Quasi-geostrophic vortex vertical alignment over bathymetry

We consider the vertical alignment of two vortices over an isolated bathymetric feature in a three-layer, quasi-geostrophic model. Vortex vertical alignment is one of the two elementary mechanisms which, with vortex merger, is responsible for the formation of large vortices. This, in turn, contributes to the inverse energy cascade in large-scale oceanic flows. In particular, vortex vertical alignment transfers baroclinic energy to barotropic energy. When the vortices' potential vorticity is of the same order as the bathymetric potential vorticity, the alignment of cyclonic vortices is favoured over seamounts and impeded over basins. Moreover, in the latter case, vortices also often strained out. However, if the bathymetric potential vorticity associated with seamount is large compared to the potential vorticity of the cyclonic vortices, the vertical alignment of the vortices may be delayed due to nonlinear effects.