VERTICAL ALIGNMENT OF GEOSTROPHIC VORTICES On the IlIfiuence of the Initial Distribution of Potential Vor,tir'ity

In a two-layer quasi-?;eostrophic numerical model, we stlldy the vprtica.l aligmnent of geostrophic vortices; we compare its efficil.'ncy for RVI condi­ tions (a disk of constant relative vorticity in each layer illitia.ll~r) to that for PVI conditions (a disk of constant potential vorticity in each layer; Polvani, 1991). The disks of radius R are initially separated by a distance rI. and Rd is the internal radius of deformation. At small Uril Hand la.rge ell R, a multipolar potential vorticity distribution is associated wit h these RVI conditions. This distribution is responsible for a much weaker efficiency of the alignment process in the RVI case than in the PVI case: indeed. the formation of horizontal or of vertical dipoles prevents ali?;n ment. Evpn mol'(' interesting is the case wherr aIignment does occur: under PVI conditions. the end state is a simple vertical column of potential vorticity, whill' for RVI vortin's it is a steadily rotating baroclinic tripolC'. a novel statiollar~r feature of stratified geostrophic dynamics.