q 2003 American Meteorological Society The Nonlinear Evolution of Barotropically Unstable Jets

The instability of jets in the context of the shallow-water model for both quasigeostrophic (QG) and non-QG parameters is studied. First, the linear stability problem is solved for a wide range of Rossby and Froude numbers to elucidate the functional dependency of growth rate on these two nondimensional parameters. Then the nonlinear evolution of the instability is investigated through the use of numerical experiments. The QG scenarios produce a vortex street with cyclones and anticyclones that are symmetric in size, strength, and shape, as predicted by QG. In the non-QG regime the instability yields cyclones and anticyclones that can be asymmetric in all three properties. The authors comment on some interesting connections this work has with the Denmark Strait overflow. 1