Destructive interactions between two counter-rotating quasi-geostrophic vortices

摘要

This paper illustrates the linear stability and the nonlinear evolution of two opposite-signed quasi-geostrophic vortices. We investigate the influence of the volume ratiobetween the two vortices as well as the influence of their vertical offset. Instability isalways found for sufficiently close vortices. A convenient measure of the separationdistance between the two vortices at their margin of stability is the horizontal gapbetween their two outermost edges. When the vortex volume ratio is very close tounity, the critical gap at the margin of stability tends to increase with the verticaloffset. However, for volume ratios greater than 1.1, it decreases with the verticaloffset. This is due to differences in the magnitude of the tilt angle of the vortices. Thenonlinear evolution of unstable equilibria tends to be destructive, often breaking onevortex or both vortices into smaller vortices.