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 Us of a linear topographic Rossby wave. For multiple vortices the westward velocities were greater than Us while for a single vortex produced by a low flow rate the velocity was less than Us. 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.