Credit: Wanming Qi and J. B. Marston (unpublished)
The series of images shows the progression of a numerical simulation of a fluid confined to the surface of a sphere. Small vortices are absorbed into larger ones, generating long-lived coherent structures that form (far right panel) a quadrapole in the vorticity field. The kinetic energy of the flow is nearly conserved, protecting the structures from being dissipated. Conservation of angular momentum (zero here) prevents coalescence into a single dipole of vorticity.