Cyclone and anticyclone formation in a rotating stratified fluid over a sloping bottom

Abstract

We discuss laboratory experiments with a continuous source or sink of fluid in a two-layer rotating environment which produces anticyclonic and cyclonic vortices, respectively. Experiments were carried out with a sloping bottom in order to simulate the β-effect and they were conducted for different values for the source/sink flow rate Q and the Coriolis parameter f. The Rossby number Ro of these vortices was small but finite and the flow was expected to be quasi-geostrophic. The qualitative behaviour of the anticyclonic and cyclonic vortices was generally similar, but it depended on the flow rate. For low flow rates, a single vortex formed at the source and extended to the west. At higher flow rates, the vortex broke free from the source and moved to the west; this vortex was then followed sequentially by other vortices behaving similarly. The westward velocity U of these vortices was calculated and compared with the speed U_s of a linear topographic Rossby wave. For multiple vortices the westward velocities were greater than U_s while for a single vortex produced by a low flow rate the velocity was less than U_s. Significant asymmetry between the anticyclonic and cyclonic vortices was observed in the transition zone from single to multiple vortices which implies that ageostrophic effects were still present in the flow.