On the spontaneous symmetry breaking of eastward propagating dipoles

The spontaneous symmetry breaking of weak eastward propagating dipoles is revealed from high-resolution numerical simulations in an equivalent-barotropic quasigeostrophic beta-plane model. The evolution of initialized Larichev-Reznik dipoles is found to depend on the initial intensity, characterized by the dipole drift speed divided by the maximum Rossby wave phase speed. We found that weak dipoles lose symmetry and eventually disintegrate due to growing perturbations. This instability is attributed to a critical, linear growing mode that is extracted from the potential vorticity anomaly. The growth rate of perturbations is found to decrease with the increasing dipole intensity.