a rotating continuously stratified fluid confined in a domain which has a shape of an inverted round cone with the upper surface being free. It is shown that under similar flow conditions (the same absolute values of the Rossby and Burger numbers) the spin-up flow remains stable and axisymmetric, while the spin-down flow undergoes a transition from axial symmetry to the formation of a regular system of large-scale anticyclonic eddies. Asymmetry between stratified spin-up and spin-down is also manifested in a qualitatively different behavior of the bottom boundary layer. The density structure of the boundary upslope flow (spin-up) remains smooth at all times, while it reveals high-frequency fluctuations for the downslope flow (spin-down), suggesting the turbulent nature of the bottom boundary layer in the latter case.