Elastic Interaction between a Vortex Dipole and an Axisymmetrical Vortex
in Quasi-Geostrophic Ocean Dynamics
Abstract
We investigate numerically the elastic interaction between a dipole and
an axisymmetrical vortex in inviscid isochoric two-dimensional (2D), as
well as in three-dimensional (3D) flows under the quasi-geostrophic (QG)
approximation. The dipole is a straight moving Lamb-Chaplygin (L-C)
vortex such that the absolute value of either its positive or negative
amount of vorticity equals the vorticity of the axisymmetrical vortex.
The results for the 2D and 3D cases show that, when the L-C dipole
approaches the vortex, their respective potential flows interact, the
dipole’s trajectory acquires curvature and the dipole’s vorticity poles
separate. In the QG dynamics, the vortices suffer little vertical
deformation, being the barotropic effects dominant. At the moment of
highest interaction, the negative vorticity pole elongates,
simultaneously, the positive vorticity pole evolves towards spherical
geometry and the axisymmetrical vortex acquires prolate ellipsoidal
geometry in the vertically stretched QG space. Once the L-C dipole moves
away from the vortex, its poles close, returning the vortices to their
original geometry, and the dipole continues with a straight trajectory
but along a direction different from the initial one. The vortices
preserve, to a large extent, their amount of vorticity and the resulting
interaction may be practically qualified as an elastic interaction. The
interaction is sensitive to the initial conditions and, depending on the
initial position of the dipole as well as on small changes in the
vorticity distribution of the axisymmetrical vortex, inelastic
interactions may instead occur.