Simulations of dual-vortex interaction within environmental shear

For over a century it has been known that each vortex in a multiple vortex configuration will move in response to the other vortices. However, despite advances since that time, the complexities of multiple vortex scenarios wh en sheared environments are present are still not completely understood. Th e interaction of binary vortices within horizontal environmental shear is e xplored here through shallow water simulations on a beta plane. Due to nonl inear feedbacks, the combination of environmental vorticity (or vorticity g radient) and shear, as well as the multiple vortex situation, results in a more complicated track than for a storm experiencing any individual compone nt. Despite the complexity of these vortex-environment interactions, the us e of previous single-vortex studies greatly aids interpretation. Centroid-r elative motion of the individual vortices is considered, as well as the pro pagation of the vortex pair centroid, to understand motion effects of the d ifferent vortex-environment combinations. As the vortices interact, vortex Rossby waves are generated through distort ion of the symmetric vorticity field by the opposing vortex. Initially, the high-frequency waves have an insignificant effect upon vortex intensity or propagation, and beta-induced wavenumber one asymmetry dominates as expect ed. However, as the waves approach a critical radius (zeta = 0), wave poten tial vorticity filamentation and stretching by the circulation of the adjac ent vortex leads to a coupling of the two vortices. This vortex coupling re sults in enhanced propagation speeds of the two vortices proportional to th e effective size of the dual-vortex system. The sign of vorticity of the environmental flow can act to enhance or negat e beta-drift such that single- or dual-vortex propagation is altered. Furth er, when environmental vorticity is present: the rate of mutual orbit from Fujiwhara rotation is altered. When the environmental flow is cyclonic, the cyclonic mutual rotation of the vortices is accelerated. Conversely, when the environmental flow is anticyclonic, the mutual rotation of the vortices is substantially decelerated. but remains cyclonic.