Stability and evolution of two opposite-signed quasi-geostrophic shallow-water vortex patches

Abstract

We examine the equilibrium forms, linear stability and nonlinear evolution of two patches having opposite-signed, uniform potential vorticity anomalies in a single-layer shallow-water flow, under the quasi-geostrophic approximation. We widely vary the vortex area ratio, the potential vorticity anomaly ratio, as well as the Rossby deformation length to unravel the full complexity of possible interactions in this system. Opposite-signed vortex interactions turn out to be far richer than their like-signed counterparts, comprehensively examined in a previous study (Jalali and Dritschel 2018, Geophys. Astrophys. Fluid Dyn. 2018, 112, 375). Unstable equilibria may evolve into a myriad of forms, many unsteady and aperiodic, and the original two vortex patches may break up into many patches which survive for long times, perhaps indefinitely.