Journal of Fluid Mechanics

An experimental study of unstable barotropic vortices in a rotating fluid

R. C.  Kloosterziel a1p1 and G. J. F.  van Heijst a1
a1 Institute of Meteorology and Oceanography, University of Utrecht, Princetonplein 5, 3584 CC Utrecht, The Netherlands

Article author query
kloosterziel rc   [Google Scholar] 
van heijst gj   [Google Scholar] 


Laboratory experiments on barotropic vortices in a rotating fluid revealed that the instability behaviour of cyclonic and anticyclonic vortices is remarkably different. Depending on its initial vorticity distribution, the cyclonic vortex has in a number of experiments been observed to be unstable to wavenumber-2 perturbations, leading to the gradual formation of a stable tripolar vortex structure. This tripole consists of an elongated cyclonic core vortex adjoined by two anticyclonic satellite vortices.

In contrast, the anticyclonic vortex shows a rather explosive instability behaviour, in the sense that it is observed to immediately split up into two dipoles. Under somewhat different circumstances the higher-order mode-3 instability is observed, in which the anticyclonic core has a triangular shape, with three smaller cyclonic satellite vortices at its sides.

A modified version of Rayleigh's instability criterion offers a qualitative explanation for this apparent difference between unstable cyclonic and anticyclonic vortices.

(Published Online April 26 2006)
(Received April 13 1990)

p1 Present affiliation: Institute for Nonlinear Science, La Jolla, CA 92093, USA.