FROM QUASI-GEOSTROPHIC TO STRONGLY NONLINEAR MONOPOLAR VORTICES IN A PARABOLOIDAL SHALLOW-WATER-LAYER EXPERIMENT

We perform a detailed experimental study of large-scale vortices propa gating in the rotating shallow-water layer in a paraboloidal vessel. A specific data acquisition technique is used in order to ensure precis e measurements of the free-surface elevation. We find two qualitativel y different types of vortex behaviour controlled by the relative eleva tion value. For small elevations we observe a standard quasi-geostroph ic pattern with an asymmetric secondary circulation around an initiall y symmetric vortex which leads to a meridional drift and Rossby wave r adiation. This type of behaviour is exhibited by both cyclonic and ant icyclonic vortices. For relative elevations larger than 1 (nonlinear r egime) the necessarily anticyclonic vortices are drifting strictly zon ally maintaining their circular symmetry during the viscous decay. By varying the initial latitude of the vortex we were able to check that in the nonlinear regime the vortex lifetime is not sensitive to the be ta-effect, while it is the case in the quasi-geostrophic regime. In th e same way we show that the observed difference in cyclone-anticyclone lifetimes is not influenced by the beta-effect.